US3127666A - Electric heating element - Google Patents

Description

April 7, 1964 L. E. FENN ELECTRIC HEATING ELEMENT Filed July 10, 1955 R o 9. mm F 3 w 3 5 M 6 e m H m 8 w N a a z a f 2 U G F QR W 2 v w. 8% w W A fl U n H g n w; a E A w fl H m y 3 m 2 ATTORNEYS United States Patent 3,127,666 ELECTRHQ HEATING ELEMENT Lawrence Fenn, Bridgeport, Conn, assignor to Case!) Produem Corporation, Bridgeport, Conn, a corporation of Connecticut Filed July 10, 1953, Ser. No. 367,233 6 Claims. (Ci. 29--155.e2)

,T'his invention relates to electric cigar lighters, and particularly to low-voltage heating elements for cigar lighters of the type commonly used in automobiles, boats and aircraft.

For many years pleasureautomobile electric systems have been standardized as .to voltage, operating at substantially six volts as obtained from a three-cell lead-acid storage battery.

Electric cigar lighters for six-volt use in pleasure cars have comprised a tubular holder and a plug-like igniting unit receivable in the holder and removable therefrom for use, said igniting unit having at its inner end an economically produced heating coil formed of flat metal ribbon wound in a pancakeshaped spiral with air-spaced turns, said coil being mounted in a shallow metal cup of slightly less diameter than the tubular holder.

Commercial vehicles having 12-volt electric systems, and aircraft with 24-volt systems have in the past been supplied with cigar lighters wherein a more costly heating coil was used, having more turns of ribbon of thinner cross section and greater length, the coil being permeated with a ceramic cement which, when it hardened, supported the coil and insured proper spacing of the turns and freedom from short circuit and burn out. Such coils, in addition to being more costly, sometimes failed due to the unequal expansion in the coil loosening the ceramic and permitting it to fall out.

It is now proposed to standardize pleasure-car electric systems at twelve volts, requiring that the present econominal and highly satisfactory six-volt heating coil be altered to accommodate the higher voltage by the use of ribhon of thinner cross section or greater length, or both. Such an altered coil wound in the customary manner and without the ceramic support cannot be readily used with the existing mounting cup since the added length and lesser thickness render it mechanically unstable to the extent that it loses its fiat shape and also since the adjacent turns easily touch and short-circuit each other, burning out the coil.

An object of the present invention is to provide an improved, economical and highly satisfactory low-voltage heating coil for cigar lighters of automobiles, boats, airoraft and the like, which coil can be readily used with existing holder and igniting plug structures, including the shallow metal mounting cup for the coil, without the turns of the coil easily short-circuiting and burning out.

Another object of the invention is to provide an improved low-voltage heating coil as above set forth, which is mechanically strong and self-supporting, doing away with the necessity of seperate or additional supporting means such as ceramic cement, etc.

A further object of the invention to provide an improved low-voltage heating coil in accordance with the above which may be readily and economically produced, and which will be reliable in use and capable of many cycles of operation.

Yet another object of the invention is to provide an improved low-voltage heating coil as above set forth, which will withstand limited over-voltages to an appreciable extent and for an appreciable time before burning out.

A still further object of the invention is to provide an improved low-voltage heating coil for a. cigar lighter,

ice

which will retain its igniting heat for a relatively long time.

Further objects of the invention include the provision of improved methods for producing heating coils as set forth above.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

FIGURE 1 is a side elevational View of a cigar lighter igniting unit, and a vertical axial section of part of the holder, the heating element of the igniting unit, as made in accordance with the invention, being shown in vertical section.

FIG. 2 is an end elevational view of the igniting unit, showing the improved heating coil of the invention.

FIG. 3 is a plan view of a heating coil during its fabrication, after it has been wound and confined against unwinding, this figure illustrating a step in the method of the invention.

FIG. 4 is a fragmentary sectional view taken on line 4-4- of FIG. 3.

FIG. 5 is a plan view of a heating coil after being wound and confined, showing a different kind of confining means.

FIG. 6 is a diagrammatic view illustrating the annealing step in the method of forming heating coils according to the invention.

FIG. 7 is a diagrammatic view of a circuit used to carry out steps in the method of the invention, relating to oxidizing and insulating the heating coil.

FIG. 8 is a vertical sectional view of an annealing furnace, used as an alternative to the high frequency heating apparatus shown in FIG. 6.

H6. 9 is a diagrammatic view showing another apparatus by which oxidizing and insulating of the coil is accomplished.

The cigar lighter illustrated in FIGS. 1 and 2 comprises a holding device 1d consisting of a tubular metal shell 11 and a clamping sleeve 12 by which the shell 11 is attached to a supporting panel 13.

