JPH02217499A - Method for controlling concentration of electroplating bath of alloy - Google Patents

Abstract

PURPOSE:To form a plated alloy layer little in fluctuation of composition with excellent adhesive properties by regulating the concn. of metallic ions and the concn. of free acid in plating liquid by both electricity conductive amount for plating and the ratio of the rate of change in concn. of plating liquid due to analysis and the rate of change in target concn. during a plating stage in the case of electroplating alloy. CONSTITUTION:In the case of electroplating Fe-Zn alloy on the surface of steel, etc., for example, by plating liquid of Fe-Zn alloy consisting of a sulfuric acid bath, one part of plating liquid is extracted from a plating line 1 and introduced into a circulation tank 2 of plating liquid. The ions of Zn and Fe, sulfuric acid and water, etc., are added to the tank 2 from a zinc dissolving tank 3, a free acid tank 4, a water tank 5 and an iron dissolving tank 6 respectively and this mixture is regulated to plating liquid having proper concn. As the respective loadings, consumption of Fe<2+>, Zn<2+> and sulfuric acid is calculated by measured value of plating electricity conductive amount. Further the replenishment of the respective components is properly performed by both concn. of the respective components of plating liquid and comparison of the rate of change in the concn. and the rate of change in target concn. Thereby the composition of plating liquid is made proper and a plated Fe-Zn alloy layer free from fluctuation of alloy composition is formed with excellent adhesive force.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling bath concentration in alloy electroplating.

[Prior art and problems to be solved by the invention] As a method for controlling the bath concentration of an alloy electroplating bath, for example,
As disclosed in Japanese Patent Publication No. 8-151489, metal ions are dissolved and replenished into a plating bath.
As disclosed in Japanese Patent Publication No. 28600 (Japanese Patent Publication No. 61-36600), it is known that a part of the plating bath is taken out, subjected to electrolytic reduction, and returned to the bath again to control the bath concentration.

In this type of bath concentration control, since it is simply replenished according to the analysis value, it is directly affected by measurement errors or concentration variations in the plating solution, making it difficult to control the concentration to a facultative level over a long period of time. In particular, in the case of alloy plating production, this has the disadvantage of leading to serious defects such as poor plating composition and poor plating adhesion.

The present invention has been made to advantageously solve these drawbacks.

[Problems to be solved by the invention] The present invention is characterized by measuring the amount of plating current applied,
A method for controlling bath concentration in alloy electroplating, which comprises calculating metal ion consumption based on the measured value and adjusting one or more of metal ions, free acid, and water in the plating bath.

and the plating bath concentration to understand the actual concentration and actual concentration change rate, and on the other hand, calculate the target concentration change rate for adjusting to the preset target concentration, and calculate the actual concentration change rate and target concentration change rate. 1. A method for controlling bath concentration in alloy electroplating, the method comprising controlling metal ions and/or free acids in a plating solution.

3. The method of controlling bath concentration for alloy electroplating according to claim 2, wherein the plating bath concentration is controlled based on the measured value of the plating current amount.

It is.

A sulfuric acid bath for iron-zinc alloy electroplating will be described below as an example of a bath for alloy electroplating. First, there are four components in the bath: divalent ions of zinc, divalent iron ions, trivalent iron ions, and sulfuric acid. The consumption of divalent ions of zinc and iron is achieved by plating the steel plate with electricity,
Replenishment is accomplished by supplying zinc and iron in the form of solids (zinc plates, zinc grains, iron plates, iron grains) or liquids (zinc sulfate, iron sulfate). When supplied in solid form, the dissolution reaction is carried out by two fl types: an oxidative dissolution reaction by sulfuric acid and an oxidative dissolution reaction by trivalent iron ions. In addition, divalent iron ions are consumed by an oxidation reaction caused by current flow on the surface of the anode. Next, trivalent iron ions are consumed by an oxidative dissolution reaction when zinc and/or iron are supplied in the solid form, and replenishment is achieved by an oxidation reaction of divalent iron ions on the anode surface and oxygen in the plating solution. This is done by an oxidation reaction caused by the incorporation of . The sulfuric acid is consumed by an oxidative dissolution reaction when zinc and/or iron is supplied in solid form, and by a light reaction by energization, and the supply is accomplished by immersion in sulfuric acid. In this way, all changes in the concentration of each component in the plating are caused by plating current, excluding the supply system, and by measuring the amount of plating current, the change in concentration can be calculated. Therefore, for the supply of divalent iron ions, divalent zinc ions, and sulfuric acid, the input amounts may be calculated based on these calculated values. Additionally, if the trivalent iron ions increase as a result of the equipment specifications, it will be necessary to add water, but even in that case, the increase in iron trivalent ions can be expressed by the amount of plating current applied. Therefore, the input amount can be calculated from the amount of plating current applied, and the amount of divalent iron ions, divalent zinc ions, and sulfuric acid to be supplied can also be calculated by taking into account the total dilution caused by the water input. The present invention is thus a bath concentration control method for alloy electroplating that calculates the increase or decrease in the components in the plating bath by measuring the amount of plating current applied, and determines the supply amount of the components in the bath.

