3 The
wire guide tube, also called ”contact tube”, is made of copper and is
used to bring welding power to the wire
as well as direct the wire toward the work. The torch (and guide tube) is connected
to the welding power source by the power
cable. Because the wire must feed easily through the guide tube and also make
good electrical contact, the bore diameter of the tube
is important. The instruction booklet, supplied with every
torch, lists the correct size contact tube for each wire size. The tube, which
is a replaceable part, must be firmly locked
to the torch and centered in the shielding gas cup. The
shielding gas cup directs a protective mantle of gas to the welding zone. Large
cups are used for high- current work where
the weld puddle is large. Smaller cups are used for low-current welding.
The wire conduit and its liner are connected between the
torch and wire drive (feed) rolls. They direct the wire
to the torch and into the contact tube. Uniform wire feeding is necessary for
arc stability. When not properly
supported by the conduit and liner, the wire may jam. The liner may be either
an integral part of the conduit or supplied
separately. In either case, the inner diameter and material of the liner are important.
When using steel wire electrodes, a steel spring liner
is recommended. Nylon and other plastic liners should be
used for aluminum wire. The literature supplied with each torch lists the recommended
conduits and liners for each wire size
and material. Continued on next page...
WELDING CONTROL AND WIRE-FEED MOTOR
The welding control and wire-feed motor are often supplied
in one package (wire feeder) as shown in
Figure 2-1.
Their main function is to pull the welding wire from the spool and feed it to
the arc. The control maintains pre-determined
wire-feed speed at a rate appropriate to the application. The control not only
maintains the set speed independent of load, but also
regulates starting and stopping of wire feed on signal from
the torch switch. Shielding gas, water,
and welding power are usually delivered to the torch through the control box.
Through the use of solenoids, gas and water
flow are coordinated with flow of weld current. The control determines
the sequence of gas flow and energizing of the power
supply contactor. It also allows some gas to flow before
and after arc operation.
