US2491210A - Tube furnace for producing metal - Google Patents

Description

Dec 13 1949 R. F. RENNLE 2,491,210

TUBE FURNACE FOR PRODUCING METAL original Filed Jan. 7, 1945 2 sheets sn t 1 ATTORNEY INVENTOR l?. F.' )PENN/ WW Mm m n MN mw WN )ANN Y uw WNNW Dec. 13, 1949 R. F. RENNIE TUBE FURNACE FOR PRODUCING METAL 2 Sheets-Sheet 2 original Filed Jan. 7, 19u-45 INVENTOR fa. F: PENN/5 BY @Xg Mm ATTORNEY Patented Dec. 13, 1949 TUBE FURNACE FOR PRODIUGING METALv Robert Fredrik Rennie, Lake Forest, Ill., assignor to Westinghouse Electric Corporation, a corporation of Pennsylvania Original application January '7, 1943, SerialNo.

471,604. Divided and thisY application November 24, 1945, Serial No. 630,669

4 Claims.

This application is a division of my applica tion', Ser. No. 471,604, filed January 7, 1943, now Patent No. 2,402,084, dated June 11, 1946, on Continuous reduction of molybdenum compounds.

This invention relates to the manufacture of molybdenum, and more particularly to a furnace adapted for continuously reducing compounds of molybdenum, such as the trioxide and ammonium molybdate, for that purpose.

The principal object of my invention, general# ly considered, is in shortening and otherwise improving 'on the manufacture of molybdenum, starting with a reducible compound, avoiding slow reduction due to keeping the reaction temperature low, and continuously moving the compound through the furnace in a direction opposite to that of the reducing gas.

Another object of my invention is the reduction of molybdenum troxide, or other reducible compound, to molybdenum, while continuously moving the same in a direction opposite to the flow of the reducing gas.

A further object of my invention is the reduction of a molybdenum compound to molybdenum, by moving it in the furnace continuously through heat zones of increasing temperatures, while passing reducing gas through said furnace in a direction opposite to that of said movement, at the same time stepwise increasing by effective` concentration the strength of said reducing gas,

to improve the quality of the metal produced andv in'order to avoid a runaway reaction.

Other objects and advantages of the invention, relating to the particular features will become apparent as the description proceeds.

Referring to the drawing:

Figure 1 is a vertical longitudinal sectional view, with parts in elevation and parts shown diagrammatically, of a furnace and associated apparatus .for reducing molybdenum compounds to molybdenum.

Figure .2 is a vertical, longitudinal, sectional Y View, with parts in elevation and parts shown diagrammatically, of another embodiment of. afurnace and associated apparatus for practicing myfnvention.

Figure Szs a view-similar to. Fig. 2,exceptva furnacepart is shown yfiagmentarily in elevation,

andthe loadingend of. the furnace is open while the unloading vmechanism is shown in engagement with .boats for the purpose of removing them fromithe` furnace In"` my copending application,Se`rial No. 413,118,v illedlOctober' 1-,l .19141, now.Y Patent` No1. 2,385,843, datedOctobexff 231945.1 havezdi'sclosed a. methodf process is fan improvement over that previouslyv employed, but is not continuous in that the molybdate is introduced into the furnace and the reducing atmosphere and temperature varied as desired until it is changed to molybdenum, whereupon it is withdrawn.

In my copending application, Serial No. 458,106, filed September 12, 1942, now Patent No. 2,398,114, dated April 9, 1946, I have disclosed a method of reducing ^molybdenum trioxide to molybdenum, which is similar to that of reducing ammonium molybdate to molybdenum, as disclosed in my application above-mentioned, except that the material is preferably granulated before reduction and I suggested using vreducing agents other than hydrogen, it of course being understood that in the reduction of the trioxide there is no ammonia in# herently available for reducing purposes.

The present invention involves a furnace especially adapted for practicing an improvement over the above-mentioned processes for stationary reduction r of molybdenum compounds by various reducing gases, in that I propose to move the lcharge to be reduced forward at constant speed into zones of' increasing temperature and in a direction opposite to that of the flow of the reducing gas, whereby said gas may be introduced when in its most concentrated or highly reducing condition, and reduced in strength, not

only by' the steam evolved during the reduction process, but also by the addition of desired amounts of Vsteam along the length of the furnace, thereby avoiding a runaway reaction at the beginning, of' the reduction process, and improv'- ing the quality of the-metal which is produced.

