JPS62116724A - Strip cooler for continuous annealing furnace - Google Patents

Abstract

PURPOSE:To uniformly cool a strip at a high speed by specifying the distance between the tip of an each cooling gas blowing nozzle and the strip and the projecting length of the nozzle and pressing the strip perpendicularly with press rolls which are so disposed as not to face each other. CONSTITUTION:The strip S subjected to heating and soaking is introduced into a cooling zone where the cooling gas is blown from the nozzles 18 of gas injectors 15 disposed to face each other along a passing line of the strip S to cool the strip. The nozzles 18 are projection type round hole nozzles which are provided zigzag in a large number on the front face 17 of a cooling chamber 16. The distance Z between the strip S and the tips of the nozzles 18 is specified to <=70mm and the projecting length (h) of the nozzles is specified to >=(100-Z)mm. A pair of the press rolls 31 are disposed diagonally to the strip S to press the strip surface in the perpendicular direction by a driving device 33. The fluttering of the strip S is thereby thoroughly prevented and the uniform cooling of the strip in the transverse direction thereof is efficiently executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a strip cooling device in a continuous annealing furnace, and more particularly to a device for cooling a strip with a high cooling capacity using gas.

PRIOR ART Continuous annealing furnaces heat, briefly soak, cool and optionally overage the steel strip in a known manner.

By the way, in order to obtain the desired material properties of the strip, in addition to the heating temperature (annealing temperature) and soaking time, how to cool the strip is important. For example, aging resistance and fluting resistance are important. It is said that in order to improve the properties of steel, it is better to increase the cooling rate and then perform an overaging treatment.

Currently, various cooling media are used as a method for cooling the strip after heating and soaking, and the speed at which the strip is cooled varies depending on the selection of the cooling medium.

Among these, when wood is used as a refrigerant, a considerably high cooling rate can be obtained, and cooling to the so-called ultra-rapid cooling range is possible, but the problem is that the strip shape may be distorted due to quenching distortion. Also, contact with water forms an oxide film on the strip surface, which requires separate equipment to remove, and is therefore not economically advantageous.

On the other hand, as a method to solve the above-mentioned problems, a so-called roll cooling method has been developed and put into practical use, in which water or other refrigerant is passed inside the roll, and the strip is cooled by contacting the cooled roll surface. However, this method includes the following problems. In other words, the strip passing through the continuous annealing furnace does not necessarily maintain flatness, and therefore, when it comes into contact with the cooling roll, there may be a local non-contact (non-uniform cooling), which causes the strip to This may cause the shape of the product to deteriorate. Therefore, a means for flattening the strip before contact with the cooling roll is required, which increases equipment costs.

As another cooling method, a method using gas as a refrigerant has been put into practical use and has achieved many successes. Although this method has a slower cooling rate than the aforementioned water cooling or roll cooling, it allows relatively uniform cooling. As such a cooling device, for example, the device disclosed in US Pat. No. 3,088,58B is known.

The gas cooling means in a vertical continuous annealing furnace is usually such that the strip is suspended between rotating conveyance rolls provided at the upper and lower parts of the furnace, and a plurality of cooling gas chambers are installed between the conveyance rolls. Cooling gas is sprayed directly onto the strip from a nozzle attached to the strip. During cooling, as mentioned above, for example, in order to improve the fluting resistance of the strip, it is necessary to further increase the cooling rate.

(Problems to be Solved by the Invention) In order to further increase the cooling rate as described above, it is conceivable to increase the amount of gas blown onto the strip.

In this case, if the distance between the strip and the nozzle tip is large, the gas flow velocity reaching the strip will be significantly attenuated compared to when it is ejected, making it impossible to achieve the objective. This method is not advantageous in terms of cost, equipment space, and running cost. Therefore, it is necessary to make the distance between the nozzle tip and the strip relatively small and to enable efficient cooling.

