JP2009256739A - Method for manufacturing hot-dip galvanized steel sheet and device for monitoring height of deposit in hot-dip galvanizing bath - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure an amount of deposited bottom dross with a simple structure, inhibit the production of the bottom dross and eliminate the bottom dross at optimal timing. <P>SOLUTION: In a process of manufacturing a hot-dip galvanized steel sheet by immersing a steel sheet in a hot-dip galvanizing bath and galvanizing the surface of the steel sheet by passing it in the hot-dip galvanizing bath, this manufacturing method includes: measuring an electric resistance value in the hot-dip galvanizing bath (step S1); estimating a height of a deposit in the hot-dip galvanizing bath based on the measurement result (step S2); and inhibiting the deposit from being produced and/or from depositing on the steel sheet based on the estimated result (step S3 to step S11). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a hot-dip galvanized steel sheet for producing a galvanized steel sheet, and a deposit height monitoring device for monitoring the height of deposits generated during the production of a hot-dip galvanized steel sheet by a continuous galvanizing method. It is.

The production of a hot dip galvanized steel sheet by a continuous galvanizing method that has been conventionally performed is performed by immersing the steel sheet in a plating bath and passing it through the plating bath.
FIG. 17 shows a schematic diagram of a conventional manufacturing method. As shown in the figure, in the conventional manufacturing method, the steel plate 100 is fed to the plating bath 102 filled with molten zinc through the snout 101 and circulates the sink roll 103 installed in the plating bath 102. Is passed through and rises in the plating bath 102. And the steel plate 100 goes out of the plating bath 102 through the support roll 104 in a bath.

In such a manufacturing process, in the plating bath 102, the Fe eluted from the steel plate 100 is alloyed with Al and Zn, thereby generating dross containing FeZn ₇ as a component. Among the components of the dross, FeZn ₇ is mainly deposited as a bottom dross 200 at the bottom of the plating bath 102, and Fe ₂ Al _{5 and the} like float on the surface of the plating bath and become the top dross 201.
A part of the bottom dross 200 is wound up by the flow in the bath due to the rotation of the sink roll 103 and the like, and floats in the plating bath 102. Although it is possible to remove the top dross 201 by using a net or the like, it is difficult to remove the dross floating in the plating bath 102. Therefore, the dross floating in the plating bath 102 adheres to the surface of the steel plate 100 passing through the plating bath 102 and deteriorates the surface quality of galvanization. On the other hand, it is difficult to eliminate the occurrence of dross in the hot dip galvanizing method.

For this reason, Patent Document 1 discloses a method for making it difficult to wind up the accumulated dross by changing the shape of the bottom of the plating bath. Further, Patent Document 2 discloses a method of pumping a bottom dross into a subpot and accelerating dross settlement in the subpot. Patent Document 3 discloses a method of preventing the dross from rolling up by controlling the flow in the plating bath with a rectifying plate, a raised part at the bottom, or the like. Patent Document 4 discloses a method for controlling the line speed, inductor output, and zinc ingot charging timing so that the flow velocity in the molten metal plating bath is in a flow velocity range in which the accumulated bottom dross does not roll up. .
JP-A-3-68746 Japanese Patent Laid-Open No. 5-17859 JP-A-7-97669 JP-A-9-170057

By the way, even if it is going to control the flow in a plating bath like patent document 1, patent document 3, and patent document 4, when the accumulation amount of dross increases, eventually, dross rolling up will occur. Therefore, as in Patent Document 1, Patent Document 3, and Patent Document 4, in order to control the flow in the plating bath and prevent the dross from rolling up, it is necessary to frequently remove the dross.
However, the shape of the plating bath differs from line to line, and depending on the line, it may be necessary to lift the sink roll and perform the dross removal operation. In this case, even if the dross removal work is performed, the dross removal work is substantially performed every periodic repair day, but if the dross removal work is performed on the regular repair day, the amount of bottom dross accumulated in the plating bath is reduced. It is necessary to determine whether or not the allowable height at which no hoisting occurs is exceeded, that is, it is necessary to know an appropriate work timing for the dross removal work. For this purpose, it is necessary to frequently measure the amount of bottom dross accumulated. However, conventionally, the amount of bottom dross accumulated is measured manually by an operator by inserting a long rod, etc. It becomes excessive.

Further, there is no problem if the bottom dross can be pumped into the subpot reliably at a timing equal to or lower than the allowable height by the method disclosed in Patent Document 2. However, in that case, it is necessary to install a device for pumping out, and furthermore, the cost for securing the location of the subpot and keeping the subpot warm is also required, so that the installation is considerably restricted. Moreover, unless the bottom dross becomes zero, there is a concern about new flow by returning from the subpot to the pot again.
An object of the present invention is to measure the amount of bottom dross deposited with a simple configuration, and to suppress and eliminate the occurrence of bottom dross at an optimal timing.

  In order to solve the above-mentioned problem, the method for manufacturing a hot dip galvanized steel sheet according to claim 1 according to the present invention comprises immersing the steel sheet in a hot dip galvanizing bath and passing it through the hot dip galvanizing bath. In the manufacturing method of the hot dip galvanized steel sheet, the surface of the hot dip galvanized steel sheet is manufactured by galvanizing the surface, and the electric resistance value in the hot dip galvanizing bath is measured. A deposit height of the deposit is estimated, and a galvanized steel sheet is manufactured while suppressing the generation of the deposit and / or the adhesion of the deposit to the steel sheet based on the estimation result. .

