JPH0543263A - Method for heat-treating and producing ceramic cast - Google Patents

Abstract

PURPOSE:To improve the mechanical strength of a glass ceramic cast by heat treatment by sufficiently relieving the thermal stress generated in the cast in a short time. CONSTITUTION:The ingot of a glass ceramic is kept at 1450 deg.C for 4min in a platinum resistance heating furnace, the molten glass is introduced into a casting mold kept at 575 deg.C and centrifugally cast at 1200r.p.m. for 1min. The cast is let stand in a heating furnace held at 575 deg.C, and then the cast is heated to 750 deg.C in 1hr, held at 750 deg.C for 2hr, further heated to 900 deg.C at the rate of 4 deg.C/min and crystallized. The cast is then allowed to cool to room temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ceramics heat treatment method for removing thermal strain after casting.

[0002]

2. Description of the Related Art In general, as a dental prosthesis, castable ceramics, which is formed by casting glass ceramics in a mold, is used. To manufacture a dental prosthesis made of this castable ceramics, for example, first,
The molten glass-ceramic is cast by centrifugal casting in which it is cast into a rotating mold. Then, after allowing to cool, the mold is removed and heated at a predetermined temperature for crystallization treatment.

As described above, in the ceramic casting by centrifugal casting, the structure is densely cast by the centrifugal force. However, the portion exposed to the air generated during centrifugal rotation of the casting and the air inside the casting mold are in contact with each other. Since a temperature difference is generated between the casting and the non-existing portion, thermal distortion occurs inside the casting.
As described above, the mechanical strength after crystallization is remarkably reduced in a cast product having an inherent thermal strain caused by non-uniform thermal stress inside the cast product.

Conventionally, in order to remove such thermal strain, a mold in which glass ceramics is cast is placed in a mold at a temperature of the strain point of the glass ceramics (the viscosity of the glass ceramics is 1
A heat treatment for removing thermal strain is carried out by leaving it in a heating furnace maintained at a temperature around 0 ^14.5 poise) and slowly cooling it.

[0005]

However, in the conventional heat treatment, since the treatment temperature is set to a temperature near the strain point of the glass ceramics, it is necessary to sufficiently remove the thermal strain in the casting. Had to be heat treated for a long time. As a result, it takes a long time to manufacture a dental prosthesis, and if the crystallization treatment is performed while the removal of thermal strain is incomplete, the mechanical strength of the obtained dental prosthesis is significantly reduced. there were.

The present invention has been made in view of the above points, and mechanically removes the thermal strain generated inside the cast product made of glass ceramics in a short time and sufficiently. It is intended to provide a heat treatment method and a manufacturing method of a ceramics casting capable of improving strength.

[0007]

According to the present invention, after a molten glass ceramic is cast into a mold, the mold is maintained at a temperature not lower than the transition point of the glass ceramic and lower than the yield point of the glass ceramic. There is provided a method for heat treatment of a ceramics casting, characterized by removing the thermal distortion of a casting made of the glass ceramics by leaving it in the heating furnace.

Further, a step of casting the molten glass ceramics into a mold, and leaving the mold in a heating furnace maintained at a temperature not lower than the transition point of the glass ceramics and lower than the sag point of the glass ceramics. A method for producing a ceramic cast, comprising: a step of removing thermal distortion of the cast glass ceramic; and a step of heating the cast at a predetermined temperature to perform a crystallization treatment. To do.

Here, the time required for removing the thermal strain of the glass-ceramic casting can be determined by the calculation formula shown by the formula (1) by Lowson. That is, for example, when the temperature in the heating furnace is set as the transition point, the viscosity (η) of the glass ceramics at the transition point
Is 10 ^13.5 poise, the thermal strain of the casting is 6 kg / cm ² which is equivalent to 1/100 of the energy required to break the glass-ceramic casting. The time (T) required to reach a smaller value is 5.27 minutes. T = η / (6.0 × 10 ¹² ) ... (1) T: Treatment time (min) η: Viscosity of glass ceramics corresponding to temperature in heating furnace (poise)

[0010]

According to the heat treatment method and the manufacturing method of the ceramics casting of the present invention, the transition point of the glass ceramics (the temperature at which the viscosity of the glass ceramics becomes 10 ^13.5 poise)
By keeping the temperature in the heating furnace maintained at a temperature lower than the yield point of the glass ceramics as described above, the thermal stress inside the casting can be made uniform, and the temperature of the heating furnace is set to the transition point or higher. Since it is set, the thermal strain of the casting can be removed in a short time.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

By applying the heat treatment method for the ceramics cast of the present invention, the margin thickness is adjusted to 0.5 mm, and a glass crown cast corresponding to the lower chamfered first molars is manufactured, and its mechanical strength is manufactured. Was tested.

