JPH1024318A - Descaling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely remove inner layer scale and outer layer scale. SOLUTION: Scales removed from an object by descaling are collected, dried, adjusted to a prescribed grain size, and used as a polishing/cleaning material. A feeding port 2 of the material is provided on the downstream side of a nozzle 1 for injecting high pressure water. The optimum grain size of the material is determined from an equation; the optimum grain size of the material = 1.11×(nozzle diameter)<0.5> . Using the material having a grain size of 0.8 to 1.2 times the optimum value thus determined, the material is mixed in the high pressure water from the feeding port by the volumetric component ratio above 0.05 but less than 0.40 of the flow rate of the high pressure water, and injected together with the high pressure water to the object to be descaled.

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 removing scale generated in a heating furnace to reduce scale flaws generated during hot rolling of metal materials such as slabs and steel materials. It is.

[0002]

2. Description of the Related Art 9 wt. % Or 36 wt. % Of steel (hereinafter, referred to as "9Ni steel or 36Ni steel"), such as a slab, a steel plate, or a steel ingot (hereinafter, referred to as "slab") is heated on a slab surface before hot rolling. Occasionally, an outer layer scale composed of Fe ₂ O ₃ , Fe ₃ O ₄ or FeO and an inner layer scale composed of grain boundary oxidation of FeO or internal oxidation of the base material are formed. Of these, the inner layer scale consists of two phases, metal and oxide,
It is difficult to completely remove this by ordinary descaling using only high-pressure water. Therefore, scale flaws occur due to the remaining scale during hot rolling.

As a measure for preventing the scale flaw, a method of applying an antioxidant to the surface of a slab or the like to prevent scale formation has been implemented (hereinafter referred to as "prior art 1").

On the other hand, a descaling method in which high-pressure water mixed with an abrasive is sprayed onto a surface of a heated slab or the like,
JP-A-63-235014 and JP-A-6-235014
No. 126324 (hereinafter referred to as “prior art 2”). Prior art 2 is a descaling method in which the abrasive is dispersed in water in advance, the pressure is increased, and the material is sprayed on a slab or the like. As these abrasives, sand iron, abrasive grains, and the like are used. After the descaling, the abrasive material accumulates in the pits together with the scale removed.

[0005]

However, in the prior art 1, when the antioxidant has a coating unevenness, a portion where an inner layer scale is formed due to the unevenness is present in a slab or the like. There is a problem that it is not suppressed.

In the prior art 2, it is extremely difficult to collect and reuse the abrasive material deposited in the pits, and it is necessary to supply the abrasive material by a method alternative to the above-mentioned method of recovery and reuse. However, there is a problem that the cost for this is large. In addition, since these abrasives have high strength and high hardness, the inner wall of the nozzle is liable to wear and damage. There is a problem that the obtained abrasive material causes surface flaws during the subsequent hot rolling. Furthermore, there is a problem that it is difficult to uniformly disperse the abrasive in water. In order to solve such problems, the particle size of the abrasive material must be reduced, but this does not allow the individual particles of the abrasive material to have sufficient kinetic energy for inner scale destruction. There is.

[0007] Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a steel material and a slab, particularly a slab or a billet made of 9Ni steel or 36Ni steel or the like, which generates an inner layer scale upon heating. An object of the present invention is to provide a descaling method capable of completely removing an outer layer scale.

[0008]

According to the first aspect of the present invention,
The present invention is characterized in that an abrasive having a predetermined particle size is jetted together with high-pressure water onto a material to be descaled.

According to a second aspect of the present invention, a supply port is provided in a nozzle for injecting high-pressure water, and a polishing material adjusted to a predetermined particle size is supplied from the supply port to be mixed with the high-pressure water. ,
It is characterized in that the high-pressure water is jetted from the nozzle to the material to be descaled together with the polishing material.

According to a third aspect of the present invention, in the second aspect of the invention, the optimum value of the particle size of the abrasive material is calculated by the following equation (1).
The optimum value of the particle size of the abrasive material = 1.11 × (nozzle diameter) ⁿ (1) where n is 0.5, the unit of the particle size of the abrasive material and the nozzle diameter is mm, Using a polishing material adjusted to a particle size within the range of 0.8 to 1.2 times the optimum value of the particle size of the cleaning material obtained from the equation (1), and using a flow rate of the high-pressure water of 0.05 The polishing material is mixed into the high-pressure water by a volume fraction of less than ultra-0.40, and the high-pressure water is injected from the nozzle to the material to be descaled together with the cleaning material from the nozzle. .

