Method for preventing jamming in hot rolling of steel plate, hot rolling method using the same, and method for manufacturing steel plate

Abstract

To provide a method for inhibiting galling in hot rolling where an appropriate torque correction value is automatically calculated, and where minus torque correction according to manual operation by an operator is not performed.SOLUTION: In a method for inhibiting galling in hot rolling of steel plates, rolling is implemented based on a rolling schedule calculated by using a torque constraint value. In the method, a rolling torque is calculated for every pass of a front stage, and a torque deviation rate is calculated, in order to correct the torque constraint value with respect to every pass of a subsequent stage based on the calculation results, and the corrected torque constraint value is used to re-calculate the rolling schedule.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for preventing jamming in hot rolling of steel plate, particularly to a method for preventing jamming by automatic correction of a torque constraint value, a hot rolling method using this jamming prevention method, and a method for manufacturing steel plate. [Background technology]

[0002] In conventional hot rolling using a four-high rolling mill, such as a plate rolling mill, a rolling schedule is calculated to maximize rolling efficiency. This calculation uses the predicted temperature and set plate thickness for each pass to obtain the maximum reduction amount for each pass within a range that does not exceed the maximum load and maximum torque (hereinafter also referred to as "torque constraint values") imposed by the equipment (see, for example, Patent Document 1).

[0003] Therefore, if the actual steel plate temperature is lower than the predicted steel plate temperature, the actual deformation resistance will be higher than the predicted deformation resistance. As a result, the torque required to feed the steel plate while rolling it down will be insufficient compared to the upper limit torque of the main motor that rotates the work rolls, and the steel plate may stop inside the rolling mill. This is called "biting."

[0004] Therefore, in the past, to prevent jamming, a rolling worker (hereinafter also referred to as "operator") would perform an operation called "minus torque correction," in which the rolling schedule is recalculated by manually inputting a correction value that subtracts the torque constraint value before the start of rolling and during rolling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-277616 Summary of the Invention [Problem to be solved by the invention]

[0006] The negative torque correction operation mentioned above is performed by the operator, who determines whether correction is necessary based on the slab unit weight, the tonnage of the load loss on the first pass, the degree of heating of the slab as judged from the color of the slab's appearance, etc., and if necessary, determines the correction value. This operation is performed manually, so it is affected by differences in the skill of the operator.

[0007] If the rolling torque deviates from the initial prediction, and the operator determines that there is a risk of jamming as a result, and corrects the torque constraint value by, for example, -10%, the maximum torque value in the rolling schedule calculation is also corrected by -10% and recalculated, resulting in a smaller maximum reduction. Therefore, the actually generated torque will be smaller than in the case of the initial maximum torque value, and torque exceeding the upper limit of the main motor will no longer be applied. As a result, this -10% correction can prevent jamming problems during rolling, but since the reduction amount for each pass is smaller, the total number of rolling passes will increase.

[0008] In this way, if the negative torque correction by the operator is excessive, the number of rolling passes increases more than necessary, resulting in a deterioration in rolling efficiency, and conversely, if this correction is insufficient, jamming occurs.

[0009] When jamming occurs, the work rolls come into contact with the hot steel plate for a long time, causing cracks in the work rolls, and the amount of work roll grinding increases by more than 10 times the normal amount, worsening the work roll consumption rate. In addition, steel plates that have jammed are deemed unable to continue rolling and are scrapped, resulting in a decrease in yield. Furthermore, if rolling stops, downtime for the rolling line occurs.

[0010] The present invention aims to solve the above-mentioned problems and provide a method for preventing jamming in hot rolling by automatically calculating an appropriate torque correction value instead of manual negative torque correction by an operator.

[0011] Another object of the present invention is to provide a hot rolling method for a steel plate and a manufacturing method for a steel plate using the above-mentioned method for preventing jamming. [Means for solving the problem]

[0012] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have predicted whether or not jamming will occur in a subsequent pass of hot rolling by using the torque deviation rate in a previous pass. Based on the results of this prediction, they have found that automatically correcting the torque constraint value for the subsequent pass and recalculating the rolling schedule is effective in preventing jamming, and have thus completed the present invention.

