KR20100080915A - Nozzle for continuous casting and method for manufacturing the same - Google Patents

Abstract

A nozzle for continuous casting in which durability is enhanced by arranging a refractory layer of high performance, e.g. high corrosion resistance or high adhesion preventive properties, on the inner hole side. A method for manufacturing a nozzle for continuous casting in which push breaking of the outer circumferential side layer due to the difference in thermal expansion between the inner hole side layer and the outer circumferential side layer of body material is prevented, and exfoliation of the inner hole side layer in the way of casting is prevented, is also provided. The nozzle for continuous casting has such an integral structure as the boundary portion of the inner hole side layer (2) and an intermediate layer (4) touches the boundary portion of the intermediate layer (4) and the outer circumferential side layer (3) directly wherein the bonding strength of the intermediate layer and the inner hole side layer and the outer circumferential side layer adjoining the intermediate layer is 0.01-1.5 Mpa in a 1000°C non-oxidizing atmosphere, and a compression rate K(%) of the intermediate layer in the 1000°C non-oxidizing atmosphere under the pressure of 2.5 Mpa is 10%-80%.

Description

Nozzle for continuous casting and method for manufacturing the same

The present invention consists of a tubular refractory structure having a nozzle for continuous casting of molten metal, in particular an inner cavity through which the molten metal passes, wherein some or all of the tubular refractory structure is formed in the inner cavity side layer and the intermediate layer. And a nozzle for continuous casting having an outer circumferential side layer.

In the present invention, the term "tubular" refers to any shape having the inner hole in the axial direction, and the cross-sectional shape in the direction orthogonal to the axial direction is irrespective of the shape. That is, the cross-sectional shape in the direction orthogonal to the axial direction may be circular, elliptical, rectangular, polygonal or the like.

In addition, in this invention, a "hollow side layer" means generically the refractory layer which exists in an inner side rather than an intermediate | middle layer in the horizontal cross section in any position which makes the molten steel passage direction (vertical direction) of the continuous casting nozzle full length. In this case, the inner pore side layer includes a plurality of layers, and the coefficient of thermal expansion in this case is the maximum value of any one of the inner pore side layers.

Furthermore, in the present invention, the "outer circumferential side layer" refers to the refractory layer existing on the outer circumferential side rather than the intermediate layer in the cross section, and the outer circumferential side layer is composed of a plurality of layers (eg, ZG quality other than AG quality is present). 2 layer structure etc.), and the thermal expansion rate in that case is made into the minimum value of any one of the outer peripheral layers.

Continuous casting nozzles, such as a long nozzle which discharges molten steel from a ladle to a tundish, and an immersion nozzle which injects molten steel from a tundish into a continuous casting mold, melt molten steel or the like near its axial center. It consists of a tubular refractory structure having an inner hole through which metal passes, and when molten steel passes through the inner hole, a temperature gradient occurs on the inner hole side and the outer circumferential side. In particular, when the discharge and passage of molten steel starts, the inner cavity side is rapidly heated, and the phenomenon becomes remarkable.

This temperature gradient causes stress distortion in the interior of the refractory material regardless of whether the refractory constituting the refractory structure is a single layer or a plurality of layers, and is one of the causes of cracking and the like in the outer peripheral layer. The larger the temperature gradient and the greater the thermal expansion rate of the inner pore side layer than the thermal expansion rate of the outer periphery side layer, the greater the thermal stress and the higher the risk of breakage of the outer side layer.

On the other hand, molten steel flows through the inner hole of the continuous casting nozzle while severely colliding. In particular, near the inner hole surface is weakened due to wear caused by molten steel or non-metallic inclusions in molten steel, oxidizing components in molten steel, loss, FeO, etc. Reaction with components in the molten steel of the damage is large. Also, in recent years, there has been an increase in nonmetallic inclusions in molten steel such as alumina due to high quality of steel.Adhesion of inclusions centered on alumina from the continuous hole of the nozzle for casting and blockage of the hole are among the major factors that determine the life of the nozzle for continuous casting. Become one.

In such a situation, the demand for higher contents and safety (stable casting) of the continuous casting nozzles is increasing due to the improvement of corrosion resistance and wear resistance of the pore surface, and the reduction or adhesion of non-metallic inclusions to the pore surface.

In order to meet these demands, a refractory material of excellent thermal shock resistance is applied to the main body portion of the continuous casting nozzle, that is, the outer circumferential side layer, to form a basic skeleton of the continuous casting nozzle, and to make contact with the molten steel stream. The layer on the side having a surface, that is, the pore side layer, is formed of a material having excellent abrasion resistance, corrosion resistance, or the like, or a refractory material made of a material hardly adhered to inclusions such as alumina. It is intended to extend the life.

In particular, various high functionalizations are progressing with respect to the air-porous layer, and recently, materials such as graphite or silica, which are melt-dissipating aggregates, or materials that do not contain them at all, are used for corrosion-resistant components such as Al ₂ O ₃ , ZrO ₂ , and MgO. It is made of a basic material containing high CaO component with high reactivity with Al ₂ O ₃ component in order to achieve high corrosion resistance or reduce or prevent adhesion of inclusions such as Al ₂ O ₃ to the pore surface from molten steel. Applications such as immersion nozzles incorporating a refractory layer have been advanced.

The refractory aggregate containing each of the above components for obtaining such a high functional refractory has high thermal expansion properties, and since the high functional refractory contains a large amount of such refractory aggregates, the air pore side layer tends to be highly expanded. In addition, an increase in thermal gradient due to a decrease in thermal conductivity relative to the outer circumferential layer of the inner pore side layer due to the reduction of the carbon content is added, and the difference in thermal expansion amount between the inner pore side layer and the outer periphery layer and the resulting thermal stress is further increased. The risk of fracture due to crushing of the outer circumferential side layer of the nozzle for continuous casting is further increased.

As a general countermeasure against fracture due to the temperature gradient (thermal stress) of the continuous casting nozzle, for example, a molten silica having a low thermal expansion rate, which contains a large amount of graphite in the refractory constituting the continuous casting nozzle, is added or increased. There are reductions in thermal stress due to high thermal conductivity, low expansion, and low elastic modulus. However, the increase in graphite and fused silica, on the other hand, has a detrimental effect on the wear resistance and corrosion resistance due to deterioration in oxidation resistance and increased reactivity with other refractory components or components in molten steel. There are limitations to the application and not a realistic solution.

Therefore, in order to avoid the risk of nozzle breakage for continuous casting, for example, when a molded article serving as the inner pore side layer is provided at the inner pore side of the outer peripheral side layer, it is composed of fine powder mainly composed of refractory raw materials such as oxides, By using a sludge-type mortar (mortar) made of an inorganic binder such as silicate containing a large amount, and by increasing the porosity of the mortar to a low strength, the mortar layer itself is destroyed to stress the thermal expansion of the inner pore layer Attempts to mitigate, i.e., by including a large amount of solvent, a method of avoiding the cracking of the nozzle by the application of mortar which exhibits a high porosity but relatively low adhesion has been adopted. However, the crack avoidance measures by mortar have the following problem.

(1) The mortar with excessive solvent has the property that the solvent in the mortar is absorbed in the material of the other layer by contact with the nozzle material. Especially in the case of continuous casting nozzles, etc., a thin mortar layer having a few mm is mortar layer. The porosity of is lower than the material interface side and tends to be dense, so that the stress relaxation function of the mortar layer itself after setting is reduced or lost.

(2) Control of apparent porosity is practically impossible. In other words, since it is impossible to control the pore distribution that can be buckled under a predetermined stress, the solvent must be excessive, and compatibility with adhesiveness is impossible.

(3) The stress relaxation by the mortar layer forms a margin of deformation of the inner pore layer by reversible destruction of the skeleton in the mortar layer forming the pores, thereby relieving the stress. Therefore, there is a high possibility of falling off, and accompanied by the expansion of the space after the mortar collapses due to the temperature change of the nozzle, molten steel or slug easily invades, cracks, erosion, etc. due to the intruded molten steel, etc. It often causes damage to the casting nozzle.

As another test for preventing such breakdown due to thermal stress while oriented such high corrosion resistance, for example, Patent Document 1 provides a refractory layer having high thermal expansion and high corrosion resistance that does not contain carbon only on the inner pore side. On the outer circumferential side, a refractory layer with excellent carbon-containing spalling resistance is provided to form a two-layer structure, and at least 80% or more of the contact surfaces between the two-layered refractory layers are formed of a combustible material such as polypropylene and nylon. Disclosed is a casting nozzle which is separated by a separation layer which is set at the time and is formed by disappearing it.

However, in the nozzle for casting of this patent document 1, less than 20% of the contact surface between refractory layers is adhere | attached. Even in the case of small adhesive portions, cracking stresses are transmitted from the inner pore side layer to the outer circumferential side layer through this adhesive portion, which is a starting point of the crack phenomenon. In addition, when the adhesive portion is 0%, a basic problem occurs that the inner pore side layer cannot be held as a structure. In addition, when molten steel easily penetrates into the separation layer and undergoes a temperature change, cracking occurs in the refractory due to solidification shrinkage of the molten steel or expansion of the steel during heating, and the inner layer does not adhere to the outer circumferential layer. A problem arises.

On the other hand, Patent Literature 2 includes a CaO nozzle containing 70 wt% or more of CaO and having an apparent porosity of 50% or less in an immersion nozzle for the purpose of suppressing adhesion of inclusions, and corresponding to the thermal expansion amount of the CaO nozzle between the CaO nozzle and the base metal nozzle. It is disclosed to provide a gap. It is also disclosed that a CaO nozzle is fixed by filling a thin ceramic fiber or a small amount of mortar between the end of the CaO nozzle and the base nozzle as necessary.

