Electric heating – Microwave heating – Enclosed cavity structure
Patent
1999-08-12
2000-12-19
Leung, Philip H.
Electric heating
Microwave heating
Enclosed cavity structure
746759, 746762, H05B 670
Patent
active
061630209
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention concerns a furnace for the high-temperature processing of materials with a relatively low dielectric loss factor, wherein the materials are heated by absorption of microwave energy in a resonant cavity.
A furnace of this type is known from WO95/05058 PCT/GB94/01730.
This known furnace has a design that is suitable for sintering ceramic materials which rest in a pile or heap within a cuboidal resonant cavity during sintering, within which cavity an again somewhat cuboidal space for the batch is bordered by a cuboid shaped heat insulator arrangement, which corresponds to the area or space within the resonator, within which it is presumed that a sufficiently homogeneous distribution of the electric field strength occurs. The uniformity of the electric field strength or, as the case may be, the cubic shape thereof is a precondition therefor, that the sinterable material is sufficiently "uniformly" thermally treatable. In order to be able to counter the effect, that with increasing warming of the sinterable material the radiation of heat from the outer areas of the sinter batch leads thereto, that on the inside of the batch a higher temperature exists than in the mentioned outer areas, an effect which is characteristic for microwave baking ovens, a device is provided, which makes it possible to conventionally warm the outer areas of the batch being sintered, that is, supplementation by means of a resistance heater, in order in this manner to achieve an equalization of the temperature profile within the entire batch of material being sintered.
The known furnace may be suitable for producing approximately homogeneous thermal conditions in the overall volume of material being processed, however in the case of relatively small processing volumes it is associated with the disadvantage that the thermal insulator arrangement, which is subjected to the microwave radiation, absorbs a major portion of the introduced microwave energy, which necessarily leads to a high consumption of microwave energy, which is not available for the desired thermal treatment of the material being sintered. This can be seen from the fact that, in practice, the total volume of the insulator material is significantly larger than the volume of the material being sintered. The known furnace is thus not suitable as an industrially useful furnace, since there is no efficient utilization of the microwave energy, of which the cost of production is however much higher than in the case of "conventional" heating by means of an electrical resistance heater.
While a furnace designed as a continuous heating or pusher-type furnace may be known from WO95/05058, which is designed as a tunnel oven with heating zones of various temperatures, through which the material being sintered is transported over transport rolls, wherein the supplemental heating means is arranged or provided outside of the treatment chamber and in which the thermal insulation, which insulates the surroundings against the high-temperature zone, surrounds the oven from the outside. In the case of this oven however the arrangement necessarily results in insufficient field homogeneity, that is, this oven design is only useful because relatively small objects are sintered serially and since there is a continuous movement through the non-homogeneous areas, thus there is no requirement for a homogeneous field distribution.
The known tunnel oven may be suitable for materials with high dielectric loss, which strongly absorb microwave energy, but it is however not suitable for treatment or processing of materials to be sintered with relatively weak dielectric losses, which can be processed practically only in significant numbers of pieces in a resonant cavity with high field homogeneity.
The known tubular oven would not be suitable for materials with low dielectric loss factor, which technically however are also of high interest.
It is thus the task of the invention, to provide a furnace of the above described type, which enables a high-temperature treatment of low diele
REFERENCES:
patent: 4307277 (1981-12-01), Maeda et al.
patent: 5449887 (1995-09-01), Holcome
Bartusch Wolfgang
Muller Gunter
GERO Hochtemperaturoefen GmbH
Leung Philip H.
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