US2740177A

US2740177A - Continuous metal casting process

Info

Publication number: US2740177A
Application number: US369292A
Authority: US
Inventors: Jr John S Smart
Original assignee: American Smelting and Refining Co
Current assignee: American Smelting and Refining Co
Priority date: 1953-07-21
Filing date: 1953-07-21
Publication date: 1956-04-03
Anticipated expiration: 1973-04-03
Also published as: DE1408397A1

Description

April 3, 1956 J. S. SMART, JR

CONTINUOUS METAL CASTING PROCESS Filed July 2l, 1953 5 Sheets-Sheet l JNVENToR. J'aH/v 5. SMA/PT, .m

TTURNE Y April 3, 1956 J. s. SMART, JR 2,740,177

CONTINUOUS METAL CASTING PROCESS Filed July 2l, 1953 5 Sheets-Sheet 2 .IN1/EN TOR. 10H/v 5. SMART, JA.

ATT/VE Y April 3, 1956 J. S. SMART, JR

CONTINUOUS METAL CASTING PROCESS Filed July 2l, 1953 5 Sheets-Sheet 5 INVENTOR. JOHN S. SMART, JR

Byzlmhly. MLC

A TTRNE Y April 3, 1956 J. s. SMART, JR 2,740,177

CONTINUOUS METAL CASTING PROCESS Filed July 21, 1953 5 Sheets-Sheet 4 i INVENTOR. Ja/m 5 SMARJ/,

I K' BY www# ATToR/VEY April 3, 1956 J. s. SMART, JR 2,740,177

CONTINUOUS METAL CASTING PROCESS Filed July 2l, 1953 5 Sheets-Sheet 5 INVENTOR. Ja/m s. sMARJ/.

Arran/EY United States 2,749,177 i coN'rnsrUoU's1t/murJ CASTING rnocnss John S. Smart, Jr., Westfield, YN.' l', assignor to American Smelting and RefiningCompany, New York, N. Y., a corporation of New Jersey Application royal, 1953, serial Noreen-292. 14-C1atms`.: (crac-Lattea)` This invention relates toa continuousmetal casting process. More particularly, it relates to a process of this type in which an improved surface in=the casting is produced. It especially relates to such a process in which an improved surface as well as other improved -physical characteristics are produced in thecasting.

Although many continuous casting processes have been proposed in the past, the castings from 4such prior Yprocesses have been characterized in varyingfdegreeby certain surface defects and internal faults. The surface defects in the castings from such prior processes may take the form of a plurality of small lateral `surface cracks, wrinkles,v crumpled areas which are usually-composed of minute longitudinal gouges confined to an area or zone; or rough, shaggy surfaces. In some processes,the surface cracks may oe so severerthat thecasting rnaybreak in the mold. Likewise, when casting :alloys ofnOn-,eutectic and non-peritectic composition, the surface may become so rough and shaggy, due to bleeding ofthe lower freez-V ing constituents,` that the y'casting mayA become jammed in the mold and may be broken during the withdrawal from the mold.

In addition, dissolved gases released from the molten metal during the freezing may become entrapped in the interior of the castingand cause internal faults.- Such entrapment generally results in a porous internal condition usually evidenced by small wide-generally ranging from visuall to microscopic in size, and'mayause brittleness in the casting or loweringbf tensile strength.- lnA some of the processesof the priorart the entrapment -of the gases may result in relativelyvlarge'interior voids,tand this condition may become s severe as to cause a'con tinuous channel in or adjacent Ythe center of the casting..-

The art has long and diligently attempted to overcome the difficulties and disadvantages due to such surface defects and internal faults, but rwithout success;y

The principal object and advantage ofthepresent invention resides in overcoming these difficulties of the prior art. These and other objects andadvantages -willbecome apparent from the following more detailed descriptionof the invention.

Broadly, the invention comprehends introducing molten metal intol one end of an'open-ended mold having an un cooled sectionk and a chill section .ofhigh thermal conductivity dividing the moldrinto an uncooled zoneanda chill zone which is in substantially fixed relationshipr and immediately adjacent to theuncooled zone, with eachy of the zones surrounding the metal contained Vin their re.- spective portions of the mold. Duringfthe casting the temperature of the inside surface of the uncooled zone is maintained above the melting-point of the metal and the temperature of the inside surface of the chill zone is kept below the freezing point of the metal in that zone. rl'he molten metal is introduced into'the end'of the mold containing the uncooled zone at a rate which, in' relation to the rate of metal withdrawal from' the lmold,'is sucient to maintain molten,A non-turbulent meta-lin the mold-beyond that 'plane in`theuncoo1ed :zone'which lies 2.. nearest the chill zone, and which passes through `the entire cross-section of -the mold intersecting the molds longitudinal axis and in which themetal .remains entirely molten during the process. The metal in the moldis maintained stationary with respect to the mold (i. e. -no metal is withdrawnfrom the mold.) until at least the outer surface ofthe metal in the chill vzone extending-sub? stantially to said plane, is frozen into a shell of suilicient thickness and strengthA to permit .intermittent withdrawal of the .shell fromthemoldlwithout rupture of the shell. During, the formationtofthe shell, at least .a'major por,- tion .of the `sensible andnlatent heat requiredtofreeze the metal constituting .the shell is .rapidly withdrawnsube stantially laterally from the metal .through the. surface of the chill zone due .to thehigh thermal conductivity of the wallsof-.the mold in the chill zone. The .frozen shell and anyunfrozen metal encompassed thereby are withdrawn intermittentlywith respect to the moldfrom that end of the mold which contains the chilly sectionby intermittently withdrawing the castingtherefrom. The rate `and period ofthe intermittent withdrawal of the castingis such that `a major portion of the shell of the with` drawn casting is `formed within themold while the-casting is stationary with respect thereto. The periods ,be-v tween vwithdrawalperiods arealso such that .themetal remains entirely molteninthe.intersecting plane inthe uncooled zone.

