JP2800823B2 - High active metal casting mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold used for casting a molten metal of a highly active metal such as titanium or zirconium in a vacuum or inert atmosphere. [Prior art] Conventionally, when a molten metal of a highly active metal such as titanium and zirconium or a base alloy thereof is poured into a mold and cast, the reaction between the highly active metal and the surrounding atmosphere is prevented, for example, by completely removing the molten metal from the atmosphere. A chamber of a vacuum or an inert atmosphere is formed in a closed-structure furnace which is shut off, and the highly active metal is melted in the chamber and the generated molten metal flows into the mold. [Problems to be Solved by the Invention] In the above prior art, the molten metal flows into the mold in a vacuum or an inert atmosphere, so that the reaction between the highly active metal and the surrounding atmosphere can be prevented. The molten metal reacts with the material forming the mold, for example, silica sand, silica, gypsum, etc., and becomes mixed with the silica sand, silica, etc. forming the mold in the molten metal of the highly active metal, resulting in a poor quality casting. In addition, there is a problem that labor is required for a post-finishing for removing the reaction layer on the casting surface. To solve such a problem, Japanese Patent Application Laid-Open No.
Japanese Patent No. 3041 discloses a main material containing silica and alumina as main components, one or more reinforcing auxiliary materials selected from zirconium oxide, zircon, calcium oxide, spinel and mullite, a phosphate and a base. There is disclosed a mold material for casting pure titanium or a titanium alloy, which comprises a hardening agent comprising a reactive metal oxide. However, since this titanium alloy casting mold material is a material in which a main material mainly composed of silica and alumina and a reinforcing auxiliary material such as zirconium oxide and calcium oxide are kneaded as the mold material itself, the inside of the mold is not included. Since the ratio of reinforcing auxiliary materials such as zirconium oxide and calcium oxide on the peripheral surface is almost the same as the mixing ratio,
There is a problem that the highly active metal reacts with silica contained in the main material. As a countermeasure, it is conceivable to increase the content of the reinforcing auxiliary material.However, silica that reacts with highly active metals such as titanium cannot be completely eliminated from the inner peripheral surface of the mold. However, since zirconium oxide, calcium oxide, and the like are kneaded, the compounding amount has to be extremely large, and it is expensive. JP-A-62-168631 discloses a mold characterized in that a layer made of a calcia-based refractory material containing 40% by weight or more of CaO is provided on a surface of the mold in contact with the molten metal.
The inner surface of this mold is made of a calcia refractory material having no reactivity with a highly active metal, and a high quality mold product can be obtained, but the calcia refractory material formed on the inner surface of the mold is obtained. The layer made of the material is formed by forming a layer on the inner surface of the mold using a slip casting method, that is, using solid CaO or the like as a raw material, using a binder or the like as necessary, and firing this. The thickness must be as thick as 0.3 to 2cm. For this reason, depending on the shape of the inner surface of the mold, there is a problem that the thickness of this layer tends to vary and the accuracy of the mold is reduced. Furthermore, since the inner surface of the mold will have irregularities according to the particles of the calcia refractory material such as CaO, the surface of the cast product of the obtained highly active metal will be rough and it will take time for post-finishing. There is a problem. Further, JP-A-61-116284 discloses a metal melting crucible in which zirconia is left on the surface of a vessel wall including the inner peripheral surface of a crucible made of an inorganic refractory, and this crucible is It is configured as a multilayer body composed of the main body and a denser zirconia residual layer. Then, in order to form the dense zirconia residual layer, in the metal melting crucible, an inner surface of the crucible is impregnated with an aqueous solution of zirconium chloride, dicornium sulfate or the like under a reduced pressure of 10 Torr or less under reduced pressure. In order to sufficiently penetrate the inner layer of the crucible, the vacuum impregnation treatment is repeated for 10 minutes, and then the heat treatment is performed to convert the remaining zirconium compound into zirconia. However, in this metal melting crucible, the crucible is alumina,
Made of ceramic material that is inactive with highly active metals such as zirconia, magnesia, and graphite, and the inner layer is made of zirconia by using impregnation under reduced pressure, so that it can be used repeatedly in this type of crucible. However, the material of the crucible itself is expensive, and the vacuum impregnation process is performed over time to form an aqueous zirconia solution into the inner layer of the crucible to form a zirconia residual layer. There is a problem that the number of manufacturing steps increases. Further, since the vacuum impregnation is repeated, it is expected that the zirconia layer on the inner surface of the crucible will vary. Further, Japanese Patent Application Laid-Open No. 49-97733 discloses that an underlayer is provided on the surface of a metal, and a ceramic material which is not eroded against a molten metal aluminum bath is sprayed and deposited on the surface of the underlayer. A metal protector having a topcoat layer formed of a ceramic material that does not attack molten metal aluminum together with hydroxychloride is disclosed. However, since this is for the purpose of protecting the metal, it is necessary to first form an underlayer on the surface of the metal, and an intermediate layer of ceramic and a topcoat layer are sequentially formed on this underlayer, Moreover, since the alumina layer is