JP2007217754A - Method and device for controlling temperature of molten zinc pot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for controlling the temperature of a molten zinc pot, the method and the device suppressing fluctuation in a zinc discharging flow attributable to an inductor in a molten zinc bath thereby suppressing deposition of floating substances or the like in the bath onto a steel sheet. <P>SOLUTION: In the method for controlling the temperature of the molten zinc pot which controls the temperature of the molten zinc pot by using an induction heater, the permissible value of the power change per unit time according to the output of the induction heater is set to determine the power command value to the induction heater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bath temperature control method and apparatus for a molten zinc pot in which the bath temperature of the molten zinc pot is controlled using an induction heating device.

  In general, in an equipment for manufacturing a hot dip galvanized steel sheet, an induction groove type electric heating furnace called an inductor is installed in a zinc bath for melting zinc. The inductor can heat the melted zinc in the induction furnace groove to control the bath temperature. In conventional inductors, heating power is controlled by using a transformer whose power tap can be changed intermittently as a power source. Recently, an induction voltage regulator (IVR) that can continuously change power is used. Used for heating power control.

  For example, Patent Literature 1 and Patent Literature 2 disclose a method for controlling the temperature of the plating bath to be constant by controlling the electric power of the induction heating device. The technique described in Patent Document 1 is a technique for controlling the steel plate temperature in the cooling zone immediately before the bath in order to keep the bath temperature constant. The technique described in Patent Document 2 considers the timing of ingot injection. In this technique, temperature control is performed in advance of charging, so that there is no significant change in bath temperature after charging of the ingot.

By the way, an inductor is a device that discharges a bath component (zinc) to be heated after being heated in a grooved furnace, and the higher the heating power, the faster the discharge rate.
On the other hand, in a facility for producing a hot dip galvanized steel sheet, the steel components brought into the steel sheet to be plated may melt into the bath and combine with the zinc in the bath to form a hard suspended substance. This is called “Dross” and settles when there is no flow in the bath. In some cases, the dross is wound up and adheres to the plated steel sheet due to the flow in the bath such as the convection due to the bias of the above and the discharge flow caused by the inductor. This is a cause of poor quality of the plated steel sheet.
Japanese Patent Laid-Open No. 5-78804 JP-A-9-209110

  However, in the technique of controlling the bath temperature described in Patent Document 1 or Patent Document 2 described above to be constant, the temperature can be made constant. On the other hand, if the temperature is increased, the zinc discharge flow rate increases. Therefore, there is a problem that winding of dross occurs and the plated steel sheet has poor quality.

  The present invention has been made in view of the above circumstances, and minimizes the flow fluctuation of the zinc discharge flow by the inductor in the molten zinc bath, and suppresses the adhering of floating substances in the bath to the steel plate. An object of the present invention is to provide a pot bath temperature control method and apparatus.

  The invention according to claim 1 of the present invention is a method for controlling a bath temperature of a molten zinc pot that uses an induction heating device to control the bath temperature of the molten zinc pot, and changes in power per unit time according to the output of the induction heating device. A bath temperature control method for a molten zinc pot, characterized in that an electric power command value to the induction heating device is determined by providing an allowable amount.

  And the invention which concerns on Claim 2 of this invention is the bath temperature control method of the molten zinc pot of Claim 1. WHEREIN: The output per unit time in case the output of the said induction heating apparatus is larger than a predetermined reference | standard boundary value. The bath temperature control method for a molten zinc pot is characterized in that the allowable value of the amount of power change is set to a smaller value than when the output is smaller than the reference boundary value.

Further, the invention according to claim 3 of the present invention is a bath temperature control device for a molten zinc pot that uses an induction heating device to control the bath temperature of the molten zinc pot. A bath temperature control device for a molten zinc pot, comprising a power change amount limiter for limiting a power change amount per hit, and setting a value to be limited by the power change amount limiter according to the output of the induction heating device. is there.
And the invention which concerns on Claim 4 of this invention is the bath temperature control apparatus of the molten zinc pot of Claim 3. WHEREIN: The said electric power variation | change_quantity when the output of the said induction heating apparatus is larger than a predetermined reference | standard boundary value The bath temperature control device for a molten zinc pot is characterized in that a value limited by a limiter is set to a smaller value than when the output is smaller than the reference boundary value.

