JP4600095B2 - Hot reuse of tundish - Google Patents

Description

  The present invention relates to a method of reusing a continuous casting tundish hot.

  In continuous casting, the molten steel contained in the ladle is once poured into the tundish, then the molten steel poured into the tundish is poured into the mold through a nozzle such as an immersion nozzle provided at the bottom of the tundish, and the slab Is manufacturing. Conventionally, the tundish was re-used after repairing the refractory etc. until the next casting after the residue remaining in the tundish was discharged every time the casting was finished and cooled. In the tundish used in this way, the tundish is reused while it is hot for the purpose of reducing the refractory cost and omitting the cold maintenance process.

  The point when the tundish is reused hot is to prevent the molten steel and steel rod remaining in the tundish from damaging the casting start work at the time of reuse. In other words, even if it is reused hot, the continuous casting machine requires casting preparation work such as charging dummy bars, so if it is several tens of minutes long before being reused from the previous use, There will be an interval of one hour or more. During this waiting time, the molten steel and steel slag remaining in the tundish solidified and solidified, and the molten steel outflow hole consisting of the immersion nozzle installed at the bottom of the tundish or the upper nozzle connected to the top of the immersion nozzle was blocked. In some cases, the molten steel cannot be injected and the tundish cannot be reused.

  Therefore, conventionally, in hot reuse of tundish, molten steel and steel slag remaining in the tundish are discharged as quickly as possible so that the bare metal is not attached to the immersion nozzle or the upper nozzle as much as possible. Things have been done. For example, Patent Document 1 discloses a heating means that discharges residual molten steel and steel slag immediately after use of the tundish, and then does not oxidize the attached metal in order to reuse the tundish hot. A method of using and heating a molten steel outflow hole from a tundish to a mold is disclosed. Here, the reason why the base metal is not oxidized is that when the attached base metal is oxidized, this oxide oxidizes the molten steel that has flowed into the tundish at the start of the next casting, and the oxide inclusions in the molten steel are removed. This is to prevent this from increasing and deteriorating the cleanliness of the molten steel.

  Moreover, in patent document 2, after reusing a tundish hot, after discharging the steel plate and molten steel which remain | survived in the tundish, the surface temperature of the metal | metal | money and the steel plate which adhered in the inert gas atmosphere A method of cooling and holding at a cooling rate of 5 to 10 ° C./min until the temperature reaches 1150 ° C. is disclosed. According to Patent Document 2, the surface temperature of the bullion and the steel plate is cooled to 1150 ° C. or less, thereby preventing the attached bullion from being oxidized.

Furthermore, Patent Document 3 discloses a flux for addition in a tundish that has a bulk specific gravity of 0.8 or less and is excellent in evacuation, as a flux that is added into a tundish that is reused hot. .
JP-A-8-257708 JP-A-9-76055 JP 2001-300703 A

  Thus, conventionally, when the tundish is reused hot, the molten steel and steel plate remaining in the tundish have been discharged as quickly as possible and as much as possible.

  However, the present inventors have found that this method is not necessarily accurate. In other words, the residual molten steel and steel plate in the tundish have the function of maintaining the temperature of the tundish in a high temperature state, and by discharging these, the temperature of the tundish refractory decreases, and the molten steel at the start of the next casting It has been found that there is a possibility of lowering the temperature and promoting solidification of the molten steel at the molten steel outflow hole such as an immersion nozzle. Also, when casting a slab with a small cross section size, such as a bloom continuous caster, the inner diameter of the molten steel outflow hole such as an immersion nozzle is small, so when discharging the residual molten steel and steel slag in the tundish It has been found that the molten steel outflow hole may be blocked by the residual molten steel or steel plate.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tank that can smoothly perform casting start work at the time of reuse when the tundish is reused hot in a continuous casting process. It is to provide a method for hot reuse of dishes.

