US1614330A - Electrical heating element - Google Patents

Description

Jan. 11 Q 1927. 1,614,330

E. L. WlEGAND ELECTRICAL HEATING ELEMENT Filed Augflst 31, 1923 4 Sheets-Sheet l 00o oooooooooooooo 00o ooooooooooooooo oooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo oooooooooooooooooooo ooooooooooooo'oooooo ag/M 00000000 0000 ooooooooo 00000 0000000070 00000 000000000 00000 000000000 0001000000 000000000 000000000 000000000 000000000 000000000 000000000 0000000 0000000 0000000 000000000 0000000 0000000 0000000 00000000 00000000 0000000 0000000 0000000 00000000 00000000 00000000 4 Sheets-Sheet 2' E. L. WIEGAND ELECTRICAL HEATING ELEMENT Filed August 31, 1923 Jan. 11 1927.

j {zrrx7 v 1,614,330 11 1927' E. LQWIEGAND ELECTRICAL HEATING ELEMENT Filed August 31 1925 4 Sheets-Sheet a Jan.'11,1927. 1,614,330 v E. L. WlEGAND I ELECTRICAL HEATING ELEMENT 4 Sheets-Sheet 4 Filed August 51, 1923 resistor temperature.

Patented Jan. 11, 1927.

PATENT OFFICE.

EDW IN L. WIEGAND, OF DOBHONT BOROUGH, PENNSYLVANIA.

nns-crates; naa'rnre ELEMENT.

Application filed August 81, 1923. Serial 1%.660384.

This invention relates to new and useful improvements in electrical heating elements of the type wherein the resistor is enveloped in refractory material. .More specifically the invention maybe stated'to consist of a novel class of heating elements and a process for making the same wherein. the

resistor is enveloped in a sheet metal casing.

and insulated therefrom by a compact mass of refractory material.

I am aware that aresistor in the form of a single straight conductor has been onclosed in a metal sheath and insulated there from by finely' divided refractory material-,- such a construction being commonly referred to as sheathed wire. This type of heating element has the disadvantage that it is very difficult and expensive to manufacture. During the drawing process, the

resistor wire develops irregularities in cross.

section andhence the life oftheelement is greatly shortened. The refractory material also becomes unevenly displaced, and the resistor isnot located centrally with respect to the outer metal casing and'therefore the insulation is impaired. This sheath wire is capable of being bent and massed into spiral and serpentine forms of heating elements with some degree of success, although it will be obvious that thereis adouble wall of .the refractory material and metal casing between each convolution or adjacent length of the spiral or serpentine 'type of heating element. This double wall requires space'that might well be utilized by a more massive resistor to greatly increase the efficiency of the element, as it is well known that there is a definiterelation between the area of the space available for the element and the cross section of the resistor which can be employed for a given voltage and wattage,'and there is also a definite relation between the cross section ofthe resistor and the durability of the element at a given A further serlous object to sheathed wire is that the single strand resistor is disposed along a line parallel to its support for a distance, such, -that'the ,difl'ei'ences in expansion between the resistor and support sc't up'strains on the resistor which. cause failure. I

-- I am also aware that heating elements,

A .known as tubular elements,

have been formed by introducing a long smral resistor into a metal tube and insulating it from the tube with finely divided refractory material. This type of' heating element is also very difiicult and expensive to manufacture as it is necessary to introduce the spiral r'e sister. and insulating material into, the end of the tube. Due to the fact that the element is in rod form, the ratio of emissivity to .cross section is comparatively low and the heat diffusion is not as good as with thin, flat types of elements. of resistor involves a central core of refractory material ;whi 'ch-requires useful .space and material, and the core absorbs heat from the resistor. Such units necessitate a high resistor temperature for a given rate of energy. input which tends to shorten their life and to limit the possible safe rate of energyinput. While this type of element may be massed into spiral orserpentinc shapes, it is open to the same objection as stated in connection with sheathed wire, namely, a double wall of refractory material and metal casing is interposed betweenadjacent convolutions or lengths of the resistor.

A heating element in the form of a solid cylinder has'also' been made; This type of element is formed by first coiling the resistor on a rigid rod then" inserting the same into a metal tube-and filling the intervening space between the tube and resistor wi'th finely divided refractory material.

This type of element ,cannot be shaped, and it emits heat from the *outer surface only. It will be obvious that many of the disadvantages ,fpreviously set forth also apply to this type of heatingelement.

