JPS6267125A - Method for cooling steel strip in continuous annealing furnace - Google Patents

Abstract

PURPOSE:To make the temp. distribution of a steel strip uniform in the lateral direction when the steel strip is cooled by passing through a cooling zone in contact with plural cooling rolls arranged in the zone, by dividing the rolls into two groups in the forward direction of the steel strip and cooling the strip with jets of gas between the groups. CONSTITUTION:A steel strip is cooled by passing through the cooling zone of a continuous annealing furnace in contact with four cooling rolls 7a, 7b, 7c, 7d arranged in the cooling zone. At this time, the rolls are divided into a group of rolls 7a, 7b and a group of rolls 7c, 7d in the forward direction of the steel strip and the strip is cooled with jets of gas from intermediate gas jet coolers 12 between the groups.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a steel strip cooling method in a continuous annealing furnace, which prevents the occurrence of cooling buckles by achieving uniform cooling in the width direction of the steel strip. We propose a method for obtaining steel plates with excellent shape and quality.

(Prior art) The conventional technology for cooling steel strip in a continuous annealing furnace is as follows:
There are two methods, one is to inject gas or other refrigerant, and the other is to bring it into contact with a cooling roll.Recently, the latter method has been widely adopted.

However, since the latter method involves contact between solids, it is difficult to bring them into uniform contact when there is a temperature difference between the two. As a result, temperature non-uniformity is likely to occur. This temperature non-uniformity causes a deviation in cooling rate and also causes non-uniform thermal stress such as thermal contraction. Therefore, a difference in deformation occurs in the steel strip, which disturbs the shape of the steel strip. In extreme cases, it may cause buckling (cooling buckles) or even line stoppage due to plate breakage. Furthermore, it causes non-uniformity in the mechanical properties of the steel sheet, making it impossible to manufacture steel sheets of the targeted quality. In addition, poor shape of the steel strip tends to cause meandering, leading to a decrease in the threading speed and resulting in a decrease in productivity.

In order to overcome the above-mentioned problems with cooling using a cooling roll, a proposal was made in JP-A-59-20428 to control the temperature distribution in the width direction of the steel strip by gas jet cooling before rapid cooling using a cooling roll. There is a technology that has been developed.

(Problems to be Solved by the Invention) However, in the case of the prior art disclosed in JP-A-59-20428, the method is to uniformize the temperature in the width direction of the steel strip before entering the roll cooling group, and the following Problems such as these remained.

That is, FIG. 6 shows the contact between the cooling rolls 7a to 7d and the threaded strip (steel strip S) in the roll cooling group 7 section. , strongly influenced by thermal crowns. Therefore, a large temperature difference (△Ts >) occurs in the steel strip S between the etching and etching parts, and shape disturbances of the steel strip occur in both the etching parts.
-N0140-Rule 7a to 7d, the shape disturbance gradually spreads from the 171st part to the center, and as a way of consolidating it, the width of the contact part is made smaller as shown in the figure. The temperature difference ΔTs('C) at this time is as high as about 50° C. as shown in FIG. 7, leading to the occurrence of the above-mentioned cooling buckle.

(Means to Solve the Problem) Regarding the above-mentioned problems that inevitably occur when cooling the steel strip using a cooling roll, considering that these problems are caused by incomplete contact between the steel strip and the cooling roll, we The key point was to provide gas jet cooling, which does not have to worry about complete contact, in the roll cooling zone, particularly in the middle of the cooling roll group.

That is, as a means for solving the above problems, the present invention provides a method for cooling a steel strip by passing the steel strip in contact between a plurality of cooling rolls arranged in a cooling zone of a continuous annealing furnace. 2. Correcting temperature deviation in the width direction of the steel strip during roll cooling by separately arranging a cooling roll group into a front stage and a rear stage and applying gas jet cooling to the steel strip in the separated section; The cooling roll group is arranged separately in the front stage and the rear stage, and the steel strip in the separated section is subjected to gas jet cooling by a device that can adjust the flow in the width direction. We decided to adopt a steel strip cooling method in a continuous annealing furnace that is characterized by the following: uniform temperature distribution control.

Above 1st. The gas jet cooling device used for carrying out the second method is preferably a so-called type that can qualitatively correct the temperature difference ΔTs caused by passing through the front roll. Steel strip
Plate) Some have a structure with slits extending in the width direction.

Further, as a device used in the second method, a gas jet cooling device of a type in which the flow rate can be variably controlled in the so-called plate width direction, as shown in FIG. 2, is suitable. This type of equipment is divided into multiple chambers in the board width direction, and each chamber is equipped with something like a butterfly valve, which is operated according to the output of a steel strip surface temperature measuring device. The structure is such that the flow rate flowing out from the tank can be controlled.

