US 2678371 A
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pad-A y 11, ,1954 w. P. ANDREW 2,678,371
- HEATING INDUCTOR Filed Jan. 16, 1952 Inverfibor: William FAhdr'ew, 0
b Wm His Attorngs.
Patented May 11, 1954 HEATING INDUCTOR William P. Andrew, Detroit, Mich, assignor to General Electric Company, a corporation of New York Application January 16, 1952, Serial No. 266,676
4 Claims. (01. 219-10179) This invention relates to induction heating coils, and has for its object the provision of an induction heating coil which heats a selected portion of a work-piece without heating closely adjacent portions of such work-piece.
t is often desirable to heat only a selected portion of a piece of metal in order to harden it or otherwise affect its characteristics, while at the same time it is desired not to heat closely adjacent portions of the piece of metal so that these closely adjacent portions retain their original characteristics. This invention provides an induction heating coil which permits conveniently such selective heating of magnetizable materials.
In carrying out my invention in one manner, I form an electrical conductor into an elongated induction heating coil having a plurality of spaced apart turns. In order to counteract the inductive effect of a portion of one of the endmost turns and thereby limit the heating effect of the coil beyond this end turn, I double back a portion of the conductor so that the doubled back portion is closely adjacent the endmost turn in current opposition thereto.
For a clearer and more complete understanding of the invention, reference should be had to the accompanying drawing in which Fig. 1 is a perspective view of a typical induction heating coil embodying this invention, while Fig. 2 shows the coil of Fig. 1 in position for heating a projection on a rocker arm member.
Referring to Fig. 1 of the drawing, there is shown a heating inductor I comprising a conductor II, which is preferably hollow tubing of a metal such as copper or other conductive material, formed into an elongated coil having a plurality of longitudinally spaced turns. A coil having approximately three and a quarter turns is shown for purposes of illustration, and the three turns are designated by the numerals I 2, l3 and It. It will be understood, however, that any desired number of turns may be employed, depending upon the voltage and frequency of the supply source and the size and configuration of the material to be heated.
At one end of coil I0, the conductor II is doubled back so that a portion [5 thereof is'positioned closely adjacent the upper portion [2a of endmost coil turn l2 to form a reversed part turn which is coextensive with a circumferential end portion of the coil. With this arrangement, current flows in opposite directions in corresponding part turns of the coil formed by portions l5 and IM when conductor II is connected to a suitable source of high frequency electrical potential, such as a 540,000 cycle source, and the magnetomotive forces produced by current in portions and [2a counteract each other.
In Fig. 2 of the drawing is shown a typical arrangement utilizing a coil such as that of Fig. 1
for heating a selected portion of a metal member. In this typical example, it is desired to heat only the projection l6 on a rocker arm I! of the type which is commonly used in automobile engines and the like. The projection It on the rocker arm member may have a depression 24 therein for receiving the end of a valve stem, and it may be desired to heat-treat projection IS in order to harden it and provide a good wearing surface in depression 24; while at the same time it is desired not to heat the cylindrical body portion of member l1, particularly the portion lla most closely adjacent the coil 1 0, so that the body of the rocker arm member remains relatively soft and machinable after projection It has been hardened. This desired heating effect is accomplished by positioning corresponding part turns of the coil in which current flows in opposite directions so that one of said part turns is located between the other of said part turns and that part of the work-piece in which it is desired to counteract th heating effect of the coil when its body portion encloses a part of the Work-piece in which it is desired to have a build-up of heat. Specifically as shown in Fig. 2 of the drawing, part turn l5 of coil 10 is interposed between part turn IZa thereof and a portion Ila of the work-piece I! when projection Hi thereof is positioned within coil I0. Thus less than one complete turn of the coil extending along and beyond an adjacent complete turn of the coil and connected in opposite current conducting re1ation therewith secures the desired selective heating effect of the coil on a work-piece by reason of the selective flux cancelling effect of its coil turns.
I have found that the heating inductor of this invention provides excellent selectivity in heating projection I6- without heating the adjacent body portion of the rocker arm member when the rocker arm member is positioned with the projection I 6 within coil 10 in the manner illustrated in Fig. 2. The counteracting of the magnetomotive force of portion 12a by the magnetomotive force of portion !5, in the manner described previously, substantially cancels the induction heating effect of coil I0 on adjacent portion Ila of the rocker arm member.
It, perhaps, should be pointed out at this point that the problem of heating a closely adjacent portion such as ila cannot be solved in many cases merely by moving th heating coil farther away from such part or by removing all or part of some of the turns from the coil. The number of turns on the coil is fixed within rather narrow limit by the voltage and frequency of the supply source. While, if a relatively short projection such as [5 is to be heated, one or more turns of the heating coil necessarily must be close to portion [lain order for the coil to impart heat to projection H5 at the necessary rate. The heating must be relatively rapid followed immediately by quenching in order to obtain selective heating of projection l6 only.
