JPS623711B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for secondary cooling of slabs in continuous casting equipment. In recent years, in order to improve the quality of slabs or perform direct rolling, the soft cleaning method, in which a mixture of steam and water is evenly sprayed over the entire area of slabs in the secondary cooling zone, is used to perform soft cooling. It is considered that a method can be adopted. However, in conventional continuous casting equipment, cooling water is simply supplied to a large number of air mist nozzles for secondary cooling of slabs, so the amount of water from the lower air mist nozzles is lower than that from the upper air mist nozzles. The spray is stronger due to the water head pressure, and it is not possible to evenly soft clean the slab over the entire secondary cooling area. Therefore, the present invention proposes a secondary cooling method for slabs that can evenly soft-clean the slab over the entire secondary cooling area. Hereinafter, one embodiment of the present invention will be described based on the drawings. 1 is a mold, and 2 is a conveyance path for the slab 3 pulled out from the mold 1. The circular arc portion of this path 2, which is curved with a radius of curvature R, is connected to support roll segments 4 and No. 1 to No. 1 in order from the top. .6 guide roll segments _A1 to _A6 . Each of the guide roll segments A ₁ to _{A 6} includes a pair of frames 5 and 6 and a slab supporting roll 7 that is rotatably supported by each of the frames 5 and 6. , the appropriate one is the drive roll. Reference numeral 8 denotes an air mist nozzle with a spray nozzle portion 9 at the tip thereof inserted between the rolls 7 and facing the slab 3, and has a steam/water mixing pipe 10 and an air supply pipe 11. Reference numeral 12 denotes an air chip disposed within the air supply pipe 11, which has an air throttle hole 13. Reference numeral 14 denotes a water tip disposed within the air/water mixing pipe 10, which has a water throttle hole 15. 16 has a proximal end fixed to the water tip 14 and a distal end connected to the nozzle part 9 inside the air/water mixing pipe 10.
It is a guide tube that extends to the vicinity. In this embodiment, the segments A ₁ to _{A 2} of No. 1 to No. 6 are divided into three groups, and the No. 1 segment A ₁ is divided into the first groups B ₁ , No. 2, and No. 3. Segment A ₂ , A ₃
2nd group B ₂ , No. 4 to No. 6 segment A ₄
- A ₆ are set as a third group B ₃ , and each group B ₁ 3 B ₃ is provided with a water supply main pipe 17, respectively, and is configured to control the amount of water in each group. In the first group B ₁ , the water main pipe 17 and the air/water mixing pipe 10 of each air mist nozzle 8 are connected via a branch pipe 18, and in the second group B ₂ and the third group B ₃ , the water main pipe 17 A main pipe 19 for each segment A ₂ to _{A 6} is connected to the main pipe 19 , and an air-water mixing pipe 10 of each air mist nozzle 8 is connected to the main pipe 19 via a branch pipe 18 . 20 is a water flow control valve. Here, due to the nozzle arrangement, each group
While the nozzle back pressures within B ₁ , B ₂ , and B ₃ become larger toward the downstream side due to the water head difference, the amount of water is only controlled by the control valve 20 on a group-by-group basis. Therefore, the amount of water per nozzle is larger on the downstream side than on the upstream side, and the difference is more significant in groups with a larger water head difference. In order to reduce the influence of this water head difference, it is conceivable to change the diameter of the water throttle hole 15 so that the diameter of the throttle hole becomes smaller toward the downstream side. However, depending on the water flow conditions, the diameter of the aperture becomes quite small, resulting in clogging of the holes due to impurities (dirt) contained in the water. Therefore, in this embodiment, the diameter of the air throttle hole 13 of the air chip 12 is changed for each segment within a group, and the diameter of the air throttle hole 13 of the air chip 12 is made smaller as the segment is located on the upstream side. This takes advantage of the characteristic of air mist nozzles that even if the water pressure is the same, the larger the amount of air, the smaller the amount of water. For example, regarding the second group _B2 , the air throttle holes 13 of each air chip 12 of No. 2 segment _A2
caliber D of No. 3 segment A ₃ each air tip 1
The diameter D of the air throttle hole 13 is set smaller than the diameter D of the air throttle hole 13 of No. 2. Therefore, even though the head pressure of each air mist nozzle 8 of No. 2 segment A ₂ is smaller than that of each air mist nozzle 8 of No. 3 segment A ₃ , No. 2 segment A ₂ and No. 3 segment A ₃
The amount of the air-water mixture sprayed from each air mist nozzle 8 in the above is approximately equal. Similarly, in the third group _B3 , each segment _A4 to _A6
The aperture D of the air throttle hole 13 is set to be smaller toward the top. In FIG. 2, only the roll 7 and the air mist nozzle 8 on the front edge side of the slab 3 are shown. Next, the experimental results of the example will be explained using the second group and the third group as examples. First, the second
For group B ₂ , the diameter D of the air throttle hole 13 of each air chip 12 of No. 2 segment A ₂ is 3.7φ.
mm, when the diameter D of the air throttle hole 13 of each air chip 12 of No. 3 segment A ₃ is 4.0φmm,
In the case where both apertures D are the same, the average spray amount QW per nozzle in the segment is as shown in Attached Table (1). In the attached table (1), for example, as shown in Cases 3 and 4, when the water head pressure is increased compared to Cases 1 and 2 and the water volume is increased, and the air pressure PL is set to 2Kg/cm ² , if the air restriction is the same, , the spray amount W in No. 2 segment A ₂ is 4.15/min, and the spray amount QW in No. 3 segment A ₃ is 4.5/min.
/min. Therefore, the amount of spray for both is 4.5.
A difference of -4.15=0.35/min has occurred. On the other hand, the diameter of the air throttle is 3.7φmm as mentioned above.
and 4.0φmm, the spray amount QW in No. 2 segment A ₂ is 4.5/min, and the spray amount QW in No. 3 segment A ₃ is also 4.5/min. Therefore, there is no difference in the amount of spray between the two. Furthermore, as for the third group _B3 , as shown in Attached Table (2), it can be seen that it is exactly the same as the case of the second group. Please note that the values in Attached Tables (1) and (2) below are estimated from experimentally measured nozzle characteristics.