Since the time-temperature schedules for such a reduction have been worked out for stationary reductions, as described in` the aforementioned pending applications, I have correspondingly arranged the speed with which the charge moves flow of lrydrogenaoaother.reducing gas and the" amount of diluting material during an increase in temperature of the reduction furnace.

Before this improvement was introduced, there was some difculty when one tried to decide what flow of hydrogen, or other reducing gas, to use. If the reduction tube was fed with the amount of hydrogen that is needed in the end zone, it would cause a too violent reaction in the Zones of lower temperature, or those near where the reaction is beginning. If the furnace was fed with the amount of hydrogen that is Wanted at the beginning of the reduction process, the end zone would have to be ymade impractically long to give com plete reduction.

For this reason, continuous processes for reduction of molybdenum compounds up until now have been split into two parts, the end point of the rst lpart being molybdenum dioxide, or a mixture of molybdenum oxide and molybdenum trioxide.

This invention, therefore, supplies a practical solution for a one step reduction of molybdenum compounds to molybdenum by a continuous process. I propose to feed the reduction tube with the hydrogen, or other reducing gas, necessary for speedy 'com-plete reduction in the end zone, and at different points admit controlled amounts of steam, or other diluting agent, into the reduction tube to slow down the reaction where necessary and yprevent the formation of imperfect metal.

Referring now to the drawing in detail, like parts being designated by like reference char acters, and first considering the embodiment of my invention illustrated in Fig. 1, there is shown a furnace I I consisting of a preferably slightly inclined reduction tube I 2, which may -be of about 4 internal diameter and formed of relatively refractory material, such as nichrome. This tube may be covered with suitable insulating material I3, in turn enclosed in a sheet metal envelope I4 and heated in any desired manner, as by means of resistance wires I5, I6, and I1, respectively, controlled by rheostats I 8, I9 and 2l to provide three heating zones, respectively designated as 22, 23 and 24.

The windings, insulation, and other characteristics of the furnace are such that the heating zone 22 may be maintained at about 400 C., the zone 23 at about 630" C., and the zone 24 at about 1075 C. The furnace and accessories are desirably held in position as by means of supports 25. The left hand end of the furnace has a section desirably cooled by a water jacket 26 and provided with an outlet pipe 21 for the excess hydrogen, steam and/or ammonia, or other reagent used during the process. It is closed by a hinged door or cap 28, desirably including power means for pushing or otherwise moving the molybdenum compound through the furnace, such as an air or water cylinder 29 and piston 3| for operating a rod 32 and associated pusher element 33. This or other suitable means may be used for moving the containers on boats 34, of the molybdenum compound to be reduced, at uniform speed from the left hand or inlet end of the furnace to the right hand or outlet end. The door or cap 28 may be secured in place by locking means 35, and provided with a chain 30 to a counterweight and lifting apparatus (not shown).

The outlet end of the furnace is provided with a section cooled by a water jacket or like means 36 and provided with a pipe 31 for introducing a supply of hydrogen or other reducing gas. The

extreme end of the cooling section 38 of the tube I2 is closed by a hinged lid or door 39, provided with a suitable latch or locking device 4I. Means are provided for introducing desired amounts of water, or other diluting agent, along the length of the tube I2, said means in the present embodiment comprising pipes 42, 43 and 44. Water for these pipes is supplied from a reservoir 45 kept in the desired level as by means of a float valve (not shown) in the water supply pipe 46. The flow of the water from the reservoir to the pipes 42, 43 and 44 is controlled by valves 47, 48 and 42, respectively, admitting water through gaged capillary tubes 5i, 52 and 53 and transparent connections 54, and 56, permitting observation of the flow of water.

The hydrogen or other reducing gas supplied passes to the reduction tube at a desirably continuous rate being, however, naturally steadily attenuated during the reaction process by steam and/or other reaction product, with the excess withdrawn from pipe 2l for reclamation after the condensation of any steam therefrom.

