US3701875A

US3701875A - H. f. heating apparatus

Info

Publication number: US3701875A
Application number: US45994A
Authority: US
Inventors: Noel John Charles Witsey; James Charles Clark
Original assignee: Intertherm Ltd
Current assignee: Intertherm Ltd; INTERHERN Ltd
Priority date: 1969-06-30
Filing date: 1970-06-15
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31
Also published as: FR2051464A5; NL7009519A; GB1274877A; DE2033889A1; BE752761A; CA898902A

Abstract

A high frequency dielectric heating apparatus with a novel stray-field platen. The platen comprises a first group of a parallel rod electrodes spaced apart in a first plane. A second group of parallel rod electrodes are alternately arranged between and in parallel with the first group of electrodes. In one region of the platen the rods of the second group are displaced in a direction away from the material to be heated, whereas in a second region of the platen the rods of the second group are closer to the material, or even in the same plane as the rods of the first group. The two regions produce different heating effects on the dielectric material. A high frequency generator is connected across adjacent electrodes. The spacing between the electrodes can be varied and the electrodes can be inclined at an angle to the lateral direction of the material to provide further variations in the heating effect across the platen.

Description

United States Patent 4 [151 3,701,875

. Witsey et al. g I I [451 Oct. 31, 1972 [54] H. F. HEATING APPARATUS 2,871,332 1 1/1969 Northmore et al. ..219/10.8i [72] lnvemm' 3:3 :22, 323 221: 3,082,710 3/1963 Holland ..219/10.s1 x

C P y i d S w 15 Rothstein. X .both of a- Primary Examiner-J. V. Truhe I [73] Assignee; lnterhern Limited Assistant ExaminerI-l ugh D. Jaeger Filed: June Attorney-Frank R- Tflfal'l [21] Appi. No.2 45,994 [57] ABSTRACT A high frequency dielectric heating apparatus with a [30] Foreign Application Priority Data novel stray-field platen. The platen comprises a first group of a parallel rod electrodes spaced apartin a June 30, 1969 Great Britain ..32,928/69 first plane. A Second group of parallel rod elgctmdes are alternately arranged between and in parallel with of In of platen the rods of the second group are displaced in a [58] Field of Search...2l9/ 10.81, 10.69, 10.61, 10.71 direction away from the material to be heated,

whereas in a second region of the platen the rods of [56] References the second group are closer to the material, or even in v UNITED. STATES P thesame P1338 as rods ,ofhthe first gtrfoup. The r3110 Y Y 7 .1 regions pro uce erent eating e ects on e 2,960,777 1l/1960 Doll 219/ l0.6l-'X dielectric material but, frequency genera-OHS com 3,461,263 1 i969 Manwaring "219/ 10.61 X. nected across adjacent electrodes; The spacing 3,469,054 9/ 1969 Serota .219/10-61 between the electrodes. can b varied the elec 3,364,294 H1968 Gambian et al. ....'....2l9/10.61 trodes can be inclined at an angle to the lateral 2,473,251 6/1949 HS ..219/10.61 direction of the material to provide further variations 2 in the heating effect across the platen. 2,640,141 5/1953 Yore et al. ..2l9/ 10.81 X 14 Claims, 4 Drawing Figures PATENTED UN 3 1 1912 saw 1 or 2 jliiim w i I mm 31 m SHEET 2 OF 2 PM JK/ 4 Fig.4

INVENTORS NOEL J. c. WITSEY JAMEIS c. CLARK By AGEIi having an air dielectric. When a material to be heated is brought near to-the platen, the field between the rods will divert to pass through the material and the amount of the field so diverted will depend on the dielectric constant of the material. If the material also has a high dielectric loss factor, a large amount of energy will be absorbed from the high-frequency field generated between the two electrode systems, that is the rods of the platen, as a result of the rapidly alternating voltage difference between the rods, and dielectric heating will occur in the material.

Water is a dielectric having a high dielectric constant together with a high dielectric loss factor and this property can be utilized in continuous flow production .techniquesfor the drying of materials such as, for example, leather, paper and carpets. Thus, by passing the wet material close to the surface of a stray field platen the water will absorb energy from the high frequency 2 reduce the heating effect of the high frequency field produced by theplaten when energized by the supply in comparison with the heating effect produced in the absence of said displacement. When the material to be heated has a high moisture content, the predetermined region can be that part of the platen adjacent to which the material to be heated is first passed so that excessively rapid heating and drying of the material can be prevented at the point where the water content and hence the dielectric loss is greatest. Alternatively, when heating a material exhibiting an increase in the dielectric loss factor as a function of a rise in temperature,

the predetermined region can be that part of the platen adjacent to which the material passes at a later stage of the dielectric heating process. The amount of the displacement applied to the alternate rods can be progressively changed in the direction of travel of the material to be heated. In addition, the relative spacing of the electrodes can be changed from one region to another to modify the relative heating effect. The rod electrodes can be inclinedto the direction of travel of the material to be heated at an angle other than 90.

