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For III Semester B.E., Mechanical Engineering Students

As per Latest Syllabus of Anna University - TN

New Regulations 2017

With Short Questions & Answers and University Solved Papers

MANUFACTURING TECHNOLOGY - I(Production Technology)

Dr. S. Ramachandran, M.E., Ph.D.,

Professor - MechSathyabama Institute of Science and Technology

Chennai - 119

Dr. S. Ramesh, B.E., M.Tech, Ph.D.,FIE., LM-ASME., LM-PMA

Professor / HODMechanical Engineering

KCG College of Technology, Chennai - 97

Dr. G. Nallakumarasamy,B.E., M.Tech (IITM)., Ph,D., MISTE, MSAE.,

Professor & Head Mechanical Engineering

Excel Engineering College, Namakkal - 637 303

250/-

Fourth Edition: June 2018

978-93-88084-00-0

www.srbooks.orgwww.airwalkbooks.com

ME8351 MANUFACUTRING TECHNOLOGY - I L T P C3 0 0 3

UNIT I METAL CASTING PROCESSESSand Casting: Sand Mould – Type of patterns – Pattern Materials – Patternallowances – Moulding sand Properties and testing – Cores – Types andapplications – Moulding machines – Types and applications; Melting furnaces;Blast and Cupola Furnaces; Principle of special casting process; Shell –investment – Ceramic mould – Pressure die casting – Centrifugal Casting –CO2 process – Stir casting; Defects in Sand casting

UNIT II JOINING PROCESSESOperating principle, basic equipment, merits and applications of: Fusionwelding processes: Gas welding – Types – Flame characteristics; Manualmetal arc welding – Gas Tungsten arc welding – Gas metal arc welding –Submerged arc welding – Electro slag welding; Operating principle andapplications of: Resistance welding – Plasma arc welding – Thermit welding– Electron beam welding – Friction welding and Friction Stir Welding;Brazing and soldering; Weld defects: types, causes and cure.

UNIT III METAL FORMING PROCESSESHot working and cold working of metals – Forging processes – Open,Impression and closed die forging – forging operations. Rolling of metals –Types of Rolling – Flat strip rolling – shape rolling operations – Defects inrolled parts. Principle of rod and wire drawing – Tube drawing – Principlesof Extrusion – Types – Hot and Cold extrusion.

UNIT IV SHEET METAL PROCESSESSheet metal characteristics – shearing, bending and drawing operations – Stretchforming operations – Formability of sheet metal – Test methods – special formingprocesses – Working principle and applications – Hydro forming – Rubber padforming – Metal spinning– Introduction of Explosive forming, magnetic pulseforming, peen forming, Super plastic forming – Micro forming.

UNIT V MANUFACTURE OF PLASTIC COMPONENTSTypes and characteristics of plastics – Moulding of thermoplastics – workingprinciples and typical applications – injection moulding – Plunger and screwmachines – Compression moulding, Transfer Moulding – Typical industrialapplications – introduction to blow moulding – Rotational moulding – Filmblowing – Extrusion – Thermoforming – Bonding of Thermoplastics.

INDEXA

Additives and Fillers in Plastics5.5

Additives 1.14

Adhesiveness 1.20

Air-Acetylene Welding 2.36

Air Furnace or Reverberatory Furnace1.81

Anisotropy 4.4

Arc Welding (or) Manual Metal arcWelding (or) Shielded arc Arcwelding 2.5

Arc Welding Equipment 2.38

BBacking sand 1.17

Bench Moulding1.20

Bending operations 3.68

Bending 3.4

Binder 1.13

Blanking 4.6

Blast Furnace 1.72

Blow Moulding 5.14, 5.36

Blowholes 2.109

Bonding of Thermoplastics 5.60

Bottom gates 1.103

Branched polymers 5.2

Brazing 2.95

CCarbon arc Welding 2.45

Cast Iron 1.47

Casting 5.15

Centrifugal Casting 1.127

Centrifuge Casting 1.131

Ceramic Mould Casting 1.121

Cereal binder 1.56

Chemical dip brazing2.96

Clay Content Test 1.31

Closed Die Forging (or) Impression DieForging (or) Precision Coal dust1.14

Cohesiveness 1.19

Cold chamber die casting 1.125

Cold forming 5.70

Cold Working Of Metals 3.3

Cold Spinning 3.65

Cold Working Processes

Collapsibility 1.20

Combustion zone 1.77

Compression Moulding 5.14, 5.29

Continuous Casting 1.138

Convertor 1.87

Cope and drag pattern 1.41

Core sand 1.17, 1.55

Core Making 1.56

Cores 1.54

Corn flour and Dextrin 1.14

Cracking 2.105

Cross-linked polymers 5.3

Crucible Furnaces 1.89

Cupola Furnace 1.74

Cupping Test 4.26

Cutting off 4.8

DDeep drawing (or) Cupping 3.56

Defects in Sand Casting 1.146

Dextrin 1.56

Die materials 3.31

Die design features 3.30

Dielectric welding 5.65

Diffusion Welding 2.78

Dimensional inspection 1.156

Index I.1

Dip Soldering 2.100

Dip Brazing 2.96

Direct Arc furnace 1.92

Distortion (or) Camber allowance1.53

Distortion 2.106

Draft (or) Taper allowance 1.52

Draft Angles 3.29

Draw spike 1.25

Drawing 3.4

Drives for Extrusion 3.63

Drop Forging 3.19

Dry strength 1.19

Dry sand 1.16

Dry sand moulding 1.22

EElastomers 5.11

Electric Furnaces 1.92

Electric arc Welding Processes2.37

Electro Hydraulic Forming 4.31

Electro Slag Welding2.50

Electrode Standards 2.23

Electrodes 2.12

Electron Beam Welding 2.85

Elongation 4.3

Excessive Penetration2.109

Explosive Forming 4.38

Explosive Welding 2.76

Extrusion defects 3.63

Extrusion 5.51

FFacing sand 1.16

Filler materials 2.97

Filler Materials and Fluxes in Brazing2.97

Fillers 5.6

Film Blowing and Sheet Blowing5.46

Flame Cutting 2.90

Flames Characteristics 2.33

Flasks 1.27

Flat Strip Rolling 3.39

Floor Moulding 1.21

Flowability Test 1.33

Flowability (or) plasticity 1.19

Flux Material 2.98

Flux Cored Arc Welding (FCAW)2.54

Follow board pattern 1.43

Forge Welding 2.70

Forging 3.19

Forging Tests 3.27

Forging Processes 3.6

Forging under sticking condition3.19

Forging Defects 3.25

Forming Limit Diagram (FLD)4.27

Four High rolling mill 3.36

Friction Stir Welding (FSW)2.74

Friction Welding 2.72

Furnace (or) Forge brazing 2.96

Fusion bonding 5.67

GGaggers 1.27

Gas Welding Processes 2.24

Gas Welding 2.5

Gas welding equipments 2.28

Gas Tungsten Arc Welding (GTAW)(or) Tungsten Inert Gas Welding(TIG) 2.48

Gas Metal Arc Welding (GMAW) orMetal Inert Gas Welding (MIG)2.49

Gate cutter 1.26

Gate 1.103

Gated pattern 1.43

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Gating System 1.100

Grain Fineness Test (GFT) 1.31

Grain size 4.4

Green strength 1.19

Green sand 1.15

HHand riddle 1.23

Hand forging 3.13

Hard Soldering 2.100

Heat Affected Zone (HAZ) 2.11

High rolling mill 3.35

Horizontal core 1.64

Hot Box Core 1.64

Hot twist test 3.28

Hot gas welding5.66

Hot Rolling: Hot Working Of Metals3.2

Hot chamber die-casting 1.123

Hot Extrusion 3.59

Hot-platen welding 5.65

Hot Spinning 3.65

Hydro Mechanical Forming 4.31

Hydro Forming 4.29

Hydrostatic Extrusion3.61

IImpact extrusion (or) Cold Extrusion3.60

Induction brazing 2.96

Initiators 5.6

Injecting Moulding 5.17

Injection Blow Moulding 5.37

Inspection Method 1.156

Investment casting (Lost waxcasting) 1.118

JJolt-squeezer machine 1.69

Jolt machine 1.68

LLancing 4.9

Laser Beam Welding 2.83

Laser brazing and electron beambrazing 2.97

Lifters 1.25

Linear polymers 5.2

Liquid (Dye) Penetrant Test 1.163

Loam Moulding 1.21

Loam sand 1.16

Loose piece pattern 1.40

MMachine Moulding 1.21

Machining allowance 1.52

Magnetic Particle Inspection 1.160

Magnetic Pulse Forming 4.40

Mallet 1.24

Match plate pattern 1.41

Mechanical Fastening5.62

Mechanical Testing 1.157

Melting Furnaces 1.71

Melting zone 1.77

Metal Pattern 1.47

Metal Spinning 4.35

Micro-Forming 4.46

Modern Welding Processes 2.83

Modifiers 5.6

Moisture Content Test 1.30

Moisture / Water 1.13

Molasses 1.56

Molten metal bath process 2.97

Mould Hardness Test1.35

Moulding Sand Testing 1.29

Moulding Boxes 1.27

Moulding Machines 1.67

Index I.3

Multiple Roll Mill/Cluster roll mill3.37

NNetwork polymers 5.3

Nibbling 4.9

Notching 4.8

OOne piece (or) solid pattern 1.39

Open Hearth Furnace1.85

Open Die Forging (or) Smith DieForging (or) Flat-die ForgingOperations 3.10

Overlays 2.109

Oxy - Hydrogen Welding 2.36

Oxy-Fuel Gas Welding (OFW)2.24

Oxy – Acetylene Welding 2.25

PParting sand 1.17

Parting 4.8

Pattern Materials 1.46

Pattern 1.38

Pattern Allowances 1.51

Pattern draw machines 1.71

Peen Forming 4.42

Percussion Welding 2.67

Perforating 4.10

Permeability Test 1.36

Permeability 1.18

Piercing or Seamless Tubing3.48, 3.64

Piercing 4.7

Pit Furnace 1.89

Pit Moulding 1.21

Planetary rolling mill3.39

Plasma arc Welding 2.87

Plaster-mould casting 1.135

Plasticizers 5.5

Plunger moulding 5.34

Polymerisation Process 5.5

Polymers 5.1

Poor Weld Bead Appearance (Fig.2.51) 2.108

Porosity (Fig. 2.45) 2.104

Pot Transfer Moulding 5.33

Potting & Encapsulation 5.69

Power hammers 3.14

Power shearing 4.7

Power forging 3.14

Preheating zone 1.78

Preshaping 3.31

Press forging 3.20

Pressure Die Casting 1.123

Principle Of Rod And Wire Drawing3.52

Principles Of Extrusion 3.58

Protein binder 1.56

Punching4.7

RRammers 1.24

Rapping (or) Shake allowance1.53

Reaction-Injection Moulding (RIM)5.68

Reducing zone 1.77

Refractoriness 1.18

Refractoriness Test 1.32

Resistance Spot Welding 2.59

Resistance Welding 2.5

Resistance brazing 2.97

Ring rolling process: 3.46

Riser of Casting 1.106

Rod drawing process 3.54

Roll Forging 3.23

Rolling Of Metals 3.33

Rotary Melting Furnace 1.83


Rotational Moulding 5.14, 5.42

Rubber Pad Forming 4.33

Runner 1.102

SSand Casting 1.5

Sand Mould 1.7

Sea coal and Pitch 1.14

Segmental (or) part pattern 1.45

Semi-Centrifugal Casting 1.130

Shape Rolling Operations 3.45

Shatter Index Test 1.34

Shaving 4.10

Shear Spinning 4.37

Shearing processes 3.66

Shearing 3.5

Sheet Metal Characteristics 4.2

Shell mould casting 1.114

Shell Core 1.63

Shovel 1.24

Shrinkage Cavity 2.109

Shrinkage allowance 1.51

Silica flour 1.15

Silica sand 1.12

Skeleton pattern 1.45

Skin-dried moulding 1.23

Slag Inclusion (Fig. 2.47) 2.106

Slicks 1.26

Slinging machines 1.70

Slitting 4.8

Slush-moulding 5.69

Smoothers 1.26

Soft Soldering 2.100

Solder Fluxes 2.102

Soldering 2.99

Solid State Welding 2.6

Solidification of Weld Metal2.10

Solvent Bonding5.62

Solvents 5.6

Spin Welding 5.62

Spirit level 1.26

Spray-gun 1.27

Spruce: 1.101

Sprue pin 1.24

Squeezer machine 1.68

Squeezing 3.5

Squeezing operations 3.69

Stack 1.78

Step gate 1.104

Stir casting 1.134

Strength Test 1.34

Stretch Blow Moulding (SBM)5.39

Strike off bar 1.24

Structural foam moulding 5.14

Stud welding 2.65

Submerged arc Welding 2.47

Sulphite binder 1.56

Super Plastic Forming 4.44

Surface Defects 3.48

Swab 1.26

Sweep pattern 1.44

System sand 1.17

TThermit Welding 2.62.81

Thermoforming 5.14, 5.56

Thermoplastics 5.7

Thermosetting resin 1.56

Thermosetting plastics 5.9

Thread rolling 3.47

Three-piece or multi- piece pattern1.42

Three High rolling mill 3.36

Index I.5

Torch brazing 2.96

Transfer Moulding 5.15, 5.32

Transfer moulding types 5.33

Trimming 4.10

Trowels 1.25

True Centrifugal Casting 1.128

Tube Drawing 3.55

Tube spinning 4.38

Two High reversible 3.35

Two piece (or) split pattern 1.39

Typical Shearing 4.4

UUltrasonic Welding 2.80

Ultrasonic Inspection 1.164

Undercutting and Overlapping (Fig.2.52) 2.108

Universal rolling mill 3.38

Unpressurized gating system:1.106

Upset forging (Heading) 3.21

Upsetting test 3.28

VVacuum casting 1.135

Vent rod 1.25

Vertical core 1.65

Vibration welding 5.67

Visual Inspection 1.156

WWave Soldering 2.100

Weld Defects - Types and Causes2.104

Weldability 2.6

Welding 2.42

Welding Terminology 2.7

Welding Positions 2.9

Well 1.76

White Metal 1.48

Wire drawing 3.54

Wood 1.46

Wood flour 1.15

YYield Point Elongation 4.3


Table of ContentsUnit 1: METAL CASTING PROCESSES

1.1 Introduction to Solidification Process . . . . . . . . . . . . . . . . . . 1.1

1.2 Sand Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5

1.3 Sand Mould . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7

1.3.1 Features of Sand mould . . . . . . . . . . . . . . . . . . . . . . . 1.7

1.3.2 Desirable Mould Properties and Characteristics . . . 1.9

1.3.3 Steps/ Procedure for making sand mould . . . . . . . 1.9

1.4 Constituents of Moulding Sand. . . . . . . . . . . . . . . . . . . . . . 1.12

1.4.1 Silica sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12

1.4.2 Binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.13

1.4.3 Moisture / Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.13

1.4.4 Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.14

1.4.4.1 Corn flour and Dextrin . . . . . . . . . . . . . . . . . . . . . . 1.14

1.4.4.2 Coal dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.14

1.4.4.3 Sea coal and Pitch . . . . . . . . . . . . . . . . . . . . . . . . . . 1.14

1.4.4.4 Wood flour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15

1.4.4.5 Silica flour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15

1.5 Types of Moulding Sands. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15

1.5.1 Green sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15

1.5.2 Dry sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16

1.5.3 Loam sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16

1.5.4 Facing sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16

1.5.5 Backing sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.17

1.5.6 System sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.17

1.5.7 Parting sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.17

1.5.8 Core sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.17

1.6 Moulding Sand Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 1.18

Contents C.1

1.6.1 Refractoriness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.18

1.6.2 Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.18

1.6.3 Cohesiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.19

1.6.4 Green strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.19

1.6.5 Dry strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.19

1.6.6 Flowability (or) plasticity . . . . . . . . . . . . . . . . . . . . . 1.19

1.6.7 Adhesiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.20

1.6.8 Collapsibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.20

1.6.9 Classification of Moulding Processes. . . . . . . . . . . . 1.20

1.6.9.1 Bench Moulding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.20

1.6.9.2 Floor Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.21

1.6.9.3 Pit Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.21

1.6.9.4 Machine Moulding. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.21

1.6.9.5 Loam Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.21

1.6.9.6 Dry sand moulding . . . . . . . . . . . . . . . . . . . . . . . . . . 1.22

1.6.9.7 Skin-dried moulding . . . . . . . . . . . . . . . . . . . . . . . . . 1.23

1.6.10 Hand Tools Used In Foundry Shop . . . . . . . . . . . 1.23

1.7 Moulding Sand Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.29

1.7.1 Need for sand testing . . . . . . . . . . . . . . . . . . . . . . . . 1.29

1.7.2 Moisture Content Test . . . . . . . . . . . . . . . . . . . . . . . . 1.30

1.7.3 Clay Content Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.31

1.7.4 Grain Fineness Test (GFT). . . . . . . . . . . . . . . . . . . . 1.31

1.7.5 Refractoriness Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.32

1.7.6 Flowability Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.33

1.7.7 Shatter Index Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.34

1.7.8 Strength Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.34

1.7.9 Mould Hardness Test . . . . . . . . . . . . . . . . . . . . . . . . 1.35

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1.7.10 Permeability Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.36

1.8 Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.38

1.8.1 Functions of the Pattern . . . . . . . . . . . . . . . . . . . . . . 1.38

1.8.2 Types of Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.39

1.8.3 Design Considerations for a good Pattern . . . . . . . 1.46

1.8.4 Pattern Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.46

1.8.5 Selection of pattern material . . . . . . . . . . . . . . . . . . 1.50

1.8.6 Pattern Allowances. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.51

(a) Shrinkage allowance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.51

(b) Machining allowance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.52

(c) Draft (or) Taper allowance . . . . . . . . . . . . . . . . . . . . . . . 1.52

(d) Rapping (or) Shake allowance . . . . . . . . . . . . . . . . . . . . 1.53

(e) Distortion (or) Camber allowance . . . . . . . . . . . . . . . . . 1.53

(f) Mould wall movement allowance . . . . . . . . . . . . . . . . . . 1.54

1.9 Cores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.54

1.9.1 Functions (or) Objectives of core . . . . . . . . . . . . . . . 1.54

1.9.2 Core Sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.55

1.9.3 Considerations in Selecting Core Sand. . . . . . . . . . 1.55

1.9.4 Binders for core sand . . . . . . . . . . . . . . . . . . . . . . . . 1.55

1.9.5 Core Making . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.56

1.9.6 Types of Cores and Applications . . . . . . . . . . . . . . . 1.62

1.10 Moulding Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67

1.10.1 Types and Applications of Moulding Machines. . 1.67

(a) Squeezer machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.68

(b) Jolt machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.68

(c) Jolt-squeezer machine . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.69

(d) Slinging machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70

Contents C.3

(e) Pattern draw machines. . . . . . . . . . . . . . . . . . . . . . . . . . 1.71

1.11 Melting Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.71

1.11.1 Factors responsible for the selection of furnace . . 1.71

1.11.2 Types of Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . 1.72

1.11.3 Blast Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.72

1.11.4 Cupola Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.74

1.11.5 Air Furnace or Reverberatory Furnace . . . . . . . . . 1.81

1.11.6 Rotary Melting Furnace . . . . . . . . . . . . . . . . . . . . . 1.83

1.11.7 Open Hearth Furnace . . . . . . . . . . . . . . . . . . . . . . . 1.85

1.11.8 Convertor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.87

1.11.9 Pit Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.89

1.11.10 Crucible Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . 1.89

1.11.11 Electric Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . 1.92

1.11.12 Overall Comparison Of Melting Furnaces . . . . . 1.99

1.12 Gating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.100

1.13 Riser of Casting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.106

1.14 Principle of Special Casting Processes . . . . . . . . . . . . . . 1.111

1.14.1 Advantages of Special casting techniques overconventional sand casting. . . . . . . . . . . . . . . . . . . . . . . . . 1.111

1.14.2 Classification of Special Casting Processes . . . . 1.112

1.14.4 Shell mould casting . . . . . . . . . . . . . . . . . . . . . . . 1.114

1.14.5 Investment casting (Lost wax casting) . . . . . . . . 1.118

1.14.6 Ceramic Mould Casting . . . . . . . . . . . . . . . . . . . . 1.121

1.14.7 Pressure Die Casting . . . . . . . . . . . . . . . . . . . . . . . 1.123

1.14.8 Centrifugal Casting . . . . . . . . . . . . . . . . . . . . . . . . 1.127

1.14.9 Carbon-dioxide Moulding Principle . . . . . . . . . . . 1.132

1.14.10 Stir casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.134


1.14.13 Expendable-pattern casting (lost foam process) 1.138

1.14.14 Continuous Casting . . . . . . . . . . . . . . . . . . . . . . . 1.138

1.15 Design Considerations of Castings . . . . . . . . . . . . . . . . . 1.142

1.16 Defects in Sand Casting. . . . . . . . . . . . . . . . . . . . . . . . . . 1.146

1.17 Inspection Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.156

1.17.1 Visual Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . 1.156

1.17.2 Dimensional inspection . . . . . . . . . . . . . . . . . . . . . 1.156

1.17.3 Mechanical Testing . . . . . . . . . . . . . . . . . . . . . . . . 1.157

1.17.4 Flaw detection by Non destructive testing . . . . . 1.157

1.17.5 Radiography Test (X-ray (or) -ray) : . . . . . . . . . 1.157

1.17.6 Magnetic Particle Inspection. . . . . . . . . . . . . . . . . 1.160

1.17.7 Fluorescent Penetrant Inspection (Zyglo Process) 1.162

1.17.8 Liquid (Dye) Penetrant Test . . . . . . . . . . . . . . . . . 1.163

1.17.9 Ultrasonic Inspection . . . . . . . . . . . . . . . . . . . . . . . 1.164

Unit - 2: JOINING PROCESSES2.1 Introduction to the Joining Processes . . . . . . . . . . . . . . . . . 2.1

2.2 Welding - Operating Principle. . . . . . . . . . . . . . . . . . . . . . . . 2.2

2.2.1 Classification of Welding Processes . . . . . . . . . . . . . . 2.2

2.2.2 Types of Welding Processes. . . . . . . . . . . . . . . . . . . . . 2.4

(i) Gas Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5

(ii) Arc welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5

(iii) Resistance Welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5

(iv) Solid State Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6

(v) Thermit Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6

(vi) Modern Welding Processes . . . . . . . . . . . . . . . . . . . . . . . 2.6

(vii) Related Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6

2.2.3 Weldability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6

Contents C.5

2.3 Welding Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7

2.3.1 Filler Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7

2.3.2 Fluxes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7

2.3.3 Welding Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9

2.4 Solidification of Weld Metal . . . . . . . . . . . . . . . . . . . . . . . . 2.10

2.5 Heat Affected Zone (HAZ) . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11

2.6 Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12

2.6.1.1 Selection of electrodes . . . . . . . . . . . . . . . . . . . . . . . 2.13

2.6.2 Electrodes and Their Uses . . . . . . . . . . . . . . . . . . . . 2.14

2.6.3 Electrode Coating and Specifications . . . . . . . . . . . 2.14

2.6.4 Electrode Classification (as per AWS A5.1) . . . . . . 2.21

2.6.5 Electrode Standards. . . . . . . . . . . . . . . . . . . . . . . . . . 2.23

2.7 Gas Welding Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.24

2.7.1 Oxy-Fuel Gas Welding (OFW) . . . . . . . . . . . . . . . . . 2.24

2.7.1.1 Oxy – Acetylene Welding. . . . . . . . . . . . . . . . . . . . . 2.25

2.7.1.2 Control in oxy-acetylene welding . . . . . . . . . . . . . . 2.26

2.7.1.3 Gas welding equipments . . . . . . . . . . . . . . . . . . . . . 2.28

2.7.1.4 Flames Characteristics . . . . . . . . . . . . . . . . . . . . . . . 2.33

2.7.1.5 Oxy - Hydrogen Welding . . . . . . . . . . . . . . . . . . . . . 2.36

2.7.1.6 Air-Acetylene Welding . . . . . . . . . . . . . . . . . . . . . . . 2.36

2.8 Electric arc Welding Processes . . . . . . . . . . . . . . . . . . . . . . 2.37

2.8.1 Arc Welding Equipment . . . . . . . . . . . . . . . . . . . . . . 2.38

2.9 Arc Welding (or) Manual Metal arc Welding (or) Shieldedarc Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.42

2.9.1 Merits and Demerits of Arc Welding . . . . . . . . . . . 2.44

2.9.2 Applications of Arc Welding . . . . . . . . . . . . . . . . . . . 2.44

2.10 Carbon arc Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.45


2.11 Submerged arc Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.47

2.12 Gas Tungsten Arc Welding (GTAW) (or) Tungsten InertGas Welding (TIG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.48

2.13 Gas Metal Arc Welding (GMAW) or Metal Inert GasWelding (MIG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.49

2.14 Electro Slag Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.50

2.15 Flux Cored Arc Welding (FCAW) . . . . . . . . . . . . . . . . . . . 2.54

2.16 Resistance Welding - Operating Principle . . . . . . . . . . . . 2.58

2.17 Solid State Welding Processes (pressure Welding Processes)2.70

2.18 Forge Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.70

2.19 Friction Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.72

2.20 Friction Stir Welding (FSW) . . . . . . . . . . . . . . . . . . . . . . . 2.74

2.21 Explosive Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.76

2.22 Diffusion Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.78

2.23 Ultrasonic Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.80

2.24 Thermit Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.81

2.25 Modern Welding Processes. . . . . . . . . . . . . . . . . . . . . . . . . 2.83

2.26 Laser Beam Welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.83

2.27 Electron Beam Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.85

2.28 Plasma arc Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.87

2.29 Flame Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.90

2.30 Brazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.95

2.31 Soldering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.99

2.32 Weld Defects - Types and Causes . . . . . . . . . . . . . . . . . 2.104

1. Porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.104

2. Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.105

3. Slag Inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.106

Contents C.7

4. Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.106

5. Incomplete Fusion and Penetration . . . . . . . . . . . . . . 2.107

6. Poor Weld Bead Appearance . . . . . . . . . . . . . . . . . . . . 2.108

7. Undercutting and Overlapping . . . . . . . . . . . . . . . . . . 2.108

8. Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.109

9. Blowholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.109

10. Burn Through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.109

11. Excessive Penetration . . . . . . . . . . . . . . . . . . . . . . . . . 2.109

12. Shrinkage Cavity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.109

2.33 Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.111

Unit - 3: METAL FORMING PROCESSES3.1 Hot Working and Cold Working of Metals . . . . . . . . . . . . . 3.1

3.2 Hot Rolling: Hot Working Of Metals . . . . . . . . . . . . . . . . . . 3.2

3.3 Cold Working Of Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3

3.4 Comparision Between Hot Working And Cold Working . . 3.5

3.5 Forging Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6

3.5.1 Tools used in forging . . . . . . . . . . . . . . . . . . . . . . . . . 3.6

3.5.2 Classification of Forging Processes/Methods . . . . . . 3.9

3.5.3 Open Die Forging (or) Smith Die Forging (or) Flat-dieForging Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10