Moreover, the manufacturing method of the hot dip galvanized steel sheet according to claim 2 according to the present invention is the method of manufacturing a hot dip galvanized steel sheet according to claim 1, wherein a plurality of locations in the horizontal direction in the hot dip galvanizing bath. In this case, the electrical resistance value is measured and the deposition height of the deposit is estimated based on the measurement result.
Moreover, the manufacturing method of the hot dip galvanized steel sheet according to claim 3 according to the present invention is the method of manufacturing a hot dip galvanized steel sheet according to claim 2, wherein the electrical resistance values measured at the plurality of locations are weighted. The deposit height of the deposit is estimated.

  Moreover, the manufacturing method of the hot-dip galvanized steel sheet according to claim 4 according to the present invention is the hot-dip galvanized steel sheet manufacturing method according to any one of claims 1 to 3, wherein Lowering, increasing the temperature of the hot dip galvanizing bath, increasing the pressing amount of the support roll in the hot dip galvanizing bath, and increasing the interval time of charging the zinc ingot into the hot dip galvanizing bath. By performing at least one of the above, generation of the deposit and / or adhesion of the deposit to the steel plate is suppressed.

Moreover, the manufacturing method of the hot dip galvanized steel sheet according to claim 5 according to the present invention is the method of manufacturing a hot dip galvanized steel sheet according to any one of claims 1 to 4, wherein the latest deposit is removed. When a predetermined period of time has elapsed, a process for suppressing generation of the deposit and / or adhesion of the deposit to the steel plate is performed.
Moreover, the manufacturing method of the hot dip galvanized steel sheet according to claim 6 according to the present invention is the method of manufacturing a hot dip galvanized steel sheet according to any one of claims 1 to 5, wherein a predetermined amount of hot dip galvanized steel sheet is added. When producing, the present invention is characterized in that a treatment for suppressing the generation of the deposit and / or the adhesion of the deposit to the steel sheet is performed.

  Moreover, the deposit height monitoring device in the hot dip galvanizing bath according to claim 7 according to the present invention is the deposit in the hot dip galvanizing bath through which the steel plate is passed in order to galvanize the steel plate surface. A deposit height monitoring device in a hot dip galvanizing bath for monitoring the height of the deposit in the hot dip galvanizing bath, monitoring means for monitoring the height of the deposit in the hot dip galvanizing bath, and monitoring results of the monitoring means On the basis of the generation of the deposit and / or adhesion of the deposit to the steel strip, and a means for suppressing the occurrence of a defect due to the deposit, and the monitoring means supplies a current to the hot dip galvanizing bath. The deposit of the deposit based on the voltage value measured by the electrode for current application to be applied, the voltage measurement electrode for measuring the voltage generated by the current applied by the current application electrode, and the voltage measurement electrode A deposition height estimating means for estimating the height; Characterized in that it comprises.

  Moreover, the deposit height monitoring apparatus in the hot dip galvanizing bath according to claim 8 according to the present invention is the deposit height monitoring apparatus in the hot dip galvanizing bath according to claim 7, wherein The electrode and the voltage measurement electrode constitute one probe, and the deposition height estimation means arranges the plurality of probes in a hot dip galvanizing bath and obtains a voltage value obtained for each probe. The deposition height of the deposit is estimated based on the above.

Moreover, the deposit height monitoring apparatus in the hot dip galvanizing bath according to claim 9 according to the present invention is the deposit height monitoring apparatus in the hot dip galvanizing bath according to claim 8, wherein the deposition height is measured. The estimating means weights the voltage value obtained for each probe, and estimates the deposit height of the deposit.
Moreover, the deposit height monitoring apparatus in the hot dip galvanizing bath of Claim 10 which concerns on this invention is the deposit height monitoring in the hot dip galvanizing bath of any one of Claims 7-9. In the apparatus, the means for suppressing the occurrence of defects due to deposits decreases the sheet passing speed of the steel sheet in the hot dip galvanizing bath, raises the temperature of the hot dip galvanizing bath, At least one of increasing the pressing amount of the support roll in the bath and increasing the charging interval time of the zinc ingot to the hot dip galvanizing bath is performed.

Moreover, the deposit height monitoring apparatus in the hot dip galvanizing bath of Claim 11 which concerns on this invention is the deposit height monitoring in the hot dip galvanizing bath of any one of Claims 7-10. The apparatus is characterized in that the means for suppressing the occurrence of defects due to deposits is performed when a predetermined period has elapsed since the latest deposit removal.
Moreover, the deposit height monitoring apparatus in the hot dip galvanizing bath according to claim 12 according to the present invention is the deposit height monitoring in the hot dip galvanizing bath according to any one of claims 7 to 11. In the apparatus, the means for suppressing the occurrence of defects due to the deposit is performed when a predetermined amount of hot-dip galvanized steel sheet is produced.

  According to the present invention, since the deposition height of the deposit in the hot dip galvanizing bath is estimated based on the measurement result of the electrical resistance in the hot dip galvanizing bath, the amount of bottom dross deposited can be measured with a simple configuration. it can. Since the generation of the deposit and / or the adhesion of the deposit to the steel plate is suppressed based on the estimated deposition height, the generation of bottom dross can be suppressed and removed at an optimal timing. it can.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described in detail with reference to the drawings.
(Constitution)
The first embodiment is a deposit height monitoring system to which the present invention is applied. The deposit height monitoring system is incorporated in the hot dip galvanized steel sheet manufacturing system.
FIG. 1 shows the configuration of a deposit height monitoring system. As shown in FIG. 1, a probe 1, an alarm output unit 2, and a control device 40 included in the deposit height measuring device are provided.

