US1555401A - Electric furnace - Google Patents

Description

Sepe 29, 1925 LSSSAQL c. A. CADWELL y ELECTRIC FURNACB Filed Nw. e, 1922 2 sheets-sheet 2 INVENTOR. Carfs CacZwe/ A TTORNEYS Patented Sept. 29, 1925.

UNITED. STATES PATENT OFFlCE.

CHARLES L CASDWELL, F CLEVELAND, OEIS?, ASSIGNO '10 THE ELECTRIC RAILWAY IMPROVEMENT COMPANY, 0F CLEVELAND, OHIC, A. CORFORATICN 0F 01H10.

v Application led November 8, 1922. Serial, No. 599,641.

To all whom i may concer/n:

Be itknown that l, CHARLES A. CADWELL, a citizen of the United States, and a resident of Cleveland, county of Cuyahoga, and State of Ohio, have invented a new' and useful Improvement in Electric Furnaces, of which the following is a specification, the principle of the invention being `herein explained and the best mode in which I have contemplated applying that-principle, so as to distinguish lit from other inventions.

The present improvements relate more particularly to an electric furnace of the oven type wherein a resistor -of granular material is employed, in conjunction with a plurality of electrodes so disposed relatively to said resistor that arcs are formed therebetween with resultant additional heating effect.

Electric ovens for ordinary purposes are heated by passing an electric current through metallic resistance paths, such as cast iron grids or various kinds of resistance wire. Such metallic resistance material constitutes in itself substantially all of the electrical equipment needed for any design of oven within the temperature range of such material, no auxiliar apparatus being required for control. owever, the maximum temperature of such an oven cannot be greater than that which may be derived by radiation from the metallic resistor at a safe Working temperature for the latter; although the maximum temperature thus derived' canvbe very nearly equal to such limiting temperature of the resistor, this being made possible by the uniformity of tem-- perature of every part of the 4heating element and the easy distribution of the ele-` ment itself.

Wherei-n order -to provide a higher temerature than can be obtained in' an oven lieated by such a metallic resistor, an electric arc or a granular resistor is employed, relatively elaborate and costly electrical equipment has heretofore been 'necessary for the operation and control ofthe furnace. Especially does such a'furnace lack the uniform distribution of heat V,energy characteristic of the metallic resistor'ovens,"being dependent rather upon radiation from sources of extremely high heat intensity. such an arc of large currentcapacity ort e resistance of a Y`large resistor body,y 1n' other words, where such a heating element is used, itis necessary to transform electric current from the crdinary transmission lines by means of massive transformers and conductors into current of .very large amperage and lower voltage. Such an installation is necessarily costlyin litself and requires costly control appah ratus.

Une object of the present invention, accordingly, is to provide an oven or furnace wherein the temperature obtainable may far exceed the safe limit for metallic resistor ovens and yet `in which it is possible to realize the simplicity of construction, ease of control and small cost of the latter. A further object is to render it possible to utilize current taken directly from ordinary *transmission lines without any transformation Whatever and with no more control apparatus than is used in the metallic resistor type of oven.

he need for such an oven has long been felt for purposes that require not only a higher temperature than that obtainable from the aforesaidmetallic resistor type of oven, but also require a more accurate con-y trol of the rate and uniformity of heating and of 'the gases in the heating chamber,

than can be obtained from ordinary fuel fired furnaces.

For example, in the firing of fine pottery, a slow drying heat is required at the start and at' all times the Ware must be protected against sudden changes of temperature which may occur in a fuel fired, furnace.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the means hereinafter fully desc ribedand particularly pointed out in the i claims, the annexed drawings and the following description setting forth in detail certain mechanism embodying the invention, such disclosed means constitu-ting, however, but one of various mechanical forms in which the principle of the invention may be used.

Fig. 1 is a central vertical section of a furnace embodying my present improvements; Fig. 2 is a top plan View ofthe furnace proper with the cover removed and` other accessory parts `sectioned on the plane indicated by the line 2-2, Fig. 1;"Fig. 3 is a transverse horizontal section of such furof a regular polygon in cross-section.

nace, the plane of the section being indicated by the line 3-3, Fig. 1; Fig. l is partly a plan view and partly a transverse horizontal section of certain auxiliary parts whereby the electrodes are adjustablysupported in the furnace, the plane of such section being indicated by the line 4-4, Fig. 1; Fig. 5 is a more or less diagrammatic representation of the wiring connections to the several electrodes; Fig. 6 is a sectional view oit a detail of the apparatus accessory te the furnace proper, the section being taken on the same plane as is Fig. l but on a larger scale; and' Fig. 7 is a perspective view ot another detail ot-such apparatus.