3.5.4 Hand forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13

3.5.5 Power forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.14

3.5.6 Forging under sticking condition. . . . . . . . . . . . . . . 3.19

3.5.7 Closed Die Forging (or) Impression Die Forging (or)Precision Forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.19

3.5.8 Drop Forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.19

3.5.9 Press forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.20


3.5.10 Upset forging (Heading) . . . . . . . . . . . . . . . . . . . . . 3.21

3.5.11 Roll Forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.23

3.5.12 Comparison between press forging and drop forging(Hammer forging). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.25

3.5.13 Forging Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.25

3.15.13.1 Defects Elimination/removal in forgings . . . . . . 3.26

3.5.13.2 Annealing & Normalizing of Forgings. . . . . . . . . 3.27

3.5.13.3 Forging Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.27

(i) Upsetting test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.28

(ii) Hot twist test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.28

3.5.14 Design Considerations In Forging . . . . . . . . . . . . . 3.29

3.6 Rolling Of Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.33

3.6.1 Types of rolling mills . . . . . . . . . . . . . . . . . . . . . . . . 3.34

(a) High rolling mill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.35

(b) Two High reversible . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.35

(c) Three High rolling mill. . . . . . . . . . . . . . . . . . . . . . . . . . 3.36

(d) Four High rolling mill . . . . . . . . . . . . . . . . . . . . . . . . . . 3.36

(e) Multiple Roll Mill/Cluster roll mill. . . . . . . . . . . . . . . . 3.37

(f) Universal rolling mill. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.38

(g) Planetary rolling mill . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.39

3.8 Flat Strip Rolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.39

3.9 Shape Rolling Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . 3.45

3.10 Defects In Rolled Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.48

3.11 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.50

3.12 Principle Of Rod And Wire Drawing . . . . . . . . . . . . . . . . 3.52

3.12.1 Applications of drawing . . . . . . . . . . . . . . . . . . . . . 3.52

3.12.2 Equipment used in drawing. . . . . . . . . . . . . . . . . . 3.52

3.12.3 Classification of drawing operations . . . . . . . . . . . 3.54

Contents C.9

3.13 Principles Of Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.58

3.13.1 Equipment used in extrusion . . . . . . . . . . . . . . . . . 3.58

3.13.2 Types of extrusion process. . . . . . . . . . . . . . . . . . . . 3.58

3.13.2.1 Hot Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.59

3.13.2.2 Impact extrusion (or) Cold Extrusion . . . . . . . . . 3.60

3.13.2.3 Hydrostatic Extrusion. . . . . . . . . . . . . . . . . . . . . . . 3.61

3.13.3 Drives for Extrusion . . . . . . . . . . . . . . . . . . . . . . . . 3.63

3.13.4 Extrusion defects . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.63

3.13.5 Piercing Or Seamless Tubing. . . . . . . . . . . . . . . . . 3.64

3.13.6 Hot Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.65

3.13.6 Cold Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.65

3.13.7 Cold Working Processes. . . . . . . . . . . . . . . . . . . . . . 3.65

3.13.7.1 Shearing processes . . . . . . . . . . . . . . . . . . . . . . . . . 3.66

3.13.8 Drawing operations . . . . . . . . . . . . . . . . . . . . . . . . . 3.66

3.13.9 Bending operations. . . . . . . . . . . . . . . . . . . . . . . . . . 3.68

3.13.10 Squeezing operations . . . . . . . . . . . . . . . . . . . . . . . 3.69

3.13.11 Equipment used in extrusion . . . . . . . . . . . . . . . . 3.71

Unit - 4: SHEET METAL PROCESSES4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.2 Sheet Metal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2

4.3 Typical Shearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4

4.3.1 Factors Affecting Shearing Operation . . . . . . . . . . . . 4.5

4.3.2 Stages in Shearing Action . . . . . . . . . . . . . . . . . . . . . 4.5

4.3.3 Shearing Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6

4.4 Bending Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11

4.5 Typical Drawing Operations In Sheet Metals . . . . . . . . . 4.19

4.6 Stretch Forming Operations. . . . . . . . . . . . . . . . . . . . . . . . . 4.23


4.7 Formability Of Sheet Metal. . . . . . . . . . . . . . . . . . . . . . . . . 4.26

4.8 Test Methods For Formability Of Sheet Metals . . . . . . . 4.26

4.8.1 Cupping Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.26

4.8.2 Forming Limit Diagram (FLD) . . . . . . . . . . . . . . . . 4.27

4.9 Special Forming Processes . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.9.1 Hydro Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.9.1.1 Hydro Mechanical Forming . . . . . . . . . . . . . . . . . . . 4.31

4.9.1.2 Electro Hydraulic Forming . . . . . . . . . . . . . . . . . . . 4.31

4.9.2 Rubber Pad Forming. . . . . . . . . . . . . . . . . . . . . . . . . 4.33

4.9.3 Metal Spinning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.35

4.9.3.1 Shear Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.37

4.9.3.2 Tube spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.38

4.9.4 Explosive Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.38

4.9.5 Magnetic Pulse Forming . . . . . . . . . . . . . . . . . . . . . . 4.40

4.9.6 Peen Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.42

4.9.7 Super Plastic Forming . . . . . . . . . . . . . . . . . . . . . . . 4.44

4.9.8 Micro-Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.46

Unit - 5: MANUFACTURING OF PLASTIC COMPONENTS5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1

5.1.1 Classification of Organic Materials . . . . . . . . . . . . . . 5.1

5.1.2 Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1

5.1.3 The Structure of Polymers . . . . . . . . . . . . . . . . . . . . . 5.2

5.1.4 Polymerisation Process. . . . . . . . . . . . . . . . . . . . . . . . . 5.5

5.1.5 Additives and Fillers in Plastics . . . . . . . . . . . . . . . . 5.5

5.1.6 Types And Characteristics Of Plastics . . . . . . . . . . . 5.7

5.1.6.1 Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7

5.1.6.2 Thermosetting plastics . . . . . . . . . . . . . . . . . . . . . . . . 5.9

Contents C.11

5.1.6.3 Elastomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11

5.1.6.4 Differentiate between Thermoplastic andThermosetting plastics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11

5.1.6.5 Advantages and disadvantages of plastics . . . . . . 5.12

5.2 Characteristics Of Forming And Shaping Processes . . . . 5.13

5.3 Moulding Of Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . 5.16

5.4 Injection Moulding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.17

5.5 Compression Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.29

5.6 Transfer Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.32

5.7 Blow Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.36

5.7.1 Working Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.36

5.7.2 Classification of Blow Moulding . . . . . . . . . . . . . . . 5.36

5.7.3 Strech Blow Moulding (SBM) . . . . . . . . . . . . . . . . . 5.39

5.7.4 Advantages of Blow Moulding . . . . . . . . . . . . . . . . . 5.40

5.7.5 Common plastics for blow moulding. . . . . . . . . . . . 5.41

5.7.6 Manufacture of plastic bags . . . . . . . . . . . . . . . . . . . 5.41

5.8 Rotational Moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.42

5.9 Film Blowing and Sheet Blowing . . . . . . . . . . . . . . . . . . . . 5.46

5.10 Extrusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.51

5.11 Thermoforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.56

5.12 Bonding of Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . . 5.60

5.13 Other Plastic Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.68

5.13.1 Reaction-Injection Moulding (RIM) . . . . . . . . . . . . 5.68

5.13.2 Slush-moulding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.69

5.13.3 Casting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.69

5.13.4 Potting and Encapsulation . . . . . . . . . . . . . . . . . . . 5.69

5.13.5 Cold forming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.70


Unit 1

METAL CASTING PROCESSES

Sand Casting: Sand Mould – Type of patterns – Pattern Materials –

Pattern allowances – Moulding sand Properties and testing – Cores – Types

and applications – Moulding machines – Types and applications; Melting

furnaces; Blast and Cupola Furnaces; Principle of special casting process;

Sheel – investment – Ceramic mould – Pressure die casting – Centrifugal

Casting – CO2 process – Stir casting; Defects in Sand casting

1.1 INTRODUCTION TO SOLIDIFICATION PROCESSIn manufacturing processes, the raw material is in either a liquid or is

in a highly plastic condition, and a part is created through solidification of

the material. Solidification processes can be classified according to the

engineering material being processed as:

Metal casting process

Ceramics, specifically glass working process

Polymers and polymer matrix composites (PMCs) process

Fig 1.1 Shows the Classification of solidification processes.

Po lym ers &PM C P rocess

Fig. 1.1. Classification of Solid ification Processes.

So lidificat io nProcess

G lassw orking

M etalcas ting

Expendable-m ouldC asting

Perm anen t-m ou ldC asting

Extru sion

In je ction M oulding

O th er M oulding

Spec ia l M ouldingfo r PM C

Sand C asting

Shell M oulding

Vacuum M ou ld ing

Expanded P olystyrene

Investm en t C a sting

P laste r-M ou ld C asting

C eram ic -M ould C astin g

Perm anen t-M ou ld C asting

Variations o f Pe rm anen t-M ou ld

C asting

D ie C a sting

C entr ifuga l C asting

1.1.1 Casting of metals

Casting is a manufacturing process by which a liquid material is

usually poured into a mould, which contains a hollow cavity of the desired

shape, and then allowed to solidify. The solidified part is also known as a

casting, which is ejected or broken out of the mould to complete the process.

Casting materials are usually metals or various cold setting materials that cure

after mixing two or more components together; examples are epoxy, concrete,

plaster and clay. Casting is a 6000 year old process. The oldest surviving

casting is a copper frog from 3200 BC. In comparison to other fabrication

processes, casting is the most economical.

Casting techniques are used when:

The finished shape is so large or consists of complex internal and

external part geometries.

A particular alloy is so low in ductility that forming by either hot

or cold working would be difficult.

Some casting processes can produce parts to met shape (no further

manufacturing operations are required)

Can be used with any metal that can be heated to its liquid phase

Some types of casting are suited to mass production

Casting is usually performed in a Foundry. Foundry is a factory

equipped for making moulds, melting and handling molten metal, performing

the casting process, and cleaning the finished casting. Workers who perform

casting are called foundrymen.

1.1.2 Important factors in casting operations

Important factors in casting operations are

Solidification of the metal

Molten metal into metal cavity

Heat transfer during solidification and cooling of the metal in the

mould

Influence of the type of the mould material

1.2 Manufacturing Technology I - www.airwalkbooks.com

1.1.3 Classification of Casting processes

Casting processes are classified as

1. Expendable mould processes

Permanent Pattern (e.g. Sand Casting)

Expendable Pattern (e.g. Investment Casting)

2. Permanent mould processes (e.g. Die, Centrifugal & continuous Castings)

Semi Permanent core (e.g. Sand core)

Permanent core (e.g. Metal core)

Expendable mould process – uses an expendable mould which must be

destroyed to remove casting

Mould materials: sand, plaster, and similar materials, plus binders

Advantage: more complex shapes are possible

Disadvantage: production rates often limited by time to make

mould rather than casting itself

Permanent mould process – uses a permanent mould which can be used over

and over to produce many castings

Made of metal or a ceramic refractory material

Advantage: Higher production rates

Disadvantage: Part geometrics are limited in this process as the

mold needs to open and close.

1.1.4 Capabilities and Advantages of Casting

Can create complex part geometries

Can create both external and internal shapes

Some casting processes are net shape; others are near net shape

Can produce very large parts

Some casting methods are suited to mass production

1.1.5 Disadvantages of Casting

Limitations on mechanical properties

Poor dimensional accuracy and surface finish for some processes;

e.g., sand casting

Metal Casting Processes 1.3

Safety hazards to workers due to hot molten metals

Environmental problems

1.1.6 Parts made by Casting

Big parts -Engine blocks and heads for automotive vehicles, wood

burning stoves, machine frames, railway wheels, pipes, bells, pump

housings

Small parts-Dental crowns, jewelry, small statues, frying pans

All varieties of metals can be cast - ferrous and nonferrous

1.1.7 Mould in Casting

Mould contains a cavity whose geometry determines part shape.

Actual size and shape of cavity must be slightly oversized to allow

for shrinkage of metal during solidification and cooling.

Moulds are made of a variety of materials, including sand, plaster,

ceramic.

Moulds are in two forms namely (a) open mould, simply a

container in the shape of the desired part; and (b) closed mould,

in which the mould geometry is more complex and requires a

gating system (passageway) leading into the cavity. (Fig 1.2)

Moulds are of the following types

Expendable moulds – These moulds are mixed with various types of binders

or bonding agents eg. Sand , Plaster, Ceramic Moulds. These moulds are able

to withstand high temperatures and mould is broken up to remove the casting

Permanent moulds-are moulds made of metal. These moulds are subjected to

a higher cooling rate and affects grain size. These are used repeatedly and

casting can be removed easily.

Composite moulds - are moulds made of two or more materials like sand,

graphite, metal etc.,. These moulds combines advantages of each material and

are used to control cooling rates, improve mould strength and optimize

economics of the process.


1.2 SAND CASTING

Sand casting method involves pouring a molten metal into sand mould.

Sand casting, is a metal casting process characterized by using sand as the

mould material. It is relatively cheap. A suitable bonding agent (usually clay)

is mixed with the sand. The mixture is moistened with water to develop

.

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C ast m eta l

F lask

Sand

Sand m ou ld

Fig. 1.2 (a) Open mould

Fig. 1.2. Two forms of mould


strength and plasticity of the clay and to make the aggregate suitable for

moulding. The term “sand casting” can also refer to an object produced via

the sand casting process. Sand castings are produced in specialized factories

called foundries.

Sand casting consists of following basic steps

Placing of the pattern having the shape of the desired casting in

sand to make an imprint.

Incorporating of gating, runner and riser systems.

Filling the resultant cavity with molten metal.

Allowing solidification and cooling.

Breaking the sand mould and removing the casting.

Heat treating the casting to relieve the stresses.

Cleaning and finishing the casting.

Inspecting for the casting defects.

A typical sand casting operation for production of castings is shown

in the Fig 1.3

Sand

C asting

Furnaces So lid ificationShakeou tR em oval o f rise rs

and ga tes

D e fectsPre ssu re tigh tness

D im ensio ns

Additional H eat

treatm en t

- P attern m a king- C ore m aking- G a ting syste m

Fig. 1.3. Sand Casting operation for production of castings.


1.2.1 Advantages and disadvantages of sand casting

Advantages of sand casting

Low cost of mould materials and equipment.

Large casting dimensions may be obtained.

Wide variety of metals and alloys (ferrous and non-ferrous) can

be cast (including high melting point metals) using this method.

Disadvantages of sand casting

Rough surface.

Poor dimensional accuracy.

High machining tolerances.

Coarse Grain structure.

Limited wall thickness: not higher than 2.5 to 5 mm.

1.3 SAND MOULD

1.3.1 Features of Sand mould

A typical sand mould is shown in the Fig. 1.4. with the following

parts/features:

Fig.1.4. A Typical sand m ould.


Cope / Drag: The mould is made of two parts, the top half is called the

cope, and bottom part is the drag.

Mould cavity: The liquid flows into the gap between the two parts, called

the mould cavity.

Pattern: The geometry of the cavity is created by the use of a wooden shape, called

the pattern. The shape of the pattern is (almost) identical to the shape of the part

we need to make.

Sprue: A funnel shaped cavity at the top of the funnel is the pouring cup;

the pipe-shaped neck of the funnel is the sprue – the liquid metal is poured

into the pouring cup, and flows down the sprue.

Runners: The runners are the horizontal hollow channels that connect the

bottom of the sprue to the mould cavity. The region where the runner joins

with the cavity is called the gate.

Risers: Some extra cavities are made connecting to the top surface of the

mould. Excess metal poured into the mould flows into these cavities called

risers. They act as reservoirs; as the metal solidifies inside the cavity, it

shrinks, and the extra metal from the risers flows back down to avoid holes

in the cast part.

Vents: Vents are narrow holes connecting the cavity to the atmosphere to

allow gas and the air in the cavity to escape.

Cores: Many cast parts have interior holes (hollow parts), or other cavities

in their shape that are not directly accessible from either piece of the mould.

Such interior surfaces are generated by inserts called cores.

Cores are made by baking sand with some binder so that they can

retain their shape when handled. The mould is assembled by placing the core

into the cavity of the drag, and then placing the cope on top, and locking

the mould. After the casting is done, the sand is shaken off, and the core is

pulled away and usually broken off.

Chaplets: Chaplets are metal distance pieces inserted in a mould either to

prevent shifting of mould or to locate core surfaces. The distance pieces in

form of chaplets are made of parent metal of which the casting is. These are


placed in mould cavity suitably which positions core and to give extra support

to core and mould surfaces. Its main objective is to impart good alignment

of mould and core surfaces and to achieve directional solidification.

Chills: Chills are pieces of copper, brass or aluminium and are inserted into

the mould’s inner surface. Water passages in the mould or cooling fins made

on outside the mould surface are blown by air otherwise water mist will

create chilling effect. A chill is used to promote directional solidification.

1.3.2 Desirable Mould Properties and Characteristics

The desirable mould properties and characteristics are

Strength - to maintain shape and resist erosion

Permeability - to allow hot air and gases to pass through voids in

sand

Thermal stability - to resist cracking on contact with molten metal

Collapsibility - ability to give way and allow casting to shrink

without cracking the casting

Reusability - can be reused to make other moulds

Size and shape of sand :

Small grain size - Better surface finish Large grain size - To allow escape of gases during pouring Irregular grain shapes - Strengthen moulds due to interlocking

but reduces permeability

1.3.3 Steps/ Procedure for making sand mould for a two piece pattern

The steps involved in making a sand mould is discussed below:

(Fig. 1.5)

Selection of Mould box / Flask:Select a suitable size of moulding box for creating suitable wall

thickness for a two piece pattern. The moulding box must be of proper size

to adjust mould cavity, riser and the gating system (sprue, runner, and gates

etc.).

Preparation of Drag: Place the drag portion of the pattern with the parting surface down

on the bottom (ram-up) board as shown in Fig. 1.5 (a).


The facing sand is then sprinkled carefully all around the pattern

so that the pattern does not stick with moulding sand during

withdrawal of the pattern.

The drag is then filled with loosely prepared moulding sand and

ramming of the moulding sand is done uniformly in the moulding

box around the pattern. Fill the moulding sand once again and

then perform ramming. Repeat the process three four times.

The excess amount of sand is then removed using strike off bar

to bring moulding sand at the same level of the moulding flask

height to complete the drag.

Fig. 1.5 (a)

Fig. 1.5 (b)

Drag


The drag is then rolled over by 180 and the parting sand is

sprinkled over on the top of the drag [Fig. 1.5(b)].

Preparation of Cope: Now the cope pattern is placed on the drag pattern and alignment

is done using dowel pins.

Then cope (flask) is placed over the rammed drag and alignment

is done using the aligning pins.

Then the parting sand is sprinkled all around the cope pattern.

Sprue (runner) and riser pins are placed in vertical position at

suitable locations using the support of moulding sand. It will help

to form suitable size cavities for pouring molten metal etc.

[Fig. 1.5(c)]. They should not be located too close to the pattern

or mould cavity otherwise they may chill the casting

Now fill the cope with moulding sand and ram uniformly.

Strike off the excess sand from the top of the cope.

Remove sprue and riser pins and create vent holes in the cope

with a vent wire. The basic purpose of creating vent holes in cope

is to permit the escape of gases generated during pouring and

solidification of the casting.

Sprinkle parting sand over the top of the cope surface and roll

over the cope on the bottom board.

Fig. 1.5 (c)

Sprue pin Riser p in

Cope

Lug

Drag

Aligning P in

Pattern


Cutting of Gate & Pouring of Metal

Rap and remove both the cope and drag patterns and repair the

mould suitably if needed and dressing is applied

The gate is then cut connecting the lower base of sprue basin with

runner and the mould cavity.

Apply mould coating with a swab and bake the mould in case of

a dry sand mould.

Set the cores in the mould, if needed and close the mould by

inverting cope over drag.

The cope is then clamped with drag and the mould is ready for

pouring, [Fig. 1.5(d)].

1.4 CONSTITUENTS OF MOULDING SANDThe main constituents of moulding sand are Silica sand, Binder,

Moisture content and Additives.

1.4.1 Silica sand

Silica sand (SiO2) in the form of granular quartz is the main

constituent of moulding sand having enough refractoriness which

can impart strength, stability and permeability to moulding and

core sand.

Fig. 1.5. S teps/procedure for making a sand mould.

Fig. 1.5 (d)

Pouring bas in

G ate


Along with silica small amounts of iron oxide, alumina, lime stone,

magnesia, soda and potash are present as impurities.

The presence of excessive amounts of iron oxide, alkali oxides

and lime can lower the fusion point to a considerable extent which

is undesirable.

The silica sand can be specified according to the size (small, medium

and large silica sand grain) and the shape (angular, sub-angular and

rounded).

1.4.2 Binder

The binders are added to bind the silica sands and can be either

inorganic or organic substance.

The inorganic group includes clay, sodium silicate, port land

cement etc.

Organic groups are dextrin, molasses, cereal binders, linseed oil

and resins like phenol formaldehyde, urea formaldehyde etc.

Organic binders are mostly used for core making.

In foundry shop, the clay acts as binder which may be Kaolonite,

Ball clay, Fire clay, Limonite, Fuller’s earth and Bentonite (most

common). However, this clay alone cannot develop bonds among

sand grains without the presence of moisture in moulding sand

and core sand.

1.4.3 Moisture / Water

The amount of moisture content in the moulding sand varies

generally between 2 to 8 percent.

This amount is added to the mixture of clay and silica sand for

developing bonds. This is the amount of water required to fill the

pores between the particles of clay without separating them.

This amount of water is held rigidly by the clay and is mainly

responsible for developing the strength in the sand. The effect of

clay and water decreases permeability with increasing clay and

moisture content.


1.4.4 Additives

For increasing the moulding sand characteristics some other additional

materials besides basic constituents are added which are known as additives.

Additives are the materials generally added to the moulding and core sand.

Some commonly used additives for enhancing the properties of moulding and

core sands are discussed below.

1.4.4.1 Corn flour and Dextrin

It belongs to the starch family of carbohydrates and is used to

increase the collapsibility of the moulding and core sand.

It is completely volatilized by heat in the mould, thereby leaving

space between the sand grains. This allows free movement of sand

grains, which finally gives rise to mould wall movement and

decreases the mould expansion and hence defects in castings.

Corn sand if added to moulding sand and core sand improves

significantly strength of the mould and core.

1.4.4.2 Coal dust

Coal dust is added mainly for producing a reducing atmosphere

during casting.

This reducing atmosphere results in any oxygen in the pores

becoming chemically bound so that it cannot oxidize the metal.

It is usually added in the moulding sands for making moulds for

production of grey iron and malleable cast iron castings.

1.4.4.3 Sea coal and Pitch

Sea coal is the fine bituminous coal powder which occupies the pores

of the silica sand grains in moulding sand and core sand. It can be added

from 0.02 % to 2% in mould and core sand .When heated, it changes to

coke which fills the pores and is unaffected by water and does not allow the

sand to move. Thus, sea coal reduces the mould wall movement and the

permeability in mould and core sand and hence makes the mould and core

surface clean and smooth.


1.4.4.4 Wood flour

This is a fibrous material mixed with a granular material like sand;

its relatively long thin fibers prevent the sand grains from making

contact with one another.

It can be added from 0.05 % to 2% in mould and core sand.

It volatilizes when heated, thus allowing the sand grains to expand.

It will increase mould wall movement and decrease expansion

defects.

It also increases collapsibility of both mould and the core.

1.4.4.5 Silica flour

It is called as pulverized silica and it can be easily added up to

3% which increases the hot strength and finish on the surfaces of

the moulds and cores.

It also reduces metal penetration in the walls of the moulds and

cores.

1.5 TYPES OF MOULDING SANDS

1.5.1 Green sand

Green sand is tempered or natural sand.

It is prepared by mixing of silica sand with 18 to 30 percent clay

and moisture content from 6 to 8%.

The clay and water furnish the bond for green sand.

It is fine, soft, light, and porous.

Green sand is damp, when squeezed in the hand it retains the

shape and the impression given to it under pressure.

Moulds prepared by this sand do not require backing and hence

are known as green sand moulds.

This sand is easily available and at low cost.

It is commonly employed for production of ferrous and non-ferrous

castings.


1.5.2 Dry sand

Green sand that has been dried or baked in suitable oven after the

making mould and core is called dry sand.

It possesses more strength, rigidity and thermal stability.

It is mainly suitable for larger castings.

Moulds prepared in this sand are known as dry sand moulds.

1.5.3 Loam sand

Loam is mixture of sand and clay with water to a thin plastic

paste.

Loam sand possesses high clay as much as 30-50% and 18% water.

Patterns are not used for loam moulding and shape is given to

mould by sweeps.

This is particularly employed for loam moulding used for large

grey iron castings.

1.5.4 Facing sand

Facing sand is just prepared and forms the face of the mould. It

is directly applied next to the surface of the pattern and it comes

into contact with molten metal when the mould is poured.

Initial coating around the pattern and hence for mould surface is

given by this sand.

This sand is subjected to the most severe conditions and therefore

must possess high strength refractoriness.

It is made of silica sand and clay, without the addition of any

used sand.

Different forms of carbon are used to prevent the metal burning

into the sand.

A facing sand mixture for green sand moulding of cast iron may

consist of 25% fresh and specially prepared sand 70% old sand

and 5% sea coal. They are sometimes mixed with 6-15 times as

much fine moulding sand to make facings.


1.5.5 Backing sand

Backing sand (or) floor sand is used to back up the facing sand

and is used to fill the whole volume of the moulding flask.

Used moulding sand is mainly employed for this purpose.

The backing sand is sometimes called black sand because it is old

and repeatedly used. Moulding sand is black in color due to

addition of coal dust and burning caused on coming in contact

with the molten metal.

1.5.6 System sand

In mechanized foundries where machine moulding is employed, a

so-called system sand is used to fill the whole moulding flask.

In mechanical sand preparation and handling units, no facing sand

is used. The used sand is cleaned and re-activated by the addition

of water and special additives. This is known as system sand.

Since the whole mould is made of this system sand, the properties

such as strength, permeability and refractoriness of the moulding

sand must be higher than those of backing sand.

1.5.7 Parting sand

Parting sand without binder and moisture is used to keep the green

sand not to stick to the pattern and also to allow the cope and drag to separate

without clinging. This is clean clay-free silica sand which serves the same

purpose as parting dust.

1.5.8 Core sand

Core sand is used for making cores and it is sometimes known as oil

sand. This is highly rich silica sand mixed with oil binders such as core oil

which is composed of linseed oil, resin, light mineral oil and other binding

materials. Pitch (or) flours and water may also be used in large cores for the

sake of economy.


1.6 MOULDING SAND PROPERTIESThe basic properties required in moulding sand and core sand are

described below.