[0013] That is, the present invention is as follows. [1] A method for preventing jamming in hot rolling of a steel plate, the method comprising: A method for preventing jamming in hot rolling of steel plate, characterized by calculating a rolling torque for each pass in the previous stage, calculating a torque deviation rate, correcting a torque constraint value for each pass in the subsequent stage based on the results of the calculation, and recalculating a rolling schedule using the corrected torque constraint value. [2] The method for preventing jamming in hot rolling of a steel sheet according to [1] above, wherein the preceding pass is one to five passes from the start of rolling. [3] In the above [1] or [2], the torque deviation rate is calculated by the following formula (1), and the torque constraint value is corrected by the following formulas (3) and (4) under the condition that the following formula (2) is established. Torque deviation rate = (actual torque - predicted torque) / predicted torque (1) Predicted torque × (1 + torque deviation rate) > threshold (2) Torque correction value = -{predicted torque × (1 + torque deviation rate) - threshold} / torque constraint value before correction (3) Corrected torque constraint value = Pre-corrected torque constraint value × (1 + Torque correction value) (4) [4] A method for hot rolling a steel plate, characterized in that the method for preventing jamming described in any one of [1] to [3] above is used. [5] A method for producing a steel sheet, characterized by using the hot rolling method described in [4] above. [Effects of the Invention]

[0014] According to the method for preventing jamming in hot rolling of the present invention, it is possible to prevent jamming while preventing an unnecessary increase in the number of rolling passes by automatically calculating an appropriate torque correction value, recalculating the rolling schedule, and applying it to rolling, without relying on conventional manual operations that rely on the experience and intuition of an operator. Furthermore, according to the hot rolling method and the method for manufacturing a steel plate of the present invention, it is possible to obtain the effects of improving rolling efficiency, improving the work roll consumption rate, and improving yield. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flow chart showing an embodiment of a method for preventing jamming in hot rolling of a steel plate according to the present invention. FIG. [Figure 2] FIG. 10 is a diagram showing an example of predicted and measured loads on a steel plate where jamming occurs. [Figure 3] FIG. 10 is a diagram showing the transition of the initial planned load, planned load, and actual load in Example 1. [Figure 4] FIG. 10 is a diagram showing the distribution of the number of passes for the calculated maximum torque category and the range in which jamming has occurred in the past. [Figure 5] FIG. 10 is a diagram showing a comparison between the conventional method and Example 2 in terms of the number of passes and the maximum torque correction value. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of a method for preventing jamming in hot rolling of a steel plate according to the present invention will be described below with reference to the flow chart shown in Figure 1. The operations according to this flow chart are executed by a process computer. In the present invention, first, a rolling schedule is calculated (step 100).

[0017] [Rolling schedule calculation] In this calculation, the predicted temperature and target plate thickness for each pass are used to calculate the maximum reduction amount for each pass within the range that does not exceed the maximum load and maximum torque of the equipment constraints, and the rolling torque (hereinafter simply referred to as "torque") is also calculated. The torque is calculated using the following equation (5). To=α×{RD×(Inlet side plate thickness - Outlet side plate thickness)}×0.5×(Maximum load) ‥‥(5) Here, To is the torque, also known as the predicted torque. RD is the flattening roll diameter, RD = C × (upper work roll diameter) / 2, and C is the roll flattening coefficient. α is the torque arm coefficient, α = 0.5 + 0.17 × (exit thickness / RD) × 0.5 × {1 - (entry thickness - exit thickness) / entry thickness}. The units are torque [t·m], RD, entry thickness, exit thickness [mm], and maximum load [t].

[0018] Torque Constraint Value The initial setting of the torque constraint, which is the maximum torque value of the equipment constraint, is assigned a constant value in the process computer for normal rolling material and controlled rolling material. For example, this constant is 300 to 400 t m for normal rolling material and 300 to 400 t m for controlled rolling material. After the rolling schedule is calculated, rolling begins (step 110). After rolling begins, the pass order, load, and torque results are acquired (step 120). It is determined whether the actual pass order is the final pass (step 130), and if it is "yes" (Y), rolling ends (step 190). If it is "no" (N), it is determined whether it is a previous pass (step 140).

[0019] [Previous path] The "previous pass" in step 140 refers to at least one pass included in the adjustment pass or the width setting pass among the "adjustment pass," "width setting pass," and "finishing pass" which are classified in order from the start of rolling. The adjustment pass is a pass in which the reduction amount of each pass is determined by the reduction amount constraint. The width setting pass is a pass in which the reduction amount of each pass is determined by the torque value constraint, and the finishing pass is a pass in which the reduction amount of each pass is determined by the load constraint and the shape line constraint. The preceding passes are preferably the first to fifth passes from the start of rolling, which provides a more sufficient effect of preventing jamming and unnecessary increase in the number of passes.

