PPRROOJJEECCTT RREEPPOORRTT

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RRAAIILL CCOOAACCHH FFAACCTTOORRYY,, KKAAPPUURRTTHHAALLAA WITH EFFECT FROM 07-05-2012 TO 30-06-2012

SUBMITTED BY- NAME- BRANCH- ROLL NO- UNIV ROLL NO-

INDEX

S. NO TOPICS PAGE NO. REMARKS

1.

ACKNOWLEDGEMENT

1

2. ABOUT RCF

2-3

3. TIG WELDING

4

4. MIG WELDING

5

5. SUBMERGED ARC WELDING

6

6. GAS WELDING

7

7. WELD DEFECTS

8-14

8. TYPES OF ELECTRODES

15

9. TECHNICAL TRAINING CENTRE

16

ACKNOWLEDGEMENT

With profound respect and gratitude, I take the opportunity to convey my thanks

to complete the training here.

I do extend my heartfelt thanks to Mr. R. K. SHARMA head of TTC

(Technical Training Center) and Mr. R.C. NASA head of Welding Workshop

for providing me this opportunity to be a part of this esteemed

organization.

I am extremely grateful to all the technical staff of RAIL COACH FACTORY,

Kapurthala for their co-operation and guidance that helped me a lot during

the course of training. I have learnt a lot working under their guidance and I will

always be indebted of them for this value addition in me.

ABOUT RCF

Established in 1986, RCF is a coach manufacturing unit of Indian Railways.

RCF has already carved a niche in the industrial scenario of the country at large

and Indian Railways, in particular. It has manufactured around 16000 passenger

coaches of 51 different types including Self Propelled passenger vehicles which

constitute over 35% of the total population of coaches on Indian Railways.

RCF is equipped with a state-of-the-art CAD centre and CNC machines to

undertake design and manufacture of Bogies, Shell (both with Stainless Steel

and Corten Steel), FRP interiors as per customer’s requirement. The state-of-

the-art manufacturing facilities and processes have enabled RCF to achieve

excellence in Design, Development, Manufacture, Installation and After-sales

service of Railway coaches with a view to ensure enhanced satisfaction of the

Rail customer.

RCF has a strong tradition of innovating and developing new products and has a

very wide manufacturing range of products which includes:-

• 1st AC Sleeper Coach (BG)

• 2 Tier AC Sleeper Coach (BG, MG)

• 3 Tier AC Sleeper Coach (BG)

• AC Inspection Coach (BG)

• AC Chair Car, Executive Class & Economy Class (BG, MG)

• AC Buffet Car (BG)

• AC Power Car (BG)

• MG Diesel Electrical Multiple Units

• Main Line Electrical Multiple Units (BG)

• Non-AC Sleeper Class Day Coach (BG)

• Non-AC General Coach (BG/MG)

• Non-AC Luggage-cum-Brake Van (BG/MG)

• Refrigerated Parcel Van (BG)

• Non AC Inspection Coach (BG)

• High Capacity Parcel Van (BG)

• Accident Relief Train (BG)

• Post Office Coach (BG)

• Coaching Container Flats (BG)

• Double Decker Coach (BG)

• Non-AC Day Coach (BG)

Fig:- Rail Coach Factory, Kapurthala

TIG WELDING

In the TIG (tungsten inert gas) welding process, an essentially non-consumable

tungsten electrode is used to provide an electric arc for welding. A sheath of

inert gas surrounds the electrode, the arc, and the area to be welded. This gas

shielding process prevents any oxidization of the weld and allows for the

production of neat, clean welds.

TIG welding differs from MIG (metal inert gas) welding in that the

electrode is not consumed in the weld. In the MIG welding process the

electrode is continuously melted and is added into the weld. In TIG welding, no

metal is added unless a separate filler rod is used.

TIG welding can be performed with a large variety of metals. The two

most commonly TIG welded metals in the PRL are steel and aluminum. Steel is

relatively easy to TIG weld and it is possible to produce very tight, neat welds.

Aluminum takes a little more skill, and one should have at least a little bit of

experience in welding steel before making the transition to aluminum.

However, the basic technique is essentially the same and most people can make

the jump to aluminum fairly easily.

TIG welding is an extremely powerful tool. With a little practice, it is

possible to make beautiful welds much more quickly and easily than with oxy-

acetylene welding. It also the only option currently available in the shop for

welding aluminum. Put in a little time, and you will be rewarded in spades.

MIG WELDING

MIG welding is an abbreviation for Metal Inert Gas Welding. It is a process

developed in the 1940’s, and is considered semi-automated. This means that

the welder still requires skill, but that the MIG welding machine will

continuously keep filling the joint being welded.

MIG welders consist of a handle with a trigger controlling a wire feed, feeding

the wire from a spool to the weld joint. The wire is similar to an endless bicycle

brake cable. The wire runs through the liner, which also has a gas feeding

through the same cable to the point of arc, which protects the weld from the air.

