US2553875A - Electric heating element - Google Patents

Description

May 22, 1951 H. N. sHAw 2,553,875

j ELECTRIC HEATING ELEMENT Filed June 50, 1948 2 Sheets-Sheet 1 IN VEN TOR.

May 22, 1951 H. N. SHAW ELECTRIC HEATING ELEMENT Filed June 30, 1948 2 Sheecs-Shee'fI 2 IN VEN TOR.

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Patented May 22, 1951 UNITED STATES PATENT OFFICE ELECTRIC HEATING ELEMENT Harold N. Shaw, Erie, Pa.

Application June 30, 1948, Serial No. 36,122

9 Claims. 1

This invention relates to improvements in electric heating elements and more particularly to heating elements of the type wherein the major portion of the heat is emitted by radiation. In my prior Patents Nos. 2,217,296, issued October 8, 1940, and 2,265,549, issued December 9, 1941, is disclosed the use of heating elements formed of thin, light weight metal which is substantially U-shaped in cross-section. One of the problems in connection with such an element is to provide satisfactory support against sagging or lateral displacement. In Patent No. 2,217,296, the element is arranged in helical form and there are helical supports of insulating material cooperable between the edge iianges of the element to support the turns from one another, and to provide for support of the element in spaced relationship with respect to an inclosing housing. In Patent No. 2 265,549, another` form of helical insulating support is disclosed and there is also disclosed means for supporting elongated parallel elements by means of a relatively complicated arrangement of porcelain insulator segments. While these constructions are entirely satisfactory for the purpose, nevertheless, because of the expense of the constructions, they are suitable mainly for commercial purposes and are not entirely practical for use in household heaters because they are relatively unattractive and cannot be produced at a sumciently low cost to iorm a part of a highly competitive item.

It is a general object of the present invention to provide an improved electric heating element for use more particularly in household radiant heaters, in paint drying heaters, and in infrared heaters, the said element being so constructed that it can be produced inexpensively and having advantages over other heating elements now available for similar purposes.

Such heating elements as are now available are usually exposed to allow for free radiation. Thus, they cannot be protected from accidental contact by the hand or by metal, or by splashing water, such as might result in an electric shock, There are, of course, heaters such as those used for infra-red heating purposes which are in the form of an enclosed lamp utilizing a lament type of heating element having a relatively small area and carrying a high temperature. rihe heating capacity of this type of lamp is, however, limited as is the life of the filament.

It is therefore one of the principal objects of the present invention to provide a radiant heating element wherein the electric conductor or element proper is enclosed in glass or other transparent material, the element having high capacityr large radiating area, and long life, and being capable of providing a penetrating heat while the A element proper is fully shielded from direct contact so as to be safe in the presence of children.

A further object of the invention is to provide an electric heating element as above described, wherein the element is formed of thin, lightweight i, metal and is provided with at least one edge flange, the element being so arranged in a transparent heat resisting tube as to provide an attractive, visible unit, the element being so constructed and arranged that the amount of contact with the glass which is necessary to provide for proper support is kept to a minimum whereby major surface portions of the element are maintained in spaced position from the glass to prevent local overheating of the latter and to provide for quick A heating of the element.

wire-heating element, and because there is no continuous porcelain core.

A further object of the invention is to provide a heating element, including a casing in the form of heat resistant glass, wherein the latter is part of the source of radiant heat.

A. further object of the invention is to provide a heating element comprising a tube of glass or the like having novel means in the form of caps cooperable with the ends of the'tube for supporting the heating element proper therein.

A, ing at least one edge ange and being supported in a novel manner to extend longitudinally within a heat resistant glass tube and provide an arrangement which is particularly suitable when the element is to be disposed vertically. This type of construction eliminates difiiculties which might be encountered as a result of the sagging of the turns of a helical element when the latter is enclosed in a vertical tube.

A more speciiic object of the invention is to provide an electric heating element of the class described including a tube of heat resistant transparent material, there being a conductor within the tube in the form of a ribbon of thin metal having a ilange on at least one edge, at

least part of said flange projecting toward the 3 impr-oved means for furnishing an insulating support for the helical type of element disclosed in my prior Patent No. 2,217,296.

With the above and other objects in view, the invention consists of the improved electric heating element, and all its parts and combinations, as set forth in the claims, and all equivalents thereof.

