JP4998712B2 - Cooling method for continuous cast slab - Google Patents

Description

  The present invention relates to a method for cooling a continuously cast steel slab, and more specifically, a slab installed to cool a slab cut by a gas cutter or the like after continuous casting to a predetermined temperature is put on standby. The present invention relates to a technique for efficiently cooling a slab without causing cracks in a cooling floor.

  A slab cast by a continuous casting machine and cut to a predetermined length by a gas cutting machine or the like is once cooled to a predetermined temperature or less for inspection or surface care. This cooling is usually performed in a cooling bed provided on the outlet side of the continuous casting machine. As such a cooling bed, for example, a roll conveyor (or chain conveyor) system described in Patent Document 1 or a walking beam system described in Patent Document 2 exists.

In any case, the slab cut to a predetermined length by a gas cutter or the like and conveyed to the cooling bed in the longitudinal direction of the slab by the transfer roll is the length of the slab in the cooling bed. It is configured to sequentially feed and cool in a direction orthogonal to the direction. The slab is cooled by water cooling or air cooling during this sequential feeding, and when it reaches the other end of the cooling bed, it is cooled to a predetermined temperature, for example, a temperature that can be magnetized by the lifting magnet, It is lifted and transferred to a freight car, a transport vehicle, or other transport means.
JP-A-6-9045 JP 2000-117408 A

  By the way, the above-mentioned cooling floor is usually designed and installed according to the production conditions and the target steel type assumed when the continuous casting machine is installed. In other words, the number of slabs carried into the cooling floor per unit time is determined by the slab drawing speed during continuous casting, and the cooling of the slab to a predetermined temperature is completed while the slab moves on the cooling floor. This is because the size of the cooling floor is automatically determined. Further, if the steel type is water-coolable, the cooling time can be shortened by installing a water spray on the cooling floor and water cooling, thereby compressing the size of the cooling floor.

  However, in a continuous casting facility once installed, the casting condition is often changed from the originally assumed condition. For example, in response to an increase in demand for steel materials, it is necessary to increase the slab drawing speed due to the need for increased production, or to newly cast a steel type that is not susceptible to cracking at the time of cooling. It is a case where it must be done.

  In such a case, conventionally, it was impossible to cope with other than expanding the cooling bed. In other words, if there was not enough room around the site of the continuous casting machine, it was impossible to cope with increased production and production of new steel grades.

  The present invention has been made in view of the above circumstances, and an object of the present invention is cooling installed to cool a continuous cast slab of steel cut by a gas cutter or the like after continuous casting to a predetermined temperature. In the floor, the steel slab can be cooled with significantly improved cooling efficiency compared to the conventional air cooling system, and even if it is a steel type with high crack sensitivity, it can be cooled without causing cracks, continuous It is to provide a method for cooling a cast slab.

The method for cooling a continuous cast slab according to the first aspect of the present invention for solving the above-mentioned problem is provided with a water spray nozzle when the continuously cast steel slab is on the cooling floor on the continuous casting machine outlet side. Spraying a mixture of water mist and air from the air cooling fan , evaporating the water mist in an air stream, and cooling the slab by air cooled by the latent heat of vaporization of the water mist. To do.

The cooling method of the continuous cast slab according to the second invention is characterized in that, in the first invention, an average particle diameter of water droplets sprayed from the water spray nozzle is 500 μm or less .

The method for cooling a continuous cast slab according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the slab is a 13% Cr steel slab .

  A method for cooling a continuous cast slab according to a fourth invention is characterized in that, in any one of the first to third inventions, the slab is a billet.

  According to a fifth aspect of the present invention, there is provided a cooling method for a continuously cast slab according to the fourth aspect, wherein the billet is a round billet.

  According to a sixth aspect of the present invention, there is provided the method for cooling a continuous cast slab according to the fourth or fifth aspect, wherein the mixture of water mist and air is sprayed when the billet is moved while moving the billet. And cooling.

  According to the present invention, since the continuous cast slab in the cooling floor is cooled by spraying a mixture of water mist and air, the slab can be cooled more quickly than conventional air cooling. In addition, since water droplets and water flow do not directly contact the slab, the slab is not locally cooled, and as a result, even in special steels such as 13% Cr steel with high crack sensitivity, cracks do not occur. Rapid cooling can be achieved. This makes it possible to increase the production of such cracked steel slabs with high cracking susceptibility even in a continuous casting factory where it is difficult to expand the cooling bed, and has an industrially beneficial effect.

