GB1595746A - Rolling mill - Google Patents

Description

(54) ROLLING MILL (71) We, ISHIKAWAJIMA-HARIMA JUK OGYO KABUSHIKI KAISHA, a Company organised under the Laws of Japan, of No. 2 1, 2chome, Ote-machi, Chiyoda-ku, Tokyo-to, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to rolling mills, and methods of rolling metal sheet, and one object is to provide means whereby the rolled sheet will approximate closely to a theoretical flat sheet.

Metal sheet leaving the rolls of a mill tends to have a cross section defined between upper and lower curved surfaces, so that the sheet is thicker at the centre than it is at the edges giving what is known as a crown.

It has been proposed to deform the rolls of a mill, either mechanically, or by heating in order to eliminate the crown, or to make it less pronounced, but that method has so far not been found to be successful.

Another proposed method in which the crown ratio is maintained at constant throughout the whole rolling sequence, has also been found not to solve the problem.

According to the present invention, a rolling mill comprises a pair of rolls, and means for driving them at unequal peripheral velocities, and a detector of the shape of metal sheet rolled by the rolls, a computer responsive to the output from the detector to compute the respective peripheral velocities of the rolls required for improvement of the shape of the rolled metal, and a control for the speeds of the rolls which is responsive to the computer output.

The invention includes a method of operating a rolling mill in which a computer is responsive to the output of a detector of the shape of metal sheet rolled by a pair of rolls to compute the respective peripheral velocities of the rolls to tend to improve the shape of the rolled metal, and the speeds of the rolls are controlled in response to the computer output.

The invention takes advantage of the discovery that by monitoring the shape, and particularly the crown of the rolled sheet, errors can be corrected satisfactorily by adjusting the peripheral velocities at which the upper and lower rollers are driven, and the ratio between those velocities, and that the thickness of the rolled strip can be maintained as desired by also controlling the rolling pressure or force applied between the rollers.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example with reference to the accompanying drawings, in which; FIGURE 1 is a schematic view of a rolling mill in accordance with the invention.

FIGURES 2, 3 and 4 are views used for the explanation of the relationship between the ratio between the peripheral velocities of the upper and lower work rolls and the frictional force; and FIGURE 5 is a graph illustrating the relationship between the rolling force and the thickness of the rolled metal.

Referring to FIGURE 1, an upper work roll 1, and a lower work roll 2 are driven from a reduction gear 3 and motors 4 and 5 in such a way that the rolls 1 and 2 rotate at different peripheral velocities vl and v2, respectively.

Metal sheet 1 Il of the thickness h, I is rolled between the rolls 1 and 2 to have a thickness h2 as shown at 112. The sheet 112 is continuously monitored by a shape detector 6 connected to an arithmetic unit 7. In response to the output signal from the shape detector 6, the arithmetic unit 7 delivers a shape correction signal to a control unit 8 which in turn controls the rotational speeds of the motors 4 and 5, and hence the rolls I and 2.

A roll gap control unit 10 is arranged to control roll gap setting units 9 so that in response to the shape correction signal from the arithmetic unit 7 the roll pressure is set to tend to cause the rolls to be spaced apart by the desired distance allowing for variations in the speeds of the motors 4 and 5.

Variation in the peripheral velocities of the rolls, varies the rolling force and conse quently the deformation of the rolls, which can thus be controlled so that the shape of the rolled metal may be corrected as will be described in detail hereinafter.

Referring to FIGURES 2, 3 and 4, it is assumed that the upper and lower rolls 1 and 2 have the same diameter and the thickness of the sheet metal 11, and 112 prior to and after rolling is the same in each FIGURE.

The neutral lines or points are designated by N, and N2.

FIGURE 2, shows the conventional rolling condition wherein the rolls 1 and 2 are rotated at the same peripheral velocity, the neutral points N, and N2 are on the same vertical line, and in the roll bite zones A and B the sheet metal is subjected to frictional force in the directions indicated by the arrow on the upper and lower rolls 1 and 2. As a result, the sheet metal is subjected to horizontal compression force so that the vertical rolling force is greater than if there were no frictional force.

FIGURE 4 shows the so-called rolling drawing or RD process wherein the peripheral velocities vl and v2 of the upper and lower work rolls 1 and 2 are so selected as to satisfy the following condition.

v1/v2 = hl/h2 where h1 and h2 are the thicknesses of the metal entering and leaving the work rolls.

Therefore in the roll bite zone C the friction force on the metal along the contact arc between the sheet metal and the upper roll I is opposite in direction to the frictional force on the metal along the contact arc between the sheet metal and the lower roll 2.

In other words, the upper neutral point N, is at the exit point of the upper contact arc while the lower neutral point N2 is at the entrance point of the lower contact arc. As a consequence, the sheet metal is not subject to horizontal compression force and the rolling pressure is smaller than in FIGURE 2.

In FIGURE 3. the peripheral velocities of the upper and lower work rolls I and 2 are so controlled that the upper and lower neutral points N, and N2 are displaced from the exit point of the upper contact arc and the entrance point of the lower contact arc and are not on the same vertical line. As a result on both sides of the bite zone C the sheet metal is subjected to frictional forces which are similar as in conventional rolling. Therefore the rolling force is intermediate between the rolling forces in FIGURES 2 and 4.

From the above explanation it is apparent that the rolling force may be varied by changing the ratio between the peripheral velocities of the upper and lower rolls I and 2. It has been found that, by so changing the ratio between the peripheral velocities of the upper and lower rolls I and 2 to vary the rolling force, the roll deformation can be varied, and; the sectional profile of the rolled metal can be improved, the distribution of the metal over the width of strip can be varied accordingly.

