Electromagnetic coil



July 21, 1942. E. E. FRANZ ELECTROMAGNETIC COIL Filed March 13, 1940 FIG. 2 INVENTOR E. E. FRANZ will Patented July 21, 1942 ELECTROMAGNETIC COIL Erwin E. Franz, Cranford, N. J., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application March 13, 1940, Serial No. 323,713 1 Claim. This invention relates to electromagnetic coils and more particularly to electromagnetic coils having one or more windings upon a toroidal core. Toroidal coils have a great variety of applications in the electrical arts and especially in the arts of electrical communication. Especially in the field of telephony are such coils used in great numbers and in many ways. It becomes, therefore, a matter of material importance both to improve the electrical efficiency and reliability and to reduce the mass, bulk and cost of such coils. An object of the present invention is to produce a toroidal coil capable of manufacture in a simple, inexpensive and rapid manner, having a rugged, compact and simple structure, and of enhanced reliability, constancy and efficiency of electrical properties. With the above and other objects in View, one embodiment of the invention may present a toroidal core consisting of a ribbon of magnetic material wound spirally into an annulus and radially slotted to permit of sliding the segments to adjust the width of the gap, an annular rigid sheath of non-magnetic material preformed to contain the core and retain its segments in place, and one or more conductor windings upon the sheath. Other objects and features of the invention will appear from the following detailed description of one embodiment thereof, taken in connection with the accompanying drawing in which the same reference numerals are applied to identical parts in the several figures and in which Fig. 1 is a broken plan view of a coil constructed in accordance with the invention; Fig. 2 is a sectional View on the line 2-2 of Fig. 1; Fig. 3 is a plan view of the core slotting fixture with a slotted core therein; Fig. 4 is a broken plan view of a slotted core with its segments displaced for adjustment of the gap, and form an annulus as shown. This may be conveniently done by winding the ribbon or tape flatwise around a mandrel of suitable size. The material of the ribbon, according to the purpose for which the coil is intended, will be of an appropriate magnetic alloy. Thus for a loading coil or transformer, the core will preferably be of one of the recently discovered high permeability, low retentivity alloys such as that commercially known as Permalloy and consisting, for example, of 79% nickel, 17% iron and 4% molybdenum. A temporary retainer ring or band II (Fig. 5) is then slipped over the coiled core to retain its turns in place and the core in the ring is annealed to restore the magnetic properties damaged by the cold working effected by the winding operation. The retainer ring II will be preferably of the same material as the core in order to have the same coefiicient of thermal expansion and to avoid alloying of the core, although in some instances other material may be used. The wound and annealed core is then radially slotted. This may conveniently be accomplished by transferring the core from the ring II to a slotting fixture I2 such as is shown in Fig. 3. This fixture consists essentially of two suitably recessed jaws I4 and I5, pivoted together at I6. Stop shoulders at H prevent closing together of the jaws beyond the position shown. Opposite the pivot, the jaws are formed to leave a parallel side slot I8 through which a suitable saw may enter to cut, the slot I9 radially through one side of the annular core. With suitable care and sharp tools, the slot I9 may be cut in the core with only extremely localized and negligible damage to the magnetic properties of the core. The slotted core is then transferred from the slotting fixture I2 to one of the two matching annular cups 2I and 22 which together constitute the hollow toroidal body of the sheath 2%, e. g. to the cup 2I as shown in Fig. 4. If desired, the effective width of the slot or gap I9 may now be diminished to practically any desired extent by successively displacing the segments of the core within each other from their relative position of Fig. 3 to some such relative arrangement as shown in Fig. 4. This obviates any necessity for a great variety of fixtures I2 and corresponding saws to produce cores having gaps I9 of a variety of effective widths. The core gap having thus been suitably adjusted, the other sheath cup 22 is placed in position on the core; and the sheathed core is then ready for winding. Preferably the wound core after annealing and after slotting comes from the fixture I2 minutely larger in external diameter or smaller in internal diameter than the corresponding annular recess in the cup 21 and has to be sprung a very little, Well Within its elastic limit, to fit it into the cup. The mutual friction between the core and the cups and between the successive segments of the core will then retain the gap I9 safely at its adjusted width. The cups 2! and 22 as shown have each a semi-toroidal body with an annular recess to receive the core, and are also formed with integral fins or winding separators 23 and 24 respectively extending radially inwardly and outwardly and also laterally outwardly from the body of each. Each fin on one body matches a corresponding fin on the other, so that the two fins when placed in alignment as shown form a Winding separator extending substantially entirely around the body. The two cup bodies may be so dimensioned that their opposed edges are spaced apart as shown in Fig. 2, or they may be dimensioned to have these edges abut and enclose the core completely. Preferably the two sheath halves or cups 2! and 22 are preformed, e. g. by molding, from any appropriate and suitable non-magnetic and electrically non-conductive material, such, for example, as artificial resin, casein plastic, cellulose plastic, glass, ceramic material, wood, paper pulp, or the like generally. Preferably also metallic terminal members 25 and 25 may be mounted in the outer ends of the fins 23 and 2 1, being molded directly and permanently in place when the sheath cups are made by molding. Thus the completed coil will have terminal members not only well adapted for electrically connecting the windings of the coil as desired, but which are also sufiiciently mechanically rigid and strong to serve as mechanical supports by which the coil may be mounted without extraneous clamps, slings or the like. Insulated electrical conductors are then wound on the sheathed core in any suitable manner to form the windings 3c, the ends of the windings being attached to the several terminals in whatever arrangement is desired as indicated at 3!. An outer weather covering 32 of suitable material, e. g. impregnated paper tape, may be placed over the windings, if necessary. If the winding of the sheathed core be done in a machine for winding toroidal coils, the fins on the sheath may be used as members to locate a core in the machine for winding, quickly and accurately. While the coil disclosed herein as. an illustrative embodiment of the invention has four sets of fins intercalated between four windings, the particular number of fins and windings is not a characteristic of the invention. There may be any desired number of these elements. In a very simple form there may be no fins at all. In this last case there may be a single winding only, or more than one without any separating septa such as the fins shown. In another simpler modification it may be desired to omit the slot or gap l9, the continuous spiral core being then a very little overwound after annealing to be placed whole into the cups 2| and 22. The embodiment disclosed is illustrative only and may be variously modified and departed from without departing from the spirit and scope of the invention as pointed out in and limited solely by the appended claim. What is claimed is: An electromagnetic coil including an annular core consisting of a spirally wound ribbon of elastically deformable magnetic material and having a radial slot through one side thereof to render the segments of the ribbon slidable with respect to each other to adjust the magnetic Width of the slot and to render the core as a whole elastically deformable to alter the diameter thereof, a sheath enclosing the same and comprising a plurality of members preformed of nonmagnetic and electrically non-conductive material and each formed with an arcuate recess of diameter a little difierent from the normal diameter of the core to receive and elastically deform and substantially enclose the core and to retain the segments thereof elastically in place when adjusted relatively to each other, and. a winding of electrical conductor strand upon the sheath and separated thereby from the core. ERWIN E. FRANZ.



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