Shielded Metal Arc Welding (SMAW): Equipment and Applications (2024)

After reading this article you will learn about:- 1. Introduction to Shielded Metal Arc Welding (SMAW) 2. Equipments for Shielded Metal Arc Welding (SMAW) 3. Welding Circuit 4. Metal Fusion and Weld Penetration 5. Electrode Motions 6. Applications.

Introduction to Shielded Metal Arc Welding (SMAW):

Shielded metal arc welding is one of the most versatile joining proc­esses in industry and it is extensively used the world over. In India nearly 90% of the welded fabrication is done by this process and even in the most ad­vanced countries like USA, USSR, Japan, and the West European countries it accounts for nearly 60% of the metal deposited by welding. Though its use is slowly decreasing but it is expected to remain indispensable for repairs and short-run jobs.

One of its attractive features is the lowest initial cost for a workable installation. Welding power sources for SMAW are available which can be plugged-in, if required, in domestic single phase electric supply, hence its popularity even with small volume fabricators.

Equipments for Shielded Metal Arc Welding (SMAW):

The major equipment for SMAW is the power source which may be a welding transformer, a d. c. rectifier or a d. c. motor-generator set. The selection of equipment depends upon the provision for initial investment and the range of materials to be handled.

The size and type of electrodes that are used and the penetration and welding speeds desired determine the current supply re­quirements. The welding power sources employed for SMAW are almost in­variably of the constant current type as they serve the purpose best in main­taining the arc current undisturbed even when the welder’s hand is inadvertently disturbed though temporarily.

Of the three basic types of welding power sources each one has its own definite advantages. The d.c. welding power source is very versatile in welding a variety of metals in any desired thickness. It permits portable operation and uses efficiently a large variety of coated electrodes.

The welding transformer has the lowest initial cost as well as low operation and maintenance cost. It has no moving parts so its operation is quiet. The rectified d.c. welding power source is simple in design and it combines the advantages of a welding trans­former and a d.c. welding set.

Equipment Accessories:

The equipment accessories for the welding power source include the connecting cables or leads, an electrode holder, cable connectors and the ground clamp.

The cables that carry the current in welding circuit are quite flexible and are generally made of copper or aluminium wires. These wires are very fine (0-2 mm diameter) and number between 800 to 2500 depending upon the current carrying capacity of the cable. Aluminium cables are much lighter and weigh only one-third of copper cables but their current carrying capacities are also lower being about 60% that of copper cables.

Cable connectors used for increasing the length of the welding leads should be of adequate size to carry the desired current and must fit snuggly to avoid drop in voltage. Sometimes soldering or brazing or even welding is employed to connect the cables but mechanical connectors are most popular because they can be easily assembled and dis-assembled.

Electrode, holder is generally matched to the welding cable and the cable size depends upon the current required to be carried in the welding circuit. Usually electrode holders are specified dc: ending upon the current that they can carry; the normal range being 150 to 500A .The electrode holders of the popular design have grooves cut in the jaw which facilitate the holding of electrode at different angles for easy manipulation.

The ground clamp is used to connect the other terminal of the welding circuit. It sometimes resembles the electrode holder but often it is like a C- clamp but with heavier section to avoid overheating. Occasionally the ground clamp is fitted tightly to the work table to avoid sparking, however most often it is rather loosely attached to facilitate easy detachment. Fig. 7.1 shows the different equipment accessories described above.

Operator Accessories:

The essential, operator accessories include chipping hammer, wire brush, and a welding shield to protect the face. The chipping hammer is chisel- shaped and is pointed on the other end to help in the removal of slag. The wire brush is used to remove the tenacious slag sticking usually at the weld bead edges. It is generally made of hard-ended steel wire pieces embedded in a wooden block.

Welding shield, is an essential accessory for successful and continuous welding. It not only protects the operator’s eyes from the high intensity glare of the welding are but also shields his face from the harmful effects of infra­red and ultra-violet rays which are emitted by the welding arc.

