arc welding

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2. Principle:
• Electric energy is converted in to
heat energy. Due to the resistance of
current flow. It produces heat and melted the
surface and joints it.
• Electrode coating is know as shield.
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• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles

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11. • Electrode and work piece are brought near to each other with a
small air gap of 3mm.
• While supply is switched on the current passed through the
work piece and electrode to produce electric arc.
• The electrode is also melted and hence both the workpiece
became a single piece without external pressure.
• The coating (flux) in the electrode is heated and vaporizes
due to electric arc.
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12. • The temperature of arc is above 5000˚C to 6000 ˚C.
• The ingredients in the vaporised coating on the electrode
creates a protective gas atmosphere over the weld puddle.
• The inner core is at high temperature. So it melts quickly
comparing to the coating. So it forms a cup shape at the
electrode end.
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14. • The temperature of arc is above 5000˚C to 6000 ˚C.
• Depth of fusion:
The depth to which the metal is melted and deposited is
called as depth of fusion.
• To obtain better depth of fusion the electrode is kept at 70˚
inclination on the vertical.
• Flux:
Electrode is coated with a flux. The flux is used to prevent the
reaction of the molten metal and forms a slag.
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16. • Oscillation depends on thickness and length.
• Figure 8 motion circular motion
• Weaving motion crescent motion
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• A welding generator (D.C.- direct current) or Transformer (A.C.)
• D.C generators are using I.C engine or Electric motor to run it.
• A.C generators are using a step down transformers 220V to
20V-80V.
• Specification
Generator Transformer
Power form Self excited 3
phase 50 cycles
per second
Step down
transformer,
3phase 50 cycles
per second
Current range 125A-500A 50A-40A
Efficiency 60% 85%

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• Non-consumable electrodes are made of carbon, graphite or
tungsten which do not consume during the welding.
• Non-consumable electrodes are used for D.C as well as A.C
welding.
• Its length is constant one.
• The metal of electrode is depends on kind of parent material
Work piece Electrode
Wrough iron Low carbon steel rod
Cast iron Cast iron rods
Mild steel Mild steel copper coated
rod
Brass Brass rod
Copper casting Copper rod

20. • Heavy coated electrodes are coated with 1 to 3mm
thick.(Boric acid, soda ash and small amount of
sodium chloride, ammonium sulphate and iron oxide)
• The weight of such coating is 15 to 30 % of the
electrode rod weight.
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• Arc crater is depression in the molten
metal created by the end of the welding
electrode during the welding of metal.

22. • Distance between the end of the electrode and the
surface of the molten metal on work.
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The prefix letter denotes method
of manufacturing
E-solid extrusion
R-Extruded with reinforcement
First digit:
Type of covering
1-high cellulose content
2-titania and producing viscous
slag
3- titania and producing fluid slag
4- oxides & producing inflated
slag
5- iron oxides & produce heavy
solid
Slag
6- calcuim carbonate and fluoride
7- other type none of the above

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Second digit: welding position
0-F,H,V,D,O
1-
2-
3-
9-ANY OTHER POSITION
F- FLAT
H-HORIZONDAL
V-VERTICAL
D-VERTICAL DOWN
O-OVER HEAD

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THIRD DIGIT: welding current
conditions
0- D+
1- D+, A90
2-
3-
9-D+- . A50
D+ DC with electrode positive
A90 AC with an open circuit
voltage not less than 90V

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Fourth and fifth digit:
Mechanical properties such as
tensile strength and yield
strength.
Sixth digit:
% elongation
Suffix letter:
Special properties
H- hydrogen controlled
P- deep penetration

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