JPH0155063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a phosphate-based investment material with excellent thermal expansion properties for use in precision casting of dental castings.

(Prior art) In precision casting of dental castings such as metal crowns and inlays, when the molten alloy injected into the molding cavity of the investment material is cooled and solidified, the alloy becomes approximately 1.4 to 2.3
% shrinkage, it is necessary to expand the molding cavity beforehand, and this expansion is carried out by the expansion that occurs during curing and heating of the investment material. However, if an investment material with a large hardening expansion is used, the cast body will be deformed, so it is desired that only the heating expansion of the investment material be used to compensate for the shrinkage of the alloy.

Phosphate-based investment materials, which are made by mixing refractory materials such as silica with monoammonium phosphate and magnesium oxide as binders, have high heat resistance and high strength when cast, so they can be used for nickel-chromium alloys, cobalt-chromium alloys, etc. It is widely used for casting alloys with relatively high melting points, but the thermal expansion rate of this investment material is about 1%, and heating expansion alone cannot sufficiently compensate for the contraction of the alloy. . Although various studies have been conducted on improving the coefficient of thermal expansion of phosphate-based investment materials, there is still no known investment material that exhibits almost no curing expansion and only large thermal expansion.

On the other hand, molten calcia, which is produced by heating calcia (calcium oxide CaO) at a high temperature to make it fine and solidify it rapidly, is used as a refining agent for molten steel or as a refractory material. Calcia also contains MnO ₂ , TiO ₂ , Fe ₂ O ₃ , Cr ₂ O ₃ , CaF ₂ ,
Calcia clinker, which is made by adding one or more compounds such as AlF ₃ , sintering the mixture at 1200 to 1600℃, cooling and pulverizing it, is widely used as a material with excellent digestion resistance and for gold. has been done. However, it has not yet been known to use molten calcia and calcia clinker as a thermal expansion agent for investment materials.

(Purpose of the Invention) The present invention provides a method of adding the above-mentioned molten calcia or calcia clinker to a phosphate-based investment material as a heat-expandability imparting agent, so that the investment material has almost no curing expansion and large heat expansion. This is what I did.

(Structure of the Invention) The present invention is a phosphate-based investment agent characterized in that it contains molten calcia or calcia clinker.

Molten calcia has CaO of 98% or more and contains small amounts of impurities such as MgO, SiO ₂ , Fe ₂ O ₃ and the like, and is generally commercially available as a scouring agent for molten steel. Calcia clinker is made by adding compounds such as TiO ₂ and Fe ₂ O ₃ and sintering the CaO to 90% or more, and is generally used as a metal material with excellent digestion resistance. This calcia clinker is relatively easy to manufacture since the calcination temperature is lowered by adding the above compound.

The investment material mixed with the heat expandability imparting agent is kneaded with water or a colloidal silica solution, filled into a ring, and heated by a conventional method.

(Example) Example 1 100 parts by weight of a phosphate-based investment material consisting of 80 parts by weight of SiO ₂ and 10 parts by weight of NH ₄ H ₂ PO ₄ was mixed with 3 parts by weight of various thermal expandability imparting agents. The coefficient of thermal expansion of the investment material was measured, and the relationship between the coefficient of thermal expansion and temperature is shown in the graph of FIG.

The heat expandability imparting agent of graph No. 1 is fused calcia FCA-8A manufactured by Tateho Chemical Industry Co., Ltd. No. 2 heat-expandability imparting agent was made by molding a mixture of 95 parts by weight of CaO and 5 parts by weight of Fe ₂ O ₃ by applying a pressure of about 200 kg/cm ² , baking at 1400°C for 4 hours, and after cooling it into 200 mesh pieces. This is calcia clinker that has been finely ground to the highest level.
The heat expandability imparting agent in No. 3 contains 92 parts by weight of CaO,
_This is a calcia clinker obtained by firing and pulverizing a mixture of 5 parts by weight of Fe ₂ O ₃ and 3 parts by weight of TiO 2 in the same manner as No. 2 above. Note that No. 4 is a comparative example in which no heat-expandability imparting agent was added.

The coefficient of thermal expansion is described in a report written by Hidekazu Fudemoto, ``About the deformation of a cast body using a prototype non-expandable investment material'' (Prosthetics Journal, Vol. 29, No. 2, 1980, pp. 165-185). It was measured according to the method described in

As seen in the graph of Figure 1, Nos. 1, 2, and 3 to which the thermal expansion agent of the present invention was added had a higher thermal expansion coefficient than No. 4 to which no additive was added, and the alloys at the time of casting were can sufficiently compensate for the shrinkage of Moreover, the thermal expansion coefficient increases rapidly at a temperature of 150 to 200°C. The curing expansion coefficient of the above-mentioned mixed investment material was almost 0.

Example 2 The thermal expansion coefficient of the investment material mixed with molten calcia of Example 1 was measured when the mixing ratio of molten calcia was changed, and the results are shown in the graph of FIG. Since increasing the mixing ratio of the heat-expandability imparting agent increases the heat expansion coefficient, a desired heat-expansion coefficient can be obtained by adjusting the mixing ratio of the heat-expandability imparting agent.

(Effects of the Invention) The phosphate-based investment material of the present invention is one in which molten calcia or calcia clinker is mixed as a heat-expandability imparting agent, and its heat-expansion coefficient can be improved compared to the conventional one, and the curing expansion is Since there is almost no shrinkage of the alloy during casting, it is possible to compensate for the shrinkage of the alloy only by heating expansion. Further, a desired thermal expansion coefficient can be obtained by changing the mixing amount of the thermal expansion imparting agent. Further, the heat-expandability imparting agent is one that has been conventionally used for refining molten steel and is therefore easily available.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the thermal expansion coefficient and temperature in Example 1, and FIG. 2 is a graph showing the relationship between the thermal expansion coefficient and temperature in Example 2.

Claims (1)

[Claims] 1. A phosphate-based investment material characterized by containing molten calcia or calcia clinker.