US2565959A - Method of casting metal continuously - Google Patents

Description

3 sheets-sheet i c. B. FRANCIS ET Al.

METHOD oF CASTING METAL coNTTNUoUsLY Aug. 28, 1951 Al1g- 28, 1951 c. B. FRANCIS ET AL, v 2,565,959

l METHOD OF CASTING METAL. CONTINUOUSLY Filed Oct. 4, 1949 3 Sheets-Sheet 2 r-*ndi C) C) C) C F A [M65/dons.' (wam @4A/05 mf 6400// 5 P09752,

Aug. 28, 1951 c. B. FRANCIS ET AL METHOD oT CASTING METAL coNTTNuousLY Filed Oct. 4, 1949 Patented Aug. 28, 1951 METHOD OF CASTING METAL CONTINUOUSLY ,'Gharlesr. rancis, Pittsburgh, and Ralph jB. --Portelfhlohnstowmla Application October 4, 1949, Serial No. 119,532

x1 Claim. 1

:This invention relates tothe castingxof' metals, and more Aparticularly to the continuouscasting-of iron and itsvalloys, including both carbon-and alloy steels, whereby Whole heats may tbe cast vdirectly into semi-finished products vof great .'length, such as slabs, blooms, shaped blooms and billets,heretofore'produced'by rolling from ingots,-and certain vsections which it is'most dii- :cultor impossible to form by rolling-either be- ;cause:the shape ofthe articleor the hot Working-.characteristics -of the l,alloy itself will not fpermitithe-necessary rolling or forging. The inventionisr-an improvement over theY practice dis- `iclosed in 'United States Patent No. ,2,338,781 granted to Ralph B. Porter onl January 11, 1944.. This isa continuation-impart of vour copen'ding application Serial-No. 840,*1ed January 7,1948, .andfnow abandoned.

.,-rfIhel-chiefrobjectxofthe invention is to simplify :andgreduce `the cost of forming .'serni'fnished .irongand Ysteel products, such Aas slabs, Ablooms fand billets, from which `nished products, such as plates, Ysheets, shapes and bars are rolled. I-Ieretofore, fthese `intermediate products 'have A,.-beenziormcd byn casting the lliquidsteel in-molds Y.to form solid ingots, "heating `the l ingots -to a temperaturesuitable for rolling androl'ling the gingotsrrst.onslabbing or blooming:y mills. #Not :only istheiequipment Vused for performing these :Operations very costly,;but the-process iswaste- .inl of; materials, Ytime andv labor since-1. Athe` ngots conta-in pipes and other defects,v making. it necessary to scrap %tof351% of thevsteel made, 4and alsogbecauserof the fuel :consumed inheating the ingots' and other materials required .to--con ,z dition them for rolling. Our-'invention Y reduces :theicost of the :apparatus required.` .to Aasrnall fraction of the-cost ofY abloomingmillY and the ilabor to less than one-thirdthat employed' in :presentfpractice TheA slabs and blooms, further-1 imore; are fully formed in the time now-.acquired to-pour thev ingots, and under conditions that lavoid'pipeyso that the scrap lossfislessfthan-r 1% .for any grade of steel-produced.

Further objects arev toprovide @for-fthe lmaking ;of shapes that cannotl be; rolledfand :toi improve generally on methods previously proposedifcrthe `continuous' casting of metals. 'Other objects :will become apparent. in the'A followingfdetailedfdescription -of thenprocess :of vour lnventionrzwhch y refers to the 1 accompanying'drawlngs'xfor1:illustration of a .present preferred :formlof-.apparatus .used-therein.

.lni the drawings:

:Figure i 1 :is a longitudinal @vertical 1-section through thefcenter of a'preferred formof com- .pleteassembly of all parts'of the apparatus essential in the casting of such. a product asslabs iin i accordance with our invention;

v:Figures 2 and 3,-are cross-.sections takemrespectively, along -the lines IIII andyIII- f-III'of .-Fgurel;

Figure 4 is apartial sectionshowinga portion vof Figure 1 to enlarged scale and. a stoppingvand lo withdrawing head which travels througha con- .tr-in -ucus-molcl at the startof a cast;

:Figure 5 is a View similar-to :Figurel `showing .a1-portion ofa modification;

:Figure 6 is a horizontal-section.takenalorlg .l5 the line VI-VI of Figure 5;

Figure 7 isa cross-.sectiontalzenalong; the line i/'I-f-Vil of A Figure 5 FigureS is a series of sections or shapesdiiiicult .or impossible to rollbytheconventional Ymethod Zogbutwhich vmay be continuously castby ,our invention;

Figure 9 is a `longitudinal vertical section through a portion of -the mold preferred for F.metals-such .as low-carbon steel having relatively 25,; highl melting points; and

Figure 10 is a crossfsectiontaken -along line `vX--X of Figure 9.