According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, the scale removed from the material to be descaled by the descaling is collected, and the collected scale is dried. It is characterized in that the scale is adjusted to a predetermined particle size, and the adjusted scale is used as the polishing material.

A fifth aspect of the present invention is characterized in that, in the first, second or third aspect of the present invention, pearl sand is used as the abrasive.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Among materials to be descaled such as slabs and steel ingots, in particular, those which produce an inner layer scale are descalated only with high-pressure water, and the outer layer scale can be removed by thermal shock. Inner layer scale is F
Since it is a so-called internal oxidation in which the oxide is dispersed in the base material and the grain boundary oxidation of eO, its removal is difficult.

The inner layer scale can be removed by mixing the abrasive with high-pressure water and causing the abrasive to collide and break. However, in order to destroy the inner scale, it is necessary that the abrasive particles having a kinetic energy of a certain value or more collide in a sufficiently large amount per unit time.

The abrasive material mixed with high-pressure water must be able to destroy the inner layer and the outer layer scale without being destroyed by itself when colliding with the inner layer and the outer layer scale. As such a polishing material, a scale or pearl sand removed from the material to be descaled by descaling is used.

As the scale used as the abrasive material, the scale removed from the material to be descaled by descaling is recovered and used. In this case, the material is the same as the inner and outer scales to be removed, but at the moment of collision, the temperature of the abrasive material is lower than that of the inner and outer scales, so the hardness, strength and toughness of the abrasive material Are superior to those of the inner and outer scales. On the other hand, since the scale is not as hard as sand iron or abrasive grains, the scale is very unlikely to be embedded in ground iron. Therefore, the necessary function as an abrasive can be sufficiently achieved.

The optimum particle size of the abrasive material for descaling is determined by the size of the outlet diameter of the nozzle from which high-pressure water is jetted, and can be obtained by the following equation (1). Optimum value of particle size of abrasive material = 1.11 × (nozzle diameter) ⁿ (1) where n is 0.5 and the unit of particle size and nozzle diameter of abrasive material is mm.

The abrasive material has an optimum value of 0.8-1.
It is used after adjusting to a particle size within twice the range. When the particle size of the blast material exceeds 1.2 times the optimum value obtained from equation (1), that is, the particle size of the blast material> {1.11 × (nozzle diameter) ⁿ } × 1.2 In such a case, the number of particles of the abrasive colliding per unit time is too small, and it is difficult to completely destroy and remove the inner scale.

On the other hand, when the particle size of the abrasive is less than 0.8 times the optimum value obtained from the equation (1), that is, the particle size of the abrasive <{1.11 × (nozzle diameter) ⁿ } If x0.8, the individual particles of the abrasive material cannot be given sufficient energy to destroy the inner scale. Therefore,
The particle size of the abrasive material is preferably in the range of 0.8 to 1.2 times the optimum value of the particle size of the abrasive material obtained from equation (1).

The supply amount of the abrasive is 0.05% of the high-pressure water flow rate.
A volume fraction from super to less than 0.40 is a suitable range. At a volume fraction of 0.05 or less of the high-pressure water flow rate when the supply amount of the abrasive is insufficient, the number of particles of the abrasive which collides in a unit time at the time of descaling is insufficient, and the effect of mixing the abrasive is not sufficient. I can't get it.

On the other hand, when the supply amount of the abrasive is 0.1% of the high pressure water flow rate.
At a volume fraction of 40 or more, the number of particles of the abrasive material is too large, so that sufficient energy cannot be given to individual particles, and the effect of mixing the abrasive material cannot be sufficiently obtained.

[0022]

Next, an embodiment of the present invention will be described with reference to the drawings.

