JPH0373377B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is for casting active metals such as titanium and zirconium, alloys thereof (hereinafter, alloys may also be simply referred to as metals in this specification), or high melting point metals such as chromium and vanadium. The present invention relates to a method for manufacturing a mold suitable for. [Prior Art] Calcia refractories are thermodynamically stable even at high temperatures and have a unique scouring action, so the present inventors believe that they can be applied to the melting of various high-melting point metals and highly active metals. This is becoming clear. According to the infusion method proposed by the present inventors, both high activity and/or
Alternatively, high melting point metals can be easily melted. Moreover, the obtained molten alloy is extremely clean. Therefore, in order to obtain a highly clean cast body, it is necessary to melt a highly clean molten metal and use a mold that does not contaminate the molten metal. Conventionally, known molds for casting titanium or zirconium (including alloys), which are active metals, include a lambda mold, an investment mold, a water-cooled copper mold, and a sand mold (using zircon sand, olivine sand, etc.). The rammed type is made by using graphite powder as an aggregate, molding it with a carbon-based or resin-based binder, drying it, and then firing it.
The investment mold uses tungsten in the slurry called tungsten powder coated mold.
There are three types of molds: one that uses a metallic binder, one that combines an oxide slurry with an oxide binder called an oxide mold, and one that uses a graphite slurry hardened with a carbon-containing binder. be. In addition, as mold materials for titanium or titanium alloys, hardening accelerators such as alkali metal hydrogen carbonate and aluminum powder are added to pure magnesia or magnesia mold materials mainly composed of magnesia, and aggregates mainly composed of magnesia. Mold materials are also known (Japanese Patent Publication No. 58-5749, Japanese Patent Publication No. 59-59-
218237). [Problems to be Solved by the Invention] However, when active metals are cast into these molds, a reaction occurs with the mold material, and carbon is generated in the case of graphite mold materials, and carbon is generated in the case of graphite mold materials, and In the case of molds, oxygen contamination occurs, resulting in contamination of the casting surface. Furthermore, among the investment types, those based on oxide binders have intrusion of not only oxygen but also nitrogen. Such contamination of the casting surface requires a step to remove the contaminated layer on the surface of the casting, making the casting process extremely complicated. Further, the casting method using water-cooled copper has the problem that the mold is expensive and easily worn out. Furthermore, molds made of oxides or graphite other than water-cooled copper have a high thermal conductivity, resulting in a low shrinkage position, resulting in a poor casting yield. Furthermore, since these oxide-based or graphite-based molds are dense, they have problems such as low thermal shock resistance, easy cracking, poor durability, and unsuitability for repeated use. It was hot. [Means for solving the problems] The present invention provides a calcia powder having a CaO content of 40% by weight or more, a maximum particle size of 1 mm or less, and a particle size of 0.1 mm.
Calcia powder with a fine particle size of mm or less and a content of 20% by weight or less
0.1 to 20 parts by weight of an organic binder is added to 100 parts by weight and kneaded, then injection molded into a mold shape, which is then subjected to binder removal treatment at 350 to 500°C.
The method is characterized in that the temperature and time are selected so that the sintered body becomes porous with a porosity of 10 to 40% by volume. [Function] Since the mold provided by the present invention is made of calcia which has a high melting point and is thermodynamically stable at high temperatures, it can easily cast high melting point and/or highly active metals. It is possible to obtain a casting without contamination on the casting surface. Furthermore, since the mold provided by the present invention is porous,
It has characteristics such as excellent thermal shock resistance, high heat retention, excellent durability, and can be used repeatedly.Moreover, the shrinkage point is high and the casting yield is improved. The present invention will be explained in more detail below. The molds produced according to the present invention are calcia-based. As mentioned above, calcia has a high melting point and is thermodynamically stable even at high temperatures. Since the stability and heat resistance of this calcia mold improve as the content of CaO increases, in the present invention, the resulting calcia mold contains at least 40% by weight of CaO.
(Hereinafter, % indicates weight % unless otherwise specified.) The raw materials are blended so that the content is preferably 70% or more, especially 80% or more. CaO content is 40%
If it is less than 100%, the refractory resistance to high melting point metals will decrease, and reactions with highly active metals will likely occur.
