US2456469A

US2456469A - Metallurgical furnace

Info

Publication number: US2456469A
Application number: US490256A
Authority: US
Inventors: Charles E Thomas; John S Eelter; Harold J Ness
Original assignee: Metallurgical Processes Co
Current assignee: Metallurgical Processes Co
Priority date: 1943-06-10
Filing date: 1943-06-10
Publication date: 1948-12-14
Anticipated expiration: 1965-12-14

Description

C. E. THOMAS ETAL METALLURGICAL FURNACE Bec. M, 1948.

Filed June 1o, 194s 4 Sheets-Sheet 1 4INVENTORS C. E.THOMAS J. S. FE'LTER BY nog ZI DSC. 14, 1948. Q EI THOMAS ETAL 2,456,469

K METALLURGICAL FURNACE 4 Filed June l0, 1943 I i 4 Sheets-Sheet 2 lNVENTORS CE THOMAS J. S. F ELTER H.J.NEss Y 'A R Y C. E. THOMAS E'I'AL.-

Dec. 14, 1948.

METALLURGICAL FURNACE 4 Sheets-Sheet 3 Filed June 10, 1943 INVENToRs y C.E.THOMAS J. S. FELTER H.J. NESS Dec. 14, 1948. c. E. THOMAS ETAL Y METALLURGICAI.:y FIURNACE 4 Sheets-Sheet 4 Filed June 10, 1943 INVENTORS C E. THOMAS J. SFELTER BY H. J. N ESS TTRNEY will be prevented.

burizing, depending upon the nature ofthe carrier gas. In order to prevent the muflie atmosphere may be either neutral to the work or carphere from being driven from the mufiie when the cover is removed, suitable control means is,-

arranged to be operated by removal of the cover to interrupt the operation of the circulating means and by replacement of the cover to restart the operation thereof. l

Numerous other features of the invention will be apparent as the description proceeds. i-'As will be evident from the foregoing, one of the principal objects of the inventionV is to provide a furnacenf the type described, in which there fwill be no' load upon the muiiie or upon Athe refractory furnace walls, thereby permitting -the muille to be made of thin walled alloy and the furnace walls to be made of light, porous brick of highinsulating value.

Anotherobject is to prevent 'damage to the -rnullle orv-to thefurnace walls due to frequent 'removal ofthe cover and the charge from the furnacel` and the replacement of the cover and insertion of anew charge within the muille.

FAnother object-of the invention is to support the work to be heated independently of its conif' taining mullie or of the refractory furnace walls. Another object is Ato facilitate the loading and unloading of the furnace so that these operations may beconducted quickly and conveniently and with a minimum-of heat loss from the furnace. "Still another object is to support the work parts inl the rfurnace out of contact with the walls thereof and with each other whereby there will #be no local-hot or cold spots on the work and 'whereby the furnace atmosphere will have free f access to all parts of the work.

Anotherobject is to preclude the presence of -pock'etsof trappedair in the work parts, carried into the furnace thereby,

parts, will vbe rendered nonoxidizing to the parts `byl chemical lreaction with the furnace yatmosphere. i .f

Another object is to provide `a progressively advancingA oxygen'rlxation front from the inlet of the protective atmosphere to the muille outlet,

'Still 'another object is to provide a furnace inl y' Vwhich-ahy air entering into the furnace during loading or carried into `the furnace by the work following the introduction of a load of work parts into the nuille. 1

f `Another object is to provide a muiile furnace of the pit type heated by an external combustion chamber in which leakage of r`the products of combustion from said chamber 'into the muiile Another object of the invention `is to provide a suitable,V seal containing displaceable material `material duringthe sealing support for the removable cover andfor the work parts.

A still furtherfobject is to provide an even and A uniformheating of the muille. l

Still another object is to provide a novel ar- Sentence Fig. 1 is a vertical sectional view of a pit type furnaceembodying a number of features of the present invention, taken on the line I-I of Fig. 3;

Fig. 2 is a plan view of the furnace showing the removable cover thereof; f Fig. 3 is a sectional view on the line 3 3 of Fig. l, showing the arrangement of the burners for the combustion chamber and the atmosphere inlet for the muiile;

Fig. 4 is a sectional view on the line 4'-'4-of Fig. 3, showing the lithium generator employed therewith for conditioning the furnace atmosphere;

Fig. 5 is a sectional view on the line 5-'5 o Fig. 1, showing the work parts and work retaining ring;

Fig. 6 is an elevational view of the furnace, showing the arrangement of the burners and the manifolding thereof;

Fig. '7 is a developed view of the furnace shell on a reduced scale, showing the arrangement of the burners; y

Fig. 8 is a layout view, showing the arrangement of a number of furnaces of the type shown zin Fig. l in connection with a common carrier gas rnumber of columns I5. A reinforcing ring I6 is welded about the open upper end of the shell lI0, and an annular angle I1 is welded to the shell at the floor level to serve as a support for the grating I8 forming a cover for the pit I3.

