JPH07171610A - Method and device for rolling hot rolled steel sheet - Google Patents

Abstract

PURPOSE:To suppress the generation of a secondary scale after descaling, simultaneously prevent the surface roughening on the surface of rolling roll and to prevent the generation of rough surface of steel sheet. CONSTITUTION:When the thickness of the scale on the surface of steel sheet exceeds 10mum on the inlet side of a finishing stand of a continuous hot rolling mill, descaling headers 1 are mounted just near by the inlet side of steel sheet of work rolls 3 and, after jetting spray water to the surface of a steel sheet 6 from descaling nozzles 2 at collosion pressure of >=0.15kgf/cm<2>, the steel sheet is rolled within one second with the work rolls 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling a steel sheet in a hot continuous rolling facility, more specifically, removing scale immediately near the entrance side of a rolling mill (stand) to generate secondary scale and roughen the roll surface. The present invention relates to a rolling method for producing a hot-rolled steel sheet having no scale defects and a rolling apparatus for carrying out the method.

[0002]

2. Description of the Related Art Hot-rolled steel sheets are usually produced by rough rolling a slab heated to a high temperature of 1100 to 1450 ° C. and then finish rolling. At that time, if the primary scale produced during slab heating or the secondary scale produced after removing this primary scale is rolled while remaining on the steel sheet surface,
So-called scale flaws in which scales are caught on the surface of the steel sheet are generated, which deteriorates product quality. In order to prevent the occurrence of such scale flaws, a descaling device that removes scale by jetting high-pressure water is usually installed in the rolling line, and rolling is performed while removing the primary scale and the secondary scale.

In this descaling method by jetting high-pressure water, high-pressure water is jetted from descaling headers provided at a plurality of positions on the surface of a steel sheet transferred along a rolling line to remove and remove the scale. Is.
A pair of descaling headers is provided above and below the steel plate, and multiple nozzles are attached to each header so that high-pressure water can be sprayed evenly across the upper and lower surfaces of the steel plate in the width direction. Has been done.

As a method of descaling as described above, for example, in Japanese Unexamined Patent Publication No. 48-38224, a secondary scale on the surface of a steel sheet is levitated in a low pressure spray zone, and 30 to 50 kgf /
A method of scattering a floated scale with a jet device of a water jet of cm ² is described, and in JP-A-54-162631, at least 2 pieces of high pressure water of 90 to 130 kgf / cm ² at the entrance side of the rolling mill are described. A method of injecting twice is disclosed. However, after removing the secondary scale, the scale grows thick again before rolling on the next stand.

Further, in Japanese Patent Laid-Open No. 63-68214, a high-pressure water spray having a collision pressure per unit spraying area of 25 g / mm ² or more is applied to the surface of a Si-containing steel sheet immediately before the finishing rolling mill to prevent peeling. Although a method of removing the scale is disclosed, even if the primary scale is removed, a secondary scale is produced between the rolling stands, so it cannot be said to be a sufficient descaling method from the viewpoint of preventing scale flaws.

Further, Japanese Patent Application Laid-Open No. 58-31247 discloses a descaling method using an extremely low pressure laminar flow and a spray flow instead of a high pressure water spray. However, in order to carry out this method, large-scale equipment is required, and after descaling, the distance to the next stand is large, and during that time, the secondary scale grows again and it is easy to generate scale flaws. It was

Further, in Japanese Patent Laid-Open No. 50131/1993, a descaling device consisting of a header pipe having a large number of injection nozzles capable of independently adjusting the injection amount is provided near a downstream stand of a finish rolling mill. Devices have been proposed to remove secondary scale by placement. This has a drawback that the descaling device becomes large because the opening and closing is controlled for each nozzle.

That is, the conventional descaling device is
For example, the finishing stand is provided on the inlet side A and the outlet side B of the front stage F1 stand and the outlet side C of the F2 stand (see FIG. 2 described later), but the installation location of the descaling device and the next stand. Between about 1500-40
Since there is a distance of 00 mm, there is a problem that even if the secondary scale is removed, the secondary scale grows thick again until rolling by the next stand, and scale flaws easily occur. Also, although the temperature of the outermost surface layer of the steel sheet decreases due to descaling, if the descaling device and the next stand are separated, the outermost surface layer of the steel sheet will be in a high temperature state again due to recuperation before moving to the next stand. In addition, the growth rate of the secondary scale is increased and a large heat load is applied to the rolling roll, which promotes roughening of the surface of the roll.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems, suppresses the generation of secondary scale after descaling, and prevents the roughening of the rolling rolls, thereby improving the surface of the steel sheet. It is to provide a rolling method for reducing scale flaws.

