[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.
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.