US 2182820 A
Description (OCR text may contain errors)
Dec. 12, 1939. D. PISAREV 2,182,820
INDUCTION COIL Filed Dec. 21, 1938 Patented Dec. 12, 1939 2,182,829
UNITED STATES PATENT OFFICE" '7 Claims. (Cl. 219-47) This invention relates to new and useful imred only after further heating. At any instant provements in induction coils, and more para portion of the object mi y between its ends ticularly to a novel induction coil which is pargives the appearance of a more intense redness ticularly adapted for use in high frequency heatthan the ends, an indication of higher temperamg apparatus for treating susceptors disposed ture. The efliciency of a heating device of this I externally about the induction coil. type is considerably low since the entire length At the present time induction coils employed of the article to be heated does not receive the in high frequency furnaces of this type are genfull force or action of the flux or magnetic field erally of cylindrical or tapered shape, or otherinduced. The result of this is, of course, that wise conform to the contour of the article around it requires operation ,of the furnace for a longer 10 it. It is desirable to employ a coil of this charperiod of time than should be necessary to comacter in order that the coupling between the pensate for the time required to allow the smallcoil and article being heated may be uniformly er amount of heat in the ends to reach the demaximum throughout the length of the coil. sired temperature. In any instance, consider- That is to say, since the coupling between the able heat is dissipated or lost by radiation and coil and the article being heated determines the conduction from the object being heated. and heating action, and since the coupling at any this longer period of time required for operation point along the axial length of the coil depends of the furnace consequently results in an inupon the proximity of the coil at that point to crease in such radiation and conduction losses.
the article, it is desirable to employ a coil For "skin hardening, excessive conduction into I) which conforms to the contour of the arthe interior of the article is undesirable.
ticle around it thus obtaining uniformly maxi- By the present invention, this deficiency of mum coupling and consequent maximum heatcoils of this type here involved is materially ing throughout the length of the article. minimized and at the same time the advantages as- It is-characteristic of high frequency furnaces of such'a coil are retained. This is accomplished 28 employing such a coil within a susceptor howby providing at the ends of the cylindrical type ever, that the susceptor does not heat uniformly of coil inwardly converged or converging coil exthroughout its cross section due to the fact that tensions which serve to direct the magnetic flux the magnetic field does not penetrate sufficiently more obliquely to or more toward the surroundso into the susceptor away or outwardly from the ing article, thereby providing a better distribu- 80' coil. When electromagnetic energy flows into tion of the magnetic flux and greater induc-' the interior of a conducting means, its convertance while still maintaining the same good cousion into heat starts at the surface whereit enpiing within the central section of the coil. The ters and diminishes at every point distant beconverged or converging end construction causes yond the surface. Also this peripheral heating a more rapid heating of the end portions of an 86- is not distributed uniformly along its length due object located externally around the central secto the fact that the strongest field is midway tion of the coil and increases the control of heat between the ends of the coil with the result distribution and uniformity of heating, as desired, that the conversion of energy diminishes markalong the length of the article to be heated,
o edly along the axial direction of the coil as the due to the increase in strength of the magnetic 0 distance from the centeroutwardly toward the field induced therein which results in a more ends increases. For example, in a wheel hub efficient heating apparatus. The distribution having a cylindrical inside surface surrounding of the magnetic flux around this novel coil is a cylindrical coil of about the same length, the considerably better than a coil without extengreater part of the electromagnetic energy sions since the shape of the coil follows more 5 around the coil that is converted into heat in closely the path of the magnetic flux and rethe inner cylindrical "skin of the object is duces'flux interthreadlng through the coil. low in efllciency and distributed very unevenly With the foregoing observations in mind, the along its length, and the fact that the ends of principal object of the present invention is to the objectreside in a much less intense heating provide an induction coil which is constructed so region of the coil is evidenced by the visible and arranged to direct magnetic flux more obreddening of the cylindrical surface near the liquely to or more toward a susceptor located center when an object of considerable length is externally about the coil, and this and other obfirst heated, while the end portions of the object Jects of the invention, as well as the features remain black for a considerable period becoming and details of its" construction and operation. 55 I are hereinafter fully set forth and shown in the accompanying drawing, in which:
Figure l is a vertical section through an induction coil made according to this invention;
Figures 2 and 3 are diagrammatic illustrations showing modified arrangements of an induction coil embodying said invention;
Figure 4 is a diagrammatic view of a high frequency inductive heater or furnace embodying a coil made according to the present invention; and
Figure 5 is a vertical section of still another form of coil embodying said invention.
As pointed out above, the invention consists essentially in the construction of an induction coil to provide at its ends portions arranged in inwardly converging or oil'set relation in contrast to the conventional cylindrical type of coil. The flux or magnetic field thus set up externally of the coil is directed more obliquely to or more toward a susceptor placed thereabout, and referring to the drawing, an induction coil made according to the present invention may be composed of a continuous single layer or winding of relatively fiat or round tubular wire i wound to form a lower diverging portion A which terminates at its upper end in a central portion B of cylindrical shape, which in turn, terminates at its upper end in an inwardly converging portion C. In some cases it may be desired to have the central portion B of the coil conform to the cross-sectional shape of an irregular object placed thereabout to be heated and, therefore, it is understood that the invention embraces such modification.