[0010]

Means for Solving the Problems The inventors of the present invention have identified the causes of scale defects in order to prevent scale defects caused by scales generated during hot rolling and improve the quality of hot-rolled steel sheets. A hot rolling model rolling machine and an actual machine were tested and investigated. As a result, scale flaws are closely related to the scale thickness during rolling, and if the scale thickness during rolling is 10 μm or less, it is possible to prevent the occurrence of scale flaws regardless of the roughness of the rolling roll. I found out. Then, in order to do so, the distance between the descaling device and the next stand is shortened, the time until the next rolling after removing the scale is shortened as much as possible, and the temperature of the outermost surface of the steel sheet once reduced by descaling is reheated. It was confirmed that suppressing the re-rise was effective in suppressing the growth of the secondary scale.

The present invention has been made on the basis of the above findings, and its gist resides in a hot rolling steel sheet rolling apparatus shown in the following hot rolling steel sheet rolling method.

When the scale thickness of the steel sheet surface exceeds 10 μm at the entrance side of the finishing front stand of the hot continuous rolling mill, after spraying water with a collision pressure of 0.15 kgf / cm ² or more on the surface of this steel sheet A method for rolling a hot-rolled steel sheet, comprising rolling in the finishing front stand within 1 second.

When the thickness of the scale on the surface of the steel sheet exceeds 10 μm at the entry side of the finishing front stand of the hot continuous rolling mill, spraying of spray water on the surface of the steel sheet is started.
A rolling method for hot-rolled steel sheet, comprising descaling by raising the collision pressure to 0.15 kgf / cm ² or more in 1.5 to 10 seconds, and rolling within 1 second in the finishing front stand.

An arithmetic unit for predicting the secondary scale thickness from the steel plate surface temperature at the entrance side of the hot continuous rolling mill and the steel plate speed of each stand, and pressure water is sprayed on the steel plate surface close to the entrance side of each stand. And a controller for operating an opening / closing valve of the descaling device when the predicted value of the secondary scale thickness of the computing device reaches a predetermined value.

The above-mentioned pre-finishing stand refers to a rolling stand from the steel plate entry side to the fourth from the finishing rolling mill, which is usually composed of 7 stands.

[0016]

The method of the present invention will be described in detail below.

(A) Effects of Scale Thickness and Roll Surface Roughness on Scale Defect Generation: Table 1 shows a thickness of 20 m.
A low carbon steel (C: 0.05%) steel sheet with a width of 100 mm and a width of 100 mm was rolled by a model rolling mill, and the results of an investigation of factors affecting the generation of scale flaws revealed that the scale thickness during rolling and the surface of the roll It shows the occurrence rate of scale flaws when the roughness is changed. The surface roughness of the roll
It is expressed by the center line average roughness (Ra) specified in JIS. Rolling is performed in a total of 5 passes, the total rolling reduction is 88%, and only the rolling roll for the F1 stand uses a roll whose surface roughness is changed.

[0018]

[Table 1]

According to the results shown in Table 1, the occurrence of scale flaws is affected by the surface roughness of the roll, but it largely depends on the scale thickness during rolling. When the scale thickness during rolling is 10 μm or less, It can be seen that the presence of scale defects can be prevented regardless of the surface roughness of the roll. Furthermore, even in the actual machine, the scale thickness during rolling is 10
It was confirmed that the scale flaw can be completely prevented by controlling the thickness to be not more than μm.

(B) Method of suppressing scale thickness to 10 μm or less: As a method of suppressing the scale thickness during rolling to 10 μm or less, high-speed rolling, low-temperature rolling, etc. can be considered, but application to an actual machine was considered. In this case, these methods are not preferable because they limit rolling conditions. Therefore, the method of the present invention uses a method of removing the secondary scale by descaling before rolling.

The timing of descaling can be obtained from calculation taking into consideration the scale generation rate, the decrease in the surface temperature of the steel sheet due to descaling, the reheat, and the like.
In the normal rolling temperature range, after descaling the steel plate,
If the rolling is performed within 1 second, the scale thickness can be suppressed to 10 μm or less. That is, one second before rolling the steel sheet, spray water is sprayed at the position where the steel sheet exists or at a position closer to the rolling roll than that position, and if descaling is performed, the scale thickness during rolling should exceed 10 μm. There is no.

