GB2386334A

GB2386334A - Continuous extrusion using dynamic shoe positioning

Info

Publication number: GB2386334A
Application number: GB0203529A
Authority: GB
Inventors: Phillip Thomas; Kafeel Khawaja
Original assignee: Holton Machinery Ltd
Current assignee: Holton Machinery Ltd
Priority date: 2002-02-14
Filing date: 2002-02-14
Publication date: 2003-09-17
Anticipated expiration: 2022-02-14
Also published as: GB2386334B; GB0203529D0

Abstract

A continuous extrusion machine has a wheel (2) wherein an endless groove (7) is formed, the wheel is mounted for rotation about an axis extending through the geometric centre in a machine chassis (1). A dynamic shoe (3) is shaped to envelope a part of the circumference of the shoe and is mounted on displacement means to be displaceable vertically and horizontally during extrusion so that the size and shape of a gap (12) formed between the wheel (2) and the shoe (3) can be adjusted. To sense the size of the gap (12) the width of the wheel is determined so that a region adjacent its edge is free of flash and a capacitive sensor (4) is mounted on the shoe (3) to sense the size of the gap between the wheel and the flash free region of the wheel periphery. The sensor employs capacitor plate 4'.

Description

Continuous Extrusion Using Dynamic Shoe Positioning.

The present invention is concerned with a continuous extrusion machine, and a method of operation for continuously extruding non-ferrous metals such as aluminium and copper.

5 In general a continuous extrusion machine comprises a chassis, a wheel and tooling. The tooling consists principally of a shoe and a die. The chassis supports the wheel for rotation by a motor. An endless groove is formed in the periphery of the wheel into which is entrained a feedstock which is commonly a bar of a non-ferrous metal such as aluminium or copper but may comprise metal particles or molten metal. Part of the 10 periphery of the wheel is closely enveloped by the shoe so that the groove co-operates with the shoe to form a passage in use feedstock entrained in the groove enters the passage at an open end as the wheel rotates. The other end of the passage is obstructed by an abutment which is mounted on the shoe and intrudes into the passage.

Because the feedstock is confined in the passage and the wheel continues to rotate, the 15 feedstock is heated by friction with the groove. A die is mounted in a chamber formed in the shoe immediately upstream of the abutment. Eventually the thermal and other stresses imposed on the feedstock cause the feedstock to extrude through the die.

The continuous extrusion machine is capable of continuously extruding a wide range of sections of non-ferrous metal7 for so long as feedstock is delivered to the 20 groove. In order to operate successfully it is necessary to have a small gap between the periphery of the wheel and the shoe. This gap permits a small quantity of the feedstock, known as the flash, to extrude out of the passage onto the periphery of the wheel and into the gap. The size of the gap has a significant effect on the performance of the 25 machine in terms of the speed, quality and type of extrusion which can be produced.

Conventionally the gap is set before starting the machine. However, when the machine is in operation heat causes thermal expansion of the machine components and pressure

on the wheel and chassis causes elastic deformation so that the gap size changes.

Thermal expansion typically alters the gap by up to 0.7mm while elastic deformation alters the gap by between 0.3 and 0.5mm. The effects of thermal expansion and extrusion pressures are non-uniform, will vary during start up, and may vary during 5 operation and conventionally cannot be measured accurately.

The elastic deformation is relieved when feedstock ceases to enter the machine, as at shut down, and it is essential that the shoe does not impinge on the wheel or serious damage will occur. It is consequently not possible to pre-set the machine to run with a gap of less than the elastic deformation. It is also disadvantageous that the gap 10 cannot be varied and accurately measured during machine operation in order to test the performance of various clearances in the production of an extrusion.