However, in the structure in which a gap corresponding to the thermal expansion margin of the CaO nozzles is provided between the CaO nozzle (inner cavity side layer) on the inner side and the base material nozzle (outer peripheral side layer) on the outer side, the outer base material by the high expansion CaO nozzle Although the crushing phenomenon of the nozzle can be suppressed, as described in paragraph [0022] of Patent Document 2, it is preferable to provide a gap of 3% or more of the outer diameter of the CaO nozzle at the time of preheating. It is thought that the base material nozzle of is not in close contact with each other (the thermal expansion rate of CaO-based material is about 2% or less even at the highest level of material at a temperature of about 1500 ° C.). If the CaO nozzle and the base material nozzle are not in close contact with each other during hot operation, there is a risk that the CaO nozzle may be displaced or dropped due to the compressive stress applied to the CaO nozzle. In addition, since molten steel easily penetrates between the CaO nozzle and the nozzle base material, when the temperature is changed, there is a risk of damaging the CaO nozzle or the nozzle base material on the outer circumference by solidification shrinkage or thermal expansion of the steel. In addition, deoxidation products and low-melting compounds in steel such as CaO are premised on the basis of being melted. Accompany

Thus, when the design of the joint part between the separation layer of patent document 1 and the space | interval of patent document 2 is too wide, the fall or damage of the internal pore side layer by molten steel penetration into a joint part, the outer peripheral side There is a risk of damage to the layers. When too narrow, longitudinal cracking occurs in the axial direction of the tubular refractory structure due to thermal stress in the circumferential direction from the outer circumferential layer due to thermal expansion of the inner cavity side layer, or transverse cracking damage (angle with respect to the axial direction) Cracking in a direction having a direction, so-called bending) easily occurs.

Therefore, in the case of the continuous casting nozzle incorporating a high-expansion inner layer, in addition to the function of alleviating the influence of the stress due to thermal expansion from the inner side layer, the molten metal is hard to penetrate or pass through, and furthermore, It is considered that the function of adhering the inner pore side layer to the outer circumferential side during casting is important, but conventionally, the measures for imparting these three functions or structures have been rarely studied.

In addition, as shown in the above Patent Documents 1 and 2, in the conventional built-in method, the outer peripheral side layer and the inner pore side layer, which are also main body parts of the continuous casting nozzle, are manufactured in a separate process, and mortar or the like is provided around the final process. Or a combination process is required, resulting in lower productivity, higher manufacturing cost, and the like. Furthermore, in the case of combining the refractory layers made of such individual parts, the layers are brought into contact with each other on a smooth surface, so that they are difficult to obtain mutual adhesive strength or fixing force sufficient to solve the above problems, and thus, adhesion by a separate adhesive or the like. It requires a means of strengthening strength.

Patent Document 1: Japanese Unexamined Patent Publication No. 60-152362 Patent Document 2: Japanese Patent Application Laid-Open No. 7-232249

The problem to be solved by the present invention is a continuous casting nozzle in which a high-performance refractory layer such as high corrosion resistance and high adhesion preventing property is disposed on the air pore side, and the solvent resistance is increased. The present invention provides a continuous casting nozzle which can prevent the outer peripheral layer from being cracked due to the thermal expansion difference of the alloy and prevents the inner hole side from shifting or falling off during casting. It is to provide a method for producing a stable and easy.

More specifically, it consists of a tubular refractory structure having an inner hole through which molten metal passes in the axial direction, and thermal expansion of the refractory material in the inner hole side layer is performed in a part or all regions of the tubular refractory structure in the outer peripheral side of the radially outer side thereof. In the continuous casting nozzle larger than the thermal expansion of the refractory of the layer, (1) preventing the breakage of the outer peripheral layer, (2) increasing the stability during the casting of the inner pore side layer, and (3) the molten steel between the layers including the intermediate layer In order to prevent this intrusion, in other words, to provide a continuous casting nozzle having a structure that satisfies these functions, and to provide a manufacturing method capable of optimal energy saving that can stably obtain the continuous casting nozzle There is.

The present invention,

(1) consisting of a tubular refractory structure having an inner hole in which the molten metal passes through in the axial direction, and thermal expansion of the refractory material in the inner hole side layer in some or all regions of the tubular refractory structure has a radially outer outer peripheral layer For continuous casting nozzles larger than the thermal expansion of the refractory

An intermediate layer having livestock properties exists between the inner pore side layer and the outer circumferential side layer as a multi-layer structure which is simultaneously integrated at the time of molding,

The adhesion strength in the 1000 degreeC non-oxidation atmosphere of an intermediate | middle layer, an inner side layer adjacent to this intermediate | middle layer, and an outer peripheral side layer is 0.01 Mpa or more and 1.5 Mpa or less,

Also,

Nozzle for continuous casting (Claim 1), wherein the livestock rate K (%) of the intermediate layer in a 1000 ° C. non-oxidizing atmosphere under a pressure of 2.5 MPa satisfies Equation 1.

 K ≧ [(Di × αi-Do × αo) / (2 × Tm)]... Equation 1

   Di: Outer diameter (mm) of inner side layer

   Do: Inner diameter of the outer circumferential side layer (mm)

   Tm: Initial thickness (mm) from room temperature of a middle layer

   (alpha) i: Maximum thermal expansion rate (%) in the range from room temperature to 1500 degreeC of the refractory body of an inner side layer

   αo: Thermal expansion rate (%) at the temperature at the start of the passage of the refractory of the outer peripheral layer

(2) Said intermediate | middle layer contains expandable expandable graphite particle (Hereinafter, "expanded expandable graphite particle" is called "expanded graphite particle") after heat processing in 600 degreeC or more non-oxidizing atmosphere, The description of Claim 1 characterized by the above-mentioned. Nozzle for continuous casting (claim 2),

(3) Claim 1 characterized by the above-mentioned intermediate | middle layer containing 16 mass% or more (including 100 mass%) of carbon components (except a compound with another component) after heat processing in 1000 degreeC non-oxidizing atmosphere. Continuous casting nozzle (claim 3) of Claim 2,

(4) The said intermediate | middle layer contains 16 mass% or more of carbon components (except a compound with another component) in total after heat processing in a non-oxidizing atmosphere of 100 degreeC, and remainder other than the said carbon component is oxide, carbide, nitride, The nozzle for continuous casting (claim 4) according to claim 1 or 2, characterized in that the material is a refractory raw material composed of at least one kind of metal.

(5) Consists of a tubular refractory structure having an inner hole in which molten metal passes through in an axial direction, and a part or all of the areas are provided with an inner hole side, an intermediate layer, and an outer circumferential layer in order from the inner plane to the radially outward side. As a method of manufacturing a continuous casting nozzle,

As the clay for the intermediate layer, containing 5% by mass to 45% by mass of unexpanded expandable graphite particles, 55% by mass to 95% by mass of combustible particles, and an organic binder, and the refractory for the intermediate layer in a 1000 ° C non-oxidizing atmosphere. After the heat treatment, the unexpanded expandable graphite particles and flammability so that the proportion of the carbon component of the organic binder alone (excluding compounds with other components) to the entire refractory for the interlayer is 2.5% by mass to 15% by mass. Prepare the topsoil added externally with respect to the sum of the particles,

The middle layer soils together with the inner layer soils and the outer layer layers are simultaneously pressurized and molded by a CIP apparatus,

By heat-treating the obtained molded object at 600 degreeC or more and 1300 degrees C or less, the combustible substance in the molded object of the said middle layer of clay was dissipated, and a space was formed, and then the unexpanded expandable graphite in the molded object of the said intermediate | middle layer of clay was expanded, and the said space is expanded. Method for producing a continuous casting nozzle comprising the step of filling with expanded expanded graphite (claim 5),

(6) consisting of a tubular refractory structure having axially pierced internal pores through which molten metal passes, with some or all of the regions having a vacant side, an intermediate layer, and an outer circumferential layer in order from the inner surface to radially outward As a method of manufacturing a continuous casting nozzle,

A fire-resistant raw material composed of at least 5% by mass to 45% by mass of unexpanded expandable graphite particles, at least 55% by mass to 95% by mass of combustible particles, and at least one component of an oxide, carbide, nitride, and metal. Containing a total of 40% by mass or less of the organic binder, and the interlayer refractory material of the carbon component (excluding the compound with other components) only of the organic binder after heat-treating the refractory material for the intermediate layer in a 1000 ° C. non-oxidizing atmosphere. It is added externally with respect to the sum total of the said refractory graphite particle | grains, combustible particle | grains, and the refractory raw material which consists of one or more types of components of an oxide, a carbide, a nitride, and a metal so that the ratio to the whole may be 2.5 mass% or more and 15 mass% or less. Prepare a clay,

The middle layer soils together with the inner layer soils and the outer layer layers are simultaneously pressurized and molded by a CIP apparatus,

By heat-treating the obtained molded object at 600 degreeC or more and 1300 degrees C or less, the combustible substance in the molded object of the said middle layer of clay was dissipated, and a space was formed, and then the unexpanded expandable graphite in the molded object of the said intermediate | middle layer of clay was expanded, and the said space is expanded. A method for producing a continuous casting nozzle comprising the step of filling with expanded expanded graphite (claim 6).

