USRE18420E

USRE18420E - Electric furnace

Info

Publication number: USRE18420E
Authority: US
Publication date: 1932-04-12

Description

ELECTRI C FURNACE Orlginal Filed Sept. I5. 1925 3 neets-b'heet l with consequent deterioratin of the mountl Reissued Apr. 12, 1932 f Re. 18,420

UNITED STATES PATENT OFFICE HAROLD N. SHAW, 0F LLANERCH, PENNSYLVANIA', ASSIGNOR', BY MESNE ASSIGN- lMENTS, T0 GLOBAR CORPORATION, 0F NIAGARA FALLS, NEW YORK, A CORPORATION OF NEW YORK ELECTRIC FURNACE Original No. 1,742,286, dated January "7, 1930, Serial No. 54,192`,'1ed September 3, 1925. Application for reissue filed July 11,1931. Serial No. 550,260."

This invention relates in general to electrical hea-ting apparatus, and it has more particular relation to electrically heated furnaces of the resistance type adapted for producing and maintaining relatively high operating temperatures.

In the production of high temperatures by electrical resistance heating, a-s in the case of electrical furnaces and the like for the various commercial heat treatment processes, it has been considerable of a problem to secure an electrical resistance heating unit capable of producing the desired heat and still capable of maintaining itself under these high` temperatures Without undueI deterioration, during a satisfactory commercial life, and readily renewable with little or no reconstruction of the furnace or placing of thelatter out of commission from the standpoint of production. i

A considerable partof the difiicultyhas'-y existed with respect to the connection or mounting, from both an electrical. and -a mechanical standpoint, of the active or heat-v producing portion of the resistanceheating element, being due to a considerable extent to the factthat the difference in-coeliicients of expansion between the resistance heating element and mechanical and electricallmountingsl and connections therefor, caused separation of the metallic securing and terminal means from the resistance heating element,

ing, When the heat-ingelement operated at high temperatures. Further, these high operating temperatures cause oxidation` and;

scaling or pitting of the `metallic 'terminal and mounting means, with further conse-l quent deterioration ofthe contact enga ement between the resistance element and its terminal, this deterioration increasing a't a -v'ery rapid rate'after having been oncestarted, with the consequent result that lthe 'volt-1 age across the active heat-producing portion of the heating element, and consequently the useful heat produced, are greatly reduced. These variouseifectsv contribute to and appear to multiply in causing reduced and generally uinsatisfactory commercial lifel of the heating element and its mounting.

The present invention includes and contemplates the provision of an improved electricalL ,ly heated furnace especially adapted for commercially satisfactory high temperature operation,'and wherein the heating eiects are produced .by resistance heating `elements. Also the invention includes the provision of an improved form of resistance heating unit whereinv a selffsustaining"heating element is utilized in connection with animproved form of mechanical and electrical mounting therefor, and wherein the parts may be readily renewable4 with a minimum ofshutedown andA reconstruction of the furnace. The invention more particularly contemplates the utilization of ymolded Y and self-sustaining heating elements having terminal portionsof substantially reduced resistance, and consequently reduced heat-producing capabilities, in connection with terminal mountings for the heating elements which serve to yieldingly mechanically support the heating elements in desired operative position and electrically connect the same in circuit in a readily demountable manner and substantially Wholly through pressure exerted through lbutt-end contact with the termina-l portions of the heating elements.'

vIt is anl object of the present invention to provide an improved form of electrical heating apparatus embodying a resistance heating unit of improved design and characteristics, and adapted for the production of relatively high operating temperatures with `commercially satisfactory life and under conditions involving commercially reasonable expense for maintenance and renewal.

It isf afurther object of this invention to provide apparatus of this general class for operation as an electrical furnace and Wherein the resistance heating element is of a relativelyy rigid, self-sustaining character and is yieldingly and detachably mounted in operativepbsitiofn substantially .through butt-end engagement between terminal portions of the heating element and cooperative mounting terminals.

It is a further object of this invention to.

provide electrically heated furnace apparatus ofthe resistance type wherein the resistance Other objects of this invention are the provision and utilization in electrical heating apparatus of this general class, of heating elements in the form of molded and heathardened, rod-shaped bodies essentially con-- stituted of silicon carbide and of substantially the same cross-sectional are\a throughout and having integrally formed terminal portions of increased conductivity and yieldably and detachably mounted in electrically and mechanically operative position through butt-end engagement With' conductive terminal elements embodying materials ofA raded heat resistant properties and protecte from the intense heat of the body portion of the heating element. 'l In the accompanying drawings: Y Fig. 1 is a vertical section of an electrically heated furnace of the resistance type, embodying features of the present invention.

Figs. 2, 3 and 4 are viewssimila'r to Fig. 1 showing modified forms and additional details o f the invention disclosed in Fig. 1. Fig. 5 is an enlarged, fragmental, vertical section of adetail ofthe Aapparatus shown in Fig. 4.

Fig. 6 is alvertical sectional view of a.

modified formof aterminal-mounting detail.