The oven or furnace chamber l, in the illustrative form shown in the drawings`is primarily designed for tiring pottery or t'or heating other' articles of va similar character and requiring similar treatment. Such chamber accordingly conveniently takes the form ot an approximately circular well sunl; practically Hush with the surface ot the surrounding Hoor. l A refractory wall 2 oit lire-brick or like material, whiclr may Vbe backed with heat insulatingv material,

forms the outer confines of the chamber il, while an inner cylinder 3 forms the lateral wall of the oven chamber proper.l Instead ot' the well being circular and such wall 3 of cylindrical form, both may take the form Such inner wall 3 is preferably of carborundum or ot equivalentrefractory material having a high heat conductivity and an electrical resistivity that classes it as no more than a secondary conductor. The purpose of this wall is that of a heat ditl'using and distributing medium, as well as that of a container for an oven product that requires a specified atmosphere; and where such oven product `is a melted metal, such inner wall .may take the form of a Crucible, i. e., the cylinder will be closed at the bottom and so rendered capable of being removed with the charge.

In any case'such inner chamber wall 3 rests on a layer 4 of granular carbon or equivalent material that forms the' floor of the well," and a supplemental layer 5 of the same or similar material is placed' in `the bottom oit the annular space between walls 2 and 3. Embedded in such layer 4 is a series of resistor elements 6 (best shown in Figs. l and 3), whichpreferably consist oit short pieces of cylindrical carbon rod spaced at short `intervals and laid transversely of such layer, i. e., in a general radial direction with vrespect to lthe center The general con' of vthe furnace chamber. struction of the resistor forms the subjectmatter of my co-pendinfrcapplication tiled April e9, 1920, serial o. 377,430, where such construction is broadly claimed.

Within the annular resistor space between walls 2 and 3 are suspended a number of carbon electrodes 7 at regular intervals. In' the case of a chamber having a polygonal cross-section, such electrodes will be located at the spices of the polygon and on account of the general use ot' -phase electric current, the number of such electrodes will usually be three for the smaller sizes of oven and some multiple of three for the larger sizes observing only that any electrode on phase l, for example, should be adjacent to phase 2 on one side and phase 3 on the other. Accordingly current flowing through adjacent electrodes and the portion of the resistor element consisting of the layer 5 and embedded carbon rods 6 lying between the lower ends of such electrodes, will encounter the resistance of suchl element and also that of two arcs. Aside from adding to the resistance ot the oven, these arcs also furnish a basis of control from an automatic variation of length, as will be presently described.

The voltage ot the power line determines the length of the portion of the resistor element between adjacent electrodes and hence determines the number of the latter that can be used in a given sized unit. As a means for increasing the length of the resistor element and Atherefore of the number of electrodes, without increasing the diameter of the annular resistor chamber, I may lace beneath each electrode, as shown in Figs. 1 and 3,' a cylindrical tile 8 of carborundum or equivalent'heat resistingl material and filled with granular carboni), such tile with its. Iilling resting upon the resistor element below and being placedwith its axis coincident with that of the electrode above. In this case the electrode will are to the top of such cylindrical tile into the granular filling 9 and the radiating surface of the resistor element is thereby not only increased, but better heat distribution is secured due to the vertical disposition of such added portion of the resistor.

Where the inner wall 3 of the oven is designed to remain permanently in place, the annular resistor space or chamber between said wall and outer wall 2 will be closed at its upper end by blocks 10 of refractory material, the inner edges of'which project a short distance beyond such inner wall so as' to leave an opening through which access may be had to the interior of the oven, as shown in Fig. 2. This opening is then in turn adapted to be closed by means of a cover 1'1, of similar refractory material, that may be lifted or otherwise removed when access to the oven isl desired, `W here the inner wall 3 is in the form of a crucible, which requires to be lifted out of the furnace, the blocks 10 will, bf course, have to .llO

be supported with their inner edges clear of the upper end of such wall. It may also l be found desirablev to provide a second orv false bottom (not shown) within said] wall 3 which may be raised and lowered withl a charge, without disturbing the. disposalof 5 the apparatus located over the oven' from which the electrodes 7 are suspended.

