US2724763A - High-frequency heating apparatus - Google Patents

Description

J. A. REDMOND HIGH-FREQUENCY HEATING APPARATUS Nov. 22, 1955 2 Sheets-Sheet 1 Filed Aug. 12, 1950 Network Generator L INVENTOR John A. Redmond.

ATTORNEY Nov. 22, 1955 J. A. REDMOND 2,724,763

HIGH-FREQUENCY HEATING APPARATUS Filed Aug. 12, 1950 2 Sheets-Sheet 2 Fig.3.

O O O O O O O O O O O O O O O D WITNESSES:

INVENTOR John A. Redmond.

BY92Z ATTORN EY United States p fl 2,724,163 HIGH-FREQUENCY HEATING APPARATUS John A'. -Redmond, Baltimore, Md;,-- assigno'r' {to 'Westinghouse Electric Corporation, East llittsburghyPa acorporationtofiPennsylvania Application August 12,1950, Serial No. 179,078

'4 .Claims. KC]. 219-10179) .My invention relates broadly tohigh-frequency heating; .but, more particularly, my invention is" directed .to .improvements in apparatus for the'h'igh-frequenc'y heatingof a tubular object, by tubular object meaning an object having .a central opening capable of receiving .an electrical conductor.

.A purpose of my invention-istto provide.ahighfrequency heating apparatus capable of heating a tubular metallic obect by heating currents magnetically induced .therein in a mannerthat causes the currents to flowjlengthwisqor axially of the opening in the object, instead-of in apath around the axis as taught by theprior art.

A further object of my invention is to provide .aninduction heating apparatus of a type described, capable 10f heating a tubular object, such as a small hollow shaft or bushing; the apparatusbeing such as to'be capable of simultaneously heating the inner and outer .surfacesTo'f the object.

In accordance with the teachings of my invention, I provide a pair of nested inner and outer heating conductors which are connected electrically .sothat current flows lengthwise or axially along both of them. Thecon- .ductors are spaced, and thefinnerconductor isplaced'ins'ide of the opening of the tubular object totbefheated, preferably out of contact with the conductors. When current flows through the conductors, the object .is heated. In the .case of a ferrous object, theapparatus can be arrange'difor'hardening a surface of the ferrous object by perforatinga wall of one or both of 'the conductors and passinga quenchingliquid through the perforations or openings at a suitable time.

'Objects,'features and innovations of my 'inve ntion,.in addition to the foregoing, will be discernible from thexfo'llowingdescriptionof illustrative apparatus embodying the invention. The description is ,tobe taken in conjunction with the accompanying simplified drawings, in whichudetails such as work-handling holders, and .so forth, .are omittedin the interest of clarity and brevity. In the drawings:

Figure l is asomewha't diagrammatic view of. apparatus embodying my invention;

Fig. 2 is a sectional viewsubstantia'lly on the 11inen n of Fig. '1;

Fig. '3 is a vertical sectional view of a preferred embodiment of my invention, the section-plane being indicated by the broken line 'IIIIII in Fig. 4;

Fig. 4 is a plan view of the apparatus ofFig". 3;

Fig. 5 is a sectional view substantiallyon the line'V-V .ofFig. 3; and g Fig. 6 is a sectional'view substantially onthliriVI-VI of Fig. 4.

Figs. land 2 show a simplified induction heating apparatus, illustrative of 'theibroad principle of "my invention, that can be used for heating bushings." The, apparatus comprises an induction heaterwhich is indicated in its en- "tirety 'byth'e reference numeral'Z. The inductidnheater2 comprises a straight inner heating conductor '4 and a straightouter heating'conductor 6; The conductors are'ciroi-'18,) '.are"secured.Such points on each heating conductorare axially spaced, one pair of spaced points (-as cularin cross section andkaremade of ahighly conducting metal such as copper. The outerconductor 6 is hollow so thatthe'inner conductor 4 'canbe nested therein,;prefe'rably parallel and concentric therewith. The'bottomends of the heating-conductors 4 and 6.are intimately electrically connected together by a conductor-means comprising a direct electrical connection-conductor shown as an annularplate '8 whichfis also made from ahighlyconductive metal.

