This document discusses arc welding. It describes how arc welding works by generating an arc between an electrode and base metal that melts the metals and allows them to mix and form a joint. It discusses the equipment used, including power sources, electrodes, and protective gear. It explains that electrodes can be bare or coated in flux materials. Coated electrodes provide shielding benefits and allow welding of different metal types. The document also covers polarity, electrode designations, and functions of flux materials.

1. 112 April 2020 Dr.Abhishek Sharma
By
Dr. Abhishek Sharma
Metal Joining (Arc Welding)
KME-403
Unit - IV
GL BAJAJ INSTITUTE OF TECHONOLOGY & MANAGEMENT

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Arc Welding

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Arc Welding
• Heat required to melt the base metal is obtained from an arc.
• An arc is established b/w metal electrode and workpiece.
• Heat is liberated at arc terminals which melts the base metal at the point of
contact.
• Filler material is added to the surface of metal to attain additional strength.
• Temperature of arc is around 40000C and maximum up to 55000C.
• This heat causes a small pool of metal to melt in the work.
• For filler material welding rod is used which is melted by heat of arc.
• This melted filler material is deposited into the small pool of molten metal.
• Arc agitates the molten metal in the pool causing base and added metal to mix
thoroughly, which forms a sound joint on cooling.
• Properties and composition of a weld should match those of the base metal
closely.
• Thus different types of rods have been developed for welding of different metals
• Electrodes can be flux coated or bare.
• Electrode coatings consist of a number of different compounds, including calcium
fluoride, cellulose, iron powder and TiO
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This flux is intended to perform following functions:
1. Produce gas which provides a shield around the arc to protect it from the atmosphere.
2. Forms slag by mixing with impurities of the molten metal and thus refines metal.
3. Slag being less dense floats over molten metal surface and protects the molten metal pool
from oxidation. This slag is easily chipped off with chipping hammer at the end of the
process.
• Arc is created by low voltage, high current supply.
• Arc initiation voltage: 60 to 100V and arc maintenance voltage 25 to 40V.
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Arc Welding Equipments:
1. Electric supply source: Arc can be struck either with AC or DC source.
• Arc initiation voltage may vary from 60 to 100V and arc maintenance voltage
ranges between 15 to 40V.
• Current for welding may range from 30 to 600 amperes.
• Source AC or Dc should have low voltage and high current characteristics.
• Either DC generator or AC alternator with step down transformer is used.
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 Arc can be described as a stream of incandescent metallic vapor which acts
a conducting medium for electric current from one terminal to other to
complete the circuit
A selenium rectifier is used to convert AC to DC.
2. Electrode holder
3. Welding cables
4. Ground clamps.
5. Welding electrodes.
6. Welding helmet and hand shield.
7. Hand gloves and aprons, Chipping hammer, wire brush etcetera.

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Polarity in Arc Welding:
• In AC heat generated at each pole is same because of reversal of current.
• Thus changing over connections to electrode does not effect.
• In DC positive pole of arc becomes hottest.
• If electrode is at negative of generator and workpiece at positive it is called
straight polarity.
• Reverse polarity vice versa.
• Penetration is less with uncoated electrode with reverse polarity.
Electrodes in arc welding:
1. Bare Electrodes:
• Have limited application as during welding they are exposed to O2 and N2 of air.
• This forms non metallic constituents which are trapped in rapidly solidifying
weld metal.
• Thus strength and ductility of weld metal reduces and quality obtained is also
poor.
• Used for welding wrought iron and mild steel.
• Also used where less skill is required like automatic and semi automatic welding.2 April 2020 Dr.Abhishek Sharma

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Electrodes can either be consumable or inconsumable type.
2. Coated Electrodes:
• Coating eliminates undesirable oxides and prevent their formation.
• Heavy coated electrodes are most important and used majorly.
• Type of flux coating depends on weld metal composition.
• Slag produced should have lower density than the base metal.
• Coating helps in striking arc and enables it to be stable.
• It also provides gaseous shield, preventing oxidation of molten weld metal pool.
• Coating also replenish elements like C, Mn, Ni etc which are partially lost during
combustion.
• Slag reduces cooling rate of joint and helps in refining of its grain structure.
• Ingredients of flux are like asbestos, mica, silica, steelite, fluorspar (fluorites),
titanium oxide, iron oxide, magnesium carbonate, calcium carbonate and alumina.
• Alloying elements are received from ferromanganese, potassium titanate.
• Light to medium coated electrodes have coating between 10 to 55% of total
diameter if die coated electrode.
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Designation of electrodes:
Electrode specified with 6 digits as per IS coding:
• First Digit: (1 to 8) Each numbers corresponds to covering (flux) on electrode.
• Second Digit: (1 to 6) Represents position of welding.
• Third Digit: (0 to 7) Number represents particularly suitable current condition.
• Fourth Digit: (1 to 8) Minimum tensile strength of the weld metal.
• Fifth Digit: (1 to 5): % elongation of deposited weld metal in tensile testing.
• Sixth Digit: (1 to 5) Minimum impact Load of the weld metal.
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