In the present invention for solving the above problems, in the structure of the nozzle for continuous casting,

(1) providing an intermediate layer having a function of alleviating stress between the inner and outer circumferential layers,

(2) maintaining the shape as a layer of the intermediate layer, not causing collapse, etc. due to fracture in the layer, that is, enhancing the stability of the layer,

(3) bonding and fixing between the intermediate layer, the inner pore side layer and the outer circumferential layer in a multi-layered structure simultaneously integrated at the time of molding;

Three items were taken as basic requirements.

(Hereinafter, the above (1) is referred to as "shrinkable condition", said (2) is called "stable condition", and said (3) is called "adhesive condition".)

Hereinafter, each of the above conditions will be described in detail.

(1) About condition of livestock

As described above, the air-resistant side layer has corrosion resistance for the purpose of improving corrosion resistance and abrasion resistance, restriction of elution of carbon components from the refractory of molten steel, adhesion to the internal pore surface of inclusions mainly containing non-metallic inclusions such as alumina, and prevention of nozzle clogging. there is a tendency that wear resistance or the like is used for the refractory increased the content of fine _{Al 2 O 3, MgO, ZrO} 2, CaO.

On the other hand, in most cases, the content of Al ₂ O ₃ , MgO, ZrO ₂ , CaO, etc. of the outer circumferential side layer (including the outer circumferential side layer as part of the main body part) mainly focusing on the thermal shock resistance is lower than that of the inner pore side layer. Therefore, the thermal expansion rate of the refractory of the inner pore side layer inevitably becomes larger than that of the outer periphery side layer.

Breakage of the nozzle for continuous casting caused by crushing or cracking of the outer circumferential side layer by the inner cavity side layer occurs remarkably by using the above-described refractory material having a higher coefficient of thermal expansion than the outer circumferential side layer on the inner cavity side. In addition, even if each layer of the inner layer and the outer layer is composed of refractory materials having the same or the same thermal expansion characteristics, the fracture may be relatively higher in temperature than the outer side due to preheating, rapid temperature rise, or passing through the inner side. This also occurs when a large thermal gradient occurs between them.

That is, in the present invention, in the case where the thermal expansion of the inner pore side layer is larger than the thermal expansion of the outer periphery side layer, the maximum thermal expansion rate of 1500 ° C. (substantially around the casting temperature region) of the refractory of the inner pore side layer is 1500 ° C. of the refractory of the outer periphery layer. It includes not only the case where it is larger than the following maximum thermal expansion rate, but also the said maximum thermal expansion rate or thermal expansion behavior is the same (for example, the same composition, material of the same structure, etc.), but according to the preheating from the steel or the hole. It also includes a case where the thermal expansion degree of the inner pore side layer at the time of heating due to the temperature difference (temperature gradient) between the inner pore side layer and the outer periphery side layer is larger than the thermal expansion degree of the outer periphery side layer.

If there is no function or a very small function of stress relaxation between the inner cavity layer and the outer peripheral layer, the stress caused by the inner cavity layer is a radial compressive stress on the cross section in the horizontal direction, and the outer peripheral layer is also applied to the end side in the longitudinal axis direction. In the case of an excitation structure, it acts on the outer circumferential layer as a compressive stress in the axial direction. And their compressive stress in the outer circumferential layer radially compressive in the circumferential direction, the axial compressive stress is converted into the same axial tensile stress, exceeding the tensile stress of the refractory of the outer circumferential layer In this case, a crack occurs in the axial (= longitudinal) direction in the former case and in a horizontal (= transverse) direction in the latter case, thereby damaging the outer peripheral layer.

As a means for imparting a function of relieving stress between the inner pore side layer and the outer circumferential layer in such a relationship, in the present invention, livestock and Install an adhesive interlayer.

By providing the intermediate layer, the thermal expansion of the inner pore side layer does not directly act on the outer circumferential side layer but acts as compressive stress to the intermediate layer. At this time, the intermediate layer itself reduces the thickness in the radial direction and in the case of the axial end in response to the compressive stress. In other words, by reducing the volume, it is possible to relieve the stress due to the expansion of the inner cavity layer. In the present invention, the property that can reduce such thickness or volume is referred to as livestock.

In the case of a tubular refractory material mainly made of Al ₂ O ₃ -C, which is a material of the general outer circumferential layer of the immersion nozzle, it is generally broken when a pressure of several MPa is applied to the inner wall surface of the outer circumferential layer. . For example, in the case of a refractory material of Al ₂ O ₃ -graphite having a maximum tensile strength of 6 MPa at a refractory (inner diameter φ80 mm, outer diameter φ135 mm) of an outer circumferential layer having a structure of almost the smallest radial direction, in practical use If pressure is applied from the wall surface, a pressure of about 2.5 MPa is applied to the inner wall surface by calculation from the formula of the thickness pressure cylinder, leading to breakage.

In the case where the intermediate layer and the inner side layer are disposed on the inner side of the outer side layer during preheating or casting start, the intermediate layer itself needs to exhibit deformation behavior in order to alleviate the stress on the outer side layer due to thermal expansion of the inner side layer. have. In other words, the stress applied to the outer circumferential layer in the inner pore side layer needs to be 2.5 MPa or less due to deformation (reduction) of the intermediate layer.

From the above, it is preferable to suppress the tensile stress generated in the outer circumferential layer in the process of heating or passing through the inner cavity side to 2.5 MPa or less and to reduce the tensile stress as small as possible in order to increase the safety. Under the stress value, the intermediate layer itself needs to exhibit deformation behavior.

The livestock required for the middle layer under a pressing force of 2.5 MPa can be expressed by the livestock rate K (%)

 K ≧ [(Di × αi-Do × αo) / (2 × Tm)]... Equation 1

   Di: Outer diameter (mm) of inner side layer

   Do: Inner diameter of the outer circumferential side layer (mm)

   Tm: Initial thickness (mm) from room temperature of a middle layer

   (alpha) i: Maximum thermal expansion rate (%) in the range from room temperature to 1500 degreeC of the refractory body of an inner side layer

   αo: Thermal expansion rate (%) at the temperature at the time of starting passage of the refractory of the outer peripheral layer

Di and Do are the positions of the outer circumferential side of the inner circumferential layer and the outer circumferential side with respect to the planar shape of the inner vacant side layer and the outer circumferential layer on the cross section in the axially horizontal direction of the portion targeted in all the axial directions, respectively. It means the diameter of the position of the inner pore side of the layer. When these planar shapes are not circular, the position of the outer circumferential side of the inner pore side layer is set to Di and the position of the inner pore side of the outer periphery layer on the same straight line extending radially from the center of the planar shape of the inner pore side layer on the plane. What is necessary is just to set Do as the said Formula 1 with respect to the whole shape.

The livestock property at the axial end is Di in the above formula 1 with respect to the planar shape of the inner periphery layer and the outer periphery layer on the cross section passing through the center of the axis in the axial direction (vertical direction). What is necessary is just to replace the length of the axial direction to the other end which makes into one end, and Do to the length of the axial direction of the outer peripheral side layer to the other end which makes the axial direction inner side surface position of an outer peripheral side layer one end.

Here, α i is the maximum coefficient of thermal expansion (%) in the range from room temperature to 1500 ° C. of the refractory of the inner pore side layer, which means the maximum thermal expansion rate of the inner pore layer refractory up to the molten steel temperature, and α o is the outer circumferential side The coefficient of thermal expansion (%) at the temperature at the start of the flow through the layer's refractory is the temperature at which the outer circumferential layer is exposed at the start of the flow through the molten steel according to operating conditions such as preheating conditions. It must be decided.

When the continuous casting nozzle is used without preheating, the outer circumferential layer is equal to room temperature (temperature of the surrounding environment), wherein αo can be regarded as the expansion rate from room temperature, that is, the reference point for thermal expansion coefficient measurement, that is, almost zero. Equation 1 becomes Equation 2.

  K ≧ [Di × αi / (2 × Tm)]... Equation 2

The livestock rate K satisfying Equation 2 is the livestock rate considering the most stringent condition, that is, the difference in thermal expansion between the inner and outer circumferential layers is maximum. Although not destroyed, in order to ensure safety that is hard to be destroyed, it is preferable to set the livestock rate K satisfying this expression 2 under all operating conditions.

K in Formulas 1 and 2 is a value in a condition where the refractory material of the target is not oxidized, such as in an oxidizing gas atmosphere such as air, by applying an antioxidant to a non-oxidizing atmosphere or surface in a reducing gas or an inert gas atmosphere. do. In practice, the intermediate layer in the use of a continuous casting nozzle is a non-oxidizing atmosphere. In addition, when the sample of the object is oxidized in the measurement of K, it is impossible to determine the exact property.

In the present invention, the livestock rate of the interlayer refractory described above is preferably based on 10% or more and 80% or less.

By adjusting the thickness of the middle layer according to the livestock rate of the middle layer, the expansion margin of the inner layer can be alleviated, but if it is less than 10%, the middle layer has to be thickened due to the difference in thermal expansion rate between the inner layer and the outer layer. Since the thickness of the nozzle for continuous casting is limited, as a result, the thickness of the main body material becomes thin, resulting in problems in strength as a structure. If the thickness is greater than 80%, the thickness of the intermediate layer can be designed to be thin. Therefore, the above-described problems do not occur. However, in forming a thin intermediate layer, problems such as manufacturing problems and lowering of the adhesive strength between the inner and outer circumferential layers are easily formed. Occurs. For example, assuming that the inner diameter of the outer circumferential layer near the minimum size of the continuous casting nozzle generally used is about φ 80 mm, the thermal expansion coefficient of the inner pore side layer is 2.0%, and the thermal expansion coefficient of the outer circumferential layer is 0.8%. In this case, the thickness of the intermediate layer is about 4 mm, the livestock rate required for the intermediate layer refractory becomes 10%, the inner diameter of the outer circumferential layer near the maximum size is about φ150 mm, the thermal expansion coefficient of the inner vacant side layer is 2.0%, and the outer circumferential layer. Assuming that the thermal expansion rate of is 0.8%, the thickness of the intermediate layer is about 1.2 mm, and the livestock rate required for the interlayer refractory is about 78%.

