Welding Processes
Joining two or more elements to make a single part is termed as a fabrication process.
The various fabrication processes can be classified as follows:
● Mechanical joining by means of bolts, screws and rivets.
● Adhesive bonding by employing synthetic glues such as epoxy resins.
● Welding, brazing and soldering.
The choice of a particular fabrication method depends on a number of factors
pertaining to the joint such as
● Type of assembly permanent, semi‑permanent or temporary,
● Materials being joined, steels, cast irons, aluminium, similar or dissimilar metals,
● Economy achieved, and
● The type of service required, such as assembly subjected to heavy loading, impact
loading, high temperatures, etc.
Welding:
Welding techniques is a metallurgical fusion process.
Here, the interface of the two parts to be joined is brought to a temperature above
the melting point and then allowed to solidify so that a permanent joining takes place.
Because of the permanent nature of the joint and strength being equal to or
sometimes greater than that of the parent metal makes welding one of the most
extensively used fabrication method.
Welding is not only used for making structures but also for repair work such as the
joining of broken castings.
Products obtained by the process of welding are called ‘weldments’.
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Definition: Welding is defined as ‘‘a localized coalescence of metals, wherein
coalescence is obtained by heating to suitable temperature, with or without the
applications of pressure and with or without the use of filler metal’’.
The filler metal has a melting point approximately the same as the base metal.
The most essential requirement is heat.
Pressure may also be employed, but this is not, in many processes essential.
Soldering and brazing:
Soldering. It is a process of joining two pieces of metal with a different fusible metal
applied in a molten state. The fusible metal is called ‘solder’.
It is a process of joining two metals with low melting point metal.
Brazing. It is a process of joining two metal pieces in which a non-ferrous alloy is
introduced in the liquid state between the pieces to be joined and allowed to solidify.
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Points to be noted:
Soldering and brazing are two common solid/liquid-state bonding processes.
— These are different from welding as bonding here requires capillary action and
that some degree of alloying action between the filler and the base metal always
occurs. Also the composition of filler metal is significantly different and its strength
and melting point are substantially lower than that of the base metal.
— In ‘soldering’ (very similar to brazing) the filler material is usually a lead-tin
based alloy which has much lower strength and melting temperature (about 250°C).
Also, less alloying action between the base and filler metals gives lower joint
strength. Since in this process much lower temperatures are involved, it is usually
carried out with electric resistance heating.
— In ‘brazing’ the joint is made by heating the base metal red hot and filling the gap
with molten filler metal whose melting temperature is above 427°C but below the
temperature of base metal. The filler metals, generally used for brazing are copper
alloys. This process is usually carried out with a gas flame.
Joining processes:
Base on the composition of the joint, the joining processes may be classified as
following:
(i) Autogeneous process: In this type of joining process, no filler material is added
during the joining process as in the case of resistance welding, cold welding, friction
welding, diffusion welding and hot forge welding.
(ii) Homogeneous process: This process make use of filler metal but of same
composition as the parent metal as in the case of arc, gas and thermit welding.
(iii) Heterogeneous process: In this process the filler material is soluble in both the
parent metals which themselves are insoluble in each other.
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Types of Joints:
Welding Position:
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Edge Preparation:
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Terminology used:
Backing: It is the material support provided at the root side of a weld to aid in the
control of penetration.
Base metal/Parent metal: The metal to be joined or cut is termed as the base metal.
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Bead or weld bead: Bead is the metal added during a single pass of welding. The
bead appears as a separate material from the base metal.
Crater: In arc welding, a crater is the depression in the weld metal pool at the point
where the arc strikes the base metal plate.
Deposition rate: The rate at which the weld metal is deposited per unit time is the
deposition rate and is normally expressed as kg/h.
Fillet weld: The metal fused into the corner of a joint made of two pieces placed at
approximately 90 degrees to each other, is termed fillet weld.
Penetration: It is the depth up to which the weld metal combines with the base metal
as measured from the top surface of the joint.
Puddle: The portion of the weld joint that melted by the heat of welding is called
puddle.
Root: It is the point at which the two pieces to be joined by welding is nearest.
Tack weld: A small weld, generally used to temporarily hold the two pieces together
during actual welding, is the tack weld.
Toe of weld: It is the junction between the weld face and the base metal.
