Heating – Processes of heating or heater operation – Controlling flame position or work atmosphere
Patent
1982-09-17
1984-12-18
Camby, John J.
Heating
Processes of heating or heater operation
Controlling flame position or work atmosphere
432 23, 432 25, 432 26, 432198, F27D 700, F27B 904, F27B 322, F27B 504
Patent
active
044888716
DESCRIPTION:
BRIEF SUMMARY
The invention is with respect to a process for producing uneven coloring effects on figure plate-like ceramic material, such as tiles or flags in a kiln, more specially a roller kiln, made up of a heating-up, a firing and a cooling zone, through whose atmosphere, which is oxidizing in the firing zone, the material to be fired is moved in a single layer without any burning tools for supporting it.
Such kilns, more specially in the form of roller kilns have come to be used of late in many parts of the ceramic industry on an ever increasing scale.
The useful effect of such kilns is that they make it possible to keep up a steady-enough temperature at every point in the kiln cross-section. Furthermore very much less fuel and manpower are needed for the operation of such kilns.
For firing plate-like ceramic material such kilns, in the form of roller kilns, are only run with an oxidizing effect, or, putting it differently, more oxygen is present in the kilns than is needed in theory, that is to say it is a question of operation with an oxygen excess. For this reason the fuel, for example gas or oil, used is completely combusted.
However because the kiln atmosphere has an important effect on the color produced on firing the material, it is sometimes important for the firing operation to take place in a reducing and not in an oxidizing atmosphere.
In the case of normal tunnel kilns, the tiles or the like are not moved through the kiln side by side in a single layer but are stacked on tunnel kiln carriages and are then moved in such stacks or parcels through the kiln so that, automatically, on burning in a reducing atmosphere the reducing effect will not be equally strong on all tiles or the like. In fact the tiles inside such a stack will undergo less reduction than the tiles or the like at the edge thereof where the reducing atmosphere may have a more lasting effect on the tiles. For this reason there is a certain uneven coloring effect, produced at the same time, on the tiles inside and outside, which will be seen after firing is completed so that by mixing the tiles on a face covered therewith a coloring effect may be produced.
This teaching may however not be made use of in kilns in which the material to be fired is run through the kiln in a single layer without any burning tools for supporting it. In fact, if in such a kiln the tiles were to be transported therethrough in a single layer side by side and then be reduced in the normally used way, all the tiles would be necessarily reduced to the same degree and for this reason would all have quite the same color, that is to say there would be no uneven coloring effect produced at the same time as desired. The tiles would all be plain and of the same color, this only being desired in a very small number of cases.
In the German Offenlengungsschrift specification No. 2,824,367 reducing gases, for example hydrogen, were to be supplied into kilns intermittently and under a high pressure. However the purpose in this case was burning structures, more specially made of porcelain, which were to be evenly reduced.
One purpose of the invention is that of making it possible for material fired in kilns, more specially roller kilns, through which the material is moved without any burning tools supporting it and in a single layer, so that the material has the desired uneven coloring effect.
This purpose is effected in the present invention inasfar as in or at the end of the firing zone, in a screened-off part, the material to be fired is acted upon by a partly reducing atmosphere.
These purposes can best be understood with reference to the appended drawings, a brief description of which is as follows:
FIG. 1 is a diagrammatic plan view of a first embodiment of the kiln of the present invention;
FIG. 2 is a diagrammatic plan view of a second embodiment of the kiln of the present invention;
FIG. 3 is a cross section taken along the plane of line III--III of FIG. 2;
FIG. 4 is a cross-sectional view taken generally along the same plane as FIG. 3 illustrating an alternate gas injec
REFERENCES:
patent: 2253897 (1941-08-01), Doderer
patent: 3459412 (1969-08-01), Fries et al.
patent: 4321031 (1982-03-01), Woodgate
Buchtal GmbH
Camby John J.
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