Railway workshop jhansi

S e m i n a r r e p o r t | 1

RAILWAY WORKSHOP JHANSIINTRODUCTIONJhansi Workshop is the biggest Wagon Repair Workshop of Indian Railways. It is

spread in area of 3.4 lakh square meter. The Covered area is 65000 square meter. The

Railway Board Wagon POH target for Jhansi workshop is 610 wagons per month which is

approximately 16 % of the wagon POH done in Indian Railways. Jhansi Workshop

undertakes POH of BOXN, BCN, BOBYN, BOBRN, BTPN and All types of defence

wagons i.e. DBKM, BWTN and BFAT etc. In addition, Jhansi workshop undertakes

Rehabilitation of 75 BOXN wagons per month. This is approximately 14% of the Rehab

work done by all Workshops of IR.

Jhansi workshop is a major POH wagon workshop being the largest workshop in the

Indian Railways, and handling 22% of the Indian Railway wagon-POH arising. It deal with

air brake stock, UIC stock and 4-wheeler tank wagon stock, with bulk of the outturn

pertaining to air brake stock. The out turn of air brake stock requires feed of 11 rakes per

month. This feed is received from NKJ and Bhusawal yards of WCR and CR.

North Central Railway caters to two heavy density over saturated electrified A routes

i.e. Ghaziabad Mughalsarai and Palwal Agra Bina. Line capacity utilization on these sections

has gone upto 170%. N C Railway has over all electrification of 52% of B.G. track and hauls

approximately 87% of its traffic on electric traction. North Central Railway runs

approx. 280 Mail/Express, 109 Passengers EMU-MEMU and an average POL 366.5 (Goods

+ coaching) daily on electric traction.

BRIEF HISTORY OF RAILWAY WORKSHOP JHANSI(a). 1889 Commencement of Construction of Jhansi Workshop.

(b). 1895 Steam Loco, Coach & Wagon Repair activities started by Indian Midland

Railways.

(c). 1910 Take Over by G.I.P. Railway (Great Indian Peninsula Railway)

(d). 1930 Loco Repair transferred from Jhansi to Parel Workshop.

(e). 1961 Introduction of Incentive Scheme.

(f). 1990 Introduction of POH of BOX ‘N’/ BCN wagons.


(g). 1997 Discontinuation of coach POH.

(h). 2001 ISO 9001: 2000 Certificate awarded to Jhansi workshop.

(i). 2008

[i]. Coach MLR Workshop sanctioned at a cost of Rs. 83.67 crores.

[ii]. Modernization Project sanctioned at a cost of Rs. 71.44 crores.

(j). 2009

[i]. POH of Tower Wagons started on regular basis.

[ii]. Stainless Steel wagons BOXNR turned out from May 2009 Rehabilitation

[iii]. Outturn increased from 50 per month in 2008-09 to 75 per month in 2009-10.

(k) 2010 GM Observation Car, RA Furnishing, RA Air conditioning

(l) 2011 Commencement of Turn Key Projects. BRN Conversion for Rail loading

DMT

(m) 2012

[i]. Conversion of BOXN to BOXNHAM started. First ever Rake of BOXNHAM in India

Railway has been flagged of on 25.05.12.

[ii]. Work of Turnkey Projects in progress, MBFU of Kanpur based ART has been

converted in to Air brake with BMBS.

STATISTICS OF JHANSI WORKSHOP(a). Established 1895

(b). Total area 3.4 Lakh square meter

(c). Covered area 65000 square meter

(d). Approximately no. of worker 6135

(e). Total machine and plant 576+

(f). Electric load 531253KW/month

(g). Budget sanctioned 171635100 Rs/-

(h). Average wagon holding 920

(i). Total outturn per day 24.5

(j). Outturn of tank wagon 105 per month

(k). Outturn of BOX-N/BCN 476 per month

(l). Average working days of a wagon 6 days

(m). P.O.H. unit cost of wagon 260000 Rs/-


ELECTRIC LOCOMOTIVEAn electric locomotive is a locomotive powered by electricity from overhead lines, a

third rail or on-board energy storage such as a battery or fuel cell. Electric locomotives with

on-board fuelled prime movers, such as diesel engines or gas turbines, are classed as

dieselelectric

or gas turbine-electric locomotives because the electric generator/motor combination

serves only as a power transmission system. Electricity is used to eliminate smoke and take

advantage of the high efficiency of electric motors, but the cost of electrification means that

usually only heavily used lines can be electrified.

