components should fit together firmly for the proper
operation of the gun. Insulators that are cracked or
burned should be replaced.
Contact tips are designed for operation with a
certain type and diameter of filler material and a specific
welding mode. Each mode of welding will define the
relationship of the contact tip end with the end of the gas
nozzle. As a general rule, the short contact tips are used
with the spray-arc mode, as shown in Figure 3-29; the
longer contact tips, as shown in Figure 3-30, are used
with the short-arc mode. Various types of contact tips are
shown in Figure 3-31.
When the exit hole size becomes enlarged to the
point where electrical contact with the wire cannot be
maintained, the tip must be replaced.
Continued use of an oversize hole in the contact tip
will cause arc outages, incorrect heating of the wire, cold
laps in the weld pool, and poor weld quality.
Always use the manufacturer’s recommended contact
tip for the job involved and inspect
regularly to make sure
the tip is seated firmly into the adapter seat. Since the tips
are expendable, it is suggested that several tips for each
application be kept in stock.
Gas nozzles are made by each manufacturer to fit
an individual gun, and they are not generally
interchangeable. However, manufacturers generally use
the same system for dimensioning the exit size of the
nozzle end. The exit diameter is usually dimensioned in
sixteenths of an inch. This is shown in Figure 3-32. In
some cases, where high currents are carried, the gas
nozzle will get extremely hot causing the copper to peel
or flake. To correct this condition, some nozzles have
aluminum fins on the outside to radiate heat away from
them. A finned nozzle is shown in Figure 3-33.
During the welding operation, spatter from the
molten metal will gather on the inside of the nozzle, as
shown in Figure 3-34. Such contaminated nozzles
decrease and deflect the gas flow over the molten metal,
causing oxidation of the weld metal. To prevent this
condition, use an anti-spatter compound or spray to coat
the inside of the nozzle. An anti-spatter spray is shown in
Figure 3-35. A brush or a tool like the one in Figure 3-36
also may be used to remove spatter buildup between
spraying applications.
Chapter 3 Equipment Set-up and Control 37
Figure 3-27. This unit is very safe for the operator to use, since
a very low voltage motor is used to drive the wire.
(Miller Electric Mfg. Co.)
Figure 3-28. The components of a typical gun are shown in the
cutaway view.
Contact tip
recessed
1/4″ (6.4 mm)
The contact tip should
be recessed 1/4″ (6.4 mm)
inside the nozzle
as shown
3/4″ -1″ (19 mm - 25 mm)
electrical stickout
Figure 3-29. Spray-arc contact tips fit within the nozzle area.
Contact tip
extension 0″ - 1/8″
(0 - 3.2 mm)
1/4″ - 1/2″ (6 mm - 13 mm) electrical
stickout
The contact tip should be flush with the end of nozzle
or extend a maximum of 1/8″ (3.2 mm) as shown.
Figure 3-30. Short-arc contact tips fit flush with the nozzle end
or extend beyond the nozzle tip end.
Insulator
Cable liner
Power cable
Trigger
off/on switch
Adaptor
Contact tip
Gas nozzle