WO1997003769A1

WO1997003769A1 - Extrusion

Info

Publication number: WO1997003769A1
Application number: PCT/GB1996/001759
Authority: WO
Inventors: Gordon Howard Goddard
Original assignee: Gordon Howard Goddard
Priority date: 1995-07-22
Filing date: 1996-07-22
Publication date: 1997-02-06
Also published as: GB9515089D0; AU6527696A

Abstract

Extrusion apparatus (300) comprises: a die assembly (304) including a die (352) having an orifice (362) of a desired shape and a ram (310) for forcing a portion of material to be extruded through the die orifice (362) to form an extrusion, said ram (310) being movable relative to the die (352) to a retracted position to allow a further portion of material to be extruded to be placed in said die assembly (304). Means (346) is provided for retaining on the ram (310) part of the material to be extruded, whereby the extrusion can be at least partially retracted when the ram (310) moves to the retracted position. This enables the further portion of material to be located in the die assembly (304) with the extrusion extending through a bore provided in said further portion of material.

Description

Extrusion

This invention relates to extrusion apparatus and to a method of extrusion.

In conventional extrusion processes a billet of the material to be extruded is placed into a die container. The die container has a die with an orifice shaped to correspond to the desired cross-section ofthe extrusion. The billet is then pushed through the die orifice in order to produce the extrusion. In order to produce tubing, the billet is provided with a bore in which a mandrel can be disposed. The mandrel is shaped and dimensioned to fit through the die orifice, so that, when the billet is extruded, the mandrel will create a properly shaped bore within the material.

The extrusion of metals, such as copper, has previously been carried out in large multi-stage processes. The billet of material to be extruded would typically have an initial outer diameter of about 5" to 13" (127 mm to 330 mm). The billet would be extruded into. a shell, and would then be drawn several times until it had the desired size and shape. During each drawing operation the extrusion would become longer and thinner. This conventional process has many problems. The length of the extrusion becomes so long that the extrusion has to be carried out horizontally (so that the extrusion can fit within the factory): the effect of gravity on the extrusion makes it difficult to obtain the correct alignment. Moreover, it is usually necessary to anneal the extrusion several times during the process, in order to counteract work hardening induced by the drawing steps.

I have now found a way to solve these problems which involves extruding a relatively small billet, then coextruding the extrusion with another relatively small billet to form a single, integral co-extruded product. This coextrusion can be repeated as many times as necessary in order to provide an extrusion of a desired length. This invention solves the problems in the prior art, because: (1) it is no longer necessary to draw very long extrusions, so the extrusion can be carried out vertically; and (2) the extruded product does not need to be subjected to multiple drawing steps, so it is not necessary to carry out any annealing steps.

I have also made a number of other improvements to extrusion apparatus in order to improve the efficiency ofthe extrusion process.

An extrusion apparatus according to the invention generally comprises: a die assembly including a die having an orifice of a desired shape; and a ram for forcing a portion of material to be extruded through the die orifice to form an extrusion, said ram being movable relative to the die between an extrusion position in which the ram can force the material to be extruded through the die orifice, and a retracted position in which a further portion of material to be extruded can be placed in said die assembly.

The portion of material to be extruded is typically a metal. The apparatus can be used to extrude ferrous and non-ferrous metals. The apparatus is particularly useful for extruding copper. The metal to be extruded may have been produced by a conventional continuous casting process. The portion of material to be extruded is known in the art as a "billet". The portion is typically 50 to 150 mm in length, with an outside diameter of 40 to 80 mm and an inside diameter of 10 to 25 mm - ultimately the size of the portion will depend upon the size ofthe extrusion apparatus. The portion is usually heated prior to being extruded. In accordance with a first preferred embodiment of the extrusion apparatus, I provide means for retracting the extrusion through the die when, or after, the ram moves to the retracted position, so that the further portion of material to be extruded can be located in die die assembly with the extrusion extending through a bore provided in said further portion of material. This embodiment enables a single continuous extrusion to be made from a plurality of separate portions of material to be extruded.

Advantageously, the retraction means comprises means for retaining on the ram part of the material to be extruded, whereby die extrusion can be at least partially retracted when the ram moves to the retracted position.

Preferably the retaining means comprises a retaining recess provided in me ram. It is also preferable that the depth of the retaining recess in the ram increases in a direction away from the die orifice. During extrusion, part of the material being extruded can flow into the retaining recess, and diis serves to retain the extrusion on the ram. More than one retaining recess may be provided: most preferably mere are two or three retaining recesses, and the recesses are equispaced around the ram.

Means can be provided to place the further portion of the material to be extruded within the die assembly; this means may be a conventional "pick and place" apparatus.

Means may be provided to control the temperature of the die assembly. The temperature control means may comprise a heating means for heating the die assembly, and a cooling means for cooling the die assembly - the cooling is needed to remove surplus heat during me extrusion.

After the ram has forced the portion of material through the die orifice to form the extrusion, there is always a residual amount of material that has not been extruded (this is known in the art as the "butt end"); part of this unextruded material will be in the recess on the ram. It is desirable to remove this unextruded material from the extrusion.

The ram provides a surface that can press against the portion of material to be extruded in order to force said material through the die oπfice. Preferably the ram comprises a ram support, and a ram body secured to the ram support; the ram body preferably includes a pressurising portion, and a mandrel extending from the pressurising portion.

The ram support is adapted to be secured to a support means for the ram (which is discussed below). In the preferred arrangement a ram retaining member is fixedly secured to d e support means, the ram retaining member serving to retaining the ram support on the support means. Preferably the ram retaining member defines at least one recess between the retaining member and the support means, and the ram support has a projection adapted to be received witiiin the or each recess, whereby the ram support is retained on the support means. The ram retaining member may be ring shaped, and may define a circular recess; the projection on the ram support may comprise a circular projection extending around the periphery of the ram support.

Although it would be possible for the ram body to be integral with the ram support, it is preferred that the ram body is removably secured to the ram support, whereby said support serves to hold the ram body in position, whilst allowing it to be removed, and replaced with another ram body, when desired. It is desirable that the ram body can be quickly removed from, and or secured to, the ram support, a ball lock is suitable for this purpose

Preferably the ram mcludes a longitudinal bore extendmg along part of its length, through which a coolant, such as coolmg water, can flow, this particular arrangement is conventional

The mandrel of the ram body is dimensioned to fit within the oπfice of the die, and withm the bore of the portion of matenal to be extruded The pressunsing portion has a cross-section larger than the die oπfice, and is adapted to press on the portion of matenal m order to force it through the oπfice of the die This arrangement results in the formation of a tubular extrusion, havmg a cross-section dictated by the shape of the oπfice and the shape of the mandrel Usually the tubing would be circular The thickness of the tubing depends on the difference in size between the mandrel and the die oπfice

The extrusion apparatus mav be used to produce a solid extrusion, in which case, it is not necessary to provide the mandrel on the pressunsing portion ofthe ram

It is especially preferred to provide an expansion device to expand a part ofthe extrusion mto contact with the further portion of matenal to be extruded The purpose of the expansion device is to assist with the formation of an integral connection between the extrusion and the further portion The expansion device is preferably secured to the support means to which the ram is secured An important reason for caπying out this expansion is so that the mandrel can freely enter the expanded extrusion, and therefore will not push it through the die onfice duπng extrusion