As mentioned above, the strip is supported between the upper and lower transport rolls (a distance of approximately 20 rolls, depending on the equipment), while
Since the strip passes at a speed of approximately 200 to 1000 m/win, resonance of the strip due to deformation (eccentricity) of the conveying roll and vibration called black ring due to the spraying of gas onto the strip occur. If the distance between the nozzle tip and the strip is reduced or the amount of gas blown is increased, the gas will be blown at a higher speed onto the strip surface, and this fluttering will further increase. If excessive flutter occurs, the strip may come into contact with a gas blowing device, damaging the device, or causing scratches on the strip itself.
In addition, it is non-uniformly cooled in the width direction, which tends to cause shape defects, and in severe cases, a malignant shape defect called heat buckle occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling device for a continuous annealing furnace that uses gas as a refrigerant and is capable of cooling a strip at a high rate.

Another object of the present invention is to completely prevent strip flutter and efficiently realize uniform cooling in the strip width direction. An object of the present invention is to provide a cooling device for a fu continuous annealing furnace.

(Means for Solving the Problems) In the cooling device of the present invention, a plurality of circular hole nozzles facing the strip surface are attached to the front surface of the cooling gas chamber, and the distance gIZ between the strip and the nozzle tip is 70 layers 1 The protrusion length of the nozzle from the front surface of the cooling gas chamber is (100-
z) am or more. The cooling device of the present invention also includes a pair of rotatable presser rolls that are arranged diagonally across the strip and are attached to the furnace wall so as to be able to move back and forth so as to push the strip surface in a direction perpendicular to the rolls. There is.

Furthermore, in the present invention, the most efficient nozzle opening area ratio and opening diameter have been found. That is, the opening area ratio of the nozzle group is set to 2 to 4%, and the opening diameter of the nozzle is set to be smaller than 115, which is the distance at which the cooling gas is sprayed.

The cooling device of the second invention of the present application further includes a device for detecting the circumferential speed of the conveyance roll, and a device that detects the speed of the strip passing through the presser roll based on the distance between the conveyor roll and the presser roll and the detected value. The apparatus includes a calculation device and a device that controls the circumferential speed of the presser roll so as to achieve the strip speed determined by the calculation.

(Function) When the nozzle height is set to (100 - spraying distance) 1 or more, the lateral flow velocity of the jet decreases and the strip is cooled uniformly in the width direction. In addition, by protruding the nozzle, the gas blown onto the strip surface is transferred from the gap between the strip and the nozzle tip to the free space inside the furnace, that is, the inside of the furnace excluding the space between the strip and the tip surface of the nozzle group. Since the gas can escape into the space and other sprays do not interfere with the gas flow, efficient cooling is possible.

The circulation fan is driven most efficiently when the ratio of the opening area of the entire nozzle group to the area of the front surface of the cooling gas chamber is 2 to 4%. If the opening area ratio is too large, the nozzle flow velocity will decrease for the same air volume, and the flow velocity of the jet reaching the strip will further decrease due to the influence of the lateral flow of the jet. On the other hand, if the opening area ratio is too small, the flow velocity becomes too high for the same amount of air, which increases pressure loss in the nozzle and requires more power. Also, the nozzle diameter is the distance between the strip and the nozzle tip, that is, the spraying distance is 115% of the distance z.
The smaller size results in the highest cooling capacity of the individual jets of cooling gas being densely and uniformly distributed over the cooling surface. The smaller the nozzle diameter is, the more advantageous it is from the viewpoint of the required circulation fan power, but if the nozzle diameter is made smaller under the condition of the same opening area ratio, the number of nozzles increases.

In the second invention, the circumferential speed of the conveyance roll is detected, and the speed of the strip passing through the presser roll is calculated based on the distance between the conveyance roll and the presser roll and the detected value. Then, the circumferential speed of the presser roll is controlled so as to achieve the strip speed determined by the above calculation. The speed of the strip is equal to the circumferential speed of the presser roll, and no slip occurs between the moving strip and the presser roll.

