Page 142 - Welding of Aluminium and its Alloys

MIG welding 127

7.11 MIG torches equipped with ‘pull’ wire drive rolls. Courtesy of
TPS-Fronius Ltd.

7.2.2.2 Wire feed systems

There are three basic forms of wire feeders: the ‘push’ system, the ‘pull’
system and the ‘push–pull’ system.As the name suggests, in the push system,
the wire is pushed by the wire feed drive rolls along the conduit to the
welding torch. The flexibility of aluminium wire means that the wire can
buckle and jam inside the conduit, resulting in irregular wire feeding at the
welding torch and, in extreme cases, a ‘bird’s nest’ of tangled wire at the
wire feed unit. Such wire feeders are generally restricted to a minimum wire
diameter of 1.6mm and the wire feed conduit to a length of 3.5m.
The pull system utilises a set of wire rolls in the torch handle which pull
the wire from the wire reel (Fig.7.11).This arrangement increases the weight
of the torch and does not increase the distance over which the wire can be
fed, this still being limited to around 3.5m, although the consistency of the
wire feed is improved and wire diameters down to 0.8mm can be used.
The push–pull system is a combination of the above two systems with a
set of drive rolls at both the wire reel feeder and in the torches illustrated
in Fig. 7.11.This enables small diameter wires to be fed up to 15m from the
wire reel. The final variation on this theme is the spool on gun torch which
utilises a small 100mm diameter wire reel mounted on the welding torch
and a set of drive rolls in the torch body.These rolls push the wire the short