Electric Loco Shed (Jhansi)Electric Loco Shed, Jhansi designed for a holding of 100 locos was established in

1987 with an initial holding of 17 locos. Present holding of the shed is 207 locomotives i.e.

90 WAG/7 (45 BHEL & 45 CLW make) and 117 WAG/5 (74 BHEL & 43 CLW make)

locomotive. This includes 45 Nos. newly built BHEL make WAG/7 locos and 09 no. CLW

make WAG-7 loco added to the fleet. These newly received locomotives are having some

special features viz., Crew Friendly Cab with FRP cabinet for Driver Desk and Air

conditioning & Stick type Master Controller.

ELS/JHS was the first shed in Indian Railways to acquire three prestigious

International Standards viz., ISO-14001:2004, OHSAS-18001 & ISO-9001:2008 together


WAGON REPAIRING PROCESS INTRODUCTIONVarious processes which are carried out once a wagon reaches in the workshop

premises are as follows:

(a). Firstly wagon come in pocket yard.

(b). Senior Section Engineer (S.S.E) of inspection department inspect deeply the wagon

and that time coding is done according to work.

(c). Light Repair- 1

(d). H/Repair- 6

(e). Under Frame- 5

(f). RE Floor- 6RF

(g). RE Roofing- 6RR

(h). Re Hab- RH

(i). For Condemn- U/Inspection

(j). In the yard noted that which wagon required POH, ROH & NPOH.

(k). In the inspection department the repairable part of wagon marked.

(l). From the yard the box is directly send in stripping shop.

(m). All corrosive parts separated by cutting operation and clean well.

(n). After parts is clean well and then according to work demand wagon is send to different

shops.

(o). Usually vacuum brake wagon sending in BWR shop, Heavy repairable wagon sending

in BNR-I and BNR-II and Re Hab wagon is send in Re habitation shop.

(p). Firstly in shop the BP of wagon and centre pivot pin of wagon is cut and after cut the

lifting the wagon and lowered on tassels by separating of body parts of wagon.

(q). After dismantle of wagon is sending in wagon shop and the wheel is sending in wheel

shop for the new profile with Ultrasonic Testing (U.S.T).

(r). After then lower the body parts on tassels air brake parts like as Auxiliary

Reservoir(A.R.), Controlling Reservoir(C.R.), Brake Power(B.P.), Distributor

Valve(D.V.), Dirt collector, Angle cock is separated.


Fig. 2.1: Rail Wagon

(s). All parts of air brake are sending in the air brake shop, all air brake steam tested on 10

kg/cm2.

(t). All parts after handling assemble in a wagon to make a perfect BOXN.

(u). According to painting schedule paint is done on wagon.

(v). After doing Stenciling the writing work on wagon is done.

(w). After complete this operation/s the testing of air brake is done by single wagon test

ring (S.W.T.R.).


ELECTRICAL REPAIR & TESTING ROOMCEILING FAN (1-ɸ INDUCTION MOTOR)

INTRODUCTIONA ceiling fan is a mechanical fan, usually electrically powered, suspended from

the ceiling of a room, that uses hub-mountedrotating paddles to circulate air. A ceiling fan

rotates much more slowly than an electric desk fan; it cools people effectively by introducing

slow movement into the otherwise still, hot air of a room, inducing evaporative cooling. Fans

never actually cool air, unlike air-conditioning equipment, but use significantly less power

(cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to

reduce the stratification of warm air in a room by forcing it down to affect both occupants'

sensations and thermostat readings, thereby improving climate control energy efficiency.

Fig. 3.1: Construction of Fan

WORKING AND CONSTRUCTION OF CEILING FANThe ceiling fan motor works on principle of single phase induction motor using capacitor.

Working of capacitor start motor: The stator consists of the main winding and a starting winding

(auxiliary). The starting winding is connected in parallel with the main winding and is placed

physically at right angles to it. A 90-degree electrical phase difference between the two windings

is obtained by connecting the auxiliary winding in series with a capacitor and starting switch.

When the motor is first energized, the starting switch is closed. This places the capacitor in series

with the auxiliary winding. The capacitor is of such value that the auxiliary circuit is effectively


resistive-capacitive circuit (referred to as capacitive reactance and expressed as XC). In this

circuit the current leads the line voltage by about 45° (because XC about equals R). The main

winding has enough resistance-inductance (referred to as inductive reactance and expressed as

XL) to cause the current to lag the line voltage by about 45° (because XL about equals R).