(Example) Examples of the present invention will be described below with reference to the drawings.

In FIG. 1, the continuous annealing furnace 1 is vertical, and the heating zone 2
．． Soaking zone 3. -Next cooling zone 4. It consists of an overaging zone 5 and a secondary cooling zone 6. A large number of conveyor rolls 7 are arranged vertically in the continuous annealing furnace 1, and these conveyor rolls 7
is a drive device (not shown) consisting of a motor, reducer, etc.
Rotationally driven by. The strip S is passed over these transport rolls 7 and transported up and down inside the furnace l. Before and after the continuous annealing furnace 1, conventional equipment such as a payoff roll, a pinch roll, an inlet looper, an outlet looper, a tension reel, and other equipment (none of which are shown) are arranged.

In this embodiment, the cooling device of the invention is provided in the primary cooling zone 4. Figure 2 shows an enlarged view of the primary cooling zone.In the primary cooling zone 4, a gas blowing device 15 is installed on the strip S.
Three units are placed along the sheet threading line. The gas ejection device 15 cools the strip S by ejecting cooling gas from its nozzle.

FIG. 3 shows a configuration diagram of the gas ejection device 15.

Gas blowing device! 5 is mainly a cooling gas chamber 16. It consists of a circulation fan 21 and a cooling heat exchanger 26. The cooling gas chambers 16 are box-shaped, and the front surfaces 17 face the strip S surface, and they form a pair facing each other with the strip S in between. The cooling gas chamber 18 is the furnace chamber 1.
1 and is attached to the furnace wall 12. A large number of nozzles 18 are provided on the front surface 17 of the cooling gas chamber 16 facing the strip S. Circulation fan 21
is located outside the furnace chamber II and is driven by an electric motor 22. The end of the suction pipe 23 of the circulation fan 21 opens into the furnace chamber 11, and the discharge pipe 24 is connected to the cooling gas chamber 1B.

Further, the cooling heat exchanger 26 is provided in the middle of the suction pipe 23. A large number of fin tubes 29 traverse the chamber 27 of the heat exchanger 26 . Both ends of the fin tube 29 are fixed to headers 28 attached to both side walls of the chamber 27, and cooling water is supplied to the headers 28 through a cooling water pipe 30. Suction pipe 2
The furnace atmosphere gas taken into 3 is transferred to the cooling heat exchanger 2.
6, it contacts the fin tube 29 and is cooled, and the pressure is increased by the circulation fan 22. The pressurized cooling gas turns into diene a and is ejected from the group of nozzles 18 in the cooling gas chamber 18 toward the surface of the strip S, thereby cooling the strip S.

Figure 4 shows a nozzle 18 provided on the front surface 17 of the cooling gas chamber 1B.
It shows a group. The nozzles 18 are protruding circular hole nozzles, and are arranged in a staggered manner on the front surface 17 of the cooling gas chamber 18. The distance between the strip S and the tip of the nozzle 18, that is, the spraying distance z, is 70 layers or less. Figure 5 shows the relationship between the spraying distance of 1llz and the cooling capacity (cooling rate when the plate thickness is lam). From a metallurgical perspective, in the case of cold-rolled thin steel sheets (about 1 layer thick), It is said that obtaining a cooling rate of approximately 100 c/s or higher will be effective in reducing the alloy used in high-tension materials. /s lsm thick plate equivalent) is known to be effective in fluting resistance. From FIG. 5, it can be seen that this cooling rate can be achieved by setting the spraying distance #2 to about 50 mm. Also, if the amount of gas sprayed is increased slightly, the spraying distance will be 70 + s.
It is presumed that this cooling rate can be achieved even in terms of degree. This spraying distance 2 was conventionally at least lOQm■
Generally, in vertical furnaces, the temperature is 150~150 to avoid contact of the strip with the cooling gas chamber due to fluttering.
The spraying distance z of the apparatus of the present invention, which has 200 layers, is significantly smaller than that of the conventional apparatus. The minimum value of the spraying distance 2 depends on the shape of the strip, but is generally about 20 mm.

