US1521028A - Resistor for electric furnaces - Google Patents

Description

Deb. 30, 1924. 1,521,028

G. M. LITTLE RESISTOR FOB ELECTRIC FURNACES iled May 24,, 1921 INVENTOR MZM BY 1/777 M M/u Patented Dec. 30, 1924.

UNITED STATES PATENT OFFICE.

GEORGE m. LITTLE, OF PITTSBURGH, PENNSYLVANIA. ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

nnsrsron ron ELEICTRIC FURNACES.

Application filed May 24, 1921. Serial ms. 472,094.

'1 '0 all whom it may concern:

Be it known that I, Gnoaon M. LrrrLE, 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 Resistors for Electric Furnaces, of which the followingais a specification. a y invention relates to electric furnaces and particularly to electric-resistance furnaces and it has for its object to provide a combination electric-furnace resistor -comprising carbonaceous plates and granular carbonaceous material.

"In my co-pendin application, Serial N o. 454,776,filed Marc 23, 1921, I have disclosed a resistance type of furnace in which the resistor consists of a plurality of relatively thin carbonaceous plates which are resiliently pressed against each other. The resistance of such a resistor element-is rela: tively low, so that, in order to obtain the requiredheating 'efi'ect, it is necessary to pro? videa source of electric energy of relatively low voltage and of high vcurrent capacity. The energy loss in the contact terminals and in the leads between the terminals of the furnace and the transformer or the controlpanel are, therefore, relatively high.

In practicing my invention, I provide a resistor element comprising a plurality of carbonaceous plates which are maintained in spaced-apart relation by interposing between two adjacent plates a thin layer of granular carbonaceous material or a plurality of relatively small carbonaceous plates. The built-up resistor element described above is resiliently compressed by suitable means andmaintained in its operative position in the furnace chamber by the same, compressing means; I

In the single sheet of drawings: Figure 11s a view, in vertical cross-sec tion, of an electric-resistance furnace com-,

prising the device embodying my invention: 1 Fig. 2. IS a view, in vertical cross-section of an electric resistance furnace comprising a modification of the device embodying my .invention, and 7 Fig. 3 1s a view, in perspective, of one elesurface.

work 11, provided with suitablesupporting members 12. Outerwulls 13 comprise a plurality of bricks or blocks of any suitable heat-insulating material. Inner' walls 14 comprise a plurality of bricks or blocks of any suitable high-tcmperature-resisting' material. The inner walls are suitably spaced. apart to form a furnace chamber 15 of any suitable or desired contour and dimensions.

As this type of vfurnace is intendedto be employed .for heating --metallic objects, a suitable opening 16- is provided near the bottom of the furnace chamber through which the materials to be heated may be inserted andremoved. 1;

A resistor located in the chamber 15 comprises a p'luralityof carbonaceous plates 17.

In the modification illustratedin Figure 1, the adjacent plates 1-? are spaced apart a short distance by means of a layer of man- .lar carbon. To cause the gnmular car on to adhere to a plate, itis only necessary to paint one of the. flatsurfaces. of each plate with a thin layer of adhesive, such as deli trine, and sift a thin layer of granular-carbon. on this layer of adhesive. After a sufiicie'nt number of plates have been this repared, they may be stacked. toget er,

clamped, and then dried by; the apphcation of heat, after which the resistor. is ready to be placed in the furnace chamber.

In order to provide a proper'ter al for each end of the resistor, the graphite plate .18 is located at each end ofthe-resistor and is provided with a depression in its outer An electrode 19 oonsistin of-carbonaceous material is provided, the inner end of which is adapted to operatively em. gage the depression in the graphite member 18. The electrode19 may be substantially circular'in lateral cross-section and relative- 'ly elongated to extend outwardly through the wall of the furnace.