It is prefened that the expansion device compπses an inner member and an expandable outer member, wherem the inner member is slidably disposed within a longitudmally extendmg bore of the outer member An outer surface of the inner member is preferably provided with at least one formation that mterengages at least one formation on an inner surface of the outer member, the thickness of said formaϋons mcreases longitudmally of said members, with the thickness of the formation on the inner member increasing in a direction opposite to the thickness of the formation on the outer member The arrangement is such that as the inner and outer members slide relaϋvely m one direction, the mterengagement of the formaUons, together with the increase m thickness of the formations, causes the outer member to expand radially When the inner and outer members slide relaUvely in an opposite direction, the outer member can contract radially - this contraction is preferably assisted by the provision of biasmg means adapted to bias the outer member to the radially contracted position Stop means may be provided to limit sliding movement in said opposite direc on The biasmg means may compπse a spπng, such as a leaf spπng and/ or a tension spπng

The outer member may be divided longitudinally mto at least two, and preferably three, segments, whereby the segments can separate as the outer member expands radially

The expansion device is capable of expanding the extrusion so that it bites mto the further portion of matenal to be extruded

The expansion device need not be used only m the first prefened embodiment of the extrusion apparatus it can be used m any situation where there are two coaxial tubes, and it is desirable to expand the inner tube mto engagement with the outer tube In accordance wi a second prefened embodiment of the extrusion apparatus, I provide means for retaining on the ram part of the material to be extruded, whereby the extrusion can be at least partially retracted when the ram moves to the retracted position, and cutting means for cutting the extrusion in order to separate the unextruded portion from the extrusion. T e cutting means is preferably movable between a retracted position, in which it is clear of the extrusion, and a cutting position, in which it can cut the extrusion. The cutting means may be pivotally movable between the retracted and the cutting positions. It is desirable that the movement of the cutting means takes place in a direction substantially perpendicular to the longitudinal axis ofthe extrusion.

In an alternative, the cutting means may be adapted only partially to cut the extrusion. In this embodiment, the cutting means is ananged to grip and partly cut the extrusion, so that the extrusion can be completely severed from the unextruded material by the further movement of the ram to the retracted position, while the cutting means continues to grip the extrusion. This form of cutting means preferably comprises at least two severing jaws that grip and sever the extrusion at equispaced positions around the extrusion.

In order to facilitate cutting of the unextruded portion from the extrusion, the ram may be adapted . to be retracted to a partially retracted position, where the extrusion can be cut, before being retracted to the fully retracted position.

After the unextruded portion has been separated from the extruded portion it is desirable to remove the unextruded portion from the ram. For this purpose, I provide stripping means to strip the unextruded material from the ram, after the unextruded material has been severed from the extrusion. The stripping means preferably comprises gripping means for gripping the unextruded material, whereby the unextruded material is stripped from the ram as the ram is retracted from the stripping means.

The gripping means preferably comprises at least two gripping members, which are movable into and out of engagement with the unextruded portion in order to grip d e unextruded portion, whereby the unextruded portion can be removed from d e ram by moving the ram. along its longitudinal axis, relative to the gripping members. The gripping members may be either radially or pivotally movable into and out of engagement with the unextruded portion, and may be equispaced about the ram.

In a preferred construction, each gripping member comprises a claw that is pivotally movable into and out of engagement with the unextruded portion. The direction of pivotal movement into engagement with the unextruded portion is preferably opposite to the direction of retraction ofthe ram.

In another construction, each gripping member comprises a toothed wheel that is rotatable in a direction opposite to the direction of retraction of the ram. The ram can be retracted, and at the same time the wheels can be driven in their direction of rotation, whereby the unextruded portion is removed from the ram.

Means can be provided to move the ram relatively from a position in alignment with the die assembly to a position in alignment with the stripping means.

If the die assembly and the ram are slightly out of alignment, then the extrusion will not be formed properly, and die extrusion apparatus may be damaged. In order to avoid this problem, and in accordance with a third prefened embodiment of me extrusion apparatus, I provide alignment means for aligning the ram with the die assembly. Preferably the alignment means comprises cooperating formations on the ram and die assembly, that interlock when the ram is moved relatively towards the die assembly. The cooperating formations are ananged so mat, when they interlock, conect alignment of the ram and die assembly is assured.

Advantageously, the ram and the die assembly are movable relatively in a direction radial to me direction of extrusion, whereby, as the cooperating formations on the die assembly and die ram come into engagement, the radial position of the die assembly can adjust relative to the ram in order to enable the cooperating formations to interlock.

There are many ways to implement the alignment means according to the invention. For example, the cooperating formations may comprise a recess in the ram and a projection on the die assembly, or vice versa. Preferably the recess is a frustro-conical recess, and the projection is a frustro-conical projection; most preferably the recess is provided in the ram support, and the projection is provided on the die assembly. One way to achieve the relative radial movement is to mount the die assembly and/or the ram to the rest of the apparatus using a mounting that holds the die assembly and or ram in position, but which has a slight clearance between the mounting and the die assembly and/or ram in order to allow a small amount of radial movement. One way to achieve mis is to provide a clearance between the ram retaining member and the ram support. In practice, a small clearance of about 0.5 to 1.0 mm is sufficient.

In accordance with a fourth prefened embodiment of the extrusion apparatus, I provide at least two of said rams and a support means for supporting each ram, wherein the support means is movable between a plurality of extrusion positions, each extrusion position conesponding to a position in which die longitudinal axis of one of the rams is aligned with the die aperture. Thus, if two rams are provided, men there will be two extrusion positions. If three rams are provided, men there will be three extrusion positions. It is preferred to provide three rams when the extrusion apparatus is being used to coextrude the extrusion with a further portion of material to be extruded. However, if the apparatus is being used to extrude individual portions of material (ie, without any subsequent coextrusion), then it is prefened to provide six rams.

The support means is preferably rotatably movable between the extrusion positions, and preferably the axis of rotation is at the centre of the support means; the rams are preferably equispaced around said axis of rotation. The support means is conveniently in the form of a disc-shaped member.

When the fourth prefened embodiment of the extrusion apparatus is being used in conjunction with the expansion device (which was discussed above in relation to the first preferred embodiment of me extrusion apparatus), it is highly desirable that one expansion device is placed between each ram, and that the support means is also movable between a plurality of expansion positions in which the longitudinal axis of one of the expansion devices is aligned with the die orifice. Thus, if two expansion devices are provided, then there will be two expansion positions. If three expansion devices are provided - which is prefened - then there will be three expansion positions. The expansion devices are preferably equispaced about die axis of the support means. Generally, the number of rams and expansion devices will be equal.

This arrangement allows for die sequential use of a number ofdifferent rams and expansion devices. Accordingly, the down-time of me apparatus is reduced, because two or three rams will last at least two or three times as long as one individual ram, so it is not necessary to stop the apparatus to replace the rams so often. Moreover, the use of more than one ram gives each ram the chance to cool before its next extrusion operation, which can extend d e lifetime of the ram.

In accordance wiύi a fifth prefened embodiment of the extrusion apparatus, I provide die replacement means for removing the die from the die assembly and replacing the removed die with anotiier die.

Advantageously die die replacement means comprises a die carrier for caπying at least two of said dies, said carrier is movable between a plurality of positions, and in each position one of the dies is aligned in with the die assembly in such a way that it can be inserted into die die assembly, and subsequently removed from the die assembl Advantageously the die carrier is rotatable about an axis, and the dies are preferably substantially equispaced about said axis. Witii this arrangement, each die is re-used after a complete rotation of the die earner The die carrier may carry, for example 2 to 20 dies; preferably the carrier carries 8 to 16 dies. In the prefened construction, the carrier carries 12 dies. The dies on die die carrier can be removed and replaced with new dies, when necessary. Normally each die would be used for over 100 extrusion operations before being replaced.

When die extrusion apparatus is being used to produce a continuous length of extrusion from two or more portions of material to be extruded, then the die replacement means would normally remove and replace the die after several extrusion operations, when the final length of extrusion has been formed.

