KR20070067891A - System for controlling a plating amount in hot dipping process - Google Patents

Abstract

A system for controlling a plating amount in a hot dip coating process is provided to improve a coating weight deviation on a top end portion of a coil by measuring actual coating weights controlled by air knives in a hot working state, thereby performing a feedback control, and automatically control the coating weight irrespective of type and thickness of steel by directly measuring the coating weight through a hot coating weight gauge, thereby performing a prompt feedback control. A system for controlling a plating amount in a hot dip coating process comprises: air knives(2) for ejecting air onto upper and lower surfaces of a strip(1) passing through a plating bath to adjust the coating weight; a hot coating weight gauge(3) installed right behind the air knives to measure coating weights on the upper and lower surfaces of the strip right after adjusting the coating weight; a cold coating weight gauge(4) installed at a predetermined location behind the air knives to measure coating weights on the upper and lower surfaces and a lateral coating weight of the strip having a lower temperature after plating; and a coating weight controller(6') for controlling pressure and gap of the air knives according to a preset control, a feed forward control, a feedback control, and a skew control.

Description

System for controlling a plating amount in hot dipping process}

1 is a functional block diagram showing the configuration of a conventional plating amount control system.

2 is a graph showing the plating amount control results in the case of the conventional plating amount control.

3 (a) to 3 (c) are schematic diagrams illustrating variation in the width direction plating amount which may appear in a continuous hot dip plating process.

It is a schematic diagram which shows the pass line movement state of the steel plate in a continuous hot dip plating process.

5 is a schematic diagram showing a continuous hot dip plating process to which the present invention is applied.

6 is a block diagram showing a plating amount control system according to the present invention.

7 is a graph showing the plating amount control results according to the present invention.

FIG. 8 (a) shows the plating amount measurement trajectory of the hot plating amount measuring instrument and the cold plating amount measuring instrument according to the present invention, and (b) is a schematic diagram showing a semi-bending state of the steel sheet.

* Explanation of symbols for the main parts of the drawings *

1: steel strip 2: air knife

3: Hot Plating Meter (HWG) 4: Cold Plating Meter (CWG)

5: Stabilizing roll 6: plating amount control device

7: plating layer

The present invention relates to the control of the air knife to control the amount of plating attached to the steel sheet by spraying the air of a predetermined pressure on the lower surface of the steel sheet in the continuous hot-dip plating process, and more specifically through the air knife using a hot plating amount measuring instrument It is related with the plating amount control system which improved the plating amount deviation of the coil tip part by measuring the plating amount of one steel plate immediately.

In the continuous hot dip plating process, in order to achieve uniform plating over the entire surface of the steel sheet, conventionally, a coating amount prediction model is made based on the air knife interval and pressure operation performance for a predetermined period and line speed information. Based on the plating quantity prediction model, when the weld passes through the air knife, it adjusts the gap and pressure of the air knife corresponding to the target plating amount of the next coil for a specific line speed.

However, if the pressure and the interval corresponding to the next target plating amount are set based only on the pre-calculated prediction model as described above, if the accuracy of the prediction model is inferior, the air knife gap and the pressure value for the target plating amount will be incorrectly calculated. The actual plating amount and the target plating amount of the steel sheet can vary greatly.

In order to solve this problem, the target plating amount is reached by feedback control using the measured value of the plating amount.

FIG. 1 is a functional block diagram showing an example of a conventional plating amount control system. The conventional plating amount control system is a cold plating amount measuring device 4 which measures a plating amount of a cooled steel plate located at the rear end of the air knife (approximately 200m rear end). And a plating amount control device 6 that receives feedback of the plating amount measurement value of the cold plating amount measuring device 4 and controls the air knife to adjust the plating amount according to a preset plating amount prediction model.