[0020] The reason why the first pass is preferably one of the first to fifth passes is as follows. Experience has shown that jamming occurs mainly during width rolling. This is because during width rolling, the contact area between the work roll and the steel sheet is the largest during rolling, and the torque during rolling is likely to be large. Width rolling usually begins from the third pass and ends between the sixth and eighth passes. Therefore, if the first pass is set to the sixth pass or later, the opportunity for correction will be missed, making it difficult to prevent jamming from occurring. If the pass / fail judgment in the previous step of step 140 is "No" (N), the pass order is incremented by one and the process jumps to step 120, and if it is "Yes" (Y), the torque deviation rate is calculated (step 150).

[0021] [Torque deviation rate] The torque deviation rate in step 150 is calculated, for example, by the following formula (1). Torque deviation rate = (actual torque - predicted torque) / predicted torque (1) Here, the actual torque is calculated by substituting the actual load for the maximum load in equation (5). The expected load is calculated from the predicted temperature and deformation resistance of each pass.

[0022] [Whether or not to correct the torque constraint value] Based on the calculation result of the torque deviation rate, it is determined whether or not the torque constraint value needs to be corrected in the subsequent pass (step 160). If the answer is "No" (N), the pass order is incremented by one and the process jumps to step 120. The "subsequent path" means at least one path subsequent to the preceding path. The necessity of the correction is determined using, for example, the following equation (2). Predicted torque × (1 + torque deviation rate) > threshold (2) The predicted torque in equation (2) is for the latter pass. The left side of equation (2) is the torque estimated for the latter pass, assuming that the torque deviation rate in the previous pass is maintained in the latter pass. This estimation was supported by the results of an analysis of past rolling operation results.

[0023] If the estimated torque is high, the risk of jamming is high. Therefore, a threshold value is set to be compared with the estimated torque, and if the estimated torque exceeds the threshold value, it is determined that the risk of jamming is high and that correction of the torque constraint value is "necessary."

[0024] Threshold An example of the threshold value is 370 t·m when the rolling material type is N11LXR (equivalent to Nippon Kaiji Kyokai NK standard 40A, 40D, and 40E) with a slab length of 4 to 5 m, a slab extraction temperature of 1050 to 1150°C, and a steel type of N11LXR. The threshold value for this example was determined as follows. Specifically, the distribution of the number of passes for each maximum calculated torque category and the range in which jamming has occurred were determined from an analysis of past rolling operation results, and Figure 4 was obtained. Figure 4 shows that jamming does not occur when the maximum calculated torque is 370 t·m or less. Therefore, the threshold value for this example was set to 370 t·m.

[0025] The example in Figure 4 is for the following conditions: slab length: 4 to 5 m, slab extraction temperature: 1050 to 1150°C, and steel type: N11LXR. If at least one of these conditions falls outside the range of this example, a threshold value other than 370 t·m may be appropriate. When the conditions differ in this way, the overall appropriate threshold value is in the range of 300 to 400 t·m. Therefore, it is preferable to set the threshold value as a function of at least one of the slab length, slab extraction temperature, and steel type.

[0026] For example, the relationship between multiple divided slab lengths and slab extraction temperatures and corresponding threshold values ​​for each steel type may be prepared in the form of a table, and threshold values ​​corresponding to the steel type, slab length, and slab extraction temperature of the actual rolled material may be selected from this table.

[0027] Torque Constraint Correction If the torque constraint value correction is "necessary" (Y), the torque constraint value used in the subsequent pass is corrected (step 170). For this, the following equations (3) and (4) are used, for example. Torque correction value = -{predicted torque × (1 + torque deviation rate) - threshold} / torque constraint value before correction (3) Corrected torque constraint value = Pre-corrected torque constraint value × (1 + Torque correction value) (4) Here, the "torque constraint value before correction" in equation (3) is, as mentioned above, 300 to 400 t·m for normal rolled material and 300 to 400 t·m for controlled rolled material.

[0028] [Recalculate rolling schedule] Then, the rolling schedule is recalculated using the corrected torque constraint value obtained by equation (4) (step 180). After the rolling schedule is recalculated, the pass order is incremented by one and the process jumps to step 120. Therefore, in the subsequent passes, rolling continues based on the recalculated rolling schedule.

[0029] The hot rolling method of the present invention uses the method of preventing jamming of the present invention, which makes it possible to prevent jamming from occurring, thereby improving rolling efficiency and work roll consumption.

