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Electric Arc Welding: Meaning, Procedure And Equipments Arc Welding

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Electric Arc Welding: Meaning, Procedure and Equipments

After reading this article you will learn about:- 1. Meaning of Electric Arc Welding 2. Procedure of Electric Arc Welding 3. Electric Current for Welding 4. Significance of Polarity 5. Equipments 6. Edge Preparation of a Joint 7. Electrodes.

Meaning of Electric Arc Welding:

The arc welding is a fusion welding process in which the heat required to fuse the metal is obtained from an electric arc between the base metal and an electrode.

The electric arc is produced when two conductors are touches together and then separated by a small gap of 2 to 4 mm, such that the current continues to flow, through the air. The temperature produced by the electric arc is about 4000°C to 6000°C.

A metal electrode is used which supplies the filler metal. The electrode may be flux coated or bare. In case of bare electrode, extra flux material is supplied. Both direct current (D.C.) and alternating current (A.C.) are used for arc welding.

The alternating current for arc is obtained from a step down transformer. The transformer receives current from the main supply at 220 to 440 volts and step down to required voltage i.e., 80 to 100 volts. The direct current for arc is usually obtained from a generator driven by either an electric motor, or patrol or diesel engine.

An open circuit voltage (for striking of arc) in case of D.C. welding is 60 to 80 volts while a closed circuit voltage (for maintaining the arc) is 15 to 25 volts.

Procedure of Electric Arc Welding:

First of all, metal pieces to be weld are thoroughly cleaned to remove the dust, dirt, grease, oil, etc. Then the work piece should be firmly held in suitable fixtures. Insert a suitable electrode in the electrode holder at an angle of 60 to 80° with the work piece.

Select the proper current and polarity. The spot are marked by the arc at the places where welding is to be done. The welding is done by making contact of the electrode with the work and then separating the electrode to a proper distance to produce an arc.

When the arc is obtained, intense heat so produced, melts the work below the arc, and forming a molten metal pool. A small depression is formed in the work and the molten metal is deposited around the edge of this depression. It is called arc crator. The slag is brushed off easily after the joint has cooled. After welding is over, the electrode holder should be taken out quickly to break the arc and the supply of current is switched off.

Electric Current for Welding:

Both D.C. (direct current) and A.C. (alternating current) are used to produce an arc in electric arc welding. Both have their own advantages and applications.

The D.C. welding machine obtains their power from an A.C. motor or diesel/petrol generator or from a solid state rectifier.

The capacities of D.C. machine are:


Up to 600 amperes.

Open Circuit Voltage:

50 to 90 volts, (to produce arc).

Closed Circuit Voltage:

18 to 25 volts, (to maintain arc).

The A.C. welding machine has a step down transformer which receives current from main A.C. supply. This transformer step down the voltage from 220 V-440V to normal open circuit voltage of 80 to 100 volts. The current range available up to 400 amperes in the steps of 50 ampere.

The capacities of A.C. welding machine are:

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

Current Range:

Up to 400 ampere in steps of 50 ampere.

Input Voltage:

220V- 440V

Actual Required Voltage:

80 – 100 volts.


50/60 HZ.

Significance of Polarity:

When D.C. current is used for welding, the following two types of polarity are available:

(i) Straight or positive polarity.

(ii) Reverse or negative polarity.

When the work is made positive and electrode as negative then polarity is called straight or positive polarity, as shown in Fig. 7.16 (a).

In straight polarity, about 67% of heat is distributed at the work (positive terminal) and 33% on the electrode (negative terminal). The straight polarity is used where more heat is required at the work. The ferrous metal such as mild steel, with faster speed and sound weld, uses this polarity.

(a) Straight polarity.

(b) Reverse polarity

On the other hand, when the work is made negative and electrode as positive then polarity is known as reverse or negative polarity, as shown in Fig. 7.16 (b).

In reverse polarity, about 67% of heat is liberated at the electrode (positive terminal) and 33% on the work (negative terminal).

The reverse polarity is used where less heat is required at the work as in case of thin sheet metal weld. The non-ferrous metals such as aluminum, brass, and bronze nickel are welded with reverse polarity.

Equipments Required for Electric Arc Welding:

The various equipments required for electric arc welding are:

1. Welding Machine:

The welding machine used can be A.C. or D.C. welding machine. The A.C. welding machine has a step-down transformer to reduce the input voltage of 220- 440V to 80-100V. The D.C. welding machine consists of an A.C. motor-generator set or diesel/petrol engine-generator set or a transformer-rectifier welding set.

A.C. machine usually works with 50 hertz or 60 hertz power supply. The efficiency of A.C. welding transformer varies from 80% to 85%. The energy consumed per Kg. of deposited metal is 3 to 4 kWh for A.C. welding while 6 to 10 kWh for D.C. welding. A.C. welding machine usually work with low power factor of 0.3 to 0.4, while motor in D.C. welding has a power factor of 0.6 to 0.7. The following table 7.9 shows the voltage and current used for welding machine.

