JP5582813B2 - Manufacturing method of ceramic member for molten metal - Google Patents

Description

  The present invention relates to a molten metal ceramic member used in a contact environment with a molten metal such as molten aluminum and a method for producing the same.

  Conventionally, in low-pressure casting equipment, parts for molten metal used in a contact environment with molten metal, such as stalk that constitutes a hot water supply pipe for discharging molten metal (typically molten aluminum) from a molten metal crucible It has been known.

In recent years, ceramics have been used as such molten metal parts. In particular, silicon nitride (Si ₃ N ₄ ) -based ceramic sintered products that have high heat resistance and corrosion resistance, as well as high strength, resistance to thermal and mechanical shock, and excellent stability as structural materials are used in many applications. It is practically used.

  However, even if it is a ceramic member for molten metal formed of a silicon nitride ceramic sintered product, if it is used for a long period of time, the molten metal ingot, its oxide, slag, etc. will adhere to the surface. The problem of being unusable due to deposits arises. For example, in the case of a tubular molten metal ceramic member inserted into a hole formed in the lid of the molten metal crucible, there is a problem that it cannot be removed from the hole due to the deposited deposit on the outer peripheral surface thereof.

  As a countermeasure against such a problem, a technique is known in which a surface layer is formed from a material having low wettability to molten metal (for example, boron nitride) (Non-Patent Document 1). Further, in Patent Document 1, a silicon nitride ceramic molded body is embedded in boron nitride (BN) powder, and this molded body is sintered to form a layer mainly composed of boron nitride on the surface. The technology is described. Patent Document 2 discloses a technique for forming a surface layer containing boron nitride as a main component by spraying or brushing a ceramic powder containing boron nitride together with an organic binder on a sialon-based ceramic compact and sintering. Is described.

  However, in Patent Documents 1 and 2, the surface layer containing boron nitride is obtained by sintering without being pressure-molded. Therefore, the surface layer is easily peeled off by intermittent use, and the effect cannot be stably maintained for a long time.

  Therefore, in Patent Document 3, after forming a coating film of mixed powder of boron nitride and base ceramic on the surface of a required region of the mold member constituting the mold, the mold is filled with the powder of the base ceramic and cooled. It is pressure-molded by isostatic pressing with isostatic water. And the ceramic member for molten metals in which the surface layer containing a boron nitride was formed by sintering a molded object is manufactured.

  FIG. 13 is a diagram showing the flow of the manufacturing method described in Patent Document 3. First, as shown in FIG. 13 (a), a slurry containing a mixed powder of boron nitride and base ceramic is applied to the surface of a cored bar 112 constituting the mold, and boron nitride and base ceramics are applied. Is formed. FIG. 13B shows a state in which the mixed coating film 134 is formed.

  Next, as shown in FIG. 13 (c), a cylindrical rubber mold 111 whose axis coincides with the cored bar 112 is disposed. Thereafter, as shown in FIG. 13 (d), a granulated material 121 made of a base ceramic material is filled between the core metal 112 and the rubber mold 111 and sealed with a rubber lid 114. And by pressurizing with cold isostatic press (CIP), as shown in (e) of FIG. 13, the compact 122 by which the granulated material 121 was press-molded, and its internal peripheral surface A molded body is obtained which is formed on the green compact layer 135 formed on the pressure-molded mixed coating film 134.

  Thereafter, as shown in FIG. 13F, the surface is cut so that the outer diameter of the green compact 122 becomes a predetermined dimension. Then, by sintering, the base portion 102, which is a sintered body of the raw material powder of the base ceramic, and the mixed powder of boron nitride and base ceramic formed on the inner peripheral surface of the base portion 102 are sintered. A ceramic member for molten metal including a composite layer 103 which is a bonded body is manufactured.

JP 63-190786 A (published on August 8, 1988) Japanese Unexamined Patent Publication No. 1-176289 (published July 12, 1989) Japanese Patent Laid-Open No. 5-301757 (published on November 16, 1993)

Jiro Tsuchida and two others, “Improvement of Wetting Characteristics on Silicon Nitride Ceramics Surface”, Kubota Technical Report, Kubota Corporation, No.29, P82-91, 1995

  In the technique of Patent Document 3, since the composite layer is formed by sintering the compacted layer that has been press-formed by cold isostatic pressing, the density of the composite layer is relatively high, and the base portion Adhesiveness to the composite layer is also high. Therefore, it can prevent that a composite layer peels off. However, there is a problem that the composite layer is worn out by long-term use. Therefore, it is desirable to increase the thickness of the composite layer in order to increase the service life. However, in the technique of Patent Document 3, since a mixed coating film is formed by applying a slurry containing a mixed powder of boron nitride and a base ceramic material to a mold member, the composite layer containing boron nitride is made thick. It was difficult.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a ceramic member for molten metal having a thick composite layer containing a material having low wettability with respect to the molten metal on the surface, and a method for producing the same. To do.

  The method for producing a ceramic member for molten metal according to the present invention is a method for producing a ceramic member for molten metal that comes into contact with the molten metal, and a first molded body is produced by pressure molding a raw material powder of a base ceramic material. A low wettability material, which is a material having lower wettability with respect to the molten metal than the base ceramic, between the first molding step and at least a part of the surface of the first molded body and the mold. Filling a mixed powder of the powder and the raw material powder of the base ceramic material, and forming a second molded body by pressure molding; a sintering process for sintering the second molded body; It is characterized by including.

  According to the above configuration, the second molded body is formed by filling a mixed powder of the low wettability material powder and the raw material powder of the base ceramic material between the first molded body and the molding die, and performing pressure molding. Is making. Therefore, a 2nd molded object will contain the 1st molded object and the compacting layer of the said mixed powder joined to the surface of the 1st molded object. And, by sintering the second molded body, the base part in which the first molded body made of the base ceramic material is sintered, and the low wettability material covering at least a part of the surface of the base part, A ceramic member for molten metal in which a composite layer, which is a sintered compact of a dust layer containing a base ceramic material, is integrated can be manufactured.

  Here, since the thickness of the dust layer depends on the distance between the first molded body and the mold, the thickness of the dust layer can be increased by appropriately setting the shape of the mold. Therefore, a ceramic member for molten metal having a thick composite layer on the surface can be produced.

  In addition, the shape of the 1st molded object and the 2nd molded object can be made into various shapes by selecting a shaping | molding die suitably. For example, when a hollow cylindrical mold is used in the first molding step, a hollow cylindrical mold in which a space is formed between the outer periphery of the first molded body also in the second molding step. If it uses, the ceramic member for molten metal in which the thick composite layer was formed also in the outer peripheral surface of the hollow cylindrical base | substrate part can be manufactured.

