JPH0949068A - Production of hot dip coated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the adhesion of a deteriorated flux to a steel sheet, to prevent the formation of bite flaws and to improve the yield of products by lowering the oxygen concn. of the flux deposited and suspended on a plating bath surface at the time of plating. SOLUTION: A small amt. of the flux is applied on the steel sheet A after annealing, degreasing, pickling, pre-electroplating and pre-flux treating by a flux applying device 23 prior to hot dip coating and, thereafter, the steel sheet is immersed into a plating bath 13. At this time, a nonoxidizing gas is injected into the plating bath 13 from a nonoxidizing gas introducing pipe 25 disposed in a flux vessel 12 on the surface of the plating bath, by which the oxygen concn. in the flux vessel 12 and the oxygen concn. on a flux 12' floating on the plating bath surface are kept at <=1% to prevent the deterioration of the flux 12'. The gas to be injected from the nonoxidizing gas introducing pipe 25 may be any gases, insofar as the gases are nonoxidizing gases. While the nonoxidizing gases are not specified, gaseous N2 is more preferable in terms of cost effectiveness.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a hot dip plated steel sheet using a flux.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Application Laid-Open No. 61-217565 has been known as a method for producing a hot dip plated steel sheet using a flux. This hot dip plated steel sheet will be described with reference to FIG. 4 using Zn-Sn alloy plating as an example. That is, FIG. 4 shows a conventional continuous hot-dip Zn-Sn alloy plated steel sheet manufacturing facility. In FIG. 4, reference numeral 1 is an uncoiler, 2 is a welding machine for joining the annealed steel plates A, 3 is a front looper, 4 is a degreasing device, 5 is a scrubber, 6 is a water washing device, 7
Is a pickling device, 8 is a water washing device, 9 is a pre-electroplating device,
10 is a water washing device, 11 is a pre-flux tank, 12 is a flux tank, 12 'is a floating flux on the bath surface, and 13 is Zn.
-Sn alloy plating bath, 14 plating pot, 15 unit weight adjusting device, 16 cooling device, 17 quench device, 18 chemical treatment device, 19 water washing tank, 20 drying device, 21 rear looper , 22 are coilers, and 23
Is a flux coating device, and 24 is a metal pump. In such equipment, after degreasing, pickling, pre-electroplating and pre-fluxing the annealed steel sheet A in the conventional method, a small amount of flux is applied to the steel sheet before the plating bath,
In this method, the flux separated on the surface of the plating bath is appropriately removed by a metal pump, and the thickness of the flux floating on the surface of the bath is kept constant to carry out continuous hot-dip plating.

[0003]

In this conventional plating method, when a water-soluble flux is used, the amount of the water-soluble flux applied before the plating bath increases or the amount of the water-soluble flux applied increases. At least when the speed of the steel sheet entering the plating bath increases, the new surface of the metal in the plating bath generated by bumping in the plating bath reacts with oxygen in the atmosphere due to the water of the flux brought into the plating bath by the steel sheet. Metal oxide is produced. Even when the flux is not water-soluble, when the speed of the steel sheet entering the plating bath of the steel sheet increases, the air entrained in the steel sheet reacts with the plating bath to produce metal oxides. When these metal oxides are mixed in the floating flux on the surface of the plating bath, the flux deteriorates, the viscosity of the floating flux rises, and the deteriorated flux is entrained in the plating bath together with the steel sheet and rolls in the plating bath. Entrapment between the steel plates, scratching the steel plates or pulling up from the plating pot while adhering to the steel plates will cause stains on the plating appearance and prevent the quality of the plating from being ensured. Therefore, it is feared that productivity will not increase because the steel sheet passing speed is reduced in order to suppress the above.

[0004]

SUMMARY OF THE INVENTION The present invention provides a conventional fused Z
It has been found that the above-mentioned problems associated with the method for producing an n-Sn alloy or Pb-Sn alloy plated steel sheet can be prevented by lowering the oxygen concentration on the floating flux in the plating bath and suppressing the deterioration of the floating flux. It is a manufacturing method of the hot-dip plated steel sheet that has been completed. The gist is molten Zn
A method for producing a hot-dip plated steel sheet, characterized in that the flux is suspended in a plating bath of a -Sn alloy or a Pb-Sn alloy so that the oxygen concentration on the floating flux is 1% or less.

[0005]

The method of the present invention will be described below with reference to the drawings. FIG. 1 is an example of equipment for performing hot-dip Zn-Sn alloy plating according to the present invention. A steel sheet A that has been annealed and subjected to degreasing, pickling, pre-electroplating, and pre-flux treatment is fluxed by a flux coating device 23. After being applied, Z is applied in the molten Zn-Sn alloy plating bath 13 through the flux tank 12.
n-Sn alloy plating is performed. Reference numeral 25 is a pipe for introducing a non-oxidizing gas into the flux tank, 26 is an oxygen meter for managing the oxygen concentration in the flux tank, and 24
Is composed of a metal pump for appropriately removing the floating flux 12 'accumulated in the flux tank.