The currents in each winding are therefore 90° out of phase - so are the magnetic fields

that are generated. The effect is that the two windings act like a two-phase stator and produce the

rotating field required to start the motor. When nearly full speed is obtained, a centrifugal device

(the starting switch) cuts out the starting winding. The motor then runs as a plain single-phase

induction motor. Since the auxiliary winding is only a light winding, the motor does not develop

sufficient torque to start heavy loads. Split-phase motors, therefore, come only in small sizes.

REPAIRING OF CEILING FANSteps for repairing ceiling fan

(a). Start by turning off the circuit breaker to the fan.

(b). Next, remove the cover on the fan housing or the globe light so you can access the

switch, and unscrew the nut on the outside of the switch that holds it on.

(c). Pull the switch out of the housing from the inside, leaving the wires attached.

(d). Examine the switch to see if the chain can be reattached.

(e). If not, carefully note the colors of the wires and the terminal each attaches to (take a

picture with a digital camera or cell phone or draw a diagram of the switch).

(f). Detach the wires and take the switch—along with the model and make of the fan—with

you to the home center for a replacement. Be sure to match the number of speeds, switch

size, and wattage.

(g). To install the new switch if the wires attach directly to the terminals, bend each wire

around the corresponding terminal in a clockwise direction, and tighten up the screws.

(h). If the switch has wires that attach using twist-on connectors (commonly called wire

nuts), strip 1/2” to 3/4” of insulation from each wire, wrap them together in a clockwise

direction, and twist the connector on in a clockwise direction so it is secure and the bare

wire is covered.

(i). Insert the switch in the hole in the fan housing from the inside and thread the nut on the

outside.

(j). Attach the housing cover or the globe light


MACHINE SHOPINTRODUCTIONEvery machine needs proper care and with the time there parts get worn out, so these

parts needs to replaced or maintained. This function performed in Machine shop. Here

different parts of machines are repaired. This shop has many heavy machines. For example

lathe machine, milling, shaper, grinding, radial drilling etc.

LATHE MACHINEIt is commonly known as the mother of all other machine tool. The main function of a

lathe is to remove metal from a job to give it the required shape and size. The job is secure1y

and rigid1y held in the chuck or in between centre on the lathe machine and then turn it

against a single point cutting tool which will remove metal from the job in the form of chips.

Lathe can be used to carry out other operations also, such as drilling, reaming, boring, taper

turning, knurling, screw thread cutting, grinding etc.

CENTRE OR ENGINE LATHEThis lathe is the important member of the lathe family and is the most widely used.

Similar to the speed lathe, the engine lathe has all the basic parts, e.g., bed, headstock, and

tailstock. But its headstock is much more robust in construction and contains additional

mechanism for driving the lathe spindle at multiple speeds.The engine lathe can feed the

cutting tool both in cross and longitudinal direction with reference to the lathe axis with the

help of a carriage, feed rod and lead screw. The power may be transmitted by means of belt,

electric motor or through gears.

Fig. 4.1: Centre lathe


Shaper MachineShaper is a reciprocating type of machine tool in which the ram moves the cutting tool

backwards and forwards in a straight line. These surfaces may be horizontal, Vertical, or

inclined. A shaper is used to generate flat (plane) surfaces by means of a single point cutting

tool similar to a lathe tool. A single point cutting tool is held in the tool holder, which is

mounted on the ram. The work piece is rigidly held in a vice or clamped directly on the table.

The table may be supported at the outer end. The ram reciprocates and thus cutting tool held

in tool holder moves forward and backward over the work piece. In a standard shaper, cutting

of material takes place during the forward stroke of the ram. The backward stroke remains

idle and no cutting takes place during this stroke. The feed is given to the work piece and

depth of cut is adjusted by moving the tool downward towards the work piece. The time

taken during the idle stroke is less as compared to forward cutting stroke and this is obtained

by quick return mechanism.

Fig. 4.2: Shaper Machine

Radial Drilling MachineThe radial drilling machine consists of a heavy, round vertical column supporting a

horizontal arm that carries the drill head. Arm can be raised or lowered on the column and

can also be swung around to any position over the work and can be locked in any position.

