JP2701636B2 - Descaling method of hot rolled steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for descaling a hot-rolled steel strip.

[0002]

2. Description of the Related Art Since a scale is attached to a hot-rolled steel strip (hereinafter referred to as a black-rolled hot-rolled steel strip), it is necessary to remove the scale before performing cold rolling thereafter.

[0003] The descaling method is roughly classified into an acid washing method and a mechanical descaling method. The pickling method requires a long pickling tank and a large-scale waste acid treatment equipment, occupies a large space and increases equipment costs, and is not economical due to the use of a large amount of acid, and the working environment is poor. .

On the other hand, the mechanical descaling method is intended to remove the scale by shot blasting, brushing, grinding, or the like, and has a disadvantage that the descaling cannot be performed uniformly as in the pickling method.

[0005] On the other hand, as disclosed in Japanese Patent Publication No. 57-59311, a method of pickling a continuously passing steel strip by a spray method has been proposed. Also, Japanese Patent Application Laid-Open No.
JP-A-09517 proposes a method in which high-pressure water is injected into a hot-rolled steel strip after scale breaking to remove scale efficiently at a low cost without requiring waste acid treatment.

Conventionally, in order to reduce the time required for pickling of hot-rolled steel strip, various mechanical scale breaking such as shot blasting, brushing, leveling, and rolling are performed before pickling.

A method of scale breaking and descaling using high-pressure water is proposed in Japanese Patent Application Laid-Open No. 57-109517. However, as shown in FIG. 4, the scale is not completely removed by this method alone, and the scale remains. Therefore, it is necessary to perform simple pickling and the like in the next step. The pickling includes a method using a pickling tank and a spray method. The spray method can effectively descale by simple means. Spray pickling is performed using an acid-resistant pump, but if the acid concentration can be reduced, the pump life is extended.

[0008]

An object of the present invention is to provide a method for efficiently descaling a hot-rolled steel strip with black scale.

[0009]

In the descaling method of the hot-rolled steel strip according to the present invention, the hot-rolled steel strip is bent by at least two rolls while giving a tension of 1.0% or more to the hot-rolled steel strip. Applying and / or reducing by 1.0% or more by a rolling mill while applying the tension, spraying high-pressure hot water at a temperature of 50 ° C. or more at a pressure of 100 kg / cm ² or more on the steel strip surface, a concentration of 6 wt% or less The above problem is solved by means of spraying an acid solution of the formula (1) on the surface of the steel strip.

[0010]

The method of the present invention comprises scale breaking with a rolling mill or a tension leveler, descaling with high-pressure hot water in the cold, and spray pickling. By performing scale braking, it becomes more effective when descaling with high-pressure hot water. Further, by using the high-pressure water as hot water, the temperature of the steel strip can be increased without a heating tank, thereby making it possible to reduce the pickling time and acid concentration during spray pickling. By lowering the acid concentration, the life of the pump, which was a problem during spray pickling, can be extended, and effective descaling can be performed.

[0011] The bending or rolling of the hot-rolled steel strip with an elongation of 1.0% or more or the rolling of a rolling mill by 1.0% or more is performed in order to enhance the effect of high-pressure descaling in the next cold period. -It is more effective that both the elongation rate and the rolling reduction rate are large, which is effective, and these may be combined.

The reason why the pressure of the high-pressure water is set to 100 kg / cm ² or more is that when the pressure is smaller than 100 kg / cm ² , the descaling ability is reduced. The reason why the high-pressure water temperature is set to 50 ° C. or higher is that the steel strip temperature before spray pickling is higher as shown in FIG. If the temperature of the steel strip rises to about 40 ° C. when the water temperature is 50 ° C., then the pickling time can be reduced by about 60%.

The reason why the acid concentration at the time of spray pickling may be 6 wt% or less is that the scale on the steel strip surface is almost removed by scale breaking and high-pressure water, and the temperature of the steel strip is also increased. Complete descaling is possible at low concentrations.

