JPS60166140A - Thermal expandability imparting agent for embedding material - Google Patents

Abstract

PURPOSE:To compensate shrinkage of an alloy during casting only by the thermal expansion concerning precision casting of a dental casting by adding a thermal expandability imparting agent consisting of molten calcium or calcia clinker to an embedding material. CONSTITUTION:A thermal expandability imparting agent consisting of molten calcium or calcia clinker is added to, for example, a phosphate embedding material. The embedding material mixed with such imparting agent is kneaded by water or colloidal silica soln. and is packed in a ring, then the material is heated by the conventional method. The embedding material has a high rate of thermal expansion with substantially no expansion on hardening. The shrinkage of the alloy during casting is thus compensated by only the thermal expansion.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a heat-expandable material 1 for improving the heat-expandability of the investment material by mixing it with the investment material used for precision casting of dental castings. It is a drug.

(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.
It is widely used for casting alloys with relatively high melting points, such as nickel-chromium alloys and cobalt-chromium alloys, but the thermal expansion coefficient of this investment material is about 1%, so heating expansion alone does not cause the alloy to shrink. Although various studies have been conducted on improving the coefficient of thermal expansion of phosphate-based investment materials, which cannot fully compensate, 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 obtained by heating and melting calcia (calcium oxide Cab) at a high temperature, making the particles fine in the molten state, and solidifying them rapidly, is used as a refining agent for molten steel or as a refractory material. Also, Calcia has 0g of Mn and 1t of Ti.
, Fe20g, Cr20B, CaFz, ^IFg, and other compounds are added to the calcia clinker, which is sintered at 1200-1600℃, cooled, and then crushed. Calcia clinker has excellent digestion resistance. It is widely used as a vegetable and for kumquats. However, it has not yet been known to use molten calcia and calcia clinker as a thermal expansion agent for investment materials.

(Object of the invention) An object of the present invention is to provide a heat-expandability imparting agent that causes almost no curing expansion of the investment material and increases thermal expansion by adding the above-mentioned molten calcia or calcia clinker to the investment material. It is something to do.

(Structure of the Invention) The present invention is a heat-expandability imparting agent for investment materials, characterized by comprising molten calcia or calcia clinker.

The molten calcia has Ca098% or more and M as an impurity.
It contains small amounts of gO, 5i02, 120 g of A, 20 g of Fe, etc., and is generally commercially available as a refining agent for molten steel. Calcia clinker is made by adding compounds such as TiO+ and Fe2O2 and sintering the Ca content to 90% or more, and is generally used as a kumquat with excellent digestion resistance. This calcia clinker is relatively easy to manufacture because 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 280 parts by weight of Si0, 0.10 parts by weight of N1(41(2P), and 10 parts by weight of Mg) were mixed with 3 parts by weight of various thermal expandability imparting agents, The thermal expansion coefficient of this mixed sinking material was measured, and the relationship between the thermal expansion coefficient and temperature is shown in the graph of FIG.

The heat expandability imparting agent of Graf&l is Fused Calcia FC^-8A manufactured by Tateho Chemical Industry Co., Ltd. The heat expandability imparting agent &2 is obtained by molding a mixture of 95 parts by weight of Ca0 and 5 parts by weight of Fe20B by applying a pressure of about 200 kg/cd.
Calcia clinker is calcined at 0°C for 4 hours, cooled, and then finely pulverized to 200 meshes or more. This is calcia clinker that has been calcined and crushed in the same way as Nα2. Note that Nα
No. 4 is a comparison bait to which no heat-expandability imparting agent was added.

The coefficient of thermal expansion is based on a report written by Hidekazu Fudemoto [About the deformation of cast bodies using prototype non-expandable sinking materials] (Prosthetics Journal Vol. 29, No. 2)
No., 1980, pp. 165-185).

As seen in the graph of Figure 1, Na1.2.3 to which the heat expandability imparting agent of the present invention is added is different from that of unadded Na.
It has a larger thermal expansion coefficient than No. 4, and can sufficiently compensate for the shrinkage of the alloy during casting. Also, the coefficient of thermal expansion is temperature 1
It is rapidly raised between 50 and 200°C. In addition, the hardening expansion coefficient of the mixed sinking material was almost 0.

Example 2 The thermal expansion coefficient was measured when the mixing ratio of molten calcia was changed in the investment material mixed with molten calcia of Example 1, 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 heat-expandability imparting agent of the present invention can improve the heat-expansion coefficient of phosphate-based investment materials compared to the conventional one, and has almost no hardening expansion, so the shrinkage of the alloy during casting is limited to heating expansion. It becomes possible to compensate by Further, a desired coefficient of thermal expansion can be obtained by changing the amount of the thermal expansion imparting agent mixed.

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. Figure 1 Temperature ('C) Figure 2 Temperature (0C)

Claims (1)

[Claims] (1) A heat-expandability imparting agent for investment materials, characterized by comprising molten calcium or calcia clinker.