KR20110076649A - Method for controlling the pressure of air knife in continuous galvanizing line - Google Patents

Abstract

PURPOSE: A method of controlling pressure of a width-variable air knife in a continuous galvanized line is provided to reduce plating deviation by applying optimal control gain according to pressure setting value of a secondary pressure control valve and edge mask variation of a width-variable air knife. CONSTITUTION: A proportional/integral parameter is input to a pressure control parameter input unit(2) according to the variation setting value according to the width variation of a steel sheet and pressure setting value of a second pressure control valves(7,8) on a gas pipe. The proportional/integral parameter is stored in a unit(1) for calculating control valve of a pressure control valve. The calculating unit proportionally/integrally calculates error between pressure setting value and current pressure and produces input value for first and second pressure control valve positioners(3-5).

Description

Method for Controlling the Pressure of Air Knife in Continuous Galvanizing Line

The present invention relates to a method for controlling the pressure of a width variable air knife in a continuous hot dip galvanizing line, and more particularly, a width variable air knife in which the air knife exit area in the hot dip galvanizing line can be adjusted according to the plate width change of the steel sheet. The present invention relates to a variable pressure air knife pressure control method of a continuous hot dip galvanizing line which can improve the pressure response characteristics while reducing the amount of hunting when using.

In general, steel sheets manufactured in steel mills are plated on the surface of steel sheets to improve their corrosion resistance and make their appearance beautiful. However, such a plating process is very important in the process of producing automotive steel sheets used for special purposes recently. As a work process, a typical method is a hot-dip plating process in which zinc is attached to a steel plate and plated while passing the steel plate through a bath stored in a molten plating solution.

In this continuous plating process, the spraying pressure of gas such as air from the spray nozzle (airknife) installed in the vertical direction of the steel sheet passing through the plating bath is adjusted or the gap between the nozzle and the steel sheet is controlled to control the amount of plating attached to the steel sheet. can do.

On the other hand, in the continuous plating process, in order to plate the steel plate continuously, the steel plates having different dimensions are welded and plated continuously. The target plating amount of the steel sheet varies depending on the demand, so if the steel type and the target plating amount are changed, the target plating amount is changed accordingly. The injection pressure of the injection nozzle and the distance between the steel plate and the injection nozzle should be adjusted to obtain

At this time, if the injection pressure or the position control of the injection nozzle is not suitable, the plating amount is less than the target plating amount or excessively plated phenomenon occurs, which causes product defects.

In addition, when the pressure response characteristic that the injection pressure for injecting gas from the air knife reaches the set pressure is not good, the coating amount is also affected. For example, there are three factors for evaluating the response characteristics of the injection pressure: the time at which the steady state is reached, the overshoot amount, and the pressure hunting amount at the steady state.

The variable width air knife is known to be useful for reducing the amount of nitrogen used in the hot dip galvanizing plant using a gas such as nitrogen, or to reduce the amount of dross in the upper portion of the zinc melting pot.

As shown in FIG. 1, the width variable air knifes 9 and 10 may vary the amount of opening of the outlet through which the gas is ejected according to the plate width W. The air knife uses a nitrogen gas. Increasing use of nitrogen is due to the effect of reducing the consumption of nitrogen or reducing the dross of zinc in the upper part of the bath.

However, when the variable width air knife is used, there is a problem that the pressure response characteristic cannot be used in the actual line. Particularly, as the edge mask amount of the variable width air knife 9 and 10 increases, the lip outlet injected by nitrogen gas is discharged. The smaller the area, the smaller the pressure and the higher the pressure, there was a problem that the amount of pressure hunting in the steady state is very large.

In other words, in applying the variable-variable air knife 9 and 10, which is useful for reducing the nitrogen consumption and the occurrence of dross, the pressure control response characteristics vary according to the amount of the edge mask applied and the set pressure. There was a disadvantage that the pressure hunting amount was very large.

In order to reduce the steady state pressure, setting the proportional and integral controller parameters of the pressure controller in a direction in which the pressure responsiveness decreases can reduce the pressure hunting at high pressure, but the pressure response time is reduced at low pressure.

When the variable width air knife is applied in the hot-dip galvanizing line, the area of the lip outlet through which the gas is injected from the air knife is varied and the dynamic characteristics of the flow rate and pressure are changed accordingly, especially when the plate width is narrow, the air knife exit area is It becomes narrow and the pressure hunting amount of a steady state becomes large, and the problem that a plating amount hunting becomes occurs.

On the other hand, Japanese Patent Application Laid-Open No. 2008-133507 (2008.06.12.) Is a conventional pressure control method for controlling pressure with good pressure response characteristics in a general air knife in which the exit area of the air knife lip in which gas is ejected according to the width of the plate does not change. Publication date).

