GB2153279A

GB2153279A - A method and apparatus for extrusion

Info

Publication number: GB2153279A
Application number: GB08402675A
Authority: GB
Inventors: Clifford Etherington; Harold Keith Slater; Robin John Luxmoore
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1984-02-01
Filing date: 1984-02-01
Publication date: 1985-08-21
Also published as: GB8402675D0; GB2153279B

Abstract

In extrusion, a mandrel 4 cooperable with a die orifice 2 is axially displaceable to vary the extent of the orifice available to material being extruded. The mandrel can be reciprocable between a first position (Fig. 1a) to expose the full extent of the die orifice and a second position (Fig. 1b) to partially close the die orifice to effect, respectively, extrusion of a solid section product and extrusion of a tubular section product. <IMAGE>

Description

SPECIFICATION A method and apparatus for extrusion The present invention concerns a method and apparatus for extrusion.

Extrusion is a well known and accepted process in which material is forced through a die orifice having a shape to determine the form of the extruded product. Thus, to form a rod or wire of solid cross-section the material can be extruded through an open circular die orifice. To extrude a tube, a mandrel can extend into the die orifice to form an annular extrusion zone. The mandrel is generally fixedly positioned relative to the die orifice.

According to one aspect of the present invention a method of forming an extruded product comprises extruding material through, a die orifice and simultaneously controlling the extent of the orifice available to the material to thereby determine the form of the extruded product.

According to another aspect of the present invention an extrusion apparatus comprises an extrusion chamber having a die orifice, selectively operable means within the chamber cooperable with the orifice to vary the extent of the orifice open to the chamber to thereby vary the form of an extruded product.

Preferably, the selectively operable means comprises a mandrel cooperable with the die orifice and displaceable to vary the extent of the die orifice available to the material being extruded. An end of the mandrel is moved into and out of the die orifice upon displacement of the mandrel. The end of the mandrel can be tapered. Conveniently. the mandrel is reciprocable between a first position to expose the full extent of the die orifice and a second position to partially close the die orifice to effect respectively extrusion of solid section product and the extrusion of tubular section product.

The invention will be described further, by way of example with reference to the accompanying drawings, in which: Figures 1 a to 1 d are diagrammatic representations to illustrate the principle of extrusion utilising a reciprocable mandrel cooperable with a fixed die orifice.

Figure 2 is a diagrammatic section of an embodiment of an extrusion apparatus.

n Figures 1 a to id an extrusion chamber,1 has a die orifice 2 in an end wall 3. Material within the chamber 1 is extruded through the orifice 2 on the application of an extrusion pressure to the material in a conventional and well known manner. An axially reciprocable mandrel 4 is arranged within the chamber 1 to cooperate with the orifice 2. In Figure 1 a the mandrel is in a position at which its free end is retracted clear of the die orifice with the result that the full extent of the orifice is available for the material being extruded. In Figure 1 b the mandrel has been advanced such that its free end is positioned centrally within the orifice resulting in an annular zone within the die orifice and about the end of the mandrel which is available for the material being extruded.In Figure 1 C the mandrel has been advanced further through the die orifice whereby an enlarged portion 5 of the mandrel abuts against the die orifice to close the orifice.

With the mandrel positioned as in Figure 1 a the material is extruded as solid section product for example rod or wire. In the Figure 1 b position of the mandrel the extruded product is tubular section and in the Figure 1 C position the extrusion is effectively blocked. Consequently, reciprocation of the mandrel between the different positions controls the form of the extruded product.

In the above arrangement the mandrel is a straight cylinder resulting when it is in the Figure 1 b position in a tubular section extrusion. However, the mandrel can be profiled, for example, to present portions of different diameters to impart a desired variation to the internal cross section along the product length. For example, the mandrel can be fluted or ribbed such that the internal wall of the tubular extrusion is correspondingly fluted or ribbed. The shape and profile of the mandrel will determine the internal section of the tubular product. The external section of the product will be determined by the shape and configuration of the die orifice.

Figure 1 d shows a modification in which the mandrel terminates in a taper 6 whereby the wall thickness of a tube can be varied steplessly by axial displacement of the taper relative to the die orifice.

The extrusion apparatus of Figure 2 comprises a wheel 10 carried on a shaft 1 2 for rotation in the direction indicated by the arrow thereon. A continuous circumferential groove 14 is formed in the periphery of the wheel 10. A shoe 1 6 fits about a portion of the periphery of the wheel 10, the shoe carrying a removable insert 1 8 terminating at one end in an abutment 20. The insert 1 8 projects into the groove 14 in the wheel with the abutment 20 substantially blocking the groove and hence the passage formed between the wheel 10 and the shoe 16. An orifice 22 in the insert 1 8 at or adjacent the abutment 20 communicates with a chamber 24 in the shoe. The chamber 24 constitutes an extrusion chamber having a die orifice 26 opening to the exterior of the shoe.A mandrel 28 is axially aligned with the die orifice 26 and is journalled in the shoe to cooperate with the die orifice 26. The mandrel is supported by bearings 29 and is reciprocable between a position at which the free end of the mandrel is retracted clear of the die orifice and an advanced position at which the free end thereof cooperates with the die orifice to de fine an annular extrusion zone. Drive means for reciprocation of the mandrel 28 can be arranged outside the shoe. The shoe can be provided with heating and/or cooling means 27.