The livestock rate can be measured by the following method and this measurement can be identified with the livestock rate.

The cylindrical refractory material (φ20 × 5 mmt) made of a mixture having the characteristics of livestock property after heat treatment after being formed at the same pressure as the molding pressure is put in a carbonaceous confined space having the same shape as the cylindrical refractory material, under a non-oxidizing atmosphere. Heat treatment is applied in a predetermined temperature rising pattern to burn off the flammable component to obtain a cylindrical sample (about φ 20 x about 5 mmt). The cylindrical sample after this heat treatment is disposed between the cross sections of two refractory jigs having a shape of? 20 x 40 mmL. Moreover, when pressing the inserted cylindrical sample in the longitudinal direction, in order to prevent the fall of the sample from the side surface, the guide for a cylindrical sample is made out of the refractory material of inner diameter φ20mm / outer diameter φ50mm height 78mm, and the sample outside is inserted in the sample outside. Let it be a sample for a measurement.

The sample for measurement is placed in a furnace of a material tester capable of controlling temperature, atmosphere, and pressurization rate. The temperature is raised to a predetermined temperature in a non-oxidizing atmosphere, maintained until the temperature becomes uniform, and then pressurization is started and measured. First, the initial thickness t ₀ (mm) of the cylindrical sample in a non-pressurized state is measured. Next, after holding the measurement sample at a predetermined temperature, the cylindrical sample was compressed from the up and down direction in the range of the crosshead moving speed of 0.001 to 0.01 mm / sec and pressed to 2.5 MPa, and then the displacement amount h ₁ (mm). Measure In order to measure the blank value of the sample put into the cylindrical refractory claim same load of the jig, the same temperature, and pressed in the same condition in a state that does not place a cylindrical sample and measure the displacement amount h _2. By calculating these measurements in the following equation, the livestock rate K (%) at each temperature can be obtained.

K = (h ₁ -h ₂ ) / t ₀ × 100 (%). Expression 3

In addition, the inner pore side layer is integrated with the outer periphery side layer by the intermediate layer during molding, and can also be measured from an actual casting nozzle having a continuous structure. A core boring of φ20 mm toward the central axis at right angles to the refractory central axis in the outer circumferential layer was performed to provide curvature to the inner and outer circumferential sides of approximately φ 20 mm integrated, including the inner cavities layer, intermediate layer and outer circumferential layer. Get a core sample with The livestock ratio of the middle layer is processed to the refractory jig by horizontally processing the upper and lower surfaces of the core sample to be uniformly pressurized, or to the refractory jig having the same curvature as the upper and lower surfaces of the core sample. It is processed into a measurement sample of a predetermined diameter of 20 x 80 to 100 mmL including the outer circumferential side layer. In the same manner as described above, the initial thickness t ₀ (mm) of the intermediate layer in the non-pressurized state is accurately measured, and the displacement amount h ₁ of the intermediate layer is measured in a non-oxidizing atmosphere at a predetermined temperature. At the same time, the displacement amount h ₂ at the blank value in the absence of the intermediate layer is measured to calculate the livestock rate K. By sampling from real nozzles, the liveness of the interlayer can be measured accurately.

(2) About stability conditions and adhesive conditions

After the intermediate layer satisfies the above-mentioned livestock property, it is necessary to maintain sufficient stability and adhesion with the inner and outer circumferential layers from the production of the continuous casting nozzle to the use thereof.

As described in the background art above, in the conventional method of buckling a high-volume, low-strength mortar and a meat porosity structure, that is, obtaining livestock by decay, the tissue after the buckling or decay is a simple powder. Therefore, the adhesive force between the layers cannot maintain the intermediate layer itself from the outset. If there is a space between the inner and outer circumferential layers by the intermediate layer in such a state, that is, when the layers are separated from each other without being fixed to each other, the intermediate layer itself is locally destroyed by eccentric stress, When the enlarged or intermediate layer is lost, the inner cavity layer is in a movable state, and it is easy to cause dropping or destruction, or stress concentration and breakage due to contact with the local outer peripheral layer of the inner cavity layer. In such spaces, molten steel may invade and further promote breakage of layers, peeling between layers, and the like.

From this, it is necessary to exist as an intermediate | middle layer even after compression in the intermediate | middle layer which has livestock property, and to maintain a fixed adhesiveness (it mentions later) with an interlayer.

The fact that such an intermediate layer has a certain adhesiveness with the inner pore side layer and the outer circumferential side layer is, on the premise of the adhesion, that the refractory itself of the intermediate layer has a certain level or more of strength required when expressing the adhesiveness as a layer and is in a healthy layer state. It is a premise to maintain a common sense, and it is a natural reason.

Thus, in the present invention, the adhesion between these layers is enhanced to enhance the stability of the intermediate layer itself and the fixing property between the intermediate layer and the inner pore side layer and the outer circumferential layer.

Adhesiveness, that is, bonding or fixing property, can be evaluated as the adhesive strength (as a premise of performing the adhesiveness as described above, it is regarded that there is stability more than necessary to exhibit the adhesive strength). The present inventors found out that the optimum range of the adhesive strength was 0.01 MPa or more and 1.5 MPa or less in the hot measurement in a 1000 ° C. non-oxidizing atmosphere.

The minimum value of 0.01 MPa of adhesive strength is a value obtained by repeating the experiment, and is a value for obtaining a frictional resistance between the minimum layers so that the inner pore side layer and the outer circumferential layer can maintain a predetermined installation place. When the adhesive strength is less than 0.01 MPa, even if the hole-side layer does not fall before the start of the passage, the holding capacity of the hole-side layer is low. There is a risk of falling if there is a local melting loss. Moreover, when conveying a continuous casting nozzle or installing it in a continuous casting apparatus, there is a high risk of causing the inner layer to deviate from a predetermined position, to peel off or fall off, even by their respective external forces at each stage during preheating and passing through. . In addition to such a phenomenon, there is also a part that does not meet the necessary livestock properties, so the risk of causing destruction of the inner layer or outer layer is also increased.

If the adhesive strength exceeds 1.5 MPa, this adhesive strength means that the strength of the refractory itself of the intermediate layer is also strengthened accordingly. The internal structure of the intermediate layer also becomes a high strength state at the same level as the adhesive strength, thereby impairing the liveness of the intermediate layer, and the thermal expansion of the inner cavity layer is not alleviated, and easily spreads to the outer peripheral layer, increasing the risk of breaking the continuous casting nozzle.

The measurement of this adhesive strength was carried out by measuring a cylindrical (sliced) shape having a thickness of about 100 mm parallel to the cross section of the continuous casting nozzle having a middle layer of a horizontal (orthogonal to the longitudinal direction) cross section of the nozzle for continuous casting. In the furnace maintained at a predetermined temperature, the sample 10 cut out by the pressure-resistant layer 2 is formed by a pressure body 11 (a cylindrical pusher made of a refractory material having a flat bottom) of an outer diameter approximately equal to the outer diameter of the inner hole side layer. By pressing only) and dividing the charge by the adhesive area. The temperature at the time of measurement shall be 1000 degreeC, and the atmosphere shall be non-oxidizing atmosphere.

The reason why the measurement conditions of the above-mentioned livestock and adhesive strength were set in 1000 degreeC non-oxidizing atmosphere and the refractory component of an intermediate | middle layer was made to undergo the heat processing in 1000 degreeC non-oxidizing atmosphere is 1000 degreeC in organic binder component. This is because the volatilization component is sufficiently scattered to complete the carbonaceous connective tissue and thus exhibit a stable livestock and adhesion state.

The intermediate layer of the present invention is characterized in that it has an integral plural-layer structure in which simultaneous molding is performed at the time of molding with the inner pore side layer and the outer circumferential layer in part or all regions of the refractory structure. An integrated plural-layer structure means a state in which there is no space between each layer, and the matrix structures near each layer boundary are directly in contact with each other without interposing a layer such as a third adhesive material.

As will be described later, the intermediate layer of the present invention has an integral continuous structure by simultaneously forming CIP (Cold Isostatic Pressing) molding of the inner layer, the outer layer, and the top layer for each layer.

In the method mainly for the construction technology of conventional adhesives and mortars ("adhesives or mortars" are hereinafter simply referred to as "mortars", etc.), such as forming each layer separately and adhering a molded body through a silicate-based adhesive, etc. There is the same problem.

(1) When filling a thin gap with mortar or the like, unfilled portions or large bubbles are mixed or unbonded portions are formed, resulting in unstable quality of the mortar and the like.

(2) In order to ensure workability, by containing a large amount of liquid, the liquid is absorbed by the layer to be bonded to cause shrinkage such as mortar, and the shrinkage cracks of mortar or the like itself and space (peeling) are likely to occur.

(3) Since there is a drastic change in structure at the boundary between layers, stress tends to concentrate on the boundary, and breakage of the bonded portion and peeling of the bonded portion are likely to occur.

(4) In the high temperature region such as through steel, components of the adhesive and the components of the layer react to soften or melt to degrade the adhesive strength or to cause shrinkage or deformation of the layer itself, thereby weakening the fixing force of the layer. The risk of causing dropping, peeling, or destruction of the outer circumferential side layer, etc., increases.