I will now describe a preferred reduction schedule of molybdenum trioxide to molybdenum, preferably using hydrogen on granulated material, the manufacture of which has been dcscribed in my Patent No. 2,398,114, previously referred to, although I do not wish to be limited to the use of such material, as ammonium molybdate and other reducible molybdenum compounds may be handled in a similar manner. Instead of hydrogen, mixtures thereof such as Endogas (which is mainly a mixture of hydrogen and carbon monoxide, diluted with nitrogen) and Water gas, and other reducing agents such as carbon monoxide, ammonia, and reducing mixtures, as referred to in said application, Serial No. 458,106, may be employed. It Will also be understood that other diluting agents such as nitrogen and carbon dioxide, as referred to in said application, may tbe employed instead of, or admixed with, steam or with each other. The schedule disclosed is merely illustrative and changes may be made within the broad scope of my invention.

The preferably granulated molybdenum trioxide (M003) is placed in boats 34, desirably formed of refractory metal such as nickel, preferably about 2 kilograms per boat, the material being spread out in the boats to expose as much surface as possible.

The loaded boats may be first introduced into the cool or left hand end portion of the tube I2, after opening the cap or door 28, a sufficient number of boats being placed in front of the pusher element 33 so that the process may be con tinuous for a desired number of hours without shutting off the flow of hydrogen, or other reducing gas, and replenishing the supply of material to `be reduced. After insuring that both doors 28 and 39 are closed and that cooling water is circulating through the water jackets, the hydrogen supply is turned on, as by opening the valve 51, to flush out the air in the tube I2 in order to insure that no explosion will occur when the furnace is brought to a higher temperature.

The electric current is then turned on to the resistance Wires I5, I6 and I1, or other heating source applied, until the zones of the furnace reach the desired temperatures, as may be indicated by suitable pyrometers (not shown). That is, the temperature in the zone 22 oontrolled by wire I5 is desirably 400 C., that in zone 23 controlled by wire I6 is desirably 630 C., and that in zone 24 controlled by wire I'l is del sirably 10?7'5"Z C ThezziowL of: waterrtocthefpipesi 42; 1l-3v, andi 44 istreggu'lated. f so g tha-t .we desirablyv getu about 3.: cci: per minute.: from .t thevpipe 42;A abouti 9i, cc.1.perminutefrom'f the-:pipe-v 353 .and f about 3 ccf.:` per minuteafromrthewpipe144.

The purposeis toradmit enough Water by pipe 43* to make-the reaction to.l molybdenum' dioxide, vors` intermediatereductiony product,y to: come to. an: standstill,` with approximately 100 of that prod- 6i" reduction.tube;` j asfzinrf-the embodiment describedl the-.pusl:le1nt elementif33 can: operate: onlyruntil; thefcharge :associatedgtherewith 'frea'chesgthe ends. ofthe'tube-or.1 outlet-door3 39thereoff, It;is,',. therefore, believed .desirable-:that the linlet' endy of-f, the furnace-,mr thatfcooledby; the -water 'jacketf 2; vbe of'a length :correspondingwith lthefintere mediate? or,` heatedportion thereof, and.A that. the:A outlet end; orfthha-t .cooled: `by the water jacket-36;

uctfatthepoint-cf admission-cripipe 43. Enough; 10 besef. alcorrespondneleneth; Soithat acharne'-v wa-teriis tob'e:admittedbyfpipeMitoslowzthe reacf` Y tion fromfthe'fmolybdenum trioxide, or starting zproduct;- suicientlyto prevent overheating; and@ premature'fiformation of imperfect` metal;I Corna paredgwithhe. stationary reduction described :in theaeapplications `referred Vto', moreV than propor'; tionate, amounts f of steaun` must .beaA added.; be@ cause at the point of entry oipipe;-43;there'-Will beY abouti100.% excess ofhydrogen',r andzat the point of entry oi pipe fifi therewillbe about 300 excess off hydrogen; This continued.` additionl of steaincduring the process of reductionf dee` sirablycoarsens the'metal powder-produced.: This r: explains the reason for: the steam inlet pipe 42;

which is'notfto control the speed-ofI reduction; but to control particle sizeoAreduced-metal. In: certain .casesgzhovveven it@ may; not be -necessary to add any: Water by f this -pipe 42; orl the pro'y portion oflwater' at this point may, be .va-ried, de-f pending-on the progress .of-the. reduction! as determined by experience:

At thefsame-timeair viszadm-ittedl to thefend pipe',l as .by means of fafsuitable'v controlyalve.Y (not shown) to .cause the-pusher :elementi 33;-1to start uniform movement`l of= the bo ats-;34 :through the various zonescof Athe furnace lait afrateoffsspeed-: calculated toA leave said vboatslin zone 22for about: one hour, in Zone-23l-for about21/nhours; andin zone 24 for about 31/2 hours. The lengthspfsaid zones are thus made proportionate Ato ythe times in .fwhichfthefboats are.,totremainrtherein, that fis; in the/ratiofof 1121A :3l/2.

