Welding Defects; Machine Maintenance - Cebora MIG WELD 403 S Manual De Instrucciones

• Screw the current nozzle again, making sure that the hole
diameter be the same as that the wire used.
• Insert the welding conic gas nozzle by rotating it clockwi-
se.
• Open the gas cylinder and adjust flowmeter at 8¸10 l/min.
WARNING: Check that the gas used is compatible with the
material to be welded.
5.3 WELDING CARBON STEELS.
To weld carbon steels the following things are necessary:
1) The use of a binary shielding gas which is most commonly
Argon and Carbon dioxide, in a ratio of 75¸80 % Argon and
25¸20% Carbon dioxide. Some applications, however, may
require a mix of three gases: Argon, Carbon dioxide (CO2),
and dioxide (O2). These gas mixtures generate heat during
welding and as a result the weld bead will be well filleted and
neat in appearance. The penetration, however, will not be
deep.
The use of Carbon dioxide as the shield gas results in a nar-
row weld bead with deep penetration but the ionization of
the gas will have an influence on arc stability.
2) The use of a filler wire of the same quality as the steel to
be welded. It is recommended that high quality wires be
used and that welding with rusted wires be avoided becau-
se they can give rise to defects in the weld bead. Generally,
the current range within which a wire can be used is calcu-
lated in the following manner:
Ø of wire x 100= minimum number of Amperes.
Ø of wire x 200= maximum number of Amperes.
Practical example: 1.2 Ø wire= 120 Amps minimum and 240
Amps maximum. These amperages are based on the use of
an Argon/CO2mixture as the shield gas and welding in the
Short Arc transfer mode.
3) Avoid welding on rusted work pieces or work having spots
of oil and grease present on the surface.
4) The use of a welding torch suitable to the welding currents
that are going to be used.
5) Periodically check that the two handles making up the
ground clamp are not damaged and that the welding cables
(torch cable and the work return lead) do not have any cuts
or burn marks that would reduce their efficiency.
5.4 WELDING STAINLESS STEEL
Welding stainless steels in the 300 series (the austenitic series)
must be done using a shield gas mixture of predominantly
Argon with a small percentage of O2 added to stabilize the
arc. The recommended mixture is AR/O2 in the ratio of 98/2.
Do not use CO2 or AR/CO2mixtures as the shield gas.
Do not touch the welding wire with your bare hands.
The filler metal (the wire) must be of a higher quality than the
work to be welded and the weld area must be clean.
5.5 WELDING ALUMINIUM
The following is required for aluminium welding:
1) 100% Argon as welding protection gas.
2) A torch wire of composition suitable for the basic material
to be welded.
For ALUMAN welding wire 3.5% silicon.
For ANTICORODAL welding wire 3.5% silicon.
For PERALUMAN welding wire 5% magnesium.
For ERGAL welding wire 5% magnesium.
3) A torch prepared for aluminium welding. If you only have a torch for steel wires, the same shall be
modified in the following way:
- Make sure that lenght of torch cable does not exceed 118
10
inches (it is advisable not to use longer torches).
- Remove the brass sheath-holding nut, the gas and the cur-
rent nozzles, then slip the sheath off.
- Insert the teflon sheath for aluminium and ensure it protru-
desfrom both ends.
- Screw the current nozzle so that the sheath adheres to it.
- Insert the sheath holding nipple, the O-Ring in the free end
of the sheath and secure with the nut without tightening too
much.
- Slip the brass tube on the sheath and insert both into the
adapter (after removing the iron tube which was fitted inside
the adaptor).
- Cut the sheath diagonally so that it stays as close as pos-
sible to the wire slide roller.
4) Use drive rolls that are suitable for aluminium wire. The
drive rolls, when being installed, must be tightened as tight
as possible.
5) Use contact tips that are suitable for aluminium wire and
make sure that the diameter of the contact tip hole corre-
sponds to the wire diameter that is going to be used.
6) Use abrasive grinders and tool brushes specifically desi-
gned for aluminium. Never use these tools on other materials.
REMEMBER that cleanliness equals quality.
The wire spools must be stored in plastic bags with a dehu-
midifier.

6 WELDING DEFECTS

1- DEFECT- Porosity (in, or on the surface of the weld
bead)
CAUSES • Bad wire (rust on the surface).
• Insufficient gas shielding due to:
- Inadequate gas flow due to a block in the
gas line.
- Defective flowmeter.
- Gas regulator covered with frost because
a gas heater was not used to heat the CO2
shielding gas.
- Failure of gas valve solenoid.
- Gas nozzle plugged up with spatter.
- Gas flow holes plugged up.
- Air drafts in the welding area.
2- DEFECT- Shrinkage Cracks
CAUSES • Welding wire or work to be welded dirty or
rusty.
• Weld bead too small.
• Weld bead too concave.
• Too much weld bead penetration.
3- DEFECT- Lateral cracking
CAUSES • Welding speed too fast.
• Low current and high arc voltages.
4- DEFECT Too much Spatter
CAUSES • Voltage too high
• Insufficient impedance
• No gas heater used for CO2 shielding gas.

7 MACHINE MAINTENANCE

Gas nozzle . Periodically clean the nozzle of all weld spatter
that may have accumulated during welding operations. If the
nozzle should become distorted or oval in shape then it must be replaced.
Contact tip . A good contact between the contact tip and
the wire ensures a stable arc and optimal current output.