JPH05104114A - Method and device for cooling work roll in hot rolling - Google Patents

Abstract

PURPOSE:To reduce the amount of grinding for repairing the roll surface and to prolong the roll life by continuously cooling the roll surface in a specified range from a specified start position of cooling with a specified quantity density of water to the end position of cooling. CONSTITUTION:A work roll 2 during hot rolling a steel material 1 is cooled by injecting cooling water from spray nozzles 4a-4d. The start position of cooling is taken as within 30 deg. of rotation angle from the outlet of roll bite. The surface of the roll 2 in the range from this start position of cooling to 90 deg. of rotation angle from the outlet of roll bite is cooled with the quantity density of water of 1.8-4.0m<3>/min.m<2> and then the surface of roll in the range of 90-270 deg. of rotation angle from the outlet of roll bite is cooled with the quantity density of water of <=2.0m<3>/min.m<2> to cool almost continuously the surface of the roll 2 from the start position of cooling to the end position of cooling. In this way, the surface quality of rolled sheet can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for cooling a work roll for hot rolling of steel with cooling water.

[0002]

2. Description of the Related Art There are mist cooling method, spray cooling method, water jacket cooling method and the like as cooling methods for work rolls for hot rolling of steel materials, but the most commonly used method is roll identification. It is a spray cooling method in which water is sprayed on the spot. This cooling method will be described with reference to the schematic diagram of FIG. This figure is a cross-sectional view of the upper half of the situation in which a heated steel material is hot-rolled by a four-high rolling mill as viewed from the axial direction of the roll. 1 is a rolled steel material, 2 is a work roll, 3 is a work roll. Backup rolls, 4a, 4b and 4c are spray nozzles and 5 is a drainer. In the following description, the rotation angle θ from the biting point (roll bite outlet) located directly below the work roll as shown in the figure is used to represent the cooling position. In the example of this figure, two spray nozzles are arranged on the outlet side of the work roll and one spray nozzle is arranged on the inlet side.

On the other hand, Japanese Patent Publication No. 60-18490 discloses a cooling method in which a large number of small-diameter cooling nozzles are arranged in the circumferential direction of the roll to cool the roll efficiently. According to this publication, the jetting pressure of the cooling water is 10 to 25 kg / cm ² G, and the water density of the cooling water on the roll surface is 4 to 10 m ³ / min · m ² . An outline of the arrangement of the roll cooling headers in this cooling method is shown in FIG. As shown in the figure, a header 6 having a large number of cooling water jetting tips (nozzles) 4 mounted at equal intervals is arranged on the roll 2, and the combination of the cooling water jetting pressure and the water amount density is changed over a wide range to achieve the above-mentioned optimum. The range is specified. The cooling water ejected from the nozzle directly collides with the roll, and there is no mutual collision between the cooling waters.

[0004]

According to such a conventional method, efficient cooling is performed with a minimum required amount of water, which is advantageous from the viewpoint of energy saving and water saving, but the number of nozzles is extremely large. Therefore, there is a new problem that this leads to an increase in running cost for maintenance, and according to the experiments by the present inventors, the amount of cooling water is still excessive, and it is possible to further select by effectively selecting the cooling position. It is possible to save water.

Generally, work rolls in hot rolling are
The surface layer locally undergoes thermal expansion due to heating at the contact area between the rolled material and the roll (hereinafter referred to as the roll bite), but it cannot be deformed because it is constrained by the surroundings, causing plastic deformation that is compressed in the circumferential direction. receive. The surface layer that has undergone this plastic deformation undergoes thermal contraction after leaving the roll bite, resulting in a tensile thermal stress.

When the surface of the roll is locally spray-cooled in a fine area as in the cooling device shown in FIG. 3, the cooled roll surface layer is supercooled, and the surface layer is further heat-shrinked and pulled more than necessary. You will be stressed. The greater the spray cooling capacity, the greater the tensile stress. If this is too large, heat cracks will occur and the roll will become rough. Also, if multiple small-diameter nozzles are installed, the temperature will oscillate in the spray direct area and other areas, and the thermal stress will also vibrate accordingly.
By repeating this, heat cracks become larger and larger.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a method and apparatus for efficiently cooling a roll with a smaller amount of cooling water.