With respect to such a prior art, if it is an integrated structure of the present invention, since it is an adhesive form based on mechanical entanglement of the components of each layer, the following effects can be obtained.

(1) A uniform amount of combustible particles can be uniformly dispersed throughout the soil during the manufacture of the clay, and the volume of the combustible particles disappeared by heat treatment is replaced with the expanded graphite particles having a fine space to uniformly and stable livestock quantity. Control is possible.

(2), adhesion through the binder component such as carbonaceous material in the intermediate layer is also expressed in the heat treatment process to stabilize homogeneously.

(3) The microcavity by the expanded graphite is finely dispersed throughout the tissue during the heat treatment process after molding, so that the expanded graphite particle portion with the fine layered space in the intermediate layer is stretched as the accordion is stretched, thereby causing large tissue breakdown as an intermediate layer. The adhesive force can be maintained without being accompanied, so that the expansion of the inner pore side layer can be absorbed uniformly.

From this, there is little risk of causing dropping, peeling of the inner pore side layer, or breakage of the outer periphery side layer, and firm interlayer fixation or stability of each layer can be obtained.

In addition, by the simultaneous integral molding as described above, the continuous casting nozzle having the above-described characteristics as compared with the case of performing mortar or the like in the prior art can be stably in a high-precision state with little variation in the structure and thickness of the refractory of the intermediate layer. Can be obtained (in the process of expanding the expandable graphite, the pressure caused by the expansion occurs inside the intermediate layer, and the components mainly composed of the expanded graphite in the intermediate layer are self-filled and dispersed to average the internal pressure in the space where the combustible material is lost, etc.) Uniformity), simplifies the manufacturing process, saves energy, shortens manufacturing time, and reduces costs.

In order to ensure the above-mentioned livestock property, adhesiveness and stability, the intermediate layer of the present invention has a structure in which a flake-like unit layer made of carbon having a thickness of 1 μm or less forms a layer with a space therebetween (“1 μm in thickness”). Lamellar unit layer made of carbon which is hereinafter referred to as " lamellar layer " This structural part is mainly composed of particles in a state in which expandable graphite (in the present invention, "expandable graphite") is expanded (in the present invention, "expanded graphite").

The livestock property of the intermediate layer of the present invention is mainly caused by the expansion of the expanded graphite particles having the lamellae structure by compressing the space between the layers with respect to the external force, and by the flexible deformation of the lamellae layer itself. When the thickness of the carbon flake layer is 1 μm or less, the property of flexibly deforming by external force is maintained while maintaining the shape of the carbon flake layer itself, and further, a space of about 10 μm or more and 200 μm or less between the carbon flake layers, It may be a space necessary for deformation or movement of the thin flakes of carbon. In addition, since the thin flakes and spaces of carbon are intertwined in three dimensions, stress can be dispersed in all directions, thereby improving livestock property, that is, stress relaxation effect.

In this invention, the whole refractory material for intermediate | middle layers is contained as a carbon component after heat processing in 1000 degreeC non-oxidizing atmosphere, containing 5 mass%-45 mass% of unexpanded expandable graphite particles, and 55 mass%-95 mass% of combustible particles. Non-oxidizing intermediate layer having the desired livestock ratio and adhesive strength without cracking or peeling by using the soil for intermediate layer with organic binder added externally so that the ratio occupies 2.5 mass% or more and 15 mass% or less. It becomes possible to form after heat processing in atmosphere.

Moreover, in this invention, 5 mass% or more and 45 mass% or less of unexpanded expandable graphite particle, 55 mass% or more and 95 mass% or less of combustible particle, and remainder consist of one or more types of components of an oxide, a carbide, a nitride, and a metal. The intermediate layer soil containing 40 mass% of refractory materials and the organic binder added externally so that the ratio which occupies for the whole refractory for intermediate layers as a carbon component after heat processing in 1000 degreeC non-oxidizing atmosphere may be 2.5 mass% or more and 15 mass% or less. By using it, the intermediate | middle layer which combines the desired livestock rate and adhesive force without a crack or peeling can be formed after heat processing in non-oxidizing atmosphere of 600 degreeC or more and 1300 degrees C or less.

The liveness of the intermediate layer of the present invention is caused by the replacement of the expanded graphite with part or all of its volume part in the course of the disappearance of the combustible particles in the layer and the components not forming carbon bonds in the organic binder during heating. As expandable graphite, it is preferable to start expansion in the temperature range which is substantially the same as the temperature at which an organic component starts heat dissipation, and it is selected from expandable graphite which differs suitably in the expansion start temperature according to the disappearance start temperature of a combustible particle, Generally It is suitably selected in the expansion start temperature range from 130 ° C to 350 ° C. The particle diameter of the expandable graphite is preferably 50 to 800 µm, more preferably 100 to 600 µm. If the thickness is less than 50 µm, the ability to fill a small space is excellent, but the expandability during heating is poor, and thus desired livestock properties are difficult to obtain. Moreover, when larger than 800 micrometers, since it has excellent expandability, it is excellent in livestock property, but there exists a tendency for three-dimensional entanglement of graphite particles to be small and adhesive strength falls.

As a constituent of the interlayer refractory material after heat treatment in a 1000 ° C. non-oxidizing atmosphere, the remaining portion other than the expanded graphite may include one or several kinds of refractory materials among oxides, carbides, nitrides, and metals.

Among these, the other refractory material particles as a constituent of the remainder other than the carbon component are mainly responsible for securing the corrosion resistance of the intermediate layer. Specifically, when the intermediate layer is damaged, in addition to preventing or preventing direct contact of molten steel with the outer circumferential side layer having poor corrosion resistance, the corrosion resistance and wear resistance of the intermediate layer itself are also secured. It also performs a skeletal function for maintaining the strength of the intermediate layer as a refractory.

The nozzle for continuous casting includes, for example, an immersion nozzle in addition to a damaged portion of the inner hole side layer itself, a boundary portion between the inner hole side layer and the nozzle body, and a weak portion of a weak portion such as a gas blowing portion or an interlayer junction portion for gas blowing. Like the ejection hole portion, there is already a portion directly exposed to molten steel in the state of the product of the nozzle for continuous casting. When the corrosion resistance, wear resistance, etc. of the part directly exposed to such molten steel are weak, continuous casting nozzles that are fatal in continuous casting operation such as molten steel invading between the air hole side layer and the outer circumferential layer by selective loss of the part. Destruction is caused.

As the refractory material applied to the refractory portion of the intermediate layer directly exposed to such molten steel, a refractory aggregate composed of at least one component selected from the group of Al ₂ O ₃ , SiO ₂ , MgO, CaO, and ZrO ₂ , specifically, alumina-silica System (corundum, mullite, sililliite, silanite, kyyanite, kaolinite) is also preferably selected in this order from the viewpoint of obtaining corrosion resistance to molten steel. -Magnesia-based spinel, zirconia, zircon, alkaline earth metal oxides and the like can be selected and used according to the degree of corrosion resistance required under conditions such as individual operation. A refractory material made of silica alone or a glassy refractory material including an alkali metal component is not used because it causes vaporization, oxidation of metal components, carbon components, and formation of low melts with other refractory materials in a reducing atmosphere. It is preferable not to.

Further, carbides such as silicon carbide and titanium carbide, nitrides such as BN and silicon nitride, and the like can also be included for the purpose of suppressing oxidation of the interlayer refractory.

Since the refractory material of the remaining part is not an indispensable element, the corrosion resistance and the like need not be included in consideration of individual operating conditions and damage conditions of the continuous casting nozzle, etc., unless it is necessary to depend on the refractory material of the remaining part.

Since the refractory material of the intermediate layer of the present invention is mainly composed of carbon having high stability in the high temperature range even at a temperature of about 1000 ° C. or higher at which the reaction such as sintering or low melting of an oxide or the like is initiated or increased, the stability of the intermediate layer itself is high. Of course, since the expanded graphite is dispersed to cover the other refractory material particles, the sintering, shrinkage, low melting, and the like rarely occur due to the mutual reaction of the refractory aggregates of other oxides. It is also an advantage of the present invention mainly containing expanded graphite.

The refractory material particles constituting the refractory materials of these intermediate layers are bonded to each other by a binder. This binder is preferably a carbonaceous connective tissue having a thermosetting resin, tar, pitch, or the like as a starting material after heat treatment at 600 ° C. or higher, since it maintains the liveness of the interlayer refractory and prevents softening or melting to maintain the bonding function even at high temperatures. Do.

Therefore, in the present invention, the organic binder is a component of the entire intermediate layer refractory material after heat treatment in a non-oxidizing atmosphere at 1000 ° C. in which the carbon component of the binder is heat-treated in a non-oxidizing atmosphere at 1000 ° C. (carbon other than the carbon component of the binder) It is added so that it may be 2.5 mass% or more and 15 mass% or less with respect to the component). If it is less than 2.5 mass%, it is advantageous for the expansion of expandable graphite and the livestock property of the intermediate layer, while sufficient adhesive strength between the inner pore side layer and the outer periphery layer cannot be obtained. If the content is more than 15% by mass, the adhesive strength is advantageous, while the expansion of the expandable graphite during the heat treatment is inhibited, so that it is difficult to secure livestock necessary as an intermediate layer.