'Ihe-operation,I therefore; starts at'vaboutsiOO? C. with the hydrogenor-other reducingygas diofvboatsequal ,in length'itothe heated portionr:A ot the@ tube,"v thatT issthe-4 portiorr consisting. ofi the zones: 22,. 23 and.v 24'; may;- be; started 'inthe cool-:left hand. end'; of t...e -fuinacer` and, the,l op- 15 eration continueduntilfcompleted, when .thetfene tire-=chargefawll have been-moved .to thezoutlet. end., Thereuponathehydrogen or reducinggaseVA supplyfmay bez-shutoff'; theheatingcurrent tera l ininated, the iow"A of. Water ori.' other dilutingfi 205; agentzstopped'andgf when the furnace .-is sufcient.

iyA coolV to avoid und'esiredf oxidation4 .of thefrefi duced metal, thewdoor-i may then be openedsandri. the charge of metal removed, after whichthedoora' 28. may be opened. and a new' charge. ofoxide,

25.3.01L other reducible molybdenum4 compound,- inf-f.

tr'oduced and the process repeated.

Referring now.4 to theembodiment of my 'invention illustrated :ini-Figs. Zand 3,I lthere islfrag-lmentarilyv shown a furnacesllaywhich mayg-'be"n 30;! identical with theffurnace vl I of the preceding em-H bodiment .insofart as thelfcentral I- or :heatingpsecfv tion is concernedf. However; the leftwhand: or; loading;l end of thesinclinedreduction-.tube |29#v ofthe .furnace of the fp resent embodiment; v has provided :with .an -outlet .pipe 21a for: excess-hw drogen, `steaintand/ or 'anfimonia A or otherfreagent i used duringfftheprocess, and said section-:need'i not be as long as the furnaceorfheating section 10i-ferr reasons avv-hichf will i be explained.l

otherzdiluting. agent, not only onraccountof the:I introduction ofL water, but also because, of: thee starts the reductionv ofimolybdenum-ztrioxide'; or. other compound,y toward lower f oxidation;

e30-.Pleite hand.- or I.inlet end. othe f furnacet tot` the:

righthandnor-outletend. Thezdoor or capi 28" is,-..in.the present instance,l hingedat itsY lower; endxrathery than: at its-upper end and normally" secured.4 in` pla-ceftby lockingmeans 135e. Asin;

product such. as he l dioxide; 1 avoiding by dilu gfthespreceding; instance: thefA cylindercZSe Ilis*- pro-- tion-Lof. a' runaway-reactiom atI undesired: high; temperatures: and ther` production.- ofv imperfect: metal..

Finally the vboats successively/reach the f-nextf vided Withachain-f. 39%L to'a vcounterweight and 1 lowering apparatus (not shownl..A

The outletfendnof. they furnace. is"providediwith asection,: cooled by; Waterfjacket` org; likefzmeans'r,

about 630 C.I in a reducing atmosphere. more:

concentrated than that in the 'zonef22; because" there isv not onlyv lessv Water:v admittedin. this@v zone, butthere has been less,impoverishmentoff completed so vthat vupon reaching" the2zone24; of the higher'temperature'ofabout1075 Cl, the'4 still -rnore concentratedreducing-atmospheremay or gothen:compound'xdepends:zon'ztheziength :of :thea

duction to molybdenum dioxidefisf substantially a supply of hydrogen :orother reducingi'gas: The. extreme end :of thetcooling sectionr138a `of .then rez-t duction tube" l2@ tis closed .by a cap or f lidi 3989;y provided; withr; suitable;v latch or: locking device?. The cooling j sectionrf; 33ai ot' the reduction'.A tubei. l 2?l issinizthisf instance formed intwoi:l seo-- tions which may be separated as,irr;Figf.= 2; ori connectedilas iii-Figc, cbyfclosing Vorfopeningf the gate valve 61;.