By lowering the acid concentration, the life of the acid resistant pump is prolonged, and as shown in FIG.
As compared with the case of 0 wt%, the life is 2.
5 times. In the case of spray pickling, the time required for pickling is shorter than in the immersion pickling method, and the effective length of the spray pickling is changed by changing the numerical aperture of the spray nozzle according to the passing speed of the processing material. It can be changed, and optimal pickling can be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an embodiment of the method for descaling a hot-rolled steel strip according to the present invention will be described. In the descaling method of the present invention, a bending process is performed on the hot-rolled steel strip 2 with a tension leveler 4 including at least two rolls while giving a tension of 1.0% or more in elongation, and / or the tension is reduced. The rolling is performed by a rolling mill 3 while reducing the pressure by 1.0% or more.
spraying high-pressure hot water at a temperature of 50 ° C. or more at a pressure of at least kg / cm ² onto the steel strip surface, and a concentration of 6 wt% in the spray pickling equipment 7
The following acid solution is sprayed on the steel strip surface.

In FIG. 1, 1 is a rewinding machine, 2 is a steel strip, 3
Is a rolling mill, 4 is a tension leveler, 5 is a bridle device, 6 is a high-pressure descaling device, 7 is a spray pickling facility, 8 is a pump, 9 is an acid tank, and 10 is a winding machine.

The line of FIG. 1 has a thickness of 2.0 mm and a width of 80 mm.
The descaling test was performed through a 0 mm ordinary steel strip 2. At this time, after a 1.5% reduction in the rolling mill 3, the steel strip was stretched by 3% by the tension leveler 4 to perform scale breaking. The high-pressure descaling device 6 has a descaling pressure of 120 kg / cm ² and a descaling of 4 kg / cm ^2.
Used this book. At this time, the water temperature is set to 70 by the heater 61.
Warm water heated to ° C was used. Thereafter, spray pickling was performed with 3 wt% hydrochloric acid (temperature: 80 ° C.). As a result, the scale was completely descaled even when the line speed was increased to 250 mpm. On the other hand, 10%
After depressurizing, if only descaling is performed with four high-pressure descaling devices (pressure 120 kg / cm ² ) through the tension leveler 4, residual scale will be generated on the steel strip surface. I understood.

In a test in which scale breaking, high pressure descaling, and spray pickling were combined, the descaling water temperature was set to 25 ° C. at room temperature, and a line speed of 150 mpm was required for complete descaling. was there. Similarly, in a test combining scale breaking, high pressure descaling and spray pickling, when the hydrochloric acid concentration in the spray pickling was set to 10 wt%, the line speed could be increased to 350 mpm, but the life of the pump was reduced by 1 / It decreased to about 4.

In FIG. 1, the rinsing and drying steps after pickling are omitted.

[0020]

According to the present invention, the temperature of a steel strip can be raised without a heating tank, the pickling time and acid concentration during spray pickling can be reduced, the pump life can be extended, and descaling can be performed. Efficiency can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a descaling line to which a descaling method according to the present invention is applied.

FIG. 2 is a graph showing the relationship between the temperature of a steel strip before pickling and the rate of decrease in pickling time compared to when a steel strip at normal temperature is pickled.

FIG. 3 is a graph showing, as a ratio, a change in the concentration of hydrochloric acid and a pump life.

FIG. 4 is an explanatory diagram schematically showing a steel strip surface after descaling by a conventional method in an enlarged manner.

[Explanation of symbols]

1: rewinding machine, 2: steel strip, 3: rolling mill, 4: tension leveler, 5: bridle device, 6: high pressure descaling device, 7: spray pickling equipment, 8: pump, 9: acid solution tank, 10: Winder.

Claims (1)

(57) [Claims] 1. A method for bending a hot-rolled steel strip with a tension of at least 1.0% with at least two rolls while applying a tension of 1.0% or more, and / or applying a tension of 1.0% by a rolling mill while applying the tension. A hot-rolled steel strip comprising performing the above reduction, spraying high-pressure hot water at a temperature of 50 ° C. or more at a pressure of 100 kg / cm ² or more on the steel strip surface, and spraying an acid solution having a concentration of 6 wt% or less on the steel strip surface. Descaling method.