JP2000254723A - Descaling method and descaling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently remove scale to the degree capable of preventing the occurrence of scale defects while minimizing the temperature drop of a rolled stock in various material regardlessly of silicon content. SOLUTION: Header arrays 1a-1d are arranged in the rolling direction and at least one jet nozzle 2a-2d is provided on the perspective arrays. When the scale is removed by supplying the high-pressure water jetted from the nozzles to the surface of a hot rolled material 6, when the collision pressure of the high-pressure water is defined as p and descaling time as t in each header array 1, the descaling is executed so that the total sum Σ(p×t) in the whole header arrays 1 of (p×t) becomes the optimum value which is decided in accordance with the silicon content [Si] (wt.%) of the rolled stock 6 or approaches the optimum value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling facility, and more particularly, to a descaling method and a descaling apparatus for removing scale of a rolled material.

[0002]

2. Description of the Related Art Generally, in the production of a hot-pressed steel sheet, a raw material slab is generally heated by a heating furnace in an oxidizing atmosphere at a temperature of 1100 to 1300 ° C. for several hours and hot-rolled. At this time, the scale (primary scale) generated on the slab surface in the heating furnace and the scale (2) generated between rolling passes
When the steel material is rolled in a state where the next scale is not sufficiently removed, the scale is pushed into the surface of the steel sheet as a product, and remains as scale flaws or scale patterns. Such scale flaws and scale patterns not only deteriorate the appearance of the product after rolling, but also cause irregular defects on the surface of the product after the scale is removed by pickling in a subsequent process. May adversely affect product quality. Therefore, it is important to sufficiently remove scale (descaling) in the hot rolling step.

Here, usually, as a method for removing scale, for example, a discharge pressure of 100 to 150 kgf is applied to a rolling line.
A method is employed in which a descaling device for jetting a water jet of / cm ² is installed, and the scale on the surface of the steel material is peeled off and removed, followed by rolling. However, the quality of the releasability of the scale largely depends on the composition and structure of the scale, and it is known that the releasability of the steel, which contains a large amount of Si, is significantly deteriorated. This is because the Si in the steel is selectively oxidized during the high-temperature oxidation, causing the interface between FeO (wustite) and the iron base to be 2
FeO.SiO ₂ (firelite) is formed, which is in a molten state due to its low melting point (1170 ° C.) and penetrates into the scale and the base iron in a wedge shape. This is because a scale layer is formed.

In order to solve this problem, for example, a method of mechanically peeling off the scale using a brush roll as disclosed in Japanese Patent Application Laid-Open No. Sho 59-82110, and other methods such as heating the heating temperature Light melting point (1170
° C) or more. However, all of these methods are complicated and inferior in workability, have a problem in terms of manufacturing cost, and have problems such as an increase in heating furnace load and energy consumption. Was.

Therefore, in order to achieve sufficient scale peeling without causing such a problem, for example, Japanese Patent Laid-Open No.
As described in JP-A-71330, the impingement pressure of spray water on a steel sheet is 20 to 180 (g / mm ² ) and the flow rate is 0.1 to 0.1 g / mm ^2.
A method of descaling under the condition of 0.6 (L / min · mm ² ), or as described in Japanese Patent Application Laid-Open No. 9-253733, the height of a nozzle for spraying spray water is set to 50 to 100.
mm, the collision pressure is 4 to 30 kgf / cm ² , and the ejection time is 0.5 mm.
A method of performing descaling under the condition of 002 seconds or more and less than 0.005 seconds has been proposed.

[0006]

However, the above prior art has the following problems. JP-A-6
In Japanese Patent No. 71330, only the relationship between the collision pressure and the flow rate is specified.
The descaling time is indispensable for defining conditions for achieving sufficient scale exfoliation to prevent scale flaws in the rolled material. That is, even if the collision pressure and flow rate are descaled within the range specified in this known example, if the descaling time is too short, the descaling becomes insufficient, the scale separation becomes insufficient, and the descaling time becomes long. If it is too much, descaling will be excessive and the temperature of the rolled material will decrease significantly, resulting in increased heat loss.

Japanese Patent Application Laid-Open No. 9-253,734 discloses that Si
The range of the impact pressure and the descaling time is specified for the rolled material having a content of 0.2 to 2%. Unlike the above, the descaling time is included in the conditions, and the It is stated that scaling is performed for 0.002 to 0.005 seconds. However, according to the study by the inventors of the present application, in order to define conditions for achieving scale delamination sufficient to prevent scale flaws in the rolled material, a constant value is set between the collision pressure and the descaling time. It is essential to satisfy the relationship. That is, even if the collision pressure and the descaling time are within the range specified in this known example, if both the collision pressure and the descaling time are relatively small, the descaling becomes insufficient and the scale peeling becomes insufficient. If both the collision pressure and the descaling time are relatively large, the descaling becomes excessive, and the temperature of the rolled material decreases significantly, resulting in an increase in heat loss.

An object of the present invention is to remove scale sufficiently to prevent scale flaws while minimizing the temperature drop of a rolled material for various materials regardless of the silicon content. It is an object of the present invention to provide a descaling method and a descaling device.

[0009]

According to the present invention, at least one header row is arranged in a rolling direction, and at least one injection nozzle is provided in each header row. In a descaling method in which high-pressure water ejected from an injection nozzle is supplied to the surface of a hot-rolled material to remove scale, in each header row, the collision pressure of the high-pressure water with the hot-rolled material is p, p
Let f (p) be a first function having the following as a variable, t be a descaling time, and g (t) a second function having the descaling time t as a variable. 2
The sum {f (p) × g (t)} for all header rows of the product f (p) × g (t) with the function of
The scale removal is performed such that the optimum value is determined according to the i content [Si] (% by weight) or approaches the optimum value.

When descaling is performed by injecting high-pressure water from at least one injection nozzle provided in at least one header row and supplying the high-pressure water to the surface of the hot-rolled material, descaling conditions are as follows. For example,
High-pressure water impinging pressure on hot-rolled material, flow rate of high-pressure water, pump pressure as a source of high-pressure water, height of nozzle from rolled material,
And a descaling time, etc., and variously changing them may result in insufficient descaling or excessive descaling. When the descaling is insufficient, the scale peeling becomes insufficient, the scale is pushed into the rolled material, and remains as scale flaws and scale patterns.
Conversely, when descaling is excessive, the temperature of the rolled material drops significantly, and heat loss increases. Therefore, as long as the scale can be sufficiently removed to prevent scale flaws, it is necessary to minimize the temperature drop of the rolled material, and such optimal conditions are indexed using the various descaling conditions described above. It is important to.

