JPS6254374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling steel strip in a continuous annealing furnace.

There are various ways to cool the steel strip in a continuous annealing furnace, such as by gas jet or water cooling, but in the case of cold-rolled steel sheets for deep drawing, etc., roll cooling is used to rapidly cool the steel strip by bringing it into contact with a cooling roll. Laws are proposed and implemented.

This cooling roll has a built-in water cooling jacket capable of circulating a cooling medium therein, and is configured to cool the roll body with the cooling medium. Conventionally, water has been used as this cooling medium, and this water absorbs heat from the steel strip and rolls, causing
It circulates around ℃. The surface of the cooling roll is also maintained at approximately the same temperature as the circulating water.

However, in this cooling method using cooling rolls, the steel strip temperature is around 850°C to 700°C, so if such a high-temperature steel strip is brought into contact with the rolls and rapidly cooled, the steel strip may shrink, causing the steel strip to deteriorate. The disadvantage is that the shape of the In order to prevent this, conventionally a method has been used in which a gas jet cooling zone is provided in front of the cooling roll strip to cool the steel strip in advance to about 600° C. and then cool it.

However, the cooling rate of such gas jet cooling is slow at 5°C/sec to 40°C/sec, which has the disadvantage that the quenching effect is insufficient, and the equipment for the gas jet cooling zone becomes larger and the power consumption rate decreases. There were drawbacks such as the need to operate a large capacity fan for high gas jets.

The present invention was made in order to improve the drawbacks of the conventional cooling method described above, and it involves circulating a high boiling point cooling medium with a boiling point of 200°C or more as a cooling medium in the cooling roll inside and outside the roll, and cooling medium outside the roll. The cooling rate of the steel strip is controlled by adjusting the temperature to a required temperature, thereby making it possible to obtain a high cooling rate while preventing deterioration of the shape of the steel strip.

The drawings are explanatory diagrams of the method of the present invention, and 1 is a heating zone, 2 is a soaking zone, 3 is a cooling zone, and 4 is an overaging zone.

A plurality of cooling rolls 10 are provided in the cooling zone 3, and a cooling medium having a high boiling point is heated and circulated there. This high boiling point cooling medium is circulated inside and outside the cooling roll, and is adjusted to a desired temperature outside the roll, thereby controlling the cooling rate of the steel strip. 11 is a pump for circulation, 12 is a cooling medium heating tank, 13 is a heater, and 14 is a cooling pipe for cooling.

As the cooling medium, one having a boiling point of 200°C or higher is used. Specifically, polyvinyl pyrrolide, polyalkylene glycol, polysoap, or a salt bath such as sodium nitrate or potassium nitrate can be used.

If this cooling medium is maintained at a predetermined temperature by the heater 13 and cooling pipe 14 and circulated inside and outside the cooling roll 10 by the pump 11, the surface of the cooling roll 10 can be maintained at a predetermined temperature. In particular, it is possible to maintain the surface of the cooling roll 10 at a high temperature of 100°C or more, which could not be achieved with conventional cooling water, so the cooling rate can be reduced to 20°C/sec without using a gas jet zone.
The steel strip can be precooled at a high cooling rate of ~150°C/sec.

In the example shown in this figure, a plurality of cooling rolls 20 using conventional water as a cooling medium are installed downstream of the cooling roll 10, and the configuration is such that the cooling roll 10 performs preliminary cooling and the cooling roll 20 performs final cooling. are doing.

It is also possible to use high-boiling point cooling rolls for all the cooling rolls 10, or it is also possible to change the temperature of the cooling medium or the cooling medium itself for each cooling roll or for each cooling roll group. be.

In addition, when preliminary cooling is performed, it is desirable that the surface temperature of the cooling roll 10 is about 300 to 500°C.

As explained above, according to the method of the present invention, since the surface temperature of the cooling roll can be controlled to an arbitrary temperature, it becomes possible to freely control the cooling rate of the steel strip. Therefore, there is no need for gas jet strip equipment, and it is possible to prevent the occurrence of defects in the shape of the steel strip. In addition, the surface temperature of the cooling roll can be rapidly controlled over a wide range in response to various heat cycles and changes in heat capacity during continuous annealing. Furthermore, since preliminary cooling can be performed at a high cooling rate, the quenching effect is not reduced.

[Brief explanation of the drawing]

The drawings are explanatory diagrams of the method of the present invention. In the figure, 10 is a cooling roll, 11 is a pump, 12
13 represents a cooling medium heating tank, 13 represents a heater, 14 represents a cooling pipe, and 20 represents a cooling roll.

Claims (1)

[Claims] 1 In a steel strip cooling method in a continuous annealing furnace in which the steel strip is heated and soaked and then cooled by contacting it with a cooling roll, a boiling point of 200% is used as the cooling medium for the cooling roll.
Steel strip cooling in a continuous annealing furnace, characterized in that the cooling rate of the steel strip is controlled by circulating a high boiling point cooling medium of ℃ or higher inside and outside the rolls, and adjusting the cooling medium to a required temperature outside the rolls. Method.