JPH0776438B2 - PH controller for Fe-based alloy electroplating equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pH control device for a plating cell of an Fe-based electroplating device such as an Fe—Zn alloy.

(Prior Art) In recent years, Fe-based electroplated steel sheets such as Fe-Zn alloys have been used for the purpose of enhancing the rust preventive ability of automobile steel sheets and improving paintability. In the following description, Fe-Zn alloy electroplating will be described as an example of Fe-based electroplating.

In this Fe-Zn alloy electroplating method, it is more difficult to control the components of the plating solution as compared with ordinary electrogalvanizing. This is because Fe ²⁺ , which is an ion to be plated, is easily oxidized into Fe ³⁺ ions in the plating solution, so that Fe ³⁺ ions increase significantly after the start of plating, and as a result, the cathode current efficiency increases. This is because there is a problem that it causes a decrease in power cost and an increase in power cost and a decrease in production efficiency.

Therefore, in order to solve such a problem, it is necessary to suppress the increase of Fe ³⁺ ions described above.

Therefore, conventionally, a method in which iron pieces, iron particles, iron powder, etc. are dissolved in a plating solution to perform both supply of Fe ²⁺ and reduction of Fe ³⁺ is generally adopted.

With this method, the increase of Fe ³⁺ ions is certainly suppressed, but the dissolution rate of metallic iron itself is significantly smaller than that of salts such as ferrous sulfate, so devising a method for dissolving it Is required.

FIG. 3 is a schematic explanatory view for explaining a conventional pH adjusting mechanism. In the figure, a pH meter 34 is installed in a circulation tank 32 that forms a circulation path for a plating cell 30 and a plating solution, and a pH value is set. Concentrated sulfuric acid solution is appropriately supplied to the circulation tank 32 in accordance with the fluctuation of pH to adjust the pH. The supply of the plating ions is carried out in a separately provided metal dissolution tank 36, and the necessary amount thereof is supplied to the circulation tank 32 as needed. At this time, the pH value may fluctuate, and as described above, whenever such pH value fluctuates, concentrated sulfuric acid for pH value adjustment was supplied to the circulation tank.

In the conventional plating solution circulation system of dissolving metallic iron, metallic iron is dissolved in a separately provided metal dissolving tank and supplied to the circulating tank. Therefore, since the plating solution with an increased Fe ²⁺ ion concentration due to the dissolution of metallic iron flows in the circulation tank, the pH value always fluctuates.Therefore, conventionally, the pH value has been adjusted in this circulation tank. It was That is, when a pH meter is installed in the circulation tank and pH control is performed based on the measured data, the response to the addition of concentrated sulfuric acid is significantly improved, and the feedback control method based on the pH meter's indicated value is sufficient. there were.

Certainly, this method makes pH control easy, but
The Fe-based alloy plating has a problem that the dissolution rate of metallic iron is slow. One of the causes is Fe + 2H ⁺ → Fe ₂ ⁺ + H ₂
This is because the reaction markedly increases the pH and inhibits the dissolution of metallic iron. Therefore, the Fe-Zn produced
As the alloy electroplating amount increases, a huge melting tank becomes necessary, which is uneconomical and unmelted iron particles are mixed in the plating cell, which impairs the plating quality.

Still another technique is (i) a method using a metal powder or metal particles as an ion raw material for electroplating and an electrolytic process of a system in which pH is lowered (Japanese Patent Laid-Open No. 58-93888). (Ii) By adding an acid to increase the pH,
A method of coping with vertical fluctuations of pH by pouring an alkali against a pH drop (JP-A-58-93900), (iii) a method of supplying plating ions by melting the metal. Then, a method of automating the supply using an arithmetic expression (Japanese Patent Laid-Open No. 59-41488), and (iv) as an electrolysis process, an anion exchange membrane is used to supply plating ions in the form of metal particles. Method (JP-A-1
-259197 gazette) etc. are known.

(Problems to be Solved by the Invention) However, with these techniques, it is not possible to control the pH in the plating solution accurately and constantly.

That is, in the technique shown in (i), since the electrolysis process is basically a system in which the pH is lowered, that is, the purpose is to extract the acid content by the anion exchange membrane, it is difficult to control the pH.

The technique shown in (ii) is a technique that tries to maintain the overall balance by adding an alkali, so as an actual pH control, it is automatically adjusted against changes in process conditions (for example, changes in plating current). Can't respond immediately to.

Furthermore, in the technique shown by (iii) and the technique shown by (iv), there is no direct reference to pH control.

Here, an object of the present invention is to provide a Fe-Zn alloy electroplating apparatus for the purpose of accelerating the dissolution rate of metallic iron, and capable of accurately controlling the pH in the plating solution to be constant. It is in.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have conducted various studies, and as a result, Fe ions in the Fe-Zn alloy electroplating solution, prevention of pH rise when supplying Zn ions In order to achieve this, by introducing sulfuric acid into a metal dissolution tank outside the system instead of using the conventional circulation tank, a large increase in pH in the metal dissolution tank can be suppressed, and a smooth flow of metallic iron can be achieved. The present inventors have found that it is possible to achieve lysis.

