IE46272B1 - Hydrostatic extrusion process and apparatus - Google Patents

Abstract

The blank (11) enters an elongate channel (18) ending in an extrusion chamber (19) located immediately upstream of a die (20). The channel (18) is formed by a groove (incision) (13) cut in the rotor (10) and by an end part at the entry of which the groove (incision) (13) is closed off, in a manner which is leaktight with respect to the extrusion fluid, by a relief (17) of the stator (16). The extrusion fluid is introduced, at the extrusion pressure, into a concentric zone (14) of the channel (18) by means of a nozzle (15). This device makes it possible to effect the hydrostatic extrusion of a metal blank, even one with low ductility, or, alternatively, of a blank made from synthetic resin, with a very high entrainment force, using a small-diameter rotor. <IMAGE> [CH617604A5]

Description

j This invention concerns a process and apparatus for ΐ j the hydrostatic extrusion of a workpiece which can be used ί t I ΐ iri particular for metals and alloys. t 1 ! 1 Conventional riethods of cold shaping metal wires of circular cross-section (by wire-drawings) or of any cross. section (essentially by drawing) are very old. ; ' t 1 Their disadvantages are well known: j In the case of wire-drawing: to achieve substantial reductions in cross-section from a machine wire which is pro10 duced hot, it is necessary to use a whole series of precise, i expensive dies, which often suffer rapid wear.

In the case of drawing; it is necessary to use a pluraI v lity of passes, to achieve progressive shaping in series of ί very expensive dies.

Many metals and alloys do not easily withstand these successive treatments and they must be subjected to intermediate ί -2treatments (this is the case with brass) and/or surface treatments to limit the degree of wear of the dies (this is the case with stainless steel or titanium).

To overcome these disadvantages, processes have been 5 proposed in which the reduction in cross-section is effected in a single pass, under the action of very high pressures.

However, these known processes are based on dry metalto-metal friction, which causes very substantial heating of the die and the treated articles, and this heating can even be such as to begin to cause melting of the latter, while also requiring substantial drive power.

Processes for continuous extrusion, referred to as hydrostatic processes, have also been proposed, in which a workpiece is forced through a die under the action of viscous fluid υ subjected to a very high pressure.

Such processes have many advantages, in particular: - the possibility of achieving very high ratios in respect of reduction in cross-section, even in the case of metals having a low degree of ductility; - the possibility of producing, under such conditions, a metal which has been heavily worked cold, and which is therefore mechanically very strong; - low degree of wear of the tooling; - flow of the metal without dead regions, hence resulting in sound products which are free from core inclusions, originating from the surface of the workpiece. ' -346 27 2 A process is known in which the wire is drawn into a high-pressure chamber by a winch means which is disposed in the chamber itself.

This last process is simple to perform if operation is effected at a relatively low pressure, but the ratio in respect of cross-sectional’ reduction permitted by the use of a single chamber is much too low for cold working the majority of metals. The use of multiple chambers arranged in series then results in an equipment design which is extremely heavy and expensive, bearing in mind the pressures involved.

At the present time, in spite of the high level of interest which it generates, no continuous hydrostatic extrusion process has been satisfactorily performed and put into operation, on an industrial basis.

The practical difficulty encountered hitherto by research concerning continuous hydrostatic extrusion processes lies essentially in the continuous introduction of a workpiece of indefinite length into a chamber containing a fluid under very high pressure. Extrusion of the product through a die which opens out of the chamber is then effected spontaneously.

According to the present invention in one aspect there is provided apparatus for the hydrostatic extrusion of a workpiece comprising two co-operating co-axial members, one member being rotatable relative to the other and constituting a rotor, said one member being provided with a circular or annular groove capable of receiving the workpiece to the extruded,said other member being fixed and constituting.· a stator, -.and forming a cover over a first sector of the groove substantially sealed -44 6 2 7a with respect to said ohe member, said other member also having downstream of the first sector a portion which is received in said groove and totally blocks the section of the groove over a second sector to seal it, said second member being provided with means for supplying a pressurized viscous fluid to the groove, a conduit in said stator capable of receiving the workpiece and having one end in communication with the groove in the vicinity of the second sector and its other end in communication with an extrusion chamber which communicates with at least one die orifice, said pressurized viscous fluid when supplied to the groove producing in the first sector of the groove a pressure gradient which increases from ambient pressure at the point of entry of the first sector to the extrusion pressure which obtains in the extrusion chamber, at said one end of the conduit.