In order to achieve a high cooling rate, it is necessary to increase the air volume of the gas blowing device. On the other hand, in order to improve the temperature distribution in the strip width direction, it is necessary to eliminate the influence of the lateral flow of the jet as much as possible. For this purpose, as shown in FIG. 4, the nozzle 18 is formed into a protruding shape with a height h greater than (1001-spraying distance z) m to ensure a gap between the strip S and the nozzle 18. Figure 6 shows the nozzle height as a parameter.
The temperature distribution in the width direction of the strip after cooling is shown. Further, FIG. 7 shows the relationship between the height and the relative heat transfer coefficient (heat transfer coefficient at the edge of the strip when the heat transfer coefficient at the center of the strip is 1.0). As is clear from these diagrams, when the nozzle height is set to (100 - spraying distance #z) or more, the cross flow velocity of the jet can be reduced and uniform cooling in the width direction can be obtained. Furthermore, by protruding the nozzle 18, the gas blown onto the strip surface becomes a flow b shown in FIG. By escaping into the furnace space 13 except for the space between the gas flow and the tip surface of the nozzle group 18, other blowing does not interfere with the gas flow, so efficient cooling is possible.

The ratio of the opening area of the entire group of nozzles 18 to the area of the front surface 17 of the cooling gas chamber 16 is preferably 2 to 4%. FIG. 8 shows the relationship between the opening area ratio and the required circulating fan power. According to FIG. 8, it is confirmed that 2 to 4% is the most efficient. When the opening area ratio is large, the nozzle flow velocity decreases for the same air volume, and the flow velocity of the jet reaching the strip further decreases due to the effect of the jet's lateral flow.

On the other hand, if the opening area ratio is too small, the flow velocity becomes too high for the same amount of air, resulting in increased pressure loss in the nozzle and the need for more power.

It is desirable that the nozzle diameter be smaller than the distance between the strip S and the nozzle tip, that is, the spray distance ltz, which is 175. FIG. 9 shows the relationship between the nozzle diameter and the required circulation fan power ratio with respect to the spray distance z. Gas blowing device 15
In order to achieve a higher cooling capacity, the nozzles 18 may be arranged closely so that the most cooling capacity parts of the individual jets of cooling gas are distributed densely and uniformly over the cooling surface. This is because it is advantageous. Also, the smaller the nozzle diameter is, the more advantageous it is from the perspective of the required circulation fan power;
If the nozzle diameter is made smaller under the condition of the same opening area ratio,
There is also the disadvantage that the number of nozzles increases, leading to a high build-up of the nozzle equipment. Considering both of these, 115
A value of about z or less is economical in practical terms.

Table 1 shows a comparison of the cooling capacities of the present invention and the prior art.

Table 1 An example of the specifications of the device of the present invention is shown.

Strip size: plate thickness 0.3-1.8mm.

Board width 600~18QOmm Strip temperature 2650~400℃ Strip speed: 0.8mm thickness x 1fi00m x 200mpm cooling air: 3500m3/5i
n (100℃) Circulation fan pressure 700mAq Nozzle diameter: 9.2mm Distance between nozzle tip and strip: 5hm Nozzle protrusion height: 1Oh Intestine opening area ratio: 2.7! Since the strip S fluffs due to the blowing of gas and the passing of the strip S, it is important to prevent this from occurring in order to achieve rapid cooling. Furthermore, when heat buckling occurs, it is important to pass the strip S through the plate without causing the plate to break.

