US2229680A - Polyphase high frequency heating device - Google Patents

Description

Jan. 28, 1941. u n E soMEs POLYPHASE HIGH FREQUENCY DEVICE Filed la! 13m A joward, 50mm Patented Jan. 28, 1941 UNITED fsTATEs PATENT OFFICE- Howard E. Somes, Grosse Pointe Park, Mich.

Application May 26, 1938, Serial No. 210,121

6 Claims'.

The present invention relates to induction heating by means of polyphase high frequency currents.

More specifically, it relates to an extension of J the principle involved in copending case Serial No. 101,993, filed September 22, 1936, wherein a single phase heating unit is utilized.

The present invention relates to a heating means comprising a plurality of induction heat- '0 ing means preferably, 'but not necessarily, identical with one another and usually axially alined with one another, the individual units being fed from separate phases of a polyphase high frequency supply system.

" An advantage of this arrangement is that by having a plurality of axially alined coils a greater axial extent of the article being treated can be heated simultaneously, thus speeding lup the work and also making it easier to obtain uniformly hardened articles.

A further advantage of polyphase currents over single phase currents even where several single phase units are connected in multiple or even energized individually from separate supply circuits, is that the polyphase system utilizes the leads more eillciently and thus permits having small leads for a given power output, and since the currents in the different coils are out of step with one another, cross-induction effects are largely eliminated and the distribution of the iiuxes is improved because of the exclusion of the possibility of synchronization of the individual currents or fluxes so that no resultant single flux can be produced in place of several independent "fluxes, as might occur under certain conditions with a plurality of single phase units.

Because of the fact that a plurality of alined inductors excited by polyphase current has an increased axial length,*the present device is particularly advantageous for the treating of articles of unusual length, for example, the treatment of engine cylinders of unusual length, long journals for bearings and other similar articles too numerous to catalog here.

A further advantage of polyphase induction heating of the type herein involved is that a generator of theA same power designed for polyphase output is usually more eiiicient than a single phase generator and in particular a three phase generator of the necessary power costs very much. less than would either a two phase or a single phase generator, the most expensive of all.

The individual inductors may `be connected,

.55 where three phase currents areused, in either Y (ci. 21a-13) or delta arrangement, a return conductor being afforded by the supporting means when a Y-connection is used and no return conductor being required at all when the delta system is employed.

It is contemplated that the inductors will be wound, Y-connected, in a preferred embodiment, either in three divisions, upon a single core or upon three adjoining cores, but other arrangements and numbers of phases are, of course, also within the scope of the invention.

One embodiment of the invention is disclosed in the accompanying drawing wherein:

Figure 1 is a diagrammatic axial section of a tubular metal article which is to be heat treated internally, with the three phase induction heating coils in place therein.

Figure 2 is a cross-section of the mandrel or support for the induction heating coils, theAsection being made on the plane indicated by the line 2-2 of Figure l.

Figure 3 is a diagrammatic representation'of certain electrical circuits involved in the device.

Figure 4 is a cross section of a modified form of compound cable.

Referring first to Figure 1, the article which is to be hardened, such as any tubular member I, usually of some length, is here to be hardened internally to the depth indicated by the reference character 2, the inner surface of the tubular article being indicated at 3. To do this it is necessary to heat the article I at its inner surface and this is accomplished by the following device, which is adapted to enter the bore of the tubular article and be moved therealong freely while fitting reasonably closely within it for electrical reasons, that is, to produce the minimum practicable air gap between the movable portion and the tubular article.

The movable member consists of a suitable support or mandrel l of suicient length to manipulate the coils and cores throughout the necessary portion of the article l.

Upon this mandrel 1, which is preferably hollow, there are mounted in the present case three cores 4, 5, and 6, each made of radially arranged laminations whose general direction thus extends parallel to the axis of the mandrel. This structure is illustrated in greater detail in said copending case above referred to, and certain addi- 50 `tional details of the construction may be found in such copending case.

The core 4 has a coil or winding II thereon, the core 5 similarly has a winding I2 and the core 6 carries the Winding I3. Each of these windings that the winding may carry electricity and also convey a cooling liquid, such as water. For economy of winding space it is preferred to make 'these conductors square, the successive turns being, of course, insulated from one another, in any suitable way, but other shapes of tubular conductors would, of course, also serve, if preferred for any reason.

The electricity and the cooling liquid are fed 1 into the respective coils II, I2 and I3 by conductors 8, 9 and I0, which run axially within the hollow mandrel 1, and which for economy of space are preferably of the cross sectional shapes best shown in Figure 2. These tubular conductors merge into the square tubes forming the windings by any-suitable form of joint which will preserve the continuity of the electrical and liquid conductive properties, for example by welding or by screw threaded connections, any form of joint well known in the art of liquid distribution which will also preserve the electrical continuity being, of course, available for this purpose. The welded :oint is the simplest and is the one illustrated in the present embodiment. Itwill be understood, of course, that the square tubing has sufllcient flexibility to be bent into the forms illustrated.

'Ihe three coils II, I2 and I3 terminate at their outgoing' ends in a common outlet tube Il, which is preferablv'grounded to the mandrel 1 although it need not be so grounded since the electrical energy fed into the lnductors in the form of delta-connected three phase currents needs no return conductor. In order: to stabilize the electrical. system, however, it will usually be found preferable toground the common point of the three phases which is. of course, the outlet tube or connector Il.