According to the present invention in another aspect there is provided a process for the continuous hydrostatic extrusion of a workpiece, in which the workpiece, accompanied hy a quantity of a viscious fluid is introduced into a groove provided in a drive rotor rotatable relative to a cover, said workpiece defining two separate concentric zones in said groove, the first zone being formed between the workpiece and a stator which forms said cover applied to the rotor, and the second zone being formed between the workpiece and the rotor, said first zone directly receiving the viscous fluid under pressure by an introduction means generating a pressure which progressively increases from ambient pressure at the point of entry of the workpiece in the groove to the extrusion pressure in an extrusion chamber which extrusion pressure being generally higher than that obtaining in the second zone, - 5 4 6 272 the pressure difference applying to the workpiece a force which tends to urge it into the groove and which produces a sufficient degree of friction between the workpiece and rotor for the movement of the rotor to contain the workpiece without slipping, from the upstream region, at ambient pressure, in a downstream direction to the entry of said chamber from which the workpiece issues by extrusion through at least one die orifice.

The principle of this process will first be explained with reference to Figures 1, 2 and 3 of the accompanying drawings.

We shall first consider a rotor 1 in which there is provided a circular groove 2 which is illustrated in crosssection in Figure 1, and a workpiece 3 to be extruded, which is placed in the groove so as to come into contact either with the two side walls 4 and 4' or the bottom 5 of the groove, or the side walls and the bottom; the pressure P of a Viscous fluid is applied to the upper part of the workpiece 3.

The workpiece 3, which is shown as having a circular cross-section but which can be of any other cross-sectional shape, is applied against the walls of the groove at the location of the two generating lines, at points such as X and Y.

In the bottom 7 of the groove there is a pressure which is at all points lower than or, locally, at most equal to the pressure P, and which may be equal to ambient pressure at the bottom 7 of the groove is in communication with the free air.

The workpiece 3 to be extruded therefore divides the -64 6 2 7 2 groove into two zones, an outward zone 6 in which there is a pressure P and an inward zone 7 in which there is a pressure p.

The pressure P varies progressively along the groove. If we consider a portion of length £, of the workpiece 3 to be extruded, the mean pressure upstream of & is equal to Po, and the mean pressure downstream of J is equal to Pl, the terms upstream and downstream being determined by reference to the direction of movement which is to be imparted to the work•jO piece 3 in the direction of the extrusion chamber. The abovementioned portion of the workpiece 3 is subjected to the four pressures P, p, Po and Pl, as can be seen from Figure 2. These pressures generate forces applied to the portion Z .

The condition under which the portion is driven by the rotor without slipping is that the gripping force of the work15 piece in the groove is at least equal to the resisting force due to the gradient of the pressure P, this force tending to cause the above-mentioned portion to slip in a downstream direction. This condition can be written, while neglecting in particular the influence Of the inherent mechanical strength of the workpiece: (P - ρ) βχ axK > (Pl ~ Po)s or P - p XPl - Po) x s/(d?xaxk) in which equation: -P is the mean pressure in the outward zone of the groove 2 above the workpiece 3, -74 6 2 7 2 -p is the mean pressure in the inward zone of the groove 2 below the workpiece 3, —Po is the mean pressure in the section of the groove 2 at the upstream end of the portion of the workpiece in question, -Pl is the mean pressure in the section of the groove 2 at the downstream end of the above-mentioned portion, -dis the length of the above-mentioned portion, -a is the width of the groove in the region in which the workpiece separates it into an outward zone 6 and an inward zone 7. -s is the cross-section of the workpiece, -K is an adhesion coefficient dependent on the shape and nature of the surfaces in contact.

If for example we consider a portion of metal wire of substantially circular cross-section, being 10 mm in diameter arid 5 cm in length, we have; £ = 5 x 10-2m a --10-2m -4 2 s -^0.8 x 10 m From the experience acquired in respect of hydrostatic extrusion, we can assume: Po = 5000 χ 105 Pascal (5000 bars) Pl = 6000 χ 105 Pascal (6000 bars) K = 0.1 The equilibrium condition can be set ou t as follows: P - p >(P1 - PO) s/(£x a x k) P - p >1000 χ 105 x 0.8/(5 x 0.1) P - p 5^1600 χ 105 Pascal (1600 bars) _a4 6 2 7 2 This condition can be very easily realised.

