JP2002120011A - Descaling apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hot-rolled steel sheet of good quality by improving the impact fracture force of high-pressure water descaling and sufficiently removing scale on the surface of a rolled material when hot rolling steel. And an apparatus and method for descaling. SOLUTION: A plurality of nozzles are arranged in a plurality of rows in a steel material conveying direction in which a discharge direction of a discharge flow is wide in a plane perpendicular to a nozzle axis, and water is accelerated to a discharge flow rate of 230 m / s or more. When ejecting and performing descaling, the distance between water films at the place where the droplet streams from adjacent nozzle rows collide with the steel plate is 20 mm or more and 100 mm or less, and the water film jet from the front nozzle enters the steel plate Angle from 0 ° to 4 °
A de-scaling apparatus in which the jet nozzle is installed such that the angle of incidence of the jet water film from the post-stage nozzle on the steel plate is in the range of 0 ° to −4 °.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a descaling apparatus for removing scale from the surface of a rolled material when hot rolling steel, and to a scale removing method using the descaling apparatus.

[0002]

2. Description of the Related Art During hot rolling of steel, a slab is charged into a heating furnace prior to rolling and heated to a high temperature of 1100 to 1400 ° C. The inside of the heating furnace is generally an oxidizing atmosphere,
During heating, the billet surface is oxidized and scale is formed.
The scale is mainly composed of iron oxide, and the scale thickness of the surface of the billet when extracted from the heating furnace reaches 1 to 2 mm. If rolling is performed with this scale attached to the billet surface, the scale bites into the surface of the rolled material and causes surface defects called scale flaws. Therefore, in general, a pressure of 10 to 15 MPa is applied to the steel sheet surface before rolling. , 100 ~
A method of preventing the occurrence of scale flaws by spraying and removing high-pressure water at an incident angle of 10 to 45 ° from a distance of 300 mm has been performed.

[0003] However, the ease of peeling of the scale varies depending on the composition of the steel. In particular, steel having a large Si content (Si> 0.15 mass%) is made of firelite (Fe ₂
A scale which contains a large amount of SiO ₄ ) is formed which is difficult to peel off, and the method of removing water by spraying water at a pressure of 10 to 15 MPa on the steel sheet surface before rolling cannot sufficiently prevent scale flaws. In general, equipment that adopts an angle of 10 ° to 45 ° toward the upstream in the transport direction of the steel sheet from the viewpoint of the angle of injection from the nozzle and the prevention of the scattered scale removed from the equipment.

[0004] In order to solve the above-mentioned problem of the Si-containing steel, Japanese Patent Application Laid-Open No. 6-114432 discloses that a steel slab from which the upper layer of the surface scale has been removed after extraction from a heating furnace is subjected to at least one pass before rough rolling. After the rough rolling of
A collision energy of 0 to 700 kg / cm ² of high-pressure water is used.
A method for producing a hot-rolled steel sheet of high Si steel which is sprayed under a condition of not less than 05 J / mm ² is disclosed. Here, the collision energy is (nozzle discharge pressure × flow rate per nozzle) / (1
(Injection width per nozzle x running speed of steel slab).

Further, in the conventional descaling method, as shown in FIG. 5, the collision force is weakened due to the interference at the site 6 where the water jet films 5 overlap each other at the boundary between the individual nozzles 3, and the descaling ability is reduced. In order to avoid this, the nozzle 3 has a twist angle as shown in FIG. 6 to avoid the overlapping portion of the water jet film, or the header 2 is separated into two lines as shown in FIG. As shown in FIG. 8, the overlapping portion of the water jet film has been avoided by changing the direction of the adjacent nozzle 3 and jetting.

[0006]

Problems to be Solved by the Invention
Compared with the conventional method of removing water by spraying water at a pressure of 10 to 15 MPa by the descaling method using high-pressure water as disclosed in Japanese Patent Publication No. 2 (1999), the descaling ability is improved even with high Si content steel, and Although the surface defect rate was slightly reduced, the scale was not sufficiently removed on the entire surface of the steel sheet.

[0007] In particular, the lap portion 6 formed by overlapping the water jet film at the boundary of the nozzle with a time difference on the steel plate is difficult to use for the descaling material such as Si-containing steel, even if the nozzle arrangement according to the conventional method described above is adopted. Because the scale remained without being removed, the distance between nozzles could be increased by 100 mm or more,
Although countermeasures such as approaching the nozzle were attempted, the residual ratio of the scale increased, resulting in surface defects of the product after the pickling process, resulting in a decrease in yield.