Certain of the blocks are provided with circular openings 12- fitted with short' upwardly extending iron tubes 13 through 10 y which the electrodes 7 are freely movable in a vertical direction, perforated ,plates 14 of asbestos or the'like, fitting more tightly about the electrodes, servingto close the upper ends or such .tubes 13..

The apparatus or mechanism from which the electrodes are thus suspended comprises a frame in the form of an open cage` 15 `which serves at the same time as a base 'for the distribution of current to said electrodes and as anountingpor the control device with which each electrode is provided. Said 'cage is itself suspended from a point overhead so aste -be vertically adjustable as a whole, a convenient n'ieansL for such i support andadjustment comprising aV cable 16, onev end of which passes over a pulley 17 and is attached'to said cage, while the other end is connected by means of a turn-l buclxle 18, or'like device, to a fixed point of A.30' support 19. Bly-the foregoing-means, the

cage with the electrodes suspended therefrom may be raised orlowered `so as to accurately vary the ar'c length of the electrodes as a unit.v The current -for theelectrodes is received at the upper end 'of the cage,` the three incoming conductors 2() where the current is B-phase, as hereinbefore assumed, be-

' ing cornlected to binding posts '21' corresponding in number tothe number of electrodes, as shown in Fig. 5. From the distributing point at the top of the cage pro-` vided by such binding posts, lengths /of bare Hlexible conductors 22 -of nichrorne, or otherv non-corrosive or non-oxidizing metal, ca-

v 4 5 pable of operating without injury at .a red eat, are stretched vertically. to correspondving posts-23 at 4the lower end of the cage,

, a suitable length -or such .conductors being l three feet in the case" of a furnace such as illustrated. It will be understood, of course, that the binding posts 21 and 23 are suitably insulated from the cage so that -the current 7may pass through each such conductor 22 directly to the corresponding ,electrode through a flexible copper conductor 24 extending from such last-mentioned binding posts to the electrode holder 2 5. Said holders 25 are vprovided with upwardly extending rods or stems 26 that are received and adjustably held in tubular members 27, orr equivalent clamping devices, and the'latter are in turn supported from the cagel by means of cords 28 that pass over pulleys 29 mounted in said cage and that have suitable 55 counterweghts 3Q attached at their inner ends. It will be understood that the holders 25 are, of course, insulated from the supporting means thus provided and it should be further explained that each counterweight 30 slightly overbalances the corresponding electrode and other'parts attached to the outer end of its cord 28. The resultant tendency of v'the weight to raise the electrode is,

however, restrained by a horizontall extending cord 31,the inner end of whichris attached, through the medium of an vinsulator 32, to an adjacent point on the corresponding nichrome conductor 22, `while the outer end passes around and is attached tothe periphery of a pulley 33, which pulley is fixed to the corresponding pulley 29 so that the two pulleys must always rotate together. As clearly shown in F ig. 1, the direction in which each cord 31 thus passes around its corresponding pulley 83 is such as topull on the conductor 22, to which .said cord is attached at its inner end, yas on a bow string. The lengthening or shortening of `such conductor 22 will accordingly cause a rotation in one direction or the other of the attached pulleys 33 and 29, with the result that the vertical position of the corresponding elect-rode will be changed. For example, a current flow through any con-' ductor 22, which increases c the temperature of such conductor, will, by the same token,

increase its length and so allow the counterweight attached to the corresponding electrode to raise the latter. As a result the Iare between such electrode and the resistor ing the ratio of the diameters of the pulleys 29and 33, as will be readily understood.

' In operating the oven the electrodes are first brought intocontact ,withv the resistor element by lowering the cage as a whole and by adjustment of the clamp devices, including rod 26 and tube 27,` whereby the individual electrodes are adjustably supported. Thereupon the current is switched on and the electrodes, due to the lengthenin of conductors 22, will immediately rise and start the arcs, following which the arcsare automatically maintained `at -the proper length by .the vaction of said conductors, as

has just been explained. f It' when thearcs are established and the oven is running steadily it is desired to increase the lowof current and thus increase the rate yof heating,

it is necessary only to slightly lower the cage and thus the electrodes as a whole; While to retard the rate of heating, the cage and electrodes will be similarly raised.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being madeas regards the mechanism herein disclosed, provided the means stated by any of the following claims Ior the equivalent of such stated means be employedc I therefore particularly point out and. distinctly claim as my invention l. In an electric furnace, the combination. of an approximately circular chamber; an annular resistor at one cud ofsaid chamber; and a series of electrodes extending into said chamber from the opposite end and approximately parallel with the axis thereof to viithin arcing range of said resistor,

