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(11) | EP 0 213 943 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Apparatus for continuous friction actuated extrusion |
| (57) Conform extrusion apparatus of the usual wheel-and-shoe type uses a scraper (5) to
remove the flash from at least the side walls of the groove. The scraper is mounted
for movement against a biassing force along a line at least approximating to the tangent
of the wheel at the scraper position and in the direction of the movement of the wheel
there. Preferably the working face of the scraper is inclined at least 30°, better
45°, to the local radius. |
[0001] This invention relates to 'Conform' apparatus for continuous friction-actuated extrusion of metal, especially (but not exclusively) copper, silver and other relatively hard extrudable metals.
[0002] The invention is applicable to the original Conform apparatus defined in U.K. Patent Specification 1370894 as
extrusion apparatus comprising movable and fixed members defining an elongate passageway therebetween, an abutment member arranged to project into and block the passageway, means defining at least one die orifice leading from the passageway and associated with the abutment member, means for continuously feeding material to be extruded into the passageway at a point spaced from the abutment member, the amount of the surface area of the passageway defined by the movable member being greater than the surface area of the passageway defined by the fixed member, whereby upon movement of the passageway defining surface of the movable member relative to the passageway defining surface of the fixed member the material fed into the passageway is moved by fictional drag with the surface of the passageway in the movable member towards the abutment member and is thereby extruded substantially in its entirety through the or each die orifice in the usual form in which the second member is a wheel with a groove formed in its surface into which the first member projects; it is also applicable to the improved apparatus of U.K. Patent 2069389 in which the abutment member does not completely block the end of the passageway but is of substantially smaller cross-section than the passageway and leaves a substantial gap between the abutment and the groove surface, and in the operation of which a substantial proportion of the metal (as distinct from the inevitable leakage of flash through a working clearance) extrudes through the clearance and is allowed to remain as a lining in the groove to re-enter the passageway at the entry end.
[0003] Even in the latter case, some flash will escape in a radial direction between the side-walls of the groove and the first member (usually called the 'shoe') and is liable to be oxidised and/or irregular in shape so that its re-entry into the extrusion passageway is undesirable. Fixed scrapers and/or rotary milling cutters have been used to remove it; scrapers have usually been mounted in a nearly radial position, and have been susceptible to build-up of flash leading, if unchecked, to fracture of the scraper and a serious risk of damage to main components of the apparatus as fragments of the knife, as well as large pieces of flash, may be drawn back into the extrusion passageway before the rotation of the wheel can be stopped.
[0004] The present invention provides apparatus in which the risk of flash build-up is greatly reduced and the risk of fracture of the scraper substantially eliminated.
[0005] In accordance with the invention, Conform apparatus for continuous friction-actuated extrusion comprises: a rotatable wheel formed with a circumferential groove; a shoe enclosing a portion of the groove to define a working passageway; an abutment projecting into the working passageway to obstruct passage of metal therethrough to generate a pressure therein that is sufficient to cause at least some of the metal to extrude through a die aperture in or upstream of the abutment; and a scraper to remove flash from at least the sidewalls of the groove is characterised by the fact that the scraper is mounted for movement against a biassing force along a line at least approximating to the tangent to the wheel at the scraper position and in the direction of the movement of the wheel there.
[0006] Preferably the working face of the scraper is inclined at lest 30°, or better at least 45°, to the local radius in order to derive a substantial self-cleaning action from the movement of the wheel.
[0007] The line along which the knife can move may be a straight line coincident with or making a very small angle with the tangent, or it may be an arc or other curve lying close to the tangent in the region of movement, provided that necessary clearances are maintained: this is easier when the scraper does not extend to the base of the groove.
[0008] The biassing force for the scraper is preferably supplied by a hydraulic piston-and-cylinder motor maintained at a constant pressure, but other hydraulic, pneumatic or resilient biassing means could be used.
[0009] The invention will be further described by way of example with reference to the accompanying drawings in which Figure 1 is a side view of scraping apparatus for a Conform extrusion machine; Figure 2 is an enlarged detail showing the scraper itself from the opposite side to that shown in Figure 1; Figures 3, 4 and 5 are views of the knife in the directions of the arrows III, IV and V respectively in Figure 2; and Figure 6 is a fragmentary cross-section on the line VI-VI in Figure 1.
[0010] The apparatus shown in Figure 1 comprises a pair of identical plates 1, 2 spaced apart perpendicular to the plane of the figure and mounted in any convenient way upon the frame of the extrusion machine. A first-order lever 3 extends between the two plates and is pivoted to them by a bearing 4 which provides for limited adjustment perpendicular to the plane of the figure for alignment with the wheel groove. On the upper end of the lever 3 is mounted scraper 5, the detailed shape of which will be understood from reference to Figures 3-5. The scraper is suitably made from a tool steel, such as standard tool steel ref. T15 heat treated to a hardness of about 60 Rockwell C. The scraper is adjustable in the direction of its length by a screw 6 and after adjustment is rigidly clamped to the lever by a plate 7 with screws extending in front of and behind the blade. The working face of the scraper makes an angle α of about 45° with the local radius of the wheel 9. A hydraulic piston-and-cylinder motor 8 applies a biassing force and normally holds the lever 3 at the clockwise limit of its movement. The bracket 9 is longitudinally adjustable using screws 10 working in slots 11 in the bracket to allow the angular position of the blade 5 to be adjusted.
[0011] In the event of forces in excess of the biassing force being applied to the scraper by the flash being urged into engagement with it by rotation of the wheel 9, the lever 3 revolves in an anti-clockwise direction, the clearance between the scraper and the bottom of the wheel groove being sufficient to permit this. The movement of the blade may of itself be sufficient to clear accumulated flash, but as a precaution conventional instrumentation may be fitted to give an alarm signal whenever the blade is retracted.
[0012] For extrusion of copper using machine of the kind described in specification of British Patent 2069389 with a rectangular wheel groove 14mm wide and a semi-circular abutment, a biassing force4 (measured at the position of the scraper of about 15.5kN (3,500 lbs weight) has been found suitable. Clearances between scraper and wheel groove are significant design features: for a machine of this size we recommend clearances of:
2.0 -2.5 mm (0.080-0.10 inch) between the tip of scraper 12 and the adjacent point of the copper lining 13 in the wheel groove;
1.8-2.3 mm (0.07-0.09 inch) at each side 14 of the scraper; and
0.3-0.5 mm (0.012-0.02 inch) between the peripheral surface 15 of the wheel and the adjacent shoulder 16 of the scraper.
1. Conform apparatus for continuous friction actuated extrusion comprising: a rotatable
wheel formed with a circumferential groove; a shoe enclosing a portion of the groove
to define a working passageway; an abutment projecting into the working passageway
to obstruct passage of metal therethrough to generate a pressure therein that is sufficient
to cause at least some of the metal to extrude through a die aperture in or upstream
of the abutment; and a scraper to remove flash from at least the sidewalls of the
groove characterised by the fact that the scraper is mounted for movement against a biassing force along
a line at least approximating to the tangent to the wheel at the scraper position
and in the direction of the movement of the wheel there.
2. Apparatus as claimed in Claim 1 in which the working face of the scraper is inclined
at least 30° to the local radius of the wheel.