The time of 1 second or less is calculated by converting the scale thickness into the scale weight increase amount and expressed by the following equation (1): Parabolic law [3rd Edition Iron and Steel Handbook, Vol. III (1) Rolling foundation,
Steel sheet (1980, Maruzen, page 33) was applied.

Ε ² = K _p · t (1) where K _p = A · exp (−Q / R · T) In the equation (1), ε is the scale weight increase amount [g / cm ² ]. ,
T is the surface temperature [K] of the steel sheet, t is the holding time [sec] at the surface temperature T, and R is the gas constant of 1.9843 [cal / mol · K].
Is. Further, Q is an activation energy [cal / mol] of diffusion of Fe ions in FeO, and A is a constant.

(C) Regarding Prediction Method of Scale Thickness: FIG. 1 is a diagram showing a part of the configuration of a rolling mill in which a device for controlling a descaling device is arranged. The steel plate surface temperature and the steel plate speed are required to calculate the scale thickness, but the output of the thermometer 7 on the rolling mill entrance side is used for the temperature calculation data, and the work roll rotation speed meter 8 is used for the steel plate speed. Since the output of is input to the computer of the rolling control device 12, this is diverted.

The temperature calculation is performed as heat conduction only in the plate thickness direction of the steel sheet in consideration of the working heat of rolling as heat input, frictional heat during rolling, contact with rolls as heat radiation, air cooling, and descaling. The unsteady one-dimensional heat conduction equation was derived and solved by the implicit difference method.

In this way, the surface temperature was calculated for each minute time Δt, and the scale thickness was obtained by the above equation (1). It is assumed that the scale is completely peeled off by descaling on the inlet side of the rolling mill, and that the secondary scale generated at each stand receives a reduction equal to the reduction rate. FIG. 5 is a diagram showing an example of changes in the scale thickness of each stand calculated in this way. The scale thickness of the descaled steel plate is reduced by the F1 stand and before entering the F2 stand.
Since it was predicted that the thickness would exceed 10 μm, this is an example of performing descaling before entering the F2 stand.

(D) The impact pressure of spray water on the steel plate surface
About to 0.15kgf / cm ² or more: impact pressure is derived by the following procedure.

First, from the well-known Bernoulli's theorem,
The relationship of equation (2) has become true.

[0029] _{(p 1 / ρ) + (} v 1 2/2) = (p 2 / ρ) + (v 2 2/2) ··· (2) However, p _1: water pressure in the header [kgf / m ² ] p ₂ : Water pressure at the outlet of the descaling nozzle [kgf /
m ² ] v ₁ : Flow velocity in header [m / s] v ₂ : Flow velocity at descaling nozzle outlet [m / s] ρ: Water density [kgf · S ² / m ⁴ ] where p ₂ << p can be regarded as _1, v _{1 «v 2,} by placing a _{p 2 ≒ 0, v 1 ≒} 0, (2) formula
It becomes like the formula (3).

V ₂ = (2p ₁ / ρ) ^1/2 (3) From this, the collision force (H) is given by the following equation (4) (v
₂ and p ₁ are represented by v and p respectively).

H = ρvQ = (2pρ) ¹ / 2Q (4) where Q: flow rate [m ³ ] The descaling nozzle forms an angle α with the vertical downward direction.
If it is inclined only, H = (2pρ) ^1/2 · Q · cos α (5).

Here, when the height of the nozzle from the steel plate surface is L, the opening angle of the nozzle is θ, and the spray thickness of the collision part is d, the collision area (A) of spray water is given by the following equation.

A = (L / cos α) × 2 tan (θ / 2) × d (6) Therefore, the collision pressure (P) is expressed by the following equation (7), and from this equation, the collision pressure (P ) Is determined by the injection pressure (p), the flow rate (Q), the nozzle shape (θ, α), and the like.

P = H / A = (2pρ) ^1/2 · Q · cos ² α / {L · 2 tan (θ / 2) × d} (7) In the descaling method of the present invention, injection is performed. Pressure is 50 ~
200kgf / cm ² , flow rate 50-150 liters / min, nozzle opening angle 15-45 °, nozzle height 200-600mm, nozzle inclination angle 5-20 °, scale thickness during rolling is 10μm It was confirmed by a test using a model rolling mill that it could be suppressed below. Using these values, the spray thickness d of the collision part is set to 10
When the minimum value of the collision pressure in mm in the descaling method of the present invention is calculated by the above formula (7) as mm, it becomes 0.15 kgf / cm ² . Therefore, in the descaling method of the present invention,
The impact pressure of spray water on the steel plate surface was limited to 0.15 kgf / cm ² or more. Moreover, although the upper limit is not particularly limited, similarly, the maximum value is about 6 kgf / cm ² . Even if the collision pressure is increased more than this, there is no difference in the peelability of the scale, and rather the steel sheet is supercooled, so it is desirable to set it to 6 kgf / cm ² or less.

