JPH0628776B2 - Casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to active metals such as titanium and zirconium, alloys thereof (hereinafter, alloys may be simply referred to as metals in the present specification), chromium, vanadium and the like. The present invention relates to a mold suitable for casting a high melting point metal.

Prior art and prior art Since the calcia refractory is thermodynamically stable at high temperatures and has a unique refining action, the present inventors applied it to the melting of various refractory metals and highly active metals. It is becoming clear that you will get it.

The present inventor provides the following melting method.

In a molten chromium or chromium-based alloy in a container whose inner surface is composed of calcia-based furnace material, aluminum and lanthanum are allowed to exist under vacuum or argon atmosphere, and high purity chromium or chromium-based alloy Production method (Japanese Patent Application No. 60-225450) Production of high-purity chromium characterized in that a rare earth element is allowed to exist in a molten chromium in a container whose inner surface is made of calcia furnace material under vacuum or argon atmosphere. Method (Japanese Patent Application No. 60-64307) According to such a melting method, it is possible to easily carry out melting of a highly active and / or high melting point metal, which was difficult to melt by the conventional method. Moreover, the obtained molten alloy is extremely clean.

In order to obtain a highly clean cast body, it is necessary to melt a highly clean metal melt and use a mold that does not contaminate the melt. BACKGROUND ART Conventionally, as casting molds for titanium or zirconium metals (including alloys) which are active metals, lamd type, investment type, water-cooled copper, sand type (using zircon sand, olivine sand, etc.) are known. The lamdo type has graphite powder as an aggregate and is molded and dried with a carbon-based or resin-based binder and then baked. The investment type uses tungsten in a slurry referred to as a tungsten powder coating mold, uses a metallic binder, and a combination of an oxide-based slurry called an oxide mold and an oxide binder, and There are three types of graphite molds in which graphite-based slurry is solidified with a binder containing carbon.

As a titanium or titanium alloy template material, pure magnesia or a magnesia template material containing magnesia as a main component or an aggregate containing magnesia as a main component, to which a hardening accelerator such as a hydrogen carbonate of an alkali metal or aluminum powder was added. Template materials are also known (Japanese Patent Publication No. 58-5749,
JP-A-59-218237).

[Problems to be Solved by the Invention] However, when an active metal is cast into these molds, a reaction occurs with the mold material, and in the case of the graphite mold material, carbon, and in the magnesia or zirconia material, In the case of a mold, oxygen contamination occurs and casting surface contamination occurs. In addition, among the investment type, the oxide binder type has the penetration of not only oxygen but also nitrogen. Such contamination of the surface of the casting surface requires a step of removing the contamination layer on the surface of the casting, which makes the casting step extremely complicated. Further, the casting method using water-cooled copper has a problem that the mold is expensive and there is a risk of steam explosion due to water leakage.

Furthermore, in molds such as oxide-based or graphite-based materials other than water-cooled copper, the thermal conductivity is large, so shrinkage cavities are large,
There is a problem that the yield of casting becomes poor. In addition, since all of these oxide-based or graphite-based molds are dense, they have low thermal shock resistance, are easily cracked, have poor durability, and are not suitable for repeated use. There was a problem.

It is speculated that if a high-calcia material is used as the casting material, the above problems will be solved to a considerable extent, but calcia has a problem of digestion or hydration, which is a bottleneck in practical use.

[Means and Actions for Solving Problems] A mold of the present invention is a mold composed of a mold body and a high calcia refractory material layer formed on a surface of the mold body in contact with the molten metal. The calcia-based refractory material is a calcia-based refractory material containing 40% by weight or more of CaO, and the mold body is constituted by any one of the following items. Graphite; heat-resistant oxides other than calcia;
Low calcia material with a CaO content of less than 40%.

Since the mold of the present invention is a high calcia refractory material whose surface in contact with the molten metal has a high melting point and is thermodynamically stable at high temperature, it is possible to easily cast a high melting point and / or highly active metal. Therefore, it is possible to obtain a casting having no surface contamination on the casting surface.

Further, the mold of the present invention, the portion other than the surface in contact with the molten metal,
Since it can be composed of the conventional mold material, it is possible to effectively use the existing equipment, and moreover,
It is possible to make up for defects in the strength and hydration of the calcia refractory material.

The present invention will be described in more detail below.

In the mold of the present invention, a layer of high calcia refractory material is provided on the surface of the mold body that contacts the molten metal.

In the mold of the present invention, the surface of the mold body in contact with the molten metal may be a high calcia refractory material layer containing 40% or more of CaO. As a form of installation of this high calcia refractory material layer, FIG. 1 (a) Examples such as ~ (c) are illustrated.

That is, as shown in FIG. 1 (a), a high calcia refractory material layer 2 is formed on the molten metal contact surface of a non-calcia or low calcia mold body 1 such as graphite.

As shown in FIG. 1 (b), a high calcia refractory material layer 2 is formed on a mold body 1 with an intermediate layer 3 having a relatively low CaO content interposed. In this case, the intermediate layer 3 is preferably made of an intermediate component between the material of the mold body 1 and the material of the refractory material layer 2.