  The inventors of the present invention have conducted intensive studies and studies to solve the above problems. Therefore, first, it was decided to test and verify whether or not the casting at the time of reuse cannot be started unless the molten steel is completely discharged as in the prior art.

  The test method is as follows. That is, in the continuous casting process of the bloom slab, about 4 tons of molten steel and steel plate remaining in the tundish after the completion of the casting of the previous charge is left as it is, and at least 20 minutes have passed until the start of the next casting. This tundish was used for casting. As a result, contrary to the conventional concept, the knowledge that the molten steel in the tundish was kept in a molten state without solidifying even after a maximum of 2 hours had passed, was obtained. .

The present invention has been made on the basis of the above knowledge, and the hot reuse method of a tundish according to the first invention is a continuous casting process of steel, in which an appropriate amount of molten steel is left in the tundish and continuously. This is a hot reuse method of tundish, in which the molten steel remaining in the tundish is not discharged and the tundish is reused at the next continuous casting. With the molten steel of 10 tons or less remaining, the stopper attached to the tundish is closed to finish the continuous casting, and the tundish is moved to the standby position without discharging the molten steel remaining in the tundish. When the preparation for the next continuous casting is ready, the tundish is placed immediately above the mold, and the molten steel for the next continuous casting is poured into the tundish. Allowed to stay more than half of the molten steel tundish capacity in Interview, then, it is characterized in that to release the stopper to start injection of the molten steel into the mold.

The hot reuse method of a tundish according to the second invention is characterized in that, in the first invention, the continuous casting process is a continuous casting process for producing a bloom slab.

  According to the present invention, even when the inner diameter of the molten steel outflow hole from the tundish to the mold as in the continuous bloom caster is small, the tundish can be reused stably in the hot without causing the molten steel outflow hole to be blocked. This makes it possible not only to reduce the cost of tundish refractories and save labor in the cold maintenance work of the tundish, but also to cast the molten steel remaining in the tundish as a good slab. Industrially beneficial effects such as improving the yield of good cast slabs are brought about.

  Hereinafter, the present invention will be specifically described. In the present invention, in the continuous casting process of molten steel, the tundish that receives molten steel from the ladle and relays the received molten steel to the mold is reused hot. The injection from the tundish to the mold is completed with an appropriate amount of molten steel remaining therein, and the remaining molten steel is not discharged from the tundish, and this tundish is reused for the next casting opportunity.

  That is, in a continuous casting process immediately before reuse, with a predetermined amount of molten steel remaining in the tundish, the stopper or sliding nozzle attached to the tundish is closed to inject molten steel from the tundish to the mold. finish. When the injection of molten steel from the tundish to the mold is completed, the tundish is removed from the position directly above the mold and transported to the standby position. Normally, the tundish is loaded on a tundish car and is transported to a standby position while being loaded on the tundish car.

  The amount of molten steel remaining in the tundish is preferably 3 tons or more. If the amount of molten steel to be left is less than 3 tons, the heat capacity will be insufficient, and solidification of the molten steel will progress at the molten steel outflow hole from the tundish to the mold and the side wall of the tundish during standby, or casting will begin when reused Sometimes, the molten steel outflow hole is blocked by the metal or the solidified steel sheet, and cannot be reused stably. The upper limit of the amount of molten steel remaining in the tundish is not particularly limited because the next casting start operation becomes more stable as the amount of molten steel remaining in the tundish increases, but about 10 tons is sufficient. In particular, if the component range of the molten steel remaining in the tundish is different from the molten steel to be cast next time, that is, if the steel type is different, if a large amount of molten steel is left, the component mixing range will be widened, and the good cast slab yield will be improved. The upper limit is about 10 tons.

  In the tundish, usually, the molten steel is kept warm, and at the same time, a flux for absorbing oxide inclusions floating and separated from the molten steel is added, and this flux melts to form a steel plate. Of course, this steel is not discharged.