For this purpose, in the present invention, as shown in FIG. 2, a driving presser roll 31 is provided between the gas jetting devices 15 so that it can freely enter the sheet threading line, and is arranged so as not to face each other and spaced apart in the direction of the sheet threading line, that is, vertically. It is set up. A drive device 33 is connected to the presser roll 31 . FIG. 1θ shows details of the drive device 33 for the presser roll 31. Presser foot roll 3
Both ends of the presser roll 31 are rotatably supported by a bearing box 34 outside the furnace chamber 11, and one end of the presser roll 31 is connected to an electric fi 35 for rotating the roll. The bearing box 34 is displaceable in a direction perpendicular to the strip S surface, and the bearing box 34
4 and the furnace wall 12 are connected by a snake [3B] to maintain airtightness. On the other hand, an electric motor 38 for advancing and retracting the presser roll is arranged outside the furnace chamber 11. Electric presser roll advancement/retraction f
i3B is operatively connected to the bearing box 34 via a distribution base 39 and a transmission shaft 40. As the transmission shaft 40 rotates, the bearing box 34 is rotated by a screw mechanism (not shown) provided therein.
advance and retreat. The drive device 33 sends out the presser roll 31 so as to push out the strip S from the threading line.The amount of extrusion of the presser roll 31, that is, the amount of crowding into the threading line, is determined by the roll diameter of the presser roll 31 and the threading amount of the continuous annealing equipment. Depending on the plate thickness range etc., for example θ~10hm
(in terms of wrap amount), and a minimum of 5 cm is required. Moreover, the arrangement interval of the presser rolls 31 in the sheet passing line direction is about 300 to 800 mm.

In FIG. 2, two presser rolls 31 are provided at intervals, but as shown in FIG. 11, three presser rolls 45 may be provided so as to be freely inserted into the sheet threading line. In this case, it is preferable in terms of equipment to connect the advancing/retreating drive device 47 to the intermediate presser roll 45. In this example, there is no need to adjust the sheet passing line according to the amount of crowding of the presser roll 45.

By arranging the presser rolls 31.45 in non-opposed positions and at intervals in the direction of the threading line, the strip S is pressed on one side by the rolls 31.45, and then placed in a non-opposed manner. The opposite surface is held down by the other presser roll 31, 45, and by wrapping and entering the threading line, and being held down by the amount of crowding, it is possible to control the plate thickness and resonance. Fluffling when it occurs is also completely prevented. Furthermore, the opposite side of the strip S before it contacts the presser rolls 31, 45 does not contact anything, that is, it is not clamped, so that the strip S can be threaded without causing the plate breakage even when heat buckling occurs.

In addition, if slip scratches occur between the presser roll and the strip S, the presser roll speed control (peripheral speed control)
Further, the surface of the presser roll may be subjected to a surface treatment such as thermal spraying for the purpose of preventing build-up.

To control the circumferential speed of the presser roll, the circumferential speed of the conveyor roll placed near the presser roll is detected, and based on the detected value and the distance between the conveyor roll and the presser roll, the threaded material passing through the presser roll is controlled. The circumferential speed of the presser roll is controlled by determining the speed of the presser roll. Since the accurate speed of the threaded material at the presser roll position is detected and the circumferential speed of the presser roll is controlled based on this threaded material speed, strip surface defects do not occur at the presser roll position, and the original function of the presser roll is smoothly performed. You will be able to demonstrate your skills.

As shown in FIG. 12, a distributor 51 is attached to the presser roll 31.
A rotary drive electric motor 52 is connected via.

A presser roll speed control device 54 and a speed reference calculation device 55 are connected to the zero-rotation drive electric motor vj, 52, in which a DC motor or an AC motor is used as the rotation drive motor 52. A transport roll circumferential speed calculating device 58 is connected to the upper and lower transport rolls 7 via rotation speed detectors 57, respectively.