When the nozzle 3 has a twist angle as shown in FIG. 6, the water jet films do not directly overlap with each other, but the influence of the interference after the collision of the steel sheet is large, and the descaling failure is likely to occur. As shown in FIG. 7, the method of separating the header 2 into two series increases the equipment cost and may cause scale unevenness due to the time difference between the descaling of the front and rear nozzles, which is not desirable. It is effective to perform descaling immediately before rolling, and when changing the direction of the adjacent nozzles 3 as shown in FIG. 8, the scale is bitten by the rolling roll behind the deske to generate scale flaws. Is not desirable.

The present invention improves the impact fracture force of high-pressure water descaling, solves the above-mentioned problems of the prior art, and sufficiently removes the Si scale in hot rolling of a steel material having a high Si content to obtain high-quality heat. An object of the present invention is to provide a descaling apparatus and a method capable of manufacturing a rolled steel sheet.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have investigated the angle of incidence of water jet from a nozzle onto a steel plate and the residual ratio and residual form of scale at a wide range of pressure levels. In the case of a droplet accelerated at a high speed, the impact angle has a very large effect on the droplet deformation behavior at the time of collision and the shock wave generated at the contact edge with the steel plate. However, from around 230m / s,
It has been newly discovered that by setting the collision incident angle to 4 ° or less, the destruction / removability of the Si scale is significantly improved.

Further, a plurality of nozzles are arranged in a plurality of rows in the conveying direction of the steel material in which the discharge direction of the discharge flow is wide in the plane perpendicular to the nozzle axis, and water is accelerated to a discharge flow rate of 230 m / s or more. When performing de-scaling for jetting, the mutual influence between the water films at the place where the droplet streams ejected from the adjacent nozzle rows collide with the steel plate greatly depends on the incident angle, and the influence of the interference To make harmless,
When the distance between adjacent jet water films is 20 mm or more and 100 mm or less,
The angle of incidence of the water jet from the front nozzle on the steel plate is 0 °
It is found that it is most effective to set the injection nozzle so that the angle of incidence of the water jet from the subsequent nozzle on the steel plate is in the range of 0 ° to -4 °. . In addition, as shown in FIG. 1, the front-stage nozzle refers to the nozzle 3a for applying a water jet to the steel plate 1 first, and the rear-stage nozzle refers to the nozzle 3b for applying a water jet after the front-stage nozzle 3a. The sign of the incident angle is positive when the sheet is inclined in the transport direction of the steel sheet.

Further, when the distance between the impinging water films from adjacent nozzle rows is 100 mm or less and the angle of incidence of the jet water is out of the range of the invention, the flow density of the water jet from the former nozzle is determined by It has been found that increasing the flow density of the water jet by at least 1.3 times is also effective for reducing the influence of mutual interference between adjacent jet water films.

Using a descaling apparatus as described above, 117% or more of Si-containing steel
After heating to 0 ° C or less, the distance from the injection orifice to the steel plate is 1
It was found that the steel sheet was installed so as to have a thickness of 00 mm to 200 mm, and the surface of the steel sheet was descaled to obtain a steel sheet free from surface defects due to scale after hot rolling.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors heated a steel sample to 1170 ° C. in a combustion heating furnace and caused accelerated water droplets to collide with the surface immediately after extraction to remove scale generated on the steel surface. investigated. In this case, the flight distance of the water droplet from the nozzle discharge hole to the steel surface is constant (100 mm, 15 mm).
0 mm, 200 mm), and the same water volume density was compared and investigated using only the discharge flow rate and the incident angle as variables.

FIG. 2 shows that [C] = 0.05-0.1 mass
%, [Si] = 0.01-1.0 mass%, [Mn] =
0.2-1.3 mass%, [S] ≦ 0.01 mass%, [N
i] shows the results of scale removal experiments performed on steel samples with ≦ 0.05 mass% for adjustment. The evaluation of the scale removability was performed by randomly colliding 300 droplets with an area of 5 mm square, and then measuring the remaining area of the scale. The vertical axis in FIG. 2 indicates the average scale remaining rate,
The angle of incidence is shown as an absolute value. Drop velocity 180m / s
In the following areas, the effect of the incident angle was not clear,
In the case of 230 m / s or more, when the incident angle is in the range of -4 ° to 4 ° in the range of the present invention, the destructive force of the impinging droplet can be used effectively, and scale can be almost completely removed. Was. Although the upper limit of the flow velocity is preferably as large as possible, it is practically determined by the apparatus and the equipment capacity, and thus is not particularly set here.

