JP4340090B2 - Steel strip cooling device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel strip cooling apparatus used in a continuous annealing furnace and a hot dip galvanizing facility.
[0002]
[Prior art]
In a continuous annealing furnace, a steel strip is heated, soaked, cooled, and then over-aged as necessary. By the way, in order to obtain the desired properties of the steel strip, it is important how to cool it in addition to the heating temperature (annealing temperature) and the soaking time. For example, it is said that in order to improve aging, fluting resistance, etc., it is better to increase the cooling rate and then perform overaging treatment. Various cooling media are currently used as a method for cooling the steel strip after heating and soaking, and the cooling speed of the steel strip varies depending on the selection of this cooling medium.
[0003]
Among these, when water is used as a cooling medium, a considerably high cooling rate can be obtained and cooling to a super-quenching region is possible, but due to quenching distortion, deformation of the steel strip called a clean buckle may occur. The biggest difficulty. In addition, an oxide film is formed on the surface of the steel strip due to contact with water, and another facility for removing this is required. Therefore, it is not an economically advantageous facility.
[0004]
In order to solve the above-mentioned problem, there is a roll cooling method in which water or other cooling medium is passed through the inside of the roll, and a steel strip is brought into contact with the cooled roll surface for cooling. This method has the following problems. That is, not all the steel strips passing through the continuous annealing furnace maintain flatness. Therefore, when contacting a cooling roll, it may become non-contact locally, and by this non-contact, the cooling in the width direction of a steel strip becomes non-uniform | heterogenous, and the shape of a steel strip is destroyed. Therefore, a means for flattening the steel strip is required before contact with the cooling roll, which increases the equipment cost.
[0005]
As another cooling means, a cooling method using a gas as a cooling medium has been put into practical use and has achieved many achievements. This method has a slower cooling rate than the water cooling and roll cooling described above, but relatively uniform cooling in the width direction is possible. As the cooling medium to increase the cooling rate, which is the biggest difficulty with this gas cooling, as the cooling medium to increase the cooling rate by increasing the heat transfer rate by bringing the tip of the nozzle that injects the gas as close to the steel strip as possible, The thing using hydrogen gas is disclosed.
[0006]
As a technique for increasing the heat transfer coefficient by bringing the tip of a nozzle to be sprayed close to a steel strip, there is a technique disclosed in Patent Document 1. This technology enables efficient cooling by reducing the distance between the tip of the nozzle and the steel strip. Specifically, the length of the protruding nozzle is 100 mm-Z or more (Z is the distance from the tip of the protruding nozzle to the surface of the steel strip), and a portion where the gas injected from the protruding nozzle hits the steel strip and escapes to the back is provided. Yes. Accordingly, it is disclosed that the injected gas is reduced from staying on the surface of the steel strip, and the cooling uniformity in the width direction of the steel strip is improved.
[0007]
In addition, various experiments were conducted from 50-Z to 200-Z to determine the optimum point of the heat transfer coefficient. Based on the results of this experiment, we have developed a cooling device with the most efficient cooling capacity that is normally used in the cooling zone of a continuous annealing furnace. With the development of this cooling device, the heat transfer coefficient, which was normally 116 kW / (m · K), can be increased to 465 kW / (m · K).
[0008]
However, a further increase in the cooling rate has been desired, and there is a limit to existing cooling devices that normally circulate atmospheric gas of about N ₂ : 95% + H ₂ : 5% as a cooling medium. In order to solve this problem, it has been considered to use hydrogen gas as a cooling medium. Although it has been known for a long time that the cooling capacity is improved by employing hydrogen gas, it has not been applied to actual machines due to the danger of hydrogen gas.
[0009]
Patent Document 2 discloses a technique for rapidly cooling by increasing the hydrogen gas concentration. In this technique, in the rapid cooling zone, the hydrogen concentration is set to 30 to 60%, the spraying temperature is set to 30 to 150 ° C., and the spraying speed is set to 100 to 150 m / sec. And in order to satisfy this cooling rate, the circular hole nozzle which protrudes toward a steel strip surface is used, and the distance of a steel strip and the protrusion nozzle front-end | tip is 70 mm or less.
[0010]
In this way, specific techniques for employing hydrogen gas have been developed and are being implemented.
[0011]
Also, in hot dip galvanizing equipment, the steel strip is heated, soaked, and cooled to a predetermined temperature by continuous annealing, immersed in a hot dip galvanizing bath, and the hot dip galvanized coating is applied to the steel strip, and then the cooling device It is cooling.
[0012]
An air-water cooling device is used as a cooling device for the steel strip after hot dip galvanization. This technique is disclosed in Patent Document 3. In this technology, a large number of cooling nozzle groups in which gas or liquid supply pipes are connected to a cooling device are arranged relative to a steel strip, and a liquid supply shut-off valve is provided in the middle of the liquid supply pipe. It is an apparatus in which a nozzle for draining is disposed below, and an injection blocking damper is movably disposed between the cooling nozzle groups so as to be able to block cooling at an arbitrary position in the width direction of the steel strip. .