The applicant's previously filed patent application WO 00/29141 (the contents of which is imported by reference) discloses a Conform_ extrusion machine adapted to provided dynamic shoe positioning, that is having a shoe mounted on actuators capable 15 of moving the shoe perpendicular to the axis of the wheel in accordance with the size of a gap sensed directly using a sonic capacitive sensor. However, experience with such sensors has demonstrated disadvantages such as a requirement for a reliable sensor gas feed supply. The present invention seeks to alleviate these disadvantages by the provision of a continuous extrusion machine having a chassis supporting a wheel for 20 rotation and a shoe enveloping a span of the periphery of the wheel and co-operating with a groove formed in the periphery of the wheel to form a passage, a support mechanism supporting said shoe and/or wheel to be relatively displaceable in a direction perpendicular to the axis of rotation of the wheel, a capacitive sensor system including a capacitive capacitive sensor able to sense the size of a gap between the wheel 25 periphery and the shoe when the machine is operating, and control means to adjust the support mechanism to displace the shoe relative to the wheel.

- 3 Preferably the support mechanism is adapted to be capable of adjusting the shoe position while the machine is in operation. It is also very preferable that the control mechanism is automatically responsive to the capacitive sensor system.

The capacitive sensor system may also sense the size and shape of the gap by 5 the provision of two, three or more capacitive capacitive sensors spaced circumferentially around the wheel shoe interface.

During the extrusion process some material (known as flash) is extruded into the gap. The majority of this flash is contned to the areas of the wheel adjacent to the groove. When using capacitive sensors wheels 50mm wider than is conventional may be 10 used and the sensors operate at the outer 25 mm which is clear of the flash. One capacitive sensor may be located adjacent the mouth of the start of the tooling, one at the centre of the tooling and one immediately downstream of the abutment. The capacitive sensor is mounted directly onto the shoe and connected to the rest of the gap sensor system via electrical, optical or wireless connectors.

15 According to another aspect of the present invention there is provided a method of operating a continuous extrusion machine wherein feedstock is entrained in a groove formed in the periphery of a wheel rotating in a chassis and drawn into a passage formed between the groove and a shoe, said passage being obstructed by an abutment supported by the shoe so that friction between the shoe and the abutment will cause the 20 feedstock to extrude through a die supported in the shoe, comprising the steps of: sensing the actual size of a gap between the wheel and the shoe using a capacitive gap sensor, comparing the actual size of the gap with a predetermined or previous gap size in a control means to determine if there is a difference, said control means responding to a 25 difference to control a support structure which supports the shoe and/or the wheel in the chassis to displace the shoe and/or the wheel on at least one axis perpendicular to the axis of rotation of the wheel so that the gap is changed to reduce the difference.

- 4 The desired gap size may be altered during machine operation. Thus while the method contemplates setting the gap size to that required for extrusion, and preventing significant deviation during extrusion, it also contemplates setting the gap size to one predetermined value during machine start up, altering that predetermined value during 5 continuous extrusion and possibly further altering the value during shut down of the machine. The method may also comprise the steps of sensing the shape of the gap, in particular by sensing the size of the gap at two or more peripherally spaced locations and the step of adjusting the shape of the gap to a desired shape by adjusting the 10 position of the shoe or the wheel in the horizontal (X) direction or the vertical (Y) direction. Continuous extrusion machines and a method of operating them, embodying biaxial shoe positioning in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which, 15 Figure I diagrammatically illustrates a continuous extrusion machine set up for radial shoe operation, Figure 2 diagrammatically illustrates a continuous extrusion machine set up for tangential shoe operation, Figure 3 is a diagramatic elevation of a capacitive gap sensor.

20 With reference to the drawings a continuous extrusion machine comprises a chassis 1, a wheel 2 mounted in the chassis for rotation about a horizontal axis, a shoe 3, 3'a shoe support mechanism, described in detail below and a capacitive sensor system comprising three capacitive sensors 4,4A,5 The machine is illustrated in the process of extruding a bar 6 of cast non- ferrous metal feedstock such as aluminium or 25 copper. The feedstock is entrained by means of a coining roll 8 in an endless groove 7 formed in the periphery of the wheel 2. As the wheel rotates in the direction of the arrow

A" the bar 6 passes into an enclosed passage formed between the shoe 3, 3' and the periphery of the wheel 2.