1.6.1 Refractoriness

Refractoriness is defined as the ability of moulding sand to

withstand high temperatures without breaking down (or) fusing

thus facilitating to get a sound casting.

It is a highly important characteristic of moulding sands.

Refractoriness can only be increased to a limited extent.

Moulding sand with poor refractoriness may burn on to the casting

surface and no smooth casting surface can be obtained.

The degree of refractoriness depends on the SiO2 i.e. quartz

content, and the shape and grain size of the particle. The higher

the SiO2 content and the rougher the grain volumetric composition,

the higher is the refractoriness of the moulding sand and core sand.

Refractoriness is measured by the sinter point of the sand rather

than its melting point.

1.6.2 Permeability

It is also termed as porosity of the moulding sand in order to

allow the escape of any air, gases or moisture present or generated

in the mould when the molten metal is poured into it.

All the gases generated during pouring and solidification process

must escape otherwise the casting becomes defective.

Permeability is a function of grain size, grain shape, moisture and

clay contents in the moulding sand.

The extent of ramming of the sand directly affects the permeability

of the mould.

Permeability of mould can be further increased by venting using

vent rods.


1.6.3 Cohesiveness

It is a property of moulding sand by virtue of which the sand grain

particles interact and attract each other within the moulding sand. Thus, the

binding capability of the moulding sand gets enhanced to increase the green,

dry and hot strength property of moulding and core sand.

1.6.4 Green strength

The green sand, after water has been mixed into it, must have

sufficient strength and toughness to permit the making and

handling of the mould. For this, the sand grains must be adhesive,

i.e. they must be capable of attaching themselves to another body.

Therefore sand grains having high adhesiveness will cling to the

sides of the moulding box.

By virtue of this property, the pattern can be taken out from the

mould without breaking the mould and also the erosion of mould

wall surfaces does not occur during the flow of molten metal.

The green strength also depends upon the grain shape and size,

amount and type of clay and the moisture content.

1.6.5 Dry strength

As soon as the molten metal is poured into the mould, the moisture

in the sand layer adjacent to the hot metal gets evaporated and

this dry sand layer must have sufficient strength to its shape in

order to avoid erosion of mould wall during the flow of molten

metal.

The dry strength also prevents the enlargement of mould cavity

caused by the metallostatic pressure of the liquid metal.

1.6.6 Flowability (or) plasticity

It is the ability of the sand to get compacted and behave like a

fluid. It will flow uniformly to all portions of pattern when

rammed and distribute the ramming pressure evenly all around in

all directions.

Generally sand particles resist moving around corners (or)

projections.


In general, flowability increases with decrease in green strength

and decrease in grain size.

The flowability also varies with moisture and clay content.

1.6.7 Adhesiveness

It is property of moulding sand that allows it to stick or adhere with

foreign materials also with inner wall of moulding box.

1.6.8 Collapsibility

After the molten metal in the mould gets solidified, the sand mould

must be collapsible so that free contraction of the metal occurs

and this would naturally avoid the tearing or cracking of the

contracting metal.

In absence of this property the contraction of the metal is hindered

by the mould and thus results in tears and cracks in the casting.

This property is highly desired in cores

1.6.9 Classification of Moulding Processes

Moulding processes can be classified as

(i) Classification based on the method used

Bench moulding, Floor moulding, Pit moulding., Machine moulding.

(ii) Classification based on the mould material used:

Green sand moulding, Dry sand moulding, Skin dried moulding, Core

sand moulding, loam moulding, Carbon-dioxide moulding, Shell moulding,

Plaster moulding, Metallic moulding and Loam moulding Some of the

important moulding methods are discussed below.

1.6.9.1 Bench Moulding

This type of moulding is preferred for small jobs. The whole moulding

operation is carried out on a bench of convenient height. In this process, a

minimum of two flasks, namely cope and drag moulding flasks are necessary.

But in certain cases, the number of flasks may increase depending upon the

number of parting surfaces required.


1.6.9.2 Floor Moulding

This type of moulding is preferred for medium and large size jobs. In

this method, only drag portion of moulding flask is used to make the mould and

the floor itself is utilized as drag and it is usually performed with dry sand.

1.6.9.3 Pit Moulding

Usually large castings are made in pits instead of drag flasks because

of their huge size. In pit moulding, the sand under the pattern is rammed by

bedding-in process. The walls and the bottom of the pit are usually reinforced

with concrete and a layer of coke is laid on the bottom of the pit to enable

easy escape of gas. The coke bed is connected to atmosphere through vent

pipes which provide an outlet to the gases. One box is generally required to

complete the mould, runner, sprue, pouring basin and gates are cut in it.

1.6.9.4 Machine Moulding

For mass production of the casting, the general hand moulding

technique proves un-economical and in-efficient. The main advantage of

machine moulding, besides the saving of labor and working time, is the

accuracy and uniformity of the castings and

or even the cost of machining on the casting can be reduced drastically

because it is possible to maintain the tolerances within narrow limits on

casting by using machine moulding method. Moulding machines thus prepare

the moulds at a faster rate and also eliminate the need of employing skilled

moulders. The main operations performed by moulding machines are ramming

of the moulding sand, roll over the mould, form gate, rapping the pattern and

its withdrawal.

1.6.9.5 Loam Moulding

Loam moulding uses loam sand to prepare a loam mould. It is such

a moulding process in which use of pattern is avoided and hence it differs

from the other moulding processes. Initially the loam sand is prepared with

the mixture of moulding sand and clay made in form of a paste by suitable

addition of water. Firstly a rough structure of cast article is made by hand

using bricks and loam sand and it is then given a desired shape by means

of strickles and sweep patterns. Mould is thus prepared. It is then baked to


give strength to resist the flow of molten metal. This method of moulding is

used where large castings are required in numbers. Thus it enables the

reduction in time, labor and material which would have been spent in making

a pattern. But this system is not popular for the reason that it takes lots of

time in preparing mould and requires special skill. The cope and drag part

of mould are constructed separately on two different iron boxes using different

sizes of strickles and sweeps etc. and are assembled together after baking. It

is important to note that loam moulds are dried slowly, completely and are

used for large regular shaped castings like chemical pans, drums etc.

1.6.9.6 Dry sand moulding

Dry moulding sand differs from the green moulding sand in the

sense that it contains binders (like clay, bentonite, molasses etc.)

which harden when the mould is heated and dried.

A typical dry sand mixture (for making non-ferrous castings)

consists of new silica sand 30%, coal dust 20% and bentonite 10%

A dry sand mould is prepared in the same manner as a green sand

mould; however it is baked at 300 to 70F for 8 to 48 hours

depending upon binders used and the amount of sand surface to

be dried.

Drying of moulds can be of two types: skin dried and complete

mould drying. Common methods of drying the mould are hot air

and gas or oil flame. Skin drying is accomplished with the aid of

torches directed at the mould surface.

Advantages

Dry sand moulds possess high strength.

They are more permeable as compared to green sand moulds.

Castings produced from dry sand moulds possess clean and smooth

surfaces.

As compared to green sand moulding, dry sand moulding turns

out castings with less defects.

Dry sand moulding imparts better overall dimensional accuracy to

the moulds and castings as compared to green sand moulding.


Disadvantages

Dry sand moulding involves more labour and consumes more time

in completing the mould. Mould baking is an extra work as

compared to that required in green sand moulding.

Dry sand moulding is more expensive as compared to green sand

moulding.

Dry sand moulding involves chances of hot tears occurring in the

castings.

Because of baking, a mould may distort.

Dry sand moulding involves a longer processing cycle as compared

to green sand moulding.

Dry sand moulding gives a slower rate of production as compared

to green sand moulding.

Applications

Dry sand moulding is used for making medium to large size ferrous

castings such as Large rolls, Housings, Gears, Machinery components.

1.6.9.7 Skin-dried moulding

A skin-dried mould is intermediate between green sand mould and dry

sand mould. Whereas a dry sand mould has its entire surface dried, a skin

dried mould has its (6 to 25 mm) skin dried.

Moisture of the skin is removed either by storing the mould for some

time or with a gas torch. It has some advantages of both green and dry sand

moulding. It is used for large moulds and moulds for pit moulding.

1.6.10 Hand Tools Used In Foundry Shop (Fig 1.6 (a to n))

Hand riddle

Hand riddle consists of a screen of standard

circular wire mesh equipped with circular wooden

frame used for cleaning the sand for removing

foreign material. Fig. 1.6 (a).

Fig. 1 .6 (a) Hand riddle


Shovel

Shovel consists of a steel pan fitted with a long

wooden handle. It is used for mixing, tempering,

moving and conditioning the foundry sand by hand.

Fig. 1.6 (b).

Rammers

Rammers are required for striking the

moulding sand mass in the moulding box to pack

or compact it uniformly all around the pattern. The

common forms are hand rammer, peen rammer, floor

rammer and pneumatic rammer. Fig. 1.6 (c).

Sprue pin

Sprue pin is a tapered rod of wood or iron

which is placed or pushed in cope to join mould

cavity while the moulding sand in the cope is being

rammed. Later, its withdrawal from cope produces

a vertical hole in moulding sand called sprue through

which the molten metal is poured into the mould

using gating system. Fig. 1.6 (d).

Strike off bar

Strike off bar is a flat bar having

straight edge and is made of wood or iron.

It is used to strike off or remove the

excess sand from the top of a moulding

box after completion of ramming.

Fig. 1.6 (e).

Mallet

Mallet is similar to a wooden hammer and is generally used in

carpentry or sheet metal shops.

Fig. 1.6(b) Shovel

Fig. 1.6(c) Rammer

Fig. 1.6(d) Sprue pin

Fig. 1.6 (e) Strike o ff Bar


Draw spike

Draw spike is a tapered steel rod having a

loop or ring at its one end and a sharp point at

the other. It may have screw threads on the end to

engage metal pattern for its withdrawal from the

mould. It is driven into pattern which is embedded

in the moulding sand and raps the pattern to get separated from the mould

cavity and finally draws it out from the mould cavity. Fig. 1.6 (f).

Vent rod

Vent rod is a thin spiked steel rod

or wire carrying a pointed edge at one end

and a wooden handle or a bent loop at the

other. It is utilized to pierce series of small holes in the moulding sand called

vent holes which allow the exit or escape of steam and gases. Fig. 1.6 (g).

Lifters

Lifters are also known as cleaners

or finishing tool which are used for

cleaning, repairing and finishing the

bottom and sides of deep and narrow

openings in mould cavity after withdrawal

of pattern. They are also used for removing loose sand from mould cavity.

Fig. 1.6 (h).

Trowels

Trowels are utilized for finishing flat

surfaces and joints and parting lines of the

mould. The trowels are basically employed for

smoothening or slicking the surfaces of

moulds. They may also be used to cut in-gates

and repair the mould surfaces. Fig. 1.6 (i).

Fig. 1.6 (f) Draw Spike

Fig. 1.6 (g ) Vent rod

Fig. 1.6 (h) Lifters

Fig. 1.6 (i) Trowels


Slicks

Slicks are small double ended

mould finishing tool which are generally

used for repairing and finishing the mould

surfaces and their edges after withdrawal

of the pattern. Fig. 1.6 (j).

Smoothers

Smoothers are finishing tools which are

commonly used for repairing and finishing flat

and round surfaces, round or square corners and

edges of moulds. Fig. 1.6 (k).

Swab

Swab is a small hemp fiber brush used for

moistening the edges of sand mould, which are

in contact with the pattern surface before

withdrawing the pattern. It is used for sweeping

away the moulding sand from the mould surface

and pattern. It is also used for coating the liquid

blacking on the mould faces in dry sand moulds.

Fig. 1.6 (l).

Spirit level

Spirit level is used by moulder to check whether the sand bed or

moulding box is horizontal or not.

Gate cutter

Gate cutter is a small shaped piece

of sheet metal commonly used to cut

runners and feeding gates for connecting

sprue hole with the mould cavity.

Fig. 1.6 (j) Slicks

Fig. 1.16 (k) Smoothers

Fig. 1.16(l) Swab

Fig. 1.6 (m ) Gate Cutter


GaggersGaggers are pieces of wires or rods bent at one or both ends which

are used for reinforcing the downward projecting sand mass in the cope. They

support hanging bodies of sand.

Spray-gunSpray gun is mainly used for spray coating of facing materials etc. on

a mould or core surface.

Nails and wire piecesThey are basically used to reinforce thin projections of sand in the

mould or cores.

BellowsBellows gun is a hand operated

leather made device equipped with

compressed air jet to blow or pump air

when operated. It is used to blow away

the loose or unwanted sand from the

surfaces of mould cavities. Fig. 1.6 (n).

Clamps, cotters and wedges

They are made of steel and are used for clamping the moulding boxes

firmly together during pouring.

FlasksThe common flasks are also called as containers which are used in

foundry shop as mould boxes, crucibles and ladles.

Moulding BoxesMould boxes are also known as moulding flasks. Boxes used in sand

moulding are of two types:

Open moulding boxes. Open moulding boxes are shown in Fig. 1.6(p) They are made with the hinge at one corner and a lock on the opposite

corner. A snap moulding is made of wood and is hinged at one corner. It

has special applications in bench moulding in green sand work for small

non-ferrous castings The size, material and construction of the moulding box

depends upon the size of the casting.

Fig. 1.6 (n ) Bellows


Closed moulding boxes. Closed moulding boxes are shown in Fig. 1.6(q) which may be made of wood, cast-iron or steel and consist of two or

more parts. The lower part is called the drag, the upper part the cope and

all the intermediate parts, if used, cheeks. All the parts are individually

equipped with suitable means for clamping arrangements during pouring.

Wooden Boxes are generally used in green-sand moulding. Dry sand moulds

always require metallic boxes because they are heated for drying. Large and

heavy boxes are made from cast iron or steel and carry handles and grips as

they are manipulated by cranes or hoists, etc.

Crucible and ladles

Crucibles are made from graphite or steel shell lined with suitable

refractory material like fire clay. They are commonly named as metal melting

pots. The raw material or charge is broken into small pieces and placed in

them. Metals are melted in crucibles, they are taken out and received in

crucible handle. Pouring of molten metal is generally done directly by them

instead of transferring the molten metal to ladles. But in the case of an oilfired

furnace, the molten metal is first received in a ladle and then poured into

the moulds. Fig 1.7.

Hinge

(p)

Drag

Cope

Lugs

(q)

Fig.1.6. ) Open moulding box ) C losed (p (q moulding box.


1.7 MOULDING SAND TESTING

Moulding sand and core sand depend upon shape, size, composition

and distribution of sand grains, amount of clay, moisture and additives.

1.7.1 Need for sand testing

The increase in demand for good surface finish and higher

accuracy in castings necessitates certainty in the quality of mould

and core sands.

Sand testing often allows the use of less expensive local sands.

It also ensures reliable sand mixing and enables a utilization of

the inherent properties of moulding sand.

Sand testing on delivery will immediately detect any variation from

the standard quality and adjustment of the sand mixture to specific

requirements so that the casting defects can be minimized.

It allows the choice of sand mixtures to give a desired surface

finish.

Thus sand testing is one of the dominating factors in foundry and

pays for itself by obtaining low unit cost and mould increased

production resulting from sound castings.

Generally the following tests are performed to judge the moulding and

casting characteristics of foundry sands:

Pouringspout

Hook fo r craneGear box

fo r pouring

Turnhandle

Handles

Top view

Fron t v iew

(a) (b)Fig.1 .7 Crucib le & Ladles

(a) Crane ladle, and (b) Two-m an ladle .


Moisture content Test

Clay content Test

Chemical composition of sand

Grain shape and surface texture of sand.

Grain size distribution of sand

Specific surface of sand grains

Water absorption capacity of sand

Refractoriness of sand

Strength Test

Permeability Test

Flowability Test

Shatter index Test

Mould hardness Test.

1.7.2 Moisture Content Test

The moisture content of the moulding sand mixture may be determined

by drying a weighed amount of 20 to 50 grams of moulding sand to a constant

temperature up to 100C in an oven for about one hour. It is then cooled to

room temperature and then the moulding sand is reweighed. The moisture

content in moulding sand is thus evaporated. The loss in weight of moulding

sand due to loss of moisture, gives the amount of moisture which can be

expressed as a percentage of the original sand sample.

% Moisture Content of Sand

Weight of wet sand Weight of heated/cooled sand

Weight of wet sand 100

The percentage of moisture content in the moulding sand can also be

determined in fact more speedily by an instrument known as a speedy

moisture teller. This instrument is based on the principle that when water and

calcium carbide react, they form acetylene gas which can be measured and

this will be directly proportional to the moisture content. This instrument is

provided with a pressure gauge calibrated to read directly the percentage of

moisture present in the moulding sand.

CaC2 2H2O CaOH2 C2H2


Calcium carbide Water Calcium hyrdroxide Acetylene

Some moisture testing instruments are based on principle that the

electrical conductivity of sand varies with moisture content in it.

1.7.3 Clay Content Test

The clay content of the sand is determined as follows,

Take 50 gms of dry moulding sand and transfer to a wash bottle.

Add 475 cc of distilled water and 25 cc of 35 % NaOH solution

and agitate with a stirrer for 10 minutes.

Fill the water bottle with water upto mark. After the sand is settled

down drain out the water (clay is dissolved in water and is

removed). Repeat the above step for 7 times to ensure complete

removal of clay.

Dry the settled sand and weigh it say A gms.

Weight of clay 50 – A gms.

% content of clay 50 A/50 100

1.7.4 Grain Fineness Test (GFT)

GFT determines the grain size, distribution and grain fineness.

For carrying out grain fineness test a sample of dry silica sand

weighing 50 gms free from clay is placed on the top most sieve

bearing U.S. series equivalent number 6.

A set of eleven sieves having U.S. Bureau of standard meshes 6,

12, 20, 30, 40, 50, 70, 100, 140, 200 and 270 are mounted on a

mechanical shaker (Fig. 1.8).

The topmost sieve is coarsest and bottom most finest and the

inbetween sieves are in order of fineness from top to bottom.

The above setup is vibrated for 15 minutes.

After this weight of sand retained in each sieve is obtained and

percentage distribution of grains is computed.

To obtain the AFS (American Foundry Society) grain fineness

number, each % is multiplied by a factor. The resulting products

are added and divided by total percentage of sand grain retained.


AFS grain fineness number = Sum of products / Total sum of the % of

sand retained on pan and each sieve.

1.7.5 Refractoriness Test

The refractoriness of the moulding sand is judged by heating the

American Foundry Society (A.F.S) standard sand specimen to very

high temperature ranges (1300C) depending upon the type of

sand.

Timer

Adjusting K nobClam ping strip

Side flex ib le bar

Set o f s ieve

Toggle sw itch

Levellingscrew

Indica to rlam p

Spring

Bum per

Pannel

Base

Fig.1.8. Grain fineness testing mechanical shaker.


The heated sand specimens pieces are cooled to room temperature

and examined under a microscope for surface characteristics or by

scratching it with a steel needle.

A good refractory sand retains the shape and shows very little (<

7%) expansion. A less refractory specimen will shrink and distort.

1.7.6 Flowability Test

Flowability is the ability of sand to take up the desired shape. Sand

must be able to transmit the blows throughout during ramming.

Flowability test setup is shown in the Fig. 1.9.

A standard sand/core specimen is prepared. The flowability

measurement device setup consists of a ramplunger, a flow dial indicator

whose stem rest on top of plunger, a standard prepared specimen and

supporting stand/table.

Ram plunger is dropped on the standard specimen for five times. The

movement of the plunger between the fourth and fifth drop (x) is measured

on the dial which is calibrated to give the flowability of the sand/core.

Plunger

Flow indica tor

Stem

Stand

X

1 dropst

4 dropth

5th drop

Standard specim en

Table

Ram

Fig 1.9 Flowability test


1.7.7 Shatter Index Test

In this test, the A.F.S. standard sand specimen is rammed usually by

10 blows and then it is allowed to fall on a half inch mesh sieve from a

height of 6 ft. The weight of sand retained on the sieve is weighed. It is

then expressed as percentage of the total weight of the specimen which is a

measure of the shatter index.

1.7.8 Strength Test

Green strength and dry strength is the holding power of the various

bonding materials.

The most commonly performed test is compression test which is

carried out in a compression sand testing machine (Fig. 1.10).

Generally sand mixtures are tested for their compressive strength,

shear strength, tensile strength, transverse tests and bending

strength.

For carrying out these tests on green sand sufficient rammed

samples are prepared. The process of preparing sand specimen for

testing dry sand is similar to the process as prepared before, with

the difference that a split ram tube is used. The specimen for

testing bending strength is of a square cross section.

........ .... ...

..... ........

......... ......

.............

......

... ......

............. . ..

.....

... ... .... .

Lugs

H igh PressureM anom eter

Low P ressureM anom eter

Ad justing C ock

D ia l G auge

Peep Ho leM olding Sand

S pecimen

Fig. 1.10 Strength testing Machine.

Hand whee l


The various tests can be performed on strength tester as follows:

The specimen is placed between the grips.

Hand wheel when rotated actuates a mechanism which builds

hydraulic pressure.

The dial indicator measures the deformation occurring in the

specimen.

There are two indicators. One is meant for testing low strength

moulding sand and the other relatively high strength core sand.

Each indicator has three scales one for reading compressive

strength, the other two for recording tensile (or transverse) and

shear strength respectively.

The compression strength of the moulding sand is determined by

placing standard specimen at specified location and the load is

applied on the standard sand specimen to compress it by uniformly

increasing load by rotating the hand wheel of compression strength

testing setup.

As soon as the sand specimen fractures for break, the compression

strength is measured by the manometer.

Also, other strength tests can be conducted by adopting special

types of specimen holding accessories.

1.7.9 Mould Hardness TestThis test is performed by a mould hardness tester shown in Fig. 1.11.

The working of the tester is based on the principle of Brinell hardness

testing machine. In an A.F.S. standard hardness tester a half inch diameter

steel hemi-spherical ball is loaded with a spring load of 980 gm.

This ball is made to penetrate into the mould sand or core sand surface.

The penetration of the ball point into the mould surface is indicated on a

dial in thousands of an inch. The dial is calibrated to read the hardness

directly i.e. a mould surface which offers no resistance to the steel ball would

have zero hardness value and a mould which is more rigid and is capable of

completely preventing the steel ball from penetrating would have a hardness

value of 100. The dial gauge of the hardness tester may provide direct

readings.


1.7.10 Permeability Test

Initially a predetermined amount of moulding sand is being kept in a

standard cylindrical tube and then moulding sand is compressed using slightly

tapered standard ram till the cylindrical standard sand specimen having

50.8mm diameter with 50.8 mm height is made and it is then extracted from

the cylindrical tube.

This specimen is used for testing the permeability or porosity of

moulding and the core sand.

The test is performed in a permeability meter consisting of the balanced

tank, water tank, nozzle, adjusting lever, nose piece for fixing sand specimen

and a manometer. A typical permeability meter is shown in Fig. 1.12 which

permits to read the permeability directly.

Plastic sleeve

M etallic s leeve

Need le

Dial

R ing

Tip

Fig. 1.11 Mould hardness tester


The permeability test apparatus consists of two concentric cylinder one

inside the other. The space between the two concentric cylinders is filled with

water. A bell having a diameter larger than that of the inner cylinder but

smaller than that of outer cylinder, rests on the surface of water.

Standard sand specimen together with ram tube is placed on the tapered

nose piece of the permeability meter. The bell is allowed to sink under its

own weight by the help of multi-position cock. In this way the air of the

bell streams through the nozzle of nosepiece and the permeability is directly

measured.

Permeability is volume of air (in cm3) passing through a sand specimen

of 1 cm2 cross-sectional area and 1 cm height, at a pressure difference of 1

gm/cm2 in one minute. In general, permeability is expressed as a number and

can be calculated from the relation:

Permeability (P) = vh/pat

Where

P Permeability; v = volume of air passing through the specimen in c.c.;

h Height of specimen in cm; p = pressure of air in gm/cm2; a =cross-sectional area of the specimen in cm2; t = time in minutes.

Ba lanced tank

W ate r tank

N ozzle ad justing lever

N ose p iece fo r fix in gsand specim en tube

D ia l m ete r

Specim en tube

M ou ld ing sand sam p le

Pressurem anom ete r

M ercu ry sea l

Variab le nozz leA ir

passag e

Ba lanced tank

.. ... . ..... .. . ... . . .. .. ... ... ... . .... .. . ... . .. .. ... ... ... . .... .. . ... . .. .. ... ... ... . .... .. . ... . .. .. ... .

..... ... . .... .. . ... . .. .. ... . ... ... . .... .. . ... . .. .. ... . ... ... . .... .. . ... . .. .. ... . .

.. ... . .... .. . .. ..

Be ll

Fig. 1.12 Permeability m eter


For A.F S. standard permeability meter, 2000 cc of air is passed

through a sand specimen (5.08 cm in height and 20.268 sq.cm. in

cross-sectional area) at a pressure of 10 gms/cm2 and the total time measured

is 10 seconds = 1/6 min. Then the permeability is calculated using the

relationship as given below.

P 2000 5.08/10 20.268 1/6 300.66 App.

1.8 PATTERN

A pattern is a model or the replica of the object (to be casted) except

for the various allowances. It is embedded in moulding sand and suitable

ramming of moulding sand around the pattern is made. The pattern is then

withdrawn for generating cavity (known as mould) in moulding sand. Thus

it is a mould forming tool. When this mould/cavity is filled with molten

metal, molten metal solidifies and produces a casting (product).

The quality of the casting produced depends upon the material of the

pattern, its design, and construction. It should have finished and smooth

surfaces for reducing casting defects.

Pattern may also possess projections known as core prints for producing

extra recess in the mould for placement of core to produce hollowness in

casting.

Pattern establishes the parting line and parting surfaces in the mould.

It may help to position a core in case a part of the mould cavity is made

with cores.

1.8.1 Functions of the Pattern

A pattern prepares a mould cavity for the purpose of making a

casting.

A pattern may contain projections known as core prints if the

casting requires a core and need to be made hollow.

Runner, gates, and risers used for feeding molten metal in the

mould cavity may form a part of the pattern.

Patterns properly made and having finished and smooth surfaces

reduce casting defects.


A properly constructed pattern minimizes the overall cost of the

castings.

It establishes the parting line and parting surfaces in the mould.

1.8.2 TYPES OF PATTERN

The different types of pattern are given below

(a) One piece (or) solid pattern

Solid pattern is made of

single piece without joints,

parting lines or loose pieces.

It is the simplest form of the

pattern. Typical single piece

pattern is shown in

Fig. 1.13.

It is inexpensive and is used for making a few large sized simple

castings.

It is usually made of wood or metal depending upon number of

castings.

It is placed either in cope or drag.

Example: Stuffing box of Steam engine can be cast from single

piece pattern.

(b) Two piece (or) split pattern

Fig. 1.13. Single Piece Pattern.