  Moreover, the manufacturing method of the ceramic member for molten metal which concerns on this invention is a manufacturing method of the ceramic member for molten metal which contacts a molten metal, Comprising: The 1st molded object by press-molding the raw material powder of a base material ceramics And forming the first molded body as a molding object, and the wettability with respect to the molten metal is higher than that of the base material ceramic between at least a part of the surface of the molding object and the molding die. The second molding that performs the low wettability material molding process of filling the mixed powder of the low wettability material powder, which is a low material, and the raw material powder of the above-mentioned base material ceramics, and forming an intermediate molded body by pressure molding A step of forming a second molded body by performing the low wettability material molding process at least once with the intermediate molded body as a molding target, and sintering for sintering the second molded body In each of the plurality of low wettability material molding processes, the weight ratio of the low wettability material in the mixed powder is set to the low wettability in the mixed powder used in the previous low wettability material molding process. It is characterized by being larger than the weight ratio of the material.

  According to said structure, in order to perform the low wettability material shaping | molding process of multiple times, low wettability material and base material ceramics are formed in the at least one part area | region of the surface of the base | substrate part which sintered the 1st molded object. A plurality of composite layers can be stacked.

  Further, in each of the low wettability material molding processes, the weight ratio of the low wettability material in the mixed powder is set to be larger than the weight ratio of the low wettability material in the mixed powder used in the previous low wettability material molding process. Yes. Therefore, the difference between the shrinkage rate during sintering and the thermal expansion coefficient after sintering between the first molded body and the composite layer adjacent thereto can be reduced. Similarly, the difference between the shrinkage ratio during sintering and the thermal expansion coefficient after sintering can be reduced also between adjacent composite layers. As a result, the stress generated at the interface between the first molded body and the adjacent composite layer and the interface between adjacent composite layers can be relaxed, and the quality of the ceramic member for molten metal can be improved. .

  A method for producing a ceramic member for molten metal according to the present invention is a method for producing a ceramic member for molten metal having a hollow cylindrical shape in contact with a molten metal, wherein the matrix ceramic is formed on the outer peripheral surface of a cylindrical cored bar. A coating film forming step for forming a coating film of a mixed powder of the raw material powder and a powder of a low wettability material which is a material having lower wettability with respect to the molten metal than the base material ceramic; and the columnar core Then, the base ceramic powder material powder is filled in a mold having a hollow cylindrical mold made of an elastic body whose axial center coincides with the cylindrical core metal, and is pressed by cold isostatic pressing. A first molding step for producing a first molded body by pressure molding, an arrangement step for arranging the first molded body again in the mold, and the first molded body and the hollow cylindrical mold. Filled with the above mixed powder , Characterized in that it comprises a second forming step of preparing a second molded body by pressure molding by cold hydrostatic isostatic pressing, a sintering step of sintering the second mold body.

  According to the above configuration, the low wettability material and the base material ceramics, in which the powder layer of the coating film is sintered on the inner peripheral surface of the hollow cylindrical base body which is a sintered body of the base material ceramics, The composite layer can be formed. Further, a composite layer of a low wettability material and a base ceramic is formed on the outer peripheral surface of the base body by sintering a powder layer of the mixed powder filled between the first molded body and the mold member. it can. And the composite layer formed in the outer peripheral surface can be thickened by selecting the dimension of a shaping | molding die suitably. The outer peripheral surface is highly likely to come into contact with other parts, and wear resistance is required, but with the above configuration, a thick composite layer is formed on the outer peripheral surface, so that the service life of the ceramic member for molten metal is increased. Can be lengthened.

  Moreover, since the same shaping | molding die can be used by a 1st shaping | molding process and a 2nd shaping | molding process, manufacturing cost can be held down.

  Furthermore, in the method for producing a ceramic member for molten metal according to the present invention, it is preferable that the pressure P2 for pressure forming in the second forming step is equal to or higher than the pressure P1 for pressure forming in the first forming step.

  According to said structure, in a 2nd shaping | molding process, sufficient pressure can be applied also to the mixed powder of the low wettability material and the raw material of base material ceramics, and the compacted layer of mixed powder is shape | molded more reliably. be able to.

  In addition, although P2 = P1 may be sufficient, it is more preferable that P2> P1. If P2> P1, the first molded body further contracts in the second molding step. Therefore, in the second molding step, a part of the mixed powder of the low wettability material and the raw material of the base ceramic material enters the first molded body, and the first molded body is bonded to the green compact layer of the mixed powder. Can be improved.

  Further, if P2> P1, in the first molding step and the second molding step, a molding die whose inner space is a hollow cylindrical shape is used, and in the second molding step, the inner peripheral surface of the first molded body and the molding die are used. Even when the mixed powder of the low wettability material and the raw material of the base ceramic material is filled in between, pressure can be appropriately applied to the mixed powder and molding can be performed.

  Furthermore, in the method for producing a ceramic member for molten metal according to the present invention, the base ceramic is a silicon nitride ceramic, the low wettability material is boron nitride, and the weight of the low wettability material with respect to the mixed powder. The ratio is preferably 5 to 50% by weight.

  According to the above configuration, by setting the weight ratio of the low wettability material to the mixed powder to 5% by weight or more, in the composite layer in which the mixed powder of the low wettability material and the base ceramic is sintered, low wettability is achieved. Sexual effects can be exhibited. Further, by setting the weight ratio of the low wettability material to 50% by weight or less, it is possible to provide a ceramic member for molten metal that has no problem in strength and is less likely to crack during sintering.

  Furthermore, in the method for manufacturing a ceramic member for molten metal according to the present invention, the pressure molding in the first molding step and the second molding step is preferably molding by cold isostatic pressing.

  According to said structure, a pressure can be uniformly applied to powder in a 1st shaping | molding process and a 2nd shaping | molding process. As a result, a homogeneous ceramic member for molten metal can be provided.

  Furthermore, the manufacturing method of the ceramic member for molten metal which concerns on this invention produces the said 1st molded object of a predetermined dimension by shaving the surface of the green compact obtained by pressure forming in the said 1st shaping | molding process. May be.

  According to said structure, even if there exists an unevenness | corrugation on the surface of the green compact obtained by the pressure molding of a 1st shaping | molding process, the 1st molded object of a predetermined dimension can be obtained.

  The ceramic member for molten metal according to the present invention is a ceramic member for molten metal that comes into contact with the molten metal, and sinters the green compact obtained by pressure-molding the raw material powder of the base ceramic material. A base portion, a low wettability material formed on at least a partial region of the surface of the base portion, and having a lower wettability with respect to the molten metal than the base ceramic, and the base ceramic. The composite layer is formed by press-molding the powder mixture of the low wettability material and the raw material powder of the base ceramic material and the green compact. It is characterized by being formed by sintering the green compact layer.

