JPS6116440B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for automatically controlling the concentration of a plating bath in electroplating, particularly in non-dissolving electrode type electroplating. In equipment for electroplating steel plates using insoluble electrodes such as lead, it is important to keep the plating bath concentration constant in order to maintain stable plating performance. In particular, when performing alloy plating of zinc and iron, it is necessary to maintain the concentrations of each metal ion more strictly at a constant level. Conventionally, plating bath concentration control in electroplating of zinc alone has been carried out by placing an appropriate amount of zinc lumps in a metal dissolving tank, and connecting the plating liquid circulation tank with the metal dissolving tank, as shown in Japanese Patent Publication No. 53-24897. This was done by circulating plating liquid between the tanks and adjusting the circulation flow rate or turning it on and off. However, when melting iron in electroplating of zinc and iron alloys, if the circulation of the plating solution to the metal melting tank is stopped for a long time, poorly soluble iron hydroxide will precipitate, and the amount of time required for the precipitation will be reduced. The time will vary depending on the amount of iron in the melting tank and the composition of the plating bath, but once precipitation occurs, it may become impossible to operate. For this reason, the plating solution between the plating solution circulation tank and the dissolving tank must be constantly circulated, except for short-term stops, in order to prevent iron hydroxide precipitation. Therefore, when performing alloy plating of zinc and iron, the conventional concentration control method is not appropriate and is inherently contradictory. An object of the present invention is to provide a method that makes it possible to strictly control the metal ion concentration in a plating bath even in electroplating that requires constant circulation of a plating solution in a metal dissolving tank. The automatic plating bath concentration control method of the present invention to achieve the object includes a plating liquid circulation tank, a supply device for water, a chemical solution, and an acid solution to the plating liquid circulation tank, a metal dissolution tank, and a metal dissolution tank. In electroplating in an insoluble electrode type electroplating equipment having a device for introducing metal into a tank, and a valve for bypassing the metal dissolution tank in the circulation path between the plating liquid circulation tank and the metal dissolution tank. , Calculated according to the amount of consumed metal calculated using the plating current value, the amount of metal corresponding to the amount of water, chemical solution, and acid solution replenished, and the difference between the measured value and target value of the metal ion concentration in the plating solution. The total amount of metal including the corrected amount of metal is charged into the metal dissolving tank from the metal charging device, and when the measured value of the metal ion concentration exceeds the target range, the valve is operated to bypass the metal dissolving tank. This is a characteristic feature. The present invention will be explained in detail below based on the drawings. The drawings show an example of the configuration of electroplating equipment for carrying out the method of the present invention. Although the drawing only shows one set of devices (group) surrounded by a dashed-dotted line,
Two sets of these devices (groups) are installed in facilities that perform alloy plating of zinc and iron. However, concentration control can be performed independently by focusing on each metal (zinc, iron) ion, so in the following explanation based on the drawings, zinc and iron will be explained as metals without making a particular distinction. The plating liquid in the circulation tank 1 is sent to the plating tank 4 by the pump 2, used for plating, and then returned to the circulation tank 1. On the other hand, the plating liquid is constantly sent from the circulation tank 1 to the metal dissolving tank 13 by the pump 12, returns to the circulation tank 1 via the settling tank 15 and the pump 16, and replenishes the metal consumed in the plating tank 4. Valves V-1 and V-2 are flow path switching valves. The metal to be replenished is transferred from the metal charging device 14 to the metal melting tank 1.
3 and dissolved. As the plating progresses, the plating liquid is carried away by the steel strip 5, which is the liquid material to be plated, and the liquid level in the circulation tank 1 decreases. This liquid level is measured by the liquid level gauge 6, and when the liquid level drops to a preset low level "L", the liquid level/acid concentration control device 8 controls the valves V-3 of the water tank 9 and the chemical tank 10, Open V-4 and replenish water and chemical solution in fixed amounts. On the other hand, the free sulfuric acid concentration in the circulation tank 1 is measured by the concentration meter 7, and the liquid level/acid concentration control device 8 opens the valve V-5 of the sulfuric acid tank 11 to replenish the sulfuric acid so that the concentration reaches the target concentration. This series of operations is repeated until the liquid level in the circulation tank 1 reaches a preset high level "H". Here, the PH value may be controlled instead of the free sulfuric acid concentration. The metal input amount is calculated by the plating liquid concentration control device 19. Normally, metal is added to the melting tank intermittently, at regular intervals of T.
Cutting is performed every (minutes), and the average cutting amount is adjusted by adjusting the input amount each time. In the present invention, the amount of metal introduced each time M
(Kg) is calculated using the following formula. M=M _f1 +M _f2 +M _b (1) M _f1 is the amount of metal (Kg) consumed in the plating tank 4 within the input time interval T (minutes), and is calculated by the following formula. M _f1 = K _f1・∫ ^T ₀ Idt ………(2) Here, I is the actual value of the plating current, and the value obtained by integrating this for T minutes and multiplying it by the proportionality coefficient K _f1 is the value consumed for plating. amount of metal. M _f2 is when the circulation tank 1 is refilled,
The amount of metal (Kg) corresponds to this, and is calculated using the following formula. M _f2 = K _f2 ·V (3) Here, V is the amount of liquid replenished to raise the liquid level in the circulation tank 1, and is calculated from the measured value of the liquid level gauge 6. When liquid replenishment is not performed, V is zero. V=S・(L ₂ −L ₁ ) (4) Here, S is the cross-sectional area of the circulation tank 1, and L ₁ and L ₂ are the liquid levels before and after liquid replenishment. Incidentally, the amount of replenishing liquid V may be actually measured by attaching flowmeters to each of the water, chemical solution, and sulfuric acid systems. K _f2 is a coefficient determined depending on the target concentration of metal ions. M _b is a value calculated according to the difference between the concentration C _n measured at fixed time intervals T (minutes) by the metal ion analyzer 3 installed on the outlet side of the circulation tank 1 and the target concentration C _r For example, the well-known equation
Perform PID calculation. Here, K _p , T _i , and T _d are proportional gain, integral time, and differential time, respectively. ej is the concentration difference during the current measurement, ej=C _r −C _n (6). e _j-1 is the concentration difference at the previous measurement.