The drill head containing mechanism for rotating and feeding the drill is mounted on a radial


arm and can be moved horizontally on the guide-ways and clamped at any desired position.

These adjustments of arm and drilling head permit the operator to locate the drill quickly over

any point on the work. The table of radial drilling machine may also be rotated through 360

deg. The maximum size of hole that the machine can drill is not more than 50 mm. Powerful

drive motors are geared directly into the head of the machine and a wide range of power

feeds are available as well as sensitive and geared manual feeds. The radial drilling machine

is used primarily for drilling medium to large and heavy work pieces.

Fig. 4.5: Radial Drilling Machine

Slotting MachineThe slotter or slotting machine is also a reciprocating type of machine tool similar to a

shaper or a planer. It may be considered as a vertical shaper. The chief difference between a

shaper and a slotter is the direction of the cutting action. The machine operates in a manner

similar to the shaper, however, the tool moves vertically rather than in a horizontal direction.

The job is held stationary. The slotter has a vertical ram and a hand or power operated rotary

table.

Fig. 4.6: Slotting Machine


Grinding MachineGrinding is a material removal and surface generation process used to shape and

finish components made of metals and other materials. The precision and surface finish

obtained through grinding can be up to ten times better than with either turning or milling

usually a rotating wheel brought into controlled contact with a work surface. The grinding

wheel is composed of abrasive grains held together in a binder. These abrasive grains act as

cutting tools, removing tiny chips of material from the work. As these abrasive grains wear

and become dull, the added resistance leads to fracture of the grains or weakening of their

bond. The dull pieces break away, revealing sharp new grains that continue cutting.

The requirements for efficient grinding include:

(a). Abrasive components which are harder than the work.

(b). Shock- and heat-resistant abrasive wheels.

(c). Abrasives that is friable. That is, they are capable of controlled fracturing.

Fig. 4.7: Grinding Machine


Milling machineA milling machine is a machine tool that removes metal as the work is fed against a

rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a

very fast rate with the help of multiple cutting edges. One or more number of cutters can be

mounted simultaneously on the arbour of milling machine. This is the reason that a milling

machine finds wide application in production work. Milling machine is used for machining

flat surfaces, contoured surfaces, surfaces of revolution, external and internal threads, and

helical surfaces of various cross-sections. In many applications, due to its higher production

rate and accuracy, milling machine has even replaced shapers and slottersAs the workpiece

moves against the cutting edges of milling cutter, metal is removed in form chips of trochoid

shape. Machined surface is formed in one or more passes of the work. The work to be

machined is held in a vice, a rotary table, a three jaw chuck, an index head, between centres,

in a special fixture or bolted to machine table. The rotatory speed of the cutting tool and the

feed rate of the work piece depend upon the type of material being machined.

Fig. 4.8: Milling machine


COMPRESSOR SHOP Introduction of Air CompressorAir compressor is a machine, suck low pressure low temperature air form atmosphere

and compressor it to high pressure and high temperature by reciprocating or rotary motion

of compressor. It is driven by external source like as prime mover. The compressor used

for supplying large amount of air to machine.

Use of Compressed Air(a). To start large diesel engine.

(b). To clean workshop machine.

(c). To operate blast furnaces.

(d). To operate lift, reams and pump.

(e). To inject drill, hammer, air brake for locomotive and water sprays.

(f). For supercharging of I.C. engine.

(g). For filling the air in tube of tire.

(h). To cool large building.

Classification Of Air CompressorsReciprocating Air Compressor

Single Stage Reciprocating Compressor

Construction(a). It consists of cylinder and piston assembly.

(b). Assembly of crank shaft and connecting rod.

(c). Inlet and delivery valve etc.

Fig. 6.2: Reciprocating Compressor


Working(a). The single stage reciprocating compressor is shown in figure.

(b). The single stage reciprocating compressor working is same as engine.

(c). During the downward motion of the piston, the pressure inside the cylinder falls

below the

(d). Atmospheric pressure and the inlet valve is opened due to the pressure.

(e). As the piston starts moving upward, the inlet valve is closed and the pressure is

increasing continuously until the pressure inside the cylinder is above the pressure of

delivery side which to the receiver.

(f). Then delivery valve open and air transfer to receiver.

(g). The cycle is repeated.

Two stage compressor (Multi stage compressor)

ConstructionIt consists of two cylinders, one is L.P. (Low pressure) and another is H.P. (High pressure).

