A drying apparatus has a generally conical upwardly flared housing having an upper end provided with a cover and a lower end provided with an outlet, a mixing auger mounted on and extending upward from the lower housing end in the housing and rotatable to mix particulate material in the housing, and a magnetron mounted at the upper housing end and directed downward inside the housing to irradiate and heat the particulate material in the housing. The magnetron can be mounted directly on the cover. An adapter ring can be provided on the upper end of the housing between the housing and the cover with the magnetron mounted on this adapter ring. This ring is releasably connected to the cover and housing, and it is possible for the ring to carry a plurality of such magnetrons each provided with a respective coaxial wave guide extending through the ring and into the housing.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for drying and mixing 
particulate material. More particularly this invention concerns such an 
apparatus which uses microwave energy as a heat source. 
BACKGROUND OF THE INVENTION 
Microwave energy is a particularly convenient method of heating wet 
material to dry it as described in German patent document 3,814,451 of H. 
K. Werner, European patent application 333,423 of N. Arai, and Japanese 
patents 2-52981 and 63-299086. In addition equipment is known which 
simultaneously agitates or mixes particulate material while irradiating it 
with microwave radiation. See German patent documents 3,907,248 and 
3,923,841 respectively of B. Lelanz and K. Satow, German Utility Model 
8,904,885, French patent 2,641,491 of R. Patrick, and U.S. Pat. Nos. 
3,777,095 and 3,834,038 respectively of T. Muranaka and R. Janda. 
A standard auger-type mixer, such as described in U.S. Pat. No. 3,775,863 
of L. Updegrove, has a basically conical and upwardly flared housing in 
which is provided an auger having an upper end mounted on the outer end of 
an arm whose inner end is pivoted in the cover of the housing about its 
central axis so that rotation of the arm orbits the auger inside the 
housing, churning the contents thereof. The walls and/or auger of such a 
device are heated to transmit heat to the contents and dry them. In an 
improvement on such a device to be used for drying particulate material, 
European patent application 306,563 of I. Sato proposes mounting a 
magnetron, that is a microwave emitter, in the cover of the housing. 
Such an arrangement is fairly effective, but the orbiting auger arm 
periodically passes underneath the magnetron, blocking it and causing it 
to heat the auger drive rather than the actual contents of the housing. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
apparatus for mixing and drying particulate material. 
Another object is the provision of such an improved apparatus for mixing 
and drying particulate material which overcomes the above-given 
disadvantages, that is which operates with a high degree of efficiency. 
A further object is to provide an improved such system which can be 
retrofitted to an existing auger-type conical-housing mixer/dryer. 
SUMMARY OF THE INVENTION 
A drying apparatus according to the invention has a generally conical 
upwardly flared housing having an upper end provided with a cover and a 
lower end provided with an outlet, a mixing auger mounted on and extending 
upward from the lower housing end in the housing and rotatable to mix 
particulate material in the housing, and a magnetron mounted at the upper 
housing end and directed downward inside the housing to irradiate and heat 
the particulate material in the housing. The magnetron can be mounted 
directly on the cover. 
In order to leave room for the input port, a vapor filter, a sight glass, 
and the like and to make it possible to retrofit the inventive system to a 
existing conical-housing mixer, an adapter ring is provided on the upper 
end of the housing between the housing and the cover and the magnetron is 
mounted on this adapter ring. This ring is releasably connected to the 
cover and housing, and it is possible for the ring to carry a plurality of 
such magnetrons each provided with a respective coaxial wave guide 
extending through the ring and into the housing. In fact several 
waveguides can extend from a single magnetron to distribute the microwave 
radiation while minimizing the expense for the expensive magnetrons.

SPECIFIC DESCRIPTION 
As seen in FIG. 1 a generally conical housing 1 centered on a vertical axis 
A is provided with a domed cover 2 itself provided with a vapor filter 3 
and an inlet opening 4. At its narrow bottom end the housing 1 has a 
lateral product outlet 5 and a drive 6 for an inclined product-mixing 
auger 7. According to the invention the cover 2 is fitted offset from the 
axis A on its side opposite the auger 7 with a magnetron 8 that projects 
microwave radiation into the interior of the housing 1 to irradiate ate 
and heat particles therein. Thus particles to be dried are loaded into the 
housing 1 through the inlet 4 and are simultaneously heated and mixed, 
ultimately exiting through the outlet 5. 
The system of FIG. 2 is identical in function to that of FIG. 1 except that 
it is provided between the cover 2 and the housing 1 with a cylindrical 
adapter ring 9 carrying two diametrally opposite magnetrons 10 and 11 
having coaxial wave guides 12 and 13 extending in to the housing interior 
and having downward directed ends. This system is particularly 
advantageous for retrofitting a conventional mixer with a microwave 
heater.