The shell I0 is lined with refractory brickwork composed of a base I9 of hard burned brick and a side wall 2I of alight, porous brick of high in- .sulating value. A cylindrical muille 22 is disposed v.centrally within the brickwork, resting directly upon the hard burned brick base I9 and spaced from the side wall 2I to form a combustion cham- -ber 23, and the side wall ZI is corbelled at 24 t0 `Ineetthe muiile 22, to form a roof for the combustion chamber. extending tangentially through the side wall 2l ,are arranged on an ascending helical line of in- ,creasing pitch, Fig. 6, whereby the greatest con- ,centration of burners occurs near the base of the lcombustion chamber with a progressively greater A number of burners 25y Fig. 3,

spacing vbetween the burnersV upwardly, thus compensating for the increased heat at the top of the 'muiiie due to the tendency of the heated gases to rise in the combustion chamber, and thus maintaining the mufe 22 at a substantially uniform temperature throughout its length. The circumferential spacing of the burners is such that the burners located on one turn of the helical line are 5 .positioned 'crculniereritial'ly i'intermlediate ithose on adjacent iturns. @ne Larrangemerit of fthe burners --is kshown in the developed viewof the shell "Folin Fig. 7,'infwhichburnersfare indicated -byithelettersa'tom The'spacing between burners 'of-each turn `is -such that there will befanodd xnuniber o'fburners ineach t-woiturns dfthe helix. This 4arrangement fenellil-es maximum spacing tbetween 'the eigmrners of adjacent turns 4to "be obltained, 1which promotes better bon'ding f I'the lwall 'and reduces the danger of weakwertical izon'es therein, particularly fadjlacent the "base VWhere ithe sp'iral is relatively'flat and l the=vertical spacing between burners 1is small. 'It Lalso prometes Iamore continuous spiraling Jand swirling `recess?? -formedlinthe shell'li). The burner-"exif ten'cis *through the 'Wall 'of fth'e recess 2l, and throug'ha hard-"burned 'brick 28, terminating -irr a 'molded refractory burner bloc-k A29 which 'forms 'anfoutwardlyilaringburnertunnelSD connecting 'with a passage 3'! inthe refractory side wall.

'The "angle of'the'burner and theburner tunnel is suchthat its laxisis substantiallytangent Itov the 'froid-'circumference fof 4the 'combustion chamber, `thereby p'emn'itting the combustion gases toA swirl 'aroundthecombustion chamber wit'haminimum ofinter'ference from the walls 'of the 'combustion chamber 4and with anaturalow into the gas stream issuing from Cthe rnext adjacent burner. The movement of "the Agases is thus laugmented V'by *the gases issuing from each suceeding burner,` producing a smooth spiral Liiovv oi considerable *velocity 'around vthe outer VAwall Aof the muffle 22. -*Due to Ycentrifugal action,`the gases scrub the Y"innerwall o'f the J'brickworlg Whichf'aids in'lthe extraction ofthe neatfromv'the gases and'a uniform fh'eating'd-f themuiile by' radiation from the h'otbrickwok "Fheburners `25'are provided'with a combusti- 'ble mixtureof V4air and gas lfrom a 'pair of Kmani- Tolds `32U^a;nd"?'2L (Figs, '1, y2, 3, and ii) "disposed about`sthe-shell I'Uand supportedthereontby suit- 'ablefbrackets Theupper m-ariifoldiSZU servestlre iburnersiintheupper 'halfv of the furnacegand the manifold '32L serves Ivthe lower group of burners. 'Each 'manifold vis provided with "an electricallyr "operated supply .valve SSUand SSL, whichscontrolled "by 'an individual 'pyrometer '34U and 3 5L, k*located `in the "zone serviced by jthe respective `manifold through vadjustable galvanometer switches '3 5U, 351'.. and `mercury switches "SBU, 3'BL. "Thus, 'the upper'and lower zones `of 'the 'furnace are separately controlled to aid in 4maintaining :a uniform temperature "throughouttheflength .,of the"mu"ie. The vproducts 'ofcombustion are exhautsedfrom'the chamber 23 by'twosets 'of exhaustgports STU 'and 31L, the former :consisting 'of three ports located just below fthe` upper jgroup "of burners Aandthe latter, asbest shown in'Fig.3, 'consisting of three ports located just below 'the ,'lowerset'ofburn'ers. "Each'exhaust, port-isformed fof aheat'resisting alloy tube extending through thebric'kwork and serving to conduct thegases *toia Asuitable stack Aor ventilator, not. shown. '.The mrovision "of .a `separate set 'of exhaust ,ports for 'eachof'thesets'of burners also'aidsin maintaini xlingamidiforrmternpenaturent/ithintheiuflielsinele =the two fsets of r burners 'will operate fon indifferent 61T and on`timie'intervalsluniiertheirimdis -vdual controls.

The opentupperfend'ofithexmuiileicisnlcsedby a :removable cover 39 comprised cof I. a imetal shell 4containing rrefractory 1heat insulation 'M -shell formed by two spaced discs ortplates m2 and 43 Iseparated i byff-an r annular ringffornre'd'frfa VVchannelfmeniloer M, 'an-angle '1515,:a'nd-g tlibe for pimms, eacnweluedito'lits adjoiningfmemeer. :ne annular ang`1e^f41 welded to 'the pipe 24-6 #forms a -Seat for the ilower plate 43, ywhich .is of iheat :resisting/alloy. A number ofigussetfplatesidiane `Weldedbetween Lthe pipe Alili andi-the angleito `reinforce =the same r'and 'to .absorb lanyrshock'iim# parted l'thereto'by thefcover centeringi meansdur- -`ing thelowering ofthe cover toits seat. iThis eenfteringmeans Willbe described subsequently. 'The `'toveriis reinforced by fourlsubstantially diagonal AIibe'ams '-48 subtended by `'four Ibeams 51. jshort `-section of -rI-beam 52 extends between the intersections of the I-beams 149. A-ll'ofthesemeinforcing beams are weldedto eachother and to the channel-meinteer-l'liv and are r4forthe purpose'o'f jprovi'ding a' strong, rigid structure fromwhic-hithe lheavy work parts lto b e Itreatedmay'bel-suspended Withinthe'muie, as willhereinafterfappear.