Two parallel cylinders are connected by inter-cooler.

Working(a). The two stage compressor diagram shown in figure.

Fig. 6.3: Multistage Compressor

(b). In the two- stage air compressor with inter-cooler, the air is first taken into low

pressure (L.P.) cylinder; this air is compressed in to the cylinder.

(c). Then this air is passing to inter-cooler.

(d). The air is cooled at constant pressure to its original temperature by cold water.


(e). When the air cooled to original temperature, the cooling perfect due to constant

pressure.

(f). The cooled air is passed to high pressure (H.P.) cylinder.

(g). For second stage, the H.P. cylinder compressed to final pressure then delivered to

receiver at constant pressure.

(h). The indicated diagram of H.P. and L.P. cylinder shown in figure.

ROTARY COMPRESSOR

Screw compressor

Construction(a). In screw compressor, the suction and delivery valve replaced by port and a piston

replaced by helical screw.

(b). It consists of two helical screws which are mesh with each other.

(c). An electrical motor drives a male rotor and female are driven by male rotor.

Working(a). The screw compressor is shown in figure.

(b). The screw compressor is driven by external source like electric motor.

(c). When the male rotor shaft is rotate then female is mesh with male gear.

Fig. 6.4: Screw Compressor

(d). The air, gas is drawn into the inlet port, the rotor is continuous to turn inter lobe space

increase in size, and gas, air flow continuously into compressor.

(e). Male lobe with female inter lobe space on the suction end and progressively

compresses the air in axial direction of discharge proof.

(f). At the point determine by the designed built in volume ratio, the discharge port is

uncovered and the compressed air is discharge.

(g). The cycle is repeated.


Root Blower (Lobe Type)

Construction(a). It consist of two rotor driven by externally, one of the rotor is connected to drive and

another is driven by first rotor.

(b). A very small clearance is provided between the casing and rotor to prevent wear.

Then increase the pressure ratio.

Working(a). The root blower is shown in figure.

(b). The volume of air Vs at atmospheric pressure is trapped between the left hand rotor

and casing.

Fig. 6.5: Root Blower

(c). At the same time, high pressure air rushes back from the receiver and mix irreversibly

with blower air V until pressure equalized.

(d). Then air is delivered to receiver.

(e). If two rotor has two lobes then air delivered is 4V and if three lobes then 6V per

revaluation.

(f). The delivery of air into receiver is not continuously even the rotor revolves with

uniform speed.

(g). The procedure is repeated.

Vane compressor

Construction(a). It consists of a rotor located eccentrically in a cylindrical casing.

(b). The rotor carries a set of spring located vane in the lot of rotor.


(c). It consists of vane, spring, casing, rotor etc.

WorkingThe vane compressor is shown in figure.

Fig. 6.6: Vane Compressor

(a). The volume of air V1 at atmospheric pressure P1, is trapped between two vanes in root

blower.

(b). As the rotation processed, the trapped air is first compressed reversibly from

condition 1 to d as the compression take place due to decrease in volume provide for

trapped air.

(c). Thus the air is compressed irreversibly from the pressure Pd to P2.

(d). The air is delivered to receiver after the equalization of the pressure in receiver.

Centrifugal Compressor

Construction(a). It consists of rotating impeller, diffuser, casing, driven shaft, impeller eye etc.

(b). The impeller can run at speed 20,000 to 30,000 r.p.m.

(c). The diffuser is important part of compressor which surrounding the impeller and

provides diverging passage for air flow thus increasing the pressure air.

Working(a). The centrifugal compressor is shown in figure.

(b). The impeller rotate with the shaft at high speed and air is drawn into the impeller eye

in an axial direction.

(c). The air flow radially outward through the impeller passed due to centrifugal force.

Fig. 6.7: Centrifugal Compressor


(d). The air leaves the impeller tip with high velocity and enters the diffuser.

(e). The diffuser reduce the high velocity thus by diffuser process of air in the diffuser,

kinetic energy is converted in to pressure energy.

(f). The flow from the diffuser is collected in a spiral passage from which it is discharged

form compressor.

(g). The procedure is repeated.

APPLICATION OF COMPRESSORApplication of reciprocating compressor(a). To spray painting shop.

(b). In workshop, for cleaning the machine.

(c). In automobile service station for cleaning the vehicle.

(d). For operation of pneumatic tools.

