GB2372955A

GB2372955A - The production of foamed components

Info

Publication number: GB2372955A
Application number: GB0104395A
Authority: GB
Inventors: Philip Milroy Thomas
Original assignee: Holton Machinery Ltd
Current assignee: Holton Machinery Ltd
Priority date: 2001-02-22
Filing date: 2001-02-22
Publication date: 2002-09-11
Anticipated expiration: 2021-02-22
Also published as: GB0104395D0; GB2372955B

Abstract

There is disclosed a process and apparatus whereby foamed product of non-ferrous metal may be formed continuously and in indefinite lengths using a continuos extrusion machine of the Conform ¹ type. The continuous extrusion machine is supplied with feedstock consisting of a mixture or particulate metal and a foaming agent. The feedstock is extruded through a die (9) of the extrusion machine in the usual way. The extrusion is then led to a further through mould (11) in a hot foaming condition and allowed to expand to fill the mould. The temperature of the mould is controlled to promote and/or stop the foaming process so that the product leaving the mould is set in a desired section.

Description

The Production Of Foamed Components It is known that metals and alloys can be produced with foam like structures and that foaming can be achieved in a variety of different ways. These foamed materials are typically produced with densities in the range 5-20% that of the solid metal The three most common techniques for the production of foamed materials are: (a) The addition of a foaming agent to liquid metal-that is then cast-into the required shape.

(b) Producing a preform that is a mixture of metal powder and foaming agent. The preformed components are then placed inside a mould and heated to a suitable temperature such that the foaming agent starts to foam.

(c) Pouring liquid metal into a mould that is essentially a mirror image of the shape to be produced and is itself a foam.

In all of the above cases the process to produce an end product is essentially discontinuous with a number of process steps.

The Conform process is a well known process for continuously extruding nonferrous metals, particularly but not exclusively aluminium and copper. In the process feedstock, in the form of any of cast metal bar, powder or melt is delivered to a passage formed by the cooperation of an endless groove in the rim of a rotatable wheel and a shoe which closely envelopes part of the rim of the wheel. The passage is obstructed by an abutment which causes the feedstock to be compressed and heated by friction with the wheel as it rotates towards the abutment. In consequence the feedstock reaches an extrudable condition and is forced through passages in the shoe leading out through an extrusion die. The die can be shaped to produce any of a large range of sections, including a solid and hollow section in simple shapes such as cylindrical or rectangular (especially square) and complex shapes e. g. having fins. It is common to deliver the extrusion to coiling apparatus downstream of the conform and cooling apparatus may be

located downstream to control the properties of the extrusion and to prepare it for coiling.

The present invention aims to alleviate the technical disadvantages of the known prior art and accordingly provides a process comprising the steps of: delivering a feedstock comprising a mixture of metal and foaming agent to a conform machine, extruding a preform from a die of the conform machine, conveying the preform to a mould downstream of the die, and allowing the preform to foam within the mould as it is conveyed continuously from an inlet of the mould to an outlet.

The feedstock may be either one of a mixture of molten metal and a foaming agent, or a mixture of particulate metal and a foaming agent.

The process relies on the fact that the preform exits the conform machine at a temperature in excess of the foaming temperature, the foaming temperature being the temperature which causes the foaming agent to generate gaseous products and foam the metal component of the feedstock. By then passing the preform into and through a die the shape of the foaming preform can be constrained to the shape of the die. The die, will be an external die, i. e. , a die having a continuous mould passage through it leading from an inlet to an outlet. The sectional shape of the mould passage will then be imposed upon the external section of the foamed product. The section of the mould passage may be rectangular, particularly square, circular, oval, with or without flattened surfaces.

It is preferable in many applications that the external surface of the foamed product is solid so that in section there is a solid skin and a foamed core. The invention therefore proposes the step of applying pressure to the surface of the foamed product causing the foamed surface to collapse and form a skin. Preferably this may be achieved by selecting the relative cross sectional size of the mould passage and the preform/conform die so that sufficient pressure is imposed on the surface foam of the

product, by the expansion of the foaming agent, as it passes through the die that it collapses to form a smooth skin.

The process of skin formation may be further enhanced by the step of heating the mould passage surface.

