JPH07164096A - Molding material for casting refractory metal - Google Patents

Abstract

PURPOSE:To provide a gypsum molding material exhibiting the excellent adaptability for casting of refractory metal. CONSTITUTION:A molding material is prepared as follows, 0.5-30 pts.wt. gypsum whisker is added to 100 pts.wt. of the mixture between the heat resistance material consisting of one or >=2 kinds selected among electrofused alumina, alumina, quartz, crystobalite, magnesia, zirconia and a gypsum hemihydrate, further, the powder of one or >=2 kinds selected among Zn, Al, Zr, W, Mg, Ti, Mo, Ni, Cr, Co or carbide, nitride boride of these metals are added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gypsum-based casting material for casting a high-melting-point metal, which exhibits excellent suitability for casting a high-melting-point metal.

[0002]

2. Description of the Related Art Dental metal prostheses such as crowns, bridges and inlays have been manufactured by the lost wax precision casting method, and the mold materials used at that time are roughly classified into the following two. . One is Tokuhei 4-4
A gypsum-based template material, such as quartz or cristobalite as a main component, to which hemihydrate gypsum is added as a binder, as found in Japanese Patent Application No. 0321 and Japanese Patent Application Laid-Open No. 61-193741, a gold alloy, a silver alloy, It is used for casting alloys having a relatively low melting point such as a gold-silver-palladium alloy, and the other one utilizes a reaction between a metal oxide and a phosphate as seen in JP-A-4-319039. It is a phosphate-based mold material, and is used for casting alloys having a relatively high melting point such as Ni-Cr alloys, high carat gold alloys, and low carat gold alloys.

All of these casting materials are required to expand to compensate for the shrinkage of the metal to be cast.
In the former gypsum-based mold material, about 200 of cristobalite
Comprehensive expansion that combines the rapid expansion of the transformation temperature range at ˜300 ° C. and the expansion of quartz is used to compensate for the shrinkage of the metal and obtain conformity. On the other hand, in the latter phosphate-based template material, a large expansion obtained by kneading with water or a colloidal solution of silicic acid is utilized to compensate for shrinkage of the metal to obtain a conformity.

However, in the conventional gypsum-based mold material, the total expansion of solidification expansion and heat expansion is about 1.2 to 1.9% (700
Since it is ℃), it exhibits sufficient compatibility for casting low melting point metals, but it does not have sufficient compatibility due to insufficient expansion for casting high melting point metals. When casting, casting surface roughening due to thermal decomposition of gypsum, seizure, gas absorption, etc. are difficult to cast for practical use,
Furthermore, mainly Cristobalite about 200-300 ℃
Since the compatibility has been obtained with the help of the rapid expansion of the transformation temperature region in the above, on the contrary, this phenomenon causes rapid expansion of the mold material, cracks in the mold and burrs in the cast body. Dental metal consisting of high melting point alloys such as porcelain baking alloys (precious type, semi-precious type, Ni-Cr type) and Ni-Cr type alloys for casting, which have recently been in increasing demand. It cannot be used for casting prostheses.

On the other hand, the conventional phosphate-based mold material is inferior in fluidity of the slurry as compared with the gypsum-based mold material, so that it is difficult to pour the details of the wax pattern sufficiently, and it is difficult to mold a cast body having a complicated shape. Is not suitable, and because it has high strength and little shrinkage during cooling, the molten metal does not shrink enough during solidification and solidifies with residual stress, which is why it is cast during digging and subsequent heat treatment. It is difficult to secure the dimensional accuracy due to the deformation of the body, and too strong strength easily deforms or scratches the cast body when digging the cast body, which is one of the causes of lowering the yield rate. In addition, the phosphate-based template material has a problem that it easily changes with time.

[0006]

The problem to be solved by the present invention is to solve the conventional problems as described above,
Even if it is a gypsum-based mold material, the heat shrinkage of gypsum is suppressed and it can exhibit sufficient compatibility even when casting high melting point metal, and it also prevents cracks from forming and burrs. High quality castings can be formed, and
To provide a casting material for refractory metal casting, which has excellent fluidity and can accurately mold a cast body even in a complicated shape, and can easily dig the cast body without damaging the cast body. It is in.

