US2631221A - High-frequency electrical heating apparatus - Google Patents

Description

March 10, 1953 yn-E 2,631,221

HIGH-FREQUENCY ELECTRICAL HEATING APPARATUS Filed March 26, 1951 Patented Mar. 10, 1953 UNITED STATES .PATENr oF-Ficr. f

i i inron-Fimoiinnoi fi iii'rmou"HEa'rING I --John G. Littell, Florham Park, 'N. J., ass'ignor to Krem'entz &' Company, Newark, N. 'J .,a corporation of New Jersey Application-March 2e, l9 51,-.Serial No.'217, 566

"This invention relatesto a circuit-for heatin small non-ferrous metal devices such as 'are used in "the jewelry trade.

In general this present invention relates to an improvement over Patent No. 2,493,269.. issued January 3, 1950, to Harrison 'D; Simpson. Thispatent sets forth in considerable detail'the use of high frequency'apparatus for the purpose "just'described. The patent also points out inconsiderable detail the prior art 'methods which had been in use, or at-least'tried out'prior to the filing of the application for said patent. In'view'of these disclosures it does not seem. necessary to-discuss the-'prior-art' set forth :in the patent, except tomention that the present application is directed to improvements upon the apparatus disclosed in the Simpson patent.

@In'the use "oftheSimpson-patent, there is a difference in potential of as much as350'0 volts 7 "betweenthe primary and secondary windings of I "the grid'transformer. Because these are of'ne cessity in close physical proximity to obtain close coupling, the high voltage often arcedacross betweenthese windings, causingdamage to the insulation f the transformeriwhich put it out of use until repairs wouldloe made. ,Apparently this was partly due to theout of "phaserelation-between the-primary and secondary voltages assisted by transientpeaks caused by-opening and closing of theswitch' controlling the plate cur rentas each-piece was inserted in the'work coil. Several methods of constructing the grid transformer of said'patent weretriedin order toincrease the period-of time during which the apparatus could be-maintained in operatin condition. but none ofthese methods wereiound to be per-" fectlyf satisfactory.

It is. therefore the principal object or myl'present invention to provide a grid transformer connected in the circuit in such a way as to eliminate all the trouble experienced with the apparatus of said-patent. My new arrangement comprises an auto-transformer having the grid of the vacuum tubeoscillator-connected to one end offthe transformer winding while the other end is connected to the anode-of theoscillator tube, with a ground connection made at the adjustable contact which is an adjunct of an auto-transformer. This pro-- vides an arrangement in which one portion of the transformer is connected to the anode of the oscillator tube while the other portion is connected to the grid of the tube, the relation between the two portions being adjustable by reason of the movable contact which in effect separates the transformer into primary and secondary windings with the primary being connected to the 5 Claims. (01.219-47) plate of' the tube and the secondary to the grid.

With this arrangement 'thevoltage ratio of the two'coils can'be adjustedto produce an optimum of grid feed voltage and hence maximum efiiciency.

Furthermore, because the auto-transformer. is

a" single layer coil the-differencein'potential between anytwoconductors that-'arein close'phys- "ical'proximityis reduced from'3500 volts to about 350 volts and arcing is-effectively"eliminated.

I have found that highly satisfactory-results can be obtained by using an auto-transformer the helical or single layer coil of which is made up of copper tubingand having an outside diameter of the turns of 6 /2" andawinding length of approximately 2 using approximately ten :or eleven turns. The movable contactshould be preferably arranged so that it may he readily moved to vary the relationship between-the .primary and thesecondary sections.

The circuit arrangement with which this grid transformer is used is in general the same as'that shown in the Simpson atent, however, there have been introduced certain circuit changes as can readily be seen by referring tothe single figure of the drawing. In th circuit showing my 'improvement is a step-up transformer I having a primary P which may have an ammeter A in'its circuit. The secondary 's is connected to two rectifier tubes 2 aud t which as-shown are of the gas type. Filaments of the tubes 2 and 3 are connected to the secondaryfi of the transformer 1 4 having a .-.primary 5. connected to J the a same source of l supply as the primary P of thetrans- .Iform'er .1. :The ccenterztap :offthe winding ifi' is joined by a conductor 1 througharadio frequency ."ldhdkfi zcoilig to -kee oscillations from ithe'lhigh frequency oscillating itubeT-,out of .thei'source Ofdire'ct current coming from the .tubesi'Z and 3.

