JPS6129808B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the thickness of a strip tail in rolling a metal strip using a tandem cold rolling mill.

It is well known that when strip is rolled by a tandem cold rolling mill, the thickness of the tail section generally increases. To explain this mechanism,
Now, assuming that Hi = i stand exit plate thickness, Vi = i stand roll circumferential speed, and fi = i stand tip ratio, from the well-known equation of constant volumetric flow rate, in a rolling mill with a total number of stands N, (1 + f ₁ )V ₁ H ₁ =…=(1+fi)ViHi=…=(1+
f _N ) V _N H _N = constant holds true. Therefore, the final plate thickness H _N is: H _N = (1+fi) Vi/(1+f _N )V _N・Hi
...(1) However, i = 1 to (N-1), and the fact that this right side is constant means that the final plate thickness H
_N is a constant condition. Similarly, when the tail end passes through the (i-1) stand in the rolling operation of the strip tail, each value at the stands after the i stand is indicated with a dash ('), and the final plate thickness H _N
is H _N ′=(1+fi′) Vi′/(1+f _N ′)
V _N ′・Hi′…(2) If the right side of equation (1) and the right side of equation (2) are equal, then
H _N =H _N ', and there is no variation in the final plate thickness.

However, the biggest factor that increases the final plate thickness H _N ' at the tail is that when the rear tension is removed, the neutral point (the point where the roll circumferential speed and the plate speed match within the arc of contact between the plate and the roll) moves rearward. As agreed from the well-known rolling theory that the advance rate increases with movement, the i-stand advance rate fi′ becomes extremely large compared to fi, and the secondary factor is that the i I before the stand exit side plate thickness Hi' falls out
It can be mentioned that the thickness increases from the stand exit side plate thickness Hi. In this way, the advanced rate of i-stand increases, and i
The plate thickness on the exit side of the stand increases (i+1), and the volumetric flow rate on the inlet side of the stand increases. However, (i+
1) Since the speed of the plate on the outlet side of the stand is approximately unchanged, the plate thickness on the outlet side of the stand (i+1) increases due to the law of constant volumetric flow rates on the (i+1) stand entry and exit sides. In this way, the above-mentioned plate thickness variation phenomenon is repeated in the subsequent stands one after another.

Conventionally, methods for preventing thickness variations at the strip tail due to such causes include reducing the speed of the next stand immediately after the tail end of the strip passes through one stand, or reducing the rolling reduction of the next stand. was used. However, in the above conventional method, in the case of the speed change method, although there is a thickness correction effect in the (i + 1) stand, there is almost no thickness correction effect in the i stand, and in the case of the reduction change method, the i In order to correct the sudden change in plate thickness directly under the (i+1) stand when the stand bottom comes out, a rolling down device with a sufficiently fast response speed that can follow the change in plate thickness is required, but this is not currently in practical use. Since the rolling down device has a slow response speed, there is a delay in correcting the plate thickness, and in the end, all methods are insufficient to prevent the plate thickness from increasing at the strip tail.

The present invention eliminates the drawbacks of the conventional method as described above,
This method was developed with the aim of providing a method for controlling the thickness of the strip tail end that achieves thickness correction reliably and with good response.The gist of this method is that the tail end of the strip passes through one rolling stand. By lowering the rolling reduction of the next rolling stand just before
This method of controlling the thickness of the strip tail section is characterized in that the tension of the strip between the one rolling stand and the next rolling stand is lowered in advance to 50% or less of the tension before lowering the rolling reduction. Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 is a block diagram showing a control system in an embodiment of the present invention, and for convenience of explanation, the number of rolling stands is shown as three. In Figure 1, 1 is
No. 1 stand, 2 is No. 2 stand, 3 is No. 3 stand, and S is strip. 4 is a tail end passage detector provided on the entry side of the No. 1 stand, and in this embodiment, it also serves as a plate thickness gauge. 5,
6 and 7 are load cells for detecting the rolling force of each stand, and also serve as tail end passage detectors of each stand. 8, 9 and 10 are hydraulic lowering devices for each stand. Reference numeral 11 designates a timing device that receives the tail end passing signal as input and outputs a control command signal after a preset period of time according to rolling conditions; and 12 designates a rolling down control device that outputs a rolling reduction correction signal based on the control command signal. be.

In the above-mentioned apparatus, the timing device 11 receives a signal indicating that the tail end of the strip S has passed through the tail end passage detector 4, and the timing device 11 receives the signal indicating that the tail end of the strip S has passed through the tail end passage detector 4. 0.1 seconds later), a control command signal is output to the reduction control device 12. Upon receiving the command signal, the roll-down control device 12 calculates the roll-down correction amount of the No. 2 stand 2 using a predetermined calculation formula, and outputs a roll-down correction signal to the roll-down device 9. Based on the reduction correction signal, the reduction device 9
Correct the pressure of No. 2 stand 2 in the direction of lowering it. This reduction in tension reduces the strip tension between No. 1 stand 1 and No. 2 stand 2 to 50% or less compared to before the strip tail end reaches the tail end passage detector 4. The reason for this will be explained below.

From the perspective of modifying the plate thickness at the tail end of the strip, the greater the reduction in rear tension, the more pronounced the effect will be.
The probability of occurrence of roll accidents etc. becomes extremely high, resulting in a decrease in the operating rate. FIG. 4 summarizes the relationship between the rear tension reduction amount, off-gauge amount, and operating rate.