As a result of the study by the present inventors, the optimum descaling condition for performing the scale peeling at least sufficient to prevent the scale flaw from occurring in the rolled material is as follows. The product of the function f (p) and the function g (t) of the descaling time t, ie, f (p) × g
(T), which can be indexed by using this f (p) × g (t), and its optimum value is the Si value of the rolled material.
It turned out that it changes according to content.

As described above, the optimum value of the total {f (p) × g (t)} can be obtained in accordance with the Si content of the rolled material. Various settings and controls may be performed. However, in an actual operation, it may be more realistic to determine a predetermined target range in order to perform setting or control so as to approach the optimum value as much as possible. Further, by setting a certain range in this way, it is possible to tolerate an error of a measuring instrument, an error due to a response delay during control, and the like.

In the present invention, based on the above considerations,
In performing descaling, the first function and the second function
Sum of the product f (p) × g (t) with the function Σ ｛f (p) ×
g (t)} such that the sum {f (p) × g (t)} is at or near its optimal value. For this purpose, for example, the content may be within a predetermined range according to the Si content [Si] (% by weight) of the rolled material. As a result, as described above, the optimum descaling condition can be set to almost no excess or deficiency as the descaling condition. Sufficient scale exfoliation can be performed. (2) In the above (1), preferably, the sum Σ
The scale removal is performed such that {f (p) × g (t)} falls within a predetermined range including the optimum value.

(3) In the above item (2), it is more preferable that the predetermined range is set to the sum total Σ ｛f (p) × g
(T) It is set by giving a certain width from the optimal value of｝ toward the over-scaling side.

When the total sum {f (p) × g (t)} is within a predetermined range including the optimum value, a width is provided from the optimum value to the side where descaling is insufficient, or the descaling is performed from the optimum value. Either the excess side has a width. Here, if you want to have a width on the side where the descaling is insufficient,
Insufficient scale peeling and residual scale flaws and scale patterns may adversely affect product quality, such as deteriorating the appearance of the product after rolling and leaving defects on the product surface after pickling. There is. So, for example, f
0.09 × [Si] ≦ Σ if (p) = p and g (t) = t
By providing a width on the side of excessive descaling as in (p × t), even if the temperature drop of the rolled material increases slightly, the scale is sufficiently peeled off and the adverse effect on the quality of the product is reliably prevented. be able to.

(4) In the above (2) or (3), preferably, the optimum value is the Si content [Si].
(% By weight).

(5) In order to achieve the above object, according to the present invention, at least one header row is arranged in the rolling direction, and at least one jet nozzle is provided in each header row, and jets are ejected from the jet nozzles. In a descaling method in which high-pressure water is supplied to the surface of a hot-rolled material to remove scale, a collision pressure of the high-pressure water on the hot-rolled material is set to p [kgf / cm ² ] for each header row, and descaling is performed. Assuming that the time is t [s], the sum Σ (p × t) of the product p × t of the collision pressure p and the descaling time t for all header rows is the Si content rate of the rolled material [S
i] The scale removal is performed so that the optimum value is determined according to (weight%) or approaches the optimum value.

(6) In the above (5), preferably,
The scale removal is performed so that the sum Σ (p × t) falls within a predetermined range including the optimum value.

(7) In the above (6), more preferably, the predetermined range is a range represented by 0.09 × [Si] ≦ Σ (p × t).

(8) In the above (7), more preferably, the predetermined range is 0.09 × [Si] ≦ Σ (p × t) ≦
It is a range represented by 0.09 × [Si] +0.08.

As described in the above (3), by giving the width from the optimum value to the side of excessive descaling, it is possible to reliably prevent the quality of the product from being adversely affected even if the temperature drop of the rolled material is slightly increased. However, if the width is set too large, the adverse effect of an increase in heat loss due to a decrease in the temperature of the rolled material becomes more significant, and a certain upper limit should be set for the width.

By the way, as described in the above (1),
One of the advantages of providing such a width is that it can tolerate instrument errors. When the inventors of the present application examined how much the temperature should be decreased to set the upper limit of the width, the measurement error of the temperature measuring means for measuring a high temperature exceeding 1000 ° C. was usually ± 15 ° C. , Total 30 ℃
Therefore, it was determined that it would be reasonable to provide a width on the de-scaling excess side from the de-scaling optimum value by an amount corresponding to this measurement error width. That is, 0 in the case of f (p) = p and g (t) = t.
When 30 × [Si] ≦ Σ (p × t), 30 ° C.
0.09 × [Si] ≦ Σ with the left side +0.08 corresponding to the upper limit of the width
(P × t) ≦ 0.09 × [Si] +0.08. As a result, it is possible to prevent an excessive decrease in the temperature of the rolled material and to surely prevent an adverse effect on the quality of the product while allowing a measurement error of the temperature measuring means.

(9) In any one of the above (5) to (8), preferably, all nozzles in each header row satisfy p ≧ 0.5.

As described in the above (1) and (5), the inventors of the present invention consider that one of the optimal descaling conditions for performing sufficient scale peeling at least to the extent that scale flaws do not occur in the rolled material. For example, it was found that the index can be indexed by the sum Σ (p × t) of the product of the collision pressure p of the high-pressure water and the descaling time t, and that the optimum value changes according to the Si content of the rolled material. That is, Σ (p × t) is Si
The same optimal value determined according to the content indicates the same descaling behavior even when the values of p and t are different. However, the inventors of the present application have examined in more detail that even if the optimal value of p × t is taken, if the value of the collision pressure p is too small, the peeling force of the physical scale becomes too small. , Sufficient descaling could not be performed, and the boundary was found to be at p = 0.5. Therefore, all nozzles in each header row are p ≧
By setting it to 0.5, such a possibility is avoided,
Further, sufficient descaling can be surely performed.

(10) In order to achieve the above object, the present invention provides at least one header row in a rolling direction of a rolling mill, and at least one injection nozzle is provided in each header row. In a descaling device for supplying high-pressure water to be jetted to the surface of a hot-rolled material and removing scale, an injection-pressure adjusting means for adjusting an injection pressure of high-pressure water to be injected from the injection nozzle, and a rolling speed of the rolling mill. A rolling speed adjusting means for adjusting the pressure, a pressure at which the high-pressure water impinges on the hot-rolled material is p, a first function having the collision pressure p as a variable, f (p), a descaling time at t,
The second function using the descaling time t as a variable is g
(T), the sum {f (p) × g (t)} of all the header rows of the product f (p) × g (t) of the first function and the second function is Controlling the operations of the ejection pressure adjusting means and the rolling speed adjusting means such that the optimum value is determined according to the Si content [Si] (% by weight) of the rolled material or approaches the optimum value. Control means for performing the operation.