:Referring now in vdetail tdi-.hedr-.awinesiand fforvtherpresent, to Figures 1.- 4,-theanparatus `v3,0 which-we prefer to employ in carryingoutqthe -ginvention includes, a pouring basingandL-gate'l, an-upwardly yflaring or V-shaped riser orskirnn -ymerr2 (desirable particularly in -the-'eastingf of certainsteels, particularly high alloy; steels) vand 35. a;\port;-,3. All these parts are inthe-form of flasks made of cast iron or steel plate formed by v`bending and welding and are lined with-refrac- -Y.torynf1 aterial. To providea skimmenforgfor-any other reason, gate v2 may1be-inclined-from the `40s-vertical at any angle desired.

continuous' horizontal mold `il 'ist the initial cooling and forming section of the apparatus-land ,is designed for theA continuous vcasting-.of slabs. The -mold has a cooling .jacket`5 provided with -connections for circulating :water therethrough -so.that. all parts, except the inner'faces, are; kept ibelow the temperature of .boiling .water'duringa wasting. -Thefimold comprisestwoparts, a=ribbed Linnerwallli cast in one to threesections longi- "tuclinally of a high-silicon, vflow-carbcnfalloyl :of *iron-*resistant* to heatrandswear, -such as that used for diesel engine blocks; Y and-anouterffwall V'i-.=which maybe formed of. .ordinary steelplate fby' bending and .weldingparts together. This :wall isv provided with an ,expansions jointiihlo- 3 cated at, or near, its midsection, is bolted to the casting at the ends as shown, and may be further secured by stud belts entering the ribs of the casting. These ribs strengthen the casting and direct the ow of the cooling water from the inlet to the outlet of each section.

The finish on the inner faces of the casting is oi prime importance. These faces must be flat and as smooth as it is practicable to make them, to decrease sliding friction and avoid such troubles in casting as sticking and bleeding of the form in the mold, yparticularly'at the entering or hot end. The smoothing operations are carried out after the casting has been shaken out and stress-relieved, and depend largely upon the care and means taken to produce a smooth surface in casting.

The water inlets and outlets must be large enough to permit a sufficient iiow of water through the mold. To hold the outlet water at a temperature just below boiling requires a feed of 50 lbs. per minute for each square foot of mold cooling surface.

Since the heat conductivity of iron and steel is only 1/8 that of copper, attempts have been made to use molds made of copper and its alloys, But copper, as compared with iron alloys, is a soft metal and has a low melting point (l981.4 FJ. It bonds or adheres to iron or steel at temperatures below its melting point, furthermore, and experience has taught it is not a satisfactory metal for use for this purpose. Apparently, its high heat conductivity plays a minor part in cooling after a shell is formed between it and the liquid steel.

The apparatus shown includes a final cooling section 8 adjacent the mold li. it consists of a housing provided with conveyor rolls 9 to receive the partly solidified section as it leaves the mold 4, and a number of high-pressure nozzles lll arranged to deliver jets of a cooling fluid striking the cast section on all sides as it is moved out of and away from the mold. These jets eifect rapid solidiiication of any metal remaining liquid in the central portion of the cast i section by quench cooling the outer shell formed as the section moves through the length of the mold'. The number of these sprayes depends upon the thickness and the speed of travel of the section, only one being required for a section 2 thick moving at a rate between 8 and 10 feet per minute. For a section 4 inches thick the total water required per minute by these jets is roughly equal to the weight of steel cast per minute.

A stand of motor-driven rough-surface rolls l l engage the cooled and solidiiied portion of the cast section and draw it from the mold at a uniform rate. The traction force necessary, as will be shown later, varies with the volume of the mold and the smoothness of its mold surfaces and increases as the height of the pouring basin above the mold is increased.

