US2955334A

US2955334A - Continuous casting

Info

Publication number: US2955334A
Application number: US837285A
Authority: US
Inventors: Pulsifer Verne
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1959-08-31
Filing date: 1959-08-31
Publication date: 1960-10-11
Anticipated expiration: 1977-10-11

Description

Oct. 11, 1960 v. PULSIFER 2,955,334

CONTINUOUS CASTING Original Filed Jan. 18, 1956 Mmswrwe a HUB M VE A/E PULSIFER Substituted for abandoned application Ser. Jan. 18, 1956. This application Aug.

No. 837,285 I 7 7 Claims. (Cl. 22-572 This invention relates to the casting of metals and more specifically to an improvement in continuous casting, and is a continuation of my co-pending application U.S. Serial No. 559,923 filed January 18, 1956, now abandoned, which in turn is a continuation-in-part ofmy co-pending application U.S; Serial No. 326,876 filed December 19, l952,'now abandoned.

In continuously casting metal it is desirable that the molten metal freeze in a direction toward'the feeding head rather than freezing rapidly laterally of the direction in which the sheet is being cast. Solidification from the side walls inwardly is termed lateral solidification, and solidification in a direction parallel to the direction of the sheet being cast is termed longitudinal solidification. 'In continuous casting apparatus of the type herein disclosed, lateral solidification will occur when the latent heat is removed from the'molten metal through themold; walls. When this occurs and while the molten metal is in the mushy condition, freezing shrinkage can be compensated for by mass feeding or in other words, by movement of liquid metal laterally with respect to the mold walls and into the interstices of the solidifying metal which is nucleated at the mold walls; After the primary crystals form a coherent skeleton, freezing shrinkage must be compensated for by flow of the residual liquid through narrow tortuous channels toward those portions ofthe newly cast metal where the freezing is most advanced. Since this flow is retarded, voids remain in the frozen sheet.

By removing the latent the direction of the sheet heat in a direction parallel to being cast, that is,- through the newly solidified metal and away from the feeder longitudinal solidification is obtained and the metal frozen in a direction toward the source of the molten metal, eliminating voids which would otherwise be interspersed throughout the newly solidified crystals. Additionally, it is desirable in continuous casting of metals to freeze the metal as rapidly as possible, thereby producing a denser product. By rapid freezing, the portion of the metal which would otherwise produce shrinkage voids is constantly maintained in the mass of molten metal not yet frozen, and the metal tends to freeze in layers along a more even front.

When pouring metal for continuous casting, it is de sirable to eliminate turbulence in the molten-metal and also to reduce the penetration of the molten metal into thesolidifying metal, thus preventing air and other gases from being trapped in the solidified metal and preventing disturbance of the granular structure of the solidifying metal.

States P tent Ofi being cooled is determined by Patented Oct. 1 1, less Another important consideration in continuous casting is the quality of the surface of the sheet. In order to obtain a usable surface which is free from'cracks, scars, and so forth, it is necessary to maintain proper alignment of the mold and solidifying metal. Turbulence in the pouring stream and the momentum of the stream should also be held to a minimum so that the surface of the sheet will not be disrupted as it is solidifying.

In any casting method, the distance which the growing dendrites or crystals extend into'the molten metal the rate of freezing. This does not mean'that with a fast rate of freezing a fine grain will result. In fact, very large grains may result, particularly if the pouring temperature is high; Grain size is determined by the number of nuclei present in the methods, solidification occurs on a narrow front and nuclei occur only within this narrow front. These nuclei do not have time to grow into stable crystals before the front has passed. In slow cooling methods; these nuclei can grow into stable crystals which result in an equiaxed' structure and poor working characteristics.

' In addition to the previously mentioned considerations,

and solidifyingmetal be maintained. In order to assure a short freezing time sulficient cooling medium must positively contact the hot metal, but the mass of coolant must be prevented from coming in tontactv with the solidifying metal and causing pockets or blisters on'the surface of the metal.

It is therefore an object of this invention to provide, extremely rapid longitudinal heat abstraction and theresurfaces. Other objects will become apparent from the following description'and drawings in which: Figure 1 is a schematic, vertical, sectional view of the casting apparatus;

Figure 2 is a transverse view taken on the line 2-2 in Figure 1;" i Figure 3 is an enlarged view of the left portion of the. cooling jacket and lines indicating the rate of cooling of a sheet. 1 The invention contemplates bottom feeding molten metal 3' into a mold or die 4' and continuously withdrawing the resultant cast sheet 10 or bar upwardly from the die by a pair of pinch rolls 12. At least all of the latent heat is very rapidly removed by longitudinal cool ing, that is, by'withdrawing the latent heat through the previously cast sheet or bar in a direction away. from the feeder, or the source of the molten metal. In order to remove substantially all of the latent heat and not more than the relatively small residue of superheat as rapidly as possible, a jet or flux of high pressure water is. directed by jacket 11 against the surface of the newly cast sheet.

