US2459605A

US2459605A - Induction coil

Info

Publication number: US2459605A
Application number: US632676A
Authority: US
Inventors: Warnken Elmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-12-04
Filing date: 1945-12-04
Publication date: 1949-01-18
Anticipated expiration: 1966-01-18

Description

E. WARNKEN 2,459,605

INDUCTION COIL Jan. 18, 1949.

Filed Dec. 4, 1945 I N V E N TOR, E/mew Mfl/mm Patented Jan. 18, 1949 INDUCTION COIL Elmer Warnken, Colerain Township, Hamilton County, Ohio Application December 4, 1945, Serial No. 632,676

4 Claims. 1

This invention relates to an induction coil and a method of manufacturing the same. The coil with which the invention is concerned particularly, is one adapted for use in permeability tuning of electronic devices, or of other devices embodying tuning circuits.

An object of the invention is to provide a coil of the character referred to, which will enhance the efll'ciency of a tuning circuit by offering very fine tuning characteristics and maximum control of frequency changes.

Another object is to provide a method of manufacture whereby the improved coil may be produced rapidly and inexpensively, to the extent that it may replace variable condensers in many instances and thereby materially reduce the cost of electronic devices, while at the same time increasing the efiiciency and serviceability thereof.

A further object is to provide an improved induction coil for the purposes stated, which is made mechanically rigid and durable without the use of an interior supporting core or form.

Another object of the invention is to provide a coreless induction coil, the wire convolutions of which may be disposed in exceedingly close proximity to an inner reciprocable metallic rod or slug, to gain the advantages of fine tuning and control as above mentioned.

The foregoing and other objects are attained by the means described herein and illustrated in the accompanying drawing, in which:

Fig. 1 is a side elevational view of an unmounted wire coil embodying the features of the invention.

Fig. 2 is a side elevational view, partly broken away, showing the coil mounted between a pair of end guides.

Fig. 3 is a side elevational view of a modification, part being broken away.

Fig. 4 is a side elevational view of a metallic rod or slug, and counterbalance means therefor, whereby the rod or slug may be guided in its movement longitudinally through the hollow coil.

The practice heretofore followed in producing induction coils for permeability tuning purposes, was that of winding the insulated coil wire upon a rigid hollow cylindrical form which became an essential part of the finished coil. The use of the cylindrical form was considered necessary for the support of the wire-convolutions, due to the very fine or light gauge wire used in forming the coil. Such wire in fact is so light as to possess very little strength, and even less rigidity. Since for use in permeability tuning the coil was required to accommodate a closely fitted straight metallic 2 rod or slug reciprocable lengthwise within it, the coil necessarily was maintained in a straight and rigid condition by means of the cylindrical form. The form, however, in order to impart the required strength and rigidity to the coil, had an appreciable wall thickness which limited the extent to which the slug could approach the inside con olutions of the coil. This condition was not conducive to efllciency and sharp tuning of the circuit in which the coil was connected, wherefore the aim of the coil designer has been to devise the thinnest possible form wall without sacrificing the strength and rigidity required for proper support of the wire convolutions of the coil. The limit in reducing the form wall thickness -"perently hase been reached, and conseouently the efilciency of such coils has reached its limit also.

In accordance with the present invention, the coil is made without an interior form or core, with the result that maximum proximity of the rod or slug to the innermost convolutions of the coil can be achieved. To make such a careless coil serviceable, a special reinforcing treatment is required in the fabrication thereof, as will be explained. With reference to the drawing, 5 indicates the coil of very fine insulated wire, the terminal ends of which are indicated at i and l. The coil is cylindrical in cross-section, and has an accurately formed and dimensioned inner surface I which is highly finished and smooth in character. The inside of the coil is adapted to snugly but slidably receive the metallic cylindrical slug 9, which is usually constructed of powdered iron pressed or molded to smooth rod formation. Since the coil is devoid of any inner core or form, the outer surface of the slug rests in very close proximity to the inner convolutions of the coil winding as the slug is reciprocated longitudinally therethrough incident to the tuning operation.

