US2510932A

US2510932A - Apparatus for melting and treating metal

Info

Publication number: US2510932A
Application number: US712446A
Authority: US
Inventors: Frank F Poland
Original assignee: Revere Copper and Brass Inc
Current assignee: Revere Copper and Brass Inc
Priority date: 1946-11-26
Filing date: 1946-11-26
Publication date: 1950-06-06
Anticipated expiration: 1967-06-06

Description

June 6, 1950 F. F. POLAND 2,510,932

APPARATUS FOR MELTING AND TREATING METAL Filed Nov. 26, 1946 4 Sheets-Sheet l June 6, 1950 F. F. POLAND APPARATUS FOR MELTING 'AND TREATING METAL 4 Sheets-Sheet 2 Filed Nov. 26. 1946 I i'wenior: 7c FPoY/and Hf mew ufix dy June 6, 1950 4 Sheets-Sheet 3 Filed NOV. 26, 1946 o and, MWWWV fliifys mm 4 m.. A W m n- F. A 3 m mm nm .u N..(/ mm M I II m a W 8 m y mm mw 1 mo BWwQ w M 5 SF 9v v m l av W ms mu [om June 6, 1950 F. F. POLAND APPARATUS FOR MELTING AND TREATING METAL Filed Nov. 26, I946 4 SheetsSheet 4 u L & i:

Qm MN a #0 z a w m UNITED STATES PATENT .OFFICE APPARATUS FOR MELTING AND TREATING METAL Frank F. Poland, Rome, N. Y., assignor to Revere Copper and Brass Incorporated, Rome, N. Y., a corporation of Maryland Application November 26, 1946, Serial No. 712,446

3 Claims. (Cl. 266-34) My invention relates to apparatus for melting I and treating metal.

The invention has among its objects the provision of an improved furnace for treating, or

bottom wall of the lining. Each of the furnace chamber side walls constituted by the lining is formed of a pair of superimposed elongated blocks 1 the lower of which rests upon the end portions melting and treating, metal, particularly alumiof the row of blocks 3. As shown (see Fig. 4), the num, the treatment comprising passing a gas end portions of the blocks 5 are recessed at 9 for through the molten metal in an improved manreceiving th d rt ons f the lo ks s her. Other objects of the invention will be unillustrated in Figs. 1, 4 and '7, the abutting porderstood from the following description when tions of the

blocks

3, 5 and l are keyed together read in the light of the accompanying drawings by the elongated carbon rods ll of square crossof several embodiments of the invention, the section received in and fitting complementary scope of the invention being more particularly fieyvg y g thgir eilttng Sui-gages. The 3;

eurn ca r,ason,1so g zg gg agg :a'ppended clanns' ilabs l3, prefelrablyahoff graphitef1 arril'gchaeligaeng ransverse ac oss e urnace c a er ar Fig. 1 is a section of the furnace on the line Supported the Shoulders '5 formed at the 1' 8- upper portions of the