(11) In the above (10), preferably, the ejection pressure adjusting means adjusts a discharge pressure of a pump, which is a supply source of the high-pressure water, and from the pump to the ejection nozzle. At least one of the opening adjustment means for adjusting the opening of the on-off valve provided in the pipeline.

By adjusting the discharge pressure of the pump by the discharge pressure adjusting means, it is possible to relatively easily adjust the ejection pressure of the high-pressure water.

(12) In the above (10), preferably, a plurality of the header rows are provided, and a selecting means for selecting at least one of them and performing high-pressure water injection is provided.

Depending on operational reasons, in particular, depending on the rolling speed (threading speed) and the type of steel, when trying to set the above-mentioned descaling condition to an optimum value, for example, a single header row was used. In some cases, such as when the optimum value is more easily realized or when using a plurality of header strings is easier, the number of suitable header strings may be different. Therefore, in the present invention, by providing a selecting means and selecting and using at least one necessary header from a plurality of header columns, it is possible to further easily realize the optimum value of the descaling condition.

(13) In the above (10), preferably, a plurality of the header rows are provided, and at least two of the header rows have different vertical distances from the surface of the rolled material. It is configured as follows.

As described above, the optimum descaling conditions for performing scale peeling at least sufficient to prevent scale flaws in the rolled material are the first function f (p) and the second function g (t). Can be indexed by the total sum {f (p) × g (t)}, but the optimum value is determined as one value if the Si content of the rolled material is determined. That is, Σ ｛f (p) × g
If (t)｝ is the same optimal value determined according to the Si content, the same descaling behavior is exhibited even when the values of p and t are different. Therefore, as long as the optimum value can be realized, it is possible to appropriately change the collision pressure p and the descaling time t in a wide range during the actual operation.

At this time, the former change of the collision pressure p is performed, for example, by changing the pump discharge pressure as a water source of high-pressure water, the specifications of the nozzle, and the vertical distance (height) from the header to the surface of the rolled material. Can be done by
However, replacing the nozzle in accordance with the type of steel causes the equipment to be stopped, which causes a decrease in operating efficiency. On the other hand, the pump discharge pressure can be changed relatively easily. However, since the control range is limited by the maximum discharge pressure specific to the pump, it does not extend to a wide range of changes. Therefore, by combining this with a change in the header height, it is possible to change the collision pressure over a wider range.

Here, it is not conceivable to make the header movable so that the height is variable. However, if only the height of the header is changed, the size of the spray area sprayed on the rolled material changes. Since the lap amount between sprays changes, it is necessary to compensate for this lap amount when the header height is changed, which leads to complication of the equipment. Therefore, in the present invention, at least two header rows are provided such that the vertical distances from the rolled material surface are different from each other. Thereby, they are set in advance to the required heights in advance and, for example, by providing a selecting means and selectively switching between them, equipment such as a header height elevating device is complicated. Thus, descaling at various header heights can be performed without any change, and a wide range of collision pressure p can be changed together with a change in pump discharge pressure.

[0034]

Embodiments of the present invention will be described below with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram illustrating a schematic configuration of a descaling device for hot rolling equipment that performs the descaling method according to the present embodiment. In FIG. 2, a pair of upper and lower work rolls 4a and 4b and a pair of upper and lower reinforcing rolls 5a and 5
The rolled material 6 is rolled in a rolling mill consisting of b. The driving force at this time is provided by roll drive motors 16a and 16b that drive the reinforcing rolls 5a and 5b, respectively. Two pairs of upper and lower descaling headers (hereinafter abbreviated as headers) 1a, 1b, 1c, 1d are provided on the entry side of the rolling mill.
Are arranged, and a plurality of descaling nozzles (hereinafter, abbreviated as nozzles) 2a and 2 are provided for each header.
b, 2c and 2d are attached. Each header is supplied with high-pressure water from a pump 9 via a pipe 10. From the pump 9, the descaling nozzles 2a, 2b, 2c, 2
Flow control valves 7 which are individually open / close valves
a, 7b, 7c, 7d are attached, and by controlling the opening degree thereof, it is possible to adjust (including shut off) the jet pressure of the high-pressure water independently for each header. A pressure adjusting valve 8 is provided in the pipe 10 on the downstream side of the pump 9, and it is possible to adjust (including shut off) the jet pressure of the high-pressure water for all the headers.

The descaling conditions which affect the quality of the descaling in such a descaling device include, for example, a collision pressure p of the high-pressure water on the rolled material 6, a flow rate of the high-pressure water, a discharge pressure P of the pump 9, a nozzle Vertical distance (height) H between 2a-d and rolled material 6, and descaling time t
And the like, and by varying them variously, descaling becomes insufficient or excessive. When the descaling is insufficient, the scale peeling becomes insufficient, the scale is pushed into the rolled material, and remains as scale flaws and scale patterns. Conversely, when descaling is excessive, the temperature of the rolled material drops significantly, and heat loss increases. Therefore, as long as the scale can be sufficiently removed to prevent scale flaws, it is necessary to minimize the temperature drop of the rolled material, and such optimal conditions are indexed using the various descaling conditions described above. It is important to.

The present inventors conducted descaling experiments under various conditions in order to examine the optimum descaling conditions for performing sufficient scale exfoliation at least not to cause scale flaws in the rolled material as described above. went.

FIG. 3 shows the chemical composition of the material (rolled material 6) used in the experiment. As described above, generally, Si
In the case of a steel scale containing a large amount of Si, it is known that the peelability is remarkably deteriorated.
Steel types A, B, and C different from 6, 0.37, and 1.20 were prepared. In addition, their plate thickness was 30 mm.

The descaling conditions for these three types of rolled material 6 are as follows: first, the height of the nozzles 2a and 2b (hereinafter also referred to as “header height” for convenience) H =
The headers 1a to 1d were set so that the height H of the nozzles 2c and 2d was 100 mm and the height H was 300 mm. And H
When it is set to 100 mm, the flow control valves 7c and 7d are fully closed by a valve operating means (not shown) to eliminate the water injection from the nozzles 2c and 2d, and only the headers 1a and 1b are used. When H = 300 mm, the flow control valves 7a, 7
b was fully closed to eliminate the water injection from the nozzles 2a and 2b, and only the headers 1c and 1d were used. At this time, all nozzles 2a to 2d are the same, and the specifications are as follows.
The flow rate at a pump pressure of 100 kgf / cm ² is 111 liter / min, and the spread angle in the spray long axis direction (board width direction) θ =
The spread angle in the spray short axis direction (passing direction) is 2.2 °.