  According to the above configuration, the composite layer bakes the green compact layer formed by pressing the powder of the low wettability material and the mixed powder of the raw material powder of the base ceramic and the green compact. It is formed by tying. Therefore, when the pressure molding is performed, the powder compact layer can be formed by filling the mixed powder between the compact and the mold. Moreover, the thickness of a compacting layer can be thickened by enlarging this space | interval. Therefore, the thickness of the composite layer can be increased.

  The ceramic member for molten metal according to the present invention is a ceramic member for molten metal that comes into contact with molten aluminum, and includes a hollow cylindrical base portion made of silicon nitride-based ceramic, and a surface of the base portion. A composite layer containing silicon nitride-based ceramics and boron nitride formed on at least a part of a region in contact with the molten aluminum, wherein the composite layer has a thickness greater than 0.5 mm. Features.

  According to said structure, the ceramics for molten metals which have a thick composite layer can be provided.

  The method for producing a ceramic member for molten metal according to the present invention includes a first forming step of producing a first formed body by pressure forming a raw material powder of a base ceramic material, and at least one of the surfaces of the first formed body. Filling the mixed powder of the low wettability material powder, which is a material whose wettability to the molten metal is lower than that of the base ceramic, and the raw material powder of the base ceramic, between the region of the part and the mold, It includes a second molding step for producing a second molded body by pressure molding, and a sintering step for sintering the second molded body.

  The ceramic member for molten metal according to the present invention includes a base portion obtained by sintering a green compact obtained by pressure forming a raw material powder of a base ceramic material, and at least a part of the surface of the base portion. A composite layer including a low wettability material, which is a material having lower wettability with respect to the molten metal than the base ceramic material, and the base ceramic material, and the composite layer includes: It is formed by sintering a powder layer formed by press-molding a powder mixture of a low wettability material and a raw material powder of the base ceramic material and the green compact.

  In the ceramic member for molten metal according to the present invention, the thickness of the composite layer is greater than 0.5 mm.

  Therefore, it is possible to provide a ceramic member for molten metal having a thick composite layer including a material having low wettability with respect to the molten metal on the surface, and a method for manufacturing the same.

It is a perspective view which shows the ceramic member for molten metals which concerns on one Embodiment of this invention. It is a flowchart which shows the flow of the process of a 1st manufacturing method. It is sectional drawing which shows the shaping | molding die and green compact in the 2nd type | mold filling process from the 1st type | mold filling process of a 1st manufacturing method. It is sectional drawing which shows the shaping | molding die from the 2nd mold filling process of a 1st manufacturing method to a baking process, a green compact, and a finished product. It is a flowchart which shows the flow of the process of a 2nd manufacturing method. It is a perspective view which shows an example of the ceramic member for molten metals manufactured by the 2nd manufacturing method. It is a flowchart which shows the flow of the process of a 3rd manufacturing method. It is sectional drawing which shows the shaping | molding die in a 3rd manufacturing method, a molded object, and a finished product. 2 is a view showing a cross section of a ceramic member for molten metal of Example 1. FIG. It is a figure which shows the external appearance photograph of the ceramic member for molten metals of Example 2. FIG. 6 is a view showing an external appearance photograph of the vicinity of an interface between a base portion and a composite layer in a ceramic member for molten metal of Example 2. FIG. It is a figure which shows the adhesion result of the aluminum with respect to the ceramic member for molten metals of Example 2. FIG. It is sectional drawing which shows the shaping | molding die, molded object, and completed product in the manufacturing method of the conventional ceramic member for molten metals.

  Hereinafter, embodiments of the present invention will be described in detail.

  The ceramic member for molten metal according to the present embodiment is a component that is used in a contact environment with the molten metal. Here, the molten metal is, for example, molten aluminum or molten aluminum alloy. Hereinafter, the molten metal mainly composed of aluminum is referred to as molten aluminum.

(Structure of ceramic member for molten metal)
FIG. 1 is a perspective view showing an example of a ceramic member for molten metal according to the present embodiment. As shown in FIG. 1, a ceramic member 1 for molten metal includes a base portion 2 that is a sintered body of a raw material powder of a base ceramic material excellent in heat resistance and corrosion resistance, and at least one of the surfaces of the base portion 2. And a composite layer 3 which is a sintered body of a mixed powder of a low wettability material having low wettability to a molten metal and a raw material of a base ceramic material.

  The base ceramic material used as the material of the base portion 2 may be appropriately selected in consideration of heat resistance, corrosion resistance, resistance to thermal and mechanical shocks, and the like.

As the base material ceramic, for example, silicon nitride (Si ₃ N ₄ ) -based ceramics can be used. Silicon nitride ceramics are known to have excellent mechanical strength even at high temperatures such as molten aluminum, can withstand rapid heating and quenching, and are resistant to corrosion. The silicon nitride-based ceramic is a polycrystal having silicon nitride as a main component, and may contain various sintering aids such as Y ₂ O ₃ and MgO. Silicon nitride ceramics also include sialon in which silicon and nitrogen are partially substituted with aluminum and oxygen, respectively.

  As the low wettability material included in the composite layer 3, a material having a wettability with respect to a molten metal smaller than that of the base material ceramic constituting the base portion 2 may be appropriately selected.

  Here, the wettability is generally determined by the size of the contact angle, which is the angle formed by the free surface of the liquid and the solid surface with which the liquid (here, the molten metal) is in contact with the solid surface. The wettability is lower as the contact angle is larger.

  For example, it is known that the contact angle of silicon nitride is 126 ° with respect to 1000 ° C. molten aluminum, whereas the contact angle of boron nitride is 157 ° (see Non-Patent Document 1). Therefore, when the molten metal is a molten aluminum and the base ceramic is a silicon nitride ceramic, it is preferable to use boron nitride as the low wettability material.

  For the following reasons, when the base ceramic is a silicon nitride ceramic and the low wettability material is boron nitride, the ceramic raw material constituting the composite layer 3 (that is, a mixture of silicon nitride ceramic and boron nitride). The weight ratio of boron nitride in the powder is preferably 5% by weight to 50% by weight.

  In order to exhibit the effect of low wettability of boron nitride, it is necessary to expose boron nitride to the surface of the composite layer 3 to some extent. A sintered compact obtained by sintering a green compact of a mixed powder of boron nitride and a base ceramic material was immersed in molten aluminum, and the adhesion of aluminum to the sintered body was evaluated. It was confirmed that the effect of lowering the adhesion amount of aluminum is exhibited when the weight ratio is 5% by weight or more. Therefore, the weight ratio of boron nitride is preferably 5% by weight or more.