First, an ingot of castable ceramics manufactured by Olympus Optical Co., Ltd. (hereinafter, referred to as OCC. The transition point of OCC is 573 ° C.) is housed in a high-purity alumina pot, and a platinum heating resistance furnace is used. Moored at 1450 ° C for 4 minutes. The OCC glass melt thus melted is cast into a mold heated and held at 575 ° C.,
Centrifugal casting was performed for 1 minute at a rotation force of 1200 rpm. After this,
After cooling under the conditions shown in Table 1, the mold was removed using a gypsum can, and Examples 1 and 2 and Comparative Example 1 were used.
I got a casting. Regarding the castings of Examples 1 and 2 and Comparative Example 2, the breakage condition was observed. The results are shown in Table 1.
Also described in. Table 1 Cooling conditions Observation results Example 1: After casting, for 5 minutes in a heating furnace maintained at 575 ° C .: 8% of the whole was damaged: After standing, it was left to cool at room temperature. :did.

Example 2: After casting, for 10 minutes in a heating furnace maintained at 575 ° C .: damage was observed at all: after standing, it was left to cool at room temperature. : I couldn't. Comparative Example 1: After casting, it was left to cool directly at room temperature. : 30% of the total was damaged.

As is apparent from Table 1, after casting, 575
The castings of Examples 1 and 2 in which the thermal strain inside the casting was removed by leaving them in a heating furnace maintained at 0 ° C for 5 minutes or 10 minutes, were cast and then left to cool directly at room temperature in Comparative Example 1 It was confirmed that the damage was significantly suppressed as compared with. In particular, the cast product of Example 2 left in the heating furnace for 10 minutes was
It was confirmed that the damage to the casting could be completely prevented. According to the above formula (1), when the casting is left in the heating furnace maintained at 575 ° C., the treatment time (T) required to remove the thermal strain until the damage of the casting can be prevented. )
Is 5.27 minutes, which is in agreement with the above test results.
Next, after subjecting the castings of Examples 1 and 2 and Comparative Example 1 described above to crystallization treatment, a bending test was conducted in accordance with JIS R1601.

In the crystallization treatment, the casting was heated to 750 ° C. in a heating furnace for 1 hour, moored at 750 ° C. for 2 hours, and then further heated to 900 ° C. at a rate of 4 ° C./min. After that, it was left to cool in the heating furnace. Table 2 shows the results of the bending test of JIS R1601 on the cast products of Examples 1 and 2 and Comparative Example 1 which were subjected to the crystallization treatment in this way. Table 2 Bending strength Example 1 1400 kg / cm ² ± 110 kg / cm ² Example 2 2100 kg / cm ² ± 60 kg / cm ² Comparative example 1 1100 kg / cm ² ± 80kg / cm ²

As is clear from Table 2, the castings of Examples 1 and 2 left in the heating furnace maintained at 575 ° C. all had a bending strength higher than that of the casting of Comparative Example 1 which was allowed to cool directly. It was found to be excellent. It was also confirmed that the casting of Example 2 left in the heating furnace for 10 minutes had the best bending strength.

[0018]

As described above, according to the method for heat treating a ceramic casting and the method for manufacturing a ceramic casting according to the present invention, the temperature is maintained at a temperature higher than the transition point cast in the mold and lower than the yield point. By gradually cooling in the heating furnace, it is possible to remove thermal strain inside the casting. As a result, there is a remarkable effect such that the mechanical strength of the ceramic casting can be remarkably improved.

Claims (2)

[Claims] 1. A molten glass ceramics is cast into a mold, and the mold is left in a heating furnace maintained at a temperature not lower than the transition point of the glass ceramics and lower than the deformation point of the glass ceramics. A heat treatment method for a ceramics casting, which comprises removing a thermal strain of the glass ceramics casting. 2. A step of casting molten glass ceramics into a mold, and leaving the mold in a heating furnace maintained at a temperature not lower than the transition point of the glass ceramics and lower than the yield point of the glass ceramics. A method of manufacturing a ceramic cast, comprising: a step of removing thermal distortion of the cast glass ceramic; and a step of heating the cast at a predetermined temperature to perform a crystallization treatment.