GB2306362A

GB2306362A - Rolling of metal strip

Info

Publication number: GB2306362A
Application number: GB9522220A
Authority: GB
Inventors: Peter George Grocock
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1995-10-31
Filing date: 1995-10-31
Publication date: 1997-05-07
Also published as: GB9522220D0

Abstract

To correct for tight-edge rolling of metal strip 7, the roll barrel of one of the roll 3 is heated by electrical induction means at two regions 9 which correspond to the edges of the strip being rolled to expand the roll 3 whereby for a distance along the length of the roll barrels which is greater than the width of the strip the gap 5 between the mill rolls is substantially uniform.

Description

THE ROLLING OF METAL STRIP This invention relates to the rolling of metal strip and it seeks to improve the quality of rolled strip.

It is well known that during the rolling of metal strip there is the danger that a different amount of rolling (reduction) will occur across the strip width. When this occurs it results in uneven longitudinal waves in the strip when the rolled strip is laid onto a flat surface. One example of this is when the edges of the strip are rolled to a lesser extent than the centre of the strip. This is known as "tight-edge" and if it is very pronounced the strip is unacceptable to the end-user.

Tight-edge very often results from uneven expansion of the rolls due to the heat which is generated during rolling. Figure 1 of the accompanying drawings illustrates, to an exaggerated extent, how the rolls of a rolling mill expand during rolling.

A pair of work rolls, 1,3 each have a cylindrical barrel and the rolls are spaced apart to form a gap 5 between them. A metal strip 7 is rolled between the rolls and the width of the metal strip is less than the length of the roll barrels. The part of each roll barrel which is contacted by the strip is heated during rolling due to the heat generated by the rolling process. The heating causes the roll diameter to increase. The ends 1A, 3A of the roll barrels which are not contacted by the strip do not expand to the same extent as that part which is contacted by the strip and on each roll there are two transition regions 9 between the part which is contacted by the strip and the ends which do not expand to the same extent.These transition regions 9 correspond to the lateral edges of the strip being rolled and so the lateral edges of the strip are under-rolled, and hence thicker, as compared with the remaining part of the strip. Thus under-rolling of the edges results in the tight-edge condition.

It is an object of the present invention to roll metal strip in a manner which overcomes this condition.

According to the present invention in a method of rolling metal strip, the strip is passed between a pair of rolls of a rolling mill, each of the rolls having a barrel which is longer than the width of the strip being rolled and wherein two regions of the barrel of one of the rolls corresponding to the two edges of the strip being rolled are heated by electrical induction means to expand the regions whereby for a distance greater than the width of the strip, the gap between the rolls is substantially uniform.

By ensuring that the gap between the rolls is substantially uniform for a distance greater than the width of the strip, the entire width of the strip is rolled to the same extent resulting in the substantial elimination of tight edge on the rolled strip.

The electrical induction means conveniently comprise two groups each of a plurality of inductors arranged side-by-side, and the two groups are positioned close to one roll adjacent said regions of the roll barrel. By appropriately energising one or more of the coils of each group, the regions are heated so that the gap is substantially uniform over a length of the roll barrels which is greater than the width of the strip being rolled.

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 2 is a view similar to figure 1 showing how the rolls expand in accordance with the present invention, Figure 3 is a side elevation of part of a rolling mill in accordance with the invention and Figure 4 is a front elevation of a rolling mill showing the location of the electrical inductors.

Referring to figure 2, the zones 9 of the roll barrels of the lower roll 3 are heated by electrical inductors not shown. The heat applied by the inductors cause the roll barrel at the transition regions 9 to expand.

By controlling the amount of heat applied to the transition zones, the gap 5 between the heated transition zones 9 and the upper roll 1 can be made substantially equal to the gap between the parts of the roll barrels which are contacted by the strip 7. This ensures that the gap is substantially uniform over a length of the roll barrels which is greater than the width of the strip being rolled and therefore the strip is rolled to substantially the same gauge across its entire width.

In figure 3, the rolls 1,3 are shown and the path taken by the strip 7 to be rolled is shown by the arrow 10.

One of the electrical inductors which is associated with one of the transition regions of the roll 3 is indicated by reference numeral 12. It comprises a metal core having a surface shaped to conform with the periphery of the roll and with a plurality of coils wrapped around the core. The coils are energisable separately so that one or more of the coils can be energised simultaneously as required by the user.

The inductor is conveniently cooled by passing a liquid coolant, such as kerosene through hollow coils. The inductors are mounted on a frame 13 which can be moved as required to adjust the separation of the shaped surface of the core from the roll barrel.

In figure 4, the rotatable rolls 1,3 of the rolling mill and the pass line for the strip are illustrated.

Strips having a width of between 1000 - 2000mm can be rolled in the mill. These widths are indicated on the roll barrels. Two groups of electrical inductors 15 which are associated with the roll 3 are shown.

One group 15 overlies a region of the roll barrel extending from one edge of the 1000mm wide strip to the corresponding edge of the 2000mm wide strip, and the other group 15 overlies the roll barrel from the 1000mm strip edge to the 2000mm strip edge on the other end of the roll barrel. As shown there are eight coils in the left hand group and six coils in the right hand group, but this is shown purely for convenience and it would be usual to have the same number of coils in each group. Above the coils of each group are shown graphs 16 giving the power distribution curves when each coil is energised. It can be seen that for all strip widths between 1000mm and 2000mm, one or more coils can be energised to introduce heat into the transition region of the lower roll. By energising two or more coils of each group the heat applied to the roll can be spread over a greater width of the roll barrel in order to expand the transition region to a form shown in figure 2 which brings about a uniform gap between the rolls for a length of the roll barrel which is greater than the width of the strip being rolled.

Claims

Claims:

1. A method of rolling metal strip in which each of the pair of rolls of a rolling mill has a roll barrel which is longer than the width of the strip to be rolled, the rolls are spaced apart and the strip is rolled between the roll barrels and wherein two regions of the barrel of one of the rolls which correspond to the respective edges of the strip being rolled are heated by electrical induction means to expand the regions whereby for a distance along the length of the barrels which is greater than the width of the strip the gap between the rolls is substantially uniform.

2. A method of rolling metal strip substantially as hereinbefore described with reference to figures 2-4 of the accompanying drawings.

3. A rolling mill having a pair of rolls and electrical induction means associated with two regions on the barrel of one of the rolls, said regions corresponding to the respective edges of metal strip to be rolled in the mill, to heat the regions whereby the regions are caused to expand relative to the part of the barrel between the regions.

4. A rolling mill as claimed in claim 3 wherein the induction means associated with each region comprises a metal core having a surface shaped to conform with the periphery of the roll and one or more coils wound around the core.

5. A rolling mill as claimed in claim 4 wherein each core has a plurality of separately energisable coils to enable the length and position of the region which is heated to be varied.

6. A rolling mill substantially as hereinbefore described with reference to figures 2-4 of the accompanying drawings.