[Embodiment 1] FIG. 1 is an explanatory view showing a jig for implementing the descaling method of the present invention. A nozzle 1 for injecting high-pressure water is provided in the jig 3, and a supply port 2 for supplying the abrasive to the high-pressure water is provided on a downstream side surface of the nozzle 1. The high-pressure water 4 injected from the nozzle 1 is supplied to the abrasive material 5 from the supply port 2 on the side thereof.
Is supplied to the high-pressure water 4 and mixed with the high-pressure water 4, and the high-pressure water 4 mixed with the abrasive 5 is jetted onto the material to be descaled. In this example, a scale was used as the abrasive.
In this scale, the scale removed from the material to be scaled by the descaling is recovered from the scale pits, dried, pulverized, and further adjusted to a predetermined particle size using a sieve.

In order to quantitatively evaluate the impact force of the high-pressure water mixed with the abrasive on the material to be descaled, a descaling experiment was performed using a styrene foam sample as a test piece. The impact force was evaluated based on the maximum penetration depth of high-pressure water or high-pressure water mixed with an abrasive to collide with styrofoam.

FIG. 2 is a graph showing the effect of the particle size of the abrasive material on the maximum penetration depth when a nozzle having an outlet diameter of 0.5 mmφ is used. Discharge pressure is 140kgf / c
m ² , water flow rate 1.72 l / min, scale supply amount /
The high-pressure water flow rate was set to 0.12 in volume fraction, and the nozzle / sample distance was set to 140 mm.

FIG. 2 shows that only high-pressure water and high-pressure water mixed with an abrasive having a particle size of less than 250 μm,
High pressure water mixed with abrasive material of 60 μm and particle size more than 860 ~ 1
It can be seen that, in the particle size distribution of the abrasive material mixed with 700 μm of abrasive material, the case of high pressure water mixed with abrasive material having a particle size of 250 to 860 μm is deepest in the test piece.

Next, when the diameter of the nozzle was changed, the particle size of the abrasive material when the nozzle was deepest was examined.
FIG. 3 is a graph showing the relationship between the energy supply optimum scale particle diameter and the nozzle diameter. The result is shown in FIG. FIG.
As a result, the following equation was obtained as the optimum value of the nozzle diameter and the particle diameter of the abrasive. Optimum value of abrasive material particle size = 1.11 x (nozzle diameter) ^0.5 However, the unit of abrasive material particle size and nozzle diameter is mm.

FIG. 4 is a graph showing the influence of the volume fraction of the scale supply amount (scale supply amount / high pressure water supply amount) on the high pressure water flow rate to the collision force. From FIG. 4, the case where the volume fraction of the scale supply amount is 0.05 or less, and 0.4
When it is 0 or more, it can be seen that a desired effect cannot be obtained in improving the collision amount by the scale supply.

Example 2 A slab sample made of 9Ni steel was used as a polishing material with the jig 3 shown in FIG. 1 using the jig 3 shown in FIG. High-pressure water mixed with scale, particle size 250 ~
860 μm scale mixed high pressure water and particle size 86
Descaling was performed using any of high-pressure water with a scale of more than 0 to 1700 μm. Further, descaling was similarly performed using pearl sand mixed high-pressure water adjusted to a particle size of 250 to 860 μm as an abrasive. In performing the test, the nozzle diameter was 0.5 mmφ, the discharge pressure was 140 kgf / cm ² , and the water flow rate was 1.72 l /.
min, abrasive supply / high-pressure water flow rate is 0.1 in volume fraction
2. The distance between the nozzle and the sample was set to 140 mm.

FIG. 5 is a schematic sectional view of an oxide scale formed when a slab made of 9Ni steel is heated in this embodiment.

FIGS. 6 to 10 show 9N in this embodiment.
i high pressure water only, particle size 2
High-pressure water with a scale of less than 50 μm, particle size 250-8
High-pressure water mixed with a scale of 60 μm, particle size exceeding 860 to 17
High-pressure water with a scale of 00 μm or a particle size of 250
It is a micrograph which shows the metal structure after performing a descaling using the high pressure water mixed with pearl sand of 860 micrometers. In FIG. 8, the photograph when the particle size of 250 to 860 μm is mixed is the boundary of the portion where the high-pressure water collides, and the high-pressure water mixed with the scale collides with the portion where the inner scale is completely removed on the right side. .

After the descaling was performed, the cross section of the slab was observed, and the descaling property of each of the particle size distributions of the abrasive was evaluated. Table 1 shows the results. In Table 1, A represents the case where the outer layer scale and the inner layer scale were removed, B the case where the outer layer scale was completely removed but the inner layer scale remained, and C the case where only a part of the outer layer scale was removed. Shows the evaluation of the scale peelability of each.

