Note: Descriptions are shown in the official language in which they were submitted.
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EXTRUSION OF METAL
This invention relates to machinery for extrusion of metal
of the kind in which a passa~eway is formed bet~een an arcuate first
member and a second member in the form of a wheel having a
circumferential groove formed in its peripheral surface into which
groove the first member projects, the wheel being rotatable to urge
material in the passageway towards one end (the exit end) thereof,
an abutment member extending across the passageway at the exit end
thereof and at least one die orifice through the abutment member or
throu~h a part of the arcuate first member adjacent the abutment
member.
The abutment member may be large enough to block the end
of the passageway completely (as described in the specification of
UK Patent 1370894) but especially when the material to be extruded
15 is a relatively hard metal, such as copper, we prefer that the
abutment member is of substantially smaller cross-section than the
passageway and leaves a substantial gap between the abutment member
and the groove surface and that the material being extruded is
allowed to adhere to the groove surface, whereby a substantial
20 proportion of the metal (as distinct from the inevitable leakage of
flash through a working clearance) extends through the clearance and
remains as a lining in the groove to re-enter the passage~ay while
the remainder of the metal extrudes through the die orifice(s), as
described in our UK Patent No. 2069389B.
2~ Such machinery is commonly known as "Conform" machinery,
and will be referred to as such hereinafter.
No doubt because of the extreme assymetry of the die area,
we have found that the product of Conform extrusion may differ
significantly in shape from the die through which it was produced;
30 for example a round die produces wire of appreciably oval
cross-section. It is the object of this invention to eliminate or
at least reduce this effect.
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In accordance with one aspect of the invention, a Conform
machine incorporates a die-unit for extrusion apparatus comprising a
die and a die holder in which the die is supported but is surrounded
over at least a substantial part of its length by a sleeve extending
5 from the entry end of the die between the die and the die holder and
made of a metal soft compared with the die and the die holder.
The invention includes also an extrusion method in which
such a Conform machine is used and products of the method, including
wire made by a Conform machine (as define!d) that is of circular
10 cross-section to within 0.1%.
The die unit is preferably a separate insert, but if
desired the die holder could be directly formed in the shoe, or the
abutment of the machine.
Preferably the sleeve extends to the end of the die at its
15 entry end but stops short of the exit end of the die sufficiently to
provide positi~e location and pressure-tight engagement.
Preferably the die is held in the die holder by means of a
close fitting ring of hard metal or a machined step in the die
holder.
The sleeve can be formed merely by leaving a clearance
which becomes filled with the metal being extruded, or a preformed
ring of that metal can be used; but to avoid a risk of damage to the
; die and/or the die holder when the machine is taken to pieces after
use it is lOpreferable to use a sleeve made of another metal (soft
25 compared with the die and the die holder) that will not strongly
adhere to the metal to be extruded.
For copper and aluminium and their alloys, and most metals
that are commonly extruded, mild steel is a sui~able material;
others include titanium, nickel and pure iron.
The lnvention will now be described, by way of example,
with reference to the accompanying drawings in which:-
Figure 1 is a cross-section of part of a Conform machine
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(in accordance with our UK Patent 2069389B) suitable for extrusion
of copper;
Figures 2 and 3 are mutually perpendicular views of a die
unit forming part of the known apparatus shown in Figure 1;
Figures 4 and 5 are mutually perpendicular views of a
preferred form of die unit in accordance with the invention~ and
Figures 6 and 7 are mutually perpendicular views
of another form of die unit in accordance with the invention.
In the machine shown in Figure 1, a wheel 1 (the curvature
10 of which is too s1ight to be visible at this scale) is formed with a
rectangular groove 2, that forms three walls of the extrusion
passageway 3. The fourth wall is formed by an assembly comprising a
shoe 4 (a small portion of ~hich is shown), and an abutment 5
projects into the passageway.
, A radial extrusion die 6 is formed in a die holder 7
(which is preferably a separate component, though it might be
integral with either the abutment or the shoe).
The shoe, abutment and die area are of high- strength
materials and are held in position by heavy-duty support members
20 (not shown), and cooling means is provided.
Figures 2 and 3 show a die 6 mounted conventionally in a
die holder 7 and providing a cylindrical orifice 8 relieved by a
counterbore 9 to provide a clearance around the extruded product.
Figures 4 and 5 show a die unit, in accordance with the
25 invention, comprising a die 10, a die holder 11 and a sleeve 12 of
mild s~eel (which is soft compared wi~h the die and die holder and
does not strongly adhere to copper) surrounding the die over its
whole length.
The alternative die unit of Figures 6 and 7 differs in
30 that the sleeve 12 is replaced by a hard metal ring 13 (which
positions the die) and a clearance 14 in which a copper sleeve
will be formed as extrusion commences. This die unit is effective,
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but is less satisfactory than the die unit of Figures 4 and 5 as
there is a risk of damage wnen the copper discard is pulled from the
die unit when the machine is taken to pieces after use.
We believe that during extrusion a hydrostatic stress,
5 governed by the pressure of metal at the die face, exists in the
steel or copper (as the case may be) surrounding the die.
In a particular group of examples, the die holder had
overall dimensions 20 x 15 x 15 mm and the dies used had a length of
4 mm (of which the parallel part of the bore was 3 mm) and a
10 diameter of 7 mmO
The first three dies were conventionally mounted, as
Figures 2 and 3. The first had a bore whose maximum and minimum
diameters were 2.500 and 2.496 mm and produced wire of consistently
oval cross-section with maximum and minimum diameters of 2.481 and
15 2.460 mm respectively (2~47 + 0.6%); the second had a bore whose
maximum and minimum diameters were 2,502 and 2.497 mm and produced
wire of consistently oval cross-section with maximum and minimum
diameters of 2.488 and 2.455 mm respectively (2.47 + 0.8%); the
third had a bore whose maximum and minimum diameters were 2.550 and
20 2.547 mm and produced wire of consistently oval cross-section with
maximum and minim~m diameters of 2.517 and 2.482 mm respectively
(2.50 + 0.8%).
The fourth and fifth dies were mounted as shown
in Figures 4 and 5 using a mild steel sleeve 0.5 mm thick. The
25 fourth had an almost perfectly round bore with a diameter of 2.280
mm and produced wire that was substantially round with a diameter of
2.2245 + 0.0021 mm S(better than + 0.1%). The fifth had a bore with
maximum and minimum diameters of 3.120 and 3.118 mm and produced
wire that was substantially round with a diameter of 3.0580 + 0~0028
30 mm (again better than + 0.1~).
T'ne sixth die was mounted as shown in Figures 6 and 7
using a preformed copper sleeve 0.5 mm thick and 2~5 mm long, the
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hard steel sleeve 13 correspondingly being 1.5 mm long. The sixth
die had maximum and minimum diameters of 2.500 and 2.496 mm
(substantially identical with the first die) and produced copper
wire that was substantially round with diameters in the range 2.480
to 2~476 mm (2.478 + 0.1%).
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