The process may enable the product to be coiled downstream of the formation step.

It should be u-nderstood thatTherein the terms aluminium or copper or metal may refer either to the pure metal or more usually in practice and alloy of the metal.

Further according to the present invention there is provided apparatus for the continuous formation of a foamed metal product of indefinite length comprising a continues extrusion apparatus of the conform type and a mould located immediately downstream of the extrusion apparatus having a mould passage whereby, in use, preform extruded from the extrusion apparatus and delivered at in excess of the foaming temperature is foamed as it is transported continuously from an inlet of the mould passage to an outlet of the mould passage.

The conform apparatus is adapted by substantially conventional equipment to receive feedstock in the form of either molten metal or metal powder which may already be mixed with a foaming agent.

Heaters may be provided within the mould to heat all or part of the length of the mould in order to control the rate and completion of the foaming process and to encourage the formation of a metal skin on the product. Part of the length of thpmould may be cooled in order to slow or stop the foaming process before the product exits the mould and to provide for handling the cooled product downstream.

It is known that the Conform process can be used to produce aluminium alloy preforms by feeding the Conform machine with a mixture of aluminium alloy and foaming agent. The preform extruded from the Conform machine is conventionally prevented from foaming by cooling the extruded product immediately it leaves the die area. The

present invention thus substitutes the hot moulding step for the cooling step.

The ratio of the cross section of the extrusion die to the cross section of the finished product is selected to ensure that the foamed product is of the correct density.

By way of example if it is required to produce a finished product in the form of a square with a cross section of 625 mm2 with a density of 10% of the solid metal the extrusion die should have a diameter of approximately 10mm. The finished product mould can be heated to ensure complete foaming of the product and be cooled to allow handiing of the finished product. It is possible to control the density of the finished product by selecting the correct ratio of feedstock cross sectional area to product cross sectional area. By controlling the heat input into the mould the surface characteristics of the finished product can be regulated.

An embodiment of a process and apparatus for extruding foamed product continuously will now be described by way of example only with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic sectional view of an apparatus, and Figure 2 illustrates the change of product section during foaming.

Figure 3 illustrates a second embodiment of the invention.

Referring to figure 1 the Conform machine comprises a wheel 1 which is rotatable clockwise in the direction of the arrow. A groove 2 is formed in the rim of the wheel 1 into which a mixture of powdered metal and foaming agent 4 can be delivered from a hopper 3. The metal powder and foaming agent are entrained in a passage, formed between the wheel rim and a shoe 6 and carried towards an abutment 7. At the abutment 7 the metal powder and foaming agent which forms the feedstock is compressed and heated by friction with the wheel until it extrudes through a passage 8 into a die chamber and through a die 9.

The feedstock is now in the form of a compressed preform rod 10 at a high temperature well in excess of the foaming temperature. In consequence the foaming

agent begins to decompose into gaseous products as soon as the restrain of the die and extrusion machine pressures are removed. The result is that the plastic partially fused metal expands as bubbles of gas are generated within it. To control this expansion a mould 11 is provided which consists basically of a rigid tube having an inlet to a mould passage 12 in line with the exit from the extrusion die and very close to the extrusion die, usually without any other than associated connection and support structures between the mould and the die.

The mould is of sufficient length that by the time the foamed product leaves the mould passage 12 it has finished foaming and expanding. The relative cross section of the mould passage 12 and the die is selected to control the density of the foamed product. In most applications it is desirable to form a solid skin on the surface of the product. This is encouraged by the mould which applies pressure to the surface and may be further encouraged by heaters (not shown) arranged to heat the surfaces forming the mould passage 12. These encourage the metal at the surface to remain molten or to melt after the foaming process has completed so forming a solid skin.

The finished foam product may be cooled by chillers (not shown) which may be formed in the mould downstream or upstream of the heaters. The chillers may be useful to control the speed of the foaming process in combination with the heaters. They may be useful in controlling the density and homogeneity of the foam and may ensure that the foaming process has finished before the product leaves the mould.

Downstream of the mould the product may be coiled by coiling apparatus.

Figure 2 illustrates diagrammatically the relative expansion of the preform rod 9 extruded from the die and the foamed product 13.