The welding shield is either of the hand-held type or is strapped to the head and can be flipped above the head when not required. The shield is designed to cover the entire face and the throat .It is provided with a window of the size 12 cm x 5 cm which is brought directly infront of the eyes during welding operation.

The window is fitted with a dark glass which is capable of stopping 99.5% of the harmful radiation from the arc. The proper selection of the welding glass is essential and is to be based on the process and the material to be welded. For SMAW shade numbers 9 to 11 are most popular though shades upto number 14 are in common use.

In spite of the use of welding shield an operator may develop eye pain if he welds continuously for long shifts say 6 to 10 hours. Fig. 7.2 shows differ­ent operator accessories required for SMAW.

Welding Circuit for Shielded Metal Arc Welding (SMAW):

A generalised electrical circuit for SMAW is shown in Fig. 7.9.

Metal Fusion and Weld Penetration in SMAW:

For making a good weld, it is essential that proper fusion is obtained between the parent metal and the material deposited from the electrode. To achieve that, the surface of the parent metal should be thoroughly melted so as to form an arc crater of sufficient depth, otherwise a shallow crater, if any, will result. In the latter case the metal droplets from the electrode will not be able to fuse with the parent metal. Such droplets, if deposited on the workpiece, will just sit on the surface without any fusion. The resultant weld may be just a camouflage.

To obtain a good weld the depth of penetration must not be less than 1.5 to 2 mm. In SMAW, depending upon the welding current, the penetration usually varies between 1.5 and 5 mm. An estimation of penetration can be made from observing the crater depth.

If during welding the arc is suddenly extinguished it leaves behind a weld crater on the workpiece which when solidifies has the same size as during the presence of the arc. Penetration normally extends 1 to 2 mm beneath the surface of the crater.

The depth of penetration depends upon the heat input into the work- piece per unit time, and thus depends upon the welding current. A cross- section of a number of weld beads deposited on a plate with varying currents can depict the influence of welding current on depth of penetration.

Fig. 7.12 shows a cross-section of three weld beads. Bead ‘a’ was deposited with too low a current, bead ‘b’ with an appropriate welding current, and bead ‘c’ with excess current. Due to insufficient welding current in depos­iting bead ‘a’ there was lack of penetration; infact the bead hardly has any depth of penetration. The metal from the electrode has just fused with the parent metal at the surface.

The weld toes are rounded, sharply merging into the parent metal providing a notch effect thereby forming points of stress concentration. Such a weld lacks strength and a bead like this can be peeled off completely from the surface of the workpiece with an impacting stroke of a hammer.

The toe of bead ‘b’ is merged smoothly into the parent metal. The parent metal was properly melted and adequate mixing of the weld metal from the electrode and workpiece provided good penetration of desired configura­tion.

The use of excessive current to deposit the bead ‘c’ resulted in exces­sive arc force, the crater did not get filled up with the molten metal from the electrode. This resulted in undercuts at the toes of the weld bead which re­duced the thickness of the parent metal and consequently reduced the strength of the weld and also provided points of stress concentration. These points are especially dangerous in the case of fatigue and impact loading.

For controlling penetration welding current is chosen according to the electrode grade and diameter.

However, for down-hand welding of butt joints in low carbon steel the welding current may be determined as a rough guide, from the following relationships:

I = (40-60) d………… (7.2)

I= (20+6d) d.…………(7.3)

where I is the welding current in amperes, and d is the electrode diameter in mm.

Welding current required for a thinly coated electrode is lower than that for a heavily coated electrode. The optimum current for a given electrode and workpiece may be found by trial and error, by depositing a number of beads, using equation 7.2 or 7.3.

The arc crater and the appearance of the bead can provide adequate guidance about the suitable current setting. Larger currents are required to be set for both heavier section and electrode size to achieve the desired penetration, because a heavy section acts as an efficient heat sink. First an electrode size for a given plate thickness should be chosen and then the welding current matched with it. Table 7.2 provides the guidelines for choos­ing electrode diameter for welding butt joints in steel plates.

