Method of producing ceramic products

Abstract: A method of firing ceramic materials seeks to avoid bending or deformation of a supporting plate which supports a green shaped body (1) of the ceramic materials, deformation of the green shaped body caused by its own weight, and cracks and breakage in the fired shaped body, during the firing of the shaped body of the ceramic materials. The method comprises mounting a green supporting plate (2) on a fired supporting plate (3), mounting a green structural body (1) of ceramic raw materials on the green supporting plate (2), and firing the green structural body (1) on the green supporting plate.

Description: The present invention relates to a method of producing ceramic products, particularly ceramic honeycomb structural bodies. Heretofore, in order to produce ceramic products by firing shaped green bodies of ceramic raw materials of the ceramic products in a firing furnace, a method is known of mounting and firing a shaped green body of ceramic raw materials on a supporting ceramic pillow or supporting plate without directly mounting the shaped green body on a shelf plate of the firing furnace, so as to prevent formation of cracks and adhesion of the shaped green bodies to the shelf plate. In producing ceramic honeycomb structural bodies, a method of firing shaped green bodies of ceramic raw materials is conventionally used wherein spacers are inserted between supporting plates and shelf plates, as disclosed in the applicant's US-A-4,786,542 "Setters and Firing of Ceramic Honeycomb Structural Bodies by Using the Same". This insertion method has a drawback in that, when firing a heavy honeycomb structural body, the supporting plate is bent downwardly by the weight of the honeycomb structural body itself, so that the end surface of the honeycomb structural body supported by the supporting plate is deformed. A similar defect is also found when a plurality of honeycomb structural bodies are superposed on the supporting plate exerting a heavy weight load thereon. If a green or non-fired supporting plate is used for supporting a green honeycomb structural body of raw ceramic materials at the time of firing the green honeycomb structural body, crack or breakage of ribs of the honeycomb structural body caused by friction resistive force arising between contacting surfaces of the honeycomb structural body and the supporting plate at the time of expanding and shrinking during the firing thereof can be prevented from occurring. However, in such a case, there is a drawback in that the honeycomb structural body is liable to deform with the green supporting plate due to its weight. Conversely, if a fired supporting plate is used for supporting the green honeycomb structural body at the time of firing, there arises a drawback in that crack or breakage of ribs of the honeycomb structural body is liable to occur, though the deformation of the honeycomb structural body due to its weight is easily prevented. It would be desirable to reduce or eliminate the above drawbacks. The present invention is a method of producing a ceramic product by firing a shaped green structural body of ceramic raw materials of the ceramic product in a firing furnace, comprising, mounting a green supporting plate on a fired supporting plate, mounting a green structural body of the ceramic raw materials on the green supporting plate, and firing the green structural body on the green supporting plate. The green structural body is preferably a green honeycomb structural body of ceramic raw materials. The green and/or fired supporting plates are preferably ceramic plates of honeycomb structural body having gas passages in vertical direction thereof, and cell density or cell opening of the honeycomb structure is 0.8-310 cells/cm² (5-2000 cells/in²). A plurality of superposed fired supporting plates and green supporting plates can be used. The fired supporting plate and the green supporting plate are preferably made of similar material and have the same cell density. However, they may also be used if they are made of different materials and have different cell densities. Preferably, the fired supporting plate and the green supporting plate are cordierite plates of honeycomb structure when the green structural body of ceramic raw materials to be fired is a cordierite honeycomb structure, or a mullite plate of honeycomb structure when the green structural body of ceramic raw materials to be fired is a mullite honeycomb structure. Combinations of the supporting plate and the green structural body of ceramic materials other than that described above can also be used. The fired supporting plate and the green supporting plate may have a shape of elliptical, circular, rectangular, etc., or other shape adapted to shape of the green structural body of ceramic raw materials to be mounted thereon. If a spacer is used between the shelf plate of the firing furnace and the supporting plate to provide a space therebetween, air ventilation property of the firing furnace is improved, and binder and cell-forming agent contained in the ceramic raw materials can be easily burned out, so that crack or breakage of fired structural bodies caused by unburned residue of the binder and the cell-forming agent can be decreased. By the arrangement of superposing a fired supporting plate and a non-fired or green supporting plate, deformation of the green supporting plate can be prevented as well as crack, breakage and deformation of the green structural body caused by its own weight and friction resistive force thereof. For a better understanding of the present invention, reference is made to the accompanying drawings, in which: Fig. 1 is a schematic side view of a conventional firing state of a structural body of ceramic raw materials; Fig. 2 is a schematic plan view thereof; and Fig. 3 is schematic side view of a firing state of a structural body of ceramic raw materials according to an example of the method of the present invention. Numberings in the drawings. 1 green honeycomb structural body of ceramic raw materials 2 green supporting plate 3 fired supporting plate 4 spacer Hereinafter, the present invention will be explained in more detail with reference to examples. Examples 1-4 and Referential Examples 1-2 Referring to Figs. 1 and 2, a conventional way of firing a honeycomb structural body of ceramic raw materials is shown as a reference. Referring to Fig. 3, an embodiment of the method of the present invention is shown. A green supporting plate 2 is mounted on a fired supporting plate 3, a green honeycomb structural body of ceramic raw materials 1 rests directly on the green supporting plate 2, and a spacer 4 is inserted between the fired supporting plate 3 and a shelf plate (not shown) of a firing furnace, followed by firing of the green honeycomb structural body. The green supporting plate 2 and the fired supporting plate 3 have the same shape and size. Results obtained with a variety of supports are shown in the following Table 1. As seen from the above Table 1, when a honeycomb structural body is mounted and fired on superposed fired supporting plate and green supporting plate, distortion at the end surface of the honeycomb structural body is small and deformation due to its own weight is small as compared with those of Referential Examples 1 and 2. Even when the thicknesses of the fired supporting plate and the green supporting plate are increased, distortion at the end surface of the fired honeycomb structural body can be decreased, as seen in Examples 2-4. By superposing a fired supporting plate and a green supporting plate, deformations of the green supporting plate and the green structural body caused by its own weight can be suppressed, so that deformation of a honeycomb structural body to be fired mounted thereon during firing thereof can be reduced. The present method is useful in producing general ceramic products, such as dishes, bowls, tiles, bricks, etc., and particularly useful in firing green honeycomb structural bodies and large size ceramic products. Though usually chamfering of the supporting plates is not necessary, chamfering of the supporting plates as described in US-A-4,786,542 may be effected if desired. As a subsidiary effect in case of not using a spacer at the time of firing a honeycomb structural body, difference of shrinkage distortions between the green supporting plate and the green honeycomb structural body can be mitigated as compared to the case of directly mounting the green supporting plate on a shelf plate of firing furnace, so that cracks and breakage of the ribs of the honeycomb structural body caused by shrinkage distortions can be prevented from occurring. Although the present invention has been explained with specific examples and numeral values, it is of course apparent to those skilled in the art that various changes and modifications thereof are possible.

