US 6,163,020 AGranted

Furnace for the high-temperature processing of materials with a low dielectric loss factor

AssigneeGERO Hochtemperaturoefen GmbH

InventorsWolfgang Bartusch, Gunter Muller

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Abstract

In the furnace (10) for the high-temperature processing of materials with a relatively low dielectric loss factor (tan .delta.) by heating the material by absorption of microwave energy in a resonant cavity (16), a uniform energy intensity of the microwave field is to be achieved for example by irradiating the microwave energy over a broad band and/or by varying in time the frequency of the irradiated microwave energy. The resonant cavity (16) and the radiation source (13) are tuned to each other such that the relation: (V/.lambda..sup.3). B.gtoreq.20 is satisfied. V stands for the volume of the resonant cavity (16), .lambda. for the wavelength of the microwave radiation and B its band width. V/.lambda..sup.3 equals at least 300 and the clear dimensions 1x, ly and lz of the resonant cavity (16) in the direction of the co-ordinates x, y and z are approximately equal to the cubic root of V. The wall (16.sub.1 to 16.sub.6) of the resonant cavity is made of graphite and can be heated by a heating device (28) up to the temperature of the material to be treated. The heating device is arranged outside the resonant cavity, and a heat insulting envelope (38) encloses the unit of resonant cavity (16) and heating device.

Claims28

Dependent claims

Furnace for the high-temperature processing of materials with relatively low dielectric loss factor (tan .delta.) by heating the material by absorption of microwave energy in a resonant cavity, in which the material to be treated is arranged within a central area of the resonant cavity, wherein a uniform energy density of the microwave field is achieved so that in each volume element of the treatment area the square of the electric field strength of the microwave field has the same value, at least over time, within a minor tolerance, wherein an electric heating device is provided, with which the resonant cavity wall can be heated to the same temperature as within the material to be treated and wherein a heat insulating envelope is provided, which insulates the furnace against heat loss into the environment, characterized by the following features:

a) the resonant cavity (16) and the radiation source (13) are sufficiently attuned to each other, so that the relation ##EQU8## is satisfied, wherein V is the volume of the resonant cavity (16), .lambda. is the wavelength of the microwave radiation and B is their band width, further the amount V/.lambda..sup.3 has a value of at least 300 and the transparent dimensions 1.sub.x, 1.sub.y and 1.sub.z of the resonant cavity (16) in the coordinate directions x, y and z have a value of approximately
.cuberoot.V
each;
b) the heating device (28) is arranged outside of the resonant cavity (16) in the immediate vicinity of the resonant wall, and the heat insulating envelope (38) is arranged so that it encompasses the resonant cavity (16) and the heating device (28) from the outside,
c) the resonant wall (16.sub.1 through 16.sub.6) consists of graphite or equivalent temperature maintaining and electrically conductive material.

2 more elements

A furnace for the high-temperature processing of a grouping of workpieces made of materials with relatively low dielectric loss factor (tan .delta.), and including:

a microwave energy source for producing electromagnetic radiation in the microwave range;
a waveguide in communication with said microwave energy source for propagating microwave radiation into a resonant cavity;
a resonant cavity in communication with said waveguide and dimensioned for receiving a grouping of individual workpieces made of materials with relatively low dielectric loss factor;
a detector for detecting the temperature within said grouping of the workpieces placed in said resonant cavity;
an electric heating device for heating the resonant cavity wall(s);
means for adjusting the output of said electric heating device to thereby adjust the temperature of the resonant cavity wall(s) to correspond to the temperature within said grouping of workpieces as detected by said detector;
and
a thermal insulating means provided outside said resonant cavity for insulating said furnace against heat loss into the environment,
wherein said microwave generator generates broadband microwave energy and/or wherein means are provided for varying the frequency of the irradiated microwave energy over time, such that a uniform energy density of the microwave field can be achieved within said resonant cavity and such that the workpieces within said grouping receive a substantially uniform high-temperature processing, and wherein the following conditions are satisfied:
a) the resonant cavity (16) and the microwave radiation source (13) are sufficiently attuned to each other, so that the relation ##EQU9## is satisfied, wherein V is the volume of the resonant cavity (16), .lambda. is the wavelength of the microwave radiation and B is their band width, further the amount V/.lambda..sup.3 has a value of at least 300 and the transparent dimensions 1.sub.x, 1.sub.y and 1.sub.z of the resonant cavity (16) in the coordinate directions x, y and z have a value of approximately
.cuberoot.V
each;
c) the heating device (28) is arranged outside of the resonant cavity (16) in the immediate vicinity of a resonant cavity wall(s), and the heat insulating envelope (38) is arranged so that it envelopes the resonant cavity (16) and the heating device (28) from the outside, and
c) the resonant cavity walls (16.sub.1 through 16.sub.6) consist of graphite or an equivalent temperature maintaining and electrically conductive material.

11 more elements

Dependencies are inferred from the claim text.