US2202874A - Heating element mounting construction - Google Patents

Description

June 4, 1940. E. l.. SMALLEY HEATING ELEMENT MOUNTING CONSTRUCTION Filed Aug. 3, 1937 3 Sheets-Sheet 1 INVENTOR.

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BY ATTORNEY E. L. SMALLEY HEATING ELEMENT MOUNTING CONSTRUCTION Filed Aug. 3, 1937 3 Sheets-Sheet 2 9,05 @@KN Q ATToR/VE June 4, 1940. E. 1 sMALLEY HEATING ELEMENT MOUNTING CONSTRUCTION Filed Aug. I5. 1937 3 Sheets-Sheet 3 INVENTOR.

Patented June 4, 1940 UNITED STATES PATENT OFFICE HEATING ELElVIENT MOUNTING CONSTRUCTION Application August 3, 1937, Serial No. 157,218

6 Claims.

My invention relates broadly to a construction of refractory for mounting electrical heating elements and more particularly to a heating element mounting construction in which the heating element remains free to expand or contract without restraint by the refractory while the element is being maintained in operative position.

One of the objects of my invention is to provide a construction of refractory for mounting an electrical heating element wherein the electrical heating element is supported in position without subjecting the heating elements to stresses or strains due to variations in temperature of the element.

Another object of my invention is to provide a construction or refractory support for electrical heating elements whereby the electrical heating elements may be mounted with respect to a vertical wall while remaining free to expand or contract with variations in temperature without introducing stresses or strains in the resistor.

Still another object of my invention is to provide a simple and inexpensive construction of refractory support for return bend resistor elements in a furnace wherein the return bend resistor element is free to expand and contract, and to creep o-r grow within normal limits without subjecting any portion of the resistor to compression or tension which would otherwise cause failure of the heating elements even at low operating temperatures.

A further object of my invention is to provide a construction of refractory particularly adapted for installation in the side wall of a furnace and $5 by which the horizontally extending portions of the return bend resistor may be freely supported by substantially horizontal projecting refractory ledge portions for supporting thel return bend resistor without introducing stresses or strains in the resistor as the temperature thereof changes.

A still further object of my invention is to provide a construction of radiant refractory plate and coacting supports therefor, wherein the refractory plate is shaped to receive a return bend resistor element and is provided with ledge-like portions which directly abut with faces on the coacting refractory supports for maintaining the resistor in position while the resistor is free to expand or contract or grow within normal limits without subjecting the return bend resistor to compression or tension.

Still another object of my invention is to provide a construction of refractory support for return bend resistors in a furnace in which a reversible refractory plate is associated with a return bend resistor, the refractory plate being selected for high thermal conductivity, and the return bend resistor being selected of such current density that an assembly may be effected 5 in which the plate is interposed between the supporting wall structure and the return bend resistor, or in which the return bend resistor is interposed between the plate and the supporting wall structure. lo

Other and further objects of my invention reside in the heating element mounting construction as set forth more fully in the specification hereinafter following by reference to the accompanying drawings in which: u

Figure l is a vertical sectional View taken through a fragmentary portion of a furnace equipped with the heating element mounting construction of my invention; Fig. 2 is an enlarged view showing one method of installing the heating element mounting construction of my invention in the roof of a furnace; Fig. 2A shows in the same proportions the manner of supporting the heating element mounting construction in reverse position to that illustrated in Fig. 2; Fig. 3 is 25 a fragmentary elevational view showing the heating element mounting construction of my invention as applied to a return bend resistor supported by a radiant plate having substantially horizontal extending ledges along which the horizontally extending portions of the return bend resistors are supported; Fig. 4 is a transverse vertical sectional view taken on line 4 4 of Fig. 3; Fig. 5 is a horizontal sectional view on an enlarged scale taken on line 5 5 of Fig. 3; Fig. 6 illustrates the adaptability of the assembly of the refractory support of my invention in reverse arrangement with the return bend resistor interposed between the refractory plate and the supporting wall; (the reason the resistor appears in spaced relation between the surfaces of the refractories and the face of the radiant plate in Figs.5 and 6 is that the straight strands of the return bend resistor are supported by the horizontally extending ledges) Fig. 7 is a front elevation of the radiant refractory plate employed in the mounting means of my invention and showing particularly the supporting ledges on each of the fiutings or extending projections of the refractory which coact with the refractory T supports which are mounted in the supporting wall; Fig. 8 is an end view of the radiant refractory plate shown in Fig. 7; Fig. 9 is a transverse vertical sectional view taken on line 9--9 of Fig. 7; Fig. 10 is a horizontal sectional view taken on line lU-ID of Fig. 7; Fig. 11