formed by applying and drying aluminum hydroxychloride, the thickness of the plurality of layers varies, which tends to cause a decrease in dimensional accuracy and an expensive protective structure. There's a problem. Therefore, according to the present invention, an extremely thin unreactive layer can be obtained on the inner surface of the mold at low cost by using a mold formed of silica sand, silica, gypsum, etc., and the reaction between the mold and the highly active metal can be prevented. In addition, an object of the present invention is to provide a casting mold of a highly active metal with a smooth inner surface of the mold, which can simplify post-finishing work, and has a thin layer that is not reactive with the highly active metal and a high mold accuracy. . [Means for Solving the Problems] The present invention relates to a casting mold for a highly active metal formed of silica sand, silica, gypsum or the like, into which a molten metal of a highly active metal flows in a vacuum or an inert atmosphere. The ions of the metal forming an oxide that is inactive with the highly active metal are adsorbed on the inner peripheral surface by flowing or spraying in the air, and this is heat-treated to oxidize the unreactive oxide with the highly active metal. It is a casting mold of a highly active metal having a coating layer formed thereon. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, a molten metal 3 of a highly active metal in a crucible 2 is cast into a mold 4 in a vacuum or a chamber 1 filled with an inert gas such as argon or helium. The mold 4 has a mold body 4A formed of a normal material, for example, silica sand, silica, gypsum, and the like, and an oxide film layer 5 that is inactive with respect to a highly active metal formed on an inner peripheral surface thereof. This unreactive oxide layer 5 is made of Al ₂ O ₃ , M
A coating of gO, CaO, ZrO ₂ or the like is preferable. In addition, the oxide film layer 5
As a method of forming, for example, a solution obtained by dissolving ions such as Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Zr ⁴⁺ in water or an acid and treating it in a liquid or gaseous state in the air in the cavity of the mold body 4A The above-mentioned ions are adsorbed on the inner surface of the mold body 4A by flowing or spraying the same. Next, the mold body 4A is heated in the atmosphere to oxidize the ions at a high temperature to form the oxide film layer 5 on the inner surface of the mold body 4A. When the molten metal 3 of a highly active metal is caused to flow into the mold 4 in the chamber 1 filled with a vacuum or an inert gas by using the mold 4 thus formed, the mold body 4A is formed from a reactive material. Since the inner peripheral surface of the cavity of the mold 4 which comes into contact with the molten metal 3 is covered with the non-reactive oxide film layer 5, the molten metal 3 and the mold 4
And a cast product of a high-purity highly active metal can be obtained without reacting with the above. The oxide film layer 5 is formed by adsorbing ions of a metal that forms an oxide that is inactive to a highly active metal and oxidizing the ions by heat treatment. It is extremely thin and has little variance in thickness, so it has high dimensional accuracy, and its irregularities are almost the same as the inner surface shape of the mold body 4A, so it was coated linearly with oxide particles such as CaO with a binder etc. It is smooth with less irregularities than the layer and can simplify post-finishing work. A relatively inexpensive mold 4 made of silica sand, silica, gypsum or the like makes it possible to obtain a cast of a high-purity highly active metal. Since the ions of the metal that forms the reactive oxide are adsorbed by flowing or spraying in the air and heat-treated to form an oxide film layer 5 that is not reactive with the highly active metal, The coating layer 5 can be formed on the inner peripheral surface by an inexpensive method, and an extremely thin oxide coating layer can be obtained. Can be formed. Further, since the mold 4 can be brought to a necessary high temperature state, the curing shrinkage can be corrected by adding an expanding material adjusted so that the cavity expands in accordance with the curing shrinkage amount to the material of the mold body 4A. . In addition, after performing the same metal adsorption treatment on the inner peripheral surface of the mold as in the above embodiment, a high-temperature treatment is performed in a nitrogen atmosphere filled with nitrogen gas, and a nitride film having high reactivity with a highly active metal is formed on the inner peripheral surface of the mold. A layer may be formed. It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. [Effects of the Invention] The present invention relates to a highly active metal casting mold formed of silica sand, silica, gypsum, or the like, into which a highly active metal melt flows in a vacuum or an inert atmosphere. The ions of the metal that forms an oxide that is not reactive with the highly active metal are adsorbed by flowing or spraying in the air, and this is heated to form an oxide film layer that is not reactive with the highly active metal. By using a relatively inexpensive mold made of silica sand, silica, gypsum, etc., an extremely thin unreactive layer can be obtained at low cost by pouring or spraying ions. To provide a high-active metal casting mold that can prevent reactions, has a smooth inner surface of the mold, simplifies post-finishing work, has a thin layer of non-reactivity with the highly active metal, and has high mold accuracy. Can be.

[Brief description of the drawings] FIG. 1 is a schematic explanatory view showing one embodiment of the present invention. 4 ... Mold 5 ... oxide layer

Claims (1)

(57) [Claims] In a casting mold of a highly active metal formed of silica sand, silica, gypsum, or the like, into which a molten metal of a highly active metal flows in a vacuum or an inert atmosphere, the inner surface of the casting mold has a high reactivity with the highly active metal. The metal ions that form the oxide of are adsorbed by flowing or blowing in the air,
This is subjected to a heat treatment to form an oxide film layer that is inactive with the highly active metal.