【table】

【table】

[Table] Furthermore, the results of tests conducted by incorporating this example into a practical machine will be described below. The graph shown in FIG. 4 takes the third group B ₃ as an example, and the diameter D of the air throttle hole 13 of No. 4 segment A ₄ is 3.7φmm, the diameter D of the air throttle hole 13 of No. 5 segment A ₅ is 4.0φmm,
No. 6 Segment A ₆ is set to 4.2φmm, and the results of measuring the water amount per nozzle for the most upstream and downstream nozzles in the segment are shown, and the intermediate nozzle in the segment is omitted. According to this, when the air pressure is 2 kg/cm ² , graph A is,
The vertical change in the average water flow rate per nozzle of 1.5/min is ±16.7%, and when the water flow rate is increased at an air pressure of 2 kg/ ^cm2 , graph B shows that the vertical change in the average water flow rate per nozzle of 4.15/min is ±16.7%. The change is ±4.2%. That is, it can be seen that there is almost no difference within the third group _B3 and the results are averaged. Note that the difference within a segment is caused by a difference in water head within the segment, and in this case, it can be similarly solved by making the D diameter of the orifice smaller towards the higher end within the segment. This allows for finer and more even spraying. In the above embodiment, the aperture D of each air chip 12 is made the same for each segment _A1 to _A6 , and the aperture D of each air chip 12 is made smaller as the segment goes higher to enable averaged spraying. Similarly, it was explained that more even spraying is possible by implementing the same principle within the segment, but also within each group B ₁ to B ₃ , for example,
D=3.7φ for B ₁ , D=4.0φ for B ₂ , D=4.2φ for B ₃
Needless to say, it can be implemented with the same gist. As described above, according to the method for secondary cooling of slabs in continuous casting equipment of the present invention, a large number of air nozzles for secondary cooling of slabs are divided into multiple groups along the slab conveying direction, and water is supplied to each group. Therefore, the head pressure of each group is almost the same. Furthermore, among the air mist nozzles in each group, the air aperture of the upper air mist nozzle is set to be smaller than that of the lower air mist nozzle, so that the balance between water and air can be maintained. From this, the amount of cooling water supplied to this upper air mist nozzle increases. Therefore, even though the head pressure of the upper air mist nozzle is smaller than that of the lower air mist nozzle, the amounts of spray from both nozzles are approximately equal. As a result of the above, the amount of spray from all air mist nozzles is approximately equal, and the slab can be evenly soft-cleaned across the secondary cooling region, making it possible to provide high-quality slabs. Moreover, direct rolling can be performed in good condition.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Fig. 1 is a schematic side view of continuous casting equipment, Fig. 2 is a schematic side view of the main parts, and Fig. 3 is a partially cutaway front view of the air mist nozzle. The figure is a graph showing the amount of water per nozzle. 1... Mold, 2... Slab conveyance path, 3... Slab,
7...Roll, 8...Air mist nozzle, 13...Air throttle hole, 17...Water supply main pipe, 18...Branch pipe, 19...Main pipe, _A1 to _A6 ...Segment, _B1 to _B3 ...Group.

Claims (1)

[Claims] 1 A large number of air mist nozzles for secondary cooling of slabs are divided into multiple groups along the slab transport direction, water is supplied to each group, and the upper air mist nozzles in each appropriate group are A method for secondary cooling of slabs in continuous casting equipment, characterized in that the air aperture of a mist nozzle is set smaller than that of a lower air mist nozzle and spraying is carried out.