KR100578479B1 - Control method of aluminum uniform concentration in hot dip galvanizing tank - Google Patents

Abstract

The present invention relates to a method for more uniformly managing the Al concentration in the plating bath, comprising: providing an Al concentration measuring sensor in the hot dip galvanizing bath and measuring the Al concentration of the hot dip galvanizing bath in real time; Calculating a difference between the measured value and an Al concentration target value of the hot dip galvanizing bath when the value is measured; After calculating the target difference of the Al concentration, the Zn consumption amount by plating is (double-sided plating amount) * W * L and Al consumption amount by plating is (0.3104 + 0.00199 * two-sided plating amount) * W * L, Predict Zn consumption by (6.622 + 0.0001 * two-sided plating) * W * L and Al consumption by dross to (0.0265 + 0.0001 * two-sided plating) * W * L, respectively, and calculate the target difference value and the Zn Selecting zinc ingots necessary to maintain the Al concentration target value using Al consumption prediction values; Calculating an amount of the zinc ingot into the hot dip galvanizing tank in consideration of the line speed of the hot dip galvanizing steel sheet; When the input amount of zinc ingot considering the line speed is calculated, it is a step of quantitatively injecting it into the molten zinc plating tank.

Hot dip galvanizing, Hot dip galvanizing bath, Al concentration measuring instrument, Al concentration

Description

Aluminum uniformity concentration control method of Hot zinc dipping pot

1 is a process chart showing a general hot dip galvanized steel sheet production process

2 is a state diagram showing a process for generating dross in a hot dip galvanizing tank;

3 is a schematic diagram of a state in which the Al measuring device according to the present invention is installed in the hot dip galvanizing tank

4 is a graph showing the Al concentration correction coefficient according to the present invention

5 is a graph showing the derivation of the Al concentration correction equation according to the present invention

6 is a graph showing the relationship between the plating amount and Al deposition amount according to the present invention

※ Description of main parts of drawing *

10: payoff reel 11: annealing furnace

12: plating tank 13: sink roll

14: air knife 15: cooling table

16: Top Roll 17: Top Dross

18: Bar Top Dross 20: Al measuring instrument

21: thermometer 22: holder

23: pole 24: support frame

25: signal conditioner 26: converter

27: Selection box 28: Data collection and conversion meter

29: computer

The present invention relates to a method for controlling the uniformity of aluminum in a hot dip galvanizing bath, and more particularly, a small amount of aluminum is mixed with zinc in the plating bath when the hot dip galvanized steel sheet is manufactured. To solve the defects of hot-dip galvanized steel sheet due to aluminum and to produce high-quality hot-dip galvanized steel sheet.

Al concentration control of the hot dip galvanizing bath (hereinafter referred to as "plating bath") and plating layer for producing hot dip galvanized steel sheet has an important effect on the quality characteristics of hot dip galvanized steel sheet. To produce ash;

In the production of strict material, constant concentration control (deviation reduction) inside the plating bath is required, but now concentration adjustment is done by injecting zinc ingots according to the experience and judgment of the operator, so there is a difference in work patterns and the same work mode. There existed a problem that the deviation width was not constant even inside.

The large increase or decrease of Al concentration in the plating bath increases the occurrence of TOP DROSS, and when such dross is attached to the sink roll surface, it causes steel sheet surface defects. Therefore, in this respect, optimization of Al concentration deviation management and automation thereof are required.

In this regard, there is currently automatic application of molten zinc plating bath ingot of patent application No. 1998-58123, but this method ignores the concentration of Al in the initial plating bath, which takes about 1 hour for analysis in wet analysis. Therefore, although the Al concentration changes during that time, when the ingot is actually put in automatically, the fluctuation range of Al appears large, so the reliability is very low.

In addition, when the above method was adopted, the correlation between Al deposition amount in the coated steel sheet was applied (0.4875 + 0.0014) × double-sided plating amount, which is neglected from the change of Al concentration in the initial plating bath. Appears large.

Hot-dip galvanized steel sheet, as shown in Figure 1, unwind the cold rolled steel (S), and the heat treatment through an annealing furnace (11), which is collected in the pay off reel (PAY OFF RILL (10)) to make the desired material and zinc is 460 ℃ The coating roll 12 is wound around the sink roll 13 of the plating bath 12 which is heated to a molten state and passed through the plating bath 12, and the plating amount is controlled by the air pressure 14 of the upper air knife 14, and the cooling stand 15 After passing through the top roll 16, it is commercialized.

In the plating bath 12, a small amount of aluminum is mixed to improve the glossiness of the steel sheet and the driveability of the sink roll 13 in addition to pure zinc. In this case, if the amount of aluminum is too high, the plating bath is shown in FIG. The supersaturated aluminum in (12) reacts with Fe in the steel sheet to form a compound of Fe ₂ A1 ₅ .

Since the compound has a small specific gravity, the compound floats on the surface of the water, which is called TOP DROSS (17). On the contrary, when the Al concentration is low, the compound formation amount of FeZn ₇ increases, which is due to the high specific gravity. He accumulates on the bottom of the jaw (12), so he is called BOTTOM DROSS (18).

