JP5069592B2 - Immersion nozzle - Google Patents

Description

  The present invention relates to an immersion nozzle having a gas blowing function used for continuous casting of steel.

  In the continuous casting process that uses an immersion nozzle to inject steel from the tundish into the mold, non-metallic inclusions and solidification are formed on the inner wall surface of the immersion nozzle as the amount of aluminum added to the steel increases in recent years. It has been a problem that the deposited metal (hereinafter referred to as “inclusions”) adheres and grows to block the inner hole of the immersion nozzle.

  As a countermeasure against this, an air permeable inner hole body is disposed so as to face the inner hole of the immersion nozzle, a hollow chamber is formed on the outer peripheral side thereof, and the inert gas introduced into the hollow chamber is introduced from the inner hole body. A measure is taken to prevent adhesion of inclusions or the like to the wall surface of the inner hole by blowing out the hole to form an inert gas film.

  However, even if such a measure for blowing an inert gas into the inner hole is employed, the actual immersion nozzle has the following problems.

A part of the immersion nozzle that contacts the powder line in the mold is generally made of a refractory material (hereinafter referred to as “ZG material”) mainly composed of ZrO ₂ having excellent corrosion resistance against powder and graphite having excellent thermal shock resistance. ing. In recent years, increasing the need for additional multi-continuous casting (higher life of), ZrO ₂ in the refractory to accommodate it tends to use the ZG material of high ZrO ₂ content of about 90 wt%.

ZG material of high ZrO ₂ content is called interference is poor at the time of molding due to the low graphite, for example, apparent porosity, is about 14-18% in ZG material of low ZrO ₂ content of ZrO ₂ of about 82 wt% whereas, in the ZG material of high ZrO ₂ content of ZrO ₂ of about 90 wt% tends to the order of 18-22%, rough texture.

When the texture of the ZG material becomes coarse in this way, a large amount of the inert gas in the hollow chamber is dissipated not only from the inner hole side but also from the outer peripheral surface of the immersion nozzle. Actually, when manufacturing an immersion nozzle having a gas blowing function, the air flow rate is adjusted according to individual operations. In this case, generally, the overall air flow rate (the air flow rate on the inner hole side and the outer peripheral surface side) In the case of an immersion nozzle using a ZG material containing high ZrO ₂ , the ratio of the ventilation rate on the inner hole side to the total ventilation rate (hereinafter simply referred to as “inner hole ventilation rate”) .) Tends to be lower than the immersion nozzle using the ZG material containing low ZrO ₂ .

When such an immersion nozzle using a ZG material containing high ZrO ₂ is used for continuous casting of steel, the formation of an inert gas film on the wall surface of the inner hole becomes insufficient, and the effect of suppressing the adhesion of inclusions, etc. Cannot be obtained sufficiently, and the quality of the slab is reduced due to the inclusion of inclusions in the slab. Further, when the dissipation of the inert gas from the outer peripheral surface of the ZG material increases, the immersion nozzle, the molten steel, etc. are excessively cooled, and the fluctuation of the molten metal surface in the mold is likely to occur.

Furthermore, as the casting time becomes longer, the thickness of the ZG material becomes smaller due to, for example, being melted by the powder, and the dissipation of gas from the outer peripheral surface of the ZG material tends to further increase (this is because of hydrodynamics). Is also obvious.) This phenomenon occurs not only in the case of an immersion nozzle using a ZG material containing high ZrO ₂ but also in an immersion nozzle using a ZG material containing low ZrO ₂ .

  On the other hand, various attempts have been made to improve in order to blow inert gas uniformly or effectively from the inner hole of the immersion nozzle.

  For example, Patent Document 1 shows that the inner hole body is composed of a plurality of refractories having different air permeability in the direction toward the discharge hole of the immersion nozzle, and refractories having higher air permeability are sequentially arranged toward the discharge hole. Has been. This is intended to reduce the deposition rate of inclusions and the like on the entire inner wall surface of the immersion nozzle by blowing out the inert gas more intensively in the vicinity of the discharge holes where adhesion of the inclusions is large. .

However, although the measure of Patent Document 1 has a certain effect on the reduction of the adhesion rate of inclusions and the like, the dissipation of the inert gas from the outer peripheral surface of the immersion nozzle centering on the ZG material described above cannot be prevented.
Japanese Utility Model Publication No. 60-171652

  An object of the present invention is to suppress the dissipation of inert gas from the outer peripheral surface of the immersion nozzle in the immersion nozzle that blows out the inert gas into the inner hole that becomes the flow path of the molten steel, and inclusions on the wall surface of the inner hole, etc. It is to make it possible to reliably prevent the adhesion of water.

