JPH1058027A - Descaling method for steel and descaling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and sufficiently execute the descaling of a steel sheet by removing the scale while heating by using microwave or using a chemical or mechanical means after heating a scale layer on the surface. SOLUTION: A microwave heating device 2 is provided with limiting chambers 6 before and behind a heating chamber 10, composed of a microwave generator 3, waveguide 4 of microwave, nozzle 5, wave absorber 7 for preventing the leakage of electromagnetic wave and wave deflecting plate 8 and agitating impeller 9 for equalizing the internal temp. is provided. As necessary, a microwave heating device 2a having a similar structure is also used in the underside of the steel sheet 1. By irradiating the microwave to the steel sheet 1 which is transported to the microwave heating device 2 with steel sheet transporting rollers in the heating chamber 10, only the scale layer on the surface is heated, thermal stress is increased and separability is promoted. In this way, the efficiency of descaling with the high-pressure water is improved, defects are reduced and productivity is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the surface of a steel plate (thin plate, thick plate), shaped steel, wire rod, bar steel, slab or billet, or a forged product (hereinafter collectively referred to as a steel material). And a method and apparatus for removing scales that are being generated.

[0002]

Oxide film of the Related Art steel _{(FeO, Fe 3 O 4,} Fe
₂ O ₃ or the like, or a composite oxide thereof. In the following, scale is required to be sufficiently removed before rolling, forming, surface treatment or the like in order to avoid adverse effects on the surface quality of the product.

[0003] The descaling method can be roughly classified into a chemical method (such as pickling) and a mechanical method (such as high-pressure water or shot blasting).
The finished quality is not always sufficient.

[0004] For example, descaling is performed using high-pressure water before hot rolling. In many cases, high-Si steels have poor descaling properties, making it difficult to completely remove scale. As an improvement measure, Japanese Patent Application Laid-Open No. 7-144213 discloses a steel containing Si.
Heat to 1230 ~ 1300 ℃, hit pressure 2000 before finish rolling
A method for preventing scale flaws in a hot-rolled steel sheet which is descaled with high-pressure water of K Pa or higher is disclosed. However, this method increases the heating cost, necessitates an increase in the equipment of a high-pressure water pump for descaling, and when high-pressure water is used for rolling thin materials, the rolling temperature is excessively lowered, which adversely affects the material and flat shape. Yes, there are problems.

Japanese Patent Application Laid-Open No. 61-95718 discloses that in order to realize complete descaling at high speed, the surface of a steel material is locally heated by a flame, and the scale is lifted by a difference in thermal expansion and contraction. Methods for removing this by mechanical means are disclosed. However, in this method, the burner needs to be brought closer to the steel material in order to improve the heating efficiency, so that the material may collide with the burner, and an exhaust gas treatment facility is also required, which increases the facility cost. Furthermore, in this method, not only the scale layer but also the steel base material is heated, so that there is a problem that the effect of heating on the peeling of the scale is not sufficient.

[0006]

An object of the present invention is to provide a method and an apparatus for quickly and sufficiently descaling a steel material.

[0007]

The gist of the present invention resides in the following descaling method and descaling apparatus.

(1) A method of descaling a steel material, which comprises removing the scale layer by chemical or mechanical means while or after heating the scale layer on the surface using microwaves, and a method for descaling the steel material. apparatus.

(2) A method and an apparatus for descaling a steel material, wherein the scale layer on the surface of the steel material is removed by a chemical means while heating the scale layer on the surface of the steel material using a pulsed microwave.

The present inventors selectively heat only the scale layer before or while performing the normal descaling treatment, so that the scale due to the difference in thermal expansion and contraction between the scale layer and the steel base material. That the descaling efficiency can be dramatically improved by using this phenomenon, and that the microwave heating method can rapidly heat only the scale layer without heating the steel base material,
Thus, the present invention has been completed.

The microwave has a wavelength of 1 m or more among electromagnetic waves.
Those 1cm range of short wavelength of (frequency 300 MH _z ~30GH _z). Microwaves travel straight in space and are reflected by metal surfaces. When an electromagnetic wave is applied to a dielectric material that is an electrically insulating material, a polarization phenomenon is generated in the dielectric material, which is divided into a positive charge portion and a negative charge portion under the influence of a given electric field. When positive and negative polarization phenomena are alternately repeated at a high speed by a high-frequency electric field, a part of the energy of the electric field is absorbed by the dielectric and becomes thermal energy.

