RU2741033C1 - Production plant for production of steel sheet and method of production of steel sheet - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to a production plant for the production of steel sheets and a method of producing a steel sheet. Proposed plant comprises hot rolling mill, first mould straightening device and accelerated cooling device arranged in said order. Accelerated cooling device contains water-removing rollers that limit the steel sheet from above and from below, and a control system that controls the force P applied to limit the steel plate.

EFFECT: as a result, providing uniform cooling of hot steel sheet on production line for production of flat steel sheet of homogeneous quality.

14 cl, 8 dwg, 2 tbl, 6 ex

Description

The technical field to which the invention relates

The present invention relates to a production plant for the production of steel sheet with cooling on a hot rolling line to obtain a high quality product, and to a method for the production of a steel sheet, in particular, to a production plant for the production of high flatness steel sheet and a method for the production of steel sheet.

State of the art

At present, controlled rolling to perform rolling in a low temperature range or accelerated cooling to cool rolled steel sheets, in particular thick steel sheets, is already performed. As product quality improves, high-precision temperature control, in particular high-precision temperature control with stop cooling, is becoming more and more important.

In general, in a hot-rolled steel sheet, uneven cooling appears to be caused by cooling due to uneven temperature distribution or a change in the shape or surface condition of the steel sheet immediately after rolling. In particular, the unevenness of cooling that occurs in a steel sheet having a relatively thick thickness is more likely to be related to the characteristics of the cooling device. Cooling irregularities occurring in a thick steel sheet cause deformation, residual stresses, quality changes, etc. in the thick steel sheet. In view of the above, despite the development of various types of cooling devices that can perform uniform cooling, the improvement of the cooling device alone cannot ensure complete alignment of the steel sheet, in particular after cooling. A defect in the shape of the steel sheet being cooled causes operational problems, such as problems with the passage of the sheets on the production line, or needs to be straightened during a subsequent process with a press or straightener and thus increases costs.

The reasons for the uneven cooling of the steel sheet include reasons related to the characteristics of the cooling nozzle, such as temperature fluctuations of the upper and lower surfaces or temperature stability in the width direction, and reasons related to the shape of the steel sheet before cooling.

To solve the problems associated with the cooling nozzle, such as temperature fluctuations of the top and bottom surfaces or temperature stability in the width direction, a large number of technical solutions have been developed so far. On the other hand, few technical solutions have been developed to overcome the cooling unevenness problems associated with shape defect occurring during rolling, as described below.

The first method is used to straighten the mold in front of the accelerated cooling device in order to level the mold for uniform cooling. In Patent Literature 1, a description is given for straightening the shape of a steel sheet in a first straightening device to such an extent that the water-removing rolls of the cooling device can completely drain water from the steel sheet. Patent Literature 2 describes how to determine the distance from the exit from the mold straightening device to the entrance to the cooling device in order to avoid the impossibility of leveling after cooling due to heat recovery in the steel sheet.

The second method serves to restrain the steel sheet with water-removing rolls. The dewatering rolls have two functions: 1) leveling the steel sheet using the pressure of the rolls and 2) preventing the cooling water sprayed to the cooling section from escaping outside.

Patent Literature 3 describes a technical solution that includes water-removing rolls capable of being individually raised and lowered vertically, and the rolls move up and down following the profile of the steel sheet. Patent Literature 4 describes a technical solution for applying pressure to a steel sheet by dewatering rolls with a predetermined force or higher in order to flatten the deformed steel sheet to a predetermined level to effectively retain cooling water while reducing the gaps between the steel sheet and the rolls.

List of referenced documents

Patent Literature

PTL 1: Japanese Unexamined Patent Publication No. 2002-11515

PTL 2: Japanese Unexamined Patent Publication No. 2005-74480

PTL 3: Japanese Unexamined Patent Publication No. 52-73111

PTL 4: Japanese Patent No. 3304816

Disclosure of the essence of the invention

Technical problem

At the present time, production lines that operate using the technical solutions described in Patent Literatures 1 and 2 are gaining more and more popularity, and contain a mold straightening device in front of the cooling device. However, when the cooling device, which does not contain water-retaining rolls, performs cooling, the cooling water that has flowed out from the cooling water spray portion remains on the steel sheet, particularly on the upper surface of the steel sheet, for a long time, and the upper the surface of the steel sheet, on which the accumulated water remains, is supercooled.

