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Publication numberUS3784777 A
Publication typeGrant
Publication dateJan 8, 1974
Filing dateDec 22, 1971
Priority dateDec 31, 1970
Also published asCA933600A1, DE2162851A1
Publication numberUS 3784777 A, US 3784777A, US-A-3784777, US3784777 A, US3784777A
InventorsJ Soulier
Original AssigneeJ Soulier
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Microwave furnace for the treatment of sheets or plates made of a material absorbing said waves
US 3784777 A
Abstract
A microwave furnace comprises a guide with a slot of a length corresponding to the width of a sheet which is to be treated by being continuously moved through the guide. A microwave generator is electrically connected to said guide and at least one metal plate is placed in front of said slot.
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United States Patent 1 91 1111 3,784,777

Soulier Jan. 8, 1974 MICROWAVE FURNACE FOR THE [56] References Cited TREATMENT OF SHEETS OR PLATES I UNITEDSTATES PATENTS MADE OF A MATERIAL ABSORBING SAID 3,457,385 7/1969 Cumming 219/1055 WAVES V 3,555,232 1 1971 Bleackley.... 219/1055 3,218,583 11/1965 Pon et al 333/81 A [76] Inventor 133:23ag glsf 'gggg 2,869,085 1/1959 Pritchard et al. 333/81 B France Primary ExaminerC. L. Albritton [22] Filed: Dec. 22, 1971 Assistant Examiner-Hugh D. Jaeger [21] Appl No: 210,801 Attorney-Saul Jecie's 57 ABSTRACT [30] Foreign Application Priority Data D 31 1970 g A m1crowave furnace comprises a gulde w1th a slot of BC. [311GB a eng corresponding o e of a sheet is to be treated by being continuously moved through 53 i gi 2 I the guide. A microwave generator is electrically coni 333 8l R nected to said guide and at least one metal plate is 1 o earc 5 81 placed in front of said slot.

21 Claims, 6 Drawing Figures V VI 1 I I I II PATENTEDJAI 1914 SHEET 1 BF 3 La v v MICROWAVE FURNACE FOR THE TREATMENT ABSORBING SAID WAVES The invention relates to a novelmicrowave furnace for the treatment of sheets or plates (i.e. workpieces) of great width and made of material absorbing said microwaves, said sheets or plates being made to travel through the furnace.

According to the invention, the novel furnace comprises a wave-guide, a slot, provided in said wave-guide, and having a length corresponding to the width of said sheet or plate, conveying means for moving said sheet or plate transversely with respect to said slot, a microwave generator electrically connected to said guide, and at least one metal plate placed in'front of said slot perpendicularly to the plane of and over the whole length of said slot. The plate has one side turned towards the slot and said side has an inclination decreasing in the direction of the microwave generator.

Other characteristics of the invention are shown in the following detailed description.

Embodiments of the invention are shown by way of the non-restrictive examples illustrated in the accompanying drawings in which:

FIG. 1 is a longitudinaldiagrammatic perspective section of a furnace according to the invention;

FIG. 2 is a diagrammatic top plan view of-the furnace of FIG. 1, with portions omitted for the sake of clarity;

FIG. 3 is a longitudinal perspective section, illustrating a variant embodiment of FIG. 1;

FIG. 4 is a cross-sectional view illustrating a further development of the invention;

FIG. -5 is an elevation sectional view taken online V-V of FIG. 4; and I FIG. 6 is a diagrammatic view illustrating another development of the invention.

The furnace shown in the drawings comprises a wave-guide excited on the mode TEOl; this waveguide is hereinafter called resonant cavity. The resonant cavity 1 is of a'parallelepipedal shape and into it protrudes the antenna'2 of a microwave generator 3 constituted, for example, of a magnetron and fed by a power source 4. g

As well-known in the art, the inside of the resonant cavity 1 in which ultra high frequency waves are dissipated includes matching elements 5, for example constituted by rings or plates made of polytetraflu orethylene; in addition, the resonant cavity 1 is provided, at the end thereof opposite the end into which the antenna 2 protrudes, with an absorbing load 6 whose position can be modified'by an adjusting device 7, the control 8 of the latter being placed outside the cavity 1. v

The upper wall of cavity 1 is provided with a slot 9 whose length corresponds to the width of a sheet to be heated, and which is of a material absorbing the micro waves; thewidth of sheet 10 can be for example from 0.25 m to 2.50 m or more. Such materials are technically known as polar materials and are, for example, constituted by various thermoplastic and thermosetting rubbers and resins, which are, should the occasion and vinyl acetate, nitrile' rubbers or blends thereof, chloroprene rubbers, and others.

