US2804562A

US2804562A - Arc-type oscillators

Info

Publication number: US2804562A
Application number: US463351A
Authority: US
Inventors: Wallace C Rudd
Original assignee: Magnetic Heating Corp
Current assignee: Magnetic Heating Corp
Priority date: 1954-10-20
Filing date: 1954-10-20
Publication date: 1957-08-27
Anticipated expiration: 1974-08-27

Description

Aug. 27, 1957 w. c. RUDD 2,804,562

ARC-TYPE OSCILLATORS Filed 001;. 20, 1954 2 Sheets-Sheet l Fig. 5

CARBON ARC WALLACE C. RUDD ATTORNEYS 1957 w. c. RUDD 2,804,562

ARC-TYPE OSCILLATORS INVENTOR. w}; WALLACE C. RUDD I dmd, fladlMwiSlmDmz 8 momma ATTORNEYS 'best vacuum tube oscillator circuits.

ARC-TYPE QSQILLATORS Wallace C. Rudd, ,Larchrnont, N.'Y., assignor to Magnetic Heating Corp New Rochelle, N. Y., a corporation of New York Application October 20, 1-954, Serial No. 463,351

4 Claims. (Cl. 313-447) This invention relates to oscillator circuits for generating "high frequency current and more particularly to improved arc constructions adapted for use in such circuits.

In order to produce high frequency currentfor induction heating and other purposes and by using commercially available 60-cycle alternating current supplies as the source of power, ithas fora number of years been cornmon practice to use vacuum tube oscillators where frequencies of the order of several hundred thousands of cycles are desired, or to use motor-driven alternators Where frequencies of the order of ten or more thousand cycles per second are desired. The initial cost of equipment of either type, and particularly the latter, is, however, relatively large and under some conditions the maintainence costs are excessive. Many years ago an arc-type oscillator was developed by Valdimar Poulsen, which was used to some extent for producing high frequency currents for radio purposes, his circuit being'a modification of the Dudell Musical Arc circuit. While such arc-type oscillators were relatively simple and inexpensive, they embodied various-recognized shortcomings, such that they were substantially superseded by vacuum tube type oscillators of greater reliability.

The general purpose of the present invention, however, is to provide such an improved form of arc construction for the Poulsen type oscillator circuit as to insure reliable operation with the initial cost and maintenance costs substantially below those of other types of oscillators and yet having an efficiency comparable to that of the The high frequency generators of the present invention are well adapted for use-with an ordinary 60-cycle commercial current source of 449 volts for example, to produce high frequency of the order of 10,900 cycles or higher with an output in the neighborhood of 20 kilowatts or more. These results have been accomplished by making a number of improvements in the construction and operation of the Poulsen type are, as will be-hereinafter described. Such improvements have resulted in a very reliable high frequency generator having an efficiency in the neighborhood of 5 50%, which is comparable to that of present-day induction heating equipment so far as concerns typical operating characteristics, but with the addition of greater simplicity and cheapness of construction.

Other and more specific objects, features, and advantages of the invention will appear from the detailed description given below, taken in connection with the accompanying drawings forming a part of this specification and illustrating by way of example the presently preferred embodiment of the invention.

In the drawings:

Figure l is a diagrammatic view of a conventional circuit of the Poulsen type oscillator as adapted for an alternating current source of supply;

Figure 2 is a vertical sectional View showing the improved arc construction according to a preferred embodimenLof the invention;

States Patent 2,804,562 Patented Aug. 27, 1957 Figure 3 is a somewhat schematic transverse vertical sectional view of a portion of the apparatus of Fig. 2;

Figure 4 is a diagram illustratinga means'for maintaining an atmosphere or hydrogen or other gas in the arc chamber; and t Figure 5 is a sectional view illustrating more fully-one of the electrode stop means hereinafter described.

