|Title of Invention||
PROCESS EQUIPMENT FOR THE THERMAL TREATMENT OF MATERIALS IN A MICROWAVE OVEN AND APPLICATION OF THIS PROCESS AND THIS EQUIPMENT
|Abstract||1. Process for the thermal treatment of at least one material selected from the group which consists of powders, hard metals, cermets and/or ceramics in a microwave furnace, in which the material to be treated (14) is moved relative to one or more microwave sources (13) characterized in that the material to be treated (14) being arranged and moved in a plurality of cassettes (10), which with the exception of an opening necessary for microwave irradiation, are made of material which is opaque to microwaves and at the same time form the resonance chamber, whose length, height and/or width in unloaded condition is negligible, in order to generate continuous energy distribution at the microwave frequency, but which in the loaded condition, enable a homogeneous heating, whereby preferably their length, height and/or width do not exceed 6 wavelengths of the applied microwave radiation.|
The present invention relate* to a process for the thermal treatment o-f any material in a microwave furnace, especially ponders, hard metals, cermets and/or ceramics.
Further the present invention also relates to an equipment for carrying out the thermal treatment of any material described above.
The Berman Patent under No. DE 43 24 635 Al describes a microttave
chamber oven, which is equipped for discontinuous sintering of
o ceramic bodies for temperatures upto apprOKimately 165O C. For
continuous sintcsring, tunnel furnaces with conventional heating
arrangements are known, which however have been proved as time
and energy consuming. In erdr to overcome these difficulties, a
sintering equipment is recommended, which has at least one fixed
sinter—table, on which the bodies to be sintered can be placed
and has atleast one microwave source in a tunnel shaped,
movable hood, which can be moved over the sintering table by
means of a drive mechanism. The hood is made of metal, for
instance, aluminium, in a self-contained construction. In a
concrete example of application, inside or outside the hood many
microwave sources are provided, which are in turn connected to a
measuring, controlling and ragulating device for the temperature controlled adjustment of the microwave output and/or the speed of the hood. The ceramic bodies, Mhich are to be sintered, can be arranged in a microwave transparent and heat insulated cassette, Mhich for instance, is made of an aluminium oxide fiber.
The German Patent under No. DE 36 43 649 Al also describes an equipment for continuous heating of polar, essentially temperature sensitive materials or highly viscous products under simultaneous application of microwave energy and conditioned atmosphere, in which the material to be treated, passes through a well dimensioned resonance chamber more than cnnce in alternating direction. The transportation of the material through the equipment can take place selectively by means of conveyor belts, channels, spirals or tubes with or without additional vibration, selectively with vacuum, normal pressure or excess pressure. In such an equipment, an uniform field distribution is effected by enlarging the resonance chamber, however, each of the strongly coupling bodies made of hard metal, cermet of ceramic, which are subjected to the microwave radiation, change the field distribution, uncontrolled, especially then, when as in an equipment according to DE 36 43 649 Al, which operates with many conveyor belts, the pieces have a more or less randomly oriented location when they fall on the next conveyor belt.
In Berman Patent under No. DE 41 36 416 Al an equipment for exposing materials especially starting materials for ceramics, alloys etc, to microwave radiations is recommended with a transpiartation system, Mhich is defined, in parts, through a channel or tube arrangement, whose walls have a particular microwave absorbing capacity. This equipment has a resonator which surrounds the wall at least partly as well as a generator to produce microwave radiations, whereby the walls of the channel or tube arrangement have varying microwaave absorption capacities. In order to heat the materials directly with microwave, an additional device can be connected in series to the transportaticm system, by means of which additional materials having higher microwave absorption capacity can be added. However this device is limited to the treatment of such materials, which can be shaped Cformed) by means of an extruder or transported with a spiral conveyor.
German Patent under No. DE 39 26 471 Ai describes a process for the thermal treatment of a mixed organic substance, in which the exposure to microwave radiation is carried out mainly in an allround reflectively limited resonance chamber, in which a mode and frequency splitting follows and whose leading dimensions are not less than approximately eight-times that of free space wavelength of the microwave field based on the nominal frequency. Apart from the fact, that in this publication no mention is made about the heat treatment of the hardmetals, cermets and/or
ceramics, the production technological and apparatiVe expenditure for the sinter treatment compared to the achievable low output would be uneconomical.
It is an object of the present patent to develop a process and an equipment of the type, mentioned at the beginning, in which an uniform, heat distribution in all products, which are to be heated, is achieved. One should be able to carry out the process, as far as possible, continuously and economically, whereby, a step—by-step processing of the bodies to be treated in various temperature stages can be carried exit economically with least designing efforts. This task is achieved through the process mentioned in claim i.
