Infrared Emitter

Abstract

An infrared emitter constituting a panel comprising a pair of sheets of refractory material, a heating element in the form of a continuous wire presented between said sheets and secured thereto by a narrow anchoring strip extending preferably across the central zone of said element. The remaining portions of said wire being unencumbered for expansion and contraction. A dielectric woven mesh-type refractory cover is provided for tying the components into a flat panel and with the end portions of the heating element extending rearwardly through said panel for engagement to a convenient source.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates in general to infrared radiation and, more particularly, to new and useful improvements in emitter panels.

In the field of infrared equipment as used in industry for a multiplicity of purposes, such as baking, curing, plasticizing, shrink wrapping, etc., there has been an ever increasing utilization of emitters of the flat panel type. Such panels normally embody a heating element, such as an electrical resistor, often a coiled wire, which is entirely embedded within the panel so that all sections of the element are completely encased within refractory material.

It is, therefore, an object of the present invention to provide an infrared panel type emitter embodying a heat source which is fixed to the adjacent components of the panel in but a limited zone so that the major portion of the element is substantially free to expand and contract and yet is enclosed in a dielectric material.

It is another object of the present invention to provide an infrared panel type emitter incorporating a continuous electrical resistor as the heat source and with a positioning member engaging a narrow, minor portion of said resistor for maintaining same in appropriate operative position.

It is another object of the present invention to provide an infrared panel type emitter of the type stated that may be produced in a manner providing marked economies over present manufacturing procedures; and which permits of utilization of resistors having greater coefficients of contraction and expansion than heretofore feasible in such emitters.

It is a further object of the present invention to provide an infrared panel type emitter which is extremely light and by reason thereof accelerate the "bring up time."

It is another object of the present invention to provide an infrared panel type emitter of the type stated which incorporates novel means for maintaining the heating element in position so as to conduce to the overall flexibility of the panel and rendering the same resistant to shock, thereby materially enhancing the effective life of the same.

It is a still further object of the present invention to provide an infrared panel type emitter having a relatively enhanced emissivity factor and which permits of markedly higher temperatures than currently attainable with present panels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an infrared emitter constructed in accordance with and embodying the present invention.

FIG. 2 is a front view of the emitter.

FIG. 3 is a side elevational view.

FIG. 4 is a rear view.

FIG. 5 is a horizontal transverse sectional view taken on the line 5--5 of FIG. 4.

FIG. 6 is a rear view of the panel with a portion of the rear refractory and covering sheets broken away.

FIG. 7 is a vertical transverse sectional view taken on the line 7--7 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now by reference characters to the drawings which illustrate the preferred embodiment of the present invention, A generally indicates a refractory panel for emission of infrared radiation. It is to be recognized that the panels of this invention are customarily assembled in multi-panel units incorporating support frames together with corresponding components of a gridwork for effective ray direction; such units being exemplified by the structures disclosed in U.S. Pat. No. 3,493,724. Panel A comprises a pair of sheets 1,2 fabricated of refractory material, such as, ceramic fiber; exemplary of which is a commercial product known as FIBERFRAX, being a trademark of The Carborundum Company for such fiber as made from alumina and silica, and which may contain small additions of suitable modifiers. Other mineral fibers having a melting point above the operating temperature of the heating element, to be described below, may be used. It is to be understood that the precise composition of sheets 1,2 does not form a part of the present invention since there are a multiplicity of materials which may be used. It is critical that the refractory material from which sheets 1,2 are fabricated be rendered resistant to fracturing as a result of repeated cooling and heating and possess substantial dielectric strength, together with a relatively low coefficient of thermal expansion consonant with sufficient thermal conductivity for heat transfer from one face thereof to the opposite face. Such refractory material is preferably in the form of "paper" sheets having a thickness of up to about 1/8 inch.

Provided for sandwiched disposition between sheets 1,2 is a heating element 3 being preferably a single length of electrical resistance wire, such as of NICHROME and arranged in a generally back and forth pattern, often characterized as serpentine, with such pattern being substantially coextensive with, but, understandably, slightly less than, the areas of sheets 1,2. The wire of element 3 may be, if desired, round or flat, and with the diameter or cross section being commensurate with the wattage to be accommodated. It is to be understood that other resistance wires than NICHROME may be equally effective, such as, various iron-aluminum alloys and the like, as NICHROME is simply set forth for illustration purposes. Each end portion of heating element 3, as at 4,5, is of increased cross section, such as through double twisting of the end portions, so that during energization of heating element 3, such end portions will be subject to relatively reduced expansion under the lower developed heat to thereby substantially eliminate possible fracturing of the associated components of panel A since, as shown in FIG. 4, said end portions or terminals 4,5, are led through openings in panel A for effecting connection to a convenient source of electrical power.