withdrawing .a major portion. of the sensible and latent heat required to freezethe shell by a path which substantiallyparallels the longitudinal axis of the casting .(as opposed to a path substantially .lateral of this axis) results in a process whichis too. slow to be commercially ac. ceptable. Moreover, in thecastingof alloys of .none eutectic and non-peritectic composition, such procedure .is

too slow to prevent bleeding of lower melting .constituents to the surface and their freezing thereon. In addition, the reduction or substantial elimination of surface cracks in the-castings are not obtained in the absence in the process of .any one of the other featuresset forthf inthe preceding paragraph. A ll of thefeatures of the process stated inv thatparagraph are necessary, therefore, in the sense that they. are critically y important, in :obtaining the present results as to .smooth surface characteristicscinta commercially acceptable process.,

in casting alloys Vof non-eutectic and nonperitectic cont` position, (i. e., vthose. whose lquidos-and solidus temperatures do not coincide) y,and f especiallyv those having a wide range between their.liquidus and -solidus tempera@ tures, it has been found that Yalthough the shell Vmay-be strong enoughto withstand withdrawallfrom the mold, it nevertheless may contain interdendritic channelsl through? which low melting constituents may bleed out tothe surface of the casting by capillary action and freeze ontlle.l outer surface shell. low melting constituents, especially those which yinthel solid state are-harderthanthe bodyof the casting, cause' a rough, shaggysurfacefonvthe-casting'and may-proceed to suchan extent as tojam inthe mold. l lnsuch an event; lthe casting may break due tothe tension required to with-zl drawit, orthe mold :may'break if it is constructedof a fairly brittle material such-as graphite.

Such bleeding andthe resulting'rough, shaggy surface in castings -of alloys of-noneutectic and non-peritectic composition are, as afpractical matter, entirely eliminated by holding the metal stationary with respect to azrnold having a chill sectionof high thermal conductivity/and rapidly coolingthermetal in the chill section until the temperature of at least the outer` surface of the shell `is below the freezingpoint of the lowest freezing component of the alloywhich inlthe solid state is, harder than the matrix of th'e'casting." For best' results thisouter surface is'cooled below'thefreezingpoint'ofthe lowest freezing The exudation and freezing of suchY component regardless of hardness. Rapid cooling to such temperature quickly freezes the metal in the interdendritic channels to produce a shell which is impervious to the low melting constituents before the latter material can vbleed to the outer surface of the shell. Thereafter the outer surface of the shell is maintained below this temperature during the freezing of any remaining molten metal encompassed by the shell.

In conducting the process to obtain the improved results as to smooth surface and to reduce or eliminate roughness due to bleeding in the case of an alloy of noneutectic and non-peritectic composition, the mold is preferably vertically disposed, with the uncooled zone in the upper portion and the chill zone in the lower portion of the mold. The most preferred procedure is to practice the process with a stationary mold and to withdraw the casting intermittently from the stationary mold. Another preferred feature is that the rate and period of the metal withdrawal from the mold is such that substantially all of the shell of the withdrawn metal is formed Within the mold `while the metal is stationary with respect thereto. The linear length of the withdrawal stroke preferably is not in excess of about 2". Withdrawal strokes not in excess of about l" are the more preferred, with withdrawal strokes not in excess of about 1/z as the most preferred. Preferably also, the rate of withdrawal during the withdrawal stroke is as'high as possible. Y

In conducting the process to obtain the additional beneiit of reducing or avoiding gas entrapment in the casting, most of the above preferred features are necessary. Thus, it is necessary that the mold be vertically disposed with the uncooled zone above the chill zone to allow the released gas to escape upwardly and away -from the freezing metal. Preferably, the mold is held stationary, i. e., stationary with respect to the earth, and the metal is withdrawn intermittently from the mold. Itis also necessary, in order to obtain such benefit, that the linear length of the Withdrawal stroke is not in excess of about 2 and that the period between any two adiacent withdrawal strokes, during which time the metal within the mold is stationary with respect thereto, is such that no metal in a molten state exists below the physical intersection between the uncooled section and the chill section at a distance which is greater than the largest lateral cross-sectional dimension of the mold cavity, and that molten metal only exists above the referred-to plane which intersects the longitudinal axis of the uncooled zone. Preferably, the withdrawal stroke does not exceed one linear inch and for best results the stroke is not in excess of about 1/2. Such a procedure insures the escape of the expelled gas by orderly progression and permits the gas to rise through the unfrozen metal.

The molten metal may be introduced into the mold in any desired manner. Thus, for example, the mold may be iixedly attached to the bottom of a molten metal holding furnace with the metal flowing directly into the mold so that a column of metal extends from the bottom of the casting to the top of the liquid metal in the holding furnace. Such introduction of the metal into the mold causes no turbulence in the molten metal in the mold. In such case, also, the metal has no free surface in the mold. a free metal surface in the mold, may also be practiced. For example, the metal may be led into the mold by a pipe or other conduit which terminates within the mold at, above orybelow the surface of the molten metal therein; or the metal may be introduced as a free falling stream.

The use of a free metal surface in the mold is preferred for casting shapes having a relatively large cross-sectional area, and especially solid shapes in which the smallest dimension of the cross-sectional area is greater lthan about 3". When using a free falling stream, it is important that the molten metal be introduced into the introduction of the metal so asto havevrs mold at a rate sufficient, in relation to the rate of met withdrawal from the mold, to insure the presence in the mold of a pool of molten` metal above the solidifying metal in the mold and to maintain suicient depth of metal in the pool to dampen the turbulence caused by the falling stream so as to establish a non-turbulent condition in the metal in the region in which the metal commences to freeze. If the pool of molten metal is too shallow in relation to the height of fall, the turbulence of the metal entering the mold may extend to the freezing metal and cause irregularities such as wrinkles, ripples, cold shuts and the like to be frozen into the surface of the casting. Although turbulent motion is to be avoided inV this region, it should be noted that nonturbulent motion may exist and may in some instances be desirable.