A continuous high-temperature furnace i2, represented diagrammatically in the drawing, quickly raises the temperature of the quenched shell to a bright red color, i. e., to a temperature approaching that of the interior of the cast section, to avoid quenching cracks and facilitate subsequent shearing and any further forming operations as desired. The furnace has supporting rollers l2l on opposite sides thereof. By regulating the cooling to effect solidication of the shell without excessive cooling of the central portion of the section being formed, this reheating of the outer portion can be effected in the same time as the cooling by holding the furnace temperature at around 2400 F.

A motor-driven shear I3 is mounted upon a traveling base if! to move with the piece while making a cut. A stationary shear can be used. but necessitates shutting off the water sprays and stopping the rolls 9 while making a cut. In that case, it is advisable to cut only a few long lengths during the casting of a heat, and to perform the operation of cutting to shorter lengths on a second shear. Shearing is necessary because of the great length of slab it is possible to obtain from a single heat. For example, a lOO-ton heat will give a 4 X 36 slab 400 to 410 ft. long.

In using the apparatus described to perform our method, molten steel is poured from a skimmer ladle iii into the gate l to ll it and port 3 rapidly at the beginning of a cast. As shown in Figure 2, a triangular-shaped refractory diverter i6 is disposed in the dii/erging riser 2, to divide the stream of hot metal and direct the cw along the walls where thick skulls may otherwise build up, causing the stream to channel through the center.

Figure 4 shows the construction of a preferred form of device used to stop the flow of metal through the mold at the beginning of a cast and to Withdraw the section as cast until it is long enough to enter roll stand Ii. This stopper or head Il is composed of a block i8 and bars I9 and 28, fitted neatly together and mounted on channels 2| forming a ram effective to close the mold completely except for a very small V-shaped vent in the top surface of the top bar. The bars and block are held together by three or more loosely-fitted removable pins 22. Bars i9 project beyond the bars 28 and have a number of holes drilled in them to form keys with the first metal cast which solidifies against the head and adjacent to the walls of the mold. These interlocks assure that the shell formed by solidication of the molten metal against the cold mold and stopper surfaces will move with the head as it is Withdrawn from the mold. The channels 2i are welded to the outer end of the head and are long enough to provide a rain extending entirely through the mold d, cooling section ii and traction rolls H as the latter lby frictional engagement with the channels, may serve to withdraw the head as fast as steel is fed into the mold. Once the section being cast has thus been started, the operation is continuous until the ladle i5 has been emptied.

Figure 5 is a vertical longitudinal section of a modified continuous mold and cooling section corresponding generally to the construction shown in Figure 1, similar parts being designated by the same numerals, but providing straightline now of metal through the mold and the simultaneous casting of four large blooms and one billet. In this form of apparatus the flaring or V-shaped skimmer 2 is connected as a horin zontal extension of the port 3 and is lined with dense, hard-burned refractory in the bottom but with porous, bonded, molding sand in the top to permit the escape of gases through small holes provided in the upper side of the iiask.

To facilitate the work of smoothing the inner surfaces, the mold 4' of this form of apparatus is built in three sections which are bolted together and is provided with longitudinal partitions of steel plate as shown in Figure 6. To provide cooling for these partitions, they are drilled vertically to form a large number of holes spaced apart along the center line. If preferred, these partitions maybe made thickerand castzwthta these partitions, the frontends are vshielded-.by

hard-burned refractory brick inserted :in the port, as `shown at 23 in Figure `6. .Since these partitions provide increased cooling for :the molten steel, the mold can be mad'efsomewhat shorter than a molddesigned vfor thegcasting of slabs.

Figures 9 and vloxshovv :a portionof 1a .-fmold generally similar toy those :'illustratedi; at :4 .vandali which is preferred f or `the lcasting:.o'imetalsvhaving melting points above 1.200,0? F. :and particularly for low-carbon steel, Jwhichfenters the mold at temperatures between':2780?;11.:and;28507 Each mold section'fhas an inner Vwall 2li :cast from metal similar to" thatused for. :diesel-engine cylinders, an intermediate wall .25 dening an inner cooling vchamber `and an outer ywall T25a forming an outer cooling fchamber. Cooling water is supplied through linlet 2B at `a pressure of 20 to 30 lbs. tothe inner cooling chamber from which it flows as vindicatedbyarrows tov theouter chamber from which it is discharged through outlets 27 and 21a.

