JPH04200950A - Molding material for casting metal having high melting point - Google Patents

Abstract

PURPOSE:To manufacture a casting having a little oxidation on surface by constituting the specific content of aggregate as main component with the specific metal oxide and containing phosphate as binder. CONSTITUTION:Molding material for casting a metal having high m.p. is the one adding the binder to the aggregate as the main component, and 50wt.% of the aggregate is constituted with one kind of metal oxide selected from group composed of magnesia MgO, zirconia ZrO2, alumina Al2O3, calcia CaO and ytria Y2O3 and the phosphate is contained as the binder. By this method, in order to decrease generation of gas caused by decomposition of the phosphate series binder, it is unnecessary to preheat the mold. Further, even in the case of casting titanium, it is unnecessary to cool the mold and the oxidation of surface is a little and high accurate casting is produced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a mold material for casting high-melting point metals used in the dental field, particularly an investment material for casting T1 metal, Zr metal, and their alloys. be.

[Conventional technology]

To date, in the field of dentistry, it has been common practice to use prosthetics to repair decayed or fallen teeth. metal must be cast. In recent years, various high-melting point alloys have been developed as dental metals, but when comparing corrosion resistance and biocompatibility, titanium is particularly superior.Other characteristics of titanium include: Its light weight, strength and hardness make it suitable as a dental metal.

Dental casting molds have been used to cast these dental metals, but since molten metal is directly poured into these molds, they are required to have excellent heat resistance.

The final mold material for producing a dental casting mold is made of aggregate and a binder, and generally, silica is used as the main component of the aggregate. On the other hand, binders for curing this include gypsum, phosphate, ethyl silicate, and the like. Among these, phosphate-based binders are excellent in that they have high heat resistance and can be used for high-temperature casting of alloys with melting points of 1100° C. or higher.

- Dental casting molds for boat fishing are made by filling a molding material containing a mixture of silica, the main component, and a binder, around a pattern formed with Wanx, curing it, and then heating it in an electric furnace. Create.

However, when casting is carried out by adding phosphate as a binder to aggregate mainly composed of silica according to such conventional methods, the phosphate is affected by the high temperature molten metal, such as titanium. There is a problem that phosphate gas is generated by decomposition, and in order to reduce the generation of phosphate gas, the mold should be heated at least once at a temperature of 950°C or higher for about 3 to 8 hours to prevent decomposition. The resulting phosphoric acid gas had to be removed. Although such problems can occur with metals other than titanium, titanium has a particularly large effect due to its high activity.

Furthermore, when casting with titanium, the molten titanium is very active, so it deprives the silica aggregate of oxygen and oxidizes the surface, causing it to seize with the mold. There is a problem that the inside is dyed with lη, causing a change in physical properties. For example, when a mold with a temperature of 800° C. is used in titanium casting, it is difficult to obtain a good cast product.

Therefore, in order to prevent seizure, the temperature of the mold in which titanium is cast has been cooled to at least 500°C or less, preferably 1I00°C or less. If the temperature of the mold is lowered in this way, the molten titanium will be cooled very rapidly, making it impossible to obtain castings with high dimensional accuracy, and making it impossible to produce products with uniform surface texture. It was also difficult.

[Problem to be solved by the invention]

The present invention improves the above-mentioned drawbacks, eliminates the need for heating the mold to reduce the generation of gas due to the decomposition of the phosphate binder, and also eliminates the need for heating the mold even when casting high-melting point metals. An object of the present invention is to provide a mold material for casting a high-melting point metal, which does not require cooling and can produce a casting with little surface oxidation.

[Means to solve the problem]

The molding material for high-melting point metal casting of the present invention is one in which a binder is added to aggregate, which is the main component.
At least 1% by weight is made of at least one metal oxide selected from the group consisting of magnenoir (MgO), di/l/coni7 (ZrO2), alumina (A120.), calcia (CaO), and ittria (y2o,). and is characterized by containing phosphate as a binder.

That is, the above metal oxide used in the present invention is
All have lower standard free energies for oxide formation than titanium oxide (T10.), and these may be used alone or in combination.

In the present invention, the total amount of these metal oxides must be at least 50% by weight of the aggregate, and is particularly preferably at least 70% by weight. If the proportion of commonly used silica etc. is too high, the cast product will become very porous due to the gas generated by the decomposition of the binder, making it difficult to obtain a good quality product.