Slot 9 may have various widths, but its width should preferably be in the range of about 5 to 10 mm.

The furnace being designed to treat or heat a sheet 10 which travels continuously, means are provided for advancing the sheet, such as, for example, sets of cylinders ll, 12, bands or other suitable conveyingdevices.

To prevent any propagation of microwaves in the atmosphere, it is advantageous as shown on the drawings,

that a protective cover 13 be provided above the slot 9 and preferably over the whole width of the cavity wallhaving said slot. This cover 13 is made of conductive metal and has its ends securedoutside of the cavity.

The furnace is also provided in front of slot 9 with a plate l4-made of conductive metal, for example aluminum, whose length is preferably equal to the length of said slot 9. The side l4a'of the plate 14 facing slot 9 is oblique to delimit a downwards inclination facing the antenna 2 of the magnetron 3. The plate 14 can be permanently placed into the cavity 1 so as to be supported by that inner wall of the cavity, which is opposite to the wall provided with the slot 9. However, as shown in the drawings, it is preferred that the plate 14 be located in an opening 15 and supported by one or several adjusting elements 16, so that the position of the inclination quently the sheet 10 would tend to be more heated near the edge thereof corresponding to that end portion of the slot 9 which is near from the antenna 2. The microwave power transmitted from the antenna 2 then has a tendency to decrease along slot 9, in an exponential manner from this end portion towards the other end portion of the slot.

Due to the provision of the plate 14 with the inclination 1411, the magnetic field which is produced inside the resonant cavity 1 and which extends transversely with respect to said cavity, has to pass around'plate 14 as represented by line Hm in FIG. 4. Consequently it will be noticed that the magnetic field becomes more and more concentrated at the vicinity of the slot 9 as the distance from the antenna 2 increases so that the resulting electrical field He which is shown on FIG. 4 and absorbed by the material of sheet 10, is made substantially constant over the whole width of said sheet. This prevents the edge of the sheet which is closet to the antenna 2 from being more heated than the rest and thus to tend to absorb more of the microwaves. As a result, the microwave energy applied to said sheet is more uniform over the whole lenght of the slot 9.

Since' the plate 14 is adjustable by means of screw 16, it is possible to concentrate the magnetic field more or less the cavity 1, thus enabling heating of sheets 10 of various thickness or having different absorption coefficients (tg 8.).

In the event that all the microwave power developed by magnetron should not be absorbed by the sheet 10,

then the auxiliary load constituted by the piston 6 which is made of absorbing material, prevents reflections which can cause return waves to be applied to the antenna 2 and consequently to themagnetron 3 with the resulting risks of destroying the same.

FIG. 3 illustrates a variantof the preceding embodiment wherein the plate 14 is replaced by several successive small plates 18, 18a 18n, each of them having a separate control means 19, 19a 19n. The height of plates 18 to 18nis decreases or the control means 19 to 1% are designed in order that the top 18 18a, 18a of each plate be set off substantially in step shape, as "shown. Thus it is possible, by moving the different plates upwards or downwards, to more or less concentrate the field in different areas of the slot 9 and thus to uniformly heat a sheet 10 having a non-constant thickness or having a heterogeneous structure with respect to the absorption of microwaves.

FIGS. 4 and show a development of the invention wherein the plate 14 of FIG. 1 or the various plates 18 to 18n of FIG. 3 are replaced by a part 20 of U-shaped cross section, said part 20 containing between the branches thereof a plate 21 made of polytetrafluorethylene or similar material. The part 20 is, asabove mentioned, preferably adjustable upwards and downwards by means ofcontrol devices 22 which are for example, constituted by screws as shown. In a similar way, the plate 21 is also adjustable upwards and downwards by means of a control component 23 which can be operated separately from those operating and lifting or lowering of the part 20. It is advantageous that the top 20a of the part 20 and also the top 21a of the plate 21 be parallel to each other. Due to this additional means it becomes possible, by adjusting the position of the plate 21 to adapt or match the impedance of the resonant cavity and, consequently, to prevent the formation of standing waves which are prejudicial to good operation.