Claims: A method of producing a ceramic product by firing a shaped green structural body (1) of ceramic raw materials, characterised by mounting a green supporting plate (2) on a fired supporting plate (3), mounting the green structural body (1) on the green supporting plate (2), and firing the green structural body (1) on the green supporting plate (2). A method according to claim 1, wherein the green structural body (1) is a green honeycomb structural body. A method according to claim 1 or claim 2, wherein the green supporting plate (2) and/or fired supporting plate (3) are ceramic plates of honeycomb structure having gas passages in a vertical direction thereof, and the cell density or opening of the cells of the honeycomb structure is 0.8-310 cells/cm² (5-2000 cells/in²). A method according to any one of claims 1 to 3, wherein a plurality of superimposed fired supporting plates and green supporting plates are used. A method according to claim 1, wherein the fired supporting plate (3) and the green supporting plate (2) are made of similar cellular materials with the same cell density. A method according to any one of the preceding claims, wherein the fired supporting plate (3) and the green supporting plate (2) are made of cordierite or mullite honeycomb structure. A method according to any one of the preceding claims, wherein one or more spacers are inserted between the fired supporting plate (3) and a shelf plate of the firing furnace.

Inventors: HORIKAWA OSAMU, WADA YUKIHISA, HORIKAWA, OSAMU, WADA, YUKIHISA
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1991
Main classification: C04B33
IPC codes: C04B35, F27D3, C04B38, F27D5, F27D1, C04B33