JPH0318893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a precision casting mold (particularly a metal precision casting mold for dental use such as metal casting beds, clasps, bridges, etc.) and a method for manufacturing the same.

B. Prior Art Conventionally, dental metals, such as metal casting bases, clasps, bridges, cast metal crowns, and inlays, have generally been used for casting Co-Cr alloys (for example,
Co65%, Cr28%, Mo5%, and also contains Ni and Mn), Au-Cu alloys (e.g. Au90%, Cu10
%), and even Ni alloys are used. The method for manufacturing such dental metal precision castings is as follows:
A lost wax method is known that uses a mold made of an investment material made of silica powder and a binder such as gypsum, phosphoric acid, phosphoric acid, colloidal silica, ethyl silicate, etc. added thereto.

However, in recent years, titanium or titanium alloys, which have better corrosion resistance than the above-mentioned Co-Cr alloys, have no harmful effects on the human body, and have appropriate mechanical properties, have attracted attention as dental metals.

However, when precision casting titanium or titanium alloys, the above-mentioned silica molds are easily corroded by slag containing titanium, resulting in spalling (cracks, peeling, etc.) and the precision casting itself. It becomes impossible. Therefore, instead of silica, attempts have been made to use graphite and magnesia, which have poor reactivity with titanium, as mold materials ("NIKKEI MECHANICAL").
1986.12.1) However, these materials tend to shrink when they harden as a mold, so if you take into account that cast metal generally shrinks during casting,
The cast product becomes much smaller than the set size, which is also unsuitable for precision casting. In addition, materials that cause shrinkage also have poor air permeability in the mold, making it insufficient to release gas and air generated at the interface between the mold and the molten metal during casting to the outside through the mold, resulting in poor quality. Good precision castings cannot be obtained.

C. Purpose of the Invention An object of the present invention is to provide a precision casting mold that is resistant to corrosion of cast metal in precision casting of titanium or titanium alloys, has excellent mold expansion properties, and has good air permeability.

Another object of the present invention is to provide a manufacturing method that can produce such precision casting molds with good reproducibility.

D. Structure of the invention and its effects That is, the present invention provides magnesia (MgO) and a metal powder (for example, Ti) that undergoes volume expansion through a chemical reaction.
The present invention relates to a precision casting mold made from an investment material containing (powder) as an essential component.

In addition, the present invention adds metal powder (for example, Ti) that expands in volume through a chemical reaction to magnesia (MgO).
The present invention also provides a method for manufacturing a precision casting mold, in which a binder (e.g., magnesium chloride) is added to the mixture, a binder (e.g., magnesium chloride) is added to the mixture, the mixture is kneaded, and the kneaded product is fired at a high temperature (particularly 750°C or higher). It is.

According to the present invention, magnesia (MgO) is used as a basic component of the investment material produced in the precision casting mold, and this MgO has an advantageous property that it is not easily corroded by titanium when casting titanium. Therefore, precision casting without spalling etc. is possible. Moreover, since the investment material according to the present invention is made by adding metal powder (hereinafter referred to as "expandable metal powder") that expands in volume through chemical reactions (for example, heating oxidation, chlorination, and sulfidation) to MgO, This volumetric expansion of the expandable metal powder not only suppresses the contraction of MgO, but also allows the mold itself to undergo sufficient volumetric expansion. Volume expansion coefficient (amount) of this mold
is the shrinkage rate (amount) of cast metal that occurs during precision casting
Since the size can be set to match the size, the resulting casting will always be approximately the same size as the set size. In addition, as the mold expands, the mold itself becomes moderately porous, improving ventilation during casting and allowing sufficient release of gas and air to the outside, resulting in high-quality precision castings. is obtained. Another effect brought about by adding this expandable metal powder is that the expansion is linear, which improves the stability of the mold, and once the amount of the expandable metal powder is determined, the expansion rate can be appropriately controlled. , the expansion rate can be set with good reproducibility. The heat resistance of the mold can also be improved by chemical changes (eg, oxidation) of the expandable metal powder.

Next, the investment material according to the present invention desirably has the following component blending ratio in order to achieve the above-mentioned remarkable effects.