When using technical solutions for equipping the cooling device with water-removing rolls, for example, as described in Patent Literatures 3 and 4, the steel sheet is more likely to have a shape defect due to rolling, in particular in a thin section prone to shape defect. , for example, in an area having a small thickness (for example, when the thickness is less than or equal to 30 mm) and a large width (for example, greater than or equal to 3000 mm). Thus, in a design that does not include a mold straightener upstream of the cooling device, the water removing rolls are more likely to be unable to properly contact the steel sheet to retain the cooling water, thereby allowing the cooling water to flow out of the cooling water spray section at the top. surface of the steel sheet and causing hypothermia and shape defect associated with temperature fluctuations.

The present invention has been developed in view of the above circumstances, and its object is to provide a steel sheet production apparatus capable of producing a flat steel sheet of uniform quality by uniformly cooling a hot steel sheet on a production line and a steel sheet production method.

Solution to the problem

Through careful research, the present inventors have found that high flatness steel sheets can be produced by flattening the shape of the steel sheets in the first shape straightener, preferably to a predetermined slope or less, and then appropriately restraining the steel sheets with water-removing rolls in the accelerated cooling apparatus.

The essence of the invention is as follows:

[1] A production plant for the production of steel sheet, containing

a hot rolling mill, a first mold straightener and an accelerated cooling device in this order,

wherein the accelerated cooling device comprises water-removing rolls that define the steel sheet at the top and bottom, and a control system that adjusts the pressure force P applied to restrain the steel sheet.

[2] A steel sheet production plant according to [1], in which the pressure force P satisfies the formula (1) below,

P ≤ 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1), where

P - pressure force (t),

L - length of the roll body (mm),

W - sheet width (mm),

D is the outer diameter of the roll (mm) and

d is the inner diameter of the roll (mm).

[3] The production plant for the production of steel sheet according to [1] or [2], in which the second mold straightener is located after the accelerated cooling device.

[4] A production plant for the production of steel sheet according to any one of [1] to [3], wherein the first form straightener and / or the second form straightener are / are roll straighteners / roll straighteners.

[5] A production plant for the production of steel sheet according to any one of [1] to [4], in which the first form straightening device corrects the slope of the steel sheet to below 2.0%.

[6] A method for producing a steel sheet, including:

placing the hot rolling mill, the first mold straightening device and the accelerated cooling device in this order; and

rolling the steel sheet in a hot rolling mill, then straightening the shape of the steel sheet in the first shape straightening device, and then cooling the steel sheet in the accelerated cooling device, limiting the steel sheet from above and below with water-removing rolls at a given pressure force P.

[7] The method for manufacturing a steel sheet according to [6], in which the pressure force P satisfies the formula (1) below,

P ≤ 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1), where

P - pressure force (t),

L - length of the roll body (mm),

W - sheet width (mm),

D is the outer diameter of the roll (mm) and

d is the inner diameter of the roll (mm).

[8] The method for manufacturing a steel sheet according to [6] or [7], wherein the second mold straightener is located downstream of the accelerated cooling device, and the second mold straightener further straightens the shape of the steel sheet.

[9] The method for manufacturing a steel sheet according to any one of [6] to [8], wherein the first shape straightener and / or the second shape straightener are / are roll straighteners / roll straighteners.

[10] The method for manufacturing a steel sheet according to any one of [6] to [9], wherein the first form straightener corrects the slope of the steel sheet to below 2.0%.

Advantageous Effects of the Invention

According to the present invention, flat steel sheets of uniform quality can be produced by uniformly cooling the hot steel sheets on a production line.

Brief Description of Drawings

FIG. 1 is a schematic diagram of the structure of a production plant for producing steel sheet according to the present invention;

fig. 2 is a schematic diagram showing how a steel sheet passes through a first sheet straightening device and an accelerated cooling device;

fig. 3 is a schematic view showing the gap between the steel sheet and the water removing rolls, where FIG. 3 (a) is a state where the pressure force of the water removing rolls is insufficient, FIG. 3 (b) is a state where the pressure force of the water removing rolls is excessive, and FIG. 3 (c) a state where the pressure force of the water-removing rolls is appropriate;

fig. 4 is a graph showing the relationship between pressure force and deflection of water removing rolls;

fig. 5 - determination of the slope λ;

fig. 6 is a graph showing the relationship of slope and pressure force with or without cooling water leakage, the roll diameter being 400 mm;

fig. 7 - model of the pressure force of the rolls removing water;

fig. 8 is a graph showing the relationship of the deflection value and the pressure force of the water removing rolls with or without cooling water leakage from the water removing rolls.