The. cap 3Saisaprovidedz withzan aperture:'con' taining afsleevefelernentz and hooked rodl53.' controlled: by: ai handle. 64, so..v that" they f are adapted; to be-.reeprocatedfi and" turned?` at@will?A They mayf'b .moved' toward" the entrance V'end `10i t open, as in Fig. 3, and turned so that the hooked end portion 66 of the rod 63 engages one or more of the boats 3fta to pull it, or them, to the right hand position shown in Fig. 2, whereupon the gate valve may be closed, the cap 39a and its associated sleeve and rod removed, and the boats taken out of the furnace. The sleeve 62 is desirably provided with a collar or flange 65 which is adapted to engage the forward or right hand end of a boat 311|a to tell the operator when to turn the handle 64 so that the hooked end portion 66 thereof will connect with the boat or boats 34a nearest the exit end of the furnace.

The hydrogen supply pipe 61 is desirably provided with a branch 68 controlled by a valve 69 so that the extreme right hand section of the reduction tube, or that beyond the gate valve 6|, may, prior to opening said valve to resume the reducing operation, be flushed out with hydrogen so that when said gate valve is opened an explosive mixture will not be formed. During the flushing operation the air is exhausted through pipe 1| controlled by valve 12.

The operation of the embodiment of my invention illustrated in Figs. 2 and 3 may be as follows:

The loaded boats of the reducible compound. such as the granulated trioxide, may be rst introduced into the cool or left hand end portion of the tube I2EL after dropping the cap or door 28a. Any convenient number of boatsare placed in front of the pusher element 33a. When the door 28a is open, the valve 13 in the hydrogen exhaust pipe Z'IfiL is closed as by releasing the spring actuated stem 14 thereof by swinging the adjustable pusher element of the operating arm 15 from engagement therewith. The arm 'I5 is integral with or connected to the door 28a so as to swing therewith.

At the same time the valve 'I6 is opened, as by release of its spring actuated stem 11 by disengagement of the arm-carried adjustable pusher element 80, to increase the supply of gas to the pipe 18 to change the pilot light 19 issuing therefrom to a relatively long flame 8l and thereby ignite the issuing hydrogen, or other reducing gas 82, and prevent the formation of an explosive mixture.

When the furnace is open, as represented in Fig. 3, then the charge of boats 3l!u may be introduced, as by pushing them in along a loading plate 83 by means of a pusher element 84, after which the door 28a is closed as in Fig. 2, automatically reducing the flame 8l to the pilot light 'I9 and opening the reducing gas exhaust pipe valve 73 by bringing the operating arm 'I5 into engagement therewith.

The hydrogen, or reducing gas supply is then turned on, the furnace brought up to temperature, and the reducing action started as described in connection with the embodiment of Fig. 1. The hydraulic cylinder or other operating means pushes the boats 34a a desired distance into the furnace, whereupon the pusher element 33a may be withdrawn, the filling end of the furnace opened, and some more boats placed therein, as illustrated in Fig. 3.

This pushing and withdrawing operation is repeated until it is estimated that the boats at the head or right hand end of the line are coming close to the gate valve 6I. Said gate valve 6| is then opened, the hooked rod 63 moved from the position shown in Fig. 2 to that shown in Fig. 3 and turned to engage one or more of the boats 34a and pull them to the extreme right hand position shown in Fig. 2. The gate valve 6| is then closed, the exit cap 39a and its hooked rod 63 removed therefrom and the captured boats taken out of the furnace. The. cap 39a and rod 63 are then reapplied to the furnace as in Fig. 2, the outer section or that to the right of the valve 6l iiushed out with hydrogen, the valves 69 and 'I2 closed, the gate valve 5I opened.

It will be understood that the reducing operation may be continued uninterruptedly during the operation of the loading or unloading of the furnace. The short stoppage time taken for loading is allowed for as part of the reduction time, the time taken for unloading, however, not.

affecting the reduction time because during the unloading operation the piston 3| a may operate and continue to push the boats from left to right in the reduction tube.

