Welding Theory; Manual Metal Arc Welding (Mma) - Selco Genesis 4000 PME Serie Instrucciones De Uso

Sticking
Cause Incorrect arc length.
Solution Increase the distance between the electrode and
the piece.
Increase the welding voltage.
Cause Incorrect welding parameters.
Solution Increase the welding current.
Cause Incorrect welding mode.
Solution Angle the torch more.
Cause Pieces to be welded too big.
Solution Increase the welding current.
Increase the welding voltage.
Cause Incorrect arc regulation.
Solution Increase the equivalent circuit inductive value setting.
Undercuts
Cause Incorrect welding parameters.
Solution Decrease the welding voltage.
Use a smaller diameter electrode.
Cause Incorrect arc length.
Solution Increase the distance between the electrode and
the piece.
Increase the welding voltage.
Cause Incorrect welding mode.
Solution Decrease the side oscillation speed while filling.
Decrease the travel speed while welding.
Cause Insufficient shielding gas.
Solution Use gases suitable for the materials to be welded.
Oxidations
Cause Insufficient gas protection.
Solution Adjust the gas flow.
Check that the diffuser and the gas nozzle of the
torch are in good condition.
Porosity
Cause Grease, varnish, rust or dirt on the workpieces to
be welded.
Solution Clean the workpieces carefully before welding.
Cause Grease, varnish, rust or dirt on the filler material.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Humidity in the filler metal.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Incorrect arc length.
Solution Decrease the distance between the electrode and
the piece.
Decrease the welding voltage.
Cause Humidity in the welding gas.
Solution Always use quality materials and products.
Ensure the gas supply system is always in perfect
condition.
Cause Insufficient shielding gas.
Solution Adjust the gas flow.
Check that the diffuser and the gas nozzle of the
torch are in good condition.
Cause The weld pool solidifies too quickly.
Solution Decrease the travel speed while welding .
Pre-heat the workpieces to be welded.
Increase the welding current.
Hot cracks
Cause Incorrect welding parameters.
Solution Decrease the welding voltage.
Use a smaller diameter electrode.
Cause Grease, varnish, rust or dirt on the workpieces to
be welded.
Solution Clean the workpieces carefully before welding.
Cause Grease, varnish, rust or dirt on the filler metal.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Incorrect welding mode.
Solution Carry out the correct sequence of operations for
the type of joint to be welded.
Cause Pieces to be welded have different characteristics.
Solution Carry out buttering before welding.
Cold cracks
Cause Humidity in the filler metal.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Particular geometry of the joint to be welded.
Solution Pre-heat the pieces to be welded.
Carry out post-heating.
Carry out the correct sequence of operations for
the type of joint to be welded.
For any doubts and/or problems do not hesitate to contact
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7 WELDING THEORY

7.1 Manual Metal Arc welding (MMA)

Preparing the edges
To obtain good welding joints it is advisable to work on clean
parts, free from oxidations, rust or other contaminating agents.
Choosing the electrode
The diameter of the electrode to be used depends on the thick-
ness of the material, the position, the type of joint and the type
of preparation of the piece to be welded.
Electrodes of large diameter obviously require very high currents
with consequent high heat supply during the welding.
Type of coating Property
Rutile Easy to use
Acid High melting speed
Basic High quality of joint
Choosing the welding current
The range of welding current related to the type of electrode
used is specified by the manufacturer usually on the electrode
packaging.
Use
All positions
Flat
All positions
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