Movement of the bar 6 through the passage is stopped by an abutment 8. The wheel 2 is rotated by a motor (not shown) so that friction heats and compresses the bar 5 6 until it becomes sufficiently plastic to extrude out of the passage 7 into tooling 9 which includes a die. In the case of the radial mode of operation shown in figure 1 the shoe presents the die so that the extrusion 10 passes from the machine radially with reference to the wheel 2. In the case of the tangential mode machine shown in figure 2 the shoe 3' is adapted to accommodate tooling 9' which has the extrusion 10' passing from the 10 machine at a tangent to the wheel 2.

The radial mode machine is best suited to the production of profiled sections and tube while the tangential mode is suited to sheathing and cladding a core 11.

A gap 12 is formed between the periphery of the wheel 2 and the shoe 3 which can be seen enlarged (approximately 10 times larger than life) in figure 3. The size of the gap 15 12 during machine operation is optimally approximately 0.2mm. During the machine operation some of the material of the bar 6 'extrudes' through the gap onto the circumferential surface of the wheel 2. This material is separated from the wheel 2 by means of a scraper assembly 41 shown in detail in figures 6 and 7 as described later.

The wheel 2 and the shoe 3 are subject to deformation cause by mechanical and 20 thermal strain This deformation tends to increase the gap size during extrusion. The removal of the strain when the feedstock supply is stopped results in a sudden reduction in the gap size. The machine must continue to run for a period after the feedstock supply is stopped in order to discharge feedstock from the passage. If the gap size were of the order of 0.2mm the sudden reduction in strain caused by the discharge of the passage 25 would cause the wheel to collide with the shoe resulting in serious damage.

To alleviate the aforementioned problem the shoe 3 is mounted on a support structure comprising a pair of wedge assemblies, in particular, a first vertical

- 6 displacement wedge assembly 13 for displacing the shoe 3 vertically and a second horizontal displacement wedge assembly 14 for displacing the shoe 3 horizontally.

The vertical displacement wedge assembly 13 comprises a base bearing member 15, a wedge 16 disposed with an elongate horizontal face bearing against the bearing 5 member 15 so that an elongate inclined face faces upwards.

A ramp 17 has a face inclined at the same angle as the wedge and bearing against the inclined face of the wedge 16. The ramp 17 has a horizontal face opposite the inclined face which bears against the shoe 3. A shim may be interposed between the shoe and the ramp 17. The ramp is mounted in the chassis to be displaceable in the 10 vertical direction only. The wedge 16 and ramp 17 are separated by a low friction spacer (not shown) which may be made of PTFE. Included in the wedge assembly 13 is a double acting vertical displacement hydraulic ram 19 connected to the wedge 16 by a con-rod 20. Hydraulic fluid supply to the extension chamber of the hydraulic ram 19 is controlled by a right displacement air hydraulic intensifier 21. Hydraulic fluid supply to the 15 retraction chamber of the ram 19 is controlled by a left air hydraulic intensifier 22.

The horizontal wedge assembly 14 comprises a back bearing member 23 which is removably secured by pins 23' into the chassis 1. An inner vertical face of the back bearing member 23 provides a bearing surface to support a vertical face of a wedge member 24 of the horizontal displacement wedge assembly 14. An inclined face of the 20 wedge 24 bears against a complimentarily inclined face of a ramp member 25. The ramp member 25 bears against a vertical face of the shoe 3 and is mounted to be displaceable horizontally only. A shim may be interposed between the ramp 25 and the shoe. A double acting hydraulic ram 26 is linked to the wedge 24 by a con-rod 27. An up air hydraulic intensifier 28 controls the delivery of hydraulic fluid to the up hydraulic ram 25 26. Displacement transducers 29 monitor the positions of the wedge members 16 and 24 to enable fast movement during start up and shut down.

