US3715551A

US3715551A - Twisted waveguide applicator

Info

Publication number: US3715551A
Authority: US
Inventors: R Peterson
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1971-07-01
Filing date: 1971-07-01
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06
Also published as: JPS5123064B1; FR2144350A5; DE2232065A1; DE2232065B2; DE2232065C3

Abstract

An apparatus is disclosed having an electromagnetic waveguide energy transmission structure providing applied orthogonally disposed high frequency electric fields disposed around material being processed in one complete traversal. The resultant electric field intensity distribution provides for uniform heating of products having nonuniform cross-sectional configuration. Objects, such as rubber moldings or extrusions, may be uniformly cured by the orthogonal electric field orientation. The apparatus utilizes conveyor mechanisms for continuously feeding strip materials to be treated. The transmission structure may be of a hollow rectangular or circular configuration or a combination of both. To assist in the removal of any vapors or to maintain heating temperature, fluid circulation means are disposed over predetermined zones of the oven energy applicator.

Description

United States Patent 91 Peterson 111 3,715,551 51 Feb. 6, 1973 [54] TWISTED WAVEGUIDE APPLICATOR [75] inventor: Robert A. Peterson, Canton, Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: July 1, 1971 [21] Appl.N0.: 158,919

[52] US. Cl ..219/10.ss [51] Int. Cl. ..H05b 9/06 [58] Field of Search ..2l9/l0.55

[56] References Cited UNITED STATES PATENTS 2,7l8,580 9/1955 Shirley ..2l9/l0.55 3,528,179 9/1970 Smith ..2l9/l0.55 X

Primary Examiner--J. V. Truhe Assistant Examiner-Hugh D. Jaeger AttorneyI-iarold A. Murphy et al.

[57] ABSTRACT An apparatus is disclosed having an electromagnetic waveguide energy transmission structure providing applied orthogonally disposed high frequency electric fields disposed around material being processed in one complete traversal. The resultant electric field intensity distribution provides for uniform heating of products having nonuniform cross-sectional configuration. Objects, such as rubber moldings or extrusions, may be uniformly cured by the orthogonal electric field orientation. The apparatus utilizes conveyor mechanisms for continuously feeding strip materials to be treated. The transmission structure may be of a hollow rectangular or circular configuration or a combination of both. To assist in the removal of any vapors or to maintain heating temperature, fluid circulation means are disposed over predetermined zones of the oven energy applicator.

10 Claims, 7 Drawing Figures PATENTEDFEB 6l975 3.715.551

SHEET 2 OF 2 ENERGY INPUT TWISTED WAVEGUIDE APPLICATOR BACKGROUND OF THE INVENTION The invention relates to heating by high frequency electric energy in the microwave portion of the electromagnetic spectrum and means for orienting the electric field distribution to uniformly heat a product.

Dielectric heating utilizing energy in the electromagnetic wave spectrum has found wide acceptance in the processing of nonconductive and poor thermally conductive materials, including foodstuffs, paper, wood, rubber, leather, and other materials. An energy generator of high frequency waves is the magnetron oscillator of World War II radar systems fame. The text Microwave Magnetrons, Radiation Laboratory Series Vol. 6, by G. B. Collins, McGraw-I-Iill Book Company, lnc., 1948, provides a comprehensive description of the construction and operation of such devices. The energy generator operates at frequencies within the allotted Federal Communication Commission frequency band for electronic ovens of 915 and 2450 megahertz. Other high frequency energy generators include vacuum tube oscillators and klystrons. High voltage circuits carrying many thousands of volts of electrical energy are utilized for the generator. For the purposes of the present specification, the term microwave is defined as the electromagnetic energy radiation in that portion of the spectrum having wavelengths in the order of approxi mately 1 meter to 1 millimeter and frequencies in excess of 300 megahertz.

In the treatment of various materials the electric field intensity within the oven is of paramount importance. Critical alignment of the product with relation to the input and output feed structuresand main oven section is required to provide for the propagation of the energy in certain selected modes, for example, TE, and TE, in rectangular or circular waveguide structures. A problem arises, however, in the treatment of nonuniform cross section materials wherein irregularities in heating are observed with certain hot spots and faulty curing resulting. In particular, products such as rubber extrusions and tubing in rolls can be advantageously treated with microwave energy if suitable disposition of the electric fields is provided for uniform heating. In

the treatmentof such rubber products, it is customary forthe curing operation to be carried out after the complex-shaped extrusions have been fabricated.