uppermost blocks

5 and 1. Figs. 2 and 3 are sections, on an enlarged scale, As shown, t blocks rest upon Slabs n of Of details of the metal discharge conduit Shown graphite upported a layer of insulating in Fig. 1; brick which rests upon the bottom Wall of the g. 4 is 8 Section 011 the line of 7, Wlth casing I. The slabs l'l, being of graphite, provide Pa s i elevation; an anti-friction surface for permitting relative Fig. 5 is a S ct n Of the Skim door Shown in sliding between the furnace lining and the fire= Fig. 4, correspondin to a section on the line brick insulating layer l9. Laterally the furnace -5 0 Fl 6 on an enlarged Scale; lining is surrounded by a layer of firebrick tile Fi 6 i a c i on the line of a 2i backed by a layer of insulating brick 23, the wi h Pa in elevation; space between this latter layer and the lateral Fig. 7 is a section on the line 1-7 of Fig. 4, with walls of t casing being fill d t a layer 25 Parts in elevation; of resiliently yieldable heat refractory packing Fig- 8 s a sec n On the line of 1, material to permit overally contraction and exon an en a Sc pansion of the metallic casing and furnace walls l 9 s o a detail, on an enlarged scale, enclosed by it independently of each other. As responding t0 Secliioh 011 the line of 7? shown, resting upon the edge of the lateral walls Fig. 10 is a fragmentary view illustrating a of the furnace chamber enclosed by the metallic modified form of charging means for the furnace; casing 1 is a coping g: of firebrick t i d i i 11 is a Section 011 the line of place by the angle-irons 29 welded to the lateral 1 and walls of the casing interiorly thereof and extend- Fig. 12 is a section on the line l2l2 of Fig. 11, m eohtinuoush; th t, with parts Omltliell- Interiorly of the furnace chamber is a row of Referring to the ac illustrated b Figs- 1 parallel graphite electric heating resistors 3| exto 9 0f he draw the Same cflmprises body tending transversely of said chamber. These repo A and removable Cover portlOn sistors are connected for series flow of current The body portion A of the furnace illustrated by graphite plates 3 which rest upon graphite or comprises a Sheet metal Casing l Preferably carbon plates 35 suspended from the roof slabs formed of steel plates welded together to enclose H by graphite or carbon rods 1 o t upper the four sides and bottom of said body portion to ends f t rods 3 are screwed graphite or rende i a t- The furnace Chamber C in the hon nuts 39 resting upon heat refractory electric body portion or the fu n has a lining of refracinsulating blocks 4 I, the latter resting upon blocks tory blocks preferably of hard carbon. A row of 3 of porous carbon constituting a refractory elongated later y abutting blocks 3, extending layer of relatively poor heat conductivity resting from one side of the furnace chamber to the upon t upper surfaces of th l b l3, The other, constitutes the bottom wall of this lining. pace betw en the cover and the furnace roof As shown, each of the furnace chamber end walls s1abs |3 is filled t a layer 45 of t retrecconstituted y the linin is formed of a pair of tory insulating material, preferably broken charp p s elongated b c s 5 t e lower of coal, inverted cup-like covers 41 of carbon restwhich rests upon the adjacent end block 3 of the 5 ing upon the slabs l3 being positioned over the upper ends of the suspension rods 81, nuts 39 and blocks 4| and 43 for keeping the charcoal out of contact with them. As shown, the end resistors 3| are secured by couplings 48 to extensions 49 of graphite projecting through aligned openings 5| and 53 (Fig. 4) in one of the lateral walls of the furnace. A resiliently yieldable' packing sleeve 55 of heat refractory material in the opening 53 and surrounding the extension 49 serves to render the joint between the latter and the furnace walls air tight, while a, bushing of refractory electric insulating material 51 serves to insulam from the metallic casing the extension and copper terminal lug 59 carried by the extension. The resistors and the manner of supporting them form the subject matter of applicant's copending application Serial Number 573,337, filed January it, 1945, now Patent No. 2,472,613, granted June 7, 1949 and it is believed need not be herein further described.

as shown, the cover portion B of the furnace comprises end and side channel-irons 6| welded together to form a continuous rim for the cover. These channeldrons at the sides of the furnace receive elongated blocks 59 the inner sides 65 of which are outwardly and downwardly inclined as shown in Fig. '7. Supported by these inclined sides of the blocks 63 are abutting slabs 61 of carbon extending transversely across the furnace, the abutting edges of the slabs being keyed together, as indicated at 69 in Fig. 1, in the same way that the blocks of the furnace lining are keyed together, Resting upon the slabs 61 and supported thereby and by the inclined sides 65 of the blocks 63 is a layer ll of refractory flrebrick.

Extending continuously about the lateral walls of the metallic casing I at the exterior thereof adjacent its upper edge is a laterally projecting metallic flange 13 carrying the upwardly proiecting continuous flanges l5. Carried by the channel-irons SI of the cover adjacent its upper edge is an exterior continuous laterally projecting flange 11 carrying the continuous downwardly projecting flanges 19, one of these flanges being adapted to project into the space between the two flanges l5 and the other into the space between the lateral wall of the metallic casing and the adjacent flange 15. The spaces into which the flanges 19 project are adapted to be fllled with ofl or sand, or a mixture of the two, and thus form a labyrinth seal for renderingpir tight the joint between the cover and body portion of the furnace.