  Boron nitride is a hard-to-sinter material and has low mechanical strength. Therefore, if the weight ratio of boron nitride is increased too much, the strength will decrease. In addition, the possibility of cracking during sintering increases due to the difference in coefficient of thermal expansion with silicon nitride ceramics, which are the base material ceramics. If the compounding ratio of boron nitride in the composite layer 3 is 50% by weight or less, there is no problem in strength, and cracking during sintering is less likely to occur. Therefore, the weight ratio of boron nitride is preferably 50% by weight or less. .

  The composite layer 3 is formed thicker than before by a manufacturing method to be described later, specifically, thicker than 0.5 mm. Thereby, even if it is worn down to some extent, the composite layer 3 is not lost, and the service life can be prolonged. In addition, it is preferable that the thickness of the composite layer 3 is larger than 0.5 mm, More preferably, it is 0.8 mm or more, More preferably, it is 1.0 mm or more.

  Since boron nitride has a lower strength than the base ceramic as described above, the thickness of the composite layer 3 can be increased as the weight ratio A of boron nitride in the composite layer 3 is smaller. That is, the upper limit value Dmax of the thickness of the composite layer 3 may be set in inverse proportion to the size of the weight ratio A of boron nitride in the composite layer 3. Specifically, Dmax can be set by α × (1 / A) (α is a constant set in consideration of the shape of the base body 2 and the like).

  Here, the base portion 2 has a hollow cylindrical shape as shown in FIG. 1, and when the composite layer 3 is formed on the surface thereof, the strength tends to increase as the curvature radius of the composite layer 3 increases. Therefore, when the radius of curvature of the surface of the base portion 2 on which the composite layer 3 is formed is R, α can be set to a value proportional to R.

  In FIG. 1, the shape of the base portion 2 is a hollow cylindrical shape, but the shape of the base portion 2 is not limited to this. For example, in the case of a thermocouple protection tube or a heater protection tube, it has a bottomed hollow cylindrical shape. Moreover, a box shape, a dish shape, and a plate shape may be sufficient.

(First manufacturing method)
Next, the 1st manufacturing method of the ceramic member for molten metals which concerns on this embodiment is demonstrated. FIG. 2 is a flowchart showing the flow of each process of the first manufacturing method. In the following description, it is assumed that the base ceramic constituting the base portion 2 is a silicon nitride ceramic and the low wettability material is boron nitride. Further, a case where a hollow cylindrical ceramic member for molten metal is manufactured will be described as an example.

<S (STEP) 1: Raw material weighing step>
First, the raw materials for the ceramics constituting each of the base portion 2 and the composite layer 3 are weighed. For the base 2, powders of sintering aids such as silicon nitride and Y ₂ O _{3 which} are raw materials for silicon nitride ceramics are weighed so as to have a predetermined ratio. On the other hand, for the composite layer 3, the raw material powder of boron nitride, which is a low wettability material, and a silicon nitride, a sintering aid such as Y ₂ O ₃ , which is a raw material for silicon nitride ceramics, has a predetermined ratio. Weigh. The boron nitride particles are mainly agglomerated particles, and the particle size is, for example, 5 to 20 μm.

<S2: mixing and grinding step>
Next, the powder obtained in the raw material weighing step of S1 is mixed and pulverized for each raw material of the base portion 2 and the composite layer 3. Various dry pulverizers and wet pulverizers may be used as the mixing and pulverizing method. Thereby, each of the raw material powder of the base material ceramics which comprises the base | substrate part 2, and the mixed powder of the ceramics which comprises the composite layer 3 can be obtained.

<S3: Granulation process>
Subsequently, the powder obtained in S2 is granulated into granules for each of the base portion 2 and the composite layer 3. At this time, a binder resin is added to make the powder granular. As a granulation method, for example, a spray dryer can be used. However, the granulation method is not limited to this, and a known technique can be used.

<S4: First mold filling step>
The granulated product of the raw material powder of the base material ceramics constituting the base portion 2 obtained in S3 is filled into a molding die for pressure molding.

  FIG. 3A is a cross-sectional view showing an example of a molding die filled with a granulated product 21 of a raw material powder of a base ceramic material. In the example shown in FIG. 3A, the molding die is a rubber die (hollow cylindrical shape mold) 11 having a hollow cylindrical shape, and a columnar shape arranged so that the rubber die 11 and the axis coincide with each other. A metal core (molding die) 12, a metal mold 13 attached to one opening end face of the rubber mold 11, and a rubber lid 14 attached to the other opening end face of the rubber mold 11. The hollow cylindrical space inside the mold is filled with a granulated product 21 of the raw material powder of the base ceramic material.

  Here, the case where the rubber mold 11 is used as the hollow cylindrical mold will be described as an example. However, the material of the hollow cylindrical mold is not limited to rubber, and may be an elastic body.

<S5: First pressure molding step>
Next, pressure is applied to the forming die filled with the granulated material 21 of the raw material powder of the base ceramic material to form the raw material powder of the base material ceramic material.

  For example, in the example shown in FIG. 3, the granulated product 21 of the raw material powder of the base ceramic material can be formed by pressurizing with a cold isostatic press (CIP). When CIP is used, a green compact (first molded body) 22 having a uniform density can be formed by a uniform action at a high pressure. In addition, when using CIP, it can shape | mold, for example with a pressure of about 50-150 MPa, and holding time of about 10-60 seconds.

  In addition, you may press-mold using a uniaxial press molding method.

<S6: First surface processing step>
A green compact 22 obtained by pressure-molding the granulated material 21 of the raw material powder of the base ceramic material is taken out from the mold and subjected to surface processing so as to have a predetermined size. In particular, when pressure molding by CIP is performed using a rubber mold 11 as shown in FIG. 3A, the surface in contact with the rubber mold 11 is uneven. FIG. 3B is a cross-sectional view showing the green compact 22 taken out from the mold shown in FIG. As shown in the drawing, it can be seen that the outer peripheral surface in contact with the rubber mold 11 has irregularities. Therefore, surface processing for smoothing the outer peripheral surface is performed so as to obtain a predetermined dimension. Specifically, the surface may be cut using a lathe or the like.

  In addition, when using the uniaxial press molding method using only a metal mold | die without using a rubber mold, the surface processing process of S6 may be omitted.

<S7: Second mold filling step>
The green compact 22 obtained in the step S6 is again placed in the mold. Then, the gap between the green compact 22 and the molding die is filled with the granulated product of the mixed powder of the ceramic raw material constituting the composite layer 3 obtained in S3.

  For example, when the same mold as that shown in FIG. 3A is used, a gap is formed between the outer peripheral surface of the green compact 22 and the rubber mold 11 as shown in FIG. The gap may be filled with a granulated product of a mixed powder of the low wettability material and the raw material of the base ceramic material.