is a fragmentary perspective View of a portion of the radiant plate; Fig. 12 is a side elevation of one of the refractory T supports employed in coaction with the radiant refractory plate; Fig. 13 is a top plan view of the T type refractory; Fig. 14.- is an end elevation of the refractory shown in Fig. 13; and Fig. 15 is a cross sectional view through the T refractory taken on line l5--l5 of Fig. 13.

My invention is directed to the construction of a refractory mounting for return bend resistor elements of the type, for example, which have a melting point substantially in excess of the well-known resistor alloy comprised of 80% nickel, 2.6% chromium, and which permits operating furnaces at 2350 to 2400" F. I have found that metallic resistance elements of comparatively recent development, comprising for example an alloy of approximately 37% chromium, 7% aluminum, and the balance substantially all iron, while being highly efficient as heating elements in electric furnaces, have a tendency to soften, and therefore become subject to distortion unless properly supported, at the relatively high operating temperatures. On account of the semi-plastic conditions of the alloys at the high temperatures, I so designed the refractory supporting plates that a portion of the corrugations thereon are engageable with other retaining members of the complete assembly. The high temperature element is thereby free to expand and contract, and to creep or grow within normal limits, without subjecting any portion of the heater coil to compression or tension which would otherwise cause failure of the heating elements, even at lower operating temperatures.

lViy present invention is an improvement over the heating element mounting construction of my Letters Patent 1,768,865, granted July 1, 1930 for the reason that in the construction set forth in my earlier patent there is insufhcient support provided for the horizontal strands of the return bend elements which become semi-plastic at high temperatures as elsewhere described and the flut ings of the T supports impinge directly on the return bends of the heating elements. In my present construction, the horizontal strands of the return bend elements are `directly supported and the flutings of the T supports engage shoulders `of the corrugations on the refractory plate rather than the return bends, as in my Patent No. 1,768,865 supra. It is to be noted that the resistor employed herein is of the same preformed character as that set forth in my Patent 1,768,865 supra. I provide a radiant refractory plate forming mounting means for the return bend resistor and wherein the plate is provided with shoulders or ledges with. which supporting refractories coact for maintaining the plate and the resistor in position while not subjecting the resistor to stresses or strains. For purposes of supporting the substantially horizontally extending portions of the return bend resistors, I provide ledge-like extensions which project substantially horizontally from the radiant refractory plate and form means alone which the horizontally extending portions of the return bend resistors may be supported.

The structure of my invention permits the reversal of the radiant refractory plates so that at excessively high temperatures, the plates may be reversed, as in the arch of a furnace, in which `case I select a ceramic refractory of high thermal conductivity, and utilize a lower current density than when the heater coil is exposed to the furnace chamber with higher current density, to keep the coil Well Within the safe operating temperatures of the heater elements.

Referring to the drawings in more detail, reference character l indicates the steel shell of an electric furnace which surrounds insulation material 2 disposed about the furnace chamber 3. The interior portion of the insulated wall is indicated at I9 having substantially vertically extending under-cut grooves 2li therein into which the T shaped refractories 2l are engaged. The T shaped refractories 2l each have an enlarged portion 22 serving as a groove engaging member for maintaining refractory 2l in grooves 20 in insulated wall iii. The refractories 2l are aligned as shown in Fig. 3 by means of an interlocking extension Zia on one refractory engaging a coacting recess 2lb in an adjacent refractory. The T shaped refractory 2l is provided with a fluted head 23 having engaging faces 23a thereon. The radiant refractory plate 'M has substantially horizontal projecting corrugations 25 thereon as shown more particularly in Figs. 8 and 9 forming substantially horizontally extending recesses 2215 for receiving the horizontally extending portions of the return bend resistor Ell. Each of the substantially horizontal projecting corrugations 25 has a shoulder or ledgelike portion at each end thereof as indicated at 2T. In the assembly illustrated in Fig. 5, the engaging faces 23a on refractories 2l abut with the shoulders or ledge-like portions 2'!! of the substantially horizontal projecting corrugations 25 allowing the resistor lil to expand and contract and to creep or grow within narrow limits without subjecting any portion of the heater coil to compression or tension which would cthervvise cause failure of the heating elements even at lower operating temperatures.

