Posted by
keda on Wednesday, December 23, 2009 1:29:26 AM
Single blockwire drawing machines
include means for holding the dies accurately in position and for
drawing the wire steadily through the holes. The usual design consists
of a cast-iron bench or table having a bracket standing up to hold the
die, and a vertical drum which rotates and by coiling the wire around
its surface pulls it through the die, the coil of wire being stored
upon another drum or "swift" which lies behind the die and reels off
the wire as fast as required. The wire drum or "block" is provided with
means for rapidly coupling or uncoupling it to its vertical shaft, so
that the motion of the wire may be stopped or started instantly. The
block is also tapered, so that the coil of wire may be easily slipped
off upwards when finished. Before the wire can be attached to the
block, a sufficient length of it must be pulled through the die; this
is effected by a pair of gripping pincers on the end of a chain which
is wound around a revolving drum, so drawing the wire until enough can
be coiled two or three times on the block, where the end is secured by
a small screw clamp or vice. When the wire is on the block, it is set
in motion and the wire is drawn steadily through the die; it is very
important that the block rotates evenly and that it runs true and pulls
the wire at a constant velocity, otherwise "snatching" occurs which
will weaken or even break the wire. The speed at which the wire is
drawn vary greatly, according to the material and the amount of
reduction.
Continuous wire drawing machines
differ from the single block machines in having a series of dies
through which the wire passes in a continuous manner. The difficulty of
feeding between each die is solved by introducing a block between each
die. The speeds of the blocks are increased successively, so that the
elongation is taken up and any slip compensated for. One of these
machines may contain 3 to 12 dies. The operation of threading the wire
through all the dies and around the blocks is termed "stringing-up".
The arrangements for lubrication include a pump which floods the dies,
and in many cases also the bottom portions of the blocks run in
lubricant.
Often
intermediate anneals are required to counter the effects of cold
working, and to allow more further drawing. A final anneal may also be
used on the finished product to maximize ductility and conductivity.