JP2568693B2 - Rolling roll cooling method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cooling a rolling roll, and more particularly, to a method for cooling a rolling roll having extremely high roll cooling efficiency and capable of preventing a change in a thermal crown amount.

(Prior Art) A rolling roll used for hot rolling of a steel sheet receives a large amount of heat from a material to be rolled (hereinafter, referred to as a rolled material) and its temperature rises significantly. However, since the width of the rolled material is smaller than the width of the roll, the temperature distribution in the width direction of the roll becomes lower toward the center and lower toward the ends. And it is the temperature of the rolled material,
It is greatly affected by rolling reduction, rolling speed, rolling time, and the like. The average roll temperature also depends on the rolling conditions. If the temperature distribution in the width direction of the roll or the average temperature changes, the amount of thermal expansion changes and the amount of thermal crown changes,
High-precision thickness control becomes difficult.

Therefore, various roll cooling methods and apparatuses have been proposed as follows, in which the roll is cooled by cooling water to prevent fluctuations in the thermal crown amount.

a. A method of spraying a large amount of cooling water with high pressure from a nozzle onto the roll surface.

According to this method, the rolling roll can be cooled with high efficiency. However, in this method, since the cooling water scatters after hitting the roll, only a small area can be cooled. Moreover, only the part where the cooling water is sprayed is supercooled, and is not uniformly cooled. In addition, there is a problem that the scattered cooling water falls on the rolled material and locally lowers the temperature, thereby deteriorating the temperature control.

b. As shown in FIG. 5 (a), a water-cooling jacket 2 is arranged on the outer peripheral surface of the rolling roll 1 so as to form a cooling water passage 3 to allow the cooling water 4 to pass therethrough, thereby increasing the cooling area and uniform cooling. A device for performing the operation (Japanese Patent Publication No. 55-12322).

With this cooling device, the problem caused by the cooling water spraying method of the above a was solved. However, in this apparatus, as shown in FIG. 5 (b) (enlarged view of part A in FIG. 5 (a)), a boundary layer 5 which prevents direct contact between the cooling water 4 and the roll 1 is formed on the surface of the rolling roll 1. There is a drawback that the cooling efficiency is not improved. In FIG. 5 (a), 6 is a cooling water supply channel,
7 is a cooling water drainage channel, 8 is a backup roll, and 9 is a rolled material.

c. In order to eliminate the temperature difference in the width direction of the rolling roll, a water cooling jacket as shown in FIG. 5 (a) is divided in the width direction of the roll and water is supplied separately (Japanese Patent Application Laid-Open No. 60-231507). .

According to this method, cooling in the roll width direction can be performed. However, this method has a problem that a non-uniform cooling portion is formed at a position corresponding to the partition wall portion of the water cooling jacket, and a temperature in the width direction of the roll does not change so much even if the amount of cooling water is slightly changed because a boundary layer is generated. is there.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for cooling a rolling roll in which the cooling efficiency of the rolling roll is extremely high and the thermal crown amount is not changed.

(Means for Solving the Problems) The rolling roll during hot rolling receives a large amount of heat from the material to be rolled and changes the thermal crown amount, making it difficult to perform high-precision rolling control. To prevent this, sufficient roll cooling and an appropriate cooling method in the roll width direction are required.

The present inventors have conducted various studies on efficient cooling and a cooling method in the roll width direction, and have obtained the following findings. That is, when the roll surface temperature during rolling reaches 100 ° C. or higher, the cooling water boils, and a vapor film (boundary layer) with extremely poor heat transfer is generated. In order to eliminate this boundary layer, if pressure water is jetted toward the flow of the cooling water, turbulence occurs in the water flow, the boundary layer is easily lost, and the cooling efficiency is significantly improved.

By changing the injection amount of the pressurized water, the turbulence intensity in the water film changes, and the thickness of the boundary layer can be freely changed. Therefore, if the injection amount is adjusted according to the amount of heat received in the width direction of the roll, the temperature in the width direction of the roll can be controlled steplessly, and a change in the thermal crown amount can be prevented.

The present invention has been made based on the above findings, and the gist of the invention lies in the following roll cooling method.

A jacket having a cooling water supply path and a drainage path, and having a plurality of nozzles for injecting pressure water toward the roll surface is installed facing the roll surface, and rotated by the cooling water supplied from the supply path. Forming a layered water flow on the surface of the rolling roll, and injecting the pressurized water from the nozzle toward the water flow, and adjusting the injection amount of the pressurized water according to the amount of heat received in the roll width direction. Rolling roll cooling method.

(Operation) In the conventional jacket-type cooling device as shown in FIG. 5, a cooling water passage 3 is provided between the rolling roll 1 and the jacket 2.
The cooling water 4 is supplied to the passage 3 from the cooling water supply passage 6, passed through the passage 3 in a layered manner, and drained from the cooling water drain passage 7. However, in this laminar basin, a boundary film is formed on the surface of the rolling roll 1 as described above. Therefore, in the cooling method of the present invention, a cooling device as shown in FIG. 1 is used. This device is provided with a large number of injection nozzles 13 for injecting the pressure water 13a in a direction perpendicular to the laminar flow in order to destroy the boundary layer. FIG. 2 is a cross-sectional view of the apparatus in the roll axis direction.
The injection nozzle 13 is divided into a plurality of sets in the width direction, and a valve
It is opened and closed by 14. Injection nozzle 13
Are arranged in an array pitch of about 50 to 100 mm in the roll axis direction, and the injection amount of the pressure water 13a is adjusted according to the amount of heat received in the roll width direction.