Torch: In gas welding, the torch mixes the fuel and oxygen and controls its delivery
to get the desired flame.
Weld face: It is the exposed surface of the weld.
Weld metal: The metal that is solidified in the joint is called weld metal. It may be
only base metal or a mixture of base metal and filler metal.
Weld pass: A single movement of the welding torch or electrode along the length
of the joint which results in a bead is a weld pass.
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Electric Arc Welding
In welding, generation of heat by an electric arc is one of the most efficient methods.
Approximately, 50% of the energy is liberated in the form of heat. The electric arc
welding process makes use of the heat produced by the electric arc to fusion weld
metallic pieces. This is one of the most widely used welding process, mainly because
of the ease of use and high production rates that can be achieved economically.
Principle of Arc
An arc is generated between two conductors of electricity, cathode and anode
(considering direct current, DC), when they are touched to establish the flow of
current and then separated by a small distance.
An arc is a sustained electric discharge through the ionised gas column called plasma
between the two electrodes.
It is generally believed that electrons liberated from the cathode move towards the
anode and are accelerated in their movement. When they strike the anode at high
velocity, large amount of heat is generated. Also when the electrons are moving
through the air gap between the electrodes, also called the arc column, they collide
with the ions in the ionised gas column between the electrodes.
The positively charged ions, moving from the anode and would be impinging on the
cathode, thus liberating heat.
About 65 to 75% of the total heat is liberated at the anode by the striking electrons.
A temperature of the order of 6000°C is generated at the anode.
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In order to produce the arc, the potential difference between the two electrodes
(voltage) should be sufficient to allow them to move across the air gap. The larger
air gap requires higher potential differences.
If the air gap becomes too large for the voltage, the arc may be extinguished.
For convenience of explanation, we have chosen a direct current arc for the above
description. But even with an arc of the alternating current (AC), would be similar,
with the main difference that the cathode and anode would change continuously and
as a result, the temperature across the arc would be more uniform compared to a DC
arc.
Arc Welding Equipment
The main requirement in an arc welding set up is the source of electric power. They
are essentially of two types:
(a) Alternating current (AC) machines
(i) Transformer, or (ii) Motor or engine driven alternator
(b) Direct current (DC) machines
(i) Transformer with DC rectifier, or (ii) Motor or engine driven generator
The transformer does not have any moving part and as a result operates with less
maintenance cost and also has higher efficiency.
The power used is also less expensive and practically there is no noise in operation
of the welding transformer. In AC welding, normally only transformers are used.
In DC arc welding, a rectifier or a generator can be used to supply the required DC
power. In the rectifier type, the power supply is first stepped down by means of a
transformer to the required voltage and then silicon controlled rectifiers (SCR) are
used to convert AC to DC. These rectifiers are very compact, highly reliable and
have high efficiency.
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The other type is a DC generator which is driven by either an induction motor
running on AC or an oil engine. This combination is less efficient, more expensive
and noisy in operation.
Welding Machine Types
The welding machines can also be divided into two types, based on the
characteristics.
The first one is the constant current welding machines or droop curve machines
or simply droopers, which vary the welding voltage to account for the change in the
arc gap thus maintaining the arc current.
As a result of this, the characteristics of the machine (a plot between output volts
and output amperes) are a drooping one, as shown in Fig.
Fig.(a) shows the setting of open circuit voltage (no welding) at 80 volts whereas
Fig.(b) for the same machine shows open circuit voltage is set at 50 volts.
It can be seen that for a large change in output voltage, the corresponding change in
current is so small that the quality of the weld can be maintained. This is very
essential for manual arc welding processes since the maintenance of constant arc is
nearly impossible by a human welder.
In contrast to the above, the constant voltage welding machines have a more flat
characteristic curve, as shown in Fig. The slope of the curve is so flat, that any small
change in voltage makes for an extremely large change in the output currents. These
systems are generally preferred in the automatic machines since they become
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self‑corrective. For example when the electrode comes a bit closer to the work, the
arc voltage drops raising the output current to a very high value. This current
instantly melts the electrode and thus maintains the arc gap.
Though DC arc welding is more expensive than AC welding, it is generally preferred
because of the control of heat input offered by it.
