GB2028206A - Extrusion apparatus - Google Patents

Abstract

Extrusion apparatus comprises a rotatable wheel member having a circumferential groove 13, a fixed shoe member covering part of the groove to form a passageway, a fixed abutment member projecting into the groove so as to blank off one end of the passageway and at least one die orifice associated with the abutment member or shoe member. A driving assembly for the wheel member and an annular driven part 10 secured to the driving assembly form the peripheral groove and the annular part 10 is replaceable when necessary. <IMAGE>

Description

SPECIFICATION The forming of materials by extrusion This invention relates to the forming of materials by extrusion.

Our British Patent Specification No 1,370,894 discloses and claims a process of and apparatus for the forming of materials by extrusion which can be performed continuously provided the feed material is fed in continuously. The said process in broad terms comprises the steps of feeding material into one end of a passageway fomed between first and second members with the second member having a greater surface area for engaging the material to be extruded than the first member, said passageway having a blocked end remote from said one end and having at least one die orifice associated with said blocked end, and moving the passageway-defining surface of the second member relative to the passageway-defining surface of the first member in a direction towards the or each die orifice from said one end to said blocked end such that the frictional drag of the passageway-defining surface of the second member draws the material substantially in its entirety along the passageway and through the or each die orifice.

The apparatus referred to in the said British Patent Specification No 1,370,894 in broad terms comprises 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 position spaced from the abutment member, the amount of the surface area of the passageway defined by the movable member being greater than the amount of 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 frictional 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.

A particular form of the said apparatus, disclosed in the said British Patent Specification No 1,370,894, comprises a rotatable wheel member having an endless groove therein and constituting the movable member, a shoe member covering part of the length of the groove, forming a passageway therewith, and constituting the fixed member, an abutment member associated with the shoe member and projecting into the groove and blocking one end of the passageway, and at least one die orifice associated with the abutment member or shoe member. This apparatus is capable of performing continuous extrusion through the die orifice of material fed to the said passageway, provided the wheel is rotated and the feed material is supplied continuously.

Described in our British Patent Specification No.

1,434,201 which is a Patent of Addition to our said British Patent No 1,370,894, are improvements in the apparatus specified in the preceding paragraph.

They include the improvement of the shoe member having a portion projecting into and extending over a length of the passageway in front of the abutment member and of a width substantially equal to that of the passageway. Another improvement is that the wheel member with groove comprises three abutting discs, the centre disc having a diameter less than the diameter of the abutting outer discs whereby to form the groove, together with means to maintain the discs in abutting relationship. Such means may be opposed inwardly-acting compressive forces exerted on the outer faces of the outer discs.

The three part wheel is a way of avoiding stress concentration at the abrupt changes of direction manifest by the groove corner that would exist in a groove machined into a single partweel.

During extrusion the wheel is subject to cyclic loading which is partly thermal and partly mechanical. The thermal loading derives from the temperature rise resulting from sliding friction between the feed material, the shoe member and the wheel, and from the deformation energy developed in the process. The mechanical loading derives from the pressure generated in the zones where upsetting and extrusion occur. Both of these loadings are cyclic because they occur during rotation as each part of the working surface of the wheel passes in and out of the extrusion zone. The combined cyclic loading eventually can give rise to the production of micro fatigue cracks in the groove surfaces, such cracks tending to propagate as feed material is forced into them by the said pressure until failure occurs.In the three-part wheel there is difficulty in extracting heat from the centre part which forms the root of the groove and this component is more susceptible to failure from thermal fatigue than the side parts. The present invention is capable of providing a wheel construction which reduces or overcomes this disadvantage.

It will also be appreciated that, if a one-part or three-part wheei becomes damaged, e.g. as stated in the preceding paragraph, and needs to be changed, such a change will involve considerable expense and difficulty particularly where the wheel is of large diameter, in that the replacement wheel, whether one orthree-partwill employ a large quantity of material (itself expensive where an alloy steel such as a hot working steel of the 5% chrome type, is employed) which requires heat treatment, and due to the large size and weight, also involves diffuclty in handling when removing and fitting on replacement.

The present invention seeks to provide a wheel assembly the construction of which is intended to reduce the expense and difficulties associated with a wheel change, and to provide greater flexibility of design, particularly in groove size.

According to the invention, in or for apparatus for the continuous forming of material by extrusion which employs a rotatable wheel with an endless peripheral groove, such wheel has a driving assembly for mounting on a driving shaft so that drive is transmitted thereto, and an annular driven part secured to the driving part and forming a peripheral groove in conjunction therewith, the driven part being separated from the driving shaft.