As shown in FIG. 1 (c), a mold body 1 is provided with a high calcia refractory material layer 2 in which the CaO content gradually increases toward the molten metal contact surface side. In this case, it is preferable that the mold body 1 side of the refractory material layer 2 be close to the material of the mold body 1.

Is.

Note that FIGS. 1 (d), (e), and (f) show the CaO content distributions in FIGS. (A), (b), and (c), respectively.

In the case of, the mold body 1 and the high calcia refractory material layer 2 become more compatible with each other, and the risk of peeling of the refractory material layer can be eliminated.

In the present invention, the thickness of the high calcia refractory material layer is not particularly limited and is appropriately determined depending on the scale of the mold, the activity or melting point of the metal to be cast, etc., but generally 0.3 to 2
It is about cm.

The calcia of the refractory layer formed in the mold of the present invention has a high melting point as described above and is thermodynamically stable even at high temperatures. Since the mold of the present invention has improved stability and heat resistance as the CaO content of the high calcia refractory layer increases, in the present invention, the high calcia refractory layer of the high calcia refractory layer formed in the mold body has high calcia. The refractory material preferably contains at least 40% by weight of CaO (hereinafter,% means% by weight unless otherwise specified), preferably 50% or more, and particularly 60% or more.

This high calcia refractory layer is made of halides other than CaO, oxides other than CaO, carbides, nitrides, carbon (C).
Can be included.

Examples of halides include fluorides and chlorides of alkali metals, alkaline earth metals and lead, and double salts containing them. Specifically, CaF ₂ , MgF ₂ , BaF ₂ , SrF ₂ ,
_{NaF, LiF, KF, PbF 2} , CsF, Na 3 AlF 6, CaCl 2, MgCl 2, NaCl, KCl and the like.

Originally, such a halide has much higher digestion resistance than CaO and has a low melting point. Therefore, in addition to improving the digestion resistance due to its own existence, it promotes the sintering of the base material during firing. It has the function of increasing the compactness of the sintered body structure, and these functions are superimposed to impart excellent digestion resistance to the high calcia refractory layer. Further, the strength of the obtained high calcia refractory material layer is also improved by the sintering promoting action. It should be noted that a large amount of halide is present at the grain boundaries, and a layer containing a large amount of halide comes to encapsulate the CaO particles, and it is speculated that this also improves the digestion resistance of the high calcia refractory layer. To be done. The content of this halide is 8% or less, preferably 5% or less, because if it is added too much, the fire resistance of the mold will be reduced. Further, as a matter of course, if the added amount is too small, the above-mentioned action and effect cannot be obtained. Therefore, it is preferable to set the content rate to 0.1% or more, preferably 0.3% or more.

Further, as the oxide that can be contained in the high calcia refractory material layer according to the present invention, specifically, those having a high melting point such as magnesia (MaO) and zirconia (ZrO ₂ ) are preferable.
Examples of carbides and nitrides include silicon carbide, silicon nitride and aluminum nitride. Graphite is suitable as the carbon raw material. There are natural graphite and artificial graphite in graphite,
Either of them can be used. Since graphite has a flaky shape, the formability is poor, and since the main body and reactivity are poor and it is difficult to form a ceramic bond, the strength of the obtained sintered body is likely to decrease. Therefore, when using graphite as a raw material for a high calcia refractory material, it is effective to add a small amount of metallic aluminum. When aluminum is fired in a non-oxidizing atmosphere, it produces reaction products with high corrosion resistance such as aluminum carbide and aluminum nitride, which not only enhances the corrosion resistance of the refractory material but also enhances the bond between graphite and the surrounding structure and improves the strength of the refractory material. Will be done.

As the raw material used to form the high calcia refractory material, limestone, calcined or sufficiently calcined lime, electrofused calcia melted in an arc furnace, calcium hydroxide, or the like may be used. Further, CaO-containing minerals such as ralnite, melwinite, anorthite and dolomite may be used.

In the present invention, the material constituting the mold body provided with the high calcia refractory material layer is usually graphite, which is adopted as the mold material, or a heat-resistant oxide other than calcia such as alumina, or CaO content. It is a low calcia refractory material of less than 40%. To form a layer of the high calcia refractory material on the surface of the mold body which is in contact with the molten metal, for example, the entire inner wall, the above-mentioned high calcia raw material and, if desired, the above-mentioned One or two or more of the above-mentioned halides, oxides, carbides, nitrides, and carbon are used together as a main raw material, and an appropriate binder is added to this main raw material as required to obtain a molding material. Then, in the case of a slurry, the molding material is put into the mold body, and the molding material is subjected to slurry casting (slip casting method), the molding material is applied, or without using the binder or in a small amount. Then, the molding material is pressed against the inner wall of the mold body so that the molding material adheres and is then fired.

