Electric heating – Microwave heating – Tunnel furnace
Reexamination Certificate
2000-06-30
2002-09-24
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Tunnel furnace
C219S700000, C219S738000, C219S756000, C219S762000, C034S259000
Reexamination Certificate
active
06455826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and apparatus for manufacturing ceramic materials. In particular, this invention relates to an essentially microwave emission-free apparatus and method for the continuous microwave heating and drying ceramics.
2. Discussion of the Related Art
Conventional heating or drying typically comprising convectional or a combination of convectional and radiative gas or electric resistance heating, is commonly used in the manufacturing of ceramic materials. However, the slow heating rate and poor temperature control associated with these conventional heating methods results in a high energy consumption and inconsistent product quality. Furthermore, utilization of these two modes of heating typically result in thermal differences within the ceramic body, due to the fact that these two heating modes are applied only to the surface and rely on thermal conductivity of the ceramic body to effect the temperature beneath the surface to the center of the piece.
Industrial heating by microwave radiation has been successfully used to accelerate the drying of traditional ceramics. In comparison with convectional heating, microwave heating provides a higher heating rate, where there is sufficient absorption, with better temperature control, and thus results in lower energy consumption and potentially better quality products. Furthermore, the utilization of microwave energy delivers a uniform application of the energy to the ceramic article, rather than to the article surface, as is the case for the aforementioned convectional and radiative modes of heating. Lastly, microwave heating is much faster than conventional drying because the ceramic body is heated directly through the interaction of the microwave energy with the ceramic body.
Although microwave heating is faster and more efficient than convectional and radiative heating, one disadvantage of microwave heating is the generation of microwave radiation emission. These microwave emissions must be controlled (i.e. shielded from the atmosphere) in order to comply with emissions regulations established by the relevant regulatory agencies (e.g., OSHA, FCC, CEPT). Ideally, any microwave dryer operation should be operated such that a nearly zero emission environment is maintained. Typically, the shielding of microwaves in microwave drying operations has been accomplished through the use of attenuation tunnels or water traps, and additionally the use of Aluminum curtains have been used to provide attenuation for any microwave emissions that escape past the attenuation tunnels. Although the use of attenuation tunnels, water traps and aluminum curtains provide sufficient shielding of microwave radiation emission, there are limitations on the both the size of the ceramic articles, as well as the overall load of ceramic articles, that can be dried. Furthermore, the use of attenuation tunnels, water traps and curtains, dictates that the drying operation be non-continuous, due to the fact that the drying cavity/chamber must be mechanically sealed off from the atmosphere during the drying of the ceramic articles and opened once the microwave drying is complete.
PCT Application WO 93/17449 discloses a continuous production method of forming ceramic green ware articles utilizing microwave setting (or accelerated drying) that incorporates a typical non-continuous drying operation. The drying step is accomplished by switching off the microwave and opening the doors of the microwave oven and moving pallets containing the ceramic articles into the microwave while moving out of the microwave pallets containing already dried ware and thereafter closing the doors of the microwave. This closing/sealing off and opening/shutting down of the microwave (i.e., non-continuous drying) is done in order to seal off the microwave from the atmosphere when the microwave is in operation and to allow the microwave to be opened when the microwaves are not being generated, thereby preventing the escape of any microwave radiation.
SUMMARY OF THE INVENTION
Accordingly it is an object of this invention to provide an apparatus for, and a method of, continuous microwave heating of ceramics that overcomes the shortcomings of aforementioned conventional microwave heating. Specifically, provided is an apparatus capable of the continuous drying of ceramic articles and which produces little or no microwave radiation emission.
The present invention thus provides an apparatus for microwave heating of a ceramic, comprising a microwave-heating chamber, for heating a ceramic, having an entrance and an exit end and a material flow axis along which the ceramic articles are conveyed. Positioned adjacent the entrance and exit ends of the microwave-heating chamber, respectively, are a first and second attenuation chamber each having an entrance and an exit end. An inlet chamber, having a material flow path, is connected to the entrance end of the first attenuation chamber with a portion of the material flow path disposed at an angle to the flow axis. Connected to the exit end of the second attenuation chamber is an outlet chamber having a second material flow path; again at least a portion of the material flow path is disposed at an angle to the material flow axis. Preferably, a gating mechanism separates each of the inlet and outlet chambers from the each of the first and second attenuation chambers, respectively; these gating mechanisms being provided for preventing the escape of microwave radiation emission. Lastly, the drying apparatus includes a transport system for transporting ceramic articles successively through the inlet and first attenuation chamber, microwave heating chamber and the second attenuation chamber and outlet chamber.
A second aspect of the invention involves a method for drying a ceramic material comprising placing a ceramic article on an air bearing support for supporting the ceramic article on a cushion of air. The supported ceramic article is then placed on the transport system (e.g., a conveyor) and caused to first pass the ceramic material successively through an inlet chamber and thereafter through a first attenuation chamber. The ceramic material then enters a microwave-heating chamber and is then subjected to a predetermined initial amount of heat energy by irradiating it with electromagnetic microwave radiation from an adjustable microwave power source. Thereafter, the ceramic material is caused to pass successively through a second attenuation chamber and lastly through an outlet chamber.
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Araya Carlos R.
Boyko Ronald A.
Corning Incorporated
Gheorghiu Anca C.
Leung Philip H.
Schaeberle Timothy M.
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