Dowel holes

Dowel holes

Fig.1.14. Split P iece Pattern


Pattern of intricate shapes made by single piece pattern are difficult

to withdraw from the mould cavity, hence solid pattern is split

into two parts. Fig 1.14

Split pattern is made in two pieces which are joined at the parting

line by means of dowel pins.

The splitting at the parting line is done to facilitate the withdrawal

of the pattern.

One part is placed in cope & the other in drag

Example are taps, water stop cocks etc.,

(c) Loose piece pattern

Loose piece pattern (Fig. 1.15) is used when pattern is difficult for

withdrawal from the mould.

Loose pieces are provided on the pattern (E & F) and they are

attached to pattern by dowel pins.

The main pattern is removed first leaving the loose piece portion

of the pattern in the mould.

Finally the loose piece is withdrawn separately leaving the intricate

mould.

It requires more labour & is a time consuming process.

E F

M ain pattern

Dow elPins

Fig. 1.15 Loose Piece Pattern .


(d) Cope and drag pattern

In this case, cope and drag part of the mould are prepared

separately. (Fig 1.16)

It is another form of Split pattern.

The Pattern is split about a convenient and suitable Surface or

line.

This is done when the complete mould is too heavy to be handled

by one operator.

The pattern is made up of two halves, which are mounted on

different plates by an independent moulder.

It is used for producing big casting.

(e) Match plate pattern

This pattern is made in two halves and is mounted on the opposite

sides of a wooden or metallic plate, known as match plate.

(Fig 1.17)

A number of different size and shape pattern can be attached to

one match plate.

Cope Patte rn

Drag Pattern

Fig. 1.16 Cope & Drag Pattern.


The match plate is clamped to drag with the help of locator holes.

The gates and runners are also attached to the plate.

This pattern is used in machine moulding.

It is used to produce small casting in mass scale with high

accuracy and at faster rate.

Eg. Piston rings of IC – Engine

(f) Three-piece or multi- piece pattern

Some patterns are of complicated kind in shape and hence cannot be

made in one or two pieces because of difficulty in withdrawing the pattern.

Therefore these patterns are made in either three pieces or in multi-pieces.

Multi moulding flasks are needed to make mould from these patterns.

(Fig 1.18)

R unnerPa tte rns

M atch p la te

H o le fo r locating

Fig. 1.17 M atch P late Pattern

..

.

.

.. .

..

.

.

.. .

. . ..

. . .. .

..

.. ..

.... .

..

..

. ..

. .

..

.. . .

.. .

..

..

..

.

..

.

. .

..

.

..

.

.

.

... .

.

.

. .

..

. .

...

. .. ..

...

....

...

.

..

.

..

..

..

...

..

. ..

.. .

.

1

2

3

C heek

M ou ld ing BoxC ope

Pa rt/C ast

D rag

Fig. 1.18. Three Piece Pattern.


(g) Follow board pattern

A contour corresponding to the exact shape of one half of the

pattern is made in a wooden board which is called a follow board.

(Fig. 1.19)

It is used for supporting a pattern which is very thin and fragile

and which may give way and collapse under pressure when the

sand above the pattern is being rammed.

In addition to supporting a thin section a follow board forms the

natural parting line of the mould or the casting.

(h) Gated pattern

Sand

Pattern

Follow board

Fig.1.19. Follow Board Pattern.

G ate

Pa tte rns

Runner

Fig. 1.20. Gated Pattern.


In the mass production of castings, multi cavity moulds are used.

Such moulds are formed by joining a number of patterns and gates

and providing a common runner for the molten metal, as shown

in Fig. 1.20.

These patterns are made of metals and metallic pieces to form

gates and runners are attached to the pattern.

A gated casting produce many castings at one time and are used for

mass production of small castings.

(i) Sweep pattern

Sweep patterns are used for forming large circular moulds of

symmetric kind by revolving a sweep attached to a spindle as

shown in Fig. 1.21.

Actually a sweep is a template of wood or metal and is attached

to the spindle at one edge and the other edge has a contour

depending upon the desired shape of the mould.

The pivot end is attached to a stake of metal in the center of the mould.

A sweep pattern can be used for both green & dry sand moulding.

... ... ...

....... ... ...

....... ... ...

....... ... ...

....... ... .......

... ... ...

....... ... .. .

....

... ... .. .

....... ... ...

....... ... ...

....... ... ...

....

... ... ...

....... ... ...

....... ... ...

....... ... ...

....

... ... ...

....

... ... ...

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....... ... ...

....

... ... .......

... ... ...

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Po st

Sw e ep

G reen san d

Fig.1.21 S weep Pattern.


(j) Skeleton pattern

A skeleton pattern is the skeleton of desired shape which may be a

S-bend or a chute or something else. The skeleton is made from wooden

strips and is thus a wooden frame work. When only a small number of large

and heavy castings are to be made, it is not economical to make a solid

pattern. In such cases, however, a skeleton pattern may be used. This is a

ribbed construction of wood which forms an outline of the pattern to be made.

This frame work is filled with loam sand and rammed. The surplus sand is

removed by strickle board. For round shapes, the pattern is made in two

halves which are joined with glue or by means of screws etc.

(k) Segmental (or) part pattern

Patterns of this type are generally used for circular castings, for

example wheel rim, gear blank etc. Such patterns are sections of a pattern

so arranged as to form a complete mould by being moved to form each

Pivo t

Fig.1.22. Segm ental (or) part pattern.


section of the mould. The movement of segmental pattern is guided by the

use of a central pivot.

A segment pattern for a wheel rim is shown in Fig. 1.22.

1.8.3 Design Considerations for a good Pattern

A good pattern produces a sound casting and a poor pattern will

produces poor castings. The following are design considerations for a good

pattern.

A pattern should be accurate in its dimensions and posses very

good surface finish.

Proper material selection of pattern.

A pattern should carry all proper allowances.

In split pattern, parting surface should be such that maximum

portion of pattern is in drag.

All sharp edges and corners should be rounded.

Changes in the section thickness should be smooth, gradual and

uniform. It reduces stresses, strains and minimizes crack formation.

Type of Pattern selection should be proper.

Jointed core should be avoided to obtain uniform holes.

Core prints provided with pattern should be of optimum size and

suitably located.

All patterns for repeat orders should be coated with preservatives.

1.8.4 PATTERN MATERIALS

Patterns may be constructed from the following materials. Each

material has its own advantages, limitations, and field of application. Some

materials used for making patterns are: wood, metals and alloys, plastic,

plaster of Paris, plastic and rubbers, wax, and resins.

Wood

Wood is the most popular and commonly used material for pattern

making. The main varieties of woods used in pattern-making are shisham,

kail, deodar, teak and mahogany.


Advantages of wooden patterns

Wood is cheap, easily available in abundance, repairable and easily

fabricated in various forms using resin and glues.

It is very light and can produce highly smooth surface.

It can preserve its surface by application of a shellac coating for

longer life of the pattern.

Disadvantages

Wood is susceptible to shrinkage and warpage and its life is short.

It is highly affected by moisture of the moulding sand.

After some use it warps and wears out quickly as it is having less

resistance to sand abrasion.

It cannot withstand rough handling and is weak in comparison to

metal.

Wooden patterns are preferred only when the number of castings

to be produced is less.

Metal Pattern

Metallic patterns are preferred when the number of castings required

is large. The wear and tear of this pattern is very less and hence posses

longer life. Metal pattern is easy to be shaped with good precision, surface

finish and intricacy in shapes. It can withstand against corrosion and handling

for longer period. It possesses excellent strength to weight ratio. These

patterns are not much affected by moisture of the sand. The main

disadvantages of metallic patterns are higher cost, higher weight and tendency

of rusting. The metals commonly used for pattern making are cast iron, brass

and bronzes and aluminum alloys.

Cast IronCast iron is cheaper, stronger, tough, and durable and can produce a

smooth surface finish. It also possesses good resistance to sand abrasion. The

drawbacks of cast iron patterns are that they are hard, heavy, brittle and get

rusted easily in presence of moisture.


Brasses and BronzesThese are heavier and expensive than cast iron and hence are preferred

for manufacturing small castings. They possess good strength, machinability

and resistance to corrosion and wear. They can produce a better surface finish.

Brass and bronze patterns are finding applications in making match plate

patterns.

Aluminum AlloysAluminum alloy patterns are more popular and best among all the

metallic patterns because of their high lightness, good surface finish, low

melting point and good strength. They also posses good resistance to corrosion

and abrasion by sand and there by enhancing longer life of pattern. These

materials do not withstand rough handling. They have poor repairability and

are preferred for making large castings.

Advantages

Aluminum alloy patterns do not rust.

They are easy to cast.

They are light in weight.

They can be easily machined.

Disadvantages

They can be damaged by sharp edges.

They are softer than brass and cast iron.

Their storing and transportation needs proper care.

White MetalWhite metal is an alloy of Antimony, Copper and Lead. It is best used

for lining and stripping plates. Its melting point is around 260C, it can be

cast into narrow cavities. The disadvantages of this white metal are that it is

too soft, it’s storing and transportation needs proper care and it wears away

by sand or sharp edges.


Plastic

Patterns made of plastics materials are lighter, stronger, moisture and

wear resistant, non-sticky to moulding sand, durable and they are not affected

by the moisture of the moulding sand. Moreover they impart very smooth

surface finish on the pattern surface. These materials are somewhat fragile,

less resistant to sudden loading and their section may need metal

reinforcement. The plastics used for this purpose are thermosetting resins.

Phenolic resin plastics are commonly used. These are originally in liquid form

and get solidified when heated to a specified temperature. To prepare a plastic

pattern, a mould in two halves is prepared in plaster of paris with the help

of a wooden pattern known as a master pattern. The phenolic resin is poured

into the mould and the mould is subjected to heat. The resin solidifies giving

the plastic pattern. Recently a new material has stepped into the field of

plastic which is known as foam plastic.

Plaster

Plaster belongs to gypsum family which can be easily cast and

worked with wooden tools and preferable for producing highly

intricate casting.

The main advantages of plaster are that it has high compressive

strength and is of high expansion setting type which compensate

for the shrinkage allowance of the casting metal.

Plaster of paris pattern can be prepared either by directly pouring

the slurry of plaster and water in moulds prepared earlier from a

master pattern or by sweeping it into desired shape or form by

the sweep and strickle method.

It is also preferred for production of small size intricate castings

and making core boxes.

Wax

Wax patterns are excellent for investment casting process. The

materials used are blends of several types of waxes, and other

additives which act as polymerizing agents, stabilizers, etc.


The commonly used waxes are paraffin wax, shellac wax,

bees-wax, cerasin wax, and micro-crystalline wax.

The properties desired in a good wax pattern include low ash

content up to 0.05 per cent, resistant to the primary coat material

used for investment, high tensile strength and hardness, and

substantial weld strength.

Wax patterns are made by injecting liquid or semi-liquid wax into

a split die. Solid injection is also used to avoid shrinkage and for

better strength.

Wax use helps in imparting a high degree of surface finish and

dimensional accuracy of castings.

Wax patterns are prepared by pouring heated wax into split moulds

or a pair of dies. The dies after having been cooled down are

parted off. Now the wax pattern is taken out and used for

moulding.

Such patterns need not be drawn out solid from the mould. After

the mould is ready, the wax is poured out by heating the mould

and keeping it upside down.

Such patterns are generally used in the process of investment

casting where accuracy is linked with intricacy of the cast object.

1.8.5 Selection of pattern material

The following factors must be taken into consideration while selecting

pattern materials.

Number of castings to be produced. Metal patterns are preferred

when castings are required large in number.

Type of mould material used & type of moulding process.

Method of moulding (hand or machine).

Degree of dimensional accuracy, stability and surface finish

required.

Minimum thickness required.

Shape, complexity and size of casting.


Resistance to wear and abrasion, resistance to corrosion, and to

chemical reactions

Low cost of production.

1.8.6 PATTERN ALLOWANCES

Pattern may be made from wood (or) metal and its size may not be

same as that of the casting. A pattern is always larger in size as compared

to the final casting because it carries allowances due to metallurgical reasons

(shrinkage on cooling) and mechanical reasons (machining, distortion, draft,

shake, sharp edges etc.,).

These various allowances given to pattern can be enumerated as,

allowance for shrinkage,

allowance for machining,

allowance for draft,

allowance for rapping or shake,

allowance for distortion and allowance for mould wall movement.

These allowances are discussed below.

(a) Shrinkage allowance

All common cast metals shrink a significant amount when they are

cooled from the molten state. The total contraction in volume is divided into

the following parts:

1. Liquid contraction, i.e. the contraction during the period in which the

temperature of the liquid metal or alloy falls from the pouring

temperature to the liquidus temperature.

2. Contraction on cooling from the liquidus to the solidus temperature, i.e.

solidifying contraction.

3. Solid contraction: Contraction that results there after until the

temperature reaches the room temperature.

The first two of the above are taken care of by proper gating and

risering. Only the last one, i.e. the solid contraction is taken care by the

pattern makers by giving a positive shrinkage allowance. This contraction

allowance is different for different metals.


The Shrinkage allowances for different metals and alloys are Cast

Iron-10 mm/mt, Brass-16 mm/mt, Aluminium Alloys-15 mm/mt, Steel- 21

mm/mt, Lead-24 mm/mt.

The Metal shrinkage depends upon the metal /alloy being casted,

Pouring temperature, Casting dimensions, Casting design aspects, Moulding

conditions (mould material and moulding methods).

(b) Machining allowance

Machining allowances is a positive allowance given to compensate for the

amount of material that is lost in machining or finishing the casting. If this

allowance is not given, the casting will become undersize after machining.

Machining allowance is given due to the following reasons:

1. Castings get oxidised inside mould and during heat treatment. Scale thus

formed requires to be removed.

2. For removing surface roughness, slag, dirt and other imperfections from

the casting.

3. For obtaining exact dimensions on the casting.

4. To achieve desired surface finish on the casting.

The amount of this allowance depends on

nature of metal,

the size and shape of casting,

methods of machining (grinding, turning milling boring etc.,),

casting condition,

moulding process involved,

number of cuts to be taken and the degree of finish.

In general, however, the value varies from 3 mm to 12 mm.

(c) Draft (or) Taper allowance

Taper allowance (Fig. 1.23) is also a positive allowance and is given

on all the vertical surfaces of pattern so that its withdrawal becomes easier.

The normal amount of taper on the external surfaces varies from 10 mm to

20 mm/mt. On interior holes and recesses which are smaller in size, the taper

should be around 60 mm/mt. These values are greatly affected by the size


of the pattern and the moulding method. In machine moulding, its value varies

from 10 mm to 50 mm/mt. Fig. 1.23 shows Draft allowance.

(d) Rapping (or) Shake allowance

Before withdrawing the pattern, it is rapped and thereby the size of the

mould cavity increases. Actually by rapping, the external sections move outwards

increasing the size and internal sections move inwards decreasing the size. This

movement may be insignificant in the case of small and medium size castings,

but it is significant in the case of large castings. This allowance is kept negative

and hence the pattern is made slightly smaller in dimensions 0.5-1.0 mm.

(e) Distortion (or) Camber allowance

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Pa tte rn N o a llow ance

Pa tte rn w ith a llow anceParting line

C racks in m ould

(a) (b)

Fig.1.23 D raft (or) taper allowance (a) W ithout a llowance (b) W ith allowance

Required Shape

of Casting

DistortedCasting

CamberedPattern

(i)

(a) (b) (c)

(ii)

Fig. 1.24. Distortion allowance (i) I-section(ii)(a) Without cam ber, (b) Actual casting, (c) W ith cam ber allowance


This allowance is applied to the castings which have the tendency to

distort during cooling due to thermal stresses developed. For example a

casting in the form of U shape will contract at the closed end on cooling,

while the open end will remain fixed in position. Therefore, to avoid the

distortion, the legs of U pattern must converge slightly so that the sides will

remain parallel after cooling. Another example is I shaped channel where to

avoid distortion cambered is given (Fig 1.24)

(f) Mould wall movement allowance

Mould wall movement in sand moulds occurs as a result of heat and

static pressure on the surface layer of sand at the mould metal interface. In

ferrous castings, it is also due to expansion due to graphitization. This

enlargement in the mould cavity depends upon the mould density and mould

composition. This effect becomes more pronounced with increase in moisture

content and temperature.

1.9 CORES

Cores are compact mass of core sand prepared separately, when placed

in mould cavity at required location. It does not allow the molten metal to

occupy space for solidification in that portion and hence help to produce

hollowness in the casting. The environment in which the core is placed is

much different from that of the mould. In fact the core has to withstand the

severe action of hot metal which completely surrounds it.

1.9.1 Functions (or) Objectives of core

Core produces hollowness in castings in the form of internal

cavities.

It must be sufficiently permeable to allow the easy escape of gases

during pouring and solidification.

It may form a part of green sand mould.

It may provide external undercut features in casting.

It may be inserted to achieve deep recess in the casting.

It may be used to strengthen the mould.

It may be used to form gating system of large size mould.


1.9.2 Core Sand

Core Sand is a special kind of moulding sand. The main constituents

of the core sand are pure silica sand and a binder. Silica sand is preferred

because of its high refractoriness. For higher values of permeability, sands

with coarse grain size distribution are used. The main purpose of the core

binder is to hold the grains together, impart strength and sufficient degree of

collapsibility. Beside these properties needed in the core sand, the binder

should be such that it produces minimum amount of gases when the molten

metal is poured in the mould. Although, in general the binders are inorganic

as well as organic, but for core making, organic binders are generally preferred

because they are combustible and can be destroyed by heat at higher

temperatures thereby giving sufficient collapsibility to the core sand.

1.9.3 Considerations in Selecting Core Sand

Keeping above mentioned objectives in view, the special considerations

should be given while selecting core sand. These considerations involve

The cores are subjected to a very high temperature and hence the

core sand should be highly refractory in nature.

The permeability of the core sand must be sufficiently high as

compared to that of the moulding sands so as to allow the core

gases to escape through the limited area of the core recesses

generated by core prints.

The core sand should not possess such materials which may

produce gases while they come in contact with molten metal and

The core sand should be collapsible in nature, i.e. it should

disintegrate after the metal solidifies, because this property will

ease the cleaning of the casting.

1.9.4 Binders for core sand

The common binders which are used in making core sand are as

follows:


(a) Cereal binderIt develops green strength, baked strength and collapsibility in core.

The amount of these binders used varies from 0.2 to 2.2% by weight in the

core sand.

(b) Protein binderIt is generally used to increase collapsibility property of core.

(c) Thermosetting resinThermosetting resins are popular because, it imparts high strength,

collapsibility to core sand and it also evolves minimum amount of mould and

core gases which may produce defects in the casting. The most common

binders under this group are phenol formaldehyde and urea formaldehyde.

(d) Sulphite binderSulphite binder is also sometimes used in core but along with certain

amount of clay.

(e) DextrinDextrin is commonly added to core sand for increasing collapsibility

and baked strength of core.

(f) PitchPitch is widely used to increase the hot strength of the core.

(g) MolassesMolasses is generally used as a secondary binder to increase the

hardness on baking. It is used in the form of molasses liquid and is sprayed

on the cores before baking.

(h) Core oilCore oil in liquid state, when it is mixed with the core sand, forms a

coherent solid film holding the sand grains together when it is baked.

1.9.5 Core Making

Stages in core making

Core making basically is carried out in five stages namely

Core Sand Preparation,

Core Making,


Core Baking

Core Finishing

Setting the cores

(a) Core Sand Preparation Preparation of core to get better and uniform core sand properties,

satisfactory and homogenous mixture of core using proper sand

constituents and additives, the core sands are generally mixed with

the help of any of the following mechanical means namely roller

mills, core sand mixer using vertical revolving arm type and

horizontal paddle type mechanisms. These machines perform the

mixing of core sand constituents most thoroughly.

(b) Core Making Process Small cores are made manually in hand rammed core boxes.

Cores on mass scale are rapidly produced on a variety of core

making machines – to name a few core blowing, core ramming

and core extrusion machines

I. Hand making of coresSmall sized cores for limited production are made manually in hand

filled core boxes. The steps involved in making core by hand are:

Place the core box on work bench and it is filled with the already

mixed and prepared core sand and rammed by hand and the extra sand

is removed. (weak cores are reinforced using steel wires).

Core box is inverted over the core plate to transfer the core to

the plate.

It is then baked in oven for specified period and then removed

and cooled. Now the core is ready.

II. Core making machines

(i) Core blowing machines The basic principle of core blowing machine comprises of filling

the core sand into the core box by using compressed air (at 5 to

7 bar pressure). (Fig 1.25)


The velocity of the compressed air is kept high to obtain a high

velocity of core sand particles, thus ensuring their deposit in the

remote corners of the core box.

On entering the core sand with high kinetic energy, the shaping

and ramming of core is carried out simultaneously in the core box.

The core blowing machines can be further classified into two

groups namely small bench blowers and large floor blowers.

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Ven tholes

M agazine

Sand

Core Box w ithVent holes

Floor M ounting

Compressed A ir

Fig.1.25 C ore Blowing Machine.


Small bench blowers are quite economical for core making shops

having low production and are bench type.

Big core blowing machines are either vertical or horizontal floor

mounted type.

The cartridge oriented sand magazine is considered to be a part of

the core box equipment.

However, one cartridge may be used for several boxes of

approximately the same size. The cartridge is filled using hands.

Then the core box and cartridge are placed in the machine for

blowing and the right handle of the machine clamps the box and

the left handle blows the core.

(ii) Core drawing/extrusion machines Uniform cross section and regular simple cores are extruded by

core extrusion machine.

Cores of square, round, hexagonal and oval section are widely

produced by core extrusion machine.

Fig 1.26 shows a core extrusion machine which consists of hopper

through which core sand is fed to horizontal spiral conveyor. As

the spiral conveyor is rotated it forces core sand through a die of

specified shape (square, round etc.,)

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D ie

Sp ira l conveyor

Core Sand

Hopper

Power or Hand Driven

Core out

Bench

Fig.1.26 C ore Extrusion machine.

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Long cores thus produced can be cut to the desired length.

The drawn core is then baked further before its use in mould cavity

to produce hollowness in the casting.

(iii) Core ramming machinesCores can also be prepared by ramming core sands in the core boxes

by machines based on the principles of squeezing, jolting and slinging. Out

of these three machines, jolting and slinging are more common for core

making.

(c) Core Baking Once the cores are prepared, they will be baked in baking ovens

or furnaces.

The main purpose of baking is to drive away the moisture and

harden the binder, thereby giving strength to the core. Core are

baked upto 380C. Core baking develops the properties of organic

binders.

At 100C moisture is driven out and at 125C to 225C Core oil

and other organic binders change chemically and molecularly from

liquid to solid state.

The core drying equipments are usually of two kinds namely core

ovens and dielectric bakers.

The core ovens are of two types namely continuous type oven and

batch type oven.

Continuous type ovens: Continuous type ovens are preferred

basically for mass production. In these types, core carrying

conveyors or chain move continuously through the oven. The

baking time is controlled by the speed of the conveyor. The

continuous type ovens are generally used for baking of small cores.

Batch type ovens: Batch type ovens are mainly utilized for baking

variety of cores in batches. The cores are commonly placed either

in drawers or in racks which are finally placed in the ovens. The

core ovens and dielectric bakers are usually fired with gas, oil or

coal.


Dielectric bakers: These bakers are based on dielectric heating.

The core supporting plates are not used in this baker because they

interfere with the potential distribution in the electrostatic field. To

avoid this interference, cement bonded asbestos plates may be used

for supporting the cores. The main advantage of these ovens is

that they are faster in operation and a good temperature control is

possible with them. After baking of cores, they are smoothened

using dextrin and water soluble binders.

(d) Core Finishing Core finishing is done after braking, before it is finally set in the mould.

The fins, bumps or other sand projections are removed from the

surface of the cores by rubbing or filing.

The dimensional inspection of the cores is very necessary to

achieve sound casting.

Cores are also coated with refractory or protective materials using

brushing, dipping and spraying means to improve their

refractoriness and surface finish. The coating on core prevents the

molten metal from entering into the core.

Bars, wires and arbors are generally used to reinforce core from inside.

(e) Setting of cores Setting of cores means positioning the cores in the mould.

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M ouldCavity

Core Seat

4Chap le ts

Sand

Fig. 1.27. Chaplets in setting of cores.

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In order to obtain correct cavities in the casting the cores must be

accurately positioned.

Core in mould should be firmly secured so that they can withstand

the buoyancy effect of the molten metal poured.

Small cores are set by hand while large ones by crane.

Cores are supported by chaplets to avoid sagging, shifting or

sinking of the cores.

Chaplets are metal shapes which are positioned between mould

and core surfaces. Chaplets are made of the same materials as that

of the cast. Fig. 1.27.

Various forms of chaplets are commercially available.

1.9.6 TYPES OF CORES AND APPLICATIONS

Cores are classified according to

(a) State (or) Condition of core

Green sand core and Dry sand core.

(b) Nature of core materials employed

Oil bonded core, Resin bonded core, Shell core and Sodium silicate

core.

(c) Type of core hardening process employed

CO2 Process, Hot box core, cold set process, Oil – No-Bake core

(d) Shape and position of core

Horizontal core, Vertical core, Hanging core, Balanced core, Drop core

(i) Green Sand Cores Green sand cores are made by green sand containing moist

condition about 5% water and 15- 30 % clay.

It imparts very good permeability to core and thus avoids defects

like shrinkage or voids in the casting.

They are used in green condition and are generally preferred for

simple, small and medium castings.


Such cores possess less strength in comparison to dry sand cores

and hence cannot be stored for longer period.

(ii) Dry Sand Cores Dry sand cores are produced by drying the green sand cores to

about 110C.

These cores possess high strength rigidity and also good thermal stability.

These cores can be stored for long period and are more stable

than green sand core.

They are used for large castings.

They also produce good surface finish in comparison to green sand

cores.

They can be handled more easily. They resist metal erosion.

These types of cores require more floor space, more core material,

high labour cost and extra operational equipment.

(iii) Oil bonded coresSand cores are produced by mixing silica sand with small percentage

of linseed oil. Oil bonded cores are based on the principle of Oxidation and

Polymerisation of oils containing chemical additives which can be activated

by an oxygen bearing material set in a predetermined time.

(iv) Shell CoreShell cores are made as follows: The core box is heated to a

temperature of around 400C to 600C. Sand mixed with 2-5 % of thermosetting

resin (Phenolic type) is dumped / blown to the above heated core box. The resin

is allowed to melt to the specified thickness. The resin gets cured. The excess

sand is removed. The hardened core is extracted from box and does not require

further baking.

Shell core possess very smooth surfaces and very close tolerances. High

permeability is achieved in shell cores. They can be easily stored and are

very costly.


(v) Sodium silicate – CO2 CoresClean, dry sand with sodium silicate is rammed into core box. CO2

gas is passed for several seconds through the above mixture as a result silica

gel is formed which binds sand grains into strong solid form.

