JPS59116400A - Automatic controlling method of concentration in plating bath - Google Patents

Abstract

PURPOSE:To make the soln. in a plating cell always normal, in an insoluble electrode plating device having a circulation cell and a metal dissolving cell by adding a plating current value and the replenishing amt. of metal by a replenishing soln. in replenishing the metal in accordance with a metallic ion value. CONSTITUTION:A plating current value I, a value by a analysis meter 3 for the metallic ion in an electrolyte to be fed into a plating cell 4, a value by a hydrometer 18, the control value 8 of water 9, chemical soln. 10, sulfuric acid 11 by a liquid level gage 6 and a free sulfuric acid densitometer 7 and the value from a metal level gage 17 of a metal dissolving cell 13 are inputted into a control device 19 for the concn. of the plating soln. The device 19 outputs a charging instruction to a metal charger 14 in accordance with the values inputted thereto and instructs the selection of valves V-1, V-2. A metal replenishing circuit by a pump 12 is bypassed by the selection of valves, whereby the excess concn. of the metal in a tank 1 is prevented and the troublesome settling in the system is prevented. The concn. of the metallic ion in the plating bath is thus automatically controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically controlling the concentration of a plating bath, 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 properties. In particular, when performing alloy plating of zinc and iron, it is necessary to maintain the concentration of each metal ion more strictly at a constant level.

Conventionally, plating bath concentration control in electroplating with zinc alone has been carried out by placing an appropriate amount of zinc ingots in a metal dissolving tank, for example, as seen in Japanese Patent Publication No. 53-24897, and using a plating solution circulation tank. This was done by circulating the plating solution between the plating tank and the metal dissolving tank, and adjusting the circulation flow rate or turning it off.

However, when electroplating zinc and iron alloys and dissolving iron, if the circulation of the plating solution to the metal melting tank is stopped for a long time, the precipitation of resolvable iron hydroxide will occur, and the precipitation will be affected. The time required varies depending on the amount of iron in the melting tank and the composition of the plating bath, but once precipitation occurs, it may lead to an operational failure. For this reason, it is necessary to constantly circulate the plating solution between the plating solution circulation tank and the dissolution tank in order to prevent iron hydroxide precipitation, except for short-term stops. 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 can strictly control the concentration of metal ions in a plating bath even in electroplating that requires constant circulation of a plating solution in a metal dissolving tank. Ql The method for automatically controlling the concentration of a plating bath according to the present invention to achieve this objective includes a plating solution circulation tank, a supply device for water, chemical solution, and acid solution to the plating solution circulation tank, a metal dissolution tank, and a plating solution circulation tank. (Metal bath) 9) An insoluble electrode type aeration system, which has a device for introducing metal into the metal bath, and has a valve in the circulation path between the plating solution circulation tank and the metal dissolution tank to bypass the metal dissolution tank. In electroplating in plating equipment, the amount of metal consumed using the plating current value, the amount of metal corresponding to the amount of pre-water distribution, chemical solution, and acid solution replenishment, and the measured value and target of metal ion concentration in the plating solution. The total metal amount, including the corrected metal amount calculated according to the difference between the two values, is charged into the metal dissolving tank through the metal charging device, and when the measured value of the metal ion concentration exceeds the target range, the valve is operated. This is characterized by bypassing the metal melting tank. The present invention will be described in detail below based on the drawings.

The drawing shows an example of the configuration of electroplating equipment for implementing the method of the present invention. Although the drawing only shows one set of equipment (group) surrounded by a dashed-dotted line, this equipment (#) is 2! #i is installed. However, since concentration control can be performed independently by focusing on each metal (zinc, iron) ion, in the following explanation based on the drawings, zinc and iron will be explained as metals without making a particular distinction.

