US1832419A - Electric resistance device - Google Patents

Description

Nov. 17, 1931. H. FENDER ELECTRIC RESISTANCE DEVICE Original Filed May 1925 an, Wm 9 62. qw ATTORNEY Patented Nov. 17, 1931 UNITED STATES PATENT OFFICE HAROLD FENDER, OF IEBION, PENNSYLVANIA, ASSIGNOB- '10 TN'TERNATIONAL IBE- SISTANCE COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF DELAWARE ELECTRIC RESISTANCE DEV ICE OriglnaI application filed Kay 28, 1926, Serial No. 88,327. latent No. 1,771,055, dated July 20, 1980.

vided and this application flledlugust 16, 1929. Serial No. 386,384.

This invention relates to electrical resistance devices or media.

One of the objects of this invention is to provide a medium of highelectrical resistance which is practical, uniform and efficient. Another object is to provide a resistance medium or device having certain desired characteristics in operation and freefrom certain undesirable characteristics. Another object is to provide an electrical resistance medium which is of simple construction and inexpensive. Another object is to provide a device of the above nature which is durable and capable of dependable service without ageing or deteriorating. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described, and the scope of the application of which will be indicated in the following claims.

This case is a division of application filed May 28, 1925, Serial No. 33,327, which issued as Patent 1,771,055; July 22, 1930.

In the accompanying drawings, in which is shown one of the various possible embodiments of my invention Figure 1 illustrates somewhat diagrammatically the insulating fiber forming part of my resistance device, at a certain stage in the manufacture thereof, and

Figure 2 shows somewhat diagrammatically my resistance device at various stages in its course of manufacture.

Similar reference characters refer to similar parts in both views of the drawin s.

Referring now to the drawings in etail, there is shown in Figure 2 a roll 10 upon which is wound a continuous fiberlike or threadlike member of non-conducting material shown passing from the roll 10 at 11. This non-conducting fiber or thread is referably of glass, glass havin certain a vantageous characteristics which will be later pointed out, but it is to be understood that other non-conducting material might be employed to advantage.

This glass fiber 11 is preferably formed as 1s\i llustrated in Figure 1. A glass rod 12, for e zample, about three-eighths of an inch in diameter, is fed. endwise through a heating medium, in this instance shown as a gas flame 13. As the rod is fed through the heating medium' 13 its end is softened, and this softened end is grasped, drawn out, and wound upon the roll 10, formin the fiber 11. The roll 10 is driven, in the irection indicated by the arrow in Figure 1, at a rate of speed which is predetermined with respect to the rate of feed of the rod 12, into the heating medium 13. Preferably the roll or spinning wheel 10 and the mechanism driving the rod 12 through the heating medium 13 are both driven from a common source of power, so that there is thus maintamed a constant ratio between the speed at which the filament 11 is pulled out and the speed at which the rod is moved into the heating medium. In this manner the lass fiber or thread 11 is drawn out in a uni orm d1ameter, providing the diameter of the glass rod 12 is uniform. Preferably the heating element 13, the speed of movement of the rod 12 and the speed of rotation of the roll 10 are so proportioned that the glass fiber 11 is uniformly drawn out to a diameter in the neighborhood of two-hundredths of an inch. The word fiber as used in the claims is to be construed to mean a filament of the order of one-twentieth of an inch or less.

Referring now again to Figure 2, the glass fiber 11 is rawn from the roll 10 and, after passing through various mechanisms which will be described in detail herein, is gripped between a pair of driven rollers 14 and 15. The peripheries of these feed rollers 14 and 15 are preferably covered with a yielding material such as leather, and these rollers grip the glass fiber 11, drawing it from the roll 10 through the various mechanisms which will presently be described.

Referring now to the right-hand side of Figure 2, the lass fiber 11 as it is drawn from the roll 10 first passes over a curved and trough-shaped guide 16. The guide 16 at its lower end pro erly positions the lass fiber for passage t rough a coating ,evice 17.

