US2469990A - Means for feeding high-frequency electric currents to the electrodes of dielectric heating apparatus - Google Patents

Description

J. c. QUAYLE ET AL 6 990 10 CURRENTS MEANS FOR FEEDING HIGH-FREQUENCY ELEGTR TO THE ELECTRODES OF DIELECTRIC HEATING APPARATUS May 10,1949.

2 Sheets-Sheet 1 Filed Oct. 9, 1946 i y r W ymwflamwa/wz Alton/veg 2,469,990 v ELECTRIQ CURRENTS TO THE ELECTRODES OF DIELEQTRIC HEATING APPARATUS Filed Oct. 9, 1946 May 10, 1949. J. c. QUAYLE ET'AL MEANS FOR FEEDING 'HIGHFREQUENCY 2 Sheets-Sheet 2 Mus/7Z0," J. C y V- 03:,

Patented May 10, 1949 MEANS FOR FEEDING HIGH-FREQUENCY ELECTRIC GURRENTS TO THE ELEC- TRODES OF DIELECTRIC HEATING AP- PARATUS Joshua Greer Quayle, Helsby, and Peter Jones, Kelsall, near Chester, England, assignors to British Insulated Callenders Cables Limited, London, England, a British company Application October 9, 1946, Serial No. 702,219 In Great Britain October 25, 1945 4 Claims. 1

This invention relates to the production of heat by means of electric fields alternating at high frequency in dielectric material by making use of electrodes between or adjacent to which the material is placed and between which a high potential difference is maintained. The invention deals particularly with the means for feeding high frequency electric currents from an oscillator to the electrodes in a manner particularly suitable for very high frequencies, for instance 200 megacycles per second and upwards.

In this improved arrangement we utilise an oscillator having an output circuit (tank circuit) in the form of a resonant line which structurally is wholly or in part a rigid bar or tube and we make coupling with this circuit by means of two rigid rings surrounding the bar or tube without making contact with it. These rings are not necessarily complete rings (although in general cases this will be found an advantageous form) and in the following description the word ring in this connection is to be interpreted with this proviso and in the light of the functions to be performed by the part to which the word is applied. These rings, which make capacity coupling with'the output circuit, are spaced apart appropriately on an insulating carrier and each have a projecting part which makes direct coupling with one of the electrodes. There is provision for relative movement between the rings and the line. This movement may be effected by moving the carrier along the line but in most instances it is advantageous to fix the carrier and move the oscillator relative to it. In either case the position of the coupling rings on the resonant line is varied and in this way the load on the oscillator is adjusted according to the requirements of each case, that is to say according to the nature and dimensions of the material to be heated, or according to the rate of increase of temperature which is desired.

Examples of apparatus embodying the invention will be described with reference to the accompanying drawings.

Figure l is a partly diagrammatic drawing in perspective of part of a machine for joining together sheets of thermoplastic material.

I The machine comprises a work-table I, slotted at 2 to receive a disc 3 of insulating material mounted on a shaft 4. The method of mounting the disc 3 and its construction is more clearly shown in Figure 2 which is a part cross section in a vertical plane passing through the shaft 4. The disc 3 is formed with metal rims 5 and S which act as two electrodes between which is r 5504) umhos.

maintained a high frequency alternating potential by means which will be hereinafter described. Suitable means for rortating the disc 3 and for pressing the sheets of plastic material against its upper edge, are described in co-pending application for U. S. patent, Serial No. 702,220, and United Kingdom application No. 30418/45. The work-table I is carried on four supports 1, which are shown partly cut away to disclose other parts of the machine. To these supports are joined rigid cross members 8 on which a platform 9 of insulating material is slidably mounted. The platform 9 is movable backwards and forwards in the direction indicated by the arrows on its upper surface. This platform carries a high frequency oscillator. The output circuit (tank circuit) of the oscillator is a U-shaped resonant line which consists of a tube divided into two parts H and I2 which are joined by a hollow terminator 13. The anodes M of two oscillator valves fit into the free ends of the tubular parts II and 12. These valves are of type ACT.19 manufactured by the General Electric Company, having an anode dissipation of 200 watts and a transconductance of Two valves in a push-pull circuit are rated to deliver 500 watts at frequencies up to mc./s. with forced air cooling at a rate of 25 C. F. M. The filament leads 32 of the valves (shown dotted where they pass through the tubu-' lar parts I! and I2) are connected to a suitable low tension supply (not shown). The filament circuit includes a phase adjusting reactance to maintain oscillations. The grid circuit for the two valves is a U-shaped resonant line l4 connected to the valves by grid leads l5 and supported on an insulator l6 carried on the platform 9. The resonant line M is connected at its centre through a grid choke l1 and resistor 18 to earth. The H. T. anode supply is connected through a lead 20 and an anode choke H! to a terminal 20 mounted on the centre of the terminator 3. The tubular parts I! and I2, the terminator l3 and the anodes M are all supported on insulators 2i mounted on the platform 9. The anodes l4 are formed with air ducts 22; A supply of air under pressure is fed through a pipe 30 to the terminator l3 and the escapes through the ducts 22.