[Formula] is a value that is the sum of the deviations for each measurement after the start of control. M _f1 and M _f2 are amounts to be input in terms of feed forward, and M _b
is a feedback term based on the measured value of concentration. If the size of the circulation tank is made large enough, it is possible to control only with M _b without considering M _f1 and M _f2 terms, but the concentration fluctuations are large and the metal ion analyzer If 3 fails, control becomes completely impossible. By adding the M _f1 and M _f2 terms, it is resistant to external disturbances and density changes can be suppressed to a small level. The metal input amount M is calculated in the above manner, and a loading command is issued to the metal loading device 14 to input the metal every T minutes. On the other hand, the metal dissolution rate in the metal dissolution tank 13 and the free sulfuric acid concentration fluctuation have a close complementary relationship.
For example, in the case of zinc, it is based on the following chemical reaction. Zn＋H ₂ SO ₄ →ZnSO ₄ ＋H ₂ ↑
(Reaction in metal dissolution tank 13) Zn ²⁺ +H ₂ O→Zn+2H ⁺ +1/2O ₂ ↑ (Reaction in plating tank 4) Therefore, in order to suppress temporary fluctuations in the free sulfuric acid concentration, valve V-1 It is effective to average the metal dissolution rate within the metal injection interval T minutes by adjusting the opening degree of V-2. The opening degrees of the valves V-1 and V-2 are determined by a table or an empirical formula based on the amount of metal remaining in the metal melting tank 13 and the amount of metal input M.
Also, due to changes in operating conditions, the plating consumption may decrease and the metal ion concentration in the plating liquid may increase, so if the measured value of the metal ion analyzer 3 rises above the target value, close the valve V-1 completely. At the same time, valve V-2 is fully opened to bypass the metal dissolving tank and prevent the concentration from increasing too much. In order to perform the above control smoothly, it is necessary to keep the circulation between the circulation tank 1, the metal dissolution tank 13, and the precipitation tank 15 as constant as possible. (not shown), it is effective to reduce the frequency of starting/stopping the pumps 12 and 16 by controlling the liquid level in the settling tank 15 at a fixed value. Since the method of the present invention replenishes metal in the required amount, the time during which the plating solution bypasses the metal dissolving tank 13 will not be prolonged unless there is an abnormal operation. As a result of implementing the method of the present invention in the equipment of this example, for example, the concentration fluctuation was within ±1 g/, and during the period when the plating solution was bypassed, it was about 1/20 of the time when iron hydroxide precipitation started, which was no problem. It was confirmed that it was small. Now, the proportionality coefficient K _f1 in equation (2) varies slightly depending on the plating current efficiency and the operating conditions of the equipment. Therefore(2)
M _f1 in the equation essentially has an error. So K
If _f1 is learned and brought closer to the true value, the concentration control accuracy will be further improved, and even if the metal ion analyzer 3 breaks down, if it is a short time, only the M _f1 and M _f2 terms in equation (1) can be used in the metal dissolving tank. It is possible to continue metal cutting operations. Learning of K _f1 is performed, for example, at appropriate time intervals P minutes (an integer multiple of the time interval T) using the exponential smoothing method as follows.

