GB2165476A

GB2165476A - Extrusion of metals

Info

Publication number: GB2165476A
Application number: GB08425672A
Authority: GB
Inventors: John Baird Childs
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1984-10-11
Filing date: 1984-10-11
Publication date: 1986-04-16
Also published as: GB8425672D0

Abstract

A continuous metal-extrusion process comprises applying a controlled tension to the product at the outlet from the extrusion die; continuously or repeatedly measuring at least one cross-sectional dimension of the product; and adjusting the controlled tension in response to the measured dimension(s) to maintain the dimension(s) within a desired range. Thus the size of the product being extruded can be adjusted within limits without altering the size of the die, making the process less dependent on the precise dimensions of the die and so extending the die life.

Description

SPECIFICATION Extrusion of metals This invention relates to continuous extrusion of metals to form wires, rods, tubes or other sections; and for the purpose of the invention extrusion may be considered "continuous" if its product has a length-to-diameter ratio of at least 10,000:1. The invention is thus applicable to Conform extrusion and other continuous friction-actuated extrusion processes, to twin-ram extrusion and to some hydrostatic extrusion processes.

An extrusion die is an expensive precision tool; it is subject in use to extremes of pressure, shear force and abrasion and thus has a relatively short life, the length of which may significantly affect the economics of the whole operation, or in some cases may limit the continuous length of product that can be attained. The commonest failure mode is by abrasive wear resulting in the production of a product above the maximum tolerance on cross-sectional dimensions; other significant modes are by distortion or by a build up of oxide leading to closing of the die opening and a product below minimum wire size: in both cases the die is still capable of producing an extruded product of good quality and unacceptable only because it is not the right size.

The present invention provides a means whereby the size of a product being extruded continuously can be adjusted, within limits, without alteration to the size of the die, thus making the process less dependent on the precise dimensions of the die and so extending the life of the die.

In accordance with the invention, a continuous metal-extrusion process is distinguished by applying a controlled tension to the product at the outlet from the extrusion die; continuously or repeatedly measuring at least one cross-sectional dimension of the product; and adjusting the controlled tension in response to the measured dimension(s) to maintain the dimension(s) within a desired range.

The applied tension may vary, to the extent required, within the whole range from the least tension that is sufficient to avoid buckling of the product (which may be zero) to the maximum tension that will not risk necking-down and fracture.

A laser guage or other optical instrument is normally preferred for measuring the cross-sectional dimension of the product, but other applicable techniques could be used. When the product is a round rod, tube or wire an arbitrary diameter may be a sufficient dimension, or several diameters may be measured and adjustment made in response to the average orthe extreme value, depending whether the cross-sectional area or the diameter is more closely specified.

For non-circular extrusions, one dimension will often be critical either because it is more important in the product or because it relates to the part of the die subject to greatest wear; such a critical dimension is plainly the most appropriate one to measure.

Where there is no obviously critical dimension, it may be desirable to measure several.

Adjustment of the applied tension may be effected manually, as changes will normally be slow, or it may be effected automatically by standard servocontrol or digital techniques if preferred.

Example The modified horizontal-axis Babcock '2D' Conform machine described by way of example in a British Patent No. 2069389B was fitted with a ceramic die with a diameter of 2.86 mm and used to extrude copper wire. The mean diameter of the product was found to vary with the tension applied to it, as shown in the accompanying graph, ranging from about 2.845 mm at a low tension of 50N down to about 2.79 mm at 400N. Operating conventionally with a steady tension of 250N, approximately 6 tonnes of wire with a diameter of 2.81 + .25 mm could be produced before the die aperture was so reduced that the lower tolerance limit was exceeded.

In accordance with the invention, a Beta diameter measuring system (available from Beta Instruments Limited) comprising a type LG1010 swept laser beam gauge head, a type L1800R indicator unit and a rotamaster RS2 rocking cradle unit were employed.

The function of the rotamaster unit was to enable the diameter of the product to be monitored continuously over a 180 arc, repeating nominally every 8 seconds.

The indicator unit continuously displayed a regularly updated mean diameter and also provided a separate alarm output for an excursion beyond either a lower or an upper diameter limit, each of which was preset. In the present example the intended diameter was 2.81 and the preset limits 2.56 and 3.06 respectively (better than the t 1% required to meet the requirements of British Standard BS4109).

The tension in the product was controlled by the air pressure in a cylinder acting on the dancer arm of a tension control unit of the kind described in our U.K. Patent No. 978174.

Air pressure in the cylinder was varied by means of a hand controlled valve which can admit air to or exhaust air from the cylinder, though of course an automatic control could readily be provided. If the upper tolerance alarm were given the air control valve would be adjusted to raise the cylinder pressure, causing an increase in tension until the required mean diameter was indicated, conversely if the lower tolerance alarm were given. In the particular experimental work the die diameter had a consistent tendency to decrease, and so only lower tolerance alarms were observed; these occurred at intervals of the order of an hour. By adjusting the control valve at these times until the diameter indicated on the display was restored to the nominal value of 2.81, a total of about 18 tonnes of wire within the set tolerance was provided before the tension fell to the minimum allowable value of 40N, thus increasing the life of the die (and the length of operation between die changes) about 3-fold.

If desired, by making more frequent adjustments, or by adjuring continuously by an automatic mechanis;n, the size may be held to a much closer tolerance to secure material saving and/or a technically superior product.

Claims

1. A continuous metal-extrusion process distinguished by applying a controlled tension to the product at the outlet from the extrusion die; continuously or repeatedly measuring at least one cross-sectional dimension of the product; and adjusting the controlled tension in resonse to the measured dimension(s) to maintain the dimension(s) within a desired range.

2. A continuous friction-actuated metalextrusion process distinguished by applying a controlled tension to the product at the outlet from the extrusion die; continuously or repeatedly measuring at least one cross-sectional dimension of the product; and adjusting the controlled tension in response to the measured dimension(s) to maintain the dimension(s) within a desired range.

3. A process as claimed in Claim 1 or Claim 2 in which the metal is copper.

4. A method of continuously extruding copper wire as claimed in any one of the preceding claims and substantially as described in the Example.

5. A copper wire made by the process claimed in Claim 3 or Claim 4.