JP2648996B2 - Investment for refractory metal casting - 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 for refractory metal casting, particularly titanium (T
i), refractory metals such as zirconium (Zr) and platinum (Pt), and investment materials used for casting these alloys.

[0002]

2. Description of the Related Art To date, in the field of dentistry, prostheses have been used for restoring tooth decay or missing teeth, and materials constituting such dental prostheses include:
Refractory metals such as Ti, Zr, Pt, and alloys thereof are being developed. Among them, in particular, Ti is a material that is very suitable in terms of strength, lightness, corrosion resistance, biocompatibility, price, and the like, and is widely used. When a dental prosthesis is manufactured using such a high melting point metal, a mold having a cavity of a desired shape is used,
The metal is directly injected into the cavity of the mold in a molten state and then molded, and then the mold is broken to take out a casting.

[0003] In this case, since the metals to be injected are all high temperature, when they are injected into the inside of the mold, the metal is easily oxidized on the surface in contact with the mold and seizure easily occurs. If seizure occurs, the surface condition of the resulting prosthesis will be significantly degraded. Therefore, it is preferable that the mold used has a composition that has excellent heat resistance and at the same time, reacts less with molten metal. Generally, a mold used for casting dental metal is made from an investment material in which a binder for imparting formability to heat-resistant aggregate is added, and the investment material is kneaded with water and a dedicated liquid. Is filled around the pattern formed of wax and cured, and then heated in an electric furnace to obtain a mold.

As an investment material that has been used to produce a mold for dental casting, an aggregate as a main component is silica (SiO ₂ ), and a binder for hardening the silica is gypsum. , Phosphates, ethyl silicates, etc. are generally used. Above all, investment materials containing a phosphate binder are excellent in heat resistance of a mold to be produced and have a melting point of 110.
It can also be used for high-temperature casting of alloys of 0 ° C. or higher. For example,
Japanese Patent Publication No. 61-35162 discloses an investment material containing silica as a main component (80 to 96% by weight) and a mixture of magnesium oxide, monobasic ammonium phosphate, and alumina cement. It is shown that the expansion property can be adjusted by adding alumina cement (3% by weight).

[0005] However, when casting is performed using a mold prepared from such an investment material containing silica and phosphate, the phosphate is decomposed due to the temperature of the high melting point metal, and phosphorus is decomposed. There is a problem that an acid gas is generated. To reduce the generation of the phosphoric acid gas, the mold is heated at least once at a high temperature of 950 ° C. or more for about 3 to 8 hours to remove the decomposed phosphoric acid gas. There was a problem that had to be. In particular, such generation of phosphoric acid gas occurs in the case of Ti having high activity. In addition, T
When casting is performed using i, since the molten Ti is very active, the surface is oxidized by depriving the silica of the aggregate of oxygen, and simultaneously burning with the mold occurs. There is a problem that the inside is contaminated to cause a change in physical properties. For example, when a mold at a temperature of 800 ° C. is used in casting of Ti, it has been difficult to obtain a good cast product.

For this reason, as a method of preventing burning, the temperature of the mold at the time of casting Ti is at least 500 ° C.
In the following, preferably cooling to 400 ° C. or less has also been proposed, but when the temperature of the mold is lowered in this way,
Since the molten Ti is quenched, there is a problem that defects such as insufficient running of the molten metal easily occur, and it is difficult to obtain an appropriate expansion coefficient.

Therefore, the present inventor has conducted research on an investment material which does not generate phosphoric acid gas, does not require heating and cooling of a mold, and hardly causes baking by casting.
In No. 8559, investment materials containing a specific metal oxide as an aggregate in a certain amount or more, and phosphate as a binder, compared with conventional investment materials mainly containing silica, Has been found to be able to improve the image sticking state. However, such investment materials can provide castings with improved seizure conditions, but are not sufficient for obtaining castings having surfaces without any seizure at high temperatures.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and provides a high melting point metal casting capable of producing a casting having a surface which is not oxidized and has no seizure. It is an object to provide investment materials.

[0009]

The investment for refractory metal casting of the present invention comprises 30 to 97.9% by weight of aggregate and 2 to 50% by weight.
% Alumina cement and 0.1 to 20% by weight of an auxiliary material, wherein the aggregate is made of magnesia (Mg
O), zirconia (ZrO ₂ ), alumina (Al
₂ O ₃ ), calcia (CaO), yttria (Y
_At least one metal oxide selected from the group consisting of ₂ O ₃ ) is contained as a main component of the aggregate, and the auxiliary material contains a carbonate of an alkaline earth metal.

That is, the investment material for refractory metal casting of the present invention is a powdery mixture containing three components of an aggregate, a binder, and an auxiliary material. 97.9
Accounts for% by weight. In addition, the investment material of the present invention contains the above-mentioned metal oxides (magnesia and the like) as aggregates, each of which has a smaller standard free energy for oxide generation than titanium oxide (TiO ₂ ), Zr,
It has the property of not easily reacting with high melting point metals such as Pt. In the present invention, metal oxides such as magnesia may be used alone or in combination, and these metal oxides are the main components of the aggregate.