" Other products having poor thermal conduction characteristics and irregular shapes can also be readily treated with the disclosed microwave oven apparatus. Vapors and fumes emitted during the heating cycle are rapidly removed to enhance the efficient and safe operation of the apparatus.

SUMMARYOF THE INVENTION .In accordance with the teachings of the present invention, a microwave .oven apparatus is provided for frequency alternating electric field distribution. A conveyor extends throughout the .length of the oven apparatus to transport the products through the complete heating cycle. Each end of the oven is provided with a feed structure having means to prevent the escape of electrical energy from the entrance and exit ports of the conveyor. The main oven section may, illustratively, be of a waveguide structure having a rectangular cross section provides for zone heating having orthogonally oriented electric field distribution. The first zone provides a field of predetermined intensity and a second zone provides an electric field orientation rotated with respect to the first zone. In addition, vapors may be removed by circulating air means which also aid in maintaining the temperature in the oven during processing. Alignment problems in the orientation of the traversing materials have been substantially reduced by the orthogonal orientation of the high frequency electric field distribution.

BRIEF DESCRIPTION OF THE DRAWINGS Details of illustrative embodiments of the invention will be readily understood after consideration of the following description and reference to the accompanying drawings, wherein;

FIG. 1 is an elevational view of a conveyerized oven apparatus embodying the invention;'

FIG. 2 is a detailed cross-sectional view of the waveguide transmission structure of the main oven taken along the line 2-2 in FIG. 1.

FIG. 3 is a detailed cross-sectional view taken along line 33 in FIG.1;

FIG. 4 is a cross-sectional view of an exemplary product of nonuniform cross-sectional area for treatment with the microwave oven apparatus;

FIG. 5 is an elevation view of a portion of an alternative apparatus;

FIG. 6 is an elevation view of a portion of an embodiment ofthe invention having air circulation means;

FIG. 7 is a view partly in section of an alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the main section 2 of the oven apparatus defines the heating enclosure through which the product to be processed is transported. An entrance port comprises an input feed structure 4 and an exit port by output feed structure 6. Conveyor mechanism 8 includes belt 10 and a drum and gear actuating mechanism 12 driven by suitable means (not shown)-for the sake of clarity in understanding the present invention. The entrance and exit structures provide a hollow passageway and are fabricated of a metallic material with the dimensions selectedto attenuate and substantially prevent the escapeof the electrical energy from the open ports. Square waveguide.

satisfies this requirement. Alternatively, energy attenuating means such as, for example, a curtain of -a lossy liquid can be disposed adjacent to the open ports.

foregoing arrangement provides for a symmetrical energy distribution. -In such a structure, the high frequency microwave energy fed into the oven from each end is isolated by

circulators

26 and 28 of the well-known ferrite material configuration.

Loads

30 and 32 coupled to the respective ferrite circulators attenuate and absorb energy directed to this component from opposing ends of the oven apparatus. The provision of the dual energy feeding arrangement provides for a more even distribution of the heating energy required for operation. Where desired, one of the energy sources may be eliminated and the waveguide transmission bend 24, for example, will be terminated by a metallic short circuiting member.

Intermediate waveguide transmission structure 34, between the first and

second zone sections

14 and 22, provides a transition for rotation of the high frequency electric field pattern in the manner now to be described. Referring to FIG. 2 the rectangular cross section of the waveguide section 14, provides parallel opposing narrow walls 14a and broad walls 14b. Flanges 36 having mounting holes 38 provide for the coupling of section 14 to

adjacent structure

16 and 34. In the microwave art, the propagation of energy in the transverse electric mode through uniform hollow conduit'transmission means has a configuration described in the text Microwave Engineers Handbook, 1966, Horizon. House-Microwave Inc., at page 23 for the TE mode in rectangular waveguide, and page 24 for the TE, mode for circular waveguide. It will be noted that in the rectangular transmission line, the electric fields have a varying intensity pattern between broad walls 14b with the maximum in a centered area represented by lines 40. The less intense energy fields, represented by lines 42, are adjacent to narrow sidewalls 14a. The heating of products having irregular nonuniform shapes, therefore, is uneven if the oven apparatus has only one electric field pattern throughout its length. To circumvent the problems inherent in the prior art, the invention provides for the orientation of the electric field patterns in an orthogonal manner with the electric fields rotated 90 in a second heating zone relative to the electric field orientation in a first heating zone. Transition section 34, therefore, provides a waveguide twist with the broad walls similar to those designated by the numeral 14b being rotated to assume a new position indicated by the walls 34b. In alike manner, the-narrow sidewalls having the designation a in FIG. 2 are now rotated 90 to assume the position indicated by walls 34a.