In such a structure, as shown in FIG. 1, a small amount of flux is applied by the flux applying device 23 to the steel sheet A which has been annealed and degreased, pickled, pre-electroplated and pre-fluxed before the plating bath. Then infiltrate into the plating bath. At this time, the flux separated from the steel sheet floats and accumulates on the plating bath surface in the flux tank, but by introducing the non-oxidizing gas from the non-oxidizing gas introducing pipe 25 into the flux tank,
By lowering the oxygen concentration in the flux tank, the metal oxidation of the plating bath in the flux tank is suppressed, so the deterioration of the flux on the bath surface inside the flux tank, which was observed by the conventional method, is suppressed, and the plating appearance quality is improved. It is possible to manufacture a good plated steel sheet. Here, the gas introduced into the flux tank may be a non-oxidizing gas, but N ₂ gas is more preferable from the viewpoint of cost.

FIG. 2 is a graph showing the relationship between the oxygen concentration in the flux tank and the deteriorated flux attachment rate. That is, Fig. 2 shows the oxygen concentration on the floating flux on the plating bath in the flux tank, the floating flux on the plating bath, and the deterioration attached to the steel plate when the steel plate is pulled into the plating bath and then pulled up from the plating bath. It shows the result of experimentally obtaining the relationship of the flux. Here, the flux is an aqueous solution containing hydrochloric acid and having a chlorine conversion amount of 1 to 35 wt%, and FIG. 2 shows an example of an experiment performed with a 30 wt% ZnCl ₂ aqueous solution.

It has been experimentally found that when the oxygen concentration in the flux tank becomes 1% or less, the rate of attachment of the deteriorated flux attached to the steel sheet decreases. This is considered to be because the oxygen concentration in the flux tank was set to 1% or less, whereby the oxidation of the metal in the plating bath in the flux tank was suppressed and the deterioration of the flux was suppressed. Further, FIG. 3 is a diagram showing the yield of products due to the oxygen concentration in the flux tank and the adhesion of the deteriorated flux. This figure also shows that the oxygen concentration in the flux tank is 1
The yield loss of the product was also improved by making it less than%. Further, as can be seen from FIGS. 2 and 3, when the oxygen concentration in the flux tank is 0.5% or less, the product yield loss is further improved.

[0009]

[Example] 10% Zn-Sn with a plating bath temperature of 350 ° C
Ni plating per side after degreasing and pickling while passing an annealed ultra-low carbon steel sheet having a thickness of 0.8 mm and a width of 1000 mm at a line speed of 70 m / min in each of the alloy plating bath and the 8% Sn-Pb alloy plating bath After pre-plating at 1 g / m ² and immersing in a 2% hydrochloric acid aqueous solution for pre-flux treatment, 30 wt% ZnCl ₂ aqueous solution is applied at 50 g / m ² per side to continuously penetrate the plating bath for plating. went. The flux applied before the plating bath is separated from the steel plate on the surface of the plating bath in the flux tank and ZnCl ₂ is melted and evaporated to float on the bath surface. In that state, the product yield loss due to the bite flaw on the pot roll due to the oxygen concentration in the flux tank and the deterioration flux was investigated. (Here, the product yield loss indicates the ratio of the product length removed by the bite flaw to the entire product length.) As a result, both the Zn-Sn alloy plating and the Pb-Sn alloy plating have oxygen in the flux tank. When the concentration was 1% or less, the biting by the pot roll due to the deteriorated flux was reduced, the product yield loss was improved, and stable plating operation with good plating appearance was made possible. These examples are shown in Tables 1 and 2.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

As described above, according to the present invention, the oxygen concentration in the flux tank is lowered to suppress the oxidation of the metal in the flux tank and prevent the deterioration of the flux. Staining flaws caused by biting and stains on the plating appearance due to adhesion to the steel sheet after plating are eliminated, stable flux operation is eliminated as there is no deterioration flux removal work for the purpose of improving the product yield as a plated product and eliminating flaws and stains. It has become possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of equipment for performing hot dip Zn—Sn alloy plating according to the present invention,

FIG. 2 is a diagram showing the relationship between the oxygen concentration in the flux tank and the deterioration flux adhesion rate;

FIG. 3 is a diagram showing the relationship between the oxygen concentration in the flux tank and the yield loss of products,

FIG. 4 is a view showing a conventional continuous hot-dip Zn-Sn alloy plated steel sheet manufacturing facility.

[Explanation of symbols]

 1 Uncoiler 2 Welder 3 Front looper 4 Degreasing device 5 Scrubber 6 Water washing device 7 Pickling device 8 Water washing device 9 Pre-electroplating device 10 Water washing device 11 Pre-flux bath 12 Flux bath 12 'Floating flux 13 Zn-Sn alloy plating bath 14 Plating pot 15 Balancing amount adjusting device 16 Cooling device 17 Quenching device 18 Chemical treatment device 19 Water washing tank 20 Drying device 21 Rear looper 22 Coiler 23 Flux device 24 Metal pump 25 Piping for introducing non-oxidizing gas into the flux tank 26 Oxygen meter A steel plate

Claims (1)

[Claims] 1. A molten Zn-Sn alloy or Pb-S.
A method for producing a hot-dip plated steel sheet, characterized in that the flux is suspended in a plating bath of an n-based alloy so that the oxygen concentration on the floating flux is 1% or less.