JPH06154837A - Descaling method - Google Patents

Abstract

PURPOSE:To efficiently descale steel products under a relatively low pressure by using liquid in which bubbles are dispersed at a specific volume ratio under the atm. pressure as a pressurized jet liquid. CONSTITUTION:The liquid is reduced in pressure down to the atm. pressure in a nozzle outlet and, therefore, gas expands if the liquid in which the bubbles are dispersed at least at >=1% volume ratio under the atm. pressure is pressurized and ejected from the nozzle 9. The liquid jet is parted by such expansion to liquid drops. The liquid drops are further accelerated from the ejection speed from the nozzle 9 by the rapid expansion of the bubbles. Then, the foamed gas parts the liquid jet to form discontinuous jets. Since the foamed gas accelerates the parted liquid drops, the collision pressure against the steel products 10 increases additionally. The descaling with high efficiency under the low pressure is possible if such gas dispersed liquid mixture jets are applied to the descaling. This method is thus advantagenous for quality improvement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method capable of efficiently removing oxide scale generated in the manufacturing process of, for example, steel materials, particularly steel plates, steel pipes, bar steels, and mold steels.

[0002]

2. Description of the Related Art Oxidized scales are generated on the surface of steel sheets, steel pipes, bar steels, or shaped steels during the hot manufacturing process. These scales are used to prevent surface flaws due to indentation in the rolling process. Must be removed before rolling. The scale generated in the steel manufacturing process is the primary scale generated in the heating process of the steel, that is, in the heating furnace.
Secondary scale generated in the rolling process after removal of the primary scale,
Further, it is roughly classified into a tertiary scale generated in the cooling process after rolling.

The primary scale is generally thick, although it depends on the material and the time spent in the furnace, and reaches several mm. The secondary scale is generally thinner than the primary scale and is about several hundred μm, although it varies depending on the rolling speed and rolling temperature. Furthermore, since the steel material temperature of the tertiary scale is lower than that of the former two and the scale generation rate is reduced, it becomes as thin as 100 μm or less.

Conventionally, a method of injecting a high-pressure water jet has been used for removing the hot scale. In the method of injecting the high-pressure water jet, the descaling pressure of the primary scale is that the temperature of the steel material is 1000 ° C. or higher immediately after it comes out of the heating furnace and the transport speed is slow at 10 to 100 m / min. Can be performed at a relatively low pressure, and is generally performed at 100 to 150 kg / cm ² . Further, when it comes to a secondary scale, the temperature is slightly lowered and the rolling speed is also high at 100 to 600 m / min. Therefore, it is said that the descaling pressure is required to be 150 to 200 kg / cm ² . In addition, the temperature is 5 for removing the third scale.
It is as low as 00-600 ℃ or less, and the speed is 600-1000m.
Very high speeds of up to 250/400 kg / c
It is said that a high pressure of m ² is required. In addition, from the viewpoint of preventing damage to the nozzle due to contact and collision during traveling of the steel material, the high-pressure water injection nozzle is usually installed 200 to 700 mm away from the steel material.

In recent years, steel materials have been diversified, highly functionalized, and have high performance, and alloy steels to which various elements have been added have been widely used. Unlike the conventional general carbon steel, the scale structure of such alloy steel increases the adhesion to the base steel, so the scale removal is insufficient with the current equipment equipped with the descaling pressure described above, and scale defects The problem that occurs occurs. In order to deal with this, increasing the descaling pressure has been studied, but in order to completely remove the scale of the alloy steel, even the primary or secondary scale is 400 to 70.
A high pressure of 0 kg / cm ² or higher is required. However, in order to increase the pressure, it is necessary to replace the existing equipment (high-pressure pump, piping, accumulator, header, nozzle, etc.), not to mention the equipment cost and the maintenance becomes difficult. Therefore, there is a strong demand for a method and apparatus capable of highly efficiently descaling under low pressure.

Therefore, as a low-pressure and high-efficiency descaling method, there is disclosed in Japanese Unexamined Patent Publication No. 59-76615, "a method of bringing a nozzle close to a steel material to increase a collision force to a steel material surface". Japanese Unexamined Patent Publication No. Sho 59-20480, "Method of projecting abrasives having a particle size of 0.3 mm or less", and Japanese Patent Laid-Open No. 61-119322, "Slurry of abrasives in high-pressure water jet". And a method of mixing and injecting "a method of mechanically removing with a brush roll" described in JP-A-61-1410.
"Method in which the above method and another (for example, the above) method are combined" described in 8-128216 is proposed.

[0007]

However, the above method requires measures to prevent nozzle damage due to contact and collision during traveling of the steel material described above, and according to experiments and studies conducted by the present inventor, it is possible to use nozzle proximity. There is a limit to the increase in the collision force, and the descaling of the alloy steel as described above also required the pressure increase of the water jet.