FIG. 2 shows the probe 1 attached to the plating bath 102 of the hot dip galvanized steel sheet production line. FIG. 3 shows the configuration of the probe 1.
As shown in FIG. 2, the probe 1 is disposed in a plating bath 102 filled with molten zinc. The probe 1 is configured to measure the electrical resistance in the plating bath (including molten zinc, bottom dross, top dross, etc.) in the plating bath 102. Specifically, as shown in FIG. 3, the probe 1 is composed of four electrodes, and of the four electrodes, two electrodes 11 positioned on the outer side (located at the uppermost part and the lowermost part). , 12 constitute current application electrodes 11, 12, and two electrodes 21, 22 positioned inside so as to be sandwiched between the current application electrodes 11, 12 constitute voltage measurement electrodes 21, 22. is doing.

The four electrodes are constituted by electric wires, and the electric wires pass through the heat-resistant insulating case (cover) 1a, and the tip ends thereof protrude outside the case 1a. The electric wire has a heat-resistant insulating film, and the tip part is removed to form the electrodes 11, 12, 21, and 22, and comes into contact with the molten zinc in the plating bath 102. In addition, the material of the electrodes 11, 12, 21, 22 (electric wires) is preferably a material that does not react with molten zinc. The material of the electrodes 11, 12, 21, 22 (electric wires) is preferably a material having corrosion resistance and high electrical conductivity, such as SUS.
The probe 1 provided with such electrodes 11, 12, 21, and 22 is immersed in a plating bath in the plating bath 102. At this time, the probe 1 is immersed so that the four electrodes 11, 12, 21, and 22 are aligned in the depth direction of the plating bath 102.

  FIG. 4 shows an electric circuit configuration of the deposit height measuring apparatus. As shown in FIG. 4, the electric circuit configuration is based on the premise that the current application electrodes 11 and 12 and the voltage measurement electrodes 21 and 22 are electrically connected via a medium (molten zinc), respectively. It is configured. In such a configuration, the electric circuit configuration applies a current from the constant current source 31 to the current application electrodes 11 and 12. The voltage value when the current flows through the current application electrodes 11 and 12 is measured by a voltage measuring device 32 attached between the voltage measurement electrodes 21 and 22. Note that the control device 10 includes an electric circuit configuration such as a constant current source 31 and a voltage measuring device 32.

Then, using the voltage value V (volt) measured by the voltage measuring device 32, the resistance value R (Ω) is calculated by the following equation (1).
R = V / A (1)
A is a constant current value (ampere). For example, when a current is applied to an object that is thinner than a current application electrode or a voltage measurement electrode, such as an electric wire, the current value between the voltage measurement electrodes is (1) no matter where the voltage measurement electrode is placed. ) A in the equation. Therefore, the absolute value of the electrical resistance of the portion can be obtained from the voltage measurement value. However, when current is applied to an object (plate shape, liquid, etc.) having a large area or volume with respect to the electrodes, the current flowing between the electrodes spreads, and the current distribution varies from place to place. In general, since the current spreads, the current between the electrodes is considered to be smaller than the current value A expressed by the equation (1), so that it is difficult to accurately determine the absolute value of the electrical resistance.

  In the case of a plating bath to be measured in the present embodiment, this corresponds to the latter case, and therefore the current value varies depending on the voltage measurement location, and it may be difficult to measure the absolute value of the electrical resistance. On the other hand, the current distribution is considered to be constant with no temporal change. For this reason, it is possible to obtain a relative change amount from a voltage measurement value or a calculated electrical resistance value at a certain time as a reference. Therefore, in this embodiment, as the management of the deposit height in the plating bath, the electrical resistance value is obtained from the equation (1), and the relative evaluation is performed to grasp the fluctuation of the deposit height. ing. For example, the relationship between the electrical resistance and the deposition height is obtained in advance, and the variation in the deposit height is grasped from the variation in the electrical resistance. At this time, as shown in FIG. 2, the probe 1 is installed near the height at which the bottom dross 200 accumulates and becomes a problem. More specifically, the probe 1 is installed so that the upper voltage measurement electrode 21 is positioned in the vicinity of the upper limit value of the deposit height (deposit depth). Here, the deposit height upper limit value is an upper limit value of the deposit height at which the winding of the bottom dross 200 can be controlled.

FIG. 5 shows the relationship between the position (height direction position) from the bottom surface of the plating bath where the bottom dross is deposited and the local resistance value at that position.
The reason why the bottom dross moves away from the bottom surface of the plating bath is that the bottom dross does not exist and the ratio of the bottom dross (bottom dross concentration) decreases, and the resistance value decreases. For example, the resistance value where the bottom dross ratio is high (near the bottom of the plating bath 102 at the bottom of the plating bath) is the resistance value where the bottom dross ratio is low (the top of the plating bath) (for example, about 1.8 × 10 ⁻ It becomes a large value such as 5 times or more of ⁷ Ωm (at a plating bath temperature of about 500 ° C.). This is because the bottom dross has a larger resistance value, and when the bottom dross increases (when the density increases), the current tries to flow around the bottom dross, but the area that can be bypassed decreases. Thus, the resistance value is different between the case of mere molten zinc and the case of bottom dross, and the bottom dross has a larger value.

  Using such a relationship, for example, a characteristic diagram showing the relationship between the ratio (concentration) of bottom dross and the resistance value is obtained in advance, and the amount of bottom dross deposited is estimated from the resistance value obtained based on the measured voltage value. To do. For example, when the resistance value exceeds a predetermined threshold value, it is determined that the bottom dross accumulation amount exceeds the allowable amount (the upper limit value of the accumulation height). The control device 40 is configured to perform such a determination process.

  As shown in FIG. 1, the control device 40 includes a dross accumulation height detection unit 41, a deposition height determination unit 42, an elapsed days determination unit 43, a production amount determination unit 44, a final determination unit 45, a line operation determination unit 46, and A control unit 47 is provided. The control device 40 includes an arithmetic device such as a personal computer and an electric circuit. The processing contents of these components of the control device 40 will be described along the processing procedure of one example thereof.