Next, a plurality of high-speed droplets collide simultaneously,
The scale of the steel surface was removed. The steel material in the above-mentioned component system is heated to 1000 ° C. to 1170 ° C., and jet water accelerated to an average discharge velocity of 230 to 360 m / s is jetted at a wide angle of nozzle of 20 to 60 °, a jet water film distance of 0 to 500 mm, Descaling was performed by changing the angle of incidence of the water film on the steel sheet in the range of -4 to 4 [deg.], And the residual ratio of the scale after hot rolling was investigated. In particular, as a result of investigating the region where the jet water film colliding with the steel sheet overlaps in the steel sheet transport direction, the distance between the jet water films was 10
In the case of 0 mm or less, it was found that the effect of the angle of incidence on the steel sheet of the jet water film from the adjacent nozzle was very large. That is, the distance between the water films at a place where the droplet streams discharged from the adjacent nozzles collide with the steel plate is 20 mm or more and 100 mm or more.
In the following, the angle of incidence of the jet water film from the front nozzle on the steel plate is between 0 ° and 4 °, and the angle of incidence of the jet water film on the steel plate from the rear nozzle is from 0 ° to -4 °. Only in certain cases, a scale residual ratio of less than 5%, which is a passing grade of surface quality, was achieved (FIG. 3).

In the invention as described above, if the distance between the impinging water films from the adjacent nozzle rows is 20 mm or less, the scale removing ability is reduced due to mutual interference regardless of the collision incident angle. When the distance between the impinging water films was large, the scale state (temperature, adhesion state) at the time of removal slightly changed, and a high scale retention rate was obtained regardless of the incident angle. It is thought that if the distance between the water films is large, the effect of interference between the jet water films will be small. However, in order to secure the distance between the water films, the angle of incidence must be set to 4 ° or more. On the contrary, since the descaling ability with a single nozzle is reduced, and the size and division of the nozzle header greatly increases the equipment cost, the distance between water films is desirably 100 mm or less. When the timing of the descaling is largely shifted, the results obtained also differ in the deskew effect between the front nozzle and the rear nozzle.

Interference between the jet water films can also be rendered harmless by optimizing the ratio of the discharge flow rates discharged from adjacent nozzles before and after. Water is jetted from the nozzle at a high pressure of 40 MPa or more at a discharge pressure of at least 230 m / s with a commercially available descaling nozzle, and when descaling is performed, the water jet from the former nozzle is When the flow density is made larger than the flow density of the water jet from the subsequent nozzle, as shown in FIG. 4, when the ratio is 1.3 times or more, the scale at the overlapping portion of the front and rear nozzles is increased. The residual ratio was equivalent to a site without overlap (scale residual ratio difference 0%).

In the case of an actual facility in a factory, the amount of water discharged from the nozzle is large, and when the distance between the discharge hole and the steel plate is less than 100 mm, the droplet formation is insufficient and the effect of the present invention does not appear. In addition, droplets accelerated at a high speed of 230 m / s or more are atomized in a short time, so that the effect is not sufficiently obtained even if the distance to the steel plate is too long. Therefore, the distance between the nozzle discharge hole and the steel plate is 100 mm. ~ 200 mm is desirable.

The present inventors have investigated the effect of the present invention by increasing the heating temperature to 1100 ° C. to 1250 ° C. in actual equipment in a factory.
It has been found that when the steel material is higher than 1 mass%, heating above 1170 ° C. generates a low melting point eutectic of FeO and Fe ₂ SiO ₄ , and the descaling effect is significantly reduced. Therefore, steel containing 0.15 mass% or more of Si is 11%.
It has been found that a particularly large scale removing effect can be obtained by performing descaling using the apparatus of the present invention by heating to 70 ° C. or lower.

[0021]

EXAMPLE The present invention was applied to hot rolling of steel containing 0.15 mass% or more of Si. The billet size used for rolling is about 8000 mm in length, 600 to 1500 mm in width,
The thickness is about 240 mm. Heating temperature is 1100 ° C ~ 1
Before finishing rolling at 170 ° C., the surface of the steel sheet was descaled at a distance from the discharge hole to the steel sheet of 100 mm to 200 mm. Spread angle of the jet from the discharge hole in the width direction is 10 ° ~
40 °.

Table 1 shows other experimental conditions and execution results.