The process may be practiced in connection with any ferrous or non-ferrous metal or alloy, and such material may be cast in any solid or hollow, circular or polygonal shape. The process of the invention is most effective in connection with the casting of copper and copper base alloys such as, for example, tough pitch copper, low oxygen coppers including oxygen-free copper and phosphorous deoxidized copper, brasses, bronzes and the like.

below the freezing point ofthe hard tin-rich constituents. Y

Best surfaces, however, are obtained by rapid cooling below the freezing point of theY lowest freezing constituent which, in the case ofcopper base alloys containing both lead and tin, is a soft lead-rich constituent,

although with this latter procedure longer stationary periods are required. As used in this specification and the claims, alloys include metallic mixtures in which the components are completely miscible in each other in the molten phase, as well as metal mixtures which are not miscible in this phase.

The mold may be fabricated of any suitable material, and different materials may be used in any one mold. Material of high thermal conductivity is used to fabricate the chill section. Preferably, thesurface of the uncooled section or this entire section is composed of a material which is, or is substantially, not wet or dissolved by the,

moltenV metal. In general, graphite molds are preferred, especially in the casting of copper or copper base alloys containing tin, although molds of a suitable metal may also be used. When casting with a free metal surface in a graphiteV mold, the exposed interior and exteriorwalls of the uncooled section of the mold may be protected by a ceramic or replaceable graphite insert for this section.'

Instead of such an arrangement, this section may be protected by an inert or reducing material such as nitrogen, carbon monoxide or other reducing gas, powdered magnesia, powdered graphite, charcoal, coal, orcoke breeze Y and the like. Alternatively also, thev chill section may be Y composed of a metal, especially copper, and theiuncooled section of graphite or a ceramic material. The chillV zone may be established by a jacket surrounding the chill section of the` mold through which Water or ani other fluid coolant may be circulated. The high thermal conductivity of the chill section thus affords rapid lateral extraction of heat from the metal in this portion of the mold. In the present invention, therefore, the mold is characterized in operation by cold walls in the chill section and a sharply increasing temperature gradient in the mold wall just above this section in the uncooled section.

The invention is further-illustrated in the accompanyarmar-at ing-drawings andeeXamplesz Itashouldi besurftr-,rstodI however, that the drawings and the examplesam givenw for ypurposesA of; -illustratiomand athat the invention inits broaden aspects is.'not'limited r thereto:

ln'thexdrawings:

Fig.; 1 isanfexaggerated 'view partly vin'.ver5ti tal:seet-ionf. illustrating a. preferred:-metliod anda apparat-'usifor com` ducting the fprocessot 'theii'lventiion tofcastzsmall shapes Fig.. 2 is-v arr exaggerated view=rp artly,-in verticalfsectiom illustrating-.a `preferred. Inode; and apparatus for' conduct-2y ing thev process Lto4 castflargeeshapes.

Fig. 3- is.' a fvertical section'. through" a fmoldf and; I. illuse trates a l modified: method and mold :f-for) casting t small: shapes;`

Figui is atop view of Figg along thefline 4?-4 in the. directionl of the arrows;

FigiY 5. iis;` an enlarged .-vertical.sectionI of t a mold illus= tratingttheevarious Icondi-tionsrexistinggin the'moldduringf thef practiceeof the processi 6. is. a i horizon-tal` crossssection off the --mold or- Fig. 1.

Figs.. 7 and 8 are -similar to -Figafandzshcwf m'oldssot different cross-'sectional j shapesrc c Fig. 9 :is .a specimen casting;.displaying-surfacefcracks.i

Fig. .10 isa specimen-casting simi-lar incomposition to. that fof Fig., 9 but producedin -accordancewith jthepresent process.

Fig'. 1 lis a specimen-of: arrtalloyl 'of..nonfeute ctie= andf nonfperitectic com-position` displaying a: rougir, shaggyU surface...

Fig.:12 isfa specimen .oan .alloyof-J composition .simi-.- lar to that or" Fig. 1l but castin` accordancewiththe pres-.- ent v invention. 4

Fig.. 13 vis a Yspecimen of metal {displaying-gas. entrapz-.L ment.` pl1enon1ena.

Fig.. 14 is -aspecimen castingfsimila'r incomposition to.. thatof` Fig.- 13 but cast infaccordance withlthe, present. process.-

Fig.15 is-a disc4 which. was-:cut fronrthespecimensof.

Fig; Band then..fractured.A Beforefraeturingthe. disc it was .partially severed by-l sawing .along.;the line of frac.- ture.. c

Fig. 16-'is .a disc. similarA to` Fig.; 15but specimen of Fig; 14.

Referring-.to :the drawings, .in.Fig. .l there. is showna. general assembly of a molten. metal\-holdi'1:lg..v furnace;

V

1,1 mold 2 and intermittentv withdrawing. means-indicated; generally by the .numeral 3. for. withdrawingrcastingd: fromuthe mold. The rnold-2 v extendsthroughthe bote torn of the furnace 1 and in contactwith Vthem'olten.metal 5 therein. The mold is iixedlyjattached to. thebottomof the-furnace .by means ofthreads 6which engagemating threads 7 in the furnace bottom. Thelower section ofi the-mold is surrounded by water jacket8 whichlprefe'rr ably is iixedly attached thereto. Wateror otherfcoola'nt is circulated through thejacket in any .desired'rnannerl The water jacket establishes in themolclanuneooled.'v zone 9 and a chill zonelt). The latter zoneextends yertically upward beyond the upper edge of the jacket 8 to the line C-C. The exact locationof-.thisline and of the plane passing through it isdeterminedhythe thermal conductivity of the mold materialgthe thermal -conduc` tivity of the metal being cast, the sensible and latent heat of the metal tovbe cast, the cooligcapacity of thejacket 8 in relation to the cross-sectional' dimensions of "the mold, the period during which the metal is stationary in the mold and the rate and/period of the withdrawal stroken dtu'ingfthe intern'littentv withdrawal. The plane passing` through lin-e C-C' is the lowest plane. inwhich the metal..` remains entirely molten duringthe process.'