In the accompanying drawings, illustrating several embodiments of the invention, in which the same reference numerals designate the same parts in all of the views:

Fig. l is a front elevational view of a vertical type of heating element embodying the invention, parts of the element being broken away and shown in section and fragments of end supporting structures being illustrated in section;

Fig. 2 is an enlarged fragmentary, vertical sectional view showing one end of the element of Fig. 1 and taken approximately on the line 2-2 of Fig. `1,'

Fig. 3 is a cross-sectional view taken on the line 3-3 of Fig. 1; v

Fig. 4 is a view similar to Fig. 3 showing a fragment on an enlarged scale;

Fig. 5 is an elevational view showing a fragment of the central supporting rod with one of the insulating supporting discs thereon;

Fig. 6 is a plan view of one of the insulating supporting discs alone;

Fig. 7 is a fragmentary vertical sectional view showing one of the ends of a vertical element of the type of Fig. 1, with a modified terminal arrangement;

Fig. 8 is a view principally in front elevation, showing an alternative form of heating element adapted for horizontal use wherein the electrical conductor is arranged in helical form;

Fig. 9 is a fragmentary sectional view taken on the line 9 9 of Fig. 8;

Fig. 10 is a View similar to Fig. 9, showing a fragment on an enlarged scale;

Fig. 11 is a perspective view of one of the end caps alone; and

Fig. 12 is a view similar to Fig. 4 illustrating a modification.

Referring more particularly to the form of the invention illustrated in Figs. l to 'l' inclusive of the drawing, the invention includes an elongated tube I 5 having open ends. The tube is preferably formed of a heat resistant transparent material such as Pyrex glass, but may be formed of other transparent or transluscent materials having the required low-expansion, heat-resistant, heat-transmitting and heat-radiating properties. While it is preferred to use a heat resistant glass which is transparent or translucent, nevertheless, certain transparent or translucent plastic materials are suitable. In the claims where transparent material is utilized it is contemplated that this include translucent material as well.

It is the principal concept of the p-resent invention to arrange an electric conductor in the form of a ribbon oi thin metal having a flange on at least one edge in such a manner within a tube as above described, that the flange projects toward the inner surface of the tube whereby major surface portions of the ribbon are spaced a substantial distance from the tube wall. To best accomplish this purpose, conductors IE which are U-shaped in cross-section, are employed. They may be of either the rounded crosssection illustrated in Fig. 4, or of the flat sided U-shaped formation shown in my prior Patent No. 2,265,549, and in Fig. 12. The metal is preierably very thin and light weight and capable oi having electricity pass therethrough to create heat. By the use of light weight metal quick heating and cooling is possible and the use of the U-shaped or flanged construction provides necessary increased strength to make the use of light weight metal practical. Nickel-chrome a few thousandths of an inch thiol; is very suitable.

In the form of the invention illustrated in Fig. l, a plurality of slightly inwardly bowed lengths of the conductor I6 are arranged in peripherally spaced relationship around a center axis within the tube I5 with the flanges I1 projecting outwardly. The lengths may extend approximately straight and parallel as illustrated or in any other desired manner. It is preferred to connect the various lengths in series by means of top and bottom connector pieces I8 and there may be a terminal strip I 9 at one end with the other terminal strip 20 at the opposite end. In the form of the invention shown in Fig. '7, the terminals may both be at the lower end as at 2| and 22 and connected to prongs 23 which extend through insulated openings in an end cap 24. Thus, the external portions of the prongs of the form of Fig. 7 may be inserted in spaced socket openings in the same manner that a vacuum tube is installed on a radio set.

In order to suitably hold the conductor members I6 forming the heating element proper in position, it is preferred to employ a central frame. This frame includes a centrally disposed rod 25, together with insulator discs 26 at vertically spaced intervals on the rod. The discs are formed o1 suitable insulating material such as porcelain having spaced peripheral notches 21 through which the conductor members extend in the manner shown in Figs. 3 and 4. The insulator discs 2S may be supported on the rod 25 in any suitable manner. It is preferred, however, to employ metal friction clips 28 above and below each insulator disc 26. Each clip has a central opening through which the rod 25 extends and has yielding lingers 29 on each side of the opening which yieldingly engage the rod to frictionally maintain the clips and disc therebetween in a predetermined position of vertical adjustment.

In the form oi the invention of Figs. 1 and 2 the terminal strips I9 and 20 have their outer ends welded or otherwise electrically connected to metal end caps 3D. Each end cap has inwardly projecting yielding fingers SI which extend lengthwise into and yieldingly engage the inner surface of the wall of the tube I5 in the manner shown in Fig. 2 to releasably hold the cap in position. In the type of cap shown in FigsA l and 2, the caps are formed with central sockets 32 which are engaged by buttons 32 mounted on the ends of spring mounting fingers 33. The mounting lingers 33 may have their inner ends electrically connected to a source of current so as to transmit electricity through the buttons 32', end caps 30, and conductor strips I9 to the heating element I6 proper. The mounting ngers 33 are suitably supported on insulating blocks 34, and the latter may be attached on the inner non-exposed surfaces of inner walls 35. The latter may be positioned in spaced relationship from outer walls 36 of a suitable housing. With this arrangement the heating element may be so supported that no electrical conducting parts are exposed for contact. Thus, a child may insert a metal instrument through a heater grill without danger of shock.