  FIG. 6 shows a processing procedure of the control device 40. As shown in the figure, when the process is started, first, in step S1, the control device 40 reads the sensor value. Specifically, the control device 40 reads a voltage value (measured value of the voltage measuring device 32) or a resistance value (see the formula (1)) obtained from the probe 1 (sensor). Here, the control device 40 reads a voltage value (measured value of the voltage measuring device 32) or a resistance value (refer to the formula (1)) obtained from one representative probe 1 among the plurality of probes 1. Here, the control device 10 applies a current to the current application electrodes 11 and 12 by the constant current source 31 and reads a voltage value between the current application electrodes 11 and 12. Alternatively, the resistance value is obtained based on the voltage value.

Subsequently, in step S2, the dross accumulation height detector 12 detects the bottom dross accumulation height (deposition amount, accumulation depth) based on the voltage value or resistance value read in step S1. For example, the characteristic diagram as described with reference to FIG. 5 is obtained in advance, and the bottom dross deposition height is detected with reference to the characteristic diagram.
Subsequently, in step S <b> 3, the deposition height determination unit 42 determines whether or not the bottom dross deposition height is greater than a predetermined threshold value. The predetermined threshold value here is a threshold value for determining the bottom dross deposition height. For example, a predetermined threshold value is set according to the state of the probe 1. For example, a predetermined threshold value is set according to the characteristics of the probe 1 and the installation location. Here, the accumulation height determination unit 42 proceeds to step S6 when the accumulation height of the bottom dross is larger than a predetermined threshold value. Further, the accumulation height determination unit 42 proceeds to step S4 when the accumulation height of the bottom dross is equal to or less than a predetermined threshold value.

  In step S4, the elapsed days determination unit 43 determines whether the elapsed days are longer than a predetermined threshold value. Here, the number of days elapsed is the number of days elapsed since the last bottom dross removal (the day when dross was drawn). Also, the number of days that have elapsed since the day on which periodic inspections and repairs were performed may be used. Further, the predetermined threshold value here is a threshold value for determining the number of elapsed days. For example, a predetermined threshold value is set according to the state of the probe 1. For example, a predetermined threshold value is set according to the installation location of the probe 1. Here, when the elapsed days are longer than the predetermined threshold value (when the predetermined days have elapsed), the elapsed days determination unit 43 proceeds to step S6. Moreover, the elapsed days determination part 43 progresses to step S5, when elapsed days are below a predetermined threshold value.

  In step S5, the production amount determination unit 44 determines whether or not the production amount of the steel sheet is greater than a predetermined threshold value. Here, the production amount of the steel plate is a cumulative value of the production amount of the steel plate after the last bottom dross removal (the dross pumping implementation date). The cumulative value of steel plate production from the date of regular inspection and repair may also be used. Moreover, the predetermined threshold value here is a threshold value for judging the production amount of the steel sheet. For example, a predetermined threshold value is set according to the state of the probe 1. For example, a predetermined threshold value is set according to the installation location of the probe 1. Here, if the production amount of the steel sheet is larger than the predetermined threshold value, the production amount determination unit 44 proceeds to step S6. Moreover, the production amount determination part 44 performs a process again from said step S1, when the production amount of a steel plate is below a predetermined threshold value.

In step S <b> 6, the control device 40 reads voltage values (measured values of the voltage measuring device 32) or resistance values obtained from the plurality of probes 1. Further, the dross accumulation height detection unit 12 detects the bottom dross accumulation height for each probe 1 based on the read voltage value or resistance value.
Subsequently, in step S7, the final determination unit 45 performs final determination. Specifically, the final determination of the deposition height is performed based on the bottom dross deposition height for each probe 1 detected in step S6. For example, the final judgment on the deposition height is made by comparing with a predetermined threshold value. Further, for example, a weighted average of the bottom dross accumulation height obtained by each probe 1 is calculated, and finally the determination is performed based on the weighted average. At this time, the weight of the important probe 1 is increased. For example, the weighting of the probe 1 that is highly related to the quality of the steel plate is increased.

  FIG. 7 shows an arrangement example of the plurality of probes 1 a to 1 h in the plating bath 102. FIG. 7 is a view of the plating bath 102 as viewed from above. That is, FIG. 7 shows the horizontal arrangement of the plurality of probes 1 a to 1 h in the plating bath 102. As shown in the figure, a plurality of probes 1 a to 1 h are arranged along the peripheral wall of the plating bath 102. This is because the bottom dross has a strong tendency to accumulate along the peripheral wall of the plating bath 102. In this way, the plurality of probes 1a to 1h are arranged at positions suitable for measuring the bottom dross deposition height.

As a result of the determination in step S7 using the plurality of probes 1a to 1h, the final determination unit 45 proceeds to step S8 when the deposition height is not acceptable (when the deposition height is NG). Further, when the deposition height is acceptable (when the deposition height is OK), the final determination unit 45 performs the process again from step S1.
In step S8, the control unit 47 controls the alarm control unit 2 to output an alarm. For example, a warning is given by the screen display output of the alarm output unit 2 or a warning is given by the audio output of the alarm output unit 2.
Subsequently, in step S9, the line operation determining unit 46 determines whether or not the line is moving. Here, the line operation determining unit 46 proceeds to step S10 when the line is operating. The line operation determining unit 46 proceeds to step S11 when the line is not operating (when the line is stopped).