"The cover .39 lWith `"the n/'orkfparts 4to be ssuspen'd'ed therefrom is "supported lindepen'clentlyfdf 'the mu'ile .22 and the brick side Wall 2`gl uat a part o'f 'the Y'furnace which is maintained Vat -f'a Arelatively A'lovv "temperature, For this purpose an annular angle ".53 is Welded to the interior ofthe shell with its upper -face 'slightly 'above :the 'top of the "brick sidewall 2i andthe'miilie 22, thereby .maintaining '3a space 'between *the'bot- 'tom cover plate *43 .and these members -vvvhen ithe cover 'is .resting upon "its 'seat 53. Thus, `neither the 4cover "39 wnor lthe Work parts can "imposeany loadonthe Amulileorron itsesurroun'd- 'ingbri'ckwork or'eiectany'damage thereto. A'a "consequence,v l thernu'ilie 22 may '-havefa rela- `tivelstliin Wall, su'fcient only'to Supportitsown Weight'tvhenheated- T'lhisresults in alargefsavfing of anetal antifa substantial-economyin constructioncost. It also promotesmore Arapid heat 4transfer fromrthe'combustion gases in the-'outer fchaniber'23. e

In `order to 'seal theinterior nf the muliie ""22 from *the 'combustion chamber Q3, 'an annular "trough ".54 iis Aformed 'at `the Aupper "end of the muflie in which a suitable displaceable sealing material "55 'may be contained. Preferably `this materia-l is `granular :chromeiore substantially free 'of powder and 'of a suflicient .size to 'have a`loW angle of repose,.so astopreven't packing and to "permit -l'eatly displacement 'therecif, Vailvlthough beach sand Aor other suitable 'refractory ,sealing material ,may Lbe use'd. An annular orring 56, depending from the coverplate 313, "is'providedfor .entry into the trough "54 to com lplete @the seal. This .ing56` is"beveledat itslower 'edge to facilitate yd isplacement ofthe sealing .materiaL f A similar seal, comprising ,an annular trough '5l Aformed in the brick side Wall "2l, a sealing medium 58, and a cooperating dependinggsealing ring 59, provide aheat ,seal lto'isolate.-tllercover .supporting ring 5'3 from 'the combustion gases. VThe depending 'length of thesealing rings .55 and 59 is such that they 4engage in ,the troughs "54 andl5l only after the cover 31lhas progressed into the feXtended :upper `end Aof thefshell gill a short distance, thus insuring correct centering 7 ofthe .cover over the inuiil'e and proper alignment ofthe l'sea-ling rings over their respective troughs beforey entry of the rings intoithe troughs.` Pcs'- sible damage to the sealing rings, or to the Inutile, or the .brickwork, by accidental engagement f the sealing rings therewith is thus prevented. Inorder that there will be no sudden shock irrifparted to the muiiie 22 by the sealing ring 56, transmitted through the sealing material 55, lshould the cover be lowered to its seat atan abnormal rate, the 'outer sealing ring 59 is made of considerably greater wall thickness than the ring 56 which, together with its greater diameter, gives it a much larger area of contact with the sealing material than has the inner ring 56. The 'shock of a sudden movement of the cover to its seat will, therefore, be taken up primarily by the outer ring. To stiifen the upper end of the muiile 22 and protect it from` accidental knocks, as from the work parts, if improperly loaded, and to retain the sealing medium therein, a beading 6| is formed about the upper end of each .wall of the trough 54.

3 The parts to be treated are shown in4 Fig. 1 as comprising tubular blanks 62 for use in the production of steel propeller blades for aircraft. 'Ihese lblanks are threaded at their upper ends for subsequent attachment to the propeller hub `and these threads are utilized to suspend the blanks within the muille 22. y For this purpose a `hollowplug 63, having apertures 64 therein and a hook 65 formed-thereon, is threaded into the blanks. The apertures 64 are provided for the lescape of the air contained within the tubes .when first loaded into the furnace and for cr- .culation of the protective furnace atmosphere wtlflerethrougl'i during the heat treatment, as will hereinafter appear. The blanks 62 are suspended from a plate 66 having stiffening ribs l61 cast thereon and provided with a group of Mdepending hooks 68 secured theretoy as by means ofnuts 69, for interengagement' with the hooks `65. The plate 66 extends to adjacent the side wall of the muiiie 22 and its lower surface is conca-ve so that it will serve as a baffle to direct the muiile atmosphere in a circulatory path, as will hereinafter appear. It is carried by the .cover 39 through a quickly detachable universal coupling comprising a double shackle, member 10 having its pins 1I and 12 disposed at right angles. The shackle is secured by its upper pin 1I to a rod 13 Xed to the cover I-beam Section 52, as by bolts 14, and the baille plate 66 is susjp'ended therefrom by a rod 15 passing loosely through the plate 66 and having a nut 16 on its lower end. The shacklelpin 12 is removable and passes through the eyes of the shackle and rod 15. In order to limit swinging of the plate 66 on the shackle bolts, a number of upstanding posts or lugs 11 are provided on' the plate 66 extending to adjacent the `cover 39. Swinging of the blanks 62 on the hooks 68 is prevented by concentric retaining rings 18 and 19, Fig. 5, removably carried by a depending rod l8|] vrigidly secured to the under side of the plate 66. The ring structure is spidered to a sleeved hub 8l having a pin and bayonet connection to a sleeve B2 carried by the rod 8D. Thus, after the blanks 62 have been secured to the plate 66 externally of the furnace, the retaining ring structure is slipped up over the ends of the tubes and fastened in place by the sleeve 82.

