Apparatus for dielectric heating

May 26, 1953

2,640,141

Μ. P. VORE ET AL

APPARATUS FOR DIELECTRIC HEATING

Filed Oct. 12, 1948

Sheets-Sheet 1

Fig.l.

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May 26, 1953

2,640,141

Μ. P. VORE ET AL

APPARATUS FOR DIELECTRIC HEATING

Filed Oct. 12, 1948

Sheets-Sheet 2

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INVENTORS Milton P. Vore and Robert E. Kirby.

BY zS if.

ATTORNEY

Patented May 26, 1953

2,640,141

UNITED STATES PATENT OFFICE ¢2,640,141

APPARATUS FOR DIELECTRIC HEATING

Milton P. Vore, Catonsville, and Robert E.· Kirby, Baltimore, Md., assignors! .to Westinghouse Electric. Corporation) East Pittsburgh, Pa., a corporation of Pennsylvania

Application October 12, 1948, Serial No. 54,032

Claims.

Dielectric.«heating' usually involves, a · pair/iof • spaced relatively Insulated' electrode-means «between which a high, frequency'eiectricwfield can •«beyestabttshed.· <Dielectric«material placednin, or •moving, through, this-field· will be heated.-, -A -com «mon form- of?apparatussfor’.’Such-.-heating.fon: a large scale includes one « or more dieleetric.-heat > ing-i electrodes' of, considerable;.expanse «or . area.

In .-its·.· broadestj-aspect, pur invention-relates -to ’ improvements in« this-field 'of dielectric -heating; 'Tn its-more limited.· asp.ects;‘.pur&lt;.^,.invention·,relates «to 'improved^dielectric'heating.«apparatustofithe :. aforesaid-type’’which'iutilizes:an.'impr®ved dielec• trie-heating: electrpde.’forrobtaining-improved; results and’:operationsof:the«apparatuS-’foi·. certain .purposes.

»Ini a more/speciflcvf&rm-iof,,,dielectric heating . apparatus,: «dielectric · material». is . carried ·. on, a -.conveyombetween a pair ;of, horizontalletectiOde.· means.;.’and an, air. space·is:pr.ovided'>betw.een:the material- t.andithe supper-.dielectric-heatingt electrode. Under certain: circumstances; an:,electric arc· w.ilfform in the air-gap between the material and· the: electrode. Such arcing has occurred in the edge-gluing together'of pieces of wood boards, ..or,veneering; by a veneer, etc. meaning any one «of a pluiahty of wood boards or wood pieces, regardless of sive or area, that are to be glued.togecher.r .The arcing may be due to glue drops-that «are present on the top layer of a stack of veneers • lorrarersqueezed out of .joints of veneers to be .edge..,glued. >If the dielectric-heating electrode .,-has.atphysical’y continuous surface, as is usually • the. case., the arct travels along with the-material and,idamage thereto may result.

. .An object of our invention is Lq piovitle a dielectric heating apparatus an which such obiee own able arcing is minimized In achieving _:.. this,.object,we .provide a. dielectric-heating ··.electrode- which. electrically,.pr.esents, a, substantially flat surface for the high-frequency electric field, but. .which .physically, presents, a ...discontinuous , surface for interrupting,, any arc,:.tnat strikes in the air-gap between the: material, being heated , and the upper. dielectric-heating electrode......

« In·· the aforesaid·-dielectric heat-treatment for edge-gluing- pieces of wood boards together, the pieces are ..clamped with glue between their facing edges. ’’The.-clamping- is maintained during the process, at .least until the glue or adhesive ,, at the joints has set ..sufficiently to make’clamping unnecessary '.for holding -the, pieces .together.

•In commercial production, pieces of wood stock occasionally . buckle out of the clamps. Our improved apparatus is so- builf-that buckled ’wood:

(Cl. 219—47) stock· usually hasmo;. damaging effect ion:^he-dleiectric^heating-eleetrodesfaithough.the-surface of the''upper.rone:.is«physically:discontinuous.

^l- Another· object &lt;of our .'inventions is:. to provide ^J a novel ''dieleetric^hdating.velectrode· whichvcan • have' its 'effective areacfor 'bounding a high-fre· quency eleGtrffifieldiread-ily and: Simply adjusted.