This device 17 is preferably in the form of a T-tube having a horizontal passage 18 through which the fiber 11 is drawn and a vertical passage 19 communicatin at its upper end with the first passage. container such as a bottle 20 contains the material, in the form of a fluid, with which the fiber 11 is to be coated in the coating device 17. The lower end of the bottle 20 is connected by a flexible tube 21 with the mouthof the vertical passage 19 in the coating device. The bottle 20 is preferably adjustable in a vertical direction, as by means of an adjusting screw 22.

As was mentioned above, the material with which the fiber 10 is coated in the coating device 17 is contained in the form of a liquid or a solution in the bottle 20. This material, indicated at 23, com rises preferably minute particles of a suita le electrical conducting material suspended in a suitable solution. A satisfactory material is carbon in the form of extremely minute (almost colloidal) particles suspended in solution. The character ii of the solutions employed will later be pointed out more fully herein. By adjusting the height of the bottle 20, the solution fills the tube 21 and rises through the passage 19, filling the passage 18 through which the glass fiber 11 is drawn. Capillary action prevents the solution from flowing out of the ends of the horizontal passage 18. As the glass fiber is drawn through the passa e 18 it is coated with a thin layer or film o the solution of conducting material; the thickness of the film deposited uponthe fiber may be controlled by adjustments of the height of the bottle 20.

The glass fiber thus emerges from the coating device 17 covered with a thin moist coating of the conductin material contained in solution in the bott e 20. The fiber now passes through a drying device 24 which is heated by suitable means illustratively shown as an electric light bulb 25. In this drier 24 the moist conducting coating or film is dried.

The glass fiber now passes through a heating device or furnace 26 wherein it is subjected to a more intense heat, wherein all moisture is positively driven from the glass fiber and from the conducting coating thereon, and wherein certain other chan es take lace, which will later be describe This urnace preferably takes the form of an elongated tube as shown, heated for example, by means of a Bunsen burner 2 Air is preferably excluded from the furnace 26 as the coated glass fiber passes therethrough, and it is found advantageous to substitute for the air an atmosphere of certain gases. For this purpose hydrogen is found to be particularly advantageous. A supply of hydrogen is connected with the interior of the heating tube adjacent its right-hand end as 28,

insane and the hydrogen is permitted to escape adually through the opening 29 at the leftand end, through which the glass fiber passes from the furnace. In order to prevent exit of hydrogen from the right-hand or entering end of the furnace, this end is sealed by suitable means such as mercury 30 which prevents exit of the hydro on, but permits ready drawing of the glass ber 11 therethrough. The mercury is introduced through an upper opening 31 and cannot flow out through the restricted passages 32 and 33 on either side thereof through which the glass fiber 11 is drawn. The atmosphere of hydrogen, among other advantages attained thereby, prevents oxidation of the conducting coating.

From the furnace 26 the glass fiber is drawn through a second coating device 34. In this coating device there is applied to the glass fiber, exteriorly of the conducting coating, a film of a suitable protective material in the nature of a binder which is adapted to hold the conducting coating in place upon the glass her and prevent its accidental rubbing off. The device 34 preferably takes the form of a T-tube having a funnel-shaped upper mouth 35 through which the protective solution 36 is introduced. I Capillary action prevents the solution fromrunning out of the two horizontal openings through which the glass fiber is drawn. The material 36 preferably comprises a solution of rosin in benzol, and a thin film of this solution is deposited exteriorly of the conducting coating as the glass fiber passes through the device 34.

Upon emerging from the coating device 34 the glass fiber passes through a heating de vice or drier 37 similar to the drier 24. In the drier 37 the benzol is driven off and a thin layer or film of rosin remains over the conducting coating. By adjusting the concentration of the benzol-rosin solution, the thickness of the film given in the device 34 may be controlled. In order that the resistance value of a length of the resistance device of the invention may be substantially that of the carbonaceous coating, unaffected by the film of protective material, the protective film should be of good insulating substance, rosin being such a substance. Preferably the concentration of the benzol-rosin solution is adjusted so that the protective film will be very thin; so thin that it will not appreciably alter the value of resistance of a length of the resistance with the current passing through (not along) the film, into the conducting coating, for the purpose of measuring the resistance as hereinafter described, or otherwise.

