US2434511A

US2434511A - Method of making electric coils

Info

Publication number: US2434511A
Application number: US557710A
Authority: US
Inventors: Joseph T Osterman; Alvah O Ericksberg
Original assignee: American Bosch Arma Corp
Current assignee: Ambac International Corp
Priority date: 1944-10-07
Filing date: 1944-10-07
Publication date: 1948-01-13
Anticipated expiration: 1965-01-13

Description

JM 13, 1948 J. T. osTERMAN ETAL 2,434,511

METHOD OF MAKING ELECTRIC COILS Filed Oct. 7, 1944 @M4 @dal ATTORNEY Patentedjlan. 13, 1,1948

METHOD OF MAKING ELECTRIC COILS Joseph T. Osterman,

, Ericksberg, American Northampton, and Alvah 0. Springfield, Mass., assignors to Bosch Corporation,

Springfield,

' Mass., a corporation of New York Application October 7, 1944, Serial No. 557,710

oolaims. (oies-155.57) L The present invention relates to methods of making electric coils on heat-resistant coll forms with wire terminals rigidly fastening the coil winding to the form, by bonding the end turns of the winding to separated conducting areas baked on the form. Such coils employ relatively ne wire and are used generally as for instance in sparkplugs in ignition systems of the capacitor discharge type. electrical instruments, and radio and other high frequency devices.

Heretofore it was customary to solder the ends of the coil winding to conducting areas or bands character.

strains. Preferably also the conducting areas onv the coil form constitute end bands of ysuch width as will be'covered vby a number of turns of bare wireof the size used, so as to secure rigid terminalsof uniform and permanent electrical Preferably also the same metallic material is used for producing the conducting areas on the form and' for bonding the winding ,to those areas, since such subsequent bonding lmay thenk be accomplished at a temperature,

lower than is required to produce the conducting areas withv the metallic material then penetratsometimes baked on coil forms to produce the' v coil terminals, butgthis subjected the form to heat shocks of such nature as often fractured it particularly if silver solder was used, or set up such stresses and strains as resulted in unduly fragile forms which broke upon ordinary mechan ical shock orvibration. Also, the electric contact between the wire and the conducting areas occurred at spots only, and the surface of the wire at the joints often corroded in soldering and sometimes'further thereafter so as to be faulty and non-uniform' in resistance upon completion besides deteriorating during service. Also the solder sometimes formed `lumps and otherwise lacked uniformity in dimensions, which detracted from the smooth and regular dimensions of the terminal in such wise as to prgvent reliable contact therewith in electrical devices and circuits.

, Furthermore, in application to sparkplugs in f which the coils were impregnated'in place at comparatively high temperature and also in service reached a comparatively high temperature at the location ofy the coil, the solder would sometimes melt and thereupon interrupt the electrical circuit at one or both terminals of the coil.

In accordance with our invention, the foregoing difllculties are obviated by bonding the bare end turns of the coll winding to the conducting areas .on the coil form by baking adher-v ent metallic material spread over at least a substantial part of the contacting surfaces of the winding while the endturns thereof are held against the conducting areas. In order to wind closely, insulated wire is used preferably, and to ing the coil form. .After the winding is bonded to the' conducting areas to form the coil terminals,` it is preferable to adherently coat the terminals' with lhighly conducting material to thereby increase the electric conductivity thereof.

In such colis. the coil4 form is preferably cylindrical so as to take advantage of the reduced nection between the withstand the baking and operating temperatures this insulation is of the heat-resistant type. Preferably the bonding operation, and also the operation of baking the conducting areas on the coil form, are accomplished by gradually heating the coil form to the necessary temperature and thereafter gradually cooling it to room temperature, thereby avoiding the subjection of the coil form to heat shocks and to excessive stresses and cost of cutting the forms into lengths from a long tube. However, in case a spring terminal is' required at one end of the coil to compensate for changes in dimensions in the device incorporatingl the coil, the form may have an integral cross wall to which the spring is riveted. In this latter case the outer face of the crossr wall is likewise coated with adherent metallicI material at the time the conducting areas are formed on the outer surface of the form, and the cross wall is likewise coatedwith the highly conductive ma terial, to thereby produce a good electrical conend of the coll winding and the spring.