For charging the furnace chamber with molten metal the casing is provided with an extension 8| in which is contained a body of flrebrick or other refractory material built up to form a funnel 93 into which the molten metal may be poured from a ladle. The discharge opening 85 of the funnel leads to an interior chamber 81 formed in the body of the flrebrick. One side of this chamber is formed by a tile-like slab 89 which rests upon the bottom 9| of the chamber, the bottom edge of the tile being notched, as indicated at 93, to form a passage for discharge of metal from the chamber. The passage formed by the notch 93 communicates with a vertical passage 95 extending well above the top edge 91 of the notch. At its upper end the passage 95 communicates with a conduit 99 extending through the furnace wall to the furnace chamber. When metal is poured into the chamber 91 through the funnel 93 it will discharge from said chamber into the furnace chamber by way of the notch 93,

cause the metal to seal the furnace chamber against entrance of air and discharge of treating gas. For keeping liquid between pouring operations the body of metal remaining in the chamber 81, notch 93 and passage 95 said chamber at its upper portion is shown as provided with an electric resistance heating element |0|, preferably in the form of a rod of graphite. This heating element extends across the chamber, and at opposite edges projects through openings in the lateral walls of the chamber as shown in Fig. 8,- the ends of the element carrying the copper terminal lugs Hi3 so that heating current may be passed through it. As shown, the heating element is insulated from the metallic casing, and the joint between it and the furnace walls is packed and rendered air tight, in the same ways as are the resistor extensions 49. Heat radiated through the conduit 99 from the furnace chamber C will augment the heating effect of the heatingelement |0|.

Molten aluminum may be charged into the furnace chamber 0 to fill the same to a level LL. In the furnace chamber the aluminum is purified by subjecting it to heat by bubbling chlorine gas through it. Chlorine is substantially inert with respect to molten aluminum, who: as nitrogen, usually considered as an inert gas, would form aluminum nitrides under such conditions and contaminate the aluminum. Gases such as hydrogen and carbon monoxide, which are inert with respect to many molten metals, would dissolve in molten aluminum and give it poor casting qualities.

For bubbling the gas through the molten aluminum the furnace chamber, as shown, is provided adjacent its bottom with a row of transversely extending parallel tubes I05 having closed ends I01. These tubes, according to the present invention, are formed of porous material, preferably carbon. The gas is admitted to the tubes under sufficient pressure to overcome the head of molten metal at the exterior of the tubes to cause the gas to discharge through the pores of the tubes and bubble through the metal a diffused volume of gas. The chlorine bubbling through the metal flushes out or otherwise removes carbon monoxide and hydrogen dissolved in the aluminum, which, if allowed, to remain therein, would make the aluminum cast poorly. When chlorine is employed as the gas it also converts to chlorides any zinc or magnesium commonly contained in aluminum, which chlorides go off as a fume. Further, the gas stirs up the molten metal and, being highly diffused, scours from it and carries to the surface of the melt aluminum oxide particles which are commonly contained in the aluminum, particularly aluminum scrap, which particles upon such removal float upon the surface of the melt.

During the operation of bubbling chlorine through the metal the latter is heated by passing electric current through the resistors 3|, which causes heat to be radiated downwardly on the surface of the metal to raise its temperature. It has been found that the effects of the chlorine gas are augmented if the temperature of the aluminum is raised as high as possible. However, this temperature should not exceed about 2200 F., as otherwise aluminum carbides will be 8 formed from the carbon surfaces in contact with the aluminum, which will contaminate the latter, and in fact such action will act to clog and destroy the porosity of the carbon tubes and in time cause said tubes to fail.

It will be understood, however, that the invention is not limited to treating aluminum, or to the use of chlorine, as bubbling an inert gas through molten metal, for example nitrogen through molten copper, will act to remove hydrogen and carbon monoxide therefrom and to flush out undissolved particles in the same way as the chlorine acts to remove aluminum oxide particles from molten aluminum.

The porosity of the carbon of which the above mentioned tubes are made may be such as to cause the carbon to pass 4 to 33 cubic feet of air, at 15% humidity, per minute per square foot of carbon surface at a pressure of 2 inches of water. The carbon which will pass 4 cubic feet of air under the conditions just mentioned has an average pore size of about 69 microns, and the carbon which will pass 33 cubic feet of air under the'above conditions has a pore size of about 190 microns, both being about 48% porous. Preferably the carbon employed is that which would pass about 33 cubic feet per minute under the above conditions, so as to make it possible to pass a large amount of the chlorine gas through the metal with a pressure of about 2 inches of water in excess of the head of metal on the tubes. For all practical purposes the permeability of the tubes with respect to chlorine is substantially their permeability with respect to air.