The glass fiber now preferably passes through a device 38 containing two mercury contacts 39 and 40 spread a predetermined distance apart. Across these two contacts is connected a battery 41 and a suitable resistance measuring device 42, which may be an ordinary megger. The megger 42 thus gives a constant reading of the resistance of the conducting coating per given length of the glass fiber, and this resistance will remaln substantially constant and uniform.

The coated glass fiber now passes through between the feeding rollers 14 and 15 which, as was mentioned above, draw the fiber through the series of devices just desorlbed. Emerging from the feed rollers 14 and 15, the glass fiber passes through a suitable gu de 43. Adjacent the left-hand end of the guide 43 is a solenoid 44 fed by the battery 45 and provided with a plunger 46. The lower feed roller 15 is provided on its periphery wlth a projecting contact 47 which, at each rotation of the roller, strikes a spring contact 48, complotting the circuit of the solenoid 44. Thus at each rotation of the roller 15 the plunger 46 is drawn upwardly and breaks off the glass fiber emerging from the left-hand end of the guide 43. The coated glass fiber is thus cut into predetermined lengths by the plunger 46 and these lengths are received in a suitable trough 49. In Figure 2 one of these lengths 50 is shown after it has been dropped into trough 49.

Considering now more particularly the nature of the material employed in forming the conducting coating upon the glass fiber, it has been pointed out above that a satisfactory material is carbon in the form of minute particles suspended in a solution. Excellent results are obtained by employing either a suspension of carbon in an aqueous solution of glue-like material or a suspension of carbon in a liquid hydrocarbon. As an example of the latter, a solution of lamp black and 11nseed oil may be employed. As an example of the first, a mixture of Le Pages glue and lampblack in substantially equal parts mixed into a paste and then diluted with water to the desired consistency gives satisfactory results; Another solution which gives excellent results is the commercial Higgins carbon drawing ink. This ink is a solution of carbon and appears to contain a glue-like constituent.

In the furnace 26, the temperature employed is preferably kept within the limits of 700 and 1350 F. The best results are obtained when a temperature in the neighborhood of 1200 or 1300 F. is employed. An effect of this baking in the furnace 26 is to drive off the volatile constituents of the glue or other material mingled with the carbon, leaving practically a pure carbon film. The glue is carbonized by the heat and the particles of carbon resulting therefrom appear to fill the interstices between the carbon particles which were suspended in the solution, so that a solid uniform coating of-carbon results.

From the foregoing, it will be seen that my invention is one well adapted to attain the ends and objects hereinbefore set forth in a practical and efiicient manner, and that my resistance device is one embodying practical advantages of great importance.

The glass fiber being non-porous and the conducting coating being thoroughly dried and covered with a non-hygroscopic film, the resistance device is stable in its resistance, being unaffected by changes in temperature and not suscepible to variations in its moisture content, due to weather conditions or other conditions of use. The conducting coating is deposited upon the glass fiber in such manner that it may be formed in an extremely thin film which is of a definite and substantially unvarying thickness throughout. These characteristics and others render this resistance device of particular advantage when used inwireless-receiving apparatus and other sound amplifiers. the device being particularly well adapted for use in the so-called grid-leak circuit of wire ess-receiving apparatus. It is found that this resistance device is non-microphonic, that is, it produces no hiss or frving noise when employed in a-sound amnlifving apparatus. advantages are attendant upon the use of carbon as the conducting film. although this invention in its broadest aspects is not limited to the us of carbon. In addition to the advanta es pointed out above, the temperature coefiicients of glass and carbon are approximately the same, and therefore the glass-supporting fiber and the carbon film expand approximately equally under heat. so' that there is no tendency to crack. Experiment would seem also to indicate that certain of these advantages accrue directly from the use of a glass or similar non-conducting fiber of very small diameter as a support for the,hip'h resistance conductive film of carbon. These results are of much greater consequence than might naturally be expected to follow a mere reduction in cross section. One of these results is noticeable in relation to the longitudinal expansion of the mem- Particular ber under the heating effects occurrring in the use thereof, while another appears when the transverse expansion thereof under like conditions is considered. In use, these coated filaments or fibers are mounted ri idly at their ends in a mass of some suitable metallic alloy, as, for instance, type-metal, which closes tightly about the carbon film and makes contact therewith.