In order to reduce the tendency to. form a chrome oxide, the end caps 39 are preferably made of such size as to completely close the ends of the tube l5. While a hermetic seal is not desirable, it is desirable to have a close enough nt to prevent the free circulation of air. On the other hand, there must be suii'icient room for escape of air so that when the air within the tube heats up, there is no danger of explosion. v

The insulating discs 26 are of such size and the notches 21 are of such depth that the conductors I6 are supported relatively loosely with only the ends of each bowed length touching the inner surface of the glass tube it as at 42. As these ends carry no current they operate at low temperatures and therefore have little heating effect on the glass. In the drawing the space between the glass and the bowed portion of each length is indicated at It is important that there be a minimum of contact, consistent with proper support, between the conductors it and the glass. With this arrangement, the members I6 are suitably supported without having any substantial portion of their surface in contact with the glass to cause local overheating or to slow up the capacity of the element to heat up quickly.

In the form of the invention of Fig. 12, the conductors It are shown as rectangular in crosse section rather than arcuate as in Fig. 4. In addition, there is welded or otherwise secured to each length of the conductors l5', at suitably spaced intervals, radial metal fingers 513 'which project or contact the inner surface of *he wall I5 of the glass tube. Thus, the conductor is supported by means of the contact of the fingers with the tube. These lingers keep current carrying parts of the element out of contact with the glass and are important when high element'temperatures and relatively low glass temperatures are desired.

With the form of the invention disclosed in Figs. 8 to 11 inclusive, the elongated conductor 31, forming the heating element proper, is arranged helically within the tube. The conductor 31 is formed of the same material heretofore described in connection with Figs. 1 to 7 and must include'at least one edge flange. In the arrangement illustrated, the element is U-shaped in cross-section to provide flanges S3. The element is positioned within one of the tubes l5 in the manner illustrated in Figs. 3 and 9 with the flanges 33 projecting outwardly. rlfhis form of the invention is particularly suited for use in horizontally disposed tubes, and by refer'- ring to Fig. 9 it is apparent that the conductor 31 sags into contact with the inner surface of the lower wall portion of the tube i5. The diameter of the helical coil is less than the internal diameter of the tube l5 so that there is contact with the flanges 38 only on the lower side of the helix. One end of the helix is connected by a conductor strip 39 with one of the end caps 30 and the other'end is connected by a similar conductor strip with the end cap 3S at the oppo site end. The method of support for the ends of the element may be the same as heretofore described in connection with Figs. 1 and 2, and the same reference numerals are utilized. The end caps Sil may be identical to the end caps of the form of the invention of Figs. 1 and 2, and a perspective view of one of said caps alone is illustrated in Fig. 11.

While the construction of Fig. 1 is preferred for vertical installations, it may also be used horizontally. It is also possible to utilize a helical construction, such as is shown in Fig. 8,'

but with a greater number of turns, in a vertically. disposed tube. While the turnsof the helix Vwill contact one another when the element is positioned vertically, nevertheless, the natural oxide of the metal will provide effective insulation between turns. With this design, a ribbon which is U-shaped in cross-section is particularly desirable as `the width of the ribbon can be varied to contain the desired number of turns for a required rating while still employing a ribbon which is thin enough to provide for quick heatingand cooling.

With the form of invention of Fig. 8, it is obvious that the anges 38 make the heating element proper substantially self-supporting and present only edge contact against the glass tube. Il a flat ribbon were employed it would not have sufcient strength to be self-support-V .ing and would heat Very slowly because a flat surface thereof would be in contact with the glass tube. With the present invention, a .very thin ribbon, only a few thousandths of an inch thick, is entirely practical and heating and cooling in a few seconds time is readily achieved because the ribbon has a small cross-section in relation to its surface area.

The radiant energy fromA any heating element operating at a moderate temperature, for example, around 1500 F., is largely in the long wave length infra-redv range. Glass is not entirely transparent to this energy so the light and only part of the heat is transmitted through the glass tube l5. The heat which is absorbed, however, causes the glass to heat rapidly and the glass itself then becomes a source of radiant heat. Glass is one of the best materials for radiant heat emission and, due to its low density, it heats up and cools oli rapidly. In conventional heat lamps the energy from the high temperature filament is mostly in the short wave length range and the latter is effectively transmitted by the relativelythin glass bulb usually employed.

