JP2010125455A - Continuous casting method for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method for steel wherein the parting of a liquid seal is not caused by pressing force applied to a nozzle joint, and air suction from the nozzle joint is surely prevented over a long period. <P>SOLUTION: The continuous casting method for steel is performed using continuous casting equipment where a nozzle joint is sealed by a liquid seal material 10 held between double refractory packing materials 11, 12. The respective packing materials 11, 12 are made thin at the side in contact with the liquid seal material 10 in a state where pressing force is not applied, and are made thick at the side opposite thereto, and, the thickness d<SB>0</SB>in the solidified state of the liquid seal material is controlled to 1 to 8 mm, and its width w<SB>0</SB>is controlled to ≥3 mm, thus, when pressing force is applied to the nozzle joint and the respective refractory packing materials 11, 12 are flatly crushed, the partition of the liquid seal material 10 is prevented, and, while securing the seal of the nozzle joint, the molten metal is poured to a mold. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steel continuous casting method performed using a continuous casting facility in which a nozzle joint portion is sealed with a liquid sealing material.

  As is well known, continuous casting of steel is performed while pouring molten steel from a ladle into a tundish through a nozzle, and further pouring the molten steel from a tundish into a mold through an immersion nozzle. These nozzles are made of refractory, and the ladle and tundish are all made of refractory, so it is not easy to completely seal the joint between the nozzle and the ladle or tundish (nozzle joint). . For this reason, oxygen infiltrates into the molten steel due to the suction of the air from the nozzle joint, which may cause product defects such as alumina clusters and operation troubles such as nozzle clogging.

  For this reason, conventionally, a method (Patent Document 1) is used in which a nozzle joint portion is sealed using a fireproof packing material obtained by kneading a fireproof powder mainly composed of alumina with a thermosetting resin. However, the sealing performance is still insufficient, and it is unavoidable that an inert gas such as argon is blown into the nozzle, and alumina clusters generated by oxygen that has entered the molten steel are floated and separated together with argon bubbles. The cost increases depending on the flow rate of the active gas.

  Therefore, as shown in Patent Document 2, the applicant has developed a technique for sealing the nozzle joint with a liquid sealing material made of liquid metal. For example, an Al alloy is used as the liquid sealing material. Such a liquid sealing material is held between the inner and outer double refractory packing materials and is a metal ring at room temperature, but melts and liquefies in use, and can reliably seal the nozzle joint. It is.

However, when such a liquid sealing material is used, the inner and outer double refractory packing material surrounding the liquid sealing material may be deformed by the pressing force applied to the nozzle joint. It has been found that there is a possibility that the liquid seal may be broken by covering the liquid seal material. If such a state occurs, the function of the liquid seal is lost, and the seal is made only with the refractory packing material.
Japanese Patent Publication No. 60-15592 JP 2007-69254 A

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems, and there is no breakage of the liquid seal due to the pressing force applied to the nozzle joint, and it is possible to reliably prevent the suction of air from the nozzle joint over a long period of time. It is to provide a continuous casting method.

The present invention made to solve the above-mentioned problems is a continuous casting of steel performed using a continuous casting facility in which a nozzle joint portion is sealed by a liquid sealing material held between inner and outer double refractory packing materials. In the method, the thickness of each refractory packing material is thin on the side in contact with the liquid seal material when no pressing force is applied, and thick on the opposite side, and the thickness d ₀ in the solidified state of the liquid seal material is set to 1. 〜8mm, width w ₀ is 3mm or more, and by applying a pressing force to the nozzle joint, each fireproof packing material is crushed flat to inject the molten metal into the mold while ensuring the seal of the nozzle joint with the liquid sealant It is characterized by doing.

Incidentally, as claimed in claim 2, the thickness of the side in contact with the liquid sealing material of the refractory packing material and (0.7 to 1.0) d _0, the opposite side thickness (1.1-1. 5) it is preferable that the d _0. Further, as in claim 3, it is preferable that the radial width of each refractory packing material is 10 mm or more.

  Further, as in claim 4, the pressing force applied to the nozzle joint is preferably 0.2 to 1.5 MPa, and as in claim 5, the flow rate of the inert gas blown into the nozzle is 1 ton of molten steel. It is preferable to set it to (0-1) NL. As in the sixth aspect, liquid metal or non-metallic melt can be used as the liquid sealing material.