The plating amount control device 6 performs four sub-controls largely. In other words, when the welded part of the steel plate passes through the air knife 2, there is a preset control that calculates and applies the air knife pressure and gap adjustment amount based on the target plating amount of the next coil, and there is a change in speed of the entire line. In this case, the amount of plating that can be adjusted by the air knife is changed according to the speed change, so that the feed forward control compensates for this and the difference between the actual plating amount and the target plating amount measured by the cold plating amount measuring device 4 is compensated. As shown in (b) and (c) of FIG. 3, skew control is performed at the same time to improve the variation in the plating amount in the width direction caused by the gap between the upper and lower left and right sides of the air knife nozzle and the steel sheet. .

More specifically, when the welded portion of the steel sheet passes through the air knife 2, the preset control is applied according to the output value of the preset controller 61 to control the air knife 2, and the weld portion is cold-plated. After passing through the measuring device 4, the air knife 2 by the feedback and skew control so that the deviation between the actual plating amount and the target plating amount measured by the cold plating amount measuring device 4 by the feedback and skew controller 64 becomes zero. Is controlled. In addition, when a change occurs in the line speed, a compensation amount is generated by the feedforward controller 62, which is applied to the control of the air knife 2.

However, according to the conventional plating amount control method, a considerable time delay occurs after the plating is started until the actual plating amount is measured and the feedback control is performed. Therefore, the tip portion, that is, the weld portion that is not subjected to the feedback control, is air knifed. As shown in FIG. 2, there is no way to compensate the difference even if a difference occurs between the target plating amount and the actual plating amount in the plated portion after passing through (2) and reaching the cold plating amount measuring instrument 4.

In addition, since the deviation generated in the section in which the feedback control is not performed is maintained, it takes a long time until the target plating amount is reached after the plating is started, and the variation in the plating amount for the entire coil also increases.

In addition, even when the plating amount prediction model is accurately predicted, when the thickness or steel grade of the steel sheet is different, as shown in FIG. 4, when the pass line of the steel sheet 1 moves from the center line of the hot dip plating process In this case, the gap between the air knife 2 and the steel sheet 1 is changed, thereby causing a plating amount deviation between the upper and lower surfaces of the steel sheet 1.

As a method for compensating for this, a method of compensating the gap between the upper and lower sides due to the movement of the pass line through the gap measurement value has been proposed by installing a gap measuring device immediately after the air knife (2). Since the bending degree varies from the stabilizing roll 5 located at the front end of the air knife 2 according to the thickness and the steel type of), the gap between the air knife 2 and the steel sheet 1 cannot be directly measured. It was measured indirectly by estimating the degree of bending, and thus there is a problem that the plating amount deviation of the upper and lower surfaces of the steel sheet is not completely compensated. In addition, even if the gap can be accurately measured, it does not measure the actual coating amount at that moment, and thus the plating amount deviation by feedback control until the weld passes through the cold plating amount measuring instrument 4 until the welding amount is attached to the surface of the steel sheet. There is still a problem that compensation cannot be made.

On the contrary, when the gap measuring device is installed close to the bottom with the air knife 2 for precise measurement, the air flowing from the air knife 2 is divided into the upper and lower parts and obstructs the flow of the air flowing upward. This may cause defects on the surface of the plated steel sheet.

The present invention has been proposed in order to solve the above-mentioned conventional problems, and an object thereof is to provide a hot plating amount measuring device directly at the rear end of an air knife to implement feedback control by measuring the actual plating amount controlled by the air knife in a hot state. It is possible to provide a fast plating amount feedback control without time delay, thereby providing a plating amount control system in a continuous hot dip plating process that can improve the variation of the coating amount of the tip of the coil.

In addition, another object of the present invention is to implement a rapid feedback control by measuring the plating amount directly through the hot plating amount measuring device even if the movement of the pass line due to the change in the bending amount of the steel sheet passed through the stabilizing roll according to the steel grade or the thickness change In addition, the present invention provides a plating amount control system in a continuous hot dip plating process capable of compensating for the movement of a pass line and enabling automatic plating amount control regardless of steel grade and thickness.

