US2946168A

US2946168A - Method and apparatus for sealing metal foil

Info

Publication number: US2946168A
Authority: US
Inventors: Joshua G D Manwaring; Raymond H Cota
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1957-10-08
Filing date: 1957-10-08
Publication date: 1960-07-26
Anticipated expiration: 1977-07-26

Description

July 26, 1960 J. G. D. MANWARING ETAL 2,946,168

J. G. D. MANWARING ETAI- July 246, 1960 ATUS FOR SEALING METAL FOIL 8 Sheets-Sheet 2 Flled Oct. 8, 1957 July 26, 1960 J. G, D. MA'NWARlNG ETAL 2,946,168

METHOD AND APPARATUS FOR SEALING METAL FOIL.

Filed OCT.. 8, 1957 8 Sheets-Sheet 25 Iawezzbads:

July 26, 1950 J. G. D. MANWARTNG ETAL 2,946,168

METHOD AND APPARATUS FOR SEALTNG METAL Fon.

Filed Oct. 8, 1957 8 Sheets-Sheet 4 EQ. //6b July 25, 1960 .1. G. D. MANwARaNG ETAL 2,946,168

METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8. 1957 8 Sheets-Sheet 5 8/ l .i sii? l g FIG. 7. l l l l i 1 l (fi I r`\ "um W ugr L ava /Vl x1 7M 7m Il INVENTOR:

ATTo'RNEv July 26, 1960 METHOD Filed OCt. 8, 1957 J. Gv D. MANWARING ETAL 8 Sheets-Sheet '7 T GENERATOR Eig 1 a. l f

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METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8, 1957 8 Sheets-Sheet 8 United States Patent Olice 2,946,168 Patented July 26, 1960 METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8, 1957, Ser. No. 688,963

13 Claims. (Cl. 523-230) This invention relates to methods and apparatus for use in the packaging of materials with which metal foil wrappers, such as aluminum foil, are utilized. More specifically, the invention is concerned with the packaging of chocolate covered candies and various candy products, as well as other substances, in aluminum foil wrapped containers.

In a presently employed form of aluminum foil used in wrapping candy boxes in packaging machines, there is included the metal foil itself over which is supported a thin coating of a wax-like adhesive material capable of melting in the presence of heat. The wax-like coating is in turn covered with a very thin layer of tissue or other fibrous sheet material. In sealing together overlapping surfaces of such a foil product when wrapped around a container, a suflicient amount of heat must be employed to melt or fuse the wax-like adhesive so that it will strike through the tissue and become bonded against an adjacent wrapper surface.

ln attempting to satisfy the heat requirements by conventional forms of heating equipment commonly employed in packaging machines and involving the use of heated applicator bars or similar instrumentalities, serious difficulties are encountered. In order to obtain an adequate heat flow, the package must be held in contact with the heating element over a substantial period and along a contact area of considerable length. This arises from the fact that the aluminum acts as an insulating member which tends to retard flow of heat inwardly to reach the wax-like adhesive. It will be appreciated that an adequate heat flow to permeate the aluminum foil will necessarily exert a considerable heating effect within the container, and this heat tends to become held within the foil Wrapped container since the aluminum is equally effective in preventing heat dissipation. The net result is damage to the chocolate covered candy with its appearance being changed undesirably and its quality and salability greatly impaired.

The speed of operation of conventional packaging machines utilizing other forms of wrapper material further complicates the problem, since the period required for heating the aluminum foil may require an appreciably longer period than is usually the case, and thus the eiiiciency of the packaging machine is lowered and output re tarded. The trate of packaging with conventional sealing equipment normally is usually not greater than fifty units per minute and this rate itself is less than that possible with well-known packaging machinery where sealing is not a factor.

It is an object of the invent-ion tov deal with the problems indicated above and to devise methods and apparatus for applying heat to a metal foil Wrapped container filled with chocolate covered candy, or other products, in such a manner that an adequate sealing or bonding is accomplished without undesirable heating of the container space or products held therewithin.

Another object of the inventionA is to provide a method and apparatus for increasing the speed of sealing operations for metal foil wrappers and also to increase the practical rate of operation of packaging machinery operation Vbeyond the standard output rate of machines equipped with conventional sealing apparatus. Still another object of the invention is to combine with a method and apparatus of the class described means for protecting the packaged material against excessive heating, either from exposure to excessive heating conditions or extended heating periods.