  The present invention is formed on an inner hole serving as a flow path of the molten steel from the tundish to the mold, a breathable inner hole disposed so as to face the inner hole, and an outer peripheral side of the inner hole. In an immersion nozzle that includes a hollow chamber and blows out an inert gas introduced into the hollow chamber from the inner hole body to the inner hole, at least a region corresponding to the powder line of the mold on the outer peripheral side wall surface of the hollow chamber This is characterized in that a flame-resistant fire-resistant layer having a lower air permeability than the refractory on the outer peripheral side is disposed.

Dissipation of the inert gas from the outer peripheral surface of the submerged nozzle occurs from a region corresponding to the powder line of the mold, that is, a region where a ZG material is generally used in the outer peripheral side wall surface of the hollow chamber. Among ZG material, dissipation of the inert gas from the immersion nozzle outer peripheral surface when the content of ZrO ₂ is using ZG material of high ZrO ₂ content exceeding 85 wt% is significant. Further, the amount of inert gas dissipated gradually increases due to a decrease in the thickness of the ZG material portion due to erosion outside the ZG material with the passage of use (casting) time. Although this phenomenon is remarkable when using the ZG material of high ZrO ₂ content of ZrO ₂ content exceeds 85 wt%, ZrO ₂ content occurs in ZG material of 85 wt% or less.

  Dissipation of the inert gas occurs outside the region where the ZG material is used, but generally the graphite content is higher than that of the ZG material, except in the region corresponding to the powder line where the ZG material is used. A large amount of about 30 to 40% by mass of alumina-graphite (hereinafter referred to as “AG material”) is used, and the air permeability of this AG material is much smaller than that of ZG material. In other words, since AG material emphasizes thermal shock resistance rather than corrosion resistance, it contains a larger amount of graphite than ZG material, and mainly contains alumina whose thermal expansion is smaller than that of zirconia. And the degree of inert gas dissipation is low. Therefore, the dissipation of the inert gas from the AG material portion is rarely an operational problem.

  For this reason, in the present invention, a flame-resistant fireproof layer is disposed at least in a region corresponding to the powder line of the mold on the outer peripheral side wall surface of the hollow chamber, and this flame-resistant fireproof layer is used to prevent the outer peripheral surface from being immersed from the outer circumferential surface of the immersion nozzle. The dissipation of active gas is suppressed.

  Here, in order to suppress the dissipation of the inert gas from the region corresponding to the powder line of the mold, the ventilation of the ZG material itself used in the region is reduced by reducing the size or amount of the through-holes. Even if the rate is lowered, as the thickness of the ZG material is gradually reduced by using the immersion nozzle as described above, the resistance of the inert gas passing through the ZG material is gradually reduced and the air flow rate is increased. It is insufficient as a means for suppressing dissipation of the inert gas from the outer peripheral surface of the immersion nozzle.

  On the other hand, in the present invention, since the non-breathable refractory layer is disposed on the outer peripheral side wall surface of the hollow chamber, the magnitude of the dissipation of the inert gas from the outer peripheral surface of the immersion nozzle is larger than the ventilation characteristics of the ZG material itself. Since it depends on the ventilation characteristics of the flame-resistant refractory layer, even if the thickness of the ZG material is gradually reduced due to melting damage, the dissipation of the inert gas from the outer peripheral surface of the immersion nozzle increases as the thickness decreases. This can be greatly suppressed.

  The air permeability of the flame-resistant fireproof layer needs to be lower than the air permeability of the refractory (generally ZG material) on the outer periphery side of the region where the flame-resistant fireproof layer is disposed. Otherwise, naturally, dissipation of the inert gas from the outer peripheral surface of the immersion nozzle cannot be suppressed.

The specific air permeability of the flame-resistant refractory layer is originally set individually according to the structure of each refractory part of the immersion nozzle, such as the thickness, length, diameter, etc., the air permeability of each constituent refractory, the operating conditions, etc. Should be of a relative nature. In particular, in order to suppress the increase in the dissipation of the inert gas from the outer peripheral surface of the immersion nozzle as the thickness of the ZG material decreases, the air permeability of the flame-resistant refractory layer is used for the immersion nozzle. What is necessary is just to be smaller than the air permeability of ZG material. However, in order to further reduce the absolute amount of inert gas dissipated from the ZG material when using a ZG material with a high ZrO ₂ content, such as a ZrO ₂ content of about 90% by mass, The air permeability of the layer needs to be considerably smaller than the air permeability of the ZG material used for the immersion nozzle. In terms of this degree, experience generally indicates that when the ZrO ₂ content of the ZG material used in the part in contact with the powder line of the mold is less than about 85% by mass, the air permeability of the ZG material part is the inner pore body. When the air permeability is about 20% or less, the air permeability of the hardly breathable refractory layer is the air permeability of the ZG material having a ZrO ₂ content of about 85% by mass. It is preferable to make it below, and it is more preferable to make it about 20% or less with respect to the air permeability of the inner pore.