This phenomenon is used as heating means, and is called microwave heating when the frequency of the electric field belongs to the microwave band. This heating method is an internal heating in which the object to be heated itself generates heat, and thus has a feature that heating can be performed efficiently and rapidly. Microwave ovens are this typical application. Even if the metal is irradiated with microwaves, the metal is reflected on the surface, so that the metal body is not heated. But Fe
_{O, Fe 3 O 4, Fe} 2 O 3, Cr 2 O 3, Zn O, Al 2 O 3
Or the scale of various steel materials made of these composite oxides is a dielectric, and these can be heated by microwaves as described below.

Microwaves include pulse waves as shown in FIG. 7 in addition to continuous waves (hereinafter, in the case of distinguishing between continuous waves and pulse waves in microwaves, they are simply continuous waves or pulse waves, respectively). Written as a wave). T _p shown in FIG. 7 is the duration of each pulse, T _p is the period of the pulse. The pulse time ratio of t _p / T _p is less (hereinafter, D _u) referred to.

The output power at the peak of the pulse wave (hereinafter referred to as peak output power, referred to as P _p ) and the total output power per unit time (hereinafter referred to as average power, referred to as P _m ) are expressed by the following formula. There is a relationship shown in That is, the peak output power of the pulse wave increases in half proportion to the pulse time ratio.

P _m = P _p · D _u The concept of microwave heating related to descaling, which is the basis of the present invention, will be described with reference to FIGS.

FIG. 3 is a diagram showing the relationship between the heating time and the amount of temperature rise when iron oxide is heated by microwaves. Put iron oxide (Fe ₃ O ₄ or FeO) powder of approximately 50g in a ceramic container, which was determined by heating from room temperature at which the frequency 2450MH _z, continuous wave average power 1 KW, 3
The solid line indicates the result of investigation for Fe ₃ O ₄ , and the broken line indicates the result of investigation for FeO 2.

Due to the microwave heating, the iron oxide can be
Raise the temperature by about 100 ° C. From this experimental result, it was found that local heating of only the scale layer on the steel surface can be easily performed by microwave heating.

FIG. 4 shows that the scale layer is heated by irradiating a continuous wave to a steel plate at a temperature of 700 ° C. or higher, and immediately after that, descaling is performed with high-pressure water to investigate the effect of microwave heating on the peelability of the scale. It is a figure which shows the result. The steel plates used were as follows: C: 0.07%, Si: 0.8%, Mn: 1.5% by weight.
% Of hot rolled carbon steel sheet (hereinafter, the% indication indicating the chemical composition of the steel material indicates% by weight). 1 by microwave
When descaling was performed after heating for 2 seconds, the descaling rate was improved, and when the average power was set to 20 kW, the descaling rate was improved from about 60% to more than 90%.

FIG. 5 is a graph showing the results of an investigation on the effect of microwave heating on the descaling speed when pickling a hot-rolled steel sheet. A sample obtained from a low-carbon hot-rolled steel sheet having a thickness of 3 mm and a scale thickness of 10 μm containing 0.04% of C was pickled with a hydrochloric acid solution at various temperatures for 10 seconds while being irradiated with microwaves having an average power of 100 W, The descaling ratio by pickling was determined by a gravimetric method. Pulse time ratio 10 for pulse wave
/ 10000. As a comparison, the descaling ratio when pickling was performed without irradiation with microwaves was also determined, and is indicated by a circle in the figure.

When the scale layer is pickled while being heated by microwaves, the reaction is accelerated. When a continuous wave is used, only the scale layer is heated, and the difference in thermal expansion and contraction between the unheated steel base material and the phenomenon of promoting separation at the interface between the base metal and the scale layer, It is considered that the reaction was promoted by a synergistic effect with the promotion of the chemical reaction due to the temperature rise.