In addition, the plating bath concentration is measured to understand the actual concentration and actual concentration change rate (the actual concentration change rate is calculated using the least squares method from several past points), while the target concentration is adjusted to a preset target concentration. Calculate the concentration change rate. Then, in order to correct the actual concentration change rate to the target concentration change rate, the correction amounts for the supply amounts of divalent iron ions, zinc ions, and sulfuric acid are calculated, and the corrections are made to the next supply amount settings. This is a method for controlling the bath concentration of alloy electroplating. however,
In the case of the iron-zinc alloy electroplating bath used as an example,
Since there are divalent iron ions and trivalent iron ions, it is determined whether the divalent iron ions or the trivalent iron ions are to be controlled mainly depending on the concentration transition of the components in the bath.

Furthermore, as mentioned above, by measuring the amount of plating current applied, the increase or decrease in the components in the plating bath can be calculated, the supply amount of the components in the bath can be calculated, and the concentration of the plating bath can be measured to determine the amount of components in the bath. In order to understand the actual concentration and the actual concentration change rate (calculate the actual concentration change rate using the least squares method from the past few points), decide whether to control mainly divalent iron ions or trivalent iron ions, On the other hand, a target density change rate for adjusting to a preset target density is calculated. Therefore, in order to correct the actual concentration change rate to the target concentration change rate, the correction amounts for the supply amount of divalent iron ions, divalent zinc ions, and sulfuric acid are calculated from the above plating energization amount. This is a bath concentration control method for alloy electroplating that corrects the supplied amount.

Such a plating bath control method of the present invention is applicable to plating baths in which trivalent chromium and hexavalent chromium coexist in the bath in addition to the above-mentioned iron-zinc type plating and chromium-zinc alloy plating. Reliable control can be achieved by controlling the bath concentration.

In addition, in an alloy electroplating bath such as nickel-zinc, which has only the ion of each metal, the bath concentration can be reliably controlled by controlling in the same manner.

In a general continuous electroplating line, there are double-sided plated materials and single-sided plated materials, and the amount of current required for plating differs significantly before and after welding the two. Therefore, when the basic concept is control based on the amount of plating current, as in this control, a lag between the timing of calculation and the timing of a significant change in the amount of plating current may cause instability in bath concentration control. , the welding points of double-sided plated material and single-sided plated material are tracked,
It is preferable to forcibly perform calculations and reset the control set values at the timing when passing through energized equipment.

[Example] Next, examples of the present invention will be given.

Example-1 In FIG. 1, a part of the plating solution is taken out from the plating line 1, guided to the plating solution circulation tank 2, and then transferred to the Zn dissolution tank 3,
It is added to tank 2 from free acid tank 4, water tank 5, and Fa dissolving tank 6 to control the plating concentration (composition), and then returned to plating tank 1. In this way, the concentration is continuously controlled.

Next, we will discuss concentration control of the plating solution.

The amount of plating current is measured, and the controller 7 instructs the eight tanks 3, 4° 5.6 to control the results as described below.

Concentration change of Fe3° in the plating bath over a certain time Δt ^
Fe” is V・ΔFe3+, (at I−a2fra−asfzn
-a4W) ・Δt m (a). Here, V: Total plating liquid volume an: Coefficient W: Water injection speed 1; Plating current fre, f
zn: Each melting rate of Fe+Zn. Zn
"" and Fe"+ are consumed by plating, so fFs
+f2n may be controlled to be approximately proportional to the plating current. Therefore, if rewritten, V-ΔFe"-(alI-
82grj-asgznI-adt) 'Δt In this way, the remaining water input term can also be set as control proportional to the current.

V-ΔFe”s (al-a2gra-a3gzn-a
4q) To use I”Δ for actual control, use equation (a) as ΔFe
”・O, it must be at I-azfra-asfzn-aJ-0, and respectively alI-82fra=o
(When AFe""O is obtained only by dissolving Fe)...
・(0) alI-a3fzn-0 (AFe''- only by dissolving Zn
0)...(Δ) a, r-a, W-0 (When AFe"-0 is set only by immersion in water)...(:) As a solution, fra"b+T, fzn-b2I , W-bs
Find l, (at-(cxb++βb2+7b,))I
-Oct1β10γ-1, and y, β, γ(
0++β+ant).