Fig. 7 is a view similar to Figs. 1, 2, 3 and 4, showingl a furthermodied form of the invention. Y

. Fig. 8 is an enlar ed, fragmental, vertical ectioi of a detail of the apparatus shown in ig. 9 is avertical sectional view in the plane of the line IX--IX of-Fig. 8.-

In the vembodiment of the invention disclosed in Fig. l, an electrical furnace is shown as including a metal supporting frame 10 mounted upon supporting legs`11, this frame carrying the walls of anfordinary furnace chamber of refractory material, shown as having a dome-shaped roof and; including a brick lining, indicated at 12, and a wall covering 13 of suitable refractory or heat insulating material and an enclosing Wallcovering 14 of suitable heat insulating material, there being an air space '15 between upper portions of the sides of the coverings 13 .and 14. The side walls of the refractorychamber and the covering wall v13 are provided' with through alined apertures 16, indicated as beingfairly nea-r the'dome-shaped roof of the furnace chamber. One'orany desired number of resistance heating elements 17, preferably in the form of self-sustaining, molded and heat-hardened rod-shaped bodies, are disposed in the furnace chamber with the terminals of the resistance elements projectingr into the apertures 16. The terminal portions of the heating elements 17 which extend into the aperture 16 in the` furnace Walls are preferably more highly conductive and, hence, become less nhighly heated than the body portion of the element 17. The ends of the heating element 17 are disposed in operative mechanical and electrical engagement with terminal mountings, shown here as comprising short rods or pieces 18 of heat-resistant electrically conductive material, preferably.

is preferably packed fairly tightly within the l recess under normal operating conditions;

Q and the terminal pieces 18 are preferably maintained in operative position substantially spaced from the, Walls of the aperture 16 'in the Wall of the furnace chamber with the y outer ends of these A air-spaces 15.

At the right in Fig. 1, the terminal piece 18 is mounted upon the lupper' end of a flexible and resiliently yielding heat-resistant and .electrically conductive element 21, preferably of Monel metal, the other end of the element 21 being' connected to and sup-ported by abus b ar 22 mountedon the furnace Wall. At the left in Fig. 1,' the terminal piece 18 1s connected to and supported at an intermediate point lof a conductive strap spring `member 23 of the same material as the ele- 'ment1 21 and mechanically and electrically connected to and supported by one or more -bus bars at its ends, or otherwise supported and connected to a supply liie.

An inwardly projecting lip or flange 24, in-

pieces projecting into the dicated at the'left in Fig. 1, may be provided on the side Walls of the furnace at the inner edge of the apertures 16, as by counte'rboring the outer portion of the aperture 16, for the purpose of protecting the terminal piece 18 to vsome extent from theV high temperature revailing in the body of the furnace chamer. 0r a, washer or ring ofA refractory material 25 may be placed over the terminal portion of the heating element 17 at a pointy Within the .recess 16 in the furnace Wall, as indicated at the right in Fig. 1, this ring acting as a shield to protect the terminal piece 18 from the more intense heat offthe furnace chamber. The 'inner edge ofthe portions of the terminal pieces 18 which constitute walls of the recesses 19 in which'the granular conductive material 20 is disposed may be beveled or serrated, as indicated at l26, to afford more ready dissipation of the heat developed at the points-of engagement between the ends of the heating element 17 and the terminal pieces.

The terminal pieces 18 are yieldingly maintained in operative relation to the terminal portions of the heatingv element 17, through the intermediary ofthe conductive granular material 20, through pressureexerted on the terminal pieces 18 by the resilient spring mounting 21 or 23, so as to cause the latter, or the granular contact material 20 therein, to forcibly and yieldingly maintain the element` 17 in operative position in theY furnace chamber, and with the terminal portions of the resistance element spaced from the walls of the aperture 16 in the side walls of the furnace, and to likewise maintain the desired yielding butt-end electrical engagement bef tween the end of the heating element and the granular conducting material 20.

In accordance with the disclosure of Fig. 2, the furnace includes a` refractory .liner 12, of brick or the like, and a covering of heat insulating material 13. The form, of terminal lses support and mounting for the resistance element 17, preferably of the general character of that of Fig. 1, used on the furnace wall at the right in Fig. 2 includes -a tube 32 of re fractoryV insulating material, such as lava, having a relatively easy sliding fitin lthe aperture 16 through the wall of the furnace. The outer end of the tube 32 may extend slightly beyond the outer surface of the furnace wall, as indicated. The inner end of this refractory tube 32 is counterbored to provide a central recess 34 in which is disposed a granular, heat-resistant and conductive material of a not readily oxidizable nature, such as Monelmetal, capable of maintaining itself at relatively high temperatures, this granular material being indicated at 35. As indicated, theend of the resistance heating element is in electrical engagement with the granular material 35. Passing through the axial bore of the lava tube is an electrically conductive bolt or rod 36 of Monel metal or the like heat resistant, conductive material. with its head 37 disposed in the recess 34 and its outer end extending appreciably beyond the outer end of the tube 32, this rod`36 being slightly enlarged and threaded adjacent its head into the tube 32.

Connection to a line terminal is made through the projecting portion of the conductive rod 36 and a yielding terminal mounting 38, here shown as comprising a spring or resilient supporting strip or element 39 and a relatively conductive strip 40 secured. by welding, riveting or the like, to the inner face of the resilient supporting strip 39 and provided 'at its upper end with a concave recess or pocket within which the outer convex end of the conductive rod 36 engages. The end portion of the supporting element 39 may have the same concave formation as the conltact strip 40, these end portions of the two strips being so formed as toV be nested together. The terminal mounting element 38 is held in operative position, wherein it forcibly but-yieldingly'engages the end of the rod 36, by securing the lower end of the element 38 upon a support 41, preferably the vbus-binwhich supplies current to the terminal, suitably carried by the wall of the furnace, one or more bolts or screws 42 being here shown as a means for mechanically securingv the terminal mounting in position on and insuring electrical connection thereof to the vbus-bar,41.

The resilient mounting element made up of the strips 39 and 40 may be replaced ,by

a single relatively'stiff terminal spring, of

rod 36 from the more intense heat of the furnace chamber.

It will beapparent that, during norm-al operation of a furnace equipped with the terminal connection and mounting described, the resilient mounting elementy 38 yieldingly Vurges inwardly the bolt 36 and the refractory tube 32 with the granular conductive material 35 at the inner end thereof, so as to force and y maintain the granular conductive material in intimate mechanical and electrical engagement with thev butt-end of the terminal portion of the heating element 17. This forciblecngagement may be such as to maintain the resistance element `in desired operative position within the furnace with its electrical connection to a supply linefestablished and maintained in'a satisfactory manner.

