US1715824A

US1715824A - Electrical resistance unit

Info

Publication number: US1715824A
Application number: US734871A
Authority: US
Inventors: William E Duersten
Original assignee: GLOBAR CORP
Current assignee: GLOBAR Corp
Priority date: 1924-08-29
Filing date: 1924-08-29
Publication date: 1929-06-04
Anticipated expiration: 1946-06-04

Description

June 1929- w. E. DUERSTEN ELECTRICAL RESISTANCE UNIT Filed Aug. 29, 1924 Patented June 4, 19 29.

UNITED STATES 1,715,824 PATENT- OFF-ICE.

WILLIAM E. DUERSTEN, F MILWAUKEE, WI SCONSIN, ASSIGNOR, BY MESNE ASSIGN- 15. IENTS, TO GLOIBAR CORPORATION, OF NIAGARA. FALLS, NEW YORK, A CORPORA- men or new man.

ELECTRICAL RESISTANCE UNIT.

Application 111m August 29, 1924. Serial no. 7s4,a71.

The present invention relates in general'to electrically conductive elements of the type known as resistance units, especially such a unit as is capable of producing in a commercial manner a relatively high degree of heat on the passage of an electrical current through the unit, and also of maintaining itself in an efiicient mannerduring a commercially satisfactory life; and the invention is more particularly concerned with the production of such a resistance element provided with terminals of a character especiallyada-pted to withstand high temperatures while connecting the unit in circuit in a mechanically and electrically efiicient and generally satisfactory manner.

The problem of producing a commercially satisfactory terminal in connection with a relatively inexpensive and efiicient electrical resistance element adapted to produce and withstand relatively high temperatures, has been a considerable onein the past, especially'in connection with resistance heating elements of what is knownin the art as the generally non-metallic class which have the characteristic of bein able to produce and maintain relatively high temperatures with a very small degree of expansion. One certain ty e of commercially satisfactory resistor 0? this general class has been produced and has gone into extended use, this resistor being constituted to a considerable extent of silicon carbide, with or without the addition of one or more modifying substances; and the present invention finds considerable utility in connection with this type of resistance element. 1

A great defect in connection with prior art devices of this character has been the failure to produce and maintain sufliciently intimate contact between the metallic conductive terminal and the body of the resistor and to satisfactorily dissipate to the air or other surrounding medium, theheat of the terminal; for as the resistor becomes heated, there is a tendency toward oxidation or burning or pitting of the metallic terminal with consequent final destruction thereof, due to the formation of minute arcs between the resistor-and '50 the terminal, with a consequent considerable increase in the resistance at the terminal. This results in a decrease in the effective voltage on the normal heat producing portion of the resistor and, hence, an undesirable decrease in the total heating effect of the remaintaining relatively high temperatures,

the invention being more particularly concerned with such a resistance element constituted to a considerable extent'of silicon carbide as an essential ingredient, and wherein means are provided for forming an efiic5 cient electrical connection between the body of the resistance element and a line terminal and also constituting means for supporting the resistance element, the general result including the provision of a relatively inexpensive and eflicient resistance unit adapted to produce the desired heating e'fl'ect and satisfactorily maintain itself under severe operating conditions.

It is an object of this invention to provide an improved electrical resistance unit embodymg a terminal or connection element of 1mproved design and construction and adapted to withstand a considerable degree of heat while maintaining an efiicient electrical connection and mechanical support for the resistance unit. It is a further object of this invention to provide an improved electrical resistance unit embodying a resistance element essentially constituted to a considerable degree of silicon carbide or the like, and likewise embodying one or more electrically conductive terminals attached to the resistance element, the unit as a whole constituting an inexpensive and efiicient resistance unit well adapted for producing and maintaining itself under high temperatures.

It is a further object of this invention to provide a terminal of improved design and construction for electrical resistance elements, more particularly of the heat generating type, which constitutes an eflicient electrical connection and mechanical support for the resistance element.

These and other objects and advantages are 1 obtained by the present invention, various novel features of which will be apparent from the description and drawings, disclosing embodiments of the invention, and will be more 1 particularly pointed out in the claims.

In the accompanying drawings:

Figure 1 is a view in elevation, partly in section, of a resistance element embodying features of the present invention.

Figure 2 is a sectional view in theplane of the line IIII of Figure 1.

Figure 3 is a broken sectional view showing a modification of a feature of the invention disclosed in Figure 1. v

In accordance with the disclosure of the accompanying drawings, 10 indicates a resistance element more particularly of the nonmctallic type and essentially constituted to a considerable degree of silicon carbide. The

'cnds of the element 10 are provided with metallic terminals or connectors embodying features of the present invention. As indicated, the terminal includes a hollow element or cap 12 having a central bore, the tubularwall of the bored portion being provided with external threads and longitudinally slotted at a plurality of points,-as indicated at 13, to provide spaced flexible fingers, The substantially closed end portion 14 of the cap 12 has a central or axial threaded aperture 15 in which a line or circuitattaching screw 16 may be secured, the line terminal, whether it be in the form of one or more turns or layers ofstrip or sheet metal, preferably aluminum foil, Wrapped about the end of the bar, or it may be in the form of a dense coating of aluminum or Monel metal deposited "inthe form'of minute particles a portion of which may impregnate the surface portion of the resistance element. In any case, the conductive coating 17 is of such a character that it is or may be forced into intimate engagement with the terminal portion of the resistance element which is of; a somewhat porous structure.

lIVith the end of theresistance element and its conductive coating inserted into the bore of the sleeve of the cap, a locking or clampin device or collar 18 is applied to the exterior o the sleeve for the purpose of clamping the V latter firmly upon and in intimate contact with the resistance element.

