BACKGROUND TO THE INVENTION When rolling a metal feedstock, such as a steel feedstock, the feedstock is guided through a roll-nip that is formed between two working rolls, the thickness of the feedstock being reduced in the roll-nip. Known rolling mills and rolling methods are described for example in US patent specification 4,369, 646 and US patent specification 5,839, 313. The feedstock is rolled in this case in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls. There may then be cause to control the pressure distribution in the transverse direction of the roll-nip in such a way that a predetermined pressure profile is obtained in the transverse direction of the roll-nip. The transverse direction of the roll-nip is taken to mean a direction perpendicular to the machine direction.

When rolling a feedstock it is desirable amongst other things to be able to expose the feedstock to tensile stress, in order thereby to get closer to the yield point, which is utilized in rolling. This is referred to as strip tension. It must be noted in this case that different parts of the feedstock exposed to strip tension can be of different lengths, in particular variations can occur in the transverse direction of the machine. However, strip tension is a partly self-regulating process, since shorter parts lead to greater drawing. At the edge of a feedstock there are always small notches, which give rise to a certain risk of strip breaks, in particular if the edges are exposed to high tensile stresses. Long edges are often rolled in cold-rolling, therefore, i. e. the edges are reduced more in the roll-nip than the middle part of the feedstock. This is achieved by using such a pressure distribution in the roll-nip that the pressure on the edges is higher than the pressure on the middle part of the feedstock.

However, if the edges are rolled to become too long, there is a risk that the edges are folded into three layers, which can cause major problems, for example due to the fact that the working rolls in a subsequent working station are broken, causing both a strip break and severe damage to the rolling mill. The exact pressure distribution must therefore be

determined from the prerequisites in each individual case. The strip width of the feedstock that is being rolled is of great importance in that case. However, it is not possible to count on the strip width being a constant magnitude, but on the contrary it must be taken into account that feedstock of varying width are rolled in one and the same rolling mill. One reason for working with different strip widths is that it is intended to utilize the whole length of the working rolls. The roll wear is greatest where the working surfaces of the working rolls come into contact with the strip edges (edges of the feedstock being rolled).

At the strip edges the wear can be 3-4 times greater than further in on the strip. To obtain a longer service life of the working rolls, therefore, feedstock of various widths are worked with. One method of working that exists is to start with a comparatively large strip width and then transfer to a smaller strip width. A modern cold-rolling mill can be constructed for a strip width of up to 2 m. Often the strip width is reduced successively in several stages, in order to utilize as large a part as possible of the surface of the working roll. When going from one strip width to another, it is also necessary to change the pressure distribution in the transverse direction, for reasons that have been explained above. One method of changing the pressure distribution is to use drive rolls that are conical at one end and can be moved in the transverse direction of the rolling mill. However, each drive roll in a rolling mill can be moved during operation by a maximum of 1 millimetre per metre of strip length. If the adjustment were made more quickly, the working rolls and the feedstock that is being rolled would be damaged, for example drag marks can occur. If the change in width is great enough, a strip break will therefore occur before the adjustment has been completed. If the width of the feedstock is to be changed from 1500 millimetres to 1300 millimetres, for example, at least 100 metres of the feedstock has to pass through the roll- nip before the drive roll has been moved so far in a transverse direction that a suitable pressure distribution is obtained. It is not possible during operation to let the working rolls lift up for adjustment in a transverse direction, since this would result in the feedstock having a thicker part, which is not acceptable.

The object of the present invention is to provide a rolling mill and a method of rolling that permits adjustment of the pressure distribution in a roll-nip and in particular to provide a rolling mill and a method of rolling that permits rapid adjustments of the pressure distribution in the transverse direction, so that the strip width can be changed during continuous rolling without having to stop the rolling mill. If the pressure distribution can be changed thus during operation, major productivity gains can be achieved. However, it must

be understood that the invention is not necessarily conceived to replace other methods of adjustment, such as displacement of conical rolls, for example. Instead, the invention is to be understood preferably as a complement to methods that are already known.

