Document EqM6npXkdQMQOb1n7nznnrBL

FILE NAME:McGraw-Edison (ME) DATE: & DOC#: ME0 DOCUMENT DESCRIPTION: WZZ : June 1, 1954 Filed Feb. 23, 1950 J. R. GOMERSALL ENCLOSED HEATING ELEMENT 2,680,183 3. Sheets-Sheet l WVVV777AAZZZAZAVO A awawaawaat AZ AAAAAAA NSG2),: AG 3 SaWAWAWAWAZZZZZY al M/6 12 8 - 4.2/ 2o AVAZR Y 2AZIZAZIns a/6, 25 Aaaatss INVENTOR. uMC2/77V a GOM2AeSaa.A. BY 42-ea-le-- 21-6 M June 1, 1954 Filed Feb. 23, 1950 J. R. GOMERSALL ENCLOSED HEATING ELEMENT 2,680,183 3. Sheets-Sheet 2 SI - $I4ZSNTIT f- ZZ . EP SH) WOA/W Ae. GOMIANVAEeNSTOARA. L BY Caeal-l. 3-1- ATTORNEY. June 1, 1954 Filed Feb. 23, 1950 J. R. GOMERSALL ENCLOSED HEATING ELEMENT 2,680,183 3 Sheets-Sheet 3 Zst: as 2 ees 4 es2 (SN/N 22z 25s ramm INVENTOR. John R. Gomersall 7%d. 1-- Otty. Patented June 1, 1954 2,680,183 UNITED STATES PATENT OFFICE 2,680,183 ENCLOSED EATING, EEMENT John R. Gomersail, Elgin, Ali., assignor to MpocrGatriaown oEfleDcetlraicwaCroempany, Elgin, ., a cor Application February 23, 1950, Serial No. 145,752 1. 4. Claims. (C. 219-9) ingTheelepmreenstesn.t, invention relates to electric heat 2 Fig. 5 shows a heating element of a modified It is an object of the present invention to pro construction; vide an improved electric-resistance heating ele ment suitable for electric toasters, broilers, cook in Faigm.o6unistainvgietwheorfeftohre; heating element of Fig. 5 ing Owens, drying Ovens, Space heaters and the like, that is cheaper in construction, less fragile, toaFsitge.r 7ofisFiag.Sic;hematic circuit diagram for the leSS Subject to corrosion, longer lived, and more Fig. 8 is a detail view on an enlarged scale, con pleasing in appearance than heating elements heretofore known. SFiisgt.i4n;g of a Section taken along the line 3-8 of A further object is the provision of an im 0 Fig. 9 is an oblique view, partly in section, taken dpervoivcee.d construction for an electrically heated along the line 8-9 of Fig. 8; According to my invention, I enclose a resist StrFuicgtSi.on1;0 and 11 are views of a modified con ance conductor in a tube of electric-insulating material such as glass, porcelain or plastic resin. 5 Fig. 12 is a view of a further modification; Fig. 13 is an elevation, partly in section, of a Although certain glass tube enclosures have been reflecting radiant heater having a heating ele proposed heretofore, they have been expensive Inent embodying my present invention; or of limited size, or have run the glass too hot. In the preferred manner of carrying out my in Fig. 14 is a perspective view of the heating element of Fig. 13; and vention I employ a round tube of a material that 20 Fig. 15 is an enlarged Section of the terminal is transparent to a Substantial part of the radiant, Of the heating element of Fig. 4. heat that will emanate from the heating conduc The Specific toaster of Fig. 1 includes a casing tor. I employ a ribbon-like conductor, crimp it f), oven frame members 2 and 4, a vertically into a Zig-Zag shape, and thread it into the tube having a sufficiently large bore that the con 25 nilowable rack levers i8 for 6 for Supporting a slice Supporting and moving of bread, the rack ductor is loose therein. I then form the tube f6, circuit wires 22 for the electric heating ele into a pattern that is suitable for the particular ments of the toaster, a Switch 24 for controlling device in which it is to be used. This method the circuits, and a handle 2 for controlling the of construction is simple and easy, and Subject rack and SWitch. to accurate control. It permits the conductor 30 The toaster also includes a pair of electric to be spaced easily along the length of the tube heating elements 30, each of which, as is best either at uniform intervals or in any desired pat ShoWin in Fig. 4, comprises a glass tube 32 through tern of non-uniformity and insures that it will Which is threaded a resistance conductor 34. not be damaged in the fabrication proceSS. The The tube is bent into a rectangular pattern con conductor touches the tube at only a few Spots Sisting of parallel runs 35 connected at their so that there is only slight conduction of heat ends by U-bends 38. The crimped conductor thereto. This construction permits a high con 34 extends from end to end of the tube, and ductor temperature for efficient radiation ac lead-in pieces 40, which may consist of the ends companied by a low tube temperature for max of the Wire, are sealed in the ends of the tube imum durability and Safety. 