[0008]

The cooling method of the present invention is a method for cooling a work roll during hot rolling of a steel material by injecting cooling water with a spray nozzle to cool the work roll. The rotation angle is within 30 °, and the roll surface in the range from this cooling start position to the rotation angle from the roll bite outlet to 90 ° is 1.8 to 4.0 m ³ / m
A roll surface in the range of 90 ° to 270 ° in rotation angle from the roll bite outlet with a water density of in · m ²
It is characterized in that the cooling is performed almost continuously from the cooling start position to the cooling end position with a water amount density of 2.0 m ³ / min · m ² or less.

Further, the cooling device of the present invention has a roll circumference for directly injecting cooling water onto the roll surface within a range of 30 ° to 90 ° in rotation angle from the roll bite outlet of the work roll during hot rolling of the steel material. 1 to 2 spray nozzles in one direction, and 2 in the circumferential direction of the roll, which bisects the range of 90 ° to 270 ° in the rotation angle from the roll bite outlet and directly jets cooling water to the surface of each roll. It is composed of the above wide type spray nozzle.

[0010]

[Operation] According to the present invention, since the cooling start position is set within the rotation angle θ of 30 ° when viewed from the roll bite exit side, heat is removed from the work roll surface heated in the roll bite (heat removal). Can be done efficiently. The cooling start position is less than 30 °, and the earlier the more effective, the more effective it is. However, since there is a drainer provided so that the cooling water does not directly come into contact with the rolled material, the fact is that cooling can be performed only from around 30 °. When the cooling start position is set to 30 ° or more, the heat transmitted in the roll bite penetrates into the inside of the roll so much that the heat cannot be removed efficiently.

In the present invention, θ = 30 ° -9
In the range of 0 °, the density of cooling water is 1.8 to 4.0 m ³ /
Since it is set to min · m ² , it is necessary and sufficient to cool the roll. According to the experiments by the present inventors, the water density was 4.
Even if it is 0 m ³ / min · m ² or more, there is almost no difference in the roll cooling capacity. Rather, when the water pressure is increased to increase the water volume density, the water sprayed on the roll bounces off the roll surface, rather As a result, the cooling capacity is reduced.

On the other hand, the water amount density in this range is 1.8 m ³ /
If it is less than min · m ² , the cooling capacity will be insufficient, and as rolling continues, the roll temperature will rise and wear and plastic flow of the roll surface will become apparent. In order to cool in this range, it is possible to use a wide type nozzle with a large spread and cool with one spray nozzle, but by using two spray nozzles, the water density can be changed to produce a large amount of water at an early stage. It is more effective to carry out cooling.

Next, in the present invention, θ = 90 ° to 2
In the 70 ° range, the volumetric density of cooling water is 2.0 m ³ / mi
Although the heat recovery from the inside of the roll was efficiently cooled by setting n · m ² or less, the water density was 2.0 m ³ in this range.
Although the surface temperature of the roll can be further lowered by setting it to be more than min / m ² · m ² , the temperature difference between the inside of the roll and the thermal stress increases. On the other hand, if you do not perform roll cooling at all in this range, the overall cooling capacity will be insufficient,
Inevitably, the roll temperature rises. Therefore, in this range, it is desirable that the cooling water volume density be set to the minimum required.

In this range, as is clear from the figure, there is a contact point with the backup roll in the middle, so there should be two or more spray nozzles, and cooling should be done in two minutes before and after the contact point. Become. Since the spraying range is wide in this range, it is necessary to use a wide type nozzle having a wide diffusion angle when using two spray nozzles.

As described above, in the present invention, the cooling water is continuously sprayed from the cooling start position to the cooling end position except the contact point with the backup roll, and all sprays are direct sprays from the nozzle to the roll surface. However, since the nozzle is a diffusion type with a spray angle and the roll is continuously sprayed within the cooling range, there is no temperature oscillation unlike the intermittent spray as in the previous example, and the heat load can be reduced. ..