  Usually, the tundish is equipped with a lid, but the lid has an opening for receiving molten steel from the ladle or an opening for introducing a burner flame when heating the inside of the tundish. In order to prevent heat dissipation during standby from these openings, if the tundish is transported to the standby position, it is preferable to perform curing to close these openings with a refractory simple lid or the like.

  In addition, a bare metal may adhere to the immersion nozzle and the upper nozzle connected to the upper part of the immersion nozzle at the end of the previous casting, and this bare metal causes nozzle blockage at the start of the next casting. Therefore, it is preferable to remove this bullion during standby. As a method for cleaning the adhered metal, oxidation heat generated by oxygen gas can be used.

  Specifically, oxygen gas is blown as follows. Fig. 1 shows a schematic diagram when the control method for the flow rate of molten steel from the tundish to the mold is a stopper method. Fig. 2 shows the control method for the flow rate of molten steel from the tundish to the mold in combination with the stopper method and the sliding nozzle method. A schematic diagram of the case is shown. When the stopper method and the sliding nozzle method are used in combination, the flow control from the tundish to the mold is performed by the sliding nozzle, and the stopper has a function of flowing out and stopping the molten steel. That is, the stopper in the case of combined use performs two kinds of operations, full open and full close.

  In the case of the stopper method, oxygen gas is blown into the molten steel outflow hole 10 from the gas blowing passage 3 installed in the stopper 2 to the inside of the upper nozzle 4, that is, from the tundish to the mold. Moreover, it can blow in from the upper nozzle 4 by making the upper nozzle 4 into a porous brick. In the case of the combined use of the stopper method and the sliding nozzle method, the stopper 2 is fully closed, the sliding plate 12 is fully opened, and oxygen gas is blown into the upper nozzle 4, that is, the molten steel outflow hole 10. The upper nozzle 5 can be blown from the upper nozzle 5 by using porous brick. The deposited metal is oxidized by the blown oxygen gas, is heated and melted, and is removed. Here, in FIGS. 1 and 2, 1 is a tundish, 2 is a stopper, 3 is a gas blowing flow path, 4 is an upper nozzle, 5 is an upper nozzle, 6 is a sliding nozzle, 7 is an immersion nozzle, and 8 is a tundish. Refractory material, 9 is a tundish iron skin, 10 is a molten steel outflow hole from the tundish to the mold, 11 is a fixed plate, 12 is a sliding plate, 13 is a lower fixed plate, 14 is a rectifying nozzle, and the sliding nozzle 6 is The upper fixed plate 11, the sliding plate 12, the lower fixed plate 13, and the rectifying nozzle 14. In addition, when only the sliding nozzle method is used, the present inventors cause solidification of the molten steel inside the upper nozzle 5 during standby, and therefore, when the tundish is reused by applying the method of the present invention. It is confirmed that it is inappropriate.

  In this way, preparations are waited for until the next casting opportunity. During standby, there is no need to heat the inside of the tundish by a heating means such as a burner. However, the immersion nozzle 7 is preferably preheated separately by an immersion nozzle preheating device or the like, both when it is reused and when a new one is used. During the standby of the tundish, the continuous casting machine performs casting preparation work such as charging the dummy bar into the mold.

  When the casting preparation work is completed and the molten steel to be cast next time is prepared, first, the preheated immersion nozzle is attached to the bottom of the tundish, conveyed by the tundish car, and installed at the position directly above the mold. Next, the molten steel is poured from the ladle into the tundish, and when a predetermined amount of molten steel is poured into the tundish, the stopper 2 is opened (the sliding nozzle 6 is also opened in the case of combined use), and the tundish is moved to the mold. Start pouring molten steel. In this case, it is preferable to open the stopper 2 when molten steel having a half or more of the tundish capacity stays in the tundish by molten steel injected from a new ladle. For example, when 4 tons of molten steel is left in a 50-ton capacity tundish, the stopper 2 is opened after pouring 21 tons of molten steel from the pan into the tundish.