40 at 2. Preferably the end of the wire is doubled These and other objects and advantages of back and spot-welded as at 4 in Fig. 15 to pro my invention will be apparent from the follow vide a double thickness, and therefore a lower ing description of certain specific embodiments Wire temperature in the glass seal and the ter thereof which illustrate the manner in which minal. This bent glass tube 32 is mounted on tdrhaewiinnvgeSn:tion may be put into practice. In the a metal sheet 46 (Figs. 1, 2 and 3) which has U-shaped channels 48 on opposite edges for re Figure 1 is a sectional elevation of an electric ceiving the U-bends 38. Lying within each chan toaster containing heating elements constructed nel 48 and between the metal of the plate and in accordance with the present invention; the glass of the tube 32 is a strip of asbestos Fig. 2 is a detail, consisting of a Section taken 50 paper 52 Which conforms to the shape of the On the line 2-2 of Fig. 1; channel 8 and lies around the glass tube, as Fig. 3 is a detail on an enlarged Scale, consti is shown for example in the sectional view of tuting a section taken on the line 3-3 of Fig. 1; Fig. 2. Within the curve of each of the U-bends Fig. 4 is a view of the heating element of the 38 the edge of the channel 48 is bent in as at toaster of Fig, 1; 55 54 in FigS. 1 and 3 to hold the tube in place. The channels 48 hold the glass tube loose, leav 2,680,183 4. 3 face in contact With the air, operates at a tem ing Space as at 56, 5 and 38, shown exaggerated perature far below that of the ribbon. in FigS. 2 and 3, to allow for any difference of $fig. 5 shows an alternative configuration for expansion between the glass tube and its Sup the glass tube of a heating element for a toaster porting Structure when heated. Such as that of Sig. 1. The configuration of the The metal. Sheet 46 is preferably bright so that glass tube consists of two Similar patterns of it Serves as a reflector for radiant heat and shot horizonta, runs connected by J.-cends, with thereby both confines most of the heat to the the two patterns connected together' by a single OWen Space and increases the intensity of radia long horizontal run across the top. This ar tion applied to the bread. As is shown in Fig. 2, angement permits both of the terminals to be the Owen-frame members 2 and 4 have bent O located at the botton edge of the patterin. A Out ears 3 which constitute guides within which Supporting plate for the heating eleinent of Fig. the channel pieces 46 lie for supporting the heat 5 is ShoW in Fig. 6. Theire a plate 8 has forrned ing element in the toaster. The upper lead 43 side channels 2 similar to the channels A8 of Of conductor 3A is brought out to a screw ter Fig. i and in addition has a separate channel minal 33 (Fig. 1) on the outer face of the oven piece 4 running down its center for hoiding the frame 2. The lower lead is riveted under a, U-bends near the Center of the heating element. Inetal grommet Supported by insulating washers The leads are riveted inder ninetal gronnets 6 On plate 46, to which gronmet, circuit-wire 65 Which aire insulated from the plate i) by in is AcoSnnisecsthedowbny adibaoglrta4m8m.atically in Fig. 7, the 20 Sulating Washers 8. 'he ribbon conductor bends InoSt easily about Separate heeating elements 38 of the toaster are the longer axis of its cross Section, and since it connected in parallel with each other and the is loose and therefore free to turn in the glass resulting group is connected in series circuit, with tube, the crimped ribbon in the curved parts of a terminal timer which includes a heating element the glass tube SpringS into the Orientation shown 60 and its shunt contacts 62, which are not in FigS. 1, 4 and 5 so that the plaine of the ribbon otherwise shown in the drawings, and also in is perpendicular to the plane of the curve of the Series With the main Switch 24. Power is applied