GB2198981A

GB2198981A - Axially-adjustable rolls

Info

Publication number: GB2198981A
Application number: GB08705914A
Authority: GB
Inventors: Robert Willian Gronbech
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1986-12-23
Filing date: 1987-03-12
Publication date: 1988-06-29
Anticipated expiration: 2007-03-12
Also published as: GB2198981B; GB8705914D0; GB8630797D0

Abstract

In order to selectively adjust the profile of rolled metal strip 34, a rolling mill stand has work rolls with at least one cylindrical portion and at least one frusto-conical portion 22, 24 and at least one of the rolls is axially displaceable with respect to the other roll whereby the roll(s) can be adjusted so that the gap between the rolls can either be of uniform thickness or of non-uniform thickness. <IMAGE>

Description

THE ROLLING OF METAL STRIP This invention relates to a method of, and apparatus for, rolling metal strip and" in particular, to selective profile control during the rolling of metal strip.

Metal strip may have small variations in thickness across its width which generally manifest themselves as thick centres and thin edges. In addition, during rolling, wear of the rolls and thermal crown on the rolls influence the profile of the strip being rolled. Thus, strip entering a uniform gap between the rolls of a rolling mill may mot have the required profile to produce a desired product.

Means for differentially modifying the reduction taken by the mill rolls across the width of the strip is, therefore, needed in order to produce the required profile.

According to the present invention, a rolling mill stand has a pair of work rolls, at least one of which is axially displaceable relative to the other, and the roll barrel of each roll has at least one cylindrical portion and at least one frusto-conical portion, with one roll reversed end-to-end with respect to the other roll so that, in one relative axial position of the rolls, a gap of uniform thickness exists along the entire length of the roll barrel and, in all other relative axial positions of the rolls, the gap of uniform thickness exists along part of the length of the roll barrel whilst that portion of the gap bounded by the frusto-conical sections varies with the direction and magnitude of the axial movement.

The frusto-conical portions on the two work rolls are such that, in one relative axial position of the rolls, a gap of uniform thickness exists along the entire length of the roll barrel, that is, between the cylindrical portions of the rolls and also between the frusto-conical portions. When the rolls are positioned in a different relative axial position, the thickness between the cylindrical portions of the rolls will be unchanged but the thickness between the frusto-conical portions will be different. That part of the metal strip which is rolled between the frusto-conical portions of the rolls can have its thickness varied by adjusting the axial position of one roll relative to the other.

The frusto-conicalportions of the work rolls can be provided at both ends of the work rolls and, in an alternative arrangement, the frusto-conical portions are provided as the central portions of the work rolls.

If the frusto-conical portions are provided as the central portions of the work rolls, axial movement of one or other of the work rolls will adjust the thickness of the central portion of the strip while keeping the thickness of the strip at its edges unchanged. Alternatively, if the frusto-conical portions are provided at both ends of the rolls, by adjusting one or other of the rolls, the thickness of the strip at its edges can be changed.

According to a second aspect of the present invention, in a method of rolling metal strip, the strip is passed through at least two rolling mill stands arranged in tandem, two of said stands being as claimed in any preceding claim with the relative positions of the frusto-conical portions and the cylindrical portions of the rolls on one of said stands being different from those on the rolls of the other of said stands and variations in the shape of the strip being rolled in the stands is corrected by axially adjusting the position of one roll with respect to the other roll in one or both of the stands.

For example, if one of the stands has frustoconical portions at the ends of the rolls and cylindrical portions in the centre of the rolls and the other stand has rolls with the frusto-conical portions in the centre, then axial adjustment of one of the rolls of the first stand, brings about adjustment of the thickness of the strip at its edges whereas axial adjustment of one of the rolls of the second stand brings about adjustment of the thickness of the centre portion of the strip.

It is envisaged that a profilemeter would be positioned downstream of the last stand so that an indication of the profile or cross-section of the strip which is being rolled can be obtained. From this indication of the shape it will be apparent which of the stands will need to be adjusted in order to improve the profile of the strip.

The rolling mill stands may have back-up rolls and intermediate rolls.

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 shows diagramatically a pair of work rolls of a rolling mill; Figure 2 shows the same rolls but with one of the rolls displaced axially with respect to the other; Figure 3 shows diagrammatically a different pair of work rolls; Figure 4 shows the same rolls but with one of the rolls displaced axially with respect to the other; and Figures 5 and 6 show alternative forms of work rolls.

Referring now to Figure 1, a pair of work rolls of a rolling mill stand are indicated by reference numerals 2, 4, respectively. Work roll 2 has a cylindrical portion 6 at its left-hand end and a cylindrical portion 8 of reduced diameter at its righthand end and these two portions are separated by a frusto-conical portion 10. Work roll 4 corresponds to work roll 2 except that it is reversed end-to-end in that the portion 8 of reduced diameter is at its lefthand end, the portion 6 of larger diameter is at its right-hand end and these portions are separated by a frusto-conical portion 10. As shown in Figure 1, the work rolls have the ends of their roll barrels aligned and the roll gap 12 along the entire length of the roll barrel is of uniform thickness.Consequently, if a workpiece 14 of uniform thickness across its width is passed between the rolls, it is rolled with a uniform reduction across its width.

In the arrangement shown in Figure 2, work roll 2 has not been moved axially but work roll 4 has been shifted in its axial direction towards the left.

It can be seen that the gap 12 between the work rolls is no longer of uniform thickness along the entire length of the roll barrels. The edge portions of a workpiece 14 passed between the rolls would be rolled to a uniform thickness but the centre portion of the workpiece would be rolled to a greater extent thereby producing a workpiece having edges which are thicker than the central portion.

