Apparatus for reducing the width of a steel slab by rolling

Abstract

 In order to minimise the dog-bone and fish-tail deformations of a slab (1) during width rolling, the rolling surfaces (3) of the rolling elements (8) have a radius of curvature of at least 0.6 m. The radius may be e.g. 5 m. To avoid the technical and economic drawbacks of cylindrical rolls of this radius, the rolling elements (8) have a curved surface (3) in the zone of rolling contact extending for an angular length of less than 180°, preferably less than 90°.
Preferably the rolling elements (8) are less thick, in the direction transverse to the rolling direction, than the radius of curvature of the curved surfaces (3). They may be arcuate segments running on guide rollers (14). The segments may be flexible, the radius of curvature being determined by the positions of the guide rollers (14). The curved surface may be provided by an endless conveyor (15) running on guide rollers.

Description

[0001] The invention relates to an apparatus for reducing the width of a steel slab by rolling, comprising edge-rolling elements, the rolling surfaces of which are moved in a rolling manner on the edges of the steel slab.

[0002] An apparatus of this type is known for example from US 3,757,556.

[0003] Reducing the width of a steel slab by rolling . (hereinafter called width rolling) is an important development in the field of the hot strip rolling of steel. By this technique the production of a continuous casting plant is increased and a hot connection with a hot strip rolling mill is possible. This and other advantages of width rolling are known to the expert and do not need further explanation. Sometimes width rolling is carried out directly after the continuous casting of the slab. In most cases however, it is best to carry out width rolling in the hot strip rolling mill.

[0004] The known width rolling is carried out with edge rolls. In a conventional hot strip rolling mill, the diameter of the edge rolls is up to approximately 800 mm. Only a small reduction in width, by a maximum of 40-60 mm can be obtained with these edge rolls. With a greater width reduction one experiences problems when feeding the slab into the edge rolls. For this reason, larger diameter edge rolls have been adopted, going up to 1200 mm diameter as shown in US 3,757,556. With a diameter of 1200 mm, the maximum width reduction per pass is 150 mm; at this width there is substantial dog-bone formation as will now be discussed.

[0005] One problem with width rolling is the irregular deformation of the piece being rolled. Firstly the material is not spread evenly over the width during width rolling, but ends up thicker at the edges. In a cross-section at right angles to the direction of rolling, the piece being rolled exhibits a so-called dog-bone shape after rolling. This effect can be minimized by using the caliber rolls known from US 3,757,556, but even then the maximum width reduction is limited by the formation of a dog-bone to the maximum of 100 mm per pass, after which the resulting dog-bone can largely be rolled flat during the following thickness rolling pass. Also during thickness rolling, part of the width reduction obtained by width rolling is lost as a result of expansion of the piece being rolled. Secondly, the material is not distributed evenly in the longitudinal direction during width rolling. The elongation of the slab is not uniform in the middle and at the sides, as a result of which the original square ends of the head and tail of the slab exhibit a so-called fish-tail shape after width rolling. This effect is further amplified by thickness rolling, after width rolling, in which, during rolling flat of the dog-bone shape, irregular elongation of the slab also occurs. This deformation results in a loss of material as the deformed ends have to be cut off before final rolling in the hot strip rolling mill. As a result of this the slab output is smaller for width rolling.

[0006] These problems are discussed in Japanese Laid . Open Patent Application 56-11451. The applicants in that application suggest the use of very large diameter edge rolls, so that the deformation caused by the rolling would extend right in to the middle of the slab. They propose rolls of at least 1.5 m in diameter. They find that, after the dog-bone has been rolled flat, the amount of material wasted by the fish-tails is substantially reduced.

[0007] We have found, in general agreement with JP 56-11451, that it is advantageous if the radius of curvature of the rolling surface of edge-rolling elements is at least 0.6 m. However, if the edge-rolling elements are circular-section cylindrical rolls, there are technical and economic drawbacks, especially if the rolls are very large, e.g. 5 m radius. One drawback is simply the space which they take up.

[0008] We have realised that it is not necessary for the rolling elements to be circular-section rolls. The contact surface between the slab and the rolling element is only a portion of the full circumference of the roll, and a rolling element need only provide an appropriately curved surface in the zone of rolling contact.