For large sections, that `is, Awhen'the distance from the inlet 26 of Figura-10 to theopenings 28 into the outer chamber is l'more than about 24 inches and always where this distance exceeds 36 inches, the construction should be Vmodified to provide an inlet and outlets :at both the top and the bottom, and the openings 28 `between the inner and outer chambers placed Yat the ends of the mold in locations indicated by thesymbols P and P in Figure l0. For small sections, the outer chamber may be omitted. In Yany case, the large outer chamber plays 'a minorvpart in the cooling, but serves as a temperature equalizer and safety device to condense any steam formed in the inner chamber.

With sumcient pressurein the Water main,fthe flow of water through the vcooling chambers is regulated by a valve so that thefmax'imum ten1- 1 perature of the water 'flowing from the outer chamber is below 200 F. Thus "regulated, the rate of flow of water in Ypounds Vor gallons per minute depends upon the sizeof the-section and Arate of withdrawing'steel from the mold. 'In gen r eral, l lb. of water solidies 3 lbsuofsteeland, for sections more than 2 'inches `.thick vithdravvn'at the rate of 1 foot per second,the-pounds of noch ing water required per "second Ais 25 times the perimeter of the section in feet. Any larger quantity of water may loe-used.

The advantage of this designoverthat shown in Figures l, 3, 5 :and 6iSLeXplained-asffollowsz As the liquid lsteel enters the cold mold, the rate of heat transfer;is at first very rapidbecause of the great difference iinitemperature. between the liquid steel and lthe surface of the cold mold with which-theliquidis ,in close contact, and also because of the large amount .of heat to be absorbed, which includes the heat of fusion of the steel as Well as that necessary to cool the steel to the temperature of the mold. As a consequence, the temperature ofthe inner surface of the thin mold Wallrises very rapidly to a temperature .far above "that vat which water boils, with the result that the opposite, water cooled surface becomes. covered byra Alayer or steam, which preventsy thezwaterflowing through a Vcooling chamber with `a section :as large ;as that Vshown .in Figures '1, randA-.lrbm making contact Y,-withthe hot surface-a conditionsimilar to tthat long known as the spheroidal state. It is necessary, therefore, to prevent the water adjacent the hot surface from assuming the spheroidal state and to remove and condense the layer of steam as rapidly as itis formed-results Vwe accomplish by making the cooling chamber in two parts and decreasing .the cross.- sectional area of the inner chamber s o thatfthe cooling water flows through this chamber fat a vhigh velocity. In this way, the friction between the fluid interfaces is increased to a pointwhere the `lm of steam is removed and condensed as rapidly as it forms, and the temperature of the mold wall at the inner face is prevented from rising'muchabove that of boiling water. Thus, since the mold wall is relatively thin, the rate of heat transfer from the liquid steel to the water 'becomes very rapid.

'Because the port 3 constitutes oneof thefea tures of our invention which is novel evento the art of continuous casting, .it deserves special mention. We provide means for preheating the end of Athe port adjacent the metal mold, suchas electric-resistance heaters in the form oirods .29 of cemented silicon carbide. For maximum effect two of these bars are inserted, one at the bottom and'one at the top as shown in Figure l, each separated from the mold by 1 to V2 inches of refractory, but when due precautions are taken toavoid delays in withdrawing the cast section assoon as the port is filled With liquid metal, one .rodinf serted in the bottom, as shown in Figure '5., is suilicient. These rods may be exposed to the liquid steel, as shown in Figure 1, or protected, as shovvn in Figure 5. If exposed, they Ycanbe used'but once, but if protected, theymay be used to cast several heats. vIn any case, the rods 'must be long enough to extend across the port and project through the Walls of the flask one to two inches to permit electrical connections to be made, as indicated in Figure 6. By energizing therods and properly insulating them from metal parts oi' the apparatus, they may be rapidlyheated to any temperature desired up to 2700 F., at which .temperature all steels are in a iluid or-semi-uid state. The port 3 is thus heated to a temperature approximating that at which themetal freezes. Instead of electrical-resistance heaters, refractory radiant tubes heated with any Acombustible vgas mixture that will give a high temperature lmay be used, and in some cases it maybe possible to heat this part with molten metal, as by shortening the port and shaping 'its bottom, as indicated by the dotted line 30 of Figure l. For

' general application, however, we prefer touse the rods.

