JPS6135162B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an investment material composition for precision casting.
In precision casting of dental castings such as metal crowns and inlays, wax patterns are formed by immersing a wax model in an investment material filled in a ring, and heating the investment material to dissolve or burn the wax model. It is widely practiced to produce cast products by injecting molten alloy into a mold cavity. In the above casting process, the alloy contracts by about 1.4 to 2.3% when it cools and solidifies, so it is necessary to expand the mold cavity into which the molten metal is injected in advance. This expansion of the mold cavity is caused by expansion that occurs during curing and heating of the investment material. Conventional investment materials include gypsum-based investment materials, which are made by mixing a refractory material such as silica with a gypsum binder, and phosphate-based investment materials, which are made by mixing diammonium phosphate and magnesium oxide as binders. Although it is common, the latter phosphate-based investment material is
Compared to the former plaster-based investment material, it has greater heat resistance, so it can be used for casting alloys with relatively high melting points such as nickel-chromium alloys, cobalt, and chromium alloys. It has advantages such as high strength. However, the above-mentioned known phosphate-based investment materials have low strength when kneaded with water, have almost no curing expansion, and only have a heating expansion of about 1%, so they cannot sufficiently compensate for the shrinkage of the alloy. A colloidal silica solution is used for kneading the acid-based investment material, and in this case, by increasing the silica concentration of the colloidal silica solution, the curing expansion can be improved to about 1%. Silica, a refractory material that is the main component of investment materials, has a coefficient of thermal expansion of approximately 2.5%, but as the amount of binder such as phosphate increases, the thermal expansion of investment materials decreases.
Although a decrease in thermal expansion can be prevented by reducing the amount of binder, the use of a colloidal silica solution cannot avoid the occurrence of large curing expansion of the phosphate investment material. Recently, it has been reported that the use of investment materials with large hardening expansion causes deformation of cast bodies, and it has been emphasized that only the heating expansion of the investment material should be used to compensate for the shrinkage of the alloy. However, an investment material that compensates for the contraction of the alloy using only thermal expansion has not yet been commercially available. These inventors found that even when kneading a phosphate-based investment material with a colloidal silica solution, the curing expansion was 0.3.
% or less, and yet has a strength that can be cast.
As a result of intensive research into obtaining a material with large thermal expansion, the desired objective was achieved by mixing a small amount of alumina cement into the investment material. That is, this invention contains 80 to 96% by weight of silica, 2 to 10% by weight of magnesium oxide, 2 to 10% by weight of monoammonium phosphate, and 0.05 to 3% by weight of alumina cement.
This is an investment material composition for precision casting, characterized in that an investment material mixed with % by weight is kneaded with a colloidal silica solution. The silica of the refractory material which is the main component of the investment material in this invention is preferably cristobalite or quartz. The mixing ratio of silica in the investment material is 80-96
If it is less than 80% by weight, the thermal expansion will be small and it will not be possible to compensate for the shrinkage of the cast body. Monoammonium phosphate and magnesium oxide are binders that exhibit shrinkage when heated, and have the effect of eliminating the thermal expansion properties of silica. The mixing ratio of monoammonium phosphate and magnesium oxide is 2 to 10% by weight, and if the mixing ratio is less than 2% by weight, the hardenability of the investment material will decrease, and it will take a long time to harden the kneaded composition. At the same time, the strength of the investment material after heating decreases, making it unable to withstand casting pressure and causing casting defects. Also, the mixing ratio is 10
If it exceeds % by weight, the expansion of the investment material upon heating will be small, making it impossible to compensate for the shrinkage of the cast body, and the surface of the cast body will become rough. The mixing ratio of alumina cement is 0.05 to 3% by weight.
If it is less than 0.05% by weight, the effect of reducing curing expansion will be small, and if it exceeds 3% by weight, it will shrink when heated at 100 to 200°C and the heating expansion will decrease. Furthermore, cracks occur in the investment material during heating, resulting in poor casting. The mixing ratio of each component of the investment material is appropriately adjusted depending on the expandability upon heating when kneaded with a colloidal silica solution. Generally speaking, when the amount of binder is large, the amount of alumina cement mixed is increased to suppress the occurrence of hardening expansion. When using the investment material composition obtained as described above, the expansion during curing is reduced to 0.3% or less, the expansion during heating is not reduced, and the strength of the solidified investment material is sufficient. is maintained. Examples of the present invention will be described below. Example 1 Quartz (particle size distribution that passes 90% or more through a sieve of 149 μm), cristobalite (particle size of 74 μm or less,
(manufactured by Taisei Dental Industry Co., Ltd.), ammonium monophosphate (particle size 74 μm or less, manufactured by Katayama Chemical Co., Ltd.), magnesium oxide (particle size 74 μm or less, manufactured by Taisei Dental Industry Co., Ltd.), and alumina cement (trade name: Hi-Alumina Cement Super, Electrochemical (manufactured by Kogyo Co., Ltd.) was mixed in a mixer for 30 minutes at the mixing ratio shown in Table 1 below, and 100 g of this mixture was mixed with a colloidal silica solution (silica concentration 20% by weight, trade name Snowtex 0-
28 c.c. (manufactured by Nissan Chemical Industries, Ltd.) was added and kneaded at 300 rpm in a vacuum kneader (manufactured by GC Corporation). The investment material composition shown in appendix Table 1 was used in a report by Hidekazu Fudemoto, "On the deformation of a cast body using a prototype non-expandable investment material" (Prosthetics Journal, Vol. 24, No. 2, 1980, 165 ~
The hardening expansion and heating expansion were measured according to the method described in page 185), and the strength was measured according to the method for measuring investment materials for dental castings in JIS-T6601.The results are shown in Table 1 and the drawings. Shown in a graph.

[Table] As shown in Table 1, Experiment No. 1, in which no alumina cement was mixed, had a large curing expansion coefficient and was contrary to the purpose of the present invention. Experiment number 2,
Comparing No. 3, it can be seen that as the amount of binder increases, the curing expansion coefficient becomes slightly larger and the heating expansion coefficient becomes slightly smaller. Furthermore, by comparing Experiment Nos. 3, 4, and 5, it can be seen that the thermal expansion coefficient decreases as the amount of alumina cement increases. A mold was made with the investment material composition of Experiment No. 3 above, and after hardening, it was placed in an electric furnace and heated to 700°C.
Vertical centrifugal casting machine (product name Castmart, G-C
As a result of casting K-metal by the dental casting method using a molding machine (manufactured by K.K.), a good cast product with very little deformation was obtained. Example 2 Regarding the mixture of experiment number 3 of Example 1 above,
Physical properties were measured in the same manner as in Example 1 for each composition in which the silica concentration was varied by diluting a colloidal silica solution (silica concentration 40% by weight, trade name Sunotex 0-40, manufactured by Nissan Chemical Industries, Ltd.) with water. The results are shown in Table 2.

【table】

[Table] As shown in Table 2, the curing expansion coefficient and heating expansion coefficient hardly change as the silica concentration changes, but the strength improves as the silica concentration increases. Although the strength of Experiment No. 6 was relatively low, it was within a practical range.

[Brief explanation of the drawing]

The drawing is a graph showing changes in the curing expansion coefficient and heating expansion coefficient in Example 1.

Claims (1)

[Claims] 1 Silica 80-96% by weight, Magnesium oxide 2-
An investment material composition for precision casting, characterized in that an investment material containing 10% by weight of monoammonium phosphate, 2 to 10% by weight of monoammonium phosphate, and 0.05 to 3% by weight of alumina cement is kneaded with a colloidal silica solution.