JP2000246302A - Hot rolling method of steel plate and rotary cutting equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the failure to bring the leading end of a steel plate into the work rolls in hot rolling at high draft and achieve stable rolling, by starting the hot rolling after reducing the thickness of the leading end of the steel plate. SOLUTION: Lubricating oil is applied to work rolls so that the friction coefficient μ between the work rolls and a steel plate 14 will be 0.2 or less, and the leading end of the steel plate 14 is reduced in thickness before hot rolling is done. Only the top surface of the leading end of the steel plate 14 is reduced in thickness and the hot rolling is started with the peripheral speed of the upper work roll set higher than that of the lower work roll. The taper angle θ of the leading end of the steel plate 14 and cutting amount Δh should be such as to satisfy the relationship of θ<α<β. In formulae I and II, α is the bring-in angle of the leading end, β the limit bring-in angle, Δt the plate thickness reduction volume of the steady-state portion during hot rolling, and D the diameter of the work roll. The leading end portion is cut by a rotary cutting equipment having multiple cutting tips on the outer periphery of a drum to be driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for hot rolling a steel sheet, and more particularly to a method and apparatus for performing stable rolling by preventing biting failure in hot high-pressure rolling using a lubricant. The present invention relates to a hot rolling method and apparatus.

[0002]

2. Description of the Related Art Usually, the rolling reduction limit in hot rolling of a steel sheet is determined by the rolling load / rolling torque limit and the motor power limit resulting from the equipment strength restrictions of a rolling mill such as the strength of a rolling roll. Conventionally, even at the first stand of a hot-roll finishing tandem mill that performs rolling at the highest rolling reduction, rolling with a rolling reduction of at most 60% is the limit, and most of normal hot rolling is performed under the stability of rolling. From the viewpoint of the rolling reduction of 30 to 50%.

[0003] In recent years, with the increasing demand for difficult-to-process materials and thin materials having high deformation resistance, realization of high-load rolling and high-pressure rolling has been desired, and the need for a high rolling capability of a hot rolling mill has increased. . Also, from the need for cost reduction of products, it is desired to realize a process of manufacturing hot-rolled products with a smaller number of stands than before.

[0004] As a method of realizing a high rolling reduction of a hot rolling mill, a method of reducing the diameter of a work roll to reduce a rolling load and a rolling torque, and improving the strength of equipment including a roll and increasing motor power are provided. There are methods. However, all of these methods require significant equipment modifications,
There is a problem that equipment costs increase.

[0005] In addition to the above method, there is a method of using a lubricant to reduce the rolling load and the rolling torque to reduce the pressure. The present inventor has disclosed in JP-A-63-238904,
The coefficient of friction between the rolled material (steel plate) and the work roll is 0.
Hot rolling method using a lubricant having a high lubricity such as 2 or less (hereinafter referred to as “hot lubricating rolling”
In addition, a method of applying a compressive force at the time of rolling material biting is proposed as a measure for reducing the biting property at the time of hot lubricating rolling.
% Can be increased.

[0006]

The hot lubricating rolling has the effect of greatly reducing the rolling load and rolling torque, and has the potential to realize high-pressure rolling without significant equipment modification. However, when the friction coefficient is reduced, the biteability of the tip end of the steel sheet into the work roll is deteriorated. Therefore, particularly under the condition of a large thickness, there is a problem that the amount of reduction is limited, and it is not possible to perform a more powerful reduction than before. For example, when the friction coefficient μ is 0.2, the upper limit of the biting angle is about 12 °, and the maximum rolling reduction that can be bitten is about 22 mm at most even when the work roll diameter is 1000 mm. Therefore, the plate thickness is 40 mm
In the case of, the rolling reduction is limited to about 55%, which is the same as the conventional one. When the plate thickness is 80 mm, the rolling reduction is limited to about 28% which is lower than the conventional one, so that hot lubricating rolling cannot be applied.

The method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-238904 is intended to improve the biting performance by applying a compressive force at the time of biting, but the required compressive force becomes excessive when the plate is thick. There is a problem that equipment such as a compression force applying device and a buckling prevention guide becomes large. Further, since the compressive force is limited from the viewpoint of the facility capacity, the effect of improving the biting ability is also limited.