According to the present invention, the material to be treated is
arranged in individual cassettes, which, with the exception of an
evening necessary for the exposure to microwave radiation, form
at the same time the resonance chamber and which do not exceed a
length, height and/or width of 6-wavelengthB at 2.45 GHz (in a
medium with 1 or in vacuum) of the microwave radiations
r used. Consequently a multi—mode-resonator is created, whose
maximum magnitude corresponds only to a few wave lengths of the
microwave radiation used, in such a way, that based on the
microwave lengths used, the components of the charge act as mode
mixer, which contribute to the multiple reflection of the
The distributiom of the sinter material into individual cassettes, which at the same time form the cavity, enables a sintering in a quasi-continuous process, which can be controlled similar to the conventional tunnel furnaces. Due to the marginal loading of the cassettes with material to be treated (presintered products), the field homogeneity is also accordingly maintained to a large extent. Miereas according to the state-of—the—art technic, the prevailing opinion is, that the field can be homogenized with increasing size of the resonator, experimentally it has been proved that the field distribution is mainly influenced by the charge. Therewith, the computation of the respective furnace space becomes difficult, since every different charging results in a different field distribution.
The present patent deals with small cassettes, which function as resonator and which meet the requirements defined in claim 1. A batch of cassettes can thus be moved through a series of microwave sources, whereby the radiation intensity of each of the microwave source can be suited to the desired temperatures in the cassettes. Hereby it is possible to carry out, for example, heating phase, holding phase and cooling phase one after the other and side by sidetparallel).
In a further development of this process, the individual cassettes in a series are passed through a tunnel provided with magnetrons, so that each cassette is successively exposed to the magnetron radiation. Hereby, a continuous or discontinuous movement of the cassettes in every direction, with respect to the microwave sources is passible.
As a possibility for further flexibility, the cassettes have at least one slidable side wall, which can be adjusted to the filling ratio of the material to be treated and to the irradiating microwave length, before the thermal treatment. Through this measure one can, fow instance, take into account, that the resonance chamber is suited to the charge quantity. The European Patent No. EP O 234 528 Al, has shown schematically and explained in Figure i, the sliding of a side wall or a corresponding piston. This system can also applied to the multimode—cassettes which ara used here.
The problem is further solved through the equipment described and claimed in claim 4. The equipment as per the present invention is characterized arranging many cassettes in the microwave-sinter furnace, which arc filled with the materials to be treated and which have, with the exception of the opening for the exposure to microwave radition, mainly walls which are opaque to microwave radition. Further they have a length, width and/or height suited to the loading, which without load leads to the formation of discrete modes, whereby the cassettes have a length, width and/or height, which in the unloaded condition is too low.
in order to generate a continuous energy distribution at the microwave frequency used, but which in loaded cndition ensures a homogeneous heating, mainly not exceeding 6 wavelengths of the microwave radiation used, whereby in each case the cassettes form microwave resonance chambers.
Further improvements in the equipment are described and claimed in claims S to 14.
Thus, the sinter furnace has developed as a tunnel shaped furnace with stationary microwave sources, through which the cassettes are longitudinally moveable, for example, by means of a belt conveyor provided in the tunnel. Depending upon the temperature and/or sinter furnace atmosphere, the walls of the cassettes are made of microwave reflecting material, preferably graphite, steel, molybdenum, nickel, titanium, copper, aluminium and/or their alloys. As mentioned earlier, atleast one wall of the cassette can be arrange slidable to the base, in order to suit the resonance chamber, so to say, to increase and to reduce.
According to a further develcement of this patent, the tunnel is provided with many microwave sources, which are arranged at a distance, which corresponds approximately to the length of the cassettes, preferably exceeds this by the wave guide width. For a
progressive movement in batches of the cassette rows in the microwave tunnel, at each time by a cassette length, each cassette can be exposed to microwave source, so that in each case individual radiation intensities and temperatures can be adjusted per cassette.
As per a further development of this patent, a vertical shield which is opaque to microwave radiation is provided laterally for each microwave source vertically in the tunnel, preferably at a distance, which corresponds to ^proximately the length of the cassette. Herewith it is ensured, that the microwave radiation is shielded laterally and is thus mainly directed towards the respective cassette which is just below the microwave source.
In the most simple case, the cassettes are either open at the top or have a cover, which is transparent to microwave radiation. The second option has the advantage that the cassette can be considered as an enclosed chamber towards outside.
Generally the cassettes have a rectangular form, but depending on the microwave sintering or heating technique, it can also have more complex forms, for instance, it can be polygonal, cylindrical etc.
In order to make it possible to adjust and control the atmosphere in the individual cassettes, each cassette is provided with atleast one connecting piece, closable by a valve, through which gas can be supplied or evacuated. In this way it is possible to build up an atmosphere of protective gas in the cassette.
