JPH0751730A - Method for descaling steel - Google Patents

Abstract

PURPOSE:To improve the quality of a product exterior and to reduce man-hour of repairing the surface. CONSTITUTION:In the descaling method for steel in which scales produced at the time of hot rolling of seamless pipe, hot rolled steel sheet, etc., are removed by a descaling device 2 using high pressure water, the steel surface is injected with the high pressure water having a discharge pressure of 100kgf/ cm<2> that is imparted with a frequency of 500 to 2000Hz and a pulse pressure ratio of 2 or more. Consequently, a descaling performance is greatly improved without an increase in flow rate, and the generation of surface flaws is reduced on steel products.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a descaling method for steel products, which removes scales formed on the surface of steel products produced by hot rolling.

[0002]

2. Description of the Related Art The primary scale generated when heating a steel material in a heating furnace and the secondary scale generated during the rolling process are
It has no ductility and is pressed against steel by rolling, which accelerates wear of the rolling rolls and deteriorates the surface texture of the product. Therefore, the scale is removed by spraying high-pressure water immediately before or immediately after the hot rolling stand. The scale removal on the surface of the steel material by the high-pressure water is to blow away with the kinetic energy of the high-pressure water jet. Therefore, in order to increase the descaling ability, it is necessary to further increase the pressure of the high-pressure water or increase the flow rate. However, increasing the pressure and increasing the flow rate not only increase the equipment cost but also lower the temperature of the material to be rolled, so that the normal pressure is 15 to 25 MPa (about 150 to 255 kg).
Before and after f / cm ² ), the number of nozzle stages is generally about 1 to 3.

[0003]

The above-mentioned scale removal with high-pressure water can remove the scale to such an extent that there is no problem in the product in descaling carbon steel. However, in the case of alloy steel containing a large amount of Cr and Si, C is denser and stronger than the scale of carbon steel.
Since scales composed of r-oxides, Si-oxides, and other oxides are generated, the scales cannot be removed sufficiently, and the remaining scales are pressed into the material to be printed during the rolling process and printed. It has the problem of becoming flawed.

That is, as shown in FIG. 2, the scale layer of carbon steel has _three layers of Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO from the outside.
In the layered structure, only FeO is formed on the base metal side,
As shown in FIG. 3, the scale layer of the alloy steel is composed of FeO and C.
Cr oxides such as r ₂ O ₃ , FeCr ₂ O ₄ , and Fe ₂ SiO ₄ ,
A dense and strong mixed layer of Si oxide is formed on the base material side. The descaling property due to these scale compositions is Fe
There is a difference of O> Fe ₃ O ₄ > Fe ₂ O ₃ > (FeCr ₂ O ₄ etc.). For this reason, even if the same descaling method as that for carbon steel is applied, the scale generated on the surface of the alloy steel cannot be sufficiently descaled, and the oxide is rolled while the oxide remains.

An object of the present invention is to provide a descaling method for steel products which can effectively remove scale in the hot rolling process, improve the quality of the outer surface of the product and reduce the number of surface maintenance steps.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted various tests and examinations in order to achieve the above object. As a result, the pulsating pressure is applied to the high-pressure water, whereby the high-pressure water ejected from the nozzle is dripping, and the dripping water droplets act on the scale layer at a pressure ρcv (where ρ: density, c: speed of sound in water,
It was confirmed that (v: velocity of water) is several times larger than kinetic energy 1 / 2ρv ² , and therefore, the descaling property can be greatly improved without increasing pressure and increasing flow rate, and arrived at the present invention.

That is, the present invention relates to a steel material descaling method in which a secondary scale generated during hot rolling of a seamless steel pipe, a hot rolled steel sheet or the like is removed by a descaling device using high-pressure water, and has a frequency of 500 to 2000 Hz and a pulse pressure ratio of 2
Discharge pressure with the above pulsating pressure 100 kgf / cm ²
It is a method for descaling a steel product, characterized in that the above high-pressure water is sprayed from the nozzle onto the surface of the steel product.

