A Mini Project report

On

DESIGN, SELECTION AND MANUFACTURING OF

FLEXIBLE DISC COUPLINGS

Submitted in partial fulfillment of the requirement for the award by

Ch.Umesh Chandra

(08B61A0311)

Bachelor of Technology

In

Mechanical Engineering

Under the esteemed guidance of

M.N.V.Ramesh, Associate Professor

Department of MECHANICAL ENGINEERING

Department of Mechanical Engineering

Nalla Malla Reddy Engineering College

(Approved by A.I.C.T.E., Affiliated to J.N.T.U., Hyderabad)

Divyanagar, Kachivani Singaram Village,

Ghatkesar Mandal, Ranga Reddy District- 500088.

Andhra Pradesh, India.

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ACKNOWLEDGEMENT

I express my sincere thanks and deep sense of gratitude for the inspiring guidence and kind

encouragement with unfailing support rendered by Mr. M. N. V. Ramesh, Associate Prof.,

Dept of Mechanical Engineering, Nalla Malla Reddy Engineering College.

I express my sincere thanks to Dr. T. Mohandas, HOD of Mechanical Engineering,

Nalla Malla Reddy Engineering College, for his encouragement and valuable suggestions

through out the miniproject.

I am also thankful to the staff of our Mechanical Department for their valuable support,

comments during the course of the mini-project and to all others who have directly or

indirectly contribute to the success of the mini-project.

I owe my gratitude to our Nalla Malla Reddy Engineering College for providing an

opportunity to do my project.

CH.UMESH CHANDRA 08B61A0311

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CONTENTS Page no’s

ABSTRACT 5

ABOUT EUROFLEX 6

CHAPTER 1: INTRODUCTION 7

1.1) DEFINITION 7

1.2) PURPOSE OF A COUPLING 7

1.3) TYPES OF COUPLINGS 7

1.4) REQUIREMENTS OF A GOOD COUPLING 8

CHAPTER 2: BASIC REVIEW ON TYPES OF COUPLINGS

2.1) RIGID COUPLING 9

2.1.1) SLEEVE OR MUFF COUPLING 9

2.1.2) CLAMP or SPLIT-MUFF or COMPRESSION COUPLING 10

2.1.3) FLANGE COUPLING 11

2.2) FLEXIBLE COUPLING 12

2.2.1) BUSHED PIN TYPE COUPLING 12

2.2.2) UNIVERSAL COUPLING 13

2.2.3) OLDHAM COUPLING 14

2.3) OTHER TYPES 15

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CHAPTER 3: DISC COUPLINGS

3.1) INTRODUCTION 18

3.2) DESIGN REVIEW 20

3.3) COUPLING SELECTION PROCEDURE 23

3.4) MANUFACTURING PROCESS 24

3.5) QUALITY PLAN AND INSPECTION 32

CHAPTER 4:

4.1) DISC DESIGNS 34

4.2) HOW TO SPECIFY A COUPLING 35

4.3) ADVANTAGES OF DISC COUPLING 35

4.4) APPLICATIONS OF A DISC COUPLING 36

CHAPTER 5:

5.1) TOOLS TO MEASURE AXIS ALIGNMENT CONDITION 37

5.2) MAINTENANCE AND FAILURE 37

5.3) CHECKING COUPLING BALANCE 38

5.4) USES OF DIFFERENT COUPLINGS 38

5.5) ADVANTAGES AND DISADVANTAGES OF DIFFERENT COUPLINGS 39

CONCLUSION 40

BIBLIOGRAPHY 41

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ABSTRACT

The main aim of this project is to study and examine design review, selection procedure of disc couplings and also to visually observe the manufacturing process and other post production processes such as quality planning and inspection.

A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.

The purpose of flexible disc couplings is to accept misalignment between the shafts of the connected machines. This misalignment may take the form of an axial movement of one or both the machine shafts, an angular misalignment between them or a relative radial (parallel) offset between their axis of rotation - or indeed any combination of these three.