The function of these heating elements yis important and is best explained as follows: When liquid steel comes into contact with a cold sur-- face, it starts to solidify, forming a lm or shell ,on the surface, and during the 5 to l0 seconds required to ll the gate and port, this shell may increase to a thickness of 1/4" or more, making it'impossible to move thewithdrawing head without rupturing the shell. With the heater rods in place, the difculty is easilyovercorne, for by turn ing on the current about an hour before aheat is to be cast, the rods and refractories near them `can be heated to a high temperature so that no illm or shell will be formed when the liquidsteel makes contact With them. Therefore, located'as they are, they form-a parting line kbetween the shell or metal solidified in the gate .and-'port and .75 .that solidifiedin the mold, makingitpossiblegto withdraw the head I1 and cast section even after the gate and port have been filled for several scc-- onds with metal.

With this description of the various parts of the apparatus and their functions, the principles involved in its construction and precautions to be observed in its operation are briefly discussed in the following paragraphs. With the various parts of the apparatus properly built, assembled and firmly mounted and lined up upon suitable foundations, its operation presents no diiiiculties when carried out as follows;

After making sure that the traction rolls I I are in perfect working order, the operator, 11/2 to 2 hours before the heat is to be tapped, turns the current on to heat the rods 29, slowly at nrst, and then more rapidly until they are white hot. This heating is best regulated by means of a thermo-'- couple placed near and above the rods. Unless the exit end of the mold is closed, a draft will be produced causing some of the heat to flow through the gate. This closure may be effected by inserting the withdrawing head l1 for a distance of a foot or so into the exit end of the mold. Finally, pouring basin, water in large volumes is started flowing through the mold, the current heating the rods 2Q is turned ofi', and the withdrawing head is pushed through the mold to within 2 to 6 inches of the entering end thereof, so that it will not be warmed by heat from the rods. In the meantime, the pouring ladle I is heated inside as hot as possible with a gas burner.

By the method of our invention, the metal is tapped from the refining furnace into a teeming t ladle, in which the metal is held until its temperature is approaching its liquidus point. From this ladle the metal is preferably teemed, or bottom poured into a basin, from which it flows by gravity through the gate and port into the end of the mold, the port wall or walls being previously heated 'to a temperature suicently high to prevent the liquid metal in contact with them from solidifying, and the entrance to the mold being closed by the withdrawing head just before pouring begins. The liquid metal in contact with the cold face of the withdrawing head is rapidly solidied, so that as soon as the port is full, the withdrawing head, or heads, are drawn back through the mold at a speed adjusted so that the volume displaced by the head is equal to or slightly less than the pouring rate, which is kept as low as practicable and varies somewhat not only for different steels, but also during the pouring of a heat.

By this method the dimensions of the mold, as Well as the speed of withdrawal, are adjusted to the minimum pouring rate so that the shell of solidified steel formed in the mold is thick enough and strong enough to permit the section to be withdrawn from the mold. As the rate of solidihcation, that is, the thickness of shell formed in a given time, is practically the same for all steels, and varies inversely as the square of the time, this factor and the minimum pouring rate determine the cross sectional dimensions of the mold, which is limited as to length to about six feet by other factors. From this maximum, the length of the mold may be reduced according to the thickness of the section, to 4 or 5 feet for1 a slab two inches thickA for example.