Specifically, the air permeability of a general ZG material having a ZrO ₂ content of about 85% by mass is the air permeability according to a test method for air permeability of refractory bricks (JIS R2115), and in a non-oxidizing atmosphere at 1000 ° C. After heat treatment of about 0.0007 cm ³ · cm / cm ² · cmH ₂ O · sec, after heat treatment in a non-oxidizing atmosphere at 1550 ° C., about 0.0008 cm ³ · cm ² · cmH ₂ O · sec It is. Therefore, it is preferable that the air permeability of the hardly breathable refractory layer is not more than these air permeability.

  Here, the measurement conditions for the air permeability were after heat treatment in a non-oxidizing atmosphere at 1000 ° C. and 1550 ° C., as the hardly breathable refractory layer, the firing temperature (800 to 1200 ° C.) and the actual This is because it is only necessary to exhibit the characteristics under two levels of the temperature during use (1500 to 1570 ° C.) and in an extremely low amount of oxygen. In other words, in the present invention, the non-breathable refractory layer is heated in a non-oxidizing atmosphere at 1000 ° C. corresponding to the firing conditions during the production of the immersion nozzle and in a non-oxidizing atmosphere at 1550 ° C. corresponding to the conditions for actual use. It exists without disappearing after heating, and it is necessary to satisfy the above-described air permeability conditions.

  In addition, the thickness of the breathable fire resistant layer formed in the present invention is preferably 0.1 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less. If the thickness of the flame-resistant fire-resistant layer is less than 0.1 mm, it is difficult to maintain the flame-resistant fire-resistant layer in a stable and uniform state during hot use with temperature changes. May cause delamination or damage. In addition, it is difficult to form a non-breathable refractory layer having a uniform thickness. In particular, when a thin portion is generated, the portion may be locally broken to cause gas leakage. On the other hand, if the thickness of the flame-resistant fireproof layer exceeds 0.5 mm, the flame-resistant fireproof layer itself is prone to cracking, and a relatively wide range of peeling is likely to occur, resulting in an unstable ventilation suppression effect. Furthermore, when forming not only on the ZG material part but also on the AG material part, the thickness of the refractory including the AG material part becomes small, so that the immersion nozzle as a structure becomes brittle and breaks. Defects such as cracks or the like are easily generated, and the usable time of the ZG material portion is shortened by reducing the thickness of the ZG material portion.

  In addition, the thickness of the fire-resistant fire-resistant layer in the refractory of the immersion nozzle is the most breath-resistant fire-resistant layer side of the boundary between the fire-resistant material such as ZG material as the base material and the fire-resistant fire resistant layer in the cross section. The raw material particle ends are connected with a line, and the distance between the inner surface side line and the outer surface side line is measured, and the average of the cross section of the collected sample is obtained. That is, the portion where the non-breathable refractory layer bites into the refractory in contact with the non-breathable refractory layer is excluded from the thickness of the non-breathable refractory layer.

  The non-breathable refractory layer having a preferable air permeability described above is a mixture of a refractory raw material as an aggregate and a phenol resin that forms a carbon bond having a high residual carbon ratio after heat treatment and a relatively small firing shrinkage. It can be obtained by heat treatment in a non-oxidizing atmosphere (including a reducing atmosphere).

 The shape of the refractory raw material to be an aggregate is preferably flat or nearly flat rather than nearly spherical. Here, the flat shape means one having an aspect ratio (a value obtained by dividing the square root of the area of the flaky particles by the thickness) of about 2 or more.

  The reason why a refractory raw material that is flat or nearly flat is preferred is that the flat shape or the shape close to flat, and the presence of them in the matrix in a plurality of laminated states, makes it difficult for a ventilation path to occur in the matrix portion, Even if a ventilation path occurs, the ventilation path passes through the laminated refractory raw material particle surface, and the length of the ventilation path such as the through-holes can be increased to increase the pressure loss, thereby strengthening the ventilation suppression. Because it can.

  On the other hand, when using a refractory material close to a sphere, for example, other than a flat shape or a shape close to a flat shape, an air passage is likely to occur in the matrix portion between the refractory materials close to the sphere, so Compared to the case where raw materials are used, the ventilation control is poor, and the entanglement between the refractory raw materials is reduced. Therefore, the strength tends to decrease, and peeling of the flame-resistant refractory layer or partial collapse is likely to occur. Become.