Heating element 3 is maintained in position between sheets 1,2 in a novel manner, as by means of relatively narrow strip-forming anchor 6 having a width within the range of 2 inches to 3 inches and a length coextensive with the width of sheets 1,2 to overlie the full width of the confronting portion of heating element 3. Anchor 6 is composed from a slurry of fine blown clay and coloidal silica together with ceramic fibers. The coloidal silica acts as a binder which could be any other suitable high temperature binder such as aluminum acid phosphate. Anchor 6 is thus applied in a paste or slurry form and may become set or dried by the heat generated by energization of element 3. As indicated with respect to sheets 1,2, anchor 6 may be formed of fine blown clay, kaolin, and the like. With heating element 3 disposed against the normally inner face of sheet 1, anchor 6 extends across the central zone of heating element 3 and is secured rigidly to the contacting portion of element 3 and of sheet 1, as by a suitable high temperature binder, such as, for example, colloidal silica, aluminum acid phosphate, etc. It will be seen that upon the setting of the binder only a narrow central portion of heating element 3 will be fixed to sheet 1 so that the remainder thereof, comprehending its major portion, together with the looped-like ends, as at 7, are free to the extent of being unencumbered or unencased. Sheet 2 is caused to adhere to the confronting face of anchor 6, as through a suitable binder, and thereby completing the basic sandwiching relationship but with the aforesaid portions of heating element 3 being unattached.

In accordance with accepted practice, those faces of sheets 1,2 directed toward heating element 3 may be suitably treated with a black dye for enhancing the heat absorptive and heat emissive capacities of said sheets 1,2.

It is to be observed that anchor 6 is flexible in character as distinguished from the solid ceramic compositions heretofore used for maintaining coiled resistant wires in position. By such flexibility a desired resistance to shock is provided so as to reduce any fragility of panel A.

With heating element 3 being thus held in position in but a minimal portion of its total extent, the same is freed for both contraction and expansion to extents heretofore unknown. This added capability can manifestly conduce to the provision of more effective and efficient heat supply than currently considered possible in panels of the type here involved. Also, conversely, wire of relatively reduced diameter may be utilized in view of the developed efficiency.

Panel A is completed by a covering sheet 8, as being of mesh character, and formed from a suitable high dielectric material, such as glass fibers. Said covering sheet 8 is disposed against the face of sheet 1 opposite that which confronts heating element 3 and with the marginal portions of covering sheet 8 being folded, in overlapping relationship, as at 8', about the face of sheet 2 remote from heating element 3 (see FIG. 4). Covering sheet 8 is of light weight and serves to tie the inner sandwich together while contemporaneously providing protection to panel A to render same less subject to damage through abusive handling. A binder, such as a mixture of clay and colloidal silica, or aluminum acid phosphate, is used for integrating covering sheet 8 with the retained components, as above described, of panel A. The exterior face of covering 8 is also coated black, such as by a mixture of colloidal silica and black dye, in a compatible vehicle, such as water. When dried, the solids produce a black surface which enhances the efficiency for infrared emission.

As noted hereinabove, end portions 4,5 of heating element 3 will extend through openings in sheet 2 and the folded marginal portions of covering sheet 8, as at 9.

From the foregoing it is apparent that panel A is uniquely constructed so as to present but a minimal portion of heating element 3 in secured relationship to the adjacent components thereby simplifying manufacturing procedures with attendant economies in both labor and material; as well as materially providing improved efficiency in operation.

Panel A is of relatively light weight and by virtue of such relatively reduced mass requires less time for heating to be brought to the operating temperature and consequently represents a marked advance over presently used emitters wherein the elements are fully encased by the positioning means.

A heating element constituted of wire in serpentine form with long straight lengths lowers the element or resistance wire temperature as compared with coiled wire in solidly embedded types, therefore increasing element life and distributing heat over a wider area.

Claims

Having described my invention, what I claim and desire to obtain by Letters

1. A refractory panel for emission of infrared radiation comprising a first sheet of refractory material, a second sheet of refractory material, a heating element disposed between said first and second refractory sheets, said heating element being a continuous electric resistance wire arranged in a back and forth pattern to present a multiplicity of looped end portions said end portions being covered by said sheets, an anchor for said heating element comprising a section of refractory material in narrow, strip-like form presented transversely of said heating element intermediate the looped end portions of said element and the end portions of said first and second sheets and with intermediate portions of the heating element being rigidly embedded therein, whereby the said looped end portions of said heating element are permitted unrestrained freedom of expansion and contraction, glutinous means rigidly securing said anchor to intermediate portions of said first and second refractory sheets, and covering means disposed about said first and second refractory sheets and

2. A refractory panel for emission of infrared radiation as defined in claim 1 and further characterized by the end portions of said heating element being of relatively increased thickness and being directed

3. A refractory panel for emission of infrared radiation as defined in claim 1 and further characterized by said covering means comprising a sheet of dielectric material of relatively high heat emissivity, said covering sheet being disposed against the first refractory sheet on the side thereof remote from said heating element, said covering sheet having marginal portions foldedly disposed against the second refractory sheet on the side thereof remote from said heating element, and binding means

4. A refractory panel for emission of infrared radiation as defined in claim 1 and further characterized by said anchor being substantially coextensive in length with the width of said first and second refractory sheets and being presented substantially intermediate the opposed end

5. A refractory panel for emission of infrared radiation as defined in claim 3 and further characterized by said covering means sheet being of fibrous material in mesh form.