In the present invention, as an aggregate other than the above-mentioned metal oxide, a metal oxide having a larger standard free energy for oxide generation than titanium oxide (TiO ₂ ), for example, silica which has been widely used conventionally. (SiO ₂ ) or the like can be added, but in this case, the total amount of silica or the like is set to half or less of the whole aggregate, and the total amount of the metal oxide is set to half or more of the whole aggregate. It is necessary. In the present invention, it is particularly preferable that the total amount of metal oxides such as magnesia is 70% or more of the entire aggregate. if,
If the proportion of silica or the like becomes too large and the total amount of metal oxides such as magnesia becomes smaller than the total amount of aggregates such as silica, the high melting point metal (for example, Ti) used for casting is oxidized. And the surface of the casting is seized,
The surface becomes hard and good quality cannot be obtained.

Further, the investment material of the present invention contains alumina cement as a binder, and this alumina cement also contains the above-mentioned high melting point metal, particularly T
It has a feature that it hardly reacts with i, and a commercially available grade product can be widely used. In particular, in the present invention, the content of alumina cement is 2 to 50% by weight of the entire investment material, and it is particularly preferable that the content is 10 to 35% by weight. With the above content, the curing time of the investment material becomes appropriate, sufficient strength can be obtained, and the surface state of the casting becomes fine. In addition, when such an alumina cement is added, it is generally mixed with the aggregate in a powder state, then added with water and further kneaded.

Further, the investment material of the present invention contains a carbonate of an alkaline earth metal as an auxiliary material. Such a compound prevents cracking when the mold is incinerated and improves operability. Show the function of Examples of the alkaline earth metal usable in the present invention include magnesium carbonate and calcium carbonate. The proportion of the auxiliary material in the investment material of the present invention is 0.1 to 20% by weight, particularly 0.2 to 10% by weight. % By weight.

Further, the present invention is characterized in that the investment material for refractory metal casting described above further contains an alkali metal carbonate as an auxiliary material. The alkali metal carbonate has a function of accelerating the hardening reaction of the alumina cement as the binder, and examples of such an alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Therefore, all of the investment materials of the present invention containing the above-mentioned alkali metal carbonate have an appropriate curing time and have improved operability. Incidentally, the content ratio of such an alkali metal carbonate in the entire investment material is sufficiently in the range of 0.05 to 5% by weight, and particularly preferably 0.1 to 3% by weight. In addition, zirconium or zirconium carbide may be added to the investment material of the present invention in order to adjust the thermal expansion property.

Next, a process for producing a casting (dental prosthesis) using the investment material for refractory metal casting of the present invention will be described. First, a wax pattern having a desired size and shape is prepared using dental wax. Then, water is added to the investment material of the present invention containing the metal oxide, the alumina cement, and the auxiliary material, and the mixture is uniformly mixed. Then, the wax pattern is embedded in the investment material. After being left at room temperature to cure the investment material, the mold is heated to incinerate the wax, thereby obtaining a mold in which a cavity having the same shape as the wax pattern is formed. Thereafter, the molten metal is injected into the cavity of the obtained mold to perform molding, and finally the mold is broken to take out the casting.

In this case, before casting the metal, heating using an electric furnace is performed to incinerate the wax. The incineration temperature of the mold obtained by curing the investment material of the present invention is as follows. Any temperature may be used as long as the wax can be completely incinerated, and does not require a high temperature (for example, 950 ° C. or higher) as used in conventional removal of phosphate gas, and generally may be heated to about 800 ° C. Therefore, simple use is possible.

Further, in the investment material for refractory metal casting of the present invention, phosphoric acid gas is not generated at the time of casting as in the case of using a phosphate as a binder. There is no need to heat the mold to a high temperature for the purpose of degassing. Moreover, in the case of the investment material of the present invention, cracking of the mold can be prevented by the addition of the alkaline earth metal carbonate, and the metal oxide contained in the aggregate is more oxidized than titanium oxide as described above. Since the standard free energy for product formation is small, oxidation of the molten Ti can be prevented, and burning between the Ti and the mold does not occur. Therefore, the temperature of the mold during casting need only be lower than the melting point of the metal to be cast, and it is not necessary to cool the mold as in the conventional case. For this reason, the investment material of the present invention can be cast using a mold at a temperature of 800 ° C.

In addition, the investment material of the present invention produces a dental prosthesis that is excellent in dimensional accuracy because it has little expansion upon curing and does not cause deformation of a wax pattern serving as a prototype. can do. Incidentally, the time required for the investment material of the present invention to be cured is too early, there is no time margin to bury the pattern formed by the wax,
Conversely, if the curing is too slow, the loss of time before putting into an electric furnace increases, so the time is adjusted to an appropriate time range, but the general curing time is about 10 to 60 minutes.