In step S10, the control unit 47 performs in-operation control. That is, control that can be performed during operation is performed. Specifically, the sheet feeding speed of the steel sheet in the hot dip galvanizing bath is changed. For example, the speed of a portion (for example, a roll) related to the plate passing speed of the steel plate is reduced. Specifically, the temperature of the entry plate (the steel plate entering the plating bath 102) is changed. For example, the temperature of the entrance plate is increased. Specifically, the pressing amount (force) / opening amount (force) of the support roll in bath is changed. For example, the pressing amount (force) of the support roll in the bath is increased. Specifically, the interval time at which the zinc ingot is charged into the plating bath 102 is changed. For example, the input interval time is increased.
In step S11, the line stop operation is performed. Specifically, dross is drawn. Also change the bath equipment. For example, the operator performs such line stop operation.

(Operation)
The operation is as follows.
FIG. 8 shows a processing procedure of a hot-dip galvanized steel sheet manufacturing system (manufacturing process) in which the deposit height monitoring system is incorporated. As shown in the figure, the hot dip galvanized steel sheet manufacturing system is roughly divided into a pretreatment process (step S21) consisting of casting, rolling, pickling, etc., an annealing process (step S22) consisting of continuous annealing, electrolytic cleaning, and the like. Inspect the hot dip galvanizing process (step S23), the alloying process (step S24) for reheating the plating layer immediately after passing through the plating bath, the skin pass (SK) process (step S25) for finishing the shape and surface, and the product. It consists of an inspection process (step S26).

  The bottom dross deposition height is detected in the hot dip galvanizing process in the above process. That is, the probe 1 is disposed in the plating bath 102 in order to monitor the bottom dross accumulation height. The control device 40 reads a voltage value (measured value of the voltage measuring device 32) or a resistance value (refer to the equation (1)) obtained from the probe 1, and deposits bottom dross based on the read voltage value or resistance value. The height is detected (steps S1 and S2). When the bottom dross accumulation height is larger than a predetermined threshold (when “Yes” in the determination of step S3), the control device 40 determines that the elapsed days are longer than the predetermined threshold (see above). When the determination in step S4 is “Yes”, or when the production amount of the steel sheet is larger than a predetermined threshold value (in the case of “Yes” in the determination in step S5), the process proceeds to the final determination. In other cases, the process is performed again from the beginning.

  As a process for final determination, the control device 40 reads a voltage value (measured value of the voltage measuring device 32) or a resistance value (see the formula (1)) obtained from the plurality of probes 1, and reads the read voltage value. Alternatively, the bottom dross deposition height is detected for each probe 1 based on the resistance value (step S6). Subsequently, the control device 40 performs a final determination. That is, based on the bottom dross accumulation height obtained for each probe 1, a final determination is made regarding the bottom dross accumulation height (step S7). Then, when the bottom dross accumulation height is acceptable, the control device 40 performs the process again from the beginning. In addition, when the bottom dross accumulation height is not acceptable, the control device 40 outputs an alarm (step S8), and performs processing according to the line movable state. That is, when the line is in operation, control during operation such as lowering the sheet feeding speed is performed (step S10). Further, when the line is not in operation, an operation at the time of line stop, such as drawing dross, is performed (step S11).

(Function and effect)
The action and effect are as follows.
As described above, in the operation control, the plate passing speed is changed. Alternatively, the temperature of the entrance plate is changed. Alternatively, the pressing amount (force) / opening amount (force) of the support roll in the bath is changed. Or the interval time which throws a zinc ingot in the plating bathtub 102 is changed. Alternatively, these change processes are performed in combination.
Therefore, the flow in the plating bath 102 is stabilized by changing the plate passing speed, specifically, by reducing the speed of the portion (for example, roll) related to the plate passing speed of the steel plate. For example, it is possible to prevent the bottom dross from being rolled up. Thereby, it can suppress that the bottom dross deposited on the bottom face of the plating bathtub 102 adheres to a steel plate.

Moreover, the temperature in the plating bath 102 can be raised by changing the temperature of the entry plate, specifically, by raising the temperature of the entry plate. Thereby, the reaction rate of the eluted iron and zinc, which cause bottom dross in the plating bath, can be reduced. Thereby, the generation amount of bottom dross can be suppressed.
Also, by changing the pressing amount (force) / opening amount (force) of the support roll in the bath, specifically, by increasing the pressing amount (force) of the support roll in the bath, the bottom dross adheres to the steel plate. Can be suppressed.

Moreover, the temperature drop of a plating bath can be made small by changing the time interval which throws a zinc ingot into the plating bath 102, specifically, making the charging interval time large.
Further, by outputting an alarm, an operator or the like can know that control during operation is performed. Also, the alarm output allows the operator to quickly start the bottom dross removal work.
Further, as described above, when the bottom dross accumulation height is larger than a predetermined threshold value, processing for final determination is performed, and control during operation and line stop operation are performed.

Here, FIG. 9 shows an example of the relationship between the bottom dross deposition height and the defect occurrence rate due to the bottom dross. In this example, a value is obtained for the back CE. The back CE is 1 g in FIG. As shown in the figure, when the bottom dross deposition height increases, the defect occurrence rate of the steel sheet due to the bottom dross increases. For this reason, when the bottom dross accumulation height is greater than a predetermined threshold, control during operation (such as suppression of bottom dross generation) or line stop operation (such as bottom dross removal) can be performed. The defect occurrence rate of the steel sheet can be reduced. In addition, it is possible to constantly monitor the bottom dross accumulation height without interfering with the operation, and to carry out the control during operation and the operation when the line is stopped at the optimum timing. Therefore, as shown in FIG. 9, the predetermined threshold value here is set so that the defect occurrence rate due to bottom dross is not more than a predetermined value, so that the operation is performed at an optimal timing according to the defect occurrence rate. Control and line stop operations can be performed.
Also, the bottom dross deposition height is measured (estimated) based on the electrical resistance value in the plating bath, and thus the bottom dross deposition height can be measured (estimated) with a simple configuration.
Further, as described above, when the number of days elapsed is longer than a predetermined threshold value, processing for final determination is performed, and in-operation control and line stop operation are performed.

