KR20040006739A - Apparatus and method for controlling aluminum concentration in molten zinc pot of continuous hot dip galvanizing line - Google Patents

Abstract

PURPOSE: An apparatus and a method for controlling aluminum concentration in molten zinc pot of continuous hot dip galvanizing line are provided to control concentration of aluminum so that the recommended ingot is automatically injected into the molten zinc pot by estimating concentration of aluminum and recommending an ingot for maintaining a target aluminum concentration based on the estimated aluminum concentration. CONSTITUTION: The apparatus comprises a sensor(100) for detecting strip speed, plating pickup weight, strip lead-in temperature, strip thickness, strip width, plating pot temperature and plating pot level; a control means(200) for recommending the optimum ingot comprising aluminum content that is the nearest to the estimated aluminum concentration of the present plating pot and controlling injection of the recommended ingot by converting detection signals detected by the sensor(100) into digital signals respectively, calculating aluminum content flown out from the plating pot by dross formation, reaction layer formation and plating adhesion by numerical value model using the data, calculating aluminum content flown in the plating pot by compound ingot injected and estimating aluminum concentration of the present plating pot using the plating pot inflow aluminum content and plating pot outflow aluminum content; and an injection means(300) for automatically injecting the ingot recommended according to control of the control means(200) into the plating pot, wherein the control means(200) comprises signal conversion part(210), control part(220), screen display part(230), aluminum concentration operating part(240) and ingot recommendation/injection part(250).

Description

Aluminum concentration control device of molten zinc plating bath and its method {APPARATUS AND METHOD FOR CONTROLLING ALUMINUM CONCENTRATION IN MOLTEN ZINC POT OF CONTINUOUS HOT DIP GALVANIZING LINE}

The present invention relates to an apparatus for controlling the aluminum concentration of a hot dip galvanizing bath and a method thereof. In particular, the aluminum concentration, which is a major element in the plating bath, is predicted using a numerical model based on a mass balance equation. Based on the recommended ingot for maintaining the aluminum target concentration based on the control to automatically put into the plating bath, the aluminum concentration in the plating bath can be kept constant, thereby hot-dip galvanizing bath to ensure the plating quality always An aluminum concentration control apparatus and a method thereof.

In general, hot dip galvanizing is a continuous line in which zinc ingots are added to a plating bath and melted to plate zinc in molten state on the surface of steel sheets to produce galvanized steel sheets (GI) and galvanized steel sheets (GA). In this hot dip galvanizing process, aluminum is included in the combination ingot to ensure product surface quality and plating adhesion, and is added to the plating bath, and the aluminum concentration of the plating bath is variously determined according to the plating properties of the steel sheet to be produced. In addition, the aluminum in the plating bath reacts with iron of the steel sheet to form a thin reaction layer on the surface of the steel sheet, which inhibits the development of the zinc-iron alloy layer to improve plating adhesion. Aluminum also transforms and floats high-density lower DROSS into upper dross to facilitate removal.

However, excessive aluminum may also have a bad effect on the paintability and weldability of the steel sheet. Excessive dross in the plating bath degrades the surface quality of the product, so it is necessary to minimize the occurrence of dross in the production of high-quality products such as automobile exterior materials, and is the most effective way to reduce the occurrence of dross in the plating bath. The silver plating bath temperature and the concentration of aluminum are kept constant. As described above, since the aluminum concentration in the plating bath has a great influence on the surface quality of the steel sheet, it is necessary to appropriately adjust the aluminum concentration in the plating bath according to the demanded product, order plating amount, and steel sheet dimensions.

In the related art, the operator judges the aluminum concentration in the plating bath through periodic plating bath concentration analysis, and uses a combination ingot different in aluminum content into the plating bath for proper aluminum concentration control.

However, it is difficult to manage the aluminum concentration in the plating bath in response to the complicated changes of coils such as required products, order plating amount, steel plate dimensions, etc. according to the prior art, which relies on the empirical judgment of these workers. The analysis takes at least 4 hours, and there is a problem in that the analysis error is difficult to maintain the aluminum concentration in the plating bath in a certain range.

The present invention has been made to solve the above problems, and an object of the present invention is to predict the concentration of aluminum, which is a major element in the plating bath, using a numerical model based on the mass balance equation, The present invention provides an apparatus for controlling an aluminum concentration of a hot dip galvanizing bath and a method thereof, which automatically recommends an ingot for maintaining an aluminum target concentration and controls the automatic input to a plating bath.

