JPS63140722A - Method for controlling plate thickness in cold rolling - Google Patents

Abstract

PURPOSE:To make the variation in the plate thickness at a rear end within allowable range and to remarkably reduce an off-gate by correcting the aiming thickness of monitor AGC at the outlet side of the final stand according to an estimation value for the variation in a plate thickness in the case of the bottom of a coil passing through a stand. CONSTITUTION:In the case of the bottom of a coil passing the stand of a cold rolling mill, the plate thickness is fluctuated with the speed arrangeability being disturbed by the load variation based on the tension variation. This variation in plate thicknesses is estimated from the load current of a roll driving motor and the tension between stands while under rolling. According to this variation estimation value, the target thickness of the monitor AGC at the outlet side of the final stand is corrected. Said correction is optimumly made at the value in proportion to the plate thickness variation value estimating the target thickness, i.e., about 1/2. The rear end to be rolled attaining to an off-gate is thus prevented with its variation in plate thickness being made within allowable range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the thickness of a thin plate such as a steel plate in a rolling process.

[Conventional technology]

Generally, a rolling mill has a configuration as shown in FIG.

The figure shows an example of a 5-stand rolling mill, where 1 to 5 are rolling stands and 6 to 10 are roll drive motors.

Each stand exit plate thickness h! ~ h5 and the rolling speeds (1) to (5) of each stand hold the constant mass flow law shown below.

Vl (1+f, ) ・h, = constant ・・
...(1) (I: advanced rate) Therefore, the final plate thickness h5 is determined by the i-stand exit side plate thickness h1 and the speed ratio vl/v5 of the i-stand and the 5-stand.Therefore, each motor are controlled by speed control devices 11 to 15 so as to rotate at a speed command value determined by the rolling schedule.

In addition, in order to ensure the target plate thickness h5 with high accuracy, a plate thickness gauge 16 is installed on the exit side of the stand, and a monitor AGC is installed to control the speed using the difference between the target plate thickness and the actual plate thickness. This is common (Japanese Patent Laid-Open No. 58-9708).

The configuration is such that the roll speed of the fifth stand 5 is adjusted by the automatic plate thickness control device 17 so that the plate thickness deviation between the detected plate thickness and the target plate thickness set by the plate thickness setting device 18 is zero. Specifically, when the thickness deviation is positive, the speed of the fifth stand is increased, and when it is negative, the speed of the fifth stand is decreased to make the deviation zero.

[Problem that the invention seeks to solve]

In a rolling mill with such a configuration, once the target thickness is determined by the monitor AGC at the top of the coil, the target thickness can be stably maintained thereafter. However, when the rear end of the coil passes through the stand, the tension between the stand on the downstream side and the upstream stand instantly becomes zero, so the speed temporarily increases as shown in Figure 7. The state will be as follows. In this case, according to formula (2), the plate thickness at the exit side of the fifth stand becomes thicker, and in extreme cases, the plate thickness exceeds the allowable range when the rear end of the strip passes through the first stand, as shown in Figure 8. There were times when the parts after that could not be made into a product (off-gauge).

In this case, the plate thickness variation occurs directly under the #5 stand, and it takes time for that point to reach the plate thickness gauge, so when the plate thickness variation is detected on the monitor AGC, immediately after the off-gauge has occurred. In this case, there was a problem that it could not be used as a means to prevent off-gauge.

[Purpose of the invention]

The purpose of this is to prevent off-gauge problems caused by variations in plate thickness due to load fluctuations when the rear end of the strip passes through the stands, which disrupts uniform speed between the stands and causes variations in plate thickness.

[Failure to solve the problem]

The gist of the present invention is to predict plate thickness fluctuations caused by disturbances in speed uniformity due to load fluctuations when the bottom of the coil exits the stand, and to
The purpose is to shorten the off-gauge length by changing in advance the target thickness of C to a value that will not result in off-gauge even if a variation in the predicted value occurs.

〔Example〕

FIG. 1 shows an outline of an apparatus according to an embodiment of the present invention. In the figure, numeral 19 is an arithmetic setting device that predicts and sets the plate thickness variation value ΔT. The calculation is based on the fact that when the rear end of the strip passes through the rolling stand (a+), the speed change of the next stand ('b) is due to the tension (T) between a and b before it passes and the load current N at b). Focusing on the change ΔV, ΔV=f (T, 1)...
(3) Δ■: Speed change (%) T: Tension between stands (Ton) ■= Load current (%) A method was adopted in which the plate thickness change ΔT was set as ΔT#Δ■. In addition, since the speed change is approximately constant depending on the rolling size, it is also possible to create a table of ΔT for each rolling size based on actual results. Further, as a second method for changing the target thickness of the monitor AGC, as shown in FIG. 3, it is also possible to use a method of correcting the plate thickness to a value that brings the plate thickness close to the allowable upper limit value when ΔT occurs.

A specific control example of this method is shown in FIG. #2 to 4 when the rear end of the strip passes through stands #1 to 4 from the rolling state
The result of calculating the speed change of 5 stands using equation (3) is Δ
Since V2 ~ Δ■ started to change, the target plate thickness of the monitor AGC becomes as shown in Figure 5 before that change occurs, and the plate thickness variation due to disturbance in speed consistency is within the allowable range. [Effects of the Invention] By the method described above, the variation in plate thickness at the trailing end of the rolled plate can be kept within the permissible range, Achieved a significant reduction in off-gauge.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of a rolling mill in the method of the present invention. FIGS. 2 to 5 are explanatory diagrams showing an embodiment of the present invention, and FIGS. 6 to 8 are explanatory diagrams showing a conventional method. 1-5: Rolling stand, 6-10: Roll drive motor, 11-15: Speed control device, 16: Thickness needle,
17: automatic plate thickness control device, 18: plate thickness setting device, 1
9: Calculation setting device. Rear end Figure 4 Figure 5--Wk 'i@= -4 Rugifuki O Procedural amendment (spontaneous) February 13, 1988 Commissioner of the Patent Office Kuro 1) Akio Tono 1, Display of the case Showa 1961 Patent Application No. 286222 2, Title of the invention: Method for controlling plate thickness in cold rolling 3, Relationship with the amended person's case Patent applicant address: 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (6
65) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent 101 Jino 7 5, Date of amendment order None 6, Number of inventions increased by amendment None] 8. Contents of amendment (1) Correct “ΔT” in lines 6 and 18 on page 5 of the specification and line 3 on page 6 to “Δh” (2) Correct “ΔT=J” in line 16 on page 5 to “Δh′qJ” .'z, 2 shi≧

Claims (3)

[Claims] (1) In a cold rolling mill, monitor AG on the exit side of the final stand predicts changes in plate thickness caused by disturbances in speed uniformity due to load changes when the bottom of the coil passes through the stand.
A method for controlling plate thickness in a cold rolling mill, characterized in that a target thickness of C is corrected according to a predicted variation value thereof. (2) A method for controlling plate thickness in cold rolling according to claim 1, wherein variation in plate thickness is predicted from tension between stands during rolling and load current of a drive motor. (3) A plate thickness control method in cold rolling according to claim 1, characterized in that the target thickness of the monitor AGC is corrected by a value proportional to the predicted plate thickness fluctuation value.