Continuous extrusion using dynamic shoe positioning
A continuous extrusion machine has a chassis ( 1 ) supporting a wheel ( 2 ) for rotation by a motor. An endless groove ( 7 ) extends around the periphery of the wheel ( 2 ). A shoe ( 3 ) is mounted in the chassis ( 1 ) and has an enveloping surface shaped to closely envelop an arc of the wheel ( 2 ) periphery so that the groove ( 7 ) co-operates with the shoe ( 3 ) to form a passage. An abutment is mounted on the shoe ( 3 ) to extend into the passage at a downstream end. Tooling is mounted in the shoe ( 3 ) including a die such that a material such as aluminum or copper bar fed into the groove ( 7 ) is extruded through the die as a consequence of the energy transfer via friction from the rotating wheel ( 2 ). A gap ( 12 ) exists between the enveloping surface and the wheel ( 2 ). The gap ( 12 ) is used to provide the orifice of a sonic gap ( 12 ) sensor whereby the size of the gap ( 12 ) can be accurately and directly measured. The gap ( 12 ) size sensed is used to control the position of the shoe ( 3 ) in two directions mutually perpendicular to the rotary axis of the wheel ( 2 ) by adjusting support structures which support the shoe ( 3 ). The size and shape of the gap ( 12 ) can thus be safely adjusted while the machine is extruding allowing the size and shape of the gap ( 12 ) to be adjusted for optimum performance.
1. A continuous extrusion machine having a chassis ( 1 ) supporting a wheel ( 2 ) for rotation and a shoe ( 3 ) enveloping a span of the periphery of the wheel ( 2 ) and co-operating with a groove ( 7 ) formed in the periphery of the wheel ( 2 ) to form a passage,
a support mechanism supporting at least one of said shoe ( 3 ) and said wheel ( 2 ) to be relatively displaceable in a direction perpendicular to the axis of rotation of the wheel ( 2 ) during use,
a gap sensor system able to sense the size of a gap ( 12 ) between the wheel periphery and the shoe ( 3 ) when the machine is operating, and
a control device responsive to the gap sensor system to adjust the support mechanism to displace the shoe ( 3 ) relative to the wheel ( 2 ), in each of two mutually perpendicular directions whereby the size and shape of the gap can be controlled.
2. A continuous extrusion machine according to claim 1 wherein the gap sensor system is able to detect the shape of the gap ( 12 ).
3. A continuous extrusion machine according to claim 1 wherein the support mechanism comprises a wedge assembly ( 13 , 14 ) having a wedge ( 16 , 24 ) longitudinally displaceable against a complementary ramp ( 17 , 25 ).
4. A continuous extrusion machine according to claim 3 wherein the support mechanism has a first wedge assembly ( 13 ) and a second wedge assembly ( 14 ), the first wedge assembly disposed to displace the shoe ( 3 ) in a first direction perpendicular to the axis of rotation of the wheel ( 2 ) and the second wedge assembly disposed to displace the shoe ( 3 ) ma direction perpendicular to the rotary axis of the wheel ( 2 ) and the first wedge assembly whereby the size and shape of the gap ( 12 ) can be altered during operation.
5. A continuous extrusion machine according to claim 3 wherein each wedge ( 16 , 24 ) is displaced by hydraulic rams ( 19 , 26 ).
6. A continuous extrusion machine according to claim 5 wherein the gap sensor system comprises a gap sensor ( 4 , 4 A, 5 ) which senses the gap size directly.
7. A continuous extrusion machine according to claim 6 wherein the gap sensor system provides at least two gap sensors ( 4 , 4 A, 5 ) each located peripherally spaced from the other to sense the size and shape of the gap ( 12 ).
8. A continuous extrusion machine according to claim 7 wherein the gap sensor system includes a first gap sensor ( 4 ) located at the entrance to the passage, a second gap sensor ( 4 A) located immediately upstream of the tooling ( 9 ) in the shoe ( 3 ) and a third gap sensor ( 5 ) located downstream of an abutment ( 8 ).
9. A continuous extrusion machine according to claim 6 wherein the sensor is a sonic gap sensor.
10. A continuous extrusion machine according to claim 1 further comprising a scraper blade ( 47 ) supported on a scraper carrier ( 43 ) for radial displacement with respect to the rim of the wheel ( 2 ), said scraper carrier ( 43 ) being driven by a motor ( 46 ) controlled by the control device in accordance with signals received from a gap ( 12 ) sensor ( 48 ) mounted on the carrier to detect the separation of the tip of the scraper blade ( 47 ) and the periphery of the wheel ( 2 ).
11. A continuous extrusion machine according to claim 10 wherein the motor displaces the scraper carrier ( 43 ) by rotation of an eccentric shaft ( 44 ).
12. A continuous extrusion machine according to claim 9 wherein the gap sensor ( 48 ) is a sonic gap sensor.
13. A method of operating a continuous extrusion machine wherein feedstock is entrained in a groove ( 7 ) formed in the periphery of a wheel ( 2 ) rotating in a chassis ( 1 ) and drawn into a passage formed between the groove ( 7 ) and a shoe ( 3 ), said passage being obstructed by an abutment supported by the shoe ( 3 ) so that friction between the shoe ( 3 ) and the abutment will cause the feedstock to extrude through a die supported in the shoe ( 3 ), comprising the steps of:
sensing the actual shape and size of a gap ( 12 ) between the wheel ( 2 ) and the shoe ( 3 ),
comparing the actual size of the gap ( 12 ) with a predetermined or previous gap size in a control device to determine if there is a difference, said control device responding to a difference to control a support structure which supports at least one of the shoe ( 3 ) and the wheel ( 2 ) in the chassis ( 1 ) to displace at least one of the shoe ( 3 ) and the wheel ( 2 ) on at least one axis perpendicular to the axis of rotation of the wheel ( 2 ) so that the gap ( 12 ) is changed to reduce the difference; and
adjusting a support mechanism to displace the shoe ( 3 ) relative to the wheel ( 2 ) in each of two mutually perpendicular directions whereby the size and shape of the gap ( 12 ) can be altered during operation.
14. A method according to claim 13 wherein the predetermined gap size is set to a desired gap size while the machine is extruding.
15. A method according to claim 13 wherein the gap size is sensed at least one position comprising the steps of:
i. blowing a pressurised gas through the gap ( 12 ) at at least one point adjacent the passage,
ii. adjusting the gas pressure to be sufficient to that the gap ( 12 ) is choked,
iii. sensing the gas pressure upstream of the gap ( 12 ),
iv. communicating the gas pressure to the control device,
v. calculating the actual gap ( 12 ) size from the gas pressure.
16. A method according to claim 15 wherein the gap size is sensed at at least two circumferentially spaced points adjacent the passage to determine the shape of the gap ( 12 ).