[0008] An object of the present invention is to eliminate the problem of the bite of the tip of a steel sheet into a work roll and to achieve stable rolling in hot lubricating rolling of a steel sheet for realizing high-pressure rolling of, for example, 60% or more. An object of the present invention is to provide a rolling method.

[0009]

In order to solve the above-mentioned problems, the present inventor has conducted various rolling tests and studies on the improvement of the biteability of the steel sheet tip and the securing of rolling stability during hot lubrication rolling. The following findings were obtained.

A. When hot lubricating rolling is performed, the bite of the front end is improved by performing a thickness reduction process on the front end of the steel plate in advance. The critical bite angle in the rolling of the steady part (part where almost steady state rolling is performed) after biting of the tip is about twice the limit bite angle of the tip, and the biting of the tip which is an unsteady part is stable. If this is the case, it is possible to reduce the pressure by hot lubricating rolling in a region where the plate thickness is thicker than before.

B. The thickness reduction of the steel plate tip can be easily performed by cutting using a rotary cutting device.

C. When rolling a steel sheet which has been subjected to cutting and thickness reduction only on the upper surface of the steel sheet, a downward warpage of the steel sheet called a nose nose whose tip bends downward during rolling. This downward warpage can be prevented by making the peripheral speed of the upper work roll higher than the peripheral speed of the lower work roll.

D. By performing cutting in a tapered shape and optimizing the tapered shape, stable biting can be performed.

The present invention has been made to solve the above problems, and the gist thereof is as follows. (1) A method of hot rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that the friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less, A hot rolling method for a steel sheet, comprising: reducing the thickness of a tip portion in the rolling direction of the steel sheet; and then starting hot rolling.

(2) A method of hot rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that the friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less. Cutting the upper surface of the tip portion in the rolling direction of the steel sheet, and then starting hot rolling by setting the peripheral speed of the upper work roll higher than that of the lower work roll and starting hot rolling. Rolling method.

(3) A method of hot rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that the friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less. The cutting process of the upper surface of the tip portion in the rolling direction of the steel plate is performed in a tapered shape in which the thickness is reduced toward the forefront portion, the taper angle is θ, and the cutting amount of the foremost portion is Δh. Then, the maximum bite angle α calculated from Δh by the following equation and the limit bite angle β calculated by the following equation from the friction coefficient μ satisfy the relationship of θ <α <β. A hot rolling method for a steel sheet, wherein a hot rolling is started by setting a peripheral speed of a work roll higher than that of a lower work roll.

Α = cos ⁻¹ (1− (Δt−Δh) / D) β = tan ⁻¹ μ where Δt: reduction in the thickness of the steady portion during hot rolling, D: work roll diameter.

(4) A cutting device used for cutting a front end portion in a rolling direction of a steel sheet in order to improve biting properties during hot rolling, wherein the drum is capable of driving rotation and an outer periphery of the drum. A rotary cutting device comprising a plurality of cutting tips provided on a surface.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The hot rolling method of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic side view showing an example of a hot rolling facility for implementing the method of the present invention, in which reference numeral 11 denotes a rolling mill, 12 denotes a pinch roll, 13 denotes a rotary cutting device,
14 is a steel plate, 15 is a tip, 16 is a work roll, 17
Is a backup roll, and 18 is a lubricant supply nozzle.

As shown in FIG. 1, the hot rolling equipment has a rolling mill 11 driven by upper and lower work rolls, and a pinch roll 12 and a rotary cutting device 13 on the entry side of the rolling mill.

After the steel plate 14 is fed to the rotary cutting device 13 by the pinch roll 12 and subjected to thickness reduction by cutting the upper surface of the tip portion 15, hot rolling is started by the rolling mill 11. The lubricant is supplied to the work roll 16 of the rolling mill 11 by a lubricant supply nozzle 18 installed on the entry side. The lubricant is a high lubricant having a friction coefficient μ between the upper and lower work rolls and the steel sheet of 0.2 or less, and usually, synthetic ester or mineral oil is used.

By setting the friction coefficient μ to 0.2 or less, the rolling load and rolling torque during high-pressure rolling at a rolling reduction of about 70% per pass can be significantly reduced without increasing the strength of the rolling mill. High pressure rolling can be realized.

By reducing the thickness of the tip,
Since the biting property of the leading end at the start of rolling is improved, for example, a high pressure can be reduced from a plate thickness of about 50 mm to a rolling reduction of about 70%.

