US2491579A - Electric resistance furnace - Google Patents

Description

Dec. 20, 1949 POLAND 2,491,579

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Dec; 20, 1949 POLAND 2,491,579

ELECTRIC RESISTANCE FURNACE Original Filed May 20, 1944 6 Sheets-Sheet 2 R it &

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Dec. 20, 1949 F. F. POLAND 2,491,579

ELECTRIC RESISTANCE FURNACE Original Filed May 20, 1944 e Sheets-Sheet 3 F. F. POLAND 2,491,579

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Dec. 20, 1949 Original Filed May 2O,v 1944 Dec. 20, 1949 F. F. POLAND 2,491,579

ELECTRIC RESISTANCE FURNACE Original Filed May 20, 1944 v 6 Sheets-Sheet 5 I Invenior EanIQFPOZaW/d. Zgyaa7fllm 7M W a Dec; 20, 1949 F. POLAND ELECTRIC RESISTANCE FURNACE 6 Sheets-Sheet 6 Original Filed May 20, 1944 Patented Dec. 20, 1949 1,491,579 ELECTRIC ansrs'rmon Fortunes;

Frank F. Poland, Rome, N. Ysassignor to Revere Copper and Brass Incorporated, Rome, N. Y;, a

corporation of Maryland Original application May 1944, serial No;

OFFICE 536,580, now Patent No. 2,472,612, dated June 3 Claims.

My invention relates to electric furnaces, the present application being a division of my copending application Serial Number 536,580, filed May 20, 1944, now Patent 412,472,612 issued on June 7, 1949. r

The invention, which has among its objects the provision of an electric furnace which will be air tight and free from the deleterious effects of expansion of the furnace structure, will be best understood from the following description when read in the light of the accompanying drawings of an embodiment of the invention, the scope of which latter will be more particularly pointed out in the appended claims.

in the Fig. l is section on the line 9- with parts in elevation;

Figs. 2 and 3 are, respectively, sections on the lines and of Fig. l, with parts in eleve tion;

Fig. 4 is a rear elevation of the furnace ac cording to Figs. 1, 2 and t;

5 is an isometric View, with parts broken away, of the body portion or lining of the fur nace chamber;

Fig. 6 is a section on the line 66 of Fig. i on an enlarged scale, with parts omitted;

Fig. 7 is a fragmentary elevation on an enlarged scale of parts shown by Fig. 4-; I

Fig. 8 is a section on the line 8-8 of Fig. '7; and

Fig. 9 shows a detail.

Although many features of a furnace according to the invention are of general application, the furnace shown by the drawings is particularly applicable for use in the practice of the methods disclosed by applicants co-pending application Serial Number 519,887, filed January 27, 1944, now Patent #2,429,584 issued on October 21, 1947. In such a furnace a molten copper base alloy containing zinc is treated under non-oxidizing conditions by heating it to a high temperature in the presence of carbonaceous material for removing its zinc content, the carbonaceous material constituting the lining or body portion of the furnace chamber containing the molten metal; When such a furnace is of large size it has been found necessary to build up this lining of carbon blocks, and, for insuring against entrance of air through the interstices of the furnace walls, to surround those walls with an imperforate metal casing which operatively tightly fits those walls, it being understood that entrance of air into the furnace chamber would not only make it impossible to treat the molten l of Fig. 2,

Divided and this application May 24, g I

2 metal under non-oxidizing conditions but also would destroy the carbonaceous lining by what amounts to combustion of the same. With a furnace so constructed extreme difllculty has been encountered inpreventing the metal casing from overheating and from being ruptured by stresses .imparted by expansion of the furnace walls when the latter are heated, it being understood that the interior of the furnace commonly will be at about 3200 F. and that the metal casing if heated in excess of about 350 F. will soften and lose its structural strength.