Attached to the sink roll 13 or the surface of the steel sheet damages the appearance of the surface, thereby causing a fatal damage to the quality. Therefore, in the manufacture of hot-dip galvanized steel sheet, there is an urgent need for the development of a technology that maintains the Al concentration of 0.200 ± 0.002wt%. However, until now, the Al concentration in the plating bath 12 has been changed by using a spatula-shaped device. After collecting the zinc bath in), a double Al concentration was analyzed by wet analysis, and in this state, an operator arbitrarily selected zinc ingot and put it into the plating bath by experience and judgment.

In this way, the Al concentration was about 0.10 wt%, and the Al concentration was very nonuniform, resulting in deterioration of driveability or excessive dross generation of sink rolls, and it took more than 30 minutes to perform wet analysis. Concentrations continued to change, requiring rapid response.

In addition, there are various zinc ingots, each of which can be selected according to the state of the plating bath by varying the Al concentration. Here, there are five types of zinc ingots, as shown in Table 1 below. Once the Al concentration is confirmed, the zinc ingot has been selected and adjusted according to the experience and judgment of the worker in order to meet the target Al concentration. Could not.

Table 1

division No. 2 No. 3 No. 4 No. 5 Pure Zinc AL concentration 0.30 ± 0.04 0.40 ± 0.04 0.60 ± 0.04 0.80 ± 0.04 Less than 0.002

The present invention has been invented to solve the above problems in view of the above problems, the purpose of which is to monitor the Al concentration in the plating bath in real time to analyze the amount of Al and analyze the amount of Zn, Al in the plating layer and dross to be consumed for each plating amount By developing a relationship model, we have secured the technology to make the Al concentration more uniform in the plating bath to solve the defects of the hot-dip galvanized steel sheet, and to provide high quality hot-dip galvanized steel sheet. .

Referring to the technical configuration of the molten zinc plating bath aluminum uniform concentration management method of the present invention for achieving the above object is as follows.

The present invention provides a method for managing a uniform concentration of aluminum in a hot dip galvanizing bath, comprising: preparing an Al concentration measuring sensor in a hot dip galvanizing bath and measuring the Al concentration of the hot dip galvanizing bath in real time; Calculating a difference between the measured value and an Al concentration target value of the molten zinc plating bath when the Al concentration value is measured in real time; After calculating the target difference of the Al concentration, the Zn consumption amount by plating is (double-sided plating amount) * W * L and Al consumption amount by plating is (0.3104 + 0.00199 * two-sided plating amount) * W * L, Predict Zn consumption by (6.622 + 0.0001 * two-sided plating) * W * L and Al consumption by dross to (0.0265 + 0.0001 * two-sided plating) * W * L, respectively, and calculate the target difference value and the Zn Selecting zinc ingots necessary to maintain the Al concentration target value using Al consumption prediction values; Calculating an amount of the zinc ingot into the hot dip galvanizing tank in consideration of the line speed of the hot dip galvanizing steel sheet; When the input amount of zinc ingot considering the line speed is calculated, it is a step of quantitatively injecting it into the molten zinc plating tank.

Referring to the accompanying drawings, the molten zinc plating bath aluminum uniform concentration management method of the present invention having such characteristics will be described in detail as follows.

3 is a schematic diagram of a state in which the Al measuring instrument according to the present invention is installed in the molten zinc plating bath, Figure 4 is a graph showing the Al concentration correction coefficient according to the present invention, Figure 5 shows the derivation of the Al concentration correction equation according to the present invention 6 is a graph showing the relationship between the plating amount and the Al deposition amount according to the present invention.

The present invention first measures the Al concentration in the plating bath 12 in real time, the method of measuring the Al concentration in real time, as shown in Figure 3, the Al meter 20 and the thermometer 21 and the holder 22 and Supported by the pole 23 and was connected to the ground using a support frame (24).

The Al measurer 20 is amplified by the signal conditioner 25, the measured voltage value of the thermometer 21 is converted to Celsius by the converter 26 and the signal conditioner 25 and the converter 26 It is housed in the selection box 27.

Each of the measured values is converted into the following relation by the data acquisition board 28 and displayed on the screen of the computer 29, and these values are transmitted by the operator.

(-) Pole AI (S) │ NaCI (S) + (NaCI + AIC13) (L) │ Al (in plating bath) (l) (+) pole

The concentration of AL is based on the Al shade cell consisting of NaCl-AlCl ₃ -based electrolyte saturated with solid NaCl, and its cell structure is as follows.

Since the amount of Al in a Zn-Al plating bath is aAl (Zn-Al), the electromotive force of this shade battery is E = -RT / 3F × ln (wt% Al) + Constant

Where E is the volt

       R: Gas constant (8,3,144 J)

       F: Faraday constant (96487 C)

E = -RT / 3F × LnaAl (Zn-Al) + C, which measures the electromotive force and temperature T (K) of this sensor, where C is the correction factor and the function of the correction factor and temperature, As shown in C = -0.004756T-9.078 and derived from numerous experiments, it shows the precision of Al concentration in the plating bath and is an important data source in selecting zinc ingot.