Example 2 In FIG. 2, in the same plating line as in Example 1, the plating solution after concentration control is transferred from the plating solution circulation tank 2 to the plating line 1, and then analyzed using an online analyzer 8, and the results are controlled. 7 and controlled as follows.

In iron-zinc alloy plating baths: ・Changes in Fe reduction reaction efficiency due to dissolution of Zn and Fe ・Fe changes due to aeration in the plating solution circulation flow
A situation where ΔFg"≠O occurs due to a discrepancy between the generation/control calculation timing of "" and the operation details. Therefore, the following control for modifying the rate of change in density transition is performed.

■ Concentration management of Fe "center control and Zn" and Fe "center control selection switching Fe" is basically the most important, but F
When e" moves to a low level, there is a margin for adjusting Zn" and Fe", and by making this adjustment, it becomes difficult to avoid water input as much as possible. In this control, Depending on the concentration level and the rate of change in the concentration of Fe'', the selection is switched between Fe'' center control and Zn'' and Fe'' center control.

■ Determination of target concentration and ideal concentration change rate pe2+483
+402+ and free acid each have a target concentration, and the ideal concentration change rate IOo at that time is calculated based on the analysis value.

Here, A: upper limit of concentration B: target concentration C: lower limit of concentration D: analysis value h: ideal concentration change rate at A l IC: ideal concentration change rate at C m A + m
C can be set by determining the MAX, MIN based on equipment specifications such as the rectifier container, ion supply capacity, and circulating fluid volume. When the difference between the target concentration and the analysis value is large, the ideal concentration change rate is high, and when the difference between the target concentration and the analysis value is small, the ideal concentration change rate is low.

・In order to bring the concentration of Fe'° center control Fe' closer to the target concentration at the ideal concentration change rate of Fe3+, the amount of dissolved Zn and Fe is corrected.

Here, m: Actual concentration change rate of "Fa": Fe
Ideal concentration change rate V: Total plating liquid volume a, b: Constants α and β are coefficients that determine the contribution rate distribution of Zn and Fe to the reduction of Fe, and there is a large margin up to the upper limit of the concentration. Try to put more weight on that side.

In J, due to equipment specifications etc., Fe is added by dissolving Zn and Fa.
This is a standardization coefficient because the reduction reaction efficiency of 3+ is different, and it is necessary to use Zn, Fe
Determine by considering how many grams of each must be dissolved. Here, the control gains α and β may be obtained using fractional functions as described above, but they can also be obtained using fuzzy logic with the concentrations of Zn'ゝ, Fe'' as the antecedent part and ■ and β as the consequent part. It is possible to determine β.

−Zn'', Fe'+center control The same control as Fe'+center control is performed independently for 7n'' and Fe2''''.

Zn dissolution amount correction amount = a (m-mo) V where, m
: Actual concentration change rate mo of Zn'+ : Ideal concentration change rate of Zn'' V : Total plating liquid volume a : Constant Fe dissolution amount correction amount = b (m-mo) V where, m
: Actual concentration change rate of Fe2″″ff1o : Fe”
Ideal concentration change rate V: total plating liquid volume b=constant. In addition, regarding Fe" center control, Zn", and Fe2 "center control, we can directly calculate Zn, Fe using fuzzy logic with the concentration of Fa3°, Zn", and Fe2+ as the antecedent part, and the correction amount of dissolved amount of Zn and Fe as the consequent part. It is also possible to determine the amount of dissolution amount correction.

In this way, after selecting the control, various 3゜4.5.8
This is to give instructions.

Example 3 In FIG. 3, in the same plating line as in Example 2, the amount of plating current is led from the plating line 1 to the controller 7, and on the other hand, from the online analyzer 8 to the plating solution circulation tank 2.
The results of analysis of the plating solution returned to line 1 are derived and controlled as follows.

Concentration change Δ of Fe'+ in the plating bath over a certain time Δt
Fe'+ is V・AFe"g (at I-a2frs-asfzn
-aJ) ・Δ1-(a) Here, V: Total plating liquid volume an: Coefficient W: Water injection speed ■: Plating current frs, f
zn: Dissolution rate of each of Fe and Zn. Zn
” and Fe”” are consumed by plating, so fl'l
l+f2n may be controlled to be approximately proportional to the plating current. Therefore, if we rewrite it, V・AFe”−(at
I-a2grsI-aagznl-a4W) ・+1 In this way, the remaining water input term can also be set as control proportional to the current.