In response to the output signal from the shape detector 6, which continuously detects the shape of the rolled metal 112, the arithmetic unit 7 computes an increment of decrement Ap of the rolling force required for correcting the shape of the sheet metal being rolled and the peripheral velocities v, and v2 of the upper and lower work rolls 1 and 2 required for producing the above increment or decrement Ap. In response to the output signal from the arithmetic unit 7, the motor control unit 8 controls the speed of the motors 4 and 5 and hence the peripheral velocities of the upper and lower work rolls 1 and 2.

A way of detecting the shape of the rolled metal 112 may be to measure the size of the crown prior to and after the rolling. Alternatively, the shape or size of the crown of the sheet prior to rolling may be predicted instead of actually measured, and the shape or size of the crown after rolling is measured.

However, in order to avoid deviation of the thickness of the rolled metal sheet 112 from h2, p, the intersection between the mill elastic characteristic curve b' (a characteristic of the mill relating to the bias force on the rollers to the reduction in thickness h1 - h2) and the metal plastic characteristic curve a' (a characteristic of the metal) must be at a distance along the abscissa in FIGURE 5 representing the desired outlet thickness h2, and on the same vertical lines passing a the intersection between the mill elastic characteristic curve b and the plastic characteristic curve a prior to the correction of shape as shown in FIGURE 5. FIGURE 5 shows the curve a for an inlet thickness h, for the greater rolling force and the curve a' for a lesser rolling force. The characteristics b and b' are parallel with each other and intersect the respective curves a and a' at points a and ss on the same line parallel to the ordinate representing rolling force.

Thus the roll gap between the upper and lower work rolls I and 2 must be increased or decreased by AS=Ap/K, where K is the coefficient of mill modulus relating change in gap to change in rolling force.

The arithmetic unit 7 computes the roll gap increment or decrement S in the manner described above, and the control unit 10 operates the roll gap setting units 9 accordingly.

In experiments conducted by the inventors, it was found that when mild steel is rolled by the rolling drawing process shown in FIGURE 4, the rolling force can be reduced to, approximately 1/3 of the rolling force required in the conventional rolling process shown in FIGURE 2. As a result, the crown is also reduced by approximately 1/3.

Thus there is scope for correcting the shape of the rolled sheet metal by the method described while still having a reduced rolling force as compared with a conventional process by approaching RD conditions.

WHAT WE CLAIM IS: 1. A rolling mill comprising a pair of rolls, and means for driving them at unequal peripheral velocities, and a detector of the shape of metal sheet rolled by the rolls, a computer responsive to the output from the detector to compute the respective peripheral velocities of the rolls required for improvement of the shape of the rolled metal, and a control for the speeds of the rolls which is responsive to the computer output.

2. A rolling mill as claimed in Claim 1 in which the computer is also arranged to control the bias force urging the rolls towards each other in the sense to tend to keep the thickness of the metal sheet leaving the rolls the same in spite of variations in the rolling force due to changes in the respective peripheral velocities.

3. A rolling mill as claimed in either of the preceding claims in which the detector includes an optical detector at the outlet side of the rolls.- 4. A rolling mill arranged to operate substantially as herein specifically described with reference to FIGURE 1 of the accompanying drawings.

5. A method of operating a rolling mill in which a computer is responsive to the output of a detector of the shape of metal sheet rolled by a pair of rolls to compute the respective unequal peripheral velocities of the rolls to tend to improve the shape of the rolled metal, and the speeds of the rolls are controlled in response to the computer output.

6. A method as claimed in Claim 5 in which the bias force urging the rolls towards each other is also controlled in response to the output of the computer to tend to keep the thickness of the metal sheet leaving the rolls the same in spite of variations of the rolling force due to changes in the peripheral velocities.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. process shown in FIGURE 2. As a result, the crown is also reduced by approximately 1/3. Thus there is scope for correcting the shape of the rolled sheet metal by the method described while still having a reduced rolling force as compared with a conventional process by approaching RD conditions. WHAT WE CLAIM IS:

1. A rolling mill comprising a pair of rolls, and means for driving them at unequal peripheral velocities, and a detector of the shape of metal sheet rolled by the rolls, a computer responsive to the output from the detector to compute the respective peripheral velocities of the rolls required for improvement of the shape of the rolled metal, and a control for the speeds of the rolls which is responsive to the computer output.

2. A rolling mill as claimed in Claim 1 in which the computer is also arranged to control the bias force urging the rolls towards each other in the sense to tend to keep the thickness of the metal sheet leaving the rolls the same in spite of variations in the rolling force due to changes in the respective peripheral velocities.

3. A rolling mill as claimed in either of the preceding claims in which the detector includes an optical detector at the outlet side of the rolls.-

4. A rolling mill arranged to operate substantially as herein specifically described with reference to FIGURE 1 of the accompanying drawings.

5. A method of operating a rolling mill in which a computer is responsive to the output of a detector of the shape of metal sheet rolled by a pair of rolls to compute the respective unequal peripheral velocities of the rolls to tend to improve the shape of the rolled metal, and the speeds of the rolls are controlled in response to the computer output.

6. A method as claimed in Claim 5 in which the bias force urging the rolls towards each other is also controlled in response to the output of the computer to tend to keep the thickness of the metal sheet leaving the rolls the same in spite of variations of the rolling force due to changes in the peripheral velocities.