[0009] Accordingly, the present invention provides apparatus for reducing the width of the steel slab by rolling having a pair of opposed edge rolling elements which each provide, at the zone of rolling contact with the slab, a curved surface which is a sector of angular length less than 180°. In this way, we can avoid the use of large rolls, while retaining the benefit of reduced deformation and greater output.

[0010] The roll elements no longer need to be able to rotate through 360°. After a pass corresponding to the _ arc length of the sector the roll elements can be returned to roll the next slab or the next section of the slab. Preferably the angular length of the curved surface is no more than 90°.

[0011] For edge-rolling elements with a greater diameter, it is preferable for there not to be a physical centre of rotation, as in full-circle cylindrical edging rolls, but for the edge-rolling elements to be designed such that measured in a direction at right angles to the rolling surface they are of a thickness which is smaller than the radius of curvature of the rolling surface. The rolling movement of the edge-rolling elements and the sides of the slab is here produced by an appropriate movement mechanism of the edge-rolling elements and/or slab.

[0012] In one embodiment of the movement mechanism the geometric centre of the rolling surface of the edge-rolling elements can be moved in a direction parallel to and opposite to the direction of rolling.

[0013] Advantageously the apparatus also includes a number of back-up rolls, which form a path for the edge-rolling elements and which, during rolling, cooperate to support the side of the edge-rolling elements facing away from the slab.

[0014] The edge-rolling elements are preferably designed with grooves, like caliber rolls, where the bottom of the groove forms the roll surface. By use of this design, dog-bone deformation can be kept to an especially small degree.

[0015] The edge-rolling elements may also be flexible in the direction of rolling and during rolling have a curve dependent on the track formed by the back-up rolls. Here the edge-rolling elements are preferably made in the form of caterpillar or apron conveyors, which are closed to themselves.

[0016] Embodiments of the invention, given by way of example, will now be described with reference to the accompanying drawings, in which:

Figures 1A and B show conventional width rolling.

Figures 2A and B show width rolling with large radius contact surfaces.

Figures 3, 4 and 5 show three embodiments of the present invention.

Figure 6 shows a section through the embodiment of Figure 3 along the line VI-VI.

[0017] Figure lA shows a slab I and edge rolls 2, which with their rolling surfaces 3 roll the edges 4 of the slab, while the slab is moved in the rolling direction shown by arrow 5. During this rolling the edge rolls exert a force on the slab at right angles to the direction of rolling 5, and as a result of this the width of the slab is reduced. A slab may for example be 1800 mm wide and 225 mm thick initially. The length of the slab may be more than 10 m. In the reduction of the width, the material of the slab is plastically deformed. During the reduction of the width of the slab, by width rolling, e.g. by 100 mm, the head end of the slab is elongated irregularly into a fish-tail 6. The cross-section of the rolled slab B-B in Figure 1A, is shown in Figure lB. This shows that irregular thickening, a so-called dog-bone 7 is formed.

[0018] Figure 2A shows width rolling with large radius edge-rolling elements 8 having a substantially greater radius of curvature than conventional edging rolls. The head 9 of slab 1, after width rolling, has a fairly straight end at right angles to the direction of rolling 5. The cross-section of the rolled slab, B-B in Figure 2A, is shown in Figure 2B. This shows that very little. irregular thickening occurs in this case.

[0019] The irregular deformation of the length and thickness of the slab during width rolling is smaller the greater the radius of curvature of the edge-rolling elements. A radius of curvature which is only slightly greater than the conventional maximum radius of curvature of 0.6 m of known edging rolls gives an advantage. In the following embodiments will be discussed where the radius of curvature of the edge-rolling elements is much greater than for the known edging rolls.

[0020] Edge-rolling elements with a much greater radius of curvature, when they take the form of full circle cylindrical edging rolls, have technical and economic drawbacks such as a large space requirement, the need for a heavy foundation and the need for high driving power. For such edge-rolling elements it is possible, and sufficient for practical purposes to provide sector of angleCK which is less than 360°; the length of the contact roll surface 3 being chosen in dependence on the length of slab 1 which is to be edge-rolled.

[0021] The rolling movement of the edge-rolling elements is obtained by rotation in the direction of the arrows 11 about the centres of curvature 10. The edge-rolling elements do not need to be further rotated to complete 360° to roll a following slab, but can be returned to their starting positions by reverse rotation after each rolling action.

[0022] The rolling movement can also be obtained by moving centres 10 in direction 12, parallel and opposite to the rolling direction 5.

