JP2005186125A - Casting mold made of metal, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting mold made of a metal with a required shape, which mold can efficiently produce a unidirectional solidification casting product of a metal oxide having a complicated shape, and further to provide its simple manufacturing method. <P>SOLUTION: The casting mold made of a metal is formed by metal-spraying at least one kind of high melting point metal selected from molybdenum, tungsten, tantalum, iridium, and platinum, or an alloy comprising the above high melting point metals as a main component. In the method for manufacturing the casting mold, a second metal is sprayed on the surface of a formed body made of a first metal, and then the formed body made of the first metal is removed. As a result, the casting mold made of the second metal is obtained. As the method for removing the formed body made of the first metal, there is a method for melting and flowing-out the formed body by heating, or a method for dissolving and flowing-out the formed body with an alkaline solution or an acid solution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal mold mainly used for unidirectional solidification of a metal oxide, and more particularly to a metal mold suitably used for unidirectional solidification precision casting of a metal oxide molded product having a complicated shape, and a method for manufacturing the same. It is about.

  Major unidirectional solidification methods for metal oxides include the Czochralski method that does not use a crucible and the Bridgman method that solidifies the melt in the crucible. In the latter case, a high melting point metal such as iridium, platinum, or molybdenum is used. This crucible is used. The refractory metal crucible is applied to the unidirectional solidification of metal oxide because the refractory metal has heat resistance higher than the melting temperature of many metal oxides, This is because it does not chemically bond with the melt at a temperature near its melting point. The refractory metal crucible is difficult to be molded by melting and solidification because of its high melting point, and is mainly manufactured by plastic working called drawing. At present, the refractory metal drawing process only produces crucibles with a relatively simple shape, such as a cylindrical shape with a sealed tip or a cylindrical shape with a gradually reduced diameter at the tip. . In addition, although molding by machining is possible, the depth and shape of the crucible are significantly restricted.

  By the unidirectional solidification of the metal oxide by the Bridgman method, a cylindrical metal oxide single crystal is manufactured using the crucible of the shape mainly by drawing, and is formed into a member shape mainly by machining after solidification. It is applied to various industrial uses including optical use.

  However, the metal oxide single crystal is generally a difficult-to-process material, and the processing often requires special equipment, skill and time that do not place a heavy load on the material during processing.

  Further, for example, Patent Documents 1 to 3 disclose ceramic composite materials having good mechanical strength and creep resistance at high temperatures, and these are manufactured by unidirectional solidification using a crucible. The ceramic composite material is expected to be applied to high-temperature structural members such as gas turbines because of its excellent mechanical strength and creep resistance at high temperatures. However, these parts generally have complex shapes. In addition, forming a solid body from a simple shape into a part shape requires technically sophisticated and labor-intensive machining. Therefore, in order to industrially apply the ceramic composite material as a high-temperature structural member such as a gas turbine, a mold having a part shape or a shape close to the part shape is developed, and the ceramic composite material is formed by unidirectional solidification precision casting. It is necessary to reduce the machining process as much as possible.

  As a mold for unidirectional solidification precision casting such as a nickel-base heat-resistant alloy used for turbine blades or the like, a ceramic mold called a ceramic shell mold manufactured by a lost wax method is generally applied. A ceramic shell mold is obtained by applying ceramic slurry to the surface of a wax substrate, drying it, and then melting and flowing out the wax while firing. It has sufficient heat resistance as a mold for heat-resistant alloys. In addition, unidirectional solidification precision casting of a complicated shape is possible.

  Patent Document 4 discloses a ceramic mold in which a ceramic layer is formed by spraying ceramics on the surface of a base material made of a predetermined metal, and then the base material is melted and discharged, and the ceramic layer is used as a mold. A manufacturing method is disclosed. According to this manufacturing method, it is said that a ceramic mold can be manufactured with high accuracy and high manufacturing efficiency.