• An ancillary iobject of our inventionMS’.to pro• vide a dielectric heating apparatus;.of- a’.typ&amp;'de¹⁰ scribed having·-a-pair ot spared! electrode^means providing-.a· horizontal work-receiving, passage ¹ therebetween. . The upper electrode-means «comprises a novel «adjustable¹ dielectric,-heating·,elec• trode Which covers a substantial: but,'adjustable ^io area along the work-receiving passage, but which is mechanically stiff.and will.not sag. in any of . the different adjustments of .the; novel dielectricheating electrode. 'As a-result; the'.top.'of; the work-receiving; ^passage · defined ror ;· bounded·by xo, the· electrode vwill be consistently flat, in effect.

c- Our; novel: idieIectEic»heatingi (electrode «is dis•tinguishedi.by a plurality of thin fiat bars· for the electrically, active surface d thevelectrode. .'-.The ( 'bars; are.’spaced; but are.; close..-/enough «to each 25; ./other -to: provide, m effect; a..continuous,'/electric (ifleldi-along-the passage occupied:by :,the, work; or ’- 'material beingiheat^treated.·--For apparatus, using - a,.w.ork-BarryingiConveyor_t the, bars, extend oblique to the path of travel for the material /passing ..them. . Preferably, a.plui^-alityjofi>'additipnal;simi. larbars are provided which criss-cross the/first mentioned bars. The two. groups of bars are,-thin and pivotally connected so ass.to.Torm; in,'.effect, a lazy-tong arranfzement which is expansible and । contractible, withiri limits. «Preferably,:,the'dazy^3o· tong, arrangement is supported at^; a «.plurality ,of different paints sufficient, in /.number· tp'.limit..any tendency of the thin pivoted «bars -tqisag.

Objects, features and innovations of our,invention, in addition to those specifically set. forth ⁴⁰i· 'above,, will.·be discernible from the'following, de•.•scription whichi is· to- be..taken·;in. -conjunction with the accompanying drawings. In -these «/drawings, dike reference (.numerals refer-to parts . _ haying, the same appeal ance. In the drawings, ⁴⁵ which are on different scales:

Figure 1 is an 'elevutipiial';.vie.w: of;,an.:.embpiiiment of our invehtioniimcorporating- our .'novel dielectrieTheating.'.'elestrode;

₅₀ -Fig. 2 is·, am elevational'-view of another· embodiment of our invention: incorporating «our novel dielectric-heating electrode, this view showing the dielectric'-heating· electrode as it appears ,when-viewed- at a right angle: to its^; show55 ing inFig. 1;

2,640,141

Fig. 3 is a plan view of the preferred form of our novel dielectric-heating electrode shown in Figs. 1 and 2;

Figs. 4 and 5 are detailed sectional views on the lines IV—IV and V—V of Fig. 3; and

Figs. 6 and 7 are perspective views of two forms of bars used in building the preferred form of our dielectric-heating electrode, to which, however, we are not limited.

The embodiment shown in Fig. 1 comprises a paii· of opposed generally horizontal electrodemeans which are indicated in their entireties by the reference numerals 2 and 4, respectively. These electrode-means are vertically spaced to provide a space therebetween which serves as a work-receiving passage. The electrode-means 4 comprises a horizontal metal plate 6 having turned ends 8. An endless conveyor (0 of insulating material has an upper run which rides on the plate 6. The conveyor is wrapped around drums 12, one of which may be driven by any suitable means to move the upper conveyor-run in an assumed direction shown by the arrow in Fig. 1, at the right. The conveyor carries suitable dielectric material 14 through the work-receiving passage between the electrode-means 2 and 4. The plate 6 and the conveyor 10 form a work-supporting means by means of which the material 14 is supported and carried through the apparatus in a linear travel-path. The material is of less height than the extent of the space between the electrode-means 2 and 4, so that an air-gap 16 is present between the top of the material 14 and the bottom of the electrodemeans 2.

The embodiment shown in Fig. 2 comprises generally horizontal opposed electrode-means 2 and 20 which are vertically spaced to provide a work-receiving passage therebetween. The electrode-means 20 comprises a work-supporting means in the form of metal rollers 22 which are rotated by any suitable means for conveying material 24 thereon through the work-passage in the assumed direction indicated by the arrow at the right of Fig. 2. The material 24 may be the same as or different from the material 14. An air-gap 16 is present between the top of the material 24 and the bottom of the electrodemeans 2.

