JPH0639720B2 - Method for producing zinc alloy electroplated steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a zinc alloy electroplated steel sheet, and more particularly to a method for producing a zinc alloy electroplated steel sheet using an insoluble anode.

(Prior Art) Conventionally, as a means for supplying metal ions to a zinc alloy-based electroplating bath, at the very initial stage, for example, zinc compounds such as zinc carbonate and zinc oxide, which have high solubility for zinc ions, are added and dissolved. Was to do. However, these zinc sources have the disadvantage of being expensive.

In recent years, with the spread of zinc alloy plating, especially continuous type zinc alloy electroplated steel sheets, zinc alloy electroplating equipment has become larger and faster in order to reduce production costs.
Operating conditions have come to be strictly controlled. Therefore, zinc alloy-based electroplating, especially when using an insoluble anode made of Pb or the like, it is necessary to supply a large amount of zinc ions and other metal ions to the plating bath at low cost, which is usually an inexpensive means. In pure zinc plating manufacturing, only metallic zinc is melted, and in zinc alloy plating manufacturing, metallic zinc and other alloy components are melted, respectively. However, metals such as metallic zinc have a slow dissolution rate and cannot follow a rapid concentration change to obtain a rapid response. In addition, in the case of alloy plating, more accurate concentration control is required as compared with the case of a single metal, and a direct melting means of metal of alloy component such as metallic zinc is not adopted.

In particular, in the production of galvannealed steel sheet, it is necessary to keep the concentration ratio of each metal ion to be plated in the plating bath within a certain fixed range, and to keep its accuracy at a considerably high level.

Therefore, generally, at present, Zn-Fe, Zn-Ni alloy electrogalvanized steel sheets use insoluble anodes, and plating metal ions have a dedicated supply facility for the same number of metal ion types as the manufacturing process. Is manufactured by.

And, in such metal ion supply equipment, ZnO, ZnCO ₃ , ZnSO ₄ , Zn (OH) ₂ , NiCO ₃ and Ni are used as the raw materials.
It is customary to add and use a metal salt such as (OH) ₂ , NiO ₂ , FeSO ₄ , Fe (OH) _{2 in the} form of slurry. By the way, the dissolution rate of the Zn metal salt is 2-3 minutes, but the dissolution rate of the Zn metal is several hours.

The reason for using a metal salt is that it has the advantages of good solubility, dissolution in a short time, and good response for concentration control, as compared with the case of using a simple metal (raw material).

However, in the process of refining the raw material, the metal salt is produced from a simple metal, so that the cost of the raw material must be increased considerably. Therefore, there is a great demand for reducing raw material costs in order to improve the price competitiveness of strategic electrogalvanized steel sheets.

Several means have been proposed so far for supplying such metal ions to be plated, for example, Japanese Patent Publication No. 53-2.
No. 4897 is about pure zinc plating, but ZnSO ₄
In this form, zinc metal is dissolved and placed, the consumption of zinc ions in the plating bath is constantly monitored, and each time it is replenished little by little. Also, in Japanese Examined Patent Publication No. 61-16440, which is also supplied in the form of a metal, in this case, the metal is dissolved in an amount larger than the amount of supplied metal ions, and the metal is supplied to the plating bath by controlling the flow rate. It controls the supply of ions.

By the way, when Zn ions and other metal ions are supplied in the form of metal salts, the cost of each metal salt is several times higher than the cost of the metal alone. Since the cost of plated metal, that is, the cost of raw materials, accounts for the highest percentage of the manufacturing cost of electrogalvanized steel sheets, it is a factor that significantly impedes the cost competitiveness of plated products. Also,
The method of replenishing metal ions in the form of a simple metal is inferior to the metal salt charging method in controlling the Zn concentration control and the ratio of Zn and other plating metal ions,
There is a problem in terms of ensuring stable alloy plating quality.

(Problems to be solved by the invention) Thus, an object of the present invention is to make the concentration control of each metal ion with high accuracy possible even in the electroplating of zinc alloys, for example, Zn-Fe and Zn-Ni alloys, which is less expensive. To provide the means.

(Means for Solving the Problems) Here, the gist of the present invention is, in a method for producing a zinc alloy-based electroplated steel sheet using an insoluble anode, 40 to 90% per supply of zinc ion to an acidic plating solution. Are supplied in the form of metallic zinc, and the rest are supplied in the form of metal salts in response to changes in the concentration of zinc ions in the plating bath, while all the metal ions of alloy components other than zinc are supplied in the form of metal salts. It is a method for producing a zinc alloy-based electroplated steel sheet.