However, as a result of further studies by the present inventors, the method of adding sulfuric acid to the metal dissolution tank is considerably longer than the method of adding sulfuric acid to the conventional circulation tank until the pH in the plating cell is lowered. Sometimes it takes
With this method, if the amount of sulfuric acid added to the plating cell dissolution tank is controlled by simple feedback control, overshooting of the pH in the plating cell (there is a fear that the lower limit will be severely cut) may occur due to the effect of other time lags. It was discovered that there is concern.

Therefore, as a method of solving this problem, feed-forward control, that is, the pH change of the plating cell that occurs when sulfuric acid is added to the metal dissolution tank, H ₂ SO ₄ , input amount, Fe powder input amount, Zn powder input The present invention has been completed by finding that it is possible to operate the pH in a more stable manner compared to the conventional method by performing the feed-forward control by performing the estimation calculation from the factors such as the amount.

Here, the gist of the present invention is to adjust a plating cell for performing Fe-based alloy electroplating, a plating solution circulation tank for circulating the plating solution to the plating cell, and a plating ion connected to the circulation tank. In a Fe-based alloy electroplating apparatus provided with a metal dissolving tank for supplying a plating solution, which is connected to the metal dissolving tank and which is provided with a sulfuric acid storage tank for directly supplying sulfuric acid to the metal dissolving tank, is charged into the metal dissolving tank. Based on the detection data from each detection device of the iron powder amount, other metal powder amount, and sulfuric acid input amount, and those detection devices,
A hydrogen ion concentration is calculated, and an arithmetic unit that calculates the pH of the plating solution in the plating cell, and feedforward control based on the calculated value from the arithmetic unit, adjust the supply amount of sulfuric acid into the plurality of metal dissolving tanks. It is a pH control device in a plating cell comprising a means for performing.

In the above-mentioned present invention, the arithmetic unit is based on the amount of the metal powder when other metals such as the amount of iron powder and zinc to be charged into the metal melting tank are further charged, and further based on the amount of sulfuric acid charged, It is preferable to calculate the pH of the plating solution in the plating cell and to control the amount of sulfuric acid to be added to the metal dissolving tank by feedforward control based on the calculated value.

(Operation) Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view of an Fe-based electroplating apparatus according to the present invention. In the figure, the Fe-based electroplating apparatus includes a plating cell 10 for performing Fe-based electroplating and a plating cell 10 for plating the plating cell 10. Circulating tank 12 for plating solution that circulates and supplies the solution,
And a metal dissolving tank 14 which is connected to the circulation tank 12 and supplies a plating solution with adjusted plating ions.
14 is a sulfuric acid storage tank for supplying sulfuric acid directly to the metal dissolution tank 16
Are connected. Therefore, unlike the conventional case, according to the present invention, the pH fluctuation occurs in the metal melting tank 14, and the pH fluctuation in the plating cell 10 caused by the pH fluctuation can be calculated based on the data such as the amount of the dissolved metal. Metal melting tank
A sulfuric acid flow meter is provided in the path connecting between 14 and the sulfuric acid storage tank 16.
18 and an electric valve 19 for adjusting the flow rate of sulfuric acid are provided, and a calculator 20
The supply amount of sulfuric acid is controlled by the command signal 21 from the.

Incidentally, in the present invention, the above-mentioned plating cell 10, circulation tank 12,
The structure of the metal dissolving tank 14, and further the sulfuric acid storage tank 16 itself may be the same as the conventional one, and is not particularly limited.

According to the present invention, in the metal melting tank 14, iron powder and zinc powder are charged from the hoppers 22 and 24 provided with quantitative cut-out devices, respectively, and the input amounts are input signals 25 and 26, respectively.
Is input to the arithmetic unit 20.

The plating ion supply material form is preferably supplied in the form of metal powder in order to facilitate dissolution.

A motor capable of controlling the number of revolutions may be used as a quantitative cutting device as a metal powder feeding means, and cutting may be performed by a screw feeder.

Other signals such as the total plating current value from the electroplating rectifier 28 are also sent to the calculator 20, and the pH value of the plating solution in the plating cell is calculated in advance based on these data, and the metal value is calculated based on the result. The amount of sulfuric acid added to the dissolution tank 14 is calculated and sent as a sulfuric acid input flow rate command signal 21 to a control system including a sulfuric acid flow meter 18 and a sulfuric acid flow rate adjusting electric valve 19.

The electroplating targeted in the present invention includes general ferrous alloy plating, and is usually Fe—Zn alloy, and other Fe—Ni, Fe—Cr, etc. are similarly applied. Fe-
In the case of Zn alloy plating, the Fe content is preferably 10 to 100%. The plating itself is not particularly limited whether it is a single layer or a multi-layer (multi-layer).

The plating conditions may be appropriately determined according to the type of alloy. For example, in the case of Fe-Zn alloy, the plating solution has a pH of 0.5-
2.0, the liquid temperature may be 50 to 70 ° C. An insoluble anode is used as the electrode, and concentrated sulfuric acid or dilute sulfuric acid is used as the input sulfuric acid species. The concentration is preferably as high as possible. (Ex.98% H ₂ SO ₄ )
etc.