Another object of the present invention is to provide an apparatus and method for controlling an aluminum concentration of a hot dip galvanizing bath which can maintain a constant aluminum concentration in the plating bath, thereby making the plating quality constant.

1 is a block diagram of an aluminum concentration control apparatus of a hot dip galvanizing bath according to the present invention.

Figure 2 is a conceptual diagram of the amount of aluminum change in the plating bath according to the present invention.

Figure 3 is a graph of the aluminum concentration change in the plating bath over time.

4 is a graph showing the plating liquid level change in the plating bath according to the elapsed time.

5 is a flow chart showing a method for controlling the aluminum concentration of the hot dip galvanizing bath according to the present invention.

Explanation of symbols on the main parts of the drawings

100: sensor 200: control device

210: signal conversion unit 220: control unit

230: screen display unit 240: aluminum concentration calculation unit

250: Ingok recommendation / input unit 300: input device

As a technical means for achieving the above object of the present invention, the present invention is a sensor means for detecting the steel plate speed, plating amount, steel sheet inlet temperature, steel plate thickness, steel plate width, plating bath temperature, plating bath level; The detection signal by the sensor means is converted into digital data, respectively, and by using the numerical model, the aluminum content flowing out of the plating bath by dross formation, reaction layer formation, and plating adhesion is calculated and inputted. The aluminum inflow to the plating bath is calculated by the combination ingot, and the aluminum concentration of the current plating bath is estimated using the plating bath inflow aluminum content and the outflow aluminum content, and the aluminum concentration of the current plating bath is estimated. Recommending an optimal ingot comprising an aluminum content approaching, and controlling means for controlling the input of the recommended ingot; It is characterized in that it provides an apparatus for controlling the aluminum concentration of the hot-dip galvanizing bath having a; injecting means for automatically introducing the recommended ingot to the plating bath under the control of the control means.

In addition, as another technical means for achieving the above object of the present invention, the present invention is to collect the steel grade, steel plate speed, plating amount, steel plate inlet temperature, steel plate thickness, steel plate width, plating bath temperature, plating bath level data First step; Calculate the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating adhesion by using the numerical model, and calculate the content of aluminum flowing into the plating bath by the combined ingot. Calculating and calculating the aluminum concentration of the current plating bath by using the plating bath inflow aluminum content and the outflow aluminum content; A third step of recommending an optimal ingot comprising an aluminum content closest to the predicted aluminum concentration of the current plating bath; It is characterized by providing a method for controlling the aluminum concentration of the molten zinc plating bath having a fourth step of automatically introducing the recommended ingot to the plating bath.

Hereinafter, with reference to the accompanying drawings, the aluminum concentration control apparatus of the hot dip galvanizing bath according to the present invention will be described in detail the configuration and operation.

1 is a block diagram of an aluminum concentration control apparatus of a hot dip galvanizing bath according to the present invention. Referring to FIG. 1, the aluminum concentration control apparatus of the hot dip galvanizing bath according to the present invention is characterized in that the steel sheet speed, plating amount, and steel sheet pulling temperature are shown. And the sensor means 100 for detecting the steel plate thickness, the steel plate width, the plating bath temperature and the plating bath level, and the detection signals of the sensor means 100 are converted into digital data, respectively, Calculate the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating adhesion, and calculate the amount of aluminum flowing into the plating bath by the combined ingot added; The outflow aluminum content is used to predict the aluminum concentration of the current plating bath, so that the aluminum closest to the predicted aluminum concentration of the current plating bath is It is recommended that the optimum ingot containing the content, the control means 200 for controlling the input of the recommended ingot, and the input means for automatically feeding the recommended ingot to the plating bath under the control of the control means 200 ( 300).

The sensor means 100 includes a steel plate speed sensor installed at the steel plate inlet of the plating bath, a plating weight sensor installed at the steel plate outlet of the plating bath, a steel plate inlet temperature sensor provided at the inlet of the plating bath, and an inlet of the plating bath. And a steel plate thickness sensor provided at the inlet, a steel plate width sensor provided at the inlet of the plating bath, a plating bath temperature sensor installed in the plating bath, and a plating bath level sensor provided in the plating bath to detect the plating liquid level.