In addition, in supplying zinc ions to the above-mentioned acidic plating solution, specifically, preferably, a fixing method of supplying a fixed amount of metal zinc below the lower limit of the fluctuation range of the required zinc supply rate or a required zinc supply rate. Of the required zinc supply rate calculated from the integrated value of the consumed current
It is sufficient to use the integration method in which 90% is supplied with zinc metal and the rest of the required amount of zinc is supplied with zinc metal salt. Here, the required zinc supply rate is the required amount of dissolved zinc metal and zinc metal salt to be supplied to the plating tank.

That is, according to the fixing method, which is one aspect of the present invention, metallic zinc is selected as a supply source for the concentration of zinc ions in a range not affected by the concentration fluctuation during normal operation. Then, by taking as much as possible about that portion, the raw material cost can be further reduced.

In this way, the dissolved portion of the metal content, which is determined in advance or determined each time, is not affected by the concentration fluctuation during operation, so the poor responsiveness due to the low dissolution rate does not pose a problem, and the raw material cost is rather low. The advantage of that is great. Usually, the supply ratio of such metal components is 40 to 90.
%. This also depends on the alloy composition. If the ratio of zinc is high, the ratio can be set relatively high.

As described above, according to the present invention, the Zn ²⁺ ion supply form is
The combination of simple metal and metal salt is used to reduce the raw material cost of alloy plating and to accurately control the concentration ratio of Zn and alloying component metals, thus reducing manufacturing cost. The present invention has great significance in the present-day situation that has been revealed.

(Operation) Next, the present invention will be further described with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view of an apparatus for carrying out the method according to the present invention. In the figure, a plating metal is replenished to a melting tank 1 in which a plating solution is circulated with a plating tank 12. As a device, a supply device 3 for metal salt 13 of metal other than Zn (eg NiCO ₃ etc.), a supply device 4 for metal salt of Zn (eg ZnCO ₃ etc.), a dissolution tank for metal Zn15, that is, zinc dissolution The tank 2 is provided.

The metal salt 13 of a metal other than Zn and the metal salt 14 of Zn are cut out by a predetermined amount by the quantitative cutting devices 5 and 7, respectively.
On the other hand, in the zinc dissolution tank 2, metallic zinc 15 is charged and immersed in the plating solution. The amount of zinc ions derived from metallic zinc is controlled by adjusting valve 10,
It is sent to the above-mentioned melting tank 1 through the zinc melting tank 2 by the pump P. The supply of metal ions to the dissolution tank 1 as a metal salt is also adjusted by the valves 6 and 8.

If desired, a buffer bath 11 may be provided between the plating bath 12 and the melting bath 1 to stabilize the concentration of metal ions in the plating bath.
May be provided.

The metal ions in the plating tank 12 are constantly analyzed by the plating solution analyzer 17, and the respective valves 6, 8 and 10 are controlled by the signals as described later.

The preferable shape of the melting tank 1 is a cascade type as shown in FIG. The material may be an iron plate with rubber lining. As a countermeasure against undissolved residues, it is advisable to provide a circulation path as appropriate. That is, the dissolution tank 1 is divided into three, and the metal salts from the metal salt supply devices 3 and 4 are respectively charged to the upper section a, and the liquid supply from the zinc dissolution tank 2 is also performed in this section a. . Then, the plating solution prepared in the section a is sequentially circulated and supplied to the plating tank 12 through the sections b and c. In this case, the plating solution is also circulated from the return pipe from the plating tank to the zinc dissolving tank 2. This is because it is desirable to use a branch pipe from the return pipe from the plating tank circulation system having a pH as low as possible to supply the plating solution to the zinc dissolution tank 2 in order to accelerate the dissolution of metallic zinc. Alternatively, the plating solution may be branched / supplied from the entry side of the cascade melting tank shown in FIG. See FIG. It is recommended to avoid branching / supply from sections B and C because the pH of the solution gradually rises due to the dissolution of the metal salt and the solubility decreases.

In the example shown in the figure, there are three divisions A, B, and C, but at least two divisions are sufficient.

