WO1993008941A1

WO1993008941A1 - A roll for a twin roll caster

Info

Publication number: WO1993008941A1
Application number: PCT/GB1992/002037
Authority: WO
Inventors: Peter George Grocock; Philip Milroy Thomas
Original assignee: Davy Mckee (Poole) Limited
Priority date: 1991-11-06
Filing date: 1992-11-04
Publication date: 1993-05-13
Also published as: AU2877092A; GB9123603D0

Abstract

To reduce sticking on a two roll caster, it is desirable to provide the peripheral surface of the or each roll with a surface texture which helps to retain parting agent applied to the surface. The surface texture is obtained by forming grooves on the surface of the roll. Conveniently, grooves extend in two directions of the roll so that the surface texture is substantially the same in both the longitudinal and circumferential directions of the roll.

Description

A ROLL FOR A TWIN ROLL CASTER

Twin roll casting is an established technology for the production of metal strip. In the case of aluminium alloys it is usual to produce strip of gauge in the range 6 - 10 mm. In this process, molten metal is fed into the bite of a pair of water cooled, counter rotating rolls. The molten metal solidifies and then undergoes hot deformation before exiting the casting rolls as solid strip.

One of the major problems with the aforesaid process is the tendency of the cast strip to adhere to one or both of the casting rolls. It is known that the application of a parting agent to the casting rolls - typically a suspension of colloidal graphite in water - is beneficial in reducing sticking. The parting agent is usually applied to the casting rolls as an atomised spray by means of either a traversing or reciprocating spray system.

It is also usual to prepare the surface of the casting rolls by grinding and it is normal to grind the rolls circumferentially to a smooth finish - typically 0.5 - 1.0 microns R_A.

By modifying the casting process, it is possible to extend the range of thickness that can be cast and it has been demonstrated that thicknesses of approximately 1 mm or less are achievable.

However, when casting at reduced gauges, the tendency for the workpiece to stick to the casting rolls increases significantly.

It is an object of the present invention to reduce the tendency of the workpiece to stick to the casting rolls.

According to a first aspect of the present invention, a roll suitable for use in a-twin roll casting machine is characterised in that the peripheral surface of the roll has a surface texture such that parting agent is retained on the surface.

The peripheral surface may have a turned finish.

Such a finish can be produced by rotating the caster roll at a speed in the range 300 - 400 rpm and traversing the cutting tool at a speed of approximately 0.4 mm/revolution. It has been found beneficial for the angle of the cutting tool to be between 60 - 90°.

Using the above conditions, the surface texture of the casting rolls is such that the surface of strip cast using those rolls is characterised by a series of longitudinal grooves and a transverse surface roughness of 4 - 8 microns R_A. Conveniently, the surface texture is substantially uniform in both the longitudinal and circumferential directions of the peripheral surface.

By providing the roll with a surface texture, much of the liquid parting agent applied to the surface of the roll is retained on the surface and produces an improved release between the roll surface and the strip.

The degree of surface roughness does not prevent the thickness of the cast product from being reduced in downstream rolling operations to thickness of <.10 microns. Casting rolls that have been prepared by a turning operation are characterised by differential roughnesses in the longitudinal and circumferential directions. In the circumferental direction, the rolls are essentially smooth, whereas, in the longitudinal direction, the rolls are rough and exhibit an approximately sinusoidal form. The frequency and amplitude of the waveform is dependent on the method of preparation.

According to a second aspect of the invention, the peripheral surface of a roll suitable for use in a twin roll casting machine is prepared by having grooves formed on the surface.

Conveniently, longitudinal grooves and circumferential grooves are formed on the peripheral surface.

A number of methods exist for preparing roll surfaces with uniform texture in both longitudinal and circumferential directions.

One such method is to use a roll grinder. In this method the rolls are ground sequentially in longitudinal and circumferential directions. Alternatively, the surface can be textured uniformly using a lathe in conjunction with a knurling tool. Another method of producing the required surface finish is to use an electro-spark discharge technique. Alternatively, a laser source can be employed.

Clearly, it is desirable for both rolls of a twin roll casting apparatus to have a surface texture in accordance with the invention. Aluminium strip with a gauge in the range 1 - 10 mm can be produced successfully with such apparatus.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a view to a greatly enlarged scale of the peripheral surface 1 of a roll suitable for use in a twin roll casting machine. V-shaped grooves 2 extend longitudinally of the peripheral surface and similar grooves 3 extend circumferentially of the surface. This means that the peripheral surface has a multiplicity of hollows formed by the grooves and the parting liquid is retained in the hollows.

Figures 2 and 3 are perspective views of a roll 4 having circumferentially extending grooves 3 and longitudinally extending grooves 2, respectively, on the peripheral surface.

Figure 4 is a perspective view of a roll 4 having helically arranged grooves 5 and 6 on the peripheral surface. The grooves 5 are inclined to the grooves 6 so as to provide a knurled surface.

Figures 5, 6 and 7 are plan views of a lathe 8 or the like showing a roll 4 mounted for rotation about its longitudinal axis.

In Figure 5, a cutting tool 9 is shown forming circumferential grooves or one continuous groove extending circumferentially of the peripheral surface of the roll.

Similarly, in Figure 6, a rotating grinding wheel 10 is employed to cut circumferential groove(s) on the peripheral surface of the roll.

In Figure 7, a grinding machine 10 is employed to produce grooves 2 extending longitudinally of the roll 4.

In accordance with one embodiment of the invention, the peripheral surface is provided with both circumferential grooves and longitudinal grooves in separate machining operations.

Claims

Claims :

1. A roll suitable for use in a twin roll casting machine, characterise:: m that the peripheral surface of- the roll has a surface texture such that parting agent is retained on τ.he surface.

2. A roll as claimed in claim 1, characterised in that the peripheral surface has a turned finish.

3. A roll as claimed in claim 1, characterised in that the surface texture is substantially uniform in both the longitudinal and circumferential directions of the peripheral surface.

4. A method of preparing the peripheral surface of a roll suitable for use in the twin roll casting machine comprising the steps of forming grooves on the surface.

5. A method as claimed in claim 4, in which the grooves are formed by machining the roll in a lathe or the like to form a turned finish on the surface.

6. A method as claimed in claim 5, in which the caster roll is rotated at a speed in the range 300 - 400 rpm and the cutting tool is traversed at a speed of approximately 0.4 mm/revolution.

7. A method as claimed in claim 6, in which the cutting tool is at an angle of between 60 - 90° to the surface of the roll.

8. A method as claimed in claim 4, comprising the steps of forming longitudinal grooves and circumferential grooves on the peripheral surface of the roll.

9. A method as claimed in claim 8, in which the longitudinal grooves and the circumferential grooves are formed by grinding operations.

10. A method as claimed in claim 8, in which the longitudinal grooves and the circumferential grooves are formed by electro-spark discharge techniques.