  As shown in FIG. 4A, a cored bar 12 'having an outer diameter smaller than that of the cored bar 12 may be used instead of the cored bar 12 used in the first pressure molding step. As a result, a gap is also formed between the inner peripheral surface of the green compact 22 and the cored bar 12 ′, and a granulated product of the mixed powder of the low wettability material and the raw material of the base ceramic material is also formed in this gap. 31 can be filled. In this case, the green compact 22 is placed in the mold so that the axis of the green compact 22 and the cored bar 12 'coincide.

<S8: Second pressure molding step>
Then, molding is performed again by applying pressure to the mold. Thereby, the powder layer 32 in which the mixed powder of the low wettability material and the raw material of the base ceramic is pressure-molded on at least a part of the surface of the green compact 22 of the raw material powder of the base ceramic. Can be produced.

  For example, in the example shown in FIG. 4, it can shape | mold by pressurizing by CIP. When the mold shown in FIG. 4A is used, the low wettability material and the base ceramic material are formed on the outer peripheral surface and the inner peripheral surface of the green compact 22 made of the raw material powder of the base ceramic material. It is possible to obtain a molded body (second molded body) to which the powder layer 32 of the mixed powder with the raw material is bonded.

  In addition, when the mold shown in FIG. 3D is used, a powder powder layer 32 of a mixed powder of a low wettability material and a raw material of the base ceramic material is formed on the outer peripheral surface of the powder compact 22 having a hollow cylindrical shape. A joined molded body can be obtained.

  When CIP is used, for example, the molding can be performed at a pressure of about 50 to 150 MPa and a holding time of about 10 to 60 seconds.

  The pressure P2 in the second pressure molding step may be the same as the pressure P1 in the first pressure molding step, or may be larger than the pressure P1.

  When the pressure P2 is set to a value larger than the pressure P1, the green compact 22 obtained by the first pressure molding is further contracted during the second pressure molding. Therefore, in the second pressure forming step, a part of the mixed powder of the low wettability material and the raw material of the base ceramic enters the green compact 22 obtained by the first pressure forming, and the green compact is obtained. Bondability with 22 can be further improved.

  For example, when a silicon nitride ceramic raw material powder is pressure-molded by CIP, the relative density of the molded body is about 57.0% when the molding pressure is 80 MPa, and the relative density of the molded body is about 58 when the molding pressure is 100 MPa. When the molding pressure is 150 MPa, the relative density of the molded body is about 60.0%, and it is confirmed that the density of the molded body increases as the molding pressure increases. Therefore, for example, the pressure P1 may be set to 80 MPa and the pressure P2 may be set to 100 MPa, for example.

  Further, as in the example shown in FIG. 4 (a), the gap between the inner peripheral surface of the hollow cylindrical green compact 22 obtained in the first pressure molding step and the cored bar 12 ′ is also low. Even when the mixed powder of the wettability material and the raw material of the base ceramic material is filled, it is preferable to set the pressure P2 to a value larger than the pressure P1. Thereby, in the second pressure molding step, the pressure is appropriately applied to the mixed powder filled between the inner peripheral surface of the green compact 22 obtained in the first pressure molding step and the cored bar 12. Can be added and molded.

<S9: Second surface processing step>
When the second pressure molding step is completed, the molded body is taken out from the mold and surface-treated so as to have a predetermined size again. As described above, when pressure molding by CIP is performed, the surface that has been in contact with the rubber mold 11 is uneven, and thus surface processing is performed to smooth the surface. Thereby, as shown in FIG. 4B, the low density wettability formed on the green compact 22 of the base material ceramic raw material powder and at least a part of the surface of the green compact 22. The green compact 32 of the mixed powder of the material and the raw material of the base ceramic is integrated, and a molded body having a desired shape can be obtained.

  In addition, when using the uniaxial press molding method which uses only the metal mold | die without using the rubber mold | type 11, since the surface of the molded object taken out from the shaping | molding die is smooth, you may abbreviate | omit the surface processing process of S9.

<S10: Firing step>
The molded body obtained in S9 is sintered. Specifically, first, in order to remove the binder resin added in the granulation step of S3, degreasing firing is performed at a temperature lower than the sintering temperature, and then a book for sintering the compact. Firing is performed. In this firing, a normal pressure sintering method is applied, and the temperature may be maintained at a temperature of about 1600 to 1800 ° C. for an appropriate time (eg, about 1 to 3 hours) in a non-oxidizing atmosphere. And finally, manufacture of the ceramic member for molten metals is completed by performing the process which removes the flash etc. of the baked product obtained by the baking process.

  (C) of FIG. 4 is a figure which shows the product after sintering. As shown in FIGS. 4B and 4C, the base portion 2 formed by sintering the green compact 22 of the raw material powder of the base ceramic, the low wettability material, and the base ceramic The ceramic member 1 for molten metal in which the composite layer 3 formed by sintering the powder layer 32 of the mixed powder with the raw material is sintered is completed.

(Second manufacturing method)
Next, the 2nd manufacturing method of the ceramic member for molten metals which concerns on another embodiment of this invention is demonstrated. FIG. 5 is a flowchart showing the flow of each process of the second manufacturing method. For convenience of explanation, the same steps as those in the drawings described in the first manufacturing method are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, in the second manufacturing method, the second mold filling step, the second pressure molding step, and the second surface processing step are performed a plurality of times (N times, where N is an integer of 2 or more). ) Different from the first manufacturing method in that it is repeated. The second mold filling step, the second pressure forming step, and the second surface processing step are low wettability material forming processes for forming a low wettability material on the surface of the green compact 22.

  In the second manufacturing method, the first second mold filling step to the second surface processing step (second molding step) are the green compacts (first molded body) obtained in the first surface processing step. 22 is performed as a molding target. On the other hand, in the second and subsequent second mold filling steps to the second surface processing step (third forming step), the intermediate formed body obtained in the previous second surface processing step is performed as a molding target. Thereby, the N composite layers 3 can be stacked. In the following description, the first to Nth composite layers are referred to in order from the base part 2. That is, the composite layer closest to the base portion 2 is called the first composite layer, and the composite layer formed on the nth composite layer and on the side opposite to the base portion 2 is the (n + 1) th layer. This is called a composite layer.

  FIG. 6 is a perspective view showing an example of the ceramic member 1 for molten metal manufactured by the second manufacturing method. FIG. 6 is an example in which two composite layers 3 are stacked, and includes a first composite layer 3-1 and a second composite layer 3-2.

