US2650291A

US2650291A - Microwave heating

Info

Publication number: US2650291A
Application number: US701305A
Authority: US
Inventors: Theodore P Kinn
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1946-10-04
Filing date: 1946-10-04
Publication date: 1953-08-25
Anticipated expiration: 1970-08-25

Description

Aug. 25, 1953 T. P. KINN 2,650,291

MICROWAVE HEATING Filed oct. 4, 194e Patented Aug. 25, 1953 UNITED STATES PATENT Q'FFICE MICROWAVE HEATING Application October 4, 1946, Serial No. '701,305

(Cl. 21S- 47) 9 Claims. ll

This invention relates to micro-wave heating, and has particular relation to apparatus for heating strips of material with ultra-high frequency energy.

In many industries there are dielectric heating problems involving the drying, curing or setting of resins or glues in continuous processes. In the textile industry, for example, cloth strips are to be dried after dyeing and often on a continuous basis, that is, in an operation in which the strip is continuously moving. Similar drying operations are necessary in the paper industry, where a continuous sheet is moved at a relatively high speed.

At conventional frequencies of electric energy in the usual high frequency heating range, apparatus with enough power for the drying of paper or textiles or other material is available, but frequently difficulty is encountered in getting that power into the work. Referring to the familiar relation for power in a dielectric material, it is evident that power into the work, once the frequency is set, varies only as the square of the voltage across the electrodes through which the power is transferred to the material in conventional high frequency heating apparatus. Thus,

2 Power frequency X voltage loss factor For thin materials, such as paper and cloth, it is impossible to apply sufficient voltage across the electrodes at conventional frequencies as ilashover between the electrodes takes place long before any appreciable amount of power is coupled into the dielectric work material.

lt is, accordingly, an object of my invention to provide new and improved apparatus for use in heating a moving strip of material.

Another object of my invention is to provide novel apparatus for heating a continuously moving strip of thin dielectric material.

A further object or my invention is to provide novel apparatus for heating a continuously moving strip of dielectric material in which uniform heating of the material is accomplished with a relatively small expenditure of energy.

Still another object of my invention is to provide novel apparatus for heating a moving strip of material quite rapidly while avoiding any fiashover through the material.

In accordance with my invention, l propose to heat a moving strip of material with appara.- tus which comprises a cavity resonator adapted to have high frequency electromagnetic field oscillations established therein, the resonator being positioned so that the strip is fed therethrough with the plane of the strip substantially parallel to the direction of the electric field within the resonator. However, the path of nio-vement of a point on the strip through the resonator is arranged to be angular with respect to the line of the electric eld vector, representing the direction of the field, so as to cause any given point on the strip to progress an even number of half wave length along and within the interior of the resonator in a component direction substantially perpendicular to the electric field vector. By this arrangement rapid and uniform heating of the strip of material is accomplished without danger of ashover.

rlhe features of my invention which are believed to be novel are set forth with more particularity in the accompanying claims. The invention itself together with additional objects and advantages thereof may be better understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which the single figure is a perspective view of apparatus embodying my invention.

As shown in the drawing, a hollow rectangular envelope forms a cavity resonator 3 which is adapted to have high frequency electromagnetic field oscillations established therein. This energy may be introduced into the resonator by any suitable means as, for example, through an opening -5 in a wall of the resonator through which electromagnetic energy is supplied from a hollow wave guide l. The wave guide, turn, may receive energy from any suitable high fre-- quency source and, of course, may be provide-:l with suitable matching apparatus.

The electromagnetic field within the resonator may have an electric leld vector extending in one direction as represente-d by the arrow il. A pair of slots Il and I3 are provided in opposite walls of the resonator 3 to receive a strip of dielectric material |55. The strip i5 is to be continuously moved through the resonator1 by any suitable driving means (not shown) connected to suitable rollers il. The slots il and i3 are so located that the plane of the strip iii is sul:-

stantially parallel to the arrow 9 repress: ing the direction of the electric field. In ion,

the strip. In the embodiment shown, such maximum intensities are found along a center line of the resonator, in the plane of the strip. Thus, as the strip of material passes through the resonator, it is subjected to the strong dielectric field which provides a rapid heating of the strip.

There will, of course, be a lengthwise standing wave effect along the length of the resonator 3 in the plane of the strip. Because of this standing wave effect, the material would be heated unevenly if passed straight through the resonator with the direction of motion parallel to the electric field vector. l-lowever, the slots ll and i3 have their center lines displaced by approximately n half wave lengths, where n is a whole number, preferably one-half wave length, in a direction substantially perpendicular to the electric field vector. Consequently, any given point on the strip i5, in passing through the res-- onator 3, also progresses approximately n half wave lengths along and within the interior of the res-onator in a direction substantially perpendicular the electric field vector. es a result, the standing waves exert a uniform effect over the entire width of the strip i5 with each point of strip being subjected to the same integrated heating so that uniform heating is obtained. This uniform heating is obtained by having each moving point of the strip pass through the same range of field strengths between minimum and maximum field intensities of the lengthwise standing wave. A distance or displacement of a quarter-wave length includes this range; but in the preferred embodiment described, each point passes through such range twice (one-half wave) for greater assurance of uniform heating.