(e). Blast in blast furnace.

(f). Boosting of I.C. engine.

Application of rotary compressor(a). Petrol chemical factory.

(b). Refrigeration factory.

(c). Supercharging of petrol and diesel engine.

(d). Oil refinery plant.


CRANESHEDINTRODUCTIONA crane is a type of machine, generally equipped with a hoist, wire ropes or chains,

and sheaves, that can be used both to lift and lower materials and to move them horizontally.

It uses one or more simple to create mechanical advantage and thus move loads beyond the

normal capability of a human.

Basic Lifting Parts Of The Crane(a). Lever

(b). Pulley

(c). The hydraulic cylinder

(d). A balance crane contains a horizontal beam (the lever) pivoted about a point called

the fulcrum.

(e). A jib crane contains a tilted strut (the jib) that supports a fixed pulley block. Cables

are wrapped multiple times round the fixed block and round another block attached to

the load.

(f). For stability, the sum of all moments about any point such as the base of the crane

must equate to zero.

TYPES OF CRANEOn the basis of modern crane study and advancement there are two basic types of cranes:-

1. Fixed crane

2. Mobile or movable crane

(a). A fixed crane is the type of crane which lift the loads without any appreciable

movement.

(b). A mobile crane is the type of crane which moves from one place to another as

well as movement of the crane basic tools.

TYPES OF FIXED CRANE

TOWER CRANEThe tower crane is a modern form of balance crane. Fixed to the ground (and

sometimes attached to the sides of structures as well), tower cranes often give the best


combination of height and lifting capacity and are used in the construction of tall buildings.

Specification:Lifting Capacity: - max 25t.

Working Radius: - 70 m to 75m.

Tower crane is generally used for high rise infrastructure and project.

SELF-ERECTING CRANE

Specification:Lifting Capacity: - max 6t to 8t.

Working Radius: - 45m.

Use:It is mainly used on construction –site to transport the material from one place to other place.

HAMMERHEAD CRANEThe "hammerhead", or giant cantilever, crane is a fixed-jib crane consisting of a steelbraced

tower on which revolves a large, horizontal, double cantilever; the forward part of this

cantilever or jib carries the lifting trolley, the jib is extended backwards in order to form a

support for the machinery and counter-balancing weight.

Specifications:Lifting capacity: - max 350tons.

Working radius: - up to 70m.

Use: Ship-yard work including construction of ship and heavy duty building construction.

30

OVERHEAD CRANE(a). Overhead Crane can build top running cranes, under running cranes, double girder

cranes, and single girder cranes ranging from:

(b). Capacities - 1/4 ton through 100 tons

(c). Spans - 5' through 125‘

(d). Use: The most common overhead crane use is in the steel industry.


WELDING SHOPINTRODUCTION

Welding is a process for joining two similar or dissimilar metals by fusion. It joins

different metals/alloys, with or without the application of pressure and with or without the

use of filler metal. The fusion of metal takes place by means of heat. The heat may be

generated either from combustion of gases, electric arc, electric resistance or by chemical

reaction. During some type of welding processes, pressure may also be employed, but this is

not an essential requirement for all welding processes. Welding provides a permanent joint

but it normally affects the metallurgy of the components. It is therefore usually accompanied

by post weld heat treatment for most of the critical components. The welding is widely used

as a fabrication and repairing process in industries. Some of the typical applications of

welding include the fabrication of ships, pressure vessels, automobile bodies, off-shore

platform, bridges, welded pipes, sealing of nuclear fuel and explosives, etc.

WELDING POSITIONSThere are four types of welding positions:

(a). Flat or down hand position.

(b). Horizontal position.

(c). Vertical position.

(d). Overhead position.

Fig. 8.1: Types of joints

TYPES OF WELDING JOINTS(a). Butt joint

(b). Corner and Tee joint

(c). Lap joint

(d). Edge joint

CLASSIFICATION OF WELDING PROCESSES


OXY ACETYLENE GAS WELDINGIn this process, acetylene is mixed with oxygen in correct proportions in the welding

torch and ignited. The flame resulting at the tip of the torch is sufficiently hot to melt and join

the parent metal. The oxy-acetylene flame reaches a temperature of about 3300°C and thus

can melt most of the ferrous and non-ferrous metals in common use. A filler metal rod or

welding rod is generally added to the molten metal pool to build up the seam slightly for

greater strength.

