JPS6045976B2 - Self-hardening mold material for titanium or titanium alloy casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-hardening mold material containing magnesia as a main component for casting titanium or titanium alloys.

Titanium or titanium alloys have excellent mechanical and chemical properties such as biocompatibility, corrosion resistance, abrasion resistance, and heat resistance, and low specific gravity, so in recent years they have been used as metal materials for dental castings or for various mechanical parts. It is attracting attention as a material for However, titanium material has high activity and oxidizes rapidly even during cold forging and casting, making it difficult to process and only produced in small quantities by cold forging in a vacuum atmosphere. remains.

Therefore, the present applicant previously developed a method for casting titanium castings made of pure titanium or an alloy containing titanium as the main component (Japanese Patent Publication No. 58-574) using a titanium casting mold made of magnesia molding material. Discloses a method for casting titanium or titanium alloy, and then discloses various methods of hardening acceleration in aggregate mainly composed of magnesia (MgO) in the application "Self-hardening mold material for casting titanium or titanium alloy" which precedes the present application. Although a mold material to which an agent is added has been disclosed, the present application is a further development of the latter self-hardening mold material.

In the case of the above-mentioned stowage wax molds for precision casting products, parameters such as hardening time, compressive strength, and coefficient of thermal expansion are practically important, and JIST 6601-1979 provides details regarding investment materials (mold materials) for dental castings. In other words, in the case of quartz investment materials, in the above standard, based on the test method, the solidification time (hardening time) is 5 minutes to 3 gin, and the coefficient of thermal expansion is 0.5 when heated at 700°C. % or more, and the fracture resistance (compressive fracture strength) is determined to be 9fld or more in 10.

It is believed that the magnesia-based mold material of the present application should also satisfy at least the above-mentioned required values, similar to the above-mentioned quartz investment material. The known magnesia-based mold materials have the following drawbacks.

(a) Since the solidification rate during mold manufacturing is slow, the curing time is as long as 60 minutes, making it impossible to proceed efficiently with mold manufacturing and casting operations.

(b) Since the expansion rate of the mold is small, the shrinkage rate of 1.5% in titanium casting cannot be compensated for, resulting in poor precision of the cast product, which remains a problem, especially in the casting of precision cast products such as dentures.

(c) The compressive strength of the green mold for casting does not satisfy the JIS specified value.

In order to solve the above-mentioned problems, the present invention adds at least one of an alkali metal hydrogen carbonate and an alkali metal phosphate to magnesia cement as a hardening accelerator and a binder, and also as an expansion accelerator. Added fine aluminum powder.

In the above self-hardening mold material, the solidification rate increases due to the action of soluble salts as a hardening accelerator and binder on Mg(0H)2 generated by the reaction with MgO(5H20), and the compressive strength increases due to the formation of insoluble salts. At the same time, it is thought that the expansion of the mold is significantly promoted by the action of hydrogen gas generated by the reaction of adding fine aluminum powder.

Hereinafter, experiments and experimental results regarding the mold material of the present invention will be explained.

In the following experiments, magnesia cement M4 manufactured by Nihon Kagaku Togyo Co., Ltd. was used as the magnesia cement, and its ingredient list is shown in Table 1.

In order to investigate the influence of the particle size of the magnesia cement M4, an unpulverized one (hereinafter referred to as magnesia cement 0M4) and one ground for 4 hours in a ball mill (hereinafter referred to as magnesia cement 4M4) were used.

The particle size distribution of both of the above magnesia cements is shown in FIG.
Below, various experiments and their experimental results will be explained.
W/P indicates the weight ratio of mixing water to magnesia cement.

Experiment 1 If a mold is made using only magnesia cement 0M4, the hardening speed will be slow and the compressive strength of the green mold will not be sufficient, so sodium hydrogen carbonate (NaH) was used as a hardening accelerator and binder.
The results of experiments conducted based on the JIST 166Ol-1979 standard by adding monobasic potassium phosphate (KH2PO4) are shown in FIGS. 2 to 9.

As can be seen from the results of this experiment, by adding sodium bicarbonate, monobasic potassium phosphate, etc., the curing speed can be greatly increased by these additives.

By increasing the amount added, the curing speed is increased, and on the contrary, W/P
By increasing the curing rate, the curing speed can be slowed down. Note that the values within the diagonal lines are the JIS required values (Figures 2 and 3). Furthermore, even if the above additives are added, there is no adverse effect on the coefficient of thermal expansion, and on the contrary it is slightly improved;
0.

Satisfy 5% or more (Figures 4 and 5).

Furthermore, by adding the above additives, the compressive strength of the green mold for casting is significantly strengthened, reaching the JIS required value of 10k.
9fIcr1 can be satisfied (FIGS. 6 to 9).

This is thought to be due to the formation of insoluble salts due to the additives. Experiment ■ From the results of Experiment 1, it was found that by adding sodium bicarbonate, monobasic potassium phosphate, etc., the curing rate, coefficient of thermal expansion, and compressive strength of the green mold could meet the JIS specified values. In this experiment, we added sodium bicarbonate as a curing accelerator and binder, and fine aluminum powder as an expansion accelerator, and investigated the dimensional change rate, thermal expansion rate, and clinical pattern of the green mold. The dimensional accuracy of cast products was investigated.