Because the wedge 24 must be readily removable from the machine in order to gain access to the shoe 3 it cannot be very rigidly fixed to the con rod 27. To ensure no backlash in the horizontal movement a down hydraulic ram 30 is provided to impose a constant downward pressure on the top of the wedge 24. This also helps to ensure 5 smooth movement of the wedge by overcoming any stiction which may occur between the wedge and bearing surfaces despite of friction reducing measures which may be implemented such as PTFE coatings.

The air/hydraulic intensifiers deilver a precise volume of hydraulic fluid every time they are actuated by a pneumatic air signal delivered to the intensifier.

10 Typically the volume may be 2ml. One stroke from the intensifier will therefore result in a the wedge attached to the associated hydraulic ram moving by a single increment resulting in an incremental shoe movement of typically 0.04mm. Thus when the control device compares a desired gap size with an actual sensed gap size the hydraulic rams can be driven the required number of strokes to achieve the desired gap 1 5 size In the radial mode of extrusion shown in figure 1 the radial shoe 3 forms a passage mostly in an upper quarter segment of the wheel 2. The pressure imposed on the radial shoe 3 by the feedstock in the passage has an upwardly directed resultant force. It is therefore necessary to provide a second down hydraulic ram 31 to urge the shoe 3 down 20 onto the vertical movement wedge assembly 13. An air/hydraulic intensifier 32 is arranged to control the delivery and discharge of hydraulic fluid to the second down hydraulic ram 31.

In the tangential operation mode of figure 2 the tangential shoe 31 forms the passage in a lower quadrant of the wheel 2. In consequence the pressure applied by the 25 feedstock entrained in the passage includes a large net downward component on the tangential shoe 31. Although this makes the second down hydraulic cylinder 31 unnecessary in the tangential mode of operation, the fact that the load on the shoe is

- 8 - near vertical and has only a small horizontal component makes the provision of a horizontal shoe displacement ram 31A in the chassis desirable. The horizontal shoe displacement ram 31A is mounted in the chassis I and acts directly against the shoe 31 to overcome friction between the shoe and a horizontal support plate 31 B by pushing the 5 tangential shoe 31 against the ramp 25.

It will be appreciated from figures 1 and 2 that a single continuous extrusion machine may be adapted by installation of the appropriate radial shoe 3 or tangential shoe 31 to run in either the radial or tangential modes.

The delivery of air to each air/hydraulic intensifier is co-ordinated by a control 10 device (not shown) of the control means, such as a programmable computer or dedicated processor which cause the discharge of pneumatic control air from an air reservoir 33 to the air/hydraulic intensifiers via solenoid valves 33A. Rams 31 or 31A are continuously pressurized to push the shoe 3 or 3',against either a vertical shoe support plate 31C, or the horizontal shoe support plate 31 B. The shoe support plates 31B, 31C 15 are each supported by the horizontal and vertical wedge assemblies 13 and 14. When the wedge assemblies move the system towards the opposing ram, e.g. the horizontal wedge assembly 13 moves the shoe 3 towards the ram 31 fluid is forced from the ram cylinder through the pressure relief valve and when the shoe is moved away fluid is pumped into the ram 31. Thus a pre-set fluid pressure is maintained in the ram 31 or 20 31A and corresponding force is applied to the shoe 3,; 3jo urge it against the wedge assembly 31,14 opposite the ram.

To summarise cylinders 19 and 26 are master cylinders which control the position of the wedges and the shoe. Cylinders 30, 31 and 31A are slave cylinders which are continuously pressurized to maintain a constant thrust. If the master cylinders are moved 25 oil is forced in or out of the slave cylinders to maintain the required thrust.

Each air/hydraulic intensifier is equipped with a microswitch which senses each stroke of hydraulic fluid discharge and transmits this information to the control device

- 9 - which can thus deduce the consequent displacement of the shoe 3,3'. The control means in this instance may be understood to consist of the control device and the pneumatic control system comprising the reservoir 33, the pneumatic valves and the air/hydraulic intensifiers.

