Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By mechanically introducing gas into material
Patent
1994-09-21
1996-06-25
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By mechanically introducing gas into material
432258, 432259, 501112, 501119, F27D 500, C04B 3503
Patent
active
055297323
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to underlying boards particularly suitable for firing ceramics and a method for firing ceramic moldings by using such underlying boards.
BACKGROUND ART
It heretofore has been a common practice that when, for example, green ceramic honeycomb structural bodies are to be fired, the structural bodies are fired in a tunnel kiln or a periodic kiln, while being placed on a shelf plate. In order to prevent cracking of the structural body and bonding between the structural body and the shelf plate, underlying boards called setters are interposed between the green ceramic honeycomb structural bodies and the shelf plate during firing.
Japanese patent publication No. 1-54,636 discloses, as an example of the underlying board, a setter made of a ceramic plate with a honeycomb structure and having a burred portion at an upper edge. For example, when a honeycomb structural body composed mainly of cordierite is to be fired, it is a common practice to employ an underlying board made of the same material (100% cordierite) as that of the honeycomb structural body so as to make the shrinkage factor equal between the underlying board and the honeycomb structural body to be fired.
However, in the case of the above-mentioned underlying boards, problems arise as the number of times the board is passed through the tunnel kiln increases. Specifically, the underlying board is warped when heated, and the surface of the structural body becomes coarse due to melting-out of a silica component so that the bottom end face of the honeycomb structural body is deformed, ribs of the honeycomb structural body are twisted and/or the structural body is cracked. Particularly, if the underlying board made of 100% cordierite is used in a tunnel kiln, the above problems such as warping and melting-out of the silica component are conspicuous, because such an underlying board has poor resistance against direct flame from a burner of the tunnel kiln. Owing to this, the conventional underlying boards have the problem that the number of times of passing through the tunnel kiln may be as low as 15-20.
SUMMARY OF THE INVENTION
It an object of the present invention is to solve the above-mentioned problems, and to provide a firing underlying board which has a long service life free from thermal deformation and which does not cause twisting of ribs, deformation of end faces, cracking or color change in a honeycomb structural body on firing with use of the underlying board. It is another object of the invention to provide a method for firing ceramic moldings by using such an underlying board.
The firing underlying board according to the present invention is characterized in that a main component thereof is composed of 55-85 wt % cordierite and 15-45 wt % mullite. It is preferable that a roughness, Ra, of that surface of the underlying board on which an object to be fired is to be placed is not more than 10 .mu.m. It is also preferable that the main component contains 0.3 to 1.0% by weight of Fe.sub.2 O.sub.3 and/or 0.2 to 0.8% by weight of TiO.sub.2.
The method for firing the ceramic molding by using the underlying board according to the present invention is characterized in that a green ceramic honeycomb structural body is fired in the state that the honeycomb structural body is placed on an underlying board for firing, in which a main component of the board is composed of 55-85 wt % cordierite and 15-45 wt % mullite.
In the above construction, the present inventors found out that when, for example, a green ceramic honeycomb structural body is fired with use of the underlying board in which the main component is composed of 55-85 wt % cordierite and 15-45 wt % mullite, the underlying board exhibits a long service life without being thermally deformed. Accordingly, twisting of the ribs, deformation of the end face and cracking in the honeycomb structural body due to thermal deformation of the underlying board can be prevented.
The reason why the amount of mullite is limited to 15-45 wt % is that if it is less
REFERENCES:
patent: 3954672 (1976-05-01), Somers et al.
patent: 4295892 (1981-10-01), Matsuhisa et al.
patent: 4598054 (1986-07-01), Mochida et al.
patent: 4786542 (1988-11-01), Yasuda et al.
Ideguchi Yoshiaki
Kato Norio
Tsunekawa Kyosuke
Fiorilla Christopher A.
NGK Insulators Ltd.
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