Receivable in the holder It) for storage and energization is a plug-like igniting unit 14 comprising a cylindrical body 15 having a manually engageable knob 1.6 and having a friction sleeve 17 by which the igniting unit is frictionally supported in the shell 11.

At its inner end the igniting unit 14 has a heating element assembly comprising a supporting thimble 18 removably secured to the body 15 by being threaded thereinto, comprising a shallow metal contact cup 19 attached to the thimble 18 and constituting a mounting and contact for a pancake-shaped heating coil 20.

In accordance with the present invention an improved method is provided for fabricating the heating coil, and a novel and improved heating coil 24) is provided for low-voltage applications such as in automobiles, boats or aircraft, the said heating coil being economical to fabricate and resistant to short-circuiting of the turns and burning out while at the same time being tightly wound withthe turns in intimate contact with and adhered to each other, being mechanically strong and selfsupporting without the use of separate or additional supporting means such as ceramic cement, etc., being reliable in useand capable of many cycles of operation and also capable of withstanding limited over-voltages, and being capable of retaining an igniting temperature for a relatively long time after its energization has been terminated. My improved heating coil is shown as being formed of flat metal alloy ribbon tightly wound in a pancake shape with adjacent turns in intimate contact but insulated from each other, the entire coil being rigid as to relative movement between its turns and thereby constituting a unitary structure which will hold its shape under all normal conditions of use. In forming the coil 24) I use a heat-resistant alloy having an appreciable aluminum content. One example of such alloy, known commercially as Kanthal D, consists of 3 /2 aluminum, 23% chromium, 2% cobalt and 71 %1 iron.. Variations in the proportions of these elements are possible. For example, the aluminum may vary from 3 /2 to 6 percent, the chromium from, 20 to 25' percent and the cobalt from 1 to 3 percent, and other proportions and alloys have also beenfound suitable. As a further illustration, an alloy of 6% aluminum, 20% chromium and 74% iron is suitable for the purposes of the present invention.

In carrying out the process of'theinventionby which my improved heating coil is produced, I wind a fiat ribbon of suitable metal alloy into the shape of a tight spiral, such a coil being indicated at 29a in FIG. 3. Where the coil is to be used with alZ-volt supply, it may have a resistance of 1.66 ohms and be 18" long, .010" thick and wide. While the coil Ztia is still tightly wound it is placed in a retainer ring 21 which confines the coil and prevents it from unwinding.

The ring 21, see FIG. 4, may advantageously be formed of drawn sheet metal a channel-shaped cross section, having an outer, main or a body portion 22, an inner coil-contacting portion 23 spaced inwardly from the body portion 22 and a connector portion 24 spanning the space between the portions 22 and 23. The advantage of this particular construction of the retainer 21 will be brought out later.

After the coil Zita has been wound and confined in the retainer 21 I subject it to an annealing heat by which the flat ribbon is annealed or relieved of temper caused by work-hardening incurred during its fabrication and coiling. I have found that a suitable temperature for annealing the coil Zlla is in the neighborhood of 1500 F.

The annealing of the coil 26a may be done by a high frequency electric field, in' an arrangement such as that shown in FIG. 6. In this figure a supply of high frequency energy 25 is connected to a field-concentrating coil or helix, through which a conveyor belt 27 passes. The heating coils 26a which are to be annealed are placed on the conveyor belt 27 and passed through the coil 26, and are discharged from the right-most end of the conveyor 27 in annealed condition. Where the coils 20a are confined by the retainers 21, the latter will also be heated by the high frequency field and will supply heat to the coils and facilitate the annealing thereof. Due to the thin cross section and relatively small mass of the retainers 21, as accomplished by their drawn sheet-metal construction, they will not heat abnormally fast, to the point of melting prior to complete annealing of the coil 20a, provided that the cycle of heating is not made too short. As an alternative to the retainer 21 I may provide a retainer 28, see FIG. 5, of nonmetallic material such as ceramic composition, having lugs 29 which engage and confine the spirally-formed heating coil, shown in FIG. ascoil b. Where a ceramic retainer is employed, the annealing of the coil may proceed without regard to heating or melting of the retainer, obviously.

It will be understood that in place of the high frequency heating unit shown in FIG. 6 any other suitable annealing means may be employed, such as an electric furnace 30 shown in FIG. 8 in which the heating coils 20a are supported on a removable tray 31.

After the coil 20a has been annealed it can be removed from confinement without losing substantially the initial coiled shape, the coil expanding but little, if any, upon removal from the retainer 21. I have found that in a properly annealed coil there remains but little force between adjacent turns, all turns however remaining in contact with each other and under some pressure. The importance and advantage of this'will be brought out in detail later.