(1) Regarding the dimensional change rate during condensation of the green mold, the inner surface of a cylindrical body made of tracing paper with a diameter x height of 25 = φ x 30Tf$L is lined with a sponge sheet for mold expansion.
The inside of the mold was filled with mold material kneaded with water, and the dimensional change in the height direction of the mold was measured using a differential transformer, and the results are shown in FIGS. 10 to 12.

As can be seen from Fig. 10, increasing the amount of sodium bicarbonate added improves the dimensional change rate of the green mold;
．． If it is added in an amount of 5% or more, the curing speed will be too fast, which is unfavorable in terms of workability. Therefore, it is desirable that the amount of sodium bicarbonate added should be about 0.3%. 1st
As can be seen from Figures 1 and 12, by adding fine aluminum powder, it is possible to significantly expand the green mold during hardening, and the shrinkage of 0.6% in the case without the addition is reduced by 0.6%. It can be expanded by as much as 7-0.8%.

The expansion caused by the addition of fine aluminum powder is thought to be due to hydrogen gas generated when aluminum reacts with water, as shown in the following equation.

N+2H20-+Al(0H)2H2↑ (2) Regarding the coefficient of thermal expansion during heating of the green mold A test piece for measuring the coefficient of thermal expansion during heating of the green mold was provided in the center of a thick silicone rubber split mold. Diameter x height = 5T! R
A cylindrical hole of mφ x 20 TEft was filled with kneaded mold material by vibration, and after 3 hours, it was taken out and manufactured, and the temperature rise rate was 10.
The results of measurement using a thermal expansion analyzer while heating to 3000C at C/Min are shown in FIGS. 13 and 14.

As can be seen from FIGS. 13 and 14, by adding fine aluminum powder, the coefficient of thermal expansion is not adversely affected as a whole.

However, as shown in Figure 14, magnesia cement 4M
When adding 0.1% aluminum fine powder to No. 4, some adverse effects are seen, but the effects are insignificant. (3) Dimensional accuracy of cast product based on clinical pattern A wax pattern for the crown is manufactured using a clinical abutment tooth made of epoxy resin, a titanium cast product is cast using this wax pattern, and this cast product is attached to the above-mentioned abutment tooth. Fit it into
The amount of lift was measured.

In this experiment, the purity of the casting metal was 99.8.
% or more of pure titanium (KS-50 manufactured by Kobe Steel Corporation), the mold is made of tracing paper and is lined with sponge on the inner surface to allow the mold to expand. The casting machine used was an Alcon arc melting casting machine (Iwatani Sangyo Co., Ltd.), which was filled with mold material kneaded with water, dried at room temperature for 2ff, heated to 800°C, and then held for 30 minutes. CASTMATIC) manufactured by Co., Ltd. was used.

The various parameters of the mold material used in the above experiment are shown in Table 2 below, the experimental results are shown in Table 3, and the cross-sectional photographs of the cast crown fitted to the abutment tooth are precisely traced in Figures 15-15. It is shown in FIG.

(However, 1 and 2 above are cast products manufactured under the same conditions.

) As can be seen from Table 3 and Figures 15 to 18 above,
When fine aluminum powder is added, the amount of lift from the abutment tooth of the titanium cast crown is 1.0? The above can also be improved and lowered to approximately ideal values.

(4) Regarding surface roughness using a mold model In order to investigate the surface roughness of a cast product due to hydrogen gas mixed with fine aluminum powder, a mold abutment as shown in Figure 19 was used instead of a clinical abutment tooth. A cup-shaped cast product c was cast using m, and the surface roughness of the cylindrical inner peripheral surface of the cup-shaped cast product c was measured using a surface roughness profile measuring machine (trade name: Surfcom 300B, manufactured by Tokyo Seimitsu Co., Ltd.).

The various parameters of the mold material in the above experiment are shown in Table 4 below, and the measurement results are shown in FIG. As can be seen from the above measurement results, the addition of fine aluminum powder has almost no adverse effect on the surface roughness of the cast product, and on the contrary, it can be improved depending on the conditions of the mold material.

In the above experiment, sodium hydrogen carbonate or monobasic potassium phosphate was added as a curing accelerator and binder.
Other alkali metal bicarbonates, carbonates or phosphates can also serve as accelerators and binders, as well as
It is believed that alkaline earth metal bicarbonates, carbonates or phosphates having chemical properties similar to these can also serve as curing accelerators and binders.

Further, although fine aluminum powder was used as the expansion promoter, fine powders of magnesium, iron, or zinc may also be used as the expansion promoter.

Hereinafter, a method for casting titanium or a titanium alloy without oxidizing it using a mold manufactured using the above-mentioned mold material will be briefly described.