The same considerations apply where the workpiece to be extruded is of a different cross-sectional shape from the circular shape mentioned above, for example a square or re5 ctangular section 8. The inward zone 7 in which there is the low pressure p is, as shown in Figure 3, in the form of passages 9 formed in the bottom of the groove 2.

Therefore, in these different cases, it is possible for a workpiece which is taken at ambient pressure to be entrained without slip by means of a rotor, and introduced into an ex10 trusion chamber containing a fluid at a very high pressure.

The present invention which is based on the use of the above-mentioned considerations is thus distinguished from the known processes in which the entrainment of the workpiece in15 volves very substantial metal-to-metal frictional effects. The extrusion die may be single or multiple, fixed or removable, and in one or more parts.

Some embodiments of the invention will now be described, by way of examples, with reference to the accompanying drawings, in which :20 Figures 1,2 and 3 illustrate the principle of the invention and have already been described.

Figures 4 and 5 show respectively a cross-section and a longitudinal part-section of an embodiment of the invention in which the groove is provided in the periphery of the rotor.

Figures 6 and 7 show respectively a cross-section and plan view of another embodiment in which the groove is pro-94 6 2 7 2 vided in the face of the rotor which is directed towards the stator, the stator forming a cover.

Figure 8 shows in section a particular form of the cover, in the part which is towards a workpiece, the cover being adapted to the shape of the workpiece, Figure 9 shows in section a simplified form of the cover.

Figure 10 is a diagram showing the distribution of the fluid pressures on the blank along the first sector of the groove, and Figures 11 and 12 diagrammatically show two complete installations for continuous hydrostatic extrusion, according to the invention, including the accompanying equipment, in the case where the stator encases the rotor (Figure 11), using the principle of Figures 4 and 5, and the case where the stator is in the form of a flat cover (Figure 12), using the principle of Figures 6 and 7.

Referring to Figure 4 which is a View in cross-section taken perpendicularly to the axis 0 of the rotor 10, the workpiece 11 to be extruded enters, at 12 at point N, the first 2Q sector of the groove 13 provided in the rotor 10. The first sector extends approximately between the radii OA and OB. At point N, the above-defined pressures P and p are equal to ambient pressure. The viscous fluid, under the extrusion pressure, is introduced into the first concentric zone 14 by means of a delivery conduit 15 which passes through a stator 16. In the second sector which is between the radii OB and OC, the groove 13 is blocked by a relief portion 17 of the stator 16, so as to be substantially fluid-tight with respect to the -104 6 2 7 2 viscous fluid.

When the process is started, the workpiece 11 must be engaged into the elongate conduit 18, in the extrusion chamber 19, and at the entry of a die 20; the term extrusion chamber denotes the part of the conduit 18 which is immediately upstream of the die 20. The extrusion chamber 19 can be of a shape and dimensions which are identical to or very different from those of the elongate conduit 18, without this affecting the extrusion procedure.

The die 20 is fluid-tightly secured to the end of the conduit 18, by means of a seal 21; in this way, the pressure of the fluid is constant over the whole length of the conduit 18 and in the extrusion chamber 19, and is equal to Ρθχ.

It is possible to provided one or more delivery conduits for injection of the viscous fluid at a pressure P* which is intermediate between the ambient pressure and the high pressure ΡΕχ, such as the delivery conduit 22.

Figure S is a view in cross-section ln a plane passing through the axis 0 at the location of the delivery conduit 15.

The clearance shown between the rotor 10 and the stator 16 in the sealing zone Z^; Z^ is greater than the clearance will be in an actual construction, for the sake of clarity of the drawings. In practice, this clearance will be measured in tenths of a millimeter. This also applies to all the following Figures.

Figure 6 shows a cross-sectional view of another embodiment of the invention, in which the rotor and the stator no longer co-operate by way of their external and internal peripheries -114 6 27 2 respectively, but by way of their faces 23 and 24 which are perpendicular to the axis of rotation.

The groove 25 is provided in the face 23 of the rotor which cooperates with the face 24 of the stator.

The right-hand part of Figure 6, relative to the axis of rotation, is a half-section through the viscous fluid injection passage 15 disposed at the downstream end of the first sector of the groove, whereas the left-hand part is a half-section through relief portion 27 which blocks the groove in its second sector. Pressure P obtains in the outward zone 28, and pressure p obtains in the inward zone 29.