Two horizontal members are rigidly mounted on the supports 1. Only one of these is shown under reference 23. These members carry a cross piece 24. Around each of the tubular parts I! and I2 is a metal ring 25 supported by a block 26 of polythene which is itself rigidly mounted on the cross piece 24. The inside diameter of the the platform 9 moves horizontally between the four supports 1 in the direction indicated by shown), similar to those described with reference to Figure 1, in such a way that a uniform spacing is maintained between them and the bars 53. The stirrups make capacity coupling with only one of the two anode resonant lines but by modifying the position of the anode lines so that bars 43 and M arrows, a uniform spacing between the inside surfaces of the rings 25 and the outside surfaces of the tubular parts I l and I2 is maintained. Two spring contacts 27 are mounted on the rings 25 and bear against the metal rims and 5 of the disc 3.

The tubular parts I I and I2 and the terminator l3 form a U-shaped resonant line. By applying a suitable H. T. supply to the lead 2!} and iow tension supply to the valve filaments, a standing wave of voltage is set up on each side of the line, falling from a maximum at the anodes i i of the two valves to approximately zero at the centre of the terminator [3, the effective length of each side of the line being a quarter wave-length. Accordingly, by varying the position of the canaci I coupling provided by the two rings alon 1 part of the resonant line consisting of the tub ar parts II and 12, the value of the potential dii ence picked up by the rings and applied to the electrodes, formed by the rims 5 and i of the disc 3, is adjusted, this value being decreased as the distance between the rings 25 and the anodes 14 increases. This adjustment is effected by sliding the platform 9 backwards and forwards in the direction of the arrows drawn on its upper surface. The external connections, namely the T. load 29, the filament leads 32, the grid lead iii the air pipe are all flexible to allow for this movement of the platform 9. The output resonant line may consist of a tube bent in the form of a U, similar to the grid resonant line, in which case the H. T. supply will be connected to the centre of the U and the terminator It will not be ne essary.

Figure 3 is a diagrammatic drawing of an alternative form of oscillator which may be used in a machine of the kind described with reference to Figures 1 and 2. This construction includes two valves each having two projecting anode terminals 4| and two projecting grid terminals 2. These valves are type 8012, manufactured by R. C. A. Inc., Camden, New Jersey, U. and

have a convection cooled glass envelope, an anode dissipation of 40 watts and an amplification factor of 23. The two Valves in a push-pull circuit are rated to deliver 60 watts at 500 mc/s. The anode terminals 4| are connected to metal bars 43 and 44 which are joined by metal terminators 45 and 46 to form two U-shaped anode resonant lines. The bars are of 1" x strip metal. The grid terminals are connected by metal bars ll forming two grid resonant lines. The centres of these bars are connected by a choke at which is connected to earth through a choke is and resistor 50 and to the negative terminal of the H. T. supply. The positive terminal of the H. T. supply is connected through anode chokes 5! to the centre points of the terminators i5. Provision is made for adjusting the terminators 5 with respect to the bars 43, the ter-minators being supported by studs '52 sliding in slots 53. Filament current is supplied to the valves 40 through a transformer 54.

The rings for effecting capacity coupling between one of the anode lines and the electrodes are in this construction in the form of stirrups 55. These stirrups are supported by means (not he parallel to each other as shown diagrammatically in Figure 4 and increasing the length of the stirrups 55, coupling can be made to both anode resonant lines as shown. This circuit is capable of oscillating at frequencies up to 590 mc./s. the output being of the order of 60 watts.