In Fig. 1 of the drawings, I have illustrated the return bend resistors mounted both in the side wall as Well as in the arch of the furnace. The heating elements may be mounted either in the side wall or the arch of the furnace to either directly or indirectly heat the furnace chamber. I have illustrated the heating elements in the arch of the furnace in Fig. 2 supported in reversed position which is one of the important features of the heating element mounting construction of my present invention. I have shown the supporting refractories in the arch of the furnace at ll, the refractories having fluted heads 5.

The refractory d has a longitudinally extending bore E therethrough terminating in a recess "l through which a headed bolt il extends. The headed bolt d passes through an aperture in the wall of insulation material 2 and through the steel shell i and is secured in position by any suitable means such as nuts Si. The radiant refractory plate lil is mounted adjacent the wall of insulation material and is provided with parallel extending corrugations il which terminate in a ledge-like portion or shoulder l2 at each end thereof.

The return bend resistor lil is mounted with the turns thereof intermediate the corrugations il and is free to expand and contract and to creep or grow within normal limits without sub- -jecting any portion of the return bend resistor to compression or tension which would otherwise cause failure of the heating elements even at lower operating temperatures especially when elements are used of alloys having a comparatively low melting point. The engaging surfaces a o-f the fluted head 5 of the refractory 4 do not contact the return bend resistor elements. Instead, the engaging surfaces 5a directly engage the ledge-like portions or shoulders I2 on corrugations II. 'Ihe supporting ledge is substantially perpendicular to the plane of the back face of the refractory. The return bend resistor occupies a space between the shoulder or ledgelike portion and the surface of the radiant refractory plate and when the radiant refractory plate is installed in the roof of the furnace, the resistor I4 by force of gravity rests directly against the surfaces 5a of the refractory 5 in the arrangements shown in Figs. l. and 2, and directly against the plate I0 in the arrangement shown in Fig. 2A. It will be understood that the end refractories have a fluted head extending in only one direction therefrom, whereas the intermediate supporting refractories have iiuted heads extending in opposite directions therefrom.

In Fig. 6, I have shown the manner in which a reversal of the assembly of the heating element mounting construction of my invention may ce effected in the side wall of the furnace. The radiant refractory plate 24 supporting the return bend resistor I 4a is carried directly by the flutings 23 of the refractories 2l with the corrugations 25 directed inwardly toward the wall of insulation and with the return bend resistor I4@ carried thereon. It is understood that when the heating elementi mounting construction is utilized in reverse arrangement, the radiant refractory plate is selected to have high thermal conductivity and the return bend resistor is selected to utilize a lower current density than when the heater coil is exposed to the furnace chamber.

Figs. 12-16 show in more detail the construction of the refractory 2l described in connection with Figs. 3-11. The flutings 23 are so shaped that the engaging faces 23a. abut against the shoulders or ledge-like portionsj 21 of corrugations 25 but do not Contact any portion of the return bend resistor I4. 'Ihe iluted head 23 is so shaped as to allow quick release of heat from the electrical resistor. In all forms of my invention the corrugations are proportioned of such depth with respect to the size of the return bend resistor that the distance between the ledge-like portion or shoulder I2 in the form of my invention illustrated in Figs. 1 and 2 and 2A, for roof mounting. and the distance between the ledge-like portion or shoulder 21, in the form of my invention illustrated in Figs. 3-11, of the corrugations, and the surfane of the radiant plate 24, as compared to the thickness of the resistor, is such that the resistor is always free to expand or contract and to grow or creep in accordance with changes in temperature. By this arrangement the engaging faces of the flutings abut with the shoulders on the corrugations while providing minimum coverage to the resistor so that heat may be released quickly from the ends of the return bends through the flutings on the refractories. While the resistor may rest against the head of the refractory support 4 or 2|, the resistor is not, under any circumstances clamped thereby, and is always free to expand or contract and to grow or creep in accordance with temperature changes.