Figure 7 shows a view form above, in a plane perpendicular to the axis of rotation, of the apparatus of Figure 6. The workpiece 11 enters the groove 25 of the rotor, on the left]5 hand side, and issues from the die 20 in the form of the wire» drawn product 26.

Both in the embodiment of Figures 4 and 5 and the embodiment of Figures 6, 7 and 8, the difference P-p depends on the value of the pressure injected into the outward zone of the groove, the distribution of the injection points, if there are multiple injections points, and on the cross-section and the shape of the inward and outward zones of the groove. Figure 10 shows the distribution of the pressures P and p in a particular case comprising two fluid intakes, one at M (Figure 4) at the extrusion pressure ΡΕχ,. and the other at R at the pressure Ρ'ΕχΡ/2. The point M corresponds to the orifice for the injection of the viscous fluid at high pressure ΡΕχ at the downstream end of the first sector of the groove. The -124 6 2 7 2 point N corresponds to the entry of the workpiece to be extruded into the groove, at the up-stream end of its first sector. The point R corresponds to the orifice for injection of the viscous fluid at the pressure P'=P„„/2. bz.

It is noted that the difference P - p is always relatively large, except at the point N at which P = p = the ambient pressure, and at point M at which equality as between P and p is necessary to permit the object to issue from the groove in order to pass into the orifice 18 towards the extrusion chamber 19.

It is noted that the curve P has radii of curvature which are less pronounced than the curve p. This is because the section of the axial leakage passage formed by the outward zone of the groove increases in a downstream direction. It is possible to seek to achieve this phenomenon by suitable machining of the stator, but it tends to appear spontaneously because of resilient yielding of the walls of the passage under the effect of the thrust forces applied by the viscous fluid. Conversely, the inward passage section tends to decrease in a 2Q downstream direction, because of the compacting of the blank * at the bottom of the groove.

In this case of Figures 4 to 7, it is possible to adapt the shape of the end 30 of the part of the cover which is towards the first sector of the groove, as can be seen in Figure 8 in such a way as to reduce the transverse section of the zone 28; this substantially reduces the fluid leakage flow rate in the opposite direction to the forward movement of the object to be extruded. -134 6 27 2 On the other hand, it is possible to simplify the design of the stator, as shown in Figure 9 in which the sealing zones are localised, for example at Z^.

The two possibilities may be combined.

The total leakage of the system is compensated by pumping means which reinject the viscous fluid which has escaped through the different clearances between the rotor, the stator, and the workpiece to be extruded, possibly after purification, filtration and temperature adjustment of the fluid. The above-mentioned clearances are essential for normal operation of the apparatus, but they should be reduced to a minimum in known manner, so that the power absorbed by the pumping means is not excessive. For the same purpose, the hydraulic fluid must be of relatively high viscosity.

Figure 11 diagrammatically shows a view in vertical section of a complete hydrostatic extrusion installation according to the invention, in the embodiment described with reference to Figures 4 and 5. The rotor 31 is rotated by a motor-reducing drive unit 32. The stator 33 is brought into 2θ and held in its working position by a jack 34. The workpiece passes into the extrusion apparatus at 36 and the extruded wire 37 issues from the die 38. The viscous fluid at the high pressure ΡΕχ is injected at 39, at the downstream end of the first sector of the groove in the rotor, by a tandem pre25 ssure multiplying means 40 which is itself fed with fluid by a medium pressure pump 41.

A second tandem pressure multiplying means 42 supplies fluid to an intermediate injection point 43 at a pressure P' -144 ΰ 2 'ι 2 which is lower than pressure P_v, as described above; the bA multiplying means 42 is also supplied with fluid from the pump 41.

The whole of the apparatus is mounted above a drain pit 5 44 into which flows the viscous fluid issuing from the various leakage points and which may be provided with an apparatus of known type for controlling the temperature of the leakage fluid. The viscous fluid is picked up by the low pressure pump 45 and, after filtration, passed to the low pressure accumulator 46 lg from which the multiplying means 40 and 42 are forced fed with fluid.

The jack 34 which controls the positioning of the stator 33 and its contact against the rotor is supplied with fluid from the same source as the pressure multiplying means. For this reason, the force holding the stator 33 against the rotor 31 is proportional to the extrusion pressure, and this provides for correct compensation of the force tending to separate the rotor and the stator.