Further, by manually operating a roll driving motor operating means (not shown), the sheet passing speed V is reduced to V = 2.
It was set appropriately at 0, 50, 150 m / min. Thereby, the descaling time t was variously changed. That is,
The descaling time t is t = e / V, where e is the distance in the passing direction of the spray to be sprayed on the steel plate, and the spread angle of the spraying direction of the spray to be sprayed from the nozzle, the nozzle set height H, and the like. It is uniquely determined geometrically from the relationship.

The pump discharge pressure P is set to P = 3 by manually operating a pump operating means (not shown).
0,70,100,200,300,350kgf / c
m ² was appropriately set. Thereby, the high-pressure water collision pressure p was variously changed.

The temperatures of the steel sheets during the descaling experiments were all maintained in the range of 800 to 1200 ° C.

FIG. 4 shows No. 1 to No. 2 as described above.
An experiment was conducted by setting various descaling conditions to 0, and the results of the scale peeling condition and the temperature drop of the steel sheet under each condition were shown. ○ in the peeling state indicates that the peeling was good, and X indicates that the peeling was poor.

Regarding the experimental results (Nos. 1 to 9) of steel type A, the peeling condition of the scale was bad in Nos. 1, 7, and 8, but the peeling condition was good in all other cases. Regarding the experimental results (Nos. 10 to 12) of steel type B, the peeling state of the scale was poor at No. 10, but the peeling state was good for all other cases. Furthermore, steel type C
Looking at the experimental results (Nos. 13 to 20), No. 1
At 3, 14, 16 to 19, the peeling state of the scale was bad, but in all other cases, the peeling state was good.

Based on the above results, the findings obtained by the inventors of the present invention after organizing and examining the experimental results will be described in detail below.

(1-1) Optimal Conditions for Descaling First, the quality of descaling is determined by the function f (p) (p in this example) of the collision pressure p of high-pressure water and the function g (t) (g) of the descaling time t. In this example, the product of t), ie, f
It was found that the relationship with (p) × g (t) (p × t in this example) was strong, and the index could be indexed by using this. This is shown in FIG. 1, FIG. 5, and FIG.

FIGS. 1, 5 and 6 show the experimental results for steel type A (Nos. 1 to 9), the experimental results for steel type B (Nos. 10 to 12) and the experimental results for steel type C (respectively). No.1
3 to 20). In each of these figures, the horizontal axis represents the descaling time t, and the vertical axis represents the high-pressure water collision pressure p. The numbers in the circles indicate the experiment numbers (No. 1 to 20). Respectively. Also, in each figure, for comparison reference, a conventional technology (Japanese Patent Laid-Open No.
25,734).

From these figures, the present inventors have obtained the following findings.

(1-1A) In each steel type, there is a boundary where the quality of scale peeling is divided, and the boundary is f (p) ×
g (t) (p × t in this example) coincides with a line having a constant value.

That is, in FIG. 1 (steel type A), p ×
The line at t = 0.014, p × t in FIG. 5 (steel type B)
= 0.033 line, p × t = in FIG. 6 (steel type C)
Above the 0.108 line (the side where the collision pressure p is large), the peeling was good (except for two exceptions in FIG. 1), and below the lines, the peeling was poor. Therefore, the conditions of p and t corresponding to these lines are not too small or too small as the descaling condition (that is, the temperature drop of the rolled material is minimized as long as the scale can be sufficiently removed to prevent the scale flaw). (It can be suppressed).

(1-1B) Irrespective of p and t, there is a minimum collision pressure at which scale peeling becomes defective (in the above example, the value is p 0.5 kgf / cm ² ).

In FIG. 1, although No. 1 and No. 2 are above the optimum value p × t = 0.014 (the side where the collision pressure p is large), scale peeling is poor. there were. The inventors of the present application considered this as follows. That is, if the value of the collision pressure p becomes too small,
The stripping force of the physical scale is too small to perform sufficient descaling.

Therefore, if all nozzles in each header row satisfy p ≧ 0.5, such a possibility can be avoided, and sufficient descaling can be performed more reliably.

(1-1C) The above descaling optimum value is determined (changes) according to the Si content in each steel type.

As described above, the optimal descaling value is:
In FIG. 1 (steel type A), p × t = 0.014, FIG.
(Steel type B), p × t = 0.033, and FIG. 6 (Steel type C), p × t = 0.108.
The higher the content, the higher the value. The inventors of the present application paid attention to this point, arranged the relationship between the value of p × t and the Si content, and obtained the results shown in FIG. The horizontal axis represents the Si content [Si] (weight percent), and the vertical axis represents p × t
The number in the circle is the experiment number (No. 1).
To 20). In order to prevent the drawing from being complicated, only typical results of all the results of Nos. 1 to 20 are shown, and other results are omitted. In addition, some experimental data not shown in FIG. 4 are also shown for reference.

In FIG. 7, point A is a point corresponding to p × t = 0.014 shown in FIG. 1 (steel type A), and point B is FIG.
This is a point corresponding to p × t = 0.033 indicating (steel type B), and the point C is a point corresponding to p × t = 0.108 indicating FIG. 6 (steel type C). As shown, these three points are PX
It is located on a straight line a represented by t = 0.09 × [Si]. Thus, it was found that the optimal descaling value is proportional to the Si content in each steel type (the straight line a will be described later).

(1-2) Setting target range of descaling condition As described in the above (1-1), the optimum value of the descaling condition can be obtained. May be set and controlled. However, in an actual operation, it is often more practical to determine a predetermined target range in order to perform setting or control so as to approach the optimum value as much as possible. Further, by setting a certain range in this way, it is possible to tolerate an error of a measuring instrument, an error due to a response delay during control, and the like.