2. Electrode Holders:

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

The function of electrode holder is to hold the electrode at desired angle. These are available in different sizes, according to the ampere rating from 50 to 500 amperes.

3. Cables or Leads:

The function of cables or leads is to carry the current from machine to the work. These are flexible and made of copper or aluminum. The cables are made of 900 to 2000 very fine wires twisted together so as to provide flexibility and greater strength.

The wires are insulated by a rubber covering, a reinforced fibre covering and further with a heavy rubber coating.

4. Cable Connectors and Lugs:

The functions of cable connectors are to make a connection between machine switches and welding electrode holder. Mechanical type connectors are used; as they can he assembled and removed very easily. Connectors are designed according to the current capacity of the cables used.

5. Chipping Hammer:

The function of chipping hammer is to remove the slag after the weld metal has solidified. It has chisel shape and is pointed at one end.

6. Wire Brush, Power Wire Wheel:

The function of wire brush is to remove the slag particles after chipping by chipping hammer. Sometimes, if available a power wire wheel is used in place manual wire brush.

7. Protective Clothing:

The functions of protective clothings used are to protect the hands and clothes of the welder from the heat, spark, ultraviolet and infrared rays. Protective clothing used are leather apron, cap, leather hand gloves, leather sleeves, etc. The high ankle leather shoes must be wear by the welder.

9. Screen or Face Shield:

The function of screen and face shield is to protect the eyes and face of the welder from the harmful ultraviolet and infrared radiations produced during welding. The shielding may be achieved from head helmet or hand helmet.

Edge Preparation of a Joint:

The efficiency and quality of welded joint also depends upon the correct preparation of the edges of the plates to be welded. It is necessary to remove all scales, rust, grease, paint, etc. from the surface before welding.

The cleaning of the surface should be carried out mechanically by wire brush or power wire wheel, and then chemically by carbon tetrachloride. Proper shape to the edges of the plate should be given to produce a proper joint.

The shape of edges may be plain, V-shaped, U-shaped, re­shaped, etc. The choice of various edge shapes depends upon the kind, thickness of metal to be welded. Some different types of grooves for edges of the work are shown in Fig. 7.17. BaDD

(i) Square Butt:

It is used when the thickness of the plate is from 3 to 5 mm. Both the edges to be weld should be spaced about 2 to 3mm apart as shown in Fig. 7.17 (a).

(ii) Single- V-Butt:

It is used when the thickness of the plates is from 8 to 16 mm. Both the edges are bevelled to form an angle of about 70° to 90°, as shown if Fig. 7.17 (b).

(Iii) Double-V-Butt:

It is used when the thickness of the plates is more than 16mm and where welding can be performed on both sides of the plate. Both the edges are bevelled to form a double-V, as shown in Fig. 7.17 (c).

(iv) Single and Double-U Butt:

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

It is used when the thickness of the plate is more than 20mm. The edge preparation is difficult but the joints are more satisfactory. It requires less filler metal, as shown in Fig. 7.17 (d) and (e).

Arc Welding Electrodes:

Arc welding electrodes can be classified into two broad categories:

1. Non-Consumable electrodes.

2. Consumable electrodes.

1. Non-Consumable Electrodes:

These electrodes do not consumed during the welding operation, hence they named, non-consumable electrodes. They are generally made of carbon, graphite or tungsten. Carbon electrodes are softer while tungsten and graphite electrodes are hard and brittle.

Carbon and graphite electrodes can be used only for D.C. welding, while tungston electrodes can be used for both D.C. and A.C. welding. The filler material is added separately when these types of electrodes are used. Since, the electrodes do not consumed, the arc obtained is stable.

2. Consumable Electrodes:

These electrodes get melted during welding operation, and supply the filler material. They are generally made with similar composition as the metal to be welded.

The arc length can be maintained by moving the electrode towards or away from the work.

The consumable electrodes may be of following two types:

(i) Bare Electrodes:

These are available in the form of continuous wire or rods. They must be used only with straight polarity in D.C. welding. Bare electrodes do not provide any shielding to the molten metal pool from atmospheric oxygen and nitrogen.

Hence, the welds obtained by these electrodes are of lower strength, lower ductility and lower resistance to corrosion. They find limited use in minor repair and poor quality work. They used to weld wrought iron and mild steel. In modern practice they are not used or rarely used. They are also known as plain electrodes.

(ii) Coated Electrodes:

These are sometimes also called as conventional electrodes. A coating (thin layer) of flux material is applied all-round the welding rod, and hence termed as coated electrode. The flux, during welding, provides a shielding to the molten metal zone from the atmospheric oxygen and nitrogen. This flux also prevents formation of oxides and nitrides. Flux chemically react with the oxides present in the metal and forms a low melting temperature fusible slag.

The slag is float on the top of the weld and can easily be brushed off after solidification of weld. The quality of weld produced by coated electrode is much better as compared to that of bare electrodes.