With these objectives in mind, we have conceived of a procedure for applying radio frequency heating to aluminum foil wrappers, as well as other metal foil wrapped packages, and we have devised a heating apparatus for sealing metal foil containers in conjunction with an automatic packaging operation at that point at which the metal foil wrapper has just been applied to the container. In one preferred aspect of our invention, a carefully controlled heat cycling apparatus is caused to operate and to energize a heating coil as the foil Wrapped package moves into a sealing station in the packaging mach-ine.

An important feature of the apparatus of the invention is the combination of a heating coil arranged in a special conformation, with the heat cycling means, whereby exceedingly high frequency heat may be produced for carefully limited intervals of time and along a sharply localized elongated zone of seal-ing with which folded ap portions of a metal foil wrapper may be held in register.

We find that this step of controlling high frequency heating may `be repeated at relatively high speed so that the continuous sealing or bonding operation may be satisfactorily synchronized with the conventional feeding and Wrapping cycle of a standard packaging machine without in any way impairing the efficiency or output of such machines and, in fact, the equipment of the invention renders it possible to increase the rate of output of such conventional machines.

We have also found that our method and apparatus for sealing may be successfully employed with various arrangements of flap portions and folded sections of metal foil wrappers applied either -to chocolate covered candies, other types of candies or products such as frozen foods, butter, margarine and others. The foil or other metallic wrapper may be aluminum or any other suitable electrical conductor.

These and other objects and novel features will be more fully understood and appreciated from the following description of a preferred embodiment of the invention selected for purposes of illustration and shown in the accompanying drawings, in which:

Fig. 1 is a fragmentary perspective view showing portions of a standard type of candy box packaging machine commonly employed in the trade;

Fig. 2 is another fragmentary perspective view of the machine shown in Fig. 1 but viewed from an opposite corner thereof;

Fig. 3 is a detail cross-sectional view showing a porltion of the mechanism of the packaging machine shown in Figs. 1 and 2 and particularly illustrating a metal foil wrapped container in the position in which it has been advanced to a sealing station for receiving high frequency heat in accordance with the invention;

Fig. 4 is a cross-section taken on the line 4 4 of Fig. 3.

Q Fig. 5 is a perspective view showing a metal foil wrapped candy box with portions of the wrapper having been broken away to indicate more clearly the line of sealing of the flap portions;

Fig. 6 is a diagrammatic view showing in detail the con- B formation of the work coil of the invention and its supporting base removed from the sealing station;

Fig. 7 is a plan View of transformer apparatus of the invention shown independently of electrical circuitry and coolant connections;

Fig. 8 is a cross-section taken on the line 8-8 of Fig. 7;

Fig. 9 is another ,cross-section taken on the line 9-9 of Fig. 7;

Fig. 10 is a diagrammatic view further illustrating details of the heat cycling switch means of the invention and further illustrating the electrical connection of this member with respect to other radio frequency generating equipment;

Fig. 11 is a cross-section taken on the line 11-1111 of Fig. l;

Fig. 12 is a schematic view illustrating a cooling arrangement for a portion of the radio frequency generating equipment; Y

Fig. 13 is another schematic view illustrating a second cooling arrangement for anotherY part of the radio frequency generating equipment; and

Fig. 14 is a current flow diagram employed in furnishing radio frequency current in accordance with the invention to the sealing station.

Referring more in detail to the drawings, the apparatus shown includes, in general, a sealing unit which is adapted to be held momentarily in contact with a metal foil wrapped box of candy; electrical means for inducing a high frequency heating effect in the sealing unit, heat cycling cam switch means for controlling the operation of the high frequency induction heating means; and mechanical feeding and wrapping mechanism for placing a metal foil wrapper in folded position about a box of candy and advancing the wrapped box into the sealing station where it may overlie the sealing unit.

It will be understood that the sealing unit, together with the high frequency induction means and the heat cycling switch apparatus, although shown in combination with one specic form of packaging machine, is not limited thereto, and the following description of the operation of the various parts is intended to be illustrative of application of the sealing unit and its related components to any other well-known packaging machine.