The air gap betweenA the movable cores and the interior of the article being heated is kept as small as practicable while not interfering with the free movement of the member through the tubular article. The flux paths are, illustrated and designated by reference characters I5, I6,v

and I1 respectively. It will be noted that while the ux spreads out in the laminations forming the respective cores, it doesnot penetrate to an equal extent outwardly in the tubular article because said tubular article is, of course, not laminated and, therefore, intense eddy currents as well as the skin effect and intense hysteresis effects are produced in 'the magnetic material constituting said article. All these phenomena tend to localize the heating effect to a more or less superficial zone, of limited but` appreciable depth. The tubular-articles suitable for this.

`'treatment are usually made of iron or steel or other materials which have suitable magnetic properties, such as certain alloys. C

It will be noted that important characteristics of the present device are its extreme compactness and excellent utilization of all the available space both within the hollow of the mandrel whichserves for feeding in the electrical energy, as well as the cooling medium, and also the excellent utilization of the space occupied by the cores which are made of radially tapered laminations, as disclosed in the copending case above referred to. v

I'he ,interior of the mandrel 1 may be lined with a suitable insulating .material such as I8, for example, mica or other refractory insulating material, which will prevent electrical contact between the conductors l. ,L and I0 and the mandrel surrounding the same and said conductors are further insulated from one another by sheets of :dat insulating material as indicated at I9, 20 and 2i inFigure 2.

While mica and refractory materials are preferred for the purpose it is not always necessary to have a refractory insulator because the conductors are water-cooled. However, the refractory nature of the insulation is ai decided advantage to guard against accidental injury in case the supply of cooling liquid should fail, whereupon the conductors would become abnormally heated and might injure any non-refractory insulations. Such heating could occur from two sources, first the current in the coil itself, and, second, the radiation of heat from the article being heat-treated.

- An electrical circuit suitable for cooperation with the above described device is illustrated very diagrammatically in Figure 3. Here 3l, 32, and 33 indicate input conductors preferably com'- ing from a source of ordinary commercial frequency three-phase current, `which operates the frequency converter 34, so asto produce currents of much higher frequency in the output side which are fed through conductors 35, and 31 windings 28, 28 and 3l and the Y-connected secondary or output windings 22,-23 and 24, which are connected by conductor 38 to the common ground, here indicatedas 1- It will be noted that 1 is the mandrel shown in Figure 1 and this use of the reference character 1 is intended to indicate that the mandrel 1 will form a suitable com'- mon ground. y l

While separate single phase transformers have been shownas constituting the three-phase bank, it will be obvious that any suitable arrangement of special transformers may be used if preferred and also while the primary windings have been shown delta-connected and the secondary windings Y-connected this also is purely a matter of preference, whose utility depends upon the con ditions in any given case. In fact if the. fre- 1 quency converter or other generator 3l has suitable'voltage and current characteristics it may be unnecessary to have any transformer bank whatsoever, in which case the windings II, I2 and I3 may be connected directly to the output side of the frequency converter. or other souree of high frequency current.

'Ihe degree of heating produced in the tubularv l article I and the extent to which said heat pene- Spcilically these merely controlling the rate at which the movable l inductor member moves with respect to the tubular article, thus determining the time of action.

Itwill be understood that the heating is followed by a quenching and the liquid used for cooling the inductor windings II, I2, or I3, may, of course, be used for quenching the surface which is to be hardened, in the manner disclosed in the copending case above mentioned, or a separate source of quenching liquidmay be employed, such details not being a part of the present invention.. To give some idea of the amount of energy involved in producing the heat it may be noted that approximately 15 to 20 kilowatts .cf power are exerted for every square inch of ond, although considerable variation is possible' in both the frequency and the power without departing from the scope of the'present invention.-

Where it is desired to eifect the current feed and cooling fluid supply entirely from one end t of the induction heating device through a single compound cable, such cable may take the form of that shown in section in Figure 4. Here the three individual phase tubular conductors 39 are of are shaped cross section arranged around a central common return conductor 40 of circular cross section and insulated therefromby the in terveninginsulating material 4I.

While I have herein shown and described certain preferred embodiments of my invention for the sake of disclosure, it is to be understood'that the invention is not limited to such specic embodiments but contemplates all such modifications and variants thereof as fall fairly within the scope of the appended claims.

What I claim is:

l. A polyphase high frequency internal heating device consisting of a number of separate adjacent substantially axially alined' cores of magnetic material, each having a winding thereon, and a pole piece extending radially outwardly from the cores between each pair of adjacent winding thereon and a pole piece extending radlallyoutwardlyfrom the cores between each pair of adjacent windings, at least one end of each winding being connected to an end of another winding and supply conductors connected one to one end 5 of each winding, said supply conductors being arranged closely together and in substantial alinement with the axes of the windings, and within the support.

4. A polyphase high frequency internal heating 10 device consistingv of a cylindrical hollow support. a tubular core of magnetic material telescopically mounted on said support, a plurality of separate windings of tubular conductive material thereon, and pole pieces of magnetic material extending radially fromthe core between adjacent windings, at least one end 'of each winding being connected to an end of another winding and tubular supply conductors of sector-shaped crosssection connected one to one end of each Winding', said supply conductors being arranged closely together but insulated from one another within the support, and substantially filling the hollow thereof, the tubular supply conductors and the tubular windings forming continuous open paths 25 for a liquid as well as for electricity.

5. A polyphase high frequency interior heating device comprising an elongated axially extending core of `magnetic material, a plurality oi windings thereon, and pole pieces for the core extending from the core radially outwardly across the remote ends of the end windings and between adjacent windings into close proximity to a surrounding object to be heated. y

6. A polyphase high frequency interior heating device comprising a plurality of energizing .windings extending end to end in axial alignment, and core means of magnetic material extending axial- 1y through the windings and radially outwardly between adjacent windings and across theremote 4o VIIOWARDE.- 0 -w=

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