US1721099A - Electric strip heater - Google Patents

Description

Patented July 16, 1929.

UNITED STAT-Es EDWIIN L. `'W'IEG'ANIL 0F DORMON T, PENNSYLVANIA.

ELECTRIC STRIP HEATER.

'Application med July a1, 1925. serial No. 47,224.l

This invention relates generally to the class of electrical heating units known as strip or space heaters, and more especlally to one that is peculiarly suited for use in broilers of the kind employed in hotels and restaurants where electrical appliances of this character are recuired to operate at very high tempera` tures or many hours running. The invention has to do also with a combination of my improved strip heater with a heat returning element or reiiector of suitable design. In the more complete embodiment of this combination, the heat returning element has a novel contour or shape that is related ina very definite way to the arrangement of the heating units. i

While I have stressed the importance of the invention with respect tofbrollers, it will be understood that it is of general application, another instance of its use being in connection with a ref iector type electric room heater.

Where I use the term reflector in connection with broiler equipment, it is used in its broadest sense, and in some instances may be a heat returning element or baffle constructed of lire clay or other suitable refractory material, minus the usual brilliant surface suggested by the ordinary use of the word rei fiector.

More generally the invention may be defined as consisting of the combination and arrangement of parts set out in the claims an-v nexed hereto, and the principal objects sought to be attained may be enumerated astfollows:

The provision cfa heavy duty electric heater of the strip type that is so designed as to facilitate manufacture andimpart rigidity to the strips, no intermediate or central support being required in the installation of the device;

A To provide a strip heater of the foregoing nature in which radiation is effected at the most advantageous angles;

To provide a strip heater of very high efficiency, the nature of its construction and its shape being, in part, responsible for this, and, in part, the use of such material as nickel chromium alloy or other high temperature metal for the sheath that surrounds the embedded resistor; and

To combine with a strip heater of the character above set forth, a heat returning element which coacts with the heater in a unique way to conserve and reflect that portion of the heat radiated from the strip which would otherwise be wasted thereby greatly enhancing the eficiency of the device.

The foregoing, objects, with others hereinafter appearing, are attained in the embodiments of the invention illustrated in the accompanylng drawing wherein Fig. 1 is a perspectwe View of my improved strip heater; F1g. 2 1s a fragmentary plan view showing lone end .of the strip applied to a support;

Fig. 3 is a fragmentary longitudinal section on the line 3 3 of Fig. 2; Fig. 4 isa transverse section through the strip on the line 4-4 of Fig. 3; Fig. 5 is `a sectional view through a broiler assembly incorporating, with my improved strips, a reflector or bae; and Fig. 6 is a diagrammatic representation of an electric heater of the reflector type embodying the invention.

The strip heater, which is designated generally by the reference character l, comprises an elongated sheath of suitable light sheet metal, preferably nickel chromium alloy because of` its being a high tem erature metal, and the same encloses a hig ly compacted mass of refractory, electrical insulating, heat conducting material, such as magnesium or aluminum oxid or zirconium silicate, referably magnesium oxid, in which is em edded a suitable resistor. Excepting adjacent its ends, thestrip has th'e cross-sectional shape shown in Fig. 4, the underneath or active face -1B of the heater preferabl defining a parabolic curve, while the bac lb is only slightly convex.

In building the device, the edge portions of atrough-shaped casing 2, which constitutes the major part of the sheath, areleft stand-L ing more or less upright until the mass of refractory, electrical insulating, heat conducting material 3 is placed therein. A resistor .5 is embedded within the mass or body of material 3, and the same is desirably, but not necessarily, composed of a suitable metallic ribbon o-r flat wire that is given a sinuous formation so as to distribute the resistor effectively throughout the strip.

After the body or mass ofrefractory insulating material 3, with the resistor 5 embedded therein, has been highly compressed within the casing 2, a cover 6, in the form of la metal strip, is placed on top of the material and the edges of the casing are turned over it to secure itin place. Before the edges of the casing are'turned over, however, plates sov ' commodation of binding posts 9 that are applied to 'the ends of the resistor 5. The openings8 are ampletoprovide liberal spaces about the binding posts 9 and washers 11 of insulating material surround the binding posts and serve to insulate the terminals from the sheath. The 'eXtreme ends cf the structure are flattened to provide 'attaching ears 12 having enlarged openings 13 through which screws 15 pass for binding the strip to a suitable support. ln the present instance, a support 16 is shown as constituted of an angle bar, and the screw 15 passes through a lole in one Harige of the bar and'has a nut 17 applied. to it beneath said flange, washers 18 being applied to the screw above and below the ear 12. The size of the opening 13 with respect to the screw 15 is such as will afford movement of the ends of the strip with respect to the screws to allow for expansion and contraction of the strip.

