JPH0237910A - Method of controlling thickness of strip bottom part - Google Patents

Abstract

PURPOSE:To improve thickness accuracy and product yield with tandem cold rolling mills by reducing the speed of any of respective stands and speeding up the previous stand adjacent thereto just before the tail end of a strip passes through said stand. CONSTITUTION:A pulse oscillator 1 for detecting the moving distance of the strip 7 is provided to the revolving shaft of a roll and an arithmetic unit 2 to determine the moving distance of the tail end of the strip is disposed. The respective motor speeds of the cold rolling mill are changed on the basis of the point of the time when the tail end of the strip 7 passes through the respective stands (pass-through of the tail end). Namely, tandem rolling is executed by decelerating the motor of the i-th stand and accelerating the motor of the (i-1)th stand adjacent thereto when the tail end of the strip 7 passes through the stand (i). The abrupt fluctuation in the tension between the stands on the down stream is eventually decreased at the time of the passage through the stands and, therefore, the thickness accuracy and product yield of the strip 7 are improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for controlling plate thickness in cold rolling.

[Prior art] In plate rolling using a conventional tandem cold rolling mill, when the strip bottom part (i-1) stand ash comes off,
Fluctuations occur in the motor load after the i-stand, the tension between the stands after the i-stand suddenly decreases, and the thickness of the exit side plate after the i-stand increases. On the other hand, since the advance rate of each stand after the i-stand also increases, the mass flow at the exit side of each stand increases, and even after the motor load fluctuation disappears, the tension between stands does not return to the previous value when the stand is removed, and the plate thickness increases. It remains as it is. According to Japanese Unexamined Patent Application Publication No. 144813/1983, (i-1
) Control has been proposed in which the rear tension of the i-stand is lowered in advance by lowering the pressure of the i-stand before the stand ends.

Also, according to JP-A No. 62-275517, (i-1)
Control that changes the stand pressure in a gradient manner has been proposed.

[Problem to be solved by the invention] The plate thickness control device in a conventional tandem cold rolling mill does not function when performing transient state rolling such as strip bottom rolling, and the strip tail end passes through each stand. Even if the rolling reduction is changed during the process, it is not possible to obtain a uniform plate thickness. Further, if the amount of reduction is large, there are problems such as poor shape is likely to occur.

[Means for Solving the Problems] A plate thickness control device for a tandem cold-opening rolling mill according to the present invention decelerates the i-stand before the tail end of the strip passes through the (i-1>stand). By increasing the speed of (i-1) stand withdrawal reduces the rear tension of the previous i stand, (il) reduces the motor load fluctuation after the i stand when the stand bottom comes out, and (
i-1) The tension between the stands after the i-stand after the stand has come off is restored to the previous state.

[Function] The motor speed correction method in this invention suppresses load fluctuations in the downstream stand motor when the stand is removed by reducing the front tension of the stand through which the tail end of the strip passes in advance; The tension between the stands is also restored to the state before stand removal, and the thickness of the strip bottom portion is kept within a predetermined range.

[Embodiment] Fig. 1 is a block diagram of a plate thickness control device for a tandem cold rolling mill according to the present invention, and Fig. 2 is a graph showing a pattern of changing the motor speed of each stand according to the present invention. Second
In the figure, ■1 to ■4 indicate the motor speeds of the first to fourth stands. Examples will be described using these figures.

In FIG. 1, 1 is a pulse transmitter attached to the roll rotation shaft for detecting the moving distance of the strip 7;
2 is a calculation device that counts pulses from a pulse transmitter to calculate the moving distance of the tail end of the strip; 3 is a calculation device that determines the change timing of each stand based on the signal from the strip movement distance calculation device 2. . Reference numeral 4 denotes an arithmetic device that calculates the motor speed change amount of each stand and instructs the motor speed change amount based on the change timing of the motor speed change timing determining device 3. 5.6 is the motor of the stand, which operates based on instructions from the motor speed change amount calculation device.

In Fig. 2, the motor speed of the cold rolling mill is determined at the time when the tail end of the strip 7 passes through each stand (the tail end is at the time).
Change based on. That is, the tail end of the strip 7 passes through the front stage stand, and before passing through the relevant stand, the motor speed of the relevant stand is increased, and the motor speed of the rear stage stand is decreased, to prevent sudden fluctuations in the tension between the stands downstream when passing the relevant stand. Reduce. This prevents variations in the thickness of the strip bottom portion. That is, after the tail end of the strip 7 passes through the front stage stand,
The pulse transmitter 1 and the calculation device 2 track the tail end, and before it leaves the corresponding stand, the motor speed change amount calculation device 4 determines the motor 5 of the corresponding stand and the rear stage based on the change timing of the motor speed change timing determination device 3. An instruction is issued to the motor 6 of the stand to change the motor speed based on the motor speed change pattern of each stand shown in FIG.

[Effects of the Invention] As described above, according to the present invention, it is possible to reduce plate thickness variations at the strip bottom portion of a cold rolling mill, thereby improving plate thickness accuracy and improving product yield. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a plate thickness control device for the strip bottom portion of a tandem cold rolling mill according to an embodiment of the present invention, and FIG. 2 is a graph diagram showing a pattern of changing the motor speed of each stand according to the present invention. . DESCRIPTION OF SYMBOLS 1... Pulse transmitter, 2... Arithmetic device for calculating the moving distance of the tail end of the strip, 3... Device for calculating change times for each stand, 4... Arithmetic device for instructing the amount of change in motor speed, 5 ...Motor 6 of the relevant stand...Motor 7 of the rear stand...Strip.

Claims (1)

[Claims] A method for controlling plate thickness when a strip bottom falls out in a tandem cold rolling mill, characterized in that the i-stand is decelerated immediately before the tail end of the strip passes through the i-stand, and (i-1) the speed of the stand is increased. thickness control method.