  The present invention sets an allowable value of the power change amount according to the output of the induction heating apparatus, and when the output is smaller than a predetermined reference boundary value, the allowable value of the power change amount per unit time is set large. When the value is larger than the reference boundary value, the allowable value is set to be small, so that the flow fluctuation of the zinc discharge flow by the inductor in the molten zinc bath is suppressed to a minimum, and the floating substance in the bath adheres to the steel plate. Can be suppressed. Thereby, the quality defect of the plated steel plate due to adhesion of floating substances can be reduced.

  The best mode for carrying out the present invention will be described below with reference to the drawings and equations. FIG. 1 is a diagram showing a bath temperature control block example of a molten zinc pot. In the figure, a is a temperature setting, b is a temperature sensor, c is a temperature record, d is a temperature deviation (setting-result), e is a controller, f is a power command, and g is a limit reference table ( ), H is the power variation limiter, i is the power command, j is the induction voltage regulator (IVR), k is the inductor, l is the molten zinc bath, m is the power supply, and n is the transformer. Represents each vessel.

  In this example, the actual temperature of the molten zinc bath l is measured using the temperature sensor b and fed back to the temperature setting a so that the controller e can adjust the induction voltage regulator so that the bath temperature of the molten zinc bath l becomes the set value. The output of j is controlled, thereby controlling the output of the inductor k of the molten zinc bath l. A power change amount limiter h that limits the amount of power change per unit time is provided in the power command f that is the control output of the controller e.

  A specific value of the power change amount limiter (upper limit value of power change amount) h is given from a limit reference table (function) g. FIG. 2 is a diagram illustrating an example of a limit reference table (function). In this figure, the power change amount limiter value is given as a function with the power command f as a parameter.

  Basically, it is defined as a solid line A, but it may be a characteristic such as a broken line B, a broken line C, or a broken line D in consideration of device characteristics, and is divided into a low output region and a high output region and becomes a boundary between them. The limit value (upper limit value) of the power change amount may be a predetermined constant value on the high output side from the threshold value, and may be a predetermined constant value different from the high output on the low output side. Alternatively, the low output area and the high output area may have the same value. Further, instead of placing the power change amount limiter h, the integral gain of the controller e may be changed.

  FIG. 3 is a flowchart showing an example of the processing procedure of the present invention. First, a temperature setting value that is a target temperature of the plating bath is input from a host computer that manages the operation (S1). And the signal of the temperature measurement sensor which measures the temperature of the plating bath installed in the plating bath is input, and the temperature of the plating bath of the present performance is input (S2). A difference (deviation) between the temperature set value and the actual temperature value is calculated (S3), and a power command value is obtained by the PI controller in order to perform control so as to eliminate the deviation (S4).

  Based on the power command value, the power limiter determination unit refers to the limiter reference table to obtain the upper limit value (limit value) of the power change amount corresponding to the power command value (S5). Further, a power change amount for making the power command value calculated by the PI controller is calculated from the current power setting value (or the power command value calculated by the previous control) (S6). The power change amount is compared with the upper limit value (S7). If the power change amount is larger than the upper limit value, the upper limit value is added to the current power setting value (or the power command value calculated in the previous control) (S8). Is set as a power command in the IVR which is an induction voltage regulator (S9). On the other hand, when the power change amount is equal to or lower than the upper limit value, the power command value calculated by the PI controller is set in the induction voltage regulator (IVR).

  For example, when the temperature deviation d between the temperature setting a and the temperature record c is small, the value of the power command f is also small. In this case, by referring to the limit reference table (function) g, the power change amount limiter h is used. The set value of increases. When the output is low, the discharge flow rate to the molten zinc bath l by the inductor k is small, and the influence of the dross winding is small.