The form of terminal connection and mounting disclosed at the left in Fig. 2 in'- cludes the terminal portion of the resistance heating element 1,7 extending an appreciable distance into the aperture 16 so as to bring the end of the heating element 17' into a zone of relatively reduced temperat-ure in the furnace wall.- 'A terminal piece or rod 45, of electrically conductive and heat resistant materialapreferably ofv Monel metal or ironconcave or recessed for effective engagement end ofthe terminal piece is preferably of substantially conical shape so as to insure provision of at least'multipoint or substantially line contact between the same and the end of the heating element. As indicated, the terminal piece 45 is appreciably smaller than the aperture 16, this condition insuring appreciable spacing of the surface of the` piece 45 from the walls of the aperture and promoting the transmission of heat from the point of engagement of such terminal piecev with the end of the heating element.

The terminal piece 45 is maintained in operative position, both mechanically and electrically, with its outer end appreciablyv beyond the furnace wallrwhere it maybe maintained fairly cool, through engagement of a convex outer end thereof by a correspond ingly concave or recessed portion of the terminal mounting 46, this terminal mounting vcomprising an outer resilient supporting ele- -Inent 47 and an inner contact strip 48, the

general design of this terminal mounting and the means for supporting it in operative po- J sition and connecting it to a supply line being substantially the same as indicated at the f right in Fig. 2. The design and arrange- EIO ment of the terminall mounting 46 is such as to yieldingly engage the terminal piece 45V and force the same into efficient mechanical and` electrical engagement with `the end of the heating element 17 so asv to form the desired electrical Ycontact therewith and to ef;r

fectively support the heating element with its body portion in the furnace chamber and its terminal portions spaced from' the walls of y the recess through ythe furnace wall.

It is desirable that the refractory tube 32 at the right and the terminal piece 45'at'the left in Fig. 2 be spaced to an appreciable extent from: the furnace Walls abou the aperture 16 for the purpose 'offacilitatingv the maintenance of these parts and theconductive parts associatedktherewith at satisthe linner ends of these' apertures `being cut'Y factory working temperatures. These

parts

32 and 45 may rest directly on the wall about theaperture 16, or they may rest on a supporting or spacing projection or ledge 49 at the lower side wall of the aperture 16, the eflfect of this latter method of supporting the parts being to permit more ready circula,- tion of air currents about and hence more ready heat dissipation from' the

parts

32 and 45. Y

In Fig. 3, there isl disclosed a furnace of substantially the same general construction as in Fig. 2. with its refractory lining 12, ofbrick or thelike'Vand its covering ofheat insulating material, vindicated at 13. v The side walls of the frnacechamberare shown?" as provided with aligned through apertures 16 a/t a point adj acentthe dome-shaped roof,

away or beveled for a small distance from thegnnerv wall of the chamber to form a substantially conical recess at such point, a's indicated at 53, the angle of flare being preferably 90 or between the latter value and 45. The heating element 17 extending across the furnace chamber has its ends, preferably of the more highly conductive type as described hereinabove, extending to a slight extent within the unflared portions of the apertures 16. The terminal pieces 45 of the type and characteristics of the corresponding element of Fig. 2, are disposed in the apertures 16, with the inner ends normally positioned a slight distance within the wall beyond the end of the flared portion 53, and the outer end projecting considerably beyond the furnace wall, as indicated, exceptionally good results being secured with an ironchromium-nickel alloy, such as ascoloy.

y These terminal pieces are somewhat smaller than the apertures'lt, so as to provide an air space between the terminal pieces and the surrounding Wall of the apertures, thus permitting more ready heat transmissionoutwardly along the terminal pieces, a seating and spacing projection 49 being provided on the wall at the lower side of the aperture 16, vif desired. @The inner ends of these terminal pieces 45 are provided with conical recesses Within which the appreciably rounded ends of the heating element 17 engage. y

(The terminal pieces 45 are maintained in operative position and in desired electrical and mechanical engagement with the ends of resistance heating element 17 by means of flexible and resilient terminal mounting ele-` ments 46 of the general character of that described in connection with Fig. 2. De-

sirable results are secured when both 'the resilient supporting strip 47 and the assoelated contact strip 48 are of a heat resistant,

conductin metal like Monel metal; and this y terminal e ement may likewise be., `formed of a single' resilient strip of this metal. This vterminal mounting may have a bentportion to increase the flexibility and resilience in the direction of the longitudinal axis of the ter minal piece "45. As indicated, the terminal element 46 may be mounted upon an angleiron or other correspondingly shaped support 59 secured to the furnace wall orsupporting frame. A bolt 61 extends through an aperture in the vertically extending portion of the support 59, the head of the boltl or a holding nut thereon being at the inner -side of support, with an insulating washer 62 between such bolt head. or nut and they Vvsupport and having a bushing extending yf throughthe support. x This bolt 61 is secured in operative'positionbymeans of a nut on the bolt,-w1th an insulating bearlng washer between this nut and the angle iron, the washer end of the bolt 61 passes through apertures in the lower end of the terminal mounting 46,

` lthe latter being `secured in mechanically and 'electrically operative position by a nut 68, withsuitable metal bearing washers between i element 46 and the nuts 67 and 68.