On the other hand, as the binder that can be used in the present invention, any commercially available phosphate for dental casting can be used, but ammonium phosphate and potassium phosphate are preferable. Generally, these phosphates are mixed with aggregate in powder form and then mixed with water, but they are dissolved in water in advance and then mixed with aggregate. Also good. Further, in the present invention, components such as borax may be added to adjust the curing time.

The particle size of these aggregates and binders contained in the mold material of the present invention is preferably fine in order to provide a smooth surface of the casting.

Next, the steps for manufacturing a casting using the mold material of the present invention will be explained.

First, a wax pattern having a desired size and shape is prepared using dental wax, and this wax pattern is embedded in the molding material of the present invention containing a specific metal oxide and phosphate. After the mold material is hardened, the mold is heated to burn out the wax, and finally the molten metal is poured into the resulting mold to obtain a casting.

As described above, before casting metal, heating is performed using an electric furnace to incinerate the wax, but the incineration temperature of the mold obtained by curing the mold material of the present invention is such that the wax is completely burned out. As long as the temperature is sufficient to incinerate the
C) or higher), and is generally heated to about 800°C.

Furthermore, with the mold material for casting high melting point metals of the present invention, almost no phosphoric acid gas is generated during casting, so there is no need to heat the mold to a high temperature for the purpose of degassing before casting the metal.

Furthermore, in the case of the molding material of the present invention, all of the metal oxides contained in the aggregate have a smaller standard free energy for oxide formation than titanium oxide, so that oxidation of molten titanium is prevented. This prevents burning between the titanium and the mold. Therefore, the mold temperature during casting only needs to be below the melting point of the metal to be cast, and there is no need to cool the mold as in the conventional case. Therefore, with the mold material of the present invention, it is also possible to perform casting using a mold with a temperature of 800°C.

In addition, since the molding material of the present invention does not cause deformation of the wax pattern that serves as the original model, it is possible to manufacture castings with excellent dimensional accuracy.

Note that if the mold material of the present invention is cured too quickly, there will not be enough time to embed the pattern formed with wax.
If the curing is too slow, there will be a large loss of time until it is placed in the electric furnace, so it must be set appropriately, and is generally about 10 to 30 minutes.

〔Example〕

Hereinafter, various experiments and their results regarding the high melting point metal casting mold material of the present invention and a comparative mold material will be described.

The components of the mold material used in the experiment are shown in Table 1 below.

1. Evaluation of bubble entrapment on the surface of the casting due to decomposition of the binder Examples 1 to 5 and comparative examples 1.2 consisting of the above-mentioned components
Mix each mixture until homogeneous, and add 70g of each mixed powder.
After adding 13 g of water to each and mixing uniformly, the wax pattern was buried in each mold material and dried at room temperature for about 3 hours.

The mold material after hardening was heated using an electric furnace, and the heating conditions at this time were (a) 850°C for 1 hour;
b) Two types were used: 1000°C for 6 hours.

-For the castings obtained from each of the mold materials listed in F, the state of bubble entrapment on each surface was visually evaluated.

The evaluation criteria are as follows.

○...No bubble entrapment △・・・Less bubble entrapment ×・・・Many bubbles are trapped The results are shown in Table 2 below.

Table 2 ■, Evaluation example 1 of the seizure state on the back surface of the casting
Molten titanium for dental casting (purity 99.8
% or more). At this time, the temperature of each mold is (a)
Adjusted to 50°C1 and (b) 600°C.

After casting, the baked-in (oxidation) state of the surface of the cast product was visually evaluated.

= 11- The evaluation criteria are as follows.

○...No burn-in △・・・Less burn-in ×・・・Many burn-in The results are shown in Table 3 below.

Table 3 [Effects of the Invention] In the high melting point metal casting mold material of the present invention, in order to reduce gas generation due to decomposition of the phosphate binder,
There is no need to heat the mold beforehand.

Moreover, when the mold material of the present invention is used, high melting point metals,
For example, even when casting titanium, there is no need to cool the mold, there is little surface oxidation, and high-precision castings can be manufactured.

Patent applicant Nilasin Co., Ltd.

Claims (1)

[Claims] (1) A binder is added to aggregate, which is the main component, and 50% by weight or more of the aggregate is MgO, ZrO_2, A
A mold material for casting a high-melting point metal, comprising at least one metal oxide selected from the group consisting of l_2O_3, CaO, and Y_2O_3, and containing phosphate as a binder.