I have found the heating element mounting construction of my invention highly practical and eicient in its operation with newly developed alloys used in heating) elements and although I have described my invention in certain of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

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

l. In combination with a wall of a furnace chamber, a refractory plate having corrugations on one face with shoulders on the ends of said corrugations and a plane surface on the reverse face, a preformed return bend heating element having straight portions lodged in grooves formed by said corrugations and return bend portions looped around the shoulders on said corrugations, and other refractories secured to the said wall and having uted edges engaged with the shoul ders on said corrugations for loosely confining the heating element in position with respect to said plate and for holding the said plate with the plane surface thereof adjacent said wall.

2. 1eating element mounting means comprising a refractory plate having corrugations on one face thereof projecting from a plane base portion, each of said corrugations having a stepped shoulder formed at each end, a preformed return bend heating element of circular cross section disposed between said corrugations and around said shoulders thereof, said shoulders being spaced at a distance from the plane base portion of said plate greater than the cross-sectional diameter of said heating element, and other refractories mounted in fixed positions on a furnace wall and having fluted edge portions extending substantially parallel with the plane base portion of said plate and engaged with the shoulders on said corrugations in bridging relation to said return bend heating element, for supporting said plate and loosely confining said element in mounted relation on said refractory plate.

3. Heating element mounting means comprising a furnace wall, a refractory plate disposed vertically and having horizontally extending corrugations thereon provided with substantially level upper faces, each of said corrugations having a shoulder formed at each end thereof, a preformed return bend heating element having straight portions loosely supported on said upper faces of the corrugations and return bend portions disposed around the ends of said shoulders, said heating element being operative at a temperature of 2400" F. with a characteristic softening in structure, and other refractories supported in xed positions by said furnace wall and having vertically extending fluted edge portions engaged with the shoulders on said corrugations in bridging relation to said return bend heating element for supporting said plate, said element in heated and softened condition being loosely confined by said edge portions of the last said refractories in unrestricted recumbent position on said substantially level upper faces of the corrugations.

4. In an electric furnace, mounting means for a preformed return bend heating element comprising a refractory plate with corrugations on one side thereof shorter in length than the corresponding dirnension of said plate, each corrugation having a step formed in each end, a return bend heating element disposed between said corrugations and around the stepped ends thereof within the limits of said plate, and means for supporting said plate and loosely confining said element, including a wall of said furnace with refractory members secured thereon at the opposite side of said plate from the step in said corrugations, said members having fluted edge portions engaged with the stepped ends of said corruga tions, said fluted edge portions being of suflicient width to span the marginal portion of said plate and bridge the bend of said element, whereby said heating element is confined with freedom to expand, contract and maintain constant stresses with temperature variations.

5. In an electric furnace, ceramic refractories in combination, forming support for a preformed heating element, comprising a ceramic plate with one plane face and the opposite face thereof having corrugations shorter in length than the plate, with each corrugation having a stepped portion in each end, said plate being adapted to support straight strands of a return bend element of the class described, loosely disposed horizontal- 1y on the upper faces of said corrugations which faces extend in planes substantially perpendicular to said plane face, with the lower face of each corrugation disposed at an angle obtuse to said Y plane face, and other refractories engaged with the stepped portions on opposite ends of said corrugations and supported on a Wall of said furnace at the opposite side of said plate from said corrugations, for maintaining said plate and said element in position, the heat produced in said element being reflected from the angular lower faces of said corrugations while the upper faces of said corrugations provide adequate support for the element under high temperature operating conditions, whereby said heating element is retained with freedom to expand, contract and maintain constant stresses with temperature variations.

6. Heating element mounting means for a preformed return bend heating element, comprising a refractory plate member and supporting refractory members secured to a furnace Wall; said plate member having one plane face and a plurality of corrugations on the other face thereof, having shoulders formed on opposite ends of said corrugations, the combined length of said corrugations and said shoulders being shorter than the corresponding dimension of said plate, said preformed return bend heating element being adapted to lie loosely in the grooves of said corrugations and around the ends of said shoulders within the limits of said plate; said supporting refractory members each including a Web portion and a iluted edge portion, and arranged at opposite edges of said plate with said corrugations endwise therebetween; said fluted edges portions being engaged with the shoulders on opposite ends of said corrugations for supporting said plates with the corrugated face thereof exposed for heat radiation and with the said edge portions in bridging relation to the portions of said return bend heating element disposed around the ends of said shoulders, the heating element thereby being supported by said plate members with freedom to expand, contract and maintain constant stresses with temperature variation.

EDWIN L. SMALLEY.

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