KR20020017624A - Thickness control method for top and bottom of plate - Google Patents

Abstract

PURPOSE: A method for controlling thickness of the front and back end parts of a plate is provided which is capable of reducing a thickness deviation of the front and back end parts of the rolled plate in manufacturing a thick plate by rolling a slab. CONSTITUTION: In a method for controlling thickness of the front and back end parts of a plate produced in the plate rolling process producing a plate by rolling a slab with a reversible rolling mill, the method for controlling thickness of the front and back end parts of a plate comprises the steps of storing data of rolling loads per each passes of the plate rolled in a certain length of the plate into a central control part; transmitting the stored data of rolling loads to a setup treatment part after the plate gets out of the reversible rolling mill; calculating roll gap corrections to be applied to the front and back end parts of the plate and application time points in the next pass using the data of rolling loads; and inputting the calculated roll gap corrections and the application time points into the central control part, and controlling a thickness deviation between the front and back end parts of the plate in the central control part at the next pass according to the roll gap corrections and the application time points.

Description

Thickness control method for top and bottom of plate}

The present invention relates to a thick plate thickness control method that can reduce the thickness deviation of the leading end of the rolled thick plate when rolling the slab into a thick plate having a thickness of 5mm ~ 120mm, in particular, the results of rolling load in the previous pass The present invention relates to a thickness control method of a rear plate rear end portion which reduces the thickness deviation of the rear plate rear end by controlling the rolling load by a feed forward method using data.

The general thick plate production process is to roll the slab heated in the furnace with a reversible rolling mill a number of times to produce a thick plate product of the desired thickness or the material to be used in the next process. At this time, the reversible rolling mill controls the thickness of the thick plate passing through the reversible rolling mill using an automatic plate thickness control method. The reversible rolling mill consists of one stand, and is a rolling mill in which a thick plate is rolled while the reversible rolling mill proceeds in a forward direction and rolled while proceeding in the reverse direction again.

According to the conventional thick plate automatic thickness control method, the rolling load is predicted from the thickness, width, temperature, etc. of the side material in order to obtain the target plate thickness before entering the rolling mill. Setup control for setting and calculating the roll gap from the stiffness coefficient of the mill, and detecting the load from the load detection device installed in the rolling mill after the thick plate enters the rolling mill, and the thickness deviation from the error between the detected load and the predicted predicted load predicted by the setup computer. An automatic sheet thickness control method is used in a programmable logic controller (PLC) that calculates a vehicle and controls a roll gap.

As described above, the absolute plate thickness control method using the thickness control method in the PLC is a method of calculating a predetermined roll gap change amount from a load change by feeding back the load measured from the load detector at each computer control cycle. The roll gap is controlled by using a hydraulic cylinder having a relatively high control response. This absolute plate thickness control method is most widely used as a thick plate thickness control method.

However, even if the roll gap is controlled by using a hydraulic cylinder which is relatively responsive, there is a limit in the responsiveness of the actuator, and since the absolute thickness control for detecting the load is a feedback control method, the control responsiveness is a feed forward control. There is a disadvantage that the control response is slow compared to the method.

On the other hand, in the case of such thick plate rolling, when a sudden and excessive temperature deviation of the rear plate front end occurs, the thickness variation of the rear plate front end occurs largely, which is beyond the thickness allowable range required by the consumer, thereby lowering the error rate. There is a problem that causes it. The thickness deviation generated by such a sudden temperature deviation of the rear end of the wire cannot be sufficiently reduced by the existing absolute thickness control alone.

1 is a graph showing the thickness deviation of the rear end of the thick plate rolled by the thickness control method according to the prior art, Figure 2 is a rolling load at the last pass rolling to the thickness deviation of the rear end shown in FIG. The graph shown.

The graph shown in Figure 1 shows the thickness deviation measured by the x-ray thickness meter installed on-site the thickness of the final thick plate product produced by the thick plate rolling. The thickness deviation graph of FIG. 1 is a result of thick plate thickness deviation to which absolute thickness control is applied, and it can be seen from the graph of FIG. 1 that a large thickness deviation has occurred especially at the rear end. Due to the rapid temperature fluctuation, the load deviation occurred greatly. As described above, the thickness variation of the rear end was largely caused by several factors such as the responsiveness of the hydraulic cylinder and the absolute thickness control caused by the feedback control. It can be estimated.