The induction coil is preferably wound upon a suitable mandrel having a surface configuration which conforms approximately to the desired contour of the coil. The angles at which the opposite end sections A or C are disposed with respect to the central section B may be varied as desired to suit performance requirements, and the number of turns per unit of length in the same or other sections of the coil need not be uniform therein. Furthermore, the number of turns or coils of wire employed in the end portions A or C of the coil may vary as desired to provide any desired ratio between the number of turns or coils of wire in the said portions A or C and the central portion B and, of course, as the length of the said central portion B decreases or is decreased, the more critical or narrow will become the region of concentration of the magnetic field thereabout. The limiting case of this involves a coil such as that shown in Figure 5 of the drawing wherein the central section B' is of minimum length or height having but a single turn. An arrangement such as this enables concentrated heating of a small length of a susceptor and at the same time, the advantages of a multiple turn coil are retained.
The induction coil contemplated by this invention is not restricted to the particular configuration or shape illustrated in Figure 1 of the drawing, and similar results are obtained, for example. by constructing an induction coil to provide at opposite ends of the central portion B portions A or C' which curve concavely inwardly and axially of the, coil as shown in Figure 2 or as shown in Figure 3 wherein inwardly and axially curving convex portions A" or Cf, respectively, are provided at opposite ends of a central portion B". Other forms and shapes may, however, be employed with satisfactory results.
By directing the fiux or magnetic field more toward the susceptor or article to be heated, a coil constructed in accordance with this inven- 5 tion may be employed to advantage to materialb' increase the efficiency of heat treating apparatus such as high frequency furnaces, one form of which is shown in Figure 4 of the drawing, and comprises an induction coil 3 suitably mounted within a susceptor 4 and spaced therefrom by suitable insulation indicated by reference numeral 5, although in some cases no insulation is needed or desirablef As shown, the induction coil I comprises a plurality of turns of wire wound to the general shape or form shown in Figure l and consists of a central portion B and inwardly converging end portions A and C, a high frequency current being supplied to said coil 3 through the extrem- -ities of the end portions 8 and 1 thereof or at intermediate points as desired. For the purpose of cooling the coil, water or other cooling fluid may be passed through the tubular wire forming said coil through the openings aflorded at the extremities of the end portions 8 and I or at intermediate points of the coil. Use of the coil 3 for heating purposes as described is confined essentially to the central portion thereof in order to obtain maximum coupling and consequently maximum heating of the susceptor, and so that the inwardly and axially converging end portions A and C thereof will function fully to direct the magnetic field more obliquely to and more toward the susceptor to be heated so that the entire length of the object may receive the full force or action of such fiux or magnetic field. The heating efilciency and control of heat distribution of the coil is thus materially increased with the result that the length of time required to heat an object, the amount of power consumed, and equipment necessary are each substantially reduced. In some instances of use of the coil where it is desired to further aid in completion of the magnetic path through the coil, it may be desirable to place steel laminae within said coil.
While my description of the invention has been confined to the embodiment or adaptation thereof to high frequency induction heaters and furnaces, it will be obvious, of course that the use of said invention is not limited to a device of that nature butmay be employed to advantage in any instance where it is desired to obtain a maximum magnetic field strength in a susceptor about the coil and where the length of the central portion is decreased the more narrow or critical is the region of concentration of the magnetic field thereabout.
1. An inductive heating device comprising an induction coil consisting of a winding of wire having a central heating portion of wire arranged for disposition within a susceptor to be heated,
and end portions of wire arranged in inwardly flafi'set relation with respect to said central nor.-
2. An inductive heating device comprising an induction coil consisting of a winding of wire having a central substantially cylindrical portion 1. arranged for disposition within an object to be heated, and end portions leading fromthe ends of said central cylindrical portion and offset with respect thereto in a direction toward the axis of the coil, said end portions constituting means for 1.
' amaeao directing the lines of flux more toward the object to be heated.
3. An inductive heating device comprising an induction coil consisting of a winding oi wire having a substantially straight-sided heating portion arranged for disposition within a susceptor to be heated, and end portions oflset inwardly toward the axis with respect to the straight-sided portion to control the distribution of heat in the susceptor alongthe axial direction thereof.
4. An inductive heating device comprising an induction coil consisting of a winding otwire having a central substantially cylindrical portion consisting of at least one turn of the wire arranged for disposition within a susceptor to be heated, and end portions ofl'set inwardly with respect to the central portion, said end portions constituting means for directing the magnetic flux more toward the susceptor.
5. An inductive heating device comprising an induction coil consisting of a winding of wire having a central substantially straight-sided portion arranged for disposition within a susceptor to be heated and curving end portions leading away from the ends of said central portion and onset with respect thereto in a direction toward the axis of the coil.
6. An inductive heating device comprising an induction coil consisting of a winding of wire having a central heating portion conforming substantially to the internal contour of and arranged for disposition within a susceptor to be heated and end portions arranged in inwardly offset relation with respect to the central portion, said end portions constituting means for controlling the disnae disposed within the coil for the purpose'of improving and controlling the magnetic path in the coil. i
' D AVID 'PISAREV.