The` casting 4 is withdrawnintermittentlyl -fromther moldby WitlnirawalV means whichgincluderolls llt-jat:` least'one of which; as'shown', may be drivenby.electricsv motor 12;.by. means `ofqbelt 13. OperativelyL connected 1to1' cut. from` the themotor 4121s startinigandstoppngswitchnlltttorfoperate- 75":

.' metal ow's into the `rnoldv of :the-'falling stream 23,'

6 ngsthe. motor "intermittently anditherebytocause the casting toifbe@withdrawn@intermittently iffromzthef mold-. TheV 'means-3. may .also include' any suitable lbraking means suchias is AillustratedI bythe shoe15` which engagesithe brake drum leon-.the roll 111.' The lshoemay-beoperatively connected :by .levers 17 andi to-switch .14 :so as to brake and quicklystopthe wheels' when 'the motor-121 is tu1ned..lotl. The-switch 14 mayxbe manually. operated or: any suitable interval timerimay be-usedlwhichsautomatically makes and brakesy the electrical supply to-motor- 12. More than one or all o the rolls-'11 mayy be posif` tively driven or positively vbraked. Any suitable-with-I drawal means vmaybe usedy in :place of thatrshown inthe drawings. For bestfresults, thejwithdra'wal means-is onewhich will start the-rolls 11 at arelatively high speedV soas' to lowerthe castingrt -fquickl-ycduringhe intermintent withdrawal andr tobrake A'the downward' 'motion of the. casting` when the motor `12.fis:=1turned=-otto obtainv relatively prompt stoppage;` ofrthefcasting'fwithout unduev coasting.-

In conducting theprocess in apparatus ofthe type illus-` trated in'Fig. l, the level ofzmoltenmetal in the hold-v ing furnace l is maintainedabovethe upper. edge 19` of the/mold 2. As the castingtis withdrawn, the molten and the mold is thereby main-1` tained lled with a column of metal. With this type ofapparatus there is no free moltenxrnetal surfaceinthe moldas lthe 'entire mold lis=lled with metal. Also, no turbulence .exists .in themolten metal in the mold such i. as would be the case if the metal were introduced as a free falling: stream.

Fig.2` shows a graphitemoldin'which the process mayibe conducted with afree metal surfaceinthe'mold,` preferably for casting large-shapes; Asislrown, thernold 2r providedwith water jacket'Sis supported 'by legsitwhich 21 which may, iny turn,` 5

maybe disposedin water tankl rest onythe foundationZZ. Moltenmetal 1in the'form of a free falling stream 23 -is supplied tothe mold by means of tilting'furnace 215 and launder 25.

Any suitable tilting furnace. may be used. As illustrated, the furnace may bepivotahly mounted on support 27 and may be tilted -as desired byhydraulic jack 28 suit-v` ably'. attached to the furnace at 29. The launderZS likev wisermay Dbe mounted on pivots .30* toadjustfthehei'ght which f height .preferably .isasA short as-possibiet Y in operation, thefu-rnace 24-is tilted to deliverfmolten` metal at a rate which, in relation to the rate of withdrawal. of the casting 4f, maintains a pool vof metal lin themold 2 of sufficient depth'v to dampen the'turbulence in ythepool caused by the falling streamso as tov establish a non-turbulent condition in the molten'metal' in the bot torn of the pool in the region-above'the- 32 below which the metal isin a frozen state."

The casting. f4' may be vwithdrawn intermittently-from the mold by. rollsl l in the same manner as' described in Fig. vl. In passing to the rolls l1. thecasting may pass through vwater tankZ- which may beprovided witha suitable seal 33, such as a rubber; gasket." Suitable severingmechanism (not shown) vmay blused `in the'amnaratus of.Figs. l and 2 below thero-lls 11 to sever the castiuginto-v any desired length. Also, in startingeither type'off'ap'pa `v ratus-.a solid bar. may-be placed-in the rollsll' 'sofas-*tol extend up into the mold. After the initially vintroducedmetal has been frozen, the starting harl is withdrawn.

The:k apparatus large shapes4 and inasmuch as the illustratediu Fig. i2 isffusefulin casting .particularly for ycasting shapes of "copper air. To minimize' contactfoff' themetal being' cast withair 'or oxidizingL gas," a layer-'oflpowdered material 34? curved line l lengtho? ther-free vfalling streanr may be controlled-- to minimizeor control' the lamount of" oxygen Yabsorbed by the copperwhen itis vpoured=through pool 31 breaks Vthe fall of the stream of metal 23 and therefore tends to reduce turbulence in the pool of metal 31. Accordingly, the minimum depth of the pool, to provide the desired quicscence in the bottom of the pool, may be correspondingly reduced. As used herein, a pool of metal of sufcient depth to establish the desired nonturbulence includes one in which a portion of the metal is replaced by a protective layer of solid material. Y Where, due to the temperature of the molten metal, oxidation of the outside of the uncooled section of a graphite mold also presents a problem, this section may be protected by a wall 3S surrounding this portion cf thc mold. A space 36 between such a wall `and the mold may also be filled with the protective material. instead of the construction illustrated in Fig. 2, the uncooled section of the mold may contain a ceramic or a replaceable graphite insert protecting the inner or both the inner and outer surfaces of this section of the mold. The chill section also may be fabricated of a metal such as copper and the uncooled section of the mold, as well as the launder 25 and the space in furnace 24, may be protected by an inert or reducing gas. it should be noted that the construction of Fig. 2 affords good insulation and assures the maintenance of a temperature in the uncooled zone of the mold, which is above the melting point of the metal being cast. This is especially advantageous where the uncooled section of the mold is fabricated of a material of high thermal conductivity such as graphite. Heat, if and when necessary, may also be applied to this section of the mold.