A protective atmosphere is introduced into the muiile 22 under slight pressure through a conduit 83 and is exhausted therefrom by a vent 84 extending through the cover 39. The' ess caping gases are ignited by a pilot burner 85 carried by a pipe 86 extending over the cover 39.Y The' pipe 66 is threaded in the elbow of a swivel coupling 81 bolted through a squared iiange '89. to a bracket@ carried by the furnace shell. The coupling 81 communicates with a gas supply conduit 9B, Fig. 2, having a suitable valve 9| for regulating the length of the ,pilot name. The burner 85 is adapted to be moved away from the cover 39 and back into position to re-ignite the vented gas, upon the removal and displacement of the cover, by a lever 92 pivoted on the sleeve section 93 of the coupling and clamped at 94 to the pipe 86. The outwardly extending end of the lever 92 is pivotally connected by a link 95 to the plunger rod 96 of a piston 91 contained within the cylinder 9815ecured to the bracket 88 by the lugs 99. Air under pressure is admitted alternately above and below the piston 91 by a reversing valve 100 operated by a solenoid |01 controlled by a switch |92 in accordance with the position of the cover 39. A switch operating lever |03 pivoted on the bracket 88 has one end extending through the shell I0 into the path of the cover 39 so that with the cover in closed position the lever will be depressed and its outwardly extending arm will be held out of engagement with the contact arm 104. Therefore, contacts [92 will remain open and contacts |05 will be closed. In this condition of the switch, solenoid 16| will be deenergized, and the reversing valve IUD will be s o positioned as to admit air to the under side of the piston 91 whereby to retain the piston in its uppermost position so that the pilot burner 85 will be located over the cover 39 of the fur;- nace in position to keep the exhaust gases from the furnace ignited. However, upon the initial movementfof the cover upwardly, lever 103 will rock under action of the spring 106 to close contacts |02, and energize the solenoid HHV so as to reverse the valve l. Air pressure will then be applied above the piston 91 to draw the ylink 9 5 downward, and thus rock the lever 92 and pipe 86 to the vertical dotted line position away from the cover 39. On return of the cover 39 to its seat, the reverse action occurs, and the pilot burner is returned to its horizontal position over the furnace to reignite the gases escaping from the vent 84. Since the vent 84 is disposed substantially centrally of the cover, the pilot flame will ignite the escaping gases irrespective of the angular position of the cover on its seat; thereby no indexing of the cover is required. Withl a commercial size furnace, the pipe 86 will be sufliciently long to elevate the burner above the iioor at such height as to produce no hazard. It will .be understood that the pilot burner will be pivoted at the side of the shell l0 remote from ,the direction of loading andl unloading of the muiile.

The loading and unloading of the furnace is effected by a traveling crane or hoist having a chain gear which engages the cover 39 by means of four eyes 108 suitably anchored to the lower flange of the channel frame member 44. The operation of unloading the furnace comprises the lifting of the cover and its load of Work parts vertically so that the work parts clear the top of the furnace and a lateral movement of the cover to a point where the work parts may be lowered between a pair of suspendedrails upon which the plate 66 may rest. With the load thus removed from-the cover 39, the shackle pin ."12

9? may: be." removed:4 the cover, positioned. over another.t plate 6&6# carrying. an cold load; I'heY shackle` pin:` is:` reinseifted and: the cover andi cold; load... conveyed a pointl. vefticallyf above' the: muffle- 22? and then: lowered in pla-ce.y In order: to..l center the coveru in: thefsh'ell. 0i and; align ther sealing.. rings 56 and: 591 with: their troughs;-, a number: ciz centering guides lilili are. secured: to\ the'fupperzedge` of the turnacefshell... Eachbf.- the guides lSr comprises# a U-shaned. brackets. the upper" edges of-r which slopeA outwardly. from the: cover, and .aiseriesz oflneedle :rollers |P| loosely.- journaled in. grooves; |=|-|.r im the: opposite: arms ofi theebracket.. The brackets aref securedy to. thefshell in any suitable manner, as by We1ding;. In@ lowering' the` cover. into position; should it be slightly? oft center', ,thefafnnulan pipefdz; Awhiehzhas:- a-.relatively-1ar-ge radius, will: engagesl onefor-theother. offthefguidestolgive-it the. required laterali movement.- tocenter it withI respect-Lto? the munie.- L

and enable it. to pass' freely intox ther furnacef opening..v

To. promote.L the circulation off the atmosphere? through* and around the blanks; er fan: |.|2f' is.

provided; inthe; base of. the` muflle-,. driven. from u asuitablev motor |f| 3. by,r meansoir a. belt. Movandl ashaft M5.. The. shaft. ||15 extendsi through. a" tubular. extensionr of the. muiilef 2lM and is: provided with a... pressed: graphitel bearing; lli!A within. the tube: andrwitha pair. ci ball,P or.V

roller bearings.. |.|8, carriedbya. bracket irl-hse tube H1B" is sealed by a.. gland |2ll' and:l is. pro vided'- with anumben otheatA insulating. disks |'2.ll: fn baiting; theJ iiow.v ofi. hot tube |16.' andfoi; conducting; the heat. away.y from the shaft ISand'theglandfl-Zilr Ii desired the; gland;v may. be cooled by either an air streamer' by ci'rculatihr; water. thereabout, asby thecoil. |22. E tubular fan.. housing |231 elevatedlfrom, the iloor of the. muiileA onlegsf or. brackets sur rounds theV fan. |.'|'2 andlt'ends to. direct. the.at.- mospliere stream upwardly through=and around.' the work parts G22. It.. is. coveredl witlrafwirefl mesh. |211 to diffuse the. gases. andr guettent-injury tof the' i'an. by any.A Work. parts. or.. other. objects.` dropped'int'o' the muilie accidentally.