A fourth-type-of heating element;-'is procore, or other core having an insulating film The spiral form duced by winding the resistor on a mica applied thereto, then applying a.layer of.

mica insulation thereabout, and finally sheathing the element in metal. This type of insulation is not truly refractory and."

hence the element will not stand thermal abuse. The res stor is not in intimate contact wlth a heat receiving'material ;over

its entire surface and is susceptible to, oxi? dation. Inasmuch as such fragile material I asmica is used for insulation, it will at once be apparent that .theseheating elements' cannot be bent or'shaped without great risk of damage tothe insulation which would result'in ultimate break down,

the chief objection to this type of heating unit being the inability of mica or other less refractorv insulation to continuously withstand high temperatures, as well as the lack of density of the element or conductive intimacy between the resistor, insulation and support.

In so far as I am aware, a relatively thin and light weight heating element consisting of a resistor enveloped in a highly compacted mass of refractory material and having a sheet metal casing applied thereto, has never been successfully produced, and it is the general object of the present invention to provide a novelclass of heating elements and a process for making the same wherein the resistor is completely enveloped in a highly compacted mass of refractory material, with the wholecontained in a sheet metal casing, and the elements in each instance having relatively thin walls and large ratio of surface area to mass, so that maximum heat emissivcly is obtainable.

Another object is to provide a novel class of heating elements which by nature of their construction and relatively thin walls and cross section may be easily shaped to lie in intimate contact with the object to be heated and thereby obtain minimum resistance to transfer of heat from the element to the object.

Another object is to provide a class of heating elements of the aforesaid character which may be entirely enclosed in an imperforate sheet metal casing and thus afford ample protection for the resistor against moisture or other foreign matter, or where conditions permit may be enclosed in a partially or wholly perforated metal casing so that the casing and refractory material will form an interlock with each other and add to the. rigidity of the elements to prevent warping and also maintain the integrity of the element and facilitate the displacement of the metal casing during the forming or shaping operation hereinafter referred to.

A still further object is to provide a group of heating elements which may be adapted, by forming or shaping when necessary, to numerous uses, and which sliall be simple in construction, inexpensive to manufacture and which shall be highly etllcient and durable in operation.

\Vith these and other objects inview, the invention consists in the various novel features of construction and arrangement or combination, all of which will be fully described hereinafter and pointed out inthe appended claims.

In the accompanying drawings wherein I.

have shown various illustrative embodiments of my invention but Without intent to limit myself thereto, Fig. 1 is a plan View of a strip from an element with parts broken away to more clearly show-the construction; Fig. 2 is a side elevation thereof with parts broken away; Fig. 3 is an enlarged trans-v verse section of the element shown in Figs. 1 and 2; Fig. 4 is an enlarged fragmentary view of a slightly modified form of element; Fig. 5 is a fragmentary plan view of a perforated cover employed in some instances; Figs. 6 and 7 are side elevations of an element such as shown in Figs. 1 and 2 and showing the same bent into two dilferent forms; Fig. 8 is a plan View of an irregularly shaped plate illustrating another form of my invention; Fi 9 is a sectional view taken on the line 9-9 of Fig. 8; Fig. 10 is a side elevation of the plate showing the same bent into a suitable shape; Fig. 11 is a plan view of a heating element in the form of a disk provided with a perforated casing; Fig. 12 is a sectional view through a dist: which has been cupped; Fig. 13 is a plan view of a disk provided with an imperforate casing; Fig. 14tis a plan view with parts broken away of ring type of element; Fig.

15 is a sectional View taken on the line 1515 of Fig. 14-; Figs. 16, 17 and' l8 are plan views of modified forms of heating elements; Fig. 19 is a perspective view, with parts broken away, of a hollow cylindrical ty e of heating element; Fig. 20 is a longitu' inal view through a cylindrical element; and Figs. 2l25 are sectional views showing the various steps in my process for forming the elements.

Referring particularly to Figs. l7 inclusive, wherein I have shown a strip type of heating element, 1 denotes the resistor wh ch is preferably bent into serpent-inc form froma suitable resistance ribbon. This resistor is molded in and completely enveloped by a hard and compact mass of cement like refractory material 2 which not only supports the ribbon at all points, due to its intimate contact therewith, but also prevents oxidation of the resistor. Each end of the resistor is connected to a terminal 3 which may be of any suitable type but prefcrably similar to that disclosed in my copending application Serial No. 555,870,

filed Apr-i121, \1922. These terminals are each provided with an insulating washer i which prevent contact of the terminals with a sheet metal casing composed of a channel receptacle 5 and a cover. plate 6 which completely surround the refractory material. The side edges 7 ofthc receptacle are deflected over the cover plate as clearly shown in Figs. 1 and 3, and the ends of the casing, beyond the terminals 3 are flattened as indicated at 8 and are provided with apertures 9 so that the element may be conveniently supported on a frame or fastened to an object to be heated. If desired the seam formed by deflecting the side edges 7 over the cover plate may be welded, although for ordinary conditions, folding over the edges under high pressure will prove sufficient.

fractor'y material and easing together.