On the other hand, in the case where the thickness difference between the leading end and the rear end of the thick plate is obtained, the rolling load drops significantly from the rear end, and as a result, the load of the rear end continues until the last pass as shown in FIG. 2. It can be seen that this greatly falls. It can be seen that when the thickness deviation of the rear end comes out thinner than the target thickness, the rolling load of the last rolling pass of the rear end is less than the load of the middle of the heavy plate. That is, it can be seen that the magnitude of the thickness deviation of the trailing end is in proportion to the magnitude of the rolling load deviation (the actual rolling load-the average rolling load) of the trailing end. Similarly, if the thickness variation of the trailing edge portion hardly occurs, the trailing edge rolling load deviation of the previous rolling pass is also small.

The factor causing the variation in the rolling load of the trailing end is due to the temperature of the trailing end. Due to the rapid temperature change of the trailing edge, the rolling load of the trailing edge changes abruptly, resulting in a large thickness deviation of the trailing edge.

In order to compensate for this disadvantage, "Korean Patent Application No. 1999-46001 (Invention name: thickness control method of the front end and the rear end of the plate in the thick plate rolling process)" refers to the front end of the thick plate, that is, from the front end in the longitudinal direction of the thick plate. In order to avoid the thickness from 0.3m to 0.6m thicker than the target thickness, and from 0.6m to 1.5m thick at the tip of the thick plate, the roll gap is set in the setup computer from the thickness of the tip to the thicker part. In the area where the thickness of the thick plate is smaller than the target thickness, on the contrary, the thickness is controlled by increasing the roll gap by a predetermined amount than the roll gap set in the setup computer, and improving the thickness variation of the rear end of the thick plate. To achieve this, when the rear end of the thick plate is at the calculated thickness, increase the absolute thickness control gain by about 20 to 40% from the existing set amount. It was used as the method of reducing the thickness variation portion. In this way, in order to improve the thickness deviation of the tip portion, the magnitude and sign of the thickness deviation that will actually occur should be well predicted to obtain a high degree of control. However, in "Korean Patent Application No. 1999-46001 (Invention name: thickness control method of the leading end and rear end of plate in thick plate rolling process), the thickness deviation amount of this part is proportional to the plate thickness for the thick part of the tip. Although the relationship between the positive and negative thickness gap roll gap correction amounts is varied according to the target plate thickness, there is no mention of how to determine the compensation amount of the portion where the plate thickness is thinner than the target thickness. none.

On the other hand, "Japanese Patent Laid-Open No. 6-277726 (Invention name: Method for controlling plate thickness of thick plate rolling)" is intended to reduce the thickening of the plate due to the retraction of the cylinder by the impact load of the heavy plate immediately after the plate is bitten by the rolling mill. The method of calculating the roll gap amount ΔG2 for compensating the tip abnormality region on the basis of the roll gap setting amount ΔG1 and the steel grade, thickness, width, etc. of the thick plate, and applying it in combination with the absolute automatic thickness control calculation amount will be described. According to the present invention, it is described that the absolute thickness control gain is reduced from 100% to 70% for the portion where the compensation amount ΔG2 and the absolute value of the absolute thickness control are added, but in this manner, an important part is the absolute thickness. There is an appropriate choice of control gain. This is because the size of the gain plays a big role in reducing the thickness variation of the tip. If the size of the gain is not properly changed according to the disturbances such as temperature deviation and thickness deviation of the material, which affect the thickness deviation, there is a problem in that there is no thickness control effect or deterioration in control performance. In addition, the method described in Japanese Patent Laid-Open No. 6-277726 (name of the invention: a method for controlling plate thickness of thick plate rolling) is mentioned only for the thickness deviation correction of the leading end of the thick plate, and there is no mention of the thickness deviation control of the rear end. . Therefore, there is a problem that the thickness deviation of the rear end of the thick plate proceeds in the same manner as in the conventional control.

The present invention is provided to solve the problems of the prior art as described above, and provides a method for controlling the thickness deviation of the front and rear ends of the thick plate by using the rolling load performance data of the previous pass of the thick plate rolled through the reversible rolling mill Its purpose is to.