The methods (1) and (2) enable high-efficiency descaling at low pressure, but if the cleaning material is not sufficiently cleaned after descaling, indentation defects due to the polishing material are likely to occur. In addition, since the peripheral cleaning equipment is also worn by the abrasive cleaning material that has bounced back, it is necessary to provide protective equipment therefor and maintenance thereof is difficult.

In the method (1), the brush is heavily worn and the brush must be replaced frequently, resulting in high maintenance cost. Further, although the method (2) has very good scale removal efficiency, it also has the above-mentioned drawbacks, and thus has a large problem of maintenance.

It is an object of the present invention to provide a low-pressure, high-efficiency descaling method that does not have the above-mentioned problems at all.

[0011]

[Means for Solving the Problems] Compared with a steady jet (continuous jet) in which a liquid is jetted from a nozzle at a constant pressure, the unsteady jet (discontinuous jet) in which the steady jet is temporally changed is It is well known that the impact pressure on an object increases due to the onset of the striking action.
By the way, the unsteady jet has a short duration, but its collision pressure is about an order of magnitude higher than that of the steady jet. Therefore, it is considered to use this unsteady jet for processing, cleaning, and destruction, and various methods of applying mechanical, electrical, or self-excited resonant vibration to the steady jet have been devised (Katsuhiro Yamamoto, Nomi) Motohiko; On unsteady high-speed water jet, Turbo Machine, Vol. 17, No. 11, 1989 1
January).

In view of the above findings, the present inventor has conducted various investigations and experiments on the erosion characteristics of high-speed water jets, and has developed a method for generating fluctuations from the inside of a liquid in the above external fluctuation imparting method. Invented and established the following invention.

That is, the descaling method of the present invention is a descaling method in which a high-pressure liquid jet formed by ejecting a pressurized liquid from a nozzle is made to collide with an object to remove scale, and the bubbles are liquids. The gist of the present invention is to use a liquid in which is dispersed at least 1% in volume ratio under atmospheric pressure. In the method of the present invention, bubbles having a required diameter or less are at least 1% in volume ratio under atmospheric pressure in the liquid ejected from the nozzle.
The above dispersion is based on the experimental results described later.

[0014]

When a liquid in which a small amount of air bubbles are dispersed and mixed is pressurized and jetted from a nozzle, the liquid is depressurized to the atmospheric pressure at the nozzle outlet, so that the gas foams. This foaming divides the liquid jet into droplets, and the rapid expansion of the bubbles accelerates the droplets further than the ejection speed from the nozzle.

That is, if the flow velocity immediately above the nozzle is sufficiently smaller than the ejection velocity from the nozzle and is ignored, then the velocity Vl (m of the liquid jet ejected from the nozzle is
/ Sec) is represented by the following formula 1 where P0 (Pa) is the pressure immediately above the nozzle, Pa (Pa) is the atmospheric pressure of the jetted liquid jet, and ρl (kg / m ³ ) is the density of the liquid. It It should be noted that in Equation 1, C is a nozzle flow coefficient, which varies depending on the shape of the nozzle and the finishing condition, but is 0.9 to 1 for a well-finished circular nozzle.

[0016]

## EQU1 ## Vl = C [2 (P0-Pa) /. Rho.l] ^1/2

On the other hand, if the flow velocity just above the nozzle is sufficiently smaller than the jet velocity from the nozzle and this is ignored,
The velocity Vg (m / sec) of the gas jet ejected from the nozzle immediately after the nozzle exit is Ta (K), the atmospheric temperature of the ejected gas jet portion, κ (−) the specific heat ratio of the gas, and the gas constant When R (J / kg / K) is given, it is represented by the following mathematical formula 2.

[0018]

[Equation 2]

By the way, when jetting into the atmosphere at a nozzle pressure of 100 kg / cm ² , the discharge flow velocity is 140 m / sec when the nozzle flow rate coefficient is 1 for normal temperature water, but it is 798 m / sec for normal temperature air. The speed is about 5.7 times that of water and a shock wave is generated.

Then, when a liquid in which gas is dispersed and mixed is jetted from a nozzle, the gas is foamed due to a sudden pressure reduction, and the speed thereof is higher than that of the liquid. Therefore, the bubbling gas breaks the liquid jet to form a discontinuous jet, and the bubbling gas accelerates the broken droplets, so that the collision pressure on the object is further increased.

As described above, if such a gas-dispersed mixed liquid jet is applied to descaling, it is possible to remove scale with high efficiency at low pressure. The method of the present invention utilizes the gas dispersion mixed liquid jet described above.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in the accompanying drawings. FIG. 1 is an explanatory view showing one embodiment of an apparatus for carrying out the method of the present invention.