MgO 60-95% by weight Expandable metal powder 25% by weight or less Binder 0.5-5.0% by weight Here, the MgO used may be in the particle size range generally used for refractory materials, but the proportion Total amount of material (100% by weight: same below)
If it is less than 60% by weight, the original performance (fire resistance) as an investment material tends to deteriorate, and if it exceeds 95% by weight, the proportion of other additive components decreases, weakening the desired expandability and caking properties. Tend. The content of MgO is
Practically speaking, the content is preferably 60 to 85% by weight, although it varies depending on the desired performance (expandability of the mold, etc.).

Further, examples of the expandable metal powder include metal titanium powder, metal iron powder, metal aluminum powder, metal zinc powder, and metal tin powder, which are extremely important in determining the expansion rate of the mold.
The content of expandable metal powder is preferably 25% by weight or less in order to exhibit its effect, but 25% by weight or less
(However, if the performance as an investment material can be maintained, 25
(% by weight may be exceeded). The content of this expandable metal powder varies depending on the desired expansion rate, but it is usually practical to set it at 1 to 20% by weight. Further, the particle size is preferably 50 to 500 meshes (for example, 300 meshes). Note that the expandable metal powder used may be a pure metal, but
It may be an impure metal (containing impurities).

Further, the above-mentioned binder is necessary to harden the investment material, and for example, magnesium chloride (MgCl ₂ ), magnesium sulfate (MgSO ₄ ), tribasic magnesium phosphate (MgPO ₃ ()), etc. can be used. . This binder is usually mixed with water and kneaded with the above-mentioned MgO and expandable metal powder. At this time, the amount of the binder is preferably 0.5 to 5.0% by weight. Also, MgO,
The molar ratio between the binder and water is (3 to 8)
It is best to use MgO, MgCl ₂ , (10-18) H ₂ O, but in any case, if there is too little binder, it will be difficult to harden the investment material, and if there is too much, it will be difficult to harden the investment material.
MgO becomes less.

According to the present invention, the investment material having the composition described above is heated and fired at a high temperature to form a precision casting mold. During this high temperature treatment, especially the expandable metal powder in the investment material undergoes a chemical change and expands in volume. As expandable metal powder
When using Ti powder, it is oxidized during heating and firing,
Since it is transformed into titanium oxide that has expanded from its original volume, this contributes to the desired expansion of the mold by a predetermined proportion. This expansion of the mold varies depending on the amount of expandable metal powder, but is generally sufficient and sufficiently offsets the amount of shrinkage of the cast metal such as Ti, which will be described later. Furthermore, it has been found that the volumetric expansion of the mold is sufficiently maintained even when the temperature is lowered. This mold also has good release from the mold (mold release) for Ti and Ti alloys that are cast metals.

It is also convenient that the titanium oxide produced during the above-mentioned firing does not react with Ti, which is the cast metal. In addition, expandable metals such as metal Ti react with binders such as magnesium chloride and are partially converted to metal chlorides, so there is no generation of chlorine gas, etc.
It's advantageous. Also, when adding Fe powder to investment materials, it is usually best to use it together with Ti powder;
Mixing Fe powder improves the thermal conductivity of the investment material.
This is because it has the effect of promoting the oxidation of Ti (titanium oxide reduces thermal conductivity, but Fe powder prevents this from happening). however,
In particular, Fe powder does not contribute much to expansion at relatively low temperatures, but when fired at high temperatures, its expandability becomes sufficiently large that it may be necessary for mold expansion. In this case, Fe powder can be used instead of Ti powder. Note that the Fe powder used may be impure iron other than pure iron, but the latter has less risk of ignition.

It is preferable to perform the above firing at a high temperature due to the above reasons, but it is usually 750℃ or higher, and even 800℃ or higher.
It is best to set the temperature to 1100℃. Further, the firing is performed at normal pressure after the first hardening of the kneaded material (for example, at 70° C. for 1 hour), but the firing time and temperature control can be set according to the desired expansion coefficient.

E. Examples Next, the present invention will be specifically explained in more detail by way of examples.

An expansion test of a precision casting mold according to the present invention was conducted as follows.

Example 1 Investment material components were prepared with the following blending ratios.

MgO (magnesia clinker) 90% by weight MgCl _{2.6H 2} O 1% by weight Ti powder (300 mesh) 9% by weight Add 15 c.c. of water (per 100 g) to these ingredients and knead for 30 seconds. Pour into a film case with diameter 25mmφ x length 45mm, diameter 25mmφ x length 28.5
A sample of mm was used. Then, this was first cured (precured) at 70° C. for 1 hour, then heated and fired at the following temperature increase, and the thermal expansion (longitudinal direction) of the sample at each firing temperature was measured.