1 is a graph showing the thickness deviation of the rear end of the thick plate rolled by the thickness control method according to the prior art,

FIG. 2 is a graph showing the rolling load at the last pass rolling with respect to the thickness deviation of the rear end shown in FIG.

3 is a graph showing a roll gap control amount for the thickness deviation of the rear end of the thick plate in the thickness control method of the rear end of the thick plate according to the present invention,

Figure 4 is a graph showing the roll gap control amount for the thickness deviation of the rear plate rear end in the thickness control method of the rear end of the thick plate according to the present invention,

FIG. 5 is a graph comparing thickness deviations of thick plate thicknesses according to the thickness control method of the thick plate front and rear ends shown in FIGS. 3 and 4 and thickness deviations of the thickness control method according to the prior art.

According to the present invention for achieving the object as described above, in the thickness control method of the rear end of the thick plate to control the thickness of the front end and the rear end of the thick plate produced in the thick plate rolling process to produce a thick plate by rolling with a reversible rolling mill, Storing each pass rolling load of the thick plate rolled by the central control unit at a predetermined length interval, transmitting the stored rolling load data to a setup processing unit after the thick plate is removed from the reversible rolling mill, and transmitting the rolling load data. Calculating a roll gap correction amount and an application time point to be applied to the front and rear ends of the thick plate in a next pass, and inputting the calculated roll gap correction amount and the application time point to the central control unit, wherein the central control unit applies the roll gap correction amount and the application time point. Depending on the time point, the thickness deviation of the front and rear ends of the thick plate This thickness control method for sequencing the end plate is provided comprising the step of.

In addition, the roll gap correction amount calculating step of the present invention calculates the average rolling load sampled to a predetermined length of the thick plate of the previous pass process, and to the point where a positive (+) thickness deviation of the thick end of the thick plate occurs with respect to the average rolling load Calculate the load difference, calculate the average value (ΔFTM1) of the load difference, calculate the roll gap correction amount (ΔGT1) as shown in Equation 4, from the point where the negative (-) thickness deviation of the thick end of the plate to the point 3m The deviation between the average load and the actual load is calculated, and the average value of the deviation (ΔFTM2) is calculated to calculate the roll gap correction amount (ΔGT2) for the negative thickness deviation of the leading end through Equation 7, and the thickness deviation of the rear end of the thick plate. The roll gap correction amount is calculated from the difference between the rolling load from the rear end L-3m to L and the load average value when the length of the rolled thick plate is L, and the load deviation (ΔFBM) is calculated. The roll gap correction amount (ΔGB) at the rear end is calculated as in Equation 10 from the load deviation.

In addition, the timing calculation of applying the rear end roll gap correction amount of the rear plate of the present invention sequentially calculates the amount of change in load with respect to the unit length change (ΔL) from the rear end L-3m to L when the length of the rear plate is L. Calculate the ratio of the plate length to the total plate length, multiply the predicted calculation plate length at the next pass rolling by the ratio, and calculate the starting point of the roll gap correction at the trailing end of the next pass; The variation of the load against is calculated as in Equation (11).

In the following, with reference to the accompanying drawings a preferred embodiment of the thickness control method of the rear end portion of the thick plate according to the present invention will be described in detail.

The slab is rolled to the desired thickness while passing through a reversible rolling mill a number of times while heated in a furnace.

Here, the number of rolling passes is determined in consideration of the load of the rolling mill, the thickness of the final product, and the like in the setup computer. In the present invention, the thickness control method of the rear end portion of the thick plate is a method of determining the next pass front end thickness control compensation amount and the control application time using the rolling load performance data after the previous pass rolling. Thus, in determining the pass roll gap correction amount, using the rolling load deviation of the previous pass can predict the magnitude and the sign of the thickness difference of the trailing end that will occur at the next pass using the magnitude of the rolling load deviation of the leading and trailing ends. Because

Figure 3 is a graph showing the roll gap control amount for the thickness deviation of the rear end of the thick plate in the thickness control method of the rear end of the thick plate according to the present invention, Figure 4 is the rear plate of the rear plate in the thickness control method of the rear end of the thick plate according to the present invention FIG. 5 is a graph showing the roll gap control amount with respect to the thickness deviation, and FIG. 5 compares the thickness deviation of the thick plate thickness according to the thickness control method of the rear end portion of the thick plate shown in FIGS. 3 and 4 with the thickness deviation caused by the thickness control method according to the prior art. One graph.

