[0001] The invention relates to an extrusion die, comprising a body of hard, wear-resistant
material in which one or more extrusion apertures are formed by means of spark erosion.
[0002] Such an extrusion die is known from, for example, GB-A-2,143,448, in which a steel
body is used.
[0003] Although these extrusion dies are very satisfactory for, for example, the extrusion
of aluminium sections, their service life is limited, in other words, after a certain
extrusion period the apertures are enlarged through wear in such a way that the extruded
sections no longer meet the set requirements. For, extrusion takes place at high pressure
and high temperature.
[0004] It is known to fit inserts of ceramic material in a steel die, in which case the
extrusion aperture(s) is (are) situated in the insert or in each insert. The contour
of the insert then fits precisely into a recess in the die. However, due to the difference
in coefficient of expansion, this produces problems in practice.
[0005] The material H.P. titanium diboride TiB₂, which can be pressed to a body under high
pressure and temperature and then has a very high density of at least 98%, is now
available on the market.
[0006] The chemical composition is 31.12% B and 68.88% Ti.
[0007] The melting point lies at 3390 ± 50 K.
[0008] Applicants have now found that this very hard and wear-resistant material is very
suitable for manufacturing extrusion dies from it through spark erosion. The service
life is thereby greatly increased.
[0009] According to the invention, the entire body is thus made from titanium diboride.
[0010] The use of a die body of titanium diboride requires a special die holder, which is
characterized in that it is made internally stepped, so that an antechamber is present
in front of the inlet side of the extrusion die.
[0011] In the schematic drawing the block of aluminium, called a billet, is indicated by
1. The die plate of titanium diboride is indicated by 2. In the example this plate
has a die aperture 3 formed by spark erosion.
[0012] The die plate 2 is accommodated in a die holder 4.
[0013] This die holder 4 is according to the invention made stepped, so that the plate 2
rests against a step.
[0014] An antechamber 5 is in this way formed in the die holder 4 to the left of the die
plate 2.
[0015] Situated to the right of the die plate 2 is a supporting tool 6 which supports the
die plate 2 in the die holder during extrusion.
[0016] During extrusion the heated billet 1 is pressed through the extrusion aperture 3
in the known manner.
[0017] On completion of the extrusion process the aluminium still remaining in front of
the antechamber 5 must be cut off.
[0018] The cutting-off now takes place at a distance from the die plate (antechamber depth
approx. 30 mm).
[0019] Besides, in that position the die plate can be given sufficient space on the diameter
to bridge the difference in coefficient of expansion.
1.Extrusion die, comprising a body of hard, wear-resistant material in which one
or more extrusion apertures are formed by means of spark erosion, characterized in that the entire body is made of titanium diboride.
2.Die holder for the extrusion die according to Claim 1, characterized in that the die holder is made internally stepped, so that an antechamber is present in front
of the inlet side.
