US1572893A - Electric furnace - Google Patents

Description

Feb, 16 11926., 1572,89?)

e. M. LQTTLE ELECTRI C FURNACE Filed Nov. 1, 1922 2 Sheets-Sheet 1 Fig.5.

WITNESSES:

INVENTOR W George M Linnea a v ,z m 1 45 ATTORNEY Feb. 16 1926. 1,572,893

G. M. LITTLE ELECTRI C FURNACE Filed Nov. 1, 1922 2 Sheets-Sheet 2 Fig.6. F g,

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INVENTOR Ge ch39 M. L. ittle ATTORNEY WITNESSES:

Patented Feb. l6, 1926.

UNITED STAES FATE GEORGE M. LITTLE, OF PITTSBURGH, FPENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA.

ELECTRIC FURNACE.

Application filed November 1, 1922. Serial No. 598,316.

To all whom it may concern:

Be "it known that I, GEORGE M. Lrrrnn, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Electric Furnaces, of which the following is a specification. Y

My invention relates to furnaces and, particularly, to electric-resistance furnaces.

One object of my invention is to provide an electric furnace havin a carbonaceous resistor which is enclosed in a substantially air-tight heating chamber.

Another object of my invention is to provide a refractory plate constituting a diahragm above the resistor and a layer of finely divided carbonaceous material located on the diaphragm to protect the plate and gated end block having provisions for maintaining them in axial alinement.

Carbonaceous resistors-have a negative temperature coefiicient of resistance and if a set of flat carbonaceous plates are in operative engagement over substantially their entire flat surface area and are supported directly by the furnace structure, that part of the plate immediately adjacent the support Will operate at a higher temperature than the rest of the plate owing to the pocketing of the heat by the supporting,

structure. This higher temperature results in a lowered resistance permitting a larger portion of current to'fiow'through this part of the platesthereby causing a still higher temperature at a part of the" resistor where it is not wanted and where it may be detrimental. Another object of my invention is to provide a built-up supported carbona ceous resistor so constructed that the largest percentage of heat generated therein is produced in a portion of the resistor relatively distant from the support.

In the drawings,

Figure 1 is a View, in vertical longitudinal section, of a part of an electrical-resistance furnace embodying my invention;

Fig. 2 is a view, in vertical lateral section, of a portion of an electrical furnace embodying my invention;

Fig. 3 is a fragmentary view, invertical lateral section, of an electric furnace embodying my invention and comprising a modified form of resistor;

Fig. 4 is a top plan View of the resistor illustrated in Fig. 3; l

Fig. 5 is a view, in vertical lateral section, of another modification of a resistor embodying my invention;

Fig. 6 is a top plan view of the resistor illustrated in Fig. 5;

Fig. 7 is a view, in vertical lateral section, of another modification of a resistor em bodying my invention; i I

Fig. 8 is a top plan view of the resistor illustrated in Fig. 7 i

Fig. 9 is a view, in vertical lateral section, of a still further modification of a resistor embodying my invention; and v Fig. 10 is a top plan view of the resistor illustrated in Fig. 9.

Referring more particularly to Figs. 1

and 2 of the drawings, a furnace structure,

designated generally by the numeral 11, embodies an outer lining 12 comprising side,

end and bottom walls of any suitable refractory heat-insulating bricks or blocks. An inner lining 13 may be provided and comprises a plurality of refractory hightemperature-resisting blocks or bricks, the

inner-lining walls being so spaced apart as to provide a furnace chamber 14 of any suitable or desired contour and dimensions.

Heretofore, in an electric-resistance furnaceoperating at a relatively high temperature, it has been customary to place the carbonaceous resistor directly in the furnace chamber and to either enclose it in a' substantially non-oxidizing container or to pro vide means, such as an inert gas, to prevent oxidation thereof. Another. means for pre venting oxidation, of the carbonaceous resister in furnaces havlngila work-rece v ng ep mnz o the weavec m e mpnaeshaped as to conform to; (e shape means for producing an accretive atmosphere or gas in the furnace chamber. It has also been found desirable in such furnaces to. support the carbonaceous resistor free of the furnace walls in order to protect them against the relatively high temperatures.

In the present embodiment of m inven-. tion, I divide the furnace chamber into two parts and place the carbonaceous resistor in, preferably, the lower part of the furnace chamber. A built-up heating element, disignated generally by the numeral inFigs. 1 and 2, comprises a )lurality of relatively thin, fiat, long, refractory carbonaceous plates 16 which are spaced apart by relatively short, thin, flat carbonaceous plates 17 alternating therewith, and located at the upper end of the long plates 16. The lower ends of the long carbonaceousvplates 16 extend to substantially the bottom of the furnace chamber 14 and may rest on a flat re fractory electrical-non-conducting plate 18.