As explained earlier, about 70% of the heat is liberated near the anode in DC arc
welding. Hence if more heat is required at the work piece side, such as for thicker
sheets or for the work materials which have higher thermal conductivity such as
aluminium and copper, the work piece can be made as anode, liberating large heat
near it. This is termed as ‘straight polarity’ or DCEN (direct current electrode
negative). This gives rise to a higher penetration as shown in Fig.(a).
However for thinner materials, where less heat is required in the weld zone, the
polarity could be reversed by making the work piece as negative. This is termed as
‘reversed polarity’ or DCEP (direct current electrode positive). In reversed polarity,
the penetration is small, as in Fig.(b).
In the case of AC welding, the bead obtained is somewhere in between the above
two types and is as shown in Fig.(c).
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DC arc welding is generally preferred for difficult tasks such as overhead welding,
since it can maintain a stable arc.
A typical AC arc welding setup using the transformer is shown in Fig.
The work piece is kept on a metallic table to which the ground lead of the secondary
windings of the welding transformer is connected. The other lead of the secondary
is connected to an electrode holder into which the electrode is gripped. When the
electrode is brought into contact with the work, the welding takes place.
The arc welding machines are normally specified by means of
● Maximum rated open circuit voltage,
● Rated current in amperes, and
● Duty cycle
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The maximum rated open circuit voltage which is the voltage between the output
terminals when no welding is being done, is normally fixed at about 80 V. This is
the maximum and normally, a voltage of the order of 40 to 50 V should be enough
for starting an arc, whereas for continuous welding 20 to 30 V is sufficient. The
minimum welding load voltage Vm can be calculated as
Vm = 20 + 0.04 I
Where, I is the load current in amperes.
The rated current specifies the maximum current in amperes (A) that a welding
machine is capable of supplying at a given voltage. The preferred current ratings as
per BIS: 1851‑1966, are 150, 200, 300, 400, 500, 600 and 900 A.
The duty cycle as defined by American Welding Society (AWS) is “The percentage
of time in a 10 minute period that a welding machine can be used at its rated output
without over loading”.
Most of the welding machines need not have to operate the full time, since a good
length of time is spent in setting up, metal chipping, cleaning and inspection.
Normally, a 60% duty cycle is suggested.
The Indian standard specifies 5 min as the cycle and hence for every 5 min of
welding transformer operation, 3 min is for welding and 2 min is for no‑load
operation. But continuous, automatic welding machines may require the welding
machine to operate at 100% duty cycle.
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Sometimes the suggested duty cycle can be lowered for high ambient temperatures,
insufficient cooling air quality and low line voltage.
Electrodes:
The electrodes used for providing heat input in arc welding are of two types,
the consumable and the non‑consumable electrodes.
When the arc is obtained with a consumable electrode, the weld metal under the arc
melts as also the tip of the electrode. The molten metal from the electrode and that
obtained from the base metal gets intimately mixed under the arc and provides the
necessary joint after solidification. So in this process, once the arc is initiated, the
electrode is continuously consumed and hence, the electrode should be moved
continuously towards the work piece to maintain the constant arc length. Since the
electrode continuously melts, it also acts as the filler rod to provide the filler metal
into the joint. Thus, the functions of providing a filler metal and heat are both built
into a single electrode. This, however, does not mean that the welding speed should
be lowered for want of proper penetration. Wide ranges of electrodes and welding
machines are available which can be used to get the proper heat input as well as the
metal deposition as required. Consumable electrodes are made of various materials
depending on the purpose and chemical composition of the metals to be welded.
Thus, they may be made of steel, cast iron, copper, brass, bronze or aluminium.
It is also possible to use non‑consumable electrodes made of carbon, graphite or
tungsten. The carbon and graphite electrodes are used only in DC welding, whereas
tungsten electrodes are used for both AC and DC welding. The filler metal required
has to be deposited through a separate filler rod. Thus, in this welding method it is
possible to properly control the heat input as well as the amount of filler metal
deposited, since both are separately controlled.
When consumable electrodes are used, the welding process is called metal arc
welding whereas when non‑consumable electrodes are used they are termed by the
electrode material used, for example, carbon arc welding or tungsten arc welding.
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A consumable electrode, used in welding, can be either bare or coated. The coated
electrode also called stick electrode, is used for the manual arc welding process. The
coating on the electrodes serves a number of purposes which are detailed as follows
with reference to Fig.