On the other hand, when die extrusion apparatus is being used to produce a single extrusion from a single portion of material to be extruded, then the die replacement means would normally remove and replace the die after each single extrusion operation.

Preferably die gripping means is provided to insert the die aligned witii the die assembly into die die assembly, and subsequently to remove said die from the die assembly. It is preferred diat a separate die gripping means is provided for each die, so that each die is carried on die die carrier by its respective gripping means.

Means may be provided to move die die gripping means towards and away from d e die assembly: the entire carrier may be movable, or the individual gripping members may be movable.

The or each gripping means preferably comprises a pair of gripping members that are adapted to grip one ofthe dies therebetween. The gripping members may be pivotable between a gripping position, in which they grip and hold the die, and a release position, in which they do not grip or hold the die. Means can be provided to open and close the gripping members in order to release or grip the die.

The gripping means is movable between a retracted position in which it is clear ofthe die assembly, and an extended position in which it is within the die assembly. When a die is being inserted into the die assembly the gπppmg means gπps the die until the die is m position within the die assembly, whereupon the gπppmg means releases the die and moves to the retracted position When a die is bemg removed from the die assembly the gπppmg means moves to the extended position, then gπps the die. tiien moves back to the retracted position while gπppmg the die

It is prefened that the gπpping means mcludes a die pushing member that is adapted to bear against the die m order to push the die away from the gπppmg means The force with which the die pushing member pushes the die is less than the force with which the die is gnpped by the gπppmg means, so the die pushing member does not push the die out of die gnpping means when it is being gnpped by the gπpping means The die pushing member ensures that the die is held m the die assembly after die gnpping means has released the die within the die assembly and is moving to the retracted position

It is especially prefened that the die is removed and replaced along an axis that is at an angle to the axis of extrusion, this angle is most preferably substantially perpendicular to the axis of extrusion This arrangement differs from conventional arrangements, in which the die is removed and replaced via the top of the die assembly An aperture can be provided in the die assembly to facilitate removal and replacement

Each of the prefened embodiments of die extrusion apparatus descπbed above provides a distinct advantage for an extrusion apparatus It is prefened to use all these prefened embodiments of the extrusion apparatus, because that provides die most advantageous extrusion apparatus However, it will be appreciated that any combination of these prefened embodiments may be used, dependmg upon the particular extrusion apparatus required

Accordmg to another aspect of the present mvention, I provide a method of extrusion compπsmg extruding a first portion of matenal through a first die havmg an oπfice of a desired shape to form a first extrusion, coextrudmg a second portion of matenal witii a part of said first extrusion either through the first die. or through a second die havmg an oπfice of desired shape, to form a second extrusion compπsmg said first and second portions of matenal

This process may be repeated with third, fourth, fifth, etc , portions of matenal to form a final extrusion of a desired length It is particularly prefened that the extrusion is m the form of a tube, the cross- sectional shape ofthe tube would typically be circular, but it may be of any desired shape

Whilst it is possible to use a different die for each extrusion step, and it is even possible for the dies to have oπfices ofdifferent shape, it is prefened that the first die is used for all d e extrusion steps

Each portion of matenal to be extruded is desirably provided witii a bore therethrough In addition, the die oπfice is preferably smaller than the bore m each portion of matenal to be extruded - this causes the outer diameter of each extrusion to be smaller than the diameter of said bore, so that the extrusion can be placed mside the bore of the portion of matenal with which it is to be coextruded Advantageously, each extrusion is at least partly expanded mto contact with the portion of matenal with which it is to be coextruded, before the coextrusion is earned out

Each newly formed extrusion is advantageously partially retracted through the die, before a further portion of material to be extruded is placed in the die assembly. The extrusion may be retracted on the ram, and may be severed from an unextruded part of die material on the ram. The unextruded part of material may be stripped from the ram.

The temperature of the die assembly may be controlled by a combination of heating means and cooling means. The heating means may be used to ensure that the die assembly is at the conect temperature before extrusion; and the cooling means may be used to cool the die assembly during extrusion.

The method and apparatus according to d e invention permits a coextrusion to be foπned that has a homogeneous microstructure, ie. the coextrusion does not have any joins, even though it is formed from several different portions of material.

The method and apparatus of the present invention allows an extrusion to be formed widiin about 7 seconds, which is much quicker than is possible with prior art techniques.

Reference is now made to the accompanying drawings, in which:

Fig. 1 is a side elevation of one embodiment of extrusion apparatus according to the invention;

Fig. 2 is a side elevation of part of a ram for use in the extrusion apparatus shown in Fig. 1 ;

Fig. 3 is a cross-sectional view of the part of the ram shown in Fig. 2, with an extrusion attached thereto;

Fig. 4 is a cross-sectional view of part of an embodiment of extrusion apparatus, showing an embodiment of a cutting means for removing an unextruded portion from an extrusion;

Fig. 5 is a side elevation of an extrusion formed by the extrusion apparatus of Fig. 4, showing longitudinal indents formed by the cutting means;

Fig. 6 is a plan view ofthe extrusion shown in Fig. 5;

Fig. 7 is a cross-sectional view of an embodiment of stripping means according to d e invention;

Fig. 8 is a plan view ofthe stripping means shown in Fig. 7;

Fig. 9 is a cross-sectional view showing an embodiment of expansion means according to the invention;

Fig. 10 is an end view of a second embodiment of extrusion apparatus according to the invention;

Fig. 11 is a side view of die extrusion apparatus shown in Fig. 10;

Fig. 12 is a plan view ofthe extrusion apparatus shown in Fig. 10;

Fig. 13 is a side view of part of die extrusion apparatus shown in Fig. 10, on an enlarged scale, just before an extrusion operation begins;

Fig. 14 is a view similar to Fig. 13, just after extrusion has been completed;

Figs. 15 A, 15B and 15C are side, end and plan views, on an enlarged scale, of a ram body of the extrusion apparatus shown in Fig 10;

Figs 16A and 16B are side and plan views, on an enlarged scale and partly in section, of part of a die assembly ofthe extrusion apparatus shown in Fig. 10;

Fig. 17A is a plan view, on an enlarged scale, of part of a die replacement means for use in the extrusion apparatus shown in Fig. 10, showing a die gripping means in a gripping position; Fig. 17B is a plan view similar to Fig 17A, showing the die gripping means in a release position;

Fig. 17C is a view along lines C-C of Fig. 17B;

Fig. 18 is a side view of expansion means for the extrusion apparatus shown in Fig. 10;

Figs. 19A is a side view of an outer expandable member of tiie expansion means shown in Fig 18;

Fig. 19B is a plan view ofthe outer member shown in Fig. 19A

Fig. 20 is a side view of an inner member ofthe expansion means shown in Fig. 18;

Figs. 21 A, 2 IB and 2 IC are side, end and plan views of a stripping means for use with the extrusion apparatus shown in Fig. 10; and

Figs. 22A and 22B are side and end views of a machine for housing the extrusion apparatus shown in Fig. 10.

Referring to Figs. 1 to 9, and particularly to Fig. 1, an extrusion apparatus generally designated 10 comprises three rams 12, each of which is capable of being brought into alignment with a die assembly 16. In Fig. 1 only one ram 12 is visible.

Each ram 12 is of circular cross section, and comprises a ram support 20 and a ram body 13; die ram 12 is shown in greater detail in Figs. 2 and 3. The ram body 13 comprises a mandrel 18 and a pressurising portion 40. The pressurising portion 40 has a generally frustro-conical surface 52 that is adapted to press against a portion of a material to be extruded.

