22
poor quality welds. General rule of thumb for down hand welding is to have an arc length no
greater than the diameter of the core wire.
Electrode Angle
The angle that the electrode makes with the work is important to ensure a smooth, even transfer
of metal. When welding in down hand, fillet, horizontal or overhead the angle of the electrode is
generally between 5and 15 degrees towards the direction of travel. When vertical up welding the
angle of the electrode should be between 80 and 90 degrees to the work piece.
Travel Speed
The electrode should be moved along in the direction of the joint being welded at a speed that will
give the size of run required. At the same time, the electrode is fed downwards to keep the correct
arc length at all times. Excessive travel speeds lead to poor fusion, lack of penetration etc, while
too slow a rate of travel will frequently lead to arc instability, slag inclusions and poor mechanical
properties.
Material and Joint Preparation
The material to be welded should be clean and free of any moisture, paint, oil, grease, mill scale,
rust or any other material that will hinder the arc and contaminate the weld material. Joint
preparation will depend on the method used include sawing, punching, shearing, machining, flame
cutting and others. In all casesedges should be clean and free of any contaminates. The type of
joint will be determined by the chosen application.
•
3.2.5. MMA Welding trouble shooting
The following chart addresses some of the common problems of MMA welding. In all cases
of equipment malfunction, the manufacturer’s recommendations should be strictly adhered to
and followed.
NO.
Trouble
Possible Reason
Suggested Remedy
1
No arc
Incomplete welding circuit
Check earth lead is connected. Check all
cable connections.
No power supply
Check that the machine is switched on
and has a power supply
2
Porosity − small
cavities or holes
resulting from gas
pockets in weld metal
Arc length too long
Shorten the arc length
Work piece dirty, contaminated
or moisture
Remove moisture and materials like
paint, grease, oil, and dirt, including
mill scale from base metal
Damp electrodes
Use only dry electrodes
3
Excessive Spatter
Amperage too high
Decrease the amperage or choose a
larger electrode
Arc length too long
Shorten the arc length
