JPS5810480B2 - Method for controlling electrical conductivity of electroplating bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for maintaining high electrical conductivity of a plating bath during electroplating of steel plates and the like.

Conventionally, methods have been used to reduce the consumption of electric power used for plating by adjusting the electrical conductivity in an electroplating bath to be high.

To adjust the electrical conductivity, add sodium sulfate (Na2SO,
) is commonly added to the plating bath liquid. However, as the days pass, the sodium sulfate that is added to the plating bath liquid flows out, the concentration decreases, and the power consumption increases, so it may take several days. A method is used in which a fixed amount of Glauber's salt is added at regular intervals.

Regarding the adjustment of mirabilite, there is a problem that if the content of mirabilite is too high, it will adhere to the surface of the plated steel sheet and impair the quality of the steel sheet, and if the content is too low, the electrical conductivity will decrease and power consumption will increase.

This invention proposes a control method to ideally manage the electrical conductivity of the electroplating bath by considering the balance between the quality of the steel sheet and the power consumption. This method is characterized by measuring temperature and hydrogen ion concentration, and controlling the amount of electrical conductivity regulator added based on these measured values.

The present inventors have conducted various studies on the electrical conductivity in the electroplating bath solution for steel sheets. As a result, the electrical conductivity in the bath solution depends on the concentration of Glauber's salt during the night, the temperature of the bath solution, and the hydrogen ion concentration (PH) of the bath solution. I found that there was a big change.

FIGS. 1, 2, and 3 are diagrams showing how the concentration of mirabilite in the bath liquid changes, and how the electrical conductivity in the liquid changes depending on temperature and hydrogen ion concentration (PH).

The horizontal axis is the passage of time, and the vertical axis is the electrical conductivity in the bath liquid.
These are liquid temperature and hydrogen ion concentration.

In the figure, curve a is the change curve of electrical conductivity, curve 2 is the temperature curve of the bath liquid, and curve C is the hydrogen ion concentration 1 (
PH) change curve.

In Figure 1, electrical conductivity curve a shows the state of the bath solution containing mirabilite when mirabilite was added to the bath solution after approximately 1.4 hours. This shows that the electrical conductivity at night changes to 399/l with the addition of Glauber's salt.

In Figure 2, the hydrogen ion concentration curve C of the liquid shows the electrical conductivity curve a when the pH value is lowered from 2.7 to 2.3 after about 50 minutes, and the lower the hydrogen ion concentration, the more electrical conductivity. The conductivity is shown to increase.

Furthermore, FIG. 3 shows a comparison between the temperature curve of the bath liquid and the electrical conductivity curve a, clearly showing that as the temperature of the bath liquid increases, the electrical conductivity in the liquid increases.

Based on this knowledge, we investigated the relationship in more detail.

FIG. 4 is a diagram showing the relationship between the concentration of mirabilite in the liquid and the electrical conductivity.

The horizontal axis shows the concentration of mirabilite in the liquid, and the vertical axis shows the electrical conductivity.

As is clear from the figure, there is a strong correlation between mirabilite concentration and electrical conductivity.

FIG. 5 is a diagram showing the relationship between liquid temperature and electrical conductivity at various concentrations of mirabilite at pH values of 2 and 5.

As is clear from the figure, there is also a linear relationship between liquid temperature and electrical conductivity.

FIG. 6 is a diagram showing the relationship between the hydrogen ion concentration (PH value) and electrical conductivity of the liquid.

The horizontal axis is hydrogen ion concentration (PH), and the vertical axis is electrical conductivity.

As is clear from the figure, if the mirabilite concentration and liquid temperature are constant, the lower the hydrogen ion concentration (PH), the higher the electrical conductivity.

From the above relationship, the relationship between the electrical conductivity, temperature, and hydrogen ion concentration in the plating bath liquid is expressed by the following equation (1), and the function correction is performed to obtain equation (2).

f (λ, T, K) - M (1)
......(2) Here, λ: Electrical conductivity (μU/Cr) T: Bath liquid temperature (C) K: Hydrogen ion concentration (PH value) M: Glauber's salt concentration (i/7) *A (T, K), B (T, K) are function corrections based on liquid temperature and PH, α is a coefficient From this relationship, measure the electrical conductivity in the bath liquid, liquid temperature and PH value, and calculate the supply amount of mirabilite as follows: Obtained by the formula.

