Welding:
Welding is a
materials joining process which produces joining of materials by heating them
to suitable temperatures with or without the application of pressure or by the
application of pressure alone, and with or without the use of filler material.
v Fusion
Welding or Non-Pressure Welding
- The material at the joint is heated to a
molten state and allowed to solidify e.g.
Gas welding, Arc welding
Arc
Welding:
Arc Welding is a fusion welding process in which the welding
heat is obtained from an electric arc struck between the workpiece (base metal)
and an electrode. D.C. is preferred in most purposes but we often use A.C. in
arc welding.
Arc Welding Types:
• Carbon
arc
• Metal
arc
• Metal
inert gas
• Tungsten
inert gas
• Plasma
arc
• Submerged
arc
• Electro-slag
A.C. &
D.C.
A.C.
|
D.C.
|
More Efficiency
|
Less Efficiency
|
Less power consumption
|
Power Consumption more
|
Higher Voltage
|
Low Voltage
|
Cost of equipment is Less
|
Cost of Equipment is more
|
Shielding &
Un-shielding Arc Welding:
When
the welding rods coated with fusing materials are used then it is said to be
shielding arc welding & when a large electrode or filler rod is used for
welding , it is said to be un-shielded arc welding…
Temperature:
Temperature in arc welding is 5600◦C.
Arc Welding
Equipments:
• 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
Procedure:
Arc welding is started by touching the electrode against the
work to complete the electrical circuit before raising electrode to establish
arc.
This needs to happen quickly. Avoid touching the rod to
workpiece.
Tap starting and scratch starting are the two common methods
of starting the arc. First of all we enter the electrode into the electrode
holder cable and scratch it on the table.
Put the welding screen on your face to avoid rays coming
directly into your eyes.
Take electrode near the workpiece to produce arc.
This arc will raise
temperature to 5600◦C.
High
temperature will melt the electrode.
Molten
electrode will join the metal parts.
Oxidation
is possible in molten state of metal therefore to prevent oxidation flux is
used.
This
flux in coated on electrode, after producing arc perform welding operation by
moving the electrode slowly.
After
some time use the hammer to remove flux from welding puddle.
Clean
the surfaces by using wire brush.
Advantages:
• Most
efficient way to join metals
• Lowest-cost
joining method
• Affords
lighter weight through better utilization of materials
• Joins
all commercial metals
• Provides
design flexibility
Limitations
• Manually applied, therefore high labor cost.
• Need high energy causing danger
• Not convenient for disassembly.
• Defects are hard to detect at joints.
Precautions:
·
Always put the face screen in front of your eyes
to avoid from being infected of harmful rays.
·
Wear gloves to protect your hands from heat.
·
Wear lab coat to prevent your clothes.
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