field and evaporation will be assisted. In such a process the heating effect will occur selectivelyin the damp regions of the material since the dielectric loss factor of water is normally much greater than the dielectric loss of the base material. Thus as the wet material entersthe region of the stray-field platen alarge amount of heating will take place and a, heavy electrical load will be presented to the platen inthe initial stage of the drying process. However, as the material is fed across the platen and becomes drier, the amount of energy dissipated will be greatly reduced as the water content falls. Thus the electrical loading of the platen will be non-uniform and it will be difficult to adjust the highfrequency drive to the platen so that excessively rapid heating and drying of thematerial does not take place in the initial stages while ensuring at the same time that the material is properly dried towards the end of its passage over the platen.

H.F. heating apparatus employing a stray field platen can also be employed for curing resin and P.V.C. formulations and it has been found that some of these formulations result in a material having a dielectric loss factor which increases with an increase in temperature. In this case it is found that a heavy electrical load is presented to the platen not in the entrance region of the platen but in a later region, which may be at the exit region of the platen. However, in this case too, a similar difficulty will arise in the adjustment of the highfrequency drive to the platen.

It is an object of the present invention to provide an improved formof high-frequency heating arrangement in which the above difficulties are alleviated.

. In accordance with the present invention, there is provided a stray-field platen comprising a plurality of rod-like electrodes arranged in operation so that adjacent rods are connected across a high-frequency The material to be heated can be passed horizontally above or below the stray-field platen, or alternatively thestray-field platen can be mounted vertically and the material fed past it in a vertical direction. The electrode rods can be of curved form and can thus be arranged to present a radiused face to the material to be heated. In order to avoid the disadvantages resulting from the occurrence of standing waves in the stray-field platen, high-frequency current can be supplied to the rod-like electrodes in the manner set forth and claimed in our British Pat. Specification No. 1,017,289.

In order that the present invention may be clearly understood and readily carried into effect, certain embodiments thereof will now be described, byway of example, with reference to the accompanying drawings, in which: 1

FIG. 1 is a longitudinalisectional diagram illustrating a stray-field platen employing the invention,

FIG. 2 is a detail illustrating a method of adjustment of the electrodes, g

, FIG. .3 is a plan diagramillustrating a feature of the invention, and

no. '4 is a plan diagram illustrating a further feature of the invention.

Referring to FIG. 1 which illustrates schematically in longitudinal vertical section one arrangement of the electrodes of a stray-field platen embodying the invention and which is-adapted for drying material having a high water content. A web 1 of material in which the water content is to be reduced, such as, for example,

carpeting coated on the back with a water based emulsion of latex or P.V.C. or a pulp mat or paper, is passed over rollers 2 made of a low-loss dielectric material and beneath a stray-field platen formed by an array of

parallel rod electrodes

3 and 4 arranged to lie across j the width of the web 1. The electrodes 3 are arranged at a substantially constant height above the web 1.

Each of the electrodes 4 is arranged at a position between and equidistant from the two adjacent elec-. trodes 3, and at that end of the stray-field platen first reached by the web 1 each electrode 4 is raised above the level of the adjacent electrodes 3 to an extent dependent on the reduction in heating eflect desired over travel of the web, may give rise to standing waves along the platen. To overcome this problem, it is preferable to divide the platen up into groups of electrodes and employ the feeding arrangement described and claimed in our British Pat. No. 1,017,289 and illustrated in FIG. 1 by the series variable capacitor 7.

It will be seen that by raising the electrodes 4 above the level of the electrodes 3 in the first part of the platen, the relative amount of the high-frequency field present between the

electrodes

3 and 4 that can pass through the web 1 is reduced. Thus, where the web 1 contains the greatest amount of moisture, the heating effect of the'field is reduced.

If this were not done the heating eflect would be too great, causing the moisture to be given off too rapidly and damaging the web. Alternatively the very moist web could so load the first part of the platen that the output of the oscillator in the high-frequency power source would be reduced and the web would not be dried satisfactorily. Thus by displacing the alternate rod-like electrodes 4 in a direction away from the web 1 within the first part of the stray-field platen, these difficulties can be overcome in a simple and convenient way.

The displacement of the electrodes 4 away from the web 1 over a predetermined region of the stray-field platen can be adjusted or pre-set. One method of supporting the electrodes 4 so that their displacement can be adjusted is illustrated in FIG. 2. The electrodes 4 are mounted on brackets 10 having

slots

11, 12 cut longitudinally therein. The brackets 10 are bolted by bolts l3, 14 to a bus-bar 15 comprising two spaced parallel conducting bars 16, 17. The

bolts

13, 14 pass through the slots l1, l2 in'the brackets 10, between the

bars

16, 17, through a clamping plate 18, to be retained by nuts, not shown, on the far side of the plate 18. The electrodes 3 can be similarly attached to a further bus-bar 20.