Referring now to Figure 3, a pair of work rolls of a rolling mill stand are indicated by reference numerals 22, 24, respectively. Roll 22 has a cylindrical central portion 30 and frusto-conical portions 26, 28 at each end. The diameter of the lefthand end of the frusto-conical portion 26 is greater than the diameter of the right-hand end of frustoconical portion 28. Work roll 24 has a central cylindrical portion 30 with a frusto-conical portion 26 at its right-hand end and a frusto-conical portion 28 at its left-hand end. It will be seen from Figure 3 that, when the ends of the roll barrels are aligned, the gap 32 between the rolls is of the same thickness along the entire length of the roll barrels and a workpiece 34 of uniform thickness rolled between these rolls would receive a uniform reduction across its width.

If, however, work roll 24 is shifted axially to the left-hand side while work roll 22 remains fixed, it can be seen that the roll gap 32 is no longer uniform along the length of the roll barrels but remains uniform over the central portion of the strip and is reduced at the two end portions. Consequently, the workpiece 34 of uniform thickness rolledbetween these rolls would have less reduction and, hence, a thicker central portion than at its edge portions.

Figures 5 and 6 show alternative pairs of work rolls each of which has cylindrical end portions 46 and 48. In Figure 5, a cylindrical central portion 50 is flanked by frusto-conical intermediate portions 52, 54, respectively, and, in Figure 6, frusto-conical portions 51, 52, 54 are positioned side-by-side between the end portions. In the axial positions shown, the gap between the rolls is uniform along the length of the roll barrels but, when there is axial displacement of one roll relative to the other, the gap at the cylindrical portions remains the same but the gap at the frusto-conical portions is changed, thereby enabling portions of the strip inwardly from its outer edges to be adjusted in thickness relative to the other portions.

From a consideration of Figures 1 to 4, it will be appreciated that, when metal strip is being rolled in a plurality of mill stands, if one of the mill stands has a pair of rolls as shown in Figures 1 and 2 and another of the stands has a pair of rolls as shown in Figures 3 and 4, then, by axially moving the rolls of the stand of the type shown in Figures 1 and 2, the central portion of the strip can be over-rolled compared with the edge portions so that, if the strip entering that stand tends to be thicker at its centre than at its edges, then, as it is rolled in this stand, the central portion will be rolled to a greater extent than its edges and, by adjusting the amount of axial movement of the rolls, strip having the required uniform thickness across its width can be obtained.

Conversely, if strip which is thicker at its edges than at its centre is rolled in the stand as shown in Figures 3 and 4 with one of the work rolls displaced axially as shown in Figure 4, then the edges are rolled to a greater extent than the central portion and unsatisfactory strip can be corrected.

The cylindrical portions of the rolls enable profile corrections to be implemented with minimum disturbance to the nominal gauge reduction in the stand.

If, therefore, a rolling mill consists of a plurality of rolling mill stands, at least one of which has rolls of the type shown in Figures 1 and 2 and the other has rolls of the type shown in Figures 3 and 4, then, by suitably selecting one or other of the stands and by axially adjusting one of the rolls relative to the other, any tendency for strip having unsatisfactory shape to be rolled can be corrected.

If there are a plurality of mill stands a combination of profiled rolls with similar shapes but differing length ratios of cylindrical and frustoconical sections may be employed to improve the selectivity of profile control.

Furthermore, by employing additional stands having rolls of the type shown in Figures 5 and 6, it is possible to correct for quarter buckle which might otherwise be present'in the strip.

Roll wear tends to be more severe locally where the rolls contact the edges of the strip. By moving the work roll pair a small distance axially together in the same direction between coils the edge wear effect on the rolls can be alleviated without substantially modifying the strip profile.

Claims

Claims:

1. A rolling mill stand having a pair of work rolls, at least one of which is axially displaceable relative to the other, and the roll barrel of each roll has at least one cylindrical portion and at least one frusto-conical portion, with one roll reversed end-toend with respect to the other roll so that, in one relative axial position of the rolls, a gap of uniform thickness exists along the entire length of the roll barrel and, in all other relative axial positions of the rolls, the gap of uniform thickness exists along part of the length of the roll barrel whilst that part of the gap bounded by the frusto-conical portions varies with the direction and magnitude of the axial mcvement.

2. A rolling mill stand as claimed in claim 1, in which the frusto-conical portion of each roll is between two cylindrical end portions of the roll.

3. A rolling mill stand as claimed in claim 1, in which the cylindrical portion of each roll is between two frusto-conical end portions of the roll.

4. A rolling mill stand as claimed in claim 1, in which each roll has at least two frusto-conical portions and at least two cylindrical portions, the cylindrical and frusto-conical portionar-being arranged alternately along the length of the roll.

5. A method of rolling metal strip, in which the strip is passed through at least two rolling mill stands arranged in tandem, two of said stands being as claimed in any preceding claim with the relative positions of the frusto-conical portions and the cylindrical portions of the rolls on one of said stands being different from those on the rolls of the other of said stands and variations in the shape of the strip being rolled in the stands is corrected by axially adjusting the position of one roll with respect to the other roll in one or both of the stands.

6. A method rolling metal strip as claimed in claim 5, in which both of the work rolls in at least one of said stands are moved axially but by different amounts to correct or produce asymmetric profile about the strip centre-line.

7. A method of rolling metal strip substantially as hereinbefore described with reference to the accompanying drawings.

8. A rolling mill stand substantially as hereinbefore described with reference to the accompanying drawings.