GB2122380A

GB2122380A - Method and apparatus for variably controlling the lateral rigidity of a sheet rolling mill

Info

Publication number: GB2122380A
Application number: GB08217544A
Authority: GB
Inventors: Isao Imai
Original assignee: IHI Corp
Current assignee: IHI Corp
Priority date: 1982-06-17
Filing date: 1982-06-17
Publication date: 1984-01-11
Also published as: GB2122380B

Abstract

In a sheet rolling mill having work rolls 1, 2 and backup rolls 3, 4, rolling of flat sheets 5 is facilitated by controlling the transverse rigidity or deflection in the direction of the width of the rolls to be constant. The rolling force is detected by a load cell 14 and, based on the rolling force thus detected, the value for correcting the crown of the work roll is calculated using a transverse rigidity coefficient C set in a setter 15 and a function set by a function unit 16 and dependent on sheet width and used to control the transverse rigidity. <IMAGE>

Description

SPECIFICATION Method and apparatus for variably controlling the lateral rigidity of a sheet rolling mill The present invention relates to a method and apparatus for variably controlling the lateral ridigity of a rolling machine.

The lateral rigidity of rolling mills is a concept expressing the deflection in the direction of the width of the roll by the rolling force and is defined by the formula: Q= Rolling force/Sheet crown (in ton/mm), where the rolling force is the force acting on the rolls tending to move them apart when a strip is being rolled and the sheet crown is the difference between the thickness of the sheet at its central portion and that at its edges.

This lateral rigidity, Q, is subject to variation in dependence on the width of the sheet being rolled, as is illustrated in the graph of Fig. 1 of the accompanying drawings. The bending effect coefficient KB also, subject to variation with the sheet width, is also illustrated on the same graph. Thus, it is difficult to obtain a precise relationship between the rolling force PR and the roll bending force PB, that is to say the force applied vertically to the working roll bearing boxed to bend the working roll.

If the lateral or transverse rigidity is always kept at an optimum value regardless of the sheet width, the sheet crown can be reduced to a minimum against disturbance of the rolling force or heat crown and roll wear. The heat crown is that part of the roll crown (difference in diameters between the thickness of the working roll at its centre and the thickness of the roll at its edge) caused by the thermal expansion of the roll which in turn is caused by the heat generated by the contact of the working roll with a sheet being rolled.

This principle will now be described with reference to Fig. 2 which comprises three graphs showing the rolling force along the vertical axis plotted against the crown variation along the horizontal axis.

As shown in Fig. 2(a), if the transverse rigidity is increased from Q1 to Q2 against an increase of the rolling force PR1 to PR2, it is possible to maintain the relative crown at a constant value for rolling. Also, as shown in Fig. 2(b), if the transverse rigidity is reduced from Q, to Q3 against the heat crown CH, rolling with a constant relative crown is possible. Further, in rolling of the input sheet crown at zero, if the transverse rigidity is increased infinitely from Q to Q as shown in Fig. 2(c), there will be required a decreased bending dto correspond to the heat crown, and this is not practical.But, in such a case, if an adequate transverse ridigity (say Q3) is given to the rolling mill, it is possible to control the sheet crown against the heat crown within the range of the increased bending I so that it is possible to roll a sheet of flat crown with ease.

Heretofore, as one of the means of variable control of the rolling mill, it has been contemplated to change the contact width of the work roll with the sheet and that of the backup roll with the work roll. As a practical method, it has been disclosed to maintain the horizontal position of the upper and lower intermediate rolls of the rolling mill in a certain relationship to the sheet width (see Japanese Patent Public Disclosure Nos.

41255/1974 and 30777/1075 and Japanese Patent Publication No. 19510/1975).

However, such a method has the shortcoming of disadvantageously affecting the sheet thickness accuracy in that change of the contact width of the back-up roll with the work roll induces a substantial change of the vertical rigidity which is inherently critical in rolling mills.

Accordingly it is an object of the invention to provide a transverse rigidity control method and apparatus which permit the maintenance of the transverse rigidity of the rolling mill at a constant value regardless of the sheet width and the control of the transverse rigidity alone without affecting the vertical rigidity.

According to the present invention there is provided a method for variably controlling the transverse rigidity of a sheet rolling mill having work rolls and backup rolls comprising detecting the rolling force, calculating a value for controlling the bending of the work rolls based on the said rolling force, a transverse ridigity coefficient and a function dependent on the sheet width and correcting the bending of the work rolls by the said value to effect the control of the transverse rigidity of the rolling mill. The correcting of the work roll bending may be carried out on a roll bending setting force or on an internal pressure set value in hydraulic chambers provided in the backup rolls.