Alternatively the electrodes 4 can be mounted on an assembly which can be raised or lowered while the apparatus is operating so that adjustments can be made of the relative heating effect over different parts of the platen while the heating is taking place. Such an adjustment can be carried out manually by means of a handwheel or lever, or it can be performed by an electric motor or by hydraulic or air-actuated means, and can be controlled automatically, for example, in response to measurements of the water content of the input web of material to be dried.

It will be understood that although a gradual change in the displacement of the electrodes 4"with distance along the stray-field platen is shown in FIG. 1, the displacement can alternatively be made-to change in one or more steps until the electrodes 4 lie in the same plane as the electrodes 3.

In addition to the displacement of the electrodes 4 away from the web to be dried in the region in which a reduced heating effect is required, a further reduction in heating effect can be brought about by increasing the spacing between the electrodes is illustrated, with reference to the removal of moisture from a web, in a plan view in FIG. 3 in which the spacing between the

electrodes

3 and 4 is greater over the region where the web enters the stray-field platen and is decreased towards the exit end of the platen.

When a web having a high moisture content enters the platen there may be a tendency for too great a load to be placed across the electrodes at the input end of the platen, and this may adversely effect the power output of the high-frequency generator feeding the platen. The initial load can be further spread over the electrodes of the platen by inclining the

electrodes

3, 4 to the lateral direction as illustrated in the plan view of FIG. 4. In this way the increased load at the input end of the platen can be distributed over a number of electrode pairs 3, 4.

While the invention has been described with reference to an embodiment in which the stray-field platen is arranged above a horizontal web, the strayfield platen can be placed underneath the web in some applications and alternatively both the web and the platen can be arranged in a vertical or inclined plane if desired. The

electrode rods

3 and 4 need not be straight but can be curved, for example, they can be bowed in the direction towards the web 1.

Furthermore, by employing the invention, the relative distribution of the dielectric heating effect can readily be controlled over any predetermined region of a stray-field platen. Thus the invention can also be employed in the curing of resin formulations in which the dielectric loss and therefore the heating effect increases during the curing process and/or as a result of an increase in the temperature of the material. The embodiment illustrated in FIG. 1 can be employed for this purpose by displacing the alternate electrodes 4 near the exit in a direction away from the platen, while bringing the electrodes 4 near the entrance towards the web '1. until they are at the same distance from the web 1 as the electrodes 3. Alternatively theweb 1 could be fed in the opposite direction with respect to the original arrangement of the

electrodes

3 and 4. The invention can also be employed when a water based resin emulsion is to be cured such that it is desirable to reduce the heating effect both at the start and at the finish of the operation. In this case alternate electrodes would be displaced away from the web in the entrance and exit regions of the platen, but not over the central region.

What we claim is:

1. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rod-like electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto for the material to be heated and another group of alternate rod-like electrodes being alternately arranged on the same side of the material and between the electrodes of said one group and displaced therefrom in a direction away from the material to be heated within a predetermined region of 'ment.

2. A stray-field platen as claimed in Claim 1 in which said predetermined region is that part of the platen adjacent to which, in operation, the material to be heated is first passed.

3. A stray-field platen as claimed in claim 1 wherein the physical displacement of the other group of alternate rod-like electrodes from said travel path progressively varies along the platen in the direction of travel of the material to be heated.

4. A stray-field platen as claimed in claim 1 wherein the lateral spacing between said rod-like electrodes varies in the direction of travel of the material to be heated.

5. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rod-like electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto-for the material to be heated and another group of alternate rod-like electrodes being alternately arranged between the electrodes of said one group and being displaced therefrom .in a direction away from the material to be heated within a predetermined region of said platen to reduce the heating effect on the material by the high-frequency field produced by the platen over said region in comparison with the heating effect otherwise produced in the absence of said .displacemenL-said rod-like electrodes being arranged .in the platen at an oblique angle other than 90 relative to the direction of travel of the materialto be heated.

6. A stray-field platen as claimed in claim 1 wherein said electrodes are divided into two groups, the electrodes of the first group being arranged in parallel in a first plane across which the material to be heated will pass, and the electrodes of the second group being alternately arranged between the electrodes of the first group in a second plane and parallel to said first group of electrodes.

7. A stray-field platen as claimed in claim 6 wherein the spacing between adjacent electrodes in a direction orthogonal to the longitudinal axes thereof of a first region of the platen is different from the electrode spacing in a second region of the platen.