ILO

the aperture and the refractory tube 70 there- As indicated at the right in Fig. 3, the outer portion of the aperture through the wall of the furnace chamber is enlarged, as indicated at 69, and a refractory insulating tube 70, of material such as alunduln, is inserted in the enlarged aperture. The enlargement of in extend inwardly almost to the beginning of the flared portion 53. rlhe bore of the `tube 70 is preferably substantially the same as the diameter of aperture 16 and is such as to receive the terminal piece 45 with a loose fit,

thus providing a slight air space substantially wholly around the terminal piece, the inner end of the latter being located substantially or nearly at the inner end of the refractory tube 70. This tube 7 0 preferably extends appreciably outside the furnace wall and has 'a loose fitin the enlarged aperture 69; and

the tube may well be of substantially s quare outer cross-sectional shape and fitting in the enlarged aperture 69 of circular .cross-section,

thus providing a substantial air space between tube and the surrounding wall of the aperture. The gen-eral arrangement is such as to provide for dissipating heat from interior portions of the terminal piece and associated parts, thus; better insuring the maintenance of these parts at safe operating temcave contact portions of these terminall mounting elements forcibly and yieldingly l engage the convex outer ends of the terminal pieces 45, thus yieldingly vurging the latter into eflicient engagement with-the ends ofthe heating element 17, these ends being in v,contact with the walls of the conical recesses in the inner ends of these terminal pieces.

Through this arrangement, the heating element is efficiently maintained in operative position within the furnace andelectricallyv connected to a supply line through pressure exerted on the heating element in the direcf tion of its longitudinalxaxis; and this support of the heating element is of sujch a yielding nature as toinsure efficient electrical connection between the cooperative parts even through the maximum variation in temperatures during operating conditions.

.In accordance with the disclosure of Fig. 4, the furnace chamber may be considered as of substantially the same general construction as in Fig. 3, with the exception that additional external side wall portions 78 o'f heatV insulating material are provided, these wall portions being recessed about the outer termi- Y nal apertures so as to form chambers 7 9 which may be lined with a metal terminal box or casing structure '81, the latter cooperating with the sheet metal shell 72 to fully enclose the furnacewalls. Upon an insulating support 84 carried by the casing 81, an angleiron or like conductive support 85 is mount-- ed, the same serving as a terminal connection to a supply line. A resilient and flexible terminal mounting element 86 is carried by this conductive support and comprises a flexible and resilient leaf or strip or heat-resistant,

conductive material, such as Monel metal, and one or more resilient and relatively sti reinforcin leaves or strips, likewise preferably of onel metal or the like. The sev-- eral leaves or strips of the resilient mounting element 86, the reinforcing strip being indicated at 87 and the Contact strip at 89, may -be permanently connected together; and the element as a whole is mechanically securedr in operative position and electrically connected in circuit by one or more bolts or screws 90, at least the inner one of these strips having a suitable recessed upper end for engagement with the convex terminal portion of a

terminal piece

91, 92 disposed within the refractory tube 70, mounted in the enlarged outer portion 69 of the aperture 16, with the outer end extending of the tube 70. Instead of the ordinary form of terminal piece within the refractory tube 70, as shown in Fig. 3, the terminal *piece lmay comprise considerably beyond the end Y an inner portion of highly heat-resistant and conductive material, preferably an Viron'- chromium-nickel alloy, such .as ascoloy,`this inner portion being exposed to the more intense heat arising from the most active portion of the heating element in the furnace chamber, and an outer portion 92 of brass or other suitable metal which is relatively inexpensive and of higher electrical and'heat conductivity than the inner' portion 91. The two or more portions of the terminal piece sup- .ported within the refractorytube 70 may be separate and formed Vwith suitable abutting end engagement surfaces, either plane, rounded or generally telescoping; or these pieces may with preference be integrally united by screw threads, brazing or intimately-connectedin a permanent and self-supporting fashlon; and theouter end of the portion` 92 is preferably corrugated or slotted to increase its 'surface area and thus improve its heat-dissipating properties for the purpose of better insuring a safe operating temperature at the point of, engagement between this outer endof the portion92 'andthe terminal mounting element 86. For this purpose, the outer end of the portion 92 is shown as provided with aV plurality of diametral slits 93. With the arrangement disclosed herein, use may be made of material having relatively high heat-resistant properties such as an iron-chromium nickel alloy, which is relatively expensive, for the element in direct engagement with the end of the heating element 17, and of other material of satisfactory and suitable heat and electrically conductiveY properties, such as brass or the like, whichv '1s a. relatively less expensive material, to the final end of providing an efficient and relatlvely lnexpensivetermmal and mounting a1'- rangement which has the desired operating characteristics.

As a further means for assisting in mainf taining the conductive terminal and mount` ing elements in relatively cool operating condition, a coil'94 through which water or other cooling fluid passes, may be disposed within the terminal casing 81, and preferably surrounding the outer end of the terminal piece 92, with inlet and outlet conduits passing.

through slots in a renewable sealing cover plate 95.

With the terminal mounting elements 86 of the required' stiffness and resiliency, the heating element 17 is held, through the intermediary of the

terminal pieces

91, 92,'in

mechanically and electrically operative posi- T tion in a yielding and readily detachable manner and through butt-end engagement of the heating element with cooperative parts.

As indicated in Figs. 3, 4 and 5, the aper-V ture 16 with its inner flared portion 53 and the counterbore or enlarged portion 69 may,l forconvenience in manufacture and assembly, all be formed in a single brick or refractory lining/element by molding to the desired special conformation. Likewise, this specially formed brick or lining element may be of extended length so as to extend through the insulating wallcovering 13, thus permitting ready'removal and renewal of this 'specially shaped element, designated as 12 in Figs. 7 and 8. The importance of having the' refractory parts immediately surrounding the resistor 17 and its contact 91 so con-- structed as to be readily replaceable without major disturbance of the furnace wall structure is due to the fact that on long continued on-and-ofl' operation the face of the metal contact adjoining theresistor tends to be' come locally fused and oxidized tovan extent\` which sometimes causes it to adhere 4so tightly to the adjacent refractories as to interfere 'with `proper operation of the spring actuated contact. On suchoccasions it frequent- 1y becomes necessary to tear out the refractory as well as the metal contact in order to make repairs and it is obviously desirable that such tearing out'involve minimum damage to the furnace structure.