The plating solution 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 pump 12 constantly sends the plating solution from the circulation tank 1 to the metal dissolution tank 13, the precipitation tank 15, and the pump 1.
6, the metal is returned to the circulation tank 1, and the metal consumed in the plating tank 4 is replenished. 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 plating progresses, the plating solution is carried away by the steel strip 5, which is the material to be plated, and the liquid level in the circulation tank 1 decreases. This liquid level is measured with a liquid level gauge 6,
When the liquid level drops to a preset low level "L#", the liquid level/acidity control device 8 opens the water tank 9 and the valves V-3 and V-4 of the chemical tank 10 to release water and the chemical liquid. On the other hand, the free sulfuric acid concentration in the circulation tank 1 is measured with the # holder 7, and the liquid level/acid concentration control device 8 is used to adjust the concentration to the target concentration by adjusting the valve V of the acid tank 11. −
Open 5 and replenish. This series of operations is carried out in the circulation tank l.
Repeat this until the liquid level reaches a preset high level ゛f().
Value management may also be performed.

The amount of metal to be added to the pot is calculated by the plating solution temperature control device 19. Normally, the metal is fed into the melting tank intermittently, and 4 grams are taken out every certain period of time @ T (minutes), and the average amount of metal cut out is adjusted by the amount put in each time. Adjust by

In the present invention, the amount of metal introduced each time M (lineage) is determined by the following formula.

M=Mf1+Mf2+Mb...
(1) Mh is the amount of metal (kg) consumed in the plating tank 4 within the input time interval T (minutes) and is calculated according to the following formula.

Mft ”” Kfx 'f,, Idt
・・・・・・・・・(2) Here ■ is the actual measured value of the plating flow 'm', which is 'f': The value obtained by multiplying the value integrated over T by the proportional coefficient Kf□ is consumed for plating. amount of metal.

1VLf2 is calculated using the following formula when the circulation tank 1 is replenished with the corresponding amount of metal.

1°df2 = Kf2-V
-・-(3) Here, V is the amount of liquid diluted to raise the liquid level in the circulation tank l, and the liquid level is a
Calculate based on the measured value. When liquid replenishment is not performed, V is zero.

V=S・(L2−Ls)
−
Song・(4) Here, S is the cross-sectional area of the circulation tank l, L4 r
L2 is the liquid level before and after liquid replenishment. Alternatively, the amount of replenishment fluid V may be actually measured by attaching Meteor M1 to each string of water, chemical solution, and sulfuric acid.

Kf2 is a coefficient determined according to the level of entertainment of gold 4 ions. A4b is calculated according to the difference between the target concentration Cr and the concentration Cm measured at regular intervals T (minutes) with the metal ion analyzer 3 installed on the outlet side of the circulation tank 1, For example, perform the well-known PII) performance of the following formula.

j Mb ”Kp (e j +−Σei + Td(ej
-e, -1) -=-==(5) Ti +=s Here, Kp and Ti e Td are proportional gain, integral time, and differential time, respectively. ej is the concentration difference at the time of this measurement, ej=Cr-cm...(6). e, -4 is the difference in weight loss from the previous 1EI11 regular time.

This value is the sum of the deviations when Mf□ and M42 are feed-forward amounts, and 9 and Mbf are feedback rings based on actual measured values of concentration.

If the size of the circulation tank is made large enough, Mfl
Although it is possible to control using Mb alone without considering the +Mf2 term, if the concentration fluctuates greatly and the metal ion analyzer 3 breaks down, control becomes impossible. Mfl
By adding the +Mf2 term, it is strong against external disturbances.
Concentration changes can be kept small.

In the above manner, the metal input amount M is calculated, and a loading command is issued to the metal loading device 14 to input the metal every T minutes. In addition, due to changes in operating conditions, the plating consumption may decrease and the metal ion accuracy in the plating solution may increase. V-
Fully close valve 1 and at the same time fully open valve 2-2 to bypass the metal dissolving tank and prevent the concentration from rising too much.

Since the method of the present invention is such that metal is replenished in the required amount, the time during which the plating solution bypasses the metal dissolving tank 13 will not be prolonged unless abnormal operation occurs.