Na2SiO3 CO2 Na2CO3 SiO2 Silica gel

Core thus formed does not require baking and have more strength than

oil bonded / resin cores. Cores formed by CO2 process are used in production

of cast iron, steel, aluminium and copper based alloys. The used sand cannot

be recovered and reused.

(vi) Hot Box CoreThis uses heated core boxes (125C 225C) for producing cores. Core

boxes are made up of cast iron, steel, aluminium and possess vents and

ejectors for removing core gases. Heated core boxes are used with core sand

mixtures employing liquid resin binders and a catalyst.

(vii) Cold set CoreCold set cores are prepared by mixing binder with the accelerator. This

sand mixture has high flowability and can easily be rammed. Curing starts

immediately as soon as accelerator is added and continued until core becomes

strong. With little heating the core hardens completely. This is preferred for

jobbing operation and producing very large cores.

(viii) Oil – No-Bake coreThis process employs a synthetic oil binder which when mixed with sand,

chemically (Polymerisation reaction) reacts and produces core that can be cured at

room temperature. The sand, binder/catalyst, oil-no bake agents weight by ratio is

500kg : 7kg : 1.4kg. The process assures better depth, fast breaking, easier core

withdrawal and lower costs.

(ix) Horizontal coreIt is produced horizontally in the mould. It can be of any shape based

on cavity of cast. It is supported in core seats at both ends . These are placed

at parting line. These are commonly used in foundries (Fig. 1.28).


(x) Vertical coreIn vertical core, Cope side has more taper than in drag so as not to

tear the sand while assembling cope and drag. It is placed vertically in the

mould cavity. Core is supported by core seat at both ends. Major portion of

core remains in drag. (Fig. 1.29)

(xi) Hanging Core or Cover coreHanging core is supported from above only and it hangs vertically in

the mould cavity. It is provided with a hole through which metal can flow

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Fig. 1.28. Horizontal Core.

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Fig. 1.29 Vertical core

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in the mould cavity. It is called hanging because it hangs from above and if

it is covering the mould it is called cover core. (Fig. 1.30)

(xii) Balanced coreBalanced core is a core supported and balanced from one end only. It

requires a big core seat for support and does not sag or sink or fall. Balanced

core may be supported by chaplets. (Fig. 1.31)

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(xiii) Drop (or) Stop off coreA stop off core is employed to make a cavity which cannot be made

with other cores. A stop off core is used when a cavity is not in line with

parting surface rather it is above or below. (Fig. 1.32)

1.10 MOULDING MACHINES Moulding machine acts as a device by means of a large number

of co-related parts and mechanisms, transmits and directs various

forces and motions in required directions so as to help the

preparation of a sand mould.

The major functions of moulding machines involve ramming of

moulding sand, rolling over or inverting the mould, rapping the

pattern and withdrawing the pattern from the mould.

Most of the moulding machines perform a combination of two or

more of functions.

1.10.1 Types and Applications of Moulding Machines

Moulding machines can be classified as Squeezer Machine, Jolt

Machine, Jolt-Squeezer Machine, Slinging Machines, Pattern Draw Machines

These varieties of machines are discussed below.

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Fig. 1.32.Stop off core

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(a) Squeezer machine These machines may be hand operated or power operated.

The pattern is placed over the machine table, followed by the

moulding box. Fig. 1.33.

In hand-operated machines, the table of machine is lifted by hand

operated mechanism. In power machines, it is lifted by the air pressure

on a piston in the cylinder in the same way as in jolt machine.

The table is then raised gradually. The sand in the moulding box

is squeezed between plate and the upward rising table thus

enabling a uniform pressing of sand in the moulding box.

More pressure can be applied in power operated machines.

(b) Jolt machine This machine is also known as jar machine which comprises of

air operated piston and cylinder.

The air is allowed to enter from the bottom of the cylinder and

acts on the bottom face of the piston to raise it up.

The (platen or) table of the machine is attached at the top of the

piston which carries the pattern and moulding box with sand filled

in it.

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Sque ezer head

Sand

Flask

Pa tte rn

M ou ld board

Tab le

Fig. 1.33 Squeezer Machine


The upward movement of piston raises the table to a certain height

(30 to 80 mm) and the air below the piston is suddenly released

and the table drops down suddenly and strikes the guiding cylinder

at bottom. This sudden action causes the sand to pack evenly

around the pattern. Springs are used to cushion the table blows

and thus reduce noise and prevent destruction of mechanism and

foundation.

This process is repeated several times rapidly. This operation is

known as jolting technique.

(c) Jolt-squeezer machine

It uses the principle of both jolt and squeezer machines in which

complete mould is prepared.

The cope, match plate and drag are assembled on the machine

table in a reverse position, that is, the drag on the top and the

cope below.

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Fig. 1.34 Jolt Machine

Patte rn

Flask

G uiding cy linder

Spring


Initially the drag is filled with sand followed by ramming by the

jolting action of the table. After leveling off, the sand on the upper

surface, the assembly is turned upside down and placed over a

bottom board placed on the table.

Next, the cope is filled up with sand and is rammed by squeezing

between the overhead plate and the machine table. The overhead

plate is then swung aside and sand on the top is leveled off, cope

is next removed and the drag is vibrated by air vibrator.

This is followed by removal of match plate and closing of two

halves of the mould for pouring the molten metal. This machine

is used to overcome the drawbacks of both squeeze and jolt

principles of ramming moulding sand.

(d) Slinging machines

These machines are also

known as sand slingers and are

used for filling and uniform

ramming of moulding sand in

moulds. In the slinging

operations, the consolidation

and ramming are obtained by

impact of sand which falls at a

very high velocity on pattern.

A typical sand slinger

consists of a heavy base, a bin

or hopper to carry sand, a

bucket elevator to which a

number of buckets are attached

and a swinging arm which

carries a belt conveyor and the sand impeller head. Well prepared sand is

filled in a bin through the bottom of which it is fed to the elevator buckets.

These buckets discharge the moulding sand to the belt conveyor which

conveys the same to the impeller head. This head can be moved at any

location on the mould by swinging the arm. The head revolves at a very high

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Tab leBoard

Fig. 1.35 Sand Slinger

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speed and, in doing so, throws a stream of moulding sand into the moulding

box at a high velocity. This process is known as slinging. The force of sand

ejection and striking into the moulding box compels the sand to get packed

in the box flask uniformly. By this way, the satisfactory ramming is

automatically get completed on the mould.

(e) Pattern draw machines

These machines enable easy withdrawal of patterns from the

moulds. They can be of the kind of stripping plate type and pin

lift or push off type.

Stripping plate type of pattern draw machines consists of a

stationary (platen or) table on which is mounted a stripping plate

which carries a hole in it.

The pattern is secured to a pattern plate and the latter to the

supporting ram.

The pattern is drawn through the stripping plate either by raising

the stripping plate or by keeping the stripping plate and mould

stationary by moving the ram downwards along with the pattern

plate.

1.11 MELTING FURNACES

The metal to be casted has to be in the molten or liquid state before

pouring into the mould. A furnace is used to melt the metal. A foundry

furnace only remelts the metal to be casted, it does not convert ore into useful

metal. A blast furnace performs basic melting (of iron ore) operation to get

pig iron. Different furnaces are used for melting and re-melting ferrous and

nonferrous materials.

1.11.1 Factors responsible for the selection of furnace

Considerations of initial, repair, maintenance and operation costs.

Availability and relative cost of various fuels in the particular

locality.

Melting efficiency, speed of melting.

Composition and melting temperature of the metal.


Degree of quality control required in respect of metal purification

of refining.

Cleanliness and noise level in operation.

Method used for pouring desired metal.

Chances of metal to absorb impurities during melting.

1.11.2 Types of Furnaces

Furnaces for melting different materials are given below

For Grey Cast Iron

Cupola furnace, Air furnace (or Reverberatory Furnace), Rotary furnace

and Electric arc furnace

For Steel

Electric furnaces, Open hearth furnace and Converter

For Non-ferrous Metals

(a) Reverberatory furnaces (fuel fired) (Al, Cu) - Stationary and Tilting

furnaces

(b) Rotary furnaces - Fuel fired & Electrically heated

(c) Induction furnaces (Cu, Al) - Low frequency & High frequency.

(d) Electric Arc furnaces (Cu)

(e) Crucible furnaces (Al, Cu) - Pit type, Tilting type, Non-tilting or

bale-out type & Electric resistance type (Cu)

(f) Pot furnaces (fuel fired) (Mg and Al) - Stationary and Tilting

1.11.3 Blast Furnace

Various kinds of mined iron ores are refined and converted to pig

iron in the blast furnace.

A typical blast furnace along with its various parts is shown in

Fig. 1.36.

It is large steel shell about 9 mt. in diameter which is lined with

heat resistant bricks.

It is set on the top of brick foundation. There are four major parts

of blast furnace from bottom to top hearth, bosh, stack and top.


The hearth acts as a storage region for molten metal and molten

slag.

The charge of blast furnace possesses successive layers of iron

ore, scrap, coke, and limestone and some steel scrap which is fed

from the top of the furnace.

Iron ore exists as an aggregate of iron-bearing minerals. These

mineral aggregates are oxides of iron called hematite, limonite, and

magnetite. They all contribute to the smelting process.

Shell

Blast p ipe

Tuyere 3000 Fo

Tap hole

ReductionCoke

CokeOre

Ore300 Fo

Refractorylining

Stack

Large bell

Head absorp

Fusion

Combustion

M olten slagM olten iron

Cindernotch

Bosh

Hearth

Bed

Sm all bellTop

Fig. 1.36. Blast Furnace.

Lim estone


It takes about 1.6 tons of iron ore, 0.65 ton of coke, 0.2 ton of

lime-stone and about 0.05 ton of scrap iron and steel to produce

1 ton of pig iron.

For burning this charge, about 4 tons of air is required.The

impurities or other minerals are present in the ore may be silicon,

sulphur, phosphorus, manganese, calcium, titanium, aluminum, and

magnesium.

The output from the furnace in form of pig iron is collected in

large ladles from the tap hole existing at lower portion of furnace.

As the coke burns, aided by the air forced into the furnace, the

ore melts and collects in the hearth. As the melting process

proceeds, the entire mass settles and thus makes room for the

addition of charges at the top.

While the melting is going on, the limestone forms a slag with

the impurities.

Coke supplies the heat which reduces the ore and melts the iron.

The iron picks up carbon from the coke and impurities from the

ore. The carbon becomes part of the pig iron used in the making

of steel.

The pig iron is then processed for purification work for production

of various kinds of iron and steel in the form of ingots (large

sections) using different furnaces.

1.11.4 Cupola Furnace

Cupola furnace is employed for melting scrap metal or pig iron for

production of various cast irons. It is also used for production of nodular and

malleable cast iron. It is available in good varying sizes. The main

considerations in selection of cupola’s are melting capacity, diameter of shell

without lining or with lining, spark arrester. Cupolas are also used for melting

some copper alloys also.


1.11.4.1 Construction of cupola

1. Coke2. Flux3. M etal

Spark a rrester

Furnace Charg ing door

Stage

Steel shell

Refractory lin ing

Air box

Red

uci

ng

zone

A ir b last inlet

Tuyeres

Fettling ho le

Drop bo ttom

Legs

Sand bottom

Slag bottom

W ellTapping hole

Combustion zone

M elting zone

Pre

heat

ing

zone

Sla

ck z

one

1

3

1

3

2

2

Fig 1.37 C upola furnace


A cupola is a cylindrical shell either welded or riveted from a

boiler plate of 6-10 mm thick and is open both at its top and

bottom, lined with firebrick and clay supported on cast iron legs.

Fig 1.37

It has cast iron door at the bottom to open or close and used to drop

the left out contents of cupola.

Air from blower comes through the blast pipe and enters wind

box which surround the cupola and supplies air uniformly to

tuyeres.

Tuyeres extend through the steel shell and refractory wall to the

combustion zone and supply air necessary for combustion.

There is a tap hole at the bottom from where molten metal is

taken out to pour in mould. The fire in cupola is also lit through

the tap hole.

Slag hole is present opposite and above the tap hole. It is 250

mm below tuyeres. Slag is removed from slag hole.

Cupola is provided with charging platform and charging door at

suitable height to feed the charge.

Capacity of cupola varies from 1 to 15 tons. They are 6 m in

height and diameters vary from 750mm to 2.5mts.

Sometimes they are fitted with collector, filter and precipitator to

minimize pollution.

1.11.4.2 Various Zones of Cupola Furnace

Various chemical reactions taking place in different zones of cupola

are:

(a) Well

The space between the bottom of the tuyeres and the sand bed inside

the cylindrical shell of the cupola is called as well of the cupola. As the

melting occurs, the molten metal is collected in this portion before tapping

out.


(b) Combustion zone

The combustion zone of Cupola is also called as oxidizing zone.

Combustion of coke takes place in this zone. It is located between the upper

of the tuyeres and a theoretical level above it. The total height of this zone

is normally from 150 mm to 300 mm. The combustion actually takes place

in this zone by consuming the free oxygen completely from the air blast and

generating tremendous heat. The heat generated in this zone is sufficient

enough to meet the requirements of other zones of cupola. The heat is also

further evolved due to oxidation of silicon and manganese. A temperature of

about 1540C to 1870C is achieved in this zone. A few of the exothermic

reactions that take place in this zone are represented as :

C O2 CO2 Heat

Si O2 SiO2 Heat

2Mn O2 2MnO Heat

(c) Reducing zone

Reducing zone of Cupola is also known as the protective zone which

is located between the upper level of the combustion zone and the upper

level of the coke bed. In this zone, CO2 is changed to CO through an

endothermic reaction, as a result of which the temperature falls from

combustion zone temperature to about 1200C at the top of this zone. The

important chemical reaction that takes place in this zone is given below.

CO2 C coke 2CO Heat

Nitrogen does not participate in the chemical reaction occurring in this

zone as it is also the other main constituent of the upward moving hot gases.

Because of the reducing atmosphere in this zone, the charge is protected

against oxidation.

(d) Melting zone

The lower layer of metal charge above the lower layer of coke bed is

termed as melting zone of Cupola. The metal charge starts melting in this

zone and trickles down through coke bed and gets collected in the well.


Sufficient carbon content picked by the molten metal in this zone is

represented by the chemical reaction given below.

3Fe 2CO Fe3C CO2

(e) Preheating zone

Preheating zone starts from the upper end of the melting zone and

continues up to the bottom level of the charging door. This zone contains a

number of alternate layers of coke bed, flux and metal charge. The main

objective of this zone is to preheat the charges from room temperature to

about 1090C before entering the metal charge to the melting zone. The

preheating takes place in this zone due to the upward movement of hot gases.

During the preheating process, the metal charge in solid form picks up some

sulphur content in this zone.

(f) Stack

The empty portion of cupola above the preheating zone is called as

stack. It provides the passage to hot gases to go to atmosphere from the

cupola furnace.

1.11.4.3 Operation / Working of Cupola

The various steps in operating cupola are:

Preparation of cupola

Lightening of cupola

Charging of cupola

Melting

Slagging and metal tapping

Dropping down

Preparation Bottom doors are opened and the contents (unburned coke, slag,

metal) of previous melting are dumped under furnace and removed.

Slag, coke, iron sticking to the side walls of the furnace are

chipped off.

Damaged bricks are replaced and damaged refractory lining is

patched up and then bottom doors are closed.


Lightening Cupola is fired 3-4 hrs before molten metal is needed.

Soft, dry wood are placed on the sand bed rammed above the

bottom door. Coke is placed above the wooden pieces till the

tuyeres. Wood is ignited through tap hole.

Charging of Cupola

After the coke bed is properly ignited, the cupola is charged from

the charging door.Charging of cupola involves adding of alternate

layers of limestone (flux), metal (iron) and fuel (coke) up to the

level of charging door.

Flux is a substance aiding in formation of slag for removing

impurities. Commonly used flux are limestone, others are sodium

carbonate, fluorospar (CaF2), calcium carbide and dolomite.

Metal charge may consist of pig iron, cast iron scrap and steel

scrap.

Melting

After charging, a soak period of 30-60 minutes is given to charge

for preheating.

At the end of soaking period the blast is turned on. The coke

becomes fairly hot to melt the metal charge.

Now molten metal starts accumulating in the hearth and appears

at tap hole.

Tap hole is closed with a plug and metal is allowed to collect

after five minutes.

Slagging and metal tapping

After enough slag is accumulated the slag hole is opened and the

slag is collected in a container and disposed off.

The plug is knocked off from the tap hole and the molten metal

is tapped pouring into the mould.


Dropping down

As cupola heat charging is stopped, all the content of cupola is

allowed to melt till one or two charge is left above coke bed.

Now the air blast is switch off and the prop under bottom door

is knocked down and the remains in cupola are dropped down on

the floor or collected in bucket.

The dropped cupola remains are quenched with water and then

metal, coke remains are recovered for next use.

1.11.4.4 Applications of Cupola

Cupola is most widely used for melting practices for production

of grey cast iron, nodular cast iron, malleable cast iron and alloy

cast iron.

It can be used for melting some copper-base alloys.

It can be used in duplexing and triplexing operations for making

of steel, malleable cast iron and ductile cast iron.

1.11.4.5 Thermal Efficiency of Cupola Furnace

Thermal efficiency of cupola furnace is the ratio of heat actually

utilized in melting and superheating the metal to the heat evolved in it through

various means. The total heat evolved involves the heat due to burning of

coke, heat evolved due to oxidation of iron, Si and Mn and heat supplied by

the air blast.

During melting it is observed that approximately 48- 70 % of the

evolved heat is going as waste.

% Thermal efficiency

Heat utilized in Preheating, melting and superheatingHeat evolved in the furnace

100

1.11.4.6 Advantages of Cupola

Cupola is simple and easier in construction and easy to operate.

Low initial cost, low operation and maintenance costs compared to

other furnaces of same capacity.


It occupies less floor space

It can operate continuously for many hours.

1.11.4.7 Disadvantages of Cupola

Close temperature control is difficult.

Molten iron, coke comes into contact with certain useful elements

like Silicon, manganese and are lost. Impurities like sulphur are

picked by molten iron affecting final iron content.

1.11.5 Air Furnace or Reverberatory Furnace

This furnace is also known as puddling or reverberatory furnace.Air

furnace is used for production of malleable cast iron and high test grey cast

iron.

1.11.5.1 Construction

Fig 1.38 Shows the construction of Air furnace. It consists of a

long rectangular structure having removable arched roof sections

called Bungs over a shallow hearth made up of refractory sand

damped with clay.

It resembles open hearth furnaces except that it does not have any

regenerative chambers for preheating. Metal is charged through

bungs and temperature is less than the open hearth furnaces.

Fig. 1.38 Air furnace or Reverberatory Furnace


1.11.5.2 Working

The air furnace is charged (i.e. metal, scrap etc.,) through bungs.

Oil or pulverized bituminous coal is placed on the fire place.

The air and fuel are blown through one end of furnace so that the

flame passes over the metal charge.

The flame and hot gases heat up the air furnace roof and walls.

The heat reflected and radiated from the roof /walls is utilized to

super heat the metal charge.

Acid slag protects the molten metal from direct exposure of flame.

The molten metal is tapped from the tap hole.

1.11.5.3 Difference between air furnace and cupola furnace

S. No Air Furnace Cupola furnace

1 Time is available to analyze thesamples of molten metal andhence control of chemicalcomposition is possible.

Time is not available due tocontinuous tapping and hencecontrol in chemical compositionis not possible.

2 Only flame not fuel comes incontact with metal and henceelements like sulphur, carbon iseliminated from molten metal

Flame & fuel come in contactwith molten metal and henceelements like sulphur, carbon isadded in molten metal.

3 Melting ratio (metal to fuel) is2:1,so high working costs.

Melting ratio (metal to fuel) is10:1, so low working costs.

4 Air furnace supplies moltenmetal in large quantities inbatches therefore facilitates largecastings.

Cupola supplies small butcontinuous supply of cast iron,so it can be used for largenumber of small castings.

5 Initial costs are high. Initial costs are Low.

6 Capacity varies from 5 to 50tons.

Capacity varies from 1 to 15tons.

1.11.5.4 Advantages of Air furnaces Time is available to analyze the samples of molten metal and hence

control of chemical composition is possible.


Only flame not fuel comes in contact with metal and hence

elements like sulphur, carbon is eliminated from molten metal.

Air furnace supplies molten metal in large quantities in batches

therefore facilitates large castings.

Capacity varies from 5 to 50 tons.

1.11.5.5 Disadvantages of Air furnaces Melting ratio (metal to fuel) is 2:1, so high working costs.

Initial costs are high.

1.11.6 Rotary Melting FurnaceAir furnace used for making malleable cast iron is difficult to operate

and lot of fuel is wasted, a rotary furnace is an improvement over the same.

1.11.6.1 ConstructionA rotary furnace consists of a horizontal cylindrical steel shell lined

with refractory material and mounted on rollers (Fig. 1.39) for rotating or

rocking purposes. The cylindrical shell revolves completely at about 1 RPM.

Burner at one end burns the fuel and resulting high temperature flame

melts and reheats the metal charge lying in the shell. There is a tapping spout

to tap the molten metal. The exhaust gas is sent to the preheater to trap the

flue gas energy to the incoming cold air.

R efractory lining

Fuel & a ir

Bu rne r

Arrangem ent o f ro ta tion

Tappingspout

M oltenm etal

Exhaust box

To p re heater

S tee l shell

Fig. 1.39. Rotary Furnace


1.11.6.2 Working Rotary furnace is charged from one of the conical ends by

removing burner or exhaust box temporarily.

The melting (metal-to-fuel) ratio is 5 : 1 for pulverized coal and

6 : 1 for oil fuel.

Due to rotation of the furnace the metal get heated from the walls

and is melted more efficiently and faster.

The burner at one end burns the fuel and the resulting high

temperature flame melts and superheats the metal charge lying in

the shell.

Since molten metal does not come in contact with the fuel (such

as coal), there is no danger of carbon or sulphur pick up.

The slag floating on the molten iron protects the metal and its

constituent elements (like Si, Mn etc.) from oxidation.

After the melting is complete, plugged tap hole is opened and the

furnace is rotated slowly until the tap hole reaches the level of

molten metal in the furnace, then the same (i.e. metal) can be

poured into a ladle.

In case the tap hole is not provided in the cylindrical body, the

liquid metal can be tapped from the other end of the furnace.

Besides tapping, this end is used for charging, slagging and

evacuating the products of combustion.

1.11.6.3 Advantages A sample of molten metal can be drawn before pouring and

analyzed as regards its chemical composition which subsequently

can be accurately controlled by additions if required.

Charge in a rotary furnace can be super-heated to high

temperatures.

Cheap and light scrap like steel clippings or cast iron borings

which cannot be used in cupola, may be added in the charge

without affecting the melt quality.


The products of combustion may be sent to a preheater or

recuperator unit where they may heat the cold air to be used

subsequently in the rotary furnace.

A rotary furnace may have a capacity ranging from 1 to 50 tons

depending upon the requirements of a consumer.

1.11.6.4 Applications

Rotary furnaces find applications in producing high-duty cast irons

having alloying elements such as Mo, Ni, Cr etc. which if added

in cupola will suffer a loss.

Metals previously melted in cupola can be held and superheated

in rotary furnaces.

1.11.7 Open Hearth Furnace

An air furnace does not develop tempertures enough to melt steel because

a large amount of heat generated by the combustion of fuel is lost in the hot

waste gases which pass up the chimney. For this reason, open hearth furnaces

are now widely used in large steel foundries.

1.11.7.1 Construction

C hecker C ham bers

Tap h ole

O il Bu rne r(Id le )

Valve

C harg ing door H earth Ba th S lag

H ot flue gas to C h im ney

O il burner

Fig. 1.40. Open Hearth Furnace.Air nle t�


In open hearth furnace, pig iron, steel scrap etc. are melted to obtain

steel. The hearth is surrounded by roof and walls of refractory bricks as

shown in Fig. 1.40.

Open hearth furnaces range from 5 to 100 tons capacity, the popular being

a 25 ton furnace. Most of the open hearth furnaces are stationary but some of the

units are of tilting type also. It consists of a long shallow basin called the hearth

(about 4.5 m wide, 12 m long and half metre deep) which is lined with dolomite

in case of a basic process and with silica fire brick if the process is acidic.

1.11.7.2 Working Scrap metal, pig iron and flux are charged into the furnace through

charging doors. Heating is done by burning gaseous fuel (i.e.

natural gas, producer gas or atomised oil). Fuel is fired through

nozzles (i.e. burners working alternatively for 20 to 30 minutes

from opposite ends of the hearth. One of the burners thus remains

idle for all times.

The hot gases formed pass over the hearth to its opposite end

thereby the metal charge supported on the hearth is openly exposed

to the flames and is converted into molten metal. Molten metal is

trapped by the trap doors.

Besides being directly exposed to the flames, metal charge is also heated

by the radiations from the walls and low hot ceiling of the furnace.

After passing over the hearth, the products of combustion pass

through one checker chamber and heat it. The process then reverses,

the idle burner fires the fuel, flame passes over the hearth from the

opposite direction and the initially active burner becomes idle.

The products of combustion after sweeping over the metal charge

enter the second checker chamber and heat it up. Thus each

checker chamber is heated up alternatively.

1.11.7.3 Advantages The system of preheating air and fuel known as Regenerative

system, heats air to about 100C before it reaches the furnace

proper. The regenerative system, because of its alternating action


speeds up the melting of metal and develops temperatures enough

to melt steel.

It has high thermal efficiency.

Before tapping the molten metal into the ladle, a sample of the

same may be tested as regards its chemical composition.

1.11.7.4 ApplicationsOpen hearth furnace is used for melting steels,

It may also be used for melting Al, Cu and their alloys in large

quantities.

1.11.8 Convertor

Converters are steel-making units. A Converter actually converts pig

or cast iron into steel by blowing air through (bessemer) or over (side blown)

molten iron. Converters are of two types:

...

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.

A ir Blast

W ind box

Tuyeres

M olten m eta l

Shell

Trunnion forTilting

Refractory lining

Flue gas

Fig. 1.41 Side-blown converter


Bessemer or bottom blower Converters in which a blast of cold

air is blown from the bottom and,

Tropellas or side-blown converter in which the blast of cold air

is blown from the side of the converter.

A side blown converter can produce high temperature molten steels

(3200 3300F) which are required to pour thin sectioned steel

castings.

1.11.8.1 Working

The metal charge is melted in a cupola and it is brought to the

converter for refining the same.

The converter is tilted down, the molten cupola iron is given a

desulfurizing treatment in the ladle and is transferred to the

converter which is then tilted back to the upright position.

Cold air is blown through tuyeres located in the side of the

converter over the molten iron at a pressure of about about 0.35

bar.

The oxygen of the cold air burns (oxidizes) Mn and Si to form

slag; the carbon is oxidized out of the charge (melt) and produces

CO and CO2.