Referring to the drawings, the furnace illustrated comprises a lower portion i and a re movable cover portion 3 (Figs. 2 and 4). The lower portion comprises a metal casing, preferably of mild steel, havingthe four lateral walls 5 and a bottom wall :7, the joints between these walls being welded together to form an integral air tight structure. As shown, the bottom of the casing is supported on the spaced l-beam supports ii extending transversely of the casing. Also, as shown, the casing is reinforced by the vertical corner angle-irons it (Figs. 1 and i) welded to the walls 5, between which angle-irons extend, at the front and rear oi the furnace, the horizontal l-beams if; welded thereto, spacing strips H being placed between the l-beams and casing and welded to each so that the ii-beams as well as the angle-irons H are in substance integral with the casing. The end walls of the casing ,as shown, are reinforced by the vertically extending I-beams i 5 welded to those walls so as in substance to be integral therewith.

The cover of the furnace similarly comprises a metal casing, preferably of mild steel, having the top wall I! and four lateral walls l9 (Figs. 2 and 3), The vertical corners between the lateral walls I9 are welded to each other and to the vertical bars 20, one of which latter is placed at each corner of the cover and extends from above the top wall H downward to intermediate the height of the lateral walls. The upper edge of each of the walls i9 and the corresponding edges of the top wall I! throughout their lengths are welded to angle-iron reinforcing members 2 I, these members at each of opposite ends abutting With the bars 20 and being welded thereto. The cover portion of the casing, as shown, is further reinforced by the channel-irons 23 extending about the lateral walls i9 adjacent their upper edges, the channel-irons being welded to welded thereto, the horizontal legs of the angle-' irons 25 resting upon the horizontal legs of the angle-irons 21 when the cover of the furnace is placed on the lower portion of the furnace.

For making an air tight joint between the lateral walls of the casing for the lower portion of the furnace and the lateral walls IQ of the casing for the cover portion of the furnace, the last mentioned walls have welded thereto horizontal I-beams 29 which extend for the full length of each side of the cover, the lower ends of the bars 20 abutting with the top edges of these I-beams at the corners of the cover and being welded thereto. Carried by these I-beams is a member extending entirely about the cover comprising the horizontal top plate 3| and spaced downwardly projecting vertical plates 33, the innermost of the latter being welded to the outer sides of the I-beams. Welded to the lateral walls 5 of the casing for the lower portion of the furnace are horizontal angle-irons 35 which extend entirely around the furnace. Carried by these angle-irons are horizontal plates 31 coextensive therewith, which plates 31 carry the spaced upwardly projectin plates 39 coextensive with said plates 31. When the cover is in position the plates 33 enter the spaces between the plates 39, which spaces may be filled with oil or sand, or a mixture of the two, so as to make an air tight labyrinth seal.

As best illustrated by Figs. 1, 2, 3 and 5, the body portion or lining of the furnace chamber has a bottom formed of massive blocks 4|, of nongraphitic carbon, extending for the full width of the chamber. At one end of the furnace is a transverse block 43, of the same material, resting upon the upper surface of the adjacent bottom block 4|, the block 43 also extending entirely across the furnace. As shown, the block 43 is provided above its lower surface with an opening 45 (Figs. 2 and 5) through which extends a conduit 41 for supplying molten metal to the furnace chamber. As shown, this conduit has a downwardly projecting spout 49 which extends into a hollow 5| of a cup-shaped block 53, the metal entering the furnace through the conduit 41 overflowing the rim of the block into the furnace chamber to fill the latter with molten metal to the level L (Figs. 2 and 3), while the hollow 5| of the block is kept filled with molten metal to seal the spout of the conduit so as to prevent entrance of air into the furnace chamber and to prevent escape of zinc or other fumes therefrom. As shown, the upper surface of the bottom of the lining is recessed at 55 and the adjacent portion of the inner surface of the block 53 is recessed at 51 (Fig. 5) to receive the block 53 to hold it in position. Conveniently the conduit 41 and block 53 are formed of graphite to facilitate machining of the same.