When the surface temperature of the roll is higher than the boiling temperature of water, the cooling water evaporates, and a boundary layer having an extremely poor heat transfer coefficient (5 in FIG. 5 (b)) covers the surface, thereby significantly reducing heat transfer. Let it. Therefore, in the cooling method of the present invention, not only the laminar cooling water flow but also the pressure water 13 injected toward this water flow is used.
Using a (pressure of about 5 to 10 kg / cm ² ), turbulence is generated in the flow of cooling water, and the boundary layer is destroyed. Thereby, the cooling water is in direct contact with the roll surface, and cooling is efficiently performed. Further, by controlling the injection amount of the pressurized water, the turbulence strength of the cooling water and the thickness of the boundary layer can be changed, so that the change in the thermal crown amount of the roll can be prevented. Opening and closing control of valve 14 is a computing unit
Using 15, the heat load on the roll 1 is calculated in the axial direction based on the rolled material dimensions, rolling conditions (temperature, etc.) and rolling information such as the rolling speed and the rolling load, and the axial direction is calculated according to the heat load. An open / close command is given to each of the valves 14.

The pressure water injection nozzles 13 are arranged in a large number (arrangement pitch: about 50 to 100 mm) in the roll width direction, and adjust the amount of pressure water 13a jetted from each nozzle in accordance with the amount of heat received in the roll width direction. Thereby, the degree of cooling in the roll width direction can be changed, and the roll crown amount can be adjusted.

(Example 1) In this example, the relationship between the injection amount of pressurized water and the heat transfer coefficient of the roll surface was examined using a test roll. That is, a test roll heated to a certain temperature (diameter: 200 mm, width: 4
00 mm), a cooling device as shown in Fig. 1 was installed, and 0.3 m ³ / min of cooling water was allowed to flow down on the roll surface.
In this experiment, pressure water of / cm ² was injected while changing its amount, and the change in heat transfer coefficient at that time was examined.

FIG. 3 shows the results. As is clear from this figure, the heat transfer coefficient can be freely changed by changing the injection amount of the pressure water. The heat transfer coefficient was determined by calculating the roll surface temperature at the inlet and the outlet of the cooling device while keeping the temperature inside the roll constant from the heater.

(Example 2) This example is a case where the cooling method of the present invention is performed in actual operation. A roll cooling device as shown in Fig. 1 was installed on the finished work roll of a hot rolling mill with a diameter of 700 mm and a width of 1780 mm, and rolled at 920 ° C (thickness: 2.2 mm, width: 1200 mm)
Was rolled. And the temperature change in the roll width direction when the constant amount of pressure water is constantly injected and when it is intermittently injected,
The thickness variation of the steel sheet at that time was examined. Coolant level when pressurized water is constant 4m ³ / min to a pressure water of 8kg / cm ² 0.5m ³ /
min, cooling water volume is 4m ³ / min for intermittent injection of pressure water
0.5m ³ / min pressure water 400mm from the center of the roll width
And stop and spray for 2 seconds every 500mm
Injection of the part of 00mm or more was stopped.

As a result, as shown in FIG.
In the case of intermittent jetting (marked with ○), the temperature difference between the center and the end of the roll was not so large, but when jetting was continued for a fixed amount (marked with △), the temperature decreased greatly toward the end of the roll. And the thickness variation in the width direction of the product steel plate in the case of intermittent injection is 6 μm
Within. However, the fluctuation amount when a constant amount was injected was as large as 8 to 10 μm.

(Effect of the Invention) As described above, according to the cooling method of the present invention, the following excellent effects are obtained. That is, the roll can be cooled with high efficiency, and a change in the roll thermal crown amount can be prevented.

Even if the roll diameter changes, the cooling capacity can be easily adjusted and the accuracy is good.

Since only a small amount of pressurized water is required, fine adjustment can be made and control responsiveness is good.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the rolling direction showing an example of a roll cooling device for implementing the cooling method of the present invention, FIG. 2 is a cross-sectional view in the roll axis direction of FIG. 1, and FIG. FIG. 4 is a diagram showing the relationship between the amount and the heat transfer coefficient, FIG. 4 is a diagram showing the relationship between the distance from the center of the roll and the roll surface temperature, and FIG. 5 is the rolling direction of the cooling device used in the conventional roll cooling method. FIG. 1 is a rolling roll, 2 is a water cooling jacket, 3 is a cooling water passage, 4 is cooling water, 5 is a boundary layer, 6 is a cooling water supply passage, 7 is a cooling water drainage passage, 8 is a backup roll, 9 is a rolled material,
10 is a cooling water supply pipe, 13 is a pressure water injection nozzle, 14 is a valve, and 15 is a calculator.

Claims (1)

(57) [Claims] 1. A jacket having a cooling water supply passage and a drain passage, and having a plurality of nozzles for injecting pressure water toward the roll surface, is installed facing the roll surface, and a jacket from the supply passage is provided. A layered water flow is formed on the surface of the rotating rolling roll with the supplied cooling water, and while the pressure water is injected from the nozzle toward the water flow, the injection amount of the pressure water is adjusted according to the amount of heat received in the roll width direction. A method of cooling a rolling roll.