JP4705438B2 - Sealing method and structure of nozzle joint in continuous casting equipment for steel - Google Patents

Description

  The present invention relates to a method for sealing a nozzle joint in a continuous casting facility for steel and the structure of the seal.

  Conventionally, in continuous casting of steel, molten steel is continuously supplied into a mold by joining a ladle nozzle and a long nozzle, and a tundish lower nozzle and an immersion nozzle, respectively. The joint surfaces are joined by using an irregular refractory or a flame retardant packing material. However, since the solids are joined to each other, the problem is a decrease in airtightness due to a minute gap. Further, since molten steel flows inside the nozzle at a high speed, a negative pressure is generated and air is sucked from the nozzle joint surface. For this reason, problems such as product defects due to air bubbles mixed into the product, product defects due to alumina clusters generated by air oxidation, and nozzle clogging have occurred.

  In order to solve the above problem, a technique for improving the airtightness of the nozzle joint has been developed. The highly corrosion-resistant and air-tight packing material disclosed in Patent Document 1 contains a low-melting-point metal in a refractory powder, thereby fixing oxygen mixed from outside air as an oxide and preventing defects due to oxygen mixing. Yes. However, since the fixed oxygen forms an oxide film on the metal surface, there is a problem that the oxidation reaction rate is lowered and the oxygen absorption capacity is lowered.

  On the other hand, in the invention disclosed in Patent Document 2, the packing material contains a metal having a high binding force with oxygen and a vapor pressure of 1 atm or higher at the use temperature. In the present invention, since the metal vapor is continuously supplied, the stagnation of the reaction for fixing oxygen does not occur.

  However, in any case, oxygen contained by the inhalation of the atmosphere cannot be completely absorbed only by containing a metal as a part of the packing material. Further, since the packing material and the nozzle joint surface are in solid contact, it is impossible to prevent air from being sucked through a minute gap between the solids.

In the invention disclosed in Patent Document 3, the adhesion of the nozzle joint surface is improved by using a packing material that is softened at the operating temperature. However, in normal continuous casting of steel, the nozzle is replaced during casting, but a part of the softened packing material tends to remain on the joint surface of the tundish lower nozzle or the immersion nozzle. For this reason, adhesion of the packing material of the next mounted nozzle is hindered, and the sealing degree is lowered.
Japanese Patent Publication No. 60-15592 JP 2001-105107 A Japanese Patent Laid-Open No. 2003-25060

  An object of the present invention is to stably seal a nozzle joint surface for a long period of time and prevent product defects and operational troubles due to air suction.

In order to solve the above problems, the sealing method of the nozzle joint in the continuous casting equipment for steel according to the present invention is Al, which is liquid during casting and has a larger affinity for oxygen than iron in continuous casting of steel. Alternatively , the bonded portion of the nozzle is sealed with an Al alloy . Further , the sealing structure of the nozzle joint used in the nozzle joint sealing method is made of Al or Al alloy depending on the packing material made of an irregular refractory material or a flame retardant material and the nozzle itself to be joined. A structure having a structure for holding a liquid metal is used. More preferably, a seal structure for the joint portion is used, in which a concave portion is provided on the upper surface of the nozzle located below to fill the liquid. More preferably, a seal structure for the joint is used, in which a recess is provided on the lower surface of the nozzle positioned above and the liquid is filled.

In the present invention, the nozzle joint is sealed at the time of casting with Al or Al alloy, which is a metal having a larger affinity for oxygen than oxygen, so that a fine gap formed by joining solids is filled with the atmosphere. Can be completely prevented. In addition, since liquid metal is used, the sealing degree of the joint portion of the nozzle that remains on the joint surface when the nozzle is replaced and is subsequently mounted is not lowered. Furthermore, since it seals with Al or Al alloy, which is a metal having an affinity for oxygen greater than that of iron, it can fix the oxygen in the atmosphere that has penetrated to the outside of the liquid by the oxidation of the metal, and obtain a reliable sealing effect Can do. Therefore, it is possible to prevent product defects and operational troubles due to air suction, which can contribute to the improvement of productivity and quality. Moreover, since it can be operated without the addition of new equipment, the economic effect is great.

The present inventors have studied a method for improving the sealing performance of the nozzle joint, and have found that a method of sealing the nozzle joint with liquid metal is optimal. By using a liquid metal, it is possible to completely seal a minute gap at a joint portion between solids. Furthermore, since the reaction between the refractory constituting the nozzle does not occur, as possible out to maintain the sealing performance for a long time.

When a metal having an affinity for oxygen larger than iron is used as the liquid sealing material, it is more preferable because oxygen in the atmosphere that has penetrated to the outside of the liquid can be fixed by oxidation of the metal .

  Of the liquid sealing materials described above, Al or an Al alloy satisfies all the above conditions and is more suitable.

Further, when the nozzle joint is sealed with a liquid metal made of Al or an Al alloy, the liquid metal is removed by using a packing material made of a refractory raw material or an amorphous refractory and a structure that holds the liquid with an immersion nozzle. There is no need to install new equipment to keep it. For example, the weir 11 is installed on the periphery of the upper surface of the immersion nozzle indicated by 7 in FIG. By filling the space provided between the packing material indicated by 9 and the weir 11 with the liquid seal 10, it is possible to seal between the submerged nozzle and the tundish lower nozzle 4.