[0030] Furthermore, the method for producing a steel plate of the present invention uses the hot rolling method of the present invention, which can prevent the steel plate from being scrapped due to jamming, thereby improving the product yield of the steel plate. [Example]

[0031] [Example 1] Example 1 is an example in which the steel type is N11LXR, the slab dimensions are 245 mm x 1904 mm x 2680 mm, the rolling order dimensions are 10.2 mm x 4151 mm x 40600 mm, and the slab extraction temperature is 1120°C.

[0032] The first pass was set to passes 1 to 5. The steel plate was a conventionally rolled material, and the initial setting for the torque constraint value was 326 t m. The torque deviation rate was calculated using the formula (1) above, and the threshold value was set to 370 t m to determine whether or not correction of the torque constraint value was necessary using the formula (2) above. The torque correction value was calculated using the formula (3) above, and the corrected torque constraint value was calculated using the formula (4) above.

[0033] After the start of rolling, correction of the torque constraint value was determined to be "necessary" on the third pass, so calculation of the torque correction value, correction of the torque constraint value, and recalculation of the rolling schedule were carried out in that order, and from the fourth pass onwards, rolling was carried out based on the recalculated rolling schedule.

[0034] The transitions of the initial planned load, planned load, and actual load at this time are shown in Figure 3. Here, the plate thickness on the horizontal axis is the delivery plate thickness of each pass from the start of rolling. The initial planned load is the predicted load in the initial rolling schedule calculation, and the planned load after rescheduling is the predicted load in the recalculated rolling schedule. In this example, initially, of the 14 passes in total, the 1st and 2nd passes were the adjustment passes, the 3rd to 7th passes were the width setting passes, and the 8th to 14th passes were the finishing passes, but after rescheduling, of the 15 passes, the 3rd to 8th passes were the width setting passes and the 9th to 15th passes were the finishing passes.

[0035] As shown in Figure 3, in Example 1, the actual load in the third pass deviated higher than the initially planned load, and if this continued, the load during rolling would increase further from the fourth pass onwards, resulting in a high risk of torque shortage and jamming. Therefore, as described above, the torque constraint value was automatically corrected using the torque deviation rate, and the rolling schedule was recalculated, and from the fourth pass onwards, rolling was carried out based on the recalculated rolling schedule, thereby preventing jamming.

[0036] [Example 2] In Example 2, steel plates of normally rolled material with a finished thickness in the range of 20 to 30 mm were targeted. In the conventional method, the operator performed the above-mentioned negative torque correction. The torque correction values ​​and number of passes were compared between Example 2 and the conventional method. The number of rolled pieces was 2,000 pieces in total for one month in Example 2, and 6,000 pieces in total for three months in the conventional method. Both the torque correction value and the number of rolling passes were shown as average values ​​obtained by dividing the total across the entire range of the number of rolled pieces by the number of rolled pieces. The results are shown in Figure 5.

[0037] 5, in Example 2, the torque correction value increased by 5.5 points and the number of passes decreased by 0.7 compared to the conventional method, resulting in an improvement in rolling efficiency of approximately 22 t / h.

[0038] Furthermore, whereas the frequency of crack occurrence in the work roll was up to about 6 times per month in the conventional method, in Example 2 it was significantly reduced to less than 1 time per month (not shown). [Explanation of symbols]

[0039] 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 steps

Claims

1. A method for preventing jamming in hot rolling of a steel plate, the rolling being performed based on a rolling schedule calculated using a torque constraint value, comprising: Calculating the rolling torque for each pass in the preceding stage, calculating the torque deviation rate, correcting the torque constraint value for each pass in the subsequent stage based on the calculation results, and recalculating the rolling schedule using the corrected torque constraint value, A method for preventing jamming in hot rolling of a steel plate, characterized in that the torque deviation rate is calculated by the following formula (1), and the torque constraint value is corrected by the following formulas (3) and (4) when the following formula (2) is satisfied. Torque deviation rate = (actual torque - predicted torque) / predicted torque (1) Predicted torque × (1 + torque deviation rate) > threshold (2) Torque correction value = - {predicted torque x (1 + torque deviation rate) - threshold} / torque constraint value before correction (3) Corrected torque constraint value = Pre-corrected torque constraint value × (1 + Torque correction value) (4)

2. 2. The method for preventing jamming in hot rolling of steel plate according to claim 1, wherein the preceding passes are the first to fifth passes from the start of rolling.

3. 3. A method for hot rolling a steel plate, comprising using the method for preventing jamming according to claim 1 or 2.

4. A method for producing a steel sheet, comprising using the hot rolling method according to claim 3.

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