[Formula] is the current estimated value of K _f1 ,

[Formula] is the previous estimated value of K _f1 , and α is a coefficient, 0<α<1. K _f1 in equation (2) is

[Formula].

[Formula] is calculated using the following formula. Here, ∫ ^P ₀ Idt is the integral value of the plating current between the previous time and this time,

[Equation] is the actual total value of M _f1 and M _b during the learning period, and R _{o -1} and R _o are the remaining amounts of metal in the metal melting tank 13 from the previous and current times, which are measured by the metal level meter 17. As the metal ion analyzer 3, a fluorescent X-ray analyzer or the like is mainly used. Although the reliability of analyzers has improved in recent years, they cannot operate stably without sufficient maintenance due to the presence of slurry in the plating solution, and are somewhat unstable compared to general industrial instruments. It is useful to consider backup in case of meter abnormality.
In general, the relationship between the concentration and specific gravity of a solution containing multiple metal ions is not strictly linear, but within a small variation range of each component around the standard composition, the specific gravity and the concentration of each metal ion can be linearized. Here, σ: Specific gravity of the plating liquid a ₀ , a _i : Coefficient c _i : Metal ion concentration measured by multiple analyzers When the analyzers are normal, the metal ion concentration c _i and specific gravity ρ are measured at appropriate times. By measuring every interval H (minutes) and estimating the coefficients a ₀ and a _i each time, a ₀ , a
Keep _i closer to the true value. If one of the multiple analyzers malfunctions and the concentration of one metal ion becomes unmeasurable, using the latest measured values of a ₀ , a _i , and specific gravity, it is determined from equation (9) that the concentration of one metal ion becomes unmeasurable. The metal ion concentration can be determined by back calculating the metal ion concentration. As described above, according to the present invention, the metal ion concentration in the plating bath can be accurately and stably controlled even in electroplating where the plating solution needs to be constantly circulated between the metal dissolution tank and the circulation tank. I can do it.

[Brief explanation of the drawing]

The drawings are diagrams showing an example of the configuration of electroplating equipment for implementing the method of the present invention. 1: Circulation tank, 2: Pump, 3: Metal ion analyzer, 4: Plating tank, 5: Steel strip, 6:
Liquid level gauge, 7: Concentration meter, 8: Liquid level, acid concentration control device, 9: Water tank, 10: Chemical tank, 11: Sulfuric acid tank, 12: Pump, 13: Metal dissolution tank, 1
4: Metal charging device, 15: Sedimentation tank, 16: Pump, 17: Metal level meter, 18: Hydrometer, 19:
Mekki liquid concentration control device, V-1 to V-5: valve.

Claims (1)

[Scope of Claims] 1. A plating liquid circulation tank, a supply device for supplying water, a chemical solution, and an acid solution to the plating liquid circulation tank, a metal dissolving tank, and a metal charging device to the metal dissolving tank, Consumption metal calculated using plating current value in electroplating in insoluble electrode type electroplating equipment in which a valve for bypassing the metal dissolution tank is provided in the circulation path between the plating liquid circulation tank and the metal dissolution tank. quantity and
an amount of metal corresponding to the amount of water, chemical solution, and acid solution supplied;
The total metal amount, including the corrected metal amount calculated according to the difference between the measured value of the metal ion concentration in the plating solution and the target value, is charged into the metal dissolving tank from the metal charging device, and the measured value of the metal ion concentration is set to the target value. An automatic control method for plating bath concentration, characterized in that when the concentration exceeds the range, the metal dissolving tank is bypassed by operating the valve.