(Function) In the present invention, the cooling roll group is separated into front and rear stages and gas jet cooling is performed in the separated section. The temperature deviation in the sheet width direction that has already occurred in the front roll group is still small, so it is easy to correct, and there are fewer cases where the temperature deviation that occurs only in the rear roll group causes cooling buckles. There is a particular thing. Furthermore, compared to cooling using only gas jet cooling, since roll cooling is also used in any case, the cooling efficiency is good and rapid cooling is possible.

(Example) FIG. 1 shows a rapid cooling zone 7 consisting of four cooling roll groups.
The preceding gas jet cooling device 11 performs gas jet cooling following the next cooling zone 6, and the four cooling rolls 7a to 7d on the downstream side of the preceding stage (7a, 7b) and rear stage (7c, 7d>
an intermediate gas jet cooling device 12 separated into two and disposed in the middle; and two divided cooling rolls 7a, 7b, 7c,
An example configured with 7d is shown below.

FIGS. 3 and 4 show the temperature difference between the center and the etch when cooling was performed using the quenching zone 7 under the following two conditions.

Cooling conditions * Corresponding to Figure 3 (1) The cooling device used was a gas jet cooling device with a normal plenum chamber.In order to supercool the etch area, the slit width at the nozzle tip was set at the center of the slit. I used one with one side slightly wider.

*Corresponding to Figure 4 (2) The cooling device used was one in which the dampers 12a and 12b operate according to the temperature measured by the temperature measuring device 13 and can control the flow rate as shown in Figure 2. .

The temperature measurement by the measuring device 13 indicates that the etch part temperature is 540 at the 0 point.
℃, and the center part temperature was 520°C, and the difference ΔTs was about 20°C, but at the 0 point, the temperature was immediately after the temperature control, so the temperature between the edge and center was opposite, and the edge part (465°C) was the center part (465°C).
480°C), and the temperature difference ΔTc is controlled to about -15°C. At point 0, where cooling of the second stage roll was completed, the temperature difference ΔTs between the etched portion and the center portion could be reduced to 0, and no troubles such as heat buckling occurred.

(Effects of the Invention) As explained above, according to the present invention, the temperature difference in the width direction of the steel strip in the cooling zone can be made very small or completely uniform, so that cooling buckles can be generated in products with good shapes. It is possible to carry out continuous annealing without any need for continuous annealing, and with the improvement of cooling capacity, it is possible to increase the line operating rate and reduce equipment costs.

[Brief explanation of drawings]

FIG. 1 is a route map of a cooling zone showing one embodiment of the method of the present invention, FIG. 2 is a route map showing an example of a gas jet cooling device, and FIGS. 3 and 4 are both in accordance with the present invention. Figure 5 is a diagram showing the temperature distribution in the width direction of the steel strip during the implementation of the method. Figure 5 is a route map showing an example of a continuous annealing furnace. Figure 6 is a diagram of the contact between the roll and the steel strip when the conventional roll cooling method is implemented. FIG. 7 is an explanatory diagram showing the temperature difference between the etched part and a part of the center under the conventional roll cooling method. 1... Payoff reel 2... Cleaning section 3... Entrance side looper 4... Heating zone 5... Soaking zone 6... Primary cooling zone 7... Roll cooling group 8... Overaging zone 9... Final cooling zone 10.
...Tension reel 11...Advanced gas jet cooling device 12...Intermediate gas jet cooling device 13...Temperature measuring device Patent applicant: Kawasaki Steel Corporation Same applicant: Mitsubishi Heavy Industries, Ltd. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 IO-11 Kennyo 7 reel Figure 6 Fish 'I! +rb direction Figure 7

Claims (1)

[Claims] 1. When cooling a steel strip by passing a plurality of cooling rolls arranged in a row in a cooling zone of a continuous annealing furnace in contact with each other, the cooling roll group is divided into a front stage and a rear stage. By installing the steel strip separately in the separated section and applying gas jet cooling to the steel strip in the separated section,
A method for cooling a steel strip in a continuous annealing furnace, characterized by correcting temperature deviation in the width direction of the steel strip during roll cooling. 2. When cooling the steel strip by passing the steel strip in contact between a plurality of cooling rolls arranged in a row in the cooling zone of a continuous annealing furnace, the cooling roll group is separately arranged into a front stage and a rear stage, Steel in a continuous annealing furnace characterized by uniformizing the temperature distribution in the width direction of the steel strip by applying gas jet cooling to the steel strip in the separation section using a device capable of adjusting the flow rate in the width direction. Band cooling method.