In the descaling method (apparatus) of the present invention, since the descaling header is installed immediately near the entrance side of the steel plate of the rolling roll, if the descaling nozzle is oriented perpendicularly to the steel plate surface, The peeled and scattered secondary scale is caught in the roll bite, and scale flaws easily occur. Therefore, it is preferable to incline the descaling nozzle backward with respect to the traveling direction of the steel sheet. The tilt angle is preferably about 5 to 20 °.

The injection pressure is determined by the pressure of the descaling pump used, but as described above, it is preferably in the range of 50 to 200 kgf / cm ² .

(E) About setting a predetermined collision pressure within 1.5 to 10 seconds after the start of spray water injection: When spraying water on the surface of a steel sheet to descale, spray is started as shown by the broken line in FIG. It takes less than a second for the spray to reach the desired impact pressure. The application of descaling on the steel sheet surface by spraying water is performed before the rough rolling stand and before the finishing stand F1 stand, but by opening the valve of the descaling pipe within a short time after the start of spraying, the specified collision pressure can be achieved. Reached and the effect of descaling is immediately exerted. At this location, the problem of plate width variation is unlikely to occur even if the material to be rolled is thick and spraying is suddenly started. However, in the case of descaling before the finishing front stand as in the present invention, when the predetermined collision pressure is set within 1 second, the rolling load changes in the next rolling stand due to a rapid change in the scale thickness and the steel plate temperature, The board width sometimes changed. As shown by the solid line in FIG. 6, when the collision pressure was gradually increased after the spraying was started and the predetermined collision pressure was applied for 1.5 seconds or more, the fluctuation of the rolling load and the fluctuation of the strip width could be prevented.

The reason why the spray water is regulated within 10 seconds after the start of spraying is that there is no particular problem in preventing load fluctuation even if it is lengthened, but if it is lengthened, the effect of preventing scale defects of the product is reached until a predetermined collision pressure is reached. Since it became smaller, it was set within 10 seconds. A method of controlling the time to reach a predetermined collision pressure can be achieved by controlling the valve opening / closing speed of the descaling pipe.

It is preferable that the descaling device for carrying out the method of the present invention is generally attached to one of the finishing pre-stage stands, especially the F2 stand in a position close to the entrance side of the steel plate in a vertical pair.

Usually, careful descaling is performed on the entry side of the finish rolling mill, and the surface temperature of the steel sheet is greatly reduced. Therefore, the scale thickness does not exceed 10 μm on the entry side of the F1 stand. However, the plate passing speed is slow between the F1 and F2 stands, and the surface temperature of the steel plate is also rising due to recuperation, so that the scale is likely to grow thick. After the F2 stand, the sheet passing speed is fast, and since the descaling is performed immediately before the F2 stand, the surface temperature of the steel sheet is also lowered, and the scale does not easily grow. Therefore, the descaling device for carrying out the method of the present invention is preferably installed immediately before the entrance side of the steel plate of the F2 stand. However,
Depending on the rolling mill, there may be a stand having a scale thickness of more than 10 μm even after the present invention is applied to the F2 stand because of a low rolling speed or a high rolling temperature. In such a case, it is desirable to provide a descaling device immediately before the steel plate entry side of each stand.

In the descaling method of the present invention, spray water is sprayed on the surface of the steel sheet immediately before rolling as described above.
Therefore, since the temperature of the outermost surface of the steel sheet once lowered is rolled before it rises again due to the heat recovery, the growth of the secondary scale is suppressed and it is effective in preventing the generation of scale flaws. Further, since the heat load applied to the rolling roll is smaller than that in the case of the conventional descaling, and the surface of the roll is less likely to be roughened, there is an advantage that scale defects are less likely to occur.

[0042]

EXAMPLES The descaling method of the present invention will be described below based on examples.