Figure 3 illustrates an alternative embodiment of the apparatus and process in which a feedstock comprising metal powder and foaming agent is fed into the groove 2 in a conform wheel 1 rotating anti-clockwise towards tooling 15. The feedstock is compressed into the groove via a compacting roll 14 before entering the passage to the extrusion die (not shown) and extrusion as described above through the die and into the mould 13.

Apart from the embodiments illustrated it may also be possible to continuously form foamed products of indefinite length by feeding a mixture of molten metal and foaming agent to the machine.

Claims

Claims 1. A process for the production of foamed components comprising the steps of : delivering a feedstock comprising a mixture of metal and foaming agent to a continuous extrusion machine, extruding a preform from a die of the continuous extrusion machine, conveying the preform to a mould downstream of the die, and allowing the preform to foam within the mould as it is conveyed continuously from an inlet of the mould to an outlet. 2. A process according to claim 1 wherein the feedstock is a mixture of molten metal and a foaming agent. 3. A process according to claim 1 wherein the feedstock is a mixture of particulate metal and a foaming agent. 4. A process according to any one of the preceding claims wherein the process includes the step of applying pressure to the surface of the foamed product causing the foamed surface to collapse and form a skin. 5. A process according to any one of the preceding claims including the step of heating the mould passage surface to encourage the formation of a surface skin on the foamed product. 6. A process according to any one of the preceding claims wherein the metal is aluminium or copper. 7. A process according to claim 1 and as herein described. 8. Apparatus for the continuous formation of a foamed metal product of indefinite length comprising a continuous extrusion apparatus of the conform type and a mould located immediately downstream of the extrusion apparatus having a mould passage whereby, in use, preform extruded from the extrusion apparatus and delivered at in excess of the foaming temperature is foamed as it is transported continuously from an Inlet of the mould passage to an outlet of the mould passage. 9. Apparatus according to claim 8 wherein a heater is provided in the mould to heat all or part of the length of the mould in order to control the rate and completion of the foaming process. 10. Apparatus according to claim 9 wherein cooling means is provided in the mould whereby the mould can be cooled in order to slow or stop the foaming process before the product exits the mould and to provide for handling the cooled product downstream. 11. Apparatus according to claim 1 and as herein described with reference to the accompanying figures. Amendments to the claims have been filed as follows

1. A process for the production of foamed components comprising the steps of : delivering a feedstock comprising a mixture of metal and foaming agent to a continuous extrusion machine, extruding a preform from a die of the continuous extrusion machine, conveying the preform to a mould downstream of the die, and allowing the preform to foam within the mould as it is conveyed continuously from an inlet of the mould to an outlet.

2. A process according to claim 1 wherein the feedstock is a mixture of molten metal and a foaming agent.

3. A process according to claim 1 wherein the feedstock is a mixture of particulate metal and a foaming agent.

4. A process according to any one of the preceding claims wherein the process includes the step of applying pressure to the surface of the foamed product causing the foamed surface to collapse and form a skin.

5. A process according to any one of the preceding claims including the step of heating the mould passage surface to encourage the formation of a surface skin on the foamed product.

6-A process according to any one of the preceding claims wherein the metal is aluminium or copper.

7. A process according to claim 1 and as herein described.

8. Apparatus for the continuous formation of a foamed metal product of Indefinite length comprising: a continuous extrusion apparatus and a mould located immediately downstream of the extrusion apparatus having a mould-passage whereby in use, preform extruded from the-extrusion apparatus and delivered at in excess of the foaming temperature is foamed as it is transported continuously from an inlet of the mould passage to an outlet of the mould passage.

9. Apparatus according to claim 8 wherein a heater is provided in the mould to heat all or part of the length of the mould in order to control the rate and completion of the foaming process.

10 Apparatus according to claim 9 wherein cooling means is provided in the mould whereby the mould can be cooled in order to slow or stop the foaming process before the product exits the mould and to provide for handling the cooled product downstream.

11. Apparatus according to any one of claims 8 to 10 wherein the continuous extrusion apparatus is of the conform type.

12. Apparatus according to claim 8 and as herein described with reference to the accompanying figures.