DESCRIPTION OF THE INVENTION A rolling mill according to the present invention comprises a first working roll and a second working roll, which working rolls form a roll-nip between them, through which roll- nip a feedstock can be rolled in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls. A first drive roll is provided for driving the first working roll and a second drive roll is provided to drive the second working roll, the longitudinal axes of the first and the second drive roll being essentially parallel to the longitudinal axes of the working rolls. The first working roll has a first lateral supporting roll located on the upstream side of the first working roll in the machine direction and a second lateral supporting roll located on the downstream side of the first working roll in the machine direction. For the second working roll there is a third lateral supporting roll located on the upstream side of the second working roll in the machine direction and a fourth lateral supporting roll located on the downstream side of the second working roll in the machine direction. The working rolls are arranged to be able to be moved during operation in an arc along the surface of their respective drive rolls, so that the roll-nip can thereby be moved in the machine direction or opposite to the machine direction. For each working roll it is the case that one lateral supporting roll has a convex camber and one lateral supporting roll has a concave camber, and the lateral supporting rolls are also arranged to be able to be moved during operation in the machine direction or opposite to the machine direction. Due to the fact that the working rolls and their lateral supporting rolls are arranged movably, the pressure distribution in the roll-nip can be changed crosswise to the direction of the machine.

In one embodiment of the invention, the first and third lateral supporting rolls have a convex camber, while the second and fourth lateral supporting rolls have a concave camber.

In a second embodiment of the invention, the first and third lateral supporting rolls have a concave camber, while the second and fourth lateral supporting rolls have a convex camber.

The lateral supporting rolls are preferably arranged to be able to be moved together with the working rolls, so that each of the working rolls can be moved as a unit together with its lateral supporting rolls. It is also suitable for the working rolls and lateral supporting rolls to be arranged so as to be able to be moved during operation, so that the pressure distribution in the roll-nip can be changed during ongoing rolling.

According to a method according to the invention, a feedstock is rolled in a roll-nip between a first working roll and a second working roll in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls. The method comprises the following stages : A feedstock with a first width is rolled between the two working rolls, the working rolls being deflected in a first deflection direction that has a principal component in or opposite to the machine direction. The width of the feedstock being rolled is then changed from the first width to a second width. The working rolls are deflected in a second deflection direction with a deflection that is basically of the same magnitude as when the working rolls are in their first position, and which second deflection direction differs from the first deflection direction, so that the pressure distribution in the roll-nip crosswise to the machine direction is changed thereby. The second width will then be rolled using a different pressure distribution to the pressure distribution used when rolling the first width.

The method according to the invention can best be achieved by moving the working rolls in the machine direction from a first position to a second position, each of the working rolls also being deflected in its second position in the machine direction or opposite to the machine direction, but in a second deflection direction that is different from the first deflection direction for the respective working roll so that, in the transverse direction of the machine, the distribution of pressure on the feedstock in the roll-nip is changed thereby.

Within the scope of the invention and the attached claims it is also conceivable to use the method to change the pressure distribution also in cases where the feedstock width is unchanged, if so desired. However, the invention relates primarily to adjustment of the pressure distribution in conjunction with a change in feedstock width. The working rolls are preferably moved from their first position to their second position chiefly at the same time as the width of the feedstock in the roll-nip is changed from the first width to the second width. However, it is conceivable that the working rolls are moved immediately before the change in feedstock width or immediately after it.

