GB2209295A

GB2209295A - Continuous extrusion of tubes

Info

Publication number: GB2209295A
Application number: GB8820623A
Authority: GB
Inventors: Norman Reginald Fairey; John Baird Childs
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1987-09-03
Filing date: 1988-09-01
Publication date: 1989-05-10
Anticipated expiration: 2008-09-01
Also published as: NZ226004A; AU606198B2; GB8820623D0; AU2116288A; GB2209295B; GB8720670D0

Abstract

In continuous extrusion by the Conform process, tubes are formed (especially from relatively hard metals such as copper) using tooling located in the wheel groove. An abutment 1 obstructs the extrusion passageway at its downstream end (but preferably does not block it completely) to establish an upset region from which the metal passes through a die orifice 10, and a cantilevered projection extends from the abutment to enter the die orifice where it acts as a mandrel to define the bore of the tubular product 8. <IMAGE>

Description

CONTINUOUS EXTRUSION OF TUBES This invention relates to the continuous extrusion of tubes by the Conform process of CB-A-1370894 (United Kingdom Atomic Energy Authority) and more especially by the improved process of our GB-B-2069389, and to tooling for use therein.

Conform extrusion of aluminium tubes is now well established, and operates using an "expansion chamber" which is filled with aluminium caused to flow from the upset region created by the abutment and which discharges the still plastic metal through a tubing die.

Harder metals, such as copper, cannot be extruded in this way because it is not feasible to generate in the upset region a sufficient pressure to drive the metal through the expansion chamber.

The United Kingdom Atomic Energy Authority (paper presented by J.A. Pardoe at the Tube Production Conference organised by the Industrial Wire and Machinery Association in Birmingham, April 1987 and reprinted by the Authority in December 1978 as paper DCO Ref 7119(5), entitled "Non-ferrous tube production by the CONFORM Continuous extrusion process Development experience") experimented in 1975 with an alternative technique in which a bridge die penetrated to the root of the wheel groove, splitting the metal stream before it entered the die. Pardoe reported that the bridge was highly stressed, particularly at start up, and that after producing tubing of variable wall thickness it eventually collapsed. The experiments were evidently abandoned in consequence. Twelve years later, there is no known technique for Conform extrusion of copper tubes.

The present invention provides a process which is suitable for use in Conform extrusion of copper (as well as other metals of comparable or less hardness) and tooling for use therein.

In accordance with the invention, a method of Conform extrusion comprises feeding metal to be extruded to a passageway formed by a groove in the periphery of a rotating wheel and a stationary arcuate shoe, creating an upset region in which the metal is in a plastic state by means of an abutment which obstructs the passageway at the downstream end of the shoe and extruding the metal from the upset region through a die orifice and is characterised by the fact that a cantilevered projection extends from the abutment to enter the die orifice where it acts as a mandrel to define the bore of a tubular product.

In accordance with another aspect of the invention, tooling for Conform extrusion of tubes comprises an abutment for creating an upset region and a die defining a die orifice and is characterised by the fact that a cantilvered projection extends from the abutment to enter the die orifice where it acts as a mandrel to define the bore of a tubular product.

The upset region is subject to large forces, and the shape of the projection naturally needs to be designed to minimise frictional forces and to balance the forces due to friction and hydrostatic pressure, in order to avoid excessive bending (or other) stresses; but we have found that the reduction in frictional forces due to the omission of the support upstream of the die in Pardoe's bridge arrangement more than compensates the inherent disadvantages of using a cantilever, provided it is well-designed.

The invention will be further described by way of example, with reference to the accompanying drawings in which; Figure 1 is a plan view of an abutment forming part of the tooling in accordance with the invention (that is to say a view seer from the base of the wheel groove when the abutment is in place); Figure 2 is an end elevation in the direction of the arrows II-II in Figure 1; Figure 3 is a cross-section on the line III-III in Figure 1; Figure 4 is a plan view of a mating die member; Figures 5 and 6 are cross-sections on the lines V-V and VI-VI in Figure 4 respectively; and Figure 7 is a cross-section showing the abutment and die assembled together in their working positions, the line of section corresponding to III-III in Figure 1 and VI-VI in Figure 4.

The abutment 1 is made of a heat treated high-strength hot work steel, such as BH1OA, and comprises a body part 2 which is of the preferred shape defined in GB-B-2069389, having a semi-circular surface 3 designed to enter a rectangular wheel groove, leaving a sufficient clearance for the metal being extruded to pass also between the abutment and the base of the groove and adhere to base of the groove so as to circulate with the wheel; as seen in Figures 1 and 3, this body part 2 is slightly tapered towards the downstream end d of the abutment. The upstream end 5 of this body part is extended to form a cantilevered projection 6 which extends forwardly and then downwardly, terminating in a cylindrical portion 7 the axis 8 of which is parallel with the flat surface of the end 5.

The upstream end 5 is also formed with a pair of triangular flanges 9,9 to assist correct location with respect to the die member now to be described with reference to Figures 4 to 6.

This is an essentially rectangular block 10, formed with a counterbored die aperture 11 and with flats 12,12 on two of its corners which seat on the flanges 9 when the two parts are assembled, as seen in Figure 7.

The metal 13 being extruded remains in pressure tight contact with only a small portion of the curved surface 3, and consequently the hydrostatic pressure exerted by metal in the region 14 generates forces tending to move the abutment upwards as seen in Figure 7, towards the base of the wheel groove. In the design shown, this is countered by providing a bevelled surface 15 which tends to generate forces in the opposite direction.

Claims

Claims

1. A method of Conform extrusion comprising feeding metal to be extruded to a passageway formed by a groove in the periphery of a rotating wheel and a stationary arcuate shoe, creating an upset region in which the metal is in a plastic state by means of an abutment which obstructs the passageway of the downstream end of the shoe and extruding the metal from the upset region through a die orifice characterised by the fact that a cantilever projection extends from the abutment to enter the die orifice where it acts as a mandrel to define the bore of a tubular product.

2. Tooling for Conform extrusion of tubes comprising an abutment for creating an upset region and a die defining a die orifice characterised by the fact that a cantilever projection extends from the abutment to enter the die orifice. where it acts as a mandrel to define the bore of a tubular product.

3. A method of Conform extrusion of tubes substantially as described with reference to the accompanying drawings.

14. Tooling for Conform extrusion of tubes substantially as described with reference to and as shown in the drawings.