Accordingly, one object of the invention is to provide methods of producing electric coils having rigid terminals which are smooth and of substantially uniform dimensions and of` uniformv and permanent electrical characteristics.

Another object is to provide such methods as are applicable to the rapid and uniform production in quantity of inexpensive coils of this kind.

These and other objects and advantages of the invention will be understood from the following description of two embodiments herein, using as t asseoir 3 at each end bared for bonding to the conducting bands; Fig. 4 shows the coil of Fig. 3 after its completion, the end turns of the winding being connected to the conducting bands by means of adherent metallic material appropriately baked to mechanically and electrically secure the winding to the conducting bands to form rigid terminals therewith, and the terminals being covered with a layer of copper applied thereto by electrolytic deposition or spraying: F18. 5 is an enlarged detail oi a completed terminal of Fig. 4; and Fig. 8 shows a modified form of coil of this type provided with a spring terminal.

Referring to the embodiment of Figs. 15 the tubular coil form I consists preferably of suitable ceramic material as porcelain, such as that used in sparkplug insulators. Preferably, in order to reduce their cost, the forms are cut from long tubes while plastic before firing. the corners at I of each form being rounded on by turning or grinding. After the fired coil form. as shown in Fig. 1, is thoroughly cleansed with carbon tetrachloride to remove oil. grease and other foreign material therefrom, each of its ends is coated by l stenciling or in any other suitable way, with a band of commercial metallic paint consisting of 90% silver and. 10% platinum. Each band is of sufilcient width to underlie 'about i0-15 turns of wire subsequently wound on the coil form almost from end to end thereof. These bands are then baked on the coil form by gradually raising its temperature in a furnace to a value between 1000 F. and 1100 F. durins a period of about 3 to 5 minutes. Then the coil form is gradually cooled to room temperature. Thus in these steps of processing, the coil form is not subjected to such heat shock, either while the temperature is being increased or decreased, as might crack or break it or might produce such stresses and strains therein as would cause its fracture upon ordinary mechanical shocks or vibration, and the paint is baked into the exterior pores of the ceramic and completely around the coil form, and if desired around its end surfaces also, in sharply defined bands l of continuously conducting metal of substantially uniform width and thickness.

Instead of using porcelain, other heat-resistant coil forms, as steatite or glass-bonded mica may be used. Furthermore, the metallic band may be in the form of a paste and may contain pure silver or pure platinum or pure gold or other suitable adherent metallic materials including admixtures thereof such that after the baking operation `there is no formation of metal oxide having a relatively high electrical resistance.

Having the finished coil form with conducting end bands thereon, as shown in Fig. 2, relatively small copper wire 4 of a B and S gage between No. and No. 42 having a bare diameter of about 10 mils down to about 2.5 mils. is wound thereon substantially from end tofend oi' the coll form as shown in Fig. 3. Preferably the wire is covered with a well known insulation which is a ceramic (inorganic) insulating coating on copper, nickel and other types of wire and which may contain resin and which is heat-resistant capable of withstanding without change a temperature of at least 800 F. Other insulation materials having suitable heat resisting characteristics may be used if desired. About 10 to l5 turns at each end of the winding I depending upon the size of wire making lup about the width of the bands 3, are bared of its insulation in any suitable way as by scraping. The bare end turns B are then given a coating of paint, preferably of the same'oomposition as the adherent metallic material of the end bands I. While these coated turns are held down tightly against the bands 8 by spring clips or tape. and the winding I on that portion of the coil form therebetween maintained tight, the wire-wound coilA form is baked in a furnace at a graduallyincreasing temperature up to about 500 F. during a period of 3 to 5 minutes. and then gradually cooled. to bond the end turns i of the winding to the bands l. The spring clips or tapes are then removed. This temperature of about 500' F., instead of the baking temperature of between 1000 F. and 1100 Il'. for the bands 8. suiiices for the bonding operation between the end turns I and bands I because the first coating of paint requires a higher temperature for penetration of the ceramic while the second coating of paint does not require such penetration but merely a bond between two contact surfaces. Either before or after the wound coil form has its temperature from the second baking operation gradually reduced to the room temperature. a second and heavier coating l of the same paint may preferably be baked over the bonded end turns at a gradually rising temperature nnally reaching about 500' l". after a period of 2 to 21/2 hours. This additional coating assists in producing a terminal 1 in which the end turns are rigidly secured to the band in a bond of comparatively low electrical resistance capable of withstanding a temperature in service of at least 600 F. Whether or not the additional coating is applied. the terminals may then, if desired, be further covered by electrolytically plating them with copper, silver or other highly conducting metal I which does not melt at the temperature to which the coil is subjected in service, or by spraying them with suitable metal. to thereby further reduce the electrical resistance of the terminals. Whether or not the step of electrolytical deposition or spraying is used. each of the termi. nais 1 so produced is smooth all around its outer surface and of uniform dimensions, comprising a substantially continuous bond between 10-15 short-clrcuited end turns of the winding. Also, such terminals and windings made in quantity have substantially uniform electrical resistance and result in coils of substantially uniform distributed inductance and capacity. Also the terminals are mechanically rigid and not only are non-corroded when completed but do not corrode thereafter in such wise as would materially change the electrical resistance thereof. Furthermore, due to the gradual application of heat and gradual reduction in temperature. the coil form is not so apt to be cracked or broken under stresses and strains such as may result in fracture under ordinary mechanical shock or vibration in handling or service. 4