This method provides a pressure control method that can improve the pressure response characteristics when using a general air knife without an edge mask function. The compressed air from the compressor is stored in the receiver tank, and the main and branch pipes therefrom. The pressurized air is supplied to the nozzle header through the pipe, and the PI (Proportional: Integral) control controls the source pressure of the receiver tank, the primary pressure of the main pipe, and the secondary pressure of the branch pipe in the form of the set pressure. The pressure value of each secondary pressure gauge installed on one side and the other side of the steel sheet is averaged, and it is determined whether the absolute value of the difference between the average value and the set value is equal to or greater than the set value X. PI control continues, YES stops PI control, and judges on the basis of the relationship of the degree of opening to the pre-stored pressure. To obtain a valve opening degree of the pressure value in the series, and outputs a signal to the drive source of the valves in the form that the valve opening degree obtained binary.

However, in this method, when the area of the air knife outlet is changed and thus the flow and pressure dynamic characteristics are changed, when the plate width of the steel sheet is narrowed, the air knife outlet area is narrowed, and the pressure hunting amount at the steady state is increased. This causes a problem that the plating amount is hunted.

Accordingly, the present invention is to solve the above problems, the purpose of which is to change the application amount and the set pressure value of the edge mask which is changed in the process of varying the lip outlet of the width variable air knife according to the plate width change of the steel plate to be plated The present invention provides a method for controlling a variable pressure air knife pressure of a continuous hot dip plating line which can reduce the pressure hunting amount due to a pressure response characteristic that varies with a large and small, and has a fast response.

The present invention as a specific means for achieving the above object is a method for controlling the pressure of the air knife is disposed on both sides of the steel sheet in the continuous molten zinc plating line to inject gas through the lip outlet, the width change of the steel sheet Inputting the proportional / integral parameter to the pressure control parameter input unit according to the set value of the variable amount according to the set value, the pressure setting values of the primary pressure control valve provided in the main gas pipe and the secondary pressure control valve provided in the branch gas pipe: the pressure Storing the proportional / integral parameter received from the control parameter input unit into the pressure control valve control amount calculation unit; The pressure control valve control amount calculating unit reads the proportional / integral parameter of the primary and secondary pressure control valves set in advance on the basis of the width change value and the pressure setting value of the steel sheet which is changed in actual operation, and then the pressure setting value and the current pressure. And calculating an input value inputted to the primary and secondary pressure control valve positioners connected to the primary and secondary pressure control valves by proportionally / integrating the error between the values. Provides a variable width air knife pressure control method.

Preferably, the step of inputting the proportional / integral parameter to the pressure control parameter input unit is to determine the use range of the edge mask variable amount of the variable air knife from the minimum plate width and the maximum plate width from the minimum value to the maximum value, the second pressure control The size of the set pressure at the valve is determined from the minimum value to the maximum value, the specified value is divided at regular intervals, and the primary and secondary pressure control valves proportional to the primary / secondary pressure control table data corresponding to each section cell. Enter the integral parameter into the pressure control parameter input.

According to the present invention described above, continuous melting is applied by applying an optimum control gain predetermined in accordance with the edge mask variable amount and the secondary pressure control valve pressure set value of the width variable air knife disposed on both sides of the steel sheet and injecting the inert gas. It is possible to obtain the favorable pressure dynamic characteristics of the galvanized line throughout the entire line, thereby reducing the variation in plating amount, improving the quality of the steel plate, preventing product defects, and reducing the nitrogen consumption by applying variable width air knife. The effect of reducing the amount of dross generated is obtained.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

1 is a schematic view showing a variable width air knife applied to the continuous molten zinc plating line width variable air knife pressure control method according to a preferred embodiment of the present invention, Figure 2 is a continuous molten zinc according to a preferred embodiment of the present invention Plating line width variable air knife pressure control method applied to the configuration.

1 and 2, the method according to the preferred embodiment of the present invention is to control the pressure of the air knife is disposed on both sides of the steel sheet in the continuous molten zinc plating line to inject gas through the lip outlet, In this manner, continuous melting is performed including inputting a proportional / integral parameter to the pressure control parameter input unit, storing the pressure control valve control amount calculation unit, and calculating an input value input to the primary and secondary pressure control valve positioners. When using the variable width air knife 20 in the galvanizing line, the proportional gain and the integral gain of the proportional / integration controller for controlling the air knife chamber pressure to be the pressure setpoint are set to the steel width and the pressure setpoint of the secondary pressure control valve. According to the size of, it reads preset table value and performs proportional / integral control operation.