The` atmosphere. forcedf. upwardly by the fans through the center. of the muiil. into and'arcund the iubes' 62 is. deflected at. the. top offthe. muilie; by the baille plate 5B). passing, towards thesidey Wallf of the mufe and.` sweeping, dow-never the. heated* surface thereof' in. a. verticali circulatory path; A portion ofthe atmosphereipasses around. the edge of" theplate:6b"and` escapes thlloughithe vent 8`4, Where it isignitedl. 'I'lieburriingdv gases. at the vent 84. serve' as. an. indication ot the.' conditionV of themul'e atmosphere, burning. with. the`A characteristic' scarlet col'or of" lithium when the atmosphere? is properly conditioned. The opening throughthe vent 84 is of such, size as to` maintainaslight*k pressureI Within' the munie.

The operationz off' thefarr |12" is` controlled b'y t'li'ev removal and replacement or the cover S'SI through the switch contacts |05 operated'by the switch. lever |413. Withi ther comer in. position, the contactsA |05 will.. be closed. and` the motor circuit completed, but'upon removalof the cover these contacts: will be` opened tol quickly# inter'- rupt. the: motor.' circuit-L and stopthe fan so thatvlthefhotsatmosphere inftliefmuilly will. not. be driveniun aboutnthosides crit-he cover asitl. is lifted'zfrorrrl its.: seat. 'llieffan then remainssoutf ofV operationrthrouallcut the'entirefumloadingfandmeloading onerationi.

gases through the :l

the operation of 'Ilhe inlet conduit; 83. for the.- muflle Latmosiphere.

encircles ther` fan housing. |23.A below' tholower. edge thereo Ity is provided,I with. atseries of. slotsr 25.` on its inner face for theadmission of,

j. the protective gas into the Inutile;.radial-1y in the.

directionof circulation... ofthe muiile atmosphere as producedv by theA fany M2 when. it. is) in ope-r,-v ation. In addition.I toproViding. aruniformldisf.

tribution: ofthe. lithiatedl gas to. ther blower, thel extension.- ofthe` conduit 83 throughthecombusw tion chamber 2r3sand.infa long. path. inithe` base. of the muiile. enables. the incoming. gas.. to.l be. brought-K upto the. muilleV temperature' before. issuing into the. muflle; Thispreheatingof'tle;

-lithiatedgases. promotes the reaction.- of the the muflie 22, andasubstantiallvolume ona-inis also carried intoith-e mule within the tubular wor-k. parts. Toexpedite thefremovaLof, the fromthe muiiie, andior.. the. 'xationoi. theoxygen contained` therein, by. the protective. atmosphere introduced.v into'thebase .ot the. muliie, ,itis .preterable :to retain. the. blower. atrestior. ashort after thefcover-hasbeen replaced.. Eor.this..pur pose theswitchontacts. |05',v whichiareclosedby. the. replacement, of. thacoyer, ,do not immediately. energize the motor, a delay being intrtoducect'by.` a time delay. switch |2, such..as an .electrie timer or a dashpot relay, .thus holding the. blower. cirouit. open. for. aA sufficient period.. to substantially. ri'd. the.A mufle. of` the. air or. oxygen .thereirn The. time. delay switch.. |251 may be adjusted son that; its. contacts.. will. not. close until.. after. the tell,- tale scarletame.. appears at the vent. 84'..

The restoration. of; the. desired. protective. at.- mosphere inthe muleis.notdependentuponthe physical displacement. of theair by rhein-coming gas, but primarily. upon achemical fixation ofLthe oxygen andwater Vapor. content, thellattereffeetl beingV obtainedl from the lithium introduced therein. Lithiumhasa strongaaffinity. for oxygen andU permeates the munie chamber, penetratingv into the interior of" th'e tubes (i2and.chemicallyv uniting with any oxyeenor` water vapor. therein to x the same, as will. presently appear- As. stated-when the col/er 39. of the. furnaceis removed, the lithiated` atmosphere. in. the.. muiile escapes and is replacedby air. The ian. |'|2.`is.at rest at4 this time, and! the. lithiated. gases issuing; from the, apertures` 2F the. conduit, 33T into. Contact with this air burn in the base oilthe Inutile. When the cover. 39S is rst replacedthe.

fan is. still`retained`, at rest, .but asthe OXygerLad.- jacent the apertures l25iscon'sumed. the incom.n ing.lithiatedgaseswhich' are only partially. com.- bustedg' spread' out' radially 'and upwardlyfrom the conduit' 83,' forming a. substantially. continu.; ous'at'mosphere front' which'..progressesuprvardly., displacing a partv of the air. through. the,v vent 84 and consumingthe oxygen in. contact. therewith as. it advances upwardly. The oX-ygenisinpart. converted'by the CO andHz of theincomingg'ases to CO2l and H20; and these together with. any. remaining oxygenare xedby. the lithium. of the. carrier gas; By retaining` the4 fan 2 at.` rest, during thisV cleaning' up period, this combined. flame propagation' and' oxygen xation iront...is

11 permitted to advance upwardly of the mule without intermixing of the air and the carrier gas, with a progressive fixation of the oxygen and water Vapor content of the air as this oxygen xation front advances.

When the lithiated gases reach the top of the muiiie and start escaping from the Vent 84, they will be ignited byv the pilot burner 85, and this flame will gradually assume a rich scarlet color, indicating that the muille has been entirely freed of any unxed oxygen. When this scarlet flame appears, the fan ||2 may be started, and the dashpot relay |26 may be adjusted to provide a time delay sufficient for this purpose.