Where it is preferable to keep the oscillator stationary, the adjustment may be attained by mounting the support for the two rings on a carrier similar to the member 24 in Figure 1 but which can be moved horizontally through the desired range in a direction parallel with the run of the line. In this case a modified form of electrode would be used having a surface large enough, in the direction in which the spring contact members mounted on the rings move, to maintain contact with the spring contact members throughout the range of their movement.

If the two electrodes are not side by side but in some other disposition, for instance in the same plane, the spring blades may be skewed or one ring may be arranged in advance of the other. on the carrier in order that simultaneous contacts can be made between blades and electrodes.

We declare that what we claim is:

1. In apparatus for producing heat in a dielectric material by passing said material through an electric field adjacent to or between two rotating electrodes between which a high frequency alternating potential is maintained by an oscillator, a variable coupling between said oscillator and said electrodes which is adjustable to vary the potential difierence between said electrodes comprising an output tank circuit for said oscillator in the form of a resonant line which structurally includes two parallel rigid conducting members, two fixed coupling members each at least partially surrounding one of said conducting members without making contact therewith, a contact member on each of said coupling members which makes rubbing contact with one of said rotating electrodes and means for moving said oscillator and said line together in a direction parallel with the longitudinal axes of said rigid conducting members thereby effecting the required adjustment.

2. In apparatus for producing heat in a dielectric material by passing said material through an electric field adjacent to or between two rotating electrodes between which a high frequency alternating potential is maintained by a Vacuum tube oscillator comprising at least two oscillator tubes, a variable coupling between said oscillator and said electrodes which is adjustable to vary the potential difference between said electrodes comprising an output tank circuit for said oscillator in the form of a resonant line which structurally includes two parallel rigid conducting members each connected at one end to the anode of one of said tubes and connected together at their other ends by a metal member, two fixed coupling members each at least partially surrounding one of said conducting members without making contact therewith, a contact member on each of said coupling members which makes rubbing contact with one of said rotating electrodes and means for moving said oscillator and said line together in a direction parallel with the longitudinal axes .of said rigid conducting members thereby effecting the required adjustment.

3. In apparatus for producing heat in a dielectric material by passing said material through an electric field adjacent to or between two rotating electrodes between which a high frequency alternating potential is maintained by a vacuum tube oscillator comprising at least two oscillator tubes, a variable coupling between said oscillator and said electrodes which is adjustable to Vary the potential difierence between said electrodes comp-rising an output tank circuit for said oscillator in the form of a resonant line which structurally includes two parallel tubular rigid conducting members each connected at one end to the anode of one of said tubes and connected together at their other end by a metal member, two fixed coupling rings each surrounding one of said conducting members without making contact therewith, a contact member on each of said coupling rings which makes rubbing contact with one of said rotating electrodes and means for moving said oscillator and said line together in a direction parallel with the longitudinal axes of said rigid conducting members thereby effecting the required adjustment.

4. In apparatus for producing heat in a dielectric material by passing said material through an electric field adjacent to or between two rotating electrodes between which a high frequency alternating potential is maintained by a vacuum tube oscillator with a U-shaped output tank circuit in the form of a resonant line with the ends of the arms of the U each connected to the anode of one of the oscillating tubes and each of length equal approximately to one quarter wave length, standing waves of voltage being generated in each arm of the U varying from a maximum at the tube anode to a minimum at the centre of the U, a variable coupling between said oscillator and said electrodes which is adjustable to vary the potential difference between said electrodes comprising two fixed coupling members each at least partially surrounding one of the arms of said U-shaped line, a contact member on each of said coin ng members which makes rubbing contact with one of said rotating electrodes and means for moving said oscillator and said resonant line in a direction parallel with the longitudinal axis of arms of said U-shaped line thereby effecting the required adjustment.

JOSHUA CREER PETER JONES.

QUAYLE REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,149,387 Brown Mar. '7, 1939 2,370,423 Roberts Feb. 27, 1945 2,382,435 Mann et al Aug. 14, 1945 FOREIGN PATENTS Number Country Date 375,587 Great Britain June 30, 1932 417,564 Great Britain Apr. 18, 1934 OTHER REFERENCES Taylor, A Radio-Frequency Gun for Spot- Gluing Wood, Electronics, November 1943, pages 106-111 and 310, particularly page 111.

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