  On the contrary, when the temperature deviation d between the temperature setting a and the actual temperature c is large, the value of the power command f becomes large. In this case, the power change is made by referring to the limit reference table (function) g. The set value in the amount limiter h becomes small. At such a high output, the discharge flow rate to the molten zinc bath l by the inductor k is large, and the influence of dross winding is large. Therefore, by suppressing the amount of power fluctuation, the rapid flow change in the molten zinc bath is suppressed, Thereby, it is suppressed that the floating substance in a bath adheres to a steel plate. Here, the power command f is an absolute value, and the protruding flow rate of the inductor is expressed as a function of the electric energy (absolute value).

  Further, the horizontal axis “power command (%)” of the limit reference table (function) shown in FIG. 2 is a value with the inductor capacity (rated kW) as 100%. As a matter of course, the capacity (rating) of this inductor varies depending on the equipment.

  Similarly, low output at high output, low output at high output, and high output indicate not the magnitude of the change, but the magnitude of the absolute value.For example, the output at 150 kW is higher than the protruding flow at 50 kW. The protruding flow has a larger flow rate (faster flow rate). Therefore, since the flow rate as an absolute value is larger when changing from 150 kW to 200 kW than when changing from 50 kW to 100 kW, it is easier to wind up the dross.

  The reference boundary value (threshold value) for determining low output and high output may be determined as appropriate. Specifically, for example, in the case of an inductor with an output of 300 kW, the normal use range is generally 15% (45 kW) to 85% (255 kW). In this case, the low output is 100 kW or less, and the high output is It can be separated from 100kW or more. However, it is not limited to this, and there is no problem even if the boundary is set to another value such as 150 kW. Further, the reference boundary value (threshold value) may be changed depending on the pot capacity and the use range.

  In addition, the set value of the power change amount limiter in the present invention is not set to a constant value in each of the ranges of low output and high output, but as a function such as A to D shown in FIG. The setting value of the change amount limiter may be changed continuously between outputs, in which case the setting value of the limiter becomes smaller as the output is higher, without distinction between low output and high output. Become. Note that the function for determining the values shown in FIG. 4 may be other than A to D, and may be determined as appropriate according to the operating conditions.

  The power change amount limiter in the present invention is mainly intended to suppress the flow rate from fluctuating due to a sudden change in power and winding up the dross. From this point of view, basically, when the power increases. If applied, the effect can be obtained sufficiently, but it also has the effect of suppressing flow changes in the bath due to sudden flow velocity fluctuations, so it may also be applied when power is reduced.

  As described above, in the present invention, it is possible to suppress the floating substance in the bath from adhering to the steel sheet, and it is possible to reduce the defective quality of the plated steel sheet due to the adhesion of the floating substance.

It is a figure which shows the bath temperature control block example of a molten zinc pot. It is a figure which shows an example of a limit reference table (function). It is a flowchart which shows the example of a process sequence of this invention. It is a figure which shows another example of a limit reference table (function).

Explanation of symbols

a Temperature setting b Temperature sensor c Temperature record d Temperature deviation (Setting-Result)
e Controller f Power command g Limit reference table (function)
h Power change amount limiter i Power command j Inductive voltage regulator (IVR)
k inductor l molten zinc bath m power n transformer

Claims (4)

In the method for controlling the bath temperature of the molten zinc pot, in which the bath temperature of the molten zinc pot is controlled using an induction heating device,
A bath temperature control method for a molten zinc pot, wherein an allowable value of a power change amount per unit time according to an output of the induction heating device is provided to determine a power command value to the induction heating device. In the method for controlling the bath temperature of the molten zinc pot according to claim 1,
The allowable value of the amount of power change per unit time when the output of the induction heating device is larger than a predetermined reference boundary value is set to a smaller value than when the output is smaller than the reference boundary value. To control the bath temperature of the molten zinc pot. In the bath temperature control device of the molten zinc pot that performs the bath temperature control of the molten zinc pot using an induction heating device,
The power command to the induction heating device includes a power change amount limiter that limits a power change amount per unit time, and a value that is limited by the power change amount limiter is set according to the output of the induction heating device. A bath temperature control device for a molten zinc pot. In the molten zinc pot bath temperature control device according to claim 3,
A value that is limited by the power change amount limiter when the output of the induction heating device is larger than a predetermined reference boundary value is set to a smaller value than when the output is smaller than the reference boundary value. Bath temperature control device for molten zinc pot.

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