Figure 12 diagrammatically shows a view in vertical 20 section of another complete hydrostatic extrusion installation according to the invention. In Figure 12, the components which perform the same functions are denoted by the same reference numerals as in Figure 11. The extrusion system itself is of the type described with reference to Figures 6 and 7. Leakage 25 fluid is collected in a tank 47 provided with a baffle arrangement 48 and provided with a known device for temperature control (not shown); the leakage fluid is picked up by the low pressure pump 45 and passed into an accumulator 46. -154 to 2 7 2 Examgle_of_Ogerationί A continuous hydrostatic extrusion installation was constructed in accordance with the diagrammatic view of Figure 11 and on the principle illustrated in Figures 4 and 5, this installation having a rotor of a diameter of 500 mm (measured at the bottom of the groove) and being supplied with a synthetic polyoxyethylene-base oil with a viscosity of 500 strokes at 20°C.

In a first test, a 10 mm diameter workpiece of unalloyed copper was introduced, and the apparatus was supplied with viscous fluid at an extrusion pressure of about 16 kbars. The discharge die was 1.6 mm in diameter.

The speed of rotation of the rotor was controlled to 34 r.p.m., corresponding to a workpiece intake speed of 0.9 meters per second, and an extruded wire discharge speed, the wire having a diameter of 1.6 mm, of 35 meters per second.

During operation, the mean leakage flow rate of the viscous fluid was 30 mililitres per second. This mode of operation produced a wire whose surface had no defect and which was totally free from inclusion.

In a second test, a 10 mm diameter workpiece of brass known as rjz 15 (containing 15% of zinc) was introduced into the apparatus. The cross-sectional reduction ratio was fixed at 3 (entry section S - 78,5 mm', discharge section s = 25.5 2 mm , rectangular shaped member measuring about 8.5 x 3 mm).

The speed of rotation was set at 34 r.p.m., the workpiece entry speed was 0.9 meters per second, and the discharge speed of the extruded shaped member was 2.8 meters per second. -164 6 2 7 3 The viscous fluid was introduced at a pressure of about 8 kbars and the leakage flow rate was of the order of 25 millilitres per second. The extruded wire had an excellent surface condition and had neither inclusions nor traces of oxidation. The,mechanical properties of the wire correspond to those of a cold worked metal.

Compared with known hydrostatic extrusion processes, the invention has the following advantages: - The die is disposed outside of the groove, which makes it possible to determine its optimum external dimensions and shape, without being limited by the dimensions required for the groove, while also making fitting and removal of the die convenient.

- Entraining the workpiece by the rotor without slip makes it possible to develop a drive force for a very substantial length unit and in practice to use a drive rotor of reduced size (for example a diameter of 500 nun instead of a diameter of 2000 mm, in the case of a 10 mm diameter workpiece). The 2Q hydrostatic extrusion process and apparatus described above are suitable both for extruding metals and alloys, even those with a low degree of ductility, and for extruding various materials such as plastics materials. They can be used over a wide range of temperatures, depending on the nature of the materials extruded, the viscous fluid and the tools.

The invention is not limited to the examples and embodiments which have been described above.

For various reason?., in particular better balancing of -174 6 2 7 2 the hydraulic forces involved, or an increase or diversification in production, it is possible in the installations described with reference to Figures 11 and 12 to use, simultaneously or alternatively, a plurality of apparatus according 5 to the invention, which use certain components in common, for example the high pressure generators or the rotor; the rotor may comprise a groove covered by a cover comprising a plurality of members acting as a stator, or even a plurality of grooves, which may be identical or different and which are each covered by a cover comprising one or more members acting as a stator, In this way it is possible to extrude two or more workpieces simultaneously or successively.

In order to improve the dimensional regularity of the superficial qf oxide qntj/or serfage workpiece or to remove therefrom ahy^ skin /irregularities wfnch is abrasive the source of/Part:i-cles that pollute the viscous fluid, it may be of advantage to subject the workpiece to at least one shaving and/or shaping pass before it passes into the groove. The drive force generated by the rotor can be utilised to draw the workpiece through the shaving or shaping device, which can be of any known type.

It is also possible to extrude composite products by coextruding a plurality of separate articles which are introA duced jointly into the groove of the rotor and heavily pressed together as they pass through the extrusion die; for example, it is possible to operate in this way to produce a shaped member of aluminium sheathed with copper from an aluminium core member wrapped around by a sheet of copper.

