EP1175270A1

EP1175270A1 - Continuous extrusion apparatus

Info

Publication number: EP1175270A1
Application number: EP01907998A
Authority: EP
Inventors: Michael Paul Clode; George Dimitrios Orfanos
Original assignee: Kings College London
Current assignee: Kings College London
Priority date: 2000-03-03
Filing date: 2001-03-05
Publication date: 2002-01-30
Also published as: AU3585901A; WO2001064363A1; GB0005060D0

Abstract

Apparatus for the forming of material (9) by extrusion consists of a sealed chamber formed by the surfaces of two rotatable heated members (1, 2) the faces of which are inclined to each other so that, as they rotate material to be formed is compressed and gripped by the surfaces. The material (9) is fed to a die by rotation of the members (1, 2) where it is extruded through the die.

Description

Continuous Extrusion Apparatus

The present invention relates to apparatus and a method for the continuous forming of material by extrusion.

Apparatus and methods for the continuous forming of material by extrusion are disclosed in GB Patents 1370894, 1434201 , 1566152, 7590776, 2028207, 2103527 and 2176728. Such apparatus typically consists of a rotatable wheel constituting a moving member and defining an endless groove around the wheel for the material, with a stationary abutment projecting into the groove partially blocking the groove with a die orifice in it. A rod feed stick, moved by frictional drag between the feed stick and the groove, is forced through the die orifice. The shear action generates sufficient pressure and temperature to extrude the material through the die. This method is generally referred to as the conform method.

The conform method can be used for extruding complex sections and can also be used for cladding, especially for exotic and temperature sensitive materials. However the use of high pressure results in wear of the wheel and, as the friction generates the heat required, there is wear of the die especially at the start of the method before the material has warmed up to the operating temperature, in addition the faster the wheel turns the more heat is generated and so cooling can be required.

We have now devised a continuous extrusion system which reduces these problems.

According to the invention there is provided apparatus for continuous forming of material by extrusion, which apparatus comprises two spaced apart rotatable coaxial members positioned face to face and inclined to each other, so that when the members rotate the material to be formed is gripped by the members, there being a guiding means and a die, the guiding means guiding the material to be extruded from the members to the die and the material being extruded through the die, there being a heating means to heat the members. In use the members are rotated and the material to be formed is fed to the gap between the faces of the members and the members grip the material where the members are closer together and heat is conducted from the members to the material to warm it up, the material is fed towards the guiding means by the rotation of the members and, as the members rotate the grip on the material is released and the material is forced through the die

The members can be cylinders, cones, discs etc and the faces of the members should be substantially flat so that the material to be extruded is gripped between the faces There can be indentations or grooves in the faces to help grip or position the material to be formed

The members can be mounted on a common axle or they can be mounted on separate axles The inclination of the faces of the members to each other is not critical and will depend on the thickness of the material and its properties, the diameter of the members etc and an angle of one to ten degrees can typically be used e g about three degrees As the material is fed between the faces of the members it is gripped by the members and compressed until it reaches the point of smallest separation of the members The inclination of the faces of the members should be such that the material is gripped for a sufficient length of the material and with sufficient force that it can be forced through the die with substantially no slippage

Preferably external pressure is applied to the members so that they are held together with sufficient force to compress and grip the mateπal

The material to be formed need not be in the form of a rod as in the conform method but can be of any cross sectional shape and, for some applications a strip is preferred as, when the shape of the material is a strip there is a more even distribution of temperature on the material being extruded, and it will he easy to control the temperature changes accurately and closely The heat required is externally supplied and so is constantly and independently controlled

Preferably the faces of the members form a sealed chamber with the material to be extruded 'fed through an entry port in the chamber to the members as they rotate and the die being located at an exit port to the chamber so that the material is extruded through the die where it leaves the chamber

Preferably the members are separated by a spacer preferably positioned on the axle between the faces of the members and so that, the faces of the members are held apart at the right distance, even when pressure is applied to the members forcing them together to grip the material to be extruded The faces of the members are preferably sealed at their edges to form a sealed chamber so that, as the material is compressed between the faces of the members and spreads across the faces it cannot escape from between the faces of the members The seal can comprise a bead surface on the inner edge of the faces which can rotate with the members and which seals the inner edge of the chamber and a back plate which seals the gap between the members at their outer edges to seal the outer edge of the chamber

In the method of the present invention the material that enters the extrusion chamber will be under higher pressure and so the current limits of wall thickness in the products can be exceeded The material is heated up as it travels towards the die, and so there is solid metal to continuously push the softer hot metal through the die This will increase the hydrostatic pressure and will enable more complex extrudates to be formed

The apparatus and method of the present invention can be used to produce product from feedstock comprising granules or powders of metals Formation of products by extrusion of metal granules and powders as the source material has been proposed and it has been claimed that existing machines can do this, but in practice this has proved difficult in the present invention the compression or compaction of the granules or powders by the faces of the members before the material is fed to the die enables the compressed or compacted powder to behave as a feeding strip and can then be extruded through the die.

