JPH0446608A - Multistage hot rolling mill - Google Patents

Abstract

PURPOSE:To prolong the life of roll without deteriorating the shape of strip and accuracy of thickness by taking the barrel length and diameter of work roll in a type of four and more stages as a specified range. CONSTITUTION:In a hot tandem mill for wide strip, the barrel length of the work rolls 1, 2 is in a range of 1.2-2.8m and the diameter of the upper and lower work rolls 1, 2 is in a range of 300-500mm in a type of four and more stages. Thus, the temp. rising of the rolls 1, 2 is restrained, roll wear and surface roughening are prevented and the surface properties, shape and accuracy of thickness of the strip 4 after rolling can be made better.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a hot tandem finishing mill for wide strip.

<Prior Art> In general, finishing stands for wide hot strip rolling use work rolls with a diameter of about 600 to 800 mm. On the other hand, the work roll diameter should be set to 500 to 6
A technique is known in which the rolling pressure is reduced to about 00 ff1m, thereby reducing the electric power consumption and reducing the plate crown (see Fig. 3). In addition, as a work roll with an even smaller diameter,
As disclosed in Japanese Patent No. 7421, a method is known in which the diameter of one of the upper and lower work rolls is made extremely smaller than the other, thereby reducing the equivalent roll diameter and reducing the rolling load.

<Problems to be Solved by the Invention> According to rolling theory, the rolling pressure becomes lower as the work roll diameter becomes smaller. Furthermore, if the work roll diameter is small, the contact arc length between the roll and the strip is also short. Therefore, by reducing the diameter of the work roll, the rolling load can be reduced due to these two effects.

In conventional hot tandem rolling mills, large diameter rolls of 600 to 800 mm are used, and the rolling pressure is higher and the contact arc length is longer than when using small diameter rolls. Due to the high rolling pressure, a large amount of frictional heat is generated in the cutting tool due to slippage between the roll and the strip.

The work roll is in direct contact with the strip, which is at a high temperature of 800°C or more, and is rapidly heated by this frictional heat (see point A in Figure 4). The roll will be long. As a result, the roll surface becomes hot and its hardness decreases, resulting in wear and roughness, resulting in frequent surface defects on the product. In particular, a large amount of frictional heat generation occurs in the latter stage of a tandem finishing mill where high-speed rolling is performed, causing the rolls to become hot.

Furthermore, in the method disclosed in Japanese Patent Publication No. 51-47421, one of the work rolls has a large diameter and the equivalent roll diameter cannot be made sufficiently small, so the effect of reducing rolling pressure is small, and the contact arc length is not very short. Therefore, the rolls still become hot, causing wear and roughness, and the problem of surface defects on products remains unsolved.
Furthermore, since the diameters of the upper and lower work rolls are extremely different, and rolling is performed asymmetrically in the upper and lower directions, there is a problem in that a difference in texture occurs between the front and back surfaces of the strip.

In recent years, with the increase in demand for thin hot-rolled products, there has been a trend towards high reduction rolling using hot rolling mills with small diameter rolls. However, when the work roll diameter is reduced in a hot rolling mill for wide strips, the rolls tend to bend, resulting in an increase in the plate crown, resulting in a problem in that the accuracy of the strip shape and plate thickness deteriorates. Furthermore, it was thought that small diameter rolls have a small heat capacity, and that heat builds up inside the roll during rolling, resulting in a high temperature of the roll, which would easily cause wear and roughness on the roll surface. moreover,
It was believed that the number of roll transfers would increase, making it more likely that cranks would occur due to thermal fatigue.

The present invention provides the above-mentioned method for hot tandem finish rolling of wide strip. ! ! The purpose of this invention is to provide a technology that solves this problem and extends the life of the roll without reducing the accuracy of the strip shape or thickness.

<Means for Solving the Problems> The present invention provides a hot tandem rolling mill for wide strip, in which the body length of the work roll is 1 or 2 in a type of 4 or more stages.
This multi-stage hot rolling mill is characterized in that the diameter of the upper and lower work rolls is in the range of 300-500 mm.

<Function> The present inventors described above! ! ! ! In order to solve this problem, we conducted a study on how the roll surface temperature changes depending on the roll diameter under the same rolling reduction and cooling conditions in a wide strip hot tandem finishing mill.