The electrode-means 2 is swingably supported. To this end, in Figs. 1 and 2, each of a pair of spaced structural channels 28 swingably supports a pair of spaced support-arms 30 and 32, through pivots 33 that allow the support-arms to swing in planes parallel to the line of travel of the material 14 and 24. The support-arms 30 and 32 may be made either of metal or of insulation, depending on whether the electrodemeans 2 is to be grounded or insulated from ground.

Secured to the lower ends of the support-arms 30 and 32 are horizontal stub shafts 34 journalled in suitable fingers 30 which carry a metal frame 38. The frame 38 is part of the electrode-means 2. Accordingly, each point of the electrodemeans 2 can swing back or forth in a vertical plane paralleling the direction shown by the arrows in Figs. 1 and 2, in which the work travels. The parallelogram-like support of the electrodemeans 2 allows the electrode means to remain in a horizontal plane as it swings. Obviously, cables, wires, etc. will allow for .an even greater freedom of swinging and other movement.

The electrode-means 2 also comprises a plurality of support-members 40 dependently car ried by the frame 38 and a plurality of electrodebars pivotally carried by the lower ends of the depending support-members 40 and subsequently described in greater detail.

The main purpose for showing the two embodiments of Figs. 1 and 2 is to illustrate the adaptability of the upper electrode-means 2, which constitutes our novel dielectric-heating electrode, with different forms of lower electrode-means of which the electrode-means 4 and 20 serve as illustrations. Thus, for example, a conveyor, such as 10, can be made of metallic material and itself provide the lower electrode. The showing of the two modifications is also to illustrate the adaptability of the electrode-means 2 for use in different positions with respect to the travel-path of the material to be heat treated, that is, with respect to direction in which the material is moved by any suitable conveyor means. With such travel-path as a fixed reference, it is apparent that the electrode-means 2 is shown in Fig. 1 disposed at a right angle with respect to its showing in Fig. 2.

As is known to the art, in a system set up as shown, the electrode-means 2 is electrically insulated from the electrode-means 4 of Fig. 1 and 20 of Fig. 2. Such relatively insulated relation between the respective pairs of electrode-means can be obtained in any suitable way. As an example, Fig. 1 shows the electrode-means 2 grounded. Consequently, the plate 6 of the electrode-means 4 of Fig. 1 should be insulated from ground, and the support-arms 30 and 32 can be of metal. As a second example, Fig. 2 shows the electrode-means 2 insulated from ground. Consequently, the electrode-means 20 can be separately grounded, as shown at 42, and the support-arms 30 and 32 can be insulated, or made of insulating material, or any other suitable expedient used. Obviously other combinations are possible, as for example the electrode-means 2 of Fig. 1 can be insulated from ground and the plate 6 of the electrode-means 4 grounded. Additionally, instead of a grounded circuit-path, a conductor can be substituted.

Assuming, as shown in Fig. 1, that the plate 6 is insulated, a high-frequency electric field is established between the plate and the electrodemeans 2 by electrically connecting power delivering conductors 44 and 46 to the plate 6 and electrode-means 2, respectively. The conductors 44 and 46 receive power, either directly or indirectly, from a high-frequency oscillation-generator 48. The conductor 46 is shown, for convenience, as grounded at 49. For completing the electric circuit, the electrode-means 2 can be grounded either through the members which support it or through a separate grounding conductor connected through a terminal connector associated with the electrode-means in any suitable manner.

The physical construction of the electrodemeans 2 is more particularly shown in Figs. 3 through 7. The frame 38 of the electrode-means comprises support-bars in the form of two spaced, lengthwise channels 50 and 52 interconnected by a pair of outer channels 54 and 56 and an inner channel 58. The channels 54, 56 and 58 are provided with slots 60, 62 and 64, respectively, the slots extending lengthwise in the base 66 of the channels centrally between the legs 68 of the channels. Each slot receives a plurality of the support-members 40 which carry a plurality of electrode-bars. The electrode-bars ¢^640)141

Β β «comprise? narrow; strips or shapes isuch : as ( Shown in Figs. 6 and 7.