The heat of steel is tapped into a teeming ladle fitted with a one-inch diameter nozzle, the smallest practicable, and held in the ladle to 30 minutes to permit the temperature of the steel just before liquid steel is admitted to the to drop as low as practicable for pouring. The nozzle is opened for 2 or 3 seconds over the spare ladle I5, and the steel collected is quickly poured while the teeming ladle is moved by crane to center the nozzle over the pouring basin, and the stopper is raised. As soon as metal starts rising in the pouring basin, the withdrawing head is started moving slowly backward through the mold at a speed of 8 to l0 feet per minute for slabs 4 inches thick by driving the traction rolls II. If this speed of travel is not fast enough to balance the teeming rate, the teeming is checked momentarily by closing the nozzle with the stopper, and opening it again before the pouring basin is empty. As the head I1 emerges from the mold 4, the water jets are turned on full, and after the slab has been gripped by the rolls II, the channels 2 I, bars 20 and block I8 are detached from the bars I9 embedded in the casting by knocking out the removable pins 22.

Once started, teeming should be as nearly con'- tinuous as possible, feeding the metal as fast as it is withdrawn from the mold with the withdrawing head or casting moving at the uniform rate of 6 to 8 feet per minute. No attempt should be made to adjust the speed of withdrawal to the pouring rate. It frequently happens, however, that the pouring rate cannot be controlled with the stopper, as in the case of stickers or running stop-pers due to metal freezing in the nozzle or about the stopper or to defective Stoppers. In such event, the steel is allowed to flow into the ladle I5 of Figure l, which may be tilted to pour over the lip into the pouring basin at any rate desired. By tilting this ladle at the start, pouring from both ladles may proceed simultaneously so that this ladle Ycan be much smaller than the teeming ladle, say 1/3 to 1/2 the size of the latter.

At the end of the pour, there is no head of liquid metal, so that the last 5 to 6 feet of the cast may be piped and the last 2 or 3 feet, representing the metal contained in the skimmer gate and port may be undersize, since it is insuihcient to i'lll the mold. rhe pinch rolls may be designed to grip undersize as well as full-size sections, so that practically all of this metal can be withdrawn from the apparatus of the design shown in Figure 5. After each heat has been cast, however, it is necessary to remove, inspect and repair both the gate and the port sections, in preparation for the next cast. The mold itself lasts for many heats, but should be carefully inspected for signs of wear after each heat. Any pitting or deep scoring of the inner surface of any section is cause for its removal and replacement with a section having a smooth inner surface.

The principles governing the design and determining the dimensions of the mold will now be explained. Regarding the dimensions of one embodiment of the molds shown in the drawings, these are preferably six feet in length and 4 X 36, inside dimensions, to cast slabs, blooms and billets 4 inches thick, and slabs 36 inches in width, and blooms and billets of any Width desired cast in multiples to give a total width of 32 inches. Other factors besides the desired finished size should be considered in fixing these dimensions as follows:

First, the speed of withdrawal must be adjusted to the minimum pouring rate, which in large-scale operations is about two tons (4000 lbs.) per minute, equivalent to pouring a heat of tons in 50 minutes. The capacity of the mold is 6 cu. ft. and, taking the density of liquid steel to be anaverage of about 475 lbs., the rate ci *niet ser alleate thi'ccch mele lic 1% QE c c Y times the length ot the mold; on 8.4; feet per minute, making the time. thesteel: is. inthe mold approximately.. 43a seconds. As wil-1l be, shown later, this-istheminimum timerequireditosol'diy a. Shell of?k sufcient rigidityl to permitv extraction from the. mold. This speed; mayv b eincieased as thethickness` of; the, cast section is decreased., 9,1 decreased` as`-V the` thickness isl increased, if the other dimensions (length and. Width-l remain; @he same. IitheA other dimensions; arc-.changed alone with thel thickness, then the speed; must be ad,- justed according to the cubicall contentci the mold to withdraw the steel as fast as itis poured.

