AU632220B2 - Extrusion die cooling system - Google Patents

Description

i I ,WO 91/12097 PCrAU91/00043 EXTRUSION DIE COOLING SYSTEM This invention relates to extrusion dies and in particular to such dies in which heat is generated during use and which benefit from application of a cooling medium. By way of example, dies of that kind include dies used to extrude metal sections such as aluminium sections. It will be convenient to hereinafter describe the invention with particular reference to such metal extrusion dies.

It is known to use liquid nitrogen as the cooling medium for extrusion dies, but the cost benefit of that type of cooling has not been good. Use of liquid nitrogen increases the useful life of the die and allows faster extrusion speeds, but the cost benefits of those advantages are subst antially offset, if not completely offset, by the supply cost of the liquid nitrogen.

Part of the problem lies in the relative efficiency of the cooling systems which employ liquid nitrogen. Suc h systems as used to date have failed to maximise the rooling benefits of liquid nitrogen and as a consequence are not terribly efficient.

It is an object of the present invention to provide extrusion apparatus, and in particular an extrusion die having an improved and relatively efficient cooling system. It is another object of the invention to provide an improved method of cooling an extrusion die.

In accordance with one aspect of the invention, there is provided an extrusion die including, a die set comprising a die member and a backing member arranged in face to face engagement, a die opening formed through a front face of said die member which is remote from said backing member, a cavity formed through a back face of said die member and communicating with said opening, a coolant distribution passage provided in said die set and being connectable to a source of. cooling medium, and a plurality of feed passages each providing communication between said distribution passage and said cavity and each communicating with said cavity at a location adjacent said opening.

In accordance with another aspect of the invention, I: i WO 91/12097 PC/AU91/00B43 -2there is provided a method of cooling an extrusion die of the kind having a die set composed of a die member and a backing member arranged in face to face engagement, said die set having a die opening formed through a front face of said die member and a cavity formed through a back face of said die member so as to communicate with said opening, said method including the steps of feeding a cooling medium into said die set, dividing said medium into a plurality of streams either before or after it enters said die set, and directing each said stream so as to emerge in said cavity at a respective location adjacent said opening.

An extrusion die according to the invention is particularly satisfactory for extruding aluminium and similar alloys.

An ep-bodiment of the invention will now be described in detail in the following passages of the specification which refer to the accompanying drawings. The drawings however are merely illustrative of how the invention might be put into effect, so that the specific form and arrangement of the various features as shown is not to be understood as limiting on the invention.

Figure 1 is a diagrammatic side elevation view of a typical -extrusion die as known prior to the present invention.

Figure 2 is a front elevation view taken along line II-II of Figure 1 and showing a d.e aperture for forming an extruded aluminium section.

Figure 3 is a view taken along line III-III of Figure 1.

Figure 4 is an enlarged cross-sectional view taken along line IV-IV of Figure 2.

Figure 5 is an enlarged view of portion of the backing member as shown in Figure 3, but in which the backing member has been modified in accordance with one embodiment of the invention.

Figure 6 is a view similar to Figure 4 but showing the die member and the backing member modified according to the embodiment of the invention referred to in relation to Figure Figure 7 is a view taken along line VII-VII of WO 91/12097 PCT/AU91 /00043 -3- Figure 6.

Figure 8 is a view similar to Figure 6 but showing a variation of the arrangement of Figure 6.

In the drawings: Figure 9 is a diagrammatic view of extrusion apparatus incorporating a die in accordance with figures to 7, or 8.

Figures 1 to 4 illustrate part of a die set according to the prior art. That die set includes a die plate 1, a backing plate 2 and a bolster 3. The die and backing plates 1 and 2 are in face to face engagement as shown, and the backing plate 2 is in face to face engagement with the bolster 3. A die opening 4 of appropriate shape is formed through the front face 5 of the die plate as shown in Figure 2. The shape and size of the opening 4 will vary according to the nature of the extrusion to be formed by the die. The particular opening 4 shown in Figure 2 is designed to form an aluminium section.