[0007]

Means for Solving the Problems The present invention made to solve the above problems is one or more selected from fused alumina, alumina, quartz, cristobalite, magnesia, zirconia, and synthetic aluminum silicate. With respect to 100 parts by weight of the mixture of the heat-resistant material and hemihydrate gypsum,
The first invention is a casting material for high melting point metal casting, which is characterized by adding 5 to 30 parts by weight of gypsum whiskers, and is selected from fused alumina, alumina, quartz, cristobalite, magnesia, zirconia, and synthetic aluminum silicate. Mixture of one or more heat-resistant materials and hemihydrate gypsum 10
0.5 to 30 parts by weight of gypsum whiskers, Zn, Al, Zr, W, Mg, Ti, Mo, Ni, Cr, Co, or carbides, nitrides, borides of these metals, relative to 0 parts by weight. A second aspect of the present invention is a casting material for high melting point metal casting, characterized in that 0.5 to 10 parts by weight of one or more powders selected from silicides are added.

The present invention is a mold material using as a base material a mixture of a heat-resistant material and a binder used in conventional gypsum-based mold materials, and as the heat-resistant material, fused alumina, alumina, quartz, It is one or more selected from cristobalite, magnesia, zirconia, and synthetic aluminum silicate, and hemihydrate gypsum is used as the binder. In addition, the mixing ratio of both is also heat resistant material: binder = 95: 5
The ratio is about 50:50, which is almost the same as the conventional gypsum-based mold material, but the present invention is characterized in that gypsum whiskers are added to the above mixture.

The reason why gypsum whiskers are added to the above mixture is that the total expansion of solidification expansion and heat expansion should be at least 2 in order to obtain compatibility in casting refractory metals such as Ni-Cr alloys. While 3% is required, 1.2-1.9% is the limit in the conventional gypsum-based mold material,
Since it was not possible to obtain further expansion, the present inventor paid attention to the phenomenon that there is a heat shrinkage of 3.0 to 3.5% at 800 ° C. when heating the gypsum, and how to suppress this heat shrinkage. As a result of studying whether or not to do so, they have found that heat shrinkage can be suppressed by adding gypsum whiskers, and have completed the present invention. That is, even with a gypsum-based mold material, addition of gypsum whiskers ensures sufficient expansion and exhibits sufficient compatibility with casting of refractory metals.

Although the effect of suppressing the heat shrinkage by the gypsum whiskers has not been theoretically fully clarified, when the hemihydrate gypsum as the binder is heated, the heat shrinkage due to the dehydration peaks of about 200 ° C. and 400 ° C. Although it shows heat shrinkage due to subsequent transition to anhydrite, decomposition, etc., if gypsum whiskers, which are needle-like crystals of inorganic fiber substance, are added to this, gypsum whiskers are entangled with fine crystals of gypsum and suppress shrinkage. It is supposed to do. The gypsum whiskers have a diameter of about 2 to 5 μm and an average length of 50 to 100 μm.
m, an aspect ratio (aspect ratio = fiber length / diameter) of about 20 to 50 anhydrous salt type gypsum whiskers are used.

In both inventions, the amount of gypsum whiskers added is 0.5 to 100 parts by weight of the base mixture.
Add 30 parts by weight. This is because there is a close relationship between the addition amount and the expansion rate as shown in FIG. 1, and in the case of no addition, a large expansion of -3.2% is only 0.5.
It has been confirmed that the addition of 1 part by weight gives an expansion of 0%, the addition of 10 parts by weight gives an expansion of 1.4% which is the maximum value, and the addition of more than 30 parts by weight gives a negative expansion coefficient. Therefore, the addition amount of gypsum whiskers is 0.
When the amount is less than 5 parts by weight and the amount is more than 30 parts by weight, a sufficient shrinkage suppressing effect cannot be obtained.
It should be added in a proportion of parts by weight.