3 (a) shown in Figure 3 is a graph showing the thickness of the front and rear end portion of the front end of the thick plate before entering the rolling mill, Figure 3 (b) is the shape of the rear end portion as shown in Figure 3 (a) This is a graph showing the roll gap control process of the rolling mill when the leading edge of the thick plate is entered.

When the leading end of the thick plate has the leading end thickness as shown in Fig. 3A, the thickness of the leading end of the steel plate is estimated using the rolling load performance data of the previous pass, and the roll gap as shown in Fig. 3B is obtained. To control.

Referring to (b) of FIG. 3, the roll gap is reduced by ΔGT1 than the roll gap set in the setup model before the thick plate enters the rolling mill, and the average rolling load is negative at the average rolling load of minus (-) after the thick plate enters the rolling mill. Calculate the plate length (LT1) to the point where the load becomes, and when the rolled plate length reaches LT1, the roll gap correction amount is opened by ΔGT2 from the set roll gap, and becomes the average rolling load at the plus (+) average rolling load. It is a method of calculating absolute plate length (LT2) to reset the compensation amount set value to zero when the rolled thick plate length becomes LT2, and then starts absolute automatic gauge control.

In the thickness deviation control of the rear end of the rear plate, the roll gap is controlled by opening or reducing the roll gap depending on whether the sign of the load deviation of the rear end is positive (+) or negative (-).

On the other hand, Figure 4 (a) shown in Figure 4 is a graph showing the thickness deviation of the rear end by the rolling load of the rear end of the rear plate, Figure 4 (b) is the rear end of the thick plate shown in Figure 4 (a) It is a graph which shows control of a roll gap when entering a rolling mill.

When the load deviation is negative at the rear end of the thick plate having the thickness of the rear end portion as shown in (a) of FIG. 4, the roll gap of the rolling mill must be opened, and the correction amount and the timing at which the rear end roll gap compensation is performed will be described below. .

The thickness control method of the rear end portion of the thick plate of the present invention is a method of automatically determining the size of the roll gap correction amount and the roll gap control direction of the rear end portion of the rear plate. The roll gap correction amounts ΔGT1, ΔGT2, ΔGB and roll gaps in FIGS. The method of determining the compensation points LT1, LT2, and LB1 will be described in detail.

The thickness control method of the thick end of the thick plate is allocated by a memory that stores the performance data of each pass rolling load per plate length (ΔL) in the automatic thickness control computer of the PLC, and when the thick plate exits the rolling mill, It transmits to the in-setup computer, and the setup computer calculates and transmits the next pass roll gap correction amount and the time point at which the trailing edge control is applied to the PLC by using the performance data, and the PLC performs the trailing edge thickness control using this. First, the average rolling load FM is calculated from Equation 1 from the rolling load performance data per plate length ΔL output from the PLC.

FM = (F (1) + F (2) + ....... + F (N)) / N

Here, N represents the number of samples when the rolling load is sampled at the plate length (ΔL) interval.

The average rolling load FM calculated from Equation 1 and the load deviation ΔFT1 (i) from the load sample value F (i) up to the plate length LT1 are calculated through Equation 2.

ΔFT1 (i) = F (i)-FM (i = 1 to N1)

Here, N1 is a value obtained by calculating an LT1 / ΔL and taking an integer value.

Then, the average value ΔFTM1 of the load deviation ΔFT1 (i) is calculated as in Equation 3.

ΔFTM1 = (ΔFT1 (1) + ΔFT1 (2) + ....... + ΔFT1 (N1)) / N1

From the equation (3), the positive thickness deviation correction amount (ΔGT1) at the tip of the thick plate is calculated through the equation (4).

ΔGT1 = ΔFTM1 / M × a1

Here, M is a dense stiffness coefficient indicating the stiffness of the mill, a1 is an adjustment coefficient that can be applied to the control method described above in practice and then adjust the magnitude of the value according to the application result.

The sign of the average value ΔFTM1 of the load deviation in Equation 4 indicates the direction in which the roll gap is reduced or increased by ΔFTM1 / M × a1 from the roll gap set in the setup. In other words, when the average value ΔFTM1 of the load deviation is positive, it is a direction of reducing the roll gap, and when it is negative, it is a direction of increasing the roll gap.