The invention also embraces an apparatus for carrying out such a method and thus according to a further aspect of the present invention there is provided apparatus for variably controlling the transverse rigidity of a sheet rolling mill having work rolls and backup rolls comprising a decrease bender, an increase bender, bender control means having a bending force setting signal input for controlling the said benders in dependance on the said signal and roll bending force setting means for setting a roll bending force in the said bender control means, the roll bending force setting means including a rolling force detecting means, a transverse rigidity coefficient setter for for setting a transverse rigidity coefficient of the rolling mill, a function unit having a function determined by the sheet width and a sheet width setter for transmitting a signal representative of the sheet width value to the function unit, thereby calculating the rolt bending force by multiplying the said transverse rigidity coefficient and said function to a rolling force detected by the said rolling force detecting means.

Preferably the bender control means comprises valve means for controlling a bender working fluid, a servo amplifier having a roll bending force setting signal input for transmitting a control signal dependent on the input signal to said valve means and a feedback circuit for detecting a working fluid pressure in the bender and feeding the same back to said servo amplifier. A hydraulic chamber may be provided in each backup roll so that its surface profile can be changed by controlling the hydraulic pressure in said hydraulic chamber.

Preferably the rolling force detecting means comprises a rolling force detector, means for locking on and storing a rolling force signal and an arithmetic unit for comparing the rolling force signal detected by said rolling force detector with the rolling force signal stored in said device and outputting a differential signal as a correction rolling force signal.

The apparatus preferably further comprises means for controlling the backup roll internal pressure for changing the surface profile by controlling the hydraulic pressure of the hydraulic chamber and means for setting an internal pressure in the backup rolls, said internal pressure setting means including a second transverse rigidity coefficient setter, a second function unit and a sheet width setter for sending a signal indicative of the value of the sheet width to said second function unit, a backup roll internal pressure set value being calculated from the rolling force by the second transverse rigidity coefficient and the second function, thereby controlling the transverse rigidity of the rolling mill by using the backup roll internal pressure set value and the roll bending force together.

Preferably the backup roll internal pressure setting means further comprises a saturation value detector for detecting the saturation value of the backup roll internal pressure so that when the backup roll internal pressure reaches a saturation value, a roll bending force setting signal is inputted to the bender control means. In a modified construction the difference between the stored value of the rolling force and the actual rolling force at the time of saturation of the backup roll internal pressure is used as a correction rolling force signal.

Further features and details of the present invention will be apparent from the following description of certain specific embodiments which is given by way of example with reference to the accompanying drawings, in which: Figure 1, which has already been referred to, is a diagram showing the relationship between the bending effect coefficient and the sheet width; Figures 2(a), 2(b) and 2(c), which have already been referred to, are diagrams showing the effects of variations in the transverse rigidity; Figure 3 is a diagram showing the ratio of the transverse rigidity to the bending effect coefficient as a function of the sheet width; Figure 4 is a block diagram showing an embodiment of the apparatus for variably controlling the transverse rigidity according to the present invention;; Figure 5 is a block diagram showing another embodiment of the apparatus for variably controlling the transverse rigidity according to the present invention; Figure 6 is a diagram illustrating the change in the transverse rigidity in an apparatus according to the present invention; Figure 7 is a diagram showing the curve of the coefficient of effect on the sheet crown when backup rolls and variable surface profile (Vc) rolls are used in the present invention; and Figures 8 and 9 are respectively block diagrams of a still further embodiment of an apparatus for variably controlling the transverse rigidity according to the present invention.

The present invention is based on the following principle: Firstly, the relation between the transverse rigidity of a rolling mill and the crown disturbance is defined as follows:

where Q = Transverse rigidity (ton/mm); PR = Rolling force (ton); Cr = Output-side sheet crown (mm); Cw = Roll Wear (mm); C, = Initial crown of the roll (mm); PB = Roll bending force (ton); and KB = Bending effect coefficient (ton + mm) (change in strip or sheet crown under the application of a unit load).

From the forgoing formulae, it will be seen that the output side sheet crown Cr is determined by the rolling mill transverse rigidity, the rolling force, the shape of the roll and the roll bending force.

Here, the roll bending force PB is expressed by the formula

Substituting thisy?oll bending force for PB in formula (1),

By controlling in this way, a controlled equivalent transverse rigidity, Qe, is obtained.

