JP2009172675A - Method of sealing nozzle junction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nozzle junction-sealing method capable of performing sealing stably for a long period of time even relating to a nozzle junction, and surely preventing a product defect due to entrapment of air. <P>SOLUTION: The nozzle junction in a continuous casting equipment is sealed by a sealing material 13 composed of Sn or an Sn alloy which is melted in a using state to turn to a liquid metal. The width in a radical direction of the liquid metal is ≥3 mm and the thickness at an ordinary temperature is 1 to 8 mm. The nozzle junction is preferably pressurized in such a manner that the relationship between the pressing surface pressure P(MPa) and thickness (mm) at the ordinary temperature satisfies formula P≥ 1.12-0.11xd. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for sealing a nozzle joint in a steel continuous casting facility.

  In continuous casting of steel, molten steel in a ladle is poured into a tundish via a long nozzle and further poured into a mold via an immersion nozzle. These nozzles and the refractory directly above are joined by an irregular refractory or a flame retardant packing material to prevent molten steel leakage. However, since the solids are in contact with each other, it is difficult to completely prevent air from being entrained from the outside of the nozzle.

  That is, since molten steel flows inside the nozzle at a high speed, the inside is in a reduced pressure state, and if the seal at the nozzle joint is incomplete, air is easily caught. When air entrainment occurs, bubbles are mixed into the cast product, resulting in product defects, and problems such as product defects and nozzle clogging caused by alumina clusters generated by air oxidation may occur.

  Therefore, argon gas is supplied to the inside of the nozzle to maintain the inside of the nozzle at a positive pressure to prevent air entrainment and to peel off alumina clusters attached to the inner surface of the nozzle with argon gas. However, there is a risk that bubbles due to argon gas may be mixed in the steel, resulting in a product defect, and a large amount of expensive argon gas is used, resulting in high running costs.

  In order to solve the above problems, various methods for sealing the nozzle joint have been studied. For example, Patent Document 1 discloses a method in which oxygen mixed from outside air is fixed as an oxide by using a packing material in which a low melting point metal is contained in a refractory powder. However, only 0.5 to 20% by weight of low melting point metal particles are contained, and the path through which air passes through the inside of the packing material cannot be completely blocked, so that intrusion of air into the nozzle cannot be prevented. . Furthermore, since the particles are as fine as 1 to 3 mm or less, the remaining metal is reduced by the reaction with air, so that there is a problem that the oxygen absorption capacity is gradually lowered.

  Further, Patent Document 2 describes that a sealing material of a nozzle joint portion is improved by using a packing material made of a material that includes feldspar and sodium silicate and softens at a use temperature. However, when such a glassy packing material is used, if the nozzle is replaced during casting, a part of the softened packing material is likely to remain on the joint surface, and adhesion of the next mounted nozzle packing material is hindered. As a result, there is a problem that the sealing performance is lowered.

Further, Patent Document 3 discloses a method of sealing the nozzle joint with a liquid metal sealing material made of Al or an Al alloy. Since the melting point of Al is 660 ° C., a sufficient sealing effect is exhibited at the nozzle joint where the temperature is 700 ° C. or higher during the casting operation. However, in an actual casting facility, there is a nozzle joint having a temperature only reaching about 500 ° C., and thus there is a case where complete sealing cannot be performed by the sealing method of Patent Document 3.
Japanese Patent Publication No. 60-15592 Japanese Patent Laid-Open No. 2003-25060 JP 2007-69254 A

  The present invention solves the above-mentioned conventional problems, and even for nozzle joints having a temperature of only about 500 ° C., the nozzle joint can be stably sealed over a long period of time, and product defects due to air entrainment It is an object of the present invention to provide a method for sealing a nozzle joint that can reliably prevent the above.

  The present invention made to solve the above-described problems is characterized in that the nozzle joint portion in the continuous casting equipment for steel is sealed with Sn or Sn alloy that is melted in a use state to become a liquid metal. .

  In the present invention, as in claim 2, the radial width of the liquid metal is 3 mm or more, the thickness d at room temperature is 1 to 8 mm, the pressing surface pressure P (MPa) of the nozzle joint and the thickness d ( mm) is preferably pressurized so that the relationship of P ≧ 1.12-0.11 × d is satisfied.

  Further, as in claim 3, it is preferable to arrange two large and small refractory hollow disc packing materials having different diameters between the nozzle joint surfaces and hold the liquid metal in a space formed between them.

