JPH10263772A - Secondary cooling device for continuous slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the lowering of a cooling capacity by arranging a slit nozzle mounted with a slit shield plate, which moves a slit from slab both end sides with shielding while specifying a distance from a cast slab surface to a spray mouth so as to obtain an uniform water quantity distribution in a spray width and reliably conform to an optimum width cut quantity each cast slab width. SOLUTION: A slit nozzle 1, which has a slit 2 over cast slab 10 width both ends of a max casting width for a spray mouth and mounts a slit shield plate 3 moving from cast slab 10 width both ends in the width direction while shielding, is arranged at the distance of 50-2100 mm from a cast slab 10 surface to the spray mouth. By this method, the spray mouth 2 is one each for one line in the width direction, an uniform water quantity distribution is obtained in a spray width. Further, a spray distance is restricted in a narrow range of 50-200 mm, attenuation of a flow speed of a mist 5 is slight, a cooling capacity is not lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary cooling device for continuously cast slabs, and more particularly to a secondary cooling device for continuously cast slabs using mist spray. In continuous casting (continuous casting), molten steel poured into a mold is cooled (primary cooling) in contact with the mold wall surface that has water flowing inside, and a slab in a state where only the surface layer is solidified is formed. Then, it is directly cooled (secondary cooling) by spraying in a downstream roll zone to promote solidification inside.

[0002] This secondary cooling is extremely important from the viewpoint of controlling the solidification structure and preventing cracks in the slab. Above all, it is important to avoid overcooling by avoiding water in the slab corners, and therefore, how to properly adjust the spray width (spray pattern width on the slab surface) according to the slab width. This is a major issue in secondary cooling technology.

[0003]

2. Description of the Related Art Among the conventional methods for adjusting the spray width, the main ones are as follows. (1) The spray width is changed by moving a plurality of nozzles arranged in a line up and down with respect to the surface of the slab (width cutting by spraying up and down) (JP-A-59-153558). (2) The spray width is changed by adjusting the air-water ratio (Japanese Patent Publication No. 5-55222). (3) A baffle plate is installed between the nozzle near the slab corner and the slab surface to prevent direct or sidestream water from coming near the slab corner (Japanese Patent Laid-Open No. 63-174768). (4) A plurality of nozzles are arranged at a small pitch in the slab width direction,
The supply of the refrigerant is divided into a separate system at the center and at the end, and the supply of the refrigerant at both ends is cut off according to the width of the slab, and the spray width is changed (width cutting by spray cutting).

[0004] In addition, "width cutting" is to cut the spray from the end of the slab to a predetermined distance in the width direction,
This predetermined distance is referred to as “width cut amount”.

[0005]

[Problems to be solved by the invention] However, the above (1)-
The method (4) has the following problems. The water distribution characteristics of the spray vary depending on the amount of water, the amount of air, and the spray distance (distance between the nozzle and the slab). The method (1) has a wide range of change of these conditions and a wide range of change of the nozzle pitch. In addition, the spray wrap (interference between sprays from adjacent nozzles)
Therefore, it is difficult to maintain a uniform water amount distribution within the spray width. Further, the cooling capability of the mist spray depends on the flow speed of the spray, but the flow speed is reduced as the spray distance increases, so that the cooling efficiency decreases as the spray width increases.

According to the method (2), in order to reduce the spray width, the air-water ratio must be increased, and an enormous amount of air is required. When the baffle plate is placed to completely block the water near the slab corner as in the method (3), the temperature near the long side corner becomes too high and the solidification of this portion is delayed. In addition, since the thermal stress increases as the temperature difference in the width direction increases, cracks and flaws are more likely to occur in this portion.

[0007] According to the method (4), control of the piping system and the automatic valve becomes complicated. In addition, the setting of the spray width becomes stepwise, and it is not possible to precisely cope with an optimum width cutting amount for each slab width. An object of the present invention is to solve the above-mentioned problems of the prior art, that is, a uniform water amount distribution is obtained within a spray width, and faithful to an optimum width cutting amount for each slab width without complicated control. It is an object of the present invention to propose a secondary cooling device for continuous cast slab which can cope with the above problem and can reduce the temperature difference in the vicinity of the corner of the long side of the slab, which is advantageous also in terms of operation cost.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a continuous cast slab.
In the next cooling device, a slit nozzle having a slit extending over both ends of the slab width of the casting maximum width as a spray port, and a slit nozzle equipped with a slit shielding plate that can move while shielding the slit in the width direction from both ends of the slab width, A secondary cooling device for continuously cast slabs, wherein a distance from a slab surface to a spray port is set to 50 to 200 mm.

[0009]

1A and 1B show an example of the present invention. FIG. 1A is a front view, and FIGS. 1B and 1C are sectional views taken along lines II ′ and II-II ′ of FIG. is there. In FIG. 1, 1 is a slit nozzle, 2 is a slit (spray port), 3 is a slit shielding plate, 4 is a moving device for moving the slit shielding plate in the width direction, and 5 is a slit nozzle that mixes air and water to form a mist. 6 is a mist, 7 is an orifice, and 10 is a slab.