In Fig. 6, there is disclosed a modified form of terminal mounting arrangement utilizing, as a substitute for the

terminal piece

45 or 91, 92, a Huid-cooled terminal piece 100, using water, air `or the like as the cooling medium, which assists in maintaining satisfactory reduced temperatures of the parts of the terminal mounting during normal operation at extremely high furnace temperatures. .The inner end of the `element 100 has a conically recessed portion, indicated at 101, for engagement with the end of the heating element 17; The outer portion of the terminal is or has portions of reduced diameter, as indicated at 102, and has a central "bore 103. A sleeve 104 is attached to the inner or body portion ofthe terminal piece,as by screwthreada, and surrounds the reduced portion 102 leaving an annular chamber or a plurality of chambers between thesel parts. The outer end ofthe sleeve 104 may be closed by an apertured cap 106 throughl which the reduced portion 102 passes, the cap .being vided with a stuffing-box 107 and suitable packing to effectively seal the aperture about the reducedportion 102. The bore 103 communicates at'it inner end, through radial ports 108, with the chamber or chambers within the fsleeve 104, and near its outer end with a supply conduit 109 for cooling fluid. he' space within the'sleeve104 communi- Cates, as through an'aperture in the lcap 106, with a discharge conduit 110 for Athe' Huid used for cooling purposes. rlphe outer end of the bore 103 may be closed in any suitable manner, as by .having a terminal head Welded 0r otherwise secured on the outer -end 0f the reduced portion 102 so as to seal the outer resilient terminal element 113 of the chari.

acter described hereinabove. "The conduits 109 and 110 are preferably of insulating-malterial or are insulated from Vthe parts of the conductive terminal piece. These conduits maybe connected to the terminals of the cooling coil 94 or other suitable sources. The terminal piece may be divided atany desired point of the reduced portion 102 into an inner highly heat resistantportion and an outer more readily workable and conductive portion, the two portions being preferably welded to prevent leakage fromthe bore 103.

VIn the modified construction disclosed in Figs.' 7,8 and 9, the furnace Wall construe` tion is slightly modified to accommodate a terminal casing 120 -which'has incorporated therein 'or associated therewith' a metallic water or othei` Huid cooling jacket 121 the specific constructionshown herein including threaded on the end of the sleeve and prothe formation of the waterv jacket at the inner end of the casing 120, the inner end wall of the latter forming one side wall of the jacket and a partition 128 welded, or otherwise secured in a fluid-tight manner, to the Walls of the casing forming the front wall of the jacket. The partition 123 and the inner end wall of the casing are eccentrically apertured inline with the aperture 16 and its counter-bore 69, and a tube or sleeve 124 is welded, or otherwise secured in a fluid-tight manner, to the partition 123 and the inner end Wall of the casing, the tube 124 being of such interior diameter as to lit fairly closely about the refractory tube 70 and completing'v the water jacket about the latter and the terminaly piece 92'therein. The metal of the central tubular Wall 124 of the water jacket is extended inwardly to a considerabledistance into the lwall of the furnace chamber, being here shown as projecting nearly or substantially to the refractory lining 12. Acooling coil 126 is utilized as a part of the inlet connection 127 to the-lower part of the water jacket, the turns of the coil being suitably spaced from the terminal piece 92 and the resilient terminal mounting SG so as not to interfere with the removal or yreplacement of Vthe conductive terminal parts. As indicated,

the discharge from the water jacket is through a conduit 128 connected to the jacket near its uppermost point. These conduits are preferably detachably connected, either inside or immediately outside the terminal casing "to suitable supply and discharge means. A door or cover plate 131is mounted, as by hinging at its upper side, outside and serves to close the terminal casing 120 and to protect the apparatus therein. This cover plate is shown as provided with Ventilating openings, through an elongated one of which the conduits '127 and 128 or connections therefrom project,` Shutters may be provided to close off theopenings in the cover plate, if it is desired to confine the space within the casing from the surrounding atmosphere.

Through the use of the Water-jacket 121' with the inwardly extending projection 125 from the inner tubular wall ofthe jacket, heat from the inner tubular wall of the jacket, heat from the inner portions of the refractory tube 70 is transmitted directly to the metal tubular extension and more readily carried to the watercooled portion of the jacket, the arrangement thus serving to more readily dissipate heat. from the

terminal piece

91, 92 and maintain the same and more especially its terminal portions in satisfactory operating condition. "i

As indicated, aV single brickor lining element 12a may be formed to provide the aperthe tube is easily replaceable.

that this block should .also be easily replaceable.

The form` of yielding terminal mounting for applying the required butt-end pressure upon the terminals of the heating element 17, as disclosed herein, wherein the required electrical and'mechanical engagement is secured through a Contact portion. located near the end of a flexible supporting arm, permits readyremoval of the heating element and associated contact parts within the aperture 16 in the furnace wall; for after releasing the holding screw or bolt which secures the supporting arm, with a little pressure applied to such arm, it may be readily freed from the end of the terminal piece directly associated with the heating element, and then the supporting arm may readily be swung'about its securing bolt to a position wherein it does not interfere with removal of the heating element v and contact parts from the aperture 1G. Then the parts'are renewed onreassembled, the yielding supportingterminal or mounting may be readily swung back to` and secured in operative position.