These oxidizing reactions are exothermic and thus no fuel is

required for heating purposes; rather the heat generated by these

reactions raises the temperature of the metal to about 1700Cwhich is sufficient for pouring purposes.

The cold air blow is continued (only) until carbon is reduced to

about 0.1 to 0.2%.

The colour and length of the flame originating from the converter

nose gives an indication of the rate of oxidation and the order of

oxidation of the elements (like C, Si and Mn).

Photoelectric devices can be used to mark the end of the air blast.


1.11.9 Pit Furnace

Pit furnace is a type of a furnace bath which is installed in the form

of a pit and is used for melting small quantities of ferrous and non ferrous

metals for production of castings. It is provided with refractory inside and

chimney at the top. Generally coke is used as fuel. Natural and artificial

draught can be used for increasing the capability towards smooth operation

of the furnace. Fig. 1.42 shows the typical pit furnace.

1.11.10 Crucible Furnaces

In a crucible furnace, the metal charge is placed and melted in a

crucible.

A crucible is made up of silicon carbide, graphite or other refractory

materials and it can withstand high temperatures. Fig. 1.43

Crucibles are available in different sizes ranging from No.1 to No.

400. Each number indicates the amount of metal which can be

handled conveniently by that crucible.

coke

R efracto rylining

C ruciblecon ta in ing

m etal

cover

Chi

mn

ey

S tee l she ll

P it

C oncretelining

S lid ingdoor

G ateN a turalD raught

Fig. 1.42. Pit Furnace.


A crucible furnace is though mainly used for melting of nonferrous

metals and low melting point alloys, it is being used for melting

cast iron and steel also.

R efractory lin ing

.. . .

....

. ....

.. .

... .. .

....

. ....

.. .

... ..

.

..

.

Fig. 1.43 (b) Stationery Pot

C ove r

Fuel

S tee l she ll

R e fractory lin ing

L ift-ou tcruc ib le

.. . .

....

. ....

.. .

....

. ....

.. .

....

. ....

Fuel

Supp ort b lo ck

Fig. 1.43 (a) Lift ou t cruc ible

C ove r


A crucible furnace consists of a steel shell provided with refractory

(fire brick) lining inside.

There are three types of crucible furnaces

(a) Lift out crucible

(b) Stationary Pot

(c) Tilting Pot furnace

Crucible furnaces are further classified as

Gas and oil fired crucible furnaces (stationary).

Coke fired crucible furnace (stationary).

A crucible furnace has the following advantages

Low initial cost

Easy to operate

Low cost of fuel

Advantages of an oil or gas fired crucible furnace over a coke tired furnace

Oil and gas heatup more quickly than coke and provide a fast

melting rate.

(c ) Tilting pot furnaces.

Fra m e

C over

Tiltinghandle

Fuel

S tee l shell

C rucible furnace

Fig. 1.43. Three types of crucible furnaces


The furnace heating can be immediately stopped in oil fired

furnace

A coke fired furnace needs an enclosed ash pan whereas nothing

like that is required in oil or gas fired furnaces.

Floor space can be saved by using oil or gas fired furnace. It

requires less floor space, less labour with improved and easier

control of temperature.

1.11.11 Electric Furnaces

Electric furnaces are employed for the production of high quality

castings, because: the furnace atmosphere can be more closely controlled,

losses by oxidation can be eliminated, alloying elements can be added without

fear of (their) loss (due to oxidation). composition of the melt and its

temperature can be accurately controlled.

Electric furnaces are used for melting steels (including alloy steel i.e.,

tool steels and stainless steels), high-test and alloy cast iron, brasses. Capacity

of electric furnaces ranges from 250 kg to 10 tons.

1.11.11.1 Types of Electric Furnaces

Direct arc furnace.

Indirect arc furnace.

Resistance heating type.

Coreless type (or High frequency) induction furnace.

Core type (or Low frequency) induction furnace.

1.11.11.2 Direct Arc furnace

Direct arc furnace has its diameter up to 6 metres and capacity of

about 125 tons.

It re-melts steels of widely differing compositions.

Rating of the transformers supplying power to the arc ranges from

800 KVA to 40,000 KVA.

A 50 ton direct arc furnace may require arc current of the order

of 25000 Amps and arc voltage of about 250V.


1.11.11.2.1 Construction

A direct arc furnace consists of a heavy steel shell lined with

refractory brick and silica for acid lined furnaces and magnesite for

basic lined furnaces.

The roof of the direct arc furnace consists of steel roofing in which

silica bricks are fixed in position.

Depending upon whether it is a two phase or three phase electric

furnace, two or three graphite electrodes are inserted through the

holes in the roof into the furnace.

All arc furnaces rest in bearings on their two sides and bearings in

turn are mounted in trunnions, thus arc furnaces can be tilted

backward or forward for charging, running off the slag and pouring

the molten metal into the ladle. Fig 1.44.

1.11.11.2.2 Working

The interior of the furnace (i.e. refractory linings, etc.) is preheated

before placing the metal charge (either foundry cast iron scrap or

steel scrap. (Fig. 1.44)

EE E

E E lectro de

R o of

S tee l shell

S lag

U p right po s ition

Sp ou t

Fu rn ace in tilted pos ition

Tapping o f m etal

3 ph ase pow ersupply

C h arg ing door

M oltenm etal

P itLad le

... . .. ... .. .. ..... .

..

.... . . ..

.. ..

.... ...

..

Fig. 1.44 Direct arc furnace.


Preheating is done by alternatively striking and breaking the arc

between the (vertical) electrodes and used electrode pieces

(removed after pre heating) kept on the hearth.

Once the cold charge has been placed on the hearth of the furnace,

electric arc is drawn between the electrodes and the surface of the

metal charge by lowering the electrodes down till the current jumps

the gap between the electrode and the charge surface.

The arc gap between the electrode and the charge is regulated by

automatic controls

Three arcs burning simultaneously produce a temperature of the

order of 11000F, and readily melt flux, sand and the metal scrap.

The slag formed due to melting of flux, sand etc. covers the molten

pool of metal. Slag present on the top of the molten metal bath

reduces its oxidation, refines the metal, and protects roof and side

walls from the large amount of heat radiated from the molten metal.

Before pouring the liquid metal into the ladle, the furnace is tilted

backward and the slag is poured off from the charging door.

The furnace is then tilted forward and the molten metal is emptied

into ladles.

1.11.11.2.3 Advantages of Direct Arc Furnace

Direct arc furnaces undertake a definite metal refining sequence.

Molten metal is refined to a proper analysis and is heated to a

suitable pouring temperature.

Analysis of melt can be kept to accurate limits.

High thermal efficiency as high as about 70%

It is easy to control the furnace atmosphere above the molten

metal.

Alloying elements like Cr, Ni and W can be recovered from the

scrap with little losses.

It can make steel directly from pig iron and steel scrap.

Arc furnace is larger and its electrical equipment is cheaper to

install.


An arc furnace is preferred for its quicker readiness for use.

1.11.11.2.4 Limitations

Heating costs are higher than for other furnaces.

This however can be adjusted to some extent by using low cost

scrap turnings or borings as metal charge.

1.11.11.2.5 Applications

In general, high quality carbon steels and alloy steels in bulk are made

in electric direct arc furnace.

Cast iron from foundry cast iron scrap.

1.11.11.3 Indirect Electric Arc Furnace

An indirect electric arc furnace has a capacity ranging from a few

Kgs to 2 Tons and is used for smaller melts.

An electric arc is struck between two graphite electrodes and the

metal charge does not form a part of the electric circuit.

The metal comes in contact with hot refractory lining and picks

up heat for melting from the linings and also metal charge melts

because of the radiations from the arc and the hot refractory walls

of the furnace and conduction from the hot refractory (wall)

linings, when the furnace rocks and molten metal rolls over the

same.

1.11.11.3.1 Construction

An indirect arc furnace consists of a barrel type shell made up of steel

plates, having refractory lining inside.

There are two openings for the two graphite electrodes and the third

is for the charging door for feeding the metal charge into the furnace built

up with pouring spout.

Furnace is mounted on the rollers (Refer Fig. 1.45) which are driven

by a rocking drive unit to rock the furnace back and forth during melting.

While the furnace rocks, liquid metal washes over the heated refractory linings

and absorbs heat from them. In addition during rocking, metal charge

constituents get mixed up thoroughly.


Rocking of furnace speeds up melting, stirs the molten metal, avoids

refractory linings from getting over-heated and thus increases their life.

The angle of rocking of furnace is adjusted in such a manner that the

liquid metal level remains below the pouring spout.

1.11.11.3.2 Operation

The furnace is charged with pig iron and scrap is placed above.

When the electric power is on, graphite electrodes are brought

nearer till the current jumps and an electric arc is set up between

them. The heat generated in the arc is responsible for melting the

charge.

A number of alloys one after the other can be easily melted in

this type of furnace. Additions of elements like Ni, Co, Cr, W,

Mo, V etc. can be made easily and conveniently.

Chargingdoor

Electrode 1

Power Lead

Pouring Spout

Support

Ro lle rs

M olten m etal

Electrode 2

Refractory lining

ShellArc

Fig. 1.45. Indirect Electric Arc Furnace.



The initial cost of the furnace and its auxiliary equipment is high.

It is limited to melting high quality metals and in smaller

quantities.

Time available for analysing the melt composition is very small,

thus the melt charge should be carefully selected and it should be

of required chemical composition.


High frequency induction furnace is very useful for special alloy

and high quality steels in small quantities.

It is used for melting Cast iron, Steel, Copper and its alloys.

1.11.11.4 Core Type (Or Low Frequency) / Induction Furnace

Construction and working A core type induction furnace operates as an ordinary transformer.

The primary coil has many turns and is wound on a laminated steel

core whereas the secondary coil of the transformer has one turn which

is a channel or loop of liquid metal within the furnace.

The furnace uses a. c. supply of 50 cycles per second.

Secondary currents (having high current values at low voltage) are

induced in the metal bath around the core and the heat is generated

due to the electrical resistance of the metal (charge) to the flow

of secondary currents.

Channel of molten metal around the coil connects to the main

metal container above, which holds the metal charge.

The metal in the channel gets heated, circulates through and stirs

the metal in the container and thus the melting process (of the

metal charge) proceeds.

Once the melt reaches the required pouring temperature it can be

ladled out from the pouring spout (refer Fig. 1.46).


1.11.11.4.1 Advantages

A core type induction furnace is the most efficient among the

induction melting furnaces.

It has thermal efficiency of about 80%. The furnace operation is

economical.

Melting is rapid, clean hence no combustion products are present

and oxidation losses are at a minimum.

Melt is accurately controlled with regards to its composition and

temperature.

Magnetic stirring of the melt ensures uniformity of the metal.

Pouring spou t

S tee l shell

R e fractorylin ing

C ircu la tio no f m elt

P lug fo rem pty ing

C hanne l ofm olten m eta l

C ircu la tio n of m elt

P rim ary co il

M olten m eta l

Fig. 1.46. Core Type (Or Low Frequency) / Induction Furnace.



This Furnace cannot be operated on solid metal charge

Furnace operation can be started only after filling the channels

with molten metal procured from some other furnace.

If once by chance metal gets solidified in the channels it cannot

remelted by the heat created in the secondary coil.

Core type furnace is more or less restricted to melt one alloy. For

melting another alloy, the furnace should be emptied, thoroughly

cleaned and restarted with the new molten alloy.

A core type furnace is not suitable for intermittent operation.


A core type furnace is used primarily for remelting non-ferrous

metals and their alloys.

It can be used for producing malleable cast iron also.

1.11.12 Overall Comparison Of Melting Furnaces

S. NoFurnace

typeHeating Method Applications

1 Crucible

Pit type Solid fuel, oil or gas Most of alloys exceptsteel

Tilting type Solid fuel, oil or gas Most of alloys exceptsteel

Bale out Gas, oil Light casting (diecastings)

2 Cupola Coke Cast iron, steel (duplexconverter)

3 Rever-beratory(air)

Solid fuel. gas or oil Non-ferrous alloys, castiron, malleable iron.

4 Rotary Pulverized solid fuel, gasor oil

Non-ferrous alloys, castiron, malleable andspecial. Duplex holding.

5 Open hearth Oil,Gas Steel


S. NoFurnace

typeHeating Method Applications

6 Arc furnace:

Direct arc Arc on metal charge Steel, Cast Iron

Indirect arc Radiant arc Non-ferrous alloys, highalloy steel and specialirons.

7 Inductionfurnace:

Core type Low frequency induction Cast Iron, non-ferrousalloys.

Coreless High frequency induction Steel and alloy steel.

8 Resistancefurnace

Resistor Radiant resistor rod Steel, cast iron, copperalloys.

Resistance Elements (shroud orimmersion)

Non-ferrous alloys.

1.12 GATING SYSTEMThe assembly of channels which facilitates the molten metal to enter

in to the mould cavity is called the gating (or) gating system.

Pouring Basin

Sprue

Sprue W e ll

G ateR unner In G a tes

C asting

In G a tes

Fig. 1.47 Gating System


1.12.1 Necessity of the gating system

The molten metal from the ladle is not introduced directly into the

mould cavity, because it will strike the bottom of the mould cavity with a

great velocity and can cause considerable erosion at the bottom of the mould

cavity.

Because of the above mentioned reason, the molten metal is introduced

into the mould cavity from the ladle through the gating system.

1.12.2 Parts of the gating system

1. Pouring basin

2. Sprue (or) down gates

3. Runner (or) Cross gates

4. Gates (or) ingates

5. Risers

Pouring basin: This part of the gating system is made on or in the top of

the sprue that receives the stream of molten metal poured from the ladle.

Sometimes the metal is directly poured into the top of the spure which is

made with a funnel shaped opening. However better results are usually

obtained with the help of pouring basin.

The pouring basin should be made large and should be placed near to

the edge of the moulding box to fill the mould cavity quickly.

Purpose:

1. To direct the flow rate of metal from ladder to the sprue.

2. To help maintaining the required rate of liquid metal flow.

3. To reduce turbulence and vortexing at the sprue entrance.

4. Helps in seperating cross, slag etc from metal before it enters the sprue.

Spruce:

1. The vertical passage that passes through the cope and connects the

pouring basin with the runner or gate is called the sprue or downgate.

2. The cross section of a sprue may be square, rectangular or circular.


3. The sprues are generally tapered downward (2 degree to 4 degree) to

avoid aspiration of air and metal damage.

4. Sprues upto 20 mm diameter are round in section whereas larger sprues

are often rectangular in section.

5. A round sprue has a minimum surface exposed to cooling and offers

the lowest resistance to the flow of metal.

6. In rectangular sprue, aspiration and turbulence are minimized.

7. Spures may be designed with either a positive taper, a reverse taper or

with no taper at all.

Sprue well: It changes the direction of flow of the molten metal to right

angle and passes it to the runner.

The sprue is tapered with its bigger end at top to receive the liquid

metal and the smaller end is connected to the runner.

Runner

The molten metal is usually carried from sprue well to several gates

through a passage called runner. Runners are normally made trapezoidal in

shape.

The runner is generally preferred in the drag but for ferrous metals it

is provided in the cope with ingates in the drag.

The runner should be streamlined to avoid aspiration and turbulence.

When a mould has more than one cavity the common gate supplying

metal to a number of cavities is also called as runner and the branches from

the runner to the respective mould cavities are referred as ingates.

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Positive Taper Sprue(a)

R eve rse Taper Sp rue(b)

Straight (o r) no tape r sprue (c)

Fig. 1.48 Sprue design

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Gate

Gates is a passage through which the molten metal flows from the

runner to the mould cavity. The gates should break off from the casting after

solidification.

For this, at the junction to the cavity the gates are much reduced in

thickness. This will also choke the flow of metal and ensure its quiet entrance

into the mould cavity. In actual practice, the best cross-section for gates is a

trapezoidal one that smoothly passes into a rectangular section at the junction

of the cavity.

According to their positions in the mould cavity, gates are classified

as

Top gates

Parting gates

Bottom gates

Top gate

This is shown in Fig. 1.49Generally top gates are used for small

and simple moulds or for larger castings

made in moulds of erosion resistant

material.

For light and oxidisable metal

like aluminium and magnesium, top

gating is not advisable because of fear

of entrapment due to turbulent pouring.

(ii) Bottom gates

This is shown in Fig. 1.50 Here,

the molten metal flows down the

bottom of the mould cavity in

the drag and enters at the bottom

of the casting and rises gently in

the mould and around the cores.

C ope

D rag M ou ld Cavity

Fig. 1.50 Bottom Gates

Sand

CopeDrag

Pouring Cup

Sand

Strainer Core

M ould Cavity

Fig. 1.49 Top Gate


In the bottom gating system, turbulence and mould erosion are the

least. However time taken to fill the mould is more.

Also, directional solidification is difficult to achieve because the

metal continues to lose its heat into the mould cavity and when

it reaches the riser, metal becomes much cooler.

Bottom gates are best suited for large sized steel castings.

Parting gate

Here, the metal enters the mould at

the parting plane when part of the casting

is in the cope and part in the drag. (Refer

Fig. 1.51)

For the mould cavity in the drag, it

is a top gate and for the cavity in the cope

it is a bottom gate. Thus this type of gating tries to derive the best of both

top and bottom gates.

Among all the gates, preparation of parting gate is the easiest and most

economical one.

Parting gate is the most widely used gate in sand castings.

(iv) Step gateIn a step gate a number of

ingates are arranged in vertical steps.

Refer Fig. 1.52. The metal enters

through these ingates whose sizes are

normally increased from top to bottom

such that metal enters the mould cavity

from the bottom most gate and then

progressively moves to the higher gates.

Step gates are used for heavy and

large castings.

While designing a casting, it is essential to choose a suitable gate,

considering the casting material, casting shape and size so as to produce a

sound casting.

M ou ldC avity

C opeD rag

Parting L ine

Fig. 1.51 Parting Gate

Sand

Sand Inga tes

M ou ld C avity

Fig. 1.52 Step Gate


Gating ratio

The term gating ratio is used to describe the relative cross sectional

areas of the components of a gating system.

It is defined as the ratio of sprue area to total runner area to total gate

area.

i.e., sprue area : runner area : gate area.

Choke

Choke is a part of the gating system which has the smallest

cross-sectional area.

Functions of choke

1. The function of choke is to control the rate of metal flow by lowering

the flow velocity in the runner.

2. To hold back slag and foreign material and float these in the cope side

of the runner.

3. To minimise sand erosion in the runner.

The gating ratio reveals whether the cross-section increases or decreases

towards the mould cavity. Accordingly, the gating system may be classified

as,

(i) Pressurized gating system

(ii) Unpressurized gating system

Pressurized gating system

In pressurized gating system, the ingates serve as the choke.

A back pressure is maintained causing the entire gating system to

become pressurized.

Here, the molten metal enters the mould cavity uniformly.

For a given metal flow rate, pressurized systems are generally smaller

in volume than unpressurized ones.

This system is adopted for metals like iron, steel, brass, etc.

A typical gating ratio in the system can be 4:3:2.


(ii) Unpressurized gating system:

Here, the sprue base serves as the choke.

The typical gating ratios in this system can be

1:2:2,1:2:4, 1:3:3, or 1:4:4.

This gating system requires careful design to ensure them being

kept filled during pouring. Drag runners and cope gates aid in

maintaining a full runner, but careful streaming is essential to

eliminate the separation effects and consequent air separation.

This system is adopted for light, oxidisable metals like aluminium

and magnesium where the turbulence is to be minimised by

slowing down the rate of metal flow.

1.13 RISER OF CASTING

Riser is also called as feeder head.

Risers are reservoirs designed and located to feed molten metal to the

solidifying casting to compensate for solidification shrinkage. Riser is a hole,

cut or moulded in the cope to permit the molten metal rise above the highest

point in the casting. It provides a visual check to ensure filling up of mould

cavity. Riser find use in casting of heavy sections (or) of high shrinkage

alloys.

1.13.1 Functions of risers

Provide extra metal to compensate for the volumetric shrinkage.

They act as a heat source so they freeze last and promote

directional solidification.

Risers indicate to the pourer whether the metal has been

completely filled up or not in the mould cavity.

They permit the escape of air and gases as the mould cavity is

filled up with molten metal.

1.13.2 Types of risers

Risers can be classified into two types

(a) Open riser

(b) Blind riser


(a) Open riser

It is the conventional riser whose top is exposed to the atmosphere.

The molten metal is fed into the riser through the sprue and runners under

gravity. Refer Fig. 1.53 (a)

Advantages

Can be easily moulded.

Since it is open to atmosphere, it will not draw metal from the

casting as a result of partial vacuum in the riser.

Such risers serve as collectors of non-metallic inclusions floating

upto the surface.

Limitations

Their height should commensurate with the height of the cope;

this reduces the yield of the casting.

These are the holes through which foreign matter may get into the

mould cavity.

(b) Blind riser

The blind riser is enclosed by the sand mould and is designed for a

minimum surface area per unit volume. A vent or permeable core at the top

of the riser may be provided to have some exposure to the atmosphere. Refer

Fig. 1.53 (b)

Sprue

Top R iser End R iser

M ou ld Cavity Parting

L ine

(a)

M ou ldCavity

PartingLine

Blind types ide r iser

Perm eable Core

(b)Fig. 1.53 Types of Risers

Sand

Sand


Advantages

Can be removed more easily from the casting than an open riser.

Since a blind riser is surrounded on all sides by moulding sand,

therefore, it looses heat slowly which helps in better directional

solidification of the casting.

It can be smaller than a comparable open riser, therefore, more

yield is obtained.

Limitation

As the metal in it cools, metal skins may quickly form on its walls.

This results in a vacuum in the riser and the riser will not actually draw

metal from the casting. This may be avoided by inserting a permeable dry

sand core into the riser cavity, connecting it to the mould sand layers. Through

these sand layers air passes into the riser interior and thus the riser operates

under atmospheric pressure.

1.13.3 Riser shapeThe metal in the riser should remain in the molten state for a longer

time than in the mould cavity.

The heat loss in the riser should therefore be kept to a minimum level.

It means riser must freeze more slowly than the casting.

Thus their shape should be such as to give volume - to - surface ratio

a maximum value.

From this point of view a spherical shape is ideal one as it is having

the lowest surface area for a same volume.

But risers of spherical shape is difficult to mould. Therefore, a

cylindrical shape is preferred.

Height of a cylindrical riser 1.5 diameter of riser.

1.13.4 Riser sizeThe solidification time of a casting depends upon the heat in the casting

(directly) and depends (inversely) upon the surface area of the casting.

Based on the above facts, the following relations have been suggested

for determining the riser size.


1. Chvorinov’s rule (for metal casting)

Chvorinov’s rule states that total freezing (solidification) time for a

casting is a function of the ratio of volume to surface area.

solidifaction time

orfreezing time t

C

Volume VSurface area SA

2

i.e. t C

VSA

2

Where,

V – Volume of casting

SA – Surface area of casting

C – Constant of proportionality that depends uponcomposition/properties of cast metal, mould material etc.

Since the metal in the riser must be the last to solidify to achieve

solidification.

VSA

riser

2

VSA

casting

2

Best riser is one whose

VSA

2

is 10 to 15% larger than that of the

casting.

Since V and SA for the casting are known

CSA

riser

can be determined.

Assuming the height to diameter ratio for the cylindrical riser, the riser size

can be determined.

Chvorinov’s rule is not very accurate, since it does not consider

solidification contraction (or) shrinkage. This method is valid for calculating

proper riser size for short - freezing range alloys such as steel and pure

metals.

For non-ferrous alloys, there is no satisfactory relationship for

determining riser size.


2. Caine’s methodIn this method, riser size calculation size is based on experimentally

determined hyperbolic relationship between relative freezing times and

volumes of the casting and the riser.

Caine’s method states that, if the casting solidifies infinitely rapidly

the riser (feeder) volume should be equal to the solidification shrinkage of

the casting and if the feeder and casting solidify at the same rate, the feeder

should be infinitely large.

Relative freezing time (or) freezing ratio Rx

is given by

Rx SA/V casting

SA/Vriser

Volume ratio Ry

is given as

Ry Vriser

Vcasting

Caine’s formula is given by

Rx a

Ry b c

Where

a freezing characteristic constant for the metal

b Contraction into from liquid to solid

c relative freezing rate of riser and casting

Table 1.1 shows the typical value of a, b and c for commonly used

metals are given below.

Table 1.1

S.No. Cost-metals a b c

1. Grey cast-iron 0.33 0.03 1.00

2. Cast-iron, brass 0.04 0.17 1.00

3. Steel 0.12 0.05 1.00

4. Aluminium 0.10 0.06 1.08

5. Aluminium bronze 0.24 0.17 1.00

6. Silicon bronze 0.24 0.17 1.00

R y

R x

Sound C asting

D efective C asting

Fig. 1.54


Fig. 1.54 shows a typical hyperbolic curve. In order to find the riser

size for a given casting, the diameter and height of the riser are assumed.

After knowing the values of a, b, and c, the values of Rx and Ry are calculated

and plotted on hyperbolic curve figure. In case the values of Rx and Ry meet

the above curve, the assumed riser size is satisfactory, otherwise a new

assumption is made.

1.13.5 Location of the riser

In addition to the shape and size, a riser must be properly located

to obtain a sound casting. Location of riser should be such that

the riser ensures directional solidification. Since the heaviest

section of the casting solidifies last, the riser should be located to

feed this section the heaviest section will now act as a riser for

other sections which are not so heavy or thick.

1.14 PRINCIPLE OF SPECIAL CASTING PROCESSESSand moulds are single purpose moulds as they are completely

destroyed after the casting has been removed from the moulding box. It

becomes therefore obvious that the use of a permanent mould would do a

considerable saving in labour cost of mould making.

1.14.1 Advantages of Special casting techniques over conventional sand casting.

Greater dimensional accuracy with higher metallurgical quality.

High production rates and hence lower production cost (in certain

cases).

Ability to cast extremely thin sections.

Better surface finish on the castings therefore low labour and

finishing costs.

Castings may possess a denser and finer grain structure and posses

higher mechanical properties.


1.14.2 Classification of Special Casting Processes

Special Casting Processes are classified as follows

Based on Metal Mould Casting

Gravity (or) permanent mould-casting

Die casting

Cold chamber process Hot chamber process

Slush casting

Based on Non metallic Mould Casting

Centrifugal casting

Carbon-dioxide moulding

Investment mould casting (or) lost-wax process

Shell moulding

Plaster moulding

Continuous casting

Reciprocating moulds - Draw casting

Stationary moulds

Direct sheet casting

1.14.3 Gravity (or) Permanent mould-casting (or) Metallic Moulding

A gravity die (or) permanent mould casting has a permanent

mould. Fig 1.55

The mould can be reused many times before it is discarded or

rebuilt.

Molten metal is poured into the mould under gravity and no

external pressure is applied. The liquid metal solidifies under

pressure of metal in the risers, etc.

Permanent moulds are made of dense, fine grained, heat resistant

cast iron, steel, bronze, anodized aluminium, graphite or other

suitable refractories.

