US2029075A - Electric heating element - Google Patents

Description

1936- J. A. KNIGHT 2,29f95 ELECTRIC HEATI NG ELEMENT Filed April 27, 1954 ance between the resistance element and the consay that it is stiff enough to apply pressure as Patented Jan. 28, 1936 r 2,029,075

UNITED STATES PATENT OFFICE 2,029,075 ELECTRIC HEATING ELEMENT John A. Knight, Hamilton, Ontario, Canada Application April 27, 1934, Serial No. 722,694

9 Claims. (01. 21938) This invention relates to electric heating eleconductivity between the resistance ribbon and 'ments of the resistance type which are exteriorly the facing band.

applied to the outer surfaces of cylindrical tanks Behind the resistance element is positioned an or conduits to heat a fluid contained therein or insulating band 3, preferably of mica. 5 flowing therethrough, and-one object of my in- Behind the band 3 is positioned the cushioning 5 vention is to produce an element of this type band 2 which is preferably of heat insulating mawhich will present a path of very high heat conterial and is sufiiciently soft to be readily comductivity between the resistance element and the pressible, as its function is to convey a resilient exterior surface of the tank. A further object of pressure from a supporting band I to the under- 0 my invention is to produce a heating element, lying parts to hold them in close contact with which, though not flexible in the strict meaning the facing band 8 in close contact with all parts of the term, is readily adaptable to several diamof the surface of a cylindrical tank or conduit eters of tank within a limited range. A further to which the device is applied. object is to provide a durable path of low resist- The supporting band is semi-rigid. That is to necting terminals and to provide a satisfactory described but flexible enough to permit its diamsupporting connection between the heating eleeter to be varied through a limited range to fit ment and the terminals. A further object is to different diameters of tank.

provide a terminal chamber where the connec- To retain the parts in assembled relationship, I tion to the source of power is made having a comform the facing band 8 of a greater width than 20 paratively low temperature therein so that the the otherbands which are approximately of the insulation on the wires leading to the heater may same width and fold its edges over the edges of not be damaged and a good electrical connection the other bands into engagement with the back will be maintained. A further object is to proof the supporting band.

vide a convenient and practical arrangement for The preferred method of assembly is to bend 25 assembling the parts together. the metal strip 8 into the form of a straight chan- I attain these objects by means of the connel, roll the channel to ring form, assemble the structions hereinafter described and illustrated other bands within the channel, and finally roll in the accompanying drawing in which in the sides of the channel over the edges of the Fig. l is a plan view of the heating element; other bands as described. 30

Fig. 2 an inside elevation ,on an enlarged scale The completed structure has its ends in juxtaand partly broken away of part of the same; position and is clamped about a. tank by means Fig. 3 a longitudinal section on the line 3-3 in of a bolt passing through lugs 14 formed on the Fig. 2; I ends of the band I. It is found that a structure Fig.4 afront elevation partly broken away and such as described presents such a high heat- 35 partly in section of part of the same; and conductive path between the resistance and the Fig. 5 a detail illustrating the connection bewall of the tank that substantially the highest tween the resistance element ribbon and the leads possible efficiency is attained. therefor. The second feature of my invention lies in the 0 In the drawing like numerals of reference indimeans for forming a connection between the cate corresponding parts in the different figures. resistance ribbon and the source of current sup- Referring to the drawing, 8 is a very thin metal ply. For this purpose I employ a metal connecfacing band formed of a metal of high heat contion box l2 in the bottom of which is formed a. ductivity and sufficiently soft or malleable to hole I8.

readily conform to the surface to which it is ap- In the supporting band I is formed a hole I9. 45 plied. Sheet aluminum about .015" thick is A plate I! is welded to the band I and has a satisfactory. Behind thisis positioned the resisthole I8 therein alined with the hole i9. The ance element comprising resistance wire 5 wound connection box I2 is secured to the plate I! in on a mica or other insulating band 4. A thin spaced relationship, preferably by the following flat ribbon is used as it presents a large conductmeans. A block I l of insulating material carries 50 ing surface towards the facing band and thus the terminals I0, and is spaced from the bottom transfers heat more effectively. A thin band I of the box l2 bythe lugs 20. Between the botof insulation, preferably mica of a thickness of tom of the box and the block l1 are positioned about .010 is positioned in front of the resistthe block or blocks l5 of insulating material.

ance element and provides a path of high heat Through the block II, the lugs 20', the bottom of 55 til electrical resistance. 7 are then brought, out through openings in the insulation and cushioning 'band tothe terminals.

the box l2, and the blocks [5 pass the screws 2|, which are threaded into the plate I! and hold the parts together.