In the case of firing the molded body, it is preferable to dry it if necessary, then calcinate at a temperature lower than the main firing temperature, and then perform main firing and sintering. The firing temperature is preferably 900 ° C. or higher, particularly 1100 to 1700 ° C. The firing atmosphere may be an air atmosphere when the material to be fired does not contain a carbon component, but may be another atmosphere.

In the case of forming a refractory layer as shown in FIG. 1 (c), the CaO content in the slip cast slurry can be increased with time in the above method to easily increase the CaO content. It is possible to form a refractory material layer that increases toward the surface.

In the present invention, hot pressing may be performed, or a mold may be configured using a high calcia refractory material as a stamp material. Further, a high calcia refractory material may be used like ordinary foundry sand to form a mold.

In the present invention, the binder used for forming the refractory material layer is usually a non-aqueous binder. The non-aqueous binder may be either liquid or solid. As a liquid type, alcohol (monohydric or polyhydric alcohol) in which anhydrous calcium chloride or gum arabic is dissolved, oleic acid dissolved in toluene, oleic acid dissolved in alcohol, oil It is a non-aqueous liquid that does not digest calcia, such as mineral oil, animal oil, vegetable oil, etc., although oleic acid dissolved in, carbon tetrachloride dissolved beeswax, or isobutyl acetate is preferable. Anything can be used.

As the solid binder, polyethylene, polypropylene, cellulose acetate, acrylic resin, thermoplastic resin such as polyvinyl alcohol, thermosetting resin such as novolac, paraffin or the like can be preferably used, but imparts moldability. Other materials may also be used.

High melting point and / or highly active metals can be easily cast using the mold of the present invention. In the case of a refractory metal such as a pure metal such as chromium or vanadium, or an alloy containing a large amount of it, Ca is used as the high calcia refractory material layer of the mold.
Those having a high O content, for example, those containing 80% by weight or more of CaO are suitable. Also, when casting a highly active pure metal such as titanium or zirconium or an alloy containing a large amount thereof, it is preferable to form a high calcia refractory material layer having a high CaO content.

The constituent elements of the refractory metal alloy and the high activity metal alloy suitable for casting with the mold of the present invention include the following. Sc, Y, La, lanthanoid elements such as Ce and Pr having atomic numbers 58 to 71, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re,
Ru, Os, Co, Ni, Rh, Pd, Ir, Pt.

Further, examples of the alloy include those containing one kind or two or more kinds of these elements.

The mold of the present invention can be applied not only to the outer mold but also to the inner mold called a core.

For casting in the present invention, the atmosphere is preferably a vacuum or an inert gas atmosphere such as argon.

[Examples] Examples will be described below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 Sintered calcia (CaO purity 98%) was crushed and classified to 0.5 mm or less as a CaO raw material, other components were added, and molding with a composition shown in Nos. 1 to 3 in Table 1 was performed. After preparing the material, a calcia layer is formed on the entire inner wall surface of the graphite mold body by the slip casting method, then dried at 250 ° C. for 30 hours, and then baked in vacuum at 1200 ° C. for 2 hours to be baked. Bonding was performed to form a high calcia fireproof material layer. The firing was performed in the air atmosphere. The mold thus obtained had the shape and dimensions shown in FIG. 2 (in FIG. 2, 1 is the mold body, 2 is a high calcia refractory layer). An alloy composed of Ti 80% and Ni 20% was cast using this mold. Atmosphere during casting is Ar 0.2
The atmospheric pressure and the temperature of the molten metal during casting are 1600 ° C. After casting the molten metal in the mold to solidify it, O, N, and
The results of the chemical analysis of C are shown in Table 2.

Comparative Example 1 Casting was performed in the same manner as in Example 1 using an Al ₂ O ₃ mold and a graphite mold having the same shape.

Table 2 shows the results of chemical analysis of the surface of the obtained casting.

[Effects of the Invention] As is clear from the above description, according to the mold of the present invention, a highly active metal, a high melting point metal, or an alloy thereof can be easily cast. The obtained casting becomes highly clean without contamination with C, O, N, etc., and no post-treatment such as removal of the cast skin contamination layer is required. Further, the mold of the present invention is inexpensive and can be repeatedly used because of its excellent hydration resistance and strength, and it is possible to significantly reduce the casting cost.

[Brief description of drawings]

1 (a) to 1 (c) are enlarged cross-sectional views of the inner wall of the mold showing the form of formation of the high calcia refractory material layer of the mold of the present invention, and FIGS. 1 (d) to 1 (f) are CaO-containing. It is a graph which shows a rate. FIG. 2 is a dimensional diagram showing the shape of the mold used in the examples. 1 ... Mold body, 2 ... High calcia refractory material layer, 3 ... Intermediate layer.

Claims (1)

[Claims] 1. A mold comprising a mold body and a layer of high calcia refractory material formed on a surface of the mold body which is in contact with the molten metal, wherein the high calcia refractory material contains 40% by weight or more of CaO. A mold, which is a high-quality refractory material, and wherein the mold body is composed of one kind selected from the group consisting of: Graphite Heat-resistant oxide other than calcia Low-calcia material with CaO content of less than 40%