The step of inputting the proportional / integral parameter to the pressure control parameter input unit may include setting the width variable according to the width change of the steel plate traveling in one direction and the main gas pipe 11 supplied with the gas to be sprayed onto the steel plate surface. Pressure according to the pressure set value of the primary pressure control valve 6 and the pressure set values of the secondary pressure control valves 7 and 8 provided in the branch gas pipes 11a and 11b branched from the main gas pipe 11. It is to obtain the ratio and integral parameters satisfying the response characteristics by experiment and input the obtained parameters to the pressure control parameter input unit 2 connected to the pressure control valve control amount calculating unit 1.

That is, from the minimum plate width and the maximum plate width of the steel sheet produced in the hot dip galvanizing line, the use range of the variable edge mask variable amount of the variable air knife 20 is determined from the minimum value to the maximum value, and the secondary pressure control valves 7 and 8 Set the size of the set pressure from the minimum value to the maximum value, and divide it at regular intervals (for example, steel plate width variable 0 to 100 mm, set pressure 0 to 10 Kpa), and the first and second order corresponding to each section cell. The pressure control table data is determined by the experiment in the form of the best pressure response characteristics, and the primary and secondary pressure control valve proportional / integral parameters are input to the pressure control parameter input unit 2.

As shown in Tables 1 and 2, the variable amount of the variable width air knife 10 and the magnitude of the pressure set value were equally divided to test the pressure control response characteristics for each of them, and to obtain proportional and integral controller coefficients for obtaining an optimum response characteristic. After that, remember and set the obtained value.

At this time, the proportional / integral parameter for the pressure control is divided into the controller of the primary pressure control valve and the controller of the secondary pressure control valve, respectively.

Table 1 below shows the table values of the primary and secondary pressure controller proportional / integral parameters according to the secondary pressure control valve set pressure when the edge mask variable amount of the variable width air knife 10 which is changed according to the steel plate width change is 0 to 100 mm or less. Table 2 shows the proportional / integral of the 1st and 2nd pressure controller according to the set pressure of the 2nd pressure control valve when the edge mask variable amount of the variable width air knife 10 which is changed according to the steel plate width change is 100 to 200 mm or less. Shows the table value of the parameter.

number
Secondary pressure control valve set pressure
(KPa) Primary pressure control valve proportional / integral parameter Secondary pressure control valve proportional / integral
parameter Proportionality constant Integral constant Proportionality constant Integral constant One 0-10 P1 (1) (1) I1 (1) (1) P2 (1) (1) I2 (1) (1) 2 10-20 P1 (1) (2) I1 (1) (2) P2 (1) (2) I2 (1) (2) 3 20-30 P1 (1) (3) I1 (1) (3) P2 (1) (3) I2 (1) (3) 4 30 to 40 P1 (1) (4) I1 (1) (4) P2 (1) (4) I2 (1) (4) 5 40-50 P1 (1) (5) I1 (1) (5) P2 (1) (5) I2 (1) (5) 6 50-60 P1 (1) (6) I1 (1) (6) P2 (1) (6) I2 (1) (6) 7 60-70 P1 (1) (7) I1 (1) (7) P2 (1) (7) I2 (1) (7)

number
Secondary pressure control valve set pressure
(KPa) Primary pressure control valve proportional / integral parameter Secondary pressure control valve proportional / integral
parameter Proportionality constant Integral constant Proportionality constant Integral constant One 0-10 P1 (2) (1) I1 (2) (1) P2 (2) (1) I2 (2) (1) 2 10-20 P1 (2) (2) I1 (2) (2) P2 (2) (2) I2 (2) (2) 3 20-30 P1 (2) (3) I1 (2) (3) P2 (2) (3) I2 (2) (3) 4 30 to 40 P1 (2) (4) I1 (2) (4) P2 (2) (4) I2 (2) (4) 5 40-50 P1 (2) (5) I1 (2) (5) P2 (2) (5) I2 (2) (5) 6 50-60 P1 (2) (6) I1 (2) (6) P2 (2) (6) I2 (2) (6) 7 60-70 P1 (2) (7) I1 (2) (7) P2 (2) (7) I2 (2) (7)

On the other hand, even if the variable edge mask width of the variable width air knife 10 changes according to the width of the steel sheet is 300 ~ 400mm, 400 ~ 500mm, 500mm or more can be set as shown in Table 1 and Table 2.

These parameter values can be applied without modification of the program when it is necessary to adjust the control values during operation. When the table values are entered on the touch screen, the input values are entered when the touch button is pressed. It is preferably configured in a form that can be used as a table value setting area in the control amount calculating section.

The storing of the pressure control valve control amount calculating unit 1 may include the proportional / integral parameter received from the pressure control parameter input unit 2, the primary pressure control valve positioner 3 and the secondary pressure control valve positioner 4, 5. ) Is inputted and stored in a predetermined memory section within the pressure control valve control amount calculation unit 1 connected to the control unit.