The tube.'I.-has aaplate :or vanode:9,:a. grid 10 and filament H the latterof which is supplied with current from a-transformer lz'having a primary .l3.and secondary 114. Connected to the anode of 2,681,221 j j p The primary portion of the auto-transformer AT is connected in parallel across the condenser l6 and the heating coil I'l. One end of the primary is connected to the tube T through the blocking condenser 15, while the secondary of the transformer has its free end 20 connected through a parallel arrangement of a grid bias resistor 24 and by-pass condenser 25 to a parasitic suppressor composed of resistance 22 and inductance 2| arranged in parallel relationship and connected to the grid in. The movable contact l9 of the transformer along with one side of the condenser l6 and one end of the heating coil I! are connected to the ground. The center of the winding I4 of the filament transformer I2 is also grounded thereby giving a feedback circuit to the filament of the tube T. With this arrangement the connections from the secondary of the transformer to the grid are in substantially a series circuit made up of the parts as just described. I have found with this arrangement which has been used over quite a period of time that troubles I have referred to have been overcome and overall improvement in efliciency of approximately three per-cent to five per-cent have been obtained over the prior arrangement. Furthermore, the cost of the grid transformer has been materially reduced and much time is saved in the operation of the system for the reasons heretofore explained.

I claim:

1. Means for heating metal parts including a high frequency oscillator vacuum tube with means for feeding direct current to the plate of the tube, a tank condenser connected in the output circuit of the tube, a heating coil connected in parallel with the tank condenserand composed of few turns to facilitate the handling operation of the parts to be inserted into the space within said turns for heating them, an helical single layer coil having few turns of large diameter with a movable tap connected to that side of the tank condenser opposite to the side that is connected to said tube plate and also one end of the auto transformer being operatively connected to said output circuit of the tube along with the condenser while the opposite end of the transformer is operatively connected to the grid of the tube, and a blocking condenser connected between the output of said tube and said tank condenser.

.2. Means for heating metal parts as set forth in claim 1 further defined in that the connections to the grid of the tube includes a parasitic suppressor withv at least a condenser in series with. the suppressor.

3. Means for heating metal .parts, including a high frequency triode tube and means for heatingits filament, means for supplying high voltage direct current to the plate of said tube through denser being connected between the plate of the triode tube and ground through the blocking condenser, an helical single layer coil having few turns of large diameter having an adjustable contact and one portion between said adjustable contact and one end, connected in parallel with the tank condenser and heating coi1-while the other portion is operatively connected to the grid of said tube to provide a feedback voltage therefor.

4. Means for heating metal parts as set forth in claim 3 further defined in that said feedback voltage to the grid is supplied through a grid bias resistor from the filament and a grid condenser connected to the last mentioned portion of the auto transformer.

5. Means for heating metal parts including a high frequency oscillator tube with means for feeding current to the plate of the tube, a tank condenser connected in the output circuit of the tube, a heating coil connected in parallel with the tank condenser and composed of a few turns to facilitate the handling operation of the parts to be inserted into the space within said turns for heating them, an helical single layer coil having few turns of relatively large diameter and an adjustable tap, said coil having its primary end connected in parallel with the tank condenser and the heating coil and the free end of the secondary operatively connected to the grid of the tube to cause the same to deliver a high frequency current to the heating coil that will produce high heating in a matter of a very few seconds, and a blocking condenser to keep high voltage direct current away from the resonant circuit.

6. Means for heating metal parts including a grid-controlled vacuum tube with means for feeding plate current and filament current to said tube, connected as a high frequency oscillator with a tank circuit in the output circuit of said tube comprising a condenser in parallel with a heating coil composed of few turns to facilitate handling of the work within said coil for heating the work, means for producing oscillation in said circuit including an helical single layer coil in parallel with said tank circuit with one endof said helical coil connected to said tank condenser and a movable tap connected to said filament and with the other end of said coil connected through a bias resistor and grid condenser to the grid, and a blocking condenser between the output of the tube and said tank condenser.

JOHN G. LITTELL.

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

Foley et al. Feb. 6, 1951

Images