As a result of experiments, it was found that when the surface temperature of the ordinary roll material used in hot tandem finishing rolling mills exceeds 600°C, the hardness decreases and wear and roughness occur frequently, and surface defects of the strip occur. I understand. In order to prevent wear and roughness on the roll surface, it is desirable to keep the roll surface temperature below about 500°C. This figure shows how the roll surface temperature changes depending on the roll diameter when the work roll is heated. From this figure, the work roll diameter at which the roll surface temperature changes by about 500°C or less is 300 to 300°C.
It is 500m.

This result is different from the conventional idea that a small diameter roll has a higher temperature, and the inventors came up with the present invention based on this fact and the results of experiments.

In addition, in the present invention, as a means for preventing an increase in roll temperature,
The work roll is cooled by a known method such as spray cooling, and the strip can be made into a 4-, 5-, 6-, or 12-stage model by applying a known method such as straightening roll deflection using a work roll bender. This prevents deterioration in the accuracy of the shape and thickness of the plate.

According to the present invention, both the upper and lower work roll diameters are 50 mm.
Since the diameter is reduced to 0Wn or less (see Fig. 2), the rolling pressure can be lower than when rolling with large diameter rolls. As a result, generation of friction heat in the cutting tool can be suppressed, and by shortening the contact arc length, the heating time of the roll can also be shortened.

On the other hand, by setting the work roll diameter to 300 m or more, a spray that cools the roll over a wide range can be installed on the exit side in the rolling direction. This makes it possible to suppress the rise in temperature of the rolls and to reduce wear and roughness of the rolls.

As a result, the unit consumption of work rolls can be increased and surface defects of products can be reduced. In addition, it is possible to suppress the temperature rise on the roll surface, so even if the number of transfers increases,
There is less thermal fatigue, and therefore the occurrence of cracks can be reduced.

Both work roll diameters are small, and the upper and lower diameters are almost equal, making it possible to roll vertically symmetrically.
This also prevents differences in texture between the front and back surfaces of the strip.

Since the present invention performs hot tandem finish rolling of a wide strip with a work roll body length of 1.2 to 2.8 m, productivity is extremely superior compared to a rolling mill with a shorter work roll body length. operation is possible.

Since the present invention is a multi-stage rolling mill with four or more stages, it is possible to apply known methods such as correcting roll deflection using a work roll bender, thereby preventing deterioration in accuracy of strip shape and thickness. fully preventable.

<Example> (Example 1) As one example of the present invention, a case where the work roll of the seventh stand in a seven-stand tandem finishing rolling mill was rolled with a reduced diameter, and a case where the work roll was rolled using a conventional technique. The results are compared and shown in Table 1.Table 1 shows that the entry side plate thickness of the 7th stand is 2.
49m, out! 2 is a table showing the work roll surface temperature, roll surface properties, strip shape, and surface properties when rolling is performed with a 1vi thickness of 1.26-. Note that the work roll body lengths at this time were all 2.0 m.

When both the upper and lower work rolls were rolled with 700 φ work rolls, the rolls were heated to 600° C., so the hardness of the roll surface decreased, causing wear and roughness on the roll surface. This resulted in many defects on the surface of the strip.

When both the upper and lower work rolls were rolled with 150-φ work rolls, the spray for cooling the work rolls could not be installed on the exit side in the rolling direction, so the rolls could not be cooled sufficiently, and the surface temperature reached 900 mm. It was heated to ℃. Therefore, wear on the roll surface, roughness, and surface defects of the strip occurred more frequently than when rolling with large diameter rolls.

Upper work roll 400-1, lower work roll 700
When rolled in layers, the roll surface temperature could be lowered by 50°C compared to rolling with large-diameter rolls, but roll surface wear, roughness, and surface defects on the strip did not disappear. Ta. Furthermore, because the rolling reduction amounts of the upper and lower rolls were different, a difference in structure occurred between the front and back surfaces of the strip.

On the other hand, in one embodiment of the present invention, when both the upper and lower work rolls are rolled using 500 mm diameter work rolls, the surface temperature of the rolls is 80°C lower than when rolling is performed using large diameter rolls. No wear, roughness, or surface defects on the strip were observed on the roll surface. In addition, no difference in structure was observed between the front and back surfaces of the strip, and sufficient shape controllability and thickness accuracy were ensured using the known technology of work roll bender. Both upper and lower work rolls are 3001
When rolling is carried out using a 111φ work roll, the roll surface temperature is heated only to 450°C, and the roll surface temperature is only 450°C.
Similar results were obtained with the φ work roll.