Implementation of the invention

As shown in FIG. 1, a production plant according to the present invention comprises a hot rolling mill 1, a first mold straightening device 2, an accelerated cooling device 3, and a second device, a second mold straightening device 4 in this order. The steel sheet 5 is rolled in a hot rolling mill 1, then the shape is straightened in the first shape straightening device 2, controlled cooling in the accelerated cooling device 3 and, if necessary, the shape straightened in the second shape straightener 4. The arrow in FIG. 1 indicates the conveying direction of the steel sheet.

FIG. 2 schematically shows how the steel sheet 5 passes through the first mold straightening device 2 and the accelerated cooling device 3. A steel sheet 5 that has been rolled in a hot rolling mill 1 is more likely to have a shape defect such as edge waves. After flattening the sheet in the first form straightening device 2, the steel sheet 5 is subjected to controlled cooling in the accelerated cooling device 3. The accelerated cooling device 3 comprises water-removing rolls 31 that define the steel sheet 5 at the top and bottom, cooling nozzles 32 that spray cooling water passing through them, and a pressure control system 33 that controls the pressure forces P of the water-removing rolls 31. Cooling nozzles 32 can be positioned between the water removing rolls 31.

FIG. 3 schematically shows the gaps between the steel sheet 5 and the water-removing rolls 31. When the steel plate is non-planar (for example, concave downward in the width direction of the steel plate), the steel plate 5, being deformable, is pressed against the water-removing rolls 31. Thus, for example when the pressure is insufficient, the dewatering rolls 31 are unable to align the steel sheet 5 that is concave downwardly as shown in FIG. 3 (a) and leave gaps between the steel sheet 5 and itself. On the other hand, when the pressure force of the water-removing rolls 31 is excessive, the water-removing rolls 31 flex and form gaps between the steel sheet 5 and themselves (Fig. 3 (b)). In general, it is known that flattening a steel sheet with a shape defect such as an edge wave by applying pressure thereto with water-removing rolls requires a pressure force of approximately several hundred tons. FIG. 4 is a graph showing the relationship between the pressure force of the 300 mm diameter dewatering rolls (solid roll) and the 6 m roll body length applied to the 4000 mm wide steel sheet and the deflection of the stripping rolls. The deflection is measured with a feeler gauge. It is generally accepted that a clearance of at least about 1 mm or less is required for proper water retention by dewatering rollers. When the pressure force exceeds several tens of tons, the water retaining rolls deflect by more than 1 mm, with each water retaining roll forming a gap of approximately 6 mm and can no longer function as a water retaining roll.

To ensure proper clearance between the steel sheet 5 and each water-removing roller 31, as shown in FIG. 3 (c), it can be assumed that the steel sheet has a flat original shape, the pressure force of the water-removing rolls 31 is limited to a predetermined level or less, and it is required to maintain the pressure force at a predetermined level while the steel sheet passes between the water-removing rolls 31.

Further, by changing the straightening conditions (pressure value) in the first shape straightening apparatus 2 with the production apparatus shown in FIGS. 1 and 2, steel sheets of various shapes are caused to pass through the accelerated cooling apparatus 3 to check the cooling water leakage state. The steel sheets are 30 mm thick, 3500 mm wide and have a temperature of 850 ° C. The shape of each steel sheet after passing through the first shape straightening device 2 is quantified using the slope λ (%) shown in FIG. 5, determined by the following formula (2), and is appropriately controlled by the pressure in the first straightening device 2 forms. The value δ / p in formula (2) is the average value of the general shape of the edge wave in the longitudinal direction:

λ = (δ / p) × 100 (2), where

λ - slope (%),

δ - wave height (mm) and

p - wave step (mm).

With regard to the dewatering rolls 31 in the accelerator 3, solid rolls with a body length of 6000 mm and diameters of 300 mm and 400 mm are used, which correspond to the typical range of diameters of the dewatering rolls of the accelerated cooler.

