JP2538973B2 - Ceramic heater manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic heater having a structure in which a heater core wire is embedded.

(Prior Art) Conventionally, as a manufacturing method of a ceramic heater made of, for example, silicon nitride having a structure in which a heater core wire made of tungsten or the like is embedded, a hot pressing method for obtaining a molded body by uniaxial compression under heating, A sinter HIP method is known in which a molded body having a heater core wire embedded therein is once pre-baked by using the method disclosed in Japanese Patent Publication No. 61-46432 and then subjected to hydrostatic pressing to obtain a molded body.

(Problems to be Solved by the Invention) However, in the hot pressing method of obtaining a molded product by uniaxial compression under a heated state, the coiled heater core wire may be crushed during compression and, for example, silicon nitride is used for uniaxial compression. There was a problem that the core-shaped crystal bodies of No. 1 were arranged side by side and the obtained sintered body had anisotropy.

Also, in the sintering HIP method, the molded body with the embedded heater core wire is once pre-fired.
There is a problem that a gap remains between the heater core wire and the ceramics, and a gap remains around the heater core wire even if the gap is exposed to high-pressure gas.

An object of the present invention is to solve the above problems and to provide a manufacturing method capable of easily obtaining a ceramic heater having good properties.

(Means for Solving the Problems) In the method for manufacturing a ceramic heater of the present invention, the ceramic powder having the heater core wire embedded therein is 0.5 to 2.0 ton / cm ^2.
Of pre-molding with a die press at a pressure of 2, the step of calcining the pre-molded body at a temperature of 350 to 700 ℃ for binder removal, and the pre-molded body after calcination of 2.0 to 7.0 ton / cm ² . Hydrostatic pressing with pressure to obtain a ceramic molded body having a crack width of 0.8 mm or less, and a step of coating the ceramic molded body with a glass capsule and hot isostatic pressing. It is characterized by.

(Operation) In the above-described configuration, a predetermined ceramic molded body in which the heater core wire is embedded is covered with a glass capsule and subjected to hot isostatic pressing, whereby the molded body can be isotropically pressed to form a coil shape. It is possible to obtain a ceramic heater having good properties without fear of the ceramic core wire being crushed. In addition, by setting the crack width in the molded product before hot isostatic pressing using glass capsules to all 0.8 mm or less, all the cracks are closed after hot isostatic pressing, and the resulting molded product and heater The gap generated between the core wire and the ceramic can be eliminated.

Here, the crack width in the molded body before hot isostatic pressing is limited to 0.8 mm or less, as is clear from the examples described below, when the width of the crack exceeds 0.8 mm cracks in the molded body. This is because a gap remains between the heater core wire and the molded body.

In order to obtain a compact with a crack width of 0.8 mm or less, preform the ceramic powder with the heater core wire embedded therein by means such as die pressing or injection molding, and temporarily remove the preform to remove the binder. It is preferable to subject the preformed body after baking and calcination to isostatic pressing because a predetermined formed body can be easily obtained. Further, hot isostatic pressing using a glass capsule is a conventionally known technique,
For example, the technique disclosed in Japanese Patent Publication No. 59-35870 can be used.

(Example) FIG. 1 is a flow chart showing an example of a method for manufacturing a ceramic heater according to the present invention. First, after mixing silicon nitride powder as a ceramic material and a predetermined amount of a sintering aid and an organic binder, a coil-shaped tungsten core wire, for example, is installed in the mixed powder, and the pressure is 0.5 to 2.0 ton / cm ² . A preform is obtained by molding with a die press. Here, in addition to the method using a die press, a preform can be obtained by injection molding. Next, depending on the organic binder using the obtained preform 350 ~ 700 ℃
Calcination is performed at the temperature of to remove the binder. Next, the preformed body from which the binder has been removed is subjected to hydrostatic pressing at a pressure of 2.0 to 7.0 ton / cm ² to obtain a molded body in which the crack width is controlled to 0.8 mm or less. Finally, the molded body with the crack width controlled is coated with a glass capsule and hot isostatic pressing is performed to obtain a predetermined ceramic heater.

 Hereinafter, an actual example will be described.

Example A mixture of a coiled tungsten core wire having a diameter of 1 mm and a length of 60 mm, a sintering aid shown in Table 1 below and 5% by weight of polyvinyl alcohol as an organic binder preliminarily mixed with 100 g of silicon nitride. Prepare powder, 60 × 60mm
In the mold, a tungsten core wire was embedded in the mixed powder and press-molded under the pressure shown in Table 1 to obtain a 60 × 60 × 10 mm rectangular plate-shaped preform. Then, in order to remove the organic binder, it is calcined under the conditions shown in Table 1 in an atmospheric furnace,
To facilitate handling, a hydrostatic press (rubber press) was carried out at the pressure shown in Table 1 to obtain a molded product. After coating the obtained molded body with BN powder, it was sealed in a glass ampoule under vacuum and held under the conditions shown in Table 1 to carry out glass capsule HIP, and the invention of Sample Nos. 1 to 11 and A ceramic heater of a comparative example was obtained.

In the manufacturing process of each sample, the width of cracks in the molded body after rubber pressing and the presence or absence of a gap between the tungsten core wire and the silicon nitride sintered body in the obtained ceramic heater were checked by a scanning electron microscope (SEM). investigated. Further, in order to evaluate the characteristics of the ceramic heater, a square plate, which is a sintered body, was heated in a furnace at a temperature shown in Table 1 and dropped in water at 25 ° C. to check whether new cracks were generated. The results are shown in Table 1.

From the results shown in Table 1, the product of the present invention having a crack width of 0.8 mm or less in the molded body before hot isostatic pressing using glass capsules has no new generation of cracks and has a tungsten core wire and a silicon nitride sintered body. In contrast to the case where there is no gap between them, in the comparative example, some cracks were newly generated and there were gaps.

(Effects of the Invention) As is apparent from the above description, according to the method for manufacturing a ceramic heater of the present invention, a ceramic molded body in which a predetermined heater core wire is embedded is coated with a glass capsule and hot isostatic pressing is performed. By doing so, it is possible to obtain a ceramic heater having good properties, in which there is no fear that the coil-shaped ceramic core wire is crushed, no anisotropy occurs in the molded body, and no gap is generated around the heater core wire.

Further, by checking the crack width existing in the molded body before hot isostatic pressing using glass capsules, it has become possible to obtain a sintered body with good yield.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of a method for manufacturing a ceramic heater according to the present invention.

Claims (1)

(57) [Claims] 1. A step of preforming a ceramic powder having a heater core wire embedded therein by a die press at a pressure of 0.5 to 2.0 ton / cm ² , and a preform for removing a binder.
A step of calcination at a temperature of 0 to 700 ° C and a preform after calcination are hydrostatically pressed at a pressure of 2.0 to 7.0 ton / cm ² to form ceramics with no cracks with a crack width exceeding 0.8 mm. A method of manufacturing a ceramic heater, comprising: a step of obtaining a body; and a step of coating the ceramic molded body with a glass capsule and subjecting to hot isostatic pressing.