  Hereinafter, the present invention will be specifically described.

  In the present invention, a hot slab, which has been cast by a continuous casting machine and then cut to a predetermined length by a gas cutting machine, a heat saw or the like, is cooled by a cooling bed installed on the outlet side of the continuous casting machine. When spraying, a mixture of water mist and air is sprayed on the cooling bed to cool the atmosphere (air) around the cooling bed, and the hot slab is cooled mainly by the temperature-decreased atmosphere. .

  As an apparatus for spraying a mixture of water mist and air, which is an important element in the present invention, a number of water spray nozzles for ejecting water mist are arranged around the air ejection side of a normal air cooling fan outer cylinder. Is preferred. In an air cooling fan (hereinafter also simply referred to as a “cooling fan”) provided with such a water spray nozzle, water mist evaporates in the airflow from the fan, and air jetted together with the water mist by the latent heat of evaporation at that time To be cooled.

  For this reason, compared with the conventional air cooling fan which can supply only the airflow of the same temperature as atmospheric temperature, a cooling capability becomes remarkably large. Moreover, since the water mist evaporates during the flight with the airflow, when the airflow reaches the slab surface, the water droplets have already disappeared and are not in direct contact with the slab, or even very small water drops The surface of the slab is not locally cooled by water droplets and is cooled almost uniformly, so that the generation of cracks due to cooling can be prevented.

  As the performance of the water spray nozzle to be provided, it is preferable that the average particle diameter of water droplets is 500 μm or less, more preferably 100 μm or less. If the average particle diameter of the water droplets exceeds 500 μm, the water droplets do not completely evaporate in the air stream, reach the slab surface, rapidly quench the slab locally, and generate cracks. There is no specific lower limit for the average particle size of the water droplets, but when using water that may contain foreign substances such as industrial water, in order to prevent clogging of the water spray nozzle, The water spray nozzle has an average particle size of 200 μm or more and 500 μm or less. If it is a water spray nozzle that generates such water droplets, foreign substances of a size contained in normal industrial water can pass through, and nozzle clogging does not occur. In addition, when using normal tap water (clean water), there is no problem even if a water spray nozzle having a lower limit of the average particle diameter of about 10 μm is used.

  In this case, the mixture of water mist and air may be sprayed from the side surface side of the cooling bed toward the slab moving on the cooling bed or directly above the slab, or cooling. Either spraying from above the floor toward the slab moving on the cooling floor may be used. However, since the reach of the airflow ejected from the cooling fan is quite wide, spraying from the side of the cooling floor toward the slab of the cooling floor is possible because the number of cooling fans can be reduced. It is preferable to do. The number of cooling fans installed may be determined according to desired cooling conditions.

  The continuous casting equipment which is the subject of the present invention is a continuous casting equipment configured to cool a continuously cast slab to a predetermined temperature in a cooling floor and then transfer it to the next process by a freight car or a transport vehicle. As long as it is, any continuous casting equipment may be used, and the present invention can be applied.

  In particular, when the present invention is applied when continuously casting a special steel, such as 13% Cr steel, which is susceptible to cracking when cooled with water, the cooling rate can be increased without causing cracking, and the effect is particularly remarkable. . In addition, when loading slabs on freight cars or transport vehicles, it is difficult to grasp because of its small size even if it is to be grasped with tongs, etc.For that reason, it is often lifted using a lifting magnet. Exhibits great effects in continuous casting equipment. When lifting a slab using a lifting magnet, if the slab temperature is high, it will not be magnetized and will not be able to be discharged from the cooling floor, so it must be cooled to at least the temperature range in which it is magnetized on the cooling floor. It is.

  Thus, according to the present invention, the slab on the cooling floor is cooled by spraying a mixture of water mist and air, so that the slab can be cooled much more quickly than conventional air cooling. In addition, since water droplets and water flow do not directly contact the slab, the slab is not locally cooled, and as a result, cracks occur even in special steels such as 13% Cr steel, which are highly susceptible to cracking. Rapid cooling can be achieved without.

  An example in which the present invention is applied to a cooling bed provided on the outlet side of a 6-strand continuous casting machine for producing a 13% Cr steel round billet will be described. FIG. 1 shows a schematic plan view of the construction of the billet continuous casting machine and the cooling bed.