The control means 200 is a signal conversion unit 210 for converting the detection signal by the sensor means 100 into digital data, respectively, and the aluminum concentration of the plating bath using the data from the signal conversion unit 210 A control unit 220 for controlling the prediction, controlling the recommendation of the ingot corresponding to the aluminum concentration of the predicted plating bath, controlling the input of the recommended ingot, and controlling the screen display of data generated in this process; A screen display unit 230 for outputting a screen including detection data, aluminum concentration prediction of the plating bath, and data related to aluminum concentration control of the plating bath according to the control of the control unit 220; Using the data from 210, a numerical model is used to calculate the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating deposition, and The aluminum concentration calculator 240 calculates the amount of aluminum introduced into the plating bath by the combination ingot, and the plating bath inflow aluminum content and the outflow aluminum content calculated by the aluminum concentration calculator 240 are used to determine the current content of the plating bath. Ingot recommendation / injection that predicts aluminum concentration, recommends an optimal ingot containing the aluminum content closest to the predicted aluminum concentration of the current plating bath, and provides an ingot input signal corresponding to this recommended ingot. 250.

The control unit 220 of the control means 200 stores the steel sheet type, that is, steel grade data in advance in the internal memory, which may be directly input by the operator, or may be downloaded through other communication means.

2 is a conceptual diagram of the aluminum change calculation amount in the plating bath according to the present invention. Referring to FIG. 2, the aluminum (Al) concentration calculation unit 240 of the control means 200 uses the weight of the ingot and the Al concentration of the ingot. Calculate the plating bath inflow Al amount (AIN) and calculate the plating bath outflow Al amount (AOUT) by using the outflow Al amount by the steel plate plating amount, the outflow Al amount by the dross and the outflow Al amount by the reaction layer. The amount of aluminum change (AV = AIN-AOUT) inside the plating bath is calculated using the plating bath inflow Al amount (AIN) and the plating bath outflow Al amount (AOUT), and the Al conversion amount (AV) in the plating bath is calculated. Calculate the plating bath Al concentration change (AV%) according to

In addition, while the control unit 220 of the control means 200 monitors the plating bath level from the sensor means 100, if the plating bath level is lowered below the predetermined reference level due to the zinc bath zinc consumption, Configure to control the ingot input.

The feeding means 300 may include an ingot loading device for placing the corresponding ingot into the feeding position under the control of the control means 200, and an feeding device for feeding the ingot raised to the feeding position by the loading device. Can be.

3 is a graph showing a change in aluminum concentration in the plating bath with elapsed time, and FIG. 4 is a graph showing a change in plating solution level in the plating bath with elapsed time. 5 is a flowchart showing a method for controlling aluminum concentration of a hot dip galvanizing bath according to the present invention.

Operation of the preferred embodiment of the present invention configured as described above will be described in detail below based on the accompanying drawings.

According to the apparatus and method of the present invention, plating is received by a computer through measurement signals of plating bath peripheral variables such as steel grade, steel plate speed, plating amount, steel plate inlet temperature, steel plate thickness and width, plating bath temperature, and plating bath level (LEVEL). Predict the aluminum concentration in the bath using a numerical model, suggest the optimal ingot combination to reach the target aluminum concentration for the operator, and automatically manage the aluminum concentration in the plating bath by injecting the combination ingot automatically at the appropriate time. .

Referring to FIG. 5, first, in a first step S51, steel grade, steel sheet speed, plating weight, steel sheet inlet temperature, steel sheet thickness, steel sheet width, plating bath temperature, plating bath level data are collected, which is the sensor of FIG. 1. When each of the plurality of sensors of the means 100 detects the steel plate speed, plating amount, steel plate inlet temperature, steel plate thickness, steel plate width, plating bath temperature, plating liquid level of the plating bath to provide to the control means 200, the control means The signal converter 210 of 200 collects data necessary for hot-dip galvanizing of the steel sheet by converting the detection signal into a digital signal and providing the converted signal to the controller 220.

On the other hand, steel grades used in continuous zinc plating are generally low carbon steel hot rolled and cold rolled coils containing 0.3% or less of carbon. In particular, the most specific steel grade is the ultra low carbon steel cold rolled coil for forming. Since steel grade is basically a variable that cannot be recognized by the sensor, the method of recognizing steel grade in the present invention is based on the schedule of the day, and the new grades enter the network grade in the central management system of the site every time a new grade is entered. For example, a method of inputting a steel grade code into a system constructed in the present invention by handing it over to the system constructed in the present invention using TCP / IP, or whenever a person managing the operation enters a plating bath. to be. The steel plate speed, plating amount, steel sheet inlet temperature, steel plate thickness and width, plating bath temperature, and plating bath level (LEVEL) read analog signals in real time (approximately 5 seconds) from the sensor attached to the field line, Collected by the central management system and converted to a digital signal and delivered to the system built in the present invention in real time (about 5 seconds intervals) using a network (for example TCP / IP).