the newly cast sheet isotherm Sufiiciently high pressure water will prevent or greatly retard the formation of steam adjacent the surface of the newly cast sheet. Alcohol and salt may be added to the water to increase its quenching properties and to permit its introduction at a lower temperature without freezing. To insure that the latent heat is withdrawn longitudinally, the die 4 is provided with either cooling means for withdrawing practically all of the super-heat laterally of the sheet through the die walls or with heating means to prevent the latent heat from escaping laterally. Under these conditions, not more than a very small residue, if any, of the super-heat remains in the metal at the mold level of incipient fusion at which the temperature of the molten metal is continuously de tected and maintained near the melting point and at which substantially all of the latent heat is maintained in order to insure that thereafter substantially all, rather than a lesser fraction of the latent heat is longitudinally abstracted to give the desired crystal structure in the cast ingot. Whether or not heating or cooling means 6 will be required depends on the operating temperature and inherent characteristics of the metal being cast. The invention is particularly adapted to casting metals such as brass, bronze, aluminum or magnesium and alloys having a base of aluminum or magnesium as well as pure metals such as copper, titanium or zirconium.

Referring to the drawings, the insulating crucible 1 includes a reservoir 2 having an open top through which molten metal 3 may be poured. A mold member or die 4, which is preferably of the type described in the afore mentioned application, is secured in the crucible 1 and has a vertical runner 5 open at its top and bottom ends. The die member maybe provided with conventional heating or cooling means 6, such as a passageway containing a cooling fluid, or a heating coil, or both such passageway and heating coil, for cooling or heating the molten metal 3 as it passes through the die so that substantially all the super-heat will be removed from the molten metal by the cooling effect of the mold member 4 but preventing any suitable amount of the latent heat from being removed through the mold walls.

A pair of rolls 7 considerably smaller than pinch rolls 12, is provided immediately adjacent the discharge end of the mold member 4. These rolls are of a size permitting very close spacing of die 4 and jacket 11 and are provided with a reducing mold dressing supplied in any conventional manner as by sprays 8 fed through headers 9, to prevent oxidation of the surface of the newly cast sheet 10. The rolls 7 and dressing 8 further serve to prevent vapor from the cooling water directed against the sheet 10 by jacket assembly 11 from the coming into contact with the molten metal in the mold member 4 or the surface of the sheet 10 below the rolls. The sheet 10 is withdrawn from the die 4 by one or more pairs of pinch rolls 12.

The cooling jacket assembly 11 directs a jet or flux of cooling medium against the surface of the solidified sheet 10. Referring toFigure 2, the jacket 13 is a hollow, elongated donut-shaped container. T he newly cast sheet 10 passes upwardly through a central aperture 14 in the jacket. Referring to Figure 1, the jacket is hollow and has a divider or partition 15 passing through the central portion thereof. The edge of the divider adjacent the sheet has a bead-like portion 16 thereon. Thus, the jacket is divided into a lower chamber 17 and an upper chamber 18. Cooling medium inlets 19 open into the lower chamber 17 and cooling medium outlets 20 open into the upper chamber 18. The size of inlets and outlets and their location on the jacket is such as to eliminate uneven cooling of the sheet. The chambers 17 and 18 are open at the center aperture 14 in the jacket 13 to permit the cooling medium to contact the surface of the sheet 10. The spacing between the sheet and the edges 21 of the aperture is great enough so the sheet and edges do not contact each other since this would tend to mar the sheet, but this spacing must be small enough to prevent excessive loss of cooling medium and too great a reduction in the pressure of the cooling medium against the surface of the sheet.

The jacket assembly is mounted in such a manner that the distance between the molten metal in the die member, at point B and the contact between the cooling water and the surface of the sheet at A may be varied to increase the rate of cooling the newly cast metal. Movement of the jacket may be accomplished in any conventional manner, such as by a hoist or a gear and rack arrangement. The sheet is withdrawn from the die member by one or more pairs of pinch rollers.

The cooling medium is introduced through the inlets 19 into the lower jacket chamber 17, It will be noted that the lower and upper chambers 17 and 18 are tapered, thus as the high pressure cooling medium passes through the lower chamber 17 it contacts the sheet 10 adjacent the bead 16 and then is sucked and passes into the upper chamber 18. The taper between the jacket walls 22 and the jacket divider 15 is such as to provide a high water velocity because of the venturi efiect as the water is forced through the jacket. The bead-like portion 16 on the end of'the divider is shaped so as to reduce the turbulence of the cooling medium and improve the degree of contact between it and the hot casting in that vicinity and to cooperate in produc ing the venturi effect.