Here, λR: Actual electrical conductivity (μU/cl) KR: Actual hydrogen ion concentration (PH value) TR: Actual liquid temperature (C) Ml: Glauber's salt concentration at the time of measurement (E/l) λC: Target electrical conductivity (μU/Cr) Mc: Required concentration of mirabilite after correction (9/l) ■ = Volume of plating tank liquid (m3) m: Concentration of mirabilite in the mirabilite supply tank (E/l) vm: Required amount of mirabilite supply liquid (mJ) First According to the above formula (3), the current (at the time of measurement) mirabilite concentration MR
Then, find the mirabilite concentration Mc required to raise the electrical conductivity to the target value.

From the determined MR and Mc, the required amount Vm of mirabilite to be supplied is determined by the above equation (5), and the amount is added.

FIG. 7 is a diagram showing an embodiment of the control method of the present invention.

Reference numeral 1 denotes a plating tank, which is filled with a zinc sulfate bath solution and has a zinc electrode set therein.

The steel plate 2 passes through this night and is plated with zinc.

In such a plating tank, the control method of the present invention is to first collect the tank bath liquid by suction with a pump 3 and send it to an electrical conductivity meter 4 and a hydrogen ion concentration meter (PH meter) 5 to measure the electrical conductivity and P of the liquid.
After the H value is measured, the liquid is returned to tank 1.

The bath liquid temperature is measured from a liquid temperature detection point 6, and these measured values are sent to a calculator 7.

On the other hand, the measured value of the mirabilite concentration in the mirabilite supply tank 8 is also sent to the computing unit 7, and the computing unit 7 calculates the above-mentioned (3) from these measured values.
Calculate the required amount of mirabilite supply using the formulas, (4) and (5), and turn on the control valve 10 using the controller 9.

It is supplied to the tank from the supply pipe 11 under OFF control.

Reference numeral 12 denotes a timer that repeatedly performs such control every other hour to maintain the target electrical conductivity.

This invention control method was implemented in a zinc plating factory with a monthly production capacity of 12,400 T/M.

The temperature of the bath liquid is set at a maximum of 70°C to avoid the problem of fume if it is too high, and the target electrical conductivity is set at 128 x 103 μU.
/1m, the average concentration of mirabilite was 50 &/
L, electrical conductivity 108 x 103 μU/cI, mirabilite concentration 100 &/L, electrical conductivity 128 x 103 μU/cI.
77 can be increased to 12K power consumption per product base
The power consumption of the WH was saved, and the quality of the steel sheet improved.

[Brief explanation of the drawings] Figures 1, 2, and 3 are diagrams showing how the electrical conductivity changes during the night depending on the concentration of mirabilite, temperature, and hydrogen ion concentration (PH) in the bath liquid. The figure shows the relationship between the concentration of Glauber's salt and electrical conductivity. Figure 5 shows the relationship between the liquid temperature and electrical conductivity at each concentration of Glauber's salt when the pH value is 2.5. Figure 6 shows the relationship between hydrogen in the bath solution. FIG. 7 is a diagram showing the relationship between ion concentration (PH value) and electrical conductivity, and is a diagram showing an embodiment of the control method of the present invention. 1...Plating tank, 2...Steel plate, 3...
...Pump, 4...Electric conductivity meter, 5...
... Hydrogen ion concentration meter, 6 ... Liquid temperature detection point, 7 ... Arithmetic unit, 8 ... Glauber's salt supply tank, 9 ... Controller, 10... Control valve, 11... Supply pipe, 12... Timer.

Claims (1)

[Claims] 1. The electrical conductivity, bath liquid temperature, and hydrogen ion concentration in the electroplating bath are measured, and the concentration of Glauber's salt, which is an electrical conductivity regulator, is controlled using the following formula from these measured values. A method for controlling the electrical conductivity of an electroplating bath. Here, M: Glauber's salt concentration (g/l) λ: Electrical conductivity (μU/Cr) T: Bath temperature (C) K: Hydrogen ion concentration (P (value) *A (T, K), B ( T, K) are relationship corrections based on liquid temperature and PH, α is the coefficient