  Examples of the refractory raw material that is flat or nearly flat include graphite, boron nitride, β-alumina, and mica plate.

  In order to obtain 0.1 mm which is the lower limit of the thickness of the preferable flame-resistant fireproof layer, the thickness of the fireproof raw material to be the aggregate is preferably 0.1 mm or less. Furthermore, the structure of the aggregate in the thickness direction of the breathable fire resistant layer is preferably a multilayer in which thin aggregates are overlapped. With such a multilayer structure, it is possible to effectively disperse the external force applied to the breathable refractory layer and increase the toughness and strength of the breathable refractory layer. Moreover, since it becomes such a multilayer structure, the boundary between aggregates does not penetrate in the thickness direction of the flame-resistant fireproof layer, and the line connecting them becomes a complicated path, so the effect of suppressing ventilation is enhanced. .

  Also, in order to prevent the aggregate from jumping out on the surface of the breathable refractory layer and creating a gap between the aggregates, that is, to minimize the smoothness of the breathable refractory layer and the gap between the aggregates. In addition, the particle size of the refractory raw material used as the aggregate is preferably 0.5 mm or less. If it exceeds 0.5 mm, depending on the state of entanglement between the aggregates, gaps are likely to be formed in the fire-resistant fire-resistant layer, and they are likely to jump out on the surface of the fire-resistant fire-resistant layer. Here, the particle size refers to the maximum length of the surface in the direction perpendicular to the thickness, that is, the size passing through a wire mesh having a predetermined opening size (0.5 mm in the above case). Therefore, this particle size does not indicate the size in the thickness direction of the flat refractory raw material.

  Among these refractory raw materials, graphite is most preferable because it is easily wetted by phenolic resin, has high fire resistance, easily forms a carbon bond with a binder, has high deformability, and does not easily break. In general, graphite is roughly classified into artificial graphite and natural graphite. Natural graphite is produced as scaly graphite and earthy graphite, but there are various grades depending on the production area, purity, refining method, etc., and those with an aspect ratio of about 5 to 80 are generally used. The aspect ratio of earthy graphite tends to be slightly small. Artificial graphite is highly pure but often has a low aspect ratio such as granular.

  As described above, graphite having a particle size of 0.5 mm or less, more preferably 0.020 mm or more and 0.5 mm or less and a thickness of 0.1 mm or less is preferably used. If the particle size is less than 0.020 mm, the bulk of the refractory raw material becomes very large, and it becomes difficult to increase the amount added to the binder used together.

  Further, as graphite, natural graphite or artificial graphite can be used, but it is preferable not to use a raw material that impairs the stability of the non-breathable refractory layer such as expanded graphite whose thickness changes by heat treatment.

  As the binder, the phenol resin can be used in either a resol type or a novolac type.

  The mixing ratio of the graphite and the binder may be adjusted in order to obtain workability capable of forming the breathable refractory layer with a uniform thickness by coating or the like. For example, when using natural scaly graphite and a liquid phenol resin having a viscosity of about 10 to 50 MPa · s, it is easy to apply, and from the viewpoint of forming a stable flame-resistant refractory layer, 10% by mass or more of graphite. The mixing ratio is preferably about 30% by mass or less and about 70% by mass to 90% by mass of phenol resin.

  As the refractory raw materials other than those exemplified above, at least one selected from silicon carbide, boron carbide, silicon nitride, alumina, alumina-silica (including mica plate), spinel, and magnesia is used. be able to. However, many of these are not flat or nearly flat, such as a shape close to a sphere, and when using such a refractory material, when using a refractory material that is flat or nearly flat, In comparison, the line connecting the raw materials in the thickness direction of the fire-resistant fire-resistant layer is shortened, a path that facilitates ventilation is created, and the air-flow suppressing property is poor, and the entanglement between the fire-resistant raw materials is reduced. The toughness and strength of the refractory refractory layer tend to be reduced, and peeling or partial collapse of the breathable refractory layer is likely to occur. Therefore, even when these raw materials are used, it is preferable to select one having a shape as close to flat as possible or a shape having a fractured surface with many irregularities. In addition, when using the raw material which is not these flat shapes or the shape close | similar to a flat shape, it is preferable that the particle size is 0.1 mm or less.

  Moreover, in the case of the refractory raw material used as aggregates other than graphite, it is preferable that content in a flame-resistant fireproof layer is 10 mass% or more and 70 mass% or less. If the content of the refractory raw material that is an aggregate is less than 10% by mass, the airflow suppressing effect is small and inefficient, and the flame-resistant fireproof layer is liable to crack and break, making the airflow suppressing property unstable. Prone. On the other hand, if the content of the refractory raw material to be an aggregate exceeds 70% by mass, it is difficult to obtain a breathable refractory layer having a uniform thickness when forming the breathable refractory layer, and a bonded portion ( When the carbon bond portion is too small, the strength of the breathable fire-resistant layer is lowered and the stability thereof is lowered.