FIG. 2 is a schematic side view showing an example of the rotary cutting device of the present invention. Reference numeral 21 denotes a drum, 22 denotes a cutting tip, and the same elements as those in FIG. 1 are denoted by the same reference numerals. FIG.
FIG. 4 is a schematic diagram showing a cutting state of a steel plate upper surface by a rotary cutting device.

As shown in FIG. 2 and FIG.
Is provided with a plurality of cutting chips 22 in the width direction and the circumferential direction of the outer peripheral surface of the drum 21. The drum 21 is driven and rotated, and a steel sheet is fed by a pinch roll. By doing so, it is possible to perform cutting of the steel plate tip. As shown in FIG. 2, the cutting chips are preferably provided in a staggered manner in the circumferential direction of the drum 21, and the cutting power can be reduced. The material of the cutting tip is preferably a cemented carbide or tool steel having excellent wear resistance. The direction of rotation of the drum may be the same as or opposite to the traveling direction of the steel sheet.

In the example shown in FIG. 1, cutting is performed only on the upper surface of the steel plate. Alternatively, a rotary cutting device may be provided above and below the steel plate to cut the upper and lower surfaces of the steel plate. Further, the thickness reduction of the tip portion may be performed by providing a press device on the entry side of the rolling mill and reducing the press. Another method of the present invention is characterized in that the thickness of the front end is reduced by cutting the upper surface of the steel sheet, and then the hot rolling is started by setting the peripheral speed of the upper work roll higher than that of the lower work roll. .

By performing cutting only on the upper surface of the steel plate, for example, one cutting device such as a rotary cutting device may be used.
In addition, accurate adjustment of the pass line at the time of rolling, which is necessary when cutting the lower surface of the steel sheet, is not necessary. Therefore, the equipment can be simplified and rolling instability due to pass line irregularities can be prevented.

By making the peripheral speed of the upper work roll higher than that of the lower work roll, it is possible to suppress nose bending during rolling.

FIG. 4 is a schematic diagram schematically showing the nose-bending phenomenon. Reference numeral 19 denotes an exit guide, and the same elements as those in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 4, when the upper surface of the steel plate 14 is subjected to cutting and the upper and lower work rolls 16 are rolled at the same peripheral speed (this rolling is referred to as "same speed rolling"), After biting, the rolling amount of the upper work roll is slightly larger than that of the lower work roll as the rolling progresses, and the tip end 15 of the steel plate is bent downward so that the nose falls. By rolling the tip end of the steel sheet (this rolling is referred to as “variable speed rolling”) by making the peripheral speed (V _U ) of the upper work roll higher than the peripheral speed (V _L ) of the lower work roll, the nose bending is performed. Is suppressed, and operation troubles can be prevented. Peripheral speed difference ΔV (= V
When _U -V _L) to define a differential speed ratio δ ratio (ΔV / V _L) and V _L, or equal to about 1 to 10% by differential speed ratio δ is in percent. An appropriate different peripheral speed ratio can be determined within the above range by rolling conditions and cutting conditions.

The variable speed rolling is performed only in the section of the so-called unsteady portion where the steel plate tip is cut, and the other sections of the steady portion may be subjected to the same speed rolling. In this case, the switching from the variable speed rolling to the constant speed rolling may be performed after the rolling time is calculated from the length of the section subjected to the cutting and the rolling time is elapsed. Further, by utilizing the fact that the rolling load in the section subjected to the cutting process is reduced, the switching may be performed by determining the completion of the rolling in the section from the actually measured value of the rolling load. The variable speed rolling may be performed over the entire length of the steel sheet.

FIGS. 5A and 5B are schematic cross-sectional views showing examples of the shape of the tip of a steel sheet obtained by cutting the upper surface of the steel sheet. FIG. 5A is a straight taper type, FIG. C) shows a taper type with a parallel part. In the figure, Δh is the cutting amount at the forefront portion. θ is the taper angle, which is represented by the average value of the cut area.

In still another method of the present invention, as shown in FIG. 5, a cutting process is performed in a tapered shape in which the thickness decreases toward the foremost portion of the steel plate. And the limit bite angle β calculated from the following equation from the frictional coefficient μ between the work roll and the steel plate, and the bite angle α of the foremost part calculated by the following formula, satisfy the relationship θ <α <β, The hot rolling is started by setting the peripheral speed of the upper work roll higher than that of the lower work roll.