1. The coatings give off inert gases such as carbon dioxide under the arc heat, which
shields the molten metal pool and protects it from the atmospheric oxygen, hydrogen
and nitrogen pick up thus, reducing contamination of the weld metal.
2. The coatings provide flux to the molten metal pool, which mixed with the oxides
and other impurities present in the puddle, forms a slag. The slag being lighter, floats
on the top of the puddle and protects it against the surrounding air during the weld
bead solidification. The slag covering also helps the metal to cool slowly preventing
the formation of a brittle weld. When the weld is sufficiently cooled, the slag can be
removed exposing the shiny weld underneath.
3. Some elements that are required for stabilisation of the arc are also added in these
coatings. The coatings are different for AC welding and DC welding.
4. Special alloying elements can be introduced through these coatings to improve
the strength and physical properties of the weld metal.
5. Since the electrode coating is consumed at a slower rate compared to the core
(filler metal), the coating would be extended beyond the electrode as shown in Fig.
This helps in concentrating the arc and directing the filler metal in the joint. Also the
thermal losses to the atmosphere from the electrode tip are reduced. This would
increase the available heat for melting the electrode and thus help in improving the
metal deposition rate.
6. The coatings are normally insulators of electricity and thus, permit the electrode
to be used in narrow grooves, and other difficult locations without causing any short
circuiting problems.
7. It is possible to include iron powder in the coating in large amounts so that the
electrode can be kept in contact with the work piece, which may be necessary for
welding in overhead and other positions.
Also this increases the penetration and metal deposition rate.
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8. The coatings also contain materials which can control the slag to be viscous or
fluid. Viscous slag would be useful for making welds in vertical position to cover
the metal puddle for a longer time.
The stick electrodes are normally available in diameters 3.2, 4, 5, 6, 8 and 9 mm and
the length is 350 or 450 mm.
One of the major concerns with the coated electrodes is the moisture pick up by the
coating. This moisture when enters the puddle dissociates into oxygen and hydrogen
with the hydrogen being absorbed by the liquid metal and subsequently released
during solidification, causing porosity. Normally some additives are added to the
coatings to reduce the moisture pick up from the damp atmosphere. But they do not
ensure complete safety from the moisture pick up. Therefore, it is preferable that
electrodes are kept in an oven to keep them thoroughly dry. The electrodes should
be picked out of the oven only when the welding is to be done. They should not be
out of the oven for more than 30 min to 4 hours depending upon the moisture picking
time of a particular coating.
TUNGSTEN INERT-GAS (TIG) WELDING
This welding process is also called Gas Tungsten Arc Welding (GTAW)
Tungsten inert gas (TIG) welding or gas tungsten arc welding (GTAW) is an inert
gas shielded arc welding process using non‑consumable electrode. The electrodes
may also contain 1 to 2% thoria (thorium oxide) mixed along with the core tungsten
or tungsten with 0.15 to 0.40% zirconia (zirconium oxide). The pure tungsten
electrodes are less expensive but will carry less current. The thoriated tungsten
electrodes carry high currents and are more desirable because they can strike and
maintain a stable arc with relative ease. The zirconia added tungsten electrodes are
better than pure tungsten but inferior to thoriated tungsten electrodes.
A typical tungsten inert gas welding setup is shown in Fig. It consists of a welding
torch at the centre of which is the tungsten electrode. The inert gas is supplied to the
welding zone through the annular path surrounding the tungsten electrode to
effectively displace the atmosphere around the weld puddle.
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In this process the heat necessary to melt the metal is provided by a very intense
electric arc which is struck between a virtually non-consumable tungsten electrode
and metal work piece. The electrode does not melt and become a part of the weld.
On joints where filler metal is required, a welding rod is fed into the weld zone and
melted with base metal in the same manner as that used with oxyacetylene welding.
The weld zone is shielded from the atmosphere by an inert-gas (a gas which does
not combine chemically with the metal being welded) which is ducted directly to the
weld zone where it surrounds the tungsten.
The major inert gases that are used are argon and helium.
TIG process offers the following advantages:
1. TIG welds are stronger, more ductile and more corrosion resistant than welds
made with ordinary shield arc welding.
2. Since no granular flux is required, it is possible to use a wide variety of joint
designs than in conventional shield arc welding or stick electrode welding.