In the foregoing formulae, C represents the transverse rigidity control coefficient, and when C= 1, Qe = co; when C = O, Qe = Q; or when C = - co, Qe = 0.

Thus, it is possible to impart a desired transverse rigidity.

In formula (2) above, KB/Q represents a proportion of the bending force for correction of the roll deflection due to the rolling force, and the graph of this is illustrated in Fig. 3. In this case, the strip width is known before the rolling, so that the rolling is made with an appropriate value of KB/Q chosen from the sheet width and an adequate value set for the transverse rigidity control coefficient or lateral mill modulus C depending on the condition of rolling. In this way, it is possible to control the transverse rigidity to an optimum value for the sheet width. It is also possible to maintain the transverse rigidity at a constant value regardless of the sheet width. depending on the condition of rolling. In this way, it is possible to control the transverse rigidity to an optimum value for the sheet width.It is also possible to maintain the transverse rigidity at a constant value regardless of the sheet width.

In accordance with the foregoing principle, the transverse rigidity control apparatus is constructed as shown in Fig. 4.

In Fig. 4, reference numerals 1 and 2 represent work rolls; 3 and 4 backup rolls and 4 a metal sheet. Between the journal boxes of the work rolls 1 and 2 an increase bender 6 is provided, and between the journal boxes of the work rolls 1 and 2 and those of the backup rolls 3 and 4 are provided with decrease benders 7 respectively. These benders have a hydraulic pressure applied to them so that the work rolls 1 and 2 are bent in the form of a convex or concave curve by the differential pressure. These bending pressures are detected by pressure transducers 8 and 9, and the differential pressures are passed to an amplifier 10, fed back and added by a servo amplifier 11 to give a gain 1 2 for control by a servo value 1 3.

On the other hand, the rolling force PR is detected by a load cell 1 4 and is inputted through a transverse rigidity coefficient setter 1 5 and a function unit 1 6 to an adding amplifier 1 7 as a roll bending force PB. The function unit has fed to it a function KB/Q (see Fig. 3) commensurate with the sheet width given by a signal from a sheet width setter 18, while the transverse rigidity coefficient setter 1 5 has a constant transverse rigidity coefficient C set, and these are adapted to cooperate to give an output of optimum gain 1 2 from the servo amplifier 11. Setting of an external roll bending force is made by an initial setter 19.

In Fig. 4, reference numeral 20 represents a housing and 21 a hydraulic pump.

Fig. 5 shows another embodiment of the present invention, using a surface profile variable roll (Vc roll) for each backup roll.

The backup rolls 3a and 4a each have a hydraulic chamber 22 at their central part, and by applying a hydraulic pressure to the hydraulic chamber 22, the surface profile can be changed, and this surface profile changes (expands or shrinks) in proportion to the hydraulic pressure.

When rolling with such backup rolls 3a and 4a the initial crown in C* in formula (4) is given by the backup rolls 3a and 4a so that the bending control is made in accordance with the forecast value of the rolling force and the sheet width.

The increment or decrement of the sheet crown Cr in formula (4) is obtainable as below:

where AP is the increment or decrement of the rolling force.

Thus, with an initial roll crown value given to the backup rolls and locked on at an adequate sheet crown value, the transverse rigidity is controlled with reference to such point. The transverse rigidity Qe thus controlled is constant regardless of the sheet width and can take a desired value according to the transverse rigidity coefficient, as shown in Fig. 6.

Specifically, the signal of the rolling force at the time when the initial crown value is given by the backup rolls 3a and 4a to the work rolls 1 and 2 is locked on by a locking-on mechanism 23 stored in a memory 24, and the signal from the load cell 1 4 is compared with the signal from said memory 24 by an arithmetic unit 25 to obtain the difference between them, the differential signal being indicative of the rolling force. Further, in order to give a specified crown to the backup rolls 3a and 4a, there are provided an oil passage 26 to the hydraulic chamber 22, an intensifier 27 and a servo value 28 in said oil passage 26, a servo amplifier 29 generating a required signal to said servo valve 28 and a pressure transfucer 30 detecting the hydraulic pressure in the hydraulic chamber 22.The signal coming from the pressure transducer 30 is fed across an amplifier 31 back to the servo amplifier 29 to set an initial crown value by means of an initial crown value setter 32 in the servo amplifier 29 so that an initial crown is given to the backup rolls 3a and 4a.