In a multi-run weld, the first run should be made with an electrode of not more than 2 to 3.15 mm in diameter. For overhead and vertical welding the electrode should have a maximum diameter of 4 mm. Electrodes of 5 mm diameter can be used to expedite welding in down-hand welding position par­ticularly the filler and finishing runs.

Despite the high production rate achievable by 6-3 mm diameter elec­trodes it is not recommended to use these electrodes except for long, wide plates in down-hand welding position as otherwise the weld pool becomes very big and unmanageable which results in poor quality welds.

Electrode Motions in SMAW:

The width of the weld bead formed under normal welding conditions in SMAW is between 1.5 to 2.5 times the diameter of the electrode; with well penetrated and smooth passage of the deposited metal to the workpiece sur­face. To achieve this arc length is kept as short as possible without the electrode sticking to the workpiece and by giving the electrode three types of motions simultaneously.

One motion is the continuous uniform down-hand feeding of .the electrode towards the weld pool, the second motion is the advancing motion of the arc along the joint and the third motion is the sidewise or lateral oscillating motion or weaving motion across the arc. All three motions are depicted in Fig. 7.13.

When the arc is advanced without any weaving motion the width of the bead is usually 1 to 2 mm more than the electrode diameter. The bead so obtained is called a ‘stringer bead’.

Weaving motion during welding is used when a ‘spread bead’ or weave bead is required. Weave beads are commonly employed in making butt and Fillet welds.

Weaving can be accomplished in a variety of patterns depending upon the type of weld, joint preparation, and the skill of the operator. Fig. 7.14 shows different weaving patterns which are used by welding operators to achieve sound weld beads. Those shown in Fig. 7.14 (a and i) are most commonly used in butt welds. For fillet welds weaving patterns given in Fig. 7.14 (d and g) are found appropriate.

Patterns (a) to (e) are used where more heat is required to be applied to both edges of the joint; pattern (b) is found particularly suitable for heavier plates. Pattern (f) is found to be appropriate when more heat is to be applied to one edge while patterns (g) and (h) are found useful when heat is to be applied to the middle of the weld.

For consistency in bead width it is essential that the swing of the weav­ing motion is kept constant. A correct, well penetrated and sound weld of high quality can be obtained only if the operator’s movements are well controlled in all the three directions and that can be acquired only through practice and experience.

Applications of SMAW:

Applications of the SMAW process are varied and wide spread. De­pending upon the mated electrodes available it finds extensive use in all major fabrication industries which may include items of sundry repairs to shipbuild­ing and pressure vessel fabrication.

Typical electrodes used for major fabrication with their specific uses are described briefly:

1. Electrodes for Welding Low Carbon Steels:

These are very well developed electrodes and are marketed under differ­ent brand names. Most of these belong to cellulosic, rutile, and basic coated types with or without iron powder. Heavy coated variety can be used as touch electrode which is excellent for welding in vertical position.

a. Cellulose Coated Electrodes (IS: E100413; AWS E6010):

These are usually light coated, all position electrodes with a forceful penetrating arc and thin brittle slag; suitable for all position work. The weld metal deposited is highly ductile.

Applications:

Pipelines, tanks, pressure vessels, structural, and field work where deep penetration is necessary. Specially suited for pressure pipe­lines which cannot be welded from inside.

b. Rutile Coated Electrodes:

There are three main categories of rutile coated electrodes.

Category 1 (IS: E206411; AWS E6012):

It is an all position electrode with good penetration and quick freezing slag. It is easy to operate in all positions including vertical-down.

Applications:

Storage tanks, gear blanks, machinery, steel furniture, truck bodies, foundry equipment, shaft build-up, etc.

Category 2 (IS: E307411; AWS 6013):

An all position electrode which gives strong and smooth arc with me­dium penetration. It gives low spatter and easy to remove slag. The electrode is well suited for bridging gaps in joints. It gives high deposition rate.

Applications:

Structures, building construction, tanks, pipelines, ma­chinery parts, automobile bodies, steel window frames, farm machinery, etc.