It becomes difficult to suppress the reaction between the mold wall and the molten metal. In the mold manufacturing method of the present invention, raw materials that can be used other than CaO include oxides,
Examples include carbides, nitrides, carbon, and halides. Specifically, oxides with high melting points such as magnesia (MgO) and zirconia (ZrO ₂ ) are suitable. Examples of carbides and nitrides include silicon carbide, silicon nitride, and aluminum nitride. Examples of the halides include fluorides and chlorides of alkali metals, alkaline earth metals, and lead, and double salts containing them. Specifically, for example, CaF ₂ , MgF ₂ , BaF ₂ , SrF ₂ , NaF, LiF,
KF, _PbF2 , CsF, _Na3AlF6 , _CaCl2 , _{MgCl2 ,}
Examples include NaCl, KCl, etc. As for such a halide, for example, it is preferable to add one or more of the above-mentioned compounds in an amount of about 0.1 to 8%. The addition of this halide has the effect of smoothing the casting surface and facilitating the firing of the calcia mold. Further, in the mold manufacturing method of the present invention, carbon (C) can be used as a raw material other than CaO. Graphite is suitable as the carbon raw material. There are two types of graphite: natural graphite and artificial graphite, and either of them can be used. Note that graphite has a scaly shape and therefore has poor formability, and is inherently poor in reactivity and difficult to form a ceramic bond, so the strength of the sintered body tends to decrease. Therefore, when using graphite as a calcia mold material, it is effective to add a small amount of metallic aluminum. When aluminum is fired in a non-oxidizing atmosphere, it produces highly corrosion-resistant reaction products such as aluminum carbide and aluminum nitride, which increases the corrosion resistance of the mold and also improves the strength of the mold by increasing the bond between graphite and surrounding tissue. It becomes like this. In addition, as a raw material serving as a CaO source, in addition to limestone, quicklime obtained by calcining limestone, fused calcia melted in an arc furnace, calcium hydroxide, etc. can also be used. Furthermore, minerals containing CaO, such as ralite, merwinite, anorsite, and dolomite, can also be used. In order to manufacture a mold according to the present invention, the above-mentioned oxides,
One or more of carbides, nitrides, carbon, and halides are used in combination to form raw material powder. If the particle size of the raw material particles is too small, shrinkage during firing in the post-process may become excessively large, or the sintered body tends to become dense. , preferably 10% or less. Furthermore, if the grain size of the particles is excessively large, injection will be difficult, and the surface of the mold will become rough, making the surface of the casting also rough. Therefore, the maximum grain size should be 1 mm or less, preferably 0.5 mm or less, especially 0.3 mm or less. . In the present invention, an organic binder is added and kneaded to this raw material fine powder, and the mixture is injection molded. As the organic binder, a non-aqueous one that does not allow calcia to be digested is used. Examples of the binder include polystyrene, polyethylene, cellulose acetate, polyvinyl alcohol, acrylic,
In addition to thermoplastic resins such as polypropylene, thermosetting resins such as novolac are used. In addition, plasticizers, lubricants, and auxiliaries may be used in combination. Suitable plasticizers include diethyl phthalate, paraffin, diptylphthalate, wax, dioctyl phthalate, and fatty acid ester.
Further, as the lubricant, zinc stearate, aluminum stearate, magnesium stearate, diglycol stearate, bread crumbs, mineral oil, etc. are suitable. As an auxiliary agent, atactic polypropylene, multiple resin groups with different decomposition temperatures,
Sublimated products such as naphthalene, natural vegetable oils such as peanut and soybean oils, natural animal oils, etc. are suitable. The amount of organic binder added is based on 100 parts by weight of raw material powder.
The amount shall be 0.1 to 20 parts by weight. The organic binder needs to be added as a forming aid, and by adding it appropriately, a desired shape can be obtained by injection molding. However, if the amount added exceeds 20 parts by weight, it will be difficult to obtain the desired shape before sintering and there will be problems in handling, so the amount should be 20 parts by weight or less. When a plasticizer, lubricant, or auxiliary agent is used, the total amount thereof is preferably 10 parts by weight or less. Addition of a plasticizer or the like is not particularly essential since an organic binder is used as a forming aid. After adding the organic binder etc., if necessary, heat to about 80 to 150°C, stir and knead, then
Cool and solidify. This is crushed and sized to preferably 0.5 mm or less, particularly preferably 0.3 mm or less.