  Alternatively, the method shown in FIG. 3 can be used as a structure in which a liquid is held by a packing material made of an immersion nozzle and a refractory raw material or an amorphous refractory. That is, the liquid 10 can be filled and sealed between the refractory sealing materials 9a and 9b having a double circumferential structure in the same plane. Moreover, what knead | mixed the refractory raw material with the thermosetting resin can be used as a packing material. It has plasticity at room temperature and is compressed when a force is applied in the vertical direction to join the immersion nozzle to the lower tundish nozzle. At this time, the liquid sealing material stored in the gap of the packing is preferable because the gap is completely filled.

  Moreover, as shown in FIG. 4, the circumferential recessed part 12 can be provided in the joining surface of immersion nozzle upper part. When the volume of the liquid sealing material is excessive with respect to the volume of the gap in the packing, the liquid may overflow and the sealing performance may be reduced. By providing the recess, the amount of the liquid sealing material can be increased, and the sealing performance can be improved.

  Moreover, as shown in FIG. 5, the circumferential recessed part 12 can be provided in the joining surface of a tundish lower nozzle bottom part. When the volume of the liquid sealing material is excessive with respect to the volume of the gap of the packing, the liquid sealing material enters the concave portion at the upper portion, so that it is possible to prevent the liquid from overflowing and the sealing performance from being lowered.

  In addition, the joining method and the structure of the joining portion of the present invention are not limited to the joining portion between the tundish lower nozzle and the immersion nozzle, and all the fireproofs that require airtightness such as joining between the pan sliding nozzle and the long nozzle. It can be applied to the joining of objects.

In a continuous casting machine for steel composed of a combination of a tundish upper nozzle, sliding nozzle, tundish lower nozzle, and immersion nozzle, operation is performed using the joint between the tundish lower nozzle and immersion nozzle under the conditions shown in Table 1. It was. The casting speed was 1.7m / min, the casting width was 1200mm, the casting thickness was 248mm, and 1350 tons of molten steel was cast. The components of the molten steel are C = 20 ppm, Si = 0.01%, Mn = 0.2%, P = 0.02%, S = 0.01%, Al = 0.015%. In both Examples and Comparative Examples, Al ₂ O ₃ —SiO ₂ refractory powder kneaded with a thermosetting resin and molded was used as a packing material. In the comparative example, the packing material was used alone.

  In order to evaluate defects caused by atmospheric suction, the slab surface was stepped and the number of bubble defects was counted. The bubble defect here refers to a defect in which bubbles or inclusions are aggregated via bubbles among the defects observed by visual observation. Moreover, in order to quantify the amount of oxidation by the sucked air, changes in the Al concentration in the molten steel in the tundish delivery side and the mold were measured.

  In the example, it was possible to prevent air from being sucked by sealing between the tundish lower nozzle and the immersion nozzle with a liquid. As a result, neither bubble defects nor defects due to alumina clusters occurred. In addition, nozzle clogging did not occur.

  In Comparative Example 1, since casting was performed using only the packing material, air was sucked from the joint. As a result, bubble defects occurred on the slab surface. In addition, Al in the molten steel was oxidized, and the nozzles were blocked by alumina clusters.

  In Comparative Example 2, a packing material containing Al was used. As a result, the oxidation of Al in the molten steel did not occur due to the fixation of oxygen by Al. However, bubble defects occurred on the surface of the slab due to the suction of the atmosphere.

It is a schematic diagram of the ladle used for continuous casting, a long nozzle, a tundish, and an immersion nozzle. It is a longitudinal cross-sectional view of the junction part of the tundish lower nozzle for continuous casting of this invention, and an immersion nozzle. It is a junction part of the tundish lower nozzle for continuous casting of this invention, and an immersion nozzle, Comprising: It is a longitudinal cross-sectional view of the structure which combined the double cyclic | annular packing material and the liquid sealing material. FIG. 2 is a longitudinal sectional view of a structure of a junction between a tundish lower nozzle for continuous casting and an immersion nozzle according to the present invention, in which a double annular packing material and a liquid seal material are combined, and an annular recess is provided on the upper surface of the immersion nozzle. . FIG. 2 is a longitudinal sectional view of a structure in which a double-annular packing material and a liquid seal material are combined and an annular recess is provided on the lower surface of the tundish lower nozzle, which is a joint portion of the continuous casting tundish lower nozzle and the immersion nozzle of the present invention. It is.

1 Ladle 2 Sliding nozzle upper plate 3 Sliding nozzle middle plate 4 Sliding nozzle lower plate 5 Long nozzle 6 Tundish 7 Immersion nozzle 8 Mold 9 Packing material 9a Outer part of double annular packing material 9b Inner circumference of double annular packing material Part 10 Liquid sealing material 11 Weir 12 Circumferential recess

Claims (4)

In continuous casting of steel, the nozzle joint is sealed in a continuous casting equipment for steel, characterized in that the nozzle joint is sealed with Al or Al alloy which is liquid during casting and has an affinity for oxygen greater than that of iron. Method. A nozzle joint sealing structure used in the nozzle joint sealing method according to claim 1, wherein the packing material made of an irregular refractory material or a flame-retardant material and the nozzle to be joined itself are made of Al or A seal structure for a nozzle joint in a continuous casting equipment for steel, characterized by having a structure for holding a liquid metal made of an Al alloy. The sealing structure of the nozzle joint part in the continuous casting equipment for steel according to claim 2, wherein a concave part is provided on a joint surface of an upper part of the nozzle located below among the nozzles to be joined and filled with liquid metal. . 4. The nozzle joining portion in the continuous casting equipment for steel according to claim 2, wherein a concave portion is provided in a joining surface of a nozzle lower portion located above among nozzles to be joined, and liquid metal is filled therein. 5. Seal structure.

Images