- evenly distributed during the bending and A strip heating element of this general character is very thin, light in weight, and permits maximum transfer of heat from the resistor to the object to be heated. The resistor is completely enveloped in a compact mass of refractory material and hence is supported at all points and is completelyprotected against oxidation. These strips may be readily bent to various shapes to meet the particular requirements. In Fig. 4: I have shown the element bent to assume an arcuate cross section while in Figs 6 and 7 I have shown the element bent into U- shaped form and circular form respectively. The U-shaped form is suitable for application to molds and similar uses, while the circular form mayv be conveniently applied to any circular object, as for example, a pipe or water heater. A bolt 12 engaged. through apertures 9 serves to retain the element in position on the object.

In Figs. 813 inclusive, I, have shown a second group of heating elements which are characterized by "having relatively large areas and very. thin cross sections. These elements are intended to replace the spiral and serpentine t pes of heatingelements' which are forme by bending and massing sheathed wire or similar straight elements. Figs. 8 and 9 show an example of a polygonal type of heating elementmonsistlng of a sheet metal receptacle 13 which is provided with a perforated cover 14 so that the refractory material 15 will interlock therewith..

This type of element as well as those previously described may be bent into various shapes, without damage to the element or any parts thereof, and as an example, I have shown one side thereof bent over at right angles in Fig. 10. If desired the other side may also be bent as indicated in dot ted lines in this figure.

In Fi s. 11 and 12 I have shown a circular type of heatin element which has the entire casing 16 perfbrated so that the refractory material and casing are bonded on all surfaces. This type of element may be cupped as shown in Fig. 12 so that the element will contact at all points with a vessel or other object having a semi-spherical surface. The perforated casing permits the metal to be hence prevents buckling;

In Fig. 13 I have shown a circular type of heating element having an imperforate. casing 17 and which is adapted for use on a casing walls from buckling.

flat surface, or as an insert. Because of refractory material and casing, I preferably. insert therethrough a plurality of eyelets 1.8 which effectively tiethe casing and refractory material together and prevent the In Fig. 14' I have shown a ring type of heating element in which the receptacle 20 of the cas'ng is in the form of a circularchannel. The resistor-21 is completely enveloped in a compact mass of refractory material as in the types previously described. A circular metal cover 22 is laid on top of the refractory material and the inner and outer peripheral edges of the receptacle 20 are deflected over the washer as shown 'in Fig. 15. This type of heating element is somewhat similar to that. shown in;Fig. 7 exceptthat the casing is previously -.-formed into a circle about, its edge; an element.

such as. shown in Fig. 14 is .capaliIe,-of assuming various shapes'as for example the triangular form 25 shown in 16, or the an ular or V-shaped form 26ishown in Fig. 1 or a modified triangular form 27 such as shown in Fig. 18. These forms adapt themselves to various requirements. The form shown in Fig. 18 for example being suited particularly for electric irons. In Figs. 19. and 20 I have shown a hollow cylindrical type of heating elementwhich is particularly useful for application to pipes or cylinderswhich are to be heated. This element maybe conveniently formed by providin a circiimferentially wound resistor comp etely enveloped in a compact mass of refractory material and then enclosing the same in a sheet metal casing comprising an outer metal tube 29 having inturned peripheral edges 30 and an inner metal tube 31 having out-turned peripheral edges 32. This type of element emits heat from its inner and outer cylindrical surfaces and also from the ends and hence is very efficient.

In Figs. 21-25 inclusive, I have illustrated the various steps employed in my process for forming the heating elements herein'disclosed. In carrying out this process I first provide a sheet metal receptacle and fill the same with a mass of receptive refractory material 36. I nextinsert into this refractory material, a previousl formed resistor "refractory material with the resistor and the receptacle. In the case of heating elements which are to be provided with an imprforate casing I next dry the partially formed element and then apply a cover plate and either simultaneously or in separate opera.

' formed with a a perforated cover 38 before or after the preliminary compacting operation tions deflect the edges of the receptacle over the cover plate and heavily compress the element. 7

In the case of elements which are to be perforated casing, I apply dried and baked either by an external source of heat or by energizing the resistor.