An upper cylindrical portion 42 ofthe ram body 13 is provided with means for retaining an extrusion 48 on die ram 12, which is in the form of three recesses 36 that are equispaced about the ram body 13. The ram body 13 includes a locating projection 50, which extends axially upwardly into a cooperating recess 54 provided in die ram support 20. The ram support 20 is provided with a recess 80 that is capable of receiving a projection 82 on the die assembly 16.

The ram support 20 of each ram 12 is secured to support means in the form of a disc-shaped member 26. The member 26 is rotatable about an axis 27, and the rams 12 are equispaced about said axis 27, whereby rotation of the member 26 can bring a selected one of d e rams 12 into alignment witii the die assembly 16.

The support member 26 is indexed by a motor 30, which has a drive pinion 28 that meshes with gear teeth 78 on the periphery of the support member 26.

The die assembly 16 comprises a die housing 32, which is slidably movable within a die housing sleeve 86; the die housing 32 is provided with a central axial bore 33. A die 34 is mounted to a die support 84 within the housing 32 and sleeve 86; the die 34 is provided with a die orifice 35. As mentioned above, the die housing 32 is provided with a projection 82 that can be received within the recess 80.

Figs. 4, 5 and 6 illustrate cutting means in the form of three shears 58, which are provided to remove the extrusion 48 from the ram body 13. The shears 58 have circumferential V-shaped indent teeth 60 and longitudinal V-shaped indent teeth 62 that are pushed radially into the extrusion, just below a butt end 46 - the butt end 46 comprises an unextruded part of the material being extruded. The shears 58 are operated by cams or cylinders (not shown), and the indent teeth 60 and 62 penetrate the extrusion 48 to approximately 80% to 90% of the extrusion wall thickness. The circumferential indent teeth 60 each span the circumferential distance between die longitudinal indent teeth 62 and hold the extrusion 46 against further movement in a direction away from die die 34.

Figs. 7 and 8 illustrate stnpping means for stripping the butt end 46 from the ram body 13. The stripping means comprises a stnpping device 202 having a housing 204 in which a generally cylindrical, vertical through-bore 206 is formed. The bore 206 has a diameter slightly larger than the combined diameter of the cylindrical portion 42 of the ram body 13 and the butt end 46. The housing 204 houses four toothed ratchet wheels 208, which are each disposed in a recess 210 of the housing 204; each wheel 208 is rotatable about a substantially horizontal axis The toothed peripheries of the wheels 208 project into the bore 206 at positions equispaced about the ram body 13. The ratchet wheels 208 are rotatable in the direction shown in Fig. 7 (which direction is opposite to the upward direction in which the ram body 13 is retracted from the housing 204); this facilitates easy entry ofthe ram body 13 into the bore 206, but resists retraction ofthe ram body 13.

Fig. 9 shows an expansion device 14 for expanding the extrusion 48. Three expansion devices 14 are provided, each ofwhich is secured to die support member 26 via an expansion support 21. The expansion devices 14 are equispaced about the axis 27. In Fig. l only two expansion devices 14 are shown. Each expansion device 14 compnses an expansion mandrel 72, having a lower tapered portion 24, which is slidable within a spring-loaded sleeve 74. A projection 73 on die mandrel 72 provides a stop surface that limits movement of the mandrel 72 within the sleeve 74. A lower tip of the tapered portion 24 has a cross- sectional area that is smaller than die cross-sectional area of the extrusion 48, while an upper end of the tapered portion 24 has a cross-sectional area tiiat is greater than the cross-sectional area of the extrusion 46. Thus, the extrusion 46 can be expanded by forcing the mandrel 72 into the extrusion 46.

The operation ofthe extrusion apparatus shown in Figs. 1 to 9 will now be described.

A billet 76 to be extruded is first placed widiin the bore 33, on top of the die 34. The billet 76 is made of the material to be extruded (such as copper) and is typically cylinder with a central bore, and has a length of 106.7 mm, an inside diameter of 17.4 mm and an outside diameter of 58 mm. The billet 76 may be placed within the bore 33 by a conventional "pick and place" apparatus, which is known to those skilled in the art. The pick and place apparatus takes the billet 76 from a furnace (not shown); for copper the temperature ofthe billet 76 in the fumace would usually be between about 780°C and 940°C.

When the billet 76 is in place, one of the rams 12 is oriented in alignment with the longitudinal axis of the die assembly 16 (assuming that it has not already been oriented in alignment). The ram 12 is then lowered relative to the die assembly 16; this can be canied out by lowering the support plate 26. The recess 80 will receive the formation 82 therein: the internal surface of the recess 80 conesponds exactly to the external surface of the formation 82, so that when the formation 82 is received within the recess 80, the correct alignment ofthe ram 12 and the die assembly 16 is assured. The ram 12 and the die assembly 16 are movable relative to one another in a radial direction, in order to allow the conect alignment to be achieved.

After the ram 12 and the die assembly 16 have been aligned, the ram 12 applies a downward force on the die housing 32, which causes the die housing 32 to slide downwardly relative to the die housing sleeve 86 and die die 34. The mandrel 18 of the ram body 13 passes through the central bore of the billet 76, and through the die orifice 35, until tiie surface 52 of the pressurising portion 40 of the ram body 13 comes into contact with the upper surface of the billet 76. A high pressure is applied on the top surface of the billet 76 by the surface 52; this pressure may be of the order of 300 tonnes. The application of the pressure on the billet 76 causes it to be extruded dirough die die orifice 35 to produce an extrusion 48. The presence of the mandrel 18 witiiin the die orifice 35 causes the extrusion 48 to be in the form of a tube. The thickness of the extrusion 48 depends upon die difference between die size of die orifice 35 and die size of the outer surface ofthe mandrel 18.

After the ram 12 has completed its downward stroke, die majoπty of tiie billet 76 will have been extraded through the die orifice 35 to form the extrusion 48 Part of the billet 76 will be unextruded - this is called the butt end, and is designated 46 in Fig. 3. As shown in Figs 3 and 7. part of the butt end 46 has flowed into the retaining apertures 36 in the ram body 13 This serves to secure the butt end 46 to die ram body 13.

After the extrusion is complete, d e ram 12 is retracted to a partially retracted position, as shown in Fig. 4. At this time the shears 58 are activated, and move radially to gnp and cut tiie extrusion 48, below the butt end 46. Figs. 5 and 6 show die way in which the extrusion is severed The ram 12 is moved to its fully retracted position (shown in Fig. 1), while die shears 58 maintain a gnp on die extrusion 48 This causes the part of the extrusion above the shears 58, together with the butt end 46. to be separated from die part of the extrusion below the shears 58. After die ram 12 has been moved to its fully retracted position, d e shears 58 are retracted; die extrusion 48 is remains in position by virtue of the frictional force between die outside surface ofthe extrusion 48 and the periphery ofthe die orifice 35

At this time the support member 26 is rotated by 60° to bnng me ram 12 that cames the butt end 46 into alignment with die stnpping device 202. and to bnng one of die expansion devices 14 into alignment with the die assembly 16. The support member 26 is tiien moved downwardly relative to die die assembly 16 and relative to die stripping device 202. This allows d e mandrel 24 of die expansion device 14 to enter the bore of the extrusion 46, and enables die ram 12 carrying die butt end 46 simultaneously to enter die bore 206 ofthe stripping device 202.

Before the expansion device 14 is moved towards die die assembly 16, a fresh billet 76 is placed in tiie die housmg bore 33.

As the ram 12 caπying the butt end 46 enters the bore 206, the four wheels 208 are moved radially into engagement with the but end 46. Since die wheels 208 can rotate in a direction that is die same as the direction in which the butt end 46 enters die bore 206, die wheels 208 allow continued movement of die butt end 46 downwardly in the bore 206. The ram 12 is subsequently moved upwardly to the fully retracted position - during this movement the wheels 208 grip the butt end 46 and strip it from die ram body 13.