The disc coupling consists of a hub, two flexible discs and two spacers. The disc is manufactured by pressing the discs in dies before being made flat in hydraulic press. The hub is manufactured from cast iron which undergoes different operations such as drilling, grinding, milling and other operations carried out on lathe according to the design.

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ABOUT EUROFLEX

.

Euroflex Transmissions (India) Private Limited, a Joint Venture Company formed in 1991 with Euroflex Transmissions Limited of the U.K., is in the business of the design and manufacture of the High Performance Flexible Disc Couplings for applications in Gas Turbines, Industrial Steam Turbines, Centrifugal Compressors, Large Pumps, Blowers, etc.The Couplings designed and manufactured by Euroflex (India), are being exported to various parts of the World including Japan, Germany, France, U.K. Switzerland, The Netherlands, Sweden etc. apart from meeting the requirements in India.

The Euroflex designs have been found to be on par with the best and at times, even better than the rest in the field of Flexible Disc Couplings.

It has been the mission of the Company, to bring innovative, value-priced and quality assured range of Couplings to the worldwide market place. The ISO 9001 Certified manufacturing facility in India, with all the required coupling components manufactured in house, ensures a resultant high quality Product.

The Company specializes in the API (3rd Ed.) Couplings. The state of the art manufacturing facility in Hyderabad, India bears testimony to continued commitment of Euroflex (India) to its customers in terms of very high quality, both in design and manufacturing practices.

Couplings manufactured by Euroflex (India) have been proven for high reliability in operations, under severe conditions of misalignment, three dimensional thermal shifts, variations in torque and speed, etc.

Other products: In synergy with the Company capabilities in precision machining, Euroflex (India) is also into manufacture of Gas Turbines and Steam Turbines Rotor and Stator blades. It is also into machining of small Steam Turbine Rotors, and supplies fully bladed Rotors rated for 8 MW to 15 MW applications, with the rotor blades manufactured for all stages, in-house.

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CHAPTER 1

INTRODUCTION

1.1) DEFINITION

A coupling is a device used to connect two shafts together at their ends for the purpose of

transmitting power. Couplings do not normally allow disconnection of shafts during

operation, however there are torque limiting couplings which can slip or disconnect when

some torque limit is exceeded.

1.2) PURPOSE OF THE COUPLING:

Shaft couplings are used in machinery for several purposes the most common of which are:

1. To provide for the connection of shafts of units that are manufactured separately such as a motor and a generator, and to provide disconnection for repairs or alterations.2. To provide for misalignment of the shafts or to introduce mechanical flexibility.3. To reduce transmission shock loads from one shaft to another.4. To introduce protection against overloads.5. To alter the vibration characteristics of rotating units. 6. It should have no projecting parts.

1.3) TYPES OF COUPLINGS:

There are two basic classes of couplings:

1.Rigid couplings

Fig 1.1: Rigid couplings

2.Flexible couplings

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1.4) REQUIREMENTS OF A GOOD COUPLING:

A good shaft coupling should have following requirements:

1. It should be easy to connect or disconnect the coupling.

2. It should transmit the full power from one shaft to another without losses.

3. It should hold the shafts in perfect alignment.

4. It should reduce the transmission of shock loads from one shaft to another shaft. 5. It is the goal to minimise the remaining misalignment in running operation to maximise power transmission and to maximise machine runtime (coupling and bearing and sealings lifetime).

6. It should have no projecting parts.

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CHAPTER 2

BASIC REVIEW ON TYPES OF COUPLINGS

2.1) RIGID COUPLING

These types of couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life.

1. This type of coupling has no flexibility or resilience; hence it is necessary for the shafts that are to be connected to be in good alignment, both laterally and angularity, in order excessive loads on the coupling, on the shafts, or on the shaft bearings.

2. Rigid couplings do not accommodate misalignment and consequently should not be used indiscriminately.

There is three types of Rigid Couplings:

1.Sleeve or muff coupling

2.Clamp coupling

3.Flange coupling

2.1.1) SLEEVE OR MUFF COUPLING:

It is the simplest type of rigid coupling, made of cast iron. It consists of a hollow cylinder whose inner diameter is the same as that of the shaft. It is fitted over the ends of the two shafts by means of a gib head key. The power is transmitted from one haft to the other shaft by means of a key and a sleeve. It is, therefore, necessary that all the elements must be strong enough to transmit the torque.