I Theheating conductors 4 and .6 are radially spaced,i. e., they are separated in a direction perpendicular to their common axis, so as to provide awor'k-receiving space 10 'therebetween. This [space 10 is generally annular in cross section and is bounded'by the outer or facing surface of the innerheating conductor 4, "the inner or facing surface of the outer heating conductor 6, and the inner or facing surface of the connection-plate 8.

' Atubu'lar object 11in the formof a cylindrical tube, is supported 'in the work-receiving space 1'0 in any suitable manner for 'heat treatment. .A work-supporting means is shown as comprising aplurality of spaced piers 14, carried "by the connection-plate 8. Eachpier has a seat or notch for receiving .an end of the tubular object 12. The piers are made of a material that 'willstand a high temperature, and molybdenumhas been found satis'factoryfor this purpose.

- 'A't'the ends 'of the'heating conductors 4 and 6 which are opposite to those associated with the connection-plate 8, a pair of relatively insulated power-supply conductor-connections16.and' 18 are provided; the connection 16being intimately securedlo-it'he inner heating conductor 4 and "the connection 18 'being similarly secured to the outer .heatin'g'cdnductor 6. The 'relat'ive'lyin sulated power supply *conn'ect'ions16 and 18 are supplied with high-frequency energy, generatedin a'high frequency generator 20 that "feedsithe generated current to them, either directly or .through asuitablecircuit' 22 that may include a balancing networlcor transformer, or other electrical circuit-improviin'g' element, as 'isknown 'to'the 'art.

*It is necessary to provide away of placing an object to .be heat-treated into the work-receiving space '10 and "can beused.

For an understanding of the. operation of the induction 'heater '2, it maybe assumedlthat the high-frequency generator-20 is .energized'and is feeding high-frequency elec- 'trical"power'to the conductor-connections 16 and 18. It canbe' assumedzthat, atsome instant, thecurrent is flowing fromth'e connection 16, downwardly along the outer surface of'the inner conductor t, :radially outwardon the inner surface of the connectiomplate 8, and upwardly "along the :inner surface of the outer conductor 6, to the ofaxially spaced'points, one ateach of .its ends, to which 'circuivconnec'ti'ons (that is.plate 8 and a connection '16 :16'and 18)"co'nduc'torlying on one axial side of the worktreating space 10 and the other pair'of spaced points (as '4-"8-an'd'6 8) lying on'the' opposite side.

The alternating current, flowing .in the conductors 4 and 6; induces rheating currents in the metal tubular object "12 which is carried onihe'piers'14, preferably concentric with-theheatingconductors. The induced currents will fiow in e'ach "curved side of the tubular object, and in a direction opposite to the direction in which the current flows inthe' surfaces 'of the facing heating conductors.

Accordingly, at t'h'eflassumed "instant, current will flow upwardly "along the elements "of the inner "surface of the tubular-"object "and downwardly along the outer surface pleted in a radial direction at the ends of the tubular objects. The induced current heats the surfaces of the object in a manner understood in the art.

It is understood, of course, that the current flows in a thin surface-film having a thickness or depth which depends, among other things, upon the frequency of the power delivered by the high-frequency generator.

If it is found necessary to cool the'heating nested conductors 4 and 6, an outer cooling-coil 24 may be helically wrapped around the outside surface of the outer conductor 6, in good thermal contact therewith, and an inner cooling-coil 26 may be disposed in contact with the inside surface of the inner conductor 4, which can be made hollow for this purpose, as shown in Figs. 1 and 2. The outer coil 24 has a water-inlet 28 and a water-outlet 30; and the inner coil 26 has a water-inlet 32 and a water-outlet 34, extending downwardly through the open bottom of the heating conductor 4.

Figures 3-6 show a more practicable structural form of my induction heater, indicated in its entirety by the reference numeral 40. The induction heater cornprises an inner copper heating conductor 42 and an outer copper heating conductor 44. In the preferred embodiment illustrated in Fig. 3, the outside diameter of the inner conductor 42 is one inch, and the inside diameter of the outer conductor 44 is three inches. The lower end of the inner conductor 42 has an integral outwardly extending flange or connection-plate 46, to which the lower end of the outer heating conductor 44 is firmly joined, for intimate electric contact. The conductors 42 and 44 are radially spaced to provide an annular work-receiving space 48 (Fig. 3) similar to the space 10 of Fig. l.

