US1127281A - Resistance-wire for electric heaters. - Google Patents

Description

R. H. READ.

RESISTANCE WIRE FOR ELECTRIC HEATERS.

APPLICATION FILED JULY 11, 1914.

1,127,281. Patented Feb. 2, 1915.

Wummm I M W \M of economical operation.

UNITED STATES PdTFENT OFFICE- ROBERT H. READ, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RESISTANCE-WIRE FOR ELECTRIC HEATERS.

Specification of Letters Patent.

Original application filed July 19, 1910, Serial No. 572,778. Divided and this application filed July 11, 1914.

Serial No. 850,489.

lated resistance wires or elements for electric heaters or the like and is applicable in all cases where electrically generated heat is utilized or dissipated. The heating wire is of a type comprising a high resistance corewire inclosed in a continuous metallic shell or armor and separated therefrom by a firmly packed annular layer or bed of mineral fireproof insulation in the form of powder. Such wires are alloys varying in speoific resistance, but always very high relatively to a good conductor such as copper, and are therefore adapted for heating work or such as requires a large diffusion or dissipation of energy as contradistinguished from ,conducting' work where a minimum dissipation of energy is required for reasons v With a mineral oxid insulation such as ground flint the temperature may be raised very high, as such substance has a melting point above 2,000 centigrade and isnot at all damagedby temperatures below its melting point. Ground flint, magnesia and many other oxide or compounds do not become conductive when heated, the melting point being so high that they do not become conductors of the second class (Nernst eflect) except at very high temperatures. I may use any highly refractory insulating powder; I prefer, however, to use ground flint, such as ground quartz or silex because of its cheapness and better thermal conductivity than other oxids or silicates, and which insures a quicker and more desirable operation for heater or rheostat work. Other mineral oxid powders such as magnesia, alumina, emery,or sulfates, or carbonates such as chalk,-or silicates such as soapstone, clay or asbestosmay be employed. The powder should be finely divided, free from granules to permit even distribution, and should pack well, preventing the infiltration of air. I have had excellent results with a form of oWder-lmown on the market as silex, WlllCll is sold as a polisher of metals, and is finely divided silica; a good quality of powder may be made by grinding flint finely and then separating the finer particles by levigation. Before using, it should be heated strongly to expel all moisture. A finished corewire of high resistance alloy such as German silver, Climax, or a nickel chronium alloy is surrounded with the powder and telescoped within a seamless tube of metal with a good clearance around the wire and powder and is then reduced in section. The armor may be of the same material as the core-wire or a metal of the same expansion coefficient so as to avoid strains clue to differences in expansion under heat of the core and shell, or in some cases may be of copper or low brass. I provide a terminal to guard the core-wire when sharply flexed from contact with the jacket. This may be done by laying bare the core by removing a short piece of the jacket, using preferably a revolving knife such as a small pipe-cutter. A piece of copper wire may be welded to the ends of the core-wire,

and a metallictube filled with powdered flint or with cement pushed over the wire until it bears on the shell. It may be sol-- dered or brazed to the shell, thus making a rigid structure. The powder fills the tube and carries the heat away from the wire, and the copper will not get hot and may therefore be led directly to a binding post or other circuit terminal. Thus I have an armored or sheathed wire in which the shell offers a large surface of exposure to the air or other heat absorbing medium, permitting the passage of a greatly increased current without overheating and maintaining the resistance core cool throughout its length.

This application is a division of my application #572,778, filed July 19, 1910 entitled Insulated conductors and process and apparatus for making the same.

In the accompanying drawings, Figure 1 shows enlarged an armored wire powdercovered and surrounded by a seamless metallic jacket; Fig. 1*- is a cross-section of the same; Fig. 1 shows the wire reduced until the jacket is firmly shrunk upon the filled or covered wire; Fig. 1 shows the wire much reduced under the action of rolls or dies; Fig. 2 shows a step in the preparation of the heater wire; and Fig. 3 shows the terminal used at the ends of the heater wire.

Patented Feb. 2, 1915.