The annealed coil 20a is now ready for another step in my novel method, that of insulating the adjacent contacting turns from-each other and securing them to each other. This I accomplish by an oxidizing process. I prefer to carry out this process after the heating coil Zita has been incorporated in the heating element assembly such as is shown in FIGS. 1 and 2. The spiral coil 29 in such assembly has its inner end welded to a supporting and current-conducting central stud 32 and its outer end outwardly offset and welded to the inner wall of the contact cup 19. In such assembly electrical connection obviously may be readily efiected to the ends of the coil 24%. The coil is now placed in a circuit such as that illustrated in FIG. 7, wherein the stud 32 is connected by a Wire 33 to a battery 34 which is in turn connected by a wire 35 to a sliding contact 36 engageable selectively with button contacts 37, 38,739, wand 41 joined respectively to resistors 42, 43, 44, 45 and 46 whose other ends are connected to a wire 47 leading to the contact cup 19 of the heating coil assembly. The resistors 42, 43, 44, 4-5 and .46 together with the sliding contact 36 enable currents of diiferent intensities to be passed through-the heatingcoilZt. Where the heating coil 26 is intended for twelve-volt use I subject it to a potential of eight volts for an interval of 20 seconds, as by moving the slidable contact 36 in engagement with the contact button 3'7. I then terminate this energization and next subject the coil 24 to a potential of ten volts for 15 seconds by moving the sliding contact 36 in engagement with the contact button 38. I then terminate this ene'rgization and subject the coil 25) to a potential of twelve volts for 10 seconds by moving the sliding contact 36 in engagement with the contact button 39. Thereafter I terminate this energization and subject the coil 24 to a potential of thirteen volts for 10 sec onds by moving the sliding contact 36 in engagement with the contact button 4-9. I terminate this energization and then repeat it, and thereafter I subject the coil 29 to a potential of fourteen volts for 10 seconds by moving the sliding contact 35' in engagement with the contact button ill.

I have found that by energizing the heating coil 20 as above outlined an aluminum oxide coating will be formed on the ribbon and at the same time appreciable shortcircuiting between turns will be prevented. Therefore the coil 2% will not burn out during the oxidizing procedure, and the oxide which is formed will insulate the adjacent contacting convolutions from each other, and the oxide coatings will adhere to each other, rendering the turns of the coil relatively immovable under normal conditions of use. As a consequence, a unitary, solid, pancake-shaped coil is produced wherein the adjacent turns are effectively insulated and prevented from having relative movement and from becoming short-circuited. The coil is therefore mechanically rigid and stable, and will not get out of shape during use as-would otherwise occur where ribbon of thin cross section is wound in an unsupported coil of a large number of turns. Be cause of the solid mass of the coil 29 and the absence of air spaces between turns, the coil has excellent heat retention and will maintain an igniting temperature for a relatively long period of time. I have found also that a coil constructed in accordance with the above will withstand moderate over-voltages for limited intervals of time without burning out. For example it will withstand an energization of twelve volts for two minutes without burning out, and if subjected to thirteen volts will only burn out after one minute and 54 seconds. When subjected to fourteen volts it will burn. out only after one minute and 19 seconds of energization. If subjected to fifteen volts it will burn out after 45 seconds of energization. This performance is substantially better than the performance of the conventional six-volt heating coil having spaced convolutions which are out of contact with each other, since a six-volt coil when subjected to seven volts will burn out in 57 seconds as compared with the fourteen volt test wherein the twelve-volt coil lasts for one minute and 19 seconds.

In FIG. 9 I show a heating coil 20 connected to a battery 48 through a rheostat 49 by which diiferent voltages may be applied to the coil for different intervals of time, as outlined above. This arrangement might in some instances be more advantageous than the circuit found in FIG. 7.

While I have illustrated and described the construction, and the method of producing an improved twelvevolt coil for a cigar lighter, it is to be understood that twenty-four volt coils, or coils intended for other low voltages may be produced in a like manner. The improved heating coil of the present invention has been found to have an extremely long life, having withstood in excess of 20 thousand cycles of energization at 13.5 volts without showing signs of deterioration or failure, each cycle of energization lasting for 12 seconds which is sufiicient to bring the coil well up into the incandescent range required for lighting cigarettes, cigars, etc.

Variations and modifications may be made Within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. The method of making an electrical heating coil for a cigar lighter comprising the steps of Winding a flat, metal ribbon, formed of a metal alloy including iron and aluminum in its composition, into a tight, pancake-shape spiral with adjacent turns touching each other, confining the spiral to prevent appreciable unwinding and separation of the turns, heating the coil to relieve the winding strains and thereafter heating the coil sufliciently to form in situ an oxide on the surfaces of the ribbon, said oxide providing electrical insulation on the surfaces of the wire to prevent short-circuiting between the turns of the coil and providing mechanical adhesion between the contacting turns to prevent relative shifting thereof and axial deformation of the coil.

