Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By mechanically introducing gas into material
Patent
1991-07-26
1993-03-30
Derrington, James
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By mechanically introducing gas into material
414159, 432 6, C04B 3564
Patent
active
051981645
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of firing ceramic building materials, such as tiles, bricks and roofing tiles, in a roller hearth kiln.
BACKGROUND ART
The roller hearth kiln is a tunnel-shaped furnace in which a multiplicity of rollers is disposed horizontally and parallel to one another. The materials to be fired are conveyed on the rollers from the inlet to outlet of the kiln so as to be passed through the preheating, firing and cooling zones thereof.
When firing ceramic building materials, such as tiles, bricks or roof tiles, in a roller hearth kiln, it has hitherto been usual practice to feed them one after another through the kiln. It has been usual that each material to be fired has a residence time of, say, one to two hours in the kiln (the time between its charging in the kiln at the inlet thereof and its discharging therefrom at the outlet thereof).
Such a short residence time is one of the advantages arising from the use of a roller hearth kiln, and contributes to rapid firing.
The residence time as stated above is, however, so short that a roller hearth kiln can be used only for firing a material comprising a body and glaze which can be rapidly fired. Moreover, the time is too short for producing a deep color by reduction or oxidation on the material to be fired.
DISCLOSURE OF THE INVENTION
This invention provides a method of firing ceramic building materials in a roller hearth kiln, wherein the materials are stacked in a plurality of layers so as to reside in the kiln for a time of at least three hours.
The arrangement of the materials in a stack enables them to reside in the kiln for a prolonged period of time and thereby be fired for a correspondingly prolonged period of time. The use of the residence time which is as long as at least three hours with a carefully controlled firing atmosphere, enables the development of a deep color by reduction or oxidation on the materials to be fired. The method of this invention is applicable to an expanded range of materials including any material comprising a body and glaze which cannot be rapidly fired. Moreover, it can fire any material uniformly from its surface to its core, even if it may be a large material having a thickness not smaller than 25 mm, or even not smaller than 30 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a transverse sectional view of a roller hearth kiln which is employed for carrying out the method of this invention;
FIG. 2 is a perspective view of a split tile taken as one example of ceramic building material, and comprising two halves which can be separated from each other;
FIG. 3 is a perspective view of one half of the split tile shown in FIG. 2;
FIGS. 4 to 6 are each a graph showing a different heat curve employed in the roller hearth kiln; and
FIG. 7 is a side elevational view of the material as fired.
BEST MODE OF CARRYING OUT THE INVENTION
The invention will now be described by way of example with reference to the drawings.
FIG. 1 is a transverse vertical sectional view of a roller hearth kiln as employed for illustrating a method embodying this invention. The roller hearth kiln has a tunnel-shaped body made of refractories, and is equipped with rollers 3 extending through the opposite sidewalls 1 and 2 thereof. The rollers 3 are employed in a large number and lie horizontally and in parallel to one another. The rollers 3 are driven for rotation by a driving device.
Ceramic building materials 4 are stacked to form a plurality of layers on the rollers 3, and are thereby conveyed. Although the materials 4 are shown as forming a stack of four layers, it is needless to say that they can alternatively be stacked in another number of layers.
Each material 4 is a rectangular split tile having longitudinally extending cavities 4A, as shown in FIG. 2. After it has been fired, the material 4 is split along the cavities 4A into two halves each forming a tile 41, as shown in FIG. 3.
The ceramic building materials 4 are placed on setters 5 (plates of a refractory material on which the materials to be
REFERENCES:
patent: 3351687 (1967-11-01), Thome
patent: 3402834 (1968-09-01), Kelsey
patent: 4193761 (1980-03-01), Mantegani
Reed, Introduction to the Principles of Ceramic Processing, John Wiley & Sons, New York, 1988, pp. 440-445.
Hayashi Yuji
Katayama Keisuke
Mori Hiroshi
Derrington James
Inax Corporation
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