[0008]

In the present invention, the frequency is 500 to 2000.
Discharge pressure 500 with pulsating pressure of 2 Hz or more and pulse pressure ratio of 2 or more
Since high-pressure water of kgf / cm ² or more is jetted onto the steel material surface, the high-pressure water jetted from the nozzle is dripping, and the pressure P acting on the scale on the steel material surface has a density ρ and a sound velocity in water. If c and the velocity of water are v, then P = ρcv. This is several times larger than the kinetic energy 1 / 2ρv ² when simply depressurizing by injecting high-pressure water,
A stronger force can be applied to the scale layer, many cracks can be generated in the scale, and the descaling property can be improved without increasing the flow rate.

In the present invention, the frequency of the pulsating pressure applied to the high pressure water is set to 500 to 2000 Hz because the jet stream is not sufficiently dripping if the frequency of the pulsating pressure is less than 500 Hz.
This is because it is difficult to give a frequency exceeding 2000 Hz at the current technical level. Further, the pulse pressure ratio is set to 2 or more because when the pulse pressure ratio is less than 2, the difference in the pressure of water is small and the momentum of ρcv due to the droplet formation of the jet flow cannot be used. Furthermore, the discharge pressure of high-pressure water is set to 100 kgf / cm ² or more because it is 100 kgf / cm ^2.
If it is less than cm ² , the pressure is weak and even descaling becomes difficult.

The pulsating pressure may be applied to the high-pressure water by any method, for example, a method of generating cavitation by electric discharge in water, a method of mechanically interrupting a jet flow to give fluctuations, a pipe or a nozzle. There is a method to change the chamber volume by changing the chamber volume by using a piston, etc., but a mechanical method outside the nozzle that cuts a direct jet by rotating a disk with a hole or slit at the nozzle tip is a facility cost. It is a good idea from the aspect of the above.

[0011]

EXAMPLE As shown in FIG. 1, just before the stretch reducer 1, which is the final finishing rolling machine of the Mannesmann mandrel mill line, 10 nozzles, an injection angle of 20 °,
A descaling device 2 having an attachment angle of 8 ° and an injection ring diameter of 500 mm is provided, and the scale generated on the surface of the pipe 3 in the reheating furnace is descaled immediately before rolling. This descaling device has a pump discharge pressure of 500 kgf / c.
The method of the present invention in which pulsation with a frequency of 1600 Hz and a pulse pressure ratio of 3 is applied to high-pressure water of m ² to perform descaling using a jet flow of 200 L / min, and a pressure of 150 kgf / cm
^With respect to each of the conventional methods in which the high-pressure water of No. ² was jetted at a flow rate of 500 L / min to perform descaling, the occurrence rate of defective external surface quality products such as pockmark defects was measured by visual observation. As a result, it was 0.01% in the case of the method of the present invention in which pulsating pressure was applied to high-pressure water for descaling, whereas it was 0.1% in the case of the conventional method of simply injecting high-pressure water. there were.

[0012]

As described above, according to the method of the present invention, in the descaling with high-pressure water, the pulsating pressure is applied to the high-pressure water, so that the descaling property is greatly improved without increasing the flow rate. It is possible to reduce the occurrence of surface flaws in the steel product due to the residual, and to reduce the number of surface maintenance steps.

[Brief description of drawings]

FIG. 1 is a plan view showing an installation position of a descaling device in an embodiment.

FIG. 2 is an enlarged sectional view of a scale layer of carbon steel.

FIG. 3 is an enlarged cross-sectional view of a scale layer of alloy steel.

[Explanation of symbols]

 1 Stretch reducer 2 Descaling device 3 Tube

Claims (1)

[Claims] 1. A method of descaling a steel material, wherein a scale generated during hot rolling of a seamless steel pipe, a hot rolled steel sheet or the like is removed by a descaling device using high-pressure water, wherein a frequency of 5
A descaling method for a steel material, comprising: injecting high-pressure water having a pulsation pressure of 0 to 2000 Hz and a pulsation pressure ratio of 2 or more at a discharge pressure of 100 kgf / cm ² or more onto a steel material surface.