2. In an electric furnace, the combination of an approximately circular chamber; an annular resistor at one end of said chainber; and a series of electrodes extending into said chamber from the opposite end and approximately parallel with the yaxis thereof to Within arcing range of said resistor7 said resistor being constructed so as to` provide a path of least resistance for the current in passing from one of saidelectrodes to the other in a plane spaced from the adjacent end of said chamben 3. In an electric furnace, the combination of an approximately circular chamber; an annular resistor at one end of said chamber; and a series of electrodes extending into said chamber from the opposite end thereof to Within arcing range of said resistor, said resistor yconsisting of granular carbon and members of greater electrical conductivity embedded therein.

4L. In an electric furnace,y the combination of anapproximately circular chamber; an annular resistor at one end of said chamber; and a series of electrodes extending into said chamber from the opposite end thereof to within arcing range of said resistor, said resister consisting of` granular carbon and a plurality of carbonrods embedded therein, and disposed in a radial direction with respect to the axis of said chamber. ,y

5. In an electric furnace, the combination of an approximately circular chamber; an annular resistor at one end of said chamber; and a series of electrodesextending into said chamber from the opposite end thereof to Within arcing range of said resistor, said resister including elements projecting therefrom in line with said electrodes; respec tively.

6. In an electric furnace, the combination 0f an approximately circular chamber; a refractory Wall within said chamber spaced from the outer Wall thereof; a resistor at one end of said chamber disposed in the annular space between such Walls; and a series of electrodes extendin t into such space from the opposite end of geld chamber to 'Within arcing range of said resistor.

L lin any electric furnace, the combination of an approximately circular chamber; a refractory Wall Within said chamber spaced from the outer Wall thereof:I resistor at one end of said chamber disposed, in the an nular space between such walls; and a series of electrodes en Lending into such space from the opposite end of said chamber to Within arcing range of said resistor, said resistor being constructed so as to provide a path of least resistance for the current in passing from one of said electrodes to the other yin a. plane spaced from the adjacent end 'of said chamber.

8. In an electric furnace, the combination of an approximately circular chamber; a refractory Wall Within said chamber spaced from the outer Wall thereof; a resistor at one end of said chamber disposed in the annular space between such Walls; and a series of electrodes extending into such space from the opposite end of said chamber 'to Within arcing range of said resistor, said resistor including elements projecting ther from in line with said electrodes, respectively.

9. In an electric furnace, the combination of a vertically disposed, approximately circular chamber; a refractory wall Within said chamber spaced from the outer Wall thereof; a resistor at the bottom of said chamber disposed in the annular space between such walls; and a series of electrodes approximately parallel with the axis of said chamber depending .vertically from above into such space to within arcingr range of said resistor.

l0. In an electric furnace, the combination of a vertically disposed; approximately circular chamber; a refractory Wall Within said. chamber spaced from the outer Wall thereof; a resistor at the bottom of said chamber disposed in the annular space between such Walls; a series of electrodes depending vertically from above into such space to Within arcingrange of said resistor; and means affected by the flow of current to said electrodes adapted automati cally to raise and lower the same individuallyt ll. In an electric furnace, the combination of a vertically disposed., approximately circular chamber; a refractory wall within said chamber spaced .from the outer Wall thereof; -a resistor at the bottom of said chamber disposed in the annular space between such Walls; a series of electrodes depending ,vertically from above into such space to Within arcing range of said resister; means adapted to raise and lower said electrodes as a unit; and i'neans affected ltl l(it) by the flow cf current to said electrodes adapted automatically to' raise and lower the same individually..

l2. ln an electric -furnace, the combination of a vertically disposed, approximately circular chamber;a refractory wall within said chamber spaced from the outer wall thereof; a resistor at the bottom of said fchamber disposed in the annular space between suoli walls; a series of electrodes decircular chamber; a refractory wall within.'

said chamber spaced from the outer wall thereof; a resistor at the bottom of said chamber disposed in the annular space between such walls; a series of electrodes depending vertically from above into such space to within arcing range of said resistor; means adapted to raise and lower said electrodes as a unit; manually adjustable means for raising andlowering indi vidual electrodes; and means affected by the flow of current to said electrodes adapted automatically to raise and lower the same individually.