[Table 1]

No. 1 in Table 1. 1 to 19 are examples of the present invention.
Regardless of the heating temperature and the spread angle of the jet in the width direction from the discharge hole, when the incident angle from the adjacent nozzle is within the range of the present invention, the residual ratio of the scale in the overlapping portion of the jet water film is preferably 5% or less. Results were obtained. In contrast, the comparative example 20
No. 31 could not achieve a residual ratio of 5% or less because the incidence angles from adjacent nozzles were all outside the range of the present invention.

[0024]

According to the above-mentioned invention, it is possible to prevent poor descaling due to interference between the jet water films, and to manufacture a rolled steel sheet of sufficiently good quality.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the definition of the angle of incidence of a droplet from a nozzle to a steel plate and the present invention.

FIG. 2 is a view showing the influence of the droplet flow velocity and the angle of incidence of a water jet (droplet) on a single nozzle on the scale survival rate.

FIG. 3 is a diagram showing the effect of the incident angle of adjacent water jets (droplets) on the scale remaining rate in a two-stage nozzle arrangement.

FIG. 4 is a diagram showing the influence of the flow density ratio from adjacent nozzles on the scale remaining rate in a two-stage nozzle arrangement.

5A and 5B are schematic views of a conventional example of a descaling nozzle arrangement, in which FIG. 5A is a perspective view, and FIG.

FIG. 6 is a schematic diagram showing another conventional example of a descaling nozzle arrangement.

FIG. 7 is a schematic diagram showing still another conventional example of a descaling nozzle arrangement.

FIGS. 8A and 8B are schematic views showing still another conventional example of the arrangement of the descaling nozzle, wherein FIG. 8A is a perspective view and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Header 3 Descaling nozzle 3a Front stage nozzle 3b Rear stage nozzle 4 Discharged droplet flow group or jet water area 5 Water film at the place where discharged droplet flow group collided with steel plate 6 Site where jetted water film overlaps 7 Steel plate transport ( Transfer) direction

Claims (5)

[Claims] The present invention has a function of causing water droplets to collide with a steel plate at a discharge flow velocity of 230 m / s or more to break and remove scale on the steel plate surface. The angle of incidence of the water droplets on the steel plate is from 4 ° to -4 °. A descaling device, wherein the injection nozzle is installed so as to fall within the range of (1). 2. A nozzle in which a discharge direction of a discharge flow is widened in a width direction in a plane perpendicular to a nozzle axis and arranged in a plurality of rows in a steel material conveying direction, and water is accelerated to a discharge flow rate of 230 m / s or more. When performing descaling by ejecting from the nozzle, the distance between the water films at the place where the group of droplets discharged from the adjacent nozzle row collided with the steel plate is 20 mm or more and 100 mm or less, and the steel plate of the water film jet from the front nozzle Angle of incidence from 0 ° to 4
A de-scaling device, characterized in that the injection nozzle is installed so as to be between 0 ° and the angle of incidence of the water jet film from the latter nozzle on the steel plate in the range of 0 ° to -4 °. 3. A plurality of nozzles, each having a discharge flow extending in the width direction, are arranged in a plurality of rows in the steel material conveyance direction, and water is jetted from the same header through the nozzles at a discharge pressure of 40 MPa or more to perform descaling. When performing, the distance between the impinging water films at the place where the droplet streams from the adjacent nozzle rows collided with the steel plate is 20 mm or more and 100 mm or less, and the flow density of the water jet from the former nozzle is lower than that from the latter nozzle. A descaling device characterized in that the discharge port diameter is set to be 1.3 times or more the flow density of the water jet. Water is ejected from the nozzle at a discharge pressure of 40 MPa or more by using a descaling apparatus in which nozzles having a discharge direction of a discharge flow extending in a width direction are arranged in a plurality of rows in a steel material conveying direction. The distance between the impinging water films at the place where the droplet streams from adjacent nozzle rows collide with the steel plate is 20 mm or more and 100 mm or less, and the flow density of the water jet from the front nozzle is the water jet from the rear nozzle. A descaling method characterized by increasing the flow density by at least 1.3 times. 5. A steel containing 0.15 mass% or more of Si
In the hot rolling in which the steel sheet is rolled by heating to 70 ° C. or less, the distance from the injection discharge hole to the steel sheet is set to 100 mm to 20 using the descaling device according to claim 1.
A descaling method characterized in that the surface of the steel plate is descaled by being set to be 0 mm.