The calculation formula of the sulfuric acid input amount in the present invention is not limited to a specific formula, but one example is as follows.

Sulfuric acid input estimation formula: A: Sulfuric acid feed rate (l / Hr) B: Iron powder feed rate (kg / Hr) C: Iron powder reduction efficiency D: Zinc powder feed rate (kg / Hr) E: Air oxidation rate (kg / Hr) F: Total plating current (kA) G: (At plating) Hydrogen generation reaction fraction H: Activity coefficient I: Sulfuric acid concentration (specified) Regarding the iron powder feeding speed of B, digital data is sent to the CPU by the conversion formula between the rotation speed of the cutting motor and the cutting amount. The same applies to the amount of zinc powder cut out in D.

The iron powder reduction efficiency of C is the ratio of the iron powder involved in the reaction of reducing Fe ³⁺ ions in the plating solution to Fe ²⁺ with respect to the amount of iron powder added. In other words, as a dissolution reaction of iron powder, two reactions of Fe + 2H ⁺ → Fe ²⁺ + H ₂ ↑ · Fe + 2Fe ³⁺ → 3Fe ²⁺ ... occur, Becomes

E is the amount of Fe ²⁺ ions oxidized by oxygen in the air during circulation of the plating solution, and the reaction formula is as follows.

The increasing rate of Fe ³⁺ generated by the equation will be referred to as the air oxidation rate.

F is a plating energization amount when performing electric iron zinc plating. In the case of double-sided plating, it means the sum of the amounts of current applied to both sides, and in the case of single-sided plating, it means the amount of current applied to that single side.

G is a reaction fraction in which H ⁺ ions in the plating solution are consumed when the plating current is applied. In other words, this is a value obtained by dividing the current involved in (-) in the following reactions by the total current.

Anode surface: Cathode surface: And are plating reactions, and are hydrogen generation reactions.

This − means that H ⁺ is generated at, H ⁺ is consumed at, and the plating current value corresponding to the subtracted amount (H ⁺ consumption is empirically higher) is divided by the total current.

H is the activity coefficient of sulfuric acid, and takes a value of 0.3 to 0.4 at a plating solution temperature of 50 ° C.

K ₁ and K ₂ are fine adjustment terms to finally match the input estimation formula with the actual results. At K ₂ , it is possible to compensate for the increase in pH due to dragout of the plating solution.

Furthermore, the present invention will be described in detail with reference to Examples, but this is merely an example of the present invention and the present invention is not limited thereto.

Example In the Fe-Zn alloy electroplating process shown in FIG.
The pH of the plating cell was adjusted by controlling the amount of concentrated sulfuric acid supplied to the metal dissolving tank 14 using the above formula for estimating the amount of sulfuric acid input based on the calculated pH value in the plating cell.

The results are shown graphically in FIGS. 2 (a) to 2 (c). Fig. 2 (a) shows the time variation of the amount of the Fe powder charged. When the charging speed was increased, concentrated sulfuric acid was added as shown in Fig. 2 (b). When the method was controlled, the pH temporarily dropped significantly. On the other hand, when the feed-forward control was performed according to the present invention, the pH hardly changed even by adding concentrated sulfuric acid.

The conditions at that time were as follows.

Plating current: Fixed at 100KA Iron powder feeding rate: 80 to 160kg / H Zinc powder feeding rate: 10kg / H Fixed iron powder reduction efficiency: 0.6 Air oxidation rate: 50kg / Hr Hydrogen evolution reaction fraction ··································· 0.35 K ₁ = 1.02 K ₂ = 0.00 By comparing FIG. 2 (b) and FIG. 2 (c), The effect is clear.

[Brief description of drawings]

1 is a schematic explanatory view showing an Fe-Zn alloy electroplating apparatus according to the present invention; FIG. 2 (a) is a graph showing the iron powder feeding rate with time in the embodiment of the present invention; (B) and (c) are graphs showing changes in pH with time according to the present invention or a conventional method in Examples of the present invention;
And FIG. 3 is a schematic explanatory view showing a conventional Fe-Zn alloy electroplating apparatus. 10: Plating cell, 12: Circulation tank 14: Metal powder dissolving tank, 16: Sulfuric acid storage tank 20: CPU (calculator)

Claims (1)

[Claims] 1. A plating cell for electroplating an Fe-based alloy,
A plating solution circulating tank for circulating and supplying a plating solution to the plating cell, and a metal dissolving tank connected to the circulating tank for supplying a plating solution in which plating ions are adjusted are connected to the metal dissolving tank. In an Fe-based alloy electroplating apparatus provided with a sulfuric acid storage tank for directly supplying sulfuric acid to a melting tank, the amount of iron powder to be charged into the metal melting tank, the amount of other metal powder, and each detection device for sulfuric acid charge, Based on the detection data from each of the detection device, the hydrogen ion concentration is calculated, the arithmetic unit for calculating the pH of the plating solution in the plating cell,
And a pH control device in a plating cell, comprising means for adjusting the supply amount of sulfuric acid into the plurality of metal dissolving tanks by feedforward control based on a calculated value from the arithmetic device.