  Although it is possible to form a flame-resistant fire-resistant layer by heat-treating an organic binder alone such as phenol resin without containing a refractory raw material, there are more voids in the structure, and shrinkage or the like occurs. The strength of the fire-resistant fire-resistant layer tends to decrease, for example, it becomes easier to cause cracks. If the thickness of the fire-resistant fire-resistant layer is increased (for example, a thickness exceeding 0.1 mm), the fire-resistant fire-resistant layer is peeled off. And partial collapse, etc., and it is difficult to ensure the breathability, especially when the degree of breathability is significantly higher than the breathability of the ZG material provided with the flame-resistant fireproof layer. Is not preferred.

  In addition, the non-breathable refractory layer formed using an inorganic binder (such as water glass, colloidal silica, phosphate solution, etc.) that can generally be used as a refractory is in a non-oxidizing atmosphere during the production of the immersion nozzle. Disappears due to the reaction with carbon in the refractory material constituting the immersion nozzle at the firing temperature (800 to 1200 ° C.) and the actual use temperature (1500 to 1570 ° C.), or the thermal contraction of the inorganic binder itself is large It is not preferable to use them alone as a binding material because cracks are generated in the film to change the air permeability characteristics and damage such as peeling is likely to occur.

  ADVANTAGE OF THE INVENTION According to this invention, dissipation of the inert gas from an immersion nozzle outer peripheral surface can be suppressed, and stabilization of the inert gas blowing to an inner hole can be aimed at.

  Moreover, the increase in the dissipation of the inert gas accompanying the melting of the refractory that cannot be suppressed by reducing the air permeability of the refractory constituting the immersion nozzle can be significantly suppressed.

  By these, it is possible to prevent inclusions and the like from adhering to the inner wall surface of the immersion nozzle and blockage of the inner hole, to suppress the fluctuation of the molten metal surface in the mold, and to improve the slab quality. In addition, it is possible to sufficiently cope with the continuous casting of steel.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 are cross-sectional views showing examples of the immersion nozzle of the present invention.

  The immersion nozzle 10 has an inner hole 1 that becomes a flow path of molten steel, an inner hole body 2 is disposed so as to face the inner hole 1, and a hollow chamber 3 is formed on the outer peripheral side of the inner hole body 2. ing. A gas introduction socket 4 is connected to the hollow chamber 3, an inert gas is introduced into the hollow chamber 3 from the gas introduction socket 4, and the introduced inert gas is blown out from the inner hole body 2 to the inner hole 1. . Thus, since the counter-hole body 2 allows an inert gas to pass through, the counter-hole body 2 is made of a fire-resistant material having high air permeability.

Further, in the body portion of the immersion nozzle 10, the region corresponding to the template powder line of ZrO ₂ is composed of ZG material 5 High ZrO ₂ content of about 90 wt%, the other portion is constituted by AG Material 6 ing.

  In the example of FIG. 1, in order to prevent the dissipation of the inert gas from the outer peripheral surface of the immersion nozzle 10, the region corresponding to the powder line of the mold in the outer peripheral side wall surface of the hollow chamber 3, that is, the ZG material 5 is used. In the configured region, a flame-resistant fireproof layer 7 having a lower air permeability than the ZG material is disposed. Further, in the example of FIG. 2, the hardly breathable refractory layer 7 is disposed in the entire region of the outer peripheral side wall surface of the hollow chamber 3. The hollow chamber 3 may be provided with a columnar refractory material for joining the inner hole body 2 and the AG material 6. In this case, the air permeability of the columnar refractory material is poor. There is no need to arrange the refractory layer 7.

  The air permeability of the AG material 6 is much smaller than that of the ZG material as described above. Therefore, as shown in the example of FIG. If 7 is arrange | positioned, the objective of suppressing dissipation of the inert gas from the immersion nozzle 10 outer peripheral surface can be achieved.

  In the example of FIGS. 1 and 2, the inner hole body 2 is disposed up to the middle of the discharge hole 8 of the immersion nozzle 10, but may be disposed up to the lower end portion of the discharge hole 8. The hollow chamber 3 may be formed on the entire outer peripheral side of the inner hole body 2.