Next, in the second step (S52), by using a numerical model, the aluminum content flowing out of the plating bath by dross formation, reaction layer formation, and plating adhesion is calculated using a numerical model, and the combination ingot is introduced. By calculating the content of aluminum flowing into the plating bath, the aluminum concentration of the current plating bath is predicted by using the plating bath inflow aluminum content and the outflow aluminum content.

In this regard, referring to FIG. 1, the control unit 220 of the control unit 200 of the present invention controls the aluminum concentration prediction of the plating bath by using the data from the signal converting unit 210, and predicts. It controls the recommendation of the ingot corresponding to the aluminum concentration of the plated bath, controls the input of the recommended ingot, and controls the screen display of the data generated in this process.

The aluminum concentration calculator 240 of the control means 200 forms a dross by using a numerical model based on a material balance equation using data from the signal converter 210 under the control of the controller 220. In addition, the aluminum content flowing out of the plating bath by the reaction layer formation and plating adhesion is calculated, and the content of aluminum introduced into the plating bath is calculated by the combined ingot.

In more detail, first, the aluminum concentration calculator 240 of the control means 200 calculates the inflow Al amount AIN of the plating bath according to Equation 1 using the weight of the ingot and the Al concentration of the ingot. Calculate In other words, in order to predict the Al concentration of the plating bath, the amount of Al entering the plating bath and the amount of Al out of the plating bath must be calculated. The mass balance of Al in the plating bath can be calculated as follows.

Here, Al is aluminum, the ingot weight is always constant at about 1 ton, and the ingot Al concentration and type are predetermined in several ways (for example, 0.0%, 0.5%, 1.0%, 1.5% and 2.0%).

Next, the amount of Al outflow of the plating bath may be calculated as the sum of the following three, that is, the amount of steel plate plating, the dross and the reaction layer, and the dross is Fe out of the steel sheet and Zn of the plating bath. It means an intermetallic compound particle formed by this reaction. And it is known that dross contains a considerable amount of Al. Next, the reaction layer means a thin Fe—Al intermetallic compound layer formed between the steel sheet and the Zn plating layer. In this case, it is basically assumed that the deposition amount of the steel sheet contains Al at the same concentration as the Al concentration of the plating bath and is discharged out of the plating bath.

In this case, the amount of outflow Al by the amount of the plated steel plate, the amount of outflow Al by the dross and the amount of outflow Al by the reaction layer are respectively calculated according to Equation 2 below. Calculate the amount of Al outflow plating bath (AOUT) accordingly.

Here, the dross generation amount per unit area, the dross Al concentration, the reaction layer formation amount per unit area, and the reaction layer Al concentration, respectively, cannot be detected by the sensor, and the dross generation amount per unit area is the plating bath Al concentration by using a model experiment. The dross Al concentration is obtained as a function of the plating bath Al concentration as a function of the plating bath temperature, the steel sheet inlet temperature, the steel sheet speed, and the steel grade, and the reaction layer generation amount per unit area is the plating bath Al concentration, the plating bath temperature, and the steel sheet. The reaction layer Al concentration is obtained as a function of the plating bath Al concentration as a function of the draw temperature, the steel sheet speed, and the steel grade.

Next, using the plating bath inflow AL amount (AIN) obtained according to Equation 1 and the plating bath outflow Al amount (AOUT) obtained according to Equation 3, the inside of the plating bath according to Equation 4 below. The amount of aluminum change is calculated, and then the plating bath Al concentration change (AV%) according to the Al conversion amount AV inside the plating bath determined by the following equation (4) is calculated according to the following equation (5).

Next, a third step (S53) recommends an optimal ingot including an aluminum content that is closest to the aluminum concentration of the current plating bath, which is previously predicted. Referring to FIG. 1, the control means 200 will be described. Ingok recommendation / input unit (250) of the present invention predicts the aluminum concentration of the current plating bath by using the plating bath inflow aluminum content and the outflow aluminum content calculated by the aluminum concentration calculation unit 240, the current plating An optimal ingot is recommended that contains the aluminum content closest to the aluminum concentration of the bath. That is, the optimum ingot combination for reaching the target aluminum concentration is recommended using the numerical model described above by receiving the material information of the coil to be worked.