Category 3 (IS: E307412; AWS E6013):

An all position electrode for structural work. Medium penetration, least spatter. Slag is easy to detach. Smooth bead and easy to operate in all positions including vertical-down.

Applications:

Building construction, vessels, tanks and boilers, pipe­lines, bridges, railway wagons, ships, trailors.

Pressure pipelines which cannot be welded from inside, oil storage tanks, railway coach panels.

Locomotive fire-boxes, scooter frames.

c. Rutile Plus Iron Powder Coated Electrodes:

There are three main categories of these coatings.

Category 1 (IS: E307512; AWS E7014):

A medium heavy coated all position electrode containing iron powder that enables the use of heavy current which consequently leads to higher welding output with a deposition efficiency of upto 110%. The weld metal is highly ductile.

Applications:

Used for welding pressure pipelines, oil storage tanks, ships, boilers, railway wagons, etc. at high welding speeds. Also well suited for repairing steel castings.

Category 2 (IS: 327512 K; AWS E7024):

It is a heavy coated electrode with high deposition rate for down-hand butt and fillet welds as well as horizontal fillet welds. The electrode is very easy to manipulate and produces smooth welds with very low spatter loss. High welding current can be used to increase welding output and productivity. Deposition efficiency is nearly 140%. It can be used as a ‘touch electrode’.

Applications:

Used for welding of heavy structures like crane and bridge girders, assembly of earth moving equipment, heavy machinery parts, etc.

Category 3 (IS: E347512L; AWS E7024):

A super heavy coated iron powder electrode with a metal recovery rate of about 210%, suitable for high speed welding of down-hand butt, fillet, and horizontal fillet welds. It can also be used as a ‘touch electrode’.

Applications:

Useful for high speed welding of heavy structural like crane and bridge girders, assembly of earth moving equipment, and parts of heavy machinery, etc.

d. Acid Coatings (IS: E422413; AWS E6020):

A medium heavy coated electrode producing a fluid slag for down-hand, horizontal, and vertical welding. It is specially suited to welding of low carbon steel where high strength and high quality weld deposits are required; particu­larly suited to applications where resistance to high stress and fatigue is important Use of high current and high welding speeds are recommended for eco­nomical welding with these electrodes.

Applications:

Used for welding heavy structural work, bridges, cranes, locomotive fire boxes, truck chasis and frames. Excellent for continuous down-hand, horizontal fillet welds and for vertical-up welding.

e. Basic Coatings (IS: E616514 HJ; AWS E7018):

A medium-heavy coated ‘low-hydrogen’ iron powder type electrode giving an extremely smooth arc, medium penetration and least spatter. Slag is easily removable. Easy to operate in all positions. The weld metal is highly ductile and crack resistant. Specially recommended for heavy joints under re­straint and subject to dynamic loading. Deposition efficiency about 115%. It needs to be kept dry; bake before use at recommended temperature.

Applications:

Used for welding blast furnance steel work, atomic reactor shell and pipework, heavy welded fabrications as replacements for castings, bridges, penstocks, root runs in heavy and restrained joints. Also used for welding steels designed for service at sub-zero temperatures down to -33°C.

f. Special Coatings (IS: E922xxxP; AWS E6027):

A super-heavy coated iron powder electrode for deep penetration butt and fillet welds. Square butt welds in plates upto 14 mm thick can be made. It can, however, be used only in flat and horizontal welding positions.

Applications:

Used for welding of heavy deck plates, structural, etc. by the deep penetration technique thus it avoids beveling and refilling of groove. It can also be used for depositing sealing run on the backside without the necessity of chipping out the root, and for depositing fillet welds with penetration beyond the root as in plate girders for bridge work.

2. Electrodes for Welding Low Alloy and High Tensile Steels:

Some of the coated electrodes used for welding HSLA (high strength low alloy) steels for specific applications are listed.

a. Cellulose Coatings (IS: E10022A; AWS 7010 –A1):

It is a cellulosic type, light coated, all position electrode that gives a thin friable slag and good penetration. The weld metal deposited is of 0-5% Mo- steel that has good ductility and creep resistance.