The electaode-har of’Fig.· 6, comprises ai.com:.par.atively short strip· TOi having a; center:hole 72 and a pair of end holes 74 and ”76 .whichare >..B /oversize · or ^elongated.' 3The;'Othen..electeodeisbar, ;!sliown->to'®g·;,· 7j comprises* a ;strip”78 /which·-,is approximately twice as long as the’strip-JO. .-The v strip.’ IB is••.providedvWithi a'center hole’ 86>,and • oversize-’or elongated <holes’:82 and84;at’the'*ends ’l( ”Of ’.the (strip. TT-he -strip; ’78 .has'further’holes: 86 i ;and>'88; respectively-half way* between the.holes • ’80 and 82, .and the,holes80:and:’84. Preferably, the -electrode-bars · have · rounded-edges- to’ avoid • ’sharp points, and their'center and end; holes·, are countersunk oh* their undersides.

’ As 'shown in Fig.· 3”’ the electrode-bars or strips ...are arranged to* form- a lazy-tong structure. To this end, .the strips’ are· arranged* in-two-levels •-and-criss-cross each’Other.' The ’strips'in the• lower level* comprise the · long * parallel ’strips·’78 • ’and* ’ diagonally*- opposite ’short 'strips* '70. The strips in the upper * level comprise long -parallel strips 78' and diagonally opposite strips 70'. The ''bottom surfaces of-the strips ineEich level pref er a’bly¹ lie · in· a single- -plane, -within· manufacturing·· and' assembly* tolerances· which-in most cases allow considerable leeway.

• In the· arrangement shown, each lower strip ’78, /except ’ the one at the* upper end of. the lazy'tong·· arrangement, crosses three upper •strips ”78' at intermediate points-along the length of the strip 78, and meets the ends of two* strips’78' at end points of ’the sa-me‘strip-78. Likewise, an - upper strip' '78' in effect , crosses and meets, five lower 'strips -78. - Accordingly, except for the ,out*ermost-strips, -a strip’48 of -the lower level of the •-laay-tong’structure has five; junction- points with the strips 78' of the- upper level, and conversely a'similar strip 78' of the· upper level of the lazytong has five- junction- points with the lower strips '78. ’ Three of the junction points for such strips are at the channels 54; 56 and 58, ahd two are centrally between, theichannels.

Each Of the short end-strips :79 and 70' crosses a,,bar :78 of 78' at a point which is. centrally between’the-inner channel 58 and.an outer channel 54 .or 56. Each of the end-strips 70 and :70' •also has a junction point at. its. .end which,is at -the channel’58, and. a similar point, at,its end which is at a'channel:54:or’56.

The criss-crossed arrangement of, the electrode-strips 70, 70', 78 and. :78'„is. carried from the .channels 54,..56. and 53 by. a plurality of pivot means comprising;the support-members 40..,A support-member 40 is provided :at each junction point of the bar 78 and 78'. that lies at. alchaiinel-54, 56 or .58. Similar support-members .are used at each junction point of the bars 70 and 70' and at the junction points of these bars 70 and 70' and a bar 78 or 78'. In the preferred • embodiment, the support-members are substantially ’alike and : are constructed as shown in Fig. 4.

•Referring in particular to/Fig. .4,. a supportmember 40 comprises a flathea’d brass screw 90 having-an end that passes through the slot 64 in’the channel’58. The lower head-rend of the ..screw-passes-through aligned holes in the strips 18.-and-78', with:the head of the screw-seating· ,in, the., countersunk. hole in the’lower strip 78. ,A.forass:washer;,’32-;lies.between,the crossing’ elec• tiOde-b.ars... A,stop nut ;94,presses a springwash,er- 96.against.,.the,.top.of; the.-jjpperistaip 78' and .forces, the* two:strips :7,8jmcl-'7I8-(:dtotQ'.g0Od;.electri cal contact’Withthe· brass; washer.but.free.enough so that they can-twist-around.·the.screw*90.

The-·* screw .90 carries- a·’thrust-nut; 98 ’Slightly -above, the-stop* nut ®4? a--compression spring ’100 above the thrust nut;· a lower· roller means 102 ’above: the spring MO-and -below ’the-'channel 58, -an.· upper -Toller means’; 1 fl4 .above ; the channel, . andlocking nuts’; !'fl6*and4fl8.

