GB2137778A

GB2137778A - Forward Slip Control Device

Info

Publication number: GB2137778A
Application number: GB08406548A
Authority: GB
Inventors: Hiroyuki Shiozaki; Hiroaki Kuwano
Original assignee: IHI Corp
Current assignee: IHI Corp
Priority date: 1983-03-15
Filing date: 1984-03-13
Publication date: 1984-10-10
Also published as: DE3408807A1; FR2542642A1; FR2542642B1; DE3408807C2; GB8406548D0; JPS59169614A; GB2137778B

Abstract

A forward slip control device for a rolling mill having a pair of rolls (1, 2) in which the forward slip fH of a strip (3) is calculated (12) and is compared with a set value fH<I>. In response to a signal representative of difference DELTA VRL between these values, the peripheral velocity VRL of a work roll (1) is changed, thereby controlling the forward slip. As shown, the lower roll 2 rotates at a constant velocity, measured at 15 and compared in an arithmetic unit 12 with strip exit velocity V2 to obtain slip. The desired value for this may be at or nearly zero. Any slip error adjusts the velocity of the upper roll 1, which in any case is slower than roll 2. In an alternative embodiment (Fig. 4) both rolls rotate at the same speed driven by a single motor whose speed is adjusted in response to slip error. <IMAGE>

Description

SPECIFICATION Forward Slip Control System The present invention relates to a forward slip control system for a rolling mill having a pair of work rolls.

As the rolling velocity in a rolling mill is increased, the fluid lubrication occurs between the work rolls and the strip so that the no-slip line position or neutral point gradually approaches the exit end of the arc of contact and finally moves past the end of the arc of contact. As a result, the forward slip has a negative value. If the no-slip line position exceeds the arc of contact and the forward slip becomes negative, these exists no point for determining the velocity of the strip with the result that the strip velocity becomes unstable. Thus, vibration occurs, leaving chatter marks on the surfaces of the rolled strip.

Furthermore, in the case of a rolling mill in which the peripheral velocity of the upper work roll is different from that of the lower work roll (hereinafter referred to as "rolling with different roll velocities"), the rolling efficiency varies in response to the forward slip, as discussed in more detail below.

It is therefore an object of the present invention to provide a forward slip control system which can control-the forward slip to a given value in order to maintain stable rolling conditions and to improve the rolling efficiency.

According to the invention there is provided a forward slip control system for a rolling mill having a pair of work rolls, the device comprising a velocity sensor for detecting a velocity of a strip leaving a rolling mill; a velocity sensor for detecting a peripheral velocity of one of work rolls; an arithmetic unit for calculating the forward slip of the strip relative to the one work roll from signals from the velocity sensors; a control unit arranged to generate a work roll velocity correction signal in dependence upon the forward slip value obtained from the arithmetic unit, a forward slip set value and a set value for the peripheral velocity of the other work roll; and a drive controller responsive to the velocity correction signal from the control unit arranged to control the actual peripheral velocity of the other work roll in order to achieve the desired forward slip value.

In the case where the work rolls are driven at different peripheral velocities, the difference between the peripheral velocities of the work rolls is controlled. Preferably, the higher velocity roll is driven at a constant speed and the speed of the lower velocity roll is controlled.

In an alternative form, the work rolls are driven at a same peripheral velocity, and the peripheral velocity of both the work rolls is controlled.

The invention may be carried into practice in various ways and some embodiments will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic vertical section through a rolling mill showing rolling with different roll velocities; Figure 2 is a graph showing the relationships between the ratio of the peripheral velocities of the upper and lower work rolls on the one hand, and the forward slip and the rolling force on the other hand, in the case of the rolling with different roll velocities; Figure 3 is a schematic diagram showing a first embodiment of a forward slip control system in accordance with the present invention; and Figure 4 is a view similar to Figure 3 showing a second embodiment.

Figure 1 shows the situation in which two work rolls 1, 2 are driven with different roll velocities.

VRL designates the peripheral velocity of the upper work roll 1 which is lower than the peripheral velocity VRH of the lower work roll 2; va, the velocity of a strip 3 entering the work rolls 1 and 2; v2, the velocity of the strip 3 leaving the work rolls 1 and 2; yP, the frictional force developed between the work rolls 1 and 2 on the one hand and the strip 3 on the other hand; a, the no-slip line position between the strip 3 and the upper work roll 1; and p, the no-slip line position between the strip 3 and the lower work roll 2.

When the peripheral velocities VRL and VAH of the upper and lower work rolls 1 and 2 are different from each other, the no-slip line position a is displaced toward the entry to the rolls 1, 2, while the no-slip line point p is displaced toward the exit. As a result, there exists a region where the directions of the frictional forces MP between the work rolls 1 and 2 and the strip 3 are opposite to each other. Consequently, the rolling force P is decreased.

In the case of rolling with different roll velocities, the forward flip fH of the higher velocity work roll is given by

Figure 2 shows the relationships between the forward slip fh and the rolling force P on the one hand and the ratio VRH /VRL between the peripheral roll velocities on the other hand. As is clear from Figure 2, the higher the ratio VRH /VRL, the lower the forward slip fH becomes, the relationship being roughly linear and, at the same time, the lower the rolling force, though the decrease of the rolling force becomes minimal as the forward slip approaches zero.

