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Publication numberUS2499961 A
Publication typeGrant
Publication dateMar 7, 1950
Filing dateApr 30, 1948
Priority dateApr 30, 1948
Publication numberUS 2499961 A, US 2499961A, US-A-2499961, US2499961 A, US2499961A
InventorsLennox Thomas H
Original AssigneeGen Electric
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electric heating unit
US 2499961 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

March 7, 1950 T. H. LENNOX 2,499,961

ELECTRIC HEATING UNIT Filed April 30. 1948 Fig.2.

Inventor- Thomas H. Lennox,

by @Mmam His Abbot-neg.

Patented Mar. 7,- 1950 ELECTRIC HEATING UNIT Thomas H. Lennox, Plttsfleld, Mass., assignor to General Electric Company, a. corporation of New York Application April 30, 1948, Serial No. 24,208

2 Claims. (Cl. 201-67) the provision of an improved method of making an electric heater of this character.

More specifically, my sheath wire units used in flat or platen heating and oven heating in each of which it is desired to maintain a uniform temperature over a flat surface. In these types of heaters, the units are disposed parallel to each other in a plane parallel to the workpiece.

My invention provides such a planar heat source at a much reduced cost. It was found that if uniform unit resistance were used over the whole len th of the heat ng units, more heat escaped into the air from the areas nearer the ends of the heating units than the areas nearer the center of the units causing uneven heating of the workpiece area.

The remedy sou ht to be applied for this situation was coils with tapered. 01' graduated, heating characteristics that is. cois that provide more heating pe unit len th at each end than in the center. The method first tried employed a reinvention relates to sistance coil of uniform diameter. Before crimping or welding to the coil terminal arbors, a center section was stretched to fewer turns per un t len th. The coil was then centered in a sheath and insulation was vib atin ly packed around it. The entire unit was subjected to a swaging operation in which the cross-section area was reduced and the unit len thened.

This method has been found to have some disadvanta es since the prestretched section of coil is less resilient than the unstretched section and after the lengthening of the whole coil caused by swaging the unit. the resistance unit len th of the entire coil had a tendency to become uniform, instead of having the desired taper.

In carrying out my invention, I utilize helical resistance coils of diffe ent diameters for providing different rates of heat generation. In one form of my invention I use a resistance coil with its center section wound to a smaller diameter than that of its ends. It has been found that when the center section of such coil is prestretched, the resulting unit has the desired tapered heat producing characteristics.

Reference to the accompanying drawing will add to a more complete understanding of my invention, in which Fig. 1 is a sectional view of the complete tapered heat Calrod unit; Fig. 2 is a view of the coil partially wound upon its arbor; Fig. 3 is a view of the arbor alone.

Referring to the drawing of one embodiment of my invention, an arbor in Fig. 2- comprises a rod I upon which two sleeves 2 and 3 are slidably mounted and to which they are removably secured by the set screws 4 and 5 in the flanges of the sleeves, leaving the rod i uncovered by the sleeves in the middle section. The coil wire of high resistance material having considerable. resiliency such as nickel, chromium alloy is wound in a helix continuously with a uniform spacing of the turns, as shown, from one sleeve flange to the other, the outside diameters of the sleeves and the rod becoming the inside diameters of the coil. After winding the sleeves and shaft are withdrawn, leaving the coil with a middle section diameter smaller than the equal end diameters. The elongation per unit length produced by the swaging of a unit comprising a coil wound with different diameters is not uniform since the coil length of smaller diameters is less resilient than the remainder, therefore, this middle section is stretched to nearly the desired length before the swaging, rolling or drawing, operation to reduce the diameter in order to compact the powdered insulation further.

Terminal rods 6 and l of the same material as that of the coil are firmly attached to the coil at their ends 8 and 9 of larger diameter and the coil is mounted concentrically in the tubular metallic sheath l0 under tension enough to maintain its concentric position, and with terminals 6 and I firmly attached to two sheath end caps. Ceramic spacers ll, l2, I3 and M are provided at suitable intervals to maintain the coil concentric with the sheath. The sheath is held upright and continuously vibrated while a powdered insulation material, like magnesium oxide, is poured into the tube through apertures provided in one end cap for the purpose. Magnesium oxide is used as insulation because of its high heat conductivity when its powdered form is compressed. When filled the end caps are replaced by washers to which the terminal rods are securely fastened. These washers keep the packed insulation within the tube during the reduction of cross-section operation which follows.

This cross-section reduction operation increases the length 01' the unit about 20% with an accompanying decrease in diameter, packing the insulation firmly within the sheath. The sheath is then cut to the desired length leaving the terminal rods at each end projecting for attachment in an electric circuit. This assembly of the resistance unit and. sheath and subsequent swaging is described more in detail in The stretched length of-the reduced diameter center section of coil is chosen so that after.

reduction its length will be substantially equal to that of each end section. The relative diam eters in a typical heating unit are such that'the resistance of each end section is substantially equal to one and one-half the resistance of the middle section. Since the rate of heat generation in a coil is proportionate to the coil resistance, in such a typical heating unit, the heat is generated substantially one-quarter by the middle section and three-eighths by-each end section. It is to be understood that this is but one form or my invention and that these relative values may be changed at will. 1

Fig. 3 illustrates an arbor for use in another form of my invention in which the end sections of the coil are tapered toward each end from the middle section, with parts corresponding to the parts of the arbor in Fig. 2 described above and numbered accordingly.