A weak point in heaters of this type, both mechanically and electrically, is the connection between the resistance ribbon or wire and the terminals. It is desirable that such connections should be mechanically strong and electrically of low resistance to avoid transfer of heat to the terminals. I..f.orm.these connections in.the tollowing manner. "For the leads 1 from the terminals I employ pieces 6 of metal ribbon having a much lower resistance per unit of length than the ribbon 5. Preferably the pieces of ribbonfB are of the same width as the ribbonf-I5,lb1lt.thiker. The ribbon 6 is positioned beneath the ribbon .5

at its last bend over the insulating band"4"be'fore' being brought out throughmheaopeningszin the insulation band 3 and the cushioning band 2. The superimposed ribbons are then coiled around 'a mandrel, the. mandrel withdrawn andthe bands flattened together, this coiling and flattening takinggplace adjacent .to the last fold overttheeedge of the insulating band-4. .The coiling-of the bands around .a mandrel :and then flattening .them. together causes them to be forced into=.high

pressure contact each withtheother, givingaa mechanically strong connection rand-one of :low The superimposed 1 parts Very little heat: therefore'is generated in the connections which not only is conducivefto'durability, but also to efficiency; Whichis further .aided by the arrangement of .the connection '.-box in spaced and insulated relationshipitdthe supporting band.

What I claim as lny-rinventionis:

v1. "An-electrical. heating element-'-comprising a thin metal l facing band an insulated resistance element applied: to the outer-surface: of: the facing band; a cushion band applied.outsidethev resistance element; .a .semirr-igid supporting -,band

of metal formed as a split ring;r-.and.-meansfor drawing its ends .together 1 to clamp -it-=-about a cylindrical 1 surface and thus press (the ccushion against the: insulated; resistance: element; the 'resistance element against the facing band-andthe latter against thewsuriaee to which :the l heating element is applied. p

2. An electrical heating.element:comprising a thin metal facing band ;zan.- insulated resistance element .applied to thezouter; surfaceof .the. facing band. and: includinga thin broad. metalrrib- .bon laid flatwiserelative-to the 'facing..band;.-a

. cushion .bandappliedoutside .the; resistance element; a semi-rigid .supportingbandtotmetal formed as a split ringaandmeansfiordrawing its .ends together tocclamp it. about .apylindrical thereto; and a terminal box secured to the said .:'Dlate=:arfd;in.spaced relation thereto.

5.,An. electrical heating element of band form having an external metal supporting band; a metal-;plate'=.tangential to the band and welded thereto; a terminal box secured to the said plate; a-block-or blocks of heat insulating material se- .cureddmthe eboxsfrom .the plate; @and fastening rmeansengaging.thebomand;plate.and-extending. through .thewblock. V

6. An; electrical heating element of flbHiHd: form having an external metalsupportingband formed -with.-a.-hole forttheipassageof .leads for the ele- .ment; .a: metal .platealso. having a hole therein registering .with .the.,hole.in .the .bandand welded .to'. theabandtabout the-1101a;- and-a. terminal. :box secured totthesaid plate in spaced relation thereto .and .also. havingra hole-.alin'ed .withtherholes aforesaid. V

.7. An. electrical resistance. element comprising a :metallic .iibbon -:,of .high :electric :resistance wound on .an .insulating support; leads .35 formed. of. a. metallic ribbon of .lower. resistance per .unit n'f. length. than; the. first mentioned rib- ...bonjthe :ends; of .the latter .belng juxtaimposed in,flat. folds.

.. 8.. An.electrical.heatingtlement..ofband. form 740 having an external metal gsup-porting .band; .a

.terminalbox-secured; to. said. band terminals. carried, byethetbox g and .washers-.0f..,heat insulating material: spacingthehox .fromthe band and :co-

. incident .openings in the .band, [the .insulati-ng 5 washers and the boxtthreughlwhichgconnection may .be. made. fromca resistance .element; to the terminals i-ntthecbox.

9. An electrical resistance.element-comprising a metallic ribbon of high eelectricalgresistance .50

.wound on .an insulating .:-;support; .and :leads formednfametallic ribbon of ,lower. resistance iper unitcof, lengthtthantthe. first; mentioned ribbon, the two ribbons being juxtaimposed each eon. thetother. in-..a:series.ni .short; fiat contiguous folds forming.alriglnpressureconnectiomoi .low

electriealresistance.

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