A metal ribbon or tape is passed to a curling die which gradually forms it into a tube, and at the open end is supplied with previ ously heated dry insulating powder of the kind referred to, precautions being taken to provide a uniform supply of the powder as the tape is formed into a tube. A corewire of high resistance alloy' is led axially of the tube being filled and at the same speedof travel. Means are provided for keeping the seam in a right line, as a blade of steel 8 at the front of the die. The seam may be brazed or welded, but good results may be obtained without this treatment, as a seamless outer shell of the proper clearance effectually prevents leakage of the powder, by closin tight on the inner folded metal tape an preventing any tendency to I .ooze at the seam., The filled tube is slipped into a seamlessv metallic tube previously drawn down to a size to permit it to be easily slid or telescoped intoit. The structure thus provided is then drawn down in dies or otherwise reduced until the desired size is attained, when the powder will be hard packed and the core-wire central. vAs will be seen in Fig. 1 there is a good clearance between the seamless jacket and the powdercovered wire core. In Fig. 1 the jacket has been reduced and has been shrunk into intimate contact with the covered wire, while in Fig. 1 the whole has been very much reduced in section. Such a wire may be reduced or drawn down to a very few thou sandths inch in diameter.

I provide a terminal at the end of the core-wire so arranged as to provide effective 'radiation for'the heat and to prevent metallic contact with the jacket. A simple and effective plan is to lay bare thecore by removing a short piece of the jacket, using preferably a revolving knife, such as a-small pipe-cutter. A piece of copper wire may be welded to the end ofthe core-wire and a metal tube having a porcelain bead shrunk in the end and filled with powdered flint or cement, as at 1, slipped over each end of the shell, thus making a rigid structure. The powder fills the tube and carries the heat away from the wire, and as'the'copper "will not by reason of its low resistance get hot it may be led directly to a binding post or other circuit terminal. If brazed seams are'used the solder should have a sufficiently high melting point to permit annealing, or the seam should be welded or burned in an approved manner. v

I do not claim in this application a corewire of high resistance in a seamless tube with closely compacted powder insulation and a seamless metallic shell on the outside, such matter being claimed in my copending application #841,544, filed May 28, 1914, nor do I claim means for excluding moisture which is claimed in my application #843,236, filed June 5, 1914, nor do I claim inclosing a wire with powder insulation in a Having thus described my invention, what I I claim as new and desire to cover by Let ters-Patent is 1. Aninsulated resistance wire for-electric heaters or the like comprising a corewire of high resistance material, a body of heat refractory powder compacted around the core-wire, a metallic armor surrounding the insulation, and a terminal of higher conductivity than the core-wire forming a continuation thereof partly embedded in the powder. 1

2. A resistance wire for electric heaters or the like comprising a core-wire of high resistance alloy, a body of heat refractory insulating powder surrounding the corewire, a metallic armor inclosing the powder, and a terminal of higher conductivity than the core-wire embedded in the powder and projecting from the armor to carry away the heat and form a relatively cool extension thereof.

3. A resistance wire for electric heaters or the like comprising a high resistance corewire, a filling of heat refractory insulating 5. A resistance wire for electric heaters.

or the like comprising a high resistance corewire, a compact body of heatrefractory insulation surrounding the same, a metallic shell inclosing the same, copper wires metallically united with the'ends of the corewire projecting from the shell and partly inclosed within the bed of insulation.

6. A resistance wire for electric heaters or the like comprising a high resistance corewire having terminals of lower resistance, a compact body of. heat refractory insulation surrounding the same, a seamed metallic inclosure for the powder, 'a seamless metallicshell on the outside, and metallic. caps at the ends insulated, from the corewire and covering the point of decreased resistance.

7. The method of making a resistance element for electric heaters or the like, consisting in surrounding a core-wire with insulating powder, inclosing it within a metallic sheath, reducing the section of the sheath, and providing terminals of lower re sistance at the ends of the core-wire extending within the powder insulation.

8. The method of making a resistance element for electric heaters or the like, consisting in surrounding a high resistance core-wire with insulating powder, inclosing it within a seamless metallic shell, reducing the cross section of the whole, and providing it with terminals of lower resistance than the core-wire extending from a point within the powder insulation.

9. The method of making a resistance element for electric heaters or the like, consisting in surrounding a high resistance corewire with insulation, inclosing it within a loosely fitting seamless metal tube, shrinking the tube on the insulation, cutting off the ends of the tube to expose the core-wire, providing terminals of lower resistance for the core-wire, and surrounding the points of lower resistance with heat absorbing material to prevent overheating.

10. A resistance wire for electric heaters or the like, comprising a high resistance core-wire, a metal tube surrounding the same, a filling of heat refractory insulating powder between the two, a metallic cap forming a prolongation of the tube filled with insulating heat refractory material, and a terminal of better conductivity secured to the core-wire within the cap.

11. A resistance element for electric heaters or the like comprising a high resistance core-wire, a metal tube surrounding the same, a filling of heat refractory powder between the two, a terminal of better conductivitv than the core-wire at each end, and a perforated insulating bead to hold the wire central.

ROBERT H. READ. Witnesses:

E. B. MCBATH, S. C. HILL.

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