GB2157605A

GB2157605A - Rolling of metal strip

Info

Publication number: GB2157605A
Application number: GB08410338A
Authority: GB
Inventors: Harry Laurence Fred Bond
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1984-04-19
Filing date: 1984-04-19
Publication date: 1985-10-30
Also published as: GB2157605B; GB8410338D0

Abstract

A rolling mill for rolling metal strip has a pair of work rolls 12 and a pair of back-up rolls 16. At least one of the work rolls is relieved at its ends so that its barrel length is not significantly longer than the width of the strip 13 to be rolled in the mill, and the work rolls are not in contact with each other outside the lateral edges of the strip being rolled, thereby ensuring that the strips is elongated equally across its width. <IMAGE>

Description

SPECIFICATION Rolling of metal strip The rolling of metal strip material is carried out in rolling mills which consist of a pair of work rolls, between which the material is reduced in thickness and which usually are in their turn supported against the load created by the reduction process by back-up trolls.

Whilst the thickness of the material is being reduced by the above means it is desirable also to ensure that the material is elongated equally across its width so as to ensure good product shape; shape is defined as the ability of a sheet of material to lie flat on a flat surface. This equal elongation across the width of material can be achieved if the profile of the gap between the work rolls can be matched to the profile of the entering material.

One means of trying to achieve that profile match is to provide loading means at the extremities of the work rolls so that they may be flexed along their length. Those loading means consist of two sets of hydraulic cylinders, one set being disposed between the work roll bearing chocks, and one set between each work roll and its associated back-up roll. The cylinders between the work rolls are to push the work rolls apart, and the cylinders between the work rolls and the back-up rolls are to push the work rolls together.

Recent developments have been put forward to improve the effectiveness of this system and have been based on the belief that, on conventional 4 high rolling mills where the back-up barrel length approximately matches that of the work roll, the continuous support imposes a constraint on the effectiveness of the loading system which is trying to push the work rolls apart. This is particularly noticeable when rolling less than full width products.

The developments have aimed to remove the constraint by removing the support of the work roll by the back-up roll outside the width of material being rolled. In some cases this has been achieved by using a back-up roll with reduced length of barrel to suit the width of strip being rolled. In another case an axially movable roll has been interposed between each work roll and its associated back up, and the support of the back-up has been matched to the width of the strip being rolled by adjusting the position of the intermediate rolls.

However, we have found that there is yet another constraint upon the effectiveness of the roll bending system, and it is the elimination of this further constraint which is an object of this invention.

We have found that, when rolling relatively thick strip material, a gap exists between the work rolls in the area outside the width of material being rolled. In these cases,the only constraint upon the effectiveness of the work roll bending system is the support of the work roll by the back-up roll outside the width of material being rolled and the above described methods can be used to remove this constraint. Figure 1 of the accompanying drawings illustrates the use of short back-up rolls and the lines of force show how the load generated between the work roll gap and the back-up roll by-passes the work roll extremities which can be quite freely flexed by the bending cylinders.We have however found that that condition only holds true for strip thicknesses above a given figure; below the figure, which may be 0.7 mm, and because of roll flattening and flexure, the work rolls begin to contact each other outside the width of strip being rolled and the nature of the loading of the work rolls is completely changed. This is shown in Figure 2 of the accompanying drawings which illustrates how the lines of force now pass through these roll contact zones. The result is that the work rolls become prestressed together and it is the locking together of the work rolls by the pre-stress that is now another very considerable constraint imposed upon the effectiveness of the roll bending system.

In the present invention, contact between the work rolls outside the width of strip being rolled is eliminated by having the barrel length of at least one of those rolls not significantly longer than the strip width. That may be achieved by the steps of grouping together the material to be rolled by width, and of rolling each width group with a pair of work rolls, at least one of which has a barrel length only slightly longer than the group width.

The work rolls are then changed when changing from one width group to another width group. The need to change work rolls is not unduly onerous as very many coils are rolled with a similar width in any typical order and as modern mills usually have quick work-roll changing facilities.

By the invention, not only the constraint on the roll bending system imposed by preloading together of the work rolls when rolling light to midrange material, but also the constraint imposed by the back-up support, are avoided.

The invention is illustrated schematically in Figure 3 of the accompanying drawings. In that figure, each of the work rolls 12 has a barrel length only slightly greater than the width of the strip 13 being rolled. Between the barrel 12A and the roll necks 12B, which as usual are carried in chocks in the mill housings (not shown), each work roll 12 is reduced in diameter so as to prevent them coming into contact with one another, even when rolling relatively thin strip. Thereby the work roll bending equipment is rendered effective for all gauges of the strip; the equipment is shown by the arrows 14 representing piston and cylinder assemblies acting between the ends of the work rolls through the work roll chocks and the arrows 15 representing piston and cylinder assemblies acting between the ends of the work rolls and the chocks of the respective back-up rolls 16. As will be appreciated the rolling loads pass through the work rolls 12 from the back-up rolls 13 only over the width of the work and bypass the work roll extremities outside of the strip width.

Although Figure 3 shows the back-up rolls 16 having barrel lengths which are also shortened below the maximum width possible with the geome try of the mill stand, that is not essential. The backup rolls instead may have the full barrel length, since, by having the barrel length of the work rolls 12 chosen according to the width of the strip being rolled, the constraint on the work roll bending equipment imposed by such back-up rolls is eliminated.

Claims

1. A rolling mill for rolling metal strip comprising a pair of work rolls each supported by a backup roll, the ends of at least one of the work rolls being relieved so that the barrel length of the roll is not significantly longer than the width of the strip to be rolled in the mill, whereby the length of the contact between the work rolls and between said work roll and the corresponding back-up roll outside the lateral edges of the strip to be rolled in the mill are reduced.

2. A rolling mill as claimed in claim 1, in which both of the work rolls are relieved at their ends so that their barrel lengths are not significantly longer than the width of the strip to be rolled and their barrel lengths are less than the barrel lengths of the back-up rolls.

3. A rolling mill as claimed in claim 1 or 2, in which roll bending means are provided on the work rolls.

4. A method of rolling metal strip in a rolling mill having a pair of work rolls and a pair of backup rolls, wherein the work rolls are chosen so that the barrel length of at least one of these is not significantly longer than the width of the strip to be rolled and the strip is passed between the work rolls.

5. A method of rolling metal strip as claimed in claim 4, in which the profile of the gap between the work rolls is adjusted by roll bending means to substantially match it with the profile of the strip entering the gap.

6. A method of rolling metal strip substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.