As shown, the tubes I95 are supported by blocks I09, preferably of carbon, resting upon the carbon floor of the furnace chamber. As best illustrated by Figs. '7 and 9, the tubes are connected by non-porous carbon T's III and elbows II 3 to a manifold II5 of non-porous carbon. At the center portion of this manifold is shown a T I" of non-porous carbon connected by a nonporous carbon nipple II9 to the lower portion of the bore I2I of a vertically extending nonporous carbon block I23. The upper end of this bore is shown as closed by a plug I25 screwthreaded into it, and screw-threaded into the block is a conduit I21 of carbon which extends through the furnace walls to their exterior and is supplied with chlorine gas under pressure from a source of supply, a suitable valve (not shown) in the conduit being provided for establishing and interrupting flow of chlorine gas to the bore I2I. Preferably the conduit I2I communicates with the bore I2I at a point above the level of metal contained in the furnace chamber, so as to insure against the possibility of molten metal that may enter the bore I2I by leakage in the Joints submerged in the metal or by reason of seepage of metal through the pores of the tubes I 35 working into the conduit I21, which, if it did, might freeze therein and block said conduit. Any metal that enters the tubes I 05, manifold H5 and bore I2I will be kept molten by heat conduction through the tube and manifold walls and block I23, and the'chlorine gas entered into the bore I2I will blow out such metal through the pores of the tubes I05 and other points of possible leakage.

As illustrated, the blocks I adjacent the conduit I21 are recessed to form an elongated vertical groove I29 opening laterally on the interior faces of the blocks the opposite side walls of the groove being formed with longitudinally extending keyways I3I coextensive with the length of the groove. The block I23 is of the same crosssectional shape as the groove I29 so as to lie flush with the inner surfaces of the blocks I, being integrally formed with longitudinally extending keys I33 which fit the keyways I3I so as to retain the block I 23 in said groove. Preferably the block I23 is of no longer length than necessary to have the conduit I 21 positioned at a sufficient height above the level of the metal in the furnace chamber. After this block is lowered into the groove I29 an unbored block I35 of exteriorly the same cross-sectional shape is lowered into the groove so as to rest upon the top of the block I23, the block I35 being retained against vertical movement in the groove by the firebrick coping layer 21 which is subsequently installed. As shown in Fig. 7, the lower end surface of the groove I29 is inclined downwardly toward the furnace chamber, as indicated at I31, and the lower end surface of the block I23 is correspondingly shaped. This causes the block I23 to tend, under the force of gravity, to slide down said inclined surface I37 toward the furnace chamber, whereby to cause the keys I33 to bear against the sides of the keyways I3I adjacent the furnace chamber so as to take up any loose fit between the parts and thus in effect secure a rigid construction.

For discharging the treated metal from the furnace chamber, the blocks 5 at one end of the furnace are, as shown in Figs. 1 and 4, also formed with an elongated vertical groove I29 identical with that above described, said groove also having the inclined lower end I31 and keyways I3I. In the groove in the blocks 5 is received an elongated block I39 having elongated keys I fitting the keyways I3I. Also in the groove I29 receiving the block I39 is placed a block I43 which rests upon said block I39, the construction in the respects mentioned being like that heretofore described. The block I39 is formed with a vertically extending bore I45 which at its lower end opens into the furnace chamber adjacent the bottom of the latter, the upper end of the bore being closed by a plug I41 screw-threaded therein. Tapped into the block I39, and opening into the bore I45 thereof above the level LL of the metal in the furnace chamber, is a conduit I49. This conduit is connected, by a T I5I, to an upwardly extending conduit I53 and a downwardly extending conduit I55. The conduit I 53 is connected to a vacuum pump (not shown), while the conduit I55 is connected to a casting machine or the like (not shown). By exhausting the conduit I53 by means of the vacuum pump metal will be sucked through the bore I45 and conduit I49, and will flow downwardly through the conduit I55 and discharge therefrom. Only suflicient vapors need be exhausted from the conduit I53 to cause the arrangement of conduits to form a siphon. In this way the metal will be discharged from the furnace chamber without the possibility of entering air into said chamber. The molten metal in the bore I45 will act to seal said bore during the periods between metal discharging operations.

The conduits I49 and I55 and the adjacent portion of the conduit I53and fittings associated therewith are preferably formed of carbon. For preventing metal from freezing in these conduits and fittings the conduits are preferably surrounded by heatin elements comprising coils of resistance wire I51 (Figs. 2 and 3) embedded in the sleeves I59 of insulating material surround- QJIOJSQ 7 ing the conduits, these coils being provided with terminal leads I8I for supplying heating current to the coils.