14. 1in an electric furnace, the combination of a vertically disposed, approximately circular chamber; a refractory wall within said chamber spaced from the outer wall thereof; a resistor, at the bottom of said chamber disposed in the annular space between such walls; a series of electrodes depending vertically from above 4 into. such space to Within arcingrange of said resistor; conductors for supplying current to said electrodes, respectively, said conductors including sections secured to points a predetermined distance apart; and means adapted automatically to raiseand lower said electrodes individually, said means being affected by variations in length of the corresponding conductor sections due to changes in current flow therethrough.

15. in an electric furnace, the combination of a vertically disposed, approximately ci r cular chamber; a refractory wall within said chamber spaced from the outer wall thereof; a resistor at the bottom of said chamber disposed in the annular space between such walls; a series of electrodes depending vertical-ly from above into such space to within arcing range of said resistor; conductors for supplying current to said' electrodes, respective y, said conductors including sections secured to points a predetermined dista ce aoart; means connected with indivi ual electrodes tending to raise the same;

and connections between said means and the corresponding conductor sections, whereby vvariations inlengthof the latter serve to control 'said means.

16. ln an electric furnace, the combination of a vertically disposed, approximately circular chamber; a refractory wall within said chamber spaced from the outer wall thereof; a resistor at the bottom of said chamber disposed in the annular space lbe-v tween such walls; a series of electrodes depending vertically fom above' .into i such space to within arcing range of said resistor; conductors for supplying current to said electrodes, respectively, said conductors including sections secured to points a predetermined distance apart; a pulley adjacent each such conductor section; a cable connected with the corresponding electrode and passing` over such pulley, said cable being counter-weighted so as to tend t/o raise said electrode;-and a cord connecting each p'ulley with the adjacent conductor section whereby theshortening of the latter tends to lower saidelectrode.

17. In an electric furnace, the combination of a vertically disposed, approximately circular chamber; a refractory wall within said chamber spaced from the outer wall thereof; a resistor at the bottom of said Sti chamber disposed in the annular space be tween such walls; a series of electrodes depending vertically from above into such space yto within arcing range of said resister; conductors for supplying current to said electrodes, respectively, said conducf tors including sections secured to points predetermined distance apart; a pulley' ad jacent each such conductor section; a cable adjustably connected with the correspcnding electrode and passing over such pulley, said cable bein counter-weighted so as to tend to raise said electrode; and a cord connecting each pulley with the adjacent conn ductor section whereby the shortening of the latter tends to lower said electrode.

18. In an electric' furnace, the5 combination of a vertically disposed, approximately circular chamber; a refracto wall within said chamber spaced from tie outer wall thereof; a resistor at the Abottom of said chamber disposed in the annular spaceA between such walls; a series of electrodes depending vertically vfrcc'ifi above into such spa/ce to within arcing range of said resistor; a vertically adjustable frame over said chamber; conductors for su plying current to said electrodes, respective said conductors including sections secured to points 'on said frame spaced a predetermined. distance apart; a ulley mounted in said frame adjacent eac such conductor section; a cable adjustably connected with the corresponding .electrode and passing i wei hted so as to tend to raise said electro e; and a cord connecting each pulley with the adjacent conductor section whereby the shortening of the latter tends to lower said electrode.

19. In an electric furnace of the character described, the combination with a resistor and a series of electrodes movable towards and away therefrom; of conductors for supplying current to said electrodes, respectively, said conductors including sections secured to points a predetermined distance apart; and means adapted automatically to move said electrodes individually, said means being affected by variations in len th of the corresponding conductor sections ue to changes in current iiow therethrough.

20. In an electric furnace of the character described, the combinationV with a resistor and a series of electrodes movable-towards and away therefrom; of conductors for supplying current to said electrodes, respectively, said conductors including sections secured to points a predetermined distance apart; means connected with individual electrodes tending to move the same away from said resistor; and connections between said means and the corresponding conductor sections, whereby variations in length of the latter serve to control said means. f

Signed by me this 4th day of November, '1922.

CHARLES A. CADWELL.

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