Forrany mold? of a given length, the maximum speed of withdrawal is limited by the maximum nate off sol-idiication of the steel, which can be CQntrolled only toA a limited extent, as willV be evident from the following. descriptive explanation. As the liquid steelenters the mold, the surface in contact with the cold mold wall is almost instantly cooled tov 'zh liiqlidus point at which the. steel begins to solidify. Because of the great diierence in temperature betweenv the two surfaces, the mold wallabsorbs heat. from the liquidus surfaceY rapidly, QuSllg Qmplete solidication o f a thin filrn in but a fraction of a second.` Since the lm thus formed is pressed tightly against the mold wall by: internal liquid pressure. thev rapid transfer of heat continues, so that if the steel is admitted to the mold at a temperaturey but slightly above its liquidus point, the lm rst formed rapidly. increasesy in thiclgness to nearly 1A; inch in 1 second, 1A inch in3 to 5 Seconds, and 1/2 ischia 11 te 1.5 Scccals- As thc steel solidii'ies it contracts;L and with a shell 1/2 Ich thk *5116.119961* Suffe 2:9@ S191@ Well-S blak contact with the mold, slowing the rate of cooling from these surfaces slightly. below the rate from the bottom.` Theheatwhich itisu necessary to extract, in order to solidify the steel remaining liquid, is about 1 0- cais. per g. and the rate of heat ow is inversely proportional to the thickness of the shell wall and directly proportional to the diierence in temperature between the two surfaces of this wall. By water cooling the mold and making its walls thin, this'ditleienge is made much greater than when steel, is cast in a heavy metal mold, such as an ingot mold,l so that the shell formed on the bottom is about one inch thick within 45 seconds, orbythe'time it reaches the`V end oi" a mold 6 ft. long, when thev rate of travel Vis 8-i-t.'per minute. l

Here all surfaces of the sections are quenched to'at most 2004"- C. by jets of` water or otherluid, so that the time, T, in seconds, required to complete solidification may be found. from the forin which H=100 cal. per g., 770 cal. per cc. of steel, or 1540 total, 7c is the coefficient of heat conductivity for steel=0.11, S=1 sq. cm., t is the temperature m degrees C. of the liquid steel: l500 C., t' is the temperature of the outer surface=200 C., and e., the mean thickness of wal1=4 cm. Substituting these values in the formula gives 43.1 seconds as the time required to complete solidication of the section, during which time the section moves forward about 60 ciclica Thisv quick cclidicfwic,111A is imccrtant it permits the` low'iliid pressiire forcing metal fcri'vard to ll the cental'voidsnd rire-- vent piping in aslab {inchesthick nd'under, but is not rapid enough to assurecoiiiplete solidi-- ification' ofja slab "d'inches intime 'tolereventpiping entirely. 'A

The iiuid pressure within the mold is controlled by` the height' of thelpoiiriighbasinlabove the mold. Assuming that the specifici gravityof the liquid steel. at pouringl tempfejatiirel is -'7.74, as compared with watenat4f CQ, each footof meses-2,5 lbs? percaef Iii 'thc'cpcretus shown in Eigures vland 5, when'thefpuring lbasin is lle.d'with"'metal,` thel liquid level standsU 4 feet above the biittornv of)` Y the lincldgi give a iiuid pressure in the'` moldk oi.*12 l'to13'flbs. per square( inch, less a -small amount for loss'. ofhead `fl`iid flew" 'thicghwthc Scic- Thc Dcuriris basin isf made nohigher. vbecause this Pressure is sutiicient'to` f eed metal to the' mold`,"and a,J higher pressure nriayriinturev the shell formed the mold. to producel the surface "deflect known as bleeding, and`also 'rflcreas'esA the,V 'force necessary Subtract pressure l XL2 IPSec-l .l ,Y 1,723 Tctel crescere tc be @hacedns- M672 Now, the coeiicientof. friction of steel on steel varies from 0.15 f or Very smooth surfacs'toQBO foinish machined surfaces; so the tctalforce required to withdrawthe sied from 'tnoidis .35 12,672#.=3,8o2 ibs., and the power"'feqir'ed=f 60 3802, lbs.

91. @resserrer plus that required tc cpcratc cthcr equipment- Bf'eucscl Withdraw@ iS. Static@ at'the port. endl of the' m01@ 'an bicfcr haetten' a'few inchs of Siccl' is cdreittcdteriiilc'fri t iencrcldybut iii; pfcccc'tlc bjcwcr fcciuir tc. cicrctc' thc ccuigmcht is mitch' 'lilcicche thc extracting force. v. ,o If- 'tbc Pouring basic. clcicetcd tc. c, ft incstcad 01"'4 'f-t'f above'the`m`ol`d `the"'power requiredto withdraw the slab is almost doubled.