Referring more in detail'to Figs. 1 3, inclusive, arrow A denotes generally a packaging machine of the class in which a wrapping material such as metal foil is fed from a feed roll mechanism B into one side of the machine with successive lengths being cut off to provide for a continuous wrapping operation. At the left-hand end of the machine P, as viewd in Fig. 3, there is provided a conveyor 2 which is adapted to receive and advance a box filled with candy in a direction from left to right. At an intermediate point in its forward travel, the filled box of candy moves into a conventional elevator device which raises the box upwardly into engagement with a wrapper which becomes folded therearound. t

A portion of the conventional elevator and folding mechanism isl shown somewhat diagrammatically in Figs. 3 and 4 wherein numeral 4 denotes a link-actuated elevator platform. The platform is shown in Fig. 3 in a fully raised position and'supports a package P in a partly engaged position with a metal foil wrapper W. A side conveyor C furnishes the metal foil wrapper which, as suggested in one position of the elevator platform noted in Fig. 4, is first caused to assume a position in which it will be directly above the elevator in a lowered position. As a package P2 comes onto the elevator platform and starts to rise, it will come into contact with the wrapper and force it upwardly into position such as that represented in Fig. 3 by package P.

Immediately after the package P reaches the position shown in Fig. 3, a folder 6Y folds one flap portion againstv opposite ap is folded into place. It will be understood that the machine operates in such a manner that one complete cycle of operation occurs to handle a single package with each rotation of the feed roll mechanism B from which foil is delivered. Y

In the operation of conventional sealing mechanisms in well-known packaging machines, sealing may be accomplished along one side of the box in one step and along opposite ends of the box in another step. Further details of packaging machine operations of the class referred to are described more fully in United States Patents 1,308,322, 1,329,236, 1,330,354 and 1,283,342.

In accordance with the present invention, in one preferred form, inductionV heating is applied along that side of the box which is of greatest length where most difficulty has been experienced. Thereafter, the flaps at opposite ends of the box may be folded and sealed using either conventional heating alements or, if necessary to avoid overheating, a further application of induction heating of the invention. Y

The apparatus of the invention hereinafter described, therefore, has been designed specifically for applying induction heating to overlapping portions of foil at a longer side of a box, it being understood that this heating operation may be repeated by substantially similar sealing means, ifdesired, in connection with sealing folded end aps or any other foil portions which are required to be secured.

Considering'in detail the sealing unit itself, an important factor is the location of this sealing unit in a position'such that the box may pass immediately into contact therewith as soon as the aps are folded into overlapping relationship to one another. This arrangement has been indicated diagrammatically by box P1 in Fig. 3. The sealing components inthe position noted occur between the elevator mechanism 4 and a second conveyor member C2 shown at the right-handV side of Fig. 3.

A further important feature of the invention, therefore, is the combination with the elevator mechanism and foil feeding components of the machine, of a sealing unit consisting of a supporting base 10 in which is embedded a special Work coil of the invention. By locating the supporting base 10V with its upper surface lying in the plane of travel of the overlapping foil aps at the underside of the box, it is possible to hold the overlapping portions snugly against one another at all times. At one point, the box may come to rest momentarily and the high speed heating cycle of the invention may take place.

It is pointed `out that each heating cycle must take place during one cycle of operation of the metal foil feed roll mechanism and the precise points at which heating is initiated and terminated must be carefully timed to allow a wrapped box to advance to the sealing station. At the same time,Y the period of heating, because of its intensity, must be substantially less than the time remaining before the roll mechanism B has completedv a single cycle of operation. This necessitates interrupting the operation of the work coil.

In meeting the needs of an adequate sealing of the metal foil flap surfaces and yet avoiding excessively heating the box interior, we have found-it necessary'to devise a special work coil conformation and to energize this work coil by a unique transformer apparatus. The transformer. apparatus is mounted at one side of the packaging machine A and is generally denoted by the arrow T in Fig. l. 'Heat cycle cam switch means for controlling the transformer apparatus T is combinedwith a suitable rotating part of the packaging machine A, preferably at an Aopposite side thereof on a gear G (Fig, 1) associated with the metal foil feed roll mechanism B.

In Figs. 5 and 6, we have illustrated the special coil conformation found to satisfy the; particular sealing rcquirement of metal foil onboxes filled with chocolate covered candy when energized in a particular manner, as hereinafter described.V In Fig. 5, we have shown a box P2 in an inverted position after it has been sealed and also indicating a bond of sealing L with a portion of the flap turned back.