Claims (16)

1. Apparatus for the hydrostatic extrusion of a workpiece, comprising two cooperating co-axial members, one member being rotatable relative to the other and constituting a rotor, said one member being provided with a circular or annular groove capable of receiving the workpiece to be extruded, said other member being fixed and constituting a stator, and forming a cover over a first sector of the groove substantially sealed with respect to said one member, said other member also having downstream of the first sector a portion which is received in said groove and totally blocks the section of the groove over a second sector to seal it, said second member being provided with means for supply a pressurized viscous fluid to the groove, a conduit in said stator capable of receiving the workpiece and having one end in communication with the groove in the vicinity of the second sector and its other end in communication with an extrusion chamber which communicates with at least one die Orifice, said pressurized viscous fluid when supplied to the groove producing in the first sector of the groove a pressure gradient which increases from ambient pressure at the point of entry of the first sector to the extrusion pressure which obtains in the extrusion chamber, at said one end of the conduit.

2. Apparatus as claimed in claim 1, in which the die is a removable die accessible from the exterior of the stator.

3. Apparatus as claimed in claim 1 or claim 2, in which the die comprises at least two dismantleable parts. -194 6 2 7 2

4. Apparatus as claimed in claim 1, in which the die has at least two flow passages.

5. Apparatus as claimed in any one of claims 1 to 4, in which the rotor provided with a groove is covered by a cover comprising at least two identical members, each acting as a stator.

6. Apparatus as claimed in any one of claims 1 to 4 in which the rotor is provided with at least two grooves covered by a cover comprising at least two members each acting as a stator.

7. A process for the continuous hydrostatic extrusion of a workpiece, in which the workpiece, accompanied by a quantity of a viscous fluid, is introduced into a groove provided in 4 drive rotor rotatable relative to a cover, said workpiece defining two separate concentric zones in said groove, the first zone being formed between the workpiece and a stator which forms said cover applied to the rotor, and the second zone beinq formed between the workpiece and the rotor, said first zone directly receiving the viscous fluid under pressure by an introduction means generating a pressure which progressively increases from ambient pressure at the point of entry of the workpiece in the groove to the extrusion pressure in an extrusion chamber, which extrusion pressure being generally higher than that obtaining in the second zone, the pressure difference applying to the workpiece a force which tends to urge it into the groove and which produces a sufficient degree of friction between the workpiece and rotor for the movement of the rotor to entrain the workpiece without slipping, from the upstream region, at ambient pressure, in a - 20 4 6 2 7 2 downstream direction to the entry of said chamber from which the workpiece issues by extrusion through at least one die orifice.

8. A hydrostatic extrusion process as claimed in claim 7, 5 in which the viscous fluid is introduced into the groove through at least one aperture in the stator, under a high pressure generated by a generator.

9. A hydrostatic extrusion process as claimed in claim 7 or claim 8, in which the workpiece is subjected to at least one 10. Pass through a shaving device, before entering the groove of the rotor.

10. A hydrostatic extrusion process as claimed in claim 7 or claim 8, in which the workpiece is subjected to at least one pass through a shaping device, before entering the groove in the 15 rotor.

11. A hydrostatic extrustion process as claimed in any one of claims 7 to 10, when employed with the apparatus of any of claims 1 to 6, in which the viscous fluid which leaks from the said apparatus during operation is recovered and re-introduced into the 20 apparatus.

12. A hydrostatic extrusion process as claimed in any one of claims 7 to 11, in which two workpieces are extruded simultaneously, by providing a member forming two stators.

13. A hydrostatic extrusion process as claimed in any one of 25 claims 7 to 11, in which at least two workpieces are extruded simultaneously, by providing a rotor having at least two grooves covered by a cover comprising at least two members, each acting as a stator.

14. A hydrostatic extrusion process as claimed in any one of claims 7 to 13, in which the or each workpiece comprises a plurality of 30 separate members which are introduced jointly into the groove - 21 4 0 272 of the rotor and which are pressed together in their passage through the extrusion die.

15. Apparatus for the hydrostatic extrusion of workpiece, substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 or Figures 1 to 3 and 6 to 9 or Figure 11 or Figure 12 of the accompanying drawings.

16. A process for the hydrostatic extrusion of workpiece, substantially as hereinbefore described with reference to the accompanying drawings.