  In the present invention, as the fireproof packing material that surrounds both the inside and outside of the liquid seal material, a material that is thin on the side in contact with the liquid seal material and thick on the opposite side is used when no pressing force is applied. This refractory packing material is also flattened by the pressing force in use, but the compression density is lower on the side in contact with the liquid seal material than on the opposite side, so the amount of deformation is small in the region in contact with the liquid seal material. Thus, deformation that covers the liquid sealing material does not occur. For this reason, it is possible to inject molten metal into the mold while ensuring the seal of the nozzle joint with the liquid seal material, and effectively prevent product defects and operational troubles due to air suction from the nozzle joint. it can. Therefore, the flow rate of the inert gas blown into the nozzle can be reduced to (0 to 1) NL per ton of molten steel, and the production cost can be reduced.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a cross-sectional view of a continuous casting facility used in an embodiment of the present invention, wherein 1 is a ladle for conveying molten steel, 2 is a tundish, and 3 is a casting mold for continuous casting. Molten steel is poured into the tundish 2 through the sliding nozzle 4 and the long nozzle 5 provided at the bottom of the ladle 1, and the mold is further formed through the sliding nozzle 6 and the immersion nozzle 7 provided at the bottom of the tundish 2. 3 is poured.

  The upper ends of these long nozzles 5 and immersion nozzles 7 are nozzle joints pressed against the lower plates of the sliding nozzle 4 and the sliding nozzle 6, and the sealing means shown in FIG. 2 is provided at these portions.

In FIG. 2, 10 is a liquid sealing material, 11 is an outer fireproof packing material, and 12 is an inner fireproof packing material. Each of these has a ring shape surrounding a circular hole in the center of the nozzle, and has a structure in which both the inner and outer sides of the liquid sealing material 10 are surrounded by fireproof packing materials 11 and 12. The refractory packing materials 11 and 12 are made of, for example, a material in which alumina powder is kneaded with a thermosetting resin such as an acrylic resin or a phenol resin. The liquid sealing material 10 is made of a liquid metal or non-metal melt that is solid at room temperature but melts and liquefies in use. The liquid metal is preferably Al, Al alloy, Sn, or Sn alloy, and the nonmetallic melt is, for example, a metal oxide such as CaO, SiO ₂ or PbO, or a metal fluoride such as CaF ₂ or PbF _2. The low melting point compound used for the raw material can be used.

FIG. 3 is an enlarged cross-sectional view showing the main part of the present invention, and shows an initial state in which the pressing force is not applied to the portion marked with a circle in FIG. As shown in this figure, when the thickness of the liquid sealing material 10 in the solidified state is d ₀ and the width is w ₀ , d ₀ is preferably ₁ to 8 mm and w ₀ is preferably 3 mm or more. If d ₀ is thinner than this range, the sealing effect will be insufficient, and if it is thicker than this range, the liquid sealing material 10 may leak out. If w ₀ is less than 3 mm, the sealing effect is still insufficient.

In the present invention, as the refractory packing materials 11 and 12 surrounding both the inside and outside of the liquid sealing material 10, those having a shape whose upper surface is inclined as shown in FIG. 3 are used. Specifically, the thicknesses d ₁ and d ₃ of the refractory packing materials 11 and 12 in contact with the liquid sealing material 10 in the initial state where no pressing force is applied are set to (0.7 to 1.0) d _0. The thicknesses d ₂ and d ₄ on the opposite side are (1.1 to 1.5) d ₀ . As described above, when the fire-resistant packing materials 11 and 12 having a thin thickness on the side in contact with the liquid sealing material 10 and having a thick thickness on the opposite side are used, the fire resistance in the usage state with the pressing force shown in FIG. The packing materials 11 and 12 are mainly compressed strongly in the region far from the liquid sealing material 10, and the compression force is weak in the region close to the liquid sealing material 10, so that the packing materials 11 and 12 are covered on the liquid sealing material 10. No deformation occurs.

When d ₁ and d ₃ are smaller than (0.7 to 1.0) d ₀ , the ability to hold the liquid sealing material 10 so as not to leak out in use is reduced, and conversely exceeds this range. If it becomes larger, sealing is performed only by the fireproof packing materials 11 and 12, and the meaning of providing the liquid sealing material 10 decreases. When d ₂ and d ₄ are smaller than (1.1 to 1.5) d ₀ , the effect of inclining the upper surface is reduced. Conversely, when d ₂ and d ₄ are larger than this range, the liquid of the refractory packing materials 11 and 12 is reduced. Sealing is performed only by a region far from the sealing material 10, and the meaning of providing the liquid sealing material 10 is reduced.

The radial widths w ₁ and w ₂ of the fireproof packing materials 11 and 12 are preferably 10 mm or more. This is because it is difficult to obtain a sufficient sealing effect when the width is less than 10 mm. In addition, a pressing force is mechanically applied to the nozzle joint, and the pressing force is preferably in a range where the surface pressure is 0.2 to 1.5 MPa. When using the fireproof packing materials 11 and 12 in which the alumina powder as described above is kneaded with a thermosetting resin such as an acrylic resin or a phenol resin, if it is less than this range, it is difficult to obtain a sufficient sealing effect. If this range is exceeded, deformation of the refractory packing materials 11 and 12 may increase and the liquid sealing material 10 may leak out. The upper limit of w ₀ , w ₁ , w ₂ is not specified as an effective upper limit, but is limited by the packing material and the sealing material installation space at the nozzle joint, and w ₀ , w ₁ , w ₂ are It is preferable to arrange so as not to deviate from the respective lower limits.