As shown in Fig. 6, the work coil unit consists of the supporting base l comprising a plastic such as fibre glass or other well-known dielectric material in which is supported, preferably in an embedded state, a copper tubing element 16. This tubing element constitutes an electrical conductor which is reversely bent upon itself to form two adjacent coils which include outer coil sides 16a and 16b and inner `adjacent coil sides 16C, 16d and 16e. The inner adjacent coil sides 16e, 16d and 16e are carefully arranged in parallel coincident relationship in such a manner that they form inner current paths, as noted by the arrows, which Iare yadditive and which are capable of inducing an electromagnetic field of exceedingly high heating capabilities. This heating eld is concentrated in -a narrow region which may be, for example, about 1A- inch wide and of a length consistent with the length of the box side along which sealing may take place las, for example, a length of 10-15 inches.

An equally important factor in the concentration of heat thus accomplished at the region 4of sealing noted is the functioning of the outer coil sides 16a and 1Gb. These two opposite sides provide relatively low heating since they `act as high heat dissipating paths.

It is pointed out that the ability of these outer coil sides 16a and 16b to dissipate heat can be greatly increased by widening the outer coil sides by means of flanges or similar structure which `tends to spread the current so that the difference between current at the outer coil sides and current at the inner adjacent coil sides becomes even more pronounced. Such a coil conformation, we find, is capable of producing an electromagnetic field when energized by a suitable high frequency current -of an order of magnitude of from 500 kilocycles up to 1,00() -kilocycles In order to furnish the work coil with radio frequency current of the frequency characteristics indicated, we have found that it is necessary to employ a special transformer apparatus such as that illustrated in Figs. 7, 8 and 9. This transformer apparatus comprises essentially -a power supply and oscillator circuit in cornbination with a special tubular coil conformation constituting the primary and secondary of a transformer device. In this special transformer coil conformation, there are employed coils of copper tubing which extend away from a common center ground in the same direction of turning. By means of this arrangement, the coils do not buck one another and a startling increase in coupling is accomplished at a relatively low potential so that insulation difficulties are at a minimum.

Numerals

200 and 200 indicate the two primary coil components whose outer ends are connected by a conductor 200a. Numeral 400 indicates the secondary disc element. This secondary disc element `400 consists of a split annular body of short axial length and formed from a low resistance material such as copper. The split ends ofthe annular body 400 are provided with electrical output members 600 and 800. These members 600 and 800 have supported therethrough two sections of a high current type Work coil member 16, which sections are made up of tubular copper conductor portions whose ends are detachably connected by threaded couplings to respective

tubular extremities

700 and 700 of a coolant conduit 700. This conduit member is secured to the secondary 400 and extends around its outer peripheral edge, as shown in Fig. 7. A coolant, such as water, is supplied and removed through the connecting ends 140 and 160 which are, in turn, connected to a suitable supply source.

The

primary coil components

200 and 200 may, for example consist of a continuous length of copper tubing which is folded or bent over upon itself to provide a common junction or meeting point 210, as shown in Figs. 7 and 8. The two components are arranged in the form of two dished `or axially displaced spiralling coils so that the turns of each coil project outwardly from either side of the secondary 400 `and extend in the same direction to thus constitute mirror images of one another.

The two outer ends of the coils are connected to a source of R.F. power of relatively high potential, such as 5,000 volts and each coil is grounded at a common ground point through a ground strap attached to the junction 210. Power is delivered to the coils `as R.-F. high voltage impulses which are conducted along the surface of these tubular coils. A coolant, such as water, is circulated through the coils from a suitable supply source which may be taken from the same source of supply for cooling the secondary member. Each turn of the primary coils is covered with a solid type insulation material which provides limited insulation with optimum induction effects and, in addition, each of the primary turns are supported upon spacing wedges 220 located at several points around the two opposite surfaces of the secondary disc 400, as best shown in Figs. 8 and 9. These wedging members thus control the degree of axial displacement of the respective primary coils from adjacent secondary surfaces and thus provide a convenient means of decreasing the spacing of the primary coils with decreasing voltage potential which ranges from a maximum at the outer peripheral edges of the secondary to a minimum at the inner peripheral edges thereof. The water cooling system for the secondary is Ifurther shown in Fig. 12. Similarly, the cooling system -for the primary is shown in Fig. 13. Numerals 201 and 2M are rubber water coils and 263 is a tank condenser with a drain 204.