Here, FIG. 10 shows an example of the relationship between the elapsed days and the bottom dross accumulation height. In this example, values are obtained for the front CE, the sync roll OP, and the back CE. The front CE is 1b in FIG. The sync roll OP is 1e in FIG. As shown in the figure, the bottom dross deposition height increases as the number of elapsed days increases. That is, the defect occurrence rate of the steel sheet due to bottom dross increases. For this reason, when the number of days elapsed is longer than a predetermined threshold value, the defect occurrence rate of the steel sheet due to the bottom dross can be reduced by performing the operation control and the line stop operation. For example, as shown in FIG. 10, the predetermined threshold value here is set so that the bottom dross deposition height is equal to or lower than the predetermined value, so that it corresponds to the bottom dross deposition height, that is, the defect occurrence rate. It is possible to perform in-operation control and line stop operation at the optimal timing.
Further, as described above, when the production amount is larger than the predetermined threshold value, processing for final determination is performed, and control during operation and line stop operation are performed.

  Here, FIG. 11 shows an example of the relationship between the production amount and the bottom dross accumulation height. As shown in the figure, as the production amount increases, the bottom dross deposition height increases. That is, the defect occurrence rate of the steel sheet due to bottom dross increases. For this reason, if the production volume is higher than the specified threshold value, it is possible to detect defects in the steel plate due to bottom dross by performing in-operation control (such as suppression of bottom dross generation) and line stop operations (such as bottom dross removal). The incidence can be reduced. For example, as shown in FIG. 11, the predetermined threshold value here is set so that the bottom dross deposition height is less than or equal to a predetermined value, so that it corresponds to the bottom dross deposition height, that is, the defect occurrence rate. It is possible to perform in-operation control and line stop operation at the optimal timing.

  Even when the bottom dross accumulation height is equal to or lower than a predetermined threshold value, when the elapsed days are longer than the predetermined threshold value or when the production amount is higher than the predetermined threshold value (in the determination in step S3). Even if “No”, as long as “Yes” is determined in Steps S4 and S5), in-operation control and line stop operation are performed. As a result, even when the probe 1 cannot perform normal measurement due to some cause, the in-operation control and the line stop operation can be reliably performed as the fail process. Thereby, the defect occurrence rate by bottom dross can be suppressed reliably.

(Other embodiments, etc.)
This embodiment can also be realized by the following configuration.
That is, the characteristic diagram of FIG. 5 is based on the assumption that bottom dross is precipitated on the bottom surface of the plating bath. However, it is not limited to such a premise. For example, the ratio of molten zinc in the bottom dross, the component of the bottom dross, the change in the deposition state due to the change in the ambient temperature of the bottom dross (the temperature of the plating bath), and the state where the bottom dross has a low density and is in a partially floating state. In consideration of such a bottom dross state, a bottom dross region can be defined, and a characteristic diagram used for determination or a resistance value for bottom dross region determination can be set for each line.

  Moreover, in this embodiment, the probe 1 is arrange | positioned in the plating bath 102 so that the electrodes 11, 12, 21, and 22 may be located along with the depth direction (vertical direction). However, it is not limited to this. That is, the probe 1 can be disposed in the plating bath 102 so that the electrodes 11, 12, 21, and 22 are positioned side by side in the horizontal direction. By arranging in this way, it is also possible to determine whether or not the bottom dross has reached the position of the probe 1 installed horizontally (whether or not the predetermined accumulation amount has been reached).

  Further, the resistance value at that time can be measured by scanning the probe 1 in the plating bath in the plating bath 102 in an arbitrary direction (for example, up and down, left and right directions). Thereby, the accumulation state (deposition shape) of the bottom dross in the plating bath 102 can also be measured three-dimensionally. Needless to say, sufficient attention should be paid to winding up the bottom dross by scanning the probe 1.

  Further, in order to three-dimensionally measure the bottom dross accumulation state (deposition shape) in the plating bath 102, a current application electrode (not limited to one pair) and a voltage measurement electrode (not limited to two) accordingly. ) May be appropriately arranged in a three-dimensional manner at multiple points in the plating bath 102. By doing in this way, even when the bottom dross accumulation state (deposition shape) in the plating bath 102 is measured three-dimensionally, it is not necessary to scan with the probe, so that the bottom dross can be prevented from being rolled up.

  The probe may include three or more voltage measurement electrodes between a pair of current application electrodes. FIG. 12 shows the configuration of the probe 1. As shown in the figure, the probe 1 includes a plurality (seven in this example) of voltage measuring electrodes 21, 22, 23, 24, 25, 26, 27 between a pair of current applying electrodes 11, 12. I have. The probe 1 is configured such that the voltage values ΔV1 to ΔV6 (resistance values) between adjacent electrodes can be measured by the plurality of voltage measuring electrodes 21 to 27.

  FIG. 13 shows an example of measurement results of voltage values ΔV1 to ΔV6 obtained between the adjacent electrodes in the voltage measurement electrodes 21 to 27. As shown in the figure, in this example, the voltage values ΔV1 to ΔV3 above the voltage measurement electrode 24 are greatly different from the voltage values ΔV4 to ΔV6 below the voltage measurement electrode 24 (in the height direction). The voltage value greatly changes at a certain X position of h), and the voltage values ΔV4 to ΔV6 below the voltage measuring electrode 24 are larger.