[0019]

EXAMPLES Experiments and results on investment materials for refractory metal casting of the present invention (Examples 1 to 10) and conventional investment materials (Comparative Examples 1 to 3) will be described below. The compositions of the investment materials used in the experiments are as shown in Tables 1 and 2 below.

[0020]

[Table 1]

[0021]

[Table 2]

Example 1 Dental magnesia, alumina cement (trade name: Denka Alumina Cement Super S-2, manufactured by Denki Kagaku Kogyo KK)
And magnesium carbonate were mixed at the mixing ratio described in Example 1 in Table 1 above, and 13 g of water was added to 70 g of the obtained investment material powder, and kneaded until uniform. Then, a wax pattern of a large denture molded with dental wax is buried in the kneaded material, and the wax pattern is about 3 mm at room temperature.
The mold obtained by drying and curing was heated using an electric furnace (the temperature was raised from room temperature to 850 ° C., and at 850 ° C. for 1 hour) to obtain a mold for metal casting.

Example 2 An investment material containing the components described in Example 2 of Table 1 in the respective mixing ratios described above was prepared, and this was added thereto at the same ratio as described in Example 1 above. Water was added and kneading was performed to obtain a kneaded product. Then, a wax pattern of a dental caries prosthesis molded with dental wax was buried in the kneaded material, and dried and heated in the same manner as described in Example 1 to obtain a mold.

Examples 3 to 10 After preparing the investment material containing the components described in Examples 3 to 10 of Table 1 or Table 2 in the mixing ratios described, the description is given in Example 1 above. In the same manner as in the above, templates were obtained.

Comparative Examples 1 to 3 After preparing investment materials containing the components described in Comparative Examples 1 to 3 in Table 2 in the mixing ratios described,
In the same manner as described in Example 1 above, each mold was obtained.

Then, about 2000 ° C. was placed inside each of the molds prepared in Examples 1 to 10 and Comparative Examples 1 to 3.
The molten titanium for casting (purity of 99.8% or more) was cast. At this time, the temperature of each mold was set to (a) 100 ° C and
(b) The temperature was adjusted to 600 ° C. After the casting was completed, the seizure state (oxidized state) of the surface of the removed casting was visually evaluated. The results of this experiment are shown in Table 3 below. Table 3
For each of the molds produced in Examples 1 to 10 and Comparative Examples 1 to 3, evaluation results on cracks of the mold after incineration are also shown.

[0027]

[Table 3]

As shown in Table 3 above, in the investment for refractory metal casting of the present invention (Examples 1 to 10), the casting temperature was 100 ° C. and 600 ° C. A cast (prosthesis) having no seizure on the surface and having no seizure on the surface, especially when the mold temperature was 100 ° C., could be produced. Further, in Examples 1 to 10, cracks of the mold after incineration did not occur.

On the other hand, in the case of the investment material in Comparative Example 1 (an investment material containing no alkaline earth metal carbonate), even if the mold temperature is 100 ° C. or 600 ° C., Although a casting without seizure was obtained, cracks occurred in the mold after incineration. In Comparative Example 2, when the mold temperature was 100 ° C., there was no seizure on the surface of the casting, but when the mold temperature was 600 ° C., seizure was observed. Furthermore, in the case of the investment material in Comparative Example 3, the surface of the casting was remarkably seized, and only a casting having extremely poor appearance and quality could be obtained.

[0030]

The investment material for refractory metal casting of the present invention contains, as a main component of the aggregate, a metal oxide having a low reaction with the high melting point metal, especially Ti, and a bond which has a low reaction with the high melting point metal. Since alumina cement is used as the material, the surface of the obtained casting is not oxidized, and seizure does not occur. or,
By containing a carbonate of an alkaline earth metal as an auxiliary material, cracking during incineration of wax can be prevented, and operability can be improved. Further, in the present invention, the curing reaction (curing time) can be easily adjusted by adding an alkali metal carbonate to the investment material.

Since the investment material of the present invention does not contain a phosphate binder, no gas is generated due to decomposition, and a cast product having excellent appearance and uniform quality can be obtained. or,
When casting a high melting point metal, there is no need to cool the mold, and a cast with high dimensional accuracy can be manufactured.

Claims (2)

(57) [Claims] 1. 30 to 97.9% by weight of aggregate, 2 to 5
0% by weight of alumina cement and 0.1 to 20% by weight of an auxiliary material, wherein the aggregate is made of magnesia (M
gO), zirconia (ZrO ₂ ), alumina (Al ₂ O)
₃ ) at least one metal oxide selected from the group consisting of calcia (CaO) and yttria (Y ₂ O ₃ );
An investment material for refractory metal casting, comprising as a main component of the aggregate, and wherein the auxiliary material contains a carbonate of an alkaline earth metal. 2. The investment material for refractory metal casting according to claim 1, wherein the auxiliary material further contains a carbonate of an alkali metal.