The structure described is characterized by several important features, all of which combine to produce relatively heavy current carrying capacity with small loss and to cooperate with the special design of the coil 16. The principal feature to be noted is that the secondary in the particular position in which it is arranged relative to the primary is adapted to produce a very strong coupling of magnetic flux. This is because the secondary occurs in the center of the primary in the rst instance, and in the second instance, the arrangement is such that much less voltage insulation is required to `avoid trouble. By bringing the primary very close to the secondary, as is achieved by having ltwo sets of spiralling coils at either side of the secondary, a maximum of coupling is achieved at all points with the adequate amount of voltage insulation being provided for. Moreover, it is pointed out that there is a voltage condition which is at its maximum in entering the primary where the spacing of the dish spiraling coils is greatest, and the voltage tapers to a minimum` where the spacing of the two sets of coils is. at a minimum or nearly zero magnitude.

In Fig. 14, we have illustrated a current flow diagram for the transformer apparatus T. Also included are electrical power supply means, an oscillator circuit, together with the primary coil and secondary parts of Figs. 7, 8 and 9 with the latter member including the work coil 16 which, las shown in Fig. 5, is embedded in the supporting base 10 of the sealing unit.

Voltage from a suitable supply line is stepped up to a desired voltage, such as 3500 volts. Rectifier tubes 5' change the voltage to pulsating D.C. voltage. Current from the power supply plate transformer 7' flows to oscillator tube 13 passing through a tank coil 1-6' and then to the radio frequency transformer primary 200 toground.

The rectified voltage is applied between the plate of the oscillator tube 13 and the filament of this oscillator tube providing a voltage which controls the ow of electrons `from the tube `filament to the plate. The flow of electrons through the tube is partially controlled by the grid bias voltage which is negative at the grid with respect to the filament and is obtained by the flow of grid current through the grid resistor.

As soon as the voltage is applied to the oscillator tube 13', current flow starts oscillations in the tank circuit,

7 including the tank coil 264)` and coil 16'. The rate or frequency at which the current flows back and forth in the tank circuit is determined by the inductance of the tank coils 200 and 16 and the capacitance i5. A high radio frequency voltage is developed across the tank coil due yto the high current owing in the tank circuit. This high radio frequency current flowing in the primary of the transformer induces current in the secondary 461B of the transformer due to the mutual inductance of the two windings, as above described. When an electrical conducting materialis placed in the electromagnetic field formed by the radio frequency current owing in the work coil 16, current is induced into the material. Since the current is reversing at a high rate, friction is created between the molecules of the material, thereby developing heat.

In Fig. 10, we have illustrated the heat cycling cam switch apparatus which we combine with the circuit of Fig. 14 to control the operation of the work coil. As shown in Fig. l0, a shaft rotation switch 59 of some conventional nature, such as the Zero Speed Control manufactured by The Winter-burn Manufacturing Company of Putnam, Connecticut, is fixed to a shaft 52 which -is located at the upper side of the packaging machine A. This shaft is Vgeared to drive which rotates the feed roll mechanism B and is indicated in Figs. l and 2. Rotation of shaft 52 holds the contacts of switch Si? in a closed position and, as soon as the shaft i) stops turning, the circuit is opened in the conventional manner.

In series with the shaft switch Sit is a second cam activated microswitch 51 of the invention which is connected into `one side of the line running to a grid of the rectifier tube 5 in Fig. 14. This microswitch is mounted above the shaft of roll B in a position such that a spring con- -trol arm 54 normally rides on a cam 56 and maintains the circuit in a closed state. The cam S6 is supported on a suitable shaft of feed roll mechanism B, as shown in Fig. 2 and, as indicated in Fig. ll, is madeup of two cam segments 56a and 56b secured in spaced relation on the shaft by set screws as 56e and 56d. By varying the position of the cams relative to one another, a dwell 56e is provided and this dwell may be varied through any desired larc to control the period in which the switch 51 may remain closed and, in particular, a time interval of limited duration for heating is accomplished. A cam adjustment which will provide for the switch being closed for a 320 interval is suitable for properly limiting the heating period of coil 16.

With the arrangement described, a desirable protection against undesirable heating is realized either from the machine stopping or for any other reason. At the same time, a very precise cut-off of intense heating may be realized.