Thus, when the forward slip fh and the rolling force are compared, it can be seen that the lower the forward slip, the lower the rolling force becomes-and that the decrease in rolling force is limited when the forward slip fH approaches zero.

It follows therefore that when the forward slip is maintained at zero, or at a value close to zero, the rolling conditions can be stabilised and the rolling efficiency can be improved.

Referring now to Figure 3, a forward slip control system in accordance with the present invention is shown. The upper and lower work rolls 1 and 2 for rolling the strip 3 are backed by backup rolls 4 and 5 and are driven independently of each other by motors 6 and 7, respectively. The strip 3 after having been rolled by the upper and lower work rolls 1 and 2 is wound around a tension reel 8 under a predetermined tension.

A deflector roll 10 is located downstream of the rolling mill and the velocity v2 of the strip 3 leaving the work rolls 1 and 2 is detected by a velocity sensor 11 operatively coupled to the deflector roll 1 0. The strip velocity sensor 11 is coupled with a forward slip arithmetic unit 1 2 to which a signal representative of the velocity v2 is applied.

Main motor controllers 13 and 14 are connected to the motors 6 and 7, respectively, so that the rotational speeds of the motors 6 and 7 may be maintained at predetermined values, respectively. The motor 7 for the lower work roll 2 is connected to a work roll velocity detector 1 5 so that in dependence upon the rotational speed of the motor 7, the lower work roll velocity VRH is detected and is applied to the forward slip arithmetic unit 12. The output signal fH from the forward slip arithmetic unit 12 is applied to a forward slip control unit 1 6 and the output AVAIL from the forward slip control unit 16 is applied to the main motor controller 13.

In Figure 3, VRL represents the velocity of the upper work roll 1; fah0 represents a forward slip setting signal; and VRL < VRH The system operates as follows. The main motor controller 1 4 controls the motor 7 so that the peripheral velocity VRH of the lower work roll 2 is maintained at a predetermined value which is dependent upon the rolling conditions and devices and equipment associated to the rolling mill and may be decided for example by the performance of a rolled strip winding device.

Thus, the peripheral velocity VRH is used as a reference in rolling.

The peripheral velocity VRH obtained by the work roll velocity sensor 1 5 is applied to the forward slip arithmetic unit 12 which also responds to the input v2 from the strip velocity sensor 11 so as to calculate the forward slip fH based upon Equation (I) above.

A predetermined forward slip setting value H% which is zero or a value close to zero, is applied to the forward slip control unit 1 6 so as to be compared with fH. The upper work roll velocity setting signal VRL is applied to the forward slip control unit 1 6. In response to these signals applied to the forward slip control unit 16, the unit 1 6 delivers a velocity correction signal AVRL to the main motor controller 1 3 for the upper work roll so that the main motor controller 1 3 corrects the peripheral velocity of the upper work roll 1 in such a way that fH equals H0 Thus the forward slip is maintained at zero or a value very close to zero so that the rolling conditions can be stabilised and the rolling efficiency improved.

In the embodiment shown in Figure 3, the peripheral velocity of the lower velocity work roll 1 is controlled while that of the higher velocity work roll 2 is maintained constant, though it is to be understood that alternatively, the peripheral velocity of the higher velocity work roll 2 may be controlled while maintaining constant the peripheral velocity of the lower velocity work roll 1. However, the former is more desirable than the latter because the peripheral velocity of the higher velocity work roll is often used as a reference representative of a rolling velocity for controlling the tension of the rolled strip.

Figure 4 shows a forward slip control device in accordance with the invention used in conjunction with a rolling mill in which the upper and lower work rolls have the same velocity (hereinafter referred to as "rolling with same roll velocity"). Similar reference numerals are used to designate similar parts in Figures 3 and 4.

Reference numeral 1 7 denotes a transmission.

In the case of the rolling with same roll velocity, the upper and lower work rolls 1 and 2 are driven by a single motor 6. The forward slip is maintained at a predetermined value by controlling the rotational speed of the motor 6.

The mode of operation is substantially similar to that of the first embodiment described with reference to Figure 3. As described above, the forward slip can be maintained at a predetermined value so that the rolling conditions can be maintained uniform and the rolling efficiency improved.

Claims

1. A forward slip control system for a rolling mill having a pair of work rolls, the device comprising a velocity sensor for detecting a velocity of a strip leaving a rolling mill; a velocity sensor for detecting a peripheral velocity of one of work rolls; an arithmetic unit for calculating the forward slip of the strip relative to the one work roll from signals from the velocity sensors; a control unit arranged to generate a work roll velocity correction signal in dependence upon the forward slip value obtained from the arithmetic unit, a forward slip set value and a set value for the peripheral velocity of the other work roll, and a drive controller responsive to the velocity correction signal from the control unit arranged to control the actual peripheral velocity of the other work roll, in order to achieve the desired forward slip value.

2. A system as claimed in Claim 1 in which the work rolls are driven at different peripheral velocities, whereby the difference between the peripheral velocities of the work rolls is controlled

3. A system as claimed in Claim 2 in which the higher velocity roll is driven at a constant speed and the speed of the lower velocity roll is controlled.

4. A system as claimed in Claim 1 in which the work rolls are driven at a same peripheral velocity, and the peripheral velocity of both the work rolls is controlled.

5. A forward slip control system constructed and arranged substantially as herein specifically described with reference to and as shown in Figure 3 or Figure 4 of the accompanying drawings.