The method according to the invention is used in particular when changing the feedstock width during operation by welding of the feedstock being rolled to another feedstock. A feedstock with a first width is then rolled between two working rolls, each of the working rolls being located in a first position in the machine direction and the working rolls being deflected in the machine direction due to the influence of the lateral supporting rolls. The deflection direction of the working rolls does not need here to coincide completely with the machine direction, but a principal component of the deflection direction coincides with the machine direction, so that the deflection of the working rolls is effected substantially in the direction of the machine. The width of the rolling feedstock is changed during operation from the first width to a second width by welding of the rolling feedstock upstream of the roll-nip to a second feedstock, which second feedstock is of the second width and which second width is smaller than the first width. The welding can take place in a special welding station. The working rolls are moved in the machine direction from their first position to a second position for the respective working roll by moving each of the working rolls together with its respective lateral supporting rolls in an arc along the surface of its respective drive roll, so that the roll-nip is moved to its second position, which second position is located downstream of the first position. The movement of the working rolls takes place preferably at the same time as the rolling feedstock of the second width reaches the roll-nip. The working rolls are deflected in the machine direction in their second position also and the deflection in the second position is essentially of the same magnitude as when the working rolls are in their first position, but the deflection direction differs somewhat from the deflection direction in the first position, so that a different pressure distribution is used in the roll-nip when rolling the second width than when rolling the first width. The second feedstock has a downstream end, at which downstream end the second feedstock is welded to the rolling feedstock. It is preferably the case that the second feedstock at its downstream end is of the first width and that the width of the second feedstock passes over into the second width via a transition piece of decreasing width. The movement of the working rolls from the first position to the second position takes place preferably at the same time as the transition piece passes through the roll-nip.

It is also conceivable for movement of the working rolls from the first position to the second position to take place only after the feedstock that is passing through the roll-nip has attained the second width. However, it is preferred that the movement of the working rolls takes place basically at the same time as the transition piece reaches the roll-nip.

According to a variant of the method according to the invention, the second position of the working rolls is downstream of the first position and the working rolls are deflected in the machine direction.

According to a second variant of the method according to the invention, the second position of the working rolls is downstream of the first position and the working rolls are deflected in a direction opposite to the machine direction.

According to a further variant of the method according to the invention, the second position of the working rolls is located upstream of the first position and the working rolls are deflected in the machine direction. According to yet another variant of the method according to the invention, the second position of the working rolls is located upstream of the first position and the working rolls are deflected in a direction opposite to the machine direction.

BRIEF DESCRIPTION OF DIAGRAMS Fig. 1 shows a rolling mill according to the invention diagrammatically Fig. 2 shows diagrammatically how a working roll can be moved in the machine direction Fig. 3 shows various positions of the working rolls and lateral supporting rolls diagrammatically Fig. 4 shows the same rolling mill diagrammatically as in Fig. 1, but with working rolls and lateral supporting rolls in a second position.

Fig. 5 shows two different pressure curves that represent different pressure distributions in the transverse direction of the roll-nip.

Fig. 6 shows, viewed in the machine direction, a cross-section of a roll-nip in which the working rolls are located in a first position to achieve a first pressure distribution.

Fig. 7 shows, viewed in the machine direction, a cross-section of a roll-nip in which the working rolls are located in a second position to achieve a second pressure distribution.

Fig. 8 shows, seen from above, a second feedstock intended to be attached to a first feedstock.

Fig. 9 shows, seen from above, another form of a second rolling feedstock intended to be attached to a first feedstock.

Fig. 10 shows a rolling mill with a preceding welding station and a strip loop diagrammatically Fig. 11 shows, seen from above, two rolling feedstocks of different widths that have been joined to one another to form one rolling feedstock Fig. 12 shows in greater detail a possible embodiment of a rolling mill according to the invention Fig. 13 shows diagrammatically how the displacement of the rolls affects the pressure distribution Fig. 14 shows, seen from above, an embodiment in which the upstream lateral supporting rolls of the working rolls are convex and the downstream lateral supporting rolls are concave Fig. 15 shows, seen from above, an embodiment in which the upstream lateral supporting rolls of the working rolls are concave and the downstream working rolls are convex.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figs. 1-4, a rolling mill 1 is shown, comprising a first working roll 2 and a second working roll 3, which working rolls 2,3 form a roll-nip 4 between them, through which roll-nip 4 a feedstock 5 can be rolled in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls 2,3. A first drive roll