Further, in order to further suppress the heat shrinkage of gypsum, Zn, Al, Zr, W, Mg, Ti, Mo, Ni, Cr,
Co, or carbides, nitrides, borides of these metals,
One or more powders selected from silicides are added separately from the above-mentioned gypsum whiskers. This is because the added metal powder as described above changes into an oxide when heated, but the oxidative expansion at this time expands the template material to exert a more sufficient shrinkage suppressing effect. It is an invention. If the addition amount of the metal powder as described above in the second invention exceeds 10 parts by weight, the fluidity of the slurry and the surface properties of the cast body may be affected.
If it is less than 0.5 part by weight, the effect of further suppressing the heat shrinkage of gypsum is poor, so about 0.5 to 10 parts by weight is preferable. Even in the second aspect of the invention, if gypsum whiskers are not added, the intended purpose cannot be achieved, and 0.5% by weight of addition is necessary to achieve 0% expansion that occurs when gypsum whiskers are not added. Since it is indispensable, the lower limit of the addition amount of gypsum whiskers is 0.5 part by weight, and the upper limit is 30 parts by weight which does not cause the expansion coefficient to become negative.

[0013]

EXAMPLE 14.5 parts by weight of fused alumina as a heat-resistant material and 55.5 parts by weight of alumina were added to 100 parts by weight of a mixture obtained by mixing 30 parts by weight of hemihydrate gypsum as a binder.
Dental consisting of Ni-Cr alloys and precious alloys (including semi-precious alloys) among porcelain baking alloys that are refractory metals with this mold material by adding anhydrous salt type gypsum whiskers in various proportions The results of molding the metal prosthesis for use are shown in Table 1. Further, 32 parts by weight of alumina, 28 parts by weight of quartz, and 10 parts by weight of cristobalite as a heat resistant material were mixed with 100 parts by weight of a mixture obtained by mixing 30 parts by weight of hemihydrate gypsum as a binder in the same manner as described above, and an anhydrous salt type. Gypsum whiskers were added in various proportions to form a mold material, and this mold material was used to make Ni-Cr among the high melting point porcelain baking alloys.
Series alloys and precious alloys (including semi-precious alloys)
Table 2 shows the results of molding a dental metal prosthesis consisting of Further, a mixture 100 in which 30 parts by weight of hemihydrate gypsum as a binder was added and mixed to 14.5 parts by weight of fused alumina and 55.5 parts by weight of alumina as a heat resistant material in the same manner as described above.
0.5 part by weight of anhydrous salt type gypsum whisker is added to 1 part by weight or 2 or more types selected from Zn, Al, Zr, W, Mg, Ti, or carbides or borides of these metals. Table 3 shows the results when the above-mentioned powder was used as the mold material. As is clear from each table, in the present invention, while exhibiting the characteristics of the gypsum-based mold material that is excellent in the slurry fluidity and the surface properties of the cast body, the excellent compatibility with the high melting point metal is exhibited. It was confirmed that it also works. In each table, the unit is parts by weight, and
◎ means good, ○ means usable, and △ means not usable. Further, PR indicates a precious alloy.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

EFFECTS OF THE INVENTION As is clear from the above description, although the present invention is a gypsum-based mold material, the heat shrinkage of gypsum is suppressed and sufficient compatibility is exhibited even when casting a high melting point metal. In addition, it is possible to form a high-quality cast body that does not crack and does not generate burrs. Furthermore, even if the cast body is excellent in fluidity and has a complicated shape, the cast body can be accurately manufactured. It has advantages that it can be molded and that the cast body can be easily dug out without damaging it. Therefore, the present invention, as a casting material for high-melting-point metal casting that eliminates the conventional problems, contributes greatly to industrial development.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of whisker added and the coefficient of expansion of gypsum when gypsum whiskers are added to gypsum.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Yamamoto 3-36 Noritake Shinmachi, Nishi-ku, Nagoya-shi, Aichi Prefecture Noritake Company Limited Limited

Claims (2)

[Claims] 1. A mixture of 100 parts by weight of a mixture of hemihydrate gypsum and one or more heat-resistant materials selected from fused alumina, alumina, quartz, cristobalite, magnesia, zirconia, and synthetic aluminum silicate. A casting material for high melting point metal casting, characterized in that 5 to 30 parts by weight of gypsum whiskers are added. 2. A gypsum whisker based on 100 parts by weight of a mixture of one or more heat-resistant materials selected from fused alumina, alumina, quartz, cristobalite, magnesia, zirconia, and synthetic aluminum silicate and hemihydrate gypsum. 0.5 to 30 parts by weight, Zn, Al, Zr, W, Mg, Ti, Mo,
Ni, Cr, Co, or carbides or nitrides of these metals,
A casting material for high melting point metal casting, comprising 0.5 to 10 parts by weight of one or more powders selected from boride and silicide.