JPS5925990A - Method for plating ferrous metal - Google Patents

Abstract

PURPOSE:To make plating efficiency constant, by carrying out continuous plating while reducing tervalent Fe ions formed in a plating bath with Ag. CONSTITUTION:A plating vessel 1 is filled with a plating soln. contg. FeSO4, ZnSO4, (NH4)2SO4 and tervalent Fe ions, and an electric current is supplied between an anode 2 made of a Pb-Sn alloy and a cathode 3 made of a steel plate to electroplate the steel plate with an Fe-Zn alloy. Part of the plating soln. is introduced into a dissolution vessel 4 through a flowmeter 10 and brought into contact with Fe 5 and Zn 6 to supply Fe ions and Zn ions. The soln. is then introduced into reduction vessels 7, 7' packed with Ag. In the vessels 7, 7', tervalent Fe ions in the soln. are reduced by adding NH4Cl 8. The plating soln. contg. a smaller amount of tervalent Fe ions is returned to the vessel 1 through a filter 9 and reused.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously applying iron or iron alloy plating to a steel plate.

As is well known, in recent years, the use of iron or iron-based alloy plating has been widely considered for the purpose of rust prevention of steel plates or improvement of coating surface treatment.

Examples include iron single plating, iron-zinc alloy plating, iron-zinc-nickel alloy plating, and iron-nickel plating. These platings have conventionally been inspected, but when plating is carried out industrially and continuously, the biggest problem is the behavior of trivalent iron ions that are generated and accumulated in the plating bath. In other words, this trivalent iron ion (Fe3+) is generated by oxygen generated at the counter electrode during plating, or by oxidation due to aeration during circulation of the plating solution, but if the amount of Fe3+ increases in the plating bath, the plating efficiency decreases. Furthermore, since it has an adverse effect on the properties of the plated surface, it is extremely important to control it to a predetermined amount or less. For this reason, what has traditionally been considered is the use of soluble anodes (counter electrodes).
However, the situation is not necessarily satisfactory industrially, and in particular The reality is that these methods are extremely difficult to apply in high-speed plating. Therefore, the present inventors conducted various studies on applying iron or iron alloy plating continuously at high speed, and found that when plating is performed while reducing Fe''+ ions in the plating bath using a silver-filled tank, Fe3+ ions are reduced. It was discovered that there is no accumulation and extremely excellent plating can be achieved.

In other words, to continuously perform iron or iron alloy plating while circulating the plating solution, the plating solution is passed through a reduction tank filled with silver, and the plating is applied to the steel sheet while Fe3+ in the bath is reduced to Fe2+. It was discovered that plating can be performed stably by applying this method. In this case, silver with an appropriate particle size may be filled to the extent that it does not interfere with the passage of the plating solution, but in this silver filling tank or in the plating solution, at least 50% of the 02- is in the state of free ions.
It is essential to contain 0 ppm-10,00ppm.

Although the required amount of silver varies depending on the particle size, that is, its surface area, it can be determined by taking into account the amount of plating solution to be circulated and the concentration of the components. Since silver is oxidized by total reduction of Fe”+, it is necessary to reduce it and regenerate it.
This can be reused by replacing it with a separate spare silver filling tank and regenerating it during processing of the plating solution.

In this way, when performing iron-based metal plating, a silver reduction tank is provided in the plating solution circulation path, and plating is performed while constantly reducing Fe"+e with silver.
Good plating can be obtained by eliminating the adverse effects caused by the formation. In addition, the range of an- to be added is 500 to 10. O
The cIV of freθ, - is 500, which is OOppm.
This is because if it is less than ppm, the reduction rate is low and the consumption of silver is large, and if it exceeds lo, 000 ppm, the effect becomes constant and there is no point in adding a large amount.

aQ- can be added by compounds such as NH, cLHcj2, xaff%Nacj2, etc.

As described above, when performing iron plating continuously, by constantly treating the plating solution in a silver reduction tank and plating while reducing Fe3+ ions, the plating efficiency can be kept constant and the plating can be performed well. I can do it.

Next, a more detailed explanation will be given with reference to examples.

Example 1 Continuous iron-zinc alloy plating was performed using the apparatus shown in FIG. In Figure 1, a plating solution (
FeSO4・7H20380y/f! ,,ZnSO4
・7H20507/n, (Nk)2S0430 l!
/ 11, pH 1,2, Fe + 3 ion 10y7
1), an anode (Pb-5n(5) alloy) 2 and a cathode (cold-rolled steel plate with a thickness of 0.8M, width 6 cm, length 15 cm)
(cut to rn) with current density 80A/
dm2, bath temperature 40°C), plating is applied, a flow meter 10) takes out a part of this plating solution, guides it to the melting tank 4, iron 5,
Fe ions and Zn are brought into contact with zinc 6 into the plating solution.
Ions are replenished, and then reduction tank 7 (area 50111 x 5
0 word, height 70μ filled with silver 8 with a diameter of 0.5 to 3wL) and passed at a rate of 5Q/min. At this time, cQ
- Reduce Fe + 3 in the liquid by adding ammonium chloride to a concentration of 5,000 to 10,000 ppm.
The ion average was reduced to 4y/II=.

Using this method, after energizing a predetermined amount of electricity, the Fe-Z
N-alloy plating was performed and the samples were evaluated. As a comparative example, samples without silver reduction treatment were also evaluated. The evaluation results are the energization shown in Table 1. From this result, it is clear that those plated with silver while reducing Fe'' produced therefrom can have excellent brightness.

When the surface of the silver 8 in the dissolving tank 7 is oxidized and the reducing ability is reduced, the silver 8 in the reducing tank 7 is switched to the reducing tank 7'. By alternately using the dissolving tanks 7 and 7' in this way, Fe+3 in the plating solution is continuously reduced. The reduced plating solution passes through a filter 9 to remove impurities, and is returned to the plating solution tank 1. The present invention performs continuous reduction in this manner to reduce Fe+3 in the plating solution.

Example 2 Using the apparatus shown in Fig. 1, a cold-rolled steel plate with a thickness Q and f3m was plated with zinc to a thickness of 10 y/m2, and a galvanized steel plate was cut into 6 crn in diameter and 15 + cn in length, and this was used as a plated substrate. Iron plating was applied to only one side of this under the following iron plating conditions to confirm the effect of silver reduction.

Plating bath composition u Fe5o4 ・7H20350f/
11, (NH4)28041207/1. , Fe+3 ion 4y/2 and pH 1.5 (adjusted with H2SO4),
The current density was 60 A/dm2, and the bath temperature was 30°C.

As the evaluation results are shown in Table 2, it is clear that iron plating can be stably performed on galvanized steel sheets by the silver reduction method.

As described above, according to the silver reduction method, Fe-based metal plating can be stably obtained, and continuous plating (long-term use of the bath) was difficult even with the use of additives as in the conventional method. It is clear that this method can be easily carried out. Furthermore, silver itself can be recycled and reused separately, which is advantageous.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention. l...Plating solution tank, 2...Anode, 3-...Cathode, 4...Dissolution tank, -5...Iron, 6...Zinc, 7.7'.・-・Reduction tank, 8...Silver, 9...
Filter, 10... Flowmeter. Patent applicant Nippon Steel Corporation Representative Patent attorney Masao Inoue

Claims (1)

[Claims] ], An iron-based metal plating method characterized by plating continuously while reducing trivalent iron ions generated in a plating bath using silver when applying iron or iron alloy plating.