The strip S is conveyed by a conveyor roll 7 in the direction of the arrow. At this time, the rotational speeds of the upper and upper transport rolls 7 are detected by roll rotational speed detectors 57, respectively. The detected rotational speed signal is input to the roll circumferential speed calculating device 5B, and the roll circumferential speed is calculated. The calculation result is speed! (Output to the quasi-arithmetic device 55. The speed reference arithmetic device 55 determines whether the presser roll 31 is in contact with the presser roll 31 based on the circumferential speed of the upper and lower conveyor rolls 7 and the arrangement distance between the presser roll 31 and the conveyor roll 7. The speed of the strip portion is calculated, and the calculated value is output to the presser roll speed control device 41 as a circumferential speed reference signal of the presser roll 31. The presser roll speed controller t!154 controls the speed of the strip S passing through the presser roll 31. The speed of the presser roll 31 is controlled based on a presser roll circumferential speed reference signal equal to .The presser roll speed control device 54 includes:
For example, if the presser roll rotation drive motor 52 is a DC motor, there are armature voltage variable control and field variable control.
In the case of AC motors, there is variable voltage variable same wave number control.

Therefore, since the presser roll 31 is rotated at the same circumferential speed as the speed at which the strip S passes, the strip S is free from surface defects such as scratches, scratches, marks, etc., and the occurrence of flapping is prevented. . Therefore, the sheet passing speed can also be increased.

In this embodiment, a case has been described in which the circumferential speeds of the upper and lower conveyance rolls 7 are determined and the circumferential speed of the presser roll 31 is controlled based on them. Instead of this, the circumferential speed of either the upper or lower transport roll 7 is determined, and the transport roll 7 and presser roll 3 are
The strip S is attached to the presser roll 31 based on the arrangement distance of 1.
The circumferential speed of the presser roll 31 can also be controlled by determining the speed at which the presser roll 31 passes.

The vertical continuous annealing furnace was described above as an example, but
The present invention is also applicable to horizontal continuous annealing furnaces. Furthermore, the number of gas injection devices, nozzles, and presser rolls is not limited to those in the above embodiments.

(Effects of the Invention) In the present invention, by inserting the presser roll into the strip threading line and controlling the amount of crowding, it is possible to prevent strip fluffing, etc., and to insert the nozzle into the strip without damaging the strip. Can be as close as possible. Also,
Since the spraying distance of the cooling gas and the nozzle protrusion length are specified, high cooling efficiency is obtained and uniform cooling in the width direction of the strip is also achieved. Heat buckling does not occur due to uniform cooling in the width direction of the strip.

Furthermore, compared to conventional cooling devices, the cooling device of the present invention can achieve high cooling capacity with a relatively small capacity blower.

From the above, it is possible to easily secure a cooling rate that is preferable from a metallurgical point of view without installing an excessively large blower or duct, which not only reduces space and equipment costs, but also significantly reduces blower power. . On the other hand, from the perspective of product quality, it is relatively easy to obtain a high cooling rate that could not be achieved with conventional equipment due to equipment costs.
Since the above cooling rate can be obtained, overaging is promoted and tinplate with a low temper level can be easily produced. In addition, even for general cold-rolled thin sheets, the sheet thickness is 1s, which requires a particularly high degree of processing.
For products of +m or less, a cooling rate of 50@c/S or more can be obtained, making it easy to produce products with good workability. Even in high tension materials, the amount of added alloying elements can be reduced.