Α = cos ⁻¹ (1− (Δt−Δh) / D) β = tan ⁻¹ μ where Δt is the thickness reduction of the steady portion at the time of hot rolling (input side thickness−outside thickness). D: Work roll diameter.

If α is equal to or more than β, it is difficult to bite the leading end portion, and if θ is equal to or more than α, unstable rolling phenomena such as slip and undulation of the steel plate occur at the time of rolling at the tip end. In addition,
The friction coefficient μ between the work roll and the steel sheet can be obtained by back calculation from the actual measured values of the rolling load and the rolling torque. The peripheral speed of the upper and lower work rolls may be the same at the point in time when the stationary portion is reached after passing through the front end portion. As described above, the configuration of the present invention
It is possible to combine each other as far as possible.

[0036]

EXAMPLES (Example 1) Hot rolling was performed using the equipment having the basic specifications shown in Table 1 with the basic configuration shown in FIG.

[0037]

[Table 1]

The steel plate has a thickness of 50 mm, a width of 1000 mm,
Low carbon steel at a temperature of 1050 ° C. was used. The rotary cutting device has a drum diameter of 300 mm and a drum body length of 1200 mm. Cutting chips are provided in a zigzag pattern on the outer periphery of the drum, and the drum is driven by an electric motor with a power of 300 KW in the direction opposite to the direction in which the steel sheet travels. While rotating, the drum was moved up and down to cut the upper surface of the steel plate.

The diameter of the upper and lower work rolls of the rolling mill is 800
mm, the upper and lower work rolls were driven by different electric motors so that the peripheral speeds of the upper and lower work rolls were different.

As a lubricant, an oil based on a synthetic ester was used, mixed with water, and applied as an emulsion to upper and lower work rolls. The coefficient of friction μ between the steel sheet and the work roll was 0.2 when calculated backward from the measured load and the measured torque during hot lubrication rolling.

In the hot rolling, a steel sheet is fed to a rotary cutting device by a pinch roll, and as shown in FIG. 5 (A), the upper surface of the tip of the steel sheet is tapered at θ: 10 ° and the cutting amount at the tip is Δh:
Linear taper shape under the condition of 20 mm (taper length: about 110
mm), and rolling was started with a different peripheral speed of 0% (same speed rolling) and 3% (various speed rolling) and a reduction of 70% (outside sheet thickness 15 mm) while applying a lubricant. .
The variable speed rolling was performed only in a section having a taper length of 110 mm, and after the rolling in the section, switching to the same speed rolling was performed. During the rotation cutting, the moving speed of the steel plate was 200 mm / S, the drum rotation speed was 150 rpm, and the peripheral speed of the work roll was 200 mpm on average.

Table 2 shows the experimental conditions together with Comparative Examples 1 to 3. As shown in Table 2, Example 1 of the present invention is rolling at the same speed, and Example 2 of the present invention is rolling at a different speed. Comparative Examples 1 and 2 are all shown in Table 1.
Table 1 shows the conditions except that the rolling equipment shown in Table 1 was used, and Comparative Example 1 was the same as the non-lubricated constant-speed rolling without the thickness reduction processing. The conditions are the same as those of Example 2 of Invention Example 2.

[0043]

[Table 2]

Table 3 shows the biting state during rolling, the nose bending state, the rolling load during steady rolling, and the surface properties of the steel sheet after rolling.

[0045]

[Table 3]

As shown in Table 3, the steel sheet of Comparative Example 1 had surface defects and was of poor quality. Rolling load is about 3600
It is presumed that the surface pressure between the work roll and the steel plate was increased at the time of ton, and seizure of the work roll occurred. Comparative Example 2 had good biting properties, and the rolling load was almost halved compared to Comparative Example 1 and was about 20 times.
As a result, the quality of the steel sheet was good without any surface flaws. In addition, in Example 1 of the present invention, a nose descent phenomenon was observed at the time of rolling of the tip portion, but it was corrected by the delivery side guide of the rolling mill, and there was no trouble in rolling. In Example 2 of the present invention, the above-mentioned nose descent was not generated, and the rolling was extremely good.

