JPH09302452A - Non-galvanizing generation preventive method in galvanizing process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to prevent non-galvanizing to be generated in the galvanizing process by controlling the quantity of iron powder in the rolling oil stuck to the steel plate after the cold rolling. SOLUTION: In the galvanizing process of a steel sheet, the quantity of iron powder in the rolling oil stuck to the steel sheet before galvanizing is controlled to be <=200mg/m<2> . In the galvanizing process of steel sheet, rolling is performed with the mean roughness (Ra) of 0.3-0.58μm at the center line of a work roll in the cold rolling process which is the pretreatment of the galvanizing process.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for controlling the amount of iron powder in rolling oil adhering to a steel sheet after cold rolling to prevent non-plating that occurs in a hot dip galvanizing process. is there.

[0002]

2. Description of the Related Art Conventionally, the occurrence of non-plating is prevented by removing rolling oil containing iron powder adhering to a steel sheet by using electrolytic degreasing or alkaline cleaning equipment in front of a hot dip galvanizing process.

[0003]

The electrolytic degreasing and alkaline cleaning apparatus has a very high cost, and since the apparatus itself is large, a large-scale remodeling is required when it is added, which causes a problem that the cost is very high. In addition, the brush rolls used in this apparatus are clogged with deposits on the surface of the steel sheet, which causes a problem that the removal ability is reduced.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and reduces the friction coefficient of a cold-rolled work roll to reduce the amount of wear, thereby adhering to a rolled steel sheet. The amount of iron powder in the rolling oil is 40 to 200 mg / m ²
After that, the surface of the steel sheet is heated in a non-oxidizing atmosphere, and subsequently in a reducing atmosphere, followed by hot dip galvanizing to prevent non-plating.

As a result of investigating the cause of occurrence of non-plating, FIG.
As shown in, the correlation between the amount of iron powder adhering to the steel sheet after cold rolling and the occurrence of non-plating was confirmed. According to this, non-plating occurs when the amount of iron powder becomes 200 mg / m ² or more. This is because the rolling oil reacts with the iron powder to increase the viscosity and the boiling point, and C remains around the adhered iron powder, causing non-plating.

[0006]

As a result of investigating the frictional characteristics of the cold-rolled work rolls, a relationship between the rolling distance and the amount of iron powder adhered to the steel sheet was found as shown in FIG. It was found that the amount was 200 mg / m ² or less. Further, from the relationship between the rolling distance and Ra shown in FIG. 3, when the rolling distance is 50 km or more, the average surface roughness Ra of the cold-rolled work roll is 0.58 μm or less, and if rolling is performed at this roughness or less, no plating occurs. It has been found that can be prevented. The lower limit value from the post-modification adhesion amount in this figure is the lower limit value that can maintain the grip force in cold rolling, and Ra at that time is 0.3 μm.

[0007]

EXAMPLES Table 1 shows the conditions of the cold-rolled work roll used in the present invention. FIG. 4 shows the amount of adhered iron powder and the amount of oil in the case of rolling with such a low roughness work roll and the conventional case. FIG. 5 shows the occurrence of non-plating before and after changing the roughness of the cold-rolled work roll. As shown in these figures, the amount of rolling oil containing iron powder adhering to the steel sheet was significantly reduced, and along with this, the occurrence of non-plating could be significantly suppressed.

[0008]

[Table 1]

[0009]

According to the present invention, it is possible to reduce the rolling oil containing the iron powder adhered to the steel sheet, so that the non-plating can be completely prevented and the yield can be improved.

[Brief description of drawings]

FIG. 1 is a correlation diagram between the amount of iron powder adhering to the steel sheet and the occurrence of pores after cold rolling,

[Fig. 2] Correlation diagram between rolling distance and amount of iron powder deposited on steel plate,

FIG. 3 is a correlation diagram of rolling distance and cold-rolled work roll roughness (Ra),

FIG. 4 is a comparison diagram of the amount of adhered iron powder between the conventional technique and the present invention,

FIG. 5 is a comparison diagram of a non-plating occurrence state between the conventional technique and the present invention.

Claims (2)

[Claims] 1. A process for hot dip galvanizing a thin steel plate, wherein the amount of iron powder in rolling oil adhered to the steel plate before plating is controlled to 200 mg / m ² or less. Of non-plating prevention method in. 2. In the process of hot dip galvanizing a thin steel sheet, the center line average roughness (Ra) of the work rolls is rolled in the cold rolling step which is the preceding step to 0.3 to 0.58 μm. A method for preventing the occurrence of non-plating in a hot dip galvanizing manufacturing process.