Electric heating – Microwave heating – Enclosed cavity structure
Reexamination Certificate
1999-04-02
2001-05-29
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Enclosed cavity structure
C219S690000, C219S745000, C219S762000, C333S219000
Reexamination Certificate
active
06239418
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a component for a microwave oven, in particular a microwave waveguide and/or a microwave resonator (cavity) for conducting microwaves of high energy density at high temperature for sintering hard materials, which comprises a support of a highly heat-resistant material and a laminated body at least partially mounted on the support and having a surface coating.
The invention further relates to a resonator housing and to at least one flanged waveguide on it for microwave ovens equipped for microwave irradiation.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,578,658 describes a microwave resonator and a microwave waveguide for conducting microwaves with high energy density. The components consist of a support body with a multi-layer coating of a thickness of about 5 &mgr;m of copper and silver.
In the sintering of metallic/ceramic composite materials such as hard metals or cermet in a microwave oven it is necessary to heat the material to be sintered to temperatures of 1800° C. which requires thermal insulation to avoid heat losses. There are basically two ways to do this, namely to insulate the charge being sintered with a microwave-transparent insulating material inside the resonator or to externally insulate the resonator housing.
The insulating material used inside the resonator housing that mainly consists of extremely pure aluminum-oxide foamed mats is not only very expensive but has the disadvantage that for example when sintering hard metals vapors sublime in the insulation and reduce the microwave transparency of the foam mats. The result is a “burning through” of the insulation as a result of it absorbing microwaves.
Applying external thermal insulation to the resonator housing, that does not need to be transparent to microwaves, has the disadvantage that all the parts inside the resonator housing, that is the resonator walls themselves, the coupling waveguide, any sensors or the like, must be made of a heat- and gas-resistant material to which end according to the state of the art temperature resistant metals are employed as materials for the microwave parts that can be exposed both to the microwave radiation as well as to the operating temperatures. Metals that are very resistant to high temperatures, such as for example molybdenum or tungsten, are not suitable as materials for microwave components since such metals carburize readily in the carbon in the sintering atmosphere. Graphite as well as other generally known materials resistant to high temperatures and elements of the sintering atmosphere are however much worse electrical conductors than metals so that they produce considerable losses in microwave energy. A graphite resonator housing thus is of low resonator efficiency.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to provide a microwave-oven component as well as a microwave oven that can be used to sinter hard materials while avoiding the above-mentioned disadvantages.
SUMMARY OF THE INVENTION
These objects are attained in a microwave waveguide or resonator for conducting microwaves of high energy density at high temperature for sintering hard materials. The waveguide or the resonator has according to the invention a support of a highly heat-resistant material and a laminated body at least partially mounted on the support and having a surface coating consisting of nitrides, carbides, or carbonitrides of elements of the IVa to VIa groups of the periodic system and having a thickness between 0.
The material of the surface coating can be nitrides, carbides, or carbonitrides of elements of the IVa to VIa groups of the periodic system. This produces a composite body formed of a support and a surface coating at least partially mounted on the support, the support being a material resistant to high temperatures and the surface coating being of a material having a thickness between 0.1 &mgr;m and 100 &mgr;m and formed of a material resistant to the sintering atmosphere, more electrically conductive than the support, and in particular stable at high temperatures in a carburizing atmosphere. The surface coating is only applied according to the invention there where microwaves need to be conducted and where chemical reactions with the oven atmosphere need to be avoided. This relates in particular to the resonator-housing inner surface as well as to the waveguide parts arranged on the resonator housing inside the thermal insulation.
The support consists of graphite or a metal, a metal alloy, oxide ceramics, composite ceramics, SiC, Si
3
N
4
, or AlN. Metals, metal alloys (so long as they are temperature resistant) can also be used when they are protected on all sides by a tight surface coating from the carburizing gases. Preferably the material of the surface coating layer can be a carbide, carbonitride, or nitride of titanium. The surface coating can have plural layer with the individual layers made of the same or different materials. Preferred coating thicknesses are from 1 &mgr;m to 20 &mgr;m.
According to a further embodiment of the invention the surface coating or layers are applied by a CVD method at 900° C. to 1100° C.
The object is further attained by a microwave oven whose resonator-housing inner wall and/or waveguide surface inside the thermal insulation or in contact with the sintering atmosphere, in particular the waveguide inside surface or the waveguide outer surface is coated with a solid microwave-transparent body with a thickness of at most 100 &mgr;m of carbide, nitride, and/or carbonitrides of the IVa to VIa elements. Preferably the resonator housing and/or the waveguide each have a graphite substrate core whereby according to a further embodiment of the invention only the parts inside the thermal insulation of the graphite waveguide are coated.
According to a further feature of the microwave oven according to the invention there is between the insulation surrounding the resonator housing and the resonator housing an electrical heater (hybrid heater), preferably in the form of a resistive electrical heater.
REFERENCES:
patent: 4006073 (1977-02-01), Welch
patent: 5270515 (1993-12-01), Long
patent: 5478608 (1995-12-01), Gorokhovsky
patent: 5886326 (1999-03-01), Tang
K{overscore (o)}nig Udo
R{overscore (o)}diger Klaus
Dubno Herbert
Leung Philip H.
Widia GmbH
Wilford Andrew
LandOfFree
Microwave oven and components therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Microwave oven and components therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microwave oven and components therefor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2452961