As mentioned above, the immersion nozzle of this invention as shown in FIG. 1 and FIG. 2 can be manufactured according to the following processes.
(1) A step of disposing an organic material layer that disappears at a temperature of 800 ° C. or less on the outer periphery of a refractory molded body that becomes an inner hole body. Forming a layer of a refractory raw material composed of a refractory raw material mixed with a refractory raw material and a binder, or a binder alone, and then forming a shape-retaining property in the layer of the refractory raw material by a curing treatment or a drying treatment. Step of applying (3) Step of setting the structure obtained in steps (1) and (2) in a mold for static pressure molding (4) Between the structure and the outer mold Step (5): Filling the soil as a raw material constituting the submerged nozzle body and hydrostatic forming together with the structure (5) Firing the molded body obtained in the step (4) at a temperature of 800 ° C. or higher. Thus, a hollow chamber is formed in the organic material layer, and Of the outer peripheral side wall surface of the cavity, forming a air-impermeable refractory layer in a region corresponding to at least the mold powder line of

  Here, the organic layer disposed in the step (1) can be formed of wax such as paraffin, paper, plastic, or the like.

  In addition, when the layer of the refractory raw material is disposed by application by brush coating in the step (2), a relatively large amount of liquid portion of the refractory raw material is obtained in order to obtain workability such as ductility of the refractory raw material by brush (for example, 70 mass% to 90 mass%) is preferable. On the other hand, according to dry spraying (for example, a method in which graphite is pneumatically transported and mixed with a mist-like resin near the spray nozzle and sprayed onto an object to be irradiated), the liquid part of the refractory raw material is relatively small (eg, 30 mass% to 70 mass%).

  Moreover, the arrangement | positioning of the layer of a refractory raw material in a process (2) can also be performed by immersion other than the above-mentioned brush coating and spraying. Further, a layer of a refractory raw material may be prepared in advance and disposed at a predetermined position.

In this example, the ZrO ₂ content is 90% by mass and the air permeability is about 0.001 to 0.0011 cm ³ · cm ² · cm H ₂ O · sec. A breathable refractory layer was formed, and the airflow suppression effect was investigated.

  Each sample of the example was formed by forming the ZG material into a size of φ50 × 20 mm, and applying the constituent material of the breathable refractory layer shown in Table 1 only on the upper surface of the cylinder by brushing so as to have a predetermined thickness. Then, after the drying treatment, it was prepared by heating and baking in a coke breeze atmosphere at 1000 ° C. and 1550 ° C. The “thickness of the non-breathable fireproof layer before heating” shown in Table 1 is the thickness of the non-breathable fireproof layer before heating and firing.

  As the constituent material of the fire-resistant fire-resistant layer, natural scaly graphite having a particle size of 0.3 mm or less is 70% by mass, sintered alumina having a particle size of 0.1 mm or less is 100% by mass (the shape of the particles is from large coarse particles). A non-uniform one having a broken fracture surface) and a phenol resin having a viscosity of about 10 to 50 mPa · s were used. In addition, when the mixing ratio of the phenol resin and the scaly graphite was investigated in advance, it was possible to form a uniform fire-resistant fire-resistant layer without any problem with respect to the coating workability until the scaly graphite content was about 30% by mass. It was. However, when the content of scaly graphite exceeds 30% by mass, the viscosity of the mixture becomes too high to be uniformly applied, and is unsuitable for application.

  Moreover, the sample which does not form a fire-resistant fireproof layer as a comparative example was also produced.

  About each of these samples, while confirming the external appearance, the air permeability was measured by the test method of JIS R2115. Moreover, the thickness of the formed flame-resistant fireproof layer was calculated | required from the height difference of the sample before and behind the formation. The state of the breathable fire resistant layer was evaluated by visual observation. The measurement of the air permeability of the hardly breathable fireproof layer and the evaluation of the state of the hardly breathable fireproof layer are 1550 ° C corresponding to the conditions after 1000 ° C reduction firing corresponding to the firing conditions at the time of manufacturing the immersion nozzle and the actual use. Performed after reduction firing.

  Table 1 shows the results.

  In Examples A to I, in which a non-breathable refractory layer was formed and did not disappear after 1550 ° C. reduction firing corresponding to the actual use conditions of the immersion nozzle, all formed a non-breathable refractory layer. The air permeability was reduced as compared with Comparative Example A, and the airflow suppressing effect by the flame-resistant fireproof layer was confirmed.

  In particular, in Examples A, B, D, and E, in which a non-breathable refractory layer was formed from a mixture of a phenol resin and scaly graphite and the thickness thereof was 0.1 mm to 0.3 mm, the non-breathable property was used. The refractory layer was stable without cracks or peeling off, and its air permeability was reduced by 75% or more compared to Comparative Example A, and a significant airflow suppression effect was obtained.