Fig 2.1: Muff coupling

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2.1.2) CLAMP or SPLIT-MUFF or COMPRESSION COUPLING:

This coupling is a modification and a improvement of the sleeve coupling. This coupling is made in two parts which are machined to fit the shaft and are finished off around the periphery and on both ends. The two halves of the coupling are clamped tightly against the surface of the shaft ends through bolts and the torsional moment is transmitted entirely by friction.

Compression couplings are manufactured from various materials, including Brass, Copper, Plastic and Cast Iron. The most common compression couplings are made of brass. They also are available in a variety of shapes and sizes. The size of a compression coupling is determined by the outside diameter of the tube or pipe it holds.

Fig 2.2: Split-muff coupling

Fig 2.3: Rubber in compression coupling

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Fig 2.4: Clamp coupling

2.1.3) FLANGE COUPLING:

A flange coupling usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angle to the axis of the shaft. One of the flanges has a projected portion and the other flange has a corresponding recess to bring the shafts into line and to maintain alignment. The two flanges are coupled together by means of bolts and nuts.

The flange coupling is adapted to heavy loads and hence it is used on large shafting.

Fig 2.5: Flange coupling

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2.2) FLEXIBLE COUPLING

Flexible couplings are designed to transmit torque while permitting some radial, axial, and angular misalignment. Flexible couplings can accommodate angular misalignment up to a few degrees and some parallel misalignment.

These couplings are rigid under torsion, but, allow the correction of errors in the alignment of drive shafts. They are widely used in the fields of robotics or automatisms, because they are excellent for very accurate system piloting. They are also known as "precision couplings”.

Flexible Couplings may be split into three categories from the standard point of design:

1.Bushed pin type coupling, 2.Universal coupling,

3.Oldham coupling.

Fig 2.6: Flexible coupling

2.2.1) BUSHED PIN TYPE COUPLING:

1. The simplest and common type of coupling is the flexible rubber – bushed coupling. In the pin type coupling motion form one half flange is transmitted to the other half by means of pins or bolts. The pins are rigidly bolted to one flange and loosely fitted in the corresponding holes of the other flange. 2. In the various designs this type of flexible coupling is extensively used, especially where the driving and driven units are mounted on a common base plate, where excessive misalignment is not likely, for example, a prime mover connected to a

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Generator, a compressor connected to an electric motor, an electric motor connected to a centrifugal blower etc.

Fig 2.7: Bushed pin type couplingA bushed pin flexible coupling is a modification of rigid type of flange coupling.The coupling bolts are known as pins.

2.2.2) UNIVERSAL COUPLINGS:

These joints are capable of handling relatively large angular misalignment and they are widely used in agricultural machinery, machine tools and automobiles. There is a center piece through which pass two pins with mutually perpendicular axes and they connect the two fork ends such that a large angular misalignment can be accommodated.

Fig 2.8: Universal coupling

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2.2.3) OLDHAM COUPLING:

An Oldham coupling consists of two flanges with slots on the faces and the flanges are keyed or screwed to the shafts. A cylindrical piece, called the disc, has a narrow rectangular raised portion running across each face but at right angle to each other. The disc is placed between the flanges such that the raised portions fit into the slots in the flanges. The disc may be made of flexible materials and this absorbs some misalignment.

It is used to join two shafts which have lateral mis-alignments.

Fig 2.9: Oldham coupling drawing

Fig 2.10: Oldham coupling

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2.3) OTHER TYPES

Friction Coupling

Driver plate A Friction Material

Driver Shaft Driven Shaft Stationary In motion

Clutch Disengaged

Driver shaft in motion

Clutch Engaged

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Slip type couplings

Fig 2.11: Slip type couplings

Jaw type couplings:

Three jaw insert coupling Multi jaw coupling

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Gear couplings:

A gear coupling is a mechanical device for transmitting torque between two shafts that are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.

Each joint consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth.