An enlarged cavity 6 is formed through the back face 7 of the die plate 1 and communicates with the opening 4 as shown in Figure 4. The cross-sectional shape and size of the cavity 6 can vary according to requirements. A clearance passage 8 formed through the backing plate 2 in effect forms an extension of the cavity 6 whereby an extrusion emerging from the die plate 1 can pass through the die set.

A cooling medium such as liquid nitrogen can be introduced into the die set through an inlet passage 9 as shown in Figure 3, and flows through a transfer passage to enter a coolant distribution passage 11. The coolant distribution passage 11 usually extends completely around the extrusion clearance passage 8 as also shown in Figure 3, and is connected with the passage 8 through a plurality of branch passages 12.

In the particular arrangement shown in Figures 1 to 4, each of the passages 10, 11 and 12 is formed by a groove or channel in the outermost face 13 of the backing plate 2, and an overlying portion. of the back face 7 of the die plate i.

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WO 91/12097 PCT/AU91/00943 -4- All of the foregoing is in accordance with the prior art. It will be seen that coolant enters the die plate 1 through the back end of the cavity 6, and therefore has some distance to travel before reaching the die opening 4. During operation of the die, high temperatures are generated at the die opening 4 because of friction between the material being extruded and the bearing surface 14 of the opening 4. The region of the die plate 1 around and adjacent to the opening 4 is therefore the part of the die set which is most in need of cooling if the die set is to have a satisfactory working life.

The arrangement according to Figures 1 to 4 fails to achieve adequate cooling at the die opening 4 because of two factors. Firstly, only part of the coolant stream will travel towards the die opening 4 from the die plate/backing plate interface. The remainder of the coolant will flow from that interface towards the bolster 3. Secondly, the coolant flowing towards the die opening 4 will be in contact with the extruded material and consequently there will be a transfer of heat from the extrusion to the coolant. As a result, the cooling potential of the coolant will be reduced by the time it reaches the opening 4.

It will be apparent that, in the prior art arrangement, the only part of the die plate which is effectively cooled is that part adjacent to the back face 7, and that is remote from the part having the greatest need for cooling. Figures 5, 6 and 7 on the other hand, show an arrangement according to the invention in which there is effective cooling of the front part of the die plate 1, and in particular the region adjacent the die opening 4.

A feature of the arrangement shown in Figure 5 is the absence of branch passages 12 between the distribution passage 11 and the extrusion clearance passage 8.

Communication between the distribution passage 12 and the cavity 6 is achieved by way of a plurality of feed passages 15 formed in the die plate 1. Each feed passage extends from the back face 7 of the die plate 1 to connect with the cavity 6 at a location adjacent to the WO 91/12097 PCT/AU91/00043 opening 4. In the arrangement shown, a step 16 is formed at the junction of the cavity 6 and the opening 4, and each of the passages 15 connects with the cavity 6 at or adjacent that step 16.

As will be seen from Figure 7, each feed passage is spaced laterally from the other passages 15 so that it has a unique point of communication with both the distribution passage 11 and the cavity 6. The number and spacing of the feed passages 15 will vary according to the size and shape of the die opening 4.

Liquid nitrogen or other coolant which is fed into the distribution passage 11 will exhaust from that passage through the various feed passages 15 to emerge into the cavity 6 adjacent the die opening 4. That is, the body of liquid nitrogen entering the die is divided into a p]urality of streams (the number being dictated by the number of feed passages 15), each of which is directed to emerge into the cavity 6 adjacent the die opening 4 so as to optimise the cooling effect of the liquid nitrogen at the part of the die which benefits most from such cooling. There may be some diminution in the cooling effect of the liquid nitrogen because of heat transfer by conduction during its passage to the die hot zone, but the improved cooling effect of the system according to the invention remains in spite of that diminution.

Persons skilled in the relevant art will be able to determine appropriate cross-sectional sizes for the passages 11 and 15 according to particular circumstances.

It is preferred, however, that the cross-sectional size of the passages 15 be kept to a minimum so as to avoid possible vaporization of the coolant at the zone of application. The cross-sectional size of the passage 1l may be kept to a minimum for the same reason.