Firing (℃) Thermal expansion (mm) 400 0.05 450 0.15 500 0.25 550 0.35 600 0.45 650 0.55 700 0.63 750 0.77 800 0.90 850 1.06 900 1.06 950 1.06 100 0 1.06 1100 1.06 950 1.06 900 1.06 850 1.03 760 1.00 400 0.90 20 0.90 This From the results, by firing at high temperature
An expansion of 1.06mm (expansion rate is 3.7%) was achieved.
This does not change much even when cooled to room temperature,
Must be able to maintain an expansion of 0.90mm (expansion rate is 3.16
%). This indicates that the metal titanium was sufficiently oxidized and expanded during heating, and that the expansion state due to titanium oxide does not change much even when the temperature drops. It was also discovered that chlorine gas was not generated because part of the titanium metal chemically reacted with MgCl ₂ (binder).

Example 2 The composition of the investment material was changed as follows.

MgO (magnesia clinker) 90.7% by weight MgCl _{2.6H 2} O 1.5% by weight Ti powder (300 mesh) 7.8% by weight Add 15cc. film case)
The resin was poured into a container, precured for 1 hour at 70°C, and then fired. The sample starts to expand at 350℃, and at 1000℃ the sample becomes 1.26
mm expansion (lengthwise) (expansion rate 2.8%). Even if this is cooled to room temperature, the amount of expansion is 1.07
mm (expansion rate 2.38%), which was sufficient. In addition, the expansion coefficient is the same when the firing temperature is 750℃, 800℃, and 900℃.
It was the same as at 1000℃.

Example 3 The composition of the investment material was changed to the following in Example 2, and the firing treatment was performed in the same manner.

MgO (magnesia clinker) 62.5% by weight MgCl _{2.6H 2} O 2.5% by weight Ti powder (300 mesh) 17.5% by weight Fe powder (100 mesh) 17.5% by weight When the firing temperature was 800℃, the expansion of the sample was
It became 10.5%.

Example 4 In Example 2, the composition of the investment material was changed to the following, and firing treatment was performed in the same manner.

MgO (magnesia clinker) 80.2% by weight MgCl _{2.6H 2} O 0.9% by weight Ti powder (300 mesh) 18.9% by weight When the firing temperature was 800℃, the expansion of the sample was
It became 5.5%.

Example 5 The composition of the investment material was changed to the following in Example 2, and the same firing treatment was performed.

MgO (magnesia clinker) 84% by weight MgCl _{2.6H 2} O 1% by weight Ti powder (300 mesh) 3% by weight TiO ₂ 12% by weight When the firing temperature was 800℃, the expansion of the sample was
It became 1.3%.

Example 6 The composition of the investment material was changed to the following in Example 2, and the same firing treatment was performed.

MgO (magnesia clinker) 94% by weight MgCl _{2.6H 2} O 1% by weight Fe powder (100 mesh) 5% by weight When the firing temperature was set to 800℃, the expansion of the sample was
It became 3.2%.

Example 7 The composition of the investment material was changed to the following in Example 1, and the firing treatment was performed in the same manner. However, the length of the sample was 60.6 mm.

MgO (magnesia clinker) 82.4% by weight Magnesium phosphate 1.1% by weight Ti powder (300 mesh) 3.3% by weight TiO ₂ 13.2% by weight When the firing temperature was 800℃, the expansion of the sample was
It became 0.6%, and even after cooling to 20°C, it remained 0.5%.

Example 8 The composition of the investment material was changed to the following in Example 1, and the firing treatment was performed in the same manner. However, the length of the sample was 56 mm.

MgO 82.4% by weight Magnesium sulfate 1.1% by weight Ti powder (300 mesh) 3.3% by weight TiO ₂ 13.2% by weight When the firing temperature was 800℃, the expansion of the sample was
It became 0.9%, and even after cooling to 20°C, it remained 0.7%.

Example 9 (Comparative Example) The composition of the investment material was changed to the following in Example 1, and the firing treatment was performed in the same manner.

Gypsum 50% by weight Fe powder 50% by weight The relationship between temperature and sample expansion was as follows.

Firing (℃) Thermal expansion (mm) 200 0 300 0 375 −0.5/100 450 −0.5/100 475 −1/100 600 −1.5/100 675 −2/100 700 −2.1/100 725 −2.3/100 To this According to the calcination temperature of 725℃, the sample is 2.3/
It can be seen that the gypsum shrinks by 100 mm, but it was also confirmed that the gypsum decomposes at the same temperature and decomposition gas is generated. With this, the mold cannot compensate for the shrinkage of the metal, and casting at high temperatures (particularly at temperatures above 725°C) is impossible.