Applications:

Used for welding C-Mo piping, road building equipment, boilers, pressure vessels, alloy steel chain links, truck frames and bodies, high tensile steel pipelines for oil and gas transmission. Also recommended for welded fabrication to be used for service at elevated temperature upto 525°C.

b. Rutile Coatings:

Three categories of electrodes, depending upon the core wire composi­tion, are included.

Category 1, 0-5% Mo-steel (IS: E31422 A; AWS E 7013-A1):

A heavy coated rutile type all position, low alloy, medium-high tensile steel electrode that gives 0-5% Mo-steel weld deposit. The electrode gives quiet arc, low spatter, and easily detachable slag. In a butt joint of a pipe or a tube, arc is very easy to strike or restrike and hence specially recommended for pipe welding. The weld profile produced is smooth with regular ripples.

Applications:

Recommended for welding medium-high tensile and low alloy steel of 0-5% Mo, and 1% Cr-0-5% Mo compositions. Also recom­mended for welding steels used in boilers, power plant, oil refineries and chemical plants in the form of structural and pipes for elevated temperature service upto 525 °C.

Category 2,1. 2% Cr-0-5% Mo Steel (IS: E31432C; AWS E8013 B2):

A heavy-coated all position rutile type, low alloy medium-high tensile strength electrode that gives 1-2% Cr-0-5% Mo steel deposit. The electrode gives quiet arc, negligible spatter, and easily detachable slag. Easy arc initia­tion in pipe or tube butt joint; hence specially recommended for pipe welding.

Applications:

Used for welding pipes and structures in boilers, power plants, oil refineries, and chemical plants for elevated temperature service upto 550°C.

Category 3, 2. 25% Cr – 1% Mo steel (IS: E31431-D; AWS E 9013 B3):

It has characteristics similar to those for category 2 except that the weld deposit obtained is 2-25% Cr – 1% Mo steel.

Applications:

Used for welding pipes and structural in boilers, oil refineries, and chemical plants for service at elevated temperatures upto 600°C.

c. Basic Coated Electrodes:

Maximum number of electrodes used for welding HSLA steels are of the basic coated type; characteristics of a few of these, which are used for typical applications, are described under six categories.

Category 1 (IS: E611514H; AWS E 7016):

A medium-heavy coated, all position, low-hydrogen electrode suitable for welding cast steel, difficult to weld steels high in carbon and sulphur, and steel of unknown composition. The weld metal is highly resistant to cracking.

Applications:

Used for welding high carbon steel parts, high carbon steel to mild steel, low alloy steels, steels relatively high in sulphur, cast steels, and steels of unknown composition.

Category 2 (IS: E611514 HJ; AWS E7018):

A medium-heavy coated, low-hydrogen, iron powder type, all position electrode for welding of medium-high tensile structural steels, heavy sections and restrained joints in high tensile steels. The weld metal contains about 14% manganese which makes it resistant to not only hot and cold cracking but also to triaxial stresses. Deposition efficiency is about 112%.

Applications:

Suitable for welding bridges, heavy machinery, pen­stocks, heavy parts of earth moving equipment and in general for carbon steel and low alloy steel fabrications where severe service conditions are to be met. Also recommended for welding steels designed for use at sub-zero temperature down to – 40°C.

Category 3 (IS: E611515 HJ; AWS E7018 G):

A medium-heavy coated, low-hydrogen, iron powder type electrode suitable for steels which are to be used under sub-zero temperature conditions such as pressure vessels, pipelines, etc. The charpy V-notch impact values are particularly good at low temperatures upto – 60°C. Metal recovery is about 112%.

Applications:

Used for welding low-alloy steels such as Si-Mn steels and steels containing nickel upto 1%. Also used for welding high tensile steels for heavy construction work subjected to dynamic loading.