5 Figure 3 illustrates a capacitive gap sensor 4 detail. The sensor consists of a capacitor plate 4' surrounded by a guard ring 4" and connected via wire 4"' to a readout apparatus. When positioned as shown opposite the target wheel rim the sensor creates a capacitance proportional to the air gap. The sensors 4, 4a and 5 are each calibrated for a specific wheel 2 prior to installation. In operation the capacitance signal is read off 10 each sensor to an A/D converter and hence to a control system for controlling the gap size using negative feedback as discussed in WO 00/29141.

Claims

- 10 Claims

1. A continuous extrusion machine having a chassis supporting a wheel for rotation and a shoe enveloping a span of the periphery of the wheel and co-operating with a groove formed in the periphery of the wheel to form a passage, a support mechanism 5 supporting said shoe and/or wheel to be relatively displaceable in a direction perpendicular to the axis of rotation of the wheel, a capacitive sensor system able to sense the size of a gap between the wheel periphery and the shoe when the machine is operating, and control means to adjust the support mechanism to displace the shoe relative to the wheel.

2 A continuous extrusion machine according to claim 1 wherein the width of the wheel is increased to provide an area clear of flash and the capacitive sensor is located to sense the gap in the area clear of flash.

15

3. A continuous extrusion machine According to claim 1 or claim 2 wherein a plurality of capacitive sensors are deployed circumferentially spaced around the wheel to sense the shape of the gap.

4. A continuous extrusion machine according to claim 1 and as herein described 20 with reference to the accompanying figures.

5. A method of operating a continuous extrusion machine wherein feedstock is entrained in a groove formed in the periphery of a wheel rotating in a chassis and drawn into a passage formed between the groove and a shoe, said passage being obstructed 25 by an abutment supported by the shoe so that friction between the shoe and the abutment will cause the feedstock to extrude through a die supported in the shoe,

- 11 comprising the steps of: sensing the actual size of a gap between the wheel and the shoe using a capacitive gap sensor, comparing the actual size of the gap with a predetermined or previous gap size in a control means to determine if there is a difference, said control means responding to a 5 difference to control a support structure which supports the shoe and/or the wheel in the chassis to displace the shoe and/or the wheel on at least one axis perpendicular to the axis of rotation of the wheel so that the gap is changed to reduce the difference.

6. A method according to claim 5 and as herein described.

j Amendments to the claims have been filed as follows Claims 1. A continuous extrusion machine having a chassis supporting a wheel for rotation and a shoe enveloping a span of the periphery of the wheel and co-operating with a groove famed in the periphery of the wheel to form a passage, a support mechanism 5 supporting said shoe and/or wheel to be relatively displaceable in a direction perpendicular to the axis of rotation of the wheel, an electrical capacitance sensor system able to sense the size of a gap between the wheel periphery and the shoe when the machine is operating, and control means to adjust the support mechanism to displace the shoe relative to the wheel 2. A continuous extrusion machine according to claim 1 wherein the width of the wheel is increased to provide an area clear of flash and the electrical capacitance sensor is located to sense the gap in the area clear of flash.

15 3. A continuous extrusion machine According to claim 1 or claim 2 wherein a plurality of electrical capacitance sensors are deployed circumferentially spaced around the wheel to sense the shape of the gap.

4. A continuous extrusion machine according to claim 1 and as herein described -

20 with reference to the accompanying figures.

A, ('i,.: hr1 TIC - l] comprising the steps of: sensing the actual size of a gap between the wheel and the shoe using an electrical capacitance gap sensor, comparing the actual size of the gap with a predetermined or previous gap size in a control means to determine if there is a difference, said control means responding to a 5 difference to control a support structure which supports the shoe and/or the wheel in the chassis to displace the shoe and/or the wheel on at least one axis perpendicular to the axis of rotation of the wheel so that the gap is changed to reduce the difference.