The reaction rate in the case of irradiating a pulse wave was even faster, and the descaling rate was more than doubled compared to the case of pickling without irradiating a microwave. As can be seen from the equation, the peak output power of the pulse wave is much larger than that of the continuous wave. For example, when the average power is 100 W, if the pulse time ratio is 10/10000, the peak output power is 100
It becomes 100 KW which is 0 times. The heating action determined by the average power is the same for both continuous waves and pulse waves, but it is presumed that a strong electric field corresponding to the peak output power was generated in the pulse wave, and the reaction speed was further increased due to this effect.

FIG. 6 shows the result of investigation on the effect of the pulse time ratio on the pickling speed. A sample of 30 mm width and 50 mm length taken from a hot-rolled steel sheet of ordinary steel with a thickness of 3 mm and a scale thickness of 8 μm containing 0.17% of C was acidified with a hydrochloric acid solution at 80 ° C. using a pulse wave having an average power of 100 W. I washed. The vertical axis is
The descaling ratio after pickling for 10 seconds under each condition was determined by a gravimetric method.

The pulse time ratio is 7/10000 to 60/10000
It can be seen that the pickling reaction is promoted in the case of the above range. The pickling speed is highest when the pulse time ratio is 10/10000. It is speculated that the synergistic effect of the pulse time ratio and the peak output power may affect the pickling rate.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The constitutional requirements of the present invention and the effects thereof will be described below with reference to an example in which the method of the present invention is applied to descaling in a hot rolling step and pickling of a hot-rolled steel sheet. explain.

FIG. 1 is a conceptual diagram of a microwave heating apparatus when the method of the present invention is applied to descaling in a hot rolling step. This device is installed upstream of a conventional descaling device (not shown) using high-pressure water performed in front of a rolling mill. Only the scale layer of the steel sheet 1 is selectively heated by the microwave heating device 2, and thereafter, descaling is performed using high-pressure water. As a result, the thermal strain of the scale layer increases, and the releasability is promoted, and the descaling efficiency is improved.

The microwave heating device 2 is a box-shaped device having a throttle chamber 6 having a lower ceiling before and after the heating chamber 10, and includes a microwave oscillator 3, a waveguide 4 for guiding microwaves to the heating chamber,
The tip nozzle 5 of the waveguide attached to the central ceiling of the apparatus body 2 in the direction of the object to be heated, the radio wave absorber 7 attached to the ceiling of the aperture chamber 6 for preventing leakage of electromagnetic waves, and the suspension from the aperture chamber 6 And a lowered curtain-shaped radio wave reflecting plate 8. A stirring blade 9 for making the internal temperature uniform is provided in the heating chamber 10.

If necessary, a microwave heating device 2a having a similar structure is used on the lower surface side of the steel plate 1. A protective cover 11a for preventing scale and cooling water from entering the steel plate 1 is attached to the device 2a used on the lower surface side. The protective cover 11a is not heated even when irradiated with the microwave,
In addition, anything that transmits microwaves may be used, for example,
Teflon (registered trademark), polystyrene or a quartz plate may be used. It is preferable to appropriately clean the scale so that scales and the like do not accumulate on the protective cover 11a.

The steel material 1 conveyed to the microwave heating device by the steel sheet conveying roll is irradiated with microwaves like a shower in the heating chamber, and only the surface scale layer is heated. Descaled by equipment.

Normally, descaling by hot is carried out by reducing the temperature of the steel material.
The coating is carried out at a temperature of 700 ° C. or higher, but it is preferable to heat the scale layer at a temperature of 100 ° C. or higher to obtain an effect on descaling. The magnitude of the average power of the microwave heating device required for this depends on the time during which the steel is to be irradiated with microwaves (this depends on the amount of scale on the surface of the steel, the passing speed of the steel, the required heating rate and heating And the area to be irradiated (width and the like).

For example, when the present invention is applied to descaling of a hot-rolled steel sheet on the entrance side of a finishing mill, if the microwave heating time can be secured for 3 seconds or more, the average power is 20 KW per one side of the steel sheet. Well, if the average power is increased, the heating time can be shortened accordingly. When the descaling is performed hot, the microwave may be a continuous wave or a pulsed wave because the purpose is to improve the descaling property by raising the temperature of the scale layer.