While so far as the present invention is concerned, I do not limit myself to any particular kind or refractory insulating matcfacilitates bedded, electrical heating elements by prorial, one class found especially suitable for the purpose is composed of magnesiumor aluminum oxide or zirconium silicate, either individually where possible or a compound of them, together when desirable with a binding material such as clay, to give the ncessary plasticity during fabrication and to effect homogeneity in the final product.

The resistor element may be enveloped in the refractory insulating material in accordance with my Patent Number 1,136,076, issued April 20, 1915 entitled Process of producing electrical heating devices or in accordance with my Patent Number. 1.398,-'

410, issued November 29, 1921 entitled Embedding process.

Manifestly the present invention greatly the production of sheated, em-

viding a compartively shallow open sided receptacle into which the granular refractory insulating material and the resistor may be properly placed before the receptacle is closed, thus distinguishing from, and affording marked advantages over, the tubular type of element hereinbefore referred to. Having thus described my invention, what I claim is 1. As a new article of manufacture, an electrical heating element consisting of a resistor, a formed sheet metal sheath enveloping said resistor and spaced therefrom, and a mass of grandular refractory electrical insulating material of high heat conducting quality filling the space between the resistor and the sheath, the resistor being provided with terminals each accessible through an opening in the sheath.

As a new article of manufacture, an electrical heating element comprising a resistor. a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and a mass of granular refractory electrical insulating material resistor being provided each accessible through an opening in the 'a mass of grandular refractory electrical 7 of high heat conducting quality filling the space between the resistor and sheath, the with terminals sheath.

3. Asa new article of manufacture, an electrical heating element consisting of a resistor, a formed sheet metal sheath enveloplng said resistor and spaced therefrom, andinsulating material filling the space between the resistor and the sheath, the entire assembly being in a highly compacted state, the resistor being provided with terminals each accessible througlran opening in the sheath.

4. As a new article of manufacture, an electrical heating element comprising a resistor arranged in flat formation, a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and an artificially compacted mass of .granular refractory electrical insulating material filling the space between the resistor and sheath, the resistor being provided with terminals each accessible through i an opening in the sheath.

5. As a new article of manufacture, an electrical heating element comprising a resistor arranged in fiat formation, a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and an artificially compacted mass of granular refractory electrical insulating material filling the space between the resistor and sheath, said element having a relatively large area and a relatively thin cross section, the resistor being provided with terminals each accessible through an opening in the sheath.

6. As a new article of electrical heating element manufacture, an comprising a resistor, a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and an artificially compacted mass of granular refractory electrical insulating material filling the space between the resistor and sheath, the resistor being provided with terminals each accessible through'an opening in the sheath, said element having a relatively large area and a relatively thin cross section, the element being .capable of being formed to a shape other than fiat.

s a new article of manufacture, an electrical heating element comprising a resistor, a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and an artificially compacted mass of granularre fractory electrical insulating material filling the space between 135 the resistor and sheath, said element having a relatively large area and a relatively thin cross'section. the element being capableof being formed to a shape other than flat and the resistor being of sinuous formation and arranged with its sinus in a plane substantially parallel to that of the relatively large area of the element and being provided with terminals each accessible through an opening in the sheath.

, 8. As a new article of manufacture, an electrical heating element comprising a resistor, a sheet metal sheath enveloping said resistor and spaced. therefrom, the sheath comprised of parts that are held together;

by the marginal portion of one of said parts being turned over' the margin of the other, andan artificially compacted mass of granular refractory electrical insulating material filling the space between the resistor and the sheath, the resistor being provided with terminals each accessible through an opening in the sheath.

9. As a new article of" manufacture, .an

electrical heating element comprising a resistor, a sheet metal sheath enveloping said' resistor and. spaced therefrom, the sheath being comprise of an open sided sheet metal receptacle and a cover applied thereto and held to the rece tacle by the edge portion of the receptacle being turned over the edge of the cover throughout the periphery thereof, and an artificially compacted mass of granular-refractory electrical insulating material filling the space between the resistor and sheath, the resistor beingprovided with terminalseach accessible through an opening in the sheath. u 4

11. As a new article of-'inanufact-ure,-an

electrical heating element comprising a sin y sheath.

uous resistor arranged in flat formation, a sheet metalfsheath made up .of a plurality of parts enveloping said resistor and spaced therefrom, and a mass of granular refractory electrical insulatingmaterial of high heat conducting quality filling the space between the resistor and the sheath, the sheath having a flat working face from which the resistor is uniformly spaced throughout its length, and the resistor being provided with terminals each accessible through an opening in the sheath. 12. An electrical heating element comprising a sheath of sheet metal having a pair of op osed superficial faces of comparatively arge area and a pair of faces connecting the former faces that are of comparatively narrow width, thesheath enclosing a shallow cavity, granular refractory electrical insulating material artificially compacted in said cavity, and a sinuous resistor enveloped in the insulating material and the sinus whereof lie in a surface which is parallel to the aforesaid faces of larger area, the resistor bein provided with terminals each accessible t irough an opening in the sheath.

