Method for continuous friction actuated extrusion

In a continuous friction-actuated extrusion process, such as the Conform process, particulate material is fed into the extrusion passageway at a rate low enough to the rate at which material is extruded from the die orifice to be determined by and substantially equal to the rate of feeding. Feeding can be achieved by a simple hopper feeding through an adjustable constriction, preferably formed by a simple gate valve, or a gravimetric or volumetric controlled rate feed device can be used.

This invention relates to the continuous friction-actuated extrusion of 
metals (and other materials) to produce wires, strips and other elongate 
bodies of considerable length. 
By "friction-actuated" extrusion is meant a process comprising several 
steps the first consisting of feeding material into one end of a 
passage-way formed between first and second members with the second member 
having greater surface area for engaging the material than the first 
member, said passageway having an obstruction at the end remote from the 
end into which the material is fed and having at least one die orifice 
associated with the obstructed end. The next step is moving the 
passage-way defining surface of the second member relative to the 
passage-way defining surface of the first member in the direction towards 
the die orifice from the first end to the obstructed end such that 
frictional drag of the passage-way defining surface of the second member 
draws the material through the passage-way and generates in it a pressure 
that is effective to extrude it through the die orifice. The obstructed 
end of the passage-way may be blocked substantially entirely, as described 
in British Patent Specification No. 1,370,894 (United Kingdom Atomic 
Energy Authority). However in the most usual practice (the Conform 
process) the passage-way is arcuate and the second member is a wheel with 
a groove formed in its surface into which the first member projects and 
the obstructed end is defined by an abutment projecting from the first 
member, we prefer that the abutment member is of substantially smaller 
cross-section than the passage-way so that it leaves a substantial gap 
between the abutment member and the groove surface. In this way the 
material may adhere to the groove surface, as described in the 
specification of our British application publication No. 2,069,398A, 
whereby a proportion of the material extrudes through the clearance and 
remains as a lining in the groove to re-enter the passage-way at the entry 
end while the remainder of the material extrudes through the die orifice. 
The Conform process was originally developed for the extrusion of a rod 
in-feed, and the dimensions of the passage-way were chosen to ensure that 
it would be filled by the material of the feed rod without any major axial 
compression of the rod. Subsequently, when particulate feed material came 
to be used in some cases, an excess of the feed material was invariably 
supplied by the use of a hopper, so that the passage way should be as full 
as possible of the particulate material, in order to minimise the volume 
of air spaces carried into the passage-way. 
We have now discovered that this is not the ideal way of feeding 
particulate material to be extruded to a friction-actuated extrusion 
machine, and that more satisfactory results can be obtained by restricting 
the amount of material fed to such an extent that the output rate of the 
extrusion machine is controlled by the rate at which particles enter the 
passage-way. 
In accordance with the invention, therefore, a friction-actuated extrusion 
process is distinguished by feeding the material into the passage-way in 
particulate form at a rate low enough for the rate at which material is 
extruded from the die orifice to be determined by and substantially equal 
to the rate of feeding (and in particular to be substantially independent 
of the speed of movement of the passage-way-defining surface of the second 
member, within the working range). 
For optimum control, the rate of feeding may be regulated by a gravimetric 
or volumetric feed device operating without a buffer storage hopper 
downstream of it (such feed devices being commercially available); useful 
results can however be achieved for a lower cost by the use of a storage 
hopper feeding particulate material to the passage through a constriction 
of smaller cross-sectional area than the passage; such constriction is 
preferably adjustable to provide a single output speed control, and may be 
formed by a simple gate valve. The invention includes apparatus for 
friction-actuated extrusion incorporating feed rate control means of these 
or other kinds. 
The process of the invention has the advantage that the quantity of 
unconsolidated material in the passage, and consequently the energy 
consumed in frictional drag between that unconsolidated material and the 
second member, may be reduced, which is an important consideration when 
extruding relatively hard materials, such as copper and its alloys, as 
this relieves the very high stresses liable to be generated in the members 
that define the passage-way; and it allows the conditions of operation to 
be optimised during running, to secure the maximum output consistent with 
acceptable torque, stress, temperature and other variables. 
Furthermore, the output rate can be controlled, without loss of quality, 
down to very small values, something that cannot be done by slowing down 
the main members of the machine alone. This is especially valuable at the 
initial start-up of the machine, when a very low output speed allows 
continuous threading of the leading end of the product through cooling 
apparatus and onto a reel or other take-up device; it may also be useful 
during reel changeover allowing a simpler mechanism to be used.

