JPS6233284A - Jig for baking tubular silicon-nitride sintered body and baking method using said jig - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a jig for firing a silicon nitride sintered body having a tubular shape such as a ring shape or a cylindrical shape, and a firing method using the jig. be.

(Prior art) Generally, the ceramic body has a 10 to 2
When obtaining a fired tubular product as shown in Figure 1 with shrinkage of about 0χ, shrinkage errors and deformation will inevitably occur.
In order to obtain a ceramic body with the target dimensions, it was necessary to provide a considerable amount of grinding allowance in advance.

(Problems with the conventional technology) In this way, a large amount of grinding allowance is provided in advance (this means that the shape before firing becomes large and difficult to fire, and not only is the raw material wasted, but also The hardness of the sintered body (
HRA) 91 is a difficult-to-cut material with higher hardness than other alumina ceramics, 88, and zirconia, 89.
Therefore, if there is a large amount of grinding allowance, the grinding process takes time, and the grinding tool (diamond tool) used
Productivity was low due to heavy wear and tear, resulting in high production costs.

(Means for solving the problem) In view of the above, a cylinder made of a material that has greater heat resistance and a coefficient of thermal expansion than the silicon nitride sintered body and does not react with the silicon nitride sintered body to be fired. The above-mentioned problems are solved by a jig made of a solid body and a firing method using the jig.

(Example) FIG. 2 shows a perspective view of a jig j according to an example of the present invention,
The material constituting this jig J is high-purity silicon carbide (
SiC), which has the following characteristics.

■High purity silicon carbide that does not react with silicon nitride, which is the material to be fired.

(2) The coefficient of thermal expansion of silicon carbide (4.2X 10-') is larger than that of silicon nitride sintered body (3.2X 1O-6).

■The heat resistance of silicon carbide is greater than that of silicon nitride sintered bodies.

■Ordinary ceramic materials can only be processed by grinding, but silicon carbide can be formed into a predetermined cylindrical shape by cutting.

In order to use such a cylindrical jig J made of silicon carbide material, it is necessary to set the thermal expansion difference and straightening rate (0 to 10χ) in advance.
The jig J is manufactured in consideration of the following, and is fired with the jig J inserted into the inner diameter of the unfired silicon nitride molded body. That is, as shown in FIG. 3, a jig J is set in the inner diameter of a silicon nitride green compact M, and a firing temperature of 1650 to 1800° C. that matches the characteristics of the silicon nitride raw material constituting the compact M is set. By firing the silicon nitride sintered body N as shown in Fig. 4, a silicon nitride sintered body N is formed as shown in FIG. Clearance for expansion difference and temperature change 5
(S=Δd・ΔT−d) will occur, and the sintered body N
can be removed from jig J, and in the next process up to 2
% of grinding allowance is removed and precision machining is performed. In this case, it is preferable to apply boron nitride powder to the surface of the jig J in order to prevent a reaction with the silicon nitride raw material during firing.

Next, in order to obtain a silicon nitride sintered body N having the desired product dimensions, a formula for calculating the dimensions of the silicon nitride green compact M and the jig J used therein will be explained.

Here k (correction rate by jig J) = 0.02 (arbitrary) q
(Silicon nitride material shrinkage rate) = 0.825 (varies depending on composition), and if the inner diameter before firing is d +, the inner diameter after firing is d, and the inner diameter after firing without jig is dy, then d' =dy/q=d/ (1+k) ・qd= (
1+k)d)' Pa・dy y=d/1−+−k In addition, the outer diameter before firing is D, the outer diameter after firing is D, the outer diameter after firing without a jig is Dy, and the correction The outer diameter D° when the length and volume are assumed to be constant regardless of the presence or absence (L is the cylindrical length of the silicon nitride unfired molded body) is Dy2 = D" - d" + dy" = D" - d "+dy" / (1+k)"In addition, the outer diameter dx of the jig J used to obtain the inner diameter d after firing is d×(1+α,・ΔT)=d (1+α7・ΔT)1
+α0 ΔT However, α,: Coefficient of thermal expansion of jig J α7: Coefficient of thermal expansion of silicon nitride sintered body ΔT: Firing temperature of silicon nitride sintered body - room temperature (effect of the invention) The present invention as shown on the ridges According to the method, in order to obtain a silicon nitride sintered body having a desired tube shape, a columnar body made of silicon carbide having a coefficient of thermal expansion larger than that of the silicon nitride sintered body is used as a jig to carry out the firing process. Since a fired product with less grinding allowance can be obtained by grinding, the time required for the grinding process is significantly shortened, making it possible to provide highly accurate fired products at low cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a tubular sintered body to be produced by the method of the present invention, FIG. 2 is a perspective view of a firing jig according to an embodiment of the present invention, FIGS. 3, 4, and 5. Each figure is a cross-sectional view for explaining the process of producing a tubular silicon nitride fired body using the firing jig of the present invention. J... Jig M... Silicon nitride unfired molded body N... Silicon nitride fired body

Claims (4)

[Claims] (1) In order to fire a tubular silicon nitride sintered body, it has greater heat resistance and thermal expansion coefficient than the silicon nitride sintered body,
A jig for firing a tubular silicon nitride sintered body, characterized in that the jig is constituted by a cylindrical body made of a material that does not react with the silicon nitride sintered body. (2) The jig for firing a tubular silicon nitride sintered body according to claim 1, wherein the material of the cylindrical body is made of a silicon carbide sintered body. (3) A jig for firing a tubular silicon nitride sintered body according to any one of claims 1 to 2, characterized in that the surface of the cylindrical body is coated with boron nitride powder. (4) A jig made of silicon carbide, which has greater heat resistance and a coefficient of thermal expansion than the silicon nitride sintered body that is the object to be fired, and which does not react with the silicon nitride sintered body, is attached to a tubular silicon nitride sintered body. Placed in the internal space of the unfired molded body, 1650 to 1800
1. A method for firing a tubular silicon nitride sintered body, characterized by firing at ℃.