lVliile in the several furnaces disclosed, yielding and resilient terminal mountings are shown asbeing provided for both ends of the heating element 17, one of these yielding terminal mountings maybe replaced by a bar or pad of conductive material held more or less rigidly in position and provided with la recessed portion in or with whichthe convex end of the terminal piece disposed in the aperture 16 engages, the required yielding effect being secured wholly through the terminal mounting for the` other end of the heating element, this latter terminal mounting being of the ordinary lyielding type described.

of the same or different ones of the several types described herein may beused for support-ing a heating element 17 in operative position. i j f rlhe resistance heating element 17 is preferably of -a moldedand heat-hardened 'composition type and of a carbonaceous' character and preferably contains a carbide, such as silicon carbide, asan essential constituent,

the resultant heating element being rigid and self-sustainingand readily handled. The resistance element is preferablyof substantial- 13 ly the same cross-sectional area throughout, both-the vactive body portion and the terminal portions, and its terminal portions are of increased conductivity, preferably rendered so through treatment which alters both mechanical and electrical characteristics of interior and surface parts of the terminal portions during the manufacture ofy the resistance element. The manufacturing operations ordinarily leave the extreme ends of theterminals, or portions thereof,`of such a resistance element somewhat rounded, and

these ends `ofthe resistance. element and the associated elements of the terminal mountingsare intendedto be in butt-end engagement. during normal operation, being yieldingly maintained in the desired contact relation by the resiliency and normal bias of the yielding mounting element, the contact portion of which is movable about its lpoint of support due to the s ring effect of a\portion of the mounting. apability of movement 0f this contact portion of the mounti g may be secured in other manners, such as pivoting `the mounting element at its point of support or otherwise guiding the contact portion for substantially straight line y movement Aalong the axis of the heating element. The normal biasing of the 'contact portion to secure the desired movement thereof may .likewise be secured by other forms ofwsprlngs, gravity, and the like. Even in those cases where the end of the resistance element is of such contour that kelectrical engagement a'nd mechanical support of such element are initially secured only at one or more spaced points of the resistance ele.

. ment and the cooperative recessed contact member,` the heat produced at such restricted contact area during initial operation may be such as soon causes softening or melting of the metal of the contact strip or element and permits the latter to adjust or wear itself into more secure and extended electrical and me chanical engagement with the'end of the heating element, the final result being that effective contact is securedl in a relatively short time over a sufficient number of points or an area of such vsize as toI produce satisfactory and efficient operation of the heating element atthe desired high. temperatures. Certain desirable effects of heating appliances embodying preferred forms of the present invention may-be due to the ability of the conductive materials usedfor the contact portions ofthe terminal mountings to wholly or substantially withstand or prevent the formation of oxides of the metal atbthe heated contact surfaces, even when the latter are heated to a relatively high temperature, or lto the fact that, if oxides. are produced at. .these surface portions vofthe metallic terminals, theloxide 1m :produced is relatively thin and, while it may be sufficient to exclude air and prevent further or increased forma-v tion of oxide or scaling nevertheless, it is sufficiently thin so that the potential drop across above effects are ordinarily present to a greater or less extent.

Where very high temperatures are liable to bepresent, it has been,` found that Monel metal and iron-chromium or iron-chromium-nickel alloys, preferably the alloy known as ascoloy, give `especially. desirable .operating results,

the effect in the latter case being more in the nature of an absence of deleterious formation or oxide or pitting on the metallic surface in .engagement with the end of the heating element.

Desirable results may be secured byproviding the required metallic contact elements of the terminal mounting with a coating of ing on the extreme end of the resistance element. This thin sprayed coating may be particularly desirable in establishing a4 satisfactory initial electrical engagement betweent-he parts and in quickly establishing the desired normal operating condition of the contacting parts.'

The heating chamber described herein as a furnace may be any of the ordinary types of furnaces known in the art, such as melting furnaces for metals, glass and other materials, or strictly heat treating furnaces,of the open, muile or other types, for treating fully or partially manufactured articles, orfurnaces orchambers for maintaining melted or other materials at a particular high temperature. And the heating elements may well be mounted in any position other than the horizontal lposition shown.,

Resistance heating elements of the character described are capable of producing and maintainin themselves, during a commercially satis actory like, under furnace teme.y vperatures upwards of 2,400 Fahr., and'even with the terminal pieces and yielding mount'-l ings described herein. Through the use of a resistance heating element and terminal mountings for supporting the heating element in operative position in the furnace chamber and electrically connecting the element in circuit, as described herein, the heating elements may be maint-ained out of direct contact with any portion of the furnace wall andthe contact points may be maintained at sufficiently reduced temperatures to insurev satisfactory operation, even though the furnace temperature may be suiiicient to destroy the metals used for the terminal mountings and supports. And with the form of terminal mounting described, the heating elements and terminal pieces may readily be removed and replaced through the furnace Wall with little A delay or less of production of the furnace, and where a sufficient number of bars are installed in the furnace, Without shutting down the furnace at all.

By yielding or resilient in connection with the mechanicaljsupport of the heating element or its electrical engagement by aterminal member, it is intendedto convey the idea that there is, in addition to the exertion of required pressure against or on the heating element, capability of the terminal or mounting parts of automatically yielding or responding, as for the purpose of permitting any expansion or adjustment of the heating element or associated parts incident to operating conditions. And by self-sustaining, it is intended to convey the idea that the heating element is of Isuch unitary and rigid construction that it is self-supporting as for instance, it will maintain lor sustain itself when supported -only at its ends.

