Gun Maintenance
The welding gun is designed to operate properly if it
is maintained with reasonable care. Treating the gun in a
rough manner will damage the outer case and may cause
internal electrical shorts which could ruin the gun. Do not
force threaded assemblies together or use parts designed
for other guns. When changing adapters or contact tips,
use a wire brush to clean threaded areas to assure good
electrical contact. Check liner set screws often and use
dry compressed air or an inert gas to blow out the liner
assembly. Plastic or steel liners used in the front of the
gun assembly should be inspected occasionally for wear
and possible replacement.
Guns that use a pull system or a wire feeder with
segmented teeth should be checked often for proper wire
tension. The adjustment screw should be tight enough to
pull the wire without permitting the teeth of the wheel to
excessively mark the wire. Excessive marking or inden-
tation will cause flaking of the filler wire and rapidly
wear the front liner of the gun.
Ground Clamps (Work Leads)
The importance of proper ground leads and proper
clamps cannot be overemphasized in GMAW. The cable
must be of a sufficient size to adequately carry the
welding current without overheating. The cable sizes
shown in Figure 3-37 are the minimum sizes; larger
cables can always be used. The ground clamp must fit
tightly to the workpiece or an arc will be made when the
current flows through the connection. Arc outages may
occur where good contact is not made; the weld joint at
these points may not be satisfactory. Cables that are
cracked or broken must be replaced. Connections
between the clamp and the cable should be tight, since
loose connections will not allow proper current flow. To
check the ground system, hold your hand near the cable
and connections. If the cable or connections are warm or
hot, they require servicing or replacement. This is one of
the major causes of faulty welding with the GMAW short
arc mode of welding. When circular parts mounted on
positioners are being welded or the parts are rotated, a
38 Gas Metal Arc Welding Handbook
Figure 3-31. Manufacturers design contact tips for individual
guns.
Size
location
Size No.
Lengths*
Short
Regular
Long
Extra long
Special
= No. 3
= No. 4
= No. 5
= No. 6
= No. 7
= No. 8
= No. 9
= No.10
= No.11
= No.12
3/16
4/16
5/16
6/16
7/16
8/16
9/16
10/16
11/16
12/16
Measure number
of 1/16th inches
*
6
Figure 3-32. Standard nozzle diameters and lengths.
Figure 3-33. Air-cooled nozzles are used to carry heat away
from the nozzle end during high-amperage welding.
(MK Products, Inc.)
Figure 3-34. Contaminated nozzles like these will prevent
sufficient gas flow over the weld. Faulty welds will result.