Instead of conducting the process as illustrated in Figs. l and 2, in which the mold is stationary, the mold itself may be reciprocated so as to withdraw the casting inter mittently with respect to the mold. Thus, for example,

the casting may be lowered continuously with respect to a point in space and while being so lowered the mold may be lowered at the same speed as the casting during the period in which the metal is stationary with respect to the mold. The mold then is moved upwardly at the same or a dierent speed as the downward speed of the casting during the intermittent periods in which the metal is withdrawn from the mold. ln such a procedure, as well as that described inFigs. l and 2, the relative motion between the mold and the casting during the intermittent withdrawal periods preferably is as rapid as practicable. Also at the end of the withdrawal stroke the relative motion is stopped as rapidly as possible with a minimum of coasting.

Regardless of the mittent removal of the present process permits net withdrawal rates which are 20 to 30% greater than those possible with a process in which the casting is continuously withdrawn with respect to the mold. At the same time, all the enhanced surface and interior characteristics of the process are obtained.

in practicing the process to obtain an improved surface on the casting, the stationary period between any two adjacent withdrawal periods is of such duration as to form a shell of suticient strength and thickness to withstand withdrawal of the casting without rupture. This condition is evidenced by the smooth appearance of the surface of the casting'emerging from the mold, and in practice this period may be adjusted as required to obtain such surface characteristics. tends substantially to the plane C-C' in Fig. 5.

Referring further to Fig. 5, as the metal freezes into the shell 37, illustrated by the cup-shape metal between the solid curved line passing through points C-E--C and the solid curved line passing through points D-D, the metal begins to shrink. in a plane passing through the points D-D, the shell pulls away from the mold, Below this plane, the cooling effect of the chill section is reduced due to the poorer contact of the shell with the mold. Direct, and therefore highest, cooling contact between the mold and the casting exists in the area manner of accomplishing the interthe casting, it has been found that The shell thus formed ex- Lil) ' and as sharply delined as possible.

' substantially to the plane 8 C-D-D'-C' extending along the'linear length C-D' of the mold.

It is believed that one of the principal advantages of the invention resides in the fact that this area is as large Under any particular set of conditions, a thermal balance between the uncooled and the chill sections of the mold is reached in a plane passing through the points C-C above which all the metal is completely molten. Below a plane passing through points D-D, the metal does not directly contact the mold. r[he direct and rapid heat transfer over the enlarged area C-D-D'-C', while the metal is stationary with respect to the mold, results inthe rapid formation of a Yshell 37 of which the portion extending passing through points C--C is of suicient thickness and strength to withstand rupture upon withdrawal from the mold. It is further believed that this accounts for the twin benefits of enhanced surface characteristics and high net rate of casting withdrawal which are obtained by the process of the invention.

A major portion of the heat extracted during the freezing of the shell flows substantially laterally from the metal and laterally through the highly thermal conductive walls of the chill zone. When the shell 37 has become thick enough to permit withdrawal without rupture, a length of casting corresponding generally to the linear length of line C-D in Fig. 5, is withdrawn and the cycle is repeated. The rate of withdrawal is such that a major portion and preferably substantially all of the outersurface of the withdrawn casting is formed as shell 37 while the metal is stationary in the mold.Y

In conducting the process to obtain the enhanced surface characteristics only, the stationary period may be just suihciently long to form a shell of required thickness to permit withdrawal which, lin the case of alloys of non-eutectic and non peritectic composition, is also of sufn'cient duration to cool rapidly at least the outer surface portion of the shell to a temperature below the temperature of the lowest freezing component of the alloy which in the solid state is harder than the matrix of the casting. In such procedure, molten metal may exist in the interior of the casting to any desired depth below the edge of the chill section. The lowest levell at which molten metal may exist in the interior of the casting with such a procedure will depend, among other factors, upon the size of the casting, the over-all length of the water jacket 8, the amount and extentnof cooling below the plane passing through points D-D in the mold, and the duration of the stationary period.

In the case of the stationary mold, the linear length of the withdrawal stroke is affected by the speed of withdrawal and especially the starting and stopping phases of this step, depending upon the mass of the casting.Y To obtain the enhanced surface characteristics, the withdrawal stroke preferably is not in excess of about 2" in length. Very good results are obtained with withdrawal strokes not in excess of about 1", and best results with withdrawal strokes not in excess of about l. Also, to obtain the enhanced surface characteristics, the stationary period preferably is Vsufliciently long so that no molten metal exists in the casting below the intersection of the uncooled and the chill sections of the mold at a distance which is greaterthan the largest horizontal dimension of t the mold cavity. This is illustrated in Fig. l by the point E" below which no molten metal exists. The length of the line 38 extending from the top edge 39 of the water jacket 8 to the point E is not greater than the largest horizontal dimension of the mold cavity. This latter dimension is illustrated in Fig. 6 by the internal diameter 40 in the case of a mold cavity which is circular in crosssection. This dimension is 42 in the case of a rectangular mold cavity shown in Fig. 7 and bythe line`43 in Fig. 8 in the case of a mold having amandrel44 for the casting of hollow shapes.

also illustrated by the length To: obtainv .the enchanced .surfacee-characteristicss andi atfthe: same time to prevent-or reduce to afminmumfthefg: entrapment of gas.. in the interior of fthecastingr:v the r preferred conditions set forthinthe preceding-paragraph; arenecessary,fas isalso the feature thatzthefmoldmust; 51; be-:vertically disposed with vthe uncooled zone-abovethe: chill zone. Within theseilimits, the Lshallownessiofthe unfrozen pool of `metal below the plane Lpassing through 1. points'-C.-CY (Fig. 5) may be controlled .bycontrollinge th'edurationof the stationary periods. The more Vshallow" 10 thiszpool becomes :the lesszis the tendencyfor gas .tobecome..entrappedin the solidiedcastng; Substantially? noigas isentrappedwhen thestationary period :is suchthat; thefsolidied metal .extendsl torthetcurvediline L41.A