’’ Each of’the-roller means 1-02 and 104 comprises • a plate support · 1'1 &amp; having a. hole through which the- se-rew-68 ’ freely*-passes-,· a; pair of stub'.shafts • ti 2- and’ i 14 extending *in -opposite directions · out'wardly from the - plate support* Ί IS,· rollers I ί6 and- I’I S-carried· respectively*-on the-stub’shafts i-‘i42‘-'and-‘t44;--and :suitable- retaining means for holding· the rollers on’the stub-shaft·,'the- retain • -ing··’means-being* indicated, as -cotter- pins¹120.

’’Sy'turning’the* holding-nuts-ISS and* i08; the • ’distance of* the ’eleetroc¹ a-bars 70,40'· -78- and 78' ’above - the’ lower ’electrocie-ineans 4 of :20,- as the case-may be-,-can foe controlled. -Moreover; the 'different * junction- points of the bars can be individually-adjusted- so as to- make the. surface of the’electrode-strips as level as convenient-or-.de• sired. -After such, adjustment,’ the’-thrust nut 98 can be· moved· to compress· the spring··· l·GO so as · to • -determine· the force, with which the .roller means ,’ί’32 and 104 press.-against the bottom and top.of _; the channel 58.

To assure- good electrical conduction .between a.channel and the roller, means, smooth narrow brass strips’ 123 -are-secured to each-channel 54, and :58 along .-each side of the slots therein, coextensive -therewith. The strips 122 may be .35 on the: upper or ;on' the; lower Sides, of ,the chan• riels or. oh both sides.. Iri. the embodiments.sho.wn, they are only on. the lower sides. The rollers l ie and ί 18 of the ..lower roller means ..1,92 j-ide oil'these strips ‘122.· The. electric'.circuit,passes 40 through the rollers to.’the screws'90 and the strips 70, 70', 78 and 78'.

. At each of the junction points, of the electrode: strips between’; the. channel members,, .a, pivot means T24:is provided for holding: the strips, to,45 gether, and to. provide, good” electrical, contact therebetween. . A ..preferred form, of construction for such pivot means, is shown more, particularly in Fig; 5. It comprises a-.short brass screw .,1,26 / which seats in the .countersunk .seat, of, a .lower 50 electrode-strip, and. passes; through the ..crossing strips; , being held, by, a, stop nut, ,128,. pressing against a spring washer 130. To allow for ..greater freedom, of. movement., .between,,the. crossing strips .and; for, good electrical ..contact. therebe55 .tween .a brass, washer: t82&lt;;can be,provided, .therebetween.

Fig, 3. (shows.,the.....lazy-tong,..arrangement. ;of electrode-bars (slightly., extended. . The. upper ..strips,! 8'. are all,.parallel, and equally spaced; ,hav60 ing., their ends at the. slots, in the outer, channels 54 ,and;56. These strips, are,oblique to these,channels but. deviate, only slightly, from a. perpendicular .thereto. (.. The lower, strips, 78,. obliquely. cross the. ..upper .strips ,78', and ,also...have their ..end 65 ..points at the slots in the outer .channels 54,and 56. (The inner.channel 5.8 serves as a further, supporting point;,for .each, strip. ’’ The .intermediate pivot points 12 4, help , to prevent sag in,the strips at the .junction points between channels. The crossing 70 -strips ..provide a perforated electrode-means having a plurality of diamond-shaped openings,; The openings .are arranged in rows with ,the openings ..in a row being staggered with respect to the openings in the adjacent rows, the staggering being .such that no straight line can be. drawn across the

2,640,141 electrode-means without cutting across an opening. It is also to be noted that each opening provided by the criss-crossed strips has nonuniform lengths at different parts thereof, measured in parallel directions.