[Embodiment 1] FIG. 2 is a view showing the front stage F1 stand and the F2 stand of the seven finishing stands of the hot rolling mill in which the descaling device used in the embodiment is arranged. The material of the work rolls of the rolling mill is high chromium cast iron (2.7% C-17% Cr).

In FIG. 2, a pair of conventional descaling devices are provided above and below the steel plate 6 at positions A, B and C, respectively. Further, descaling for carrying out the method of the present invention at a position D near the entrance side of the steel plate of the F2 stand, that is, a position at which the steel plate can be rolled within 1 second after descaling as described below. A device (hereinafter referred to as "nearest descaler") is attached. Since the rolling speed is fast after the F2 stand and the oxidation time is short, and the steel plate surface temperature is low, it is difficult for the scale thickness to become thick, and the stand after F3 does not require a descaling device to provide the scale thickness during rolling. Is 10 μm
Never exceeded.

FIGS. 3 and 4 show an example of the latest descaler attached to the position D, which is a view showing the structure of the portion centering on the descaling header, and is processed into a drain plate on the steel plate entry side of the F2 stand. And the descaling header is added. FIG. 3 is a partial vertical sectional view,
FIG. 4 is a plan view of the descaling header and the nozzle portion. In these figures, 1 is a descaling header, 2 is a descaling nozzle, 3 is a work roll,
6 is a steel plate, the inclination of the descaling nozzle 2 is 10 °, and the distance from the tip of the nozzle 2 to the surface of the steel plate 6, that is, the injection distance is 300 mm. The distance from the position where the spray water collides with the steel plate to the point where the roll 3 contacts the steel plate 6 (the point where the perpendicular line passing through the center of the roll 3 intersects the steel plate 6) is 650 mm.

In this case, the time from descaling to rolling depends on the rolling speed and the like, but is about 0.5 to 0.8 seconds. In addition, 4 is a draining board, 5 is a rolling oil nozzle. Further, as shown in FIG. 4, each nozzle 2 is provided with a twist of 15 ° in order to avoid interference between spray water sprayed from the adjacent nozzles. The shaded area in FIG. 4 shows the spread of the spray water when it collides with the steel sheet.

With the finishing stand to which the descaling device is attached as described above, the finishing dimension is 2.3 mm and the width is 1250 for a plain steel plate having a thickness of 30 mm and a width of 1260 mm.
mm hot-rolled steel sheet was manufactured, and the surface temperature and skin roughening condition of the work roll of the F2 stand and the condition of the steel sheet surface after manufacturing were investigated. In this case, when using the nearest descaler, the descaling device mounted at the positions B and C in FIG. 2 was stopped and the descaling device at the positions A and D was used. Note that A, B and C
With the descaling device at the position of
The water pressure was 0 kgf / cm ² and the water amount was constant at 4200 liters / min, and the spray pressure and the water amount were adjusted in the nearest descaler at the position D to change the collision pressure of the spray water on the steel plate surface.

The survey results are summarized in Table 2. Inventive Examples 1 to 3 and Comparative Example 4 are cases where the descaling apparatuses A and D shown in FIG. 2 are used and the method of the present invention is applied to D, and Comparative Example 5 is the descaling apparatus A shown in FIG. , B
And C are used.

[0049]

[Table 2]

As shown in Table 2, in the invention examples (Nos. 1 to 3) in which the most recent descaler was used and descaling was performed at the collision pressure determined by the method of the present invention, both the roll surface skin and the steel plate surface condition were good. However, when the collision pressure was lower than the range specified by the method of the present invention (Comparative Example 4) even when the nearest descaler was used (Comparative Example 4), or when the nearest descaler was not used (Comparative Example 5), banding on the roll surface was observed. The surface of the steel sheet was roughened and scale flaws were generated. In addition, when the latest descaler was used, the temperature of the roll surface could be significantly lowered as compared with the case where it was not used.

[Embodiment 2] The rolled material is ordinary steel (C = 0.05).
~ 0.15%) finish dimension thickness 1.2 ~ 3.5 mm, board width 900 ~
A 1500 mm steel plate was used. High speed steel for rolling work rolls
(2% C-5% V-5% W) was used.

FIG. 1 is a diagram showing a part of the rolling apparatus used in this embodiment. This is a device in which a nearest descaler is placed on the F2 stand and the entrance side of the F3 stand, the scale thickness between the stands is predicted and calculated, and rolling is performed while controlling the opening / closing valve of the descaler. In addition, the descaler is
Similar to that shown in Fig. 3 and Fig. 4, the descaling injection pressure was 130 kgf / cm ² , and the flow rate per nozzle was 100.
The collision pressure was 1.6 kgf / cm ^{2 in} liter / min.