As a result of carrying out the method of the present invention in the equipment of this embodiment, for example, the concentration fluctuation of iron was within ±1 g1t, and during the time when the plating solution was bypassed, compared to the time when iron hydroxide precipitation started,
It was confirmed that the particle size was about /20, which was small without any problem.

In fact, the proportionality coefficient Kf in equation (2) varies slightly depending on the plating current efficiency and the operating conditions of the equipment. Therefore, Mfl in equation (2) essentially has an error. Therefore, by learning Kt and getting closer to the true value, the a-summer oscillation rate will further improve, and even if the metal ion analyzer 3 breaks down, it will only be for a short time (1
) It is possible to continue the operation of cutting out metal into the metal melting tank using only the terms RLr11M12 of the equation.

Learning of Kfl 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.

/\ (Kfl)n is the current estimated value of Kfl, (Kfl)n-
1 is the previous estimated value of K f 1, and α is a coefficient O<α<1.

Kt in equation (2) is (19)m+1 in equation (7). (1>) n is calculated using the following formula.

Here, fPIdt is the integral value of plating current between the previous and current times, and Σ(Mf1+Mb)j is Mfl and Mb within the learning period.
The actual total value of j=1, Rn-1, and Rn are the remaining amounts of metal in the metal melting tank 13 from the previous and current times, and are measured at the metal level section 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 unless sufficient maintenance is done due to slurry in the plating solution, and they are somewhat unstable compared to general industrial instruments. It is useful to have a backup plan in case the analyzer malfunctions.

Generally, the relationship between the specific gravity of a solution containing multiple metal ions is not strictly linear, but the specific gravity and the concentration of each metal ion can be linearized within a small variation range of each component around the standard composition.

ρ=Σa i ′c i tenao
""song' (9) t = 1 where ρ: specific gravity of plating solution ao, ai: coefficient C1: metal ion concentration measured by multiple analyzers When the analyzer is normal, metal ion contact ei and Measure the specific gravity ρ at appropriate time intervals H (minutes), and calculate the coefficient &o each time.
, &i, we keep 'l'o r ai closer to the truth. If one of the multiple analyzers malfunctions and one metal ion becomes unmeasurable, the latest a(1, ai) and the actual measured value of specific gravity are used to perform the measurement using equation (9). The metal ion concentration can be determined by back calculating the metal ion placement that has become impossible.

As described above, according to the present invention, even in electroplating where it is necessary to constantly circulate the plating solution between the metal dissolution tank and the circulation tank, the metal ion richness in the plating bath can be controlled accurately and stably. You can do that.

[Brief explanation of drawings]

The drawing is a diagram showing an example of the configuration of electroplating equipment for carrying out the method of the present invention. Bowl needle, 8: liquid level, acid vf 1 degree 1b
Control device q19: Water tank, 10: Chemical tank, 11:
4A enemy tank, 12: pump, 13: metal molten monk, 14
: Metal charging device, 15: Sedimentation tank, 16: Pump, 17:
Metal level meter, 18: Hydrometer, 19: Me. Liquid concentration control device, V-1 to V-5 = pulp. Applicant: New Japan M-Tetsu Co., Ltd.

Claims (1)

[Claims] A plating solution circulation tank, water to the plating solution circulation tank,
It has a replenishing device for chemical solution and acid solution, a metal dissolving tank, and a device for charging metal into the metal dissolving tank, and a metal dissolving tank is provided in the circulation path between the plating solution circulation tank and the metal dissolving tank. In electroplating in insoluble electrode type electroplating equipment equipped with a bypass valve, the amount of metal consumed calculated using the plating current value and the water,
The metal feeding device calculates the total amount of metal, which is the amount of metal corresponding to the amount of replenishment of the chemical solution and acid solution, and the amount of corrected metal calculated according to the difference between the measured value and the target value of the metal ion concentration in the plating solution. A method for automatically controlling the concentration of a plating bath, characterized in that when the measured value of metal ion concentration exceeds a target range, the valve is operated to bypass the metal dissolution tank.