In this case, either a width is provided from the optimum value to the side where the descaling is insufficient, or a width is provided from the optimum value to the side where the descaling is excessive. Here, when the width is provided on the descaling-insufficient side, the scale peeling becomes insufficient, and the remaining scale flaws and scale patterns cause deterioration of the product appearance after rolling or cause defects to remain on the product surface after pickling. May adversely affect product quality. Therefore, by providing a width on the excessively descaling side, even if the temperature drop of the rolled material increases somewhat, the scale can be sufficiently peeled, and the adverse effect on the quality of the product can be reliably prevented. However, at this time, if the width is set too large, the adverse effect of an increase in heat loss due to a decrease in the temperature of the rolled material becomes more significant, so a certain upper limit should be set for the width. Here, one of the advantages of providing such a width is that an error of the measuring instrument can be tolerated as described above. The inventors of the present application have studied how much the temperature should be allowed to fall in order to set the upper limit of this width, and the measurement error of the temperature measuring means for measuring a high temperature exceeding 1000 ° C. is usually ± 15 ° C. Total 30 ° C
Therefore, it was determined that it would be reasonable to provide a width on the de-scaling excess side from the de-scaling optimum value by an amount corresponding to this measurement error width.

FIG. 8 shows that, in order to examine how much the measurement error 30 ° C. corresponds to p × t, a separate cooling experiment was conducted for steel type B, and the temperature T and p
It is the figure arranged on the relation of xt. Experimental conditions other than p and t were H = 150 mm and V = 50 m / min. The horizontal axis is p × t, and the vertical axis is the temperature T after descaling.
Expressed in ° C.

As shown in FIG. 8, T tends to decrease with an increase in p × t, but generally has a characteristic along the downward-sloping curve shown in the figure. The point B ₁ is a point corresponding to p × t = 0.03 which indicates the optimum value for the steel type B. A position corresponding to 30 ° C. on the de-scaling excess side from the point B ₁ is a point B ₂ , and a section from the B ₁ to B _{2 in} the curve is an appropriate target range in setting the descaling condition.

This range is defined by the Si content [Si] and p × t
In FIG. 7, the straight line A in FIG. 7 is shifted from the straight line A by 0.08 in the value of p × t toward the excessive descaling side, and p × t = 0.09 × [Si ] +0.0
It is represented by 8. That is, in this example (f (p) = p, g
In the case of (t) = t), the target setting range of the descaling condition may be 0.09 × [Si] ≦ p × t ≦ 0.09 × [Si] +0.08. As a result, it has been found that an adverse effect on the quality of the product can be surely prevented while preventing an excessive decrease in the temperature of the rolled material and allowing a measurement error of the temperature measuring means.

(1-3) Effects of the present embodiment As described above, in the descaling method of the present embodiment, when descaling is performed, the product f (p) of the first function and the second function is used. × g (t) sum Σ ｛f
(P) × g (t)} is converted to the Si content [Si] of the rolled material.
(% By weight) so that the sum {f (p) × g (t)} becomes the optimum value of the descaling condition or approaches the optimum value. As a result, as described above, the optimum descaling condition can be set to almost no excess or deficiency as the descaling condition. Sufficient scale exfoliation can be performed.

Further, the descaling apparatus shown in FIG. 2 has the following effects. When realizing the above descaling optimum value, when it is desired to change the high pressure water collision pressure p variously, the pump discharge pressure P which is a water source of the high pressure water is used.
Alternatively, it can be performed by changing the specifications of the nozzle and the vertical distance (height) H from the header to the rolled material surface. However, replacing the nozzle in accordance with the type of steel causes the equipment to be stopped, which causes a decrease in operating efficiency. On the other hand, the pump discharge pressure P can be changed relatively easily. However, since the controllable range is limited by the maximum discharge pressure unique to the pump, it does not extend to a wide range of changes. Therefore, by combining this with the change of the header height H, it is possible to change the collision pressure p over a wider range. This will be further described with reference to FIG.

FIG. 9 shows, as an example of normal operating conditions, a rolled material having a Si content [Si] = 0.2 to 2% corresponding to the object of the above-mentioned prior art (Japanese Patent Application Laid-Open No. 9-253,734). In the case of targeting, the passing speed V = 20 to 300 m /
FIG. 9 shows a range of the optimal descaling value according to the present embodiment when the range is changed to a range of min. In the illustrated descaling optimum region, the upper side shows the characteristic line (p × t = 0.18) of the descaling optimum value at the Si content [Si] = 2%, and the lower side shows the Si content [ The characteristic line (p × t = 0.018) of the optimal descaling value when Si] = 0.2% is shown. In addition,
Right end part of the descaling optimum area (t = 0.01s)
Is equivalent to the above V = 20 m / min (corresponding to a general threading speed in rough rolling), and the left end portion (t = 0.001 s) of the descaling optimum area is V = 3
This is equivalent to 00 m / min. Further, FIG. 9 shows that the pump discharge pressure P = 50 to 350 k as an example under the condition of the above-mentioned passing speed V = 20 to 300 m / min.
gf / cm ² , header height H = 50,100,15
The graph shows an area that can be covered in the relationship between the collision pressure p and the descaling time t when variously changed such as 0, 200, and 300 mm.

As shown in the figure, for a header having a fixed height in one row, H = 50, 100, 150, 200, 300 mm
In each case, the area that can be covered is a rectangular area that is horizontally long in the figure, and slides to the lower right as H increases. On the other hand, the range of the descaling optimum value according to the present embodiment is represented by a parallelogram falling to the right as shown in the figure, so that H = 50, 100, 150,
No matter which of 200 mm and 300 mm is set, a single-row header cannot be realized over the full range of the wide descaling optimum value. Therefore, it is desirable to enable the header height H to be variously changed from the viewpoint of effectively utilizing the descaling optimum value range.

Here, when it is desired to change the header height H variously, if only the header height H is changed, the size of the spray area to be sprayed on the rolled material (steel plate) 6 changes. Changes. FIG. 10 is a view for explaining this, and schematically shows the size and positional relationship of the spray area when only the header height H is changed. In FIG. 10, the spray area 12 when the header height H is set relatively high,
The relationship with the spray area 11 when the header height H is changed to a relatively low value is, for example, as illustrated. When the header height H is reduced, there is a high possibility that the lap Lp between the adjacent spray areas like the spray area 11 disappears, and in that case, the descaling of that part (the part without the wrap Lp) becomes poor. Conversely, the wrap portion L
In p, since cooling is large, if the amount of lap is large, cooling of the steel sheet in that portion becomes remarkable, and if the amount of lap is too large, excessive cooling may occur. Therefore, it is necessary to determine and install the nozzle interval so that the wrap amount Lp becomes an appropriate value with respect to the set header height H. As such a conventional technique, as described in JP-A-5-177239, a method has been proposed in which a header is turned in a plane parallel to a steel plate to compensate for a lap amount.
There is a problem that equipment such as a header height elevating device is complicated.