Furthermore, in order to ensure the livestock property and sound structure required for an intermediate | middle layer, it is necessary to contain expanded graphite particle as 13.5 mass% or more as the carbon component. If it is less than 13.5 mass%, the possibility that the weak part of the structure of an intermediate | middle layer will generate | occur | produce will become high, and the possibility of shrinkage cracking of an intermediate | middle layer itself, or the adhesiveness with an inner side layer, and an outer peripheral side layer will increase.

That is, the intermediate layer of the present invention includes the expanded graphite particles and the organic binder component after the heat treatment in a 1000 ℃ non-oxidizing atmosphere, the carbon component (for example, SiC, B ₄ C in the sum of the expanded graphite particles and the organic binder component) , Except for compounds with other components such as AlC), characterized by including 16% by mass or more (including 100% by mass). That is, 16 mass% which is a lower limit of this carbon component shows the total amount of the minimum content of 13.5 mass% of expanded graphite particle, and 2.5 mass% of minimum content of an organic binder component, and the organic binder component about the part exceeding 16 mass% (Maximum content 15 mass%) and expanded graphite particle may be sufficient, and it may be comprised by carbonaceous components, such as general impression graphite and carbon black, other than the said expanded graphite particle and an organic binder component.

Moreover, 84 mass% or less of total refractory raw materials which consist of one or more types of components of an oxide, a carbide, a nitride, and a metal can be contained in the remaining part in the case of 16 mass% or more and less than 100 mass% of the said carbon component in total.

The adhesive strength is also changed by the balance between the content of the binder and the content of the combustible particles in the soil.

A binder such as silicate or phosphate containing a large amount of alkali metal is preferably not used because it may cause softening of oxides, melting, or vaporization of carbon components and the like, which may cause deterioration of the structure of the intermediate layer or other adjacent layers. Moreover, in order to maintain the structure strength especially in low temperature area | region (for example, 600 degrees C or less), it is also possible to use organic resin etc. which do not leave carbon.

Next, the manufacturing method for obtaining the nozzle for continuous casting provided with the refractory material of the intermediate | middle layer of this invention, and the refractory material of this intermediate | middle layer is demonstrated.

Continuous casting nozzle having a livestock intermediate layer of the present invention is a process for producing a dedicated clay for each layer of the inner cavity side layer, the intermediate layer and the outer peripheral layer, and forming the inner cavity side layer, intermediate layer and outer peripheral layer in the molding mold A process of providing a plurality of spaces partitioned into a predetermined size, and a step of directly contacting adjacent soils by filling each space in the molding mold with dedicated soil and removing a partition of the space; And pressurizing the clay thus directly contacted with a CIP apparatus, and forming a molded body, and heat-treating the resultant molded body at a temperature of 600 ° C. or higher and 1300 ° C. or lower in a non-oxidizing atmosphere or in an oxidizing atmosphere with an anti-oxidation treatment on the surface thereof. It can obtain by the manufacturing method to make. Prior to the heat treatment step, an independent heat treatment step for removing volatile matter, curing resin, or the like at a temperature lower than the temperature may be included.

The basic operation, work method, apparatus, etc. of each said process are the same as the manufacturing method of the nozzle for continuous casting in general, but the manufacturing method of the nozzle for continuous casting of this invention has the characteristics shown to the following 1st-3rd.

The 1st characteristic is the structure of the clay of the refractory material for intermediate | middle layers. This intermediate | middle layer topcoat is a powder part except volatilization, Comprising: (1) 5 mass% or more and 45 mass% or less of unexpanded expandable graphite particle, (2) 55 mass% or more and 95 mass% or less of combustible particle, (3) Depending on the remaining portion, the refractory raw material composed of one or more components of oxides, carbides, nitrides and metals contains 40% by mass or less (including 0% by mass), and an organic binder is added to the total of the powder portions. After heat-treating a refractory material in 1000 degreeC non-oxidizing atmosphere, the ratio which occupies for the whole refractory material for intermediate | middle layers of the carbon component (except a compound with another component) only for the said organic binder is 2.5 mass% or more and 15 mass% or less, It is made by addition.

The second feature is that CIP molding each layer as a single body at the same time seamlessly at the boundary.

A 3rd characteristic is that in the process of heat-processing an integrated molded object at 600 degreeC or more and 1300 degrees C or less, the combustible substance in the molded object of the intermediate | middle-layered clay is removed, a space is formed, and then unexpanded expandable graphite is expanded.

These features will be described in detail below.

The refractory material of the intermediate | middle layer which uses the expanded graphite of this invention as a main component already has the required livestock (similar to the livestock rate which satisfy | fills said Formula 1, hereafter simply called "product livestock") in the state of the product mentioned above. It is difficult to install with the refractory refractory material or its clay | rock, and having a simultaneous integrated structure during the shaping | molding process of a nozzle for continuous casting. That is, in the case of CIP molding (normal molding pressure is a high pressure far exceeding 2.5 MPa) on the premise of manufacturing by the apparatus, basic operation and working method according to the general continuous casting nozzle manufacturing method, the refractory having livestock property Compressed by the molding process, the refractory after molding loses livestock. Therefore, it is difficult to simultaneously produce a continuous casting nozzle using a refractory material or a clay that has the same level of livestock as the product livestock, and to obtain a continuous casting nozzle having a product livestock and having an integrated structure.

Therefore, in the step of simultaneously molding to integrate at least at a high pressure, the shaping soil has a livestock property of the degree of volumetric shrinkage according to the CIP molding of the refractory powder for continuous casting nozzles (hereinafter, to distinguish it from the above-mentioned livestock). There is little livestock on the same level as product livestock, except simply called "reduction margin".

The manufacturing method of the present invention makes it possible to obtain a nozzle for continuous casting in which the refractory material in the intermediate layer has product liveness and has an integral structure.

According to the clay of the structure shown by the said 1st characteristic, since the expanded graphite after expansion which is the main component which is responsible for the livestock in a product state exists in the unexpanded state, there is little special livestock property, and this clay has a high pressure by CIP molding. Since each component hardly reduces the volume even when exposed, the volume shrinkage of the clay can be suppressed to the extent of the reduction margin. Thereby, the predetermined volume, such as the thickness and axial dimension required as an intermediate | middle layer, can be ensured.

By the clay which can endure such CIP molding, it becomes possible to shape | mold integrally simultaneously with the clay of each refractory material for inner side and outer periphery layers other than the clay layer refractory.

It is preferable that 5 mass% or more and 45 mass% or less of the unexpanded expandable graphite particle in the said clay for the said intermediate | middle layer. If less than 5% by mass, the liveness of the refractory layer after heat treatment becomes too small, and in order to satisfy the above equation 1 regarding the liveness, it is necessary to make the thickness of the intermediate layer too large, subject to design limitations in the refractory thickness, or the layer. Variation in livestock properties for each internal part also tends to occur, which is not preferable. On the other hand, if the unexpanded expandable graphite particles exceed 45% by mass, the expandable graphite expands due to excessively exceeding the volume of the space created by the loss of the combustible particles, so that the pressure in the refractory of the intermediate layer due to expansion as the intermediate layer becomes excessively large, There is a problem that the side layer is destroyed to cause a decrease in yield.

The combustible particles in the clay for the intermediate layer are preferably 55 mass% or more and 95 mass% or less. If the content is less than 55% by mass, the space volume lost by heating the combustible particles during the heat treatment during the manufacturing process becomes too small, and the interlayer space of the expanded graphite cannot be sufficiently secured after the filling of the space due to the expansion of the expandable graphite. There is a high risk of causing a decrease. When it exceeds 95 mass%, the space volume after the disappearance becomes too large, and there is a possibility that the space including the interlayer space of the expanded graphite becomes excessive even after filling the space caused by the expansion of the expandable graphite, leading to a decrease in the strength or adhesiveness of the layer itself. It is preferable to make content of a combustible particle into the same quantity or more with respect to content of expandable graphite. As the combustible particles, polyethylene particles, polyester powder, grain flour and the like can be used. The combustible particles are preferably as small as possible with a particle size of 45 µm or smaller in order to obtain uniform space formation and uniform expanded graphite structure.

The amount of unexpanded expandable graphite particles and combustible particles in the above-mentioned intermediate layer clay may be determined by relatively adjusting to satisfy the above formula 1 relating to livestock.

The remaining part of 40 mass% or less in the said middle layer covering (the minimum amount of unexpanded expandable graphite particle is 5 mass%, the minimum amount of combustible particle is 55%, and the maximum value of remainder part is 100-5-55 = 40 And the minimum value becomes zero.) May be composed of a refractory material composed of one or more components of an oxide, carbide, nitride, and metal, which components are not essential and may not be included. These refractory materials are dependent on the conditions of the structure or shape of the individual operation, equipment, etc., that is, the degree of corrosion resistance to be provided in the intermediate layer and the amount of expandable graphite and combustible particles according to the degree of livestock (in this case, And the type, configuration, quantity, and the like may be selected and determined from the viewpoint of controlling the reactivity with the material of the inner pore side layer or the outer circumferential side layer, and the like.

Therefore, the carbon component after 600 degreeC or more heat treatment of the intermediate | middle layer refractory body of the continuous casting nozzle of this invention can also be made into the maximum 100 mass% with respect to the whole part including the binder material only when carbon type is used for the part except binder material or binder material.

Next, when other unfired expandable graphite particles, combustible particles, and other refractory material particles are included in these intermediate layers, these refractory material particles (collectively referred to as "raw particle powder") are uniform. To be mixed. And it mixes uniformly, adding the binder (solvent may be used, in that case, also a solvent) to give fluidity | liquidity, wettability, a shape retention, a bonding function, etc. to the said raw-particle powder uniformly mixed.