The desired looking or clampin effect is preferably secured by having t e outer threaded wall of the sleeve portion of the ca 12 somewhat tapered toward its inner en thatis, toward the middle of the resistance element, and providing a clamping element or nut 18 having an internal thread tapered to poi-respond to the taper of the cap, the clamping element being threaded onto the outer wall of the cap irom the inner end thereof.

As this clamping or locking element is threaded or forced onto the sleeve of the cap 12 from the inner end thereof, it has theefie'ct of pinching or contracting the spaced portions or fingers of the tubular portion 12, formed by the slots 13. into firm and rigid frictional engagement with the terminal portion of the resistance element directly or with the conductive coating, where the latter is applied to such terminal portion;

The inner end of the threaded clam ing element 18 is provided with an integral auge 21 substantially perpendicular, or preferably slightly inclined from a perpendicular, to the axis of the resistance element and cap, as indicated. This flange 21 is preferabl with spaced apertures 23 or the. may serve for engagement by a tool for forcing the locking or clamping element into operative position on the tubular portion of the cap 12. As shown at the right in Figure 1, this flange extends toward the middle of the resistance element, while at the left in this figure, the flange 21 extends away from the middle of the resistance element. In either case, the flange constitutes a shield for protecting the heated portion of the resistance element from accidental contact with external objects, and alsoa heat conducting shield which dissipates heat'from the body portion of the cap, and thus assists in preventing over heating of the end and body portion ofthe terminal; The cap 12 provided e which i and the clamping element 18 with its integral flange-like shield may be of any material having the desired conductivity and which does not readily oxidize at the normal operating temperatures of the terminal; and'the radiating surface of the terminal as a whole should be such as to keep its operating temperature belowared heat. g

In the modification shown in Figure 3,'the end of the resistance element 10'is provided with corrugations, preferably in the form of screw threads, andthe bore of the terminal cap 12 is provided with internal threads for engagement with the-threads formed ou-the I end of the resistance element, permitting v.

screwing the cap to operative position onthe terminal portion of the resistance element.

The other features may be the same as shown in Figure 1'. The pitch of the threads formed i f on the end of the resistance element may be opposite to that of thethreads formed on the exterior of the terminal cap, toassist in look ing the cap. on the end of the'resistanceelement as .the clamping element 18-isforced into operative position on the threaded outer surface of the sleeve portion of the cap A conductive coating 17 of the t pe. described in connection wit Figure l is likewise applied to the corrugated or threaded end of the resistance element prior to disposing the lat- .ter in operative'position within the bore of the terminal cap 12. The corrugationsgor of the cap 12 have the added'funct ion of providing additional surface contact between the p and threaded clamping collar surrounding terminal portion of the .resistance element and the terminal ca 12 and the intermediate conductive coating 17. The resistance element is preferably formed from a mixture containing silicon carbide as an essential element, with or without one or more metallic modifying substances, and molded and baked and burnt or fired. at a high temperature to produce aheat-hardened resistance element' of the desired mechanical and electrlcal characteristics.

With a conductive coating of the character described applied to the end of the resistance element and the latter disposed within the bore of the sleeve-like portion of terminal cap 12 and the cap clamped or locked in operative position, an efiicient mechanical and electrical connection of the parts is secured.

lVith the complete resistance unit operatively connected to a supply line through theconnection screws 16, the effect of a high degree of heat producedin the resistance element may be to weld or alloy or intimately unite,

the metallic coating 17 to the associated parts of the resistance unit. In general, the electrical and mechanical connection secured as hereinabove described is of a very efiicient character, even while the resistance unit is operating at relatively high temperature.

It should be understood that the inven-' tion claimed is not limited to the exact details of construction and design shown and described herein, for it will be apparent that obvious modifications will occur to persons skilled in this particular art.

It is claimed and desired to secure by Letters Patent: 4

1. An electrical resistance heating unit, comprising a self-sustaining resistance heating element capable of producing and maintaining itself at high operating'temperatures, a conductive terminal for Sflld' heating elem'e'nt comprising an externally tapered and threaded contractile sleeve portion at one end surrounding a terminal portion of said heating element and a substantially ri id-portio'n at the other end, and an interna ly tapered and adjustable upon said contractile sleeve portion and adapted to force and hold said sleeve in intimate engagement with said terminal portion of the heating element, said clamping collar being provided adjacent its inner end with an external flange-like shield inclined away from said inner end.

2. An electrical resistance heating unit, comprisng a self-sustaining resistance heating element capable of producing and maintaining itself at high operating temperatures and having a terminal portion of corrugated or irregular surface outline, a conductive terminal having a contractible sleeve-like portion of correspondingly irregular outline to intimatelyenga-ge with said terminal portion of the heating element when the latter is disposed within said sleeve, and annular clamping means cooperative with the exterior of said sleeve for causing said sleeve to forcibly grip and intimately engage said terminal portion of the heating element, said clamping means having at its end nearest the center of the heating element and inclined away therefrom a flange-like shield adapted to dissipate heat from the body portion of said conductive terminal.

3. An electrical resistance heating unit, comprising a self-sustainin resistance heating element capable of pro ucing and maintaining itself at high operating temperatures and having a terminal portion provided Withscrew threads, a conductive terminal having a cont'ractible sleeve-likeportion surrounding said terminal portion of the heating element, said conductive terminal being provideclwith screw threads in cooperative intimate engagement with the screw threads on said terminal portion of the heating element, and annular clamping means cooperative with the exterior of said, sleeve for causing said sleeve tov forcibly grip and intimately engage said terminal portion of the heating element, said clamping means having at its end nearest the center of the heating element and inclined away therefrom a flangelike shield adapted to dissipate heat from ,the body portion of said conductive terminal.

In witness whereof I affix my signature.

hereto.

- DUERsTEm