For venting the furnace chamber of chlorine gas, chloride fumes, carbon monoxide and hydrogen discharged from the pool of molten metal, a, conduit I63, preferably of carbon, opens into the furnace chamber above the pool of metal therein and communicates with a vent stack I85 through a gate valve I61. By regulation of the gate valve the pressure within the furnace chamber above the pool of metal therein may be regulated. Preferably this pressure is kept at slightly above atmospheric pressure so as to insure against leakage of air into the furnace chamber.

As illustrated (see Figs. 4, and 6), the furnace is provided with one or more skim ports I69 adjacent the surface of the molten metal, these ports being downwardly inclined, as illustrated in Fig. 6, so that the ports open on the exterior of the furnace at a level above the level LL of the pool of metal in the furnace. These ports, as illustrated, are normally closed by the doors I1 I. Each door is shown as swivelly connected to the inner end of a screw-threaded clamping screw I13. The clamping screw is screw-threaded through a nut I15 rigidly carried by a yoke I11, the screw at its outer-end having a handwheel I19 for turning it. The yoke at one end is pivoted at It (Fig. 5) to a door frame I83 fixedly carried by the casing I. Pivotally secured to the opposite end of the yoke at I85 is a latch I81 adapted to engage a keeper I89 rigidly carried by the door frame. When the latch is engaged, by turning the handwheel I19 the door will be forced toward the door frame. When the latch is disengaged, the yoke may be swung on its pivot IBI to o en the door. The door frame surrounds the outer opening of the port I69, and comprises the spaced projecting sleeves I! which provide between them a continuous groove I93 extending entirely about said frame, at the bottom of which groove is a packing ring I95 of heat refractory resiliently yieldable material. Rigidly carried by the door is a sleeve I91 adapted to enter the groove I93 so that its free end will be forced against the packing ring I95 when the door is forced toward the door frame by rotation of the handwheel I19. Between the sleeves I9I is welded a fiat annular plate I99 upon which the packing ring I95 seats. The plate forms at its side opposite the packing a ring-like passage 20I between the sleeves I9I extending continuously about the door frame, the inner sleeve being provided with a series of small diameter ports 203 distributed about the passage circumferentially thereof. For supplying the passage 20I with a substantially inert gas, such as city illuminating gas, is a pipe 295 controlled by a valve 201. When the door IN is opened for permitting entrance of a skimming tool into the furnace chamber for removing the zinc oxide dross from the surface of the pool of metal therein, the valve 201 may be opened to cause gas to be discharged through the ports 203. These openings are spaced close enough together so that in effect is formed a sheet of the gas across the skimming port I69, and that sheet insures against entrance of air into the furnace or escape of dangerous chlorine gas therefrom during the skimming operation. Preferably, before opening the door, the supply of chlorine gas to the furnace chamber is interrupted and the gate valve I61 is closed as soon as the pressure in the furnace drops to atmospheric.

Instead of entering the aluminum into the furnace chamber C in molten form, the same may be charged thereto in solid form, say in the form of compressed bales of scrap 8 (Figs. 10 and 11). As illustrated in Figs. 10 and 11, the casing I is extended at 209 at one end of the furnace. Leading through this extension to the interior of the furnace are one or more conduits 2| I, of rectangular cross-section, preferably of graphite. The conduits are surrounded by a mass 2 I3 of insulating brick forming a continuation of the adjacent portion of the insulating layer 23. As shown, each conduit 2| I is provided with a, pair of spaced control gates 2I5 and 2I1 adapted to be raised or lowered by the manually controlled air cylinders 2I9. Leading to the space between these two gates is a valve controlled pipe 22I for admitting city illuminating gas, or other relatively inert gas, to the space between the two gates. The gate 2", as shown, at its lower edge is formed with a notch 223, so that when gas is supplied through the pipe 22I to the space between the two gates with the gates closed the gas vwill exhaust that space of air. When the space between the gates is so exhausted the gate 2" may be raised to permit the bale S to be slid into the conduit from the table T to enter the space between the two gates, after which the gate 2I1 may be closed and the gate 2 I5 opened to permit the bale to be pushed into the furnace by means of a rod entered through the notch 223 in the gate 2I1. By properly regulating the amount of gas supplied through the pipe 22l the escape of chlorine gas from the furnace and the entrance of air thereto will be prevented.