Category 4 (IS: E61122A; AWS E7018-A1):

A medium heavy coated, all position, low-hydrogen, iron powder type electrode that gives a ductile and creep resistant 0-5% Mo-steel weld deposit. It gives a deposition efficiency of about 106%.

Applications:

Used for welding 0-5% Mo, and 1% Cr-0-5% Mo steels, high temperature pipeline, boiler tubes and boiler plates where good creep resistance is necessary. Also recommended for welding components required for elevated temperature service upto 525°C.

Category 5 (IS: E61131D; AWS E9018-B3):

A medium-heavy coated, all position, low-hydrogen, iron powder type electrode that gives weld metal which has an approximate composition of 2-25% Cr – 1% Mo steel, with a deposition efficiency of approximately 106%.

Applications:

Recommended for welding HSLA steels containing 2-25% Cr-1% Mo used in boilers, power plants, oil refineries and chemical plants in the form of structural and pipes required for elevated temperature service upto 600°C.

Category 6 (IS: MDO1 – 611; AWS E502- 16):

A medium-heavy coated, all position, low hydrogen, iron powder type electrode that gives a weld deposit with an approximate composition of 5% Cr – 0-5% Mo steel. It needs to be kept dry.

Applications:

Used for welding in oil refineries, power house and chemical plants where steels of 5% Cr-0-5% Mo are used.

3. Coated Electrodes for Welding Stainless Steels and Heat-resisting Steels:

Some of the well known categories of coated electrodes with specific industrial uses in welding stainless steels and heat-resisting steels are de­scribed in this section.

Category 1 (IS: MB01L-311; AWS-ASTM E308L -16):

An extra-low carbon, 19/10 Cr-Ni stainless steel electrode with con­trolled ferrite content of 3-7% for maximum resistance to cracking and corro­sion, and for use at elevated temperature upto 800°C. Carbon content is as low as 0 028% which eliminates the possibility of inter-crystalline corrosion in the temperature range of 425°C to 843°C. The weld metal has excellent creep strength.

Applications:

Used for welding of 18Cr-8Ni stainless steels repre­sented by AISI grades 301, 302, 304 and 308 having very low carbon contents. Welding of utensils, spoon and forks, household articles, hospital apparatus, apparatus for handling nitric acid, acetic acid and citric acid. Also used for welding components required in soap industry, dairy industries, chemical and fibre industries as well as for fabricating aircraft frame.

Category 2 (IS: MB02 Mo Nb – 311; AWS – ASTM E318-16):

A low carbon 18/13 Cr-Ni, molybdenum-niobium stabilized steel elec­trode with controlled ferrite content of 5 to 8% for maximum resistance to stress corrosion cracking, chemical corrosion and inter-crystalline corrosion. The weld metal has excellent creep strength at temperature upto 850°C.

Applications:

Used for welding 18/8 Cr-Ni, Mo-Nb or Titanium stabi­lized steels such as AISI 318 grade paper mill equipment, bleaching equip­ment, chemical plants, dyeing equipment, pickling plant, heat-resisting cast­ings, etc. Can also be used for welding non-stabilised steels of the types AISI 316 and 317 grades.

Category 3 (IS: MB01 Nb – 610; AWS-ASTM E 347-15):

A low carbon 19/10 Cr-Ni, niobium-stabilised stainless steel, basic coated type electrode with controlled ferrite content of 4 to 9% for maximum resistance to cracking, corrosion, and for use at elevated temperature upto 800°C. Niobium stabilisation prevents harmful carbide precipitation in the temperature range of 425°C to 843°C. The weld has excellent creep strength.

Applications:

Used for welding AISI steels 321 and 347 grades. Gener­ally used for welding 18/8 Cr-Ni Steels stabilised with titanium or niobium. Also recommended in the manufacture of equipment for chemical, food proc­essing and aircraft industries; for welding of gas turbines, and equipment for soap industry. Can also be used for welding un-stabilised stainless steels for ex­ample, AISI 301,302, 304 and 308 grades.