V-AFe''-(al-82gFll-83gZn-a
4Q) I”j For actual control use, AFe is used in formula (A).
”=0, it must be al 1-a2fy*-a3fzn-aJ-0, and all-a2fp, -0, respectively.
(When AFe”-0 is obtained only by dissolving Fe)...(
b) a, I-a3f, -0 (AFe”- only by dissolving Zn
0) ... (8) alI-aJ-0 (When AFe"-0 is obtained only by adding water) ... (:) As a solution, fra-btI, fzn"b21. W-b
Find sl, (a 1- (ci:b I*βb2+γ
bs)) I-06t + β + γ-1, and distribute β and γ (at 1 β ÷ γ-1) in consideration of quality such as operational cost reduction, plating efficiency, and stability of composition.

Next, the concentration of Fe'+ in the plating is measured, and the rate of change in concentration of Fe'' is calculated from the past several points by least square approximation. Depending on the division, it is determined whether to perform Fe'!center control, Zn'', or Fe'+center control.

Regarding the contents of Fe"center control and Zn", Fe"center control, each of Fe", Fe", Zn", and free acid has a target concentration, and the ideal concentration at that time is determined based on the analysis value. Calculate the rate of change mD.

Here, ^: Concentration upper limit value B: Target concentration C: Concentration lower limit value D = Analysis value I^:, Ideal concentration change rate l at A! Ic: Ideal concentration change rate at C 10A+InC
can be set by determining the MAX, MIN based on equipment specifications such as the rectifier container, ion supply capacity, and circulating fluid volume. When the difference between the target concentration and the analysis value is large, the ideal concentration change rate is high, and when the difference between the target concentration and the analysis value is small, the ideal concentration change rate is low.

・In order to bring the concentration of Fe'+central control Fe''' closer to the target concentration at the ideal concentration change rate of Fe', the dissolved amounts of Zn and Fe are corrected.

Here, m: Fe'' actual concentration change rate ff1O: F
Ideal concentration change rate of e'' V: total plating liquid volume a, b: constant 佽, β is a coefficient that determines the contribution rate distribution of Zn and Fe to the reduction of Fe'', and there is a large margin up to the concentration upper limit. Try to put more weight on that side.

j, due to equipment specifications etc. 2n, Fe due to dissolution of Fe
This is a standardization coefficient because the reduction reaction efficiency of "Fe" is different, and in reality it takes Zn,
The amount is determined by considering how many grams of Fe each must be dissolved.

=Zn'', Fe'' center control The same control as Fe'+center control is performed independently for Zn'' and Fe2°.

Zn dissolution amount correction amount = a (m-mI)) V where,
ts: Actual concentration change rate of Zn2° mo: Ideal concentration change rate of Zn'+ V2 Total plating liquid volume a: Constant Fe dissolution amount correction amount = b (m-m,) V where, m
: Actual rate of change in concentration of "Fe" lHo : Ideal rate of change in concentration of "Fe" V: Total plating liquid volume b: Perform calculations above a constant, and calculate each dissolution amount and input amount from the plating current amount and concentration change It is calculated as the sum of the correction values calculated from the speed correction and is given to each type 3, 4, 5, and 6.

[Effect of the invention] By doing so, the plating solution concentration can be reliably controlled,
The amount of plating deposited becomes uniform and quality can be improved.

In addition, the control required by adding water to the plating solution is reduced, and the waste solution treatment load can be reduced accordingly, resulting in excellent effects such as cost reduction.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are explanatory diagrams showing embodiments of the present invention. 1... Plating line 2... Plating liquid circulation tank 3... Zn dissolution tank 4... Free acid tank 5...
・Water tank 6... Fe dissolution tank 7... Controller 8... Online analyzer and 4 others Figure 2 Figure 1: Plating line 3: Zn dissolution tank 5: Water tank 7: Controller 2: Plating solution Circulation tank 4: Free acid tank 6: Fe dissolution tank 1: Plating line 3: Zn dissolution tank 5: Water tank 7: Controller 2/Plating solution circulation tank 4: Free acid tank 6: Fe dissolution tank 8: Online analyzer

Claims (1)

[Claims] 1. Measure the amount of plating current, calculate the amount of metal ions consumed in the plating bath based on the measured value, and calculate one or more of metal ions, free acid, and water in the plating bath. A method for controlling the bath concentration of alloy electroplating, the method comprising adjusting the bath concentration. 2 Measure the plating bath concentration to understand the actual concentration and actual concentration change rate, and calculate the target concentration change rate for adjusting to the preset target concentration, and compare the actual concentration change rate and target concentration change rate. 1. A method for controlling bath concentration in alloy electroplating, which comprises adjusting metal ions and/or free acids in a plating bath. 3. The bath concentration control method for alloy electroplating according to claim 2, characterized in that the plating bath concentration is controlled based on the measured value of the amount of plating current applied.