  If the nozzle joint is sealed with the sealing material having the structure shown in FIG. 3 as described above, there is no possibility that the fireproof packing materials 11 and 12 are covered with the liquid sealing material 10, and the liquid sealing Since the material 10 is not divided, stable liquid sealing is always possible. As a result, there is no air suction from the nozzle joint, and even if the flow rate of argon gas blown into the immersion nozzle 7 is reduced to (0-1) NL per ton of molten steel, it is caused by air suction. Product defects and operational troubles can be effectively prevented. Therefore, according to the present invention, it is possible to reduce the production cost.

Hereinafter, the present invention will be described in detail based on examples.
300 tons of extremely low carbon steel was melted in the converter-RH process. The molten steel in the tundish is set to 1560 to 1580 ° C., and the molten steel is injected into the mold using a three-layer sliding nozzle and an immersion nozzle, and a cast piece having a thickness of 250 mm and a width of 1200 to 1600 mm is cast at a casting speed of 1.6 to Manufactured at 2.0 m / min. The manufactured slab was cut by changing the sealing conditions of the nozzle joints in various ways, and the number of bubbles contained in the interior, the state of fragmentation of the sealing material, and the state of nozzle clogging were observed. As sealing conditions, the thickness, width, composition, and pressing surface pressure of the sealing material were changed as shown in Tables 1 and 2. The argon flow rate was also changed.

The meaning of * in the table is as follows.
* 1 All the symbols in the table indicate the height shown in Fig. 3 or the width in the circumferential direction.
* 2 ○: d1 <d2 and d3 <d4, within the scope of the present invention, x: d1 ≧ d2 or d3 ≧ d4, d1 ≧ d2 and d3 ≧ d4, outside the scope of the present invention.
* 3 All are%.
* 4 Ar gas was used as the inert gas. Ar gas was blown from the sliding nozzle plate part or the immersion nozzle part.
* 5 When the sealing surface is soundly held in the circumferential direction when the joint surface is viewed from above after casting, `` Without sealing material splitting ○ '', and the fireproof packing material is 20% in area ratio on the liquid sealing material. A case where the covering was less than% was marked as “slightly with sealing material splitting Δ”, and a case where the covering was 20% or more was marked as “with sealing material splitting ×”.
* 6 When the joint surface is viewed from the top after casting, the residual ratio of the sealing material is an area ratio of “90% or more ○”, “70 to 90% Δ”, and “<70% less than ×”.
* 7 The cumulative number of bubbles per 1m2 observed when grinding the slab surface layer 10-60mm at 5mm pitch.
* 8 “No nozzle occlusion” when no oxygen cleaning work was performed to remove deposits inside the nozzle by 7 continuous casting, “No nozzle occlusion △” when oxygen cleaning work was performed once. The case where it was carried out twice or more was designated as “No nozzle clogged”.

It is sectional drawing of the continuous casting installation used for embodiment of this invention. It is the horizontal sectional view and center longitudinal cross-sectional view of a nozzle junction part. It is an expanded sectional view of the principal part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ladle 2 Tundish 3 Mold 4 Sliding nozzle 5 Long nozzle 6 Sliding nozzle 7 Immersion nozzle 10 Liquid seal material 11 Fireproof packing material 12 on the outside 12 Fireproof packing material on the inside

Claims (6)

In the continuous casting method of steel performed using a continuous casting facility in which the nozzle joint is sealed with a liquid sealing material held between the inner and outer double refractory packing materials, the thickness of each refractory packing material is pressed thin on the side in contact with the liquid seal material in a state that is not applied, and leave thicker at the opposite side, the thickness d ₀ of the solidification state of the liquid seal material 1 to 8 mm, the width w ₀ and more than 3 mm, the nozzle connection part A continuous casting method of steel characterized by injecting molten metal into a mold while securing a seal at a nozzle joint by a liquid seal material by flatly crushing each refractory packing material by applying a pressing force to the mold. The thickness of the side in contact with the liquid sealing material of the refractory packing material and (0.7~1.0) d _0, to the thickness of the side opposite to the (1.1 to 1.5) d ₀ The continuous casting method for steel according to claim 1, wherein the steel is continuously cast.   The continuous casting method for steel according to claim 1 or 2, wherein the width in the radial direction of each refractory packing material is 10 mm or more.   The method for continuously casting steel according to any one of claims 1 to 3, wherein the pressing force applied to the nozzle joint is 0.2 to 1.5 MPa.   The continuous casting method for steel according to any one of claims 1 to 4, wherein the flow rate of the inert gas blown into the nozzle is (0 to 1) NL per ton of molten steel.   6. The continuous casting method of steel according to claim 1, wherein a liquid metal or a non-metallic melt is used as the liquid sealing material.

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