Category 4 (IS: MB02 Mo Nb-4>10; AWS-ASTM E318-15):

A low carbon 19/13 Cr Ni, molyibdenum or niobium stabilised basic coated type electrode with controlled ferrite content of 4 to 9% for maximum resistance to stress corrosion cracking and intercrystalline corrosion. The weld metal has excellent creep strength upto 850°C.

Applications:

Used for welding paper mill equipment, bleaching equip­ment, chemical plants handling sulphuric, sulphurous, hydrochloric, acetic, formic, citric, tartaric acids, etc. Dyeing equipment, pickling plant, heat resist­ing casting, and bakery equipment Also used for welding AISI 316 and 318 grades stainless steels when maximum resistance to corrosion is required.

Category 5 (IS: MB05 MoL – 610; AWS-ASTM E316L-15):

A medium-heavy coated, all position electrode with basic type coating having good performance characteristics and easy slag removal. It has a core wire composition of 25/20 Cr-Ni steel which gives a weld deposit of similar composition. The electrode is specially designed for high temperature applica­tions where greater stability and oxidation resistance are required. The weld metal can stand upto 1200°C in continuous service.

Applications:

Used for welding 25/20 Cr-Ni stainless and other grades of heat-resisting steels. For butt-welding spring steels, high temperature fur­nace parts, preheater tubes for high pressure boilers, and annealing boxes.

Also used for welding high carbon steels, air-hardening steels, high-Mn steels, cast armour steels, and rolled armour steels.

Category 6 (AWS E410-15):

A heavy coated, low-hydrogen type, all position welding electrode spe­cially designed for welding ferritic-martensitic chrome steels. The weld de­posit which contains approximately 13% Cr is air hardenable. Hardening can be avoided through preheating and stress relieving. It gives low spatter and easily detachable slag.

Applications:

Used for welding heavy sections of steel armatures and for repair of cast parts such as in turbine construction and for welding similar corrosion resistant chrome steels and steel castings; for welding low-priced stainless steel cutlery, pump parts, oil refinery equipment, coal washers, etc. Also used for welding steels required for general corrosion and heat resisting applications.

Category 7 (IS: MA01-611):

A super-heavy coated, low-hydrogen type, austenitic stainless steel electrode that gives 18/8/5 Cr-Ni-Mn steel weld deposit. The core wire is of mild steel and all the alloying elements are in the flux coating. The slag is easy to remove and the weld bead has smooth profile. The weld metal has excellent heat resisting properties upto 900°C. It is corrosion resistant to the effects of normal atmosphere, sea water, and weak acids. It gives deposition efficiency of about 135%.

Applications:

It is specially designed for welding austenitic Mn-steel (12% Mn) to mild steel for producing crack-free joints in difficult to weld steels and high alloy steels including armour plate, repairing cracks in austenitic Mn-steel castings, surfacing parts subject to wear and tear, for example, rail points and crossings, laying buffer layer on difficult to weld steels before hard facing, etc.

4. Coated Electrodes for Welding Cast Iron:

Cast iron is rarely welded in normal fabrication work, however, it is often required to be welded for urgent or emergency repairs.

Coated electrodes have been developed for use in such situations and two categories of such electrodes are:

Category 1 (AWS: E Ni-Cu B):

A light coated electrode with graphite based coating for welding cast iron without preheating and for getting a machinable weld on cast iron. The electrode gives a monel (Ni-Cu) deposit.

Applications:

This electrode is specially designed for repair of broken castings, filling defects and correcting surfaces, joining cast iron to steel, etc.

Category 2 (AWS: E NiCI):

A light coated electrode depositing nickel. Specially suited for welding cast iron the cold way. The nickel weld deposit which bonds thoroughly with cast iron does not pick-up carbon or any other element from the base metal and remains soft and tough. The weld deposit is machinable and its tensile strength is adequate for cast iron.

Applications:

Used for repairing broken castings, building up of worn surfaces on castings, correcting of machining errors on castings, welding of cast iron to steels, etc.