Instead of ithe mold shownwin :Figs 1 :and 2,2 a .fmold.:. 15 havingaiplurality of mold cavities may be used; especially inithe'casting of small'shapes;` Such ralternativeconstrucei tion is iillustrated in'Figs. 3fand 4*in.'.which"the'mold. 2 is:provided with a 4plurality of cavities'45g46 'and4'7fwith`f thechill zone being establish'edfby'a1singlewater.jacket48. 201 With such a construction the plane..passingfthrough' the pointsC-C', immediately above :whichfall the metal l the mold remainsentirelymolten; doesnot lie in -thehori-- zontal. plane.y Also,when it's desired :toobtainonlyrf the enhanced surfacecharacteristics inthe processga hori-V 25? zontally disposed mold or a bottom-fed vertical mold with" the uncooled section .below the chill section'vmayibeused.`

Example I Commercially pure copperwaszcasttin apparatus :simiei Y lartto'th'atshown in Fig. 1 'exceptrth'atitheacastingzwas withdrawn continuously from vthe moldat'a constant rates of 19% inches per minute; A `.solid cylindrical :castings-3 a inches in diameter was produced. Circulating iwater was". used'in the water jacket 8'surrounding1hel graphiteimold. 35 2; Fig. 9 is a photolithograph offa'sectionof the :casting: thusproduced. It will be'noted that 'the surface'containsa plurality of horizontal cracks'.v

Exampler II The procedure Aof Example I wasAl repeated zexcept thatv a-s0lid, cylindrical casting4 inches.in-diameterfwasproe duced and the casting was withdrawn intermittently from: the stationary mold 2. The intermittent withdrawal :periods were 3 seconds in duration, durin'geachfoffwhichthe linear length of'casting withdrzufvnzwas.` 1/sof'.an.'.'inch. Each stationary period between vadjacentxwithdr'awal: peri-pV odsl was 1 second in. duration.I Figs.10Iis-aphotolithoav graphtofthe casting thus produced. It;will befnotedthat the4 surface vof the casting` is :smoothnand free fof; surface cracks.

Example III.`

The procedure of Example I wasfrepeated-.to produce: a tubeof an alloy composedof 88%:copper, 10%.tin.v and 2% zinc. The tube produced wasl%2,-inches inout- 55 side diameter and1/2 inch'in its inside .diarneter.. Thef. graphite mold had the cross-section of .thatillustrated in Fig. 8. The water jacket surroundedftheoutside-.surfacef of the mold 2 inthe chill scctionand. no water was'scircul lated through the'mandrel 44-.\ The-tube was continufy 60' ously withdrawn from the stationary mold at a constantv rate`of.ll% inches per minute. Thesurfaceoffthe. tube thusfproducedis` shown in-Fig.; l1 Itfwill fbe noted that--Y thefsurfaceeis rough and shaggy/in appearance..- These; rough and shaggy exudations were found to.be composed 65" off low-melting,A tin-'rich constituentswhich were harder thanthe main body or matrixof thecasting.-e Solidfrodst cast from thesame alloywith similar-casting. procedureproduced the same roughand shaggy surface.

Example-I V The procedure of Example I was repeatedexcept-v that aY solid,V cylindricalv` casting 1%1"A inches: in' diameter: 'was produced fromv analloyisir'nilarto thatfoffEXampllII" containing; 90`%`" copper-"and 10%? Inftheepresentl 751y ously withdrawn from the mold atithe zcastingawas withdrawn intermitexample, however, tently( from .the stationarymold. The. intermittent withdrawal periods were2 "seconds-in duration; and yduringwell below the freezing temperature ofthe lowest'freezf ing constituent in the alloy.-v The -surface of the casting thus produced isshown in Fig. 12. It will .be noted that it s free of the rough, shaggy'exudationsV foundin Fig. ll.v

The procedure "of Example 'Iwas again'v repeated :to-- 2%'l inchesinv diameter -and *tin* andk 5%* lead.A Thel rod was continuouslyA withdrawn-'from'the stationary; Fig. 13

produce an alloy'rod stock' composed of copper, 5%'

moldat a constant rate Aof 46 inchesper minute'.l shows across-section of `a brokenspecimeny of the-rod thus cast. The interior'of thespecimen-was porous'and also contained a'continuous `void at its center. showsa wafer or disc' cut from' the rod and which was fracturedby bending; of"thecasting' is porous; Itwas'foundthat theV central` voidextended'th'e full length of the specimen.

Example.y VI The procedure-of Examplel composed of 90% copperand'10%t mold. The intermittent withdrawal periodsl were 3 seconds in duration, and during each such period 0.35 Alinear inches of casting stationary period secondV in duration.

to a temperature-well below thefreezing point of the lowest freezing constituent in the falloy'. Under these* conditions of casting, no molten metal exists'in the cast-- ingA at a'point about-one inch below the top` of `the-water#- `to Fig'. 1,' the dimension of the line 38' inch under theconditions ofthe pres-- 5 entexample; Fig. 14 showsa crossescction of a broken 16 shows a wafer cu'tA from the rodand which was fractured by bending: lt"- ythe castingis free of porosity and displays a uniformly sound structure.v

jacket.' Referring is about -one vlinear specimen of the -rod thus'v cast. Fig.

willV benoted that theinterior of Example VII rod stock 1% inches in diameter analyzing 98% 2% tin and 0.25%

copper, phosphorous.

The -rod was lcontinuthe rate of 51/2 inches perminute.- The Asurface `ofthe rod had 'the roughand shaggy surface illustratedinfl-iig.v 1l.

Example VIII Thexsame :size and'composition of rod as thatset forth inEXampleVIIwas made nlaccordance with the present invention .in apparatusxof..thetypexil1ustrated in Fig. l

casting was withdrawnalloy. The casting produced hada smooth, even: surface '12..y The net withdrawal!l rate "in tlisfintancey was: 42 greater than lthat. of :Exam-f -1 similarfto that illustrated in Fig.