In order that the furnace attendant will know when the fan ||2 is operating, a signal lamp |21 is provided mounted at any suitable position, either on the furnace or on the control panel, operated in parallel with the fan motor I I3.v

Y The inlet pipe 23 for the muiile atmosphere extends from a lithium generator |28 suitably secured to the outer Wall of the furnace, as by lugs |29, As shown in Fig. 4, this generator comprises a metal chamber |3| having aremovable cover |32 from which a plate |33 depends. Around the chamber |3| is disposed an electrical heating coil |34 contained within suitable refractory insulation, and within the chamber there is a central cylindrical recess' |35, in which is supported a metallic cup |36 containing suitable lithium compounds. A carrier gas is admitted into the lithium generator through a conduit |37, this carrier gas `being deflected by the partition plate |33 over the cup |36 and thence by way of the conduit 83 into the muffle 22.

The carrier gas may be a non-oxidizing me-- dium, such as nitrogen or hydrogen, although a gas resulting from the combustion or cracking of a liquid or gaseous fuel is preferred. Air may also be employed as a carrier gas, if desired= since the lithium fixes the oxygen therein. However, the use of air as a carrier gas requires the consumption of a greater quantity of lithium and is not preferred; Fig. 8 shows apparatus for producing a suitable carrier gas bythe combustion of an air and gas fuel. Hydrocarbon gas, such as butane, propane, or natural gas, supplied from 'a conduit |38, and air drawn in through a conduit |39, each provided with an apertured plate or disc |,4I for metering the proportion of each, are forced under slight pressure by la pump or blower |42 into a closed cracking chamber |43. The chamber |43 is heated by a series of burners |44 extending tangentially into the combustion chamber |45 of a furnace |46 in which the chamber |43 is contained. The ratio of the hydrocarbon gas to air is dependent upon the analysis of the former, and the purpose for which the muile chamber is to be used. For the heat treating of metals, where a neutral atmospher-e is desired, We prefer to employ a ratio of approximately l part of propane to 18 parts of air, whereas for carburizing a ratio of 1 part of propane to from 4 to 12 parts of air may be used, depending upon the analysis of the gas and the type, analysis n and quality of the carburized case desired.

The furnace |46 may be of similar construction to the furnace of Fig, l, with the closed cracking chamber |43 substituted for the muflle 22. The burners |44 are supplied with fuel and air from an independent source to provide heat of approximately l800 to 1900 F. for cracking of the gases in the chamber |43, as fully described in Patent No. 2,346,698 of H. J. Ness, granted April 8, 1944, and entitled CQntlOllQd 12 atmosphere furnace. Thecracked gases from the chamber |43 are passed through a condenser |41 where they are cooled and the major portion of the water is removed. A condenser suitablel for this purpose is shown in the Patent No. 2,394,002 .of H. J. Ness,` previously referred to. The cooled and partially dried gases'are conducted by a conduit |48 to a manifold |49 from which it is distributed to the lithium vaporizing chambers |28 of a number of treating furnaces A, B and C, similar to the furnace of Fig. 1 As stated, this gas in passing through the chamber 3| picks up the vapor emanating from the lithium compound in the cup |36 and carries it into the muiile 22.

The preferred charge within the cup |36 comprises a mixture of lithium carbonate and lithium chloride in the proportion of about 60% of the former and 40% of the later, by weight, which has been fused together at a temperature of about 1800" F. With a fused mixture of these proportions, sufficient vaporization occurs ata temperature of about l300 F. to create an appreciable lithiated muille atmosphere, although higher temperatures may be employed depending on the amount of lithium desired in the atmosphere. The amount of lithium salt required to produce a non-oxidizing and non-decarburizing and nonstaining atmosphere in the muiile 22 is very small. With a muilie heated to 1400 F. and having a volume of approximatelylO() cubic feet and provided with a mixture of air and gas entering the gas generator at the rate of about 1200 cubic feet per hour, a 7 to 8 ounce charge of lithium salts composed of 40% lithium chloride and 60% lithium carbonate, heated in the vaporizer toa temperature of 1800 F., will supply sumcient lithium to the atmosphere within the muille to maintain'the same for a period of 12 hours or more in a condition which is neutral to steels or other metals so that neither oxidation, nor decarburization, nor stainining thereof will occur. While it is desirable to maintain the charge in the Vaporizing chamber |3| at a temperature of at least l800 F. for the salt mixture specified, the

muille 22 may be operated at temperatures ranging from 450 F. up to the maximum temperature that the muffle will withstand.

While the exact nature of the chemical reactions occurring in the charge in the cup |36 or between the generated vapors and the combustion.

gases from the cracking chamber |43 is not fully known, the following explanation is supported by a large amount of experimental evidence.

The lithium chloride within the cup at the temperature prevailing therein is reduced to lithium metal by reaction with thehydrogen of the carrier gas in accordance with Ythe equation The hydrochloric acid so formed then reacts with the lithium carbonate or any lithium oxide in the cup to produce additional lithium chloride as follows:

2HC1 LizCOs 2LC1 -1- H2O -1- CO2 2HC1 -l- LizO 2LiC1 -i- H2O The lithium chloride formed by the above con'- version reacts with hydrogen, as set forth above, to liberate a vapor of lithium metal. i