tube. In the toaster of Fig. 1, for example, the to the two leads 63 and 64. ribbon is merely crinaged aid inOttWisted axially AS is shown more clearly in Figs. 8 and 9, the and consequently it faces edge-on toward the resistance conductor 34 preferably is in the forn 30 bread. In tins construction of FigS. 10 and ll, of a thin ribbon which is deformed and lies loose the ribbon 85 is first crimped, and then twisted in the tube. Preferably I first crimp the ribbon 90 axially at Selected points such as 36. The to give it a generally zig-zag shape so that it con riokhon conductor, so foicined, is ii. Selted in a prises a Series of longitudinal waves. A single straight gaSS tube in which it, fits loose, and the Short length of ribbon Such as this usually has 35 tube is then heated and beat into its final shape. excellent uniformity, but various samples of rib The points SS at which tile ribbon was twisted bon, even from the Same Spool, may have ma axially will have been selected to come at the terially different thicknesses. In many heaters, junctions 33 between the curved and straight Such as those used for electric sirable that the heating units toasters, it is de be provided with 40 portions part 83 3 of and the 82 of the final assembly 8T. That ribbon in the curve will orient equal electric resistances so that the several ele itself edge-on as in Fig. 1, and because of the ments of any one toaster will perform alike. Ac 90 axia, Wis at each of the pointS 36 that part cordingly, in forming the crimps, I make thern 93 in the Straight, luns Will lie broad-on. An Shalp So that the crimped ribbon will be short. axial twist is a forAnation. Wherein croSS Sections I cut the formed ribbon to the desired resistance 45 transverse the longitudinal axis of the Convolute value, Stretch it out to the required length, attach ribbon taken at Spaced pointS of Said axis have Or form the lead-ins, and insert it in a straight different orientations about that axis. glass tube. I then form the tube to the desired In Fig. 12 the construction of Fig. 11 has been shape by heating it. the tube and pinch Finally, I soften the ends of them against the wire. As 50 bent into a Surface that is part of an inder so that the Straight poitions SS erect cyl of Fig. 1 inay be seen in FigS. 8 and 9, this crimped ribbon have become curved in a horizontal plane, but conductor 34 touches the glass tube only at lon with a less sharp curvature, aid therefore longer gitudinai intervals at the crests 66 and 68 of radius of curvature, than the J-bends. Here the Waves (Fig. 9) and then only at the edges the 90 ange of axial tWist at point 86 in the of the ribbon (Fig. 8). Furthermore the Wire 55 ribbon corresponds to the difference in direction lies loose in the glass tube and so will actually of the radii of curvature of the two curved por touch the tube only at a few of these corner tions of the tube, so that the longer axis of the like points. That is to say, the edges of the rib ribbon in each part of the tube lies approximately bon at the CrestS 66 and 68 longitudinal waves contact of only some of the tube while the the 60 perpendicular to the radius of curvature of that part. The straight runs in the tubes, as in Figs. Crests of other of the waves will be spaced from 4 and 11, should be regarded as portions of Zero the tube, as shown in Fig. 8. The overall thick curvature arid therefore as having a different ness or height of the ribbon determined by the curvature thaia do the U-bends. The radius of curvature of Such straight portions must of Wave formation is such that the zone of rec tangular cross section defined by the waves (Fig. 65 course be regarded as having infinite value and 8) in its greatest dimensions will be less than the indMeytenremwinaanted idmirpercotvieond.heating element is useful diameter of the tube. Accordingly, while the heat-generating ribbon is entirely supported by also in vai'ious other cooking and heating devices, the glass tube, it touches it only at widely spaced as for example the reflecting radiant heater of Fig. 13. There a glass tube 38 having a crimped pointS and is able to conduct only a small amount, ribbon conductor 82 