Since one or two cooling nozzles are provided for each of the two cooling ranges, various cooling patterns can be set by changing the cooling water condition for each nozzle.

[0017]

FIG. 1 shows an embodiment of the present invention. 2 and 3
Similarly to this, this figure is a cross-sectional view of the upper half when the heated steel material is hot-rolled by a four-high rolling mill as seen from the roll axial direction, 1 is a rolled material, 2 is a work roll, 3 is a backup roll. , 4a, 4b, 4c and 4d are spray nozzles, and 5a and 5b are drainers.

The rolling mill is the first stand of the tandem type finishing rolling mill, and the rolling and cooling conditions in the examples are shown in Table 1 together with examples according to the prior art as comparative examples. As shown in the figure, in this embodiment, two cooling nozzles are provided in each of the two cooling ranges in the circumferential direction of the roll, and a total of four nozzles are used for cooling. Roll diameter 800
mm high chrome cast iron, the material to be rolled is general steel, and in this first stand, the sheet bar with a thickness of 30 mm is reduced to about 16 to 20 mm. The total amount of cooling water is 3.8 m ³ / mi
n.

[0019]

[Table 1]

FIG. 4 is a graph showing the temperature change in the vicinity of the roll surface during one rotation of the roll in the present embodiment. The type of line represents the depth of the measuring point from the roll surface, which is 0.05 mm closest to the surface. The solid line indicates the surface temperature. FIG. 5 is a graph showing the temperature change near the surface of the roll when the conventional cooling method shown in FIG. 2 is used as a comparative example. Comparing FIG. 4 and FIG. 5, the maximum temperature of the roll is about 700 ° C. The cooling capacity of the present invention is not inferior to that of the conventional method. On the other hand, the roll surface temperature in the spray cooling region is large up and down in the conventional method, but in the present invention, the temperature change is very small because the spray is continuous.

Observation of the roll surface after the completion of rolling revealed that the number of heat cracks generated on the roll surface was large and the depth was large in the conventional method, but the present invention showed that the heat cracks were small and the number was small. The surface condition was also beautiful with little rough skin. As a result, the amount of roll grinding that removes the heat cracks after removing the roll was about 0.25 mm, compared to 0.3 mm per diameter in the past with 50 rolling coils, improving the roll unit consumption. did.

[0022]

According to the present invention, the generation of heat cracks is suppressed, and the roughening of the roll is reduced. As a result, the amount of maintenance grinding on the roll surface is reduced and the roll life is extended.
This has the effect of improving the surface quality of the rolled plate.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a cooling system of the present invention.

FIG. 2 is a conceptual diagram of a cooling method according to a conventional technique.

FIG. 3 is a conceptual diagram of a cooling method according to another conventional technique.

FIG. 4 is a graph showing roll surface temperature according to the cooling method of the present invention.

FIG. 5 is a graph showing a roll surface temperature according to a conventional cooling method.

[Explanation of symbols]

 1 Rolled material 2 Work roll 3 Backup roll 4, 4a, 4b, 4c, 4d Spray nozzle 5a, 5b Drainer 6 Header

Claims (2)

[Claims] 1. A cooling method for cooling a work roll during hot rolling of a steel material by spraying cooling water with a spray nozzle, wherein a cooling start position is within a rotation angle of 30 ° from an exit of a roll bite. The roll surface in the range from the cooling start position to the rotation angle of 90 ° from the roll bite outlet has a water amount density of 1.8 to 4.0 m ³ / min · m ² , and the rotation angle from the roll bite outlet is 90 ° to 270 °. range roll surface 2.0 m ³ / min · m ² or less of water density of,
A method for cooling a work roll in hot rolling, comprising cooling from a cooling start position to a cooling end position almost continuously. 2. One or two rolls in the circumferential direction of the roll for directly injecting cooling water onto the roll surface in the range of 30 ° to 90 ° in rotation angle from the roll bite outlet of the work roll during hot rolling of steel material. Spray nozzles, and two or more wide-type spray nozzles in the circumferential direction of the roll that directly spray cooling water to the surface of each roll by dividing the range of 90 ° to 270 ° in rotation angle from the roll bite outlet. A work roll cooling device in hot rolling.