FIG. 6 is a graph showing the slope and pressure force with or without cooling water leakage for a roll diameter of 400 mm. FIG. 6, circles indicate cases where water does not flow between steel sheet and rolls, and crosses indicate cases where water flows between steel sheet and rolls. Cooling water leakage is visually confirmed.

The results in FIG. 6 show that an excessively large pressure force of the dewatering rolls 31 causes the cooling water to leak, and an excessively low pressure force also causes the cooling water to leak. Thus, the pressure force must be adjusted properly. The results also show that the excessively large slope of the steel sheet 5 also does not prevent the cooling water from escaping even with the pressure force control. It can be assumed that an excessively large pressure force causes the above-described deflection of the water-removing rolls 31, so that the steel sheet is in the state shown in FIG. 3 (b), while the insufficient pressure force does not prevent deformation of the steel sheet 5, so that the steel sheet is in the state shown in FIG. 3 (a).

The results in FIG. 6 show that the steel sheet 5 must be leveled to a certain level before being transported to the accelerated cooling device 3 and must be subjected to a predetermined pressure force. Thus, the preferred level of pressure force is determined based on the fact that the excessive pressure force bends the rolls.

When simulating the dewatering rolls 31 using the model shown in FIG. 7, from the point of view of the mechanical properties of the material, the deflection value δ at the center of the water removing roller 31 in the length direction of the body can be calculated by the following formula:

Calculation 1

, где

where

P - pressure force (t)

L - length of the body of the water-removing roll (mm),

W - sheet width (mm),

E - Young's modulus of the water-removing roll (21 t / mm ² ) and

I - secondary moment of inertia of the section (mm ⁴ ).

In the case of a hollow roll, the secondary moment of inertia of the section I can be described by the following formula:

Calculation 2

, где

where

D - outer diameter of the water-removing roll (mm),

d is the inner diameter of the water-removing roll (mm) and

π is the ratio of the circumference of the ring to its diameter.

In the case of a solid roll in the formula (4), which calculates the moment of inertia of the section I, the inner diameter d of the water-removing roll 31 can be determined as 0. From the above formula, it is clear that the deflection value δ of the water-removing roll 31 related to the width of the steel sheet 5 or the dimensions of the dewatering roller 31 is proportional to the following parameters:

Calculation 3

.

...

Hereinafter, the right side of formula (5) is referred to as the deflection parameter.

Subsequently, to confirm the influence of roll deflection on the ability of the water-removing rolls 31 to retain water, steel sheets of several types with a slope of 0.75% were preliminarily manufactured, after which these steel sheets were delivered to the accelerated cooling device 3, and cooling water was sprayed on them using accelerated cooling devices 3 under different pressure forces applied to the water-removing rolls 31 to confirm whether there has been a leakage of cooling water. Each of the steel sheets had a thickness of 30 mm and a width of 2500 mm, 3500 mm or 5000 mm, and the dewatering rolls, whether they were solid rolls or hollow rolls, had a diameter of 400 mm (the inner diameter of the hollow rolls was 320 mm at thickness 40 mm) and body length 6000 mm. It was visually confirmed whether there was visual leakage of cooling water or not, and a case where there was a leak between the steel sheet and the rolls was identified as a leakage of cooling water (cross indicating "unsatisfactory").

FIG. 8 is a graph showing the effect of the pressure force of the dewatering rolls 31 and the amount of deflection on whether or not cooling water leaks past the dewatering rolls 31. The graph shows that a large amount of deflection causes the cooling water to leak at a lower pressure. FIG. 8 shows that limiting the occurrence of cooling water leakage has the following relationship:

Calculation 4

.

...

Specifically, it has been found that when the outer diameter D, the inner diameter d, and the body length L of the water removing roll 31 are determined, the pressure force P satisfies the formula (1) below, according to the width W of the sheet, so that the water removing rolls 31 are not can bend and can provide a preferred drainage of water:

P ≤ 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1), where

P - pressure force (t),

L - length of the roll body (mm),

W - sheet width (mm),

D is the outer diameter of the roll (mm) and

d is the inner diameter of the roll (mm).

The lower limit of the pressure force P is preferably greater than or equal to 1.0 ton from the viewpoint of balancing out the slight curvature remaining in the steel sheet, which is affected by the roll leveler, to a minimum level of water evacuation by the pressure force of the water removing rolls.

