JP7768170B2 - Method for preventing jamming in hot rolling of steel plate, hot rolling method using the same, and method for manufacturing steel plate - Google Patents

Description

The present invention relates to a method for preventing jamming during hot rolling of steel plate, in particular a method for preventing jamming by automatically correcting torque constraint values, and a hot rolling method and steel plate manufacturing method that use this jamming prevention method.

Conventionally, in hot rolling using a four-high rolling mill, such as a plate rolling mill, a rolling schedule is calculated with the aim of maximizing rolling efficiency. This calculation uses the predicted temperature and set plate thickness for each pass to achieve the maximum reduction amount for each pass without exceeding the maximum load and maximum torque (hereinafter also referred to as "torque constraint values") imposed by the equipment (see, for example, Patent Document 1).

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 compressing it 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 "sticking."

Therefore, in the past, rolling workers (hereinafter also referred to as "operators") would perform an operation called "minus torque correction," in which they manually input a correction value that subtracts from the torque constraint value before and during rolling, and recalculate the rolling schedule to prevent jamming.

Japanese Patent Application Publication No. 10-277616

The negative torque correction mentioned above is performed by the operator, who determines whether correction is necessary based on factors such as the slab unit weight, the tonnage at which the load was removed on the first pass, and the degree of heating of the slab as judged from the external color of the slab, and if necessary, determines the correction value. Because this operation is performed manually, it is subject to differences in operator skill.

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 will also be corrected by -10% and recalculated, reducing the maximum reduction amount. Therefore, the actually generated torque will be smaller than in the case of the initial maximum torque value, and torque that exceeds 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 because the reduction amount for each pass is smaller, the total number of rolling passes will increase.

As such, if the operator applies excessive negative torque correction, the number of rolling passes increases more than necessary, reducing rolling efficiency; conversely, if this correction is insufficient, jamming occurs.

When jamming occurs, prolonged contact between the work roll and the hot steel plate causes cracks to form in the work roll, and the amount of work roll grinding increases by more than 10 times the normal amount, worsening the work roll consumption rate. Furthermore, steel plates with jamming are deemed unable to continue rolling and are scrapped, resulting in a decrease in yield. Furthermore, stopping rolling causes downtime for the rolling line.

The present invention aims to solve the aforementioned problems and provide a method for preventing jamming in hot rolling by automatically calculating an appropriate torque correction value rather than manually performing negative torque correction by an operator.

Another object of the present invention is to provide a hot rolling method for steel plate and a method for manufacturing steel plate that use the above-mentioned method for preventing jamming.

The inventors conducted extensive research to solve the aforementioned problems. As a result, they used the torque deviation rate in the preceding passes of hot rolling to predict whether jamming would occur in the following passes. Based on these prediction results, they discovered that automatically correcting the torque constraint value for the following passes and recalculating the rolling schedule is effective in preventing jamming, leading to the creation of the present invention.

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 plate according to [1], 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 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)
[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 in that the hot rolling method described in [4] above is used.

The hot rolling jam prevention method of the present invention automatically calculates an appropriate torque correction value, recalculates the rolling schedule, and applies it to rolling, rather than relying on manual operations that rely on the experience and intuition of conventional operators. This prevents jamming while preventing an unnecessary increase in the number of rolling passes. Furthermore, the hot rolling method and steel plate manufacturing method of the present invention not only improve rolling efficiency, but also improve the work roll consumption rate and yield.

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. FIG. 10 is a diagram showing an example of predicted and actually measured loads on a steel plate where jamming occurs. FIG. 10 is a diagram showing the transition of the initial planned load, the planned load, and the actual load in Example 1. 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. FIG. 10 is a diagram showing a comparison between the conventional method and the second embodiment in terms of the number of passes and the maximum torque correction value.

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. Operations according to this flow chart are executed by a process computer.
In the present invention, first, a rolling schedule is calculated (step 100).

[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 a range that does not exceed the maximum load and maximum torque of the equipment constraints, and the rolling torque (hereinafter also 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 torque, also called 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].

Torque Constraint Value
The initial setting of the torque constraint value, which is the maximum torque value of the equipment constraint, is assigned a constant value in the process computer for normal rolled material and controlled rolled material, for example, 300 to 400 t m for normal rolled material and 300 to 400 t m for controlled rolled material.
After the rolling schedule is calculated, rolling is started (step 110). After the start of rolling, 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). If the result is "yes" (Y), rolling is terminated (step 190). If the result is "no" (N), it is determined whether the previous pass is correct (step 140).

[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.

The reason why the first to fifth passes are preferable as the first pass is as follows. Experience has shown that jamming occurs mainly during width setting rolling. This is because, during width setting 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 setting rolling usually starts 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 determination 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).

[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 obtained 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.

[Whether or not correction of torque constraint value is necessary]
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 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 that for the subsequent pass. The left side of equation (2) is the torque estimated for the subsequent pass, assuming that the torque deviation rate for the previous pass is maintained for the subsequent pass. This estimation was supported by the results of analysis of past rolling operation results.

When the estimated torque is high, the risk of jamming is high. Therefore, a threshold value is set for comparison with the estimated torque, and when 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 required.

[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, or 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. That is, 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. From Figure 4, it can be seen 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.

The example in Figure 4 is for the following conditions: slab length: 4-5 m, slab extraction temperature: 1050-1150°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 conditions differ in this way, the overall appropriate threshold value is in the range of 300-400 t·m. Therefore, it is preferable to set the threshold value as a function of at least one of slab length, slab extraction temperature, and steel type.

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

[Torque Constraint Value 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, for example, the following equations (3) and (4) are used.
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)
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.

[Rolling schedule recalculation]
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.

The hot rolling method of the present invention uses the method for preventing jamming of the present invention, which prevents jamming from occurring, resulting in improved rolling efficiency and improved work roll consumption.

In addition, the steel plate manufacturing method of the present invention uses the hot rolling method of the present invention, which prevents steel plates from being scrapped due to jamming, thereby improving the product yield of steel plates.

[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.

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 set to 326 t·m. The torque deviation rate was calculated using formula (1), and the threshold value was set to 370 t·m to determine whether correction to the torque constraint value was necessary using formula (2). The torque correction value was calculated using formula (3), and the corrected torque constraint value was calculated using formula (4).

After rolling began, it was determined that correction of the torque constraint value was "necessary" on the third pass, so the torque correction value was calculated, the torque constraint value was corrected, and the rolling schedule was recalculated in that order, and from the fourth pass onwards, rolling was carried out based on the recalculated rolling schedule.

Figure 3 shows the changes in the initial planned load, planned load, and actual load at this time. Here, the plate thickness on the horizontal axis is the delivery plate thickness for 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, the first and second passes were the adjustment passes, the third to seventh passes were the width setting passes, and the eighth to fourteenth passes were the finishing passes. However, after rescheduling, of the 15 passes, the third to eighth passes were the width setting passes, and the ninth to fifteenth passes were the finishing passes.

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. From the fourth pass onwards, rolling was carried out based on the recalculated rolling schedule, preventing jamming.

[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. Conventionally, 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.

As shown in Figure 5, in Example 2, the torque correction value increased by 5.5 points and the number of passes decreased by 0.7 passes compared to the conventional method. This resulted in an improvement in rolling efficiency of approximately 22 t/h.

In addition, whereas the frequency of cracks occurring in the work rolls in the conventional method was a maximum of approximately six times per month, in Example 2 this was significantly reduced to less than one time per month (not shown).

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

Claims (4)

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