In the apparatus shown in FIG. 1, the extrusion passage-way is formed 
between a first member in the form of a shoe 1 which is fixed and forms 
one side wall of the passage-way and a rotating wheel 2 which is grooved 
to form the other three side walls of the passage-way. The shoe 1 supports 
an abutment member 3 which projects into and defines the outlet end of the 
passage-way 4, and which provides an orifice 5 through which the extruded 
product 6 emerges. In accordance with the prior invention described in our 
British Patent Application Publication No. 2,069,398A, the abutment member 
3 does not completely block the end of the passage-way, but leaves a 
substantial clearance through which a coating 7 (FIG. 4) is formed in the 
base of the wheel groove. 
The apparatus shown is fitted with a hopper 8 in order to control the 
infeed of particulate material in accordance with the present invention. 
Referring now to FIGS. 2, 3 and 4, the hopper 8 is a simple, steep sided 
funnel of rectangular cross-section discharging directly into the wheel 
groove 9 at a point a little upstream of the entry end of the passageway 
4. For controlling the rate of feed in accordance with the invention, a 
gate 10 is moveable by a screw mechanism 11 so as to extend to any 
required extent into the wheel groove and so restrict the flow of 
particles from the hopper into the extrusion passage-way 4. 
Since the manual operation of the screw mechanism 11 will be relatively 
slow, a separate obturator member 12 is moveable by a pneumatic motor 13 
into the position shown in broken lines in order to provide the facility 
for rapid complete shut-off when required, in an emergency or otherwise. 
In the operation of this machine, the wheel 2 is first driven at about half 
its full running speed, and the gate 10 is set to constrict the 
passage-way only slightly. Particulate feedstock is then introduced by 
hand into the hopper at a low rate to obtain an initial extruded product 
sufficient for threading up to any suitable take-up mechanism. The 
obturator 12 is now closed while the hopper is filled (to a level 
afterwards held steady by a simple level detection system) with 
particulate material. Extrusion is then commenced in a controlled manner 
by opening the obturator 12 and increasing the wheel speed. As full 
running speed is approached, and when necessary thereafter, the gate 10 is 
adjusted to the widest opening consistent with ensuring that neither the 
torque required to maintain the wheel speed nor the pressure on the die 
assembly exceeds chosen maximum values. This adjustment can be made 
automatically by conventional means. If desired, for instance during reel 
changes in the take up, the output speed can be reduced to a required 
level by lowering the gate 10. 
In a specific example, a "2 D" Conform friction-actuated extrusion machine, 
supplied by Babcock Wire Equipment Limited, was modified by fitting a 
semi-circular abutment as shown in FIGS. 3 to 5 of British Application No. 
2,069,389A and the hopper shown in the drawings of this application. The 
die aperture was 2.5 mm and the full running speed of the wheel 20 
revolutions per minute. The hopper was kept supplied with granulated 
cathode copper with a maximum particle size of about 3 mm. In normal 
running, the gate 10 was adjusted to a setting in the region of 3 mm 
projection into the wheel groove to limit the motor torque to 68.9 
lb/ft..sup.2 and the pressure on the die assembly to 56,580 lb/in.sup.2 ; 
under steady conditions of running, an extrusion output of 689 ft/min was 
secured. The output speed, and the torque relative to that observed at 
full speed, for greater projection depths were measured as follows: 
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Depth Output 
mm m/min Relative Torque 
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4 180 0.95 
5 150 0.85 
6 120 0.75 
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For greater projection depths, the situation is complicated by the fact 
that individual infeed particles may be unable to pass freely between the 
gate and the bottom of the groove--if it is desired to achieve very low 
output speeds without reducing the speed of the wheel, it is preferable to 
use more finely divided particles in the feed, or to use a gravimetric 
feed device instead of the gate valve.