Next, an example of precision casting of a dental metal made of titanium or a titanium alloy using the investment material described above will be described. Here, casting of a metal casting base (denture base) is illustrated, but the same applies to other cast products.

First, as shown in FIG. 1, a retroimpression model 1 is prepared by a known method using an investment material according to the present invention (for example, the investment material of Example 5). That is, a mold with an inverted shape is taken from the original model, and the investment material is poured into this mold to form the model 1. Then, a wax sheet 10 of a predetermined thickness (for example, 0.4 mm) is attached to the front surface 3 of the model 1. Wax sheet 10 includes
The wax funnel-shaped body 4 is connected via the wax connection part 5.

After creating the wax pattern 20 in this way,
As shown in FIG. 2, a wax pattern 20 is housed in a molding frame 11. Then, the above-mentioned investment material (for example, the investment material of Example 5) 13 is poured. After that, the solidified refractory block 14 is taken out from the frame 11 and placed in a heating furnace at a temperature of 750°C or higher (particularly 800°C or higher).
Bake at 1100℃). As a result, the wax in the wax pattern 20 within the block 14 melts and is removed outside. That is, the funnel-shaped body 4 shown in FIG. 2 first melts and the inner refractory material portion 13a
are also removed, and the connecting portion 5 and wax sheet 1 are also removed.
0 also begins to dissolve. Therefore, the block 14 has a thin molding space 1 having a shape corresponding to the pattern 20 described above.
5 and a sprue 17 are formed (see FIG. 4).

In this case, for the reasons mentioned above, the block (mold) 14 made of the investment material according to the invention containing MgO and expandable metal powder is heated and fired to produce a certain thermal expansion. That is, as shown in FIG. 3, the investment material 13 expands from its original shape shown exaggeratedly by the dashed line to the solid line position of the wax pattern 10 during heating and firing (the state after expansion is shown in the drawing). ing).

Next, as shown in Fig. 4, the sprue 17 of the block 14 is
Block 1 with the side facing the rotation axis 24 direction.
4 is fixed on a rotating table 26, and a crucible 28 is attached to the sprue 17. Then, molten metal (for example, metallic titanium or titanium alloy) is placed in the crucible 28, and the rotary table 26 is rotated at a predetermined speed, and the molten metal is injected into the molding space 15 through the sprue 17 using the generated centrifugal force. .

Through such centrifugal casting, a metal precision casting product (here, a casting bed) is obtained by solidifying the molten metal filled in the molding space 15, but the metal contracts during solidification (i.e., as shown in Fig. 3). It has the property of shrinking from the solid line position to the dashed-dotted line position. However, such shrinkage of the metal causes the investment material 13 described above.
Since the shape has already been compensated for by the expansion of things). Therefore, the obtained cast product always has high precision as designed and is suitable as a dental precision cast product.

Note that when the cast metal is titanium, its shrinkage rate is, for example, 0.9%, so it is preferable to use an investment material (for example, the one in Example 3) with an expansion rate that offsets this.

In addition, since the above-mentioned model 1 is also formed with the investment material composition based on the present invention, it expands during firing, and the shrinkage of the cast metal can be offset on the above-mentioned front side 3, resulting in a highly accurate cast product. It will be done.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a cross-sectional view of a wax pattern, Fig. 2 is a cross-sectional view of the wax pattern solidified with investment material, and Fig. 3 is a cross-sectional view of the wax pattern during heating and firing. FIG. 4 is a cross-sectional view of a part of the mold for explaining the expansion of the mold, and FIG. 4 is a cross-sectional view of the main part during centrifugal casting. In addition, in the symbols shown in the drawings, 1...Model, 10...Wax sheet, 13...
... Investment material, 15 ... Molding space, 17 ... Sprue, 2
0... Wax pattern, 28... Crucible.

Claims (1)

[Claims] 1. A precision casting mold made from an investment material containing as essential components magnesia and metal powder that undergoes volumetric expansion through chemical reaction. 2. A method for manufacturing a precision casting mold, in which a metal powder that causes volumetric expansion through a chemical reaction is added to magnesia, a binder is added to this mixture, the mixture is kneaded, and the kneaded product is fired at a high temperature.