As the lower tapered portion 24 of the expansion mandrel 72 enters the bore ofthe extrusion 48, the sleeve 74 also moves downwardly until it abuts the upper surface of the billet 76. The main part of the mandrel 72 has a cross sectional area greater than the cross-sectional area of the bore ofthe extrusion 48, so that the extrusion 48 is expanded into contact with the billet 76. The downward movement of die mandrel 72 continues until tiie projection 73 engages the lower end of the sleeve 74. The mandrel 72 is then pulled upwardly relative to the die assembly 16 to remove die mandrel 74 from the bore of the extrusion 48. Initially, the sleeve 74 is held in place to prevent the extrusion 48 or the billet 76 from being drawn upwardly with the mandrel 72. When the projection 73 of the mandrel engages die upper end of die sleeve 74, the sleeve 74 will be drawn upwardly witii the mandrel 72. The expansion device is then moved to the fully retracted position shown in Figure 1.

The support member 26 is then rotated through 60° to bring the next ram 12 into alignment with the die assembly 16. At this point one entire cycle has been completed, and d e ram 12 is moved downwardly relative to the die assembly 16 in order to coextrude die upper end of die extrusion 48 with the fresh billet 76.

Referring to Figs. 10 to 22 a second embodiment of extrusion apparatus is generally designated 300; die extrusion apparatus 300 is prefened to die extrusion apparatus 10.

Referring particularly to Figs. 10 to 12, the extrusion apparatus 300 comprises a base plate 302, to which a die assembly 304 is secured. The apparatus 300 includes tiiree guide pillars 306; each guide pillar 306 is slidable in a guide bush 308; die guide bushes 308 are secured to the base plate 302. Support means for a plurality of rams 310 is provided in die form of a support member 312. Three rams 310 are secured to the support member 312. aldiough only one is shown in Figs. 10 to 12. The support member 312 is rotatable about a central axis 314, and d e tiiree rams 310 are equispaced about the axis 314. Rotation means 316 is provided to rotate the support member 312 about the axis 314; the rotation means 316 may comprise a conventional motor linked to die support member 312 via a conventional drive arrangement. The rotation means 316 is arranged to rotate the support member 312 in an indexed fashion, ie, through a predetermined angle of rotation. In an embodiment having three ofthe rams 310, this predetermined angle of rotation is 60°.

The die assembly 304 and die ram 310 are shown in greater detail in Figs. 13, 14 and 15. The ram 310 comprises a ram body 318 and a ram support 320. The ram support 320 is retained on die support member 312 by means of a ram retaining ring 322, which is fixedly secured to die support member 312. The ram retaining ring 322 has in inwardly extending circular projection 324, tiiereby defining a recess 326 between the projection 324 and die lower surface of the support member 312. The ram support 320 is provided witii a cylindrical projection 328, which extends into the recess 326; the projection 324 retains the projection 328 within the recess 326. The recess 326 is larger than the projection 328, so that there is a slight gap 330 between the projection 328 and the part ofthe retaining ring 322 above the projection 324. The gap 330 (the size of which is greatly exaggerated in Figs. 13, 14 and 15) allows die ram 310 to move radially relatively to a longitudinal axis 332 of the ram 310. A recess 321 is provided in a lower surface of the ram support 320; the purpose ofthe recess 321 is described below.

The ram body 318 is shown in greater detail in Figs. 15A, 15B and 15C, and comprises a pressurising portion 334, a mandrel 336 extending downwardly from the pressurising portion 334, and a projection 338 extending upwardly from the pressurising portion 334. The purpose ofthe projection 338 is to allow the ram body 318 to be removably secured to the ram support 322 by means of a ball lock 340 (see Fig. 11). The pressurising portion 334 is provided widi a curved pressurising surface 342, which serves to press on a billet 344 of a material to be extruded - for clarity the billet 344 is only shown in Fig. 18.

The pressurising portion 334 is provided witii extrusion retaining means in the form of two recesses 346; the depth of the recesses 346 increases in a direction away from the mandrel 336. The purpose of the recesses 346 is to retain the extrusion (which is shown in Figure 18, and is designated 345) on the ram body 318 after an extrusion operation, in a similar manner to the anangement shown in Fig. 4.

A longitudinal bore 347 is provided widiin the ram 310; the bore 310 carries cooling water into the mandrel using a conventional cooling system.

Cutting means 456 is provided to cut the extrusion below the mandrel 336. The cutting means 456 is shown in Fig. 12, and comprises a cutting arm 458 that is mounted to rotate about the axis 378, and which carries a rotary cutting blade 460. The arm 458 is pivotable between a retracted position in which the cutting blade is away from the ram 310, and a cutting position in which the blade can cut die extrusion 345 below die mandrel 336.

The die assembly 304 comprises a die housing 348, a die housing sleeve 354, within which die die housing 348 is slidable, a die support 350, and a die 352 on die die support 350. The die housing 348 is slidable witiiin the die housing sleeve 354 along three return rods 356. The return rods 356 are biased upwardly in order to bias d e die housing 348 upwardly relative to die die housing sleeve 354. The lower end of the die housing 348 is provided witii a peripheral lip 500, which engages the underside of a ring 502 that is fixed to die top of die die housing sleeve 354. The lip 500 and die ring 502 prevent the return rods 356 from pushing the die housing 348 out of the top of the die housing sleeve 354. The die housing is provided with a central, axially extending bore 362, within which the billet 344 to be extruded can be received. The die housing sleeve 354 is provided with an aperture 358 through which the die 352 can be moved to and from the die support 350. The direction of movement of the die 352 is peφendicular to a longitudinal axis 360 of the die assembly 304 - the longitudinal axis 360 of die die assembly 304 is collinear with the longitudinal axis 332 of the ram 310, when the ram 310 is aligned above the die assembly 304 for extrusion.

The die housing 348 is provided with heating means (not shown) to heat the die housing 348 to a desired temperature. A cooling jacket 504 containing cooling water is provided to cool the die housing 348. The puφose ofthe cooling jacket 504 is to remove heat during d e extrusion operation.

A formation 349 is provided on an upper surface of die die housing 348. The recess 321 and die formation 349 act as cooperating formations that ensure that the ram 310 is properly aligned witii the die assembly 304. The gap 330 between the retaining ring 322 and the ram support 320 allows the ram support 320 to move radially so that the formation 349 can be interlockingly received in the recess 321.

The die support 350 and the die 354 are shown in greater detail in Figs. 16A and 16B. The die 352 is provided with a central die orifice 364; the cross-section of the die orifice 362 conesponds to the desired external shape of the extrusion to be foπned. The die support 350 is provided with a longitudinal bore 364, which is aligned with the die orifice 362. The die 352 sits on an upper surface 366 of the die support 350. The die 352 is provided wid a peripheral recess 368 which receives a projection 370 on the die support 350. The recess 368 and the projection 370 ensure that the die 352 is locked against longitudinal movement relative to the die support 350. An outer surface 372 of the die 352 is cylindrical and is a close sliding fit within the bore 364 ofthe die housing 348, so tiiat radial movement of the die 352 is not possible during the extrusion operation. The surface 372 slides over the die 352 before extrusion begins, in order to prevent extrusion taking place between the die 352 and die die housing 348.

The extrusion apparatus 300 further comprises die replacement means 374 (see Fig. 12). The replacement means 374 comprises a die earner 376, which is rotatable about a central axis 378. A plurality of arms 380 extend radially from die central axis 378, and each arm 380 carries one of die dies 352. In the embodiment shown in the drawings the die replacement means can carry up to twelve ofthe dies 352.