In FIG. 1, reference numeral 1 is a supply pipe for the injection liquid, and the supply amount of the injection liquid supplied into the tank 3 through the supply pipe 1 is adjusted by a liquid flow rate adjusting valve 2. Compressed air is supplied to the tank 3 through a compressed air supply pipe 4, and the compressed air is bubbled through, for example, a ceramic filter 6 after the supply amount is adjusted by a gas flow rate adjusting valve 5. , For example 300
Micro bubbles having a size of μm or less are dispersed and mixed in the jet liquid.

The jet liquid in which fine bubbles are dispersed and mixed is guided to the high-pressure pump unit 7, where it is pressurized to the required jet pressure, and then the descaling nozzle header 8 is added.
It is supplied to a · 8b and jetted from the nozzle 9 toward the front and back surfaces of the steel material 10.

In this jetting process, the fine bubbles dispersed and mixed in the jetted liquid divide the liquid jet and accelerate the liquid droplets, and collide with the steel material 10 in a state where the collision force is strengthened, and a good descaling ability is obtained. Demonstrate.

Next, the results of an experimental examination of the effect of the method of the present invention will be described in comparison with the conventional method. The experiment was carried out by heating a steel material in an electric furnace in an air atmosphere to generate a scale, and then injecting an unsteady jet according to the method of the present invention to observe the peeling removal state of the scale.

The steel material used is firelite (2Fe
O. SiO ₂ ) has a chemical composition shown in Table 1 below, which is said to have poor scale removability due to the generation of O.
Si killed steel was used.

[0028]

[Table 1]

The method of the present invention used in this experiment was carried out using the apparatus shown in FIG. 1 having the following specifications. Note Tank internal volume: 100 liters High pressure pump unit; 55KW Electric motor drive capacity is 5
00Kg / cm ² × 52l / min Triple Plunger Pump Ceramic Filter; 100mesh

In this experiment, a nozzle having an inner diameter of 1.5 mm was used, and the nozzle was attached to a linear cylinder driven by compressed air, and the scale was removed by moving it on the steel material at a constant speed. In addition, the conventional method was carried out by directly supplying water without air bubbles to the high pressure unit without performing air bubbling in the tank. The results of the experiment are shown in Table 2 below. In this experiment, as shown in Table 2, descaling was evaluated by visually observing the scale remaining rate of the descaling portion (the portion hit by the jet). Table 2
In the table, ⊚ indicates that the scale residual rate is 1 to less than 2%, ∘ indicates 2 to 5%, Δ indicates 5 to 10%, and x indicates that the percentage exceeds 10.

[0031]

[Table 2]

As shown in Table 2 above, a high pressure of 400 to 500 Kg / cm ² was required in the conventional method in order to perform sufficient descaling in Si killed steel having a poor scale removal rate. In the method of the present invention, the bubble inclusion rate is 1
%, The descaling effect will appear, and the bubble inclusion rate will be 3
It was confirmed that the descaling can be efficiently performed at a pressure of about 200 to 300 Kg / cm ² which is about half the pressure of the conventional method when it is set to%.
In the method of the present invention, descaling can be efficiently performed at a low pressure as compared with the conventional method, but since gas foaming occurs after being jetted from the nozzle, the jet spouting noise is slightly larger than in the conventional method, but in practical use. , There is no hindrance.

[0033]

As described above, according to the present invention,
The descaling of the steel material can be efficiently performed at a relatively low pressure, which is advantageous for quality improvement. Further, the cost can be reduced as compared with the case where descaling is performed using the conventional method and apparatus.

In this embodiment, only the descaling of the steel material has been described, but the technique of the present invention is not limited to this, and the surface cleaning and peeling of the structure, that is, the cleaning of the inner and outer walls of the building, the floor and the ceiling, the concrete, It is also applicable to cleaning and peeling of surfaces, peeling and washing of coating materials on structures, peeling and washing of deposits on ships, excavation of rock mass, etc.

[Brief description of drawings]

FIG. 1 is an explanatory view showing one embodiment of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 1 Injection Liquid Supply Pipe 3 Tank 4 Compressed Air Supply Pipe 6 Ceramic Filter 7 High Pressure Pump Unit 9 Nozzle 10 Steel Material

Claims (1)

[Claims] 1. A descaling method in which a high-pressure liquid jet formed by ejecting a pressurized liquid from a nozzle is collided with an object to remove scale, and the liquid is bubbles in a volume ratio under atmospheric pressure. A descaling method comprising using a liquid in which at least 1% or more is dispersed.