Fig 2.12: Gear coupling

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CHAPTER 3

DISC COUPLINGS

3.1) INTRODUCTION

Disc coupling: by definition, transmits torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack.

Disc couplings transmit torque by a simple tensile force between alternating driving and driven bolts on a common bolt circle. Misalignment arises from the flexibility that comes from the length of material between the bolts. Disc couplings have been around for years, but with the use of finite element analysis, they can be and have been optimized for optimum characteristics. These couplings are composed completely of metal and do not require lubrication. The discs are usually continuous and of various shapes-circular, square, or scalloped but can also be individual links.Most disc couplings use multiple thin discs rather than one thick disc or link.

There are two different styles of disc coupling:

1. Single Disc: Style couplings are composed of two hubs and a single, flat, stainless steel disc spring.2. Double Disc: Style coupling is also composed of two hubs, but has an additional center spacer sandwiching two disc springs. The center spacer can be made out of the same material as the hubs, but is sometimes available in insulating acetal, which makes the coupling electrically isolating.

The difference between the two styles is that single disc couplings cannot accommodate parallel misalignment due to the complex bending that would be required of the lone disc. Double disc styles allow the two discs to bend in opposite directions to better manage parallel offset. The discs are fastened to the hubs (and center spacer on double disc styles) with tight fitting pins that do not allow any play or backlash between the disc and the hubs. The discs can be bent easily and as a result, disc couplings have some of the lowest bearing loads available in a motion control coupling.

Torsionally stiff and flexible, disc couplings are a great solution for high speed applications. The downside is that they are more delicate than the average coupling and can be damaged if misused.The Basic DISC coupling consists of two hubs, a spacer and two flexible discs. The disc is an assembly of thin metal laminations.

Misalignment is taken through bending in the link between the bolt holes.

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Fig 3.1: Hub

Fig 3.2: Disc coupling assembly drawing

Fig 3.3: Finished Discs

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3.2) DESIGN REVIEW

The principal reasons why, the disc couplings, out perform others in its class is on account of the two fundamental design principles adopted:It is this design feature of the flexible element which enables the couplings to offer smaller diameters, for a given torque, than, would otherwise have been possible.

Fig 3.4: 6-bolt disc

A) Flexing Element Design:

In the design, the flexible elements have a polygonal outer profile with a circular central hole. The design ensures that, all the forces in the flexible elements are purely tensile and also provides for the maximum material at the points of bending, leading to very low bending stresses, while permitting high misalignment capacity.

B) Coupling Bolt:

The coupling bolts in the design are manufactured out of high tensile steel and are adequately sized to transmit torque through friction rather than shear.

Fig 3.5: Coupling bolt

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Thereby inducing a large tensile load in the bolts, which is adequate to prevent both bending of the bolts as well as slip between the flexing elements. The prevention of slip is very important to prevent the flexing elements from fretting.

Misalignment Capacity:

Misalignments arise in all rotating machinery due to various reasons, like temperature variations, bearing wear, foundation settling etc.

The type of misalignments are:

Axial Misalignment:Axial misalignment is the variation in axial distance between the shafts of the driving and driven machinery.

AngularMisalignment:Angular misalignmnet is the effective angle between the two shaft centerlines and is usually quantified by measuring the angle between the shaft centerlines as if they were extended till they intersect. If the shafts are flanged, it is simply enclosed angle between them if they were to be brought to a position of contact.

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Radial Misalignment:Radial or Parallel misalignmnet is the transverse distance between the two shaft centerlines and is quantified by measuring the radial distance between the centerline of one shaft if it were to be extended to overlap the other.

The couplings are designed to accept Axial, angular and radial misalignments and the degree of misalignment is limited by the imposed stresses in the flexing element.

The axial misalignments imposes a tensile bending stress in the flexing element, which is dipicted by the bending of the beam between the anchor points (see figure), while angular or radial misalignment introduces a bending in the span of the flexing element

Thus the permitted amount of axial and radial misalignments is dependent on the number ofbolts and geometry of the flexing element.