MIG welding is most commonly used in fabrication shops where production is

high, and the possibility of wind blowing away your gas shielding is unlikely.

SUBMERGED ARC WELDING

Submerged arc welding (SAW) is a common arc welding process. Originally

developed by the Linde - Union Carbide Company. It requires a non-

continuously fed consumable solid or tubular (flux cored) electrode. The

molten weld and the arc zone are protected from atmospheric contamination

by being “submerged” under a blanket of granular fusible flux consisting of

lime, silica, manganese oxide, calcium fluoride, and other compounds. When

molten, the flux becomes conductive, and provides a current path between the

electrode and the work. This thick layer of flux completely covers the molten

metal thus preventing spatter and sparks as well as suppressing the intense

ultraviolet radiation and fumes that are a part of the shielded metal arc

welding (SMAW) process.

GAS WELDING

Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas

welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and

oxygen to weld and cut metals, respectively. French engineers Edmond Fouché

and Charles Picard became the first to develop oxygen-acetylene welding in

1903.[1]

Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to

increase the flame temperature to allow localized melting of the workpiece

material (e.g. steel) in a room environment. A common propane/air flame burns

at about 3,630 °F (2,000 °C), a propane/oxygen flame burns at about 4,530 °F

(2,500 °C), and an acetylene/oxygen flame burns at about 6,330 °F (3,500 °C).

Oxy-fuel is one of the oldest welding processes. Still used in industry, in recent

decades it has been less widely utilized in industrial applications as other

specifically devised technologies have been adopted. It is still widely used for

welding pipes and tubes, as well as repair work. It is also frequently well-suited,

and favored, for fabricating some types of metal-based artwork.

WELD DEFECTS

TYPES OF DEFECTS:-

1.Cracks

Defects related to fracture.

Arc strike cracking

Arc strike cracking occurs when the arc is struck but the spot is not welded. This

occurs because the spot is heated above the materials upper critical temperature

and then essentially quenched. This forms martensite, which is brittle, and

micro-cracks. Usually the arc is struck in the weld groove so this type of crack

does not occur, but if the arc is struck outside of the weld groove then it must be

welded over to prevent the cracking. If this is not an option then the arc spot can

be postheated, i.e., the area is heated with an oxy-acetylene torch, and then

allowed to cool slowly.

Cold cracking

Residual stresses can reduce the strength of the base material, and can lead to

catastrophic failure through cold cracking, as in the case of several of the

Liberty ships. Cold cracking is limited to steels, and is associated with the

formation of martensite as the weld cools. The cracking occurs in the heat-

affected zone of the base material. To reduce the amount of distortion and

residual stresses, the amount of heat input should be limited, and the welding

sequence used should not be from one end directly to the other, but rather in

segments.

Cold cracking only occurs when all the following preconditions are met:

susceptible microstructure (e.g. martensite) hydrogen present in the microstructure (hydrogen embrittlement) service temperature environment (normal atmospheric pressure): -100 to

+100 °F high restraint

Eliminating any one of these will eliminate this condition.

Crater crack

Crater cracks occur when a crater is not filled before the arc is broken. This

causes the outer edges of the crater to cool more quickly than the crater, which

creates sufficient stresses to form a crack. It may form a longitudinal or

transverse crack or form multiple radial cracks.

Fusion-line crack

Creep crack growth and fracture toughness tests were performed using test

material machined from a seam welded ASTM A-155-66 class 1 (2.25Cr-1Mo)

steel steam pipe that had been in service for 15 years. The fracture morphology

was examined using SEM fractography. Dimpled fracture was found to be

characteristic of fracture toughness specimens. Creep crack growth generally

followed the fusion line region and was characterized as dimpled fracture mixed

with cavities. These fracture morphologies were similar to those of an actual

steam pipe. It was concluded that creep crack growth behavior was the prime

failure mechanism of seam-welded steam pipes.

Hat crack

Hat cracks get their name from the shape of the cross-section of the weld,

because the weld flares out at the face of the weld. The crack starts at the fusion

line and extends up through the weld. They are usually caused by too much

voltage or not enough speed.

Hot cracking

Hot cracking, also known as solidification cracking, can occur with all metals,

and happens in the fusion zone of a weld. To diminish the probability of this

type of cracking, excess material restraint should be avoided, and a proper filler

material should be utilized. Other causes include too high welding current, poor

joint design that does not diffuse heat, impurities (such as sulfur and

phosphorus), preheating, speed is too fast, and long arcs.

Underbead crack

An underbead crack, also known as a heat-affected zone (HAZ) crack, is a crack

that forms a short distance away from the fusion line; it occurs in low alloy and

high alloy steel. The exact causes of this type of crack are not completely

understood, but it is known that dissolved hydrogen must be present. The other

factor that affects this type of crack is internal stresses resulting from: unequal

contraction between the base metal and the weld metal, restraint of the base

metal, stresses from the formation of martensite, and stresses from the

precipitation of hydrogen out of the metal.