As is clear from FIG. 4, the relationship between these two and the rear tension reduction allowance is contradictory. However, as shown in FIG. 4, it has been found that there is an optimal range of the rear tension reduction amount α that reduces the amount of off-gauge and does not reduce the operating rate. This optimal range of values is
From the results of various experiments conducted by the inventors, generally
It was concluded that 50% to 90% is optimal. That is, if the tension of the strip is lowered in advance to 50% or less of the tension before the reduction, the amount of off-gauge can be reduced without adversely affecting the operating rate.

Furthermore, when using the present invention, the rear tension reduction margin α may be appropriately determined within the above range based on the characteristics of the rolling equipment and work. In this example, the known
The following formula is derived from _Hill 's formula, and based on this formula, a formula for calculating the reduction correction amount is determined.

P: Rolling force during steady rolling P': Rolling force after reduction correction t _f : Forward tension t _b : Backward tension: Average deformation resistance α: Backward tension reduction (50 to 90%) Example of operation of the above-mentioned equipment To give an example, when the original strip thickness is 3 mm, the tension between No. 1 and 2 stands is 12 Kg/mm ² before the reduction correction.
After the strip tail passes the tail end passage detector 4
After 0.1 seconds, tighten the No. 2 stand by 500μ to reduce it to 3Kg/mm ² . In this way, by lowering the strip tension between No. 1 and No. 2 stands in advance just before the strip tail end exits No. 1 stand 1, no. .2 It is possible to reduce the variation in plate thickness caused by the loss of rear tension in the stand, and as a result, it is possible to reduce the length of the part where the plate thickness on the exit side of the final stand is off-gauge.

A time chart of the above operation is shown in FIG.
The solid line in the figure shows the relationship (state of change) between the time (timing) when implementing the method of the present invention, the strip tension between No. 1 and 2 stands, and the thickness of the exit side of No. 2 stand, and the dashed-dotted line This figure shows the state of change when the reduction is corrected using the conventional method. As is clear from the figure, according to the present invention, by reducing the tension between No. 1 and 2 stands in advance before the strip tail end of No. 1 stand comes off, the strip tail end of No. 1 stand comes off. It is possible to reduce the variation in the thickness of the plate on the exit side of the No. 2 stand. Next, the tail end of the strip is No.2.
In response to the signal passing through the stand 2 (when the rolling force detected by the load cell 5 falls below a certain threshold value), the timing device 11 outputs a control command signal to the rolling control device 12 after a preset certain period of time. do. Note that the timing at which the control command signal is output is not after a certain period of time as described above, but when the tail end of the strip is output using a signal from a speed detector (not shown).
The control command signal may be output at a timing when the vehicle has advanced a certain distance from the No. 1 stand 1. Based on this control command signal, the roll-down control device calculates the amount of roll-down correction for No. 3 stand 3 using a predetermined calculation formula, and outputs a roll-down correction signal to the roll-down device 10. Based on the reduction correction signal, the reduction device 10 adjusts No. 3.
Correct the pressure of stand 3 in the direction of lowering it. This reduction correction reduces the variation in the plate thickness on the exit side of the No. 3 stand in the same manner as in the case of the reduction correction of the No. 2 stand 2 described above. If the number of stands is four or more, the above correction operation may be repeated in sequence.

FIG. 3 shows an example of the effect of reducing plate thickness variation on the exit side of the final stand due to the above-mentioned reduction correction. In Fig. 3, the horizontal axis is the distance from the tail end of the strip (lengthwise position), and the vertical axis is the deviation from the reference plate thickness at each position. shows the state of plate thickness variation when conventional reduction correction is performed. In this example, the standard thickness of the strip after cold rolling is
It is 0.6mm. As is clear from the figure, in the case of the conventional method, the off-gauge part of the strip tail (the part outside the allowable range) is approximately 9 m long from the tail end, whereas when the method of the present invention is implemented, the off-gauge part The part is approximately 3m long from the tail end,
Off-gauge parts have been drastically reduced.

As described above, the method of the present invention is a method in which the strip tension between the rolling stand and the next rolling stand is lowered in advance just before the tail end of the strip passes through one rolling stand. This is extremely effective in minimizing the effect on the plate thickness due to the loss of rear tension in the next rolling stand when the end passes through the rolling stand, and as a result, reducing the length of the off-gauge section of the strip tail.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a control system in an embodiment of the present invention, Fig. 2 is a time chart showing control timing in an embodiment of the present invention, and Fig. 3 shows an example of effects in an embodiment of the present invention. It is a graph. FIG. 4 is a graph showing the relationship between the rear tension reduction amount and the off-gauge amount. 1: No.1 stand, 2: No.2 stand, 3: No.
3 stands, 4: tail end passage detector, 5 to 7: load cells, 8 to 10: reduction device, 11: timing device, 12: reduction control device.

Claims (1)

[Claims] 1. In rolling a metal strip by a tandem cold rolling mill, the strip between said one rolling stand and the next rolling stand is reduced by lowering the rolling reduction of the next rolling stand just before the tail end of the strip passes through one rolling stand. A method for controlling the thickness of a strip tail, characterized in that the tension of the strip is lowered in advance to 50% or less of the tension before the reduction.