The first shape straightening device 2 can be either a push pass straightening machine or a roll straightening machine for multiple bending. In the present invention, when the front end portion of the steel sheet 5 is curved, it may not be possible to insert the steel sheet 5 between the water-removing rolls 31 of the accelerated cooling device 3. Thus, the front end portion of the steel sheet 5 is preferably straightened in a roll straightening machine capable of performing multiple bending and providing more efficient straightening modes than a temper leveler, which provides less efficient straightening modes for the longitudinal curvature that occurs at the rear end portion of the steel sheet. sheet 5.

When the first shape straightening device 2 is to straighten the steel sheet 5, the slope of the steel sheet 5 is preferably straightened to a value below 2.0%. More preferably, the slope is adjusted to below 1.0%.

The accelerated cooling device 3 is not suitable for adjusting the flow in the direction of the width of the steel sheet in order to ensure a completely uniform flow. Thus, temperature fluctuations during controlled cooling can cause slight bending, so that preferably the second shape straightening device 4 further straightens the steel sheet 5 after controlled cooling in the accelerated cooling device 3. A roll straightening machine capable of performing multiple bending is preferably used as the second form dressing devices 4.

Each dewatering roll 31 may have either a hollow structure or a solid structure. From the point of view of minimizing the deflection of the water-removing roll 31, a solid structure (solid roll) is more preferable because the roll is more rigid. The rigid structure can also reduce additional pressure forces such as hydraulic pressure by using the weight of the water-removing rolls.

The cooling nozzles 32 are not limited to specific nozzles. The examples used include multiple cylindrical jet nozzles, slot nozzles, a spray nozzle that sprays only water, such as a flat spray, angle spray, full cone spray or oval spray, or a mist spray nozzle of the same shape that mixes water and air.

The pressure force control systems 33 can be any system that can apply a predetermined pressure, such as a spring, pneumatic pressure, or hydraulic pressure. In the present invention, it is important that the pressure control systems 33 maintain a pressure such that the water-removing rolls 31 do not bend. Thus, a control system that can maintain a given pressure force is preferable. However, in the case of a spring system, the amount of pressure changes according to the shape of the steel sheet 5, and thus the pressure force also changes to a large extent. Thus, in the case of a spring adjustment system, the steel sheet should have a low slope (preferably less than 1.0%) during straightening of the steel sheet in the first shape straightener 2. Thus, a control system using hydraulic pressure or pneumatic pressure, which is characterized by having a predetermined pressure force, is preferable.

Preferably, the present invention relates to a steel sheet having a thickness less than 30 mm and / or a width greater than or equal to 3000 mm, and capable of reducing shape defects associated with rolling.

Example 1

The steel sheets were produced in the production plant shown in FIG. 1. Steel sheets 5 with a thickness of 25 mm and a width of 3500 mm were produced in a hot rolling mill 1, then their shape was corrected in the first device 2 for adjusting the shape to obtain a predetermined steepness, after which the steel sheets were directed to the device 3 for accelerated cooling. The slope of the steel sheets 5 was adjusted by adjusting the pressure force settings of the first shape straightening device 2. As required, the steel sheets 5 were straightened in a second shape straightener 4. The steel sheets 5 that had curvatures after straightening in the second shape straightener 4 were re-straightened in the cold rolling straightener.

As shown in FIG. 2, an accelerated cooling device 3 was used as an example, which contains ten nodes located in the transport direction of the steel sheets 5, each receiving unit contains water-removing rolls 31, cooling nozzles 32 located between the water-removing rolls 31, and pressure control systems 33 ... The pressure force control systems 33 were pneumatic pressure systems. The water removing rolls 31 were hollow rolls with a body length of 6000 mm, an outer roll diameter of 400 mm and an inner roll diameter of 320 mm.

First of all, the relationship between the slope of the steel sheets 5, the pressure force P of the water removing rolls 31, the temperature distribution of the cooled steel sheets, and the resulting shapes (Examples 1 and 2 and Comparative Examples 2 to 4) was investigated.

After controlled cooling, from the point of view of checking the temperature fluctuations in the width direction of the steel sheets and achieving the target quality, the steel sheets having the temperature fluctuations in the width direction of the steel sheets in the range of 25 ° C were evaluated as acceptable. The material having temperature fluctuations in excess of 25 ° C was re-straightened in a cold-rolling straightener to a level that meets the specified manufacturing specifications.

The results are shown in Table 1.