It is necessary to secure the refractory strength after shaping | molding and heat processing at the time of shaping | molding and a subsequent process. Therefore, in the present invention, the ratio of one or more organic binders such as various tars, pitches, phenol resins, furan resins, etc., to the entire refractory for the intermediate layer in terms of carbon components after heat treatment in a 1000 ° C. non-oxidizing atmosphere is 2.5% by mass to 15% by mass or less. Add to The more specific amount of the organic binder added is the sum of the solids mass (total amounts of carbon components after heat treatment in a non-oxidizing atmosphere at 1000 ° C. and 1000 ° C.) relative to a total of 100 parts by mass of the powder part composed of the expandable graphite, combustible particles, and the remaining refractory material. It is preferable to set it as 5 mass parts or more and 30 mass parts or less by external appearance with the other organic binder which does not remain a carbon component after heat processing in a non-oxidizing atmosphere, in solid content except the solvent from room temperature. It is because the fluidity | liquidity at the time of clay shaping | molding, compressibility, the strength after shaping | molding, etc. will fall when solid content addition amount of an organic binder exceeds 5 mass parts or 30 mass parts.

In order to ensure the strength in the low temperature range of about 300 degrees C or less from normal temperature, such as the main purpose of the shape retention after shaping | molding, you may use together the organic binder which does not remain a carbon component (carbon bond) at about 600 degreeC or more. .

As an organic binder which does not leave a carbon component (carbon bond), organic adhesives, resins, etc., such as an acrylic resin, a vinyl acetate type resin, a polyester resin, and a polyacrylonitrile resin, can also be used together.

When using together an organic binder which does not leave such a carbon component (carbon bond), the total amount of solid content (room temperature) excluding a solvent and the amount of the carbon component after heat treatment in a 1000 ° C. non-oxidizing atmosphere of the organic binder is externally added. What is necessary is just to add so that it may become 5 mass parts or more and 30 mass parts or less.

In order to improve the intensity | strength after heat processing in manufacture of the nozzle for continuous casting of this invention, it is preferable to raise the use ratio of pitches. This strength is based on the premise that the strength of the refractory itself of each layer is more than the adhesive strength, and the binder which produces the said carbon bond contributes also to the strength provision of the intermediate | middle layer itself.

In particular, in the case of adhering (or constituting a layer corresponding to the intermediate layer) with, for example, mortar using an inorganic binder such as silicate mainly using a common oxide commonly used in the prior art, hot 1000 ° C to 1500 ° C In the temperature ranges below, the reaction between the oxide component and the alkali metal oxide causes them to soften and the adhesive strength gradually decreases or melts at 1200 ° C. or higher, resulting in a significant decrease in the adhesive strength, shrinkage or melting or collapse of each layer. In addition, the sound structure of the nozzle for continuous casting is often damaged by creating a space between the layers and the like.

With respect to such a prior art, according to the bonding structure of the present invention, since the structure mainly contains carbonaceous bonds, it does not include components accompanied with sintering acceleration or low melting, and hardly deteriorates even at high temperatures. Can be solved.

Apart from the above-mentioned intermediate layer of clay, dedicated clay is produced for each layer of the inner and outer circumferential layers.

The clay of this inner pore side and outer periphery side layer can be arbitrarily arbitrarily determined so that it may be suitable for individual continuous casting conditions and objectives. However, it is assumed that all the properties such as co-molding in CIP, for example, filling property, shape retention, strength expression, and the like.

Next, a plurality of spaces partitioned to a predetermined size are formed in the molding mold for CIP to form the inner cavity side layer, the intermediate layer, and the outer peripheral side layer, and each of the predetermined spaces is filled with predetermined clay.

Thereafter, these adjacent topsoils are brought into direct contact with each other without being separated from each other. In this process, individual spaces for filling the tops of each layer are separated in advance by partition plates or the like, and each tops are filled in the spaces for each layer, and thereafter, the partitions are removed to adjoin the topsoil and the adjacent layers. It is possible to employ a method of directly contacting each layer of clay without boundaries. Alternatively, one or two of the topsoils for the intermediate layer, the inner side layers and the outer circumferential layers are temporarily formed (to produce a molded body), and this is installed in a mold for CIP molding, and the layered tops adjacent to the molded body are prescribed. It is also possible to employ a method of filling the space. In addition, it is also possible to integrate by pressurizing several times step by step each time filling each clay in the same mold and finally pressurized simultaneously.

Next, it presses by a CIP apparatus and shape | molds. The conditions, such as pressure and pressurization time at the time of shaping | molding, may be the same as the shaping | molding of a general continuous casting nozzle (about 150 MPa).

By these processes, the integral molded object in which the refractory for each layer became a multilayer structure can be obtained.

Although the obtained molded object may be dried about several hundred degrees C or less, etc., it heat-processes 600 degreeC or more and 1300 degrees C or less in non-oxidizing atmosphere or in the oxidizing atmosphere which surface-treated antioxidation. In this heat treatment step, the combustible materials (flammable particles, solvents, etc.) are lost in the molded body of the intermediate layer clay to form a space, and thereafter, the unexpanded expandable graphite is expanded to remove the combustible material, thereby expanding the formed space. (Expanded graphite) is filled.

That is, the volume portion occupied by the combustible particles in the clay is replaced by the carbonaceous layer after expansion of the expandable graphite and the multilayered structure particles with the space, and thus has a fine and uniform space volume, thereby providing a refractory layer having livestock properties. You can get it.

Loss of the combustible material and expansion of unexpanded expandable graphite proceed from about several hundred degrees Celsius, but in order to complete such a change, it is preferable to treat at a temperature of 600 degrees Celsius or more. On the other hand, when the heat treatment temperature exceeds 1300 ° C., the maximum temperature is 1300 ° C. or less because the physical properties of the refractory parts other than the refractory material of the continuous casting nozzle body and other intermediate layers of the present invention are likely to cause undesirable changes in terms of thermal shock resistance and the like. desirable.

After that, all processing such as cutting, polishing, and anti-oxidation treatment can be performed as required. Through each of these steps, the nozzle for continuous casting of the present invention can be obtained.

According to the manufacturing method having the characteristics of the present invention, not only can the nozzle for continuous casting excellent in livestock property, adhesiveness, etc., but also the continuous casting nozzle according to the prior art, that is, to manufacture individual parts for each layer and combine them with adhesive materials. Compared with the manufacturing method by the step of joining and drying again with mortar or the like, it is possible to realize a significant reduction in the number of steps and costs, and to improve the productivity as well as the accuracy of the dimensions of the nozzle for continuous casting.

The continuous casting nozzle according to the present invention has a high function such as high corrosion resistance and high inclusion prevention resistance at the pore side, that is, a continuous casting nozzle having a higher refractoriness by arranging a refractory layer having a higher thermal expansion rate than the outer periphery side layer. In addition, even if the inner and outer circumferential layers have the same degree of thermal expansion characteristics, the outer circumferential layer is depressed due to the difference in thermal expansion between the inner and outer circumferential layers. Can prevent cracking.

In addition, since the layers are integrated with each other, no special adhesive is required, and the adhesion between the layers and the fixing force superior to the bonding method by an adhesive or mortar can be obtained.

By these, the thermal shock resistance, stability, etc. of a continuous casting nozzle can be improved significantly, and the realization of the high functionalization, high internalization, etc. of a continuous casting nozzle by multilayer can be promoted.

Furthermore, by the manufacturing method of the present invention, simultaneous and integral molding are possible, so that the continuous casting nozzle having the excellent features as described above can be stably obtained with high precision and high quality, while simplifying the manufacturing process, saving energy, and manufacturing. The time required and cost reduction can be realized.

1 is a cross-sectional view showing a long nozzle to which the present invention is applied.
2 is a cross-sectional view showing another application example of the present invention.
3 is an explanatory diagram showing a method for measuring hot adhesive strength of an intermediate layer.

Best Mode for Carrying Out the Invention The best embodiment of the present invention will be described based on examples.

<Examples>

The present invention has been applied to tubular refractory structures called long nozzles used for molten steel transfer between ladle and tundish in a continuous casting process.

As shown in FIG. 1, the arrangement structure of the material with respect to the long nozzle 1 (pore diameter: φ140 mm, linear motion outer diameter: phi 226 mm, length 1500 mm) is 1500 degreeC as an inner pore side layer 2. As shown in FIG. MgO-C material (MgO = 77% by mass, C = 19% by mass) having a maximum coefficient of thermal expansion of up to 1.8% was disposed in the entire inner surface at a thickness of 10 mm and was not immersed in the molten steel bath as the outer circumferential side layer (3). Al ₂ O ₃ -SiO ₂ -C material (Al ₂ O ₃ = 50 mass%, SiO ₂ = 25 mass%, C = 25 mass) having a maximum coefficient of thermal expansion up to 1500 ° C. in the non-immersed portion (not immersed side). %) Was arrange | positioned at the thickness of 30 mm, and the intermediate | middle layer 4 for alleviating the thermal expansion of the inner cavity side layer 2 was made into the thickness of 3.0 mm.

In the clay for the intermediate layer 4, unexpanded expandable graphite particles as an expanding agent, polyethylene particles as combustible particles, alumina and magnesia fine particles as fire resistant aggregates are mixed, and pitch powder and acrylic resin are used as organic binders. After addition by external addition and granulation treatment in a high speed mixer, the residual volatiles were adjusted by a flow drying furnace to adjust the plasticity during molding. The granulated soil after granulation obtained by drying after that was sieved to 1 mm or less, and it was set as the compound for intermediate | middle layers.