As a constituent means for realizing the above object, the plating amount control system in the continuous hot dip plating process includes an air knife for adjusting the plating amount by spraying air on the upper and lower surfaces of the steel sheet passing through the plating bath; A hot plating amount measurer installed immediately after the air knife to measure an upper and lower plating amount of the steel sheet immediately after the plating amount adjustment; A cold plating amount meter installed at a predetermined position at the rear end of the air knife to measure the upper and lower plating amounts and the width direction plating amount of the steel sheet having a lower temperature after plating; Preset control for calculating the pressure and gap adjustment amount of the air knife based on the target plating amount of the coil according to a predetermined plating amount prediction model when the welded part of the steel plate passes through the air knife, and according to the speed and gap change of the pass line. Feed forward control for compensating the pressure and gap of the air knife, feed back control for controlling the pressure and interval of the air knife on the basis of the deviation between the plating amount and the target amount measured from the hot plating amount meter, and the cold And a plating amount control device for controlling the pressure and interval of the air knife according to skew control for reducing the variation in the width direction plating amount of the steel sheet based on the deviation between the actual plating amount and the target plating amount measured by the plating amount measuring device.

Hereinafter, a plating amount control system in a hot dip plating process according to the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals and the same elements among the referenced drawings are represented by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

5 is a schematic diagram showing a hot dip plating process to which a plating amount control system according to the present invention is applied.

Referring to FIG. 5, the plating amount control system according to the present invention includes an air knife 2 for spraying air on the upper and lower surfaces of the steel plate 1 passing through the plating bath, and immediately after the air knife 2 to adjust the plating amount. Hot plated amount measuring device 3 for measuring the upper and lower plating amount of the steel plate 1 immediately after the coating amount adjustment and the steel plate 1 which is installed at a predetermined position at the rear end of the air knife 2 and the temperature after plating is lowered. The air knife 2 based on the target plating amount of the coil in accordance with a predetermined plating amount prediction model when the cold plating amount measuring instrument 4 for measuring the upper and lower plating amounts and the welded portion of the steel sheet 1 pass through the air knife 2. Preset control for calculating the pressure and spacing amount of the gas, a feed forward control for compensating the pressure and spacing of the air knife 2 according to the speed and spacing of the pass line, and the hot plating amount measuring instrument 3 A feedback control for controlling the pressure and interval of the air knife 2 based on the deviation between the plating amount and the target amount measured from the steel plate, and the steel sheet based on the deviation of the actual plating amount and the target plating amount measured by the cold plating amount measuring instrument 4. And a plating amount control device 6 'that controls the pressure and spacing of the air knife 2 in accordance with skew control for reducing the variation in the width direction plating amount in 1).

In the plating amount control system of the present invention configured as described above, after the hot plating amount measuring device 3 is installed at the rear end (about 1 m rear end) of the air knife 2, the actual plating amount is measured using this to perform feedback control. As shown in FIG. 7, the target plating amount can be reached more quickly without time delay.

Therefore, according to the present invention, as the result of the plating amount deviation control results in a rapid convergence of the actual plating amount from the tip of the coil to the target plating amount as shown in the graph of FIG. 7, the variation in the plating amount of the product is greatly improved. In addition, even if the accuracy of the preset control by the predictive model falls, fast feedback control is performed, thereby allowing immediate compensation.

In the plating amount control device 6 ', skew control is performed using the measured value of the cold plating amount measuring device 4 as in the related art.

As shown in (a) of FIG. 8, the cold plating amount measuring device 4 measures the plating amount while the hot plating amount measuring device 3 draws a straight trace, while drawing a trace in the diagonal direction of the steel sheet 1. The plating amount is measured. The cold plating amount measuring device 4 draws a trajectory in an oblique direction so that the plating amount measuring method in the width direction of a commercially available cold plating amount measuring device simultaneously measures the plating amount for the full width, but the head portion of the measuring sensor is Since the measurement is performed at a predetermined time period while reciprocating in the width direction, the speed of the steel sheet and the lateral reciprocation of the sensor head are combined.