Molten metal may be discharged from the furnace chamber through a conduit 59, preferably formed of graphite, the bore of which conduit communicates with said chamber at the level of the upper surface of the blocks 4|, as illustrated in Fig. 2, so that all the molten metal in the chamber may be drained therefrom when desired. The adjacent end wall portion of the furnace chamber with which the molten metal con tacts is constituted by a block 6|, of non-graphitic carbon, which extends for the full width of the chamber, this block having an opening 62 through which the conduit 59 passes. To insure against leakage of metal about the exterior of the conduit it is necessary for it tightly to fit the opening in the furnace walls through which it passes, which assurance cannot be had if the block 6| should rest on the extreme top of the adjacent block 4| as does the block 43 at the opposite end of the furnace. Consequently the adjacent block 4| is downwardly recessed as shown at 63, while the block 6| is extended downward to fill said recess, thus enabling the walls of the opening 62 to be wholly constituted by the block 6|. The upper portion of the transverse wall comprising the block 6| may be built up to the level of the top of the transverse block 43 by a block 65 of the same length as the block 6|, the two preferably having a tongue and groove fit as indicated at 61 (Figs. 2 and 5). Normally the conduit 59 is closed by a removable screw-threaded graphite plug 69 which may be turned by a key wrench inserted through the exterior open end of the conduit, and to insure against leakage the portion of the conduit at the right of the plug, as viewed in Fig. 2, may be normally filled with fireclay and closed by a removable cap I Zinc fumes and the like may be discharged from the furnace chamber through a suitable conduit 12, which in practice, when the furnace is used for treating zinciferous metal, leads to a closed zinc condenser.

As shown, the opposite longitudinal walls of the body portion or lining of the furnace chamber are constituted by blocks I3 extending for the full length of the chamber, the transverse blocks at the ends of the chamber being recessed as indicated at I5 (Figs. 1 and 5) for receiving the end portions of the blocks 13.

Preferably the carbon blocks constituting the body portion or lining of the furnace chamber are accurately machined to fit with each other, adjacent surfaces being formed with keyways H which receive elongated non-graphitic carbon keys 19 to lock the parts together. These keyways also act to prevent escape of molten metal from the furnace chamber should the same tend to leak through the joints between the blocks. For further insuring against such leakage the lateral walls of the chamber are surrounded by an integral layer 8| of carbonaceous material. This material may be applied in the form of a thick paste rammed into the space between the carbon blocks and the surrounding brickwork, a space several inches in width being left between the carbon blocks and the surrounding brickwork to permit entrance of the paste. This paste may be the material known as green electrode paste consisting of a mixture of comminuted carbon and coal tar, and being the material commonly employed for making molded carbon electrodes. After the furnace is in operation the paste will bake and form an integral layer of hard carbon. As shown, the exterior sides of the blocks 43 and 6| at the two extreme transverse sides of the carbon lining project slightly beyond the adjacent sides of the end blocks 4| forming the bottom of the lining so as to provide shoulders 83, which shoulders act to prevent any tendency of the layer 8| to move upward, that is to say, they act to lock the layer to the lining.

As shown in Figs. 2 and 3, the body portion or ,metal when the pool of the latter is about 6 inches deep, these resistors may be about 6 inches in diameter spaced about 16 or 17 inches apart.

As shown, the ends of the resistors are connected for series flow of current by plates I2I, preferably of graphite, these plates being supported on the shelves II1 by blocks I22 of heat refractory electric insulating material such as sintered aluminum oxide A1203 of high purity, say about 99.5%, the ends of the resistors being screw-threaded, as shown in Fig. 1, and secured to the plates by graphite clamping nuts I23. As shown in Figs. 1 and 6, the openings I25 in the plates I21 through which the resistors extend are elongated lengthwise of the plates so that the resistors, although securely clamped thereto by the nuts I23, may slide longitudinall of the plates to permit expansion and contraction of the series of resistors longitudinally of the farnace particularly when the walls of the latter expand and contract, it being understood that graphite has high lubricating or anti-friction qualities when heated to incandescence. As shown, the ends of the resistors are secured by means of graphite coupling sleeves I21 to larger diameter graphite extensions I29 projecting through openings I3I in the adjacent carbon block v13 in spaced relation to the walls of such opening. In alignment with the openings I3I the furnace walls and easing are formed with openings through which the enlarged diameter portions I30 of the resistor extensions I29 lead to the exterior of the furnace, the openings through the brickwork, as shown, being constituted by the bores of sleeves I33 (Fig. 1), which sleeves are of heat refractory electric insulating material preferably alundum. As shown, the space between the walls of each sleeve and associated extension is packed with a yieldable layer I35 of asbestos or other yieldable heat refractory material, so that the extension despite the packing remains operatively in spaced relation to the surrounding walls of the sleeve in the sense that relative movement between them transversely of the extension is not prevented.