It is also possible, as shown in FIG. 6, for the plate 14 to have a top 14b substantially shaped as an exponential curve. This isadvantageous when the exponential function of absorbtion decrease of a material having to be heated is exactly known. Actually, then, by replacing said function in the configuration of the top 14b of plate 14 it becomes possible to compensate the absorption decrease very accurately and, consequently, to obtain strictly uniform heating over the whole width of the sheet 10.

The invention is not restricted to the embodiments shown and described in detail, for various modifications can be employed without departing from the scope of the invention. Especially in the event when all the microwave power developed from the magnetron would not be absorbed by the wave-guide, then the energy could be returned into one or several similar waveguides through appropriate bends.

l Claim:

1. A microwavefurnace for the treatment of sheetshaped or plate-shaped workpieces whose material is capable of absorbing microwaves, comprising a waveguide having a wall bounding an interior cavity and provided with a slot having a length corresponding to the width of the workpieces to be treated;

conveying means for conveying a workpiece to be treated exteriorly of said cavity across said slot transversely to the elongation thereof;

a microwave generator electrically connected with said wave-guide for producing in said cavity of the latter an electric field to which the successive increments of the advancing workpiece are to be exposed through said slot, and which tends to be nonuniformly absorbed over the surface area of said slot by the material of the workpiece; and

field-equalizing means in said cavity for equalizing said electric field over the entire area of said-slot so that the material of the workpiece will uniformly absorb the field during advancement of the workpiece across said slot.

2. A microwave furnace as defined in claim 1, wherein said field-equalizing means comprises at least one metal plate located in said wave-guide in front of the slot and extending normalto the plane and over the entire length of the same, said plate having a surface facing said slot and inclined in direction toward the same from the region of said microwave generator.

3. A microwave furnace as defined in claim 2; and further comprising control means associated with said plate for moving the same toward and away from said slot normal to the plane of the latter.

4. A microwave furnace as defined in claim '2; and further comprising a plurality of additional plates similar to the first-mentioned plate and all aligned in a common plane extending longitudinally of said slot; and control means associated with said plates and operative for individually moving each plate toward and away from said slot. j

5. A microwave furnace as defined in claim 2, wherein said surface of said plate has a rectilinear inclination. I

6. A microwave furnace as defined in claim 2, wherein said surface of said plate has a step-shaped inclination.

7. A microwave furnace as defined in claim 2, whereinsaid surface of said plate has an exponentially shaped inclination.

8. A microwave furnace as defined in claim 2, wherein said plate comprises one portion of substantially U-shaped cross-section having an open side facing said slot, and another portion of material sensitive to microwaves arranged in said one portion and having said surface which faces said slot at said open side; and

further comprising control means associated with said I other portions for moving the same toward and away from said slot normal to the plane of the same.

9. A microwave furnace as defined in claim 2, said wave-guide having another wall opposite the firstmentioned wall and provided with an opening through which said plate in'part extends to the exterior of said wave-guide; and further comprising a cupped cover fixed to the outer side of said other wall over said opening.

10. A microwave furnace as defined in claim 2; and further comprising a cupped cover secured to said wall at the outer side thereof and overlying said slot, said cover defining with said wall a guide passage for travel of said workpiece across said slot;

11. A microwave furnace for treating a workpiece in the form of an elongated band, comprising a substantially electrically continuous cavity having a longitudinal axis and being bounded by circumferential walls;

a source of microwave power to energize the cavity for propagating therein microwave energy along said longitudinal axis;

one longitudinally extending slot provided in one of said walls, said slot having a length substantially equal to the width of the elongated band;

travelling means for moving said elongated band along its own longitudinal plane and transversally to said longitudinal axis in front of said slot and exteriorly of said cavity; and

at least one metal plate inside the resonant cavity in front of said slot perpendicularly to a plane limited thereby and over all the length thereof, said metal plate having one side turned towards the slot and provided with a slope generally decreasing in direction of the source of microwave power.