Japanese Patent No. 3128044 Japanese Patent No. 3216683 Japanese Patent No. 3128044 JP 2002-192300 A

  However, the molds described in Patent Documents 1 to 4 above are ceramic molds and can be used for unidirectional solidification precision casting of metals such as nickel-base heat-resistant alloys, but the metal oxides as described above When the unidirectional solidification is used, there is a problem that the metal oxide and the mold react with each other, and it is impossible to carry out the unidirectional solidification precision casting of the metal oxide by the known technique.

  In addition, as described above, the high melting point metal crucible currently used for unidirectional solidification of metal oxides is manufactured by plastic working called drawing, and because of its high melting point, molding by melt solidification is possible. Since it is difficult, a metal mold capable of obtaining a desired molded body has not been developed. The

  The present invention has been made in view of the above-described problems, and an object of the present invention is to enable precision casting for efficiently producing a unidirectional solidification casting product of a metal oxide having a complicated shape. It is to provide a mold made of a metal having a shape and a simple manufacturing method thereof.

  The present invention relates to a metal mold comprising, as a material, at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy containing the refractory metal as a main component. Preferably, the metal mold of the present invention is characterized in that the material is formed by thermal spraying.

  According to the present invention, a metal mold made of the second metal is characterized in that the second metal is thermally sprayed on the surface of the molded body made of the first metal, and the formed body made of the first metal is removed. It relates to the manufacturing method.

  In the metal mold manufacturing method of the present invention, the first metal is a metal whose melting point is lower than the melting point of the second metal, and the method of removing the molded body made of the first metal is melted by overheating. It is the method of letting it flow out.

  In the metal mold manufacturing method of the present invention, the second metal is mainly at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium or platinum, or the refractory metal. It is characterized by being an alloy as a component.

  Furthermore, as a preferred embodiment, the first metal is copper or an alloy containing copper as a main component.

  In the metal mold manufacturing method of the present invention, the first metal is a metal having a lower resistance to an alkaline solution or an acidic solution than the second metal, and the molded body made of the first metal is removed. The method is characterized in that the method is a method of dissolving and discharging with an alkaline solution or an acidic solution.

  The metal mold manufacturing method of the present invention is characterized in that the molded body made of the first metal is obtained by coating the surface of a graphite molded body with the first metal.

  According to the present invention, by using a mold made of at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy mainly composed of the refractory metal. Thus, precise unidirectional solidification of a metal oxide having a desired shape is possible. Also, by producing a mold by spraying the refractory metal and its alloy, a metal mold having a desired shape capable of precision casting is provided, and precise unidirectional solidification of the metal oxide is possible.

  Hereinafter, the mold of the present invention and the production method thereof will be described in detail. The metal mold of the present invention has a heat resistance equal to or higher than the melting temperature of a desired metal oxide, and is composed of a desired metal oxide melt and a substance that does not chemically bond at a temperature near its melting point. It is a metal mold that can be easily formed into a desired shape.

  That is, the metal mold of the present invention is composed of at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy containing the refractory metal as a main component. It is a metal mold. An alloy containing a refractory metal as a main component may be any alloy that contains refractory metal in an amount of 50 wt% or more of the alloy. Here, the mold is a mold intended to obtain a desired shape when a solidified product is obtained from a melt, and does not include a crucible intended to simply obtain a solidified product from a melt. The material constituting the metal mold of the present invention is preferably formed by thermal spraying, and a metal mold having a desired shape can be provided by a method using thermal spraying.

  The metal mold can be manufactured, for example, as follows. These layers are obtained by spraying at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium and platinum or an alloy containing the refractory metal as a main component onto the surface of a metal molded body having a desired shape. Is formed on the surface of the metal molded body, and then the metal molded body is melted (or melted) out.

  As another production example, a graphite molded body having a desired shape is coated with a metal in advance, and the surface of the graphite molded body coated with the metal is coated with the refractory metal or an alloy containing the refractory metal as a main component. Then, after these layers are formed on the surface of the metal of the graphite molded body, the first coated metal is dissolved (or melted) out on the graphite molded body, and the graphite base material is used as the refractory metal. Alternatively, it is obtained by extracting from a shell-like molded product (that is, a mold) of a layer composed of the alloy.