FIG. 2 shows a process of pickling a hot-rolled steel sheet.
It is the figure which showed the concept of the equipment arrangement | positioning at the time of pickling while irradiating a microwave. The steel sheet 1b is immersed in the pickling liquid 13 by, for example, a dipping roll 14 in the pickling tank 12, and is pickled.
The microwave heating device 2b is installed close to the upper part of the pickling tank 12, and the microwave is irradiated from the waveguide 4b toward the steel plate, whereby the scale layer on the steel plate surface is selectively heated. As a result, it is possible to reduce the pickling time due to the effect of promoting separation at the scale interface due to the difference in thermal expansion and contraction, and the effect of promoting a chemical reaction due to the effect of local temperature rise and pulse waves.

The structure of the microwave heating device is basically the same as that used in the above-mentioned hot rolling mill. In order to avoid the effect of pickling fumes, it is preferable to attach a protective cover 11b similar to that used for descaling the lower surface during hot rolling shown in FIG. The protective cover 11b may be any material that is not heated by microwaves, that transmits microwaves, and that can withstand corrosion caused by vapor generated from an acid solution, such as Teflon (registered trademark) or a quartz plate. .

When the microwave heating method is applied to descaling by a chemical method, for example, a steel plate at room temperature is heated to 50 ° C.
As described above, it is effective that the chemical treatment is performed by heating at preferably 60 ° C. or more. Although either a continuous wave or a pulse wave may be used, it is preferable to use a pulse wave from the viewpoint of improving the reaction speed. In particular, the pulse time ratio is 7/10000 to 60 /
It is more preferable to use a pulse wave having a range of 10,000 and an average power of 20 kW or more. This is because the electric field generated by the extremely large peak output power that is characteristic of the pulse wave promotes the descaling reaction.

The opposite side of the steel sheet is treated in the same manner by using the apparatus shown in FIG. 2 after the front and back surfaces of the steel sheet are turned over using a roll or the like to turn the original back side to the front side. Good.

When descaling by a chemical method after applying microwave heating, a device for irradiating microwaves on both upper and lower surfaces in front of the pickling tank is installed in the same manner as in descaling by hot. There are methods such as doing. Depending on the arrangement of the equipment, the microwave heating device may be installed in a vertical direction instead of the horizontal direction shown in FIG. An existing method such as a magnetron may be used for the microwave oscillator 3. Frequency is regulated by the Radio Law 915 ~ 2450MH
Any of the ranges of z may be used. Due to the characteristics of the microwave, there is no adverse effect on heating even if the distance between the waveguide tip nozzle 5 and the steel material 1 is large.

The method of the present invention utilizes the difference in thermal expansion and contraction between the scale layer and the steel material to increase the releasability of the scale layer from the steel material. In addition, the descaling property is improved by utilizing the effect of the strong electric field generated by the pulse wave on the reaction.
To promote. Therefore, the microwave heating is performed in addition to the conventional descaling means to improve the descaling efficiency. For this reason, the method of the present invention is a mechanical method using high pressure water or shot blasting,
It may be used in combination with any means such as a chemical method using hydrochloric acid, sulfuric acid, nitric acid or a mixed acid thereof, or a combination of a mechanical method and a chemical method.

The method of the present invention may be applied to the entire surface of the target steel material, or may be selectively applied to only necessary surfaces or portions. For example, if only one surface of the steel sheet is good, microwave heating is applied to only that surface to obtain a desired product more efficiently or more economically than to apply it to both surfaces. Can be

The effects of the method and apparatus of the present invention are effective without being affected by differences in the form or composition of the steel material, and are not limited to the above examples, and may be applied to steel plates (thin plates, thick plates),
The present invention can be applied to the removal of scale formed on the surface of a slab such as a wire, a bar, a slab or a billet, or a forged product. The steel type of the steel material can be applied not only to ordinary steel such as carbon steel but also to special steel such as stainless steel.