6 is provided for driving the first working roll 2 and a second drive roll 7 is provided for driving the second working roll 3. The longitudinal axes of the first and the second drive roll 6,7 are basically parallel to the longitudinal axes of the working rolls. The first working roll 2 has a first lateral supporting roll 8 located on the upstream side of the first working roll 2 in the machine direction and a second lateral supporting roll 9 located on the downstream side of the first working roll 2 in the machine direction. For the second working roll 3, there is a third lateral supporting roll 10, which is located on the upstream side of the second working roll 3 in the machine direction and a fourth lateral supporting roll 11 located on the downstream side of the second working roll 3 in the machine direction. The working rolls 2,3 are arranged to be able to be moved in an arc along the surface of their respective drive rolls 6,7, so that the roll-nip 4 can thereby be moved in the machine direction or opposite to the machine direction. For each working roll 2,3 it is the case that one lateral supporting roll 8,9, 10, 11 has a convex camber and one lateral supporting roll 8,9, 10,11 has a concave camber and the lateral supporting rolls 8,9, 10, 11 are also disposed to be able to be moved in the machine direction or opposite to the machine direction. It is perceived that the cambered lateral supporting rolls achieve a deflection of the working rolls in the machine direction or opposite to the machine direction. The pressure distribution in the roll-nip crosswise to the machine direction can thereby be changed when the working rolls are moved. It is to be understood that the drive rolls 6,7 can be driven in many different ways, for example the drive rolls 6,7 can be driven by supporting rolls 16,17. Realistic dimensions for the components forming part of the rolling mill can be as follows. The supporting rolls 16,17 can have a diameter that exceeds 1 m and 1150 mm can be stated as a conceivable measurement for these. For the drive rolls 6,7, approx. 355 mm can be indicated as a suitable diameter measurement. The working rolls 2,3 can have a diameter of 140 mm, while the lateral supporting rolls 8,9, 10,11 can have a diameter that is less than the diameter of the working rolls.

According to an embodiment of the rolling mill according to the invention, the first and third lateral supporting rolls 8,10 have a convex camber and the second and fourth lateral supporting rolls 9,11 have a concave camber. According to a second embodiment of the rolling mill 1 according to the invention, it is the case that the first and third lateral supporting rolls 8,10 have a concave camber, while the second and fourth lateral supporting rolls 9,11 have a convex camber.

The lateral supporting rolls 8,9, 10,11 are preferably arranged to be able to be moved together with the working rolls 2,3, so that each of the working rolls 2,3 can be moved as a unit together with its lateral supporting rolls 8,9, 10,11. The working rolls 2,3 and lateral supporting rolls 8,9, 10,11 are preferably also arranged to be able to be moved during operation, so that the pressure distribution in the roll-nip 4 can be changed during ongoing rolling.

According to a method according to the invention, a feedstock is rolled in a roll-nip 4 between a first working roll 2 and a second working roll 3 in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls 2,3. A freedstock 5 with a first width is rolled in this case between the two working rolls 2,3 and the working rolls 2,3 are deflected in a first deflection direction that has a principal component in the machine direction or opposite to the machine direction, so that the working rolls 2,3 are deflected in the machine direction or opposite to the machine direction. The width of the rolling feedstock 5 is then changed from the first width to a second width. On rolling of the second width, the working rolls 2,3 are deflected in a second deflection direction with a deflection of essentially the same magnitude as when the working rolls 2,3 are located in their first position. However, the second deflection direction is different to the first deflection direction, so that the pressure distribution in the roll-nip 4 crosswise to the machine direction is changed thereby. The method according to the invention can best be achieved by displacing the working rolls in the machine direction from a first position to a second position, each of the working rolls 2,3 being deflected in its second position also in the machine direction or opposite to the machine direction, but in a deflection direction that is different to the first deflection direction for the respective working roll so that, in the transverse direction of the machine, the distribution of pressure on the feedstock in the roll- nip 4 is changed thereby. Within the scope of the invention and the attached claims it is also conceivable to use the method to change the pressure distribution even in the event that the feedstock width is unchanged, if so desired. However, the invention relates primarily to adjustment of the pressure distribution in connection with a change in feedstock width.

The deflection of the working rolls 2,3 is at best essentially of the same magnitude in the second position of the working rolls as in the first position, even if the deflection direction is different. The working rolls 2,3 are best moved from their first position to their second

position principally at the same time as the width of the feedstock 5 in the roll-nip 4 is changed from the first width to the second width.