Rotation means 382 is provided to rotate die die carrier 376 about die axis 378; the rotation means 382 may comprise a conventional motor linked to die die earner 376 via a conventional drive arrangement. The rotation means 382 is ananged to rotate die die carrier 376 in an indexed fashion, ie, dirough a predetermined angle of rotation In an embodiment having twelve of die dies 352. this predetermined angle ofrotation is 30°.

The rotation means 382 is mounted to a piston 384 and cylinder 386 arrangement, which serves to provide means to slide the die earner 376, in a direction towards or away from the die assembly 304, along an axis peφendicular to the axis 360 of die die assembly 304.

Each die 352 on die die earner 376 is held by a separate gripping means 388, which is shown in Figs. 17A, 17B and 17C. The gripping means 388 comprises a pair of gripping members 390, each of which has a recess 392 shaped to receive part of one of the dies 352. Each pair of gripping members 390 is pivotally mounted to one of die arms 380, so that they can pivot between a gripping position (shown in Fig. 17A), in which the one of the dies 352 is gnpped between die gripping members 390, and a release position (shown in Fig. 17B), in which the die 352 is released by die gripping members 390.

Operating means 394 is provided to move the gripping members 396 between the gripping and the release position. The operating means 394 comprises an operating member 396, which is biased by springs 398 towards an extended position (as shown in Fig. 17A). The operating member 396 has an enlarged end 400 having camming surfaces 404 that engage cooperating camming surfaces 402 provided on each gripping member 390. When the operating member 396 is in the extended position, the action ofthe camming surfaces 404 on the camming surface 402 causes the gripping members 390 to pivot towards the gripping position.

A die pushing member 406 extends from the end ofthe operating member 396 nearest to the die 352. The die pushing member 406 is slidably mounted within a housing 408 between a retracted and an extended position; the die pushing member 406 is biased towards the extended position by a spring 410. The arrangement is such that when die die 352 is gripped by die gripping members 396, the die pushing member 406 either does not push against the die 352, or pushes only widi a small force that is less than the force by which the gripping members 396 grip the die 352. When die gripping members 396 move to the release position, the die pushing member 406, applies a pressure on the die 352 to push the die 352 away from the gripping members 396. The piupose of this feature is explained below.

Figures 18 to 20 show an expansion device generally designated 412 disposed in position in the die assembly 304. Like the rams 310, the expansion device 412 is secured to d e lower surface of the support member 312. There are tliree expansion devices 412: they are arranged equispaced around die axis 314, between the rams 310. For clarity, the expansion devices 412 are not shown in Figs. 10 to 12.

The expansion device 412 comprises an inner member 414 that is disposed widiin, and slidable relative to, an expandable outer member 416. The expandable outer member 416 is divided longitudinally into three identical segments 418. which can move radially apart. The upper part of the inner and outer members 414 and 416 are housed witiiin an expansion device housing 420, which is fixedly secured to the support member 312.

The inner member 414 is resiliently mounted to the housmg 420 by three springs 422. The outer member 416 is mounted to the housing 420 by means of a cylindrical projection 424 at the upper end of the outer member 416, which projects into a conesponding recess 426 of the housing; a spring (not shown) can be provided in the recess 426 to bias the segments 418 of the outer member 416 towards die unexpanded position. In addition, a tension spring 427 is wrapped around the upper end of die outer member 416 to bias die segments 418 to the unexpanded position.

An outer surface of the inner member 414 is provided widi a plurality of formations 428, which interengage a plurality of formations 430 on an inner surface of die outer member 416; die diickness of the formations 428 and 430 increases longitudinally of die inner and outer members 414 and 416, widi the thickness of the formations 428 on the inner member 414 increasing in a direction opposite to the thickness ofthe formations 430 on the outer member 416. The arrangement is such that as the inner and outer members 414 and 416 slide relatively in one direction, the interengagement of the formations 428 and 430, together with die increase in thickness of d e formations 428 and 430, causes die segments 418 of die outer member 416 to expand radially outwards. When die inner and outer members 414 and 416 slide relatively in an opposite direction, die segments of the outer member 416 can move radially inwards - this contraction is assisted by the provision of the spring within the recess 426, and by d e spring 427. The lower end of die inner member 414 is provided widi a formation 436 that is shaped to hook around die lower end of the outer member 416; this helps to keep the segments 418 of the outer member 416 together, when the outer member 416 is in the radially contracted position. The formation 436 has a stop surface 432 that engages a stop surface 430 at the lower end of die outer member 416, in order to limit relative movement of the inner and outer members 414 and 416 in said opposite direction.

Figures 21 A, 2 IB and 21C illustrate a stripping device generally designated 438. The stripping device 438 is provided to strip an unextruded part of the billet 344 (ie, the "butt end") from the ram body 318 after an extrusion has been carried out. The stripping device 438 is provided on a die mounting plate 303 on the base 302, but it is not shown in Figs. 10 to 12, for clarity.

The stripping device 438 comprises a housing 440 within which two stripping claws 442 are pivotally mounted. The claws 442 are each slidably mounted on a separate rail 444. An activation member 446 is also slidably mounted on each rail 444. The activation member 446 can be slid upwardly on die rail 444 in order to pivot die claws 442 in a direction towards die ram body 318. When die activation member 446 slides downwardly, the claws 442 pivot away from the ram body 318 under the influence of gravity.

Figures 22A and 22B show a machine 448 for housing the extrusion apparatus 300. The machine 448 comprises a housing 450, within which the extrusion apparatus 300 is disposed - for clarity die extrusion apparatus is not actually shown in the housing 450. The housing 450 is provided widi a window 452, through which the operation ofthe extrusion apparatus can be monitored by an operator. A separate control box 454 is provided for controlling the operation of the extrusion apparatus 300. A hydraulic press 456 is provided, which is located above die apparatus 300, and applies d e pressure on the ram 310 needed for the extrusion operation.

The operation ofthe extrusion apparatus 300 will now be described.

A billet 344 to be extruded is first placed widiin die bore 362 on top of the die 352. The billet 344 is made of the material to be extruded (such as copper) and is typically a cylinder with a central bore, having a length of 106.7 mm, an inside diameter of 17.4 mm and an outside diameter of 58 mm. The billet 344 may be placed within the bore 362 by a conventional "pick and place" apparatus, which is known to those skilled in the art. The billet 344 would usually be heated prior to placing it in die bore 344 - tins assists the extrusion operation. The temperature of the die housing 348 would have been raised to a desired temperature by its heating means.

When the billet 344 is in place, one of the rams 310 is oriented in alignment with the longitudinal axis of the die assembly 304 (assuming that it has not already been oriented in alignment). The ram 310 is then lowered relative to the die assembly 304; this can be carried out by lowering the support plate 312. The recess 321 will receive the formation 349 therein: the internal surface of the recess 321 conesponds exactly to the external surface of the formation 349, so that when the formation 349 is received witiiin the recess 321, the correct alignment of the ram 310 and the die assembly 304 is assured. The ram 310 and die die assembly 304 are movable relative to one anotiier in a radial direction, in order to allow die conect alignment to be achieved.

After the ram 310 and die die assembly 304 have been aligned, just before extrusion begins, the relative positions of the ram 310 and the die assembly 304 are shown in Fig. 13. It will be noted tiiat the lower surface of the die housing 348 is a small distance (eg, 5 mm) below the upper surface ofthe die 352 - this prevents the extrusion of die billet 344 between the housing 348 and die die 352.