Axial and Parallel misalignments are inversely related, in other words, when one increases, the other decreases. Further this misalignment capability is determined by assessing the combined steady and fluctuating stresses experienced by the flexible elements.

The hallmark of the design is the expertise to accurately determine the cylical stresses under all conditions of coupling operations.

3.3) COUPLING SELECTION PROCEDURE

There are usually four steps that a coupling selector should take to ensure the proper selection of a flexible coupling for critical or vital equipment:

1. Review the initial requirements for a flexible coupling and select the type of coupling that best suits the system.

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2. Supply the coupling manufacturer with all the pertinent information on the application so that the coupling can be properly sized, designed, and manufactured to fit the requirements.

3. Obtain the flexible coupling’s characteristic information so the interactions of the coupling with the system can be checked to ensure compatibility and prevent the unleashing ofdeterminental forces and moments.

4. Review the interactions, and if the system conditions do change, contact the coupling manufacturer so that the new conditions and their effect on the coupling selected can bereviewed. Continue this process until the system and the coupling are compatible.

Flexible couplings generate their own forces and can also amplify system forces. This may change the system’s original characteristics or operating conditions. The forces and momentsgenerated by a coupling can produce loads on equipment that can change the alignment, decrease the life of a bearing, or unleash peak loads that can damage or cause failure of the coupling or connected equipment.

Listed below are some of the coupling characteristics that may interact with the system. The coupling selector should obtain the values:

1. Horsepower2. Operating speed3. Interface connect information 4. Torque5. Angular misalignment6. Offset misalignment7. Axial travel8. Ambient temperature

Based on these the selector must work on:

1. Torsional stiffness 2. Torsional damping 3. Amount of backlash 4. Weights 5. Coupling flywheel effect 6. Center of gravity 7. Amount of unbalance 8. Axial force And should analyze;

1. Size of bore including tolerance or size of shaft and amount of clearance or interfearence required2. Lengths3. Taper shafts4. Minimum strength of hub material or its hardness5. If keyways in shaft a. How many b. Size and tolerance

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c. Radius required in keyway (minimum and maximum). d. Location tolerance of keyway respective to bore and other key ways

Final CheckThe coupling selector should use the coupling characteristics to analyze the system axially, laterally, thermally, and torsionally. Once the analysis has been completed, if the system’s operating conditions change, the coupling selector should supply this information to the coupling manufacturer to ensure that the coupling selection has not been sacrificed andthat a new coupling size or type is not required. This process of an exchange of information between the coupling manufacturer and the coupling selector should continue until the system and coupling are compatible. It is the only way to ensure that the system will operate successfully.

3.4) MANUFACTURING PROCESS

The disc coupling is used for a large size range of drives, from fractional horsepower to very large (100,000 hp). In general we can categorize disc couplings into two groups, one for general--purpose applications and one for high-speed applications. The general-purpose disc coupling’s torque-transmission components are made of low- to medium-carbon steels. Its flexing discs are usually made of spring steel. The high-speed disc coupling’s torque-transmission components are usually made of alloy steels. Its flexing disc is usually made of corrosion- resistant steel.

The main parts of the flexible disc coupling are two hubs, a spacer and two flexible discs.

The Basic disc coupling consists of two hubs, a spacer and two flexible discs. The flex disc is an assembly of thin metal laminations. In figure shown below, flex disc holes A & C are bolted to the hub and holes B & D are bolted to the spacer. Torque is transmitted in direct tensions from A to B and from C to D through the flex disc. Misalignment is taken through bending in the link between the bolt holes.

The discs are manufactured from heavy sheet metal gauge which are in turn made of HSS because high speed steel can withstand wide range of temperatures. First, the heavy sheet metal gauges are taken and cut according to the required square shape depending on the number of holes.

These sheets are brought together by pressing them against each other with heavy weights using hydraulic press.

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A hydraulic press is a machine used to generate a compressive force using hydraulic force. It uses the hydraulic equivalent of a mechanical lever.

After the sheets are made flat they are bought together by putting them in dies and are made as a unit.

Fig 3.6: Finished discsThe ends of the formed metal sheets are grinded for safety purpose and also for accurate finishing and high efficiency.