3. There is little weld metal splatter or weld sparks that damage the surface of the
base metal as in traditional shield arc welding.
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Applications:
(i) The TIG process lends itself ably to the fusion welding of aluminium and its
alloys, stainless steel, magnesium alloys, nickel base alloys, copper base alloys,
carbon steel and low alloy steels.
(ii) TIG welding can also be used for the combining of dissimilar metals, hard facing,
and the surfacing of metals.
METAL INERT-GAS (MIG) WELDING
This welding process is also called Gas Metal Arc Welding (GMAW).
Metal inert gas arc welding (MIG) or more appropriately called as gas metal arc
welding (GMAW) utilises a consumable electrode and hence, the term ‘metal’
appears in the title. There are other gas shielded arc welding processes utilising the
consumable electrodes, such as flux cored arc welding (FCAW) all of which can be
termed under MIG. Though gas tungsten arc welding (GTAW or TIG) can be used
to weld all types of metals, it is more suitable for thin sheets. When thicker sheets
are to be welded, the filler metal requirement makes GTAW difficult to use. In this
situation, the GMAW comes handy.
The typical set up for GMAW (or MIG) process is shown in Fig. The consumable
electrode is in the form of a wire reel, which is fed at a constant rate, through the
feed rollers. The welding torch is connected to the gas supply cylinder which
provides the necessary inert gas. The electrode and the work piece are connected to
the welding power supply. 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.
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The inert-gas consumable electrode process, or the MIG process is a refinement of
the TIG process, however, in this process, the tungsten electrode has been replaced
with a consumable electrode. The electrode is driven through the same type of collet
that holds a tungsten electrode by a set of drive wheels. The consumable electrode
in MIG process acts as a source for the arc column as well as the supply for the filler
material.
MIG welding employs the following three basic processes.
1. Bare-wire electrode process
2. Magnetic flux process
3. Flux-cored electrode process.
Advantages:
1. It provides higher deposition rate.
2. It is faster than shielded metal-arc welding due to continuous feeding of filler
metal.
3. Welds produced arc of better quality.
4. There is no slag formation.
5. Deeper penetration is possible.
6. The weld metal carries low hydrogen content.
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7. More suitable for welding of thin sheets.
Limitations:
1. Less adaptable for welding in difficult to reach portions.
2. Equipment used is costlier and less portable.
3. Less suitable for outdoor work because strong wind may blow away the gas shield.
Applications:
Practically all commercially available metals can be welded by this method.
It can be used for deep groove welding of plates and castings, just as the submerged
arc process can, but it is more advantageous on light gauge metals where high speeds
are possible.
SUBMERGED ARC WELDING
The submerged arc process (which may be done manually or automatically) creates
an arc column between a base metallic electrode and the work piece.
— The arc, the end of the electrode, and the molten weld pool are submerged in a
finely divided granulated powder that contains appropriate deoxidizers, cleansers
and any other fluxing elements.
— The fluxing powder is fed from a hopper that is carried on the welding head. The
tube from the hopper spreads the powder in continuous mount in front of the
electrode along the line of the weld.
— This flux mound is of sufficient depth to submerge completely the arc column so
that there is no splatter or smoke, and the weld is shielded from all effects at
atmospheric gases. As a result of this unique protection, the weld beads are
exceptionally smooth.
— The flux adjacent to the arc column melts and floats to the surface of the molten
pool; then it solidifies to form a slag on the top of the welded metal. The rest of the
flux is simply an insulator that can be reclaimed easily.
— The slag that is formed by the molten flux solidifies and is easy to remove. In
fact, in many applications, the slag will crack off by itself as it cools.
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— The unused flux is removed and placed back into the original hopper for use for
the next time.
— Granulated flux is a complex, metallic for silicate that can be used over a wide
range of metals.
The process is characterised by high welding currents. The current density in the
electrode is 5 to 6 times that used in ordinary manual stick electrode arc welding,
consequently the melting rate of the electrode as well as the speed of welding is
much higher than in the manual stick electrode process.
Welds made by the submerged arc welding process have high strength and ductility
with low hydrogen or nitrogen content.
Advantages:
1. Higher welding speeds can be employed, effecting saving in welding time.
2. Very high deposition rate.
3. Flux acts as a deoxidiser to purify the weld metal.
4. Shallow grooves can be used for making joints, requiring less consumption of
filler metal.