  In this manufacturing method, the weight ratio of the low wettability material in the mixed powder of the low wettability material and the raw material of the base ceramic material, which is filled in the second mold filling step of the nth time, is set to the (n-1) th It is made larger than the weight ratio of the low wettability material in the mixed powder filled in the mold filling step. For example, when two composite layers 3 are laminated, the weight ratio of the low wettability material in the first second mold filling step is set to 5% by weight, and the low wetting in the second second mold filling step is performed. The weight ratio of the functional material is 10% by weight. Thereby, the weight ratio of the low wettability material in the first composite layer 3 can be reduced, and the weight ratio of the low wettability material can be increased in order along the direction away from the base portion 2.

  The base material ceramic and the low wettability material have a difference in shrinkage ratio during sintering and thermal expansion coefficient after sintering due to the difference in composition. If the difference in shrinkage rate during sintering is large, cracks may occur at the interface between the base portion 2 and the composite layer 3 in the sintering process. In addition, when the difference in thermal expansion coefficient is large, a relatively large thermal stress is applied to the interface between the base portion 2 and the composite layer 3, and the service life of the molten metal ceramic member may be shortened.

  However, according to the present manufacturing method, the weight ratio of the low wettability material in each composite layer 3 can be gradually increased as a plurality (N layers) of composite layers 3 are formed and separated from the base portion 2. Therefore, even when the difference between the shrinkage rate and the thermal expansion coefficient during sintering between the base ceramic material and the low wettability material is large, the shrinkage during the sintering of the base portion 2 and the first composite layer 3 is performed. The difference in the coefficient of thermal expansion and the coefficient of thermal expansion after sintering can be reduced. In addition, the difference between the shrinkage ratio during sintering and the thermal expansion coefficient after sintering between the nth composite layer 3 and the (n + 1) th composite layer 3 can also be reduced. As a result, at the interface between the base portion 2 and the first composite layer 3 and at the interface between the adjacent composite layers 3, the stress is caused by the shrinkage rate during sintering and the difference in the thermal expansion coefficient. Stress can be relieved and the quality of the ceramic member for molten metal can be improved.

(Third production method)
Next, the 3rd manufacturing method of the ceramic member for molten metals which concerns on another embodiment of this invention is demonstrated. FIG. 7 is a flowchart showing the flow of each process of the third manufacturing method. For convenience of explanation, the same steps as those in the drawings described in the first manufacturing method are denoted by the same reference numerals and description thereof is omitted.

  In the first manufacturing method described above, when producing a ceramic member for molten metal having a hollow cylindrical shape and having a composite layer formed on the inner peripheral surface thereof, the method shown in (a) of FIG. 3 and (a) of FIG. As shown, the diameter of the cored bar 12 ′ of the mold used in the second pressure molding process was made smaller than the diameter of the cored bar 12 of the mold used in the first pressure molding process. Therefore, it is necessary to prepare two cored bars, which increases the cost.

  As a ceramic member for molten metal, which has such a hollow cylindrical shape and both the inner peripheral surface and the outer peripheral surface are in contact with the molten metal, there is a stalk that constitutes a hot water supply pipe line in a low-pressure casting apparatus. It is conceivable that the outer peripheral surface of the stalk rubs against other members during the operation of removing the stalk from the container in which the molten metal is stored. Therefore, the outer peripheral surface is more easily worn than the inner peripheral surface, and it is desired to form a thick composite layer.

  Therefore, in the third manufacturing method, the composite layer 3 is formed on the inner peripheral surface using the technique described in Patent Document 3, and the composite layer 3 is formed on the outer peripheral surface using another method. Thereby, the thick composite layer 3 can be formed in the outer peripheral surface where abrasion resistance is required. Hereinafter, the third manufacturing method will be described with reference to FIG. Note that, as shown in FIG. 7, the third manufacturing method is different from the first manufacturing method in that it has a slurry blending step (S12) and a coating film forming step (S13), so this point is mainly described. To do.

<S12: Slurry blending process>
In this manufacturing method, in addition to the granulation step of S3, slurry preparation for producing a slurry containing a mixed powder of a low wettability material and a raw material of the base ceramic material in order to form the inner peripheral surface side composite layer 3 Perform the process. The method for preparing the slurry is roughly divided into the following two. One is a method of preparing a slurry by mixing and suspending a raw material powder (mainly granulated material) of a base material ceramic and a powder of a low wettability material in a dispersion medium at a desired blending ratio. In this case, the granulated material 21 of the raw material powder of the base ceramic produced in S3 can be used. The other one is a granulated product 31 of a mixed powder prepared by the same method as S3, in which a raw material powder of a base ceramic and a powder of a low wettability material are mixed in a desired blending ratio. This is a method for producing a slurry by suspending in a dispersion medium. In addition, what is necessary is just to adjust a slurry to the density | concentration (for example, solid content 10-40%) suitable for application | coating by using ethyl alcohol etc. as a dispersion medium.

  For example, 20 parts by weight of boron nitride powder (average particle size: 6 μm) as a low wettability material is mixed with 100 parts by weight of silicon nitride ceramic powder (including 10 parts by weight of a sintering aid component) as a base material ceramic. Further, 130 parts by weight of ethyl alcohol is added to form a slurry (solid content concentration: 48%).

<S13: Coating film forming step>
Next, as shown in FIG. 8 (a), the slurry produced in S12 is applied to the surface of the core metal (cylindrical core metal) 12 of the mold member by spraying or brushing, etc. A mixed coating film 34 including a mixed powder of the wettability material and the raw material of the base ceramic material is formed. Note that the mixed coating film 34 may be formed by pouring and applying the slurry prepared in S12 from the upper part of the cored bar 12 to the cored bar surface. The coating thickness is, for example, 200 to 500 μm.

<About steps after S4>
Thereafter, as shown in FIGS. 8B and 8C, a rubber mold (hollow cylindrical mold) 11 is installed, and a granulated product 21 of the raw material powder of the base ceramic material is filled in the mold. After that, it is sealed with a rubber lid 14 (S4). Then, the first pressure molding step of S5 is performed. In addition, it is desirable to perform filling and pressure molding of the granulated material 21 of the base material ceramics into the mold in which the mixed coating film 34 is formed while the mixed coating film 34 is in a wet state. . Thereby, when the granulated material 21 of the raw material powder of the base ceramic material is filled in the mold, it is possible to prevent the mixed coating film 34 from being peeled off. Further, it is possible to improve the bonding property between the mixed coating film 34 and the granulated material 21 of the raw material powder of the base ceramic material.

  When the mixed coating film 34 of the low wettability material and the base ceramic material is applied to the mold member and the base ceramic powder is pressure-molded as described above, the mixed coating film 34 is filled in the mold. The mixed coating film 34 and the matrix ceramic powder in the mold are integrated by pressure molding, and the mixed coating film 34 becomes a surface layer of the obtained molded body.