After that holes are drilled at the marked places with the help of a drilling machine and these holes are finished to perfection. Washers are induced into each and every hole to fit the bolts perfectly.

Fig 3.7: Assembled disc coupling

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The hub is manufactured from cast iron. Cast iron as a raw material undergoes rust removal process and undergoes different operations in lathe machine, drilling machine, grinding machine, milling machine and cnc machine to form a standard hub according to the required dimensions.

Different operations on different machines are done to produce hub and the spacer according to the design.

Since there are three parts of a disc coupling i.e. a spacer, two hubs and two discs these three parts are manufactured separately and joined together after manufacturing.The manufacturing work of the spacer is done mostly on the lathe machine since it is a cylindrical part consisting of three sections as shown in the figure.

A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as boring, drilling, tapping, turning, facing, threading, polishing, grooving, knurling etc. with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.

First, the cylindrical shaped iron bar undergoes the turning operation where the upper layer of the cylindrical bar is removed so that the bar is clean from all impurities such as rust.

Fig 3.8: Turning process

Fig 3.9: Lathe machine

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During the process of turning or any other operation carried out on lathe, coolant is sprinkled so that tool won’t get damaged due to the heat developed during the constant turning process.Rough turning is used to remove large flakes of metal since the cross-section of the middle section of the spacer is less than the outer ends.

The holes at the two ends of the sections are drilled either on a drilling machine or using drill bits which are held stationary in the tail stock or tool turret of the lathe.

Fig 3.10: Turning operation on lathe

In the manufacturing of the spacer, CNC milling machine plays a vital part.To achieve high complex geometry and high product quality CNC milling machines are employed to achieve consistency.

Most CNC milling machines (also called machining centers) are computer controlled vertical mills with the ability to move the spindle vertically along the Z-axis. This extra degree of freedom permits their use in die sinking, engraving applications. When combined with the use of conical tools or a ball nose cutter, it also significantly improves milling precision without impacting speed, providing a cost-efficient alternative to most flat-surface hand-engraving work.

The spacer and hub undergoes the milling operations in a CNC machine since the ability of the spindle to move in the z-axis.

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Fig 3.11: CNC milling machine

The data required for the operation of the milling operation is entered in the computer screen that is located on the outside of the machine.the numerical are entered under three axis namely x,y and z.The latest CNC milling machines are provided with additional axis C or Q allowing the horizontally mounted workpiece to be rotated, essentially allowing asymmetric and eccentric turning. The B axis controls the tilt of the tool itself. When all of these axes are used in conjunction with each other, extremely complicated geometries can be made with relative ease with these machines. But the skill to program such geometries is beyond that of most operators. Therefore, 5-axis milling machines are practically always programmed with CAM.

The hub is manufactured on the lathe machine involving operations such as turning,rough turning and the hole part is done on a drilling machine.A horizontal drilling machine id used to drill the holes of large diameter.Also the deep hole drilling machines are used to drill very large holes.

Fig 3.12: Drilling machine

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Also a slotting machine is used to slot a key way in the hub. In the slotting machines, single point (straight or formed) reciprocates vertically (but without quick return effect) and the workpiece, being mounted on the table, is given slow longitudinal and / or rotary feed. Also grinding machine is used for the removal of smallest chips on the surface through each grain of abrasive on the wheel's surface.After undergoing all these machine operations, the produced hub is painted black as a process of BLACKENING.

BLACKENING is a conversion coating for ferrous materials, copper and copper based alloys, zinc, powdered metals. It is used to add mild corrosion resistance and for appearance. To achieve maximum corrosion resistance the black oxide must be impregnated with oil or wax. One of its advantages over other coatings is its minimal buildup.

Fig 3.13: blackened spacers and hubs

3.5) QUALITY PLAN AND INSPECTION

Inspection of disc couplings is also plant-friendly. They can be inspected for condition, wear and performance without disassembly.

Additionally, you can inspect them while the equipment is running with the use of a strobe light. Under a strobe, you can see the discs flex and move. You can also see any damage. In

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the event that a disc pack needs replacement, certain coupling styles allow for a center section (containing the disc packs) to be removed without removing either shaft hub.

