JPH082771B2 - Rapid heating type investment material composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an investment material composition used for molding a dental mold, which enables rapid heating of the mold.

[0002]

2. Description of the Related Art As an investment material composition used for molding a dental mold, quartz or cristobalite is used alone or in a mixture as a refractory material, and a plaster or phosphate-based material is used as a binder. Cristobalite and quartz are widely used because they have a large coefficient of thermal expansion and can compensate for metal casting shrinkage.

[0003]

However, since quartz changes from α-type to β-type at 573 ° C., the coefficient of thermal expansion sharply rises at this temperature. Therefore, the melting point of quartz is increased by using a mold made of quartz as a refractory material. When casting a metal or alloy of 1000 ° C. or higher, if the mold is directly put into an electric furnace having a temperature of 700 ° C. or higher for the purpose of incineration of the wax pattern and preheating of the mold, and a rapid heating is performed, cracks are generated in the mold. In order to prevent this, it is necessary to slowly raise the temperature from room temperature to 700 ° C. over a long period of 2 to 4 hours,
It was extremely inefficient. Further, cristobalite has a transition point at 220 ° C., and the coefficient of thermal expansion sharply increases at this temperature, so that it has the same drawbacks as the above-mentioned quartz.

In the present invention, since the thermal expansion coefficient is relatively small, tridymite, which has been considered unsuitable as an investment material, is mixed with the above refractory material, which enables rapid heating of the dental mold, and at the time of casting. The time required for incineration of the wax pattern and preheating of the mold in step 1 is greatly shortened.

[0005]

That is, the present invention provides:
A rapid heating type investment material composition comprising a refractory material and a binder, wherein the refractory material is obtained by adding tridymite to at least one of quartz and cristobalite.

The binder used in the present invention is the same as that used for refractory materials such as quartz and cristobalite, and is based on a phosphate-based material such as a mixture of magnesia clinker and monoammonium phosphate. The thing and gypsum are suitable. And, the compounding amount of the binder is preferably 10 to 25% of the total weight of the refractory material and the binder. Also,
The blending amount of tridymite is preferably 5 to 50% of the total weight of the refractory material and the binder.

[0007]

When the investment material composition of the present invention uses gypsum as the binder, it is kneaded with water and molded into a mold. Also,
When a phosphate-based binder is used as the binder, it is kneaded with colloidal silica and molded into a mold. Thus, the tridymite added in the present invention has a smaller coefficient of thermal expansion than quartz and cristobalite, and has a temperature of 117 ° C and 16 ° C.
Since it has two transition points at 3 ° C. and the rising curve of the coefficient of thermal expansion is gentle, rapid thermal expansion at the time of rapidly heating the mold is suppressed, and cracks are prevented from occurring. However, if the blending amount of tridymite is less than 5% of the total weight of the refractory material and the binder, there is no effect of the addition. On the contrary, if it exceeds 50%, the thermal expansion of the entire mold is insufficient and the amount of metal Insufficient compensation for casting shrinkage.

[0008]

Example 1 32 g of water was added to 100 g of an investment material composition consisting of 60 parts by weight of quartz, 10 parts by weight of cristobalite, 10 parts by weight of tridymite and 20 parts by weight of gypsum, and kneaded to form a mold for a crown. Then, put this mold in an electric furnace at 700 ° C,
When it was taken out after 30 minutes, no crack was observed. Then, a gold alloy having a melting point of 1000 ° C. was poured into the above-mentioned mold and cast to obtain a crown with good accuracy.

Example 2 20 cc of colloidal silica was added to 100 g of an investment material composition consisting of 60 parts by weight of quartz, 10 parts by weight of cristobalite, 10 parts by weight of tridymite, 10 parts by weight of magnesia clinker and 10 parts by weight of ammonium primary phosphate, and kneaded. When the mixture was soaked and a crown crown mold was molded, and the mold was put in an electric furnace at 800 ° C. and taken out after 30 minutes, no crack was observed at all. Then, the above-mentioned mold has a melting point of 1300 ° C.
A nickel-chromium alloy was poured and cast to obtain a highly accurate crown.

Example 3 Quartz 60 parts by weight, tridymite 20 parts by weight and gypsum 2
32 cc of water per 100 g of investment material composition consisting of 0 parts by weight
Was added and kneaded, and a mold for a crown was molded in the same manner as in Example 1, put in an electric furnace at 700 ° C. and taken out after 30 minutes to obtain a mold without cracks. A gold alloy having a melting point of 1000 ° C. A good dental crown was cast.

Example 4 20 g of colloidal silica was added to 100 g of an investment material composition consisting of 40 parts by weight of cristobalite, 40 parts by weight of tridymite, 10 parts by weight of magnesia clinker and 10 parts by weight of ammonium primary phosphate, and kneaded. Two
Mold a dental crown mold in the same manner as in, place it in an electric furnace at 800 ° C and take it out after 30 minutes to obtain a mold without cracks, melting point 1
A good crown made of nickel-chromium alloy at 300 ° C was cast.

Comparative Example 1 32 g of water was added to 100 g of an investment material composition consisting of 80 parts by weight of cristobalite and 20 parts by weight of gypsum and kneaded to form a mold for a crown, and the mold was placed in an electric furnace at 700 ° C. When it was taken out 30 minutes after being put in, it was unusable due to cracking. However, from room temperature to 700 ° C 2
When the temperature was slowly raised over the time, it was possible to cast without cracking.

Comparative Example 2 20 cc of colloidal silica was added to 100 g of an investment composition consisting of 40 parts by weight of quartz, 40 parts by weight of cristobalite, 10 parts by weight of magnesia clinker and 10 parts by weight of ammonium monobasic phosphate, and kneaded to prepare a crown. A casting mold was molded, and the mold was put in an electric furnace at 800 ° C. and taken out after 30 minutes. As a result, a crack was generated and it was unusable. Then, in order to prevent cracks from being generated in the similarly molded mold, it was necessary to slowly raise the temperature over 2 hours or more.

[0014]

INDUSTRIAL APPLICABILITY As described above, the investment material composition of the present invention has a relatively small coefficient of thermal expansion of quartz and cristobalite, which is excellent in the capability of compensating the casting shrinkage of the metal, and has a thermal expansion coefficient which is accompanied by a temperature rise Since it is replaced with tridymite that does not have a rapid increase in expansion coefficient, when molding a mold with the above-mentioned investment material composition, there is no occurrence of cracks even if it is directly heated in a high-temperature electric furnace and rapidly heated. During casting, the time required to incinerate the wax pattern, which also serves to preheat the mold, can be greatly reduced to less than 1/4 of the conventional time, and the above compensation performance of the refractory material such as quartz and cristobalite is impaired. And high-precision casting is possible.

Claims (1)

[Claims] 1. A rapid heating type investment material composition comprising a refractory material and a binder, wherein the refractory material is obtained by adding tridymite to at least one of quartz and cristobalite.