In the foregoing case where Vc rolls are used for the backup rolls, if the profile diametrice increment of the backup roll at the strip width is represented by CB, the coefficient of effect otv onto the sheet crown Cr is given by

where the coefficient of effect represents the rate or ratio of the change of the sheet crown by means of the work roll bender or the Vc roll.

As stated above, the hydraulic force Pv and the backup roll diametric crown Cv are in proportional relationship to each other, and its coefficient ss is approximately a square function of the sheet width. As Fig. 7 indicates, the effect coefficient av as a function of the sheet width has a constant value if the hydraulic force Pv is constant.

Fig. 8 shows a further embodiment of the control with a bender interlocked with the backup roll internal pressure. The principle of this embodiment is as follows: Where Vc rolls are used as the backup rolls, the sheet crown is related to the changing rolling force given by the formula:

In this case, the hydraulic force Pv of the backup roll is obtainable by

so that the sheet crown is given by

Here, the transverse rigidity is controlled as

for PB = O by changing the Pv value.

However, if the absolute value of bending by the rolling force is great enough over the value of the backup roll diametric crown by the hydraulic force Pv, control is so effected as to add the bender force with Pvrna, maintained to satisfy the transverse rigidity control.

Thus in this system, the rolling force with that proportion which is converted to the value of the hydraulic pressure Pv is substracted from it is given as a quantity for adjustment of the bender, and the system is expressed by the formula

where PRC represents the rolling force corresponding to that part of the bending which may be modified by control of the Vc roll. The value of APR thus obtained may be corrected on the bender, or

(where PBO represents that value of bending modifiable by control of the Vc roll which has been converted from Vc roll pressure into bender pressure) may be deducted from the PB value calculated from the rolling force for use as a set value of the bender.

The control apparatus of such a system will be described with reference to Fig. 8. The backup rolls 3a and 4a each have a hydraulic chamber 22 at the central part of the roll, as in the case of Fig. 5, so that the surface profile can be changed by applying hydraulic pressure to the hydraulic chamber 22, and the surface profile is adapted to change in proportion to the hydraulic force applied. This hydraulic pressure (internal pressure) is given by the servo valve 28 and the intensifier 27, and it is fed back to the servo amplifier 29 via the pressure transducer 30 and the amplifier 31.

On the other hand, the signal indicative of rolling force PR detected by the load cell 14 is inputted through a first transverse rigidity coefficient setter 15a and a first function unit 1 6a having a function of KB/Q to the adding amplifier 1 7. Here, the backup roll internal pressure setting force Pv to be inputted to the servo amplifier 29 is calculated as the signal of the rolling force PR detected by the load cell 14 passes through a second transverse rigidity coefficient setter 1 sub and a second function unit 1 6b having a function of 1 /avss.

The function KB/Q in the first function unit 1 6a and the function 1 /avss in the second function unit 1 6b are determined by the sheet width, and the signal of the value of sheet width from the sheet width setter 1 8 is given to the first and second function units 1 6a and 1 6b. Further, there is provided a saturated value detector 33 which detects when the backup roll internal pressure set value has reached a saturated value. When the saturation detector 33 detects a saturated value, a switch 34 is actuated to feed the signal passing through the first function unit 1 6a into the adding amplifier 1 7 so that the control shown in Fig. 4 operates as a transverse rigidity control loop.Simultaneously, the signal passing through the second function unit 1 6b is fed through a converter 35 into the adding amplifier 29. This converter is to deduct the initial crown components of the backup rolls 3a and 3b and has KBavss set as a function.

This function is also subject to change by the sheet width.

The rolling force may be stored and locked on at the point at which the internal pressures of the backup rolls 3a and 4a have reached saturation so that the transverse rigidity control loop is operated as shown in Fig. 5.

Further, the control of the internal pressure and that of the bender pressure may be effected together. In such a case, control is not made by detecting the saturation of the internal pressure but by distributing the change of the rolling force proportionally to the internal pressure and the bender pressure.

That is, the sheet crown is controlled as

while the transverse rigidity is controlled as

so that by supplying a proportion of the transverse rigidity coefficients C, and C2, it is possible to control the equivalent transverse rigidity. This block diagram is shown in the block diagram of Fig. 9 in which reference numeral 36 represents a first transverse rigidity coefficient proportional setter and 37 represents a second transverse rigidity coefficient proportional setter. In Figs. 8 and 9, the same components are designated by the same reference numerals.

The effects and advantages of the present invention may be summarized as follows.