  In this way, by performing the first pressure forming step (S5), as shown in FIG. 8D, the pressure of the hollow cylindrical shape in which the raw material powder of the base ceramic material is pressure formed. A molded body (first molded body) in which the powder 22 and the green compact layer 35 formed by pressure molding the mixed coating film 34 formed on the inner peripheral surface of the green compact 22 is obtained.

  Thereafter, as shown in FIG. 8E, the green compact 22 having a predetermined size is formed by performing the first surface processing step (S6). Then, the second mold filling step (S7) is performed as in the first manufacturing method. (F) of FIG. 8 is a figure which shows the cross section of the shaping | molding die in a 2nd type | mold filling process. As shown in the drawing, a low wettability material and a base material ceramic are provided between the outer peripheral surface of the green compact 22 having a green compact layer 35 on which the mixed coating film 34 is press-molded on the inner peripheral surface and the mold. A granulated product 31 of a mixed powder with the raw material is filled. By performing the second pressure forming step (S8) and the second surface processing step (S9) by CIP, as shown in FIG. 8 (g), the green compact 22 and the green compact are obtained. Thus, a molded body (second molded body) formed on the outer peripheral surface 22 and integrated with the powder layer 32 of the mixed powder of the low wettability material and the raw material of the base ceramic material can be obtained. Then, through the sintering process, as shown in FIG. 8 (h), the hollow cylindrical base 2, the composite layer 3 covering the inner peripheral surface, and the composite covering the outer peripheral surface A ceramic member 1 for molten metal having the layer 3 can be manufactured.

  According to this manufacturing method, the composite layer 3 formed on the outer peripheral surface is obtained by pressure-molding the granulated material 31 filled between the green compact 22 and the molding die, so that it is thickened. Can do. As a result, the service life can be extended even if there is wear due to contact with other members.

<Application example>
The molten metal ceramic member 1 manufactured by the first to third manufacturing methods is used in various applications. For example, in a low-pressure casting apparatus, a stalk that constitutes a hot water supply pipe for discharging molten metal (typically molten aluminum) from a molten metal crucible. That is, it can be used as a hot water supply pipe that is inserted into a container in which molten aluminum is stored and increases the atmospheric pressure in the container to send the molten aluminum in the container to the outside. In this case, both the inner peripheral surface and the outer peripheral surface are in contact with the molten metal. However, as described above, the outer peripheral surface is required to have higher wear resistance than the inner peripheral surface. Therefore, at least the composite layer 3 on the outer peripheral surface is formed by pressure-molding the mixed powder of the raw material of the low wettability material and the base ceramic material and the green compact 22 that becomes the base portion 2 by sintering. Preferably it is formed.

  In addition, the present invention can also be applied to a thermocouple protection tube for protecting a thermocouple for measuring the temperature of the molten metal and a heater protection tube (heater tube) for protecting a heater for supplying heat to the molten metal. Furthermore, it can be applied as a degassing shaft (pipe) that is inserted into a container in which molten metal is stored, supplies an inert gas into the molten metal, and removes fine bubbles and the like in the molten metal. .

  Note that the thermocouple protection tube and the degassing shaft have relatively small mechanical and thermal repetitive stress applied during use, compared to the stalk and heater protection tube. Therefore, the upper limit value of the thickness of the composite layer 3 in the thermocouple protection tube and the degassing shaft can be set larger (for example, twice) than the upper limit value of the thickness of the composite layer 3 in the stoke and heater protection tube.

  For example, when the ceramic member 1 for molten metal of this embodiment having a hollow cylindrical shape is used as a stalk or heater protective tube, the diameter of the surface of the base portion 2 on which the composite layer 3 is formed is Rmm, and boron nitride in the composite layer 3 is made of When the weight ratio is A wt%, the thickness of the composite layer 3 is preferably R / A mm or less. On the other hand, when the hollow cylindrical ceramic member 1 for molten metal according to the present embodiment is used as a thermocouple protection tube or a degassing shaft, the thickness of the composite layer 3 is preferably 2 × R / Amm or less.

  Examples of the ceramic member for molten metal manufactured by the first manufacturing method will be described.

<Example 1>
(1) Raw material weighing step to (2) Mixing and pulverizing step to (3) Granulation step As the granulated product 21 of the raw material powder of the base ceramic material to be the base portion 2, the following was produced.

Raw material: Silicon nitride ceramics KN-101 (manufactured by Kubota Corporation)
Average particle size of the granulated product: about 70 μm
Moreover, the following was produced as the granulated product 31 of the mixed powder to be the composite layer 3.

Mixed powder: boron nitride powder (average particle size: 6 μm) 20% by weight, silicon nitride ceramics (including 10% by weight of sintering aid) 80% by weight
Average particle size of the granulated product: about 50 μm (granulated with a spray dryer).

(4) First mold filling step to (5) First pressure molding step The molding die shown in FIG. 3 was used. The outer diameter of the cored bar 12 is 96 mm. The molding die was filled with the granulated powder 21 of the raw material powder of the base ceramic material constituting the base portion 2 and subjected to pressure molding by CIP.

  Pressure: 100 MPa, holding time: 30 seconds.

(6) Surface processing step The outer peripheral surface of the green compact 22 was cut by a lathe so that the outer diameter other than the flange portion was 120 mm.

(7) Second mold filling step to (8) Second pressure molding step The molding die shown in FIG. 4 was used. A cored bar 12 ′ having an outer diameter of 92 mm was used. The green compact 22 after the surface processing step is arranged in the mold so that the core 12 ′ and the axis coincide with each other, and in the gap between the mold and the green compact 22, the composite layer 3 and The resulting mixed powder granulated powder 31 was filled. Thereafter, pressure molding was performed by CIP.

  Pressure: 120 MPa, holding time: 30 seconds.

(9) Surface processing step The outer peripheral surface of the molded body was cut with a lathe so that the outer diameter was 124 mm.

(10) Firing step Atmospheric gas: Nitrogen gas Temperature: 1750 ° C., Time: 2 Hr.

  Through the above steps, a low pressure casting stalk having the composite layer 3 on a part of the outer peripheral surface and the inner peripheral surface of the base portion 2 as shown in FIG. In the low-pressure casting stalk of Example 1, the thickness of the base portion 2 was 10 mm, and the thickness of the composite layer 3 was 1.5 mm. Further, the relative density of the base portion 2 was 99%, and the relative density of the composite layer 3 was 72%.

<Example 2>
Example 2 was produced by using the core metal 12 having an outer diameter of 96 mm in the second mold filling step and the same conditions as in Example 1 except that the pressure in the second pressure forming step was 100 MPa. That is, since the core metal 12 having the same outer diameter is used in the first mold filling process and the first mold filling process, no composite layer is formed on the inner peripheral surface.