[0023] For edge-rolling elements which have a very large radius of curvature and which are in the form of a sector of a complete circular edging roll and physically include the centre of curvature 10, the technical and economic drawbacks stated above still apply to some extent.

[0024] Figure 3 shows an embodiment where the edge-rolling elements 8 are so designed that they do not extend in the direction at right angles to the rolling surface 3 for the entire radius of curvature of the rolling surface.

[0025] The edge-rolling elements 8 are arcuate in shape and each have a swivelling point 13 at each end. By means of a movement mechanism not shown, which is linked with swivelling points 13, the edge-rolling elements 8 are moved so as to roll the edges 4 of the slab with the two rolling surfaces 3.

[0026] The length of the rolling surface of the edge-rolling elements can be selected such that with these edge-rolling elements a slab of maximum envisaged length can be rolled in one pass. The length selected can also be smaller, as shown in Figure 3, and the slab rolled in a number of passes with the edge-rolling elements.

[0027] Figure 4 shows another embodiment of the apparatus with edge-rolling elements of a thickness of less than the radius of curvature of the rolling surface. Here the edge-rolling elements 8 are supported, guided and possibly driven by a number of back-up rolls 14, which form a track for the edge-rolling elements 8. With this embodiment the edge-rolling elements can be flexible in the rolling direction 5, with the curvature of the rolling surfaces during width rolling being dependent on the path formed by the back-up rolls 14.

[0028] Figure 5 shows an embodiment in which the edge-rolling elements are flexible and form caterpillar or apron conveyors 15, which are closed loops.

[0029] As shown in Figure 6, the edge-rolling elements 8 can have a caliber groove 16. This reduces the formation of a dog-bone in slab 1 still further. The bottom of the groove 16 forms the rolling surface 3 mentioned above.

EXAMPLE

[0030] With an apparatus in accordance with Fig. 2 a test was carried out in which the width of the slab was substantially reduced. Plasticine was used as the slab material. The expert knows that at room temperature plasticine behaves similarly to steel during hot rolling.. The test was carried out on a scale reduced by 10. The dimensions of the plasticine slab were 180 x 22.5 x 600 mm. The radius of curvature of the roll elements was 1000 mm.

[0031] The width reduction was 15 mm.

[0032] After one pass the deformation of the head and tail was measured. In addition the rolled plasticine slab was carefully cut at right angles to the direction of rolling and the dog-bone measured. It was found that little or no dog-bone or fish-tail was formed.

Claims

1. Apparatus for reducing the width of a steel slab by rolling, comprising a pair of opposed edge-rolling elements (8,15) having rolling surfaces (3) which, during rolling, engage the edges of the slab, and which have a radius of curvature of more than 0.6 m,
characterized in that
the said edge-rolling elements (8,15) each provide, at the zone of rolling contact with the slab, a circularly cylindrical rolling surface (3) which is a sector of angular length less than 180°.

2. Apparatus according to claim 1 wherein the angular length of the said circularly cylindrical rolling surfaces (3) is not more than 90°.

3. Apparatus according to claim 1 or claim 2 wherein the mathematical centres (10) of the rolling surfaces of the edge-rolling elements are arranged to be moved during rolling in the direction parallel to and opposite the rolling direction (5).

4. Apparatus according to any one of claims 1 to 3 wherein the edge-rolling elements (8,15) have a thickness which, as seen at the zone of rolling contact in the direction transverse to the rolling direction, is less than the radius of curvature of the rolling surface (3).

5. Apparatus according to claim 4 further comprising a set of back-up rolls (14) for each edge-rolling element (8,15), the back-up rolls forming a track for the edge-rolling elements and supporting the faces of the edge-rolling elements facing away from the slab during rolling.

6. Apparatus according to any one of the preceding claims wherein the edge-rolling elements (8) are sectors of rigid cylinders (Figs. 2,3 and 4).

7. Apparatus according to claim 5 wherein the edge-rolling elements (15) are flexible so as to bend in the rolling plane and during rolling have a curvature at the rolling zone determined by the track formed by the back-up rolls (14) (Fig. 5).

8. Apparatus according to claim 7 wherein the edge-rolling elements are elongate flexible endless elements (15).

9. Apparatus according to any one of the preceding claims wherein the edge-rolling elements each have a groove, of which the bottom is said rolling surface and the side walls of which engage the main slab surfaces during rolling.

Drawing