Al calculated as the voltage is again measured in real time when the experiment to convert the concentration to the concentration is automatically monitored in real time, the correlation with the wet analysis value as shown in FIG. Alternative analysis is possible.

As a model that can automatically select zinc ingot in the next two stages, this predictive model is based on measfloor balance, and when zinc ingot is added by the amount of Zn and Al consumed by plating and the amount removed by dross The amount of Zn and Al in the tank is always constant.

Therefore, if the amount of zinc and Al coated on the steel sheet can be predicted, it is possible to inject zinc ingots as much as the consumption amount at an appropriate point, thereby maintaining the appropriate plating bath level.

In addition, the Zn consumption and Al consumption escaping to the plating adhesion and dross are predicted as shown in Table 2 below through the regression analysis of the relationship between the order plating amount and Zn consumption and Al consumption through wet analysis based on experiment and specimen analysis data. Got. The constants of the above-described prediction equations are not simply calculated in consideration of the order plating amount, but comprehensively include the amount of galvanized steel sheet to be continuously operated, the size and thickness of the steel sheet, and thus the plating amount and the line speed of the steel sheet in the plating bath. Is considered. For example, the steel sheet to be galvanized is all different in size, thickness, plating amount, etc. according to its use, and accordingly, the line speed passing through the plating bath also varies by operation. Al has a high reactivity with Fe, which is a major component of the steel sheet, and therefore, when the line speed is fast, the area of contact with Fe increases and reacts rapidly. Therefore, Al consumption is higher than the same time when the line speed is slow. The following formulas are optimized to predict Al consumption in the smallest error range through repeated experiments considering all factors that can be changed according to the zinc plating operation.

Table 2

division Item Prediction Remarks Plated Zn consumption   (Double Sided Plating) * W * L Al consumption   (0.3104 + 0.00199 * Double Sided Plating) * W * L 6 Dross Zn consumption   (6.622 + 0.023 * 2-sided plating amount) * W * L Al consumption   (0.0265 + 0.0001 * 2-sided plating amount) * W * L

Based on the above equation, the prediction point of zinc injecting is calculated. When the Zn content and Al content are calculated by dividing the amount of Zn into 5㎡, the zinc in which the deviation value between OUT-PUT and IN-PUT is minimum is selected as the optimal zinc ingot. Input instruction at the time of one consumption. The series of operations are automatically calculated and controlled by the central control computer.

Hereinafter, a description will be given of the molten zinc plating bath aluminum uniform concentration management method of the present invention by way of examples.

(Example)

After the work plan for the hot-dip galvanizing of cold rolled steel sheets with the material thickness of 0.5 ~ 2.0mm and the width of 910 ~ 1830mm to 60 ~ 600g / m2 respectively, the Al prediction program was applied directly to the field line.

After transferring the current work instruction unit to the central control computer, the program was started and the zinc ingot was automatically injected by the Al prediction program, and the Al concentration value after the zinc ingot injection based on the operator's experience was compared with the analytical practice performance value. .

As a result of the analysis, it was possible to manage Al uniform concentration by comparing the Al prediction value and the Al analysis value of the actual plating tank sample. On the basis of the Al concentration analyzed in real time, an automatic selection model of zinc ingot was developed. The development was achieved to save the Al concentration analysis time by the manual operation and to minimize the deviation.

As described above, the present invention measures the Al concentration of the hot dip galvanizing bath in real time, calculates a difference between the measured value and the Al concentration target value of the hot dip galvanizing bath, selects a zinc ingot corresponding to the Al concentration target, and selects the zinc ingot. After considering the line speed of the plated steel sheet, calculate the amount to be injected into the hot dip galvanizing bath and quantitatively inject it into the hot dip galvanizing bath to uniformly manage the Al concentration of the hot dip galvanizing bath to solve the problem of conventional hot dip galvanized steel sheet It has the unique effect of eliminating defects and producing high quality hot dip galvanized steel sheet.

Claims (1)

Providing an Al concentration measuring sensor in the hot dip galvanizing bath and measuring the Al concentration of the hot dip galvanizing bath in real time; Calculating a difference between the measured value and an Al concentration target value of the molten zinc plating bath when the Al concentration value is measured in real time; After calculating the target difference of the Al concentration, the Zn consumption amount by plating is (double-sided plating amount) * W * L and Al consumption amount by plating is (0.3104 + 0.00199 * two-sided plating amount) * W * L, Predict Zn consumption by (6.622 + 0.0001 * two-sided plating) * W * L and Al consumption by dross to (0.0265 + 0.0001 * two-sided plating) * W * L, respectively, and calculate the target difference value and the Zn Selecting zinc ingots necessary to maintain the Al concentration target value using Al consumption prediction values; Calculating an amount of the zinc ingot into the hot dip galvanizing tank in consideration of the line speed of the hot dip galvanizing steel sheet; When the amount of the zinc ingot considering the line speed is calculated, the step of quantitatively injecting it into the hot dip galvanizing bath; Aluminum uniform concentration management method of the hot dip galvanizing tank comprising a.

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