extending therethrough is of heat thereto. Since glass is transparent, most formed in the shape of a bifilar tapered helix. of the heat that radiates from the ribbon passes The Specific Shape of this helix is best Seen in out through consequently the the glass glass, without Since it heating it, has a large and sur 75 Fig. 14. A metal rod 84 extending through the S 2,680,188 helix provides support at the outermost part of S the tube. For Such exposed constructions, the sectional area the ribbon would be less stiff. heating element of my present invention is Su Consequently the ribbon is more compliant and perior to unenclosed heating conductors because exerts far Smaller forces against the tube, and it presents far less danger to persons from burns So has less tendency to Set up noise when it moves and electric shock. For the same reasons my slightly as it expands under rising temperature. aetlmeomsepnhterisesf.ar more suitable for use in explosive The fact that the crimped ribbon lies loose further limits the mechanical forces it can exert against For use in toasters and the like, I now prefer that the insulating tube be made of borosilicate the Wall of the tube and so further reduces any tendency to generate noise. glass such as Pyrex glass. Such glass is trans O Although glass is an excellent electric insulator parent to a Substantial part of the radiation from at room temperature it is likely to become suffi the conductor, which is operated at red heat, ciently conducting at high temperatures, for ex and withstands the temperatures of 800-1000 ampie, when the glass reaches red heat, to Con F. to which it may be subjected. For greater 5 duct currents that night be dangerous to a person heat resistance I may employ a high-silica, glass. handling the toaster or other appliance in which For uses involving lower temperatures, as for ex the heating element was employed. The ability ample certain warming ovens, drying ovens and of the glass tube to operate at a low temperature space heaters, I may employ resinous insulating in my heater construction reduces the hazards materials such as polytrifluorochloroethylene, 20 from such possible leakage currentS. methyl silicones, polystyrene, methyl meth The asbestos paper spacers 52 that hold the acrylate, or nylon. Such Substances do not re glass tube out of direct contact With the metal sist heat, as well as does glass, but they are leSS supporting channels 48 not only provide a Soft brittle and for that reason will be preferred for and yielding mounting for the tube and reduce certain uses when the temperatures involved are 25 rattling that might result from the loose mount low enough. Porcelain, though far leSS trans ing, but also add materially to the electric insula parent, and less easily formed, is mechanically tion. In particular they provide a low-leakage stable at higher temperatures than is glass, and support for the glass tubes when they become hot so may be preferred When the higher trans enough to conduct objectionable electric cur parency and pliability are not tetrafluoroethylene is resistant required. to higher Poly ten 30 rents. Although asbestos may be somewhat hy groscopic and by itself inight contain enough peratures than are the other resins but is inited moisture at room temperatures to permit danger to uses in which pliability is inot required. ous leakage currents, nevertheless, as the toaster Because enclose my heat-generating metal heats up, the moisture is thoroughly expelled to conductor, it is kept out of direct contact with 35 leave the asbestOS paper non-conducting by the the atmosphere and only a limited supply of oxy time the glass reaches a temperature at which gen is available for its chemical erosion. AC the glass, by itself, might conduct current. The cordingly I can operate a glass enclosed element asbestos and glass consequently provide a Com of my present invention at a higher temperature, posite insulating construction which assures free and obtain comparable a longer life than open-wire heating is possible elementS. with The 40 dom from dangerous, or even current at room temperature, aniloying, leakage at high operating higher permissible