Vapourisation of the coolant can have the consequence of creating back pressure in the system such as to inhibit or prevent flow of further coolant to the hot zone of the die.

Very high temperatures are generated in large dies, and the cooling demands will generally be greater under those circumstances. The normal approach to higher cooling demand is to increase the coolant flow rate to the WO 91/12097 PCT/AU91/00043 -6hot zone by increasing the cross-sectional size of the passage or passages through which coolant flows.

According to one embodiment of the present invention, such an increase in size is not the preferred approach, or at least is not the only approach. It is preferred to keep the cross-sectional size of the feed passages 15 to a minimum and to meet the demand for increased cooling, at least in part, by increasing the velocity of flow of coolant to the hot zone. That increase in velocity may be achieved by including a cryogenic pump in the system.

Furthermore, it may be desirable to also keep the cross-sectional size of the passage 11 to a minimum.

It is thought that the risk of vaporization is minimised by reducing the residence time of the coolant within the flow passages, and an increase in flow velocity is a means to that end. Furthermore, any increase in cross-sectional size of the flow passages naturally increases the surface area of the coolant body which is exposed to the hot die, and that also increases the risk of vaporization. It is therefore preferred to keep the cross-sectional size of the passages 15, and possibly the passage 11, to a minimum and to rely at least in part upon increased flow velocity to meet any increase in cooling needs. Under some circumstances, the normal feed pressure of the coolant may be adequate.

It will be apparent that the invention can be applied to die set arrangements different to that shown in the drawings. For example, the distribution passage 11 need not be formed in the manner described, and it may be located other than at the interface of the two plates 1 and 2.

and 2.Figure 8 shows a modification in which each feed passage 15 is reduced in cross-sectional size adjacent to the opening 4. In a typical arrangement, involving the feed passages of either Figure 6 or Figure 8, the axis of each passage 15 may extend at an angle in the range of 200 to 500 inclusive relative to the longitudinal axis of the die set.

Extrusion apparatus according to the invention is shown diagrammatically in Figure 9. The die plate 1 may WO 91/12097 PCT/AU9!/00043 -7be in accordance with Figures 6 or 8, or it may be of some other suitable form. An extruder 17.is operable to feed material to be extruded (eg, aluminium) to the die opening 4 and from there to the die cavity 6.

In a preferred arrangement, the cooling medium is liquid nitrogen, and a source of that cooling medium is represented by the block 18. Liquid nitrogen is fed under pressure to the die plate 1 through a supply passage 19 and the feed passages 15, and a pump 20 is provided to control that feed.

The arrangement is preferrably designed so that conversion of the liquid nitrogen to gas is inhibited until the coolant emerges into the die cavity 6, and that emergance occurs at or adjacent to the die opening 4. The coolant has optimum cooling effect at the time of that conversion, and the area of the die opening 4 is the area of the die set which is most in need of cooling. Design perameters which are thought to have an influence on the time and location of the conversion (expansion) of the coolant to a gas are the cross sectional size of the various passages through which the coolant is transported, positioning of the exit ends of the feed passages 15, and the internal pressure of the coolant during its transport to the die opening 4.

A number of factors may contribute to maintennance of a suitable internal pressure for the coolant, and passage cross-sectional size is one such factor. Velocity of transport of the coolant is another, and that may be controlled, at least to some extent, by an adjustable pressure regulator 21 located on the outlet side of the pump 20. Appropriate selection of the pump 20 is also relevant to the matter of coolant velocity. An objective of the arrangement is to move the coolant through the system at a velocity such as to minimize residence time and thereby minimize vapourisation of the coolant during its transport to the exit ends of the feed passages It will be apparent from the foregoing description that the invention is characterised in that coolant is fed from the distribution passage 11 to the opening 4, or a region adjacent the opening 4, and as a consequence is Ir -~-LIU ICIIIC--- L -CI-L-~ WO 91/12097 PCI/AU91/00043 -8directly applied to that part of the die plate 1 which benefits most from effective cooling. Such an arrangement not only extends the useful working life of the die, but also allows use of higher operating speeds and improves the surface finish of the extrusion.