While certain specific embodiments have been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. The appended claims are, therefore, intended to cover any such modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent oi the United States is:

1. A metallic sheathed heating unit having greater heat generation in a section at each end than in the remaining central section, comprising a tubular metallic sheath, powdered heat refractory insulating material compacted to a hard dense mass in said sheath, and a continuous helical coil of resistance wire in said sheath extending lengthwise thereof and em bedded in said insulating material having [its turns spaced apart substantially uniformly throughout-its length and being provided with at least three sections each having turns of uniform diameter, there being a section at each end having a substantially greater diameter than the remaining central section to provide a greater length of said resistance wire in said end sections per unit length oi said sheath for the generation of a greater amount of heat per unit length in said end sections as compared with said central section.

2. A metallic sheathed heating unit having greater heat generation in a section at each end than in the remaining central section, comprising a tubular metallic sheath, powdered heat refractory insulating material compacted to ahard dense massin said sheath, a continuous helical coil of resistance wire in said sheath extending lengthwise thereof and embedded in said insulating material having its turns spaced apart substantially uniformly throughout its length and being provided with at least three sections each having turns of uniform diameter, there being a section at each end having a substantially greater diameter than the remaining central section to provide a greater length of said resistance wire in said end sections per unit length of said sheath for the generation of a greater amount of heat per unit length in said end sections as compared with said central section, an electric terminal rod projecting fromeach end of said sheath having its inner end embedded in said insulating material, and en-' larged portions on the inner ends of said terminal rods secured respectively to the ends of said eoii.

' THOMAS H. LENNOX.

The following references are of record in the file of this patent:

UNI'IED STATES PATENTS Number Name Date 563,032 Hadaway, Jr. June 30, 1896 essence Lightfoot Nov. 16, 1920 1,755,444 Von Brockdorii Apr. 29, 1930 1,901,892 Ejorkman et a1. Mar. 21, 1933 1,911,063 Daiy May 23, 1933

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US563032 *Jun 30, 1896 William s
US1359400 *Jun 22, 1920Nov 16, 1920Cutler Hammer Mfg CoElectric heater
US1756444 *Feb 7, 1929Apr 29, 1930Schutte & Koerting CoElectric heating means
US1901892 *Dec 7, 1929Mar 21, 1933Edward Bjorkman GeorgeHair curler
US1911063 *Nov 30, 1929May 23, 1933Gen ElectricElectrical heating unit
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2725453 *Apr 8, 1952Nov 29, 1955Westinghouse Electric CorpHeating apparatus
US2756362 *Feb 2, 1955Jul 24, 1956La Rue Albert DCathode heater
US2817740 *Nov 28, 1955Dec 24, 1957Jackson Robert Alfre FrederickElectric heaters
US2875312 *Sep 27, 1956Feb 24, 1959Thermel IncHeating assembly and method of production thereof
US3027285 *Aug 28, 1958Mar 27, 1962American Photocopy Equip CoOffice laminating machine
US3121154 *Oct 30, 1959Feb 11, 1964Babcock & Wilcox LtdElectric heaters
US3158787 *Jun 20, 1961Nov 24, 1964Magneti Marelli SpaGlow plugs equipped with armoured resistances
US3180973 *Dec 15, 1961Apr 27, 1965Robertson Photo Mechanix IncApparatus for fusing master plates
US3227854 *Feb 8, 1963Jan 4, 1966Reynolds Metals CoApparatus for perforating thermoplastic film
US3393292 *Jul 27, 1965Jul 16, 1968Werner & PfleidererPressure plate for a press
US3927301 *Sep 17, 1974Dec 16, 1975Hasco Normalien Hasenclever CoElectrical heating cartridge
US4117311 *Mar 14, 1977Sep 26, 1978Von Roll Ag.Electric welding muff
US4626665 *Jun 24, 1985Dec 2, 1986Shell Oil CompanyMetal oversheathed electrical resistance heater
US4704514 *Jan 11, 1985Nov 3, 1987Egmond Cor F VanHeating rate variant elongated electrical resistance heater
US5159179 *Mar 9, 1990Oct 27, 1992Chimica Edile Artigiani Di Ghini & Pasquini S.N.C.Heating device for accelerating the action of expansive mortars
US5412181 *Dec 27, 1993May 2, 1995The B. F. Goodrich CompanyVariable power density heating using stranded resistance wire
US5908569 *Apr 4, 1996Jun 1, 1999Eos Gmbh Electro Optical SystemsApparatus for producing a three-dimensional object by laser sintering
US6919542 *Oct 22, 2003Jul 19, 2005Seb S.A.Sheathed heating element with positive temperature coefficient
US7769278 *Jul 26, 2005Aug 3, 2010Lg Electronics Inc.Carbon heater
EP0388368A1 *Mar 1, 1990Sep 19, 1990CHIMICA EDILE ARTIGIANA DI GHINI & PASQUINI S.N.C.Method for accelarating the action of expansive mortars
EP0703036A2 Nov 7, 1991Mar 27, 1996Dtm CorporationSelective laser sintering apparatus with radiant heating
EP0764079A1 Apr 4, 1996Mar 26, 1997EOS GmbH ELECTRO OPTICAL SYSTEMSDevice for producing a three-dimensional article by laser sintering
Classifications
U.S. Classification219/541, 338/218, 338/238, 219/546, 219/531, 219/544, 219/553, 219/552, 100/320
International ClassificationH05B3/42, H05B3/48
Cooperative ClassificationH05B3/48
European ClassificationH05B3/48