By means of the combination of special work coil shape and special transformer apparatus for energizing this work coil shape, an intense narrow band of heating is accomplished in a carefully limited time interval. Highly intensied heat is developed by fthe particular electro-V magnetic eld induced in a metal foil surface which is momentary held above the work coil 16. As a result, we nd that we are enabled to melt or fuse the wax-like adhesive on the metal foil, earlier described, in such a rapid manner that theY melted adhesive instantly strikes through the tissue backing of the aluminum foil and a part of this fused or melted adhesive becomes transferred onto an adjacent ymetal foil surface of an underlying flap.

the outer exposed surfaces of the metalV foil. rIhis is irnportant'since the metal foil is found .to take a ne finish of printed material greatly enhancing the value of the foil as a wrapping material. By controlling our heating operation in the manner described, there is no change in this printed material on exposed surfaces ofthe wrapper.

Still a further advantage realized in this rapid high intensity heating step is an increase in the capacity of the machine as compared with its capacity when using conventional heating means. We find that we may utilize our induction heating method and apparatus to step up the rate of operation, for example, from 50 sealing operations per minute up to to 1GO sealing operations per minute `or higher. This is a substantial improvement in package machine operations using metal foil. The heat cycling cam switch apparatus, in addition to performing the described control of the heating period, affords another desirable advantageV in that exceedingly long life may be realized from the apparatus described and the possibility of breakdown or early wearing outof more conventional parts, such asY time control relay mechanisms, is avoided. Finally, in conjunction with all of the above recited advantages, there is realized a simplification of installation of heating 4means in any standard type of packaging machine and a much greater degree of exibility in the use of such machines is present.

it is contemplated Vthat the method and apparatus of the invention may be modified in various respects wherein the basic combination of special work coil shape and special Vtransformer energizing means may be adapted to varying types of packaging machinery and to meet the requirements of varying demands in shapes and sizes of metal foil wrapped containers for a wide range of products.V Although a single band of sealing has been disclosed with the special work coil shape of the invention, it will be appreciated that two or more bands of sealing or various other arrangements of bonding overlapping surfaces may be accomplished by the invention.

Therefore, while we have shown and disclosed preferred embodiments of the invention, it will be understood-that changes and modifications may be resorted to within the scope of the appended claims.

Having thus described our invention, what we claim is:

I. An induction heating apparatus -for sealing metal foil, said apparatus comprising a sealing unit consisting of a supporting base and a work coil embedded in theV supporting base, said supporting base presenting an upper at surface for receiving a foil wrapped package with overlapping foil portions occurring at the underside of the package, said embedded work coil means including two elongated inner coil sides occurring in parallel spaced relation -to one another in close proximity to the surface vof the supporting base thereby to form inner current paths of high intensity and said coil further including two outer coil sides which provide high heat dissipating paths and said inner coil sides being spaced to define a narrow elongated zone of heating which substantially corresponds to the area along which the said foil portions overlap and electrical transformer means for energizing said work coil.

2. A structure according to claim l in which the work coil consists of a continuous length of electrically conductive tubing.

3. An apparatus according to claim 1 including switch means for controlling the Voperation of the transformer, said switch means including adjustable cam segment mechanism for controlling the time interval during which the transformer remains energized.

4. ln a packaging machine for applying `a foil wrapper to a container, means for advancing and supporting a container in a position to receive the wrapping material, means for folding the wrapping material :about the container to provide over-lapping foil portions, a heat seal unit for temporarily supporting the container while the overlapping wrapper portions are held in contact with one another at the underside of the container, said sealing unit including a dielectric base having a at supporting surface, a work coil embedded in the dielectric base 1n close proximity to the flat supporting surface, said work coil including inner coil sides which dene current paths of high intensity yand outer coil sides which constitute high heat dissipating paths.

5. An apparatus according to claim 4 in which the inner coil sides are arranged in spaced relation to define a zone of heating which corresponds approximately to the area included by the overlapping foil portions.

6. An apparatus according to claim 4 including transformer means for energizing said Work coil 4and switch means for controlling operation of said transformer, said switch means consisting of a cam segment mechanism and micro switch which opens and lcloses a circuit through the transformer during each wrapping cycle of the packaging machine and said cam segment mechanism being adapted to vary the period during which the transformer is energized during each machine cycle.

7. In -a packaging machine for applying a foil wrapper to a container, means for 'advancing and supporting a container in a position to receive the wrapping material, means for folding the wrapping material about the container to provide overlapping foil portions, a heat seal unit for temporarily supporting the container While the overlapping wrapper portions are held in contact with Ione another at the underside of the container, said sealing unit including a dielectric base having a flat supporting surface, a work coil embedded in the dielectric base in close proximity to the flat supporting surface, said work coil including inner coil sides which deline current paths of high intensity and outer coil sides which constitute high heat dissipating paths, transformer means for energizing said coil, electrical switch means for controlling the operation of the transformer, said switch means including means for interrupting operation of the transformer whenever the packaging machine cornes to rest and a second micro switch mechanism for providing a predetermined dwell during which period the transformer is held in operative position while the packaging machine is running.