A permanent mould is made in two halves in order to facilitate

the removal of casting from the mould.


The mould walls of a permanent mould have thickness from 15

mm to 50 mm and can remove greater amounts of heat from the

casting.

Pouring cup, sprue, gates and riser are built in the mould halves

itself. The two mould halves are securely clamped together before

pouring.

Simple mechanical clamps (latches, toggle,clamps etc.) are

adequate for small moulds whereas larger permanent moulds need

pneumatic, or other power clamping methods.

C avity

C ore

F

Fig. 1.55 (b) Cores (if used) are inserted and m ould is closed

Stationarym ou ld section

Spray nozz le

H ydraulic cy linderto open and c lose m ou ld

M ovablem ou ld section

Fig. 1.55. Mould is preheated and coated (a)



Permanent mould casting process are costly and is generally limited to

those applications only where an economic or engineering gain is obtained.

Examples are Carburetor bodies, Hydraulic brake cylinders, Refrigeration

castings, Washing machine gears and gear covers, Connecting rods,

automotive pistons, aircraft and missile castings.

1.14.4 Shell mould casting

1.14.4.1 Working Principle

Fig 1.56 Shows the process of Shell mould casting

The 2-piece pattern is made of metal (e.g. aluminum or steel), it

is heated to between 175C 370C and coated with a lubricant,

e.g. silicone spray.

Each heated half-pattern is covered with a mixture of sand and a

thermoset resin/epoxy binder. The binder glues a layer of sand to

the pattern, forming a shell. The process may be repeated to get

a thicker shell.

The assembly is baked to cure it.

The patterns are removed and the two half-shells joined together

to form the mould and then metal is poured into the mould.

F

(c) M olten meta l is poured into the m ould, where it solidifies.

Fig. 1.55. Permanent Mould Casting


When the metal solidifies, the shell is broken to get the part.

Fig.1.56 shows Steps in Shell Casting (1) A match-plate or

cope-and-drag metal pattern is heated and placed over a box containing sand

mixed with thermosetting resin.

(2) Box is inverted so that sand and resin fall onto the hot pattern,

causing a layer of the mixture to partially cure on the surface to form a hard

shell;

(3) Box is repositioned so that loose uncured particles drop away;

(4) Sand shell mould is heated in oven for several minutes to complete

curing;

(5) Shell mold is stripped from the pattern

(3) (4)

. .. .. .... .... ... . .. .. ... ..

...... ... .. .. .

. .. .... ... ... . . .. .. .

..... ... . . ..

..

..

.

.. . ...... ..

. . .... . ....... . .

. ...

. . . ... . ....

. .. ... . .. ..... ....

.. . . .... ...

. .... .....

.

Shell

Fig. 1.56

Sandw ithresinb inder

D um pbox

H eated pa tte rn

(1)

. . . ...

. .. . . ..

....

. . ... .. ...

...

.....

.. .

..

.... . ... .. .

... .

...

...

.. ...... ... . . . . .....

.. ...... ..... .

... .. .. . ..

.. ... ..

.. ... .. .

. . .. .

. ... ..

..... ..

.......

......

.. . . .

...

(2)Fig 1.56


(6) Two halves of the shell mold are assembled, supported by sand or

metal shot in a box and pouring is accomplished.

(7) The finished casting with sprue is removed.

1.14.4.2 Advantages

Castings as thin as 1.5 mm and of high definition can be casted

satisfactorily.

Good dimensional accuracy - machining often not required.

(5)Fig. 1.56

Shell m ou ld

Pa tte rn

... ... ..

....

... ..

.

. . ... . .. .

Shell m oulds M etal shotFlask

(6)

(7)


Mould collapsibility minimizes cracks in casting.

It can be mechanized for mass production.

There is no surface chilling or skin hardening of castings, since

shell is an excellent heat insulator.

Cooling rate of cast metal being slow, castings possess grain sizes

larger than those obtained in green sand moulds.

Shell mould made castings possess excellent surface finish and

high tolerance of the order 0.002 to 0.003 mm per mm is possible.

Shell moulding faithfully reproduces details with sharp clean edges

thereby rendering fettling and machining unnecessary.

Smoother cavity surface permits easier flow of molten metal and

better surface finish.

1.14.4.3 Disadvantages

Shell moulding is uneconomical on small scale production. Resin

costs are comparatively high.

Heavy weight castings weighing greater than 10 kg may not be

able to be casted by shell moulding.

Moulds are not normally economically recoverable.

Shapes in which proper parting and gating cannot be obtained are

not suitable for production with shell moulding process.

The maximum size of the casting is limited by the maximum size

of the shell which can be feasibly produced and poured.

Low carbon steels castings made by shell moulding may show

depressions on their upper surface.


Components cast by shell moulding are: Automotive rocker arms,

valves, small pipes, camshaft, bushings valve bodies, spacers, brackets,

manifolds, bearing caps, shafts and gears.

Shell moulding is ideal for mass production of small castings where

the degree of intricacy causes high rejection rates in green sand

moulding.


Various alloys which can be satisfactorily cast by shell moulding

are: aluminium alloys, copper alloys, cast irons, stainless steels etc.

A number of small hydraulic castings in stainless steel and corner

alloys are produced by shell moulding.

Shell moulding is suited to ferrous and non-ferrous alloy castings

in the range 0.1 to 10 kg.

1.14.5 Investment casting (Lost wax casting)


Investment casting uses a wax pattern which is coated with refractory

materials to form a mould. The wax is then melted out and the mould cavity

is filled with molten metal. Cast metal is cooled and the slurry broken to get

the castings. It can be used for high precision complex shapes from high

melting point metals that are not readily machinable.

1.14.5.2 Steps involves investment casting

Fig 1.57 shows the step by step method of performing investment

casting.

Pattern creation – (Fig 1.57 (1),(2)) The wax patterns are typically injection moulded into a metal die

and are formed as one piece.

Several of these patterns are attached to a central wax gating

system (sprue, runners, and risers) to form a tree-like assembly.

The gating system forms the channels through which the molten

metal will flow to the mould cavity.

Mould creation – (Fig 1.57 (3),(4),(5)) This "pattern tree" is dipped into a slurry of fine ceramic particles,

coated with more coarse particles and then dried to form a ceramic

shell around the patterns and gating system.

This process is repeated until the shell is thick enough to withstand

the molten metal it will encounter.


Waxpatte rn

(1 )

Waxsprue

(2)(3 )

(4 )

Wax

Heat

(5 ) Heated in oven

(7)

Fig. 1.57 Steps involved in process of Investment casting

Ceram ic partic les

S lurry of fineceramic partic les

Fina lp roduct

Pouring m olten m etal


The shell is then placed into an oven and the wax is melted out

leaving a hollow ceramic shell that acts as a one-piece mould,

hence the name “lost wax” casting.

Pouring – (Fig 1.57 (6))

The mould is preheated in a furnace to approximately 1000C and

the molten metal is poured from a ladle into the gating system of

the mould, filling the mould cavity.

Pouring is typically achieved manually under the force of gravity,

but other methods such as vacuum or pressure are sometimes used.

Cooling After the mould has been filled, the molten metal is allowed to

cool and solidify into the shape of the final casting.

Cooling time depends on the thickness of the part, thickness of

the mould and the material used.

Casting removal (Fig 1.57 (7)) After the molten metal has cooled, the mould can be broken and

the casting removed.

The ceramic mould is typically broken using water jets, but several

other methods exist.

Once removed, the parts are separated from the gating system by

either sawing or cold breaking (using liquid nitrogen).

FinishingMost often finishing operations such as grinding or sandblasting are

used to smooth the part at the gates. Heat treatment is also sometimes used

to harden the final part.


Investment casting is used for making components like parts for

sewing machines, locks, rifles, beer barrels and burner, nozzles,

engines, textile cutting machines, motion picture projectors,

pulverizing equipments and chemical industry equipments, dentistry

and surgical implants


To fabricate difficult-to-machine and difficult-to-work alloys into

highly complex shapes such as hollow turbine blades.

For casting jewellery and art castings.

1.14.5.4 Advantages

Parts of greater complexity and intricacy can be cast.

Close dimensional control 0.075 mm.

Good surface finish.

Irregular parts which cannot be machined or difficult to machine

may be cast by investment casting process.

The lost wax can be reused.

Additional machining is not required in normal course.

Al, Cu, Ni, Carbon and alloy steels, tool steels etc. are the common

materials.

Cast does not have disfiguring.


Process is expensive and time consuming (slow).

Pattern making is additional cost.

Size of the casting is limited.

Cores cannot be used

Preferred for casting weight less than 5 kg, maximum dimension

less than 300 mm.

Thickness is usually restricted to 15 mm.

1.14.6 Ceramic Mould Casting

1.14.6.1 Classification of ceramics

Glasses –optical, composite, containers, house hold

Clay products – White ware, bricks

Refractory – Bricks for high temperature (furnaces) Al2O3-SiO2,

ZrO2, Al2O3

Abrasives – Sand paper, cutting and polishing - SiC

Cements – Composites, structural


Advanced ceramics – Engine rotor, valves, bearings, Sensors -

Si3N4, ZrO2, Al2O3.

1.14.6.2 Working Principle of ceramic mould casting

A suspension of ceramic powders in water, called a slip, is poured

into a porous plaster of paris mould where the water from the mix is absorbed

to form a firm layer of clay. The slip composition is 25% to 40% water. It

is similar to plaster mould. Ceramic slurry mixture of fine grained Zircon

(ZrSiO4), aluminum oxide and fused Shell is baked at high temperature and

casted.

Two principal variations:

Drain casting - the mould is inverted to drain excess slip after a

semi-solid layer has been formed, thus producing a hollow product

Fig 1.58

Solid casting - to produce solid products, mould not drained.

Fig. 1.58. Sequence of steps in drain casting, a form of slip casting:

(1) slip is poured into mould cavity, (2) water is absorbed into plaster

m ould to form a firm layer, (3) excess slip is poured out, and

(4) solid casting in which part is removed from m ould and trim m ed



High temperature alloys, stainless steel or tool steel parts: examples

impellers, cutters, dies etc.

This process can be used to make very good quality castings of

steel or even stainless steel, it is used for parts such as impellor

blades (for turbines, pumps, or rotors for motor-boats).

1.14.7 Pressure Die Casting

In pressure die casting, molten metal is forced into permanent mould

(die) cavity under pressure. The pressure is generally obtained by compressed

air or hydraulically. The pressure varies from 70 to 5000 Bars and is

maintained while the casting solidifies. Associated with externally applied high

pressure, is the high velocity with which the liquid metal is injected into the

die, and these conditions give a unique capacity for the production of intricate

components at relatively low cost. This process is called simply die casting.

There are four main types of die-casting machine which are given as

under.

1. Hot chamber die casting machine

2. Cold chamber die casting machine.

3. Air blown or goose neck type machine

4. Vacuum die-casting machine

Some commonly used pressure die casting processes are discussed here.

1.14.7.1 Hot chamber die-casting

Hot chamber die-casting machine can produce about 60 or more

castings of up to 20 kg each per hour and several hundred castings per hour

for single impression castings weighing a few grams. The melting unit of

setup comprises of an integral part of the process. This process may be of

gooseneck or air-injection type or submerged plunger type-air blown or goose

neck type machine as shown in Fig. 1.59

It is capable of performing the following functions:


Holding two die halves finally together, closing the die, injecting

molten metal into die, opening the die and ejecting the casting out of the

die.

1.14.7.1.1 Construction and working

A die casting machine consists of four basic elements namely frame,

source of molten metal and molten metal transfer mechanism, die-casting dies,

and metal injection mechanism. A cast iron gooseneck is so pivoted in the

setup that it can be dipped beneath the surface of the molten metal to receive

the same when needed. The molten metal fills the cylindrical portion and the

curved passageways of the gooseneck. Gooseneck is then raised and connected

to an airline which supplies pressure to force the molten metal into the closed

die. Air pressure required for injecting metal into the die is of the order of

30 to 45 Bars. The two mould halves are securely clamped together before

pouring. On solidification of the die cast part, the gooseneck is again dipped

beneath the molten metal to receive the molten metal again for the next cycle.

The die halves are opened out and the die cast part is ejected and die closes

in order to receive a molten metal for producing the next casting. The cycle

. . . . . .. . . . ... . . ........ . . ........ . . ........ . . . ....... . . . ...... .

. . . . . . . . . .. . . . . .. .. . ...... ............ . . . ....... . .. ....... . . ........ .. ...

AirStationarydie

M ovabledie

Ejectorpins

Gooseneckin jector

Refractorylining

M etal potFire box

Burner

M oltenm etal

.. . ... . . . ..... . . . ...... . . .. ....... .. ... .. ... ..... .. ... . .

. .

. .. .. . . ... . . . .. .. . ... . . . .. .. . ....... . . ....

. . . ... . . . ......

Fig. 1.59 Air b lown (or) goose neck type die casting setup


repeats again and again. Generally large permanent moulds need pneumatic

or other power clamping devices. A permanent mould casting may range in

weight from a few grams to 150 kg. for aluminum.


Die casting is widely used for mass production and is most suitable

for non-ferrous metals and alloys of low fusion temperature. The

casting process is economic and rapid.

The surface achieved in casting is so smooth that it does not

require any finishing operation.

The material is dense, homogeneous and has no possibility of sand

inclusions or other cast impurities.

Uniform thickness on castings can also be maintained.

The principal base metals most commonly employed in the casting

are zinc, aluminum, copper, magnesium, lead and tin.

Under low category involves zinc, tin and lead base alloys.

Under high temperature category aluminum and copper base alloys

are involved.

1.14.7.2 Cold chamber die casting

Cold chamber die casting process differs from hot chamber die casting

in following respects.

1. Melting unit is generally not an integral part of the cold chamber die

casting machine. Molten metal is brought and poured into die casting

machine with help of ladles and a piston injects metal under high

pressure into die cavity (Fig 1.60)

2. Molten metal poured into the cold chamber casting machine is generally

at lower temperature as compared to that poured in hot chamber die

casting machine.

3. For this reason, a cold chamber die casting process has to be made use

of pressure much higher (of the order of 200 to 2000 Bars) than those

applied in hot chamber process.

4. High pressure tends to increase the fluidity of molten metal possessing

relatively lower temperature.


5. Lower temperature of molten metal accompanied with higher injection

pressure will produce castings of dense structure, sustained dimensional

accuracy and free from blow-holes.

6. Die components experience less thermal stresses due to lower

temperature of molten metal. However, the dies are often required to

be made stronger in order to bear higher pressures.

. .... . ....... ............................................ ....... ...... .......................................

Shot chamber

Ram

Ladle

M ovabledie half

Ejectorpins

Cavity

Fixed d ie ha lf

(1)Fig. 1.60

F

(2)

...........................................

........

..................

.......................................................

.

Fig. 1.60 Cycles in cold-chamber casting: (1) W ith die closed and ram withdrawn, m olten m etal is poured into the cham ber

(2) Ram forces m etal to flow into die, m aintain ing pressure during cooling and solidification.


1.14.7.2.1 Advantages

It is a very quick process and is used for mass production with

improved surface finish

Variation in size and shape of the castings is less

Thin section (0.5 mm Zn, 0.8 mm Al and 0.7 mm Mg) can be

easily cast.

Good tolerances with low rejection rate.

Cost of production is less.

Process requires less space.

Life of die is long.

1.14.7.2.2 Disadvantages

Cost of die is high and only thin casting can be produced.

Special skill is required and not suitable for low production.

Unless special precautions are adopted for evaluation of air from

die-cavity, some air is always entrapped in castings causing

porosity.


Aluminum, brass and magnesium alloys can be cast.

Low melting-point alloys (zinc, tin, lead) are easy to be cast.

1.14.8 Centrifugal Casting

Centrifugal casting uses a permanent mould that is rotated about

its axis at a speed between 300 to 3000 rpm as the molten metal

is poured.

Centrifugal forces cause the metal to be pushed out towards the

mould walls, where it solidifies after cooling. Parts cast in this

method have a fine grain microstructure, which is resistant to

atmospheric corrosion; hence this method has been used to

manufacture of hollow pipes and other annular shapes.

Since metal is heavier than impurities, most of the impurities and

inclusions are closer to the inner diameter and can be machined

away.


Surface finish along the inner diameter is much worse than along

the outer surface.

Centrifugal- casting techniques are usually classified as.

1. True centrifugal casting.

2. Semi-centrifugal casting.

3. Centrifuge casting.

1.14.8.1 True Centrifugal Casting

Molten metal is poured into a rotating mould to produce a tubular

part. In some operations, mould rotation commences after pouring

Fig. 1.61 (a) True centrifugal casting

End view

Free ro lle rM ou ld

M ould

Pouring bas in

Side viewRo lle rs

Fig 1.61 (b)


rather than before. A cylindrical mould is made to rotate on its

own axis at a speed such that the metal being poured is thrown

to the outer surface of the mould cavity. The metal solidifies in

the form of a hollow cylinder (Fig 1.61). The cylinder wall

thickness is controlled by the amount of liquid metal poured.

Casting cools and solidifies from outside, toward the axis of

rotation, thereby providing conditions which set up directional

solidification to produce castings free from shrinkage.

They have more or less a symmetrical configuration (round, square,

hexagonal etc.) on their outer contour and do not need any center

Core.

Advantages

1. Relatively lighter impurities within the liquid metal such as sand, slag,

oxides and gas float more quickly towards the centre of rotation from

where they can be easily machined out thereby giving a clean metal

casting.

2. Dense and fine grained metal castings are produced by true centrifugal

casting techniques.

3. There is proper directional solidification from outside (surface) towards

inwards of the casting.

4. There is no need of a central core or gating system required to make

a pipe or tube.

Disadvantages

1. True centrifugal casting is limited to certain shapes.

2. Equipment costs are high.

3. Skilled workers are required for operation and maintenance.

Applications

Parts such as cast iron pipes, alloy steel pipes, tubing/annular

sections, bushings and rings.

Liners for I.C. Engines, rings, short or long pots and other annular

components.


1.14.8.2 Semi-Centrifugal Casting

Centrifugal force is used to produce solid castings rather than tubular

parts Fig.1.62

Moulds are designed with risers at center to supply feed metal.

Density of metal in final casting is greater in outer sections than

at center of rotation.

Often used on parts in which center of casting is machined away,

thus eliminating the portion where quality is lowest.

Advantages1. Semi centrifugal casting ensures purity and density at the extremities of

a casting such as a cast wheel or pulley.

2. Since the poorer structure forms at the center of the casting, it can be

readily machined out if it is objectionable.

Applications

Wheels and pulleys are casted by this process

Po uring bas in

H u b C ore

Straine r C ore

C o pe

C a stin g

D rag

.. . . . . . .. . . . . . .. . . . . . ......... . .. . . . . ..

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..........

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Sa nd.. .

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sha ft

Fig. 1.62 Semi-centrifugal casting


1.14.8.3 Centrifuge Casting

Parts not symmetrical about any axis of rotation may be cast in a group

of moulds arranged in a circle (Fig. 1.63) to balance each other.

The axis of mould and that of rotation do not coincide with each

other so that molten metal poured into mould is distributed to

these cavities by centrifugal force.

The set-up is revolved around the center of the circle to induce

pressure on the metal in the moulds.

Mould is designed with part cavities located away from axis of

rotation.

Used for smaller parts.

. . . . . . . .......... . . . . . . .

... ...

..

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..

.. .

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Core Central sp rue

Cope

Casting

Drag

Central sp rue

...

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.. ........ .. ..

. ......

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........

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... .. .. . .... .... . ....

Fig. 1.63 Centrifuge Casting


1.14.9 Carbon-dioxide MouldingPrinciple

The highly flowable mixture of pure dry silica sand and sodium

silicate binder is rammed or blown into the mould or corebox.

Carbon-dioxide gas at a pressure of about 1.5 bar is diffused

through the mixture (of sand and sodium silicate) to initiate the

hardening reaction which takes from a few seconds to a few

minutes depending upon the size of core or mould.

Passage of carbon-dioxide through the sand containing sodium

silicate produces carbonic acid in the aqueous solution, this causes

a rise in the SiO2-Na2O ratio and the formation of a colloidal

silica gel which hardens and forms a bond between the sand grains.

This reaction is represented by the following equation

NaSiO3 CO2Sodium Silicate

NaCO3 SiO2Silica gel

1.14.9.1 Operation

The mould material consists of pure dry silica sand (free from

clay) and 3 to 5% sodium silicate liquid (water) base binder,

mulled for about 3 to 4 minutes. The moisture in the mixture is

generally less than 3%.

. . . . .. . .. . . .

.. .. .. .

. . .. . . ......... .. .. ......

. . .... ... .. .CO 2

.. ... ... ... ... . .... . .

Hollow patte rn.

(a) Gassing through hollow pattern


Small amounts of starch or clay may be added to improve green

strength of the mix. Sodium silicate may contain additives such

as sugars to help in breakdown of the core in casting (to improve

collapsibility).

After the moulding mixture has been rammed around the mould

boxes or core boxes by means of hand ramming or machine jolting,

Carbon dioxide gas is forced into the mould or core at about 1.4

to 1.5 Bars. Fig.1.64.

After gassing, core (or) mould is given a refractory coating and

system is ready for pouring.

Core

CO 2

(b) Gassing previously stripped cores

Fig. 1.64. M ethods of gassing m ould and cores

.

.

...

..

..

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.. .. .

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..

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.

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...

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...

..

..

.....

. ..

..

.... .

C O 2

M old

(c) Gassing m ould a fter drawing out pattern


1.14.9.2 Advantages

Low cost of production and process can be mechanized.

No skilled labour is required.

Hollow cores can be made easily.

Improved surface finish & dimensional accuracy can be obtained.

Mould hardens quickly and hence metal can be poured frequently.


Reclaim of sand is difficult.

Poor collapsibility and moisture susceptibility to core.

It is less suitable for non ferrous castings.

It is also less suitable for small and thin sections.


It is used for making heavy and thick walled casting, larger cores,

cores for iron, copper and its alloys.

1.14.10 Stir casting

It is an economical process for the fabrication of metal matrixcomposites.

Stir casting is a liquid state method of composite materials fabrication,

in which a dispersed phases - ceramic particles and short fibers are mixed

with a molten matrix metal by means of mechanical stirring. Then the

liquid composite material is cast by conventional casting methods and may

also be processed by conventional metal forming technologies.

There are several parameters in this process, which affect the final

microstructure and mechanical properties of the composites.

Among the variety of manufacturing processes available for

discontinuous metal matrix composites, stir casting is one of the best method

mostly used everywhere. This process is widely used due to its simplicity,

flexibility and applicability to large quantity of production with cost

advantage. The main difficulty in this process is to obtain sufficient wetting

of particle by liquid metal and to get a homogeneous dispersion of the

particles.


1.14.11 Vacuum castingThis process is also called counter-gravity casting. It is basically the

same process as investment casting, except for the step of filling the mould.

In this case, the material is sucked upwards into the mould by a vacuum

pump. The Fig. 1.65 shows the basic idea – how the mould appears in an

inverted position from the usual casting process, and is lowered into the flask

with the molten metal.

One advantage of vacuum casting is that by releasing the pressure a

short time after the mould is filled, we can release the un-solidified metal

back into the flask. This allows us to create hollow castings. Since most of

the heat is conducted away from the surface between the mould and the metal,

therefore the portion of the metal closest to the mould surface always

solidifies first. The solid front travels inwards into the cavity. Thus, if the

liquid is drained a very short time after the filling, then we get a very thin

walled, hollow object etc.

1.14.12 Plaster-mould castingThe mould is made by mixing plaster of paris (CaSO4) with talc and

silica flour. This is a fine white powder, which, when mixed with water gets

C astingVacuum

M olten m etal

M ou ld

G ate

Induction furnace

Fig. 1.65. Vacuum Casting


a clay-like consistency and can be shaped around the pattern (it is the same

material used to make casts for people if they fracture a bone). The plaster

cast can be finished to yield very good surface finish and dimensional

accuracy. However, it is relatively soft and not strong enough at temperature

above 1200C, so this method is mainly used to make castings from non-ferrous

metals, e.g. zinc, copper, aluminum and magnesium. Since plaster has lower

thermal conductivity, the casting cools slowly, and therefore has more uniform

grain structure (i.e. less warpage, less residual stresses). Fig. 1.66.

Plaste rs lu rry

Pa tte rn

(b) Mould m aking

Plaster slu rry(gypsum +water)

Stirrer

(a) Slurry making


1.14.12.1 Advantages

In plaster moulding, very good surface finish is obtained and

machining cost is also reduced.

Slow and uniform rate of cooling of the casting is achieved

because of low thermal conductivity of plaster and possibility of

stress concentration is reduced.

Metal shrinkage with accurate control is feasible and thereby

warping and distortion of thin sections can be avoided in the

plaster moulding.


There is evolution of steam during metal pouring if the plaster

mould is not dried at higher temperatures. To avoid this, the plaster

mould may be dehydrated at high temperatures, but the strength

of the mould decreases with dehydration.

The permeability of the plaster mould is low. This may be to a

certain extent but it can be increased by removing the bubbles as

the plaster slurry is mixed in a mechanical mixer.

D rag

(c ) Assembly

copePouring bas in

Fig. 1.66. Plaster - m ould casting


1.14.13 Expendable-pattern casting (lost foam process)

The pattern used in this process is made from polystyrene (this is the

light, white packaging material which is used to pack electronics inside the

boxes). Polystyrene foam is 95% air bubbles, and the material itself evaporates

when the liquid metal is poured on it. The pattern itself is made by moulding

– the polystyrene beads and pentane are put inside an aluminum mould, and

heated; it expands to fill the mould, and takes the shape of the cavity. The pattern

is removed, and used for the casting process, as follows - The pattern is dipped

in a slurry of water and clay (or other refractory grains), it is dried to get a hard

shell around the pattern. The shell-covered pattern is placed in a container with

sand for support, and liquid metal is poured from a hole on top. The foam

evaporates as the metal fills the shell; upon cooling and solidification, the part

is removed by breaking the shell. Fig 1.67.

The process is useful since it is very cheap, and yields good surface

finish and complex geometry. There are no runners, risers, gating or parting

lines – thus the design process is simplified. The process is used to

manufacture crank-shafts for engines, aluminum engine blocks, manifolds etc.

1.14.14 Continuous Casting

Round ingots, slabs, square billets and sheets can be cast by continuous

process directly from molten metal.

m olten m etal

polystyreneburnsgas escapes

supportsand

patternpolystyrenepattern

.

.. .

.

... . .

.. . .

..

.. . . . . . . .

.. .

..

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. ..

Fig. 1.67 Expendable-pattern casting (lost foam process)

..

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Asarco process is one of the most commonly used process and is

shown in Fig. 1.68.

Molten metal is transferred from the holding furnace into special

ladle called a tundish from where the metal is poured into the top

of a bottomless graphite mould of the desired shape.