On the contrary, the hot plating amount measuring device 3 measures the plating amount by drawing a straight line trajectory without measuring the plating amount over the entire width direction of the steel sheet, as shown in FIG. 8B at the rear end of the air knife 2. Since the steel sheet 1 often has a C-shaped curvature, when the plating amount is measured while moving in the width direction, the distance between the sensor head and the steel sheet is changed, which may cause a problem in the reliability of the measurement data.

Therefore, in the present invention, by performing the feedback control using the actual plating amount measured in the hot plating amount measuring device 3 for measuring the coating amount while drawing the trace of the straight line, the cold plating amount measuring instrument for measuring the coating amount while drawing the trajectory of the oblique line ( By performing skew control using the actual plating amount measured in 4), the plating amount control in the width direction can be simultaneously performed with the fast feedback control.

Fig. 6 shows a block diagram of the plating amount control device 6 'operating as described above.

Referring to FIG. 6, the plating amount control device 6 ′ includes a preset controller 61 for calculating a pressure and an interval of the air knife 2 by applying a predetermined plating amount prediction model to a target plating amount, and hot dip plating. A feedforward controller 62 which calculates the pressure and spacing adjustment amount of the air knife to compensate for the plating amount variation due to the change in the moving speed and the spacing of the pass line of the process, and the actual plating amount measured by the target plating amount and the hot plating amount measuring machine 3 In the first subtractor 66 to obtain a deviation from the plating amount, the second subtractor 67 to obtain a deviation between the target plating amount and the actual plating amount measured by the cold plating amount measuring instrument 4, and the first subtractor 66. A feedback controller 68 for calculating a control amount for the pressure and interval of the air knife 2 so that the deviation between the obtained target plating amount and the actual plating amount is reduced; and the target plating amount and actual plating obtained by the second subtractor 67. A skew controller 69 which calculates a control amount for the pressure and interval of the air knife 2 so that the widthwise plating amount is uniform by using the deviation of the amount; and the preset controller 61 and the feedforward controller 62 And a summer 69 for adding the pressure and interval control amounts of the air knife calculated by the feedback controller 968 and the skew controller 69 to the air knife 2.

More specifically, the preset controller 61 calculates the air knife pressure and the gap adjustment amount for the next coil by using a plating amount prediction model as shown in Equation 1 below, which is made by using the operation results of the past period.

    K, a, b, c of the above formula (1) is determined by the regression equation, W is the plating amount, V is the feed rate of the steel plate, D is the interval between the nozzle and the steel plate of the air knife, P is the air knife nozzle Outlet pressure.

That is, if the target plating amount TW is given and the ratio of the plating amount to be reflected in the transfer of the gap in the mother plating amount TW is R, the ratio to be reflected in the pressure is (1-R), and thus the gap of the air knife And the pressure regulation amount are determined as in Equation 2 below.

Next, the feedforward controller 62 infers the pressure adjustment according to the change of the line speed, and when the pass line moves, the movement interval from the change in the plating amount measured using the hot plating amount measuring device 3. Reward that amount.

The amount of pressure adjustment by the line speed change in the feedforward controller 62 is determined as in Equation 3 below.

라 하면, 상기 도금량 변화를 하기의 수학식 4와 같은 에어나이프의 간격 조정을 통해 보상한다.When the plating amount change due to the movement of the pass line occurs, the plating amount measured by the hot plating amount measuring device 3 is measured.

In this case, the plating amount is compensated for by adjusting the gap of the air knife as shown in Equation 4 below.

Next, the feedback controller 68 compares the actual plating amount and the target plating amount measured by the hot plating amount measuring device 3 to feedback-control the interval and pressure of the air knife 2, and the average plating amount and the front and rear plating amount averages. The difference e _p is controlled by the air knife pressure P as shown in Equation 5 below.

Here, TW is the target plating amount, W _T is the actual plating amount of the steel plate Top, W _B is the actual plating amount of the steel plate Bottom, Gp is the preset pressure gain value, P _T-new , P _B-new represents the value corrected by the feedback control for nozzle pressure on the upper and lower steel plates, respectively, and P _T-old and P _B-old represent the upper and lower nozzle pressure values of the steel sheet before feedback control.