As best illustrated in Fig. 8, screw-threaded on the enlarged diameter end portion I30 of each resistor extension I29 is the base I31 of a terminal I39, preferably formed of copper, the base being insulated from the walls of the metallic furnace casing by a washer I4I of yieldable refractory insulating material such as asbestos. As shown, the base I31 is provided with the radial water passages I42 with which communicate the water supply passage I43 and water discharge passage I44 leading to the end of the terminal for connection to suitable hoses. The water circulated through the base and terminals keeps them and the adjacent portions of the resistor extensions I29 cool. Because of the cooling water and the increased diameter of the resistor extensions as compared to the diameters of the heating resistors, although the latter are heated to incandescence the terminals and adjacent portions of the extensions, including the portions of the latter within the sleeves I33, are kept relatively cool.

As shown, each terminal I39 extends through an opening I45 in a plate I46 of insulating material, to which plate the base portion I31 of the terminal is clamped by a nut I48 screwthreaded on the terminal. This plate, as shown. is relatively thick, say about 1 inch, so as to give it considerable strength. Preferably the material of the plate is one of those used for panels of radio instruments as, for example, material sold under the name "Micarta. Surrounding the base of the material is shown a sleeve I41 which is stiiily flexible transversely of its axis but nonextensible. This sleeve in detail may have the construction shown by Fig. 9, that is to say, may have the interlocked spirally wound portions I49 which are packed with asbestos or the like, as indicated at I5I, to render the sleeve air tight. At its outer end the sleeve, as shown, is welded at I53 to a metal ring I55 which is secured to the plate I46 by bolts I51, a packing I59, preferably of asbestos, being placed between the ring and the plate for rendering the joint between them air tight. At its opposite end the sleeve, as shown, is welded at I6I to a metal ring I93 which is secured to the metal furnace casing, preferably by welding as shown at I65.

The sleeves I41 in conjunction with the pack ings I35 insure against entrance of air into the furnace chamber through the openings in the furnace wall through which the resistor extensions I29 pass. At the same time the sleeves being laterally yieldable prevent undue stresses being imparted to the resistor extensions when the metal casing of the furnace expands, and likewise permits the resistor extensions to move relative to the casing in so far as they tend to so move by reason of relative expansion between the metal casing and the walls of the furnace interiorly of the casing.

For supporting the terminals I39 and the resistor extensions against the stresses of the cables connected to the terminals, in the embodiment of the invention shown the two insulating plates I46 are connected to the opposite ends, respectively, of a bar I61, which latter is rigidly supported by posts I69 (Fig. 4) carried b a plate I" (Fig. 3) secured to the projecting ends of the I-beam supports 9 for the furnace. As shown, metal plates I13 are welded at I15 to the ends of the bar I61, while the insulating plates I46 are secured to these metal plates by bolts I11, the perforations I 19 in the plates I13 through which the bolts pass being elongated in the direction of the fixed bar I61 so as to permit relative movement longitudinally of the furnace between the plates I45 and that bar.

The current employed for energizing the resistors commonly will be in the order of 6,000 to 10,000 amperes, and when this is an alternating current a very strong alternating electro-magnetic field is set up about the terminals and resistor extensions I29. It has been found that this field is sufficient seriously to overheat the portions of the casing walls adjacent the resistor extensions when the casing is of steel because of the hysteresis phenomena involved. To avoid this eifect, in the present embodiment of the invention the portion of the lateral walls 5 of the casing adjacent each resistor extension is constituted by an insert I 8I of non-magnetic material, preferably silicon bronze which has a tensile strength in the order of steel. As shown, each insert is of the same thickness as the rest of the lateral walls of the casing and is secured thereto by a metal frame I83 welded to the insert and the lateral walls 5. As shown, the inserts extend farther from the terminals toward the center of the length of the furnace than toward the ends of the furnace because the electro-magnetic field is strongest between the two terminals. When an alternating current is employed, also the bar I61 preferably is provided with an insert I85 of non-magnetic material, such as copper or silicon bronze, for breaking the magnetic path between the regions adjacent the terminals, as otherwise the bar I57 is liable to overheat and weaken. Likewise the metal of the sleeve I41 and the rings I55 and IE3 associated with said sleeve are preferably of nonmagnetic material, such as bronze, to prevent their overheating when an alternating current is employed.