In the fourth step (S54, S55), the recommended ingot is automatically introduced into the plating bath, which causes zinc in the plating bath to be consumed so that the plating bath level drops below a certain value, and the plating bath level gauge signals the heavy-duty treatment apparatus. When sent, the central processing unit sends a signal to the ingot input device to automatically feed the recommended ingot to the plating bath to control the plating bath aluminum concentration.

According to the present invention, the Al concentration of the current plating bath is calculated using the above-described formula model, and if there is a plating bath Al concentration targeted by the operation manager, the amount of Al necessary to make the Al concentration of the current plating bath as the target value is determined. The combination ingot (eg, 0.0, 0.5, 1.0, 1.5, 2.0% Al) containing Al nearest to the calculation is selected and placed on a loading apparatus for ingots in the plating bath. On the loading device, the field worker can directly load the selected combination ingot by using a forklift truck, or the ingot can be automatically selected and loaded on the loading device by a crane. The ingot placed on the loading device is automatically put into the plating bath when the level of the plating bath falls below the standard.

On the other hand, the screen display unit 230 of the control means 200 of the present invention controls the aluminum concentration of the plating bath, including the detection data, the aluminum concentration prediction of the plating bath, the recommended ingot under the control of the controller 220. Outputs the relevant data screen.

FIG. 3 compares the concentration of aluminum in the plating bath with the concentration of aluminum in the plating bath measured through chemical analysis as an example of calculation results obtained using the collected field measurement signals and the numerical model described above. . Overall, the calculated results track the change of the experimental value well, and the difference between the calculated value and the experimental value is not large. Therefore, the numerical model described above is reliable in predicting the plating bath aluminum concentration.

Fig. 4 compares and shows changes in the plating bath level before and after introducing the method of automatically injecting the ingot by treating the plating bath level with the measurement signal of the gauge of the level. After using the plating bath level as a measurement signal, it can be seen that the width of the plating bath level changes with time earlier than before.

According to the present invention described above, by real-time prediction of the plating bath aluminum concentration by the numerical model, recommendation of the combination of the ingots and automatic injection of the ingots, the target aluminum concentration for each working mode can be kept constant so that high-grade zinc plating such as automobile exterior materials In the production of steel plate (GI) and galvanized steel sheet (GA), it is possible to reduce the amount of dross that causes surface defects and to improve productivity by reducing the work load of the operator by utilizing the ingot automatic injection function. have.

According to the present invention as described above, an ingot for predicting the concentration of aluminum, which is a major element in the plating bath, by using a numerical model based on the mass balance equation, and maintaining the aluminum target concentration based on the predicted aluminum concentration. By recommending the control to automatically put into the plating bath, it is possible to maintain a constant aluminum concentration inside the plating bath, thereby to ensure the plating quality at all times.

In other words, in contrast to the method of controlling the aluminum concentration of the plating bath according to the subjective experience and judgment of the operator, it is not possible to cope with the change of the operation variables such as the steel sheet dimension, the adhesion plating amount, the steel sheet inlet temperature and the steel sheet speed in the existing process. By real-time prediction of plating bath aluminum concentration, recommendation of ingots, and automatic injection of ingots, it is possible to maintain the target aluminum concentration in each work mode. Therefore, high-quality galvanized steel sheets (GI) and galvanized steel sheets (GA) ) It can reduce the amount of dross that causes surface defects during production, and it can improve productivity by reducing the worker's workload by utilizing ingot automatic injection function.

The above description is only a description of specific embodiments of the present invention, and the present invention is not limited to these specific embodiments, and various changes and modifications of the configuration are possible from the above-described specific embodiments of the present invention. It will be apparent to those skilled in the art to which the present invention pertains.

Claims (8)

