US1555258A

US1555258A - High-frequency dielectric furnace

Info

Publication number: US1555258A
Application number: US671113A
Authority: US
Inventors: Chester T Allcutt
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1923-10-27
Filing date: 1923-10-27
Publication date: 1925-09-29
Anticipated expiration: 1942-09-29

Description

c. T. ALLQUTT HIGH FREQUENCY .nmnnc'rme FURNACE Filed Oct. 27. 1 923 WITNESSES: INVENTOR 2 4 7 Chas fer T A//cuf7.

, ATTORNEY Patented Sept. 2 9, 192 5.

UNITED sTm'Es PATENT onl -cs.

CHESTER 'r. ALLCUTT, or rrrrsnvaen, rENNsYLvANrA, ASSIGNOR TO WESTING- HOUSE ELECTRIC. & MANUFACT RING COMPANY, A conroRATIoN or PENNSYL- vANIA.

HIGH-FREQUENCY DIELECTRIC FURNACE.

Application filed October 2 7, 1928.- Serial No. 671,113.

To all whom it may concern:

Be it known that I, CHESTER T. ALLCUI'I, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Hi h-Fre-' (f uency Dielectric Furnaces, of which the ollowing is a specification.

-My invention relates to electric heating and particularly to heating-by means of a high-frequency electric fleld.

The object of my invention is to provide a system of, and means for, heating by the use of a high-frequency electric field.

In practicing my invention, I provide a source of high-frequency electric current and connect the terminals thereof to two electrodes between which is located a member oi imperfect dielectric material which becomes heated when subjected to the high-- frequency electric field produced between the electrodes. 1

In the single sheet of drawings, Figure 1 1s a schematic view of a high frequency source of electric ener y operatively associated with a furnace, i lustrated in section, embodying my invention,

Fig. 2 is a schematic view of a modified form of high-frequency system embodying my IIIVGIltiOIl,

Fig.3 is a View, in section, of a. further modification of a device comprising a part of a system embodying my invention,

Fig. 4 is a view, in section, of another modification of a device embodying my invention, 1 1 I Fig. Sis a schematic view of a still further modification of a high-frequency heating system, and

Fig. 6 is a schematic view, in side elevation, of a commercial application of high frequency dielectric heating.

Referring more particularly to Fig. 1' of the drawin a source of alternating current is here indicated by the conductors 11 that are connected to the terminals of the primary winding 12 of a suitable transformer.

The secondary winding 13 is connected t6 the terminals of a condenser 14', of suitable type, and the connections empldyed are such as to provide. a source, of sustained electric current of high frequency and of high voltage delivered to the conductors 15 and 16. A crucible 17 of any suitable or convenient form has located thereon an enclosing the conductor 16. A mass 19, of a material to be heated, is located within the crucible 17 and is electrically connected to the con ductor 15.

The crucible 17 is made of a material that is an imperfect dielectric and which, when subjected to the action of the high-voltage alternating electric field existing between the mass of material 19 and the outer electrode .18 when the system is energized, is heated by the loss of energy in the dielectric material itself. As is well known, the energy loss in a member of imperfect dielectric material when subjected to anfialternating electric field is dependent upon the geometrical dimensions of the member,-the material of which it is made, the frequency ofthe field and the squareof the applied voltage.

In general, this loss is relatively small for such members where the dimensions of the crucible are relatively limited and it is,

- therefore, advisable tolemploy a frequency that is ashigh as is commercially possible and a voltage that is as high as is practicable.

The crucible 17 may, for instance, be made of clay, porcelain or glass that will be heated Whensubjectedto the action of a high frequency and high-voltage electric field and that will, at the same time, serve as a container for materials to be heated therein, the heat being generated directly in the crucible of dielectric materialand imparted to the material located therein by conduction.

Dielectric materials of the ordinary kind that may be employed ascontainers are usually relatively poor conductors of electricitywhen cool but become much better conductors when heated, that is, they have a relatively high negative temperature coefficient of resistivity. It is advisable, therefore, to provide some means for counteractingthis effect, which would result in a tendency of the current flowing through a member of dielectric material to concentrate at any point that. had a relatively high loss, such as mightbe caused by a defect in the materiaL- Such means may be provided by a condenser or by an air gap placed in series relationtto the imperfectdielectric and such means is illustrated more particularly in Fig. 2 of the drawing, where the crucible 17 has an electrode 21 surrounding it but spaced therefrom. This construction, of

course, reduces the inherent capacity of the structure, but provides .means for insuring that the current traversing the-member of imperfect dielectric material shall be substantially uniform over substantially its entire surface since the air between the

members

17 and 21 is a relatively perfect dielectrio and there will be no tendency for the current to concentrate at certainpoints.