[0033]

[Table 1]

As shown in Table 1, when descaling was performed using only high-pressure water, high-pressure water mixed with scale having a particle size of less than 250 μm, and high-pressure water mixed with scale having a particle size of more than 860 to 1700 μm, the outer layer scale was reduced. Was completely removed, the inner layer scale remained, and the evaluation was B or C. On the other hand, particle size 25
When descaling was performed using high-pressure water mixed with scale of 0 to 860 μm and high-pressure water mixed with pearl sand having a particle size of 250 to 860 μm, the scale was completely removed up to the inner layer scale.

[0035]

As described above, according to the present invention, the abrasive material is mixed into the high-pressure water, and the high-pressure water mixed with the abrasive material is jetted from the nozzle. The impact of the abrasive material on the material surface becomes uniform, the inner scale that was difficult to remove by the conventional descaling method can be removed, and scale flaws generated during hot rolling can be significantly reduced, Further, since the abrasive is supplied on the downstream side of the nozzle, there is no wear and damage on the inner wall of the nozzle due to the abrasive, and the durability is improved. Thus, an industrially useful effect is provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a jig for implementing a descaling method of the present invention.

FIG. 2 is a graph showing the effect of the particle size of the abrasive on the maximum penetration depth when a nozzle having an outlet diameter of 0.5 mmφ is used.

FIG. 3 is a graph showing a relationship between an optimum energy supply scale particle diameter and a nozzle diameter.

FIG. 4 is a graph showing the influence of the volume fraction of the scale supply amount (scale supply amount / high-pressure water supply amount) on the high-pressure water flow rate to the collision force.

FIG. 5 is a schematic cross-sectional view of an oxide scale generated when a slab made of 9Ni steel is heated.

FIG. 6 is a micrograph showing the metal structure of a slab made of 9Ni steel after descaling the slab using high-pressure water.

FIG. 7 shows a particle size of 25 for a slab made of 9Ni steel.
It is a microscope picture which shows the metallographic structure of a slab after performing descaling using high-pressure water mixed with a polishing material of less than 0 μm.

FIG. 8 shows a particle size of 25 for a slab made of 9Ni steel.
It is a microscope picture which shows the metallographic structure of the slab after performing descaling using 0-860 micrometer abrasive material mixing high pressure water.

FIG. 9 shows a particle size of 86 for a slab made of 9Ni steel.
It is a microscope picture which shows the metallographic structure of the slab after performing descaling using the high-pressure water mixed with a polishing material of more than 0 to 1700 μm.

FIG. 10 shows a particle size of 2 for a slab made of 9Ni steel.
It is a microscope picture which shows the metal structure of the slab after performing a descaling using the pearl sand mixing high pressure water of 50-860 micrometers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle 2 Supply port 3 Jig 4 High-pressure water 5 Cleaning material

Claims (5)

[Claims] 1. A descaling method comprising spraying an abrasive having a predetermined particle size together with high-pressure water onto a material to be descaled. 2. A nozzle for injecting high-pressure water is provided with a supply port, and a polishing material adjusted to a predetermined particle size is supplied from the supply port and mixed with the high-pressure water. A descaling method, wherein water is sprayed on the material to be descaled together with the abrasive material. 3. The optimum value of the particle size of the abrasive material is obtained from the following equation (1), and the optimum value of the particle size of the abrasive material = 1.11 × (nozzle diameter) ⁿ (1) N is 0.5, the unit of the particle size of the abrasive and the nozzle diameter is mm, and the optimal value of the particle size of the abrasive obtained from the equation (1) is 0.8 to 0.8.
Using a polishing material adjusted to a particle size within a range of 1.2 times, mixing the polishing material into the high-pressure water by a volume fraction of more than 0.05 to less than 0.40 of the flow rate of the high-pressure water. The descaling method according to claim 2, wherein the high-pressure water is jetted from the nozzle to the material to be descaled together with the polishing material. 4. The scale removed from the material to be descaled by descaling is collected, the collected scale is dried, the dried scale is adjusted to a predetermined particle size, and the adjusted scale is cleaned by the polishing. 4. The descaling method according to claim 1, wherein the method is used as a material. 5. The descaling method according to claim 1, wherein pearl sand is used as the polishing material.