It should be understood that the invention set forth herein is not limited to the specific details of construction vand operation described; but it is desired that the claims cover the ordinary and obvious modifications -that may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. In combination a furnace chamber having its wall recessed,

' a self-sustaining electrical resistance heating a. furnace chamberhaving its wall recessed,;

a unitary self sustaining electrical resistance heating element inthe form of a heat-hardened composition product having integral. terminal portions thereof of increased conductivity lone of which extends into' a recess provided with through in an electrical furnace,

" in said chamber land in the furnace wall, and lmeans for yielding- 'ly supporting said resistance element in operative position Within said furnace and in electrical connection with a line circuit, said means comprising a yieldable conductive terminal element, and an .intermediate barshaped terminal element disposed in said re-\ cess in the furnace Wall and interposed between said yieldable terminal and the conductive end of said heating element, saidintermediate element being of material more highly heat-resistant than said terminal element and provided with a recess at its inner end Within which the conductive terminal of said heating element -is yieldingly held in electri- .caland mechanical engagement.

3.` In combination in an electrical furnace, a furnace chamber comprising spacedv walls apertures, a unitary self-sustaining-electrical resistance heating element disposed within said furnace and having integral terminal portions thereof extending into the and terminal mountings forsaid heating element including yieldable current carrying elements supported outside of said furnace wall and exerting pressure on the ends of the terminal portions of said leating element in the direction of its longitul inal axis, said mountings being operative to yieldingly maintain said heating element in operative position substantially said furnace chamber.

4. In combination a furnace cham r comprising opposed walls provided with through apertures, a self-sustaining, rod-shaped electrical resistance heatapertures in said spaced Walls, l

free of the walls of Y in an electrical furnace,

ing element of a substantially non-metallic I I character and having terminal portions thereof of increased conductivity extending into apertures in said walls, and means for .yield-v ingly supporting said heating element 1n operative position substantially wholly through pressure exerted in the direction of the longitudinal axis of said heating element, said means comprisingv metallicterminal pieces having theirinner ends in said apertures, and

a resilient conductive element supported out- -side one of said tion in contact pieces. 5. In combination in an electrical furnace, a furnace chamber comprising opposed walls provided with alined apertures, a self-sus*- taining, electrical resistance heating element l having its ends projecting into said apertures, and means for yieldingly supporting "said resistance element in operative position and in electrical connection with asupply circuit, said means comprisinglexible and resilient conductive elements supported outside of said furnace walls, and intermediate conductive elements within said apertures' and having portions of different heat-resistant qualities with the more highly apertures and havmg -a porwithA one 'of said terbminal heat-resistant portions in electrical and mechanical engagement `with the terminals of said resistance elements.'

6. In combination in an electrical furnace, a furnace chambercomprising side walls provided with a lined apertures, the walls of. said apertures being counterbored at the `ment within said furnace and'having termiouter end thereof and being outwardly flared at the inner end thereof, a refractoy tube disposed in the counterbored portion of said walls, a self-sustaining, electrical resistance heating element of rod-shape and of su'bstantially the same cross-sectional area throughout, said heating element having terminal portions of increased conductivity extending into said refractory tube, and means for yieldingly support-ing said heating element in operative position within said furnace, said means comprising yieldable ter- .minal elements supported in position outside nal portions extending into said apertures,

` and means for yieldingly supporting said resistance element in operatlve position in said furnace and in electrical connection With a line circuit, said means comprising a terminal supported outside of said -furnace wall, and an intermediate electrically conductive and heat-resistant element containing a substantial amount of-chromium interposed between the end of said resistance element and said terminal, said terminal having associated therewith meansfor yieldingly supporting said resistance element and said intermediate element in operative position and connected to a line circuit wholly through butt-end pressure exerted on the parts in the direction of the axis of the heating element. l

8. In combination in an electrical furnace, a furnace chamber having side walls provided with alined through apertures, a selfsustaining electrical resistance heating element. of a substantially non-metallic character disposed in said furnace chamber and having terminal portions of increased, con ductivity extending intoV apertures in the furnace walls, a terminal casing on the outl sideof the furnace wall and aperturedin alinement with the aperture in the furnace wall,` -a yieldable conductive' terminal supported within saidterminal casing, an intermediateconductive and heat-resistant Velement interposed between the terminal portion of said resistance elementand said terminal, said terminal being yieldingly urged in the direction of the longitudinal axis of said re-` sistance element and operative to mechanicallyv and electrically maintain said resistance element in operative position through buttend vengagement between the terminal, the intermediate element and the resistance element. l y V 9. f In combinationinv an electrical furnace, a furnace chamber having side Walls provided with alined through apertures having 'portions of polygonal cross-sectional outline,

a refractory tube disposed within` a portion of an aperture of polygonal cross-sectional outline in said furnace wall, said refractory tube being of substantially cylindrical form and fitting loosely within said polygonal Yaperf ture, a self-sustaining heating element of a non-metallic character disposed in said furnace and having-terminal portions ofincreased conductivity, a terminal casing on the outside of the furnace wall vand capertured in alinement with the aperture in the furnace wall, said refractory tube extending outwardly beyond said furnace Wall and into the said term- 1 inal box, and means for mounting and maintaining'said heating element in mechanically and electrically operative position through yielding butt-end engagement with said heatlng element.

10. In an electrical furnace, a furnace chamberhaving apertured walls, a self-sus taining resistance heating element having Va heat-producing body portion within said furnace chamber and a terminal'portion of increased conductivitydisposed within an aperture in a wall of said chamber, a refractory tube within said aperture and spaced at points from 'the wallsof said aperture and surrounding said terminal portion of the heating element, and means for supporting said heating element in operative position and connecting the same to a supply circuit, said means comprising a terminal piece of heat-resistance conductive metal having its inner portion within said refractory tube, and means for yieldingly urging said terminal piece into butt-end supporting and electrical engagement with said terminal portion of the aperture in a wall of said chamber, a refractoryytube within said aperture and spaced at points from the wallsof said aperture and surrounding said terminal portion of the hea-tingelement, and means for supporting said heating element in operative position and connecting the same to a supply circuit,

s'aid means comprising a terminal piece of vheat-resistant,conductive metal having its inner portion within said refracftbry tube,'and

an inner tubular wall surrounding and closely adjacent said refractory tube.