8. A stray-field platen as claimed in-claim 6 wherein the electrodes of said first and second groups are arranged at a non-perpendicular angle relative to the direction of travel of the material to be heated.

9. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rod-like electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto for the material to be heated and another group of alternate rod-like electrodes being alternately arranged between the electrodes of said one group and being displaced therefrom in a dire on awga fgorn the material to be heated witgg a pre etermln gm of sai p aten to reduce the ing effect on the material by the high-frequency field produced by the platen over said region in comparison with the heating efiect otherwise produced in the absence of said displacement, and wherein the distance between given ones of said alternate rod-like electrodes and said material varies along a portion of the platen in the direction of travel of the material. A

10. A high frequency heating apparatus for a material to be heated as it is moved along a given path of travel comprising, a source of high frequencyelectric energy, a stray-field platen assembly that includes two groups of rod electrodes sequentially arranged adjacent the path of travel of said material to be heated and on the same side thereof, the electrodes of one group being spaced apart and equidistant from the material as it moves along said travel path, the electrodes of the other group being alternately located between the electrodes of said one group with at least some of theelectrodes of said other group positioned at a greater distance from said material than the electrodes of said one group, and means for connecting the electrodes to the terminals of said energy source whereby different regions of the platen in the direction of travel of the material produce difierent heating effects on the material adjacent thereto.

11. A heating apparatus as claimed in claim 10 wherein the electrodes of said one group are mounted in parallel in a first plane and at least some of the electrodes of said other group are mounted in parallel in a second plane and parallel to said one group of electrodes.

12. A heating apparatus as claimed in claim 11 wherein the lateral spacing between adjacent electrodes in a first region of the platen is difierent than the lateral spacing between adjacent electrodes in a second region of the platen.

13. A heating apparatus as claimed in claim 10 wherein said electrodes are arranged in parallel in the platen at an oblique angle relative to said path of travel of the material. I

14. A heating apparatus as claimed in claim 10 including means for mounting other ones of the electrodes of said other group in positions at a still greater distance from said material to be heated.

Claims

1. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rodlike electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto for the material to be heated and another group of alternate rod-like electrodes being alternately arranged on the same side of the material and between the electrodes of said one group and displaced therefrom in a direction away from the material to be heated within a predetermined region of said platen to reduce the heating effect on the material by the high-frequency field produced by the platen over said region in comparison with the heating effect otherwise produced in the absence of said displacement.

5. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rod-like electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto for the material to be heated and another group of alternate rod-like electrodes being alternately arranged between the electrodes of said one group and being displaced therefrom in a direction away from the material to be heated within a predetermined region of said platen to reduce the heating effect on the material by the high-frequency field produced by the platen over said region in comparison with the heating effect otherwise produced in the absence of said displacement, said rod-like electrodes being arranged in the platen at an oblique angle other than 90* relative to the direction of travel of the material to be heated.

8. A stray-field platen as claimed in claim 6 wherein the electrodes of said first and second groups are arranged at a non-perpendicular angle relative to the direction of travel of the material to be heated.

9. A stray-field platen for high-frequency heating apparatus comprising a high frequency energy supply, a plurality of rod-like electrodes arranged in operation so that adjacent rod-like electrodes are connected across said high-frequency supply, one group of alternate electrodes being spaced apart so as to define a path of travel adjacent thereto for the material to be heated and another group of alternate rod-like electrodes being alternately arranged between the electrodes of said one group and being displaced therefrom in a direction away from the material to be heated within a predetermined region of said platen to reduce the heating effect on the material by the high-frequency field produced by the platen over said region in comparison with the heating effect otherwise produced in the absence of said displacement, and wherein the distance between given ones of said alternate rod-like electrodes and said material varies along a portion of the platen in the direction of travel of the material.

10. A high frequency heating apparatus for a material to be heated as it is moved along a given path of travel comprising, a source of high frequency electric energy, a stray-field platen assembly that includes two groups of rod electrodes sequentially arranged adjacent the path of travel of said material to be heated and on the same side thereof, the electrodes of one group being spaced apart and equidistant from the material as it moves along said travel path, the electrodes of the other group being alternately located between the electrodes of said one group with at least some of the electrodes of said other group positioned at a greater distance from said material than the electrodes of said one group, and means for connecting the elecTrodes to the terminals of said energy source whereby different regions of the platen in the direction of travel of the material produce different heating effects on the material adjacent thereto.

12. A heating apparatus as claimed in claim 11 wherein the lateral spacing between adjacent electrodes in a first region of the platen is different than the lateral spacing between adjacent electrodes in a second region of the platen.

13. A heating apparatus as claimed in claim 10 wherein said electrodes are arranged in parallel in the platen at an oblique angle relative to said path of travel of the material.