The conventional circuit, as shown in Fig. 1, comprises an arc with carbon electrodes-as indicated, supplied from a source of low frequency alternating current through a reactance with a laminated iron core as indicated at R. In parallel with the arc electrodes, a capacitor C and'an inductance I are connected in series. When the arcis struck by bringing the electrodes together and then-sen arating same, a negative resistance characteristic is produced. This negative resistance characteristic (according to which the greater the current, the lower the voltage drop across the arc) causes such circuit to operate as an oscillator to produce high frequency alternating current in the capacitor-inductance circuit. Since high frequency current flows in this circuit, it may be conveniently used for induction heating, and various other purposes, for example by placing the object to be heated inside the inductance I, such inductance in this case being the work coil, or of course such circuit may be used by making the inductance I the primary of a high frequency transformer, the secondary of which feeds a conventional work coil and load combination.

Poulsen improved the Dudell musical arc circuit by installing a direct current magnetic field at right angles to the arc electrodes which were fed with direct current. Such magnetic field caused the arc to be blown over to one side of the electrodes and to remain at a predetermined position. With the Poulsen construction, the electrodes were constructed respectively of a carbon rod and a water-cooled copper block, each with its own direct current polarity. The carbon rod was rotated and automatically advanced axially in order to compensate for the carbon consumption during the operation.

For a variety of reasons, I have found that high frequency current is most efiiciently produced with this circuit if carbon or graphite electrodes are used and if the arc is maintained in an atmosphere of hydrogen, or one containing considerable hydrogen. However, an atmosphere of other gases such as illuminating gas may be used, but a carbon deposit will then be created on the inside of the gas chamber which would require periodic cleaning. if the arc chamber is filled with air, only a very small amount of high frequency current is produced, but if hydrogen or some other gas or vapor containing hydrogen is used, the production of high frequency current is made possible with a quite satisfactory efiiciency.

Since for widespread present-day use, such equipment should be designed for use with an alternating current source of supply, the Poulsen copper electrode is eliminated and carbon or graphite is used for both electrodes according to the present invention. An to insure uniform burning of the carbon, the Poulsen arc magnetic field is used, but in the form of an alternating current field, and preferably the reactance R of the supply circuit is used to supply such a field to blow the are into a stable position at one side of the electrodes while the electrodes are being rotated, preferably relatively rotated and preferably, but not necessarily, in opposite directions.

However, with the arrangement as thus far described there would remain two problems which so far as known have not heretofore been satisfactorily solved in any simple, practical and depend-able way, viz. first the arc would be irregular and variable in length because of the difficulties of axially feeding the electrodes .at the proper rate toward each other to insure an arc of constant length as the carbon or graphite becomes burned away, and secondly with the are blown to the peripheries of the ends of the electrodes, such peripheries would become burned away more rapidly than the central portions so that the central portions, when fed toward each other, would either come into contactl and eliminate the arc or provide a shorter path causing irregularities in the arc. Efforts to avoid these difficulties were made with a variety of electrode arrangements such as with electrodes at various angular relationships or with one electrode offset with respect to the other or concentric with the other, but by far the most satisfactory arrangement was found to be with the electrodes in spaced end-to-eud alignment and with each electrode formed with a hollowed-out center, the central cavities being sulficinetly large so that the arc, as the electrodes are oppositely rotated, will uniformly burn away all of the carbon, since the carbon is located only at the peripheral portions at the end of each electrode. While the construction of the electrodes in hollow cylindrical form with means to uniformly and relatively rotate same about their axes, insures against creation of any grooves or irregular unburned areas at the ends of the electrodes, still this leaves no way in which to predict the rate (which may sometimes vary) at which the electrodes should be fed toward each other. And since the electrodes are to be contained within a gas-filled chamber, it is difiicult to determine visually whether or not they are being fed at the proper speed. However, according to the present invention, this problem is solved by using the ends of the electrodes in the are chamber as the actual reference points for determining the rate of feeding. This is accomplished by arranging two insulated water-cooled spacers or stop means located in contact with the facing ends respectively of the electrodes, while each of the electrodes are separately urged by spring means or otherwise, constantly into contact with the respective stop means. In this way, the electrode spacing is satisfactorily maintained at a constant value.