With reference to Figs. 3,4, 10 and 11, a particularly suitable variant of the method according to the invention shall now be explained. A feedstock 5 is rolled in a roll-nip 4 between a first working roll 2 and a second working roll 3 in a machine direction that is essentially perpendicular to the longitudinal axes of the working rolls 2,3. Each of the working rolls 2,3 is driven by a drive roll 6,7 and supported by a lateral supporting roll 8, 10 located upstream and a lateral supporting roll 9,11, located downstream, one lateral supporting roll 8,9, 10,11 having a concave form and the other lateral supporting roll 8,9, 10,11 having a convex form for each working roll 2,3. A first feedstock width is rolled between the two working rolls 2,3, each working roll 2,3 being located in a first position in the machine direction and the working rolls 2,3 being deflected in the direction of the machine due to the influence of the lateral supporting rolls 8,9, 10, 11. The width of the rolling feedstock 5 is changed during operation from the first width to a second width by welding the feedstock 5 upstream of the roll-nip 4 to a second feedstock 12, which second feedstock 12 is of the second width and which second width is less than the first width. The welding is done in a welding station 18 situated upstream of the roll-nip 4. So that the operation is not to be disrupted, a strip looper (accumulator) 19 is arranged between the welding station 18 and the nip 4. Figure 10 shows diagrammatically how the strip looper 19 is provided with a movable looper roller 20. During the welding operation, the strip is fed from the strip looper to the roll-nip 4 so that operation does not need to be interrupted. It is perceived that more than one looper roller 20 can be used (2-12 can be used) to achieve a suitable strip looper 19. The working rolls 2,3 are moved in the machine direction from their first position to a second position for the respective working roll 2,3 in that each of the working rolls 2,3 is moved together with its respective lateral supporting rolls 8,9, 10, 11 in an arc along the surface of its respective drive roll 6,7, so that the roll-nip 4 is moved to its second position. The second position is located downstream of the first position and the working rolls 2,3 are also deflected in their second position in the machine direction and the deflection in the second position is essentially of the same magnitude as when the working rolls 2,3 are in their first position, so that a different pressure distribution is used in the roll-nip when rolling the second width than when rolling the first width. The second deflection direction of the working rolls 2,3 is different to the first deflection direction. The difference in deflection direction does not have to be great, but can in practice be very little.

The second feedstock 12 has a downstream end 13, at which downstream end 13 the second feedstock 12 is welded to the rolling feedstock 5, so that the feedstocks 5,12 are joined with a weld seam 15 to form a rolling feedstock 5. The second feedstock 12 is best shaped so that at its downstream end 13 it is of the first width and the width of the second feedstockl2 passes over into the second width via a transition piece 14 of decreasing width, preferably a continuously decreasing width. The movement of the working rolls from the first position to the second position takes place preferably at the same time as the transition piece 14 passes through the roll-nip. However, it is conceivable for the movement of the working rolls 2,3 from the first position to the second position to be effected only after the rolling feedstock 5 that is passing through the roll-nip 4 has attained the second width. It is also conceivable for the change in width to be made in such a way that one goes from a narrower feedstock to a wider feedstock. The transition piece 14 can then have a transition from a smaller width to a larger width, as is evident from Fig. 9.

The working rolls 2,3 are located in their second position suitably downstream of the first position of the respective working roll and the working rolls 2,3 are deflected in the machine direction.

According to another embodiment of the method according to the invention, the working rolls 2,3 are located in their second position downstream of the first position for the respective working roll 2,3 and the working rolls 2,3 are deflected in a direction opposite to the machine direction.

According to a further embodiment of the method according to the invention, the second position of the respective working roll is located upstream of the first position of the respective working roll 2,3 and the working rolls 2,3 are deflected in the machine direction.

Within the scope of the invention, it is finally conceivable for the second position of the respective working rolls to be located upstream of the first position of the respective working roll 2,3 and for the working rolls 2,3 to be deflected opposite to the machine direction.

With reference to Fig. 13, it shall now be explained in greater detail how the displacement of the working rolls affects the pressure distribution in the roll-nip 4. Figure 13 shows how the working roll 2 takes up a first and a second position. In the second position, the working roll 2 is displaced by a distance x in the machine direction in relation to the first position.