In order to begin extrusion, the support member 312 is forced downwardly by pressure from the hydraulic press 456. This causes the ram support 320 to apply a downward force on the die housing 348, which causes the die housing 348 to slide downwardly relative to the die housing sleeve 354 and the die 352. The mandrel 336 of the ram body 318 passes through the central bore of the billet 344, and through the die orifice 362, until the surface 342 ofthe pressurising portion 334 ofthe ram body 318 comes into contact witii the upper surface of the billet 344. A high pressure is applied on the top surface of the billet 344 by the surface 342; this pressure may be ofthe order of 300 tonnes. The application ofthe pressure on the billet 344 causes it to be extruded through the die orifice 362 to produce an extrusion 345. The presence ofthe mandrel 336 within the die orifice 362 causes the extrusion 345 to be in the form of a tube. The thickness of the extrusion 345 depends upon die difference between the size of the orifice 362 and the size of the outer surface ofthe mandrel 336.

After die ram 310 has completed its downward stroke, the majority of the billet 344 will have been extruded through the die orifice 362 to form the extrusion 345. Part ofthe billet 344 will be unextruded - this is called the butt end - it is not specifically shown in Figs. 10 to 22, but it is similar to the butt end designated 46 in Fig. 3. Part of die butt end flows into die retaining apertures 346 in the ram body 318. This serves to secure the butt end to the ram body 318.

After the extrusion is complete, the ram 334 retracted to a partially retracted position, which is not specifically shown. At this time the cutting arm 458 is swung towards the ram 310, so that the cutting blade 460 can cut the extrusion 345 below the butt end. It should be noted that the ram 310 must be retracted far enough that the lower end of d e mandrel 336 is clear of die cutting blade 460. After the extrusion 345 has been severed from the butt end, die arm 458 retracts, and die ram 310 is moved to its fully retracted position.

Next, the support member 312 is rotated by 60° to bring the ram 310 that carries the butt end into alignment with the stripping device 438, and to bring one of d e expansion devices 412 into alignment with the die assembly 304. At the same time the die replacement means may be activated to exchange die die 452.

The support member 312 is tiien moved downwardly relative to die die assembly 304 and relative to the stripping device 438. This allows the inner and outer members 414 and 416 of the expansion device 412 to enter the bore of the extrusion 345, and enables die ram 310 caπying the butt end simultaneously to enter the housing 440 ofthe stripping device 438.

Before the expansion device 412 is moved towards die die assembly 304, a fresh, heated, billet 344 is placed in the die housing bore 362, over the freshly cut end of die extrusion 345 diat has just been formed.

As the ram 12 carrying the butt end 46 enters the bore housing 440 ofthe stripping device 438, the activation member 446 is driven upwardly to pivot the claws 442 towards the butt end on the die body 310. When the claws 442 have gripped the butt end, the ram 310 is subsequently moved upwardly to the fully retracted position, whereby the butt end is stripped from the ram body 318.

When the expansion device 412 is lowered towards die die assembly 304, die outer member 316 is in the radially contracted position, and die formations 428 and 430 are in an interlocking relationship. When the lower surface ofthe housing 420 engages the die housing 348, the inner member 414 continues to move downwardly against the spring force in the spring 422. The relative sliding movement between the inner and outer members 414 and 416 causes the formations 428 and 430 to move apart, which forces the segments 418 to the radially expanded position. When in the radially expanded position, the outer member 416 has a cross sectional area greater than the cross-sectional area ofthe bore ofthe extrusion 345, so that the extrusion 344 is expanded into contact with the billet 344. After the expansion is complete, the expansion device 412 is then pulled upwardly relative to the die assembly 304 to remove the inner and outer members 414 and 416 from the bore ofthe extrusion 345. The biasing force ofthe spring 422 causes the inner member 414 to slide upwardly relative to the outer member 416 The mandrels are moved back to die radially contracted posiUon with the assistance of the spnng in the recess 426 The expansion device is then moved to its fully retracted position

The replacement of the die 352 takes place as follows First, die piston 384 and cylinder 386 are activated to slide the die earner 376 towards the die assembly 304 As this sliding movement takes place, a pair of the gnpping members 390 move through the aperture 358 in the die housmg sleeve 354, and gnp the die 352 within the die housing sleeve 354 The operatmg member 396 is moved to its retracted position shown m Figure 17A, so that d e camming surfaces 404 and 402 mteract to move the gπpping members 390 to the gripping position The piston 384 and cylinder 386 arrangement are then re-activated to slide the die earner 376 away from the die assembly 304, which causes the die 352 to be removed from the die support 350 through the aperture 358 in d e die housmg sleeve 354 Duπng this retraction the die pushing member 406 acts to push the die 352 out from between the gπppmg members 390, but the force applied on die die 352 by the gπppmg members 390 is large enough for them to be able to keep a gnp on the die 352

After the die earner 376 has been moved back to its retracted position, die rotation means 382 is activated to rotate the earner 376 by 30° This brings another pair of gπppmg members 390 , which carry another die 352, mto alignment with the aperture 358

The piston 384 and c\ linder 386 anangement is re-activated to move the earner 376 towards the die assembly 304, so tiiat the gnpping members 390, together with the die 352 tiiat they are gπppmg, move through the aperture 358 When die die 352 is in posiUon on the die support 350, die operatmg member is moved to its extended posiUon, as shown in Figure 17B, so that the camnung surfaces 404 and 402 mteract to prevent the gπpping members 390 from gπppmg the die 352.

The piston 384 and cylinder 386 anangement is again re-activated to move die die earner 376 to its retracted position Duπng this retraction, the gπppmg members 390 no longer gnp the die 352, and the die pushing member 406 pushes agamst the die to ensure that the die 352 remains in position on die die support 350 duπng retracϋon The die 352 and the die housmg 348 are provided with cooperating angled surfaces (not shown) that engage when the die housmg 348 moves downwardly relative to die die 352 - this helps to re-align the die 352 on die die support 350, m the event that the die 352 moves radially slightly out of position

The support member 312 is tiien rotated dirough 60° to bnng the next ram 310 mto alignment with the die assembly 304 At this pomt one entire cycle has been completed, and die ram 310 is moved downwardly relative to the die assembly 304 m order to coextrude the upper end of the extrusion 345 with the fresh billet 344

It will be appreciated tiiat modificauons may be made to die embodiments of extrusion apparatus descπbed above. For example, if the desired length of extrusion can be made from a smgle billet, then it is not necessary to coextrude the extrusion with further billets In these circumstances the expansion devices will not be necessary. Furthermore, it may not be desirable to provide the die earner when the extrusion apparatus is being used to coextrude an extrusion and a billet.

Claims

1 Extrusion apparatus compnsing a die assembly mcludmg a die havmg an onfice of a desired shape, a ram for forcmg a portion of matenal to be extruded through the die onfice to foπn an extrusion, said ram bemg movable relative to die die between an extrusion position in which the ram can force the matenal to be extruded through the die onfice, and a retracted position in which a further portion of matenal to be extraded can be placed m said die assembly, and means for partially retracting the extrusion through the die when, or after, the ram moves to the retracted position, so tiiat the further portion of matenal to be extraded can be located in the die assembly with die extrusion extendmg dirough a bore provided m said further portion of matenal

2 Extrusion apparatus according to claun 1, wherem die retraction means compnses means for retaining on the ram part of the matenal to be extraded, whereby die extrusion can be at least partially retracted when the ram moves to the retracted position

3 Extrusion apparatus according to claun 2, wherem die retaining means compπses a retaining recess provided m die ram, whereby, duπng extrusion, part of the matenal bemg extruded can flow mto die retaining recess to retam the extrusion on the ram

4 Extrusion apparatus accordmg to claim 3, wherem d e deptii of the retaining recess m the ram increases m a direction away from the die onfice

5 Extrusion apparatus accordmg to claim 2. 3 or 4, further compπsing cutting means for cutting the extrusion, after it has been at least partially retracted, m order to separate die extrusion from the part of the matenal to be extruded tiiat has been retamed on die ram

6 Extrusion apparatus accordmg to claim 5, wherem the cutting means is movable between a retracted position, in which it does not cut die extrusion, and a cutting position, m which it cuts the extrusion, the cutting means bemg pivotally movable between the retracted position and the cutting posiϋon along an axis that is substantially peφendicular to die directton of extrusion

7 Extrusion apparatus accordmg to any one of ciauns 2 to 6, further compnsing stnpping means to remove the part of the matenal retamed on the ram, and wherem the ram is movable from the die assembly and mto the stnpping means

8 Extrusion apparatus accordmg to claun 7, wherem the stnpping means compπses gπppmg means for gnppmg the part of the matenal retamed on the ram, whereby the unextruded matenal is stπpped from the ram as the ram is retracted from die stripping means.