Longitudinal crack

Longitudinal cracks run along the length of a weld bead. There are three types:

check cracks, root cracks, and full centerline cracks. Check cracks are visible

from the surface and extend partially into weld. They are usually caused by high

shrinkage stresses, especially on final passes, or by a hot cracking mechanism.

Root cracks start at the root and extent part way into the weld. They are the most

common type of longitudinal crack because of the small size of the first weld

bead. If this type of crack is not addressed then it will usually propagate into

subsequent weld passes, which is how full centerline cracks (a crack from the

root to the surface) usually form.

Reheat cracking

Reheat cracking is a type of cracking that occurs in HSLA steels, particularly

chromium, molybdenum and vanadium steels, during postheating. It is caused

by the poor creep ductility of the heat affected zone. Any existing defects or

notches aggravate crack formation. Things that help prevent reheat cracking

include heat treating first with a low temperature soak and then with a rapid

heating to high temperatures, grinding or peening the weld toes, and using a two

layer welding technique to refine the HAZ grain structure.

Root and toe cracks

A root crack is the crack formed by the short bead at the root(of edge

preparation) beginning of the welding, low current at the beginning and due to

improper filler material used for welding.Major reason for happening of these

types of cracks is hydrogen embrittlement. These types of defects can be

eliminated using high current at the starting and proper filler material. Toe crack

occurs due to moisture content present in the welded area,it as a part of the

surface crack so can be easily detected. Preheating and proper joint formation is

must for eliminating these types of defects.

2. Distortion

Welding methods that involve the melting of metal at the site of the joint

necessarily are prone to shrinkage as the heated metal cools. Shrinkage then

introduces residual stresses and distortion. Distortion can pose a major problem,

since the final product is not the desired shape. To alleviate certain types of

distortion the workpieces can be offset so that after welding the product is the

correct shape. The following pictures describe various types of welding

distortion.

Transverse shrinkage Angular distortion

Longitudinal shrinkage Fillet distortion

Neutral axis distortion

3.Gas inclusion

Gas inclusions is a wide variety of defects that includes porosity, blow holes,

and pipes (or wormholes). The underlying cause for gas inclusions is the

entrapment of gas within the solidified weld. Gas formation can be from any of

the following causes: high sulphur content in the workpiece or electrode,

excessive moisture from the electrode or workpiece, too short of an arc, or

wrong welding current or polarity.

4.Inclusions

There are two types of inclusions: linear inclusions and isolated inclusions.

Linear inclusions occur when there is slag or flux in the weld. Slag forms from

the use of a flux, which is why this type of defect usually occurs in welding

processes that use flux, such as shielded metal arc welding, flux-cored arc

welding, and submerged arc welding, but it can also occur in gas metal arc

welding. This defect usually occurs in welds that require multiple passes and

there is poor overlap between the welds. The poor overlap does not allow the

slag from the previous weld to melt out and rise to the top of the new weld bead.

It can also occur if the previous weld left and undercut or an uneven surface

profile. To prevent slag inclusions the slag should be cleaned from the weld

bead between passes via grinding, wire brushing, or chipping.

Isolated inclusions occur when rust or mill scale is present on the base metal.

5. Lack of fusion and incomplete penetration

Lack of fusion is the poor adhesion of the weld bead to the base metal;

incomplete penetration is a weld bead that does not start at the root of the weld

groove. Incomplete penetration forms channels and crevices in the root of the

weld which can cause serious issues in pipes because corrosive substances can

settle in these areas. These types of defects occur when the welding procedures

are not adhered to; possible causes include the current setting, arc length,

electrode angle, and electrode manipulation.

6. Lamellar tearing

Lamellar tearing is a type of welding defect that occurs in rolled steel plates. It

has rarely been an issue since the 1970s because steel produced since then has

less sulfur.

There is a combination of causes: non-metallic inclusions, too much hydrogen in

the material, and shrinkage forces perpendicular to the face of the plates. The

main factor among these reasons is the non-metal inclusions, of which the sulfur

is the main problem. Lamellar tearing is no longer a problem anymore because

sulfur levels are typical kept below 0.005%.

Some things that are done to overcome lamellar tearing are: reducing amount of

sulfur in the material or adding alloying elements that control the shape of

sulfide inclusions, such as rare earth elements, zirconium, or calcium. A more

drastic option is change the workpieces to castings or forgings because this type

of defect does not occur in those workpieces.

TYPES OF ELECTRODES

In an electrochemical cell, there are two electrodes, positive and negative. Each

electrode constitutes a half cell or a single electrode. Although a number of

electrodes are possible but the more important of these electrodes are grouped

into the following types:

(i) Metal-metal ion electrodes

(ii) Metal-metal insoluble salt electrodes

(iii) Metal-amalgam electrodes

(iv) Gas-ion electrodes

(v) Oxidation-reduction or redox electrodes

TECHNICAL TRAINING CENTRE