12. A microwave furnace as defined in claim 11, wherein an aperture is provided in the cavity in a wall thereof opposite the slot, control means being connected to at least one metal plate for supporting and adjusting it through said apreture.

13. A microwave furnace as defined in claim 11, wherein said at least one metal plate is composed of a succession of plates, means being provided for supporting and adjusting each plate in position.

14. A microwave furnace. as defined in claim 11,

wherein said at least one metal plate has a rectilinear wherein said at least one metal-plate has a U-shaped cross-sectional shape and is supported by means for adjusting the position thereof with respect to the slot.

18. A microwave furnace as defined in claim 11, wherein a first protective cover is fixed outside the cavity on the wall thereof which is provided with a slot, said protective cover forming a passage for the band to be treated.

19. A microwave furnace as defined in claim 12, wherein a second protective'cover is fixed outside the cavity on the wall thereof which is provided with an ap erture, said protective cover enclosing said control means of at least one metal plate.

20. A method of treating elongated sheet-shaped or plate-shaped workpieces of material capable of absorbing microwaves, with the aid of a microwave furnace, comprising the steps of producing a microwave field in a microwave furnace having a wall provided with a slot;

advancing a workpiece over said wall and transversely of said slot outside said microwave furnace for exposing successive increments of the workpiece through said slot to said microwave field;

and equalizing the microwave field over the entire surface area of each increment exposed in said slot whereby to assure uniform absorption of the microwave energy of the field by the material of said workpiece.

21. A method as defined in claim 20, wh ereinthe step of equalizing said field comprises varying the field over the surface area of the respective increment exposed in said slot as a function which is the inverse of the exponential function of absorption decrease of the material of the workpiece.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2869085 *Jan 19, 1954Jan 13, 1959Raytheon Mfg CoSelective absorbers
US3218583 *Aug 30, 1963Nov 16, 1965Textron IncHigh frequency attenuator with constant phase shift
US3457385 *Jul 7, 1966Jul 22, 1969Canadian Patents DevApparatus for dielectric heating
US3555232 *Oct 21, 1968Jan 12, 1971Canadian Patents DevWaveguides
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3949328 *Mar 20, 1975Apr 6, 1976C.G.R.-MevVariable-reflectivity device for varying output power of microwave generator
US4179595 *Aug 15, 1977Dec 18, 1979Saint-Gobain IndustriesMultimodal resonant cavity for very high frequency heating
US4259561 *May 1, 1978Mar 31, 1981Agence Nationale De Valorisation De La Recherche (Anvar)Microwave applicator
US4689459 *Sep 9, 1985Aug 25, 1987Gerling John EVariable Q microwave applicator and method
US4711983 *Jul 7, 1986Dec 8, 1987Gerling John EFrequency stabilized microwave power system and method
US4991539 *Dec 19, 1988Feb 12, 1991Sarda Jean LucienMicrowave unit for thermographic printing
US5371342 *Nov 4, 1993Dec 6, 1994Saitoh; YoshiakiElectromagnetic-wave-operated heating apparatus having an electric field concentrating member
US6054696 *Jan 5, 1998Apr 25, 2000International Business Machines CorporationFeedback system to automatically couple microwave energy into an applicator
US6072167 *Jan 5, 1998Jun 6, 2000International Business Machines CorporationEnhanced uniformity in a length independent microwave applicator
US6121595 *Jan 5, 1998Sep 19, 2000International Business Machines CorporationApplicator to provide uniform electric and magnetic fields over a large area and for continuous processing
US6590191 *Apr 19, 2001Jul 8, 2003Industrial Microwaves Systems, Inc.Method and apparatus for electromagnetic exposure of planar or other materials
US6965099 *Aug 28, 2001Nov 15, 2005Georgia Tech Research CorporationGeometry for web microwave heating or drying to a desired profile in a waveguide
US7470876Dec 14, 2005Dec 30, 2008Industrial Microwave Systems, L.L.C.Waveguide exposure chamber for heating and drying material
US20100282741 *Nov 17, 2008Nov 11, 2010Dow Global Technologies Inc.Method for controlling and optimizing microwave heating of plastic sheet
Classifications
U.S. Classification219/693, 219/696, 333/81.00B, 219/750
International ClassificationH05B6/78
Cooperative ClassificationH05B6/788
European ClassificationH05B6/78T