Although I have shown and described a preferred embodiment of my invention, l am aware that many modifications thereof be without departing from the spirit of the invention. I do not intend, therefore, to limit ny invention to the specic embodiment disclosed.

claim as my invention:

l. Apparatus for use in heating a moving elongated insulating material comprising a hollow envelope providing a cavity resonator to have frequency electromagnetic field oscillations having an electric field vector in one direction established therein, said rez nator having openings in different sides thereof, and means for guiding said strip through said openings and through said resonator with the material substantially parallel to the vector of the electric field and with the path of movement of said material through said resonator such as to cause any given point on the material to progress approximately n half-wave lengths along and within the interior of the resonator in a direction. substantially perpendicular to said electric field vector, where n is a whole number.

2. Apparatus for use in heating a moving strip insulating material comprising a hollow envelope providing' a cavity resonator adapted to have high frequency electromagnetic field oscillations established therein having an electric field vector in one direction, said resonator having a pair of slots therein on opposite sides thereof, and means for feeding said strip in one of said slots and out the other, said slots being located to that the plane of said strip is substantially parallel with said electric eld vector with the centers of the slots displaced substantially one half-wave length in a direction substantially perpendicular to said electric eld vector, any

given point on said strip progressing in a direction substantially perpendicular to said electric field vector as the strip is fed through the cavity resonator.

3. Apparatus for heating an elongated insulating material, comprising a hollow envelope providing a cavity resonator adapted to have highfrequency electromagnetic field oscillations established therein and a standing wave with an electric held vector in one direction, said resonator having opposite Sides, each of said sides having a hole therein, said holes being in registry in a plane including said direction, and means for guiding said material into one of said holes and out of the other, said holes being displaced in a direction perpendicular to said direction of said electric field, the displacement being at least a distance substantially equal to a quarter-wave length of said standing wave, any given point on said material progressing in a direction substantially perpendicular to said electric field vector as the material passes through the cavity resonator.

4;. Apparatus for use in heating a moving strip of insulating material, comprising a hollow enelope providing a cavity resonator adapted to have high-frequency electromagnetic oscil- "ia-tions established therein with an electric I'coto in direction, said resonator having sides, each of said sides having a slot g entirely within and from the edges side, and means for feeding said 'ip in one of said slots and out of the other, c slots lying substantially in a plane substantially parallel to said direction of the electric Q nd provided by said oscillations, and said strip being fed through the cavity resonator such that any given point on the strip progresses in a direction substantially perpendicular to the electric field vector and substantially parallel to the direction of said slots.

5. An invention comprising that of claim 4, but further characterized by said slots being located in said opposite walls with their midpoints displaced in a direction lying in the associated side.

6. in invention including that of claim 5 but characterized by said slots comprising portions `of a size corresponding to the strip passing therethrough, said portions being displaced by substantially n half-wave lengths in a direction parallel to their lengths.

'2. Apparatus for use in heating a s rip of insulating material, comprising a hollow envelope providing a cavity7 resonator yadapted to have high-frequency electromagnetic field oscillations established therein providing a standing wave therein, said resonator having a pair of opposite sides, each of said sides having a slot, said slots being substantially ccplanar, means for feeding said strip through said resonator, through one of said slots and out of the other, said slots being constructed and arranged in said opposite sides so as to be displaced from each other a distance substantially egual to at least a quarter of a wave length of the standing wave as a reference, said slots being of substantially the same size as the width of said strip with sufcient clearance being provided between the slots and said strip such that the strip freely passes through the slots.

8. An ultra high frequency heater co crising walls made of an electrically conducting material forming a chamber provided with diagonally opposite openings in its ends, means for pass- 5 ing a material to be heated diagonally through Said chamber between said openings, and a high frequency supply source connected to said chamber for producing an electric field mode in said chamber thereby to heat the material uniformly as it passes through said chamber.

9. An ultra high frequency heater comprising Walls made of an electrically conducting material forming a chamber provided with diagonally opposite openings in its ends, means for passing a material to be heated diagonally through said chamber between said openings, and a high frequency supply source connected to said chamber for producing a transverse electric eld mode in said chamber thereby to heat the material uniformly as it passes through said chamber.

THEODORE P. KINN.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Number Name Date 2,197,122 Bowen Apr. 16, 1940 2,226,871 Nicholas Dec. 31, 194C- 2,364,526 Hansell Dec. 5, 1944 2,370,161 Hansen Feb. 27, 1945 2,398,606 Wang Apr. 16, 1946 2,400,777 Okress May 21, 1946 2,427,094 Evans Sept. 9, 1947 2,433,067 Russell Dec. 23, 1947 2,500,752 Hanson et al Mar. 14, 1950 FOREIGN PATENTS Number Country Date 417,564 Great Britain Apr. 18, 1934 518,691 Great Britain Mar. 5, 1940 OTHER REFERENCES- Skilling, Physical Behavior of Wave Guides, Electronics, March 1943, pages 76-80 inclusive. Electronic Heat, Steel, November 12, 1945, page 92.