When employing the form of furnace shown by Figs. 10, 11 and 12, the furnace-may be initially charged with sufficient molten aluminum to cover the tubes I95, 50 that bales of scrap entered into the furnace may float on such metal while being melted and thus properly distribute the charge. This initial charging of molten aluminum'into the furnace may be done by entering into the furnace chamber through the conduit 2 from the exterior of the furnace the end portion of the spout of a funnel, from the lower portion of the body of which funnel the spout projects laterally, said body being supported on the table T, whereupon molten aluminum may be poured into the body of the funnel to cause said metal to discharge through the funnel spout into the furnace chamber.

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. A furnace having means forming a furnace chamber adapted to maintain a pool of metal therein, blocks forming a lining for said chamber, means forming a passage from the exterior of said chamber at one level to the interior of said chamber at a lower level comprising a vertically extending block having a, vertically extending passage therein, a lateral wall of said lining being formed to provide a vertically extending groove opening laterally into said chamber, in which groove said vertically extending block is received, said groove being formed with a vertically extending shoulder facing the vertically extending bottom of said groove, said vertically extending block having an oppositely facing vertically extending shoulder slidably contacting with the shoulder of said groove for retaining said block in said groove, said block and groove at their lower ends having cooperating contacting inclined surfaces for causing the weight of said block to hold said shoulders in contact.

2. A furnace having means forming a furnace chamber adapted to maintain a pool of metal therein, blocks forming a lining for said chamber, means forming a passage from the exterior of said chamber at one level to the interior of said chamber at a lower level comprising a vertically extending block having a vertically extending passage therein, a lateral wall of said lining being formed to provide a vertically extending groove opening laterally into said chamber, in which groove said vertically extending block is received with a lateral wall of said vertically extending block flush with the exposed surface of said wall, said groove being formed with a vertically extending shoulder facin the vertically extending bottom of said groove, said vertically extending block having an oppositely facing vertically extending shoulder slidably contacting with the shoulder of said groove for retaining said block in said groove, said block and groove at their lower ends having cooperatin contacting inclined surfaces for causing the weight of said block to hold said shoulders in contact.

3. A furnace for treating metal having, in combination, walls forming a substantially closed furnace chamber adapted to maintain therein a pool of molten metal having an upper free surface, means for heating such pool of metal, means inert with respect to chlorine at the temperature of the melt for diifusing chlorine gas and bubbling it through the metal of such pool for stirring and scavenging it, which last mentioned means presents a gas receiving cavity having a wall exteriorly exposed to the interior of said chamber in position to contact with the metal of said pool below its upper free surface, said wall of said cavity being of chlorine gas pervious porous carbon capable of conducting through its pores chlorine gas supplied to said cavity under pressure for discharge from said pores in diffused state at the exposed metal contacting surface of said wall, the furnace being formed with passage mans leading through its walls from the exterior of the furnace for supplying such gas under pressure to said cavity, vent means for the furnace chamber at its upper portion above the upper free surface of the pool of molten metal adapted to be maintained therein, which vent means is adapted to maintain above said upper free surface an atmosphere of the chlorine gas bubbled through such pool, a skim door for said chamber, and gas discharge means at said door for projecting gas across the door opening for preventing entrance of air to and escape of chlorine gas from said chamber when such door is open.

FRANK F. POLAND.

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

UNITED STATES PATENTS Number Name Date 728,261 Mark May 19, 1903 1,472,139 Reid Oct. 30, 1923 1,674,947 Bunce June 26, 1928 1,690,273 Gope Nov. 6, 1928 1,719,888 Ipsen July 9, 1929 1,836,196 Snelling Dec. 15, 1931 2,054,922 Betterton Sept. 22, 1936 2,058,947 Betterton Oct. 27, 1936 2,140,607 Thompson Dec. 20, 1938 2,214,612 Greenberg Sept. 10, 1940 2,256,481 Hulme et a1 Sept. 23, 1941 2,265,284 Hulme et al Dec. 9, 1941 2,269,838 Wroblewski Jan. 13, 1942 2,402,084 Rennie June 11, 1946 2,447,672 Smith, Jr. et al Aug. 24, 1948 OTHER REFERENCES Carbon and Graphite Products, National Carbon Co., Inc., 30 E. 42nd Street, New York, N. Y. Published July 1946. Page 9.