On the other hand, in the descaling apparatus shown in FIG. 2, the nozzles 2a and 2b and the nozzles 2a having different vertical distances (= heights) H from the surface of the rolled material 6 are different from each other.
Two rows of headers 1a and 1b and headers 1c and 1d respectively provided with c and 2d are provided. As a result, by setting them in advance to the required heights in advance as described above, and selectively using these two rows of headers by using the flow control valves 7a to 7d, It is possible to perform descaling at various header heights H without complicating the equipment. Therefore, it is possible to easily change the collision pressure p in a wide range together with the change in the pump discharge pressure P. That is, in the configuration example at the time of the above-described experiment, the height H of the nozzles 2a and 2b was set to 100 mm, and the height H of the nozzles 2c and 2d was set to 300 mm. However, when the operation conditions shown in FIG. 2a, 2b
Height H = 50 mm, nozzles 2c, 2d height H = 10
By setting it to 0 mm (or 150 mm), most of the descaling optimum value range shown in FIG. 9 can be easily covered, and this range can be used effectively.

In this case, the conventional technique (Japanese Patent Laid-Open No. 9-2
The following is further clear as an effect of the present embodiment in comparison with Japanese Patent Application Laid-Open No. 53,734).

As described above, this prior art uses a collision pressure of 4 to 30 kg for a Si content of 0.2 to 2.0%.
f / cm ² , and the ejection time is 0.002 seconds to 0.005 seconds. As is clear from FIG. 9, in this setting range, there is a descaling failure region in which a part of scale removal is insufficient. turn into. The inventors of the present application performed a descaling experiment in the descaling failure region shown in FIG. 9 just in case, and in accordance with the knowledge of the present embodiment described so far, the descaling in this region is actually performed. Was insufficient. Therefore, the setting of the descaling condition according to the above-described conventional technique cannot be said to be correct in the sense that the condition for achieving sufficient scale exfoliation to prevent scale damage of the rolled material is specified.

The range of the descaling optimum value according to the present embodiment is, as described above, the parallelogram region falling to the right in FIG. 9, and its width is clearly larger than the range defined by the above-mentioned prior art. The present invention includes a short-time descaling (high-speed passing) side and a long-time descaling (slow-speed passing) side than the conventional technology. That is, the present invention does not include a descaling defective region as in the above-described conventional technology, or does not limit the region to an unnecessarily small size, and a condition for achieving sufficient scale peeling to the extent that scale damage of a rolled material can be prevented. Can be correctly defined.

A second embodiment of the present invention will be described with reference to FIG. This embodiment is an embodiment in which the same descaling experiment as in the first embodiment is performed using two rows of headers. The same reference numerals are given to the same contents as those in the first embodiment, and the description will be appropriately omitted.

In this embodiment, in the descaling apparatus shown in FIG. 2, the header 1 is set so that the heights H of the nozzles 2a, 2b, 2c and 2d are all H = 100 mm.
a to d are set, and the flow control valves 7a, 7b, 7c, 7d
Were used as fully open. Other experimental conditions are
It is as follows.

As the rolled material 6, only the steel type C having a Si content [Si] (% by weight) of 1.20 was used. The plate thickness was 30 mm as in the first embodiment. Nozzles 2a-d
Is the same as that of the first embodiment. Passing speed V
Was fixed at V = 150 m / min. Thereby, the descaling time t was also fixed at 0.0030 s. Pump discharge pressure P is P = 250, 300, 350 kgf / c
m ² was appropriately set. Thereby, the high-pressure water collision pressure p was variously changed.

FIG. 11 shows Nos. 21 to N as described above.
An experiment was conducted by setting various descaling conditions up to o.23, and the results of the scale peeling condition and the temperature drop of the steel sheet under each condition were shown.

In FIG. 11, Nos. 22 and 23 correspond to the first
Headers for Nos. 16 and 17 in the embodiment of FIG.
Equivalent to using columns. As shown in FIG.
Regarding o.23, even if good stripping was not obtained with No.17 in a row of headers, the descaling effect can be easily improved by changing the number of headers used (in this case, doubling). It could be confirmed.

Based on the above results, the findings obtained by the inventors of the present invention by organizing and examining the experimental results will be described in detail below.

(2-1) Optimal Descaling Condition In the first embodiment having only one column of header,
The quality of the descaling is determined by the function f of the collision pressure p of the high-pressure water.
(P) (eg p) and the function g of the descaling time t
The product of (t) (eg, t), ie, f (p) × g (t)
(For example, p × t) could be used as an index, and an optimal descaling value and an appropriate target range including the same could be set.

The inventors of the present invention have proposed that when a plurality of rows of headers are provided as in this embodiment, the above f (p) × g (t)
(For example, p × t) for the header column (in this case, 2
Column) can be indexed. This will be described with reference to FIG. In FIG. 6, f (p) in Nos. 13 to 20 of the first embodiment.
Instead of × g (t) (p × t in this example), {f (p) × g (t)} (｝ (p × t) in this case) is used in Nos. 21 to 23 of the present embodiment. Thus, it can be understood that the same optimum characteristic line Σ (p × t) = 0.108 can be arranged on the same diagram as an index. At this time, the aforementioned No.
For No. 23, compared to No. 17 in the header row,
Since the value of (p × t) doubles, it can be evaluated that the descaling effect has been improved.

(2-2) Extension and Generalization of Optimal Descaling Condition In the first embodiment of one header row, $ f (p)
× g (t)} is equal to {f (p) × g (t)} as it is. Therefore, from the knowledge obtained in the above (2-1),
In the various findings obtained in (1-1A) to (1-1C) of the first embodiment, f (p) × g (t) is all Σ
It is understood that the definition may be replaced with {f (p) × g (t)}. Below, they will be organized and re-posted.

(2-2A) In FIGS. 1, 5 and 6,
Steel type A is Δ (p × t) = 0.014, steel type B is Δ (p × t)
t) = 0.033, steel type C is Σ (p × t) = 0.108
Are the lines indicating the optimal descaling values.

(2-2B) In FIG. 7, the descaling optimum value is proportional to the Si content in each steel type.
× t) = 0.09 × [Si].

(2-2C) In FIG. 8, the appropriate target range when the descaling condition is set in consideration of the measurement error 30 ° C. is 0.09 × [Si] ≦ Σ (p × t) ≦ 0.09 × [Si] +0 It should be .08.

By expanding as described above, regardless of the number of header rows, the descaling conditions that can sufficiently remove the scale to the extent that scale flaws can be prevented while minimizing the temperature drop of the rolled material are defined as follows. Can be set correctly.