It is a feature of the invention that there is continuous deformation along the path of the faces of the members and so the grip is greater compared to the conform method and due to the grip obtained the pressure can be higher and so different shaped products can be formed. It is also easy to change the die to form a range of products. As well as for forming metals the apparatus and method of the invention can be used to form products from polymers, ceramics, foods such as chocolate etc. and any material which can be extruded. The invention can also be used for cladding material such as metals, optic fibres etc.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of the members of the invention from the side Fig. 2 is a schematic view of the members from the front Fig. 3 is a side view of an embodiment of the invention

Fig. 4 is a sectioned perspective view of the apparatus Fig. 5 is an perspective expanded view of the apparatus

Fig. 6 is a disassembled view of the apparatus showing the component parts and Fig. 7 is a side view of an embodiment of the device in use. Referring to the figures, in particular figures 1 and 2, the apparatus consists primarily of two mutually inclined members 1 and 2 supported for rotation about an axis X-X. Each member 1 and 2 is annular and has an aperture 1a, 2a whereby it is mounted over an axle 3. The axle consists of a shaft 3a supporting a wheel part 3b. The wheel part 3b provides a rim 3c which defines one wall of an annular chamber. The wheel part and the axle is be rotatable.

Each member 1 and 2 has a substantially annular radial surface 1 b, 2b. Each member 1 and 2 is supported so that the radial surfaces 1 b, 2b are mutually inclined and spaced in the axial direction The lowermost edge of the radial surfaces 1 b, 2b sea ngly engages the wheel nm 3c at a sealing bead surface C so forming two opposing sides of the chamber The wheel nm 3c need not be cylindrical but may be wholly or partially spherical Because of the arrangement of the inclination of the members relative to the axis X-X the sides 1 b,2b of the chamber converge progressively from a feedstock inlet region to an extrusion region adjacent an abutment 8 In the figures the inlet region is located at the top and the extrusion region towards the bottom The members 1 and 2 together with the wheel and axle form the principle members of the rotor assembly

A shoe 6 is statically (non-rotatably) mounted on a machine frame (not shown) and has an arcuate inner sealing surface 6a which complements the outer peripheral surfaces of the members 1 and 2 and extends seahngly around part of the circumference of the peripheries of each of the members 1 and 2

At the top the shoe 6 provides a feedstock entry port 7 As shown in figure 2 feedstock, which is in the form of a cylindrical rod in this example, is fed into the feedstock entry region and engaged by the radial surfaces 1 b, 2b As the members are rotated by engagement with a drive mechanism, the feedstock is compressed and carried towards the extrusion region where it meets the abutment structure 8 The abutment structure 8 forms a part of the stator assembly together with the shoe 6 and intrudes into the chamber between the radial surfaces 1b and 2b Heaters are provided (not shown) in order to heat the feedstock as it progresses through the chamber The heaters are preferably provided in the members 1 and 2 and may comprise electrical heating of resistive or induction type The members may be heated by heaters mounted within the members 1 and 2 or within the shoe 6

In use the members are heated to their working temperature and rotated by rotation of the axle 3 Axle 3 can be rotated by conventional hydraulic or electric motors (not shown) and feedstock material 9 is fed into the chamber through the entry port 7 As it progresses through the chamber the radial faces of the members grip the feedstock, compress it and heat it When the heated feedstock within the chamber reaches the abutment 8a it is upset and extrudes through an extrusion passage formed upstream of the abutment 8a either in the abutment structure 8 or the shoe 6 In the present example the extrusion passage through which extrudate 10 passes from the chamber, is formed in the abutment structure 8 as can best be seen in figure 4

For hot extrusion of metals a temperature above 0 5TM (T_m = half the melting temperature of the material in Kelvin) is normally required and the present invention enables this to be achieved easily The material entering the chamber at the feedstock entry region is cold and relatively hard whereas the material at the extrusion region B is relatively soft and this facilitates extrusion through the die

Two frame (or casing) halves 5a and 5 b which form a frame (or casing) 5 as can be most readily seen in the exploded figure 5 The frame 5 provides support for the shoe 6 Each of the frame halves 5a, 5b has an annular end plate part 4a, 4b each with a cylindrical bearing housing to accommodate axle bearings 15 which rotatably support the axle 3 Each of the frame halves 5a and 5b is formed with internal radially extending shoulders 16 which provide support for an inclination plate 18 The inclination plate 18 takes the form of a disc which is wedge shaped in cross section Each inclination plate 18 supports a thrust bearing 17 which provide support, one each for each member 1 and 2 as it rotates The wedge angle of the inclination plate 18 determines the relative inclination of the members 1 and 2

The frame 5 provides means by which an axial force is applied urging each member toward the other

In figure 6 the abutment structure can be seen exploded showing an extrusion die part 8b As can be seen in figure 5, the abutment structure is held in a die holder 19 formed in the frame 5 In essence the die holder is an aperture shaped to accommodate the abutment structure 8. A further cleaning and heating opening 20 is formed in the frame 5.