Table 1

Steel sheet thickness
(mm) Steel sheet width
(mm) Steepness
(%) Pressure force of water-removing rolls
(t) Pressure force P according to the formula (1)
(t) Temperature deviation after cooling
(° C) Re-edit Example 1 25 3500 0.75 ten 15.3 12 Not required Example 2 25 3500 1.5 ten 15.3 22 Not required Comparative example 2 25 3500 0.75 thirty 15.3 72 Required Comparative example 3 25 3500 1.5 thirty 15.3 69 Required Comparative example 4 25 3500 2.5 thirty 15.3 58 Required

P = 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1)

Examples 1 and 2 are examples where the dewatering rolls 31 had a pressure force of 10 tons, which is less than or equal to the pressure force P (15.3 tons) expressed by formula (1) in the present invention. In Examples 1 and 2, the slope was 0.75% and 1.5%, respectively, and the temperature fluctuation in the width direction of the sheets was 12 ° C and 22 ° C, which was an acceptable range. After straightening in the second form straightening device 4, the steel sheets remain flat without the need for re-straightening. During mechanical tests, the tensile strength was satisfactory without hesitation. When comparing Examples 1 and 2, the steel sheet of Example 1, having less curvature, had less temperature fluctuation.

Comparative examples 2 to 4 are examples where the dewatering rolls 31 had a pressure force of 30 tons, which is greater than the pressure force P (15.3 tons) expressed by formula (1) in the present invention. Regarding these examples, regardless of the slope of the steel sheets 5, large temperature fluctuations (58 to 72 ° C) were observed towards the tire of the sheets. During the examination, a large amount of accumulated water was observed on the steel sheet, particularly in the center in the direction of the sheet width. This is probably the result of the inability to retain the cooling water by the water removing rollers 31. The accumulated water remained in the center in the width direction, which was probably caused by temperature fluctuations. The steel sheets of Comparative Examples 2 to 4 had a large curvature after straightening in the second shape straightener 4 and required re-straightening in the cold rolling straightener, which was associated with additional production costs. In addition, mechanical tests carried out on the steel sheets of Comparative Examples 2 to 4 showed large fluctuations in tensile strength.

Further, as a second embodiment, the relationship between the width of the steel sheets, the pressure force of the water-removing rolls 31, the temperature distribution of the cooled steel sheets, and the resulting molds for the steel sheets 5 before their accelerated cooling was investigated, the steel sheets 5 being aligned in the first mold straightening apparatus 2 and had a slope of 0.75% and were then subjected to controlled cooling in the accelerator 3 (Examples 3 and 4 and Comparative Examples 5 and 6).

The study was carried out on steel sheets with a thickness of 30 mm and a width of 2000 mm and 5000 mm. As in the first embodiment, steel sheets having temperature fluctuations in the width direction of the steel sheets in the range of 25 ° C were judged to be acceptable. As in the first embodiment, the material having temperature fluctuations exceeding 25 ° C was re-straightened in a cold-rolling straightener.

The results are shown in Table 2.

table 2

Steel sheet thickness
(mm) Steel sheet width
(mm) Steepness
(%) Pressure force of water-removing rolls
(t) Pressure force P according to the formula (1)
(t) Temperature deviation after cooling
(° C) Re-edit Example 3 thirty 2000 0.75 thirty 34.5 18 Not required Comparative example 5 thirty 2000 0.75 50 34.5 100 Required Example 4 thirty 5000 0.75 fifteen 19.7 ten Not required Comparative example 6 thirty 5000 0.75 thirty 19.7 40 Required

P = 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1)

Example 3 was an example where the water removal roll 31 had a pressure force of 30 tons, which is less than the pressure force P (34.5 tons) expressed by formula (1) in the present invention. In example 3, the temperature fluctuation in the width direction was 18 ° C, which is small and corresponds to an acceptable level without the need for straightening in the second shape straightener 4. During the study in example 3, no water accumulation was observed. On the other hand, Comparative Example 5 was an example where the dewatering rolls had the same width as in Example 3 and a pressure force of 50 tons, which is greater than the pressure force P (34.5 tons) expressed by formula (1) in the present invention. In Comparative Example 5, large temperature fluctuations (100 ° C) were observed in the width direction of the sheet. A large amount of accumulated water was observed on the steel sheet, particularly in the center in the sheet width direction. This is probably a result of the inability to retain the cooling water by the water removing rolls 31. As in the above comparative examples, the steel sheets of Comparative Example 5 had a large curvature after straightening in the second shape straightener 4 and required re-straightening in the cold rolling straightener, which associated with additional production costs. In addition, mechanical tests showed large fluctuations in tensile strength.