The process is started by placing a dummy bar in the mould upon

which the first liquid metal falls. The liquid metal gets cooled and

is pulled, by the pinch rolls along with dummy bar.

Vertical cooling chamber cools the hot metal. A skin of solid metal

forms quickly at the mould-metal interface and shrinks from the

mould walls.

Cutting device

Straightening m echanism

W ithdrawal m echan ism

Bendingm echanism

Casting floor(20+m aboveground level)

Lad leTundish

M ould

Vertica l cooling cham ber

M olten m eta l

X-Ray M /c

Fig. 1.68 Continuous casting


The shrinking effect provides a very small gap between the metal

and the mould, thereby reducing friction between the two and

permitting cast shape to move continuously through the mould.

Pinch and guide rolls regulate the rate of settling of cast shape

and keep proper alignment.

As the casting passes out of the pinch rolls it is cut to desired

length by a saw or oxyacetylene torch moving briefly along with

the casting. The cut lengths may be straightened, rolled (if desired)

and inspected before shipping.

Argon provides an inert atmosphere to avoid atmospheric

contamination of the molten metal.

X-ray unit controls the pouring rate of molten metal from the ladle.

1.14.14.2 Advantages

Casting surfaces obtained are better than that can be got with static

ingots.

The process is cheaper than rolling from ingots and there is no

need of rough forming and breakdown rolling.

Reduced segregation, grain size and structure of the casting can

be regulated by controlling cooling rates

The casting structure is more dense.

The process is essentially automatic and thus unit labour cost is

low.

100 percent casting yield can be achieved.


It can produce continuous casting of square, rectangle, hexagonal,

fluted, toothed gears, hollow sections.

Production of blooms, billets, slabs and sheets.

Bushings and gears pump.

Copper (wire) bar.


1.14.15 Slush castingSlush casting is a form of permanent mould casting and its usage is

limited to tin-Zinc (or) lead-base alloys.

Here, the molten metal is filled in a mould cavity, but not allowed to

completely solidify inside it.

When the desired thickness is obtained during solidification of the skin,

the remaining molten metal is poured out.

In this process, hollow castings can be produced without the use of

cores.

Casting processSlush casting process requires a split mould of metal similar to that

used in gravity die casting.

The open die halves are cleaned properly and coated with die lubricant.

Then the halves are assembled together by leaving a small hole to pour

molten metal in the mould cavity. Usually the hole is provided at the bottom

of the object.

The Fig 1.69 shows the method of slush casting a hollow statue.

The molten metal is filled inside the mould cavity through the bottom

hole. The metal is retained inside the mould cavity till the solidification of

a skin of required thickness is formed.

After the skin has frozen, the mould is turned upside down (or) slung

to remove the remaining liquid from the mould cavity.

C over M olte n

M etal Pouring

So lidified Sk in

L iquid M etal D ie

(a) M eta l Filling

So lid M etal

P in

D ieH a lf

D ra in in g o f Excess M eta l

(b) Draining of Excess M etal

C asting

C over

(C) Ejection of Casting

Fig. 1.69


The mould is kept for some more time to bring the temperature low,

inorder to get sufficient strength for the shell cast.

Finally, the die halves are opened to eject the casting out.

Advantages1. Light and thin castings of hollow shape can be cast successfully.

2. No core is required to form the hollow shape.

3. Intricate shapes like statues ornaments, etc. can be produced using

non-ferrous metals.

4. Very good external surface finish is obtained.

5. The process is applicable in permanent moulds (or) non-metallic

materials also.

6. Cost of production is low.

Limitations1. The thickness of the casting will not be uniform.

2. The internal surface is not smooth and a required internal shape cannot

be obtained.

ApplicationsSluch castings, find wide application in the production of products such

as toys, ornaments and decorative objects like flower vases, bowls, candle

stands, models, etc.

Statues and animal miniatures of non-ferrous metals are generally

produced by slush casting method.

1.15 DESIGN CONSIDERATIONS OF CASTINGS

The design of a cast part should ensure good working characteristics

viz. strength, rigidity, stiffness, tightness and corrosion resistance. Casting

problems can be minimized with proper design done in collaboration between

the designer and the foundry engineer. The important factors in the design

of castings are

Design for

directional solidification

minimum stresses


metal flow

minimum casting

expected tolerances

function

The above are related in general with

the following considerations:

1. Castings should be simple. This reduces

cost.

2. Section thickness of cost part, as far as

possible, should be uniform. This

prevents improper solidification and

shrinkage defects (porosities, cracks,

etc).

3. Complex large castings should be

divided to be easily cast. Then the divided cast parts can be joined to

produce ‘cast-weld’ construction. This prevents wrap (or) tear.

4. Sharp corners and abrupt section changes should be eliminated by

employing fillets and blending radii to prevent stress concentrations

resulting in hot check (or) hot tear. Also smoothly tapered sections

should be used to eliminate high stress concentrations. Refer Fig. 1.71.

Poros ity

Poor

G oo d

(a)

H otTear

Poor

Be tte r (b)Fig. 1.71

Poor

G ood

Best

Fig. 1.70


5. The number of sections coming at a

junction should be minimum. This

reduces hot spots. Refer Fig. 1.72.

6. Joining thin ribs to heavier sections

cause high stresses and cracking and

therefore should be avoided.

7. The appropriate location where

material should be fed into the part

should be determined since gas blow

holes may form on the upper surface

of the cast part. Critical surfaces of the castings should lie at the bottom

part of the mould.

8. Bosses lugs, etc (or) under cuts should be avoided for easy removal of

pattern from the mould. Refer Fig. 1.73.

9. Parting lines should be in a single plane, if practicable. This reduces

cost and also plane parting can be used in the process of moulding.

Refer Fig. 1.74.

Boss

Undercut

Inco rrect Correct Fig. 1.73

(a) Bad (b) GoodFig. 1.74

Por

osity

Poor Better

Fig. 1 .72


10. Minimum section thickness of the casting walls should be considered.

This depends on the size and mass of the casting, its material, fluidity

of the molten metal and molten metal temperature. The fluidity of

molten metal is important to determine the minimum section thickness,

except for cast iron.

11. Ribs are used to increase stiffness or to reduce weight. They should

not be too shallow in depth or two widely spaced. Generally, thickness

of ribs should be 0.8 times the casting thickness. Also staggered ribs

cause less distortion than regularly spaced ribs. Refer Fig. 1.75.

12. Iron castings should not be used for impact or shock loading.

13. Strength of cast iron castings decreases above 300C. Hence they should

not be used at such temperatures.

14. In places where holes are drilled, the design of castings should be such

that the drilled holes must be normal to both top and bottom surfaces

to eliminate drill breakage and loss of material. Also drilling time is

reduced. Refer Fig. 1.76.

15. Design of castings should be such that removal of core materials and

reinforcements is simple. Also cleaning and fetting after the shake out

operation should be made easy.

16. The mould should have a minimum number of cores or no cores, if

possible.

17. The locating surfaces (used for machining cast parts) should lie in the

same mould half, so that relative displacements of mould parts and cores

do not affect the accuracy of these surfaces.

(a) Good (b) Bad Fig. 1.75


18. A thorough analysis of the design should be carried out as the function

of the casting is more important than its cost, ease of manufacture or

appearance.

1.16 DEFECTS IN SAND CASTING

Various defects can develop in manufacturing processes depending on

factors such as materials, part design and processing techniques. While some

defects affect only the appearance of the parts made, others can have major

adverse effects on the structural integrity of the parts. Defects found in

castings may be divided into three classes:

(i) Defects which can be noticed on visual examination or measurement of

the casting.

(ii) Defects which exist under the surface and are revealed by machining,

sectioning or radiography.

(iii) Material defects discovered by mechanical testing of the casting.

Defects in the casting may occur due to one or more of the following reasons:

Fault in design of pattern.

Fault in design of mould and core.

(a ) Bad (b) Good

Fig . 1.76


Fault in design of gating system and riser.

Improper choice of moulding sand.

Improper metal composition.

Inadequate melting temperature and rate of pouring.

1.16.1 Classification of Defects

Defects caused by patterns and moulding box equipment

Examples are Mismatch /Mould Shift, Fins - Flash – Strain, Crush,

Variation in wall thickness of the Casting

Defects caused by molten metal.

Examples are Misruns, Cold-shut, Excessive penetration, Tin and lead

sweat, Hot tears, Sand cuts and Washes, fusion, Gas porosity, Gas-holes,

sponginess, Shot metal, Rattails and buckle, swells.

Defects due to improper mould drying and core baking.

Examples are Sand Washes, Scabs, Blowholes, Rough surface, Metal

penetration and undersized holes.

Defects caused by moulding, core making, gating etc

Examples are Hot tears, Shifts, Fins and Flash, Crush, Cold laps (shuts)

and mis-run.

Defects due to improper moulding and core making materials

Examples are Blowholes, Drop, Scab, Pin holes, Metal penetration and

Rough surface, Hot Tears (Pulls)

Defects due to improper sand mixing and distribution

Defects occurring while closing and pouring the moulds

Examples are Shift or mismatch, Mis-run, Cold laps or cold shuts,

Crush, Run out.

Defects due to cast metal

Examples are hard spots.

Defect called Warpage.

Various casting defects, their causes and their remedies are discussed

in the table.


surf

ace

of

cast

ing

Blo

w h

ole


Mou

ld Mis

run

Mou

ld

.

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Por

osity


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TT

EA

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etra

tion


San

d m

ould

Was

h

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lack

of f

usio

n


CO

RE

FIN

SP

AR

TIN

GLI

NE


1.17 INSPECTION METHOD

Inspection is the act of checking the acceptability of the casting both

dimensionally & functionally. Inspection method is broadly classified into five

categories

Visual inspection

Dimensional inspection

Mechanical Testing

Flaw detection by Non destructive methods

Metallurgical inspection

1.17.1 Visual Inspection

Visual Inspection is carried out for all the castings to detect the

surface defects.

It is carried out either by naked eyes or magnifying glass.

Defects like surface cracks, tears, blow holes, metal penetration,

swells, roughness, shrinkages etc., are easily detected by visual

inspection.

It is the simplest, fastest and most commonly used method for

detecting defects in casting.

It ensures that none of the casting features are eliminated and also

the presence of any modeling errors.

1.17.2 Dimensional inspection

Dimensional Inspection is a very important activity in those

castings which need to be further machined.

It is required for checking out the availability of various machining

allowances in the castings.

It is required in accepting/rejecting of castings.

It is required to check for the correctness of the core, pattern, core

boxes.

It is done by various commercially available instruments like

Micrometer, Gauges, Coordinate measuring machine, 3D inspection

station (Machine vision station).


1.17.3 Mechanical Testing All the castings need to be tested for their mechanical properties

like Tensile/ Compression strength, Hardness, Toughness, Fracture,

Fatigue, Impact testing, Soundness, Pressure/leak testing for tubes

and piping, Creep testing etc.,

All the above tests are done using different commercially available

testing machines like Universal testing machines, Rockwell

hardness testing machines, Fracture testing machines etc. with

standard test procedures.

1.17.4 Flaw detection by Non destructive testing Non-destructive testing is a powerful weapon in foundry industry

with potential for reducing costs, improving product quality, and

maintaining a given quality level. It can play an important role in

improving the competitive position of a casting producer.

The proper nondestructive test, applied at the earliest point in the

production process at which reliable inspection is possible, will

discover defective materials or parts and eliminate further

fabricating costs on units with internal defects.

Non-destructive tests make castings more reliable, safe and

economical.

The most common methods of non-destructive testing used in foundries are:

Radiography (X-ray and -ray).

Fluorescent-Penetrant inspection.

Ultrasonic inspection.

Magnetic particle inspection.

1.17.5 Radiography Test (X-ray (or) -ray) :

The use of X-ray and -ray radiography are used in inspecting castings

for such defects as blow holes, cracks, shrinkage cavities and slag inclusions

.These defects are of special importance in components designed to withstand

high temperatures and pressures employed in power plants, atomic reactors,

chemical and pressure vessels etc., because they cause stress concentration

which may frequently lead to part failure.


1.17.5.1 Principle

Radiography technique is based upon exposing the castings to short

wavelength radiations in the form of X-rays or gamma () rays from a suitable

source such as an X- ray tube or Cobalt-60.The characteristic feature of X-ray

or -ray which makes them to work is their power to penetrate matters opaque

to light.

1.17.5.2 Procedure for X-ray Radiography Test

X-rays are produced in an X-ray tube as shown in Fig. 1.77. The

portion of the casting where defects are suspected is exposed to X-rays.A

cassette containing X-ray film is placed behind and in contact with the casting,

perpendicular to the rays. During exposure, X-rays penetrate the casting and

thus affect the X-ray film. Since most defects possess lesser density than the

sound metal of the casting, they transmit X-rays better than the sound metal

does; therefore the film appears to the more dark where defects are in line

of the X-ray beam.The exposed and developed X-ray film showing light and

dark areas is termed as Radiograph (or) Exograph.

Fig 1.78 Shows a X-ray Radiograph (a) Sound casting (b) Casting

having blowholes (c) Casting having porosity.

Targe t

Electronflow

F ilam en t

Lead shield

X-Rays

W eldm ent

F ilm

Leadback ing

Filam ent heatingtransform er

R heosta t

AC line

Hig

h v

olta

ge

Fig. 1.77 X - Ray Radiography Test


1.17.5.3 Gamma Ray Radiography Test

It is used for thicker castings.

Scattering of Gamma rays is less and hence are more satisfactory

than X-ray techniques for varying casting thickness.

It is a slower method than X-ray technique.

It can be used to inspect number of casting at a time.

C a stin g

Film

C o -60

Fig. 1.79 Gam m a Ray Radiography

CastingBlow

Ho les

X rayX ray

.... ........... ........ ......

............... ...

.......... . ...........

Po ros ity

X ray

(b )(a ) (c)Fig. 1.78 X-Ray Radiograph


Gamma-ray equipment being small possesses better portability and

convenience of use for certain field inspections.

Unlike X-rays, gamma-rays from its source are emitted in all

directions, therefore a number of separate castings having cassette

containing film, fastened to the back of each casting, are disposed

in a circle around the source placed in a central position as shown

in Fig. 1.79.

1.17.6 Magnetic Particle Inspection

This method of inspection is used on magnetic ferrous castings for

detecting invisible surface or slightly subsurface defects. Deeper

subsurface defects are not satisfactorily detected because the

influence of the distorted lines of magnetic flux (owing to a

discontinuity) on the magnetic particles spread over the casting.

Fig 1.80.


The defects commonly revealed by magnetic particle inspection are

quenching cracks, thermal cracks, seams, laps, grinding cracks,

overlaps, non-metallic inclusions, fatigue cracks, hot tears, etc.

1.17.6.1 Principle

When a piece of metal is placed in a magnetic field and the lines of

magnetic flux get intersected by a discontinuity such as a crack or slag

inclusion in a casting, magnetic poles are induced on either side of the

discontinuity. The discontinuity causes an abrupt change in the path of

magnetic flux flowing through the casting normal to the discontinuity,

resulting in a local flux leakage field and interference with the magnetic lines

of force. This local flux disturbance can be detected by its effect upon

magnetic particles which are attracted to the region of discontinuity and pile

up and bridge over the discontinuity.

A surface crack is indicated (under favorable conditions) by a line of

fine particles following the crack outline and a subsurface defect by a fuzzy

collection of the magnetic particles on the surface near the discontinuity.

Maximum sensitivity of indication is obtained when the discontinuity lies in

a direction normal to the applied magnetic field and when the strength of

magnetic field is just enough to saturate the section being inspected.

Fig. 1.80 Shows M agnetic Particle Inspection


1.17.7 Fluorescent Penetrant Inspection (Zyglo Process)

Fluorescent penetrant inspection is also carried out to detect small

surface cracks, but it has the advantage that it can be used for testing both

ferrous and non-ferrous castings. Zyglo is the registered trade mark of the

Magnaflux Corporation. This method is sensitive to small surface

discontinuities such as cracks, shrinkage and porosity open to the surface

which tend to retain penetrant inspite of the rinse. Smooth or machined casting

surfaces provide more satisfactory conditions for the test.

1.17.7.1 Procedure for Fluorescent Penetrant Inspection

Clean the surfaces of the object to be inspected for cracks etc. Fig1.81

Apply the fluorescent penetration on the surface by either dipping,

spraying or brushing. Allow a penetration time up to one hour.

The fluorescent Penetrant is drawn into crack by capillary action

Wash (the surface) with water spray to remove penetrant from

surface but not from crack.

Apply the developer. The developer acts like a blotter to draw penetrant

out of crack and enlarge the size of the area of Penetrant indication.

The surface is viewed under black light. Black light causes

penetrant to glow in dark.


Used for locating cracks and shrinkage in ferrous and especially

non-ferrous castings: cracks in the fabrication and regrinding of

......... ......................... ... ....... ...................

.. ......... ...... ......... ......................... .. ....... ...................

.. ........ ....

.............................

...............

...............

...... ...............

.... .

.. ... ....

......... ......................... .. ...... ...............

.. ................. ......................... .. ...... ...............

.. ........ ........

Pene tra te(a )

W ash(b )

....... .. . .

.... ..

...

......... ...... ... .. .. ..

.. ....... . ........

...

.. ....... .

...

D eve lo p(c)

Inspect(d )

Fig. 1.81 Procedure for Penetrant Inspection


carbide tools, cracks and pits in welded structures, cracks in steam

and gas turbine blades, ceramic insulators for spark plugs and

electronic applications.

It can also be carried out on parts made up of other materials such as

plastics, ceramics, glass, etc.

1.17.8 Liquid (Dye) Penetrant Test

A liquid penetrant test is non-destructive type and can detect flaws that

are open to the surface e.g. cracks, seams, laps, lack of bond, porosity, cold

shuts etc. It is effectively used in inspection of ferrous metals, non-ferrous

metal products, non-porous, non-metallic materials such as ceramics, plastics

and glass.


The principle of liquid penetrant test is that the liquids used enter small

openings such as cracks or porosities by capillary action. The rate and extent

of this action are dependent upon such properties as surface tension, cohesion,

adhesion and viscosity. They are also influenced by factors such as the

condition of the surface of material and the interior of the discontinuity.

For the liquid to penetrate effectively, the surface of the material must

be thoroughly cleaned. After cleaning, the liquid penetrant is applied evenly

over the surface and allowed to remain long enough to permit penetration

into possible discontinuities. The liquid is then completely removed from the

surface of the component and either a wet or a dry developer is applied. The

liquid that has penetrated the defects will then bleed out onto the surface,

and the developer will help delineate them. This will show the location,

general nature and magnitude of any defect present.

The oil-whiting test is one of the older and cruder penetrant tests used

for the detection of cracks too small to be noticed in a visual inspection. In

this method, the piece is covered with penetrating oil, such as kerosene, then

rubbed dry and coated with dry whiting. In a short time the oil that has

seeped into any cracks will be partially absorbed by the whiting, producing

plainly visible discoloured streaks delineating the cracks.


1.17.9 Ultrasonic Inspection

1.17.9.1 Principle

Ultrasonic inspection is employed to detect and locate defects such

as shrinkage cavities, internal bursts or cracks, porosity and large

non-metallic inclusions.

Ultrasonic waves are usually generated by the Piezoelectric effect

which converts electrical energy to mechanical energy. A quartz

crystal is used for the purpose.

Ultrasonic inspection for flaw detection makes use of acoustic

waves with frequencies in the range between 20 KHz and 20 MHz,

which can be transmitted through solids (even liquid and air as

well) and get reflected by the subsurface defects. Ultrasonic waves

form a basis for detection, location and size estimation of defects.

1.17.9.2 Steps in Ultrasonic inspection

The surface of casting is made fairly smooth

Ultrasonic inspection employs separate probes, one for transmitting

the waves and other to receive them after passage through the

castings. The ultrasonic waves are transmitted as a series of

intermittent pulses and the same crystal may be employed both as

the transmitter and receiver (Fig. 1.82).

Defect

Soundwave

1 2 3

Casting

Transm itterp robe Receiver

p robe

Input pu lse-p ip

1 Defect echo

CR Oscreen

23

Backecho

Time d is tancescale

(reduced)

Fig. 1.82 Princip le of Ultrasonic Inspection


Before transmitting waves, an oil film is provided between the

probe and the casting surface.

Now an ultrasonic wave is introduced into the metal and the time

interval between transmission of the outgoing and reception of the

incoming signals are measured with a Cathode Ray Oscilloscope

(CRO).

The time base of CRO is so adjusted that the full width of the

trace represents the section being examined.

To start with, as the wave is sent from the transmitter probe, it

strikes the upper surface of the casting and makes a sharp (peak)

or pip (echo) at the left hand side of the CRO screen.

If the casting is sound, this wave will strike the bottom surface

of the casting, get reflected and indicated by a pip towards the

right hand end of CRO screen.

In case a defect exists in between the top and bottom casting

surfaces, most of the beam striking this defect will get reflected

from the defect, reach the receiver probe and indicate a pip (echo)

on the CRO screen, before the pip given by the waves striking

the far end of the casting and returning.

1.17.9.3 Advantages

It is a fast, highly sensitive, economical and reliable method of

non-destructive inspection.

This method of locating flaws with metal objects is more sensitive

than radiography.

Big castings can be systematically scanned for initial detection of

major defects.

1.17.9.4 Limitations

Ultrasonic inspection is sensitive to surface roughness. Since the

as-cast surfaces will in most cases be too rough, some preliminary

machining of castings will be required.


In complex castings the interpretation of the CRO trace may not

be easy. Waves reflected from corners or other surfaces may give

a false indication of defects.


Ultrasonic vibrations can be used to locate defects in ferrous and

non-ferrous metallic objects as well as in plastics and ceramics.

Inspection of large castings and forging, for internal soundness,

before carrying out expensive machining operations.

Inspection of moving strip or plate for laminations and thickness.

Routine inspection of locomotive axles ,wheel pins for fatigue

cracks, rails for bolt-hole breaks.

PROBLEMS IN CASTING

Problem 1.1 What will be the solidification (or) freezing time for a 1200mm diameter and 35 mm thick casting of aluminium if the mould constant

is 2.2 sec/mm2

Given

Diameter of casting, d 1200 mm

Height/thickness of casting, h 35 mm

Mould constant, C 2.2 sec/mm2

Solution

Volume of the casting, V 4

d2 h

4

12002 35 39584067.44 mm3

Surface area of the casting, SA 2 4

d2

2 4

12002 2261946.71 mm2

Using chvorinov’s rule,


Solidification time, t

t C

VSA

2

2.2 39584067.442261946.71

2

673.75 sec or 11.23 min. Ans.

Problem 1.2 Two castings of the same metal have the same surface area.One casting is in the form of sphere and other is a cube. What is the ratioof the solidification time for the sphere to that of a cube.

Let, V Volume of casting, and

A Surface area of casting

Also, Asphere Acube ...(Given)

According to Chvorinov’s rule,

Solidification time, t

VSA

2

Ratio of solidification time (or) freezing time for the sphere to that

of cube,

tspherettube

Vsphere

SAcube

2

43

R3

a3

162 R6

9a6 Ans.

Where, R Radius of sphere

a Side of the cube.

Problem 1.3 In a sand mould, a sprue of 220 mm height and 1162 mm2

top area is provided to maintain the flow rate of liquid at

1,738,000 mm3/s. What should be area at the base of down sprue to prevent

aspiration of molten metal? Take g 9815 mm/s2.


Given:

h 220 mm Top area = 1162 mm; Flow rate, Q 1,738,000 mm3/s,

g 9815 mm/s2

Solution

Area at the base of down sprue

Velocity is down sprue, v 2gh

2 9815 220 2078.12 mm/s

Area at the base of down sprue to maintain the flow rate,

A Qv

1,738,0002078.12

836.33 mm2

Problem 1.4 An aluminium cube of 13 cm side has to be cast along acylindrical riser of height equal to its diameter. The riser is not insulated onany surface. If the volume shrinkage of aluminium during solidification is 5percent; Find(i) Shrinkage volume of cube on solidification.(ii) Minimum size of the riser so that it can provide the shrinkage volume.

Given:

Side of the aluminium cube, a 13 cm

Diameter of cylindrical riser, d height of riser h

Volume shrinkage of aluminium during solidification = 5%

Solution

Shrinkage volume of cube on solidification

Volume of casting a3 133 2197 cm3

Shrinkage volume 5% 5

100 2197 109.85 cm3

(Normally this shrinkage, depending upon metal, varies from 2.5 to

7.5%)


Minimum size of the riser

A riser should be designed with minimum possible volume while

having a longer solidification time than the casting.

Now from practice, minimum volume of riser is approximately three

times the shrinkage volume.

Minimum volume of riser 3 109.85 329.55 cm3

4

dr2 hr 329.55

where suffix ‘r’ stands for riser, suffix ‘c’ stands for casting.

Problem 1.5 Compare the solidification times for castings of three differentshapes of same volume : Cubic, cylindrical (with height equal to its diameter)and spherical.

Solution

Let, A Surface area of casting, and

V Volume of each casting = unity (say) ...(Given)

Using Chvorinov’s rule,

Solidification time, t C

VSA

2

,

where C is a constant of proportionality.

(i) Cubic casting

Consider l be the side of the cube.

V l3 1

l 1

Surface area, of cube SA 6l2 6 12 6 units,

t C 16

2

0.0278 C


(ii) Cylindrical casting

Consider r and h be the radius and height of the cylinder.

h 2r

V r2 h r2 2r 1 ...(Given)

(or), 2 r3 1 r

12

1/3

0.5419 unit.

Surface area of the cylinder

SA 2 r2 2 rh

2 r2 2 r 2r 6 r2 6 0.54192 5.53 units

t C

15.53

2

0.0327 C.

(iii) Spherical casting

Consider R be radius of the sphere,

V 43

R3 1 or R

34

1/3

0.62 unit

Surface area of the sphere SA 4 R2 4 0.622 4.83 units

t C

14.83

2

0.0429 C.

Result

Therefore we found that cubic casting has the least solidification time,

hence it will be solidifying at faster rate. Spherical casting has the maximum

solidification time, hence it will solidify at slower rate.

Now, hr dr

4

dr2 dr 329.55 or dr 7.486 cm

...(Given)


In order to have a sound casting, the metal in the riser should be the

last to cool, that is, the riser should have a longer solidification time than

the casting, so

SAV

r

SAV

c

or

VSA

r

VSA

c

,

Now, SAV

r

dh 2

4

d2

4

d2 h

r

d d 2

4

d2

4

d2 d

r

d2

2

d2

4

d3

r

6dr

6

7.486 0.8014

and, SAV

c

6 13 13

13 13 13 0.461

As is clear SAV

r

is SAV

c

, which is not desirable

SAV

r

SAV

c

0.461

or 6dr

0.461,

6

0.461 dr or dr

60.461

or 13

Minimum size of riser = 13 cm diameter 13 cm height.

i.e., {Vr 4

132 13 1725.52 cm3


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