Note that instead of crushing, granulation may be performed by extrusion or the like. The injection raw material thus obtained is supplied to an injection molding machine, and is injected and molded into a mold to obtain a molded article. Various types of injection molding machines can be used, such as a screw-in-line type and a plunger type. In this molding machine, as is well known, the injection raw material is plasticized by heating and kneading in a heating cylinder, and is injected into a mold by advancing a screw or plunger. This mold has a shape as a female mold of the intended mold. The obtained molded body is finished into a predetermined shape by cutting, grinding, or polishing, as required, and then subjected to a binder removal treatment. To perform this binder removal treatment, the temperature is gradually raised to 350 to 500° C. in an air atmosphere, and the resin components are removed by decomposition, sublimation, oxidation, or the like. 350 due to the presence of organic binders
If the binder removal treatment temperature is less than 350°C, the binder will not be completely removed, which may cause defects during firing, so the temperature should be 350°C or higher. Further, the reason why the temperature is 500° C. or lower is sufficient to remove the binder, and high-temperature treatment exceeding this temperature is disadvantageous in terms of cost. After that, a sintered body is fired. However,
In the mold manufacturing method of the present invention, the sintered body obtained when performing this main firing has a porosity of 10 to 40% by volume.
The temperature and time are selected so that the material becomes porous.
The firing conditions vary depending on the components other than CaO in the mold, and the firing temperature will be lower if the composition contains relatively large amounts of halides or oxides that form low melting point compounds with CaO. Baking time is also shorter. Furthermore, as a matter of course, the higher the firing temperature, the shorter the firing time, and the lower the firing temperature, the longer the firing time. Specifically, the CaO content is
For compositions between 40 and 80%, typically 850
Baking is performed at about 1350°C for about 1 to 10 hours. In addition, if the CaO content exceeds 80%, 1000
It is preferable to carry out the firing at a relatively high temperature of 1500°C to 1500°C for about 1 to 5 hours. The sintered body obtained by such firing is subjected to finishing processes such as grinding and polishing as necessary to form a mold. The mold of the present invention is porous, with a porosity of 10 to 40% by volume, preferably 15 to 30% by volume. When the porosity is less than 10% by volume, the thermal shock resistance of the mold decreases and the heat retention effect decreases. If the porosity exceeds 40% by volume, it is not preferable because mold strength decreases and molten metal seepage defects are likely to occur. According to the mold of the present invention, it is possible to easily cast a metal with a high melting point and/or a high activity. For high melting point metals such as chromium, vanadium, pure metals, or alloys containing large amounts of them, as a mold.
A material having a high CaO content, for example, a material containing 80% by weight or more of CaO is suitable. In addition, highly active titanium,
Even when casting a pure metal such as zirconium or an alloy containing a large amount of pure metal, it is preferable to use a mold with a high CaO content. Incidentally, the following metals by weight and highly active metals are suitable for casting using the mold of the present invention. Sc, Y, La, atomic number 58-71
Lanthanide elements such as Ce and Pr, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re,
Ru, Os, Co, Ni, Rh, Pd, Ir, Pt. Furthermore, examples of the alloy include those containing one or more of these elements. Note that the mold manufacturing method of the present invention can be applied not only to the manufacturing of an outer mold but also to the manufacturing of an inner mold called a core.
Furthermore, since CaO has digestibility, the template produced according to the present invention can be removed by hydration using this digestibility. When casting a high melting point metal, a highly active metal, or an alloy thereof using the mold of 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 unless the gist of the invention is exceeded. Example 1 0.3 mm to 0.1 mm of fused calcia (CaO purity 98%)
Mix 80% by weight of crushed and classified powder, 10 parts by weight of commercially available grade 1 CaOO ₃ , and 10 parts by weight of magnesia clinker crushed to 0.5 mm or less to make 100%
Parts by weight of raw material powder and granules were prepared. Further, 5 parts by weight of polyethylene powder was prepared. These raw material powders and polyethylene were put into a stirrer equipped with a heater, heated to 150°C, kneaded well, and then cooled. This was crushed using a Raikai machine, and then sieved to a size of 0.3 mm or less.