Figure 3 shows the left hand portion of the jacket to an enlarged scale. The cooling medium, such as water 23, is forced through the lower chamber 17 and contacts the surface of the sheet 10 as it passes the head 16 on the divider 15. It will be seen that adjacent the hottest portion of the sheet the water vaporized into steam 24 but that adjacent the upper chamber of the jacket, the contact is substantially continuous between the water and the surface of the sheet. The edges of the opening in the jacket adjacent the surface of the sheet will be spaced apart between one-fourth inch and onehalf inch for a sheet of approximately one-half inch thickness. The edge of the bead nearest the sheet will be spaced from the sheet approximately one-eighth inch and the pressure developed by the water flowing between the edge of the sheet and the bead, as at point A, will be for all practical purposes at the relatively high pressure of approximately 2,000 p.s.i. A pressure of this magnitude will, of course, retard the formation of steam on the surface of the sheet, but in addition to this effect the scrubbing action of the water as it flows against the surface of the sheet also tends to prevent the formation of steam or to dissipate any steam which might form. As mentioned previously, the spacing between the edges 21 of the jacket aperture and the surface of the sheet 10 must be sufficiently small to prevent any appreciable escape of water 23 or steam 24 and the accompanying reduction in water pressure. Because of the velocity of water adjacent the sheet, the water temperature will remain substantially constant in this area. Isotherm lines 26 shown on the sheet indicate the relative rate of cooling of the newly cast sheet. The temperatures designated on the isotherm lines are intended merely for purposes of illustration and relate to a cast aluminum sheet and these figures will, of course, vary depending on such factors as the initial temperature of the water, the temperature of the molten metal, and {.116 spacing of the water jacket from the molten meta In starting the apparatus in operation, a previously cast sheet or bar of the same size and configuration as the mold member 4 is inserted through the pinch rolls 12 and jacket aperture 14 and into the mold member runner 5. The level of the molten metal in reservoir 2 is then raised to provide the proper hydrostatic head in the mold member 4. The cooling water passing through jacket 11 causes the molten metal 3 to solidify in the die 4 and the sheet or bar-is then withdrawn by the pinch rolls 12. The cooling'or heating means 6 in the die 4 are then adjusted so that all'except a small residue, if any, of the super-heat, but substantially none of the latent heat, in the molten metal is withdrawn through the die member 4. It should be noted that the majority of the cooling medium contacting the newly cast sheet 10 will be dissipated through the outlets 20, but some means must be provided to prevent. thewater from contacting the molten metal 3 in the die'4 and rolls 7 and the applied dressing 8, thelatter of which not only keeps coolant from prematurely contacting the hot metal, but also serves to reduce the effective clearance at the lowermost edge 21 of jacket 11 and excessive escape therefrom of coolant, are particularly adapted for this purpose.

By bottom feeding inclusions and blow holes are eliminated, the entrapment of gas is prevented, and a better surface is provided, both by eliminating oxidation and by the tendency of the solidified casting to shrink away from the mold surface so that almost all frictional contact between the newly cast sheet or bar and the apparatus is eliminated. The rolls 7 maintain the alignment of the newly cast material with the die, thus preventingscarring of the sheet or bar by the die 4 and jacket 11 and these rolls also protect the mold. It should also be noted that by providing a reducing mold dressing to the surface of the rolls 7, the newly cast sheet is coated with this dressing immediately upon emerging from the die. The shape .of the crucible prevents any dross from getting into the die and, furthermore, a crucible having a reservoir of this nature makes it extremely simple to vary the hydro static head on the molten metal in the die. By providing a controlled head, any voids which may form in the internal structure of the sheet will more easily fill with molten metal, thereby providing a sounder and denser sheet. The reservoir furthermore permits the introduc tion of molten metal 3 with no appreciable disturbance of the molten metal in the die 4. The water in the jacket '11 provides rapid cooling of the molten metal 3 in the die member 4 and it is merely necessary to increase the quantity of water delivered against the newly cast'sheet, reduce the water temperature or decrease the distance between the jacket and molten metal in the die 3 to increase the rate of cooling.

It is to be understood that provision for heating and/or in the die may be provided. Although certain specific embodiments, components and details are set forth in the foregoing, it will be understood that various changes in such embodiments, components and details will be apparent to one skilled in the art and that such changes may be made without departing from the spirit and scope of this invention and that this invention is therefore not to be solimited except as set forth in the appendent claims.