Fig. 15

It'will benoted that the interior wasl repeated except ythat' a. solid,"cylindrical casting 2%'Pinch`es in diameter and tin'was produced byA withdrawing the casting intermittently Vfrom the` stationary were withdrawn-from the-mold. Each" between the withdrawalpcriods was'el During the stationary periods thesurface of the outer shell of therod was rapidly reduced 11 Example IX The procedure of Example VII was repeated to produce rodV stock l/s inches in diameter and analyzing 84% copper, tin, 295% lead and Bti/2% nickel. The rod was withdrawn continuously from the stationary mold at a constant rate of 51/2 inches per minute. The produced rod has a surface which was even more rough and shaggy than that of Example Vll.

Example X The same size and composition of rod as that of Example iX was made in accordance with the present invention using apparatus of the type illustrated in Fig. l and which was equipped with a graphite mold. The casting was withdrawn intermittently from the stationary mold using Withdrawal periods of three seconds duration. In each withdrawal period 0.465 linear inches of rod were withdrawn from the mold; this rate amounting to a net withdrawal speed of '7 inches per minute. The stationary periods were l second in duration. The outersurface of the shell of the rod formed in the mold was rapidly reduced during the stationary periods to a temperature well below the freezing point of the tinrich constituents of the alloy but not below the freezing point of the lead-rich constituents. The casting had an exceptionally smooth, even surface of the type illustrated in Fig. l2.

ln operating the process on a plant-size scale over a period of several months, cycles varying from a withdrawal period of one second and a stationary period of 4 seconds to a withdrawal period of 4 seconds and a stationary period of one second have been used with satisfactory results.

From the foregoing it will be seen that the present invention provides a continuous method of casting ailoys of non-eutcctic and non-peritectic composition to eliminate the rough surface caused by low melting components which in the solid state are harder than the body of the casting and which in prior processes bleed to and freeze on the surface of the casting. The invention also provides a method for casting metals and alloys so as to reduce or eliminate surface cracks. ln addition, it provides a step for eliminating surface imperfections caused by turbulence in the molten metal irnrnediately before freezing, such as is encountered with molds having a free metal surface into which molten metal is introduced as a free falling stream. The invention further provides a process in which castings are produced which have enhanced surface characteristics and at the same time improved internal characteristics by eliminating or reducing internal faults due to entrapment of gases which are released by the molten metal as it freezes.

What is claimed is:

l. A continuous metal casting process comprising introducing molten metal into one end of an open-ended mold having an uncooled section and a fixed cooled section of high thermal conductivity dividing the mold into an uncooled zone and a chill zone immediately adjacent to said uncooled zone with each of said zones surrounding the metal contained therein, continuously maintaining the temperature of the inside surface of said uncooled zone above the melting point and the temperature of the inside surface of said chill zone below the freezing point of the metal contained in the respective zones, said molten metal being introduced into the end of the mold containing the uncooled zone at a rate which in relation to the rate of cast metal withdrawn from the mold is suiicient to maintain molten and non-turbulent metal in the uncooled zone of thc mold in the vicinity of a plane which intersects saidY zones and in which plane the metal remains entirely molten, maintaining the metal stationary with respect to the mold in the chill zone until at least the outersurface of the metal extending substantially to said plane is frozen into a shello'f suicient thickness and strength to overcome the surface friction forces between the mold` and' the shellv to permit motion oflthe shell with respect tok the mold without rupture of the shell, said shell being g formed by withdrawing at least a major portion of thel sensible and.' latent heat required to freeze said shell` substantially laterally from the metal through the surface of `said chill zone, thereafter Vwithdrawing a predetermined length of cast metal from the otherV end of the mold,V stopping said cast metal withdrawal before shellk formation takes place on a major portion of the outersurface of the molten metal moving beyond said plane into said chill zone during said metal withdrawal, and

repeating said shell freezing and said Vcast metal withdrawal steps until a casting of desired length is obtained, whereby aV major proportion of the shell of thethus withdrawn metal is formed within the mold while stationary with respect thereto thereby enhancing the surfacecharacteristics on the said withdrawn casting.

2. A continuous metal casting process comprising introducing molten metal into one end of an open-ended mold having an uncooled section and a fixed cooled section of high thermal conductivity dividing the mold into an uncooled zone and a chill zone immediately adjacent to said uncooled zone with each of said zones surrounding the metal contained therein, continuously maintaining the temperature of the inside surface of said uncooled zone above the melting point and the temperature of the-inside surface of said chill zone below the freezing point of the metal contained in the respective zones, said molten metal being introduced into the endof the mold containing the uncooled zone at a rate-which in relation to the rate of cast metal withdrawn from the mold is .suicient to maintain molten and non-turbu lent metal in the uncooled zone of the mold inthe vicinity of a plane which intersects said zones and in which plane `the metal'remains entirely molten, rnain-.v taining the metal stationarywith respect to the mold;

in the chill zone until at least the outersurface of the metal extending substantially to said plane is frozen into a shell of sulhcient thickness and strength to overcome the surface friction forces between the mold and the shell to permit rapid motion of the shell with respect to the mold without rupture of the shell, said shell-being formed by withdrawing at least a maior portion of g is obtained, whereby substantially all ofthe shell Vof the thus withdrawn metal is formed within the mold while stationary with respect thereto thereby 'obtaining a high net casting rate and a uniformly smooth surfacev free of surface cracks on the said withdrawn cast.

ing; Y

3. A process according to claim 2 in which said molten metal is introduced into the top of a vertically'disposed mold having said uncooled zone in the upper portion vand said chill zone in the lower portion thereof.

4. A process according to claim 3 in which said mold is maintained stationary'during the process and the metal is withdrawn intermittently from the stationary mold.