In FIG. 3, the downstream orientation of the applied electric field pattern within the waveguide transmission structure after rotation is illustrated. Narrow sidewalls 22a are now'disposed in an orthogonal manner with respect to the narrow sidewalls 14a of the first heating zone section 14. Similarly, broad walls 22b are now positioned orthogonally to broad walls 14b. The electric field distribution lines between the broad walls 22b indicate that the maximum intensity is provided in the region of the narrowly spaced lines 44 while the fields of lower intensity are indicated by lines 46. Flange members 48 at the opposing ends of section 22 provide for mating with flange members disposed at the ends of transition section 34 and waveguide bend 24. Coupling apertures 50 provide for the introduction of means for securing the mating flanges of therespective components of the waveguide transmission structure.

It will be evident that material being heated in the first zone is exposed to an electric field pattern indicated by lines 40 and 42, extending from left to right. The same material is exposed to an electric field distribution represented by lines 44 and 46 in the downstream or second heating zone during the complete traversal through the waveguide transmission structure 2. Irregular shaped products, particularly such items as rubber molding or extrusions, which are originally processed from the crude rubber material in rolls may be continuously fed into the microwave oven apparatus to be uniformly cured by exposure to such orthogonally oriented electric fields. An example of a product of nonuniform cross-sectional configuration is shown in FIG. 4. The elongated strip molding 52 comprises a plurality of hollow sections 54 and 56 within the main body 58. Such products are often employed in structures to support dielectric panels within metallic channels.

In FIG. 5, transition section 60 is provided with

flange members

62 and 64 and tapered

waveguide sections

66 and 68 are disposed intermediately to the previously described rectangular waveguide

heating zone sections

14 and 22. In this embodiment, transition section 60 is constructed of a larger dimension hollow waveguide configuration capable of supporting, for example, microwave energy in a lower frequency range or L-band. The

adjacent mating sections

14 and 22 with the orthogonal electric field distributions are capable of supporting energy in a higher S-band frequency band. The twisting broad and narrow walls of transition section 34 provide for a constriction and reduction of the internal cross-sectional area available for the products to be heated. The provision of the larger dimensioned transition waveguide section 60 permits the resultant internal access passageway to be of a larger dimension to handle larger products. The tapering waveguide sections provide for the provision of a continuous path for the applied energy within the oven apparatus. In an exemplary embodiment rectangular waveguide, designated by the standard code WR650, has an I. D. dimension of 6.500 for the broad walls and 3.250 for the narrow walls. The higher frequency waveguide or S-band WR340 has I. D. dimensions of 3.400 by 1.700. The tapered

waveguide sections

66 and 68 are then suitably dimensioned to accommodate the mating of the respective waveguides.

In FIG. 6 a plurality of pipes 70 are shown extending through the narrow and broad walls of the

waveguide sections

14, 34 and 22 comprising the main waveguide transmission structure of the oven. Fluid circulation means, including fans as well as plenums, are attached to these pipes for exhausting any resultant fumes or vapors throughout the length of the oven. Additionally, such exhaust and circulation means can supply any desired atmosphere within the oven to assist in the heat treatment. In the case of rubber moldings or extrusions, the circulation of heated air removes any vapors emitted during the curing operation which may coat the interior of the oven walls and be difficult to remove.

In FIG. 7 another variation of the invention is illustrated with particular regard to the transition region between the orthogonal rectangular waveguides, such as

section

14 and 22. A conveyor mechanism, including belt 10, is illustrated traversing an input feed structure 4 joined to the outer wall of waveguide bend 16 provided for the introduction of applied energy from the source. A resonant cavity 72 defined, for example, by cylindrical walls 74, is coupled by means of

flange members

76 and 78 to the

waveguide sections

14 and 22. The circular cavity dimensions are selected to support multi-mode orthogonal distributions of the electric fields and has, for example, an overall length of onehalf of a wavelength of the operating frequency range of, for example, 2450 MHz. The material to be treated is transported through the resonant cavity by the belt with appropriate support means. A dielectric material, such as fiber glass, is preferred for the belt to permit the microwave energy to permeate the products carried by the conveyor. Numerous other resonant cavity structures will be evident to those skilled in the art of the multimode configuration to provide for the transition between the orthogonal electric fields in the manner specified in the present invention.