Mostly the cassettes can be transported through the tunnel in such a way, that the upper edge of their side walls has minimum possible distance from the lower edge of the vertical shields located lateral to the microwave sources. Hereby an optimal shielding is ensured, that means, the interference of microwave fields of two adjacent sources is ruled out.
Further, the tunnel has heating ranges of varying intensities, such as, for instance, the ones needed during sintering:
In the first temperature range upto 600°C, preferably from 200°C to 500°C, the sinter bodies can be dewaxed, for which suitable suction-equipment is provided, the sintering range should be beatable to temperatures between 400°C to 1800°C, preferably between 600°C to 1400°C, the cooling range can either be mildly or not at all heated, if necessary, a flushing with a protective gas, inert gas, reactive gas and/or gas mixture is to be carried out.
Further individual zones of the furnace can also be heated conventionally. Further the microwave treatment of the material can be restricted to individual stages of the process.
The process and/or the equipment can even be advantageously used for the synthesis of WC and also for separate thermal treatment of compcwients.
Examples of application are presented in the drawings. They shows Figure 1 and 2 schematic side views of a row of 5 cassettes in
varying relative positions to the microwave
sources respectively and
FiguB-e 3 an alternative version of the microwave tunnel
As can be seen from Figure 1 and 2, the sinter material is distributed in individual cassettes 1O, which are arranged in a row one after the other and which can be passed through the tunnel 11 in the discretion of the arrow 12. In the tunnel 11, the microwave sources 13 (magnetrons) are arranged at an equidistance, under which the row of cassettes are passed. The cassettes are packed with the material to be treated, here precompacted cutting inserts 14, made of hardmetals, cermets or cermics. The varying power densities or radiation intensities of the microwave sources 13 are identified through different blackenings. In the present case, the last source 13 radiates with the maximum intensity, so that the material to be treated 14, is heated more intensely while moving continuously from left to right-
The same row of 5 cassettes, after certain advancing movement, is shown in Figure 2. In the position shown in Figure 2, each microwave source 13 is directed centrally over the concerned cassette lO. The cassettes are, toward the microwave sources 13, electro conductively connected with the tunnel wall, preferably through eliding contact.
In the version shim in Figure 3, additionally shielding IS are provided, whose bottom edge ends slightly above the upper edge of the side wall Ih. Herewith it is ensured, that the cassettes to in a centralized politics below the respective magnetron 13, are exclusively exposed to their radiation. In this position, field interferences, which are caused through the microwave radiation of adjacent sources are ruled out, in all other positions they are possible.
The cassettes lO can either be open at the top or have a rover which is transparent to microwaves. The side walls 16 and the base are made of material which is opaque to microwaves. Through this measure, that means, the distribution of the sintering material in small cassettes, which at the same time form the so called cavity, sintering is possible in a quasi-continuous process, which can be regulated similar to the conventional tunnel furnace. The dimensions of the sinter boxes are suited to the irradiated microwaves, »#iereby through an uniform loading an
optimal field homogeneity can be achieved. This field homogeneity is independent of the flow rate, since this is determined by the speed of movement of the cassettes lO. By segmenting the tunnel into similar sections, which in each case femur an enclosed resonator with separate microwave sources 13, the flexibility of the process can be enhanced. Thus it is possible to set various temperature ranges Just as it is possible to accelerate the heating and cooling phases due to small number of sinter units. Herewith one can utilize the advantage to carry out the complete sintering cycle in approximately 2 hours. Longer cooling durations, which are nectar in case of larger charges in the conventional microwave furnaces, are completely eliminated.
For dew axing of corpsmen’s, many cassettes 1O loaded in one layer
with a charge of hard metal indexable inserts containing wax at a
distance of 3 mm from each other, were passed through the tunnel
-1 at a speed of frequency with increasing power density. The maximum temperature
o which was achieved here is 500 C. The evaporating wax is
continuously sucked from the openings at the top of the tunnel.
The bemires which were dew axed in this manner are subsequently fed
into a sintering furnace, which is heated conventionally or by
means of microwaves.
For the heat treat«net of tungsten-carbon-compacts of high
porosity many graphite cassettes 10 with the dimensions
3 50 X 50 K 30 cm , each loaded with many compact tablets of high
porosity, which consist of a thoroughly mixed tungsten-carbon
powder mixture, are passed through the tunnel at a speed of -1 cm min and subjected to microwaves of 2.45 GHz frequency with
variable power density. Hereby, due to the microwave dissipation,
the mixture is converted to tungsten carbide powder at
o o temperatures between lOOO C to 1800 C.