Based on such a result, between the voltage value (resistance value) between the voltage measurement electrodes 23 and 24 and the voltage value (resistance value) between the voltage measurement electrodes 24 and 25, molten zinc and bottom dross The bottom dross deposition height is measured on the assumption that the boundary surface of the bottom dross exists in the vicinity of the voltage measurement electrode 24.
For example, when the bottom dross deposit height varies greatly (the measurement dynamic range is large), it is necessary to increase the distance between the current application electrodes 11 and 12. On the other hand, if the distance between the pair of voltage measurement electrodes is increased, the resolution (accuracy) of measurement of the voltage value (resistance value) by the voltage measurement electrode may be reduced. For this reason, a plurality of voltage measurement electrodes are provided between the current application electrodes 11 and 12 so that the voltage value (resistance value) between adjacent electrodes can be measured. Even when there is a large fluctuation, the amount of bottom dross deposited can be measured with high accuracy.

  Here, FIG. 14 shows an example of measurement results of voltage values ΔV1 to ΔV6 obtained between the adjacent electrodes in the voltage measurement electrodes 21 to 27. As shown in the figure, this example shows a result in which there is no clear difference in voltage values ΔV1 to ΔV6 obtained between adjacent electrodes. In such a case, it is determined that the boundary layer between the molten zinc and the bottom dross is wide, that is, the concentration change of the bottom dross is gradual. to decide.

  Also, the current applied between the current application electrodes can be a rectangular wave (step wave). When an electrode generates a thermoelectromotive force, it may appear as noise (such as drift) in the voltage value. In this case, the resistance value (bottom dross deposition height) cannot be measured with high accuracy due to the influence of noise. However, the influence of such noise can be prevented by making the current applied between the current application electrodes a rectangular wave (step wave).

  FIG. 15A shows a rectangular wave current applied between the current application electrodes 11 and 12 in the third embodiment. The current is, for example, a rectangular wave that changes by ± 1 (A). At this time, the voltage waveform that can be measured by the voltage measurement electrode (for example, two voltage measurement electrodes 21 and 22 in the case of the first embodiment) is as shown in FIG. In both the negative side and the initial stage (area A in the figure), a large fluctuation occurs due to the influence of the thermoelectromotive force and the like. Therefore, a difference value (for example, a difference between a smooth portion after rising on the positive side in the voltage waveform that can be measured by the voltage measuring electrode (B region in the figure) and a smooth portion after rising on the negative side in the voltage waveform (the C region in the same figure). ) (Corresponding to the offset δ shown in the figure), and the resistance value is calculated based on the difference value. Thereby, even when noise (drift, for example, offset OS shown simultaneously) occurs due to the thermoelectromotive force or the like at the beginning of the voltage waveform measured by the voltage measuring electrode (both plus and minus sides), The resistance value can be calculated based on the voltage value from which the influence of noise has been removed. As a result, the bottom dross deposition height can be detected with high accuracy.

  Further, the two probes can be provided with a current application electrode and a voltage measurement electrode separately. FIG. 16 shows the configuration of the probes 50 and 60. As shown in the figure, the current application electrode housing probe 50 includes two current application electrodes 51 and 52 at distant positions. On the other hand, a plurality of voltage measurement electrode probes 60 (seven in this example) are provided so as to be within the distance between the two current application electrodes 51 and 52 provided in the current application electrode housing probe 50. The voltage measuring electrodes 61 to 67 are provided. As shown in the figure, the current application electrode housing probe 50 and the voltage measurement electrode probe 60 are opposed to each other in the plating bath and between the current application electrodes 51 and 52 in the height direction. Voltage measuring electrodes 61 to 67 are positioned. When the current is applied between the current application electrodes 51 and 52 on the current application electrode storage probe 50 side, the voltage between the adjacent electrodes in the voltage measurement electrodes 61 to 67 is detected by the voltage measurement electrode probe 60. A value (resistance value) is measured (see the second embodiment). Thereby, for example, the state of the bottom dross can be measured three-dimensionally.

  In the description of this embodiment, the probe 1 and the control device 40 realize monitoring means for monitoring the deposition height of the deposit in the hot dip galvanizing bath, and the deposition height determination unit 42 of the control device 40. The elapsed days determination unit 43, the production amount determination unit 44, the final determination unit 45, the line operation determination unit 46, and the control unit 47 generate the deposit and / or the deposit based on the monitoring result of the monitoring unit. This realizes a means for suppressing the occurrence of defects due to deposits that suppress the adhesion of steel to steel plates. The current application electrodes 11 and 12 realize a current application electrode for applying a current in the hot dip galvanizing bath, and the voltage measurement electrodes 21 and 22 are applied by the current application electrode. The voltage measuring electrode for measuring the voltage generated by the current is realized, and the voltage measuring device 32 and the dross accumulation height detecting unit 41 of the control device 40 are based on the voltage value measured by the voltage measuring electrode. A deposit height estimating means for estimating the deposit height of the deposit is realized.

  Moreover, in this embodiment, the steel sheet is immersed in a hot dip galvanizing bath and passed through the hot dip galvanizing bath, so that the surface of the steel sheet is galvanized to produce a galvanized steel sheet. In the method, the electrical resistance value in the hot dip galvanizing bath is measured, the deposition height of the deposit in the hot dip galvanizing bath is estimated based on the measurement result, and the deposit is estimated based on the estimation result. The manufacturing method of the hot dip galvanized steel plate which manufactures a galvanized steel plate is implement | achieved, suppressing generation | occurrence | production of this and / or adhesion to the steel plate of this deposit.