There is disclosed a very efficient microwave oven apparatus for the provision of uniform heating by applied microwave energy of products having nonuniform cross-sectional configurations. While the invention has been described in a rectangular hollow conduit waveguide configuration, the concept is equally applicable to other transmission structures capable of supporting orthogonal microwave electric field distribution. Circular hollow waveguide or a combination of both circular and rectangular may be employed. Alignment problems which have plagued processing of irregularly shaped objects, particularly those of poor thermally conductive materials, have been considerably reduced by the orthogonal rotation of the electric fields with resultant uniform heating during the traversal of the product through the apparatus.

Other variations, alterations or modifications, of the disclosed apparatus will be evident to those skilled in the art. It is intended, therefore, that the foregoing description of the invention and illustrative embodiments be considered in the broadest aspects and not in a limiting sense.

I claim:

1. Microwave oven apparatus comprising:

a source of electromagnetic energy at a predetermined operating frequency;

a hollow waveguide transmission structure for propagating said energy and a product along a predetermined path with changing electric field distribution patterns of said energy as said product traverses separate sections of said structure to symmetrically heat the product;

said structure including a first waveguide section having a predetermined electric field distribution pattern and a secondwaveguide section having the electric fields oriented orthogonally to said first waveguide section; and

transition means disposed between said first and second waveguide sections capable of supporting both electric field orientations.

2. Microwave oven apparatus as set forth in claim 1 wherein said waveguide transmission structure is of a hollow rectangular cross-sectional configuration.

3. Microwave oven apparatus as set forth in claim 1 wherein said waveguide transmission structure is of a hollow circular cross-sectional configuration.

4. Microwave oven apparatus as set forth in claim 1 wherein said transition means comprise a section of hollow rectangular waveguide having a continuously twisting outer wall configuration.

5. Microwave oven apparatus as set forth in claim 1 wherein said transition means comprise a hollow circular resonant cavity.

6. Microwave oven apparatus as set forth in claim 1 wherein said transition means comprise a section of hollow rectangular waveguide having larger boundary wall dimensions relative to said first and second zone waveguide sections.

7. Microwave oven apparatus as set forth in claim 1 wherein said energy is coupled from said source at opposing ends of said waveguide transmission structure.

8. Microwave oven apparatus comprising:

a source of electromagnetic energy;

a hollow waveguide transmission structure for propagating said energy and a product along a predetermined path with orthogonally oriented electric field distribution patterns of said energy in first and second waveguide sections during complete traversal of said product along said path to symmetrically heat the product;

transition means disposed between said first and second waveguide sections capable of supporting both electric field orientations; and

means for transporting the product through the waveguide transmission structure sections.

9. Microwave oven apparatus as set forth in claim 8 wherein said transportation means comprise a continuously moving belt conveyor.

10. Microwave oven apparatus comprising:

a source of electromagnetic energy;

a hollow waveguide transmission structure, for propagating said energy and a product along a predetermined path with orthogonally oriented the electric field distribution patterns of said energy in first and second waveguide sections during complete traversal of said product along said path to symmetrically heat the product;

means for circulating a fluid medium within the transmission structure.

Claims

1. Microwave oven apparatus comprising: a source of electromagnetic energy at a predetermined operating frequency; a hollow waveguide transmission structure for propagating said energy and a product along a predetermined path with changing electric field distribution patterns of said energy as said product traverses separate sections of said structure to symmetrically heat the product; said structure including a first waveguide section having a predetermined electric field distribution pattern and a second waveguide section having the electric fields oriented orthogonally to said first waveguide section; and transition means disposed between said first and second waveguide sections capable of supporting both electric field orientations.

8. Microwave oven apparatus comprising: a source of electromagnetic energy; a hollow waveguide transmission structure for propagating said energy and a product along a predetermined path with orthogonally oriented electric field distribution patterns of said energy in first and second waveguide sections during complete traversal of said product along said path to symmetrically heat the product; transition means disposed between said first and second waveguide sections capable of supporting both electric field orientations; and means for transporting the product through the waveguide transmission structure sections.