9. Extrusion apparatus according to any preceding claim, further comprising an expansion device to expand a part ofthe extrusion into contact with the further portion of material to be extruded.

10. Extrusion apparatus according to claim 9, wherein die expansion device comprises an inner member and an outer, expandable, member, the inner member being slidably disposed within a longitudinally extending bore of the outer member, an outer surface of the inner member being provided with at least one formation that interengages at least one formation on an inner surface of the outer member, the thickness of said formations increasing longitudinally of said members, with the thickness of the formation on the inner member increasing in a direction opposite to die duckness of die formation on the outer member, whereby as the inner and outer members slide relatively in one direction, die interengagement of the formations, together with the increase in thickness ofthe formations, causes the outer member to expand radially.

11. Extrusion apparatus according to claim 10, wherein the outer member is divided longitudinally into at least two, and preferably tiiree, segments, whereby the segments can separate as the outer member expands radially.

12. Extrusion apparatus according to any preceding claim, further comprising alignment means for aligning the ram with the die assembly.

13. Extrusion apparatus according to claim 12, wherein the alignment means comprises cooperating formations on the ram and die assembly, that interlock when the ram is moved relatively towards die die assembly, the cooperating formations being arranged so tiiat, when they interlock, correct alignment of the ram and die assembly is assured.

14. Extrusion apparatus according to claim 13, wherein the ram and die die assembly are movable relatively in a direction radial to the direction of extrusion, whereby, as the cooperating formations on the die assembly and the ram come into engagement, the radial position of the die assembly can adjust relative to the ram in order to enable die cooperating formations to interlock.

15. Extrusion apparatus according to claim 13 or 14, wherein the cooperating formations comprise a recess in the ram and a projection on die die assembly, or vice versa.

16. Extrusion apparatus according to any preceding claim, further comprising support means having at least two of said rams secured thereto, wherein the support means is movable between a plurality of extrusion positions, each extrusion position conesponding to a position in which the longitudinal axis of one of the rams is aligned with the die aperture.

17. Extrusion apparatus according to claim 16, wherein the support means is rotatably movable between the extrusion positions, the support means is rotatable about a central axis, and the rams are equispaced around said axis of rotation.

18. Extrusion apparatus according claim 16 or 17, when dependent upon claim 9, 10 or 11, wherein an expansion device is placed between each ram, and the support means is also movable between a plurality of expansion positions in which the longitudinal axis of one of die expansion devices is aligned widi die die orifice.

19. Extrusion apparatus according to claim 16, 17 or 1.8, when dependent upon claim 7 or 8, wherein when one of the rams is aligned with the die assembly, anotiier of the rams is aligned with the stripping means.

20. Extrusion apparatus according to any preceding claim, further comprising die replacement means for removing the die from the die assembly and replacing die removed die witii another die.

21. Extrusion apparatus according to claim 20, wherein the die replacement means comprises a die carrier for carrying at least two of said dies, said carrier is movable between a plurality of positions, and in each position one ofthe dies is aligned in with the die assembly in such a way that it can be inserted into the die assembly, and subsequently removed from the die assembly.

22. Extrusion apparatus according to claim 21 , wherein the die carrier is rotatable about an axis, and the dies are substantially equispaced about said axis.

23. Extrusion apparatus according to claim 21 or 22, wherein the die replacement means further comprises die gripping means adapted to insert the die aligned widi the die assembly into die die assembly, and subsequently to remove said die from die die assembly.

24. Extrusion apparatus according to claim 23, wherein the die gripping means comprises a pair of gripping members that are adapted to grip one of the dies therebetween, the gripping members being pivotable between a gripping position, in which they grip and hold the die, and a release position, in which they do not grip or hold the die.

25. Extrusion apparatus according to claim 23 or 24, wherein the gripping means is movable between a retracted position in which it is clear of the die assembly, and an extended position in which it is within the die assembly, and die gripping means further comprises a die pushing member that is adapted to bear against the die in order to push die die away from the gripping means, the force with which the die pushing member pushes the die being less than the force with which the die is gripped by the gripping means, so the die pushing member does not push the die out of the gripping means when it is being gripped by the gripping means.

26. Extrusion apparatus according to any one of claims 20 to 25, wherein the die replacement means removes and replaces die die along an axis diat is peφendicular to die axis of extrusion.

27. Extrusion apparatus comprising: a die assembly including a die having an orifice of a desired shape; a ram for forcing a portion of material to be extruded through the die orifice to foπn an extrusion, said ram being movable relative to die die between an extrusion position in which the ram can force the material to be extraded through the die orifice, and a retracted position in which a further portion of material to be extraded can be placed in said die assembly; means for retaining on the ram part of the material to be extraded, whereby the extrusion can be at least partially retracted when die ram moves to the retracted position, and cutting means for cutting die extrusion in order to separate die unextruded portion from die extrasion.

28. Extrusion apparatus comprising: a die assembly including a die having an orifice of a desired shape; a ram for forcing a portion of material to be extruded dirough die die orifice to form an extrasion, said ram being movable relative to die die between an extrusion position in which the ram can force the material to be extraded through die die orifice, and a retracted position in which a further portion of material to be extraded can be placed in said die assembly; and alignment means for aligning the ram with the die assembly in a direction radial to the direction of extrusion.

29. Extrasion apparatus comprising: a die assembly including a die having an orifice of a desired shape; a ram for forcing a portion of material to be extraded dirough die die orifice to form an extrusion, said ram being movable relative to die die between an extrusion position in which the ram can force the material to be extraded through the die orifice, and a retracted position in which a further portion of material to be extraded can be placed in said die assembly; and support means having at least two of said rams secured thereto, wherein the support means is movable between a plurality of extrusion positions, each extrasion position corresponding to a position in which the longitudinal axis of one ofthe rams is aligned with the die aperture.

30. Extrusion apparatus comprising: a die assembly including a die having an orifice of a desired shape; a ram for forcing a portion of material to be extraded through the die orifice to form an extrusion, said ram being movable relative to the die between an extrusion position in which the ram can force the material to be extraded through the die orifice, and a retracted position in which a further portion of material to be extraded can be placed in said die assembly; and die replacement means for removing the die from the die assembly and replacing the removed die witii another die.

31. A method of extrusion comprising: extruding a first portion of material through a first die having an orifice of a desired shape to form a first extrasion; coextrading a second portion of material with a part of said first extrasion either through the first die, or through a second die having an orifice of desired shape, to form a second extrasion comprising said first and second portions of material.

32. A method according to claim 31, further comprising repeating the coextrusion step a preselected number of times witii a preselected number of further extrusions, in order to produce an extrasion of a desired length.