[0013]
[Patent Document 1]
Japanese Patent Publication No. 2-16375 [0014]
[Patent Document 2]
Japanese Patent Laid-Open No. 9-235626
[Patent Document 3]
Japanese Patent Publication No. 58-56029 [0016]
[Problems to be solved by the invention]
In general, when the H ₂ concentration is increased by cooling with an atmospheric gas mainly composed of N ₂ gas and the discharge flow rate from the nozzle is set to 100 to 150 m / sec and sprayed onto the steel strip for cooling, the discharge is 100 to 150 m / sec. Since a flow rate is required, a large amount of gas is required as a gas sprayed on the steel strip. Although the cooling capacity is improved by spraying this large amount of gas, the temperature distribution in the width direction of the steel strip due to the gas after sprayed on the steel strip becomes a problem. The gas that has collided with the steel strip bounces off and flows out from the widthwise side opening of the steel strip while forming a gas layer along the steel strip. At that time, a temperature difference occurs in the width direction of the steel strip due to the gas layer after spraying, but in the technique disclosed in Patent Document 1 described above, the length of the protruding nozzle is set to (50-Z) to (200-Z) mm. It is considered that the gas blown as can flow out from the back of the protruding nozzle. However, since it is necessary to cool the steel strip by blowing a large amount of gas onto the steel strip, there is a slight effect in the above range, but the temperature difference in the width direction of the steel strip has not been solved. In addition, the press roll is installed between the cooling devices so as to keep the flutter of the steel strip stationary by high-speed spraying, but the place where the press roll is placed is also limited. However, the current situation is that we cannot expect much effect.
[0017]
In addition, in the air / water cooling device, after being injected into the steel strip, an exhaust port for exhausting gas is installed above the air / water cooling device so that water after air / water cooling does not leak below the cooling device. In addition, a drainer is required. It is necessary to install such an accessory device, which requires equipment space.
[0018]
The object of the present invention is to provide a cooling device that minimizes the temperature difference in the width direction of the steel strip generated by high-speed spraying in view of the above reasons, and prevents the flapping of the steel strip to maximize the effect of the pressing roll. There is.
[0019]
[Means for Solving the Problems]
The steel strip cooling device of the present invention is a steel that projects a plurality of nozzles on the surface of a pair of cooling boxes opposed to a steel strip that runs in the vertical direction, and jets gas from the projecting nozzles to cool the steel strip. in the cooling device of the band, along the running direction of the steel strip running between the protruding nozzles that face of the pair of cooling boxes, at predetermined intervals a plurality of baffle plates in the width direction of the steel strip, the projecting nozzle It is characterized by being erected between the two.
[0020]
Further, the steel strip cooling device of the present invention projects a plurality of nozzles on the surfaces of a pair of cooling boxes facing a steel strip traveling in the vertical direction, and cools the steel strip by ejecting gas from the projecting nozzles. In the steel strip cooling device, a plurality of baffle plates are spaced at predetermined intervals in the width direction of the steel strip along the travel direction of the steel strip that travels between the opposed protruding nozzles of the pair of cooling boxes . A guide plate having a linear cross section is provided on both side surfaces of the pair of cooling boxes that are erected between the protruding nozzles and face each other, and both sides of the cooling box are connected by a guide blade. Is.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
1 is a schematic view of a rapid cooling zone in a continuous annealing furnace, FIG. 2 is a view taken along the line AA in FIG. 1, FIG. 3 is a schematic view of a cooling device installed in the rapid cooling zone, and FIG. It is the schematic which shows the flow of the blowing gas in the cooling device of invention.
[0022]
In FIG. 1, rolls 3 and 4 for conveying the steel strip 2 are arranged up and down, and a plurality of cooling devices 5 are arranged in a plurality of stages along the traveling direction of the steel strip 2 so as to face the surface of the steel strip 2. is doing. In order to prevent the steel strip 2 from fluttering between the upper and lower sides of the cooling device 5, press rolls 6 and 7 are disposed so as to sandwich the steel strip 2.
[0023]
2 is an AA arrow view of FIG. 1, and the gas blown to the steel strip 2 by the cooling device 5 is sucked from the gas suction port 8 provided in the furnace body 1, and the heat exchanger 9 and the circulation blower 10 are made to flow. Then, it is returned to the cooling device 5 again and sprayed onto the steel strip 2. The heat exchanger 9 and the circulation blower 10 are connected via a circulation duct 11 to circulate and use the gas in the furnace.