(Example 2) Sheet thickness 90 mm, sheet width 1000
mm, low-carbon steel sheet with a temperature of 1050 ° C., the upper surface of the steel plate tip is tapered at θ: 10 °, and the cutting amount at the tip is Δh: 4
Linear taper shape under 5 mm condition (taper length: about 260 m
m), a lubricant is applied by a rolling mill having a work roll diameter of 1000 mm (the specifications other than the work roll diameter are the same as in Table 1), and a different peripheral speed rate of 2%
The hot rolling was performed at a rolling reduction of 70% (outside plate thickness 27 mm) in the steady portion. The variable speed rolling at a different peripheral speed ratio of 2% was performed only in a section having a taper length of 260 mm, and after the rolling in the section, switching to the same speed rolling was performed. The coefficient of friction μ is 0.2
Met.

Table 4 shows experimental conditions together with comparative examples. In addition, as shown in Table 4, the comparative example was used under conditions of lubricant application without cutting.

[0049]

[Table 4]

Table 5 shows the state of biting during rolling, the bending of the nose, and the surface properties of the steel sheet after rolling.

[0051]

[Table 5]

As shown in Table 5, in the examples of the present invention, the biteability is good, the occurrence of falling down the nose is small, and there is no practical problem. confirmed. In the comparative example, rolling was not possible because biting was impossible.

[0053]

According to the present invention, the hot lubricating rolling can be applied to a wide area with a large thickness because the inferior biting property of the tip of the steel sheet into the work roll during hot lubricating rolling is eliminated. Rolling under high pressure becomes possible. Therefore, high-pressure rolling can be performed with simple equipment modification, and economic effects such as reduction in manufacturing cost and equipment cost due to reduction in the number of stands can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of a hot rolling facility for implementing a method of the present invention.

FIG. 2 is a schematic side view showing an example of a rotary cutting device.

FIG. 3 is a schematic diagram showing a cutting state of an upper surface of a steel plate by a rotary cutting device.

FIG. 4 is a schematic diagram schematically showing a nose bending phenomenon.

FIG. 5 is a schematic cross-sectional view showing an example of the shape of a steel plate tip portion obtained by cutting the upper surface of the steel plate, and FIG.
FIG. 1B shows a polygonal line type, and FIG. 1C shows a taper type with a parallel portion.

[Explanation of symbols]

11: rolling mill, 12: pinch roll, 13: rotary cutting device, 14: steel plate, 15: tip, 16: work roll, 17: backup roll, 18: lubricant supply nozzle, 19: delivery guide 21: Drum, 22: cutting tip.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23C 3/12 B23C 3/12 Z

Claims (4)

[Claims] 1. A method for hot-rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that a friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less. A hot rolling method for a steel sheet, comprising: reducing a thickness of a tip portion in a rolling direction of the steel sheet, and then starting hot rolling. 2. A method for hot-rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that the friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less. Cutting the upper surface of the tip portion in the rolling direction of the steel sheet, and then starting hot rolling by setting the peripheral speed of the upper work roll higher than that of the lower work roll and starting hot rolling. Rolling method. 3. A method for hot rolling a steel sheet by applying a lubricant to the upper and lower work rolls so that a friction coefficient μ between the upper and lower work rolls of the rolling mill and the steel sheet is 0.2 or less. The cutting process of the upper surface of the tip portion in the rolling direction of the steel plate is performed in a tapered shape in which the thickness is reduced toward the forefront portion, the taper angle is θ, and the cutting amount of the foremost portion is Δh. At this time, the bite angle α of the foremost part calculated from Δh by the following equation and the limit bite angle β calculated by the following equation from the friction coefficient μ satisfy the relationship of θ <α <β, and then the upper workpiece A hot rolling method for a steel sheet, wherein a hot rolling is started by setting a peripheral speed of a roll higher than that of a lower work roll. α = cos ⁻¹ (1− (Δt−Δh) / D) β = tan ⁻¹ μ where Δt: amount of reduction in the thickness of the stationary part during hot rolling D: work roll diameter 4. A cutting device used for cutting a front end portion in a rolling direction of a steel sheet for improving biting property during hot rolling, wherein a drum capable of driving rotation and an outer peripheral surface of the drum are provided. A rotary cutting device, comprising: a plurality of cutting tips provided in the rotary cutting device.