As shown in FIG. 1, it is preferable to provide a backwash type filter 16 on the way of returning the plating supply solution from the zinc dissolution tank 2 to the dissolution tank 1. This is because metal ions other than Zn (Fe ²⁺ or Ni ²⁺ etc.) in the plating solution are substituted and deposited during the dissolution of metal Zn, which is likely to be an inhibitory factor to plated products.
This is to remove those foreign matters. However, even if it is not a backwash filter, it can be applied even if it is thickener type as long as it is effective in removing foreign matters.

The general specifications of the plating solution adjusted in this way are:
It is usually as follows. pH ≦ 2.0, temperature: 45 to 80 ° C., bath composition (plating metal ion concentration) is not particularly limited. However,
It is necessary to limit the Zn concentration to about 70 g / or less.

Next, the manner of controlling the supply of metal ions, especially zinc ions, will be described.

The control target in the present invention is the analytical data by the plating solution analyzer 17 of FIG. 1, which is received online and is the required dissolution amount based on these data, that is, the total amount of metallic zinc and zinc metallic salt. Required zinc supply rate V _Zn (kg / h
r) is calculated. Once the required dissolution amount is known, the required ion amount is supplied from the zinc dissolution tank 2 by operating each valve. In the case of a metal salt, the cutout amount is adjusted. These operations can be manual or automatic.

Next, in the present invention, it is important to determine the ratio of supplying zinc ions from metallic zinc and the ratio of supplying metallic ions from metallic salts. There are fixed method, variable method and multiplication method.

(1) Fixing method: As shown in FIG. 3, the maximum consumption V _Znmax determined in advance from plating equipment, specifications, etc. is determined, and the supply ratio K of metallic zinc is 40 to 90%. Think in the range of.
At this time, the required zinc supply rate V _Zn (kg / hr) constantly fluctuates, so K is determined in a range such that the fluctuation can be absorbed by the addition of the zinc metal salt. For that purpose, the maximum fluctuation range is empirically known, and the ratio is determined so that the metal zinc dissolution rate VM _-Zn (kg / hr) is slightly lower than the maximum fluctuation range. That is, V _M-Zn = K · V _{Zn max} (K
= 0.4 to 0.9) to ensure the amount of dissolved zinc metal. When the fluctuation range is large, the unnecessary amount of the metal salt is increased, and the original effect of the present invention may not be sufficiently exhibited.

In addition, the Ni content is appropriately converted into a metal salt each time.

(2) Variation method: Based on the above-mentioned V _{Zn max} , the operating condition at that time, that is, the plate width
(W: mm), unit weight (C: g / m ² ), line speed (v: m / min)
V _Zn is determined by adding the correction of each term of

V _Zn = f (v, w, c) V _{Zn max} Corresponding to the predicted value of the zinc supply amount determined by the above formula, the metal zinc supply amount is determined by the ratio of K determined in advance, and Similarly, it is supplied to the dissolution tank.

As described above, Ni is appropriately added as a metal salt in each case.

In these methods, the opening of the valve 10 is adjusted or the pump flow rate of the circulation pump 9 is adjusted based on the correlation between the circulation pump 9 and V _MZn (melting rate of metallic zinc) which is known in advance. In the case of an AC motor itself, it is controlled by a rotational speed control means such as VVVF. Depending on the variation of V _Zn ,
The amount of zinc metal dissolved varies and requires valve control.

If the fluctuation of the metal zinc dissolution rate is within 5%, the response is not so bad. Therefore, if the fluctuation amount is suppressed to that extent, the data of the plating solution analyzer will not be predicted as described above. It is also possible to control it.

(3) Integration method: In this method, first, the absolute value of the Zn ²⁺ concentration, that is, the consumption amount is determined online by the plating solution analyzer 17, and a predetermined control value is set based on that value. In other words, it is the setting of the Zn consumption limit. Then, the density increase / decrease from that time is evaluated by the consumed current, and the density control is performed so that the consumed current is integrated and balanced. _Assuming that the zinc consumption is V _zn , for example, However, I = load current during alloy plating η = current efficiency (≦ 0.95) 65.4 / 2 = Zn 1 g equivalent (current efficiency depends on quality).

That is, as shown in FIG. 4, the current efficiency is set first, and then the integrated current value is set. This is a calculation of the amount of zinc consumed. The consumption amount at this time is the consumption amount of metal zinc, zinc metal salt, and metal salts other than Zn, that is, the required supply amount is calculated by setting the current proportional division ratio. This is because the required supply time is immediately calculated with a known metal ion dissolution rate and the valve operation is commanded.