2. The method of making an electrical heating coil for use in a low-voltage cigar lighter, which includes the steps of winding a flat metal ribbon, having a composition whose oxide is electrically insulating, into a tight, pancake-shaped spiral with adjacent turns touching each other, confining the spiral to prevent appreciable unwinding and separation of the turns thereof, subjecting the coil to heat to anneal the coil, and thereafter passing heating currents through the coil in successive stages to oxidize the surfaces of the ribbon and provide electrical insulation and mechanical adhesion between adjacent contacting turns of the coil.

3. The method of making an electrical heating coil for use in a low-voltage cigar lighter, which includes the steps of winding a flat metal ribbon, having a composition whose oxide is electrically insulating, into a tight, pancake-shaped spiral with adjacent turns touching each other, confining the spiral to prevent appreciable unwinding and separation of the turns thereof, subjecting the coil to heat to anneal the coil, and thereafter passing a heating electrical current of lesser value than the intended electrical heating current through the coil to oxidize the surfaces of the ribbon and provide electrical insulation and mechanical adhesion between adjacent contacting turns of the coil.

4. The method of making an electrical heating coil for use in a low-voltage cigar lighter, which includes the steps of winding a fiat metal ribbon, having a composition whose oxide is electrically insulating, into a tight, pancake-shaped spiral with adjacent turns touching each other, confining the spiral to prevent appreciable unwinding and separation of the turns thereof, subjecting the coil to heat to anneal the coil, and thereafter passing successive heating electrical currents of lesser value than the intended electrical heating current through the coil to oxidize the surfaces of the ribbon and provide electrical insulation and mechanical adhesion between adjacent contacting turns of the coil.

5. The method of making an electrical heating coil for use in a low-voltage cigar lighter, which includes the steps of winding a flat metal ribbon, having a composition Whose oxide is electrically insulating, into a tight, pancake-shaped spiral with adjacent turns touching each other, confining the spiral to prevent appreciable unwinding and separation of the turns thereof, subjecting the coil to heat to anneal the coil, and thereafter passing successive heating electric currents of lesser value than the intended electrical heating current, but each successively greater than the preceding, through the coil to oxidize the surfaces of the ribbon and provide electrical insulation and mechanical adhesion between adjacent contacting turns of the coil.

6. The invention as defined in claim 5 in which the successive currents of increasing value are maintained for intervals which are successively longer each than the preceding interval.

References Cited in the file of this patent UNITED STATES PATENTS 515,280 Brown Feb. 20, 1894 1,946,434 Bach Feb. 6, 1934 2,062,701 Cohen Dec. 1, 1936 2,157,050 Bilger et a1. May 2, 1939 2,269,394 Cuno et a1 Jan. 6, 1942 2,287,460 Wagenhals June 23, 1942 2,465,864 Freeman et a1. Mar. 29, 1949 2,585,037 Robinson et a1. Feb. 12, 1952 2,596,325 Cerny May 13, 1952 2,652,622 Charbonneau Sept. 22, 1953 2,702,935 Kyle Mar. 1, 1955 2,975,262 Schnick Mar. 14, 1961 OTHER REFERENCES Woldman & Metzler: Engineering Alloys; 2nd Edition, 1945; published by American Society for Metals; page 200 (Copy in Div. 3).

Woldman: Engineering Alloys; 3rd Edition; 1954; published by American Society for Metals; pages 238, 810 (Copy in Div. 3).

Claims (1)

1. THE METHOD OF MAKING AN ELECTRICAL HEATING COIL FOR A CIGAR LIGHTER COMPRISING THE STEPS OF WINDING A FLAT, METAL RIBBON, FORMED OF A METAL ALLOY INCLUDING IRON AND ALUMINUM IN ITS COMPOSITION, INTO A TIGHT, PANCAKE-XHAPE SPIRAL WITH ADJACENT TURNS TOUCHING EACH OTHER, CONFINING THE SPIRAL TO PREVENT APPRECIABLE UNWINDING AND SEPARATION OF THE TURNS, HEATING THE COIL TO RELIEVE THE WINDING STRAINS AND THEREAFTER HEATING THE COIL SUFFICIENTLY TO FORM IN SITUAN OXIDE ON THE SURFACES OF THE RIBBON, SAID OXIDE PROVIDING ELECTRICAL INSULATION ON THE SURFACES OF THE WIRE TO PREVENT SHORT-CIRCUITING BETWEEN THE TURNS OF THE COIL AND PROVIDING MECHANICAL ADHESION BETWEEN THE CONTACTING TURNS TO PREVENT RELATIVE SHIFTING THEREOF AND AXIAL DEFORMATION OF THE COIL.

Images