In the feedback controller 68, the deviation of the plating amount average appearing between the upper and lower surfaces of the steel sheet is divided by the deviation of the upper and lower plating amounts by 2, as shown in Equation 6 below, and the upper and lower nozzle intervals are reversed back and forth in the opposite direction as corresponding to the calculated value. Control by Generating.

Next, the skew controller 69 is a control means for reducing the variation in the plating amount in the width direction of the steel sheet, and the distance between the work side WS side of the air knife nozzle as shown in Equations 7 and 8 according to the variation in the width direction plating amount. Adjust the distance on the drive side (DS) side.

Equation (7) represents the widthwise plating amount deviation of the upper surface of the steel sheet (TOP) and the gap adjustment amount of the nozzle of the air knife located on the upper surface side of the steel sheet, and Equation (8) is the widthwise plating amount variation of the bottom surface of the steel sheet (Bottom) The gap adjustment amount of the air knife nozzle located on the lower surface side of the steel sheet is represented by the equation.

In Equations 7 and 8, W is the actual coating amount, T is the upper surface of the steel sheet, B is the lower surface of the steel sheet, ds is the drive side located on one side when viewed from the steel sheet in the continuous melting process, ws is The work side located on the opposite side, D denotes a gap between the nozzle of the air knife and the steel sheet, and e denotes a variation in the plating amount in the width direction of the steel sheet.

As shown in Equations 7 and 8, the skew controller 69 divides the width direction deviation by 2, and then, by the amount proportional to the width direction deviation divided by 2, both sides of the air knife (that is, the drive). The nozzle spacing between the side and the work side is adjusted in opposite directions.

According to the above-mentioned structure and operation | movement, this invention uses the actual plating amount measured using the hot-plating amount measuring device 3 for feedback control which adjusts the deviation from the actual plating amount with the target plating amount, as shown in FIG. Since the welding part of the steel plate coil passes through the air knife 2 and can immediately compensate the difference between the target plating amount and the actual plating amount without time delay, the coil tip, more specifically, the cold plating amount measuring instrument 4 operates normally. It is possible to reduce the variation in the amount of plating on the tip portion that has been passed before.

In addition, even if the upper and lower plating amount variation of the steel sheet is caused by the pass line moving from the center line according to the thickness or steel grade of the steel sheet, the fast compensation is performed by feeding back the plating amount without time delay by the hot plating amount measuring device 3. can do.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

As described above, the present invention is to measure the plating amount without time delay through the hot plating amount meter immediately after the air knife in the continuous hot-dip plating line, so that the deviation from the target plating amount and the plating amount variation due to the movement of the pass line is not delayed. Since it can be compensated by the feedback immediately, there is an excellent effect of improving the overall quality by minimizing the occurrence of variation in the amount of plating in the tip portion of the steel sheet.

Claims (8)