FIG. 12 and FIG. 1 show a third embodiment of the present invention.
3 will be described. This embodiment is an embodiment in a case where the descaling condition is automatically controlled and optimized based on a given operation condition. Portions common to the first and second embodiments are denoted by the same reference numerals, and description thereof will not be repeated.

FIG. 12 is a diagram showing a schematic configuration of a descaling apparatus for hot rolling equipment according to the present embodiment. First
The embodiment differs from the descaling device of FIG. 2 described above in that the input device 13, the arithmetic device 14, and the control device 1
5, a discharge pressure adjusting means (for example, a regulator for adjusting the tilt angle of the swash plate) provided along with the pump 9, and an opening adjusting means (for example, a solenoid for not shown) provided along with the flow control valves 7a to 7d. ) And the operation of the roll drive motors 16 a and 16 b are controlled by a control signal from the control device 15.

That is, the operator can select the type of rolled steel, rolling temperature,
When operating conditions such as rolling speed and the like are input from the input device 13, they are transmitted to the arithmetic device 14. Arithmetic unit 14
Is based on the operating conditions and in accordance with the principle described in the first and second embodiments, the Si content [S
i] (weight%), the optimal descaling condition, ie, the first function f (p) (for example, p) and the second function g
(T) (for example, t) The sum of all products f (p) × g (t) (for example, p × t) ヘ ッ ダ ー f (p) ×
g (t)} is calculated. Then, the control device 15 performs the above-described ejection so that the collision pressure p and the descaling time t become the optimum value {f (p) × g (t)} or approach the optimum value. A control signal is output to the pressure adjusting means, the opening degree adjusting means, and the roll drive motors 16a and 16b as needed, so that the discharge pressure P of the pump 9 and the flow rate control valves 7a to 7a are controlled.
The opening degree d and the drive speed of the roll drive motors 16a and 16b are controlled.

The control method at this time is a passing speed priority method in which the passing speed V input by the input device 13 is prioritized without control intervention, and the discharge of the descaling pump p is performed according to the input passing speed V. The pressure P is changed.
As in the first embodiment, the height H of the nozzles 2a and 2b is 100 mm, and the height H of the nozzles 2c and 2d is 300.
mm, and the flow rate control valves 7a, 7b,
Headers are automatically selected and used by control signals to 7c and 7d.

In the above configuration, the descaling pump 9 provided with the discharge pressure adjusting means and the flow rate control valves 7a, 7b, 7c, 7d provided with the opening degree adjusting means include:
A jet pressure adjusting means for adjusting the jet pressure of the high-pressure water jetted from the jet nozzle constitutes a roll drive motor 16a, 16
b constitutes a rolling speed adjusting means for adjusting the rolling speed of the rolling mill. Further, the flow control valves 7a, 7b, 7c, 7d
Also constitutes selection means for selecting at least one of the plurality of header rows to perform high-pressure water injection.
Further, the arithmetic unit 14 and the control unit 15 constitute control means for controlling operations of the ejection pressure adjusting means and the rolling speed adjusting means.

Using the descaling apparatus, the present inventors conducted descaling experiments (Nos. 24, 25 and 26) similar to those of the first and second embodiments. This will be described with reference to FIG.

As shown in FIG. 13, as the rolled material 6,
In Experiment No. 24, the Si content [Si] (% by weight)
Using a steel type B having a value of 0.37,
In No. 26, steel type C having a Si content [Si] (% by weight) of 1.20 was used. The plate thickness was 30 mm as in the first embodiment. The running speed V as an operating condition input by the input device 13 is V = 50 m / m in Nos. 24 and 25.
In No. 26, v = 100 m / min.

After the start of the experiment, in No.
Finally, the discharge pressure P of the pump 9 = 190 kgf
/ Cm ² and the flow control valves 7a, 7b
Was controlled to be fully closed and the flow control valves 7c and 7d were fully opened, whereby only the headers 1c and 1d having a header height H = 300 mm were used. During operation, Σ ｛f (p) × g (t) (in this case, Σ (p × t), the same applies hereinafter) that defines the descaling condition is in an appropriate range (0.033 to 0.133) corresponding to steel type B. , FIG. 4), and the scale peeling condition was good.

In No. 25, the discharge pressure P of the pump 9 is controlled to 210 kgf / cm ² by the control device 15, and the flow control valves 7c and 7d are fully closed and the flow control valves 7a and 7b are fully open. State, whereby only the headers 1a, 1b with a header height H = 100 mm were used. During operation, Σ (p × t), which defines the descaling condition, is in an appropriate range (0.1
08 to 0.188 (see FIG. 4), and the scale peeling condition was also good.

Further, in No. 26, the discharge pressure P of the pump 9 is controlled to 315 kgf / cm ² by the control device 15, and the flow control valves 7c, 7d or 7a, 7b are selectively controlled to be fully opened. Thus, the headers 1a and 1b having the header height H = 100 mm and the headers 1c and 1d having the header height H = 300 mm were selectively used as appropriate. Specify the descaling conditions during operation.
(P × t) is an appropriate range (0.108) corresponding to steel type C.
０．１0.188, see FIG. 4), and the scale peeling condition was also good.

As described above, according to the descaling device of the present embodiment, the input device 13, the arithmetic device 14, and the control device 15 are provided, so that the almost optimal descaler is automatically provided for various rolling conditions. Descaling can be performed under scaling conditions.

The following effects are also obtained. That is, depending on the operational reasons, in particular, depending on the rolling speed (sheet passing speed) and the type of steel, when trying to set the above-mentioned descaling condition to an optimum value, for example, as in the case of Nos. In some cases, it is easier to realize the optimum value by using a header string, and in other cases, it is easier to achieve by using a plurality of header strings as in No. 26 described above. In the present embodiment, the control signal from the control device 15 selects and uses at least one required header from the plurality of header columns 1a to 1d, thereby making it easier to realize the optimal value of the descaling condition. it can.

In the first to third embodiments, as described above, as an example of the function f (p) of the collision pressure p of the high-pressure water, f (p) = p and the function g of the descaling time t
Although the case of f (t) = t has been described as an example of (t), the gist of the present invention is not limited to this.
For example f (p) = p ^m and g (t) = t ^n, etc., even if the other functions using an idea of the above-described embodiment, their product f (p)
The optimal descaling value can be indexed using × g (t). At this time, it goes without saying that they are also included in the scope of the concept of the present invention.

Further, in the first to third embodiments, at most two rows of headers having nozzles are used, but the present invention is not limited to this. That is, three or more header columns may be provided in the descaling device, and the number of header columns to be used therein may be determined as appropriate.