  As in claim 4, it is preferable to use a Sn—Pb alloy or a Sn—Zn alloy as the Sn alloy.

  Further, as in claim 5, a method of blowing an inert gas of 1 L or less per ton of molten steel into the nozzle and suppressing air entrainment from the nozzle joint can be used in combination.

  According to the present invention, since the nozzle joint is sealed with Sn or Sn alloy, Sn or Sn alloy is melted and liquefied even in the nozzle joint where the temperature reaches only about 500 ° C. For this reason, a stable seal is possible over a long period of time, and even when the nozzle is replaced, there is no possibility that the sealing property of the nozzle mounted next will be hindered and the sealing performance will deteriorate. In particular, a more complete seal can be achieved by pressurizing the nozzle joint so as to satisfy the conditions of claim 2.

Preferred embodiments of the present invention are shown below.
In FIG. 1, 1 is a ladle for conveying molten steel, 2 is a sliding nozzle provided on the bottom of the ladle 1, 3 is a long nozzle connected below the sliding nozzle 2, 4 is through a long nozzle 3 A tundish that receives the molten steel flowing down, 5 is a sliding nozzle provided on the bottom surface of the tundish 4, 6 is an immersion nozzle connected below the sliding nozzle 2, and 7 is a casting mold for continuous casting.

  As is well known, the sliding nozzles 2 and 5 have a three-plate structure of an upper plate, an intermediate plate, and a lower plate, and the long nozzle 3 and the immersion nozzle 6 are joined to the lower surface of the lower plate. The molten steel in the ladle 1 flows into the tundish 4 through the long nozzle 3 and is further supplied into the casting mold 7 through the immersion nozzle 6 so that continuous casting is performed as in the conventional case.

  FIG. 2 is an enlarged cross-sectional view of the nozzle joint, in which the nozzle joint between the upper end surface of the immersion nozzle 6 and the lower surface of the lower plate of the sliding nozzle 5 is shown. The joint between the sliding nozzle 2 and the sliding nozzle 2 has a similar structure.

  Inner and outer double annular packing materials 11 and 12 are arranged concentrically at the nozzle joint, and a seal material 13 made of Sn or Sn alloy is arranged between them. As the annular packing materials 11 and 12, an amorphous refractory or a flame retardant packing material, for example, alumina powder mixed with phenol resin or acrylic resin can be used.

  The sealing material 13 made of Sn or Sn alloy is melted in a use state to become a liquid metal. Since Sn has a melting point of 232 ° C., it melts into a liquid metal even when the temperature of the nozzle joint reaches only about 500 ° C., and can exhibit a sealing effect. However, if Sn—Pb alloy or Sn—Zn alloy is used, the melting point is further lowered. The melting point of Sn-10% Pb alloy is 217 ° C., the melting point of Sn-20% Pb alloy is 205 ° C., and Sn-30% Pb alloy. The melting point of 192 ° C., the melting point of Sn-10% Zn alloy is 217 ° C., and the melting point of Sn-20% Zn alloy is 220 ° C. Can be used.

  Regarding the size of the sealing material 13 made of Sn or an Sn alloy, the radial width is preferably 3 mm or more, and the thickness d at room temperature is preferably 1 to 8 mm. Since the outside air is entangled in the nozzle joint portion in the radial direction, the radial width is preferably 3 mm or more, and the maximum width is about 30 mm in order to prevent this. As a result of the experiment, the sealing effect was insufficient when the thickness d was less than 1 mm, and the sealing effect was lowered even when the thickness d exceeded 8 mm. In addition, it can be said that if the residual ratio after injection of molten steel of the sealing material 13 made of Sn or Sn alloy is 90% or more in the area ratio as viewed from the molten steel injection direction (upward direction), the almost perfect seal state is maintained. The number of bubbles in the slab is small. If the residual ratio is less than 90%, the number of bubbles in the slab increases due to air entrainment and nozzle clogging occurs, which is not preferable.

  In order to reliably prevent the outside air from being sucked, the nozzle joint is preferably used in a pressurized state. The pressing force can be easily applied by pressing the nozzle upward with a spring, for example. As a result of the experiment, the relationship between the pressing surface pressure P (MPa) of the nozzle joint and the thickness d (mm) of the sealing material 13 at room temperature satisfies the formula P ≧ 1.12-0.11 × d. It has been found that a complete sealing effect is exhibited by pressurizing the nozzle joint.

