JPS6320108A - Rolling method for slab - Google Patents

Abstract

PURPOSE:To remarkably reduce dimensional fraction defective by correcting the target thickness value of the final finish pass within the allowable range based on actual slab thickness and length measured at a pass preceding to the final finish pass. CONSTITUTION:A draft position Si and a rolling load Fi from a drafting device 2 at the time of rolling a steel slab at a pass preceding to the final finish pass are inputted to a gage mater 3 and an actual thickness Hi is found. On the other hand, an actual slab length Li is found based on the number of pulses from a pulse generator 4 through a rolling length gage 5. The Hi, Li and a command thickness Haim, a command length Laim are inputted to a target thickness computing element 6 to find the target thickness value H'aim minimizing a fraction defective. The H'aim is inputted to a drafting position controller 7 to perform a draft control by a control signal S. Therefore, this method reduces the fraction defective by 0.25% in comparison with a conventional method.

Description

[Detailed description of the invention] "Industrial application field" The present invention relates to a method for rolling thick plates.

``Prior art'' In rolling thick plates, the yield of thick plates is determined by reducing the deviation of finished product dimensions and minimizing the weight of the slab.
Determined based on the dimensional accuracy of the plank.

If the commanded yield is set too high, the expected product cannot be obtained, leading to a high rejection rate.
As shown in page 168 of ``Published in May 1980'', there is an optimal balance point between the order yield and rejection rate at which the order yield is the highest (see Figure 4). .

Therefore, in order to obtain the highest yield, the thickness target for the final pass is determined at the time of designing the slab to an appropriate value that will result in the incidence of under-thickness and under-length.

In order to reduce the incidence of defects such as insufficient thickness and length, the weight of the slab is actually measured before rolling, or the width of the plate is measured after tentering rolling, and the target thickness is allowed according to this value. A method of changing within the range has been proposed (Special Public Interest Publication Act 1986-
(See Publication No. 16845).

"Problems to be Solved by the Invention" By the way, the above-mentioned conventional methods only reflect a very small part of the factors that should be taken into consideration, and other undetermined factors, such as scale loss. There is a problem in that it is impossible to comprehensively reflect the amount of plate crown, the amount of plate crown, etc., and it is difficult to find the optimal point for reducing the defect rate.

"Means for Solving the Problems" The present invention was made to solve the above-mentioned conventional problems, and its gist is that first, a slab designed according to the shape of the product is In a thick plate rolling method in which the plate is tentered to the desired width and then finished rolled to a predetermined thickness, the final finish is calculated based on the actual plate thickness and actual plate length measured in passes before the final finishing pass. A method of rolling a thick plate is characterized in that rolling is performed while correcting a target value of plate thickness in a double pass within an allowable range.

``Structure and Function J'' The present invention provides that, assuming that there is no variation in the target plate thickness, various variations in plate rolling, such as slab weight, scale loss amount, and tenting accuracy variation, are all caused by the plate length at the end of rolling. Focusing on the fact that it appears aggregated as a deviation in thickness, estimate the deviation before the final finishing pass, and set this value to an appropriate value, that is, so that the incidence of insufficient length and insufficient thickness after rolling is balanced. They discovered that the overall failure rate could be reduced by correcting the final target plate thickness within the allowable range.

The method of the present invention will be explained below based on FIG.

In the plate rolling mill 1, the rolling position Si and rolling load Fi from the rolling device 2 when rolling a steel plate in a pass before the final finishing pass are input to the gauge meter 3, and the actual result is calculated by this gauge meter 3. In addition to obtaining the plate thickness, the actual plate length Li of the steel plate at this time, the number of rotation pulses of the rolling roll from the biting of the steel plate to the blowout by the pulse generator 4 connected to the rolling roll, and the rolling pressure of the steel plate. It is obtained via a flattening length meter 5 which converts it into length.

The actual plate thickness from the gauge meter 3, the actual plate length Li from the rolling length meter 5, the commanded rolled board thickness 11aim, and the commanded rolled board length La1m are calculated so as to minimize the defective rate. The plate thickness target for the final finishing pass is input to a plate thickness target calculator 6 that calculates the plate thickness target, and a revised plate thickness target value H'aim is obtained from the plate thickness target calculator 6.

Then, this plate thickness target value H'ajm is input to the rolling position controller 7, and the rolling device 2 is controlled by the rolling position control signal Sn of the final finishing pass from this rolling position controller 7, and the rolling of the final finishing pass is controlled. This is what we do.

"Embodiment" The following equation may be used as the calculation formula for the plate thickness target value I+'aim by the plate thickness target calculator 6.

α-1, i×old/Haim-ΔLc-(1
1αt = (Cn-Latm) /Laimxβt
-(21+1'a+m -Max(He+ r ・
σt, (14-αt)
Plate thickness lower limit tolerance, γ・σt; Target plate thickness accuracy margin. The rolling length meter 5 is, for example, as shown in FIG. and a steel plate tip detection sensor 8.9 disposed at each predetermined position on the exit side of the rolling mill 1 with a mutual interval β, and detects the number of rotational pulses of the rolling roll from biting to biting out of the steel plate. P1, number of rotation pulses P2 of the rolling roll from injection to detection of the tip of the steel plate by the steel plate tip detection sensor 8, number of rotation pulses P3 of the rolling roll from biting to detection of the tip of the steel plate by the steel plate tip detection sensor 9, and each The actual plate length Li of the steel plate may be determined from the mutual distance l between the steel plate tip detection sensors 8 and 9 using the following formula.

The rolling length meter 5 shown in FIG. 2 above simply converts the number of rotational pulses of the rolling roll from biting through the steel plate to the rolling length of the steel plate, as shown in FIG. 1. It is preferable to use the rolling length meter 5 shown in FIG.

"Effects of the Invention" According to the method of the present invention described above, compared to the conventional method of actually measuring the slab weight and correcting the target plate width and thickness within the allowable range according to this value, As shown in FIG. 3, the dimensional defect rate could be reduced by 0.25%, and the yield could be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the method of the present invention, Fig. 2 is a block diagram showing another embodiment of the rolling length meter, and Fig. 3 is a diagram showing the dimensional defect occurrence rate between the conventional method and the method of the present invention. A graph showing the comparison, FIG. 4, is a graph showing the relationship between instruction yield and failure rate.

Claims (1)

[Claims] Results measured in passes before the final finishing pass in a thick plate rolling method in which a slab designed according to the product shape is first tentered rolled to a predetermined width and then finished rolled to a predetermined thickness. A thick plate rolling method characterized in that rolling is performed by correcting the target thickness of the final finishing pass within an allowable range based on the plate thickness and actual plate length.