The details are shown in Table 1. The livestock rate and hot adhesive strength (compressive shear strength) of the intermediate | middle layer of Table 1 were measured by the method demonstrated above. In the long nozzle 1 of this embodiment, the livestock rate required for the intermediate layer by the formula 1 is 34% or more.

For comparison, Comparative Example 1 was prepared by inserting the inner pore side layer 2 into the outer circumferential side layer 3 using mortar of a general sludge type. In this comparative example 1, the livestock property of the intermediate | middle layer measured by the actual shape was not acquired, and the crack and peeling of the inner periphery side layer generate | occur | produced in the 1st pouring test.

In Comparative Example 2, 50 mass% of expandable graphite was included, the remaining part was 50 mass% of combustible particles, and 5 mass parts of pitch were added by external addition. In the heat treatment process at the time of manufacture, cracking occurred by pressing on the outer peripheral layer. . This is because the expandable graphite exceeded the upper limit of 45% by mass at 50% by mass, and the outer peripheral layer was pressed by the expansion force of the expandable graphite during the heat treatment.

Examples 1 to 3 and Comparative Examples 3 and 4 are made of 45% by mass of expandable graphite, an organic binder, and a carbon component of a pitch component in terms of the carbon component amount in a 1000 ° C. non-oxidizing atmosphere (hereinafter referred to as the “pitch component” It is the result of changing to 2.0-16 mass%.

The increase in adhesive strength is observed with the increase in the pitch coal component.

In Examples 1 to 3 and Comparative Example 3, the expandable graphite was sufficiently expanded during the heat treatment to fill the space occupied by the polyethylene particles, thereby obtaining a large livestock rate. However, in Comparative Example 3 in which the pitch coal component was reduced to 2% by mass, sufficient adhesive strength could not be obtained, and the inner body was dropped by the pouring test. Moreover, in the comparative example 4 which is a case where the pitch coal component was increased to 16 mass%, adhesive strength became too strong and sufficient livestock property was not acquired, and the crack generate | occur | produced in the pouring test 1st time.

In Examples 1 to 3, even if the actual yield and pouring test were repeated, no problems occurred and good results were obtained.

Comparative Example 5 is a case of not using the expandable graphite, but the necessary level of both livestock and adhesive strength could not be obtained, and peeling phenomenon occurred in the pouring test.

Example 4 to Example 6 were cases where the combustible particles were further increased, but both livestock and adhesive strength could be sufficiently obtained to obtain good results.

Comparative Example 6 is a case where the flammable particles were further increased. The livestock property was sufficient, but the adhesive strength could not be obtained, so that the dropping phenomenon occurred by the pouring test.

Example 7 and Example 8 are a case where a part of combustible particle is substituted by fire resistant particle. Livestock and adhesiveness could be obtained sufficiently and good results could be obtained. In Comparative Example 7, although the refractory particles were increased more than in Example 7, sufficient animal properties could not be obtained, and shrinkage cracks appeared in the intermediate layer, so that sufficient adhesive strength could not be obtained. As a result, in the pouring test, a phenomenon in which the inner air side layer fell off occurred a second time.

The above embodiment is applied to the long nozzle shown in FIG. 1, but the present invention is not limited thereto, and can be applied to, for example, the tubular refractory structure shown in FIG.

2 (a) and 2 (b) are applied to the same long nozzle as in the example of FIG. 1, the example of FIG. 2 (a) also arranges the refractory of the outer peripheral layer 3 at the lower end of the long nozzle 1. And the intermediate | middle layer 4 is arrange | positioned also between the lower end part of the inner cavity side layer 2, and the outer peripheral layer 3. In addition, in the example of FIG. 2 (b), the refractory of the outer circumferential side layer 3 is also disposed at the upper end and the lower end of the long nozzle 1, and also between the upper end and the lower end of the inner vacant side layer 2 and the outer circumferential side layer 3. The intermediate layer 4 is arrange | positioned.

The example of FIG. 2 (c) is applied to an immersion nozzle. In the immersion nozzle 1 'shown in Fig. 2C, the outer circumferential side layer 3 is composed of an AG material 3a and a ZG material 3b, and the discharge hole 5 is formed on the side with a bottomed structure. Prepared. The inner pore side layer 2 also had a bottomed structure, and the intermediate layer 4 was disposed entirely between the inner pore side layer 2 and the outer circumferential side layer 3.

1 long nozzle
1 'immersion nozzle
2 inner layer
3 outer circumferential floor
3a AG Material
3b ZG material
4 mezzanine
5 discharge hole
10 samples
11 Pressurized Body

Claims (6)

Consisting of a tubular refractory structure having an axially oriented internal hole through which molten metal passes, and thermal expansion of the refractory of the inner circumferential layer in some or all of the region of the tubular refractory structure is carried out by In the nozzle for continuous casting larger than the thermal expansion,
An intermediate layer having livestock properties exists between the inner pore side layer and the outer periphery side layer as a multi-layer structure which is integrated at the same time during molding.
The adhesion strength in the 1000 degreeC non-oxidation atmosphere of an intermediate | middle layer, an inner side layer adjacent to this intermediate | middle layer, and an outer peripheral side layer is 0.01 Mpa or more and 1.5 Mpa or less,
Also,
A continuous casting nozzle, wherein the livestock rate K (%) of the intermediate layer in a 1000 ° C. non-oxidizing atmosphere under a pressure of 2.5 MPa satisfies the following expression (1).
K ≧ [(Di × αi-Do × αo) / (2 × Tm)]... Equation 1
Di: Outer diameter (mm) of inner side layer
Do: Inner diameter of the outer circumferential side layer (mm)
Tm: Initial thickness (mm) from room temperature of a middle layer
(alpha) i: Maximum thermal expansion rate (%) in the range from room temperature to 1500 degreeC of the refractory body of an inner side layer
αo: Thermal expansion rate (%) at the temperature at the start of the passage of the refractory of the outer peripheral layer The method of claim 1,
The said intermediate | middle layer contains expanded expandable graphite particle (Hereinafter, "expanded expandable graphite particle" is called "expanded graphite particle") after heat processing in non-oxidizing atmosphere of 600 degreeC or more, The continuous casting nozzle characterized by the above-mentioned. The method according to claim 1 or 2,
A nozzle for continuous casting, wherein the intermediate layer contains at least 16 mass% (including 100 mass%) of carbon components (excluding compounds with other components) after heat treatment in a non-oxidizing atmosphere at 1000 ° C. The method according to claim 1 or 2,
After the heat treatment in a non-oxidizing atmosphere at 100 ° C., the intermediate layer contains 16 mass% or more of carbon components (excluding compounds with other components), and the remaining portions other than the carbon components are one of oxides, carbides, nitrides, and metals. Continuous casting nozzle, characterized in that the refractory raw material consisting of more than a kind of components. Continuous casting nozzles consisting of a tubular refractory structure having axially pierced inner pores through which molten metal passes, with some or all of the regions having an inner cavity side, an intermediate layer, and an outer circumferential layer in turn from the inner surface to radially outwardly As a manufacturing method of
The clay for intermediate | middle layer contains 5 mass% or more and 45 mass% or less of unexpanded expandable graphite particle, 55 mass% or more and 95 mass% or less of combustible particle, and also contains the organic binder and the refractory material for said intermediate layer is 1000 degreeC non-oxidization. The unexpanded expandable graphite particles such that the ratio of the carbon component of the organic binder alone (excluding compounds with other components) to the entire refractory for the intermediate layer after heat treatment in an atmosphere is 2.5% by mass or more and 15% by mass or less. And the clay added to the sum of flammable particles externally,
The middle layer soils together with the inner layer soils and the outer layer layers are simultaneously pressurized and molded by a CIP apparatus,
By heat-treating the obtained molded object at 600 degreeC or more and 1300 degrees C or less, the combustible substance in the molded object of the said intermediate | middle layered clay was lost, and a space was formed, Then, the unexpanded expandable graphite in the molded object of the said intermediate | middle layered clay was expanded, and the said space was made A method for producing a nozzle for continuous casting comprising the step of filling with expanded expanded graphite. Continuous casting nozzles consisting of a tubular refractory structure having axially pierced inner pores through which molten metal passes, with some or all of the regions having an inner cavity side, an intermediate layer, and an outer circumferential layer in turn from the inner surface to radially outwardly As a manufacturing method of
A fire-resistant raw material composed of at least 5% by mass to 45% by mass of unexpanded expandable graphite particles, at least 55% by mass to 95% by mass of combustible particles, and at least one component of an oxide, carbide, nitride, and metal. Containing a total of 40% by mass or less of the organic binder, and the interlayer refractory material of the carbon component (excluding the compound with other components) only of the organic binder after heat-treating the refractory material for the intermediate layer in a 1000 ° C. non-oxidizing atmosphere. It is added externally with respect to the sum total of the said refractory graphite particle | grains, combustible particle | grains, and the refractory raw material which consists of one or more types of components of an oxide, a carbide, a nitride, and a metal so that the ratio to the whole may be 2.5 mass% or more and 15 mass% or less. Prepare a clay,
The middle layer soils together with the inner layer soils and the outer layer layers are simultaneously pressurized and molded by a CIP apparatus,
By heat-treating the obtained molded object at 600 degreeC or more and 1300 degrees C or less, the combustible substance in the molded object of the said intermediate | middle layered clay was lost, and a space was formed, Then, the unexpanded expandable graphite in the molded object of the said intermediate | middle layered clay was expanded, and the said space was made A method for producing a nozzle for continuous casting comprising the step of filling with expanded expanded graphite.

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