1. Process for the thermal treatment of at least one material selected from the group which consists of powders, hard metals, cermets and/or ceramics in a microwave furnace, in which the material to be treated (14) is moved relative to one or more microwave sources (13) characterized in that the material to be treated (14) being arranged and moved in a plurality of cassettes (10), which with the exception of an opening necessary for microwave irradiation, are made of material which is opaque to microwaves and at the same time form the resonance chamber, whose length, height and/or width in unloaded condition is negligible, in order to generate continuous energy distribution at the microwave frequency, but which in the loaded condition, enable a homogeneous heating, whereby preferably their length, height and/or width do not exceed 6 wavelengths of the applied microwave radiation.
2. The process as claimed in claim 1, wherein the individual cassettes (10) in a row are passed through a tunnel (11), which is provided with magnefrons (13), preferably continuously and'or discontinuoxisly relative to the microwave sources.
3. The process as claimed in claim 1 or 2 wherem by adjusting the geometry and size of the cassettes (10), preferably by sliding at least one wall of the cassette before the thermal treatment, the said individual cassettes can be adjusted to the filling ratio and type of the material to be freated (14) and the irradiated microwave length.
4. Equipment for the thermal treatment of at least one material selected from the
group which consists of powders, hard metals, cermets and/or ceramics in a
microwave sintering furnace, in which the material to be treated (14) can be
moved relative to the microwave sources (13) characterized in that a plurality
of cassettes (10) filled with the material to be treated (14) are arranged in the
microwave sintering furnace, which with the exception of an opening
necessary for the microwaves irradiation, have mainly walls (16) which are
opaque to microwaves and whose length, width and/or height, in unloaded
condition is negligible, in order to generate continuous energy distribution but
in the loaded condition enable a homogeneous heating and which does not
exceed preferably 6 wavelengths of the microwave radiation applied, whereby
each of the cassettes (lOj^crowave resonance chambers.
5. Equipment as claimed in claim 4, wherein the said microwave sintering
furnace tunnel (11) with spaced apart microwave sources (13), through which
Do) the cassettesiare longitudinally movable.
6. Equipment as claimed in claim 5, wherein a conveyor belt is provided for carrying the cassettes (10) in the tunnel.
7. Equipment as claimed in any one of claims 4 to 6, wherein the cassette walls (16) are made of graphite, steel or out of molybdenum, nickel, titanium, tantalum, copper, aluminium and/or their alloys.
8. Equipment as claimed in any one of claims 4 to 7, wherein at least one cassette wall (16) can be slided in order to change the size and/or geometry of the cassette.
9. Equipment as claimed in any one of claims 5 to 7, wherein the tunnel (11) has many microwave sources (13), which are arranged at a distance corresponding approximately to the length of the cassettes (10), preferably the wave guide width.
10. Equipment as claimed in any one of claims 5 to 9, wherein vertical shields (15), which are opaque to microwaves are provided at the side of each microwave source (13) preferably at a distance, which corresponds ^>proximately, to the length of the cassette.
11. Equipment as claimed in any one of claims 4 to 10, wherein the cassettes (10) are open at the top or have a microwave transparent cover.
12. Equipment as claimed in claiml 1, wherein every cassette (10) has at least one connecting piece, which can be closed by a valve for adjusting the pressure and/or gas atmosphere in the inside of the cassette.
13. Eqiupment as claimed in any one of claims 10 to 12, wherein the cassettes (10) can be transported through the tunnel (11) in such a way that the upper edge of their side walls (16) has minimum possible distance from the lower edge of the vertical shields (15).
14. Equipment as claimed in any one of claims 4 to 13, wherem the tunnel (11) has sections including a temperature zone up to 600°C for dewaxing with suction, a sintering zone between 600°C and 1400°C and a cooling region, which can be flushed mainly with protective gas such as N2 or an inert gas.
15. A method of synthesizing tungsten carbide which comprise the steps of:
a) providing a plurality of cassettes having microwave impermeable walls
and each formed with an opening enabling microwave energy to pass into
said cassettes, said cassettes being dimensioned when charged with
articles to form microwave-resonant cavities at a microwave frequency;
b) charging said cassettes with a plurality of pressed articles containing
tungsten and carbon particles;
c) thereby synthesizing tungsten carbide from the tungsten and carbon of said
|Indian Patent Application Number||67/MAS/1996|
|PG Journal Number||30/2009|
|Date of Filing||16-Jan-1996|
|Name of Patentee||M/S. WIDIA GMBH,|
|Applicant Address||MUNCHENR STRASSE 90, D-4300, ESSEN 1,|
|PCT International Classification Number||H05B6/78|
|PCT International Application Number||N/A|
|PCT International Filing date|