A water-cooled metallic. contact terminal 20 is mounted ontheouter end of the electrode 19, and is provided with a central air erture 21, substantially conical in form to fit No. 464,290, filed April 25, 1921. It may be on the tapering outer end of the electrode noted that the area of contact of a grain of 19. the granular carbonaceous material with the Resilient compressing means are provided plate 17 may be relatively very small, and, and comprise an adjustable screw 22 and a in some cases, may even form a point conhelical spring 23, one end of which is tact. If any soot is deposited around this pressed against the outer end of the contact grain of. material, the area of contact beterminal 20, an insulatin r member 24 being tween it' and the adjacent plate will be inplacedbetween the end 0 the spring 23 and creased to a very appreciable extent, thus, of

the contact terminal 20 to roperly insulat e course, decreasing the resistance of the rethe two members from eac otherQ It is to i'sistor element. be understood that the resilient compress- By making the area of the small plates 28 ing means, as illustrated, is schematic only relatively small, 'as compared to the area of and that any suitable or desired resilient the plate 17., the resistance of such a built-up compressin means may be employed.

An annu ar member 25, which may conor even greater han, that of the combined 'sist of asbestos, is placed around the contact plate and granular carbonaceous material,

terminal 20 to effectively insulate this terand the efi'ect of soot deposited around the.

minal from the small plates 28 is not as great as is the case furnace. when As the temperature of the electrode is used; ence, the resistance is not reduced relatively very high at itsinner end where as much as in the modification illustrated in it engages the graphite member 18 and may Fig. 1 be almost as hot in the walls 13 and 14,1 It may be noted that I have illustrated a provide means for preventing the oxidation single built-up resistor element so that the of this heated electrode by air which may two terminal electrodes are located on oppometallic framework of the resistor may be ade substantially equal to,

ranular carbonaceous material is leak past the contact terminal 20. This site walls of the furnace but this is not essen means comprises a well or hopper 26 in tial and I may use two parallel resistonelewhich is located a mass 27 of granularcar: merits, each one resiliently pressed against bonaceous material which may be tightly ne sidewall of the furnace, the two tar-- tamped in place around the electrode 19. minal electrodes being, therefore located in Further description of this part of the furone sidewall of. th'efurnace. nace is believed unnecessary, inasmuch as it an essential element of my invention, howconstitutes the subject of my co-pending ap ever, and in nowise affects the inventive plication Serial No. 472,093, filed May 24, idea. I

1921. It may be noted that the device embodying In the modification illustrated in 2, my invention provides a relatively simple This is not the means for separating the adjacent plates uil -up IeSiStOI w ic has g a 17 comprise a pluralityof plates 28 of carsistance than the resistor built up onl of bonaceous material of relatively small area. flat plates and that this resistor is relativelv' These plates may be caused to adhere to the inexpensive and easy to make. The higher flat surface of the plate 17 by substantially inherent resistance permits the use of a the same means as hercinbefore described in smaller current to obtain the same heating connection with the resistor illustrated in effect as is obtained with a built-up carbon- Fig. 1. The modified form of resistor illusp e resistor he etofore used. irated in Figs. 2 and 3 has an advantage over Various modifications may be made in the that illustrated in Fig- 1, in that the thickdevice embodying my invention without dencss of the means spacingapart the adjaparting from the s irit and scope thereof cent plates 17 are more uniform in thickness. and I desire that on y such limitations shall This is of advantage in preventing breakage be placed thereon as are imposed by the prior of the plates 17 when they are compressed art or are specifically set forth in the apby the resilient compressing means hereinpended claims. before described. I claim as my invention:

I have found that, while the resistance of the resistor illustrated in Fig. 1 is relatively a plurality of thin flat plates of refractory high at the beginning, it decreases a relamaterial, means comprising granular electively large amount in the first few days of trio-conducting material for electrically conits use and I attribute this result to the acnecting said plates-over. only a relatively tion of the sooty vapor which I use in fursmall portion of their area, said means servnaces of this type to protect the carbonaceous in also to maintainsaid plates in substan resistor against the oxidizing effect of air tia ly spaced-apart relation, and means for entering the opening 16. Means for promaintaining said resistor under substanducing such a sooty va por are described and tially constant compression.

claimed in my co-peud mg ipplication Serial 2. In an electric furnace, a plurality of 1. An electric furnace resistor comprising furnace walls enclosing a furnace chamber, their area and for spacing said successive a resistor in said chamber comprising a plates apart, and means for holding said plurality of thin flat plates of refractory resistor in said chamber free of said walls. electrical-conducting material, refractory In testimony whereof, I have hereunto 5 granular electrical-conducting means for subscribed my name this 18th day of May connecting the Hat surfaces of ad'acent 1921. plates over only a relatively small portion of GEORGE M. LITTLE'

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