This was put into a screw-in-line injection molding machine and injected into a mold. After deburring the obtained compact, it was heated to 500°C in air and held for 3 hours to remove the binder, then heated to 1200°C and fired for 3 hours to form a cylindrical container. It was made into a mold. FIG. 1 is a dimensional drawing of this mold. Note that the porosity of the mold was 24% by volume. Pure Ti was cast using this mold. The atmosphere during casting was Ar1 atm, and the temperature of the molten metal during casting was 1700.
It is ℃. After pouring molten metal into a mold and solidifying it, chemical analysis of O and N on the surface of the casting was conducted.
In addition, the casting was cut and the height of shrinkage was measured. The results are shown in Table 1. Example 2 A mold was produced and casting was carried out in the same manner as in Example 1, except that the conditions were changed as shown in (a) to (f) below. (a) The ingredients are mixed as follows. Dolomite clinker (CaO64.5%, MgO30.9
%, _{Fe2O3 2.3} %, SiO2 _1.8 %, _{Al2O3 0.4} %)
90 parts by weight of crushed and classified limestone to 0.3 mm to 0.1 mm, 10 parts by weight of limestone crushed to 0.3 mm or less. (b) Use polyethylene powder as a binder. (c) The mixing ratio of the above solid raw materials and binder is 100:
5. (d) The conditions for main firing are 1100°C x 3 hours. (E) The casting alloy is 60% Zr and 40% Co. (F) The temperature of the molten metal during casting is 1500℃. Table 1 shows the chemical analysis of the surface of the obtained casting and the measurement results of the shrinkage height. The porosity of the mold is
It was 30% by volume. Example 3 A mold was manufactured and casting was carried out in the same manner as in Example 1 except that the conditions were changed as shown in (a) to (f) below. Note that the porosity of the mold was 32% by volume. (a) The ingredients are mixed as follows. Commercially available quicklime (CaO98.0%, SiO ₂ 0.08%)
60 parts by weight of crushed and classified 0.5 mm to 0.1 mm, 10 parts by weight of Ca(OH) ₂ , dolomite clinker (same as Example 2) crushed to 0.3 mm or less
30 parts by weight. (b) Polypropylene is used as a binder. (c) The mixing ratio of the above solid raw materials and binder is 100:
5. (d) The conditions for main firing are 1100°C x 3 hours. (e) The casting alloy is pure Cr. (F) The temperature of the molten metal during casting is 1950℃. Comparative Example 1 Casting was carried out under the same conditions except that the mold of Example 3 was used as a metal mold (made of steel). Table 1 shows the chemical analysis of the surface of the obtained casting and the measurement results of the shrinkage height.

[Table] [Effects of the Invention] As is clear from the above description, the mold produced by the present invention allows easy casting of highly active metals, high melting point metals, or alloys thereof. The resulting casting is highly clean without contamination with C, O, N, etc., and post-treatment such as removal of the casting surface contamination layer is not necessary. Further, according to the mold manufactured according to the present invention, it is possible to increase the shrinkage position to prevent the occurrence of shrinkage cavities in the central part and to increase the casting yield. According to the present invention, molds can be easily mass-produced, and the resulting molds are inexpensive and can be used repeatedly due to their excellent thermal shock resistance, making it possible to significantly reduce casting costs. .

[Brief explanation of drawings]

FIG. 1 is a dimensional drawing of the mold.

Claims (1)

[Claims] 1 Organic binder: 0.1 parts by weight for 100 parts by weight of calcia fine particles having a CaO content of 40% by weight or more, a maximum particle size of 1 mm or less, a particle size of 0.1 mm or less, and a fine powder content of 20% by weight or less. ~20 parts by weight was added and kneaded, injection molded to form a mold shape, and after debinding at 350 to 500°C, the sintered body became porous with a porosity of 10 to 40% by volume. A method for producing a porous calcia mold, characterized in that firing is performed by selecting a temperature and time.