In fabricating the coil 5, a smooth metallic mandrel or temporary form, cylindrical in crosssection, is first coated with a suitable wax or other releasing agent. and then is wound with fine insulated wire to form upon the mandrel a coil of any desired winding pattern. Either during the winding operation or subsequently thereto, the winding is to be impregnated or saturated with a resinous material or binder which will set or harden to an inert state without checking or cracking, The resinous material or binder having been set or cured while the coil remains upon the mandrel, imparts to the coil the characteristics of mechanical rigidity and hardness such that it may be stripped from the mandrel and handled without liability to distort, bend or disintegrate. Due to the smoothness of the mandrel and the presence of the releasing agent upon it, the stripping of the coil from the mandrel is easily accomplished, with the coil leaving the mandrel accurately shaped and dimensioned to nicely accommodate a slug or rod such as Fig. 4 illustrates. Application of heat to the waxed mandrel will generally facilitate and expedite the stripping operation.

The binder used in producing the coil is preferably a resin of a type which, when cured or set to the hardened state, will possess the qualities of high resistance to abrasion, moisture absorption, and current leakage. It should also be resistant to checking or cracking upon setting, even when generously applied to the coil windings. A highly satistfactory material that may be used as the binder, is a highly plasticized thermosetting phenol formaldehyde resin. A synthetic resin of this type is obtainable under the designation of P- 162, a product of The Ironsides Company, at Columbus, Ohio.

Various other binders which will set up to a hardened state, may be employed with the attainment of satisfactory but generally less desirable results, among them being the thermoplastic resins, the contact or monomeric resins, and asphaltic compounds or binders such as shellac, spar varnish, and enamels. The phenol formaldehyde resin, however, is more acceptable because of its high mechanical strength when cured to the inert state, and its disposition to cure in thick films without cracking or checking. Should there be any tendency of the resin toward frothing or blistering during the curing cycle, the reaction may be readily controlled with the use of defoaming agents or anti-skinning agents, examples of which are compounds of the class of capryl alcohol, and hexone.

As was stated previously herein, the binder may be applied either during the winding of the wire upon the mandrel, or subsequently thereto. One procedure is that of passing the wire through a vat, spray, or other applicator of binding substance as the wire is fed to the mandrel. To hasten setting of the binder, heat may be applied to the coated wire before it reaches the mandrel, or, if desired, heat may be played upon the coil as the winding proceeds. Such treatment will serve to precure the binder and hasten completion of the process.

As an alternative procedure, the insulated wire may be coiled upon the mandrel prior to application of the binder material, and as a separate step of the process the coil while remaining upon the mandrel may be impregnated or saturated with binder material by dipping, spraying, coating or otherwise. Thereafter, the binder material may be set or cured to the hardened state by means of a baking or air-drying treatment, after which the coil may be stripped from one end of the mandrel as a rigid self-sustaining unit accurately shaped and dimensioned as to its inner wall surface 8.

To prepare the coil for use as a permeability tuning device, it will preferably be furnished with end guides such as are indicated at Ill upon Fig. 2 of the drawing. These guides may be in the form of cylindrical sleeves of insulating material applied to the opposite ends of the rigid coil, the internal diameter of each being the same as the internal diameter of the coil. The necessary connection may be effected between the coil ends and the sleeves, by shouldering or counterboring the sleeves as at l2, and forcing them over the ends of the coils. The sleeves may be cemented or otherwise secured in place upon the coil ends if necessary. The terminal ends of the coil winding may be projected through holes in the sleeves (not shown).

Instead of applying the sleeves in the manner illustrated by Fig. 2, they may be applied in accordance with Fig. 3, wherein |3--l3 are plain sleeves of insulating material or the like endbutted at M to the opposite ends of the coil. These sleeves are of an internal diameter approximating or conforming to the inside diameter of the coil, and may be held in axial alignment therewith by means of a wrapper or adhesive sheet of paper, cloth, or similar flexible material covering the exterior surfaces of the sleeves and the coil, and serving as a retainer I5. The means of applying guide sleeves to the ends of the coil is a matter of immateriality to the invention, and is capable of considerable variation in practice. The principal function of the sleeves is to lend support to the slug or rod 9 as it is reciprocated axially through the coil from end to end thereof, or to a position at which the slug is substantially withdrawn from the confines of the coil interior. The slug itself may be supported by means of small rollers l6 and I1 embracing an extension it of the slug. Movement of the slug or rod 9 axially of the coil serves to change the frequency of the tuning circuit of which it is a part. Because of the fact that no supporting form or core is present in the coil, the outer surface of the slug moves always in very close proximity to the innermost convolutions of the coil, with the result of attaining the finest possible tuning and accuracy of control. This result is not merely a lineal phenomenon, but rather a logarithmic factor which further enhances the behavior of the coil.