The transverse rigidity can be controlled at a constant value against change of the sheet width and the transverse rigidity thus controlled can be set at a desired value.

The system is applicable to four-stage rolling mills, with no change in the contact width between the backup rolls and the work rolls, so that the vertical rigidity does not change even if the transverse rigidity is changed thereby ensuring no adverse effect on the accuracy of the sheet thickness.

Variable control of the transverse rigidity is effected by control apparatus so that the machine can be simplified and the manufacturing cost can be reduced.

Compared with six-stage rolling mill intermediate roll moving systems for transverse rigidity variable control of this type, the present invention has the advantages of fewer rolls, less wearing of the rolls and a lower running cost. Also, a four-stage rolling mill in accordance with the present invention is of symmetrical construction thus avoiding zig-zag movement of the sheet.

Claims

1. A method of variably controlling the transverse rigidity of a sheet rolling mill having work rolls and backup rolls comprising detecting the rolling force, calculating a value for controlling the bending of the work rolls.

based on the said rolling force, a transverse rigidity coefficient and a function dependent on the sheet width and correcting the bending of the work rolls by the said value to effect the control of the transverse rigidity of the rolling mill.

2. A method as claimed in Claim 1 in which correcting of the work roll bending is carried out on a roll bending setting force.

3. A method as claimed in Claim 1 in which correcting of the work roll bending is carried out on an internal pressure set value in hydraulic chambers provided in the backup rolls.

4. A method of variably controlling the transverse rigidity of a sheet rolling mill substantially as specifically herein described with reference to any one of Figs. 4, 5, 8 and 9 of the accompanying drawings.

5. Apparatus for variably controlling the transverse rigidity of a sheet rolling mill having work rolls and backup rolls comprising a decrease bender, an increase bender, bender control means having a bending force setting signal input for controlling the said benders in dependence on the said signal and roll bending force setting means for setting a roll bending force in the said bender control means, the roll bending force setting means including a rolling force detecting means, a transverse rigidity coefficient setter for setting a transverse rigidity coefficient of the rolling mill, a function unit having a function determined by the sheet width and a sheet width setter for transmitting a signal representative of the sheet width value to the function unit, thereby calculating the roll bending force by multiplying the said transverse rigidity coefficient and said function by a rolling force detected by the said rolling force detecting means.

6. Apparatus as claimed in Claim 5 in which the bender control means comprises valve means for controlling a bender working fluid, a servo amplifier having a roll bending force setting signal input for transmitting a control signal dependent on the input signal to said valve means and a feedback circuit for detecting a working fluid pressure in the bender and feeding the same back to said servo amplifier.

7. Apparatus as claimed in Claim 5 or 6 in which a hydraulic chamber is provided in each backup roll so that its surface profile can be changed by controlling the hydraulic pressure in said hydraulic chamber.

8. Apparatus as claimed in Claim 5 in which the rolling force detecting means comprises a rolling force detector, means for locking on and storing a rolling force signal and an arithmetic unit for comparing the rolling force signal detected by said rolling force detector with the rolling force signal stored in said device and outputting a differential signal as a correction rolling force signal.

9. Apparatus as claimed in Claim 7 further comprising means for controlling the backup roll internal pressure for changing the surface profile by controlling the hydraulic pressure of the hydraulic chamber and means for setting an internal pressure in the backup rolls, said internal pressure setting means including a second transverse rigidity coefficient setter, a second function unit and a sheet width setter for sending a signal indicative of the value of the sheet width to said second function unit, and backup roll internal pressure set value being calculated from the rolling force by the second transverse rigidity coefficient and the second function, thereby controlling the transverse rigidity of the rolling mill by using the backup roll internal pressure set value and the roll bending force together.

10. Apparatus as claimed in Claim 9 in which said backup roll internal pressure setting means further comprises a saturation value detector for detecting the saturation value of the backup roll internal pressure so that when the backup roll internal pressure reaches a saturation value, a roll bending force setting signal is inputted to the bender control means.

11. Apparatus as claimed in Claim 9 in which the difference between the stored value of the rolling force and the actual rolling force at the time of saturation of the backup roll internal pressure is used as a correction rolling force signal.

1 2. Apparatus for variably controlling the transverse rigidity of a sheet rolling mill substantially as specifically herein described with reference to any one of Figs. 4, 5, 8 and 9 of the accompanying drawings.

13. A rolling mill including apparatus as claimed in any one of Claims 5 to 12.