  On the other hand, in Examples C and F in which a fire-resistant layer having a thickness of 0.5 mm was formed from the same mixture of phenol resin and scaly graphite as described above, the reduction rate of the air permeability relative to Comparative Example A was about 45% to about It was 30%, and the air flow suppressing effect was inferior to Examples A, B, D, and E. This is presumably because microscopic cracks and peeling tendency occurred in the non-breathable refractory layer because the non-breathable refractory layer was thicker than Examples A, B, D, and E. Although not shown in Table 1, when the thickness of the flame-resistant fireproof layer was 0.7 mm, the cracks and peeling tendency were more prominently generated in the flame-resistant fireproof layer. These microcracks and the tendency to peel off are considered to have been likely to occur in the test method of this example because the breathable refractory layer of the sample was flat and relatively narrow with a diameter of 50 mm and the periphery was open. .

  In an actual immersion nozzle, the flame-resistant fire-resistant layer is curved and its entire end is constrained, so cracks and delamination are considered less likely to occur than the test conditions of this example, and the tendency to delaminate from the ZG material As long as the flame-resistant refractory layer does not break down, the inert gas does not immediately leak into the ZG material due to the separation, so that it can be used without any problem up to a thickness of 0.7 mm. However, when the thickness is 0.7mm, remarkable microcracks and the like were observed in the fire-resistant fire-resistant layer, so that the effect of suppressing air flow deteriorates due to the progress of crack expansion and peeling especially during long-term use. Therefore, from the knowledge of the test of this example, the thickness of the breathable fire resistant layer is preferably up to 0.5 mm.

  From the results of the above examples, in order to obtain a stable flame-resistant fire-resistant layer and a stable air-flow suppressing effect, in the case of a mixture of phenol resin and scaly graphite, the thickness of the flame-resistant fire-resistant layer is 0.1. It is preferably 0.5 mm or less and more preferably 0.1 mm or more and 0.3 mm or less.

  Next, in Example G in which a hardly breathable refractory layer was formed from a mixture of phenol resin and alumina, about 40% after heat treatment in a non-oxidizing atmosphere at about 1000 ° C. with respect to the air permeability of Comparative Example A, about 1550 ° C. After the heat treatment in a non-oxidizing atmosphere, a reduction effect of about 30% was obtained, and a practically sufficient ventilation suppression effect was obtained. However, as compared with the case of scaly graphite having the same mixing ratio and thickness with the phenol resin (Example E), about 53% after heat treatment at 1000 ° C. and about 38% after heat treatment at 1550 ° C. The degree and the airflow suppression effect are inferior. This is thought to be due to the shape factor that alumina is nearly spherical compared to flat scaly graphite, and even if the shape of the alumina or other refractory raw material is more flat, the airflow suppression effect is further enhanced. it is conceivable that.

  On the other hand, in Examples H and I in which a fire-resistant fire-resistant layer was formed from a phenol resin alone that does not contain an aggregate of a fire-resistant raw material, the reduction rate of the air permeability with respect to Comparative Example A was as small as about 8 to 19%. When it was formed with a thickness of 1 mm, microcracks were generated in the fire-resistant fire-resistant layer. From this, it can be seen that the hardly breathable fire-resistant layer made of a phenolic resin alone containing no aggregate of the fire-resistant raw material is not preferable for Comparative Example A, although it has an air-flow suppressing effect.

In Table 1, as Comparative Example B, as a Comparative Example C, the same evaluation as described above was performed on a ZG material having a ZrO ₂ content of 85% by mass without forming a non-breathable fireproof layer. FIG. 5 also shows the results of the same evaluation as described above, without forming a non-breathable refractory layer, for a general inner-pore body material having 70% by mass of Al ₂ O _{3 and} 18% by mass of graphite. .

  In this example, the material and thickness of the non-breathable refractory layer are changed for the submerged nozzle provided with the non-breathable refractory layer of the present invention, so that the inner hole, the outer peripheral surface and the entire air flow rate of the submerged nozzle are difficult. This was investigated in comparison with a conventional immersion nozzle (Comparative Example D) in which no breathable refractory layer was disposed.

The structure of the immersion nozzle was the structure shown in FIG. 1 for the example, and the structure shown in FIG. 3 was obtained by removing the non-breathable fireproof layer from the structure of FIG. The dimensions of the main part of this immersion nozzle are as follows: the outer diameter of the ZG material part is 150 mm, the outer diameter of the hollow chamber is 100 mm, the inner hole diameter is 80 mm, the axial length of the hollow chamber is 450 mm, and the axial length of the ZG material part Is 200 mm. The ZG material, ZrO ₂ is used to ZG material of high ZrO ₂ content of 90 wt%, _Al 2 _{O 3} is 65 wt% to AG material portion other than ZG material portion, AG material of graphite 30% A breathable refractory having 70% by mass of Al ₂ O _{3 and} 18% by mass of graphite was used for the inner pores.