Next, the method for calculating the roll gap correction amount ΔGT2 will be described in detail.

The load deviation ΔFT2 (i) of the average rolling load FM calculated from Equation 1 and the rolling load performance value F (i) from LT1 to the point 3m from the tip is calculated through Equation 5.

ΔFT2 (i) = F (i) -FM (i = N1-N2)

Here, N1 represents the performance load of the plate length at the LT1 point, and N2 represents the performance load of 3m from the tip.

On the other hand, the average value ΔFTM2 of the load deviation ΔFT2 (i) calculated from Equation 5 is calculated using Equation 6.

ΔFTM2 = (ΔFT2 (N1) + ΔFT2 (N1 + 1) + ..... + ΔFT2 (N2)) / (N2-N1)

In this way, the tip roll gap correction amount ΔGT2 is calculated as shown in Equation 7 by using the average value of the calculated load deviations.

ΔGT2 = ΔFTM2 / M × a2

Here, a2 is an adjustment factor that can adjust the size of the value according to the application result.

Next, the process of calculating the roll gap correction amount ΔGB will be described in detail.

When the total plate length rolled from the previous pass is L [m], the difference between the rolling load performance (F (i)) and the average load (FM) from plate length L-3m to point L (ΔFB) Calculate as in Equation 8.

ΔFB (i) = F (i) -FM (i = N3-N4)

Here, N3 represents the performance load at the point L-3m, and N4 represents the performance load at the point L L.

On the other hand, the average value ΔFBM of the difference between the rolling load performance and the average load (ΔFB (i) (i = N 3 to N 4) calculated in Equation 8 is calculated as in Equation 9.

ΔFBM (i) = (ΔFB (N3) + ΔFB (N3 + 1) + ...... + ΔFB (N4)) / (N4-N3)

The rear end roll gap correction amount ΔGB is calculated using Equation 10 using the average value ΔFBM calculated through Equation 9.

ΔGB = ΔFBM / M × a3

Here, a3 is an adjustment factor that can adjust the size of the value according to the application result.

On the other hand, below, the method of setting the roll gap control time points LT1, LT2, LB1, and LB2 at the rear end of the thick plate shown in FIG. 4 will be described. The LT1 calculates the average value of the thickness of the thick plate and how long the plate length lasts from about 0 to 0.5m at the tip of the thick plate after sufficient data on the thickness deviation of the plate length is obtained. Set the plate length to LT1. LT2 is basically set up by taking the correlation data of thickness deviation and plate length for the thick plate whose thickness deviation is negative, taking the average value and adjusting it according to the application result.

In the following description, a method of setting the time point LB1 at which the rear end thickness control is started will be described. Here, LB1 is set by recognizing the point where the rolling load sharply drops or increases from the rolling load performance data of the previous pass to the rear ends L-3 to L [m]. At this time, the difference between the rolling load performance (F (i)) and the average load (FM) from the rear end L-3 ~ L [m] calculated by Equation 8 to automatically recognize the sudden change of this load The change amount ΔDFB of ΔFB is calculated by using Equation 11 below.

ΔDFB (i) = ΔFB (N3 + i)-ΔFB (N3 + i-1) (i = 1 to N4-N3)

While calculating ΔDFB (i) sequentially by increasing i by one in Equation 11, if the condition ΔDFB (i) ≧ x is satisfied, an abrupt change point LBS of the rear end load is expressed by Equation 11 Calculate as 12 At this time, the determination of the threshold value x of the load variation is set to a value in which the load variation is well recognized by analyzing the performance rolling data.

LBS = L-3 + i × ΔL [m]

The ratio LB occupied by the sudden fluctuation point LBS of the load in the total plate length L [m] is calculated by Equation 13.

LB = LBS / L × 100 [%]

From the equation 13, the next pass rear end control compensation point LB1 is calculated from the equation (14).

LB1 = LN × LB / 100 [m]

Here, LN is the plate length calculated by the difference pass prediction calculated by the setup computer.

The point LB2 that resets the rear end control amount to zero is determined immediately after the plate exits the rolling mill.