The same effect may be obtained byemploying a member of relatively perfect solid, die ectric material between the crucible and the outer electrode. This is illustrated more particularly .in Fig. 3 of the drawing, wherein the crucible 22 for containin the mass of materialLto be heated is ma e of glass and is surrounded by a crucible 17, of quartz, an electrode 18 being fitted closely around a portion-of the peri heral surface of the quartz crucible 3L7. s quartz is a much better dielectric than glass, it will operate to prevent what may be termed local hot s ots in the crucible 22 and insure substantially uniform distribution of current traversing the member 22.

The crucible 17 of quartz, illustrated in' Fig. -3 of the drawing, will also be heated when sub'ected to the action of a high voltage and ighfrequency electric field and will therefore assist in increasing the temperature of the mass of material located within the inner crucible 22.

A structure that may be used in heating non-conducting materials is illustrated in Fig. 4. A conducting electrode 23 is inserted in crucible 24 of dielectric material, but is spaced therefrom by a mass of mate,- rial 25 to be heated. A second conducting electrode 26 surrounds the crucible but is spaced therefrom as in the structure shown in. Fig. 2. When a source-13, of high-freuenc electromotive force, is connected to Q t e e ectrodes 23 and 26, the losses in the sir dtemps mass 25 of non-conducting material to be heated, supplemented by such losses as may occur in t the material in the crucible to attain the derature.

In Fig. 5, I have illustrated a relatively narrow. and elongated crucible or container 27 of a suitable imperfect dielectric mateor the source of high and high voltage currentfhere illustrated u are of relativ thereby increasin crucible27. larly adapted for use in case the materialrial. Electrodes 28 and 29 connected-to the frequency as a' seconds coil 13Qof. a transformer,

large surface area and ma be located a re tivel short distances a capacitance o the device and, there one, the power loss in the This modification is particucontained .in the crucible is non-conductiinlg In Fig. 6, I have'illustrated schematic y one form in which the system embodying my invention may be employed 0 mediately incorporated in t e dielectric crucible 24, will cause cially. A sheet or strip 31, of high grade' moisture and when subjected'to the action of a high-frequenc electric field is heated and any moisture t at may be in the paper will be driven out thereby and the aper will, therefore, be thoroughly dry, i?

e condenser and suitably protected against reabsorption of moisture. This method is particularly advantageous because of the fact that the losses and consequent heating of the paper are more or less restricted to such of the paper as contain undesirab e moisture. Portions 'of the paper that do not contain an undesirable quantity of moisture will have relatively low dielectric losses'and will be but slightly heated. Obviously, a saving in power will result. Furthermore,

this method permits ofIvery rapid drying without danger of overheating since the losses diminish as the paper dries and overheating is thereby automatically prevented. Where I have referred to a source of sustained electric current of high-frequenc I include fre uencies not less than t ose usually emp oyed in radio telegraphy and radio telephony and suchhigher frequencies as may be commercially roduced for such applications. A sustaine alternatin current of high frequency is particular aplicable for my purpose, as the disc arge rom'a series 0 high-frequency wave trains, such as produced by an oscillatory ark discharge, will not produce the desired eatin efl'ects.

ortions I arious modifications and changes may be i made herein without departing from the s irit and scope of the invention, and I desire, therefore, that only such limitations shall placed thereon as are b the prior art or are specifically set forth in the a pended claims.

I c aim as my invention: j 1. In combination, a pair of terminal -members, a memberof imperfect dielectric material therebetween, and a source'ofhighfrequency current supply connected t id terminal mem rs.

. v l C 2. In a heatingsystem,a container of im- -perfect dielectric material, and means for subiecting said. container to the action I of a big frequency current.

3. In an electric furnace, in combination,-

5. In an electric furnace, in combination,

a dielectric member and a source of highfrequency electromotive force having its'terminals electrically connected to opposite sides of said dielectric member.

6. In combination, a member of im rfect dielectric material, a pair of termina mem-' bers, a source of high-frequency current supply connected to said terminal members, and means for insuring a substantially uniform energy loss throughout the mass of said dielectric member.

7.. In combination, a member ofimperfect dielectric material, a pair of terminal members, a, source of high-frequency current supply connected to sald terminal members, and means for insuring a substantially uniform current density throughout the mass of said dielectric member under all conditions of operation. 7

8. In combination, a member of imperfect dielectric material, a source of high-frequency current supply, a pair of terminal members connected to said terminals, operatively associated with said member of dielectric material, and means havin a higher dielectric strength than said first named dielectric material interposed between said terminal members and said member of imperfect dielectric material."

9. The method of heating a mass of material which com rises subjecting a member of imperfect die ectric material to a highfrequency electric field and causing the heat I generated therein to heat said mass of material.

10. The method ofheating 21 mass of material located in .a container of imperfect ing the container to the action of a highfrequency electric field.

11. The method otheating a mass of ma terial located in a container of imperfect dielectric material which comprises connecting one terminal of a high-frequency circuit to said mass of material, connecting the other terminal of said circuit to a terminal member located outside of said container, and energizing said circuit.

In testimony whereof,-I have hereunto subscribed my name this 22nd day of October, 1923.

CHESTER T. ALLCUT'I dielectric material which comprises subject-,