The inner conductor 42 is hollow, having an open lower end and a closed upper end 50 that terminates in an upwardly extending threaded portion 52 which projects above the upper end of the outer heating conductor 44. The hollow part of the inner conductor 42 forms a channelmeans 54, which is defined by the cylindrical wall 56 of the conductor 42, and which is perforated to provide ou'tlet quench-openings for a quenching-liquid which is fed into the channel 54 in any suitable manner. Thus, said channel 54 may be supplied with a quenching-liquid through a pipe 58. The inner heating conductor 42 may be cooled, if necessary, by a helical cooling coil 60, which contacts the inside of the wall 56 and which is provided with water inlet and outlet-pipes 62 and 64, respectively, which extend downwardly through the lower end of the inner heating conductor 42.

The outer heating conductor 44 is ,also constructed so as to permit the outside of the work-piece to be quenched. To this end, the outer heating conductor 4.4.is hollow to provide an annular channel-means 68 therein. Specifically the outer conductor 44 comprises a solid or imperforate outer tubular wall 70, and a perforated inner tubular wall '72. Quenching liquid is supplied to the annular channel 68 of the outer heating conductor 44 by means of one or more liquid-supply pipes 76. For keeping the inner wall '72 of the outer heating conductor 44 cool, a

cooling coil 74 is helically wound around it in intimate thermal contact therewith. This cooling coil is provided with water inlet and outlet pipes which liquid-tightly pass through the outer wall of the outer heating conductor.

The work to be heat-treated is represented, in Figs. 3-5, as a ferrous bushing 78. 80, which in turn are replaceably and snugly carried in grooves of a turntable 82 which is adapted to rotate around the lower end of the inner heating conductor For rotating this turntable, a belt 84 is provided which passes through tubes 86 passing through the outer heating conductor 44.

The upper end of the outer heating conductor 44 has an integral flange or copper plate 90,-that closes the upper end of the annular channel 68 in said conductor 44.

It is carried on notched piers diameter to the inner diameter of the wall 72. Secured tube-oscillator generators. as shown in Fig. 3, I have successfully hardened both to the underside of this top-plate 90 is a conductorconnection 92. Resting on the top-plate 90 is a layer of insulation 94 which separates said plate from a second conductor-connection 96. The connections 92 and 96 are equivalent to the connections 18 and 16 of Fig. 1. As shown in Fig. 4, the insulation 94, the lower connectionplate 92 and the upper connection-plate 96 have U-shaped cutout portions 98 that extend beyond a side of the outer heating conductor 44.

For electrically connecting the connection 96 to the inner heating conductor 42, a narrow copper securingbar 100 is provided, having three spaced holes, the central one of which receives the extending threaded portion 52 of the inner conductor 42, and the end ones of which receive threaded bolts 102 and 104 that extend upwardly from the connection 96. Nuts 106 clamp the securing bar 100 in intimate contact with the connection 96 and with a flange 108 at the top of the inner heating conductor 42. Accordingly, whenever work is to be inserted into, or removed from, the work-receiving space 48, the securing bar 100 is first removed.

Assuming that work to be heated is in the space 48, the securing bar 100 is tightly bolted down, and the relatively insulated connections 92 and 96 are energized from any suitable source of high-frequency energy. The turntable 82 is rotated for rotating the Work carried on the piers 80. After the desired heating interval, quenchingliquid is supplied to the channel-spaces 54 and 68 for hardening the inner and outer surfaces of the bushing. Quenching liquid may flow out of the work-receiving space 48, through a plurality of spaced openings 109 in the bottom connection-plate 46. It is also to be observed that the connection-bar 100 is of less width than the inner diameter of the outer heating conductor 44. Consequently, quenching-liquid can also flow upwardly through the resulting opening, including the cutout portions 98.

