GB2251569A

GB2251569A - Continuous extrusion of pre-heated billets

Info

Publication number: GB2251569A
Application number: GB9024095A
Authority: GB
Inventors: Roger Pedley
Original assignee: Alform Alloys Ltd
Current assignee: Alform Alloys Ltd
Priority date: 1990-11-06
Filing date: 1990-11-06
Publication date: 1992-07-15
Also published as: GB9024095D0

Abstract

In a method of Operating a Continuous Extrusion Machine it is well known to continuously extrude metals, particularly aluminium and its alloys, in a continuous extrusion machine known as a Conform machine. Conventionally cold metal stock bar is fed to the machine which, by friction. heats and pressurises the metal until it can be forced through an extrusion die. Attempts to extrude small cross sectional area products from large cross sectional area stock bar result in unacceptable power consumption, undesirable changes in the metallurgical properties of the product and low productivity. The present method involves preheating the stock bar to in excess of 200 DEG C before extrusion enabling small cross section (16mm<2> to 800mm<2>) extrusion to be produced from large section (1000mm<2> to 1300mm<2>) stock. The extrusion product does not require further metallurgical treatment to produce a finished product.

Description

CONTINUOUS EXTRUSION The present invention is concerned with apparatus and a process for continuously extruding aluminium and its alloys from cast aluminium bar. Hereafter, aluminium should be taken to mean pure or alloyed aluminium. Moreover the invention may enable the continuous extrusion of other metals such as copper and its alloys.

The invention applies to the operation of a continuous extrusion machine of the type commonly known as a Conform extrusion machine. These machines consist of a rotatable wheel in which is formed an endless peripheral groove. A segment of the groove is closed by a non-rotating shoe to form a passage. The shoe also mounts a tooling assembly including an abutment which intrudes into the groove, and a die. Metal introduced to the passage is heated and compressed by frictional engagement with the walls of the passage and the abutment. When compressed and sufficiently heated, the metal in the region of the abutment flows into and through the die to be continuously extruded. The flow is believed to be plastic.

It is desirable to be able to extrude finished products of any dimension from stock bar of a single size.

However, when the extrusion has a cross section which is small in comparison with the cross section of the stock bar this may be either impossible or result in a product in which the properties of the aluminium have been undesirably changed, for example, when cold stock bar having a cross section of 1200mm2 is fed to a continuous extrusion machine to extrude conductor cable, the tensile strength of the material changes from 68 Nmm-2 to 95 Nmm-2 so that subsequent annealing is necessary.

It is an object of the present invention to provide a method of operating a continuous extrusion machine which alleviates the aforementioned problems.

Accordingly there is provided a method of operating a continuous extrusion machine to extrude finished metal products comprising the step of: feeding stock bar of large cross section to the machine preheated to a temperature in excess of 2000C and, extruding finished products therefrom.

It is found that by preheating the stock bar the change in tensile strength is greatly reduced, or completely eliminated. In this case the cross section of the stock bar will be of the order 1000 to 1300mm2.

It has previously been known to feed large cross section cast stock bar to an extrusion machine and to extrude unfinished product with a reduction in cross section of around 16%, e.g. from 1200mm2 to 1000mm2. To finish the product it was necessary to roll the extrusion in a wire rolling mill. This would lead to changes in the tensile strength and other properties of the product which, at least for some applications, then requires annealing.

According to another aspect of the present invention there is provided a method of operating a continuous extrusion machine wherein stock bar having a cross section of the order of l100mm2 is preheated to a temperature exceeding 2000C and fed directly to a continuous extrusion machine whereby extruded finished metal products with a cross sectional area in the range between 16mm2 and 800mm2 are produced.

By virtue of the present invention, a finished product requiring no further metallurgical processing is produced. In addition to this advantage it has been found that the continuous extrusion machine runs with significantly less power consumption while the working life of the tooling is increased.

In a preferred form of the invention it is advantageous to combine the continuous extrusion machine with a continuous casting machine such as the apparatus disclosed in the applicant's co-pending application GB 9014437.9. In this case the hot cast bar leaving the continuous casting machine is kept at a temperature in excess of 2000C and fed directly into a continuous extrusion machine. Thus the costs of apparatus and power required to heat the stock bar from cold are avoided.

There follows an example of the application of a process embodying the present invention and, by way of comparison, the application of a conventional continuous extrusion process to a similar cast aluminium bar. The example is not intended to limit the scope of the present invention.

A stock bar of 99.7% pure aluminium was used. The Feedstock cast bar with a cross section area of 1133mm2 and maximum section dimensions of 42mm by 37mm was fed to a conventional continuous extrusion machine adapted to extrude product with a cross sectional area of 150mm2 and of approximately triangular section.

In the first test the bar was fed to the extrusion machine cold, i.e., at a temperature of approximately 200.

In the second test the bar was fed to the extrusion machine at a temperature of 2100C. The results for each test are tabulated below.

TEST 1 TEST 2 Wheel Speed: 13 13 D.C.Volts: 600 600 D.C.(Amps): 750 580 Ultimate tensile strength of extrusion (N/mm2): 84 69.7 Power consumption (KW) 450 348 Production rate (Kg/He) 2876 2846 Specific power consumption (KW,H/Tonne) 156 122

Claims

Claims: 1. A method of operating a continuous extrusion machine to extrude finished metal products comprising the step of feeding stock bar of large cross section to the extrusion machine said stock bar being preheated to a temperature in excess of 200 C and extruding finished products therefrom.
2. A method according to claim 1 wherein the cross sectional area of the stock bar is in the range 1000mm2 to 1300mm2 .
3. A method according to claim 1 or claim 2 wherein the finished extrusion product has a cross sectional area in the range of 16mm2 to 800mm2.
4. A method according to any one of the preceding claims wherein the stock bar is formed by casting in a continuous casting machine and fed directly to the continuous extrusion machine with the temperature of the cast bar being kept in excess of 200 C.
5. A method of operating a continuous extrusion machine to extrude finished metal products as herein described.