. In this manner the lithium carbonate is gradually converted to the chloride and thus to the metal, as the process proceds. The proportion of 40% lithium chloride and 60 %v lithium carbonate appears to be so balanced as to render the hence, a sharply peaked secondary voltage, .the eifect of which is accented by a tuning condenser |16 across the secondary winding.' The rapid vibrations of the armature |13 are communicated through the rod |69 to the plate |'65,'and thence to the sealing ring 56' and to the sealing material 55 adjacent thereto, causing the latter to become fluid and enabling the sealing ring to readily penetrate the same as the cover islowered to its seat. A switch |11 in the vibrator circuit permits the vibrator to be operated only during the cover opening and closing operations. The switch |11 is normally open but is arranged to bel operated by a slide |18 extending through a slideway in a block carried by the furnace shell Il! into the path of the ringA |19 which encircles the outer end` of the' I-beam's |59. Consequently as the rings 56' and 59 approach the sealing medium in their associated troughs, the slide |18 is engaged by the ring |19 and cammed outwardly thereby to close the vibrator vircuit. This circuit remains closed until the sealing rings are substantally fully engaged in the sealing medium and the cover fully seated upon the support |62 whereupon the' slide is released to open the vibrator circuit;

` The disc |80 rests on an enlarged portion |89 of the stud I9! by which it is carried from the shackle 10 by the removable pin 12. The lower end of the stud |S| has a cylindrical recess |92 therein adapted to receive a vertical stanchion orpost, not shown, to support the disc and its load of work parts when it is removed from the furnace for cooling. The furnace of Fig. 9 is otherwise similar to that shown inFigs. l to 4.

`Itwill be understood, of course, that many modifications and alterations of the structure shown'and described may be `made without departing from the essential attributes of the invention, and all such changes are contemplated a-s coming within the scopel of the appended claims.

What is claimed is:

. l. A furnace comprising a vertical heat treatl ing chamber having an open top, heating'means for said chamber, a removable closure member for said chamber, means for supporting said closure member on said furnace structure independent of said heat treating chamber and a plurality of concentric gas seals between said heat treating chamber and said supporting means, one of said seals being disposed between said heating means and said supporting means and another of said seals being disposed between said heat treating chamber' and said heating means.

2. A furnace comprising a heating chamber, a muflle disposed in said heating chamber and hav- -ing an open top, a closure member for said'mufile, means vcarried by said closure member for forming a gas seal between said heating chamber and said mufe, a support for said closure member disposed rem'ote from the heating chamber and a heat sealv between said heating chamber and said support adapted to be closed by said closure member.

3. A furnace comprising a heating chamber, a muiiie disposed in said heating chamber and having an open top, a closure member for said muiiie, means carried by said closure member for forming a gas seal between said heating chamber and said muie, a support for said closure member disposed remote from the heating chamber, a heat seal between said heating chamber and said support adapted to be closed by said closure member, and work supporting means carried by said closure member.

4. In a furnace structure, the combination of two co-operative chamber forming members movable into inter-engaging relation to form a closed chamber, a displaceable sealing medium carried by one of said members and engaged by the other to seal said chamber and means for vibrating one of said members to facilitate displacement of said medium.

5. In a furnace structure, the combination of two co-operative chamber forming members movable into inter-engaging relation to form a closed chamber, a displaceable sealing medium carried by one of said members and engaged by the other to seal said chamber, means for vibrating one of said members during the inter-engaging movement of said members and means for interrupting said vibrating means upon full engagement of said members.'

6. A furnace comprising a heat treating chamber having a channel at its upper end for holding a displaceable sealing medium, a closure member for said chamber having a flange disposed in said sealing medium and removable for access to said chamber and means carried by said closure' memb'er adapted to vibrate the same to facilitate displacement of said sealing medium about said ange.

7. A furnace comprising a heating chamber having side walls, a muiiie disposed Within said chamber, a channel at the upper end of said side walls for holding a displaceable sealing medium, a channel at the upper end of said muille for holding a displaceable sealing medium, a closure member for said chamber and muiiie having depending flanges adapted to be disposed in said sealing mediums, and means carried by said closure member for vibrating said anges to facilitate the displacement of said sealing medium thereabout.

8. A furnace comprising a heating chamber having side walls, a muffle disposed within said chamber, a channel at the upper end of said side walls for holding a displaceable sealing medium, a channel at the upper end of said muifle for holding a displaceable sealing medium, a closure member for said chamber and muifle having depending flanges adapted to be disposed in said sealing mediums, the iiange associated with said first channel having a greater displacement than the flange associated with said second channel, whereby impact shock of said closure member will be received primarily by said side walls.

9. A furnace comprising a heating chamber having side walls, a muiiie disposed within said chamber, a channel at the upper end of said side walls for holding a displaceable sealing medium, a channel at the upper end of said muiile for holding a displaceable sealing medium, a closure member for saidachamber..andimuille having depending ilanges adapted to'be disposed in said sealing ime'diums, :the `rising'e"lfass'o'ci'atedwithfsaid first channel being adapted toi engage-lits associE ated sealingmediumprior-to engagement of the ange associated with said second channel with its associated sealing medium; vvherebyimpac't shock ofsaid closuremember v'vlillbe received primarily by'said'sidewalis."

A furnace compri-sing"arheatinggchainber having an" openingdn 'its`"uppe1'j,:end, a"cl'os'ure member for: said opening'supported'independently of said. "chamber, a"botton1^' plate icarrie'd' .byA said closure' member' adjacent' the^center thereof:V and having-its' outered'ges free; saidplate being' exposedto the' direcrheatorsaidbnamberandbeing free to'expa'ri'dlaterallyrelativeto sa'id'closure member.