13. As. a new article of manufacture, an electrical heating element comprising a resistor 'a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, a mass of granular refractory electrical insulating material filling the space between the resistor and sheath, the resistor bein provided with terminals each accessible tirough an opening in the sheath, and means for tyin the opposit-e walls of said sheath toget er to prevent warping thereof, said means being locatedwithin the area of the active surface of the element. v

-14.As a new article of manufacture, an electrical heating element comprising a-re-c sistor a sheet metal sheath made up of a plurality of parts enveloping said resistor and spaced therefrom, and a mass of gran-- ular refractory electrical insulating material filling the space between the resistor .of the active surface of the element, and

the resistor ,beipg provided with terminals each'access'ible through an opening in the In testimony whereof, hereunto aflix mysignature. k

EDWI L, WIEGAND.

and the sheath, theopposite walls of said DBSOLAIMER l,614,330.1'5dwia L. l Viegand, Dormont Borough, Pa. ELECTRICAL HEATING ELEMENT. Patent dated January 11, 1927. Disclaimer filed November 2, 1938, by the patentee; and the licensee, Edwin L. Wiega'ad Company.

Herebyenter this disclaimer:

A.- To so much of claim 1 of said Letters Patent as may cover any electrical heating element in which the sheath surrounding the resistor is not relatively thin and wide in cross section, or does not constitute a surface of relatively large area for the transfer of the heat from the element, or does not define a relatively shallow cavity of relatively small capacity, or in which the resistor is not arranged in a formation correspondingly relatively thin and wide in cross section, or in which the electrical insulating material is not compacted, or in which no part of the electrical insulating material is integrated into formation positively spacing the resistor from the sheath.

B. To so much of claim 3 of said Letters Patent as may cover any electrical heating element in which the sheath surrounding the resistor is not relatively thin and wide in cross section, or does not constitute a surface of relatively large area for the transfer of the heat from the element, or does not define a relatively shallow cavity of relatively small capacity, or in which the resistor is not a resistance conductor arranged in a formation correspondingly relatively thin and wide in cross section, or in which the electrical insulating material is not of high heat conducting quality, or in which the electrical insulating material is not in heat-conduction contact both with all parts of the surface of said conductor over substantially the entire length of said conductor and with all parts of the interior of the sheath surrounding the resistor and adapted to conduct the heat generated in the resistor arranged in said relatively thin and wide formation substantially from all parts of the surfa e thereof readily and directly to all parts of said relatively large area heat-transfer surface, or in which no part of the electrical insulating material is in integrated condition and disposed in position positively spacing the resistor from the sheath. Cl To so much of claim 5 of said Letters Patent as may cover any electrical heating element in which the electrical insulating material is not of high heat conducting quality, or in which the sheath surrounding the resistor is not relatively thin and wide in cross section, or does not constitute a surface of relatively large area for the transfer of the heat from the element, or does not define a relatively shallow cavity of relatively small capacity, or in which the resistor is not a resistance conductor arranged in a formation correspondingly relatively thin and wide in cross section, or in which the electrical insulating material is not in heat-conduction contact both with all parts of the surface of said conductor over substantially the entire length of said conductor and with all parts of the interior of the sheath surrounding the resistor and adapted to conduct the heat generated in the resistor arranged in said relatively thin and wide formation substantially from all parts of the surface thereof readily and directly to all parts of said relatively large area heat-transfer surface.

D. To so much of claim 12 of said Letters Patent as may cover any electrical heating element in which the electrical insulating material is not of high heat conducting quality, or in which the sheath surrounding the resistor is not relatively thin and wide in cross section, or does not constitute a surface of relatively large area for the transfer of the heat from the element, or does not define a relatively shallow cavity of relatively small capacity, or in which the resistor is not a resistance conductor arranged in a formation correspondingly relatively thin and wide in cross section, or in which the electrical insulating material is not in heat-conduction contact both with all parts of the surface of said conductor over substantially the entire length of said conductor and with all parts of the interior of the sheath surrounding the resistor and adapted to conduct the heat generated in the resistor arranged in said relatively thin and wide formation substantially from all parts of the surface thereof readily and directly to all parts of said relatively large area heat-transfer surface.

[Ofiicial Gazette December 6', 1.938.]

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