In the modincation shown in Fig. 6, the ooil form l has near one end an integral cross wall il which is perforated at I l. whereas the remainder of the coil form is tubular as before. The bond between the bared end turns of the winding and the end bands or conducting areas are formed as before. but the initial coating of adherent metallic material is extended over the inner surface.

. form, preferably after the winding is secured in place, with its ends connected to the conducting area on the cross wall by a brass rivet Il. Buch a coil, with a spring electrically connected toone terminal thereof. is useful in mounting in devices,

such as sparkplugs, having mounting dimensions which are variable within the `compensation afforded by the spring I 3. Obviously, this electric coil has the mechanical and electrical characteristics of the embodiment of Figs. 1-5.

It will be apparent that in either of the embodiments of Figs. 1-5 or Fig. 6, the wire of the coil may be bare instead of insulated, the turns t then being maintained in spaced relation in the well known way as by forming in the coil form a helical groove in which the wire is wound. 'This and other changes and modifications may be made without departingfromthe spirit of the invention as embodied within the broad terms of the appended claims.

paint on separated areas on the coil form, heat-4 ing the paint to a temperature between substantially 1000 F. and 1 100 F. during a period of Having thus described our invention, what we claim is:

1. The method of making an electric coil hav- `ing terminals and a heat-resistant inorganic coil form, which consists in spreading an adherent metallic material on separated areas on the coil form, heating the metallic material to a temperstufe at which it `is baked on the coil ferm to produce conducting areas thereon, winding wire on the coil form over the conducting areas and the portion therebetween, covering at least a part of the surface of the bare end turns of the winding with a coating of an adherent metallic material, and baking the metallic material on the end turns while in contact with the conducting areas to thereby bond the metallic materials into coil terminals rigidly fastening the winding to the coil form.

2. The method of making an electric coil havwinding wire on the coil form over the conducting about 3 to 5 minutes to bake the paint on the coil form and produce conducting areas thereon,

areas and the portion therebetween, covering at least a part of the surface of the bare end turns of the winding with a coating of platinum-silver paint, and bakingthe .paint on the end turns while in contact with the conducting areas at a temperature of substantially 500 F. to thereby bond the metallic materials on the end turns and the conducting areas into coil terminals rigidly fastening the coil to the coil form.