A refractory, relatively elongated, ,car bonaceous end block '19; has its, inner end, operatively engaging one end of the built up heating element 15. 'At its outer'end, it is provided with an axial and-longitudinally-extending bore 21 which is adaptedto'receive the inner end of a relatively-"small metallic water-cooled terminal electrode 22.

,The electrode 22 com. rim 9, l ti g- ,thfim wall tubular member avin' its inneii'end so I bf'the bottom of the bore 21 inthe end block 19. The member 22 is provided with aninner,

V longitudinally-extending conduit .23 which,

27, one end of whic at its outer end, is secured to anend member 24 which has screw-threaded engagement with the outer end of the terminal electrode 22. Fluid inlet and outlet pipes 25 and 26 engage, respectively, the end member 24 and the conduit 23, and the tubular member 22 intermediate its" ends, to permit of circulating a cooling-fluid'through the tubular member 23 to within a short distance of theinner end of the terminal electrode 22 and then outwardly through the outlet pipe 26.

Resilient means for pressing the terminal electrode 22, the end block 19, and the plates 16 and 17, into close operative engagement with each other com uses a helical spring operatively engages the end member 24 and the other end of which is located in a socket member 28 having an insulating lining 29 therein. An adjusting screw 31, -provided with a hand wheel 32 at its outer end, engages the socket jmember 28 and permits of varying the pressure applied between the various members of the built-up resistor, the'end block and the terminal electrode.

A terminal lug 33 may be suitably secured against the terminal electrode 22 to permit of connecting one end of a supply circuit 1 enses thereto. If it is desired to employ only one heating-element, substantially as illustrated in Fig. 1 of the drawing, two end blocks 19 and terminal electrodes 22 may be employed therein located in axial alinement with each other and in opposite walls of the furnace. If it is desired to emplo two resistors, the terminal members hereinbefore described may be located in the same wall of the furnace in spaced-apart relation, and the rear ends of the built-u resistors may be electrieally connected by any suitable means, such as a carbonaceous plate which is pressed against the rear wall of the furnace by the action of the resilient compressing means hereinbefore described. The relatively deep axial bore 21 permits of locating a relatively large portion ofthe terminal electrode 22 therein whereby an alini-ng eifect of the electrode relatively to the end block 19 is obtained.

The water-cooling means hereinbefore described permits of operatin the inner end of the metal electrode and t e outer end of the end'block 19 at a'relatively low temperature but, if desired, 1 may provide means for still further reducing the oxidation of the outer end surface of the end block 19 by providing a well 34 solocated in the walls of the .furnace as to receive the outer end of the end block 19 and may place therein a mass 35 of finely dividedgranular carbonaceous material. It is, of course. understood that the end block 19 rojects through a suitable opening in the urnace wall, as does also the metal electrode 22 to permit of their having longitudinal movement relatively to the Wall of theflfurnace through which'they extend. This construction permits of air entering the opening, and flowing past or along the outer surface oflth metal electrode and the carbonaceous and block and, it the temperature of the carbonaceous.

If the plate 36 is of graphite, v

bonaceous material, such as coke or charcoal.

The upper surface of the mass 37 may be made substantially flush with the bottom of I a work-receiving opening 38-. It is, of course, apparent that the greatest oxidizing action of air entering the furnace chamber 39 Within which material to be heat-treated is placed; will occur close to the work-receiving opening 38, and the depth of the granular carbonaceous material 3? is ma the greatest immediately 'adjacentf the I introduced-to replace that-which has been destroyed by tha -oxidizing action.

- If 'carborundum,-' alundumor fireclay plates are employed as diaphragms, they may be placedin a substantially horizontal position and no protecting layer of carbona'ceous material is necessary.

Figs. 1 and 2 of th'efdrawings, in which the a substantially horizontal direction and 'are a separated by alternating plates '17 of relatively small area of cross-section located intermediate the ends of the long plates. Theouter ends of'the'large plates 16 may be supported on.suitable shoulder portions 41'- constituted by integral portions of the furnace walls-which are so built as to provide these shoulder portions. Substantially the same results in foperatioriare obtained from .a built-up resisto'r'in which thejeonnecting plates 17 are located intermediate the ends of the relatively ilar eor. wing plates 16,.

as was 'hereinb'efore escribed in connection with the modification illustrated in Figs. 1

and 2 of thegdrawings.

F igs. 5*aiid- 6 illustrate, a still farther modifie'atiomof a built-up resistor in which a relatively small number of wing plates '16 are employed and ajrelatively large number of smaller plates 17 which are, in turn, spaced apart by relatively narrow carbonaceous bars The outer ends of the wing plates 17 may be supported on integral shoulder portions 41, as hereinbefore described in connection with the modification illustrated'in Figs. 3 and 4. If the furnace is-to be operated at amelatively high tem-, perature, I may employ a plurality of bricks or blocks 43' to protect the side walls of the furnace chamber, locating .them on integral shoulder-portions 44, also c oiistituted by the 'furnace wall: structure.