The step of calculating the input values input to the primary and secondary pressure control valve positioners 3, 4 and 5 is based on the width change value of the steel sheet and the pressure set value of the secondary pressure control valve, which are changed in actual operation. The proportional / integral parameter of the primary and secondary pressure control valves, which are stored in the pressure control valve control amount calculating unit 1, are read in advance, and then the proportional / integral operation of the error between the pressure set value and the current pressure value is performed. It is to calculate the input values respectively input to the primary and secondary pressure control valve positioners 3, 4 and 5 connected to the secondary and secondary pressure control valves 6, 7, and 8 to control the gas supply pressure.

That is, the edge mask application amount A of the width variable air knifes 9 and 10 is calculated from the width information of the steel sheet and from the preset margin value B, which is the overall width of the variable width air knifes 9 and 10. Is 2000 mm, the sheet width W is 1000 mm, and the margin value B is 100 mm, the edge mask application amount A of the width variable edge knife 9, 10 to be applied is determined based on the driving side or the working side. Is calculated as

Edge mask application amount (A) = (total width of air knife / 2)-(plate width / 2)-margin value = 1000-500 -100 = 400mm.

Accordingly, when the sheet width of the steel sheet is 1000 mm and the margin value is set to 100 mm, the reference value of the edge mask application amount 400 to 500 mm is referred to, and the reference table number is determined according to the set pressure of the secondary pressure controller. .

For example, if the plate width of the steel plate is 1000mm and the set pressure of the secondary pressure control valve is 35Kpa, the proportional constant parameter P1 (4) (4) of the primary pressure control valve is read and I1 (4) (4) is read as the integral upper parameter. P2 (4) (4) is read for the secondary pressure control valve, and I2 (4) (4) is read for the integral upper parameter.

Then, the pressure control valve output value is calculated through the read proportional value, the integral value and the set pressure value. That is, the output values of the primary and secondary pressure control valves are calculated by the calculation unit 1 by using the proportional, integral and set pressure values read above, and the primary and secondary pressure control valves are output according to the calculated output values. The output can be controlled.

As described above, the predetermined optimum is set according to the edge mask variable amount of the variable width air knife 9, 10 which is disposed on both sides of the steel sheet and injects the inert gas, and the pressure set value of the secondary pressure control valves 7, 8. By applying the control gain of, it is possible to obtain the favorable pressure dynamic characteristics of the whole hot dip galvanizing line, and to reduce the variation in plating quantity, improve the quality of steel sheet, prevent product defects, and change the width of the air knife (9,10). In addition to the reduction of nitrogen consumption by the application, it is possible to reduce the amount of dross generated on the upper surface of the bath.

While the invention has been shown and described with respect to particular embodiments, it will be understood that various changes and modifications can be made in the art without departing from the spirit or scope of the invention as set forth in the claims below. It will be appreciated that those skilled in the art can easily know.

1 is a schematic diagram showing a variable width air knife applied to the continuous hot dip galvanizing line width variable air knife pressure control method according to a preferred embodiment of the present invention.

2 is a configuration diagram applied to the continuous hot dip galvanizing line width variable air knife pressure control method according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: Pressure control valve control amount calculating unit

2: Pressure control parameter input unit

3: Primary pressure control valve positioner

4,5: Secondary pressure control valve positioner

6: Primary pressure control valve

7,8: secondary pressure control valve

9,10: Width variable air knife

11: main gas pipe

11a, 11b: branch gas pipe

Claims (2)

In the continuous hot dip galvanizing line is disposed on both sides of the steel sheet to control the pressure of the air knife to inject gas through the lip outlet, Inputting a proportional / integral parameter to a pressure control parameter input unit according to a set value of a variable amount according to a width change of the steel plate and a pressure set value of a secondary pressure control valve provided in a branch gas pipe branched from a main gas pipe; Storing the proportional / integral parameter received from the pressure control parameter input unit into a pressure control valve control amount calculation unit; The proportional / integral parameter of the primary and secondary pressure control valves, which are set in advance on the basis of the width and pressure setting values of the steel sheet which are changed in actual operation, is read from the pressure control valve control amount calculating unit, Calculating an input value inputted to the primary and secondary pressure control valve positioners connected to the primary and secondary pressure control valves by proportionally / integrating an error; Width variable air knife pressure control method of the continuous molten zinc plating line comprising a. The method of claim 1, The step of inputting the proportional / integral parameter to the pressure control parameter input unit may determine an edge mask variable amount use range of the variable air knife from the minimum plate width and the maximum plate width of the steel sheet from the minimum value to the maximum value, Set the size of the set pressure from the minimum value to the maximum value, divide the fixed value at regular intervals, and adjust the proportional / integration parameters of the primary and secondary pressure control valves in the table data for primary and secondary pressure control corresponding to each section cell. The variable width air knife pressure control method of the continuous hot-dip galvanizing line characterized in that the input to the pressure control parameter input unit.

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