In use, an extrudable feed material, which for example can be metal or plastics, is fed into the open end of the passage formed between the wheel 10 and the shoe 1 6.

Rotation of the wheel in the indicated direction causes the feed material to be drawn along the passage towards the abutment 20 by frictional drag in the manner as described, for example, in British Patent Specifications Nos 1,370,894 and 1,434,201. Upsetting of the feed material occurs in the vicinity of the abutment and the material flows through the orifice 22 into the extrusion chamber 24 to emerge through the die orifice 26.

With the mandrel in the retracted position with its free end clear of the die orifice 26 the full extent of the orifice 26 is available to receive the material. Consequently, the extruded product emerging from the orifice 26 is in the form of a rod of solid cross-section.

Upon advancing the free end of the mandrel into the die orifice to define an annular extrusion zone the extruded product is in the form of a tube. Reciprocation of the mandrel results in the continuous extrusion of alternate solid and tubular lengths of extruded product. The extruded product emerging from the die orifice 26 can be chopped into discrete individual lengths by means of a cutter blade 30.

Such a cutter blade can be coupled to operate in response to movement of the mandrel. For example the cutter can be arranged to function when the mandrel is in the retracted position and with a solid section rod emerging from the die orifice. This will result in the production of separate individual lengths of extruded product each comprising a hollow section having solid opposite ends. 8uch individual lengths could find use as structural members, for example in aircraft frames, or again as example each individual length can be cut in half to provide two identical cylinders.

In an alternative form of the apparatus the mandrel 28 can be tubular, that is provided with an axial bore extending the length thereof. As before, the mandrel is reciprocable to form alternate solid and tubular lengths of extruded product. During the interval that the mandrel is in its advanced position to effect extrusion of tube a material to be encapsulated can be delivered through the hollow mandrel into the extruded tube as it is being formed. The delivery of the material to be encapsulated will be stopped prior to retraction of the mandrel from the die orifice to effect solid section extrusion which will form an integral end cap for the tube.The delivery of the material to be encapsulated can be synchronised with the movement of the mandrel such that such material only passes through the bore in the mandrel when the mandrel is in a position relative to the die orifice to effect a tubular extrusion. The continuous extruded product emerging from the die orifice can be separated into individual filled and sealed containers by a cutter blade operable to shear through the sections of solid extrusion.

In an alternative form of apparatus the shoe 1 6 can cooperate with two or more wheels 10 each arranged to feed material into the chamber 24 for extrusion through the die orifice 26. For example with reference to Figure 2 the shoe can be modified to accept a second wheel 10 with the mandrel 28 being located between the two wheels. Yet again, a wheel can be provided with two or more grooves communicating with the chamber 24.

As alternatives to the wheel or wheels to create the extrusion forces it is possible to utilise a ram or hydrostatic pressure to effect extrusion at the die orifice 26.

Claims

1. A method of forming an extruded product which comprises extruding material through a die orifice and simultaneously controlling the extent of the orifice available to the material to thereby determine the form of the extruded product.

2. A method as claimed in claim 1 which comprises arranging a mandrel to cooperate with the die orifice and selectively displacing the mandrel relative to the die orifice.

3. Extrusion apparatus comprising an extrusion chamber having a die orifice, selectively operable means within the chamber cooperable with the orifice to vary the extent of the orifice open to the chamber to thereby vary the form of an extruded product.

4. Extrusion apparatus as claimed in claim 3 in which the selectively operable means comprises a mandrel reciprocable to vary the extent of the die orifice.

5. Extrusion apparatus as claimed in claim 4 in which the mandrel is reciprocable between a first position to expose the full extent of the die orifice and a second position to partially close the die orifice to effect respectively extrusion of solid section product and tubular section product.

6. Extrusion apparatus as claimed in claim 5 in which the mandrel is reciprocable between a third position to close the die orifice and the first and second positions.

7. Extrusion apparatus as claimed in claim 4, 5 or 6 in which an end of the mandrel cooperable with the die orifice is tapered.

8. Extrusion apparatus as claimed in any one of claims 3 to 7 including cutter means for severing extruded product emerging from the die orifice into individual lengths.

9. Extrusion apparatus as claimed in claim 8 in which the cutter means is synchronised for movement with the mandrel.

1 0. Extrusion apparatus comprising a rotatable wheel member having an endless groove therein, a stationary shoe member overlying part of the length of the groove to define a passageway therebetween, an abutment associated with the shoe to block the passageway, an outlet at or adjacent the abutment leading from the passageway to a chamber having a die orifice and a reciprocable mandrel cooperable with the die orifice and operable to vary the extent of the die orifice.

11. A method of forming an extruded product substantially as herein described with reference to the accompanying drawings.

1 2. Extrusion apparatus substantially as herein described with reference to and as illustrated in the accompanying drawings.