According to this method, when the integrated value of the consumed current reaches a predetermined critical value, the plating metal raw materials of the respective components commensurate with the current are replenished. In other words, it is the supplemental consumption metal. The time lag during this period can be improved by increasing the total amount of the plating solution, preferably by providing the buffer tank 11 of FIG. 1 or the like, and aiming at the buffering effect against fluctuations or shortening the interval of the integration time, and there is no practical problem. . Especially, it is better to adopt the latter as the effect.

This will be described below with reference to an example.

When electroplating a Ni-Zn alloy (Ni: 13%), Q _Ni : Q _Zn = 13 / 58.7: 87 / 65.4 Q _Ni = 0.143 x Q, Q _Zn = 0.857 x Q (Q: current x time) As described above, 0.857 is multiplied by K ″ to be allocated to two sources of metallic zinc and zinc metallic salt. The consumption Zn (W _Zn : kg) at that time is as follows.

However, α: constant.

Therefore, with the supply device of metal zinc dissolution rate VM _-Zn (kg / hr)
(W _Zn / VM _-Zn ) time is applied. The state at this time is shown in FIG.

In actual operation, current consumption does not necessarily equal zinc consumption. It is a drag-out of the plating solution (outflow from the system)
This is because there are not a few. This increase in consumed zinc is large due to each plating cell structure, but the correction term (D
A value obtained by adding _Zn ) such as W _Zn + D _Zn may be used instead of W _Zn . For D _Zn, it is necessary to understand the characteristics by conducting a characteristic survey in advance.

Incidentally, the property of metallic zinc is not particularly limited, and it is usually 9
Any simple substance of metal having a Zn purity of 9.9% or more may be used, and the shape may be plate-like, granular, or powder.

Next, the present invention will be described more specifically by way of examples.

Example When Ni-Zn alloy electroplating (Ni: 13% target) is performed to produce a plated steel sheet, Ni is supplemented with NiC according to the present invention.
Replenishment of O ₃ and Zn 80% by metal zinc particles, the remaining 20%
Was supplied with ZnO.

As a comparative example, an operation was also performed in which all zinc was supplied with metallic zinc.

The Zn supply amount was adjusted by the integration method described above.

With respect to the target value of Zn concentration, when the plating solution total amount of 100 m ³ had a variation of ± 3 g / in the case of only metallic zinc, when the metallic zinc + metal salt was supplied according to the present invention, the variation was within ± 1 g /. Fit in.

By the way, when zinc was supplied with the total amount of ZnO, the accuracy at that time was ± 0.5 g /.

According to the present invention, the raw material cost could be reduced by 40%.
This means that, assuming that 50 tons of metallic zinc is used per month, the current price will be 60 to 90 million yen on an annual basis.

As described above, the present invention is inferior in accuracy to the total amount of metal salt charging method, but the degree is practically no problem, while the cost is overwhelmingly advantageous. You can see how significant the practical use of is.

[Brief description of drawings]

FIG. 1 is a flow chart showing the method of the present invention; FIG. 2 is a schematic explanatory view showing a modification example of a melting tank; FIG. 3 is a schematic explanatory view of a method of distributing metal zinc and zinc metal salt; FIG. 4 and FIG. 5 are schematic explanatory views of the integration method.

Claims (2)

[Claims] 1. A method for producing a zinc alloy-based electroplated steel sheet using an insoluble anode, wherein 40 to 90% is supplied in the form of metallic zinc when supplying zinc ions to an acidic plating bath, and the rest is zinc ions in the plating bath. Of zinc alloy-based electroplated steel sheet, characterized in that it is supplied in the form of a metal salt in response to the fluctuation of the concentration of Al2O3, while all the metal ions of alloy components other than zinc are supplied in the form of a metal salt. Method. 2. When supplying zinc ions to an acidic plating solution,
A fixed method of supplying a fixed amount below the lower limit of the fluctuation range that is 40 to 90% of the required zinc supply rate with metallic zinc, or predicting the fluctuation of the required zinc supply rate from operating conditions,
Using the variation method of supplying 90% with metallic zinc or the integrating method of supplying 40 to 90% of the required zinc supply rate calculated from the integrated value of consumption current with metallic zinc, the remaining required amount of zinc is zinc metal salt. The method for producing a zinc alloy-based electroplated steel sheet according to claim 1, which is supplied by.