The common types of failures seen in disc couplings are:

The most common form of failure is disc fatigue due to excessive flexure. This is usually caused by poor initial alignment of the connected machines. It can also be brought about by operational conditions. Machines connected with flexible couplings should be aligned with the greatest possible accuracy. The better the initial alignment, the more capacity the coupling has to take care of subsequent operational misalignment. Changes from the initial condition can occur throughbearing wear, settling of foundations, base distortion due to torque thermal changes, and vibrations in the connected machines. The alignment of the machines should be checked at regular intervals and corrected as necessary.

1. Disc failures such as Misalignment failure, Fatigue failure, elongated bolt holes.2. Distorted disc packs such as Compression damage of a disc pack, Elongation damage of a disc pack.3. Torque-overload failure.

Following are some of the more evident visual inspection criteria and recommended corrective procedures:

1. The disc is broken through the bolt hole. This indicates loose coupling bolts. Replace the disc pack and tighten bolts to the specified torque value.

2. Discs are embedded in the bolt body. This is usually the result of a loose bolt or a severe torque overload. This may also appear when the bolt is turned during installation. Replace thebolt and tighten the locknut to the proper torque. Do not turn the bolt during the locknut-tightening process.

3. The disc pack is wavy, and the dimension between flange faces is smaller than indicated on the installation instructions or applicable assembly drawing. The coupling has been installed in a compressed condition, or equipment has shifted axially during operation. Check for thermal growth problems.

Chemical Mechanical NDT machining is the manufacturing process carried out as a part of the quality plan.

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Fig 3.15: Balancing and inspection

NDT methods may rely upon use of electromagnetic radiation, sound, and inherent properties of materials to examine samples. The inside of a sample can be examined with penetrating electromagnetic radiation, such as X-rays or 3D X-rays for volumetric inspection. Sound waves are utilized in the case of ultrasonic testing. Contrast between a defect and the bulk of the sample may be enhanced for visual examination by the unaided eye by using liquids to penetrate fatigue cracks.

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CHAPTER 4

4.1) DISC DESIGNS

4-BOLT DISC-

Straight sided flex disc,1 degree angular misalignment.

Ideal for general industrial applications with motor or turbine drivers and smooth to moderate load conditions.Low to moderate speed ranges.

6-BOLT DESIGN-

Straight sided disc.0.7 degree angular misalignment.

Ideal for motor or turbine drivers with any load conditions.Use for reversing, reciprocating or other rough load conditions.

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4.2) HOW TO SPECIFY A COUPLING

Proper selection has been made based on:

1. Application and type of duty.

2. Type of prime mover, power and speed.

3. Shaft types and sizes, keyway dimensions, hub length.

4. Expected misalignments.

5. Type of driven equipment.

6. Coupling type, size and distance between shaft ends (DBSE).

7. Space limitations.

4.3) ADVANTAGES OF DISC COUPLING

NO LUBRICATION & ZERO MAINTENANCE COSTS - The Flexible disc couplings is a dry coupling not requiring any lubrication. The coupling also has no relative moving parts and maintenance is reduced to a periodic visual inspection, during any convenient shut down.

HIGH TORQUE / SPEED CAPACITY WITH LOW MASS - Due to the unique approach in design, disc couplings meet all torque and speed requirements. By using light and high strength alloys for components even lower mass can be achieved.

GOOD DYNAMIC BALANCE - By ensuring excellent accuracy in manufacture residual unbalance is kept to a minimum. All couplings can be dynamically balanced to international standards as required.

TORSIONAL RIGIDITY - Disc couplings are essentially torsionally rigid although adjustment to stiffness can usually be made at design stage to suit the requirements of any torsional analysis.

MISALIGNMENT CAPABILITY - Disc couplings offer the capability to accept significant angular, radial & axial misalignment with no sacrifice of operating performance.

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4.4) APPLICATIONS OF A DISC COUPLING

Disc couplings are used in variety of applications.The most common use is in medium- horse power pumps. These couplings are also used in: 1. Marine drives 2. Cooling tower drives 3. Generators 4. Compressors 5. Mill equipment 6. Machine tools.