8. In a packaging machine, means for feeding a container forwardly, means for applying 1a metal lfoil wrapper about the container with its edges in overlapping relationship to one another, mechanism for advancing the foil wrapped container into a sealing station, a container supporting member located in the sealing station and having a Work coil embedded therein, said Work coil being arranged to define a heating `area which extends in a relatively narrow zone coinciding lwith the overlapping portions of the metal foil wrapper, transformer apparatus for furnishing radio -frequency ycurrent to said Work coil, and means for interrupting the ilow of current from the transformer to the work coil periodically, said means for interrupting the flow of current comprising a switch which is normally closed when the machine is applying the metal foil wrapper to the said container and which is opened lwhen the packaging machine is at rest, and ya second cam actuated switch arranged to open a ycircuit from the transformer apparatus to the work coil after a time interval has elapsed of a duration less than the time interval required for the machine to make one cycle of operation.

9. A structure according to claim 1 in which the transformer device includes a secondary electrical conductor, a primary electrical conductor consisting of two spacedapart coils supported at opposite sides of the secondary electrical conductor, Said coils being joined together at a common central ground point and having their outer ends connected to a common terminal, each of said coils having its constituent turns originating in close proximity to the secondary electrical conductor and extending away from the common ground point in the same direction, whereby high voltage impulses applied to the primary will produce flux paths for the two coils, which flux paths combine in series and are additive.

ll0. An apparatus for sealing metal foil comprising a supporting base for receiving an enclosure body which presents overlapping metal foil portions, means in said supporting base for selectively applying heat which is localized on adjacent surfaces Iof the said overlapping metal foil portion to bond the surfaces without appreciable change in temperature within the enclosure body, said means for applying heat including an electrical transformer device for producing radio frequency current and work coil means mounted in the supporting base for receiving said radio frequency current and producing a lacalized electromagnetic iield of high voltage characteristics, said -work coil consisting of a tubular conductor consisting of two loop portions, said loop portions being arranged one -beside another to define two opposite outer loop sides land two inner adjacent loop sides, said inner loop sides occurring in substantially parallel relationship to coincide with one another and to form inner current paths which are additive and which are capable of inducing a relatively high heating effect, and said opposite outer loop sides providing relatively low heating, high heat dissipating paths.

l1. In an induction heating device for sealing metal foil surfaces to one another, electrical transformer means for producing radio frequency current and work coil means constructed and arranged to receive radio frequency current from said electrical transformer means, said work coil means comprising a tubular conductor consisting of two loop portions, said loop portions being arranged to fdene two opposite outer loop sides and two inner adjacent loop sides occurring 'm substantially parallel overlapping relationship to coincide with one another and to form additive inner current paths -for inducing a relatively high heating eifect and said opposite outer loop portions providing Irelatively low heating current paths.

12. A structure according to claim 4 in which the transformer apparatus comprises in combination a secondary electrical conductor, a primary electrical conductor consisting of two spaced-apart coils supported at opposite sides of the secondary electrical conductor, said coils being joined together at a common central ground point and having their outer `ends connected to a common terminal, each of said coils having its constituent turns originating in close proximity to the secondary electrical conductor and extending away from the common ground point in the same direction, whereby high voltage impulses Lapplied to the primary will produce flux paths for the two coils, which ux paths combine in series and are additive.

13. A structure according to claim 8 in which the cam actuated switch includes an adjustable cam body which is adapted to make one revolution during each cycle of operation of the packaging machine, said adjustable cam consisting of two cam segments removably secured together, each of said segments presenting recessed dwell surfaces which may vbe variabley spaced with respect to one another.

References Cited in the tile of this patent UNITED STATES PATENTS 2,195,222 Neumair Mar. 26, 1940 2,342,532 Doelker Feb. 22, 1944 2,446,414 Farrell et al Aug. 3, 1948 2,676,444 Gaubert Apr. 27, 1954 2,723,517 Mittelmann Nov. 15, 1955 2,818,483 Blume Dec. 31, 1957