Again, when the shell formed in the mold is IAL thick, the strength of the solidified section will probably not exceed 400 lbs. per square inch, so that the total force per inch of cross-section the shell can withstand is lbs. This force is exceeded by the force of friction when the ferrostatic head is 11 feet, and raising the pouring basin to this height would result in tearing the shell as fast as it is formed, so that the section may be bleeding as it is withdrawn from the mold. As the detached portions of the shell would remain in contact with the mold, they would gradually grow thicker until eventually4 they would block the free movement of metal through the mold in the parts tc which they are attached. y

As the various limiting factors make it i1n practical to attempt complete solidification in the mold, we resort to the use of high pressure water jets I directed against all surfaces of the section as it is withdrawn from the mold, to effect complete solidication of the central portion in a minimum period of time and before the section reaches the withdrawing rolls il which of necessity exert considerable pressure upon at least two surfaces of the section. If the section were passed through these rolls while the central portion is still in a iiuid or semiuid state, the section would be deformed to a considerable extent, and the central portion would be defective in that it would be characterized by a Weak, porous structure, similar to that obtained when an ingot is rolled before the central portion has solidified.

Rapid cooling at this point to effect complete solidification also permits feeding of liquid metal to compensate for the contraction or solidication, and assures a solid section free of pipe or remnants of pipe.

The application of the cold water jets has the effect of chilling or quenching the surface to a temperature Well below the critical range, or in the range 300 F. to 700 F., leaving the central portion at a much higher temperature, which will vary according to the thickness from about 800 F. for a slab 2 inches thick to about 1800 F. for a slab 4 inches thick. This treatment, therefore, hardens the surface, particularly of the higher carbon steels, develops stresses in the section, and makes it diicult to cut the section into lengths by either shearing or sawing, the only methods of cutting that are rapid enough for the process. To overcome this difficulty, as Well as to improve the quality of the product, we pass the section through a reheating furnace I2 to restore the heat to the surface metal and make the temperature of the section more nearly uniform for cutting into lengths suitable for the next forming operation,

From this description, it will be observed that the method of our invention consists essentially of continuously introducing the molten metal through a preheated refractory port into a metal mold, supported in a horizontal or nearly horizontal position and designed for the rapid abstraction of heat to form a shell of solidified metal conforming to the section desired; con-V r, unuousiy withdrawing this sneu from the mold and rapidly cooling it by direct application of a uid cooling medium to complete the solidiflcation of the section progressively toward the exit end of the mold so that the liquid metal, under a low head will flow forward to compensate liquid-to-solid contraction of the metal; and

subsequently applying heat to the quenched or chilled surfaces to restore the temperature of the shell to substantially that of the interior and thus relieve stresses developed in cooling and soften the structure for cutting into lengths desired for the next operation.

Having thus described the apparatus used, recited the principles to be observed and the precautions to be taken in designing and constructing it and explained the method to be followed in the continuous casting of steel, we wish to point out that it may also be applied to the casting of other metals, such as copper and nickel, and that various modifications may be introduced in its design and construction without exceeding the scope of the invention as defined by the following claim.

We claim:

ln a method of progressively casting an elongated mass of metal of indefinite length, the steps including preheating to a temperature near the freezing point of the metal, the outlet end of a U-tube gate connected to the entrance end of a horizontal mold open at both ends, thereby preventing formation of a shell of solidified metal adjacent said entrance end of the rnold, inserting a closure head into the mold from the other end, pouring molten metal into a basin surmounting the inlet end of said gate above the level of the mold whereby the metal flows into said entrance end and against said head, circulating cooling liquid about the mold thereby causing partial solidication of the metal therein, withdrawing said head and thereby pulling from the mold a continuous mass of metal preliminarily shaped therein, discharging sprays of cooling liquid onto the mass immediately it emerges from the mold, to accelerate freezing of the interior thereof, then passing the mass directly through a continuous furnace thereby reheating it eX- teriorly and tending to equalize the interior and exterior temperatures thereof and finally shear ing said mass into predetermined lengths as it emerges from the furnace.

CHARLES B. FRANCIS. RALPH B. PORTER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 894,410 Trotz July 28, 1908 944,370 Monnot Dec. 28, 1909 944,668 Douteur Dec. 28, 1909 2,058,447 Hazelett Oct. 27, 1936 2,121,280 Bell June 21, 1938 2,225,373 Goss Dec. 17, 1940 2,242,350 Eldred May 20, 1941

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