  Next, the method for producing a metal mold of the present invention will be described in detail. The metal mold manufacturing method of the present invention is characterized in that the second metal is sprayed on the surface of the molded body made of the first metal, and the molded body made of the first metal is removed. In this case, the metal component of the metal mold is made of the second metal.

  The first metal and the second metal may be any metal that can spray the second metal on the first metal and can remove the first metal after the spraying. The present invention provides a new method for producing a metal mold, and is not limited to the metal of the metal mold of the present invention described above.

  As a method for removing the first metal, for example, there are a first method using melting by heating and a second method for chemically eluting the first metal using an alkaline solution, an acidic solution, or the like. is there.

  In the method of melting and flowing out by the first heating, the melting point of the first metal is lower than the melting point of the second metal. By melting and flowing out the molded body made of the first metal at a temperature that is not higher than the melting temperature of the second metal (high melting point metal or alloy thereof) that is a material and does not chemically bond both, A metal mold made of the second metal can be obtained.

  In the method of dissolution and outflow with the second acidic solution or alkaline solution, the first metal is in a relationship that the resistance to the alkaline solution or acidic solution is lower than that of the second metal, and the molded body of the first metal is A second metal layer is formed on the surface of the molded body of the first metal in a solution that can be dissolved and the second metal (refractory metal or alloy thereof) mainly does not dissolve the second metal. The first metal can be dissolved and discharged by immersing the molded body.

  In either of the method of melting and flowing out the first metal by the first heating and the method of dissolving and flowing out the first metal by the second acidic solution or alkaline solution, the second metal, that is, the mold material Is preferably at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy containing the refractory metal as a main component. This is because it is chemically stable and has high heat resistance, so that the reaction with the metal oxide to be unidirectionally solidified hardly proceeds, and a metal oxide solidified product having a desired shape can be obtained. Furthermore, molybdenum is particularly preferably used as the second metal. Molybdenum has a high melting point of about 2600 ° C. and has a very low reactivity with metal oxides. Therefore, molybdenum is suitable as a material for holding a melt of many metal oxides, that is, as a mold. Molybdenum is generally cheaper than other refractory metals, and is a material suitable as a mold used for casting metal oxide from an industrial viewpoint.

  In the method of melting and flowing out the first metal by the first heating, when molybdenum is selected as the second metal, the first metal is preferably the second metal sprayed at the melting temperature. There is no particular limitation as long as it is a material that is low in reactivity with metal, that is, molybdenum, and is not easily damaged by heat during thermal spraying, but copper or an alloy containing copper as a main component (50 wt% or more) can be used. Particularly preferably used. This is because copper has a melting point of about 1080 ° C., which is lower than that of molybdenum, and molten copper does not chemically bond to molybdenum below 1300 ° C. When the first metal is copper, the copper can be melted out from the molybdenum mold by heating to a temperature of about 1080 ° C. or higher, which is its melting point. A change in which the molybdenum mold cannot be used as a mold is not caused by melting and flowing out of copper by heating.

  In the method of dissolving and flowing out the first metal with the second acidic solution or alkaline solution, for example, when molybdenum is selected as the second metal, the first metal is compared with the second metal to be sprayed. The material is not particularly limited as long as it is a material that is extremely easily dissolved in an acidic solution or an alkaline solution and is not easily damaged by heat during thermal spraying. However, copper or copper is a main component (50 wt% or more). Alloys are particularly preferably used. When the first metal is copper, for example, copper can be dissolved out from the molybdenum mold by immersion in dilute sulfuric acid at room temperature (around 20 ° C.). This immersion in dilute sulfuric acid does not cause a change in which the molybdenum mold cannot be used as a mold.