[0024]
The cooling device 5 has a cooling box 12, and a protruding nozzle 13 having a circular hole is provided on the surface of the cooling box 12 on the steel strip 2 side. The projecting nozzle 13 employs the projecting nozzle described in Patent Document 1 described above, and employs a nozzle opening area of 2 to 4% with respect to the surface of the cooling box 12. Since the tip of the protruding nozzle 13 can be disposed close to the steel strip 2 by the protruding nozzle 13, the cooling capacity can be greatly improved. Moreover, the most efficient cooling capacity was set by setting the aperture area of the nozzle to 2% to 4%.
[0025]
FIG. 3 is a schematic view of the cooling device of the present invention, in which a cooling box 12 is disposed opposite the steel strip 2. Projecting nozzles 13 are disposed on the entire surface of the steel strip 2 of the cooling box 12 with the opening ratio as described above.
[0026]
A baffle plate 14 is erected on the cooling box 12 along the traveling direction of the steel strip 2 between the protruding nozzles 13. And both the side surfaces of the cooling box 12 are connected by the guide plate 15 so that the circulating gas blown to the steel strip 2 is not exhausted from the side.
[0027]
FIG. 4 is a view taken along the line B-B in FIG. 3, and shows how the circulating gas sprayed on the steel strip 2 bounces off the steel strip 2 and is discharged from the upper and lower surfaces of the steel strip 2. Thus, the circulating gas sprayed on the steel strip 2 collides with the steel strip 2 and rebounds, passes between the nozzle groups, and is discharged from the upper and lower sides of the cooling box 12. Since the baffle plate 14 is disposed between the protruding nozzles 13, the circulating gas passing through the nozzle group is discharged along the baffle plate 14 from above and below the cooling box 12 into the furnace. Further, since the circulating gas blown to the edge portion of the steel strip 2 is also provided with guide plates 15 on both side portions of the cooling box 12, the circulating gas is discharged from above and below the cooling box 12 along the guide plate 15. The
[0028]
In the cooling device in which the baffle plate 14 and the guide plate 15 of the present invention are not disposed, the gas blown to the central portion of the steel strip 2 collides with the steel strip 2 and rebounds along the surface of the cooling box 12. It flows out in the direction of the edge part of the steel strip 2 in a certain layer. Further, the gas blown to the central part of the steel strip 2 rebounds after collision with the steel strip and moves to the cooling box side, and the gas layer blown to the central part prevents the rebound of the gas after the collision. The part tries to flow out to the edge part of the steel strip while staying between the tip of the protruding nozzle and the steel strip.
[0029]
This is because the cooling box 12 has a greater distance in the height direction than the width direction of the steel strip 2, and the circulating gas is discharged from the width direction of the steel strip 2 due to pressure loss. For this reason, fluttering occurs in the steel strip 2 due to the gas discharge balance.
[0030]
From the above, when the gas blown to the steel strip flows to the edge of the steel strip, the edge of the steel strip is supercooled, a temperature difference occurs in the width direction of the steel strip, and the outflow of this gas The gas outflow balance at the edge portion is broken, and the fluttering (amplitude) of the steel strip occurs.
[0031]
【The invention's effect】
As described above, by arranging the baffle plate and the guide plate in the cooling device for the steel strip, the gas flow after cooling can be discharged in the vertical direction of the steel strip, and the temperature in the plate width direction due to cooling is The difference can also be suppressed. In addition, since the gas stay at the edge of the steel strip is alleviated, the flutter of the steel strip can be suppressed, and the load of the pressing roll that suppresses the flutter of the steel strip can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic view of a rapid cooling zone in a continuous annealing furnace.
FIG. 2 is a view taken in the direction of arrows AA in FIG.
FIG. 3 is a schematic view of a cooling device installed in a rapid cooling zone.
FIG. 4 is a schematic view showing the flow of blowing gas in the cooling device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Furnace 2 Steel strip 3 Top roll 4 Bottom roll 5 Cooling device 6 Press roll 7 Press roll 8 Atmospheric gas suction port 9 Heat exchanger 10 Circulating blower 11 Circulating duct 12 Cooling box 13 Protruding nozzle 14 Baffle plate 15 Guide plate

Claims (2)

In the steel strip cooling device for cooling a steel strip by projecting a plurality of nozzles on the surface of a pair of cooling boxes opposed to a steel strip that runs in the vertical direction, gas is ejected from the projecting nozzle. A plurality of baffle plates are erected between the projecting nozzles at predetermined intervals in the width direction of the steel strip along the traveling direction of the steel strip traveling between the projecting nozzles facing each other in the box. Steel strip cooling device to do. In the steel strip cooling device for cooling a steel strip by projecting a plurality of nozzles on the surface of a pair of cooling boxes opposed to a steel strip that runs in the vertical direction, gas is ejected from the projecting nozzle. A plurality of baffle plates are erected between the projecting nozzles at predetermined intervals in the width direction of the steel strip along the traveling direction of the steel strip that travels between the projecting nozzles facing the box. A steel strip cooling device, wherein a guide plate having a linear cross section is provided on both side surfaces of the pair of cooling boxes, and both sides of the cooling box are connected to each other by a guide blade.

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