An air knife for spraying air on the upper and lower surfaces of the steel plate passing through the plating bath to adjust the plating amount; A hot plating amount measurer installed immediately after the air knife to measure an upper and lower plating amount of the steel sheet immediately after the plating amount adjustment; A cold plating amount meter installed at a predetermined position at the rear end of the air knife to measure the upper and lower plating amounts and the width direction plating amount of the steel sheet having a lower temperature after plating; Preset control for calculating the pressure and gap adjustment amount of the air knife based on the target plating amount of the coil according to a predetermined plating amount prediction model when the welded part of the steel plate passes through the air knife, and according to the speed and gap change of the pass line. Feed forward control for compensating the pressure and spacing of the air knife, feedback control for controlling the pressure and spacing of the air knife based on the deviation between the plating amount and the target amount measured from the hot plating amount measuring instrument, and the cold plating amount Plating amount control in the hot-dip plating process including a plating amount control device for controlling the pressure and the gap of the air knife according to the skew control to reduce the variation in the width direction plating amount of the steel sheet based on the deviation between the actual plating amount and the target plating amount measured by the measuring device system. The method of claim 1, The measurement trace of the hot plating amount measuring device draws a linear trace along the moving direction of the steel sheet. The method of claim 1, The cold plating amount measuring device to measure the plating amount in the width direction of the steel sheet while drawing a measurement trace of the diagonal form from one side of the steel sheet to the other side. According to claim 1, wherein the plating amount control device A preset controller applying a predetermined plating amount prediction model to a target plating amount to calculate a pressure and an interval of the air knife; A feedforward controller for calculating pressure and spacing adjustment amounts of the air knife to compensate for the variation in the plating amount due to the change in the movement speed and the change in the spacing of the pass line of the hot dip plating process; A first subtractor for obtaining a deviation between a target plating amount and an actual plating amount measured by the hot plating amount measuring device; A second subtractor for obtaining a deviation between a target plating amount and an actual plating amount measured by the cold plating amount measuring instrument; A feedback controller for calculating a control amount for the pressure and interval of the air knife so that the deviation between the target plating amount and the actual plating amount obtained in the first subtractor is reduced; A skew controller that calculates a control amount for the pressure and interval of the air knife to make the widthwise plating amount uniform by using the deviation between the target plating amount and the actual plating amount obtained by the second subtractor; And a totalizer configured to add pressure and interval control amounts of the air knives calculated by the preset controller, the feedforward controller, the feedback controller, and the skew controller, respectively, and apply them to the air knife. The method of claim 4, wherein the preset controller

Where Dnew and Pnew are the air knife gap and pressure calculated by the preset controller, TW is the target plating amount, R is the ratio of the target plating amount to the air knife interval, and 1-R is the target plating amount. It represents the ratio to be realized through the pressure of the air knife, V is the feed rate of the steel plate, P is the nozzle outlet pressure of the air knife, D is the distance between the air knife and the steel plate, K, a, b, c is the plating amount prediction model Is a variable obtained by Plating amount control system in the hot-dip plating process characterized in that for calculating the interval and pressure of the air knife to implement the target plating amount by. The method of claim 4, wherein the feedforward controller is

Here, Pnew is the pressure control amount of the air knife, TW is the target plating amount, V is the feed rate of the steel sheet, D is the interval of the air knife, K, a, b, c is a variable determined by the plating amount prediction model. ) Calculate the pressure control amount Pnew due to the speed change of the pass line by

Where Dnew is the amount of airknife adjustment

Is the coating amount measured by the hot plating meter, V is the feed rate of the steel sheet, P is the pressure of the air knife, and K, a, b, and c are variables determined by the plating amount prediction model.) The plating amount control system in the hot-dip plating process characterized by calculating the interval adjustment amount by the plating amount change by the movement of the pass line. The method of claim 4, wherein the feedback controller is Substituting the difference e _p between the target plating amount and the average surface plating amount into the following equation, the upper and lower pressure adjustment amounts (P _T-ne w, P _B-new ) of the air knife are controlled.

Where Pp _-new and P _B-new are the nozzle pressure adjustments at the top and bottom of the steel plate, and P _T-old and P _B-old are the steel sheets before feedback control. Up and down nozzle pressure value) The deviation e _D of the average of the plating amount appearing between the upper and lower surfaces of the steel sheet is expressed by the following equation.

(Where D _T-new and D _B-new represent the amount of adjustment of the air knife gap on the upper and lower steel plates, and D _T-old and D _B-old indicate the air knife gap on the upper and lower steel plates) The plating amount control system in the hot-dip plating process characterized by controlling the air knife gap on the upper and lower surfaces of the steel sheet. The method of claim 4, wherein The skew controller is represented by the following equation,

,

(W is the measured plating amount, D is the gap between the nozzle and the steel plate of the air knife, Gp is the preset gain, T is the upper surface of the steel sheet, B is the lower surface of the steel sheet, ds is based on the steel sheet in the continuous melting process) Drive side located on one side, ws is the work side located on the opposite side, e is the width variation of the steel plate in the width direction) Plating amount control system in the hot-dip galvanizing process characterized in that the compensation in the width direction plating amount variation for each of the upper and lower surfaces of the steel sheet by adjusting the gap of the air knife.

Images