The steel plate surface temperature and the steel plate speed are fetched from the rolling control device (computer) 12 into the sequential calculation device 10,
Calculate the scale thickness just before each stand. The calculated scale thickness data is sent to the controller 11,
If this exceeds 10 μm, the descaling valve 13 is opened with the tip of the steel plate biting into the next roll. In this rolling schedule, the descaling method of the present invention was applied to the F2 and F3 stands, and the scale thickness immediately before rolling did not exceed 10 μm in the stands after F4.

When the F2 stand exceeds 10 μm, the F2
By starting descaling in front of the stand and adjusting the opening / closing degree of the valve 13 shown in Fig. 1, the collision pressure is 1.6 kgf / cm.
^The time to reach ² was changed and the rolling situation was investigated.

The test results are shown in Table 3. Impact pressure 1.6 kgf / cm
^{When the} time to reach ² was short, the F2 stand rolling load fluctuated and the strip width locally decreased. However, when the time to reach the predetermined collision pressure was 1.5 seconds or more, the load fluctuation was suppressed and the plate width fluctuation was reduced. The surface quality of the steel sheet was all good.

[0056]

[Table 3]

[0057]

By applying the rolling method of the present invention during hot rolling of a steel sheet, it is possible to suppress the generation of secondary scale after descaling and at the same time prevent the surface of the rolling roll from being roughened. It is extremely effective in preventing the occurrence of scale flaws on the surface. In particular, when the material of the rolling roll is high-speed steel, the roll is used for a long period of time and scale defects tend to occur frequently, and the effect of the present invention is remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing a partial configuration of a rolling mill in which a device for controlling a descaling device is arranged.

FIG. 2 is a diagram showing a partial configuration of a hot finish rolling mill in which a descaling device for carrying out the method of the present invention is arranged.

FIG. 3 is a partial vertical cross-sectional view showing an example of a part of the descaling device for carrying out the method of the present invention.

FIG. 4 is a plan view of a descaling header and nozzle portion of an example of a descaling device for carrying out the method of the present invention.

FIG. 5 is a diagram showing a time-dependent change in scale thickness during rolling.

FIG. 6 is a diagram showing a pattern for increasing the collision pressure of the descaler to a predetermined pressure.

[Explanation of symbols]

1: Descaling header 2: Descaling nozzle 3: Work roll 4: Drainer
5: Rolling oil nozzle 6: Steel plate 7: Thermometer
8: Tachometer 9: Backup roll 10: Secondary scale thickness prediction calculator 11: Controller 12: Rolling controller 1
3: Open / close valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Hikaru Okada, Sumitomo Metal Industries, Ltd. 4-53, Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture (72) Haruhiko Ishihara, 4-chome, Kitahama, Chuo-ku, Osaka-shi, Osaka 5-33 Sumitomo Metal Industries, Ltd. (72) Inventor Kunio Goto 4-53-3 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Sumitomo Metal Industries Ltd. (72) Inventor Tomoya Suzuki Kashima, Kashima-gun, Ibaraki Prefecture No. 3 Hikari, Chozai, Sumitomo Metal Industries Kashima Works

Claims (3)

[Claims] 1. When the thickness of the scale on the surface of the steel sheet exceeds 10 μm at the entrance side of the finishing front stand of the hot continuous rolling mill,
A method for rolling a hot-rolled steel sheet, comprising spraying spray water at a collision pressure of 0.15 kgf / cm ² or more on the surface of the steel sheet, and rolling within one second with the finishing front stage stand. 2. When the thickness of the scale on the steel sheet surface exceeds 10 μm at the entrance side of the finishing front stand of the hot continuous rolling mill,
1.5 after starting spraying spray water on the surface of this steel plate
A rolling method for hot-rolled steel sheet, which comprises descaling by raising the collision pressure to 0.15 kgf / cm ² or more in about 10 seconds, and rolling within 1 second with the finishing front stage stand. 3. An arithmetic unit for predicting a secondary scale thickness from a steel plate surface temperature at the entrance side of a hot continuous rolling mill train and a steel plate speed between stands, and a steel plate surface close to the entrance side of each stand. A hot rolling apparatus comprising: a descaling device for injecting pressurized water; and a control device for activating an opening / closing valve of the descaling device when the predicted value of the secondary scale thickness of the computing device reaches a predetermined value.