Oxy Acetylene Welding SetupAcetylene and oxygen gas is stored in compressed gas cylinders. These gas cylinders

differ widely in capacity, design and colour code. However, in most of the countries, the

standard size of these cylinders is 6 to 7 m3 and is painted black for oxygen and maroon for

acetylene. An acetylene cylinder is filled with some absorptive material, which is saturated

with a chemical solvent acetone. Acetone has the ability to absorb a large volume of

acetylene and release it as the pressure falls. If large quantities of acetylene gas are being

consumed, it is much cheaper to generate the gas at the place of use with the help of

acetylene gas generators. Acetylene gas is generated by carbide-to-water method.

Fig. 8.3: Oxy-Acetylene Welding


METAL INERT GAS WELDINGMetal inert gas arc welding (MIG) or more appropriately called as gas metal arc

welding (GMAW) utilizes a consumable electrode. MIG welding uses a welding wire that is

feed automatically at a constant speed as an electrode. A short arc is generated between the

base metal and the wire. The resulting heat from the arc melts the welding wire and joins the

base metals together. Since the wire is fed automatically at a constant rate, this method is

called semiautomatic arc welding.

During the welding process, either inert gases or active gas shields the weld from the

atmosphere and prevents oxidation of the base metal. The type of inert gas used depends on

the base material to be welded. For most steels welds, carbon dioxide is used a shield gas.

The power supplies are always of the constant voltage type only. The current from the

welding machine is changed by the rate of feeding of the electrode wire. Normally DC arc

welding machines are used for GMAW with electrode positive (DCRP).

Fig. 8.4: Mig Welding Set Up

TUNGSTEN INERT GAS WELDINGIn this process a non-consumable tungsten electrode is used with an envelope of inert

shielding gas around it. The shielding gas protects the tungsten electrode and the molten

metal weld pool from the atmospheric contamination. The shielding gases generally used are

argon, helium or their mixtures. Both AC and DC power source can be used for TIG welding.

DC is preferred for welding of copper, copper alloys, nickel and stainless steel whereas DC


reverse polarity (DCRP) or AC is used for welding aluminium, magnesium or their alloys.

Fig. 8.5: Tig Welding Set Up

WELDING DEFECTSLack of Penetration

It is the failure of the filler metal to penetrate into the joint. It is due to

(a). Inadequate de-slagging.

(b). Incorrect edge penetration.

(c). Incorrect welding technique.

Lack of Fusion

Lack of fusion is the failure of the filler metal to fuse with the parent metal.

(a). Too fast a travel

(b). Incorrect welding technique

(c). Insufficient heat

Porosity

It is a group of small holes throughout the weld metal. It is caused by the trapping of gas. It is

caused by the trapping of gas during the welding process, due to

(a). Chemicals in the metal

(b). Dampness


(c). Too rapid cooling of the weld.

Slag Inclusion

It is the entrapment of slag or other impurities in the weld. It is caused by

(a). Slag from previous runs not being cleaned away,

(b). Insufficient cleaning and preparation of the base metal before welding commences.

Undercuts

These are grooves or slots along the edges of the weld caused by

(a). Too fast a travel

(b). Bad welding technique

(c). Too great a heat build-up.

Cracking

It is the formation of cracks either in the weld metal or in the parent metal. It is due

(a). Unsuitable parent metals used in the weld

(b). Bad welding technique.

Poor Weld Bead Appearance

If the width of weld bead deposited is not uniform or straight, then the weld bead is

termed as poor. It is due to improper arc length, improper welding technique, damaged

electrode coating and poor electrode and earthing connections.

Distortion

Distortion is due to high cooling rate, small diameter electrode, poor clamping and slow arc

travel speed.

Overlays

These consist of metal that has flowed on to the parent metal without fusing with the defect is

due to

(a). Contamination of the surface of the parent metal

(b). Insufficient heat

Blowholes

These are large holes in the weld caused by

(a). Gas being trapped, due to moisture.

(b). Contamination of either the filler or parent metals.

Burn Through


It is the collapse of the weld pool due to

(a). Too great a heat concentration

(b). Poor edge preparation.

Excessive Penetration

It is where the weld metal protrudes through the root of the weld. It is caused by

(a). Incorrect edge preparation

(b). Too big a heat concentration

(c). Too slow a travel.

Fig. 8.6: Types of Welding Defects

Railway workshop jhansi

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