Preferably the driving assembly of the wheel is in two adjacent parts with provision for being keyed to the said driving shaft, the annular driven part being trapped between the two driving parts with means for transmitting drive therebetween, and means being provided for holding the driving parts and the annular parts in close engagement.

A constructional embodiment of the invention will now be described by way of example with reference to the accompanying drawings, wherein Figure lisa side elevation of one of two similar elements of a wheel assembly for continuous extrusion apparatus, Figure2 is an end view in section on line ll-ll of Figure 1, Figure 3 is a side elevation of another element of said wheel assembly, Figure 4 is a end view in medial section of the element of Figure 3, and Figure 5 is a fragmentary end view in section of the assembled elements.

Referring to Figures 1 and 2 of the drawings, one of two elements for the driving part of a wheel assembly for apparatus for continuous forming of extrusion of the kind disclosed in our British Patent Specifications Nos. 1,370,394 or 1,434,201 consists of a disc-like member 1 having four equispaced keyways 2 for driving engagement via keys 3 with a driving shaft 4, both keys and driving shaft being shown in dot-and-dash outline in Figure 1. The member 1 has a plain vertical side 5 (Figure 2) and its opposite side 7 is relieved at 6 and has four lateral holes 8 extendinyg from further relieved portions 9 and equiangularly spaced around the member 1. The other element is a mirror image of the one described.

Referring now to Figure 3, another element is shown, consisting of an annulus 10 provided with cut-out portions 11, formed as half-circules in crosssection which correspond in spacing and in diametral position with the holes 8 of the members 1. The annulus 10 is rectangular in cross-section, and when assembled with the two members 1, see Figure 5 which shows part only of the assembly, the members 1 trap the annulus 10 between them with the non-relieved parts of sides 7 facing each other with clearance beneath the annulus 10, the relieved portions 6 accommodating the annulus 10 between them and engaging therewith, and the further relieved portions 9 providing annulus channels 12 around the assembly.Pegs (not shown) engage the holes 8 and cut-out portions 11 and prevent relative rotation between the two members 1 and annulus 10 so that, when drive is transmitted to the members 1 via keys 3 and keyways 2, it is also transmitted to the annulus 10. The latter, being cf lesser diameter than the external diameter of members 1, forms with the latter a peripheral groove 13 which is active in the performance of continuous extrusion as setforth in the said British Patent Specifications Nos. 1,370,894 and 1,434,201.

In order to lessen the effects of thermal cycling as aforesaid, the channels 12 may be employed for cooling the groove sides and floor by having coolant fed to them via a suitable radial feed channel (not shown) or, with one or more connecting channels (not shown), via the clearance between faces 7 (Figure 5) and a radial coolant duct (not shown) in the driving shaft 4 (Figure 1).

As in the three-part wheel referred to in connection vvith our British Patent Specification No.

1,434,201, a side loading is applied to each member 1 acting in an inward direction.

Claims (4)

1. Apparatus for the continuous forming of materials by extrusion which apparatus comprises a rotatable wheel member having an endless groove therein and constituting a movable member, a shoe member covering part of the length of the groove, forming a passageway therewith and constituting a fixed member, an abutment member associated with the shoe member and projecting so far into the groove as to block one end of said passageway and constituting another fixed member, and at least one die orifice associated with the abutment member or shoe member, the amount of the surface area of the passageway defined by the movable member being greater than that defined by the shoe member, and the said endless groove being a peripheral groove disposed in the periphery or peripheral region of the wheel member, wherein the wheel member has a driving assembly for mounting on a driving shaft adapted to be rotated by drive means so that drive is transmitted to said driving assembly, and an annular driven part secured to the driving part for rotation thereby and forming, in conjunction with said driven part, the said peripheral groove, the driven part being separated from the driving shaft.

2. Apparatus according to claim 1, wherein the said driving assembly of the wheel is in two adjacent parts with provision for being keyed to said driving shaft, the annular driven part being trapped between the two driving parts with means for transmitting drive therebetween, means being provided for holding the driving parts and the annular part in close engagement.

3. For apparatus substantially as set forth in claim 1, a wheel assembly substantially as hereinbefore described with reference to the accompanying drawings.

4. Apparatus substantially as setforth in claim 1, including a wheel assembly according to claim 3.