11; A furnace comprising' a heating chamber havingr anopen'ing in" its' upper. end, .acclslure member forsaid'opening'suppor'ted indep, "d", Atlyof saidchamber, a bottomlplat'ecarriedb said closurelmember adjacent thecenter there'o'i and having itsoute'r edges freesaid4 plate being, exdosed-to. the heat OfSai'dLChamber-and being-4free tofeXpandlat-erally relative togsaid closuremember,` a channel disposed" abouttha upperedge of 'said chamber for holdingaa.,displaoeablesealing mediumland aflange dependingfmm said?l plate for reception in saids'ealingI medium.

l2. A furnace comprising,awheatingechamber having an opening in its upper end, a closure member for said opening supported independently of said chamber, a bottom plate carried by said closure member adjacent the center thereof and having its outer edges free, said plate being exposed to the heat of said chamber and being free to expand laterally relative to said closure member, a channel disposed about the upper edge of said chamber for holding a displaceable sealing medium, a ange depending from said plate for reception in said sealing medium and means for vibrating said plate to facilitate entrance of said iiange into said sealing medium.

i3. A furnace comprising a combustion chamber, burners extending therein, a muilie having an open top disposed in said combustion chamber, a closure member extending over the top of said muiiie and said combustion chamber, a support for said closure member disposed remotely from said combustion chamber, and means carried by said closure member for forming a gas seal between said mule and said combustion chamber and between said combustion chamber and said support.

14. A furnace comprising a heating chamber having a removable cover, means for introducing a gaseous medium into said chamber, a conduit in said cover for egress of said medium, removable means positioned over said cover, adjacent to said conduit, for igniting the gaseous medium escaping therefrom, and means operated by the removal and replacement of said cover for moving said removable means to a position at one side of said cover and back to a position over said cover.

l5. A furnace comprising a heating chamber having a removable cover, means for introducing a gaseous medium into said chamber, a conduit in said cover for egress of said medium, means positioned over said cover, adjacent to said conduit, for igniting the gaseous medium escaping therefrom, said last means being movable to a position at one side of said cover to permit removal of the cover, and means for retaining said means in each position.

Crl

1.6;;Affurnaoezcomprising asubstantially-cylindribaly Shell,Iasrefractoryglining:within said shell forming.: a: chamber,V heating,- means for said chamberyasubstantially-gewindricalmunie within said'f chamberysa-id mulilehaving` an open top, ai'closure imembergextending. ,overy said muilie and said refraetoryqlining, means'fcarried by -said shell forrsupporting Aesaid closing'member outA of contactfiwithfsaid refractory-'lining and/said mufile, a Work support carried by said closure .member forsuspending the Workato be heated Within said muniey andmeansefor,:preventing gas vtransf er between saidgchamberfandsaid muflie. y

17.` Alfur-nace comprising a/,heat treating chamberfhaving-gamopening .therein for loading andlgunloadingf.theffurnace aremovable closure member :'for vsaid openingi an .inlet conduit for introducingv a gaseous atmosphere into said cl1a1nber,=n a.vent-.forsaid chamber, meansV for circulating said atmosphere Within; the chamber andI means :operate'dbyasaid closure member for controlling;l the; operation of said circulating means...

18; i Afurnace. comprising` a, heat treating chamberihavingaan'opening therein for loading .and unloadihgthexfurnace; aaremovable closure member for'V said-opening?, means forintroducing a gaseous atmosphereintosaid' heat treating chambefr, means foricirculating said atmosphere within the heat treating chamber and meansy operated upon the openingoisaid closure member to interrupt the operationfof saidcirculating means and upon theclosing offfsaid* closure member for restarting the operation of said circulating means.

19. A furnace comprising a heat treating chamber having anopening therein for loading and unloading the furnance, a removable closure member for said opening, means for introducing a gaseous atmosphere into said heat treating chamber, means for circulating said atmosphere within the heat treating chamber, means operated upon opening of said closure member to interrupt the operation of said circulating means and upon the closing of said closure member for restarting the operation of said circulating means, and means for delaying the restarting of said circulating means for a predetermined time after the closing of said closure means.

20. A furnace comprising a furnace casing having an opening therein, a heat treating chamber in said casing, a closure member for sai-d chamber extending into said opening, means for circulating a gaseous medium in said chamber and means engageable by said closure member when in said opening for controlling said circulating means.

21. A furnace comprising a furnace casing having an opening therein, a heat treating chamber in said casing, a seat Within said casing, a closure member for said chamber extending into said opening and resting on said seat, means for circulating a gaseous medium in said chamber and switch means engageable by said closure member on movement to and from said seat for controlling said circulating means.

22. A furnace comprising a heat treating chamber, heating means for said chamber, gas circulating means Within said chamber, a drive shaft for said circulating means extending through Wall of said chamber, a tube surrounding said shaft and extending into said chamber, a seal for the outer end of said tube and gas non' retard-- ing means in said tube between said seal and said chamber.

23. A metallurgical furnace having a heat treating chamber, heating means for said chamber, means for introducing a gaseous atmosphere into said chamber, and a revoluble fan Within said chamber for circulating said gaseous atmosphere, said gas introducing means comprising a conduit disposed about said fan and having inlets for directing the incoming atmosphere substantially in the direction of circulation of said atmosphere as produced by said fan and substantially uniformly with respect to the axis of said fan. l v

24. A furnace comprising an open top heat treating chamber, a removable closure member forsaid chamber, means for introducing a gas atmosphere into'said chamber, circulating means for said gas, a bale plate adjacent to and spaced from the top of said chamber and extending to adjacent the sides thereof for deiiecting the gases towards the side of said chamber and means for supporting said baille plate from said cover.

25. A furnace comprising an open top heat treating chamber, a removable closure member for said chamber, means for introducing a gas atmosphere into said chamber, circulating means for said gas, a baille plateadjacent to and spaced from the top of said chamber and extending to adjacent the sides thereof for deilecting the gases towards the sides of said chamber, means for detachably supporting said bafe plate from said cover, and work holding means carried below said baille plate. f

CHARLES E. THOMAS, JOHN S. FELIER. HAROLD J. NESS.

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

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