The arrangement of 'the strip heaters in broiling apparatus is shown in Fig.. 5, the active faces 1a being presented to a suitable grid 20 on which food to be broiled or toasted may be supported, and a suitable heat obstructing element or reflector 22 is situated above theheaters in spaced relation to their backs 1b. The light line arrows appearing in said view indicate the radiation of heat from the strip heaters, while the heavyline arrows represent the heat that is radiated by the heat obstructing elementor reflector 22, which, in the present instance, is preferably composed of suitable refractory material, such as fire brick, and its surface adjacent the strip heaters is corrugated to provide ribs 23 that are disposed directly above the backs of the-strips Heat is pocketedwithin the grooves between the lribs 23 and this heat, with that absorbed ,by the reflector, serves'as a secondary radiator to intensify the primary radiation in the vertical zones between the strips. It will be seen from this that the design of the strip heaters 1 and the relation thereto ofthe heat obstruct- -,a very even distribution of the heat delivered to an object sustained by the grid 20. -For instance, immediately below the heaters 1, the heat is thrown directly downwardly from the active faces of the heaters, while that which is thrown generally laterally therefrom has a greater distance to travel and accordingly is relatively less effective. However, throughout this area of less 4effective direct radiation, the heat that is radiated' upwardly by the .backs of the strips is reflected .downwardly by the heat obstructing element 22 to augment the direct radiation thereby to equalize, so to spek, the heat throughout the area of the By the use of well known circuit arrangements, at the option of the operator all of the strip heaters, or groups thereof less in number than that constituting the entire series, may be energized.

The embodiment of my improved strip in a room heater of the reflector type is illustrated in Fig. 6the strip heaters 1 being disposed transversely of the structure immediately in front of a reflector 25, the active faces of the strips radiating heat directly into the room while the heat radiated from the backs of the strips is returned to the room by the reflec- -tor 25.

The construction 'and cross-sectional shape of my improved strip heater make it very still and rigid and not liable to becoming warped or distorted by the intense heat under which it is required to operate for many hours at a time. rlhis obviates the use of undesirable central or intermediate supports which so frequently have to be resorted to in the use of tubular or strip heaters of prevailing kinds.

Having thus described my invention, what I elaimis:

1. As a new article of manufacture, an electric strip heater comprising a resistor, a

Ahighly compacted mass of refractory, elecportion intermediate said ends .is slightly convexed along one side while along the other side it has a pronounced transverse parabolic curvature so as to increase the radiating surface of said side and more widely dilfuse the heat therefrom.

2. An electric strip heater comprising a resistor, a compacted mass of refractory, electrical insulating, heat conducting material enveloping said resistor, a thin metal sheath completely'enclosing said material and consisting of atrough-shaped casing member that extends about the active facel of the heater, and a cover which extends along the back of the heater in contact with the refractory material, the edges ofthe casing member beingl turned over said cover and meeting each other along the medial line thereof, the active face of the element having a pronounced transverse parabolic curvature so as to increase the radiating surface of said face and more widely diffuse the heat therefrom.

3. An electric strip heater comprising a resistor that extends substantially from one end'of the heater to the other, a terminal at each end of the resistor, a highly compacted mass of refractory, electrical insulating, heat conducting material, enveloping said resistor 4and portions of the terminals, a metal casing the active face thereof, a cover applied to said mass along the back of the heater and end plates set Within the casing member beyond the ends of the strip and having perforations through which the terminals project, the

,lateral edges of the casing member being each end of the resistor, a highly compacted mass of refractory, electrical insulating, heatconducting material enveloping said resistor and portions of the terminals, a metal sheath enclosing said mass of refractory material and consisting of a trough like casing member which extends throughout the .length of theheater and about the active face thereof, a

'cover consisting of a metal strip ,applied to said massief material along the vback ofthe heater, and end plates set within the casing member and overlapping the ends of the cover and having pcrforati'ons through which the aforesaid terminals project, the'lateral edge portions of the casing member'being turned over the cover and ovei` said end plates to hold them in place, the said end plates and casing member being pressed together beyond the. `mass ofjinsulating -materialto provide attaching means, the active face of the element being transversely curved and of considerably greater area than the back. l

In testimony whereof,1 'hereunto alhx my signature.

E. L. WIEGAND.

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