  Before pouring into the mold, the molten steel with a capacity of 1/2 or more of the tundish capacity is retained in the tundish, so that the previous steel type remaining in the tundish and the steel type to be cast this time are different. However, the mixing of the components is relaxed, the mixing range of the components is within the bottom crop, and the good slab yield is not reduced. Further, by retaining molten steel having a capacity of 1/2 or more of the tundish capacity in the tundish, the oxide inclusions contained in the molten steel are levitated and separated, and a clean slab can be obtained.

  The present invention is particularly effective when applied to a bloom continuous casting machine where the molten steel outflow hole has a small inner diameter and the molten steel outflow hole is likely to be blocked by a metal or a steel plate, but compared with the bloom continuous casting machine. The slab continuous casting machine with a large molten steel outflow hole also exhibits the same effect.

  As described above, according to the present invention, even when the molten steel outflow hole from the tundish to the mold as in the bloom continuous casting machine is small, the tundish is stably kept hot without causing the molten steel outflow hole to be blocked. Thus, the cost of the tundish refractory can be reduced and the labor saving of the tundish cold maintenance work can be achieved.

  Also, even when the tundish is not reused, in order to prevent the steel spill from flowing out of the tundish into the mold, the molten steel is usually left in the tundish and the casting is finished, and the present invention is applied. Thus, the remaining molten steel can be cast as a good slab, and the yield of good slab can be improved.

  The present invention was carried out when aluminum killed steel was cast in a bloom continuous casting machine in which the control method of the flow rate of molten steel from the tundish to the mold was a stopper method. The tundish capacity is about 30 tons.

  The stopper was closed leaving about 4 tons of pre-charged molten steel in the tundish, the tundish was moved to the standby position, and the immersion nozzle was removed at the standby position. During standby, oxygen gas was blown into the molten steel outflow hole from the tip of the stopper to wash the adhered metal, and the tundish opening was covered with a refractory lid to prevent heat dissipation. When the next casting was ready, an immersion nozzle preheated by a separate preheater was attached to the upper nozzle, and the tundish was conveyed and placed directly above the mold.

  And the molten steel in the ladle was poured into the tundish. When the amount of molten steel in the tundish reached 15 tons, the stopper was released, and molten steel was poured into the mold from the tundish to start continuous casting.

  As a result of reusing the tundish in this way, the casting success rate at the time of reuse reached 99%. Here, the casting success rate is a ratio at which the molten steel outflow hole is not blocked and started smoothly. In addition, the component mixing range was all within the bottom crop, and the amount of residual metal generated in the tundish could be reduced from 0.25% to 0.10%.

It is the schematic when the molten steel flow rate control system from a tundish to a mold is a stopper system. It is the schematic when the molten steel flow rate control system from a tundish to a mold is used together with a stopper system and a sliding nozzle system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tundish 2 Stopper 3 Gas injection flow path 4 Upper nozzle 5 Upper nozzle 6 Sliding nozzle 7 Immersion nozzle 10 Molten steel outflow hole

Claims (2)

In a continuous casting process of steel, and exit the continuous casting leaving a suitable amount of molten steel in the tundish, without discharging the molten steel was remaining in the tundish, to reuse the tundish during the next continuous casting, A method for hot reuse of tundish,
With 3 to 10 tons of molten steel remaining in the tundish, the stopper attached to the tundish is closed to finish the continuous casting, and the molten steel remaining in the tundish is not discharged and the tundish is discharged. When the next continuous casting is ready, place the tundish directly above the mold and inject the molten steel of the next continuous casting into the tundish. Of tundish, and then injecting the molten steel into the mold by releasing the stopper and starting the injection of the molten steel into the mold . The method for hot reuse of tundish according to claim 1, wherein the continuous casting process is a continuous casting process for producing a bloom slab.

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