As shown in Figure 21, at temperatures below about 1700°C. Since the oxide formation energy of magnesia is smaller than the oxide formation energy of titanium, titanium or titanium alloy is heated in an oxygen-free manner while maintaining the temperature of the magnesia-based mold below about 1700'C. Casting in an atmosphere prevents oxygen atoms from entering the molten metal from the mold, making it possible to produce unoxidized casts of titanium or titanium alloys. The self-hardening mold material for casting titanium or titanium alloy according to the present invention has the following effects, as can be seen from experimental results. (1) A mold made by kneading this mold material with water has a hardening accelerator that accelerates its solidification, shortens the hardening time to an appropriate value, and satisfies the JIS specified values. Manufacturing and casting work processes can proceed efficiently.

(2) A mold made by kneading this mold material with water generates hydrogen gas due to the action of fine aluminum powder as an expansion accelerator, suppressing shrinkage of the mold, and depending on the amount of fine aluminum powder added. can be expanded by at least about 0.7 to 0.8%.

Furthermore, since the coefficient of thermal expansion of the mold at a mold temperature of approximately 700 to 800'C during casting is approximately 0.5 to 0.6%, the total value of both coefficients of expansion is approximately 1.2 to 1. 4%, the shrinkage rate during casting of titanium or titanium-based alloys is approximately 1.
Approximately 5% can be compensated. Therefore, using this self-hardening mold material, it is possible to cast a substantially complete precision cast product such as a denture made of titanium or a titanium alloy. (3
) The mold made using this mold material has improved compressive strength due to the effects of the hardening accelerator and binder, and satisfies the JIS standard values.

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between grinding time and particle size distribution for magnesia cement M4, and Figure 2 is a chart showing the relationship between magnesia cement M4 and particle size distribution.
Figure 3 is a diagram showing the relationship between the amount of sodium bicarbonate added and the curing time for a mold made with W/P = 0.13 using a mold material with monobasic potassium phosphate added.
The figure shows a mold material made by adding sodium bicarbonate or dibasic potassium phosphate to magnesia cement 0M4, W/P = 0.
．． Figures 4 and 5 are diagrams showing the relationship between each addition amount and curing time for the molds manufactured as No. 17, respectively, for mold materials in which sodium hydrogen carbonate or monopotassium phosphate was added to magnesia cement 0M4, respectively. W/P=0.1
Figures 6 and 7 are diagrams showing the relationship between heating temperature and coefficient of thermal expansion of the mold manufactured as No. 3, respectively, using magnesia cement 0.
Figures 8 and 9 are bar graphs showing the relationship between the amount of each addition and the compressive strength of molds made with M4 containing sodium bicarbonate or monopotassium phosphate, with W/P = 0.13. The figure is a bar graph showing the relationship between the amount of each addition and the compressive strength of molds made with W/P = 0.17 using mold materials in which sodium bicarbonate or monopotassium phosphate was added to magnesia cement ■4. 10th
The figure is a diagram showing the relationship between the condensation time and the dimensional change rate during condensation of a mold made with magnesia cement 0M4 and sodium hydrogen carbonate added, with W/P = 0.14. Relationship between condensation time and dimensional change rate during condensation of molds manufactured with W/P = 0.14 using mold materials made by adding 0.3% sodium bicarbonate to 0M4 and each percentage of fine aluminum powder. Figure 12 is a diagram showing the magnesia cement core ■.
A mold material containing 3% of sodium bicarbonate and each percentage of aluminum fine powder added, W/P=0.
A diagram showing the relationship between the condensation time and the dimensional change rate during condensation of the mold manufactured as No.
A mold material made by adding 0.3% sodium hydrogen carbonate to M4 and each percentage of fine aluminum powder.
Figure 14 is a diagram showing the relationship between the heating temperature of a mold manufactured with /P=0.14 and the coefficient of thermal expansion during heating. Figures 15 to 18 are diagrams showing the relationship between the heating temperature and the coefficient of thermal expansion during heating for molds manufactured with mold material containing fine aluminum powder and W/P = 0.16. Longitudinal front view of the state fitted to the abutment tooth,
Fig. 19 is a longitudinal sectional front view of the mold support and cup-shaped cast product, Fig. 20 is a bar graph of the center line average roughness of the surface of each cast product,
FIG. 21 is a diagram of the energy for forming oxides such as magnesia and titanium oxides.

Claims (1)

[Claims] 1 Titanium obtained by adding at least one of alkali metal hydrogen carbonate and alkali metal phosphate as a hardening accelerator and binder to magnesia cement, and adding fine aluminum powder as an expansion accelerator. or self-hardening mold material 2 for casting titanium alloys In the self-hardening mold material for casting titanium or titanium alloys described in claim 1, sodium hydrogen carbonate (NaHCO_3) is used as a hardening accelerator and a binder. 3. The self-hardening mold material for casting titanium or titanium alloy as set forth in Claim 1, in which monopotassium phosphate (KH_2PO_4) is used as a hardening accelerator and binder. 4. Claim 4 In the self-hardening mold material for casting titanium or titanium alloys described in item 1, magnesia cement is mixed with magnesia (MgO) and silica (SiO_
2), sodium oxide (Na_2O), ferric oxide (F
e_2O_3) and alumina (Al_2O_3) added.