  FIG. 10 is a view showing an external appearance photograph of the molten metal ceramic member 1 of Example 2. FIG. FIG. 11 is a view showing an enlarged photograph of the vicinity of the interface between the composite layer 3 and the base portion 2. As shown in the figure, it was confirmed that a composite layer of about 2 mm was formed on the outer peripheral surface. Further, it was confirmed that there was no crack at the interface between the composite layer 3 and the base portion 2 and there was no problem in the bonding property.

  Next, the adhesion test of the molten metal was performed using the piece of Example 2 as a test piece. In the adhesion test, a test piece was immersed in the following molten metal bath in the vertical direction for 3 minutes, then pulled up on the bath, and after 3 minutes, immersed again in the bath (repetition number: 260 times).

Molten metal bath: Aluminum alloy (JIS H5202 AC-4B)
Bath temperature: 720 ° C.

  The upper part of FIG. 12 is a diagram showing a state on the composite layer 3 of the test piece immediately after immersion. As shown in the figure, it can be seen that the aluminum is about to peel off. Thereafter, as shown in the lower part of FIG. 12, it was confirmed that all the aluminum was peeled off and no aluminum was adhered to the surface of the composite layer 3. Thus, it was found that the adhesion preventing effect was excellent.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be applied to uses such as stalk, a thermocouple protection tube, a heater protection tube, and a degassing shaft, which are molten metal hot water supply pipes used in a contact environment with molten metal.

DESCRIPTION OF SYMBOLS 1 Ceramic member for molten metal 2 Base part 3 Composite layer 11 Rubber mold (hollow cylindrical shape mold, mold)
12.12 'Core (molding die)
13 Mold 14 Rubber lid 21 Granulated product 22 Green compact 31 Granulated product 32 Green compact layer

Claims (7)

A method for producing a ceramic member for molten metal that contacts a molten metal,
A first molding step for producing a hollow cylindrical first molded body by pressure-molding the raw material powder of the base ceramic material;
A surface processing step of performing a surface processing to smooth the surface of the first molded body;
Between the outer peripheral surface and at least a part of the inner peripheral surface of the first molded body on which the surface treatment has been performed, and the mold, the material is lower in wettability with respect to the molten metal than the base ceramic material. Filling a mixed powder of the low wettability material powder and the raw material powder of the base ceramic material, and forming a second molded body by pressure molding;
A sintering step of sintering the second molded body,
The base material ceramic is a silicon nitride-based ceramic, the low wettability material is boron nitride,
Of the sintered body obtained by the sintering step, a portion where the first molded body is sintered is a base portion, a portion where the mixed powder is sintered is a composite layer, and the composite layer in the base portion is In the second molding step, when the radius of curvature of the interface is R and the weight ratio of the low wettability material in the composite layer is A wt%, the thickness of the composite layer is 2 × R / A or less. A method for producing a ceramic member for molten metal, comprising producing the second molded body. A method for producing a ceramic member for molten metal that contacts a molten metal,
A first molding step for producing a hollow cylindrical first molded body by pressure-molding the raw material powder of the base ceramic material;
A first surface processing step of performing a first surface processing to smooth the surface of the first molded body;
The first molded body that has been subjected to the first surface processing is a molding target, and the wettability to the molten metal is between the outer peripheral surface and at least a part of the inner peripheral surface of the molding target and the molding die. Low wettability material molding process that fills a mixed powder of low wettability material powder, which is a lower material than the above-mentioned base ceramic material, and raw material powder of the above-mentioned base ceramic material, and produces an intermediate molded body by pressure molding A second molding step of performing
A second surface processing step for performing a second surface processing for smoothing the surface of the intermediate molded body;
A third molding step for producing the second molded body by performing the low wettability material molding process at least once on the intermediate molded body on which the second surface processing has been performed ;
A sintering step of sintering the second molded body,
In each of the plurality of low wettability material molding processes, the weight ratio of the low wettability material in the mixed powder is greater than the weight ratio of the low wettability material in the mixed powder used in the previous low wettability material molding process. Make it bigger
The base material ceramic is a silicon nitride-based ceramic, the low wettability material is boron nitride,
Of the sintered body obtained by the sintering step, a portion where the first molded body is sintered is a base portion, a portion where the mixed powder is sintered is a composite layer, and the composite layer in the base portion is In the third molding step, when the radius of curvature of the interface is R and the weight ratio of the low wettability material in the composite layer is A wt%, the thickness of the composite layer is 2 × R / A or less. A method for producing a ceramic member for molten metal, comprising producing the second molded body. A method of manufacturing a ceramic member for a molten metal having a hollow cylindrical shape in contact with a molten metal,
A coating film of a mixed powder of a raw material powder of a base ceramic material and a powder of a low wettability material, which is a material having lower wettability with respect to the molten metal than the base ceramic material, is formed on the outer peripheral surface of a cylindrical cored bar Coating film forming process;
The raw material powder of the base material ceramic is filled in a forming die having the cylindrical cored bar and a hollow cylindrical mold made of an elastic body whose axial center coincides with the cylindrical cored bar, and cold isostatic A first molding step for producing a first molded body by pressure molding with an isotropic pressure press;
A surface processing step of performing a surface processing to smooth the surface of the first molded body;
An arrangement step of arranging the first molded body subjected to the surface treatment again in the mold;
A second molding step for producing a second molded body by filling the mixed powder between the outer peripheral surface of the first molded body and the hollow cylindrical mold and press-molding it with a cold isostatic press. When,
A sintering step of sintering the second molded body,
The base material ceramic is a silicon nitride-based ceramic, the low wettability material is boron nitride,
Of the sintered body obtained by the sintering step, a portion where the first molded body is sintered is a base portion, a portion where the mixed powder is sintered is a composite layer, and the composite layer in the base portion is In the second molding step, when the radius of curvature of the interface is R and the weight ratio of the low wettability material in the composite layer is A wt%, the thickness of the composite layer is 2 × R / A or less. A method for producing a ceramic member for molten metal, comprising producing the second molded body.   The pressure P2 for pressure molding in the second molding step is equal to or higher than the pressure P1 for pressure molding in the first molding step. A method for producing a ceramic member.   The method for producing a ceramic member for molten metal according to any one of claims 1 to 4, wherein a weight ratio of the low wettability material to the mixed powder is 5 to 50% by weight.   The pressure molding in the first molding step and the second molding step is a molding by cold isostatic pressing, 6. Manufacturing method of ceramic member for molten metal.   The said 1st molded object of a predetermined dimension is produced in the said 1st shaping | molding process by shaving the surface of the green compact obtained by pressure forming, The any one of Claims 1-6 characterized by the above-mentioned. A method for producing a ceramic member for molten metal as described in 1.