When the present element is installed, as shown in Figs'. `1 and 8, all metal conducting parts for electricity are inaccessible from accidental con tac't. Therefore, the danger of shock, which is present with open-coil heating elements, lis practically eliminated.

Various changes and modifications may be made without departing from the spirit of the invention, and all of such changes are contemplated, as may come within the scope ofthe claims.

What I claim is:

1. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor within said tube in the form of thin metal ribbon having an edge flange, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis within the tube, leach of said lengths being inwardly bowed, in-

r sulator means arranged within said peripherally jecting toward the inner surface ofthe tube, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis within the tube, means providing for the connection of the ends of said ribbon with an external source of electricity, said ribbon having spaced portions located out of the main path of flow of electricity and projecting toward and contacting the inner surface of the tube to maintain major portions of the ribbon out of contact with said inner surface, and insulator means arranged within said peripherally spaced lengths of ribbon.

3. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor Within said tube in the form of a thin metal ribbon having an edge flange and having spaced portions which are out of the main path of flow of electricity projecting toward the inner surface of the tube, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center `axis Within the tube, means providing for the connection of the ends of said ribbon with an external source of electricity, and means having longitudinally spaced insulating members thereon maintaining said spaced projecting portions of the ribbon adjacent the inner surface of the tube, the lengths of the conductor being positioned between the edges of the spaced insulating members and the inner surface of the tube with major portions of the ribbon out of contact with said tube surface.

4. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor within said tube in the iorm of a thin metal ribbon having an edge flange and having spaced portions which are out of the main path of flow of electricity projecting toward the inner surface of the tube, said ribbon comprising a plurality of connected lengths arranged in pee ripherally spaced relationship around a center axis within the tube, insulating means having longitudinally spaced insulating discs thereon provided with peripheral notches, the lengths of the conductor ribbon extending through said notches and adjacent the Wall of the tube with major portions of said lengths out of contact with said tube surface, and means providing for the connection of the ends of said ribbon with an external source of electricity.

5. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor rwithin said tube in the form of a thin metal ribbon having an edge ange and having spaced portions which are out of the main path of flow of electricity projecting toward the inner surface of the tube, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis within the tube, a rod extending axially of the tube, insulating discs at longitudinally spaced intervals around said rod, the lengths of the conductor ribbon being positioned between the peripheries of said discs and the inner surface of the tube with major portions of the length of said ribbon out of contact with said tube surface, and means providing for the connection of the ends of said ribbon with an external source of electricity.

6. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor within said tube in the form of a thin metal ribbon, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis Within the tube, means providing for the connection of the ends of said ribbon with an external source of electricity, said ribbon having spaced portions located out of the main path of flow of electricity and projecting toward and contacting the inner surface of the tube to maintain major portions of the ribbon out of contact with said inner surface.

l`7. An electric heating element comprising a tube of heat resistant transparent material, an electric conductor within said tube in the form of a thin metal ribbon, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis within the tube, means providing for the connection of the ends of said ribbon with an external source of electricity, metal fingers projecting from said ribbon toward the inner surface of the tube, and insulator means maintainingl said ribbon lengths in peripherally spaced relationship.

8. An electric heating element'comprising a tube of heat resistant transparent material, an electric conductor within said tube in the form of thin metal ribbon, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis Within the tube, means providing for the connection of the ends of said ribbon with an external source of electricity, metal ngers projecting from said ribbon toward the inner sur face of the tube at spaced intervals, and means having longitudinally spaced insulating members thereon maintaining said connected lengths oi the ribbon in peripherally spaced relationship, the lengths of the conductor being positioned between the edges of said spaced insulating inembers and the inner surface of the tube with major portions of the ribbon out of contact with said tube inner surface.

9. An electric heating element comprising a tube, of heat resistant transparent material, an electric conductor Within the tube in the form of a thin metal ribbon, said ribbon comprising a plurality of connected lengths arranged in peripherally spaced relationship around a center axis within the tube, metal fingers projecting at spaced intervals from said lengths toward the inner surface of the tube, means having longitudinally spaced insulating discs thereon provided with peripheral notches for receiving the lengths of said ribbon, and means providing for the connection of the ends of said ribbon with an external source of electricity.

HAROLD N. SHAW.

REFERENCES CITED Themfollowing references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 791,998 Ball June 13, 1905 1,032,267 Bastian July 9, 1912 1,255,326 Macnicol Feb. 5, 1918 1,533,292 Woodson Apr. 14, 1925 1,608,005 Schoeppler Nov. 23, 1925 2,217,296 Shaw Oct. 8, 1940 2,265,549 Shaw Dec. 9, 1941 FOREIGN PATENTS Number Country Date 3,191 Great Britain Feb. 9, 1909

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