Depending on the coating factor or thickness of flux coating, coated electrodes are divided in three groups:

(a) Lightly coated electrodes.

(b) Medium coated electrodes.

(c) Heavily coated electrodes.

A comparison of three types of coated electrodes is given in the Table 7.10:

Advantages of Flux Coated Electrodes:

The flux coating on welding electrodes has may advantages. Some of them are following:

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

1. It protects the welding zone from oxidation by providing an atmosphere of inter gas around the arc.

2. It produces low melting temperature slag, which dissolves the impurities present in the metal like oxides and nitrides, and floats on the surface of the weld pool.

3. It refines the grain size of the welded metal.

4. It adds alloying elements to the welded metal.

5. It stabilizes the arc by providing certain chemicals which have this ability.

6. It reduces the spattering of weld metal.

7. It concentrates the arc stream and reduces thermal losses. This result in increased arc temperature.

8. It slows down the cooling rate of weld and accelerates hardening process.

9. It increases the rate of metal deposition and the penetration obtained.

Constituents of Electrode Coatings:

The electrode coating may consists two or more ingredients. Different type of coatings used for different type of metals to be welded.

The constituents of typical electrode coatings and their functions are given in table 7 11. Some of them are discussed here:

1. Slag Forming Constituents:

The slag forming ingredients are silicon oxide (Sio2), Manganese oxide (Mno2), iron oxide (FeO), asbestos, mica, etc. In some cases, aluminum oxide (Al2o3) is also used but it makes the arc less stable.

2. Constituents to Improve Arc Characteristics:

The ingredients to improve arc characteristics are sodium oxides (Na2O), Calcium oxides (CaO), magnesium oxides (MgO), and titanium oxide (TIO2).

3. De-Oxidising Constituents:

The deoxidising ingredients are graphite, powdered aluminum, wood flour, calcium carbonate, starch, cellulose, dolomite, etc.

4. Binding Constituents:

The binding materials used are sodium silicate, potassium silicate and asbestos.

5. Alloying Constituents:

The alloying elements used for improvement of weld strength are vanadium cobalt, molybdenum, aluminum, chromium, nickel, zirconium, tungsten, etc.

Specification of Electrodes:

The specification of electrodes are provided by Bureau of Indian standard IS : 815-1974 (second revision).

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

According to this, the coated electrodes are specified by:

(i) A prefix letter.

(ii) A six digit code number.

(iii) A suffix letter.

(i) Prefix Letter:

The prefix letter indicates the method of manufacturing of electrodes.

These prefix letters with method of manufacturing of electrodes are given in the Table 7.12:

(ii) A Six Digit Code Number:

The six digit code number indicated the performance characteristics and mechanical properties of the weld metal deposit.

The meaning of each individual digit from one to six is given in the Table 7.13:

(iii) Suffix Letter:

The suffix letter indicates the special properties or characteristics of the electrode.

These are given in the Table 7.14:

The first digits of the code number essentially explain the type of covering used on the electrode and this covering signifies the performance characteristics.

There are seven types of covering representing the first digit number are given in the Table 7.15:

The second digit of the code indicates the welding position, as per Table 7.16 given below:

The third digit of the code number indicates welding current conditions recommended by the manufacturer of electrode.

These are given in the Table 7.17:

Electric Arc Welding: Meaning, Procedure and Equipments arc welding

The fourth, fifth and sixth digits of the code number represents tensile strength, maximum yield stress and percentage elongation with impact value.

These are given in the Table 7.18:

In addition to the coding given above, all electrodes must conform to the test requirements of IS: 814 (part I and II) – 1974. Each packet of electrodes must have a marking indicating coding and specification.


IS: 815 coding: E 315 – 411K

Specification: Ref: 814 (Part-1)

The significance of above example is that:

(i) The electrode is manufactured by solid extrusion and is suitable for metal arc welding of mild steel. [E].

(ii) The electrode covering has an appreciable amount of titanium with basic materials and will produce fluid slag. [3].

(iii) The electrode is suitable for welding in the flat, horizontal, vertical and overhead position. [1].

(iv) The electrode is suitable for welding with direct current, with electrode being +ve or -ve. It is also suitable of welding with an alternating current with open circuit voltage less than 90 volts. [5].

(v) The electrode has range of tensile stress of deposited metal is 410 to 510 N/mm2. [411].

(vi) The electrode has a maximum yield stress of deposited metal is 330 N/nm2. [411].

(vii) The electrode has a minimum percentage elongation in tensile test of deposited metal is 20 percent on a gauge length of 5.65 √So and average impact test value of deposited metal is 47J at 27°C. [411].

(viii) The electrode has iron powder in the covering, giving a metal recovery of 130 to 150 percent.

(ix) The electrode conforms to IS: 814 (Part-I)-1974.

Electric Arc Welding: Meaning, Procedure and Equipments

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