  In both the first and second methods, since the surface roughness of the molded body made of the first metal affects the surface roughness of the inner surface of the metal mold, the first metal is often used. It is desirable that the surface roughness of the formed body is small.

  The molded body made of the first metal may be a molded body having a hollow inside, or may be a molded body in which the first metal is coated on another molded body. As an example of the latter, a graphite molded body whose surface is coated with a first metal is preferably used. The first metal layer may be coated by any method as long as a desired metal layer can be obtained, but a thermal spraying method or a PVD method is preferably used. In this case, the graphite molded body needs to be designed in consideration of the thickness of the first metal layer to be coated. Further, the thickness of the first metal layer to be coated is preferably 0.5 mm or less. When the thickness of the metal layer to be coated becomes thicker than 0.5 mm, in the case of the thermal spraying method, the unevenness on the outside of the metal layer to be coated becomes large, and the surface roughness of the inner surface of the metal mold to be obtained is reduced. This is because the time required for coating becomes longer in the case of the PVD method.

  When the inside of the molded body made of the first metal is composed of a molded body made of graphite, the coating layer composed of the first metal is dissolved (or melted) or is dissolved (or melted). After flowing out, the graphite molded body is extracted from the mold made of the second metal (a refractory metal or an alloy thereof) to obtain a metal mold having a hollow portion of a desired shape. Since the graphite base material is not dissolved like the metal base material, it can be repeatedly used as a base material.

  The method of spraying the second metal on the surface of the molded body made of the first metal may be any of flame spraying, explosion spraying, arc spraying, plasma spraying, and line explosion spraying. It is preferable to carry out the plasma spraying under a reduced pressure at which densification is easiest. Moreover, although any of a powder material, a wire material, or a rod material may be used as the thermal spray material, it is preferable to use a powder material in the case of plasma spraying. The particle size of the powder material is not particularly limited as long as the powder can be supplied to the spray gun, but when directly spraying the metal base material surface, the surface roughness of the inner surface of the metal mold In order to reduce the thickness, it is preferable to use a powder material having a small particle diameter, specifically, a powder material having a particle size of 70 μm or less in the initial stage of thermal spraying.

  The thermal spraying of the second metal on the surface of the molded body made of the first metal may be performed while rotating the metal base material, and according to the shape of the metal base material, a spray gun and / or It may be performed while moving the metal base material.

  The second metal layer formed by thermal spraying needs to have a thickness that does not spoil the shape during unidirectional solidification precision casting, and is generally 0.5 mm, depending on the shape of the metal mold. The above thickness is necessary.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Example 1)
The copper molded body shown in FIG. 1 was obtained by machining. While rotating this copper molded body, molybdenum powder was sprayed so that a molybdenum layer having an average thickness of 2 mm was formed on the surface. Plasma spraying was performed using a molybdenum powder in which 90% or more of the particles had a particle diameter of 10 to 53 μm as a raw material while rotating a copper molded body under reduced pressure to obtain a molybdenum-coated copper base material shown in FIG. .

  This molybdenum-coated copper molded body is heated to 1200 ° C. in a high-frequency induction furnace maintained in a vacuum, so that the copper molded body is melted and flown out from the metal mold opening side, and the molybdenum-made product shown in FIGS. 3 and 4 is used. A mold was obtained.

  The obtained metal mold is heated up to 200 hours in a vacuum of 2000 ° C., and there is almost no change in the shape of the metal mold before and after that, and water from the metal mold when filled with water at room temperature. It was confirmed that there was no leakage. Table 1 shows the surface roughness of the surface of the copper molded body, the inner surface of the metallic mold after melting and flowing out of copper, and the inner surface of the metallic mold heated in a vacuum at 2000 ° C. for 200 hours.