[0098]

According to the present invention, regardless of the silicon content, it is possible to reduce the temperature of the rolled material to a minimum while minimizing the temperature drop of the rolled material and to sufficiently prevent the scale from being damaged. Can be removed.

[Brief description of the drawings]

FIG. 1 is a view showing experimental results (Nos. 1 to 9) of steel type A in a descaling experiment of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of a descaling apparatus for a hot rolling facility that performs a descaling method according to a first embodiment of the present invention.

FIG. 3 is a diagram showing a chemical composition of a material used in a descaling experiment according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a result of a scale peeling state and a temperature drop of a steel sheet under each condition in a descaling experiment of the first embodiment of the present invention.

FIG. 5 is a view showing experimental results (No. 10 to 12) of steel type B in a descaling experiment of the first embodiment of the present invention.

FIG. 6 is a diagram showing experimental results (Nos. 13 to 20) of steel type C in the descaling experiment of the first embodiment of the present invention.

FIG. 7 is a diagram showing the relationship between the value of p × t and the Si content regarding the optimal descaling value.

FIG. 8 is a diagram in which cooling test results of steel type B are arranged in a relationship between the temperature T after descaling and p × t.

FIG. 9 shows the range of the optimal descaling value when the rolling speed is changed to a range of 20 to 300 m / min for a rolled material having a Si content [Si] = 0.2 to 2%. FIG.

FIG. 10 is a diagram showing a comparison between a spray area when the header height H is set relatively high and a spray area when the header height H is changed relatively low.

FIG. 11 is a diagram showing experimental results (Nos. 20 to 23) in a descaling experiment according to the second embodiment of the present invention.

FIG. 12 is a diagram illustrating a schematic configuration of a descaling device for hot rolling equipment according to a third embodiment of the present invention.

FIG. 13 is a diagram showing experimental results (Nos. 24 to 26) in a descaling experiment according to the third embodiment of the present invention.

[Explanation of symbols]

1a-d Descaling header 2a-d Descaling nozzle (spray nozzle) 4a, b Work roll (rolling roll) 5a, b Reinforcement roll (rolling roll) 6 Rolled material (hot rolled material) 7a-d Flow control valve ( Opening / closing valve, ejection pressure adjusting means, selecting means) 8 pressure adjusting valve 9 descaling pump (ejection pressure adjusting means) 10 piping 14 arithmetic unit (control means) 15 control unit (control means) 16a, b roll drive motor (rolling speed) Adjustment means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenjiro Narita 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power & Electricity Development Division, Hitachi, Ltd. 3-1-1, Inside Hitachi, Ltd. Hitachi Plant

Claims (13)

[Claims] At least one header row is arranged in a rolling direction, and at least one spray nozzle is provided in each header row, and high-pressure water sprayed from the spray nozzles is supplied to the surface of a hot-rolled material to remove scale. In each of the header rows, p is a collision pressure of the high-pressure water on the hot-rolled material, f (p) is a first function having the collision pressure p as a variable, and t, when a second function having the descaling time t as a variable is g (t), a product f (p) × g of the first function and the second function
Sum of all header columns of (t)） f (p) × g
(T) The scale removal is performed so that な る becomes or approaches an optimum value determined according to the Si content [Si] (% by weight) of the rolled material. Descaling method to use. 2. The descaling method according to claim 1, wherein the scale removal is performed such that the sum {f (p) × g (t)} falls within a predetermined range including the optimum value. A descaling method characterized in that: 3. The descaling method according to claim 2, wherein the predetermined range is defined as the sum Σ ｛f (p) × g
(T) A descaling method characterized in that the value is set by giving a certain width from the optimum value of｝ toward the overscaling side. 4. The descaling method according to claim 2, wherein said optimum value changes in proportion to said Si content [Si] (% by weight). 5. At least one header row is arranged in the rolling direction, at least one injection nozzle is provided in each header row, and high-pressure water ejected from the injection nozzles is supplied to the surface of the hot-rolled material to remove scale. In each of the header rows, the pressure at which the high-pressure water impinges on the hot-rolled material is p [kgf / cm ² ], and the descaling time is t.
[S], the product p × of the collision pressure p and the descaling time t
The sum Σ (p × t) of all the t header rows is set to an optimum value determined according to the Si content [Si] (% by weight) of the rolled material, or approaches the optimum value. ,
A descaling method comprising performing the scale removal. 6. The descaling method according to claim 5, wherein the scale removal is performed such that the sum Σ (p × t) falls within a predetermined range including the optimum value. Scaling method. 7. The descaling method according to claim 6, wherein said predetermined range is a range represented by 0.09 × [Si] ≦ Σ (p × t). 8. The descaling method according to claim 7, wherein the predetermined range is a range represented by 0.09 × [Si] ≦ Σ (p × t) ≦ 0.09 × [Si] +0.08. A descaling method characterized by the following. 9. The descaling method according to claim 5, wherein all nozzles in each header row satisfy p ≧ 0.5. 10. At least one header row is arranged in a rolling direction of a rolling mill, at least one injection nozzle is provided in each header row, and high-pressure water jetted from the injection nozzles is supplied to the surface of the hot-rolled material. In a descaling device for removing scale, an ejection pressure adjusting means for adjusting the ejection pressure of high-pressure water ejected from the ejection nozzle; a rolling speed adjustment means for adjusting a rolling speed of the rolling mill; The impact pressure on the hot-rolled material is p, the first function using the impact pressure p as a variable is f (p), the descaling time is t, and the second function using the descaling time t as a variable is g. (T), the sum {f (p) × g (t)} of all the header rows of the product f (p) × g (t) of the first function and the second function is , Si content of the rolled material [Si] (Weight%), and control means for controlling the operations of the ejection pressure adjusting means and the rolling speed adjusting means so as to become or approach the optimum value determined in accordance with the weight ratio. Scaling device. 11. A descaling apparatus according to claim 10, wherein said ejection pressure adjusting means adjusts a discharge pressure of a pump which is a supply source of said high-pressure water, and said ejection pressure adjusting means includes a means for adjusting a discharge pressure from said pump to said ejection nozzle. A descaling device comprising at least one of the opening adjustment means for adjusting the opening of the on-off valve provided in the pipeline. 12. The descaling device according to claim 10, wherein said header row is provided in a plurality of rows, and a selecting means for selecting at least one of them and performing high-pressure water injection is provided. A descaling device characterized by the above-mentioned. 13. The descaling apparatus according to claim 10, wherein a plurality of header rows are provided, and at least two of the header rows have different vertical distances from the rolled material surface. A descaling device characterized in that it is configured as follows.