Figs. .7 and 8: illustrate another modification in which wing plates 16 only are employed and arelocated at substantially right angles relatively to each other, with their, upper ends operatively engagin each other andthe lower ends operative y engaging either the bottomor the side walls. of the furnace or both, as illustrated particularly inFig. 7. It may be noted that the current-carrying area of each of the plates is relatively small in proportion to the total area of the plate.

' Figs. 9 and 10 illustrate a still further modification in which wing plates 16 only are employed and are so located as tohave on y a portion of the flat surfaces of the opposite directions.

, plates plates adjacent one end thereof in close placed. The outer ends 0 the bars 16 may rest on refractory electrical-non conducting v blocks 47. A graphite diaphragm 36 may 'Figs. 3"and 4 illustrate a'modification of the resistor described in connection with bricks or blocks 48 located at the side of the furnace chamber. It is, of course, un-

10h aYiother refractory. 'electrical-non-conducting plate 46 maybe derstood that the resilient .compressing means described in connection with Figs. 1 and 2 is employed with all of these modifications.

provides a resistor for an electric-resistance furnace comprising a plurality of' wing plates which are electrically conducting but are so arranged as to conduct current through only a relatively small portion thereof, the outer end of the wing plates serving The device embodying my invention thus of. sealing the carbonaceous resistor eifectively against the oxidizing action of air entering the portion of the furnace chamber which receives the work or materialto be heat-treated.

The hereinbefore-described construction a relatively small metal water-cooled. electrode which fits into a carbonaceous or graphite terminal block results in obtaining an alining'eifect between the. two members which is of value in maintaining the alinemont of thebuilt-up resistor, the terminal block and the metallic electrode with the resilient compressing meansprovided to maintain all of these members in close operative engagement under the varying operating conditions of the furnace.

This application is closely related to my copending application's SerialNo. 598,317, filed November 1, 1922, and Serial N o. 598,- 318, filed Novemberl, 1922, both assigned to the Westinghouse Electric & Manufactub plurality of refractory members, an elongated refractory end block operat vely engaging said heating element and having a longitudinally-extending axial opening in its outer end, and a metallic terminal electrode operatively engaging said end block and extending into said axial opening.

2. In. an elect-ric furnace; in combination, a refractory heating element, an elongated refractory end block operatively engaging said heating element, and having a longitudinally-extending axial opening in its outer end, and a metallic terminal electrode operatively engaging said end block and extending into said axial opening.

3. In an electric furnace, in combination, a refractory heating element, an elongated refractory end block, of. relatively large cross-sectional area, operatively engaging one end of said heating element and having a longitudinally-extending axial openingjn its outer end, and a metallic terminal electrode, of relatively small cross-sectional area operatively engaging said end block and extending into said axial opening, whereby an axial alinement of said electrode and said end block and a relatively large area of contact therebetween is obtained.

l. In an electric furnace, in combination, a refractory heating'element, an elongated refractory end block operatively engaging said heating element, and having a longitudinally-extending axial opening in its outer end, a water-cooled metallic terminal electrode operatively engaging said terminal block and extending into said axial opening and resilient means for maintaining said electrode, end block and heating element in close operative engagement with each other.

5. In an electric furnace, in combination, a heating element comprising a plurality of refractory members having integral noncurrent-carrying and weight-supporting ex-' tensions.

6. In an electric furnace, in combination. a heating element comprising a plurality of relatively thin refractory plates,'each having one portion of relatively small area traversed by an electric current and another portion integral with said first portion for supporting the weight thereof.

7. In an electric furnace, in combination, a heating element comprising a plurality of relatively thin refractory plates each having integral non-current-carrying and weightsupporting extensions and resilient compressing means for maintaining said plates in close operative engagement with each other in said furnace.

8. In an electric furnace, in combination, a pluralityof walls surrounding a furnace chamber, a refractory carbonaceous heatingelement in said chamber, a refractory carbonaceous diaphragm in said chamber dividing the same into two compartments, and a layer of finely divided carbonaceous material-on said diaphragm for preventing access of air to said heating element.

9. In an electric furnace, in combination, a plurality of walls defining a furnace chamber, an opening in one of said walls adjacent the upper part of said chamber, a refractory carbonaceous heating element in the lower portion of said chamber, a refractory carbonaceous diaphragm in said chamber between said opening and said heating element, and a layer of comminuted carbonaceous material on said diaphragm, the thickness of said layer being a maximum adjacent said opening.

10. In an electric-resistance furnace, in combination, a furnace chamb'er having a work-receiving opening thereto, a refractory carbonaceous heating element in said chamber, a refractory diaphragm in said chamber between said work-receiving opening and said heating element, and a layer of heatconducting comminuted granular oxidizable material on said diaphragm, the thickness of said layer being in accordance with the distance from said work-receiving opening.

In testimony whereof, I have hereunto subscribed my name this 27th day of October, 1922.

GEORGE M. LITTLE.

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