12. In an' electrical furnace, a furnace chamber having apertured walls, a self-sustaining resistance heating element having a heat-producing body portion within said furnace chamber and a terminal portion of increased conductivity disposed Within an aperture in a wall of said chamber, a refractory tube within saidaperture and spaced at points from the Walls of said aperture and surrounding' said terminal portion of the heating element, and means for supporting said heating element in operative position and connecting the same to a supply circuit, said means comprising a terminal ,piece of heat-resistant conductive metal having its inner end recessed and disposed within said refractory tube, and means for yieldingly maintaining said terminal piece in forcible engagement with the end of said terminal portion in the recess of said terminal piece, and a cooling jacket carried by the wall of the furnace and having an inner tubular Wall surrounding and closely adjacent said refractory tube.

13. In anelectrical furnace, a chamber having a wall including an element of refractory material provided with a throughk aperture having an enlargement atthe point where'it opens into the furnace chamber, a

unitary self-sustaining resistance heating' element disposed Within said furnacecham ber and having an integral terminal portion thereof extending into the aperture of vsaid refractory element beyond the enlargement of said aperture, and a conductive terminal element within said'aperture maintained in operative engagement with the end of said heatin element.

14. n an electrical furnace in combination,

l an enclosed chamber, apertures in the walls of the chamber, silicon carbide resistor rods which may be inserted through said apertures and which extend -across the chamber into the apertures,-metallic terminal elements in said apertures to mechanically support said resistorQ elements by butt-end engagement and to conductthe electric current outside of the walls of the chamber, and resilient terminal members having cup-shaped portions which support both the terminal 'elementsand the resistor elements and conduct the electric current,'said resilient members being so mounted'on the voutside of the furnace that by loosening a single bolt eaclimay ofthe resistor element and-terminal element.

be rotated to permit insertion or withdrawal 15. In an electric furnace, an enclosed chamber having apertures through which 1a insertion butt-end engagement at points within the apertures but adjacent the openings of the aperturesand t0 the chamber, said apertures 73' being flared outwardly toward the interior of the muilie to provide for freer dissipation 0f the heat developed at the junction of the resistor element and the terminal elements.

16. In an electric furnace using rigid heat- '75 i ing elements, a wall element adapted for the and support of a heating element and its terminal connection, said Wall element comprising a refractory block having an aperture therethrough and a refractory S0 tube loosely supported in said aperture and extending only partially through the said aperture, said tube being of larger internal diameter than said heating element and its terminal contact piece.

17. In an electric furnace, a rigidl self-supporting resistor, a furnace wall including` an y element adapted for the insertion and support of said resistor, said furnace wall element comprising a refractory block having an 90, n

opening therethrough and a refractory tube; loosely mounted in said aperture, said tube being of larger diameter than the resistor and its terminal support, and a terminal lmember extendinh into the the end o the resistor within the said tube. v18. In an electric furnace, a heating chamber, a rigid resistor element'extending across said chamber and lsupported from its ends," and a refractory block in having an aperture extending therethrough, a refractory tube inserted wittliin the said aperture, and a terminal member extending only partially through the said aperture and engaging the end of the resistor within the 105 said aperture.

19. The furnace wall described in claim 18 in which the aperture in the refractory block is of larger diameter adjacent the heating chamber than at points in'said aperture a no little further removed from the heating chamber. v v Y 20. In an electric furnace wall, a support for a resistor rod and for a terminal connector thereof, said Support comprising a' remi fractory block to be inserted in a furnace wall, -which block contains a passageway therethrough v of sufficient diameter to permit passage'of a. resistor rod, the end of the` passageway adjacent the'` hotter side of ythel furnace wall being of greater diameter than at points in the passageway a little further removed from the hotter side of the wall.

21. The electric lfurnace wall described in claim 20 in which the end of the ,refractory 1:5

block `remote from -said enlarged aperture abuts a water-cooled chamber. i

22. Inj an electric furnace wall, a support for a resistor rod and for a terininal connector thereof, said support ,comprisingl a rei .u

said tube'and engaging 95 one of said -walls v 12 4 A l 113,4aoV

fractory member surrounding the resistor and connector at their point ofcontact, said member being readily replaceable in the furnace wall.

23./In an electric furnace wall, a support fora resistor rod and for a terminal connector thereof, said support comprising a refractory block and a. refractory sleeve adjacent said rod and connector, the block and the sleeve forming a slip fit therearound, the sleeve beiug slip t in said block and said block having a stop therein-tov prevent the sleeve from slipping vinto the furnace.

24. The Wall element described in claim- 16, in which the refractory tube is of the same Y internal diameter as a portion of the aperv ture in the block immediately adjacent the end of the tube. 1 t

25. In an electric furnace wall, a refractory block having an aperture therethrough, the said aperture having a flared portion, a middle portion of substantially constant cross section" along its length, and a third portion also of 'substantially constant cross section and of larger cross section than the said middle portion, the said third portion of the aperture being adapted to receive'a refractory tube of larger external diameter than the diameter of the said middle port-ion of the aperture.

Q6. In an electric furnace,' a refractoryv block having an aperture therethrough for the reception of an end of a rigid resistor, a portion of the said aperture being of Substantially uniform cross section along its length, a second portion also of substantially uniform cross section alon its length and of larger diameter than the rst mentioned portion, and a non-conducting refractory tubewvithin the said second portion of the aperture and terminating Within the aperture in the said block. .1)

In testimony whereof I aix my siV ature.

" HAROLD N. S W.