6. The method of making an electric coil having terminals and a heat-resistant inorganic coil form, which consists in spreading platinum-silver ing terminals and a heat-resistant inorganic coil form, which consists in spreading an adherent metallic material on separated areas on the coil form, heating the metallic material to a temperature at which it is baked on the coil form to produce conducting areas thereon', `winding wire on the coil form over the conducting areas and the portion therebetween, covering at least a part of the surface of the bare end turns of the winding with a coating of an adherent metallic material, baking the metallic material on the end turnswhile in contact with the conducting areas to thereby bond the metallic materials into coil terminals, spreading a layer of adherent metallic material over the coil terminals to embed the end turns, and baking said layer to bond it onto the terminals. y

3. The method of making an electric coil having terminalsv and a heat-resistant inorganic form, which consists in forming bands 'of anadpaint on separate areas onlthe coil form, heating the paint to a temperature between substantially 1000 F. and 1l00 F. during a period of about 3 to 5 minutes to bake the paint on the coil form and produce conducting areas thereon, winding l wire on the coil form over the conducting areas herent metallic material at the ends of the coil A form, heating the metallic material `to a temperature at which it is baked on the coil form to produce conducting bands thereon, winding wire on the coil form over the end bands and the portion therebetween, covering the entire surface of the bare end turns of the winding with a coating of an adherent metallic material, and baking the metallic material on the end turns while in contact Awith the conducting bands to thereby bond the metallic materials into coil terminals rigidly fastening the coil to the coil form.'

4. The method of, making an electric coil having terminals and a' heat-resistant inorganic coil form, which consists in coating an adherent metallic material on separated areas on lthe coil form, heating the metallic material to a tem'- perature at which it is baked on the coil form to produce conducting areas thereon, winding wire on the coil form over the conducting areas and the portion therebetween, covering at least a part of the surface of the bare end turns of the winding with a coating of platinum-silver paint, baking the paint on the end turns while in contacts with the conducting areas at a temperature of substantially 500 F. .during a period of about 3 to 5 minutes to thereby bond the metallic materials of the paint into coil terminals, spread'- 'ing a Ilayer of platinum-silver paint over the terminals, baking said layer at atemperature of substantially 500 F. fora period of about 2 to 21/2 hours, and thereafter cooling the coll to thereby rigidlytfasten the winding to the coil terminals.

7. The method of making an electric coil having terminals and a heat-resistant inorganic coil form, which consists in spreading an adherent metallic material on separated areas on the coil form, heating the metallic' material to a temper,- aturel at which it is baked on the coil form to produce conducting areas thereon, winding wire on the coil form over the conducting areas and the portiontherebetween covering at least apart of the surface of the bare end turns of the winding with a coating of an adherent metallic material, baking the metallic material on the' endr turns while in' contact with the conducting areas to thereby bond the metallic material into terminals rigidly fastening the winding to the coil form, and adherently coating a layer of highly conductive material on the terminals to increase' the conductivity thereof.

8. .The method of making an electric coil having terminals and a heat-resistant inorganic coil form, which consists in forming bands of an adhercnt metallic material near the ends of the coil rorm,'heating the metallic material to a temperature at which it is baked on the coil form to 7 produce conducting bands thereon. winding heatresistant insulated wire on the coil form over the conducting bands and the portion therebetween, baring the end turns of the. winding of the insulation thereon, covering at least a part of the `surface of the bare end turns of the coil with an adherent metallic'material, baking the metallic material on the end turns while in contact with the conducting bands to thereby bond the metallic materials into coil terminala rigidly fastening the coil to the coil form, and depositing a coating of conducting material thereover by electrolytically plating the terminala with high conductive material to increase the conductivity thereof.

9. The method of making`an electric coil having one rigid terminal and one resilient terminal and also having a heat-resistant inorganic coil form of tubular section with an inner cross wall, which consists in spreading an adherent metallic material near one end oi' the coil form and also spreading adherent metallic material in a continuous mass over the other end of the coil form and over the cross wall, heating the metallic A material to a temperature at which it is baked 8 on the coil form to produce conducting areas thereon. winding wire over the outer surface of the coil form and over the conducting areas and the portion therebetween, covering at least a part of the surface of the bare end turns of the winding with a coating of an adherent metallic material, baking the metallic material on the end turns while in contact with the conducting areal to thereby bond the metallic materials into coil terminala rigidly fastening the coil to the ooil form, and fastening a resilient terminal to the croaa wall in contact with the conducting area thereon.

JOSEPH T. OBTERMAN. ALVAH 0. ERI.

REFERENCES CITED The following references are of record in the ille of this patenti l UNITED STATES PATENTS Number Name Date 2,075,515 Fisher Max'. 30. 1037 1,871,371 Jackson Aug. 9, i932 Schellenger Nov. 5, 1985