With the above considerations in mind, the construction of Fig. 2 will now be described. The two carbon or graphite hollow cylindrical electrodes are indicated at and 11 respectively, positioned in spaced end-to-end aligned relation within a gas chamber 12 formed of copper or brass, for example. This chamber may be protected from overheating as by application of circulating cooling fluid conduits as at 13 on the exterior thereof. The electrodes protrude into the chamber respectively through openings 14, 15, and outside the chamber portions of the electrodes are surrounded by insulation cylinders at at 16, 17 formed of quartz, for example, and protected against overheating as by coils containing cooling fluid as indicated at 18 and i9 surrounding metal flanges 2t 21 formed about the chamber openings 14 and 15. The outer ends of the insulation cylinders 16, 17 may be closed as by metal plates 22, 23 suitably apertured to receive the electrodes and carrying copper or brass bearing members as at 24, 25, within which the electrodes may rotate.

The outer ends of the electrodes respectively may be covered by brass or copper cap members as at 26, 27, upon which sprockets as at 28, 29 are mounted in position to be driven from motors 30, 31 respectively through belt or chain means as shown at 32, 33.

Each of the cap members 25, 2'! and thus also the electrodes, are constantly urged inwardly of the are chamber by helical springs 34, 35 respectively, which may bear against frame means as at 36, 37. The plates or

frame parts

22, 36 and 23, 37 may be secured together as by rods 38 and the frame means at one end of assembly may be clamped or supported by a suitable insulation clamping means or the like (not shown) with respect to the frame means at the other end of the assembly and so as to hold the quartz cylinders 16 and 17 4 in the positions shown. The two electrical terminal connections for the source of power may be applied to the rods 38 and as indicated at 40, 41.

The stop means, such as above referred to, are indicated at 42, 43 for engaging the facing ends of the electrodes as pushed toward each other by the springs 34, 35. These stop means may comprise angularly shaped blocks of copper or brass as shown supported upon pairs of tubes as at 42, 43' which form conduits for streams of cooling fluid to prevent overheating of the stops.

As best shown in Fig. 3, the stop means 4-2, 43 may preferably be located at positions Spaced angularly apart about the electrodes by about 120 and at the same time they will then each be located at positions spaced also about 120 from the normal position of the are, as indicated at 45, assuming that the source of the magnetic field for blowing the are into this position is located below the chamber. Preferably as above indicated, the source of the magnetic field comprises the iron core re actance R above referred to in connection with the circuit of Fig. l.

The cooling fluid conduits which support the

stops

42, 43 may, as shown, extend through suitable insulation supporting means as at 46, 47 mounted on the walls of the arc chamber.

Various known means for starting the arc may be used, but in the form shown in Figs. 2 and 3, a wedge-shaped piece of carbon 48 is mounted upon a suitable inwardly slidable insulation rod 49. Thus after the current source is connected to the terminals 4t 41 as per the circuit of Fig. l, the carbon wedge 4% is momentarily thrust i11- wardly of the arc chamber to the position shown at 48 in Fig. 2 and then withdrawn, leaving established a single are between the ends of the electrodes 19 and 11. And if the reactance R is positioned as shown, the alternating field maintained thereby will act to retain the arc in the upper position as shown in Fig. 3. Since the current flowing through the arc is alternating (from a -cycle source, for example), it will be appreciated that the electromagnetic field used to retain the arc in this position should also be alternating and in phase with the alternating arc current, but of course this is assured by using the reactance R of the power supply source for the double purpose of establishing the field for controlling the arc and for properly limiting the supply of alternating current to the oscillating circuit.

Before the arc is started, the chamber 12 should be purged of air and the air replaced by the desired gaseous atmospher, such as hydrogen. And since there maybe some slow leakage of gas from the arc chamber, the chamber is preferably constantly supplied with gas in the manner shown in Fig. 4. Here a small constant supply of hydrogen is provided through a conduit 52 which extends down to near the bottom of a chamber 53 containing a small volume of liquid 54 such as mercury. The gas thus is allowed to bubble up through the mercury and from the chamber 53 into the arc chamber through a conduit 55. Gas may constantly be withdrawn in small quantities from the arc chamber through a conduit 56 which extends down close to the bottom of another chamber 57, also containing a body of liquid 58, such as mercury, through which the discharged gas bubbles up and finally escapes to a desired discharge point through a conduit 59. in this way an atmosphere of the desired gas may be readily maintained at a substantially constant pressure above atmospheric pressure in the arc chamber and acting to exclude any possibility of leakage of air into the arc chamber.