Claims

1 Apparatus comprises two spaced apart rotatable coaxial members positioned face to face and inclined to each other, so that when the members rotate the material to be formed is gripped by the surfaces of the members, there being a guiding means and a die, the guiding means guiding the material to be extruded from the members to the die and the material being extruded through the die, there being a heating means to heat the members

2 Apparatus as claimed in claim 1 in which the inclination of the faces of the members to each other is at an angle of one to 10 degrees

3 Apparatus as claimed in any one of claims 1 or 2 in which there are means to apply pressure to the members so that they are held together with sufficient force to compress and grip the material

4 Apparatus as claimed in any one of claims I to 3 in which the surfaces of the members form a sealed chamber with an entry port in the chamber through which the material to be extruded is fed to the gap between the members as the members rotate and the die being located at an exit port to the chamber so that as the material is extruded through the die it leaves the chamber

5 Apparatus as claimed in claim 5 in which the inner circumferential surfaces of the members are sealed by a bead surface which can rotate with the members and the gap between the outer surfaces of the members is sealed by a back plate

6 Apparatus as claimed in any one of claims 1 to 5 in which the members are separated by a spacer positioned between the members.

7. A method for continuous forming of material by extrusion, in which method the material to be extruded is fed between the faces of two spaced apart rotatable coaxial members positioned face to face and inclined to each other, and the members rotated and heated so that the material to be formed is compressed and gripped by the members as they rotate, the material is fed from the members to a die and the material extruded through the die.

8. A method as claimed, in claim 7 in which the inclination of the faces of the members to each other is at an angle of one to five degrees

9. A method as claimed in claim 8 in which the inclination of the faces of the members is such that the material is gripped for a sufficient length of the material and with sufficient force that it can be forced through the die with substantially no slippage.

10. A method as claimed in claim 8 or 9 in which external pressure is applied to the members so that they are held together with sufficient force to compress and grip the material.

11. A method as claimed in claim 8 to 10 in which the surfaces of the members form a scaled chamber and the material to be extruded is fed through an entry port in the chamber to the gap between the surfaces of the members as they rotate and the die being located at an exit port to the chamber so that as the material is extruded through the die it leaves the chamber.

12. A method as claimed in claim 8 to Ii in which the members are separated by a spacer positioned between the members so that the members are held apart even when pressure is applied to the members forcing them together to grip the material to be extruded and as the members rotate the sphere also rotates

13 A method as claimed in claim 8 to 12 in which the' material being formed is granules or powders of metal or metals

14 A continuous extrusion apparatus comprising a rotor assembly capable of rotation around an axis (X-X) and accommodated in an enveloping stator assembly such that the rotor assembly cooperates with the stator assembly to form a chamber which reduces in cross sectional area from a feedstock inlet region, to an extrusion region

15 Apparatus according to claim 14 wherein the rotor assembly comprises a pair of members (1 ,2), mounted for rotation about mutually inclined axis, each member (1 ,2) providing a radially extending surface (1 b, 2b) in opposition to the other which define radial walls of the chamber such that the surfaces are separated by a gap which is greatest at the feedstock inlet region and least at extrusion region

16 Apparatus according to claim 15 wherein the members (1 ,2) are annular and mounted for rotation about an axle (3), said axle (3) having a wheel part (3b) providing an axially extending nm (3c) which sealingly engages the annulus of each member (1 ,2) to further define the chamber

17 Apparatus according to claim 16, wherein the stator assembly includes a shoe (6) which extends in sealing engagement partway around the cylindrical outer nm of each member to further define the chamber

18 Apparatus according to claim 18 wherein the stator includes an abutment structure providing an abutment which intrudes into the passage formed between the radial surfaces (1 b, 2b) and the nm (3c) to obstruct the passage of feedstock

19 Apparatus according to claim 18 wherein an extrusion passage is formed in one of the shoe (6) or the abutment structure (8)

20 Apparatus according to any one of claims 14 to 19 wherein heaters are provided to heat the feedstock in the chamber

21 Apparatus according to any one of claims 15 to 20 wherein each member (1 ,2) is supported by thrust bearings which bear against an enclosing frame (5) by means of an inclination plate (16) which sets the angle of mutual inclination of each member (1 ,2)

22 Apparatus according to any one of claims 16 to 21 wherein the members (1 ,2) are rotated by the action of rotating the axle (3) said axle projecting from the frame (5) to be coupled to a motor

23 A method for continuously extruding a material comprising the steps of feeding the material into an enclosed chamber formed in an axially extending gap between two endless rotating radially extending surfaces which move progressively towards each other in the axial direction

24 A method according to claim 23 comprising the step of heating the feedstock within the chamber by means of heaters

25. A method according to claim 24 wherein the radial surfaces of the chamber move endlessly toward each other by virtue of the mutual inclination of the axis of rotation of members (1 ,2) which provided the surfaces (1b, 2b) and the rate at which the surfaces move toward each other is altered by changing the relative inclination of the axis according to the nature of the product to be extruded.