(Example 2)
A graphite molded body having the same shape as in Example 1 was obtained by machining. While rotating this graphite-made formed body, copper powder was sprayed so that a copper layer having an average thickness of 0.5 mm was formed on the surface. Next, in the same manner as in Example 1, a molybdenum layer having an average thickness of 2 mm is formed on the surface of the graphite molded body covered with the copper layer having an average thickness of 0.5 mm, and the graphite layer is in contact with the graphite molded body. A graphite molded body coated with copper as one layer and molybdenum as the second layer was obtained.

  The graphite-molded body coated with copper and molybdenum is heated to 1200 ° C. in a high-frequency induction furnace maintained in a vacuum, so that the graphite-molded body is coated from the metal mold opening side. Copper was melted out to obtain a molybdenum mold having the same appearance as the molybdenum mold shown in FIGS.

  The obtained metal mold is heated up to 200 hours in a vacuum of 2000 ° C., and there is almost no change in the shape of the metal mold before and after that, and water from the metal mold when filled with water at room temperature. It was confirmed that there was no leakage. Table 1 shows the surface roughness of the surface of the copper molded body, the inner surface of the metallic mold after melting and flowing out of copper, and the inner surface of the metallic mold heated in a vacuum at 2000 ° C. for 200 hours.

(Example 3)
A graphite molded body having the same shape as in Example 1 was obtained by machining. The surface of this graphite molded body was covered with a copper layer having an average thickness of 0.2 mm by PVD using copper as a target material. Next, in the same manner as in Example 1, a molybdenum layer having an average thickness of 2 mm is formed on the surface of the graphite molded body covered with the copper layer having an average thickness of 0.2 mm, and the graphite layer is in contact with the graphite molded body. A graphite molded body coated with copper as one layer and molybdenum as the second layer was obtained.

  From the graphite molded body coated with copper and molybdenum, the copper layer and the graphite molded body were removed in the same manner as in Example 2 to obtain a molybdenum mold.

  The obtained metal mold is heated up to 200 hours in a vacuum of 2000 ° C., and there is almost no change in the shape of the metal mold before and after that, and water from the metal mold when filled with water at room temperature. It was confirmed that there was no leakage. Table 1 shows the surface roughness of the surface of the copper base material, the inner surface of the metal mold after melting and flowing out of the copper, and the inner surface of the metal mold heated in a vacuum at 2000 ° C. for 200 hours.

FIG. 1 is a photograph of a copper molded body showing an example of the shape of a metal molded body used in the production of the metal mold of the present invention. FIG. 2 is a photograph showing that a molybdenum layer is formed on the surface of the copper molded body by thermally spraying molybdenum on the surface of the copper molded body shown in FIG. FIG. 3 is a photograph of a molybdenum mold obtained by melting and flowing copper from a copper molded body having a molybdenum layer formed on the surface. FIG. 4 is a photograph of a molybdenum mold obtained by melting and flowing copper from a copper molded body having a molybdenum layer formed on the surface.

Claims (8)

  A metal mold comprising, as a material, at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy containing the refractory metal as a main component.   The metal mold according to claim 1, wherein the material is formed by thermal spraying.   A metal mold made of the second metal is manufactured by spraying a second metal on the surface of the molded body made of the first metal and removing the molded body made of the first metal. Method.   The first metal is a metal whose melting point is lower than the melting point of the second metal, and the method of removing the molded body made of the first metal is a method of melting and flowing out by overheating. A method for producing a metal mold according to claim 3.   The second metal is at least one refractory metal selected from molybdenum, tungsten, tantalum, iridium, or platinum, or an alloy containing the refractory metal as a main component. 3. A method for producing a metal mold according to 3.   4. The method for producing a metal mold according to claim 3, wherein the first metal is copper or an alloy containing copper as a main component.   The first metal is a metal having a lower resistance to the alkaline solution or the acidic solution than the second metal, and the method of removing the molded body made of the first metal is dissolved and discharged by the alkaline solution or the acidic solution. The method for producing a metal mold according to claim 3, wherein the method is a method.   4. The method for producing a metal mold according to claim 3, wherein the molded body made of the first metal is obtained by coating the surface of a graphite molded body with the first metal.

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