Furthermore, since the circumferential speed of the conveyor roll is detected and the circumferential speed of the presser roll is controlled based on the detected value, no slip occurs between the moving strip and the presser roll, and the strip has a good surface without slip scratches. You can get the product.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an outline of a continuous annealing furnace in an embodiment of the present invention, Fig. 2 is an enlarged view of a cooling device in an embodiment of the invention, and Fig. 3 is a perspective view of a gas injection device. , 4th
Figures (a) and (b) are a cross-sectional view and a front view of a cooling gas chamber equipped with a protruding nozzle, respectively, Figure 5 is a graph showing the relationship between spray distance and cooling capacity, and Figure 6 is a graph showing the relationship between nozzle protrusion length and cooling capacity. A graph showing the relationship between temperature distribution in the strip width direction after cooling,
Figure 7 is a graph showing the relationship between nozzle protrusion length and relative heat transfer coefficient, Figure 8 is a graph showing the relationship between opening area ratio and required circulation fan power, and tJ59 is a graph showing the relationship between nozzle diameter and spray distance. Graph showing the relationship between circulation fan power, 1st
Figure 0 is a plan view showing the configuration of the drive device for the presser roll.
Figure 1 is a drawing showing another embodiment of the presser roll and the first
FIG. 2 is a system configuration diagram of presser roll circumferential speed control. l... Continuous annealing furnace, 4... Cooling zone, 7... Conveyance roll, 11... Furnace chamber, 12... Furnace wall, 15...
Gas blowing device, 1B...cooling gas chamber, 17...gas chamber front,! 8... Nozzle, 21... Circulation fan, 2
B... Cooling heat exchanger, 31... Presser roll, 33
. . . Presser roll drive device, 38 . . . Electric motor for advancing and retreating the presser roll, 54 .
・・Speed reference calculation device, 57 ・・Rotation speed detector, 58
... Conveyance roll circumferential speed calculation device.

Claims (3)

[Claims] (1) A furnace chamber that forms a passage for the strip, a conveyor roll rotatably supported within the furnace chamber and around which the strip is wound, and attached to the furnace wall with the front facing the strip surface and facing each other with the strip in between. a pair of cooling gas chambers, each having a plurality of circular hole nozzles mounted in front of each cooling gas chamber to cool the strip by blowing pressurized gas onto the moving strip, communicating into the furnace chamber through a suction pipe. ,
In an apparatus equipped with a gas forced circulation device communicating with the cooling gas chamber via a discharge pipe and a gas cooling device provided in the middle of the suction pipe, the distance Z between the strip and the nozzle tip is 70 mm or less. , the protrusion length of the nozzle from the front surface of the cooling gas chamber is (100-z) mm or more, and the nozzle is arranged diagonally across the strip, and is movable back and forth so as to push the strip surface in a direction perpendicular to the nozzle. 1. A strip cooling device for a continuous annealing furnace, comprising a pair of rotatable presser rolls attached to a furnace wall, and a presser roll advancement/retraction device for setting the presser rolls at a predetermined position. (2) A patent in which the ratio of the opening area of the entire nozzle group to the area of the front surface of the cooling gas chamber is 2 to 4%, and the opening diameter of the nozzle is 1/5 or less of the distance Z between the strip and the nozzle tip. A strip cooling device for a continuous annealing furnace according to claim 1. (3) A furnace chamber that forms a trip passage, a conveyor roll that is rotatably supported within the furnace chamber and has the strip wrapped around it, and is attached to the furnace wall with the front facing the strip surface and facing each other with the strip in between. a pair of cooled gas chambers,
A plurality of circular hole nozzles are installed in the front of each cooling gas chamber and blow pressurized gas onto the moving strip to cool the strip, communicating with the furnace chamber through a suction pipe and communicating with the furnace chamber through a discharge pipe. In an apparatus equipped with a gas forced circulation device communicating with the cooling gas chamber and a gas cooling device provided in the middle of the suction pipe, the distance Z between the strip and the nozzle tip is 70 mm or less, and the distance from the front of the cooling gas chamber is The protruding length of the nozzle is (100-z) mm or more, and the rotating nozzle is arranged diagonally across the strip and is attached to the furnace wall so as to be able to move forward and backward so as to push the strip surface in a direction perpendicular to the nozzle. A pair of presser rolls that can be freely moved, a presser roll advancing and retracting device that sets the presser rolls at predetermined positions, a device that detects the circumferential speed of the conveyance roll, and a distance between the conveyance roll and the presser roll and the detected value. a device for calculating the speed of the strip passing through the presser roll based on the above calculation; and a device for controlling the circumferential speed of the presser roll so that the speed of the strip is determined by the calculation. Strip cooling device.