An induction heater in accordance with my invention may be used with practically any of the more common frequencies now used for induction heating. I have used electric power derived from rotating alternators and from In a particular setup, such surfac'esof a six-inch bushing by using current at a frequency of about ten thousand cycles per second and flowing at eight thousand amperes. I have also used similar equipment for hardening with currents at considerably higher frequencies. The wave lengths are considerably longer than the work- piece 12 or 78, so that there are no significant standing-wave effects in the heating apparatus, to produce non-uniform heating patterns in the workp ece.

In general, the object to be heated should have its axial- 'ly extending curved surfaces radially spaced about equally from the heating conductors. Non-equal radial spacing causes non-uniform current-distribution in Fig. 2. In

'Fig. 3, rotating the workpiece 78 produces even heating;

even though the radial spacing may be non-equal. For this reason, it is desirable to rotate the piece.

While I have described my invention in connection with an embodiment which is at present preferred, it is obvious that this embodiment is subject to considerable changes and modifications, and that the principles of my invention have considerably larger application, beyond that described in connection with the preferred embodiment.

I claim as my invention: 4 1. High-frequency inductive-heating apparatus, including a supporting-means for holding a hollow cylindrical conducting object having interior and exterior surfaces to be heated, and high-frequency inducing-current means comprising an inner tubular inductor member and an outer 'tubular inductor member respectively positioned adjacent the interior and exterior surfaces of said object, for subjecting said surfaces to high-frequency current-inducing fields such as to induce high-frequency surface-skin cur rents which flow axially and in opposite directions along the respective interior and exterior surfaces of said object and radially at the ends of said object.

2. High-frequency inductive-heating apparatus, including a supporting-means for holding a hollow cylindrical conducting object to be heated, said object having substantially parallel interior and exterior surfaces, motor means for rotating said supporting-means about an axis which is approximately coincident with the axis of said object, and high-frequency inducing-current means comprising inner and outer tubular inductor members, said latter members being positioned adjacent respectively the interior and exterior surfaces of said object for subecting said surfaces to high-frequency current inducing fields such as to induce high-frequency surface-skin currents which flow axially and in opposite directions along the interior and exterior surfaces of said object and radially at the ends of said object.

3. High-frequency heating apparatus of a type described, comprising, in combination, a plurality of nested heating conductors including an inner tubular induction heating conductor and an outer tubular induction heating conductor, said conductors extending in the same general lengthwise direction and being radially spaced to provide a work-treating space therebetween, work-supporting means for holding an axially extending workpiece in said space, said workpiece being positioned substantially parallel relative to said conductors, and circuit-means for supplying high-frequency current to said conductors, said circuit-means including circuit-connections between a pair of spaced connection-points on each of said conductors, said pairs of points being on opposite sides of the work-treating space, said circuit-connections including a direct cross-connection between a first of said points on said inner conductor and a first of said points on said outer conductor, said first points lying at the same end of said work-treating space.

4. An induction heater of a type described, comprising, in combination, a pair of nested substantially parallel tubular induction heating conductors, said conductors being radially spaced to form a space for receiving work to be heated, conductor-means directly connecting an end-portion of the inner of said conductors to an endportion of the outer of said conductors, said conductorrneans being at an end of said space, means for supporting a metallic object in said space, with the inner conduc tor passing through said object, means for providing access to said space for loading and unloading said metallic object to and from said space, said means being at the other end of said space, and power-supply means associated with said conductors for causing high frequency currents to flow axially in said conductors.

References Cited in the file of this patent UNITED STATES PATENTS 1,566,500 Northrup Dec. 22, 1925 1,987,458 Adams Jan. 8, 1935 2,145,864 Denneen et al Feb. 7, 1939 2,181,921 Schlup Dec. 5, 1939 2,294,413 Marshall Sept. 1, 1942 2,359,285 Bennett Oct. 3, 1944 2,364,623 Denneen et al Dec. 12, 1944 2,404,987 Rudd July 30, 1946 2,449,325 Rudd et al. Sept. 14, 1948 2,483,623 Clayton Oct. 4, 1949 2,517,098 Dreyfus Aug. 1, 1950 2,556,236 Strickland, Jr. June 12, 1951

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