In addition, although the case where the diameter of the work roll of the seventh stand is reduced is explained in the above embodiment, the present invention is not limited to this, and the work roll of other stands may be reduced in diameter, or the work roll of a plurality of stands may be reduced in diameter. The work roll may be made smaller in diameter.

Table 1 (Example 2) As an example of the present invention, the results of rolling with different work roll body lengths on the 7th stand of a 4-stage type of a 7-stand tandem finishing mill are compared and shown in Table 2. Table 2 shows that the board thickness on the entry side of the 4-tier model No. 7 stand is 1.49 m, the board thickness on the exit side is 1.26 m, and the diameters of both the upper and lower work rolls are 5 m.
3 is a table showing the shape and thickness accuracy of the strip and the production efficiency of the rolling mill when rolling is carried out at 00 m.

When the work roll body length was set to 1.0 m, the roll deflection was small and the shape and thickness accuracy were good, but production could only handle narrow width materials and the daily production amount was 4000.
It was a ton. On the other hand, the work roll body length is set to 3.
When it is set to 0m, the deflection of the roll becomes large, so
The shape has deteriorated significantly. This resulted in problems with threadability such as throttling, and both rolling efficiency and yield deteriorated.

On the other hand, when the work roll body length is 2.0 m, sufficient shape properties and thickness accuracy can be ensured by using known techniques such as a work roll bender, and high quality strips can be produced. was completed. Additionally, both narrow and wide materials can be rolled, making it possible to produce products that meet a wide range of demands. As a result, the production amount per day is 1
2,000 tons, making it possible to lower costs and operate with high efficiency.

In the above embodiment, the seventh stand is of a four-stage type, but the present invention is not limited to this, and the work rolls can be reduced in diameter in multi-stage rolling mills of five, six, and 12 stages. Good too.

The present invention is a hot tandem finishing mill for wide strips with a work roll body length of about 1.2 to 2.8 m, and the diameters of the upper and lower work rolls are made to be the same within the range of 300 to 500 m. It was possible to reduce the rolling pressure compared to rolling with diameter rolls. As a result, we were able to suppress the occurrence of friction within the cutting tool, and by shortening the contact arc length, we were able to shorten the heating time of the roll.

At the same time, we were able to install a sprayer that cools the rolls over a wide area on the exit side in the rolling direction. This makes it possible to suppress the rise in temperature of the rolls, thereby reducing wear and roughness of the rolls. As a result, we were able to increase the unit consumption of work rolls and reduce surface defects on products.

Since the temperature rise on the roll surface can be suppressed, even if the number of transfers increases, there is little thermal fatigue and, therefore, the occurrence of cranks can be reduced.

Since the diameters of the work rolls were both small to the same extent, it was possible to roll the strip almost symmetrically from top to bottom, thereby preventing differences in structure between the front and back surfaces of the strip.

The present invention is a multi-stage rolling mill with 4, 5, 6, or 12 stages, and can apply known methods such as correcting roll deflection using a work roll bender, thereby achieving precision in strip shape and thickness. The decline could be sufficiently prevented.

<Effects of the Invention> According to the present invention, as described above, it is possible to suppress the rise in temperature of the rolls, prevent roll wear and roughness, and improve the surface properties, shape, and thickness accuracy of the strip after rolling. .

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing the relationship between work roll diameter and work roll surface temperature, Fig. 2 is an explanatory drawing showing an example in which the present invention is applied to stands 5 to 7, and Fig. 3 is an example. FIG. 4 is an explanatory diagram showing the entire conventional seven-stand tandem type four-high finishing mill. FIG. 4 is an explanatory diagram showing the work rolls and strip during rolling. 1...Small diameter work roll, 2...Large diameter work roll, 3...Back unroll, 4...Strip.

Claims (1)

[Claims] In hot tandem rolling mills for wide strips, the work roll body length is from 1.2 m to 2.8 m in models with 4 or more stages.
A multi-stage hot rolling mill characterized in that the diameter of the upper and lower work rolls is within the range of 300 mm to 500 mm.