JP2735872B2 - Adjustment of plating bath composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a Zn-Ni-based alloy added as a plating bath composition when adjusting the composition of a nickel-containing hot dip galvanizing plating bath. The present invention relates to a method for adjusting the composition of a plating bath, wherein Ni in a zinc zinc mother alloy is dissolved in a plating bath in a good yield and in a uniform state.

[Prior art] Conventionally, as materials for pipes, general steel materials, small parts, etc.,
A steel material containing 0.02 to 0.30% by weight of Si and 0.05 to 0.10% by weight of P and subjected to immersion plating of molten zinc is widely used.

However, when such a steel material is subjected to hot-dip galvanizing with plain zinc, the Fe-Zn alloy layer develops abnormally,
The surface of the plated product loses its luster and exhibits a so-called "burn" phenomenon, or the amount of zinc attached becomes abnormally large.
The tendency to cause a cost increase phenomenon was strong.

As a means for solving such a problem, a method has been devised in which nickel is contained in a zinc bath in an amount of 0.05 to 0.2% by weight.
It is running.

In this case, with the progress of the plating operation, the capacity of the plating bath decreases and the composition of the plating bath also fluctuates. Therefore, while continuing the plating operation, it is necessary to adjust the component composition in the plating bath within a predetermined range. Is required.

The adjustment of Ni in the plating bath is usually performed by adding a Zn-Ni-based Ni-containing zinc master alloy containing about 3% by weight of nickel in a lump form. Even if the mother alloy is put into the plating bath as it is, it easily reacts with the Zn-Fe dross present at the bottom of the plating bath, and the degree of its reactivity varies. It was not easy to keep in the range of 0.2% by weight.

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the above-mentioned adverse effects and to stabilize the composition of a plating bath for hot dip galvanizing treatment.
Nickel addition that regulates the amount of nickel deposited on the hot dip galvanizing bath as much as possible in order to regulate the amount of plating applied to the plated product and to enable the shipment of plated products in a stable plating state. Is to provide a way.

[Means for Solving the Problems] The present inventors have conducted various studies in order to achieve the above object, and as a result, have found that a plating bath for hot dip galvanizing treatment in which a Zn-Fe-based dross layer is present below. When a certain amount of nickel is added to adjust the composition, the dross layer and the Ni-containing zinc master alloy are added until the Ni-containing zinc master alloy is completely dissolved in the plating bath. To prevent contact,
It is based on the finding that the problem can be solved by dissolving nickel in the plating bath.

Therefore, in the method for adjusting the plating bath composition of the present invention, Zn and
For the purpose of adjusting the composition of the hot dip galvanizing plating bath having a dross layer mainly composed of Fe, 0.10
Using a Ni-containing zinc master alloy containing up to 2.5% by weight of Ni, preventing contact between the dross layer and the Ni-containing zinc master alloy until the Ni-containing zinc master alloy is completely dissolved in the plating bath; It dissolves Ni into the plating bath.

Further, according to one embodiment of the present invention, the plating bath is a Zn bath.
This is a hot-dip galvanizing bath composed of a plating layer containing Ni as a main component, a dross layer mainly containing Zn and Fe, and a lower layer mainly containing Pb.

[Operation] Hereinafter, the operation of the present invention will be described.

0.15 to 2.5 wt% Ni, for example Zn-2 wt% Ni
Ni-containing zinc alloy of 500 ℃ which is the normal zinc alloy production temperature
When melted at up to 600 ° C., the metal structure of the Ni-containing zinc alloy is composed of an η phase mainly composed of pure zinc and a γ phase of a Zn—Ni alloy. Since the melting point of the γ phase is 880 ° C., the Ni-containing zinc alloy containing most of nickel in the γ phase is:
At a normal zinc plating bath temperature of 430 to 470 ° C., nickel is difficult to dissolve in the plating bath. Therefore, even if a Ni-containing zinc alloy is put into a plating bath in which a Zn-Fe-based dross layer exists under the plating layer, the dissolution of nickel in the plating layer is not performed quickly, and most of the nickel is removed. It will enter the Zn-Fe-based dross layer. This dross layer is composed of an η phase composed of pure Zn and a ζ phase composed of Zn—about 7 to 9 wt% Fe (melting point
530 ° C.), where Zn—about 15% by weight N
When the γ phase of i is mixed, the ζ phase and the γ phase are united to form a ternary alloy phase of Zn—about 6 wt% Fe—about 5 wt% Ni, and nickel dissolves in the plating phase. Will be gone.
From this, conventionally, even if the Ni-containing zinc master alloy is additionally added, nickel dissolved in the plating layer is small, and most of the nickel becomes a Zn-Fe-Ni alloy phase in the dross layer, Nickel yield was extremely poor.