Preferably, a large number of strips are provided in order to produce the electrical effect of an electrode-means consisting of a solid metallic sheet. It is known that a perforated metallic sheet can provide the effect of a solid piece of metal for bounding an electric field if the openings in the structure are not too large. In a typical lazy-tong structure, such effect was obtained by using long aluminum strips of close to 60 inches in length, and short aluminum strips slightly more than half that long. The number of strips used correspond to the number shown in Fig. 3, in a frame having dimensions that were approximately 56 inches by 46 inches, the shorter dimensions being that in which the lazy-tong structure could be expanded and contracted. With the arrangement of the electrode-strips in the manner shown, with their flat faces facing the opposed electrode-means 4 or 20 and their narrow edges upstanding, the strips as a whole can be said to lie on the same level when they are spaced far enough from the opposed electrode-means 4 or 20 and they are sufficiently thin. In the specific embodiment described, the strips were A inch thick, and the work-receiving passage 1 to 3 inches high.

Obviously, by loosening the thrust nuts 98, the lazy-tong structure can readily be spread out or collapsed for increasing or decreasing the crisscrossed area encompassed by the structure. The nuts can then be retightened. Loosening the nuts 106 and 108 also permits the lazy-tong structure to be extended or contracted, but may require more caution in order not to change the vertical spacing between the electrode-means.

The holes 74, 76, 80, 82 and 84 in the electrodebars or strips are sufficiently oversize or elongated to allow the lazy-tong electrode-means 2 to be adjusted so as to occupy any desired portion of the area of the frame 38, from a maximum determined by the length of the slots 60, 62 and 64 to a minimum determined by the width of the strips. By adjusting the angle which the strips make with each other, and corresponding with the angle which each strip makes with the channel members of the frame, the effective area for the electrostatic field of the electrode-means 2 is correspondingly changed.

If the electrode-means 2 is arranged as shown in Fig. 1, the overall length of the electrostatic heating field can be changed in the direction of movement of the material 14. Such an arrangement is more likely to be used where the width of the material being heat treated remains fairly constant. If the electrode-means 2 is disposed as shown in Fig. 2, the overall width of the electrostatic heating field can be changed in a direction transverse to that in which the material 24 moves. Such an arrangement is more likely to be used where the width of the material being dielectrically heated will vary from time to time and it is desirable to adjust the electrode-means to a corresponding width. In this latter arrangement, should an arc strike from the material to one of the electrode-strips, it will ultimately reach an opening formed in the criss-cross arrangement of the strips. As the point of origin of the arc moves into the opening, the arc elongates and becomes extinguished. In the meantime, the spot of glue or other material which caused the arc to strike has a chance to become burned out. For such arc-extinguishing operation, it is desirable to provide a minimum spacing between electrode-strips on the same level, the spacing being such that an opening will always be encountered by an arc moving with the material.

Oblique strips in a single layer only also provide an open space for elongating any arc occurring in the air-gap 16.

If a more direct contact for an electrical circuit to the electrode-means 2 is desired, one or more of the electrode supporting-members 40 can be provided with a terminal connector 134, as shown in Fig. 4. The connector is held in place on a screw 90 by a holding nut 136. The terminal connector 134 receives a conductor 138 which maybe insulated or grounded so as to correspond to the conductor 46 of Fig. 1. In order to carry the electricity readily from the connector to the various electrode-strips, the parts of the electrode supporting members 40 that may be called up to carry current are preferably made of brass, and for economy the channels of the frame 38, and the various electrode strips 70, 70', 78 and 78' can be of aluminum.

There is a distinct advantage in providing a plurality of support-members 40 for carrying the criss-crossed strips. The relatively elongated screw 90 of each support-member allows for limited vertical adjustment of the levels of the strips 70, 70', 78 and 78', through raising or lowering the holding nuts 106 and 108. The nut 98 can be adjusted for a suitable compression of the spring 100.

A swinging support for the lazy-tong, such as provided for Fig. 2, and obviously also applicable to Fig. 1, also has a distinct advantage in case any material being dielectrically heated should buckle. The electrode-means 2 can swing when a piece of buckled board should hit it, as may sometimes occur in edge gluing where a plurality of elongated narrow veneers or boards are placed lengthwise on the conveyor means with their upright edges to be glued together. A safety switch such as 140 can stop the conveyor motor through a motor controlling relay 142, when the electrodemeans swings. The buckled boards can then be removed, or the electrode-means swing out of the way to permit the boards to pass.

While we have described our invention in fairly particular detail, it is obvious that these details are subject to wide variations and that many modifications can be made thereof.