  In FIG. 1, a billet continuous casting machine 1 includes a tundish 2, a guide roll band 3, a gas cutting machine 4, and a transport roller table 5, and 13% Cr steel held in a ladle 6 above the tundish 2. The molten steel (not shown) is poured into a mold (not shown) immediately below the tundish 2 and cooled by the mold to form a solidified shell. The solidified shell is used as an outer shell and the inside is used as an unsolidified phase. The slab is cooled by the secondary cooling water in the guide roll band 3 while being continuously drawn below the mold, and solidification to the inside is completed. Thereafter, the slab is cut into a predetermined length by the gas cutter 4 to manufacture the billet 11. The billet 11 cut to a predetermined length by the gas cutter 4 is transported by the transport roller table 5 and then introduced into the cooling bed 7 by the chain conveyor 7a that moves in a direction orthogonal to the transport roller table 5. The The chain conveyor 7 a is installed up to the tip of the cooling floor 7.

  In this case, the cooling floor 7 has a length of 60 m, and has a billet 11 corresponding to about one charge of the ladle, specifically, a length in which 150 billets 11 are arranged. The billet 11 is a chain conveyor 7a. Therefore, it moves to the carry-out side while rolling, that is, rolling. The unloading-side sorting skids 8 and 9 are each provided with a lifting magnet type crane, and the billet 11 is configured to be loaded on a transport vehicle (not shown) by the lifting magnet type crane.

  The surface temperature of the billet 11 when it was carried into the cooling bed 7 when a 13% Cr steel round billet having a diameter of 170 mm was continuously cast was 700 ° C.

  When the ambient temperature is 25 to 30 ° C., a cooling fan 10 that sprays a mixture of water mist and air on one side of the cooling floor 7 (longitudinal direction with respect to the billet 11) ((stock) 20) Ikeuchi manufactured: Cool Jetter) were arranged at equal intervals, and the billet 11 moving on the cooling floor 7 was cooled.

The number of water spray nozzles installed per cooling fan was 15, the amount of water was 18 L / min, and the average particle size of water mist was 260 μm. In addition, the diameter of the cooling fan was 370 mm, and the air flow rate was 75 m ³ / min. As a result of cooling under this condition, the surface temperature of the billet became 170 ° C. in 3 hours, and the billet was magnetized on the lifting magnet and could be carried out from the sorting skid 8 or the sorting skid 9.

  As a result, when the molten steel for one charge of the ladle is cast by billet continuous casting, the billet can be taken out from the cooling bed, and so-called “continuous casting” is possible in which the molten steel of the next charge is continuously cast. . The inventors have confirmed that the magnetization temperature of 13% Cr steel is 200 ° C. or lower, preferably 170 ° C. or lower.

  On the other hand, when the billet is cooled without using a cooling fan for comparison, when the billet for one charge of the ladle is lined up on the cooling floor (the billet at the start of casting reaches the carry-out side of the cooling floor) At the time of 3 hours from the start of casting, the billet surface temperature is still 218 ° C., not magnetized, and then allowed to cool for 1 hour 30 minutes, and finally the billet surface temperature reaches 170 ° C. Declined. Thereafter, the billet was transferred from the sorting skid to the transport vehicle by the lifting magnet. For this reason, continuous billet casting machines cannot be cast continuously, and casting of only one charge has been forced.

It is a schematic plan view of the structure of a billet continuous casting machine and a cooling bed.

Explanation of symbols

1 Billet Continuous Casting Machine 2 Tundish 3 Guide Roll Band 4 Gas Cutting Machine 5 Transport Roller Table 6 Ladle 7 Cooling Floor 7a Chain Conveyor 8 Sorting Skid 9 Sorting Skid 10 Cooling Fan 11 Billet

Claims (6)

When the continuously cast steel slab is on the cooling floor on the continuous caster exit side, a mixture of water mist and air is sprayed from an air cooling fan provided with a water spray nozzle, and the water mist is air-flowed. A method for cooling a continuous cast slab, characterized in that the slab is cooled by air evaporated in the air and cooled by the latent heat of evaporation of the water mist . The method for cooling a continuous cast slab according to claim 1, wherein an average particle diameter of water droplets sprayed from the water spray nozzle is 500 μm or less . The method for cooling a continuous cast slab according to claim 1 or 2, wherein the slab is a 13% Cr steel slab .   The method for cooling a continuous cast slab according to any one of claims 1 to 3, wherein the slab is a billet.   The said billet is a round billet, The cooling method of the continuous cast slab of Claim 4 characterized by the above-mentioned.   6. The continuous cast slab according to claim 4, wherein when the billet is rolled and transferred to the cooling bed, the mixture of water mist and air is sprayed and cooled. Cooling method.

Images