Computations and comparisons have proven that a gain in proximity of the slug area to the inside convolutions of the coreless coil has been increased by more than ninety percent, over the proximity characteristic obtainable with conventional coils wound upon plastic or paper cores or forms which remain within the coil. As a result of the present construction, much finer tuning and better control have been assured in application of the improved coil to permeability tuning of electronic equipment.

What is claimed is:

1. As a new article of manufacture, an electric coil devoid of internal supporting form comprising convolutions of insulated wire wound to hollow cylindrical formation, the convolutions thereof being fixed relative to one another by a hardened binding material to render the coil rigid and self-sustaining, notwithstanding the absence of a stationary core, and a cylindrical sleeve of insulating material having an internal diameter closely approximating the inside diameter of the coil, fixed to an end of the coil in axial alignment therewith, the innermost convolutions of the wire being included in the circumference of a coaxial imaginary cylinder which includes the inner surface of the sleeve.

2. A tuning device which comprises in combination, a coil of insulated fine wire wound to hollow cylindrical formation, the coil being devoid of internal supporting form the convolutions of which are cemented together to impart rigidity to the coil, a cylindrical sleeve having an internal diameter closely approximating the inside diameter of the coil fixed to an end of the coil in axial alignment therewith, the innermost convolutions of the wire being included in the circumference of a coaxial imaginary cylinder which includes the inner surface of the sleeve and a metallic substantially cylindrical slug fitted within the coil for reciprocating movement in the sleeve and in unobstructed relationship to the innermost convolutions of the coil winding.

3. A tuning device which comprises in combination, a coil of insulated fine wire wound to hollow cylindrical formation, the coil being devoid of internal supporting form the convolutions of which are cemented together to impart rigidity to the coil, a cylindrical sleeve having an internal diameter closely approximating the inside diameter of the coil fixed to an end of the coil in axial alignment therewith, the innermost convolutions of the wire being included in the circumference of a coaxial imaginary cylinder which includes the inner surface of the sleeve and a metallic substantially cylindrical slug fitted within the coil for reciprocating movement in the sleeve and in physical contact with the cemented inner convolutions of the coil winding.

4. As a new article of manufacture, an electric coil devoid of internal supporting form comprising convolutions of insulated wire wound to hollow cylindrical formation, the convolutions thereof being fixed relative to one another by a hardened binding material to render the coil rigid and self-sustaining, notwithstanding the absence of a stationary core, and a sleeve of an internal diameter closely approximating the inside diameter of the coil, fixed to an end of the 0 coil in axial alignment therewith, the innermost convolutions of the wire being included in the circumference of a coaxial imaginary cylinder which includes the inner surface of the sleeve.

ELMER WARNKEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 824,048 Thomson June 19, 1906 1,372,850 Turney Mar. 29, 1921 1,409,352 Adair Mar. 14, 1922 1,587,252 Hill June 8, 1927 ,643,998 Scott Oct. 4, 1924 1,674,934 Victo'reen June 26, 1928 ,827,571 Fiene Oct. 13, 1931 1,874,723 Dawson Aug. 30, 1932 1,887,005 Apple Nov. 8, 1932 1,944,870 Apple Jan. 30, 1934 1,994,534 Robinson Mar. 19, 1935 2,137,392 Cobb Nov. 22, 1938 2,245,373 Weiss June 10, 1941 2,280,981 Schuh Apr. 28, 1942 2,298,275 Bohren Oct. 13, 1942 2,375,911 Foster May 15, 1945 FOREIGN PATENTS Number Country Date 159,997 Great Britain Mar. 11, 1921 115,025 Australia Apr. 17, 1942