[0039]

【Example】

[Embodiment 1] As shown in FIG. 1, the average electric power is reduced immediately before a descaling device in front of a hot rolling mill for steel sheets, which is a conventional method.
Microwave heating devices 2 capable of outputting up to 50 KW were installed above and below a steel sheet conveying roll, respectively, and a test for improving descalability by microwave heating was performed. The dimensions of the heating chamber 10 are
The width is 2000 mm, the length is 10,000 mm, and the height from the surface of the steel material 1 to the ceiling of the heating chamber 10 is 1000 mm. The descaling apparatus, in order to perform descaling of high Si steel, 20 mP _a
Of high pressure water was used. The steel sheet 1 used is a hot-rolled high-tensile steel sheet specified in JIS G 3141 and contains 0.8% of Si.
The dimensions at the entry side of the rolling mill are 50 mm in thickness, 1500 mm in width, and the passing speed is 120 m / min. Continuous wave irradiation was performed with an average power of 50 KW and an irradiation time of 1 to 2 seconds, and immediately descaling was performed using high-pressure water. The microwave irradiation raises the temperature of the scale layer on the steel surface by 100 ° C and the water pressure for descaling increases by 15 ° C.
Obtain sufficiently good descaling results MP _a, the surface of the steel sheet after hot rolling was good without scale defects. When descaling was performed using high-pressure water of 20 MPa without applying microwave heating, _a small amount of scale remained on the steel sheet surface, resulting in failure.

[Embodiment 2] As shown in FIG.
A microwave heating device 2b is installed at the top of the
Pickling was performed while heating only the upper surface of b with microwaves. The average power of the microwave heating device 2b is a device capable of outputting up to 20KW. The pickling liquid used was an HCl 10% solution, the temperature of the liquid was 80 ° C., and the distance between the steel plate and the pickling liquid surface at the position of the immersion roll 14 was 50 mm. The steel plate used was 5mm thick and width
A hot-rolled high-strength steel sheet of 1500 mm containing C: 0.07%, Si: 0.8%, and Mn: 1.5%. This steel sheet does not have good descaling properties in ordinary pickling due to its high Si content.

Table 1 shows the results of comparison of pickling properties under various conditions.
Shown in

[0042]

[Table 1]

When the conventional microwave heating was not applied, a good surface could not be obtained even if the passing speed was greatly reduced and the pickling time was increased, but the method of the present invention is applied. By doing so, while obtaining good descaling results,
Pickling can be performed at high speed. In particular, if a pulse wave is used, pickling becomes easier, and a good surface can be obtained at high speed.

[0044]

As described above, the descaling efficiency when hot descaling by high-pressure water or descaling by acid is improved, the quality is improved by reducing the scale defect and the rolling temperature, and the power and energy are saved. Is effective in improving productivity in the pickling step.

[Brief description of the drawings]

FIG. 1 is a diagram showing the concept of the structure of a microwave heating device when the present invention is applied to descaling at the hot rolling mill entry side.

FIG. 2 is a diagram showing an example of equipment arrangement when the present invention is applied to pickling of a steel sheet.

FIG. 3 is a diagram showing a temperature rise characteristic when iron oxide is heated by microwaves.

FIG. 4 is a diagram showing the results of investigating the effect of improving descalability by locally heating a scale layer with microwaves on the entry side of a hot rolling mill.

FIG. 5 is a diagram showing the relationship between the descaling ratio and the pickling temperature when the scale layer is pickled by heating with microwaves.

FIG. 6 is a diagram showing an influence of a pulse time ratio of a pulse wave on a descaling ratio.

FIG. 7 is a diagram illustrating the concept of a pulse wave.

[Description of Signs] 1 Steel material 2 Microwave heating device 3 Microwave oscillator 4 Microwave waveguide 5 Microwave waveguide tip nozzle 6 Restriction chamber 7 Radio wave absorber 8 Radio wave reflection plate 9 Stirring blade 10 Heating chamber 11 Protective cover 12 Acid Washing tank 13 Pickling solution 14 Dipping roll

Claims (4)

[Claims] 1. A method for descaling a steel material, wherein the scale layer is removed by chemical or mechanical means while or after heating the scale layer on the surface using microwaves. 2. A method for descaling a steel material, comprising removing the scale layer by chemical means while heating the scale layer on the surface of the steel material using a pulsed microwave. 3. A microwave heating apparatus for heating the scale layer and descaling at a position where heating of the scale layer by microwaves and removal of the scale layer by chemical or mechanical means can be performed simultaneously. A descaling apparatus for steel material, comprising: a chemical or mechanical means. 4. A descaling apparatus for a steel material, comprising a microwave heating device for heating the scale layer on the upstream side of the chemical or mechanical means for removing the scale layer on the surface of the steel material.