Solid insulator and method of manufacturing the same

Details Solid insulator and method of manufacturing the same Solid insulator and method of manufacturing the same

1994-05-24

1996-05-14

Kincaid, Kristine L.

Electricity: conductors and insulators

Insulators

Combined

264 66, C04B 3564

Patent

active

055169872

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a solid insulator and a method of manufacturing the same.


PRIOR ART

In the technical field of this kind of solid insulator, there have been developed a solid insulator made of cristobalite porcelain containing cristobalite crystals, and a solid insulator made of non-cristobalite porcelain without any cristabalite crystal or the like. In these solid insulators, high mechanical strength and electrical strength are required.
The former solid insulator made of cristobalite porcelain containing cristobalite crystals in an amount of more than 20 wt % is superior in strength to a solid insulator made of cristobalite porcelain containing cristobalite crystals in an amount of less than 10 wt %, the latter solid insulator made of non-cristobalite porcelain or the like. From the manufacturing point of view, however, the latter solid insulator made of non-cristobalite porcelain is superior to the former solid insulator since the sintering temperature can be easily controlled in a wide range during the firing process.
A method for increasing strength of insulators is disclosed on pages 1260 to 1261 of "Ceramics Industry Engineering Handbook" issued by Gihodo, Feb. 15, 1971. In such a method for increasing strength of insulators, a raw material easier for forming cristobalite crystals is used as a raw material of the insulator body, and a firing condition easier for forming the cristobalite crystals is adapted to increase the thermal expansion coefficient of the insulator body more than that of a glaze layer on the surface of the insulator during the sintering process, thereby causing compressive stress in the glaze layer during the cooling process for increasing the tensile stress and bending strength of the insulator by 10 to 40%.
In the solid insulator made of cristobalite porcelain containing cristobalite crystals in an amount of more than 20 wt %, the foregoing method is useful for increasing the thermal expansion coefficient of the insulator body during the sintering process. In the solid insulator containing cristobalite crystals in an amount of less than 10 wt % or the solid insulator made of non-cristobalite porcelain, however, the thermal expansion coefficient of the insulator body may not be increased during the firing process. It is, therefore, difficult to adjust the thermal expansion coefficient of glaze for increasing a difference in thermal expansion coefficient between the insulator body and the glaze layer. For this reason, the foregoing method is useless in manufacturing of the latter solid insulator. Since the glaze layer formed on the surface of the insulator is extremely thin in thickness, the glaze layer is damaged when slightly cracked during handling of the insulator products. For this reason, the foregoing method is not always useful in manufacturing of the former solid insulator made of cristobalite porcelain containing a large amount of cristobalite crystals.


SUMMARY OF THE INVENTION

It is, therefore, an object of present invention to provide a high strength solid insulator made of cristobalite amount of less than 10% wt % or made of non-cristobalite porcelain, and a method of manufacturing the high strength solid insulator.
MEANS FOR SOLVING THE PROBLEM:
According to the present invention, there is provided a solid insulator made of cristobalite porcelain containing cristobalite crystals in an amount of less than 10 wt % or made of non-cristobalite porcelain in which internal strain of a columnar body of the insulator in the direction of compression is larger in the diametrically outer portion thereof than in the diametrically inner portion thereof, and in which a difference Y between the internal strain in the diametrically outer portion of the columnar insulator body and that in the diametrically central portion thereof is determined to be Y>(1.76.times.10.sup.-6)X, where X(mm) represents the diameter of the columnar insulator body and is determined to be 20.ltoreq.X.ltoreq.250.
In the present invention, the internal strain

REFERENCES:
patent: 3723593 (1973-03-01), Ono
patent: 4659680 (1987-04-01), Guile
patent: 4866014 (1989-09-01), Cassidy et al.
patent: 5425909 (1995-06-01), Fu et al.

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