Sensor means (100) for detecting the steel sheet speed, plating amount, steel sheet inlet temperature, steel sheet thickness, steel sheet width, plating bath temperature, plating bath level; Convert the detection signal by the sensor means 100 into digital data, and calculate the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating adhesion by numerical model using these data. The aluminum content of the plating bath is estimated by using the ingot aluminum content and the outflow aluminum content, and the aluminum content of the current plating bath is estimated. A control means 200 for recommending an optimal ingot comprising an aluminum content closest to the concentration, and controlling the input of this recommended ingot; Injecting means for automatically injecting the recommended ingot into the plating bath according to the control of the control means 200; Aluminum concentration control device of the hot-dip galvanizing bath characterized in that it comprises a. The method of claim 1, wherein the sensor means 100 A steel plate speed sensor installed at the steel plate inlet of the plating bath; A plating adhesion sensor installed at the steel plate outlet of the plating bath; Steel plate inlet temperature sensor installed at the inlet of the plating bath; A steel plate thickness sensor installed at the inlet of the plating bath; A steel plate width sensor installed at the inlet of the plating bath; A plating bath temperature sensor installed in the plating bath; And a plating bath level sensor installed in the plating bath to detect the plating liquid level. The method of claim 1, wherein the control means 200 A signal converter 210 for converting the detection signal of the sensor means 100 into digital data, respectively; Controlling the aluminum concentration prediction of the plating bath using the data from the signal conversion unit 210, controlling the recommendation of the ingot corresponding to the aluminum concentration of the predicted plating bath, and controlling the input of the recommended ingot. A controller 220 for controlling a screen display of data generated in this process; A screen display unit 230 for outputting a screen including detection data, aluminum concentration prediction of the plating bath, and data related to aluminum concentration control of the plating bath under the control of the controller 220; Using the data from the signal conversion unit 210, by using a numerical model, the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating adhesion is calculated, and the combined ingot is added to the plating bath. An aluminum concentration calculator 240 for calculating the amount of aluminum introduced; The aluminum concentration of the current plating bath is predicted using the plating bath inflow aluminum content and the outflow aluminum content calculated by the aluminum concentration calculation unit 240, and includes the aluminum content that is closest to the aluminum concentration of the current plating bath. An ingot recommendation / injection unit 250 which recommends an optimal ingot to provide an ingot input signal corresponding to the recommended ingot; Aluminum concentration control device of the hot dip galvanizing bath comprising a. According to claim 3, wherein the aluminum concentration calculation unit 240 of the control means 200 Using the weight of the ingot and the AL concentration of the ingot, calculate the amount of AL in the plating bath (AIN), The outflow AL amount (AOUT) of the plating bath is calculated by using the outflow AL amount by the steel plate plating amount, the outflow AL amount by the dross and the outflow AL amount by the reaction layer, Calculate the aluminum change amount (AV = AIN-AOUT) inside the plating bath by using the plating bath inflow AL amount (AIN) and the plating bath outflow AL amount (AOUT), The aluminum concentration control device of the hot dip galvanizing bath, characterized in that for calculating the plating bath AL concentration change (AV%) according to the AL conversion amount (AV) in the plating bath. According to claim 3, wherein the control unit 220 of the control means 200 While monitoring the plating bath level from the sensor means 100, when the plating bath level falls below a predetermined reference level due to the zinc consumption of the plating bath, the ingot injection is controlled. Aluminum concentration controller. A first step of collecting steel grade, steel sheet speed, plating deposition amount, steel sheet pulling temperature, steel sheet thickness, steel sheet width, plating bath temperature, plating bath level data; Calculate the aluminum content flowing out of the plating bath by dross formation, reaction layer formation and plating adhesion by using the numerical model, and calculate the content of aluminum flowing into the plating bath by the combined ingot. Calculating and calculating the aluminum concentration of the current plating bath by using the plating bath inflow aluminum content and the outflow aluminum content; A third step of recommending an optimal ingot comprising an aluminum content closest to the predicted aluminum concentration of the current plating bath; And a fourth step of automatically adding the recommended ingot to the plating bath. The method of claim 6, wherein the second step (S52) Using the weight of the ingot and Al concentration of the ingot, calculate the amount of Al in the plating bath (AIN), The outflow Al amount (AOUT) of the plating bath is calculated by using the outflow Al amount by the steel plate plating amount, the outflow AL amount by the dross and the outflow Al amount by the reaction layer, Calculate the aluminum change amount (AV = AIN-AOUT) inside the plating bath l using the plating bath inflow Al amount (AIN) and the plating bath outflow Al amount (AOUT), A method for controlling the aluminum concentration of the hot dip galvanizing bath, characterized in that the plating bath Al concentration change (AV%) is calculated according to the Al conversion amount (AV) in the plating bath. The method of claim 6, wherein the fourth step (S54, S55) is Plating bath When zinc is consumed and the plating bath level drops below a certain level and the plating bath level gauge sends a signal to the heavy equipment, the central processing unit sends a signal to the ingot input device and automatically puts the recommended ingot into the plating bath. A method for controlling the aluminum concentration of a hot dip galvanizing bath, characterized in that the bath aluminum concentration is controlled.