It will be understood that the description of the apparatus of Fig. 2 is to be supplemented by the description of the apparatus of Fig. l, insofar as the details of the furnace or heating portion of the apparatus is concerned. The essential difference between the two embodiments is that in connection with the second the loading pistonr will periodically move back to accommodate charges, that is, move at a substantially continuous and uniform rate punctuated only by the brief loading intervals, and the reduced metal will be withdrawn without stopping the furnace, while in the first embodiment the charge is started at the loading end and pushed on through to the unloading end without opening the furnace or stopping the movement of the boats in any manner.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

I claim:

1. Apparatus for manufacturing molybdenum comprising a furnace consisting of an inner reduction tube of refractory material, a plurality of heating coils of resistance Wire surrounding said tube and independently controlled, insulating material enclosing said coils and tube, one of said coils serving to heat an intermediate portion of said tube and coils at opposite ends thereof serving, respectively, to heat portions of said tube toward its opposite ends, whereby said tube may be heated to different temperatures along its length, a door closing the loading end of said tube, a rod reciprocable in said door, a fiuid-pressure cylinder connected to said door, a piston in said cylinder and connected to said rod for pushing containers of molybdenum oxide along said reduction tube, a gate valve which when closed divides the other end portion of said tube into two parts, a door for the unloading end of said tube, a hooked rod slidable in said door, a handle on the outer end of said rod to pull containers of reduced metal from one side of said valve to the other, pipe connections for introducing gas to said tube portion at both sides of said valve, and pipe connections adjacent the ends of said tube for exhausting said gas, so that when said valve is' closed, said tubev between said gate valve and un-"' loading end door may be flushed out by said gas, whereby a periodically replenished charge of molybdenum oxide may be substantially continuously moved along said reduction tube and the reduced metal withdrawn at desired time intervals without stopping the reducing operation.

2. Apparatus as defined in claim 1 in which a water jacket surrounds a portion of said reduction 9 tube beyond one oi said end coils adjacent the loading end of said tube, and another water jacket surrounds the other end portion or" said tube beyond said other end coll adjacent the end of said tube.

3. Apparatus for manufacturing molybdenum comprising a furnace consisting of an inner` reduction tube or" refractory material, a plurality of heating coils of resistance wire surrounding said tube and independently controiled, insulating material enclosing said coils and tube, one oi said coils serving to heat an intermediate portion of said tube and coils at opposite ends thereof serving, respectively, to heat portions of said tube toward its opposite ends, whereby said tube may be heated to dilerent temperatures along its length, a fluid-pressure cylinder connected to said door, a piston in said cylinder and connected to said rod for pushing containers of molybdenum oxide along said reduction tube, a door ior the unloading end of said tube, a pipe connection for introducing combustible gas to said tube, another pipe connection for exhausting the gas irom said tube, a valve in said other pipe connection, a pipe from a supply of combustible gas for normally providing a pilot light near the loading end ci said tube, a normally only partly open vaine in said pipe, and an arm connected to sflng with the door closing the loading end of said tube and so related to said Valv es that it closes the Valve in the exhausting pipe connection and further opens the valve in the pilot light pipe, as the door is opened, so as to then allow all of the gas in the tube to flow out of the loading end thereof and be met 10 by a relatively-long flame, instead of a mere pilot light, to thereby ignite the gas from said tube and prevent the formation of an expiosive mixture.

4. Apparatus as dened in claim 3 in which a water jacket surrounds a portion of said tube beyond one of said end coils adjacent the loading end of said tube and another water jacket sur rounds the other end portion of said tube beyond said other end coil adjacent the unloading end of said tube.

ROBERT FREDRIK RENNIE.

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

UNITED STATES PATENTS Number Name Date 1,283,286 Pfanstiehl Oct. 29, 1918 1,289,896 Pfanstiehl Dec. 31, 1918 1,736,248 Brook Nov. 19, 1929 1,827,413 Ament Oct. 13, 1931 1,979,820 Bowling Nov. 8, 1934 2,054,921 Betterton Sept. 22, 1936 2,116,554 Bardue May 10, 1938 2,149,883 Coviolis Mar. 7, 1939 2,239,370 Osborne et al Apr. 22, 1941 2,269,838 Wooblewski Jan. 13, 1942 2,323,305 Burruss et al. July 6, 1943 2,337,042 Gloss Dec. 21, 1943 2,385,843 Rennie Oct. 2, 1945 2,402,084 Rennie June 11, 1946

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