5. A process according to claim 2 in which a free falling stream of molten metal is introduced into the top of a vertically disposed mold having said uncooled zone in the upper portion and said chill zone in the lower portion thereof, and in which there is maintained in the uncooled zonea pool of molten metal of sufcient depth to dampen the turbulence caused by the incoming stream of metal and to establish non-turbulent metal in said vicinity of said plane.

6. A process according to claim 2 in which the molten metal introduced into said mold is an alloy of non-eutectic and non-peritectic composition, and said metal is held stationary with respect to the mold until the temperature of at least the outersurface of said shell is below the freezing point of the lowest freezing component of said alloy which in the solid state is harder than the body of the casting.

7. A process according to claimv 6 in which the temperature of said outersurface of said shell is cooled below the freezing point of the lowest freezing component of said alloy.

8. A process according to claim 6 in which a copper base alloy is introduced into said mold, and the mold is a graphite mold.

9. A process according to claim 8 in which said alloy contains at least 4% tin.

10. A process according to claim 8 in which said alloy contains tin and lead, and in which said outersurface of said shell is cooled to a temperature below the freezing point of the lowest freezing component of said alloy.

1l. A process according to claim 2 in which metal selected from the group consisting of copper and copper base alloys is cast and the mold is a graphite mold.

l2. A process according to claim l1 in which an upright mold with an uncooled zone above the chill zone is used, free mold surface exists in the mold during the casting procedure, and the exterior and exposed interior surfaces of the mold are protected from direct contact with air.

13. A process according to claim 2 in which a vertical moldhaving an'uncooled zone above the chill zone s used, said mold is maintained stationary during the process, the length of the withdrawal stroke is not in excess of about two inches, and the stationary period between any two adjacent Withdrawal periods is such that no metal in a molten condition exists below said plane at a distance which is greater than the largest horizontal dimension of the mold cavity thereby also reducing entrapment of gas in the freezing metal.

14. A process according to claim 13 in which said withdrawal strokes are not in excess of one-half inch.

References Cited in the tile of this patent UNITED STATES PATENTS 2,128,943 Hudson Sept. 6, 1938 2,136,394 Poland et al Nov. 15, 1938 2,195,809 Betterton et al. Apr. 2, 1940 2,225,416 Junghans Dec. 17, 1940 2,242,350 Eldred May 20, 1941 2,527,545 Goss Oct. 31, 1950 2,667,673 Harrison Feb. 2, 1954 2,682,691 Harter July 6, 1954 FOREIGN PATENTS 598,385 Great Britain Feb. 17, 1948

Claims

1. A CONTINUOUS METAL CASTING PROCESS COMPRISING INTRODUCING MOLTEN METAL INTO ONE END OF AN OPEN-ENDED MOLD HAVING AN UNCOOLED SECTION AND A FIXED COOLED SECTION OF HIGH THERMAL CONDUCTIVITY DIVIDING THE MOLD INTO AN UNCOOLED ZONE AND A CHILL ZONE IMMEDIATELY ADJACENT TO SAID UNCOOLED ZONE WITH EACH OF SAID ZONES SURROUNDING THE METAL CONTAINED THEREIN, CONTINUOUSLY MAINTAINING THE TEMPERATURE OF THE INSIDE SURFACE OF SAID UNCOOLED ZONE ABOVE THE MELTING POINT AND THE TEMPERATURE OF THE INSIDE SURFACE OF SAID CHILL ZONE BELOW THE FREEZING POINT OF THE METAL CONTAINED IN THE RESPECTIVE ZONES, SAID MOLTEN METAL BEING INTRODUCED INTO THE END OF THE MOLD CONTAINING THE UNCOOLED ZONE AT A RATE WHICH IN RELATION TO THE RATE OF CAST METAL WITHDRAWN FROM THE MOLD IS SUFFICIENT TO MAINTAIN MOLTEN AND NON-TURBULENT METAL IN THE UNCOOLED ZONE OF THE MOLD IN THE VICINITY OF PLANE WHICH INTERSECTS SAID ZONES AND IN WHICH PLANE THE METAL REMAINS ENTIRELY MOLTEN, MAINTAINING THE METAL STATIONARY WITH RESPECT TO THE MOLD IN THE CHILL ZONE UNTIL AT LEAST THE OUTERSURFACE OF THE METAL EXTENDING SUBSTANTIALLY TO SAID PLANE IS FROZEN INTO A SHELL OF SUFFICIENT THICKNESS AND STRENGTH TO OVERCOME THE SURFACE FRICTION FORCES BETWEEN THE MOLD AND THE SHELL TO PERMIT MOTION OF THE SHELL WITH RESPECT TO THE MOLD WITHOUT RUPTURE OF THE SHELL, SAID SHELL BEING FORMED BY WITHDRAWING AT LEAST A MAJOR PORTION OF THE SENSIBLE AND LATENT HEAT REQUIRED TO FREEZE SAID SHELL SUBSTANTIALLY LATERALLY FROM THE METAL THROUGH THE SURFACE OF SAID CHILL ZONE, THEREAFTER WITHDRAWING A PREDETERMINED LENGTH OF CAST METAL FROM THE OTHER END OF THE MOLD, STOPPING SAID CAST METAL WITHDRAWAL BEFORE SHELL FORMATION TAKES PLACE ON A MAJOR PORTION OF THE OUTERSURFACE OF THE MOLTEN METAL MOVING BEYOND SAID PLANE INTO SAID CHILL ZONE DURING SAID METAL WITHDRAWAL, AND REPEATING SAID SHELL FREEZING AND SAID CAST METAL WITHDRAWAL STEPS UNTIL A CASTING OF DESIRED LENGTH IS OBTAINED, WHEREBY A MAJOR PROPORTION OF THE SHELL OF THE THUS WITHDRAWN METAL IS FORMED WITHIN THE MOLD WHILE STATIONARY WITH RESPECT THERETO THEREBY ENHANCING THE SURFACE CHARACTERISTICS ON THE SAID WITHDRAWN CASTING.