As shown in FIG. 1, the present invention has, as a spray port (an opening for ejecting a mist), slits 2 extending over both ends of a slab 10 having a maximum casting width, and a width from both ends of the slab 10 width. A slit nozzle 1 equipped with a slit shielding plate 3 that can move while shielding the slit 2 in the direction, with the distance from the surface of the slab 10 to the spray port 2 being 50 to 200 mm. It is a secondary cooling device for cast slabs.

According to the present invention, since the slit nozzle 1 having the slit (spray port) 2 having the longest side of the slit extending over both ends of the slab 10 having the maximum width of the casting is employed, the number of the spray ports 2 is one per row in the width direction. In addition, the spray wrap portion generated when a plurality of nozzles are arranged in a line as in the method (1) is eliminated, and a uniform water amount distribution within the spray width can be obtained. Further, since the spray distance is limited to a narrow range of 50 to 200 mm, the flow rate of the mist 5 is slightly attenuated and the cooling capacity is not reduced. If the spray distance is less than 50 mm, it will be susceptible to radiant heat from the slab, equipment failure such as nozzle deformation will easily occur, and there is a concern that the slab may hit the nozzle slab due to bulging of the slab. In addition, the flow rate of the spray decreases, the cooling ability decreases, and depending on the roll pitch, the roll and the nozzle interfere with each other. Further, the gap (slit short side length) of the slit 2 is preferably in the range of 1 to 5 mm.

Further, a slit nozzle mounted with a slit shielding plate 3 slidably engaged with the slit 2 and driven by the moving device 4 to slide and slide while blocking the slit 2 from both ends of the slab 10 in the width direction. Since it is set to 1, it is possible to continuously change the width cutting amount without complicated control, and it is possible to faithfully cope with the optimum width cutting amount for every 10 widths of the slab, and the method (4) has a disadvantage. do not do.

The moving device 4 may be a hydraulic cylinder, an air cylinder, a hydraulic motor, an electric motor, or the like. Also, since it is not necessary to increase the amount of air in order to narrow the spray width, the method (2) does not have the disadvantages and is advantageous in terms of operating costs. Since the width end of the slit 2 is only shielded and the width end of the slab 10 is not directly shut off, the cooling of this portion can be controlled appropriately, and the disadvantage of the method (3) can be compensated.

FIGS. 2A and 2B show the surface temperature distribution in the slab width direction after the secondary cooling. FIG. 2A shows the present invention, and FIG. 2B shows the conventional one. As shown in the figure, in the case where the conventional width cutting is not performed, the temperature drop near the corner is large, and the corner crack easily occurs at the correction point. In order to improve this, if the area near the corner is waterproofed with a baffle plate as in the above-mentioned conventional method (3), cooling near the corner is excessively suppressed, and a high temperature section about 100 ° C. higher than the center side is formed, delaying solidification. Along with
Corner key cracking and surface flaws near the corner are likely to occur. In contrast, according to the present invention, the temperature difference from the center side is reduced to 50 ° C. or less, and the temperature difference near the corner is also 10%.
Since the temperature falls within 0 ° C., such a problem can be prevented.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous casting machine having a secondary cooling device (slit gap 2.5 mm) shown in FIG.
For 40 medium carbon steel slabs with more than 08 wt% and less than 0.2 wt%, the occurrence rate of corner cracks (corner key cracks + surface flaws near the corners) ((number of occurrences / total number of sheets) x 100%) was investigated. According to the method (3), baffle plate installation), the occurrence rate was reduced from about 10% to 2.5%, and the effect of the present invention was recognized.

[0016]

[Table 1]

[0017]

According to the present invention, the following various effects can be obtained in the continuous casting operation. (1) Since a slit nozzle having a slit (spray port) extending across both ends of the slab width, which is the maximum casting width, is used, the number of spray ports is one per width direction, and there is no spray wrap, and the spray nozzle is uniform within the spray width. Water volume distribution is obtained. (2) The spray distance is limited to a narrow range of 50 to 200 mm, so the mist flow rate is slightly attenuated and the cooling capacity does not decrease. (3) Since the slit nozzle is equipped with a slit shielding plate that can move while blocking the slit in the width direction from both ends of the slab, the optimum width cutting amount for each slab width can be achieved without complicated control. Can respond faithfully. (4) Since only the width end of the slit is shielded and the slab width end is not directly waterproofed, it is possible to obtain an appropriate width direction temperature distribution without excessively suppressing cooling of this portion, Corner slab cracks and surface defects near corners are reduced. (5) There is no need to increase the amount of air in order to narrow the spray width, which is advantageous in terms of operating costs.

[Brief description of the drawings]

FIG. 1A is a front view showing one example of the present invention, FIG.
(C) is a sectional view taken along the line II ′ and a line II-II ′ of (a).

FIGS. 2A and 2B are surface temperature distribution diagrams of a slab after secondary cooling, in which FIG. 2A shows the present invention, and FIG.

[Explanation of symbols]

 Reference Signs List 1 slit nozzle 2 slit (spray port) 3 slit shield plate 4 moving device 5 mixer 6 mist 7 orifice 10 cast slab

Claims (1)

[Claims] In a secondary cooling device for a continuous cast slab, a slit extending over both ends of a slab having a maximum casting width is provided as a spray port, and the slit is moved from both ends of the slab in the width direction while shielding the slit. A secondary cooling device for continuously cast slabs, wherein a slit nozzle equipped with a slit shield plate capable of being installed is provided with a distance from the slab surface to the spray port of 50 to 200 mm.