In the case of a resistance element having a glass rod of really appreciable diameter as a support for the conductive material, the longitudinal expansion of said rod, when heated, and its subsequent contraction when cooled, often causes a. transverse fault to occur in the conductive coating, adjacent the point where the glass enters the terminal members. Such cracks or faults inevitably cause hissing or frying noises when such a device is used as a grid-leak in a radio receiver. My device is substantially free from this great defect largely because of the pliability of the small glass fiber which permits the resistance ele- I ment to bend or warp slightlybetween its points of contact with the metal mounting. In this way, cracking of the conductive coating is prevented, or if it occurs at all, it is to so slight a degree as to produce no noticeably audible disturbance.

Also, when a resistance element of relatively large diameter is heated as mentioned above, it is subject to lateral or circumferential expansion within the metal alloy. Under these conditions the glass support may be crushed, the carbon film fractured or distorted, or the metal may be forced to recede from its close contact with the element. In any one of these cases the device becomes practically useless. If the glass is crushed it is ruined. In case the film is fractured or distorted, microphonic faults occur, which render the grid-leak unsatisfactory in use, and should the third condition arise, namely, the withdrawal of the metal from its close contact with the carbon film, then and thereafter imperfect contact results, which again produces hissing and frying noises when the device-is used as a grid-leak.

It should be noted further that grid-leaks of very small dimensions, both as to length and diameter, may be made with the present coated fiber and yet have the high resistance values necessary in practical use. Resistances of circular cross section vary in absolute resistance inverse-1y as the square of their diameters, and directly in proportion to their lengths. This is true whether the conductor be a tube or solid, providing when tubular conductors are compared the same thickness of conductive material is maintained. Thus, in order to obtain a highresistance of the order now under consideration with a resistance device having a relatively large rod as a support, the devices must attain relatively great lengths, but resistances made in accordance with my invention, with their fine fiber support and film of conductive material, may be produced in units of very high resistance without exceeding in length the standards established as desirable in radio design.

As many possible embodiments may be made of the above invention, and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In an electrical resistance device, in combination, a glass fiber of sufficiently small diameter to be pliable, and a coating of solid carbon of'substantially uniform thickness and continuity upon the surface of said. fiber, said coating consisting of fine carbon particles and a carbonized material filling the interstices between said articles, said coating bein of a thickness and texture to be pliable, wit out ru turing, throughout the range of pliability 0? said glass fiber.

2. In an electrical resistance device, in combination, a glass fiber of; sufiiciently small diameter to-be pliable, and a coating of solid carbonaceous material of substantially uniform thickness and continuity upon the surface of said fiber, said coating being of a thickness and a texture to be pliable, without rupturing, throughout the range of pliability of said glass fiber.

3. In an electrical resistance device, in combination, a glass fiber of sufiiciently small diameter to be pliable, a coating of solid carbonaceous material of substantially uniform thickness and continuity upon the surface of said fiber, said coatin being of a thinness and a texture to be pliable, without rupturing, throughout the range of pliabihty 0 said glass fiber, and a non-hygroscopic protective insulating film upon said coating.

In testimony whereof, I have signed in name to this s ecification this twenty-fourth day of June, D. 1929.

HAROLD FENDER.

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