temperature not only provides temperatures and during the transition from One a more intense radiant heat but also permits the to the other. use of a smaller element, particularly With a It will be apparent to those skilled in the art shorter total length of conductor with a consequent Saving in cost. and glass tube, 45 that Iny invention is capable of numerous modi fications and variations Within the Scope of the In many heating elements, as for example those appended claims. used in toasters, it is desirable that the heat I claim: storage capacity be low so that it can cause very 1. An electric heating element comprising a little delay in the heating and cooling of the 50 tube of heat-resistant electric-insulating material heating element. Such delay adds to the diffi and of curved cross-section and a crimped metal culties of controlling the toaster to make toast of electric heating resistance ribbon extending the same color regardless of the temperature to through the tube having longitudinal Waves de which the toaster may have been heated by fining a Zone of rectangular CrOSS-Section, Said previous operations. The low temperature of the ribbon making contact only at longitudinal inter tube helps to hold down the amount of heat that vals and only at its edges at crests of waves With is stored in this manner. In addition, my present the wall of the tube. construction provides adequate support for the 2. Aheating element comprising a tube of heat tube and puts little or no strain upon it. Con resistant electric insulating material and of cir sequently the tube can have a thin wall to fur ther reduce the mass and the heat storage capac 60 cular cross Section having a Series of extending in spaced parallel relation portions and U ity of the heating element. shaped bends in the tube connecting each adja I have found that under certain conditions a cent pair of said parallel portions, and a crimped conductor in a tube will produce a high-pitched, metal electric heating resistance ribbon having squeal-like noise as it pears to be produced heats up. This noise by the movement of ap the 65 longitudinal waves defining a zone of rectangular cross section extending continuously through all heated metal of the conductor across the Surface of said parallel tube portions and said tube bends, of the tube, and to occur in the curved parts of said ribbon making contact only at longitudinal the tube. I find that this noise can be at least intervais and only at its edges at Crests of Waves reduced, and usually eliminated by using a thin ribbon conductor and by having it fit loose in 70 with the wall of the tube and the opposite ends of said ribbon having sealed connections With and the tube. As between a ribbon and a round Wire projecting outwardly beyond the opposite ends of having the same heat dissipating Surface per the tube. unit length, the ribbon has the Smaller CrOSS 3. An electric heating element as in claim 2 sectional area, and even. With the Same croSS 75 wherein the greatest dimensions of the Zone of rectangular cross section defined by the Wayes of 2,680,188 7 the ribbon are shorter than the diameter of the 1,104,054 tube and the edges of the ribbon at recurrent 1,334,850 1,395,963 Wave crests are Spaced from the Wall of the tube. 4. A heating element according to claim 2 2.061,516 Whereiin the faces of the Waves of the ribbon in 5 each U-bend of the tube lie substantially per 2,150,285 2,244,960 pendicularly to the bend plane and the faces of 2,332,392 2,344,908 the Waves of the ribbon in the parallel tube por tions lie substantially perpendicularly to the wave 2,464,147 faces in Said U-bends of the tube. O References Cited in the file of this patent UNITED STATES PATENTS Number 4:25,043 Number Name Date 5 1,032,267 Bastian ------------- July 9, 1912 3. Linder ------------- July 21, 1914 George et al. -------- Mar. 23, 1920 Kuppers ------------- Nov. 1, 1921 Frese -------------- Nov. 17, 1936 Marek et al. -------- Mar. 14, 1939 Nelson ------------- June 10, 1941 Minter ------------- Oct. 19, 1943 Whitman ---------- Mar. 21, 1944 Myers -------------- Mar. 8, 1949 FOREIGN PATENTS Country Date Great Britain -------- Mar. 4, 1935