The specific example of the apparatus above described was designed to operate from a source of 60-cycle current supply at 446 volts to provide a high frequency generator having an output of 20 kilowatts at a frequency of about 10,000 cycles per second, the 60-cycle alternating current being translated into high frequency current with an efficiency of about 50%. This was accomplished by using a current of about 100 amperes (when having unity power factor). With this particular example of the apparatus, it was found that the most desirable operating characteristics were obtained when the capacity C was about 11.2 microfarads and when the inductance I had a value of about 25 microhenries. These factors will, of course, vary depending upon the particular design of the apparatus, the particular high frequency desired and other characteristics thereof, but although such factors are fairly critical, for best results the values thereof may readily be determined by trial. With the particular installation as described, the value of the reactance R was 6.4 millihenries, The electrodes and 11 had an outside diameter of about 2 inches and a quarter inch wall thickness. When the motors 30, 31 rotates such electrodes in opposite directions at a speed in the neighborhood of three revolutions per minute, the electrode walls were consumed by the arc gradually and completely as same were advanced by the springs 34, 35 and held in contact with the

stops

42, 43, respectively. The space between electrodes may be of the order of A to A".

While the electrodes may be conveniently and preferably rotated in opposite directions to insure uniform consumption thereof at all points around their end edges, yet satisfactory results may be obtained by rotating them both in the same direction but at somewhat different speeds. Since the arc is held in a stationary position by the magnetic field, it will have opportunity to come into contact successively with all points on the end edges of the electrodes if the electrodes are rotated about their axes and whether or not they are rotated at different speeds or in opposite directions. But by relatively rotating them, irregularities in the burning tend to be more safely avoided and rotation thereof in opposite directions at the same speed will generally be most convenient.

Although one particular embodiment of the invention is here disclosed for purposes of explanation, various modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. An arc construction adapted for use in an oscillator circuit and comprising a pair of hollow cylindrical electrodes formed of carbon material, means for supporting said electrodes substantially in endwise alignment with an arc gap between the ends thereof, means for relatively rotating same about their axes, fluid cooled stops for engaging portions on the facing ends thereof respectively to maintain the gap therebetween of predetermined length, means for normally constantly urging each of said electrodes against said stops respectively, means for maintaining a magnetic field in said gap with lines of force running transversely of the electrodes to cause an are between the electrode ends to assume a position spaced from said stops, a chamber for enclosing the region of the arc, and means for maintaining a hydrogen-containing atmosphere normally above atmospheric pressure in said chamber.

2. An arc construction comprising a pair of electrodes formed of carbon material and having annular ends, means for supporting said electrodes substantially in endwise alignment with an arc gap between said annular ends, means for rotating said electrodes about their axes, stops for engaging said annular ends respectively to maintain the gap therebetween of predetermined length, means for maintaining said ends as they burn away in contact with said stops respectively, and means for maintaining a magnetic field in said gap to cause the arc to assume a predetermined position between said annular ends.

3. In an arc construction, a pair of electrodes formed of carbon material, means for supporting said electrodes substantially in endwise aligmnent with an arc gap between the ends thereof, means for relatively rotating same about their axes, and means for maintaining a magnetic field in said gap with lines of force running transversely of the electrodes to cause an arc therebetween to be blown to one side of the gap and confined to the peripheries of the electrodes, the said end portions at least of said electrodes being hollowed out to an extent whereby the whole end surfaces will be burned away by the arc.

4. An arc construction comprising a pair of hollowended electrodes formed of carbon material, means for supporting said electrodes with an arc gap between such ends, means for rotating same about their axes, stops for engaging portions on the facing ends thereof respectively to maintain the gap therebetween of predetermined length, means for maintaining said electrodes with their ends as they burn away in contact with said stops respectively, and means for maintaining a magnetic field in said gap with lines of force running transversely of the electrodes to cause the arc between the electrodes to assume a substantially stable position spaced from said stops.

References Cited in the file of this patent UNITED STATES PATENTS 1,906,491 Spieth May 2, 1933 2,449,552 Gorham Sept. 21, 1948 2,450,477 Huff Oct. 5, 1948 2,456,902 Treuthart Dec. 21, 1948