Various alterations, modifications and/or additions may be introduced into the construction and arrangement of parts previously described without departing from the spirit or ambit of the invention as defined by the appended claims.

Claims (19)

1. An extrusion die including, a die set comprising a die member and a backing member arranged in face to face engagement, a die opening formed through a front face of said die member which is remote from said backing member, a cavity formed through a back face of said die member and communicating with said opening, a coolant distribution passage provided in said die set and being connectable to a source of cooling medium, and a plurality of feed passages each providing communication between said distribution passage and said cavity and each communicating with said cavity at a location adjacent said opening.

2. An extrusion die according to claim 1, wherein at least part of said distribution passage is formed in said backing member.

3. An extrusion die according to claim 1, wherein at least part of said distribution passage is composed of a channel which is formed in the face of said backing member which is adjacent to and engaged by said back face of the die member, and each said feed passage extends from said back face towards said front face to communicate with said cavity.

4. An extrusion die according to any preceding claim, wherein a step is formed at the junction of said cavity and said opening and extends laterally outwards from said opening, and each said feed passage communicates with said cavity at a location adjacent said step.

An extrusion die according to any preceding claim, wherein the end of each said feed passage at the distribution passage is spaced from the corresponding end of each other said feed passages, and end of each said feed passage at the cavity is spaced from the corresponding end of each other said feed passages.

6. An extrusion die according to any preceding claim, including a plurality of said die openings, each said opening having a respective said cavity, a respective said distribution passage, and respective said feed passages, associated therewith.

7. Extrusion apparatus including a die according to any 1YI I14CIUIIIC WO 91/12097 PCT/AU91/00043 one of claims 1 to 6, a cooling medium source, a supply passage connecting said source to, said distribution passage, and a pump operable to cause cooling medium to be conveyed under pressure from said source and through said supply passage.

8. Apparatus according to claim 7, further including pressure regulating means connected to said supply passage and being operable to regulate the pressure of said cooling medium being conveyed through that passage.

9. Apparatus according to claim 8, wherein said pressure regulating means is adjustable.

Apparatus according to any one of claims 7 to 9, wherein said cooling medium is liquid nitrogen.

11. Apparatus according to claim 10, wherein the cross-sectional size of said feed passages and the velocity at which said cooling medium is conveyed through said supply and feed passages, are predetermined so that conversion of said liquid nitrogen to a gas is inhibited until said liquid nitrogen arrives at or adjacent said front face of the die member.

12. A method of cooling an extrusion die of the kind having a die set composed of a die member and a backing member arranged in face to face engagement, said die set having a die opening formed through a front face of said die member and a cavity formed through a back face of said die member so as to communicate with said opening, said method including the steps of feeding a cooling medium into said die set, dividing said medium into a plurality of streams either before or after it enters said die set, and directing each said stream so as to emerge in said cvvity at a respective location adjacent said opening.

13. A method according to claim 12, wherein said cooling medium is liquid nitrogen.

14. A method according to claim 13, wherein said liquid nitrogen is converted to a gas at or adjacent said front face of the die member.

A method according to claim 12,13, or 14 wherein said division of the cooling medium is effected through a distribution passage which receives said cooling medium from a supply source, and a plurality of feed passages C i I~LL~r I ~L J L~rr: i RECEIVEb :YUB JL A A J A U each of which communicates with said distribution passage at a respective location within that distribution passage and also communicates with said cavity at a respective location within that cavity.

16. A method according to any one of claims 12 to wherein the velocity 'at which said cooling medium is transported through said die set is controlled at least in part by regulating the internal pressure of said cooling medium.

17. An extrusion die substantially as herein described with particular reference to what is shown in Figures 5 to 7, or 8, of the accompanying drawings.

18. ExtrUsion apparatus substantially as herein described with particular reference to what is shown in figure 9 of the accompanying drawings.

19. A method of cooling an extrusion die substantially as herein described with particular reference to what is shown in Figures 5 to 7, or 8 and 9, of the accompanying drawings. Uuf' A~l4~tv. C, 0 0 0 SUBSTITUTE SHEET _J I