It will be understood that within the scope of the appended claims wide deviations may be made from the form of the invention described without departing from the spirit of the invention.

I claim:

1. An electric furnace having, in combination, built up walls forming a furnace chamber, an outer metallic casing surrounding said walls for supporting them and rendering them air tight, heating means in said chamber comprising a row of rigid heating resistors connected together by rigid end members, a rigid resistor extension at each end of said row extending through aligned openings formed in said walls and casing in operatively laterally spaced relation to the walls of said openings to the exterior of said casing, air tight laterally flexible metallic sleeves carried by said casing at the exterior thereof, which sleeves receive the portions of said resistor extensions at the exterior of said casing in laterally spaced relation to said portions, the end of each sleeve adjacent the easing having an air tight connection thereto, and means including an electric insulator adjacent the opposite end of said sleeve connecting that end in air tight insulated relation to said portion of said resistor extension received by the sleeve.

2. An electric furnace having, in combination, built up walls forming a furnace chamber, an outer metallic casing surrounding said walls for supporting them and rendering them air tight, heating means in said chamber comprising a row 01' rigid heating resistors connected together by rigid end members, a rigid resistor extension at each end of said row extending through aligned openings formed in said walls and casing in operatlvely laterally spaced relation to the walls of said openings to the exterior of said casing, air tight laterally flexible metallic sleeves carried by said casing at the exterior thereof, which sleeves receive the portions of said resistor extensions at the exterior of said casing in laterally spaced relation to said portions, the end of each sleeve adjacent the casing having an air tight connection thereto; and means including a terminal carried by each of said portions of said extensions and an electric insulator adjacent the end of each sleeve remote from the casing. through which insulator such terminal projects, for securing that end of the sleeve in insulated air tight relation to said portion of said extension.

3. An electric furnace having, in combination, built up walls forming a furnace chamber, an outer metallic casing surrounding said walls for supporting them and rendering them air tight, heating means in said chamber comprising a row of rigid heating resistors connected together by rigid end members, a rigid resistor extension at each end of said row extending through aligned openings formed in said walls and casing in operatively laterally spaced relation to the walls of said openings to the exterior of said casing, air tight laterally flexible metallic sleeves carried by said casing at the exterior thereof, which sleeves receive the portions of said resistor extensions at the exterior of said casing in laterally spaced relation to said portions, the end of each sleeve adjacent the casing having an air tight connection thereto, a terminal carried by each of said portions of said extensions, which terminals have base portions received by said sleeves in laterally spaced relation thereto, and electric-insulators carried by the ends of the sleeves remote from the casing in air tight relation thereto, which insulators are formed with openings through which said terminals project in fluid tight relation thereto.

FRANK F. POLAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 513,602 Thomson Jan. 30, 1894 685,042 Gibbs Oct. 22, 1901 1,054,371 Tone Feb. 25, 1913 1,450,543 Gronwall Apr. 3, 1923 1,472,139 Reid Oct. 30, 1923 1,498,990 Beyer June 24, 1924 1,533,224 Colby Apr. 14, 1925 1,547,002 Ruckstahl July 21, 1925 1,572,881 Brace Feb. 16, 1926 1,617,359 Westberg Feb. 15, 1927 1,641,764 Keenan Sept. 6, 1927 1,692,478 Weintz Nov. 20, 1928 1,749,762 Fitzgerald et al Mar. 11, 1930 1,832,872 Millar Nov. 24, 1931 1,837,178 Benner et al. Dec. 15, 1931 2,073,597 Northrup Mar. 9, 1937 2,123,158 Ridgway July 5, 1938 2,126,454 Crocker Aug. 9, 1938 2,325,521 Lambert July 27, 1943 FOREIGN PATENTS Number Country Date 35,632 Norway Aug. 28, 1922 45,407 Sweden Oct. 19, 1917 558,972 Great Britain Jan. 28, 1944

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