  FIG. 3 is a graph obtained as a result of an experiment in which the inside of the nozzle was depressurized to 0 atm, and the pressing surface pressure P of the nozzle joint and the thickness d of the seal material 13 were variously changed. Is in the range of 250-700 ° C. As shown in this graph, in the range where d is 1 to 8 mm and P ≧ 1.12−0.11 × d, complete sealing can be achieved even when the inside of the nozzle is decompressed. The upper limit of the pressing surface pressure P is determined by the strength of the nozzle material used and the structure of the nozzle support device. For example, in the case of alumina graphite, the bending strength at a joint temperature of 600 ° C. is 8 MPa, and the value taking into account the safety factor is the upper limit. If the safety factor is 0.5, the upper limit is 8 MPa × 0.5 = 4 MPa.

  As described above, according to the sealing method of the nozzle joint portion of the present invention, it is possible to effectively prevent the outside air from being entrained. It is also possible to use a method in which gas is blown and the air entrainment from the nozzle joint portion is more reliably suppressed. However, if the argon flow rate is increased, air entrainment can be prevented, but argon bubbles increase. Here, 1 L or less may be an amount corresponding to 1 L or less at room temperature and 1 atmosphere.

  In addition, if molten steel is used, which is deoxidized with Al and added with one or more rare earth elements (REM) of Ce, La, Pr, and Nd in an amount of 0.1 to less than 10 ppm, generation of alumina clusters is suppressed. Therefore, it is possible to more reliably prevent problems such as product defects and nozzle clogging caused by alumina clusters.

Examples of the present invention are shown below.
The sealing conditions of the nozzle joint in the molten steel continuous casting equipment were changed variously, and the cast slab was cut to observe the number of bubbles contained in the inside and the clogged state of the nozzle. As sealing conditions, the thickness, width, alloy composition, and pressing surface pressure of the Sn sealing material were changed as shown in Table 1, and the argon flow rate was also changed as shown in Table 1. In addition, the temperature of a nozzle junction part is 300 degreeC.

No. In Examples 1 to 15, the relationship between the pressing surface pressure P (MPa) of the nozzle joint and the thickness d (mm) of the sealing material 13 at room temperature satisfies the expression P ≧ 1.12−0.11 × d. The number of bubbles per 1 m ^{2 of} the slab cut surface is less than 500, which is significantly less than that of the comparative example, and is extremely effective against product defects. In contrast, no. In Comparative Examples 16 and later, the number of bubbles per 1 m ² of the slab cut surface was large, at least 680, and more than 1000, and the nozzle was clogged due to imperfect sealing.

On the other hand, in the method of sealing with a liquid metal sealing material made of Al or Al alloy disclosed in Patent Document 3, sealing is impossible. In addition, when a flame retardant packing material in which alumina powder was added to phenol resin was used, not only the number of bubbles was 500 / m ² or more, but also nozzle clogging occurred.

It is sectional drawing which shows the continuous casting equipment of steel. It is an expanded sectional view of a nozzle joined part. It is a graph which shows the influence which the pressing surface pressure P of a nozzle junction part and the thickness d of a sealing material have on the sealing performance under pressure reduction of 0 atm inside the nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ladle 2 Sliding nozzle 3 Long nozzle 4 Tundish 5 Sliding nozzle 6 Immersion nozzle 7 Mold for continuous casting 11 Annular packing material 12 Annular packing material 13 Sealing material

Claims (5)

  A method for sealing a nozzle joint, comprising: sealing a nozzle joint in a continuous casting facility of steel with Sn or an Sn alloy that melts in a use state to form a liquid metal.   The radial width of the liquid metal is 3 mm or more, the thickness d at room temperature is 1 to 8 mm, and the relationship between the pressing surface pressure P (MPa) of the nozzle joint and the thickness d (mm) at room temperature is P ≧ 1. 2. The method for sealing a nozzle joint according to claim 1, wherein the nozzle joint is pressurized so as to satisfy an expression of 12-0.11 * d.   The nozzle according to claim 1 or 2, wherein two or more refractory hollow disc-shaped packing materials having different diameters are arranged between the nozzle joining surfaces, and a liquid metal is held in a space formed between them. How to seal the joint.   The method for sealing a nozzle joint according to claim 1, wherein an Sn-Pb alloy or an Sn-Zn alloy is used as the Sn alloy.   The method for sealing a nozzle joint according to claim 1, wherein an inert gas of 1 L or less per ton of molten steel is blown into the nozzle to suppress air entrainment from the nozzle joint.

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