As shown in Figure 5, Figure 5 (a) is a graph showing the thickness deviation of the steel plate front end according to the thickness control method according to the thickness control method according to the prior art and the rear plate front end portion of the present invention, Figure 5 (b ) Is a graph showing the thickness deviation of the rear end of the steel sheet.

As can be seen from (a) and (b) of Figure 5, it can be seen that the thickness deviation of the thick plate according to the thickness control method of the rear end portion of the thick plate of the present invention is smaller than the thickness control method according to the prior art. .

As described in detail above, in the thickness control method of the rear end of the thick plate according to the present invention, the roll gap is controlled according to the thickness of the rear end of the steel sheet after estimating the thickness of the rear end of the steel sheet after receiving the previous rolling load performance data by the feedforward method. As a result, control responsiveness is fast, and by controlling the roll gap appropriately according to the shape of the thickness of the front and rear ends of the steel sheet, there is an advantage that the shape defect of the thickness of the front and rear ends of the steel sheet can be reduced.

In the above description, the technical idea of the thickness control method of the rear end portion of the thick plate of the present invention has been described together with the accompanying drawings, but this is only illustrative of the best embodiment of the present invention and is not intended to limit the present invention. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (3)

In the thickness control method of the rear end portion of the thick plate to control the thickness of the front end and the rear end of the thick plate produced in the heavy plate rolling process to produce a thick plate by rolling with a reversible rolling mill, Storing every pass rolling load of the thick plate rolled by the central control unit at a predetermined length interval, Transmitting the stored rolling load data to a setup processing unit after the thick plate is removed from the reversible rolling mill; Calculating a roll gap correction amount and an application time point to be applied to the front and rear ends of the thick plate in the next pass using the rolling load data; And inputting the calculated roll gap correction amount and the application time to the central control unit, wherein the central control unit controls the thickness deviation of the front and rear ends of the thick plate in the next pass according to the roll gap correction amount and the application time. Thickness control method of the rear end of the thick plate. The method of claim 1, The roll gap correction amount calculating step calculates the average rolling load sampled from the thick plate of the previous pass process to a certain length, calculates the load difference to the point where the positive thickness deviation of the thick end of the thick plate occurs with respect to the average rolling load By calculating the average value (ΔFTM1) of the load difference, the roll gap correction amount (ΔGT1) is calculated as shown in Equation 1, The deviation between the average load and the actual load from the point where the negative thickness deviation occurs at the tip of the thick plate to the point of 3m at the tip is calculated, and the average value (ΔFTM2) of the deviation is calculated to calculate the roll gap correction amount for the tip thickness minus deviation ( ΔGT2) is calculated from Equation 2, The roll gap correction amount for the thickness deviation of the rear end of the thick plate is calculated from the difference between the rolling load from the rear end L-3m to L and the load average value when the length of the rolled thick plate is L, and the load deviation (ΔFBM) is calculated. The thickness control method of the thick plate front and rear end parts which calculates the roll gap correction amount ((DELTA) GB) of a rear end part from the deviation as shown in Formula (3). [Equation 1] ΔGT1 = ΔFTM1 / M × a1 Here, M is a stiffness coefficient indicating the stiffness of the mill, a1 is an adjustment coefficient that can adjust the size of the value according to the application result. [Equation 2] ΔGT2 = ΔFTM2 / M × a2 Here, a2 is an adjustment factor that can adjust the size of the value according to the application result. [Equation 3] ΔGB = ΔFBM / M × a3 Here, a3 is an adjustment factor that can adjust the size of the value according to the application result. The method according to claim 1 or 2, The timing calculation for applying the rear end roll gap correction amount of the rear plate sequentially calculates the variation in load with respect to the unit length change (ΔL) from the rear end L-3m to L when the rear plate length is L, and the plate length Calculates the ratio occupied by the total plate length, and calculates the starting point of the roll gap correction of the trailing edge of the next pass by multiplying the ratio by the above-mentioned ratio. The thickness control method of the rear end portion of the thick plate, characterized in that the variation in the load for the unit length change (ΔL) is calculated as in Equation 4. [Equation 4] ΔDFB (i) = ΔFB (N3 + i)-ΔFB (N3 + i-1) (i = 1 to N4-N3) Here, ΔFB is the difference between the rolling load performance and the average load from the plate length L-3m to the L point, N3 represents the performance load at the L-3m point, and N4 is the plate length L Performance load.