In some cases no edge preparation is at all needed.
5. No chance of weld spatter (since the arc is always covered under flux blanket).
6. If required, the flux may contain alloying elements and transfer them to the weld
metal.
7. Can be employed with equal success for both indoor and outdoor welding work.
8. Less distortion.
9. Few passes are required due to deep penetration.
10. It is often used in automatic mode.
Limitations:
1. This process can be performed only in flat and horizontal welding positions.
2. In order to obtain good weld the base metal has to be cleaned and made free of
dirt, grease, oil, rust and scale.
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3. Flux may get contaminated and lead to porosity in weld.
4. Normally unsuitable for welding of metal thickness less than 4.8 mm.
5. Removal of slag is an additional follow-up operation. In multi passes beads it has
to be done after every pass.
Applications:
This process is suitable for welding low-alloy, high tensile steels as well as the mild,
low carbon steels.
This process is also capable of joining medium carbon steels, heat resistance steels,
and many of high-strength steels.
Also the process is adaptable to nickel, monel and many other non-ferrous metals.
The submerged arc process is also capable of welding fairly thin gauge materials.
THERMIT WELDING
It is the method of uniting iron or steel parts by surrounding the joint with steel at a
sufficient high temperature to fuse the adjacent surfaces of the parts together.
— Here a wax pattern of desired size and shape is prepared around the joint or region
where the weld is to be affected.
— The wax pattern is then surrounded by sheet iron box and the space between box
and pattern is filled and rammed with sand.
— After cutting, pouring and heating gates and risers a flame is directed into the
heating oven due to which the wax pattern melts and drains out, the heating is
continued to raise the temperature of the parts to be welded.
— The thermit mixture (finely divided aluminium iron oxide) is packed in the
crucible of conical shape formed from a sheet-iron casting lined with heat resisting
cement and is ignited with magnesium or torch yielding a highly superheated (nearly
3000°C) molten-iron and a slag of aluminium oxide
(the reaction is : 8Al + 3 Fe3O4 = 4 Al2O3 + 9Fe + heat).
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— The molten iron is then run into the mould which fuses with the parts to be welded
and forms a thermit collar at the joint. The welds thus obtained are metallurgically
very sound and strong.
Advantages:
1. Can be used anywhere.
2. Low set-up cost.
3. Not a highly skilled operation.
4. Most suitable for welding of thick sections.
Limitations:
1. Only thick sections can be welded.
2. High set-up and cycle time.
Applications:
The process is widely employed in the shipping, steel and railroad industries.
It can also be used for welding non-ferrous parts by selection of a mixture of oxides
which on reduction with aluminium will provide an alloy approximating the material
to be welded.
E 6013
~HERE first two digits indicates tensile strength of electrode material in 1000PSI
(pound per square inch ) .
Welding means making a joint having similar properties to the base metal. So
electrode material should also have the same chemical composition and mechanical
properties.
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Let us understand it by example how to select electrode for a particular metal.
If it is Mild Steel then
Tensile strength =410 MPa
1.) First two digit would be Tensile strength of base metal in 1000PSI.
So 410MPa =59500 PSI =59.5 kPsi
So first two digits are 60
2.) Third digits indicates position of welding
1-Any position
2 -Vertical
3-Horizontal
4-Overhead
So if you want to use in any position then choose third digit as 1.
3). Last digit indicate type of flux coating and current condition
0-DCRP
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1-DC or AC Reverse polarity
2-DC or AC Straight Polarity
3-DC or AC Straight or Reverse Polarity
And if it is used with any current condition then our digit will be 3.
This is how electrode for mild steel is E 6013.
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Texts:
1. A Ghosh and A K Mallik, Manufacturing Science, Wiley Eastern, 1986.
2. P Rao, Manufacturing Technology: Foundry, Forming and Welding, Tata
McGraw Hill, 2008.
3. M.P. Groover, Introduction to Manufacturing Processes, John Wiley & Sons,
2012
Page 26 of 27
JU
Compiled & prepared by Suman Nihar, Mech. Enggg. Dept.,
4. Prashant P Date, Introduction to Manufacturing Technologies Principles and
Technologies, Jaico Publications, 2010 (new book)
Page 27 of 27
JU
Compiled & prepared by Suman Nihar, Mech. Enggg. Dept.,