Therefore, the present inventors, when throwing the Ni-containing zinc master alloy into the plating bath, do not directly throw the zinc master alloy into the plating bath, put in a basket or hang a chain, etc., the plating layer It has been found that by holding and dissolving in it, the desired amount of nickel can be added to the bath.

Here, 0.10% or more of the Ni content of the Ni-containing zinc master alloy and 2.5% or less.
When the Ni content in the plating bath is less than 0.15%, it is difficult to adjust the Ni content in the plating bath to 0.05 to 0.2%, which is an appropriate plating bath composition, because the Ni content is small and conversely, it exceeds 2.5%. This is because nickel contained in the nickel-containing zinc mother alloy precipitates as a γ phase, and the yield of nickel effectively acting in the plating bath is reduced.

The same effect can be obtained in a plating bath in which a layer mainly composed of lead is laid below.

[Example] (Comparative example) Using distilled zinc and electric nickel as raw materials, a Ni-containing zinc mother alloy containing Zn-2 wt% Ni was used in a graphite crucible using a resistance heating furnace.
Melted at 560 ° C.

Then, distilled zinc 2 was placed in a black smoke crucible using a resistance heating furnace.
After melting 5.1 kg at 480 ° C., dross of Zn-1.2 wt% Fe composition was added to molten zinc in an amount of 1.5 to reproduce the actual operating condition.
After charging Kg and stirring sufficiently, the mixture was allowed to stand. As a result, the plating bath was composed of a hot-dip galvanized plating layer and a Zn-Fe-based dross layer thereunder.

In this manner, a plating bath in which molten zinc and Zn-Fe-based dross coexist was prepared, and 1.4 kg of the Ni-containing zinc mother alloy was directly charged into the plating bath, and left at 450 ° C. for 7 days.
A sample was taken from the plating layer and the Ni content was analyzed. According to the analysis results, only 0.021% by weight of Ni was detected from the sample with respect to 0.1% by weight of Ni in the prepared composition, revealing that much of the nickel in the master alloy had dissolved in the dross. Became.

(Example) In the same manner as in the comparative example, when introducing 1.4 kg of Ni-containing zinc master alloy into molten zinc containing Zn-Fe-based dross, the Ni-containing zinc mother alloy was stored in a stainless steel mesh basket, By suspending in the plating layer, contact with the dross existing at the bottom of the plating bath was avoided, and other processes were performed in the same manner as in the comparative example, and then an analysis sample was collected from the plating layer. According to the analysis value of this sample, the detected Ni content was 0.090% by weight, and it was found that most of the added amount of 0.1% by weight was dissolved in the plating layer.

[Effects of the Invention] The present invention proposes a method of dissolving nickel, which is a precious raw material, in a hot-dip galvanizing bath according to a target composition with a high yield, and contributes to the industry together with its easy handling. There is something big to do.

Claims (2)

(57) [Claims] When a nickel-containing zinc master alloy is used to adjust the composition of a hot dip galvanizing plating bath in which a dross layer mainly composed of Zn and Fe is present, the nickel-containing zinc mother alloy is applied to the plating bath. Dissolving the Ni-containing zinc master alloy in the plating bath so as to prevent contact between the dross layer and the Ni-containing zinc master alloy until completely dissolved in the plating bath, and a method of adjusting a plating bath composition. . 2. The method according to claim 1, wherein the Ni-containing zinc master alloy contains 0.10 to 2.5% by weight of N.
The method for adjusting the composition of a plating bath according to claim 1, wherein i is included.