Example 4 was an example where the dewatering rolls 31 had a pressure force of 15 tons, which is less than the pressure force P (19.7 tons) expressed by formula (1) in the present invention. In Example 4, the temperature fluctuation in the width direction was 10 ° C, which is preferable, and the flat shape was also maintained after straightening in the second shape straightener 4. On the other hand, in Comparative Example 6, the temperature fluctuation was 100 ° C, and severe hypothermia was observed. In Comparative Example 6, a large amount of accumulated water was observed on the steel sheet, particularly in the center in the width direction. This is probably due to the inability to retain the cooling water by the water removing rolls 31. As in the above comparative examples, the steel sheet of Comparative Example 6 had a large curvature after straightening in the second shape straightener 4 and required re-straightening in the cold rolling straightener, which associated with additional production costs. In addition, mechanical tests showed large fluctuations in tensile strength.

The above study has shown that limiting the steel sheet to water-removing rolls with a predetermined pressure force simultaneously with leveling the steel sheet ensures an even temperature distribution of the steel sheet to obtain a high flatness steel sheet, and that changing the pressure force appropriately depending on the sheet width ensures an even temperature distribution of the steel sheet. sheet for the production of high flatness steel sheet.

List of item numbers

1 - hot rolling mill

2 - the first device for dressing the form

3 - accelerated cooling device

31 - water removing roller

32 - cooling nozzle

33 - pressure control system

4 - the second device for dressing the form

5 - steel sheet

W - sheet width

L - roll body length

P - pressure force

δ - wave height

p - wave step.

Claims (30)

1. A production plant for the production of steel sheet, containing a hot rolling mill, a first mold straightener and an accelerated cooling device in this order, wherein the accelerated cooling device comprises water-removing rolls that define the steel sheet at the top and bottom, and a control system configured to adjust the pressure force P applied to limit the steel sheet. 2. An installation according to claim 1, in which the pressure force P satisfies the formula (1) below, P ≤ 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1), where P is the pressure force (t), L - length of the roll body (mm), W - sheet width (mm), D is the outer diameter of the roll (mm) and d is the inner diameter of the roll (mm). 3. An installation according to claim 1, in which a second mold dressing device is located after the accelerated cooling device. 4. An installation according to claim 2, in which a second mold straightening device is located after the accelerated cooling device. 5. Installation according to any one of paragraphs. 1-4, in which the first shape straightener and / or the second shape straightener are / are roll straighteners / roll straighteners. 6. Installation according to any one of paragraphs. 1-4, in which the first form straightener corrects the steel sheet slope to below 2.0%. 7. An apparatus according to claim 5, wherein the first form straightener corrects the slope of the steel sheet to below 2.0%. 8. Method for the production of steel sheet, including: using a production plant comprising a hot rolling mill, a first mold straightener, and an accelerated cooling device in this order, and rolling a steel sheet in a hot rolling mill, then straightening the shape of the steel sheet in the first shape straightening device and then cooling the steel sheet in an accelerated cooling device while limiting the steel sheet from above and below by water-removing rolls at a given pressure force P. 9. The method according to claim 8, wherein the pressure force P satisfies formula (1) below, P ≤ 37 × ((LW) × W ² / (D ⁴ -d ⁴ )) ^-1.25 (1), where P is the pressure force (t), L- length of the roll body (mm), W - sheet width (mm), D is the outer diameter of the roll (mm) and d is the inner diameter of the roll (mm). 10. The method according to claim 8, wherein after the accelerated cooling device there is a second mold straightening device, in which additional straightening of the steel sheet is performed. 11. A method according to claim 9, wherein after the accelerated cooling device there is a second mold straightening device, in which additional straightening of the steel sheet is performed. 12. The method according to any one of claims. 8-11, in which the first shape straightener and / or the second shape straightener are / are roll straighteners / roll straighteners. 13. The method according to any one of claims. 8-11, in which the first mold straightener corrects the steel sheet slope to below 2.0%. 14. The method of claim 12, wherein the first shape straightening device corrects the slope of the steel sheet to below 2.0%.

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