The vertical position of the working roll 2 has then been displaced by a distance y. If the radius of the drive roll is R, it is generally true that tg a = x/ (2R-y) and that tg a = y/x and, as a result of this, that y = x2/(2R-y).

When one working roll 2 is moved in the machine direction, the roll-nip will be changed by double the value of the vertical displacement y, since the second working roll 3 is also displaced. Assuming that the lateral supporting rolls of a convex and concave shape respectively give the working roll 2 a deflection of 1 mm maximum (at the middle of the roll in the transverse direction of the rolling mill) and that the radius of the drive roll 6 is 350 mm, the following result is obtained. If the displacement of the working roll in the machine direction amounts to 0 mm, it is the case at the edges of the working roll that x = 0 and y = 0. At the centre of the working roll, however, x = 1 and y = 1/350 0.0029 mm.

The difference in the width of the roll-nip between the edge of the nip and its middle is then 2 (yi-yo) = 2*0. 0029 mm = 0.0057 mm. If on the other hand the displacement of the working roll in the machine direction increases to 12 mm, the following result is obtained.

At the edges it is the case that x = 12 mm and y = 144/350 0.411 mm. At the centre of the working roll, however, x = 13 mm and y 0.483 mm. The difference in the width of the roll-nip between the edges and the middle of the nip is then 2 (yi-yo) = 2 (0.483-0. 411) = 0.143 mm. Due to this, the pressure on the edges of the rolling feedstock is higher than the pressure on the middle of the rolling feedstock. It is also perceived that displacement of the working rolls from a first position in which x = 0 to a second position in which x = 12 will change the distribution of the pressure/force in the roll-nip 4. As is evident from the example cited above, the displacement of the working rolls does not have to be great for a substantial effect to be obtained. The change in deflection direction of the working rolls is therefore very little in practice.

With reference to Fig. 5, the effect of moving the working rolls in the machine direction is shown. In the figure, curve B shows a pressure profile in the transverse direction where the pressure is distributed relatively evenly. In this case the working rolls are in a first position.

Curve B can then be imagined to correspond to a pressure distribution in a roll-nip according to Figure 6. Curve A shows the pressure distribution when the working rolls have been moved to a second position. The pressure at the edges of the rolling feedstock is higher here than the pressure on the middle of the feedstock. Curve A can be imagined to correspond to the pressure distribution in a roll-nip according to Figure 7. However, it should be understood that the movement from the first position of the working rolls to the second position could equally well result in a change in the pressure profile of the opposite kind, so that the pressure was distributed more evenly.

With reference to Figure 12, an advantageous embodiment of the rolling mill according to the invention is shown. The working rolls 2,3 are placed in a rolling mill with convex and concave lateral supporting rolls 8,9, 10, 11. The lateral supporting rolls are each placed in a cassette 21,22, 23,24 that is supported swivellably around a pin 25,26, 27,28. On movement of the working rolls, each cassette 21,22, 23,24 is swivelled around its respective pin 25,26, 27,28. The lateral supporting rolls and working rolls are then moved as a unit.

Due to the present invention, a possibility is provided of controlling the pressure distribution in a roll-nip. Due to the fact that the working rolls can be moved along the surface of the drive rolls, friction is avoided and the working rolls can be moved quickly.

The advantage is thereby achieved that the pressure profile in the transverse direction of the machine can be changed very quickly. This in turn facilitates width changes during operation, which increases productivity in the rolling mill.

The method according to the invention/rolling mill according to the invention can also be used if it is desired to make quick transverse profile changes at strip ends. The invention can also be used when different parts of the same strip are to be rolled to different thicknesses.

In the enclosed figures it is shown how the roll-nip is displaced in the downstream direction in relation to a plane that coincides with the axes of rotation of the drive rolls. It should be understood, however, that the roll-nip can also be displaced in an upstream direction in relation to this plane. Such a displacement can be made prior to a reduction in the strip

width and will then cause the conical drive rolls to move inwards and so that the transition to a narrower width is thereby prepared.

The invention is especially suitable for use in conjunction with cold-rolling and can be used in connection with cold-rolling of black material without the prior removal of oxide.

However, it should be understood that the invention can also be used in connection with other rolling.