It is a block diagram which shows the structure of the deposit height monitoring system of embodiment of this invention. It is a figure which shows the installation state of the probe in a plating bath. It is a figure which shows the structure of a probe. It is a figure which shows the electric circuit structure for measuring deposit height. It is a characteristic view which shows the relationship between the height from the plating bath bottom face where the bottom dross has settled, and resistance value. It is a flowchart which shows the process sequence of a control apparatus. It is a top view which shows the example of arrangement | positioning of the some probe within a plating bath. It is a flowchart which shows the process sequence of a hot-dip galvanized steel plate manufacturing system (manufacturing process). It is a characteristic view which shows an example of the relationship between the deposition height of bottom dross, and the defect incidence by bottom dross. It is a characteristic view which shows an example of the relationship between elapsed days and bottom dross deposit height. It is a characteristic view which shows an example of the relationship between a production amount and bottom dross accumulation height. It is a figure which shows the other structure of a probe. It is a figure which shows the example of the measurement result of the voltage value by the probe shown in FIG. It is a figure which shows the other example of the measurement result of the voltage value by the probe shown in FIG. It is a figure which shows the electric current of the rectangular wave applied between the electrodes for electric current application. It is a figure which shows the other structure of a probe. It is the figure used for description of the conventional manufacturing method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Probe, 2 Alarm output part, 11, 12 Current application electrode, 21, 22 Voltage measurement electrode, 31 Constant current source, 32 Voltage measuring device, 40 Control apparatus, 41 Dross accumulation height detection part, 42 Deposition height Determination unit, 43 Elapsed days determination unit, 44 Production amount determination unit, 45 Final determination unit, 46 Line operation determination unit, 47 Control unit, 102 Plating bath, 200 Bottom dross

Claims (12)

In the method for producing a hot dip galvanized steel sheet, the steel sheet is crushed in a hot dip galvanizing bath and passed through the hot dip galvanizing bath, and the galvanized steel sheet is produced by galvanizing the steel sheet surface.
The electrical resistance value in the hot dip galvanizing bath is measured, the height of the deposit in the hot dip galvanizing bath is estimated based on the measurement result, and the generation of the deposit is based on the estimated result. A method for producing a hot-dip galvanized steel sheet, comprising producing a galvanized steel sheet while suppressing adhesion of the deposit to the steel sheet.   The electrical resistance value is measured at a plurality of locations in the horizontal direction in the hot dip galvanizing bath, and the deposition height of the deposit is estimated based on the measurement result. Manufacturing method of hot dip galvanized steel sheet.   The method for producing a hot-dip galvanized steel sheet according to claim 2, wherein the accumulated height of the deposit is estimated by weighting electrical resistance values measured at the plurality of locations.   Decreasing the sheet passing speed of the steel sheet, increasing the temperature of the hot dip galvanizing bath, increasing the pressing amount of the support roll in the hot dip galvanizing bath, zinc ingot to the hot dip galvanizing bath The generation of the deposit and / or the adhesion of the deposit to the steel plate is suppressed by performing at least one of increasing the charging interval time. A method for producing the hot dip galvanized steel sheet according to item 1.   The process which suppresses generation | occurrence | production of the said deposit and / or adhesion to the steel plate of the said deposit when the predetermined period has passed since the removal of the latest deposit is characterized by the above-mentioned. The manufacturing method of the hot dip galvanized steel plate of any one of these.   6. When producing a predetermined amount of hot-dip galvanized steel sheet, a process for suppressing generation of the deposit and / or adhesion of the deposit to the steel sheet is performed. A method for producing the hot dip galvanized steel sheet according to item 1. A deposit height monitoring device in a hot dip galvanizing bath for monitoring a deposit height in a hot dip galvanizing bath through which the steel plate is passed in order to galvanize the steel plate surface,
Monitoring means for monitoring the height of deposits in the hot dip galvanizing bath;
Based on the monitoring result of the monitoring means, the deposit generation and / or adhesion to the steel strip to suppress the occurrence of defects due to the deposit,
The monitoring means includes a current applying electrode for applying a current into the hot dip galvanizing bath, a voltage measuring electrode for measuring a voltage generated by the current applied by the current applying electrode, and the voltage measuring electrode. And a deposit height estimating means for estimating the deposit height of the deposit based on the voltage value measured in step (d).   The current application electrode and the voltage measurement electrode constitute one probe, and the deposition height estimating means arranges a plurality of the probes in a hot dip galvanizing bath for each probe. 8. The deposit height monitoring device in a hot dip galvanizing bath according to claim 7, wherein the deposit height of the deposit is estimated based on the obtained voltage value.   The deposit in the hot dip galvanizing bath according to claim 8, wherein the deposit height estimating means weights the voltage value obtained for each probe to estimate the deposit height of the deposit. Height monitoring device.   The means for suppressing the occurrence of defects due to the deposit is to lower the sheet passing speed of the hot dip galvanizing bath, to increase the temperature of the hot dip galvanizing bath, and to support the hot dip galvanizing bath in the bath. 10. The method according to claim 7, wherein at least one of increasing a pressing amount of a roll and increasing a charging interval time of a zinc ingot to the hot dip galvanizing bath is performed. Deposit height monitoring device in hot dip galvanizing bath.   The hot dip galvanizing bath according to any one of claims 7 to 10, wherein the means for suppressing the occurrence of defects due to deposits is performed when a predetermined period has elapsed since the last deposit removal. Inside sediment height monitoring device.   The deposit in the hot dip galvanizing bath according to any one of claims 7 to 11, wherein the means for suppressing the occurrence of defects due to the deposit is performed when a predetermined amount of hot dip galvanized steel sheet is produced. Height monitoring device.

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