  For each immersion nozzle manufactured in a product state, the total ventilation amount and inner hole ventilation amount of the immersion nozzle were measured. Specifically, air was supplied at a normal pressure from a gas introduction socket at a pressure of 0.1 MPa, and the total air flow rate and inner hole air flow rate were measured with a mass flow meter. And the inner-pore aeration rate was computed from the ratio. The air flow rate on the outer peripheral surface was determined from the difference between the total air flow rate and the inner hole air flow rate. Moreover, the defect at the time of manufacture was investigated by the X-ray transmission inspection.

  The results are shown in Table 2.

  Examples J, K, and L in Table 2 are obtained by disposing the flame-resistant refractory layers of Examples A, B, and E, which had good evaluation in the previous examples, as the flame-resistant refractory layers, respectively. .

  Whereas the air permeability of the inner hole of Comparative Example D was 62.5%, the air permeability of the inner hole was 80% or more in all the examples, and the effect of suppressing gas leakage from the ZG material to the outside could be confirmed. It was.

  In addition, manufacturing defects in the X-ray transmission inspection, that is, cracks that cause gas leakage in the refractory are not confirmed, and it can be seen that the result of this example is due to the effect of the breathable refractory layer of the present invention.

It is sectional drawing which shows an example of the immersion nozzle of this invention. It is sectional drawing which shows the other example of the immersion nozzle of this invention. It is sectional drawing which shows the conventional immersion nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Immersion nozzle 1 Inner hole 2 Inner hole body 3 Hollow chamber 4 Gas introduction socket 5 ZG material 6 AG material 7 Breathable fireproof layer 8 Discharge hole

Claims (6)

An inner hole serving as a flow path of molten steel from the tundish to the mold, a breathable inner hole body arranged to face the inner hole, and a hollow chamber formed on the outer peripheral side of the inner hole body In the immersion nozzle that blows out the inert gas introduced into the hollow chamber from the inner hole body to the inner hole,
An immersion nozzle comprising a flame-resistant fire-resistant layer having a lower air permeability than a refractory on the outer periphery side of at least a region corresponding to a powder line of a mold in an outer peripheral side wall surface of a hollow chamber.   The immersion nozzle according to claim 1, wherein the thickness of the flame-resistant fireproof layer is 0.1 mm or more and 0.5 mm or less. A non-oxidizing atmosphere having a breathability of 0.0007 cm ³ · cm ² · cm ² · cmH ₂ O · sec or less after heat treatment in a non-oxidizing atmosphere at 1000 ° C. and a non-oxidizing atmosphere of 1550 ° C. ^3. The immersion nozzle according to claim 1, wherein the immersion nozzle is about 0.0008 cm ³ · cm / cm ² · cmH ₂ O · sec or less after the lower heat treatment.   The immersion according to any one of claims 1 to 3, wherein the non-breathable refractory layer contains 10% by mass or more and 30% by mass or less of graphite having a particle size of 0.5 mm or less, and the balance is made of carbon other than the graphite. nozzle.   One kind selected from silicon carbide, boron carbide, silicon nitride, alumina, alumina-silica (including mica plate), spinel, and magnesia, each of which has a particle size of 0.1 mm or less. The immersion nozzle according to any one of claims 1 to 3, wherein the refractory raw material is contained in an amount of 10 mass% or more and 70 mass% or less, and the balance is made of carbon other than the refractory raw material. It is a manufacturing method of the immersion nozzle in any one of Claims 1-5, Comprising:
(1) A step of disposing an organic material layer that disappears at a temperature of 800 ° C. or less on the outer periphery of a refractory molded body that becomes an inner hole body;
(2) A layer of a refractory raw material composed of a refractory raw material mixed with a refractory raw material and a binder or a single binder is formed on the outer periphery of the organic material layer to form a fire-resistant fire-resistant layer by firing at 800 ° C. or higher. Then, a step of imparting shape retention to the layer of the refractory raw material by a curing treatment or a drying treatment,
(3) a step of setting the structure obtained in the steps (1) and (2) in a form for static pressure molding;
(4) filling the earth as a raw material constituting the submerged nozzle body between the structure and the outer formwork, and hydrostatic forming with the structure;
(5) The molded body obtained in the step (4) is baked at a temperature of 800 ° C. or higher to form a hollow chamber in the organic material layer, and at least of the outer peripheral side wall surface of the hollow chamber. And a step of forming a breathable fire-resistant layer in a region corresponding to the powder line of the mold.

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