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CHAPTER 5

5.1) TOOLS TO MEASURE AXIS ALIGNMENT CONDITION

It is possible to measure the alignment with dial gauges or feeler gages using various mechanical setups.

It is very convenient to use laser shaft alignment technique to perform the alignment task within highest accuracy.

It is required to align the machine better, the laser shaft alignment tool can help to show the required moves at the feet positions.

5.2) MAINTENANCE AND FAILURE

Fig 5.1: Coupling failure

Coupling maintenance is generally a simple matter, requiring a regularly scheduled inspection of each coupling. It consists of:

Performing visual inspections, checking for signs of wear or fatigue, and cleaning couplings regularly.

Checking and changing lubricant regularly if the coupling is lubricated. This maintenance is required annually for most couplings and more frequently for couplings in adverse environments or in demanding operating conditions.

Documenting the maintenance performed on each coupling, along with the date.

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Even with proper maintenance, however, couplings can fail. Underlying reasons for failure, other than maintenance, include:

Improper installation

Poor coupling selection

Operation beyond design capabilities.

The only way to improve coupling life is to understand what caused the failure and to correct it prior to installing a new coupling. Some external signs that indicate potential coupling failure include:

Abnormal noise, such as screeching, squealing or chattering.

Excessive vibration or wobble.

Failed seals indicated by lubricant leakage or contamination.

5.3) CHECKING COUPLING BALANCE

Couplings are normally balanced at the factory prior to being shipped, but they occasionally go out of balance in operation. Balancing can be difficult and expensive, and is normally done only when operating tolerances are such that the effort and the expense are justified. The amount of coupling unbalance that can be tolerated by any system is dictated by the characteristics of the specific connected machines and can be determined by detailed analysis or experience.

5.4) USES OF DIFFERENT COUPLINGS

• To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alternations.

• To provide for misalignment of the shafts or to introduce mechanical flexibility.

• To reduce the transmission of shock loads from one shaft to another.

Eg:*A coupling is used to join the output shaft of an electric motor to the input shaft of a gearbox in machine tools.*Also used to connect output shaft of an engine to the input shaft of a hydraulic pump to raise water from the well.

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5.5) ADVANTAGES AND DISADVANTAGES OF DIFFERENT COUPLINGS

1. Rigid couplings can accommodate almost no misalignment; should some misalignment occur, from assembly inaccuracy or from thermal expansion during operation, the use of rigid couplings can result in large reactive forces on support bearings.

2.Oldham couplings can accommodate large radial, small angular, and moderate axial misalignment; they offer good peak torque rating and torsional stiffness, , very low reactive forces, and low cost, and are a good all-around choice for a flexible coupling in most applications. 

3. Bellows couplings have a thin-walled flexible metallic element, and can accommodate large misalignments with low reactive forces, but are useful only for low torque, and have low torsional stiffness when measured at torques that approach the peak torque. Like the beam coupling, these are moderate-cost units that will eventually fatigue. 

4. Gear, grid, and chain couplings are very robust designs meant for large shafts (over two inches in diameter), very high torques, and rough applications. 

5. Pin-and-bushing couplings are large-diameter assemblies that accommodate small misalignments and offer small torsional dampening.

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CONCLUSION

Advances in couplings and universal joints are a continuing process as the needs of power transmission increase. Couplings play an important role in the mechanical life by connecting two shafts which may be straight or misaligned. Almost each and every machine run by human have coupling as a part of its system which shows how important a coupling is to run a particular machine. Its use is found in plumbing, automobiles, turbines, generators and many other machine components thus is a vital component for the whole mechanical world. As with the ancestor of flexible couplings, the universal joint, technological improvements in materials, design, and manufacturing will help upgrade couplings so they can handle the ever increasing needs and demands of power transmission equipment.

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BIBLIOGRAPHY:

1. Machine Design by R.S.Khurmi

2. Industrial Machinery Repair by R. Smith and K. Mobley 3. Wikipedia

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