I have found that it is possible by the use of my invention to heat successfully small projections and other similar parts which cannot be selectively heated successfully by any other known type of coil including hairpin, single turn and multiple turn without the doubled back portion, nor by any other known arrangement including various types of shielding between the coil and the main body portion such as IT.
As mentioned above it is necessary to quench the heated portion is of rocker arm member I! immediately after it is heated, in order to prevent the heating of the body of the rocker arm member by conduction from portion H's, and this quenching operation can be carried out in any well known manner.
When the portion 55 of the conductor is positioned as illustrated in order to counteract the inductive effect of a portion of the end turn of the induction heating coil, the heating time is increased slightly, perhaps 1 or 2 seconds, over the time required if an inductor without this doubled-back portion is employed. In a typical case in which this invention is employed, the heating time is approximately 6 seconds. However, my inductor provides excellent selectivity of heating, which more than compensates in many situations for the slightly increased time required.
In the operation of coil Ill, the two projecting ends thereof are connected to a sou "cc of high frequency electrical energy, as illustrated schematically by connections l8 and it to a source of energy lit. The projecting ends of coil ill may also be connected by suitable connections 21 and 22 to a source of cooling water (not shown). Cooling of inductor it, by circulating water through the hollow tubing H, or by other suitable means, is generally necessary in order to prevent overheating the inductor.
Rocker arm members of the type illustrated in Fig. 2 generally have two or more projections, and another projection 23 on rocker arm member ll may be heat-treated simultaneously with projection it if desired, by employing another inductor lilo. (shown in dashed lines in Fig. 2) similar to inductor Ill. Likewise, two or more inductor coils it may be supplied in series or parallel from a single source 20, if desired.
While I have shown in the drawing a coil Ii] which is approximately rectangular in transverse crosssection, it will be readily understood that any desired cross-section may be employed, and generally this is chosen to correspond with the cross-section of the part to be heated. It will be understood also that any desired portion of the end turn It. ma have the inductive effect thereof counteracted by an adjacent doubledbacls'. portion of conductor H. In the induction heating coil illustrated, approximately one-quarer or" the end turn has a doubled-back portion positioned closely adjacent thereto, but this can be any part of the end turn from none up to the complete turn, as necessary to secure the desired confining effect on the heating of coil I0.
It will be apparent also to those familiar with induction heating coils that a similar arrangement can be employed on both ends of the inductor if desired. Such an arrangement makes it possible, forexample, to heat a selected intermediate section of an elongated member, such as a rod, without heating the'portions of the rod closely adjacent to each end of the selected section.
Another arrangement is to locate a portion of conductor H in current opposition closely adjacent a selected portion of one of the intermediate turns of the coil, such as turn 13 in the drawing, for example. In this manner the inductive effect of such selected portion is counteracted, with a resulting heating discontinuity on the member heated by the coil.
Therefore, while I have described and illustrated one preferred embodiment of my invention, it will be understood that modifications may be I intend to cover by the appended claims all such modifications as may fall within the true spirit and scope of my invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
l. A high frequency induction heating coil having less than one complete turn thereof located closely adjacent and along a circumferential portion of a complete turn thereof and connected in opposite current conducting relation therewith whereby the flux cancelling effect of said less than one complete turn of said coil controls the in-- ductive heating ffect of said coil on a portion of a work-piece associated therewith.
A. hi h frequency induction heating coil having at one end thereof less than one complete turn connected in opposite current conducting relation with and extending along and beyond a corresponding circumferential portion of a complete turn of said coil and between said complete turn and a portion of a work-piece in which a build-up of heat to be avoided.
3. A multiple turn induction heating coil having corresponding part turns thereof connected to 'te current conducting relation with one another, said part turns being positioned relatively to one in said coil so that one of said turns is located between the other of said part turns and that part of a work-piece in which it is desired to counteract the heating effeet or" said coil when said coil is inductively coupled with said workpiece.
4. A high frequency induction heating coil which in use has at one end thereof a circumferential portion located closely adjacent a part of a work-piece in which a build-up of heat is to be avoided when said coil encloses another part of said work-piece in which a build-up of heat is desired, said coil having coextensive with said circumferential portion of said one end thereof a part turn which is closely adjacent a corresponding part of a complete turn thereof with which it is connected in opposite current conducting relation.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,401,899 E-ierwirth et al. June 11, 1946 2, l52,162 Stanton et a1. Oct. 25, 1943 2,452,801 Storm Nov. 2, 1948 2,479,341 et a1 Aug. 16, 1949 2,512,893 Gehr June 27, 1950 FOREIGN PATENTS Number Country Date 983,746 France June 27, 1951 OTHER REFERENCES High Frequency Induction by Frank W. Curtis, January 1950, McGraw-Hill Book Co.