What is claimed is:

1. In a continuous metal casting apparatus, a cooling jacket having a cooling medium stream inlet end, a cooling medium stream outlet end and a pair of spaced edges defining an intervening opening intermediate said stream inlet and outlet ends, said edges being adapted to be positioned circumferentially in closely spaced relationship adjacent the periphery of the freshly cast portion of a casting emerging from a casting die, a partition member in said jacket forming on one side thereof with said jacket a channel terminating at said opening for admitting cooling fluid to said portion directly, and said partition forming on the opposite side thereof with said jacket a channel terminating at said opening for admitting cooling fluid to said portion directl and said partition forming on the opposite side thereof with said jacket a second channel originating at said opening for removing said cooling medium, said first channel communicating with said inlet end and converging to said opening and said other forms of dies having cooling the molten metal second channel communicating with said outlet and diverging from said opening, said channel separating partition having a circumferential edge spaced from said periphery in excess of the spacing therefrom of said edges of the opening whereby said medium is applied and withdrawn at said periphery with a venturi effect at high pressure and velocity with a minimum of entrained gas.

2. The cooling jacket of claim 1 wherein the first channel is positioned in'proximity with the discharge end of a casting die and the second channel is positioned more remotely therefrom.

3. In the cooling jacket of claim 1 wherein the partition edge at the opening is a bead, said first and second cooling medium conveying channels are directed with respect to said opening so that said cooling medium impinges said newly cast bar or sheet at an acute angle and 's deflected therefrom around said bead into said second channel, thereby engaging said newly cast sheet longitudinally with a scrubbing action.

4. The continuous casting apparatus of claim 1 including a casting die having walls defining a vertical bore pass ing therethrough, a molten metal reservoir having means to feed molten metal into the bottom of said die bore and place a hydrostatic pressure on the molten metal in said die against the emerging solidified metal suflicient to fill any voids in the solidifying metal, anti-friction guide means to withdraw the solidified metal upwardly out of the die in fixed alignment with said bore substantially at the rate of solidification, and heat exchange means at said die tomaintain substantially all of the latent heat of fusion in the portion of the molten metal at and near the melting point adjacent the bottom of the emerging solidified metal by reversible interchange of heat through said walls of the vertical bore.

5. A continuous casting apparatus comprising a die member having a vertical bore passing therethrough, a molten metal reservoir having means to feed molten metal into the bottom of the die member and to maintain a hydrostatic pressure on the molten metal in said die member sutficient to fill any voids in the solidifying metal, driven guide means to withdraw the solidified metal upwardly out of the die member substantially at the rate of solidification, means at said die to maintain substantially all of the latent heat of fusion in at least the portion of the molten metal near the melting point in the mold adjacent the bottom of the solidified metal by adding or withdrawing heat through the walls of said vertical bore in said die member and high pressure, high speed fluid jet cooling means applied simultaneously around a peripheral portion of the metal below said driving guide means and closely spaced with respect to said die member to Withdraw the latent heat of fusion longitudinally of the solidified metal from said adjacent molten metal, said means for withdrawing the solidified metal from the mold comprises a pair of pinch rolls and including further alignment and shield means adjacent the die member to maintain the solidified metal in the die member aligned with the walls of the vertical bore of the die member, and to prevent said cooling medium from contactnig the metal in the die member, said further means comprising a second pair of rollers immediately adjacent the discharge end of said die member.

6. The continuous casting apparatus of claim 5 including means for applying a reducing dressing to said second pair of rollers for subsequent application of said dressing as an adherent oxidation retarding coating to the solidified metal.

7. A process for continuously casting metals comprising feeding molten metal upwardly through a vertical die in heat exchange relationship with the metal while subjecting the molten metal in the die to a hydrostatic pressure sufliciently high to fill any voids between solidified crystals with metal and simultaneously maintaining in substantially all of the molten metal in the die an amount of heat substantially equal to the latent heat of fusion of the metal being cast by varying the exchange of heat transversely of the metal to and from the die, continuously coating substantially all of the periphery of the emerging solidified metal with a dressing material immediately after withdrawal from the die, and thereafter rapidly abstracting substantially all of the latent heat of fusion upwardly through the solidified metal from the underlying portion of molten metal being near the melting point and adjacent the solidified metal by intimate contact with a longitudinal stream of refrigerant at relatively high pressure continuously impacting substantial portion of the periphery of the solidified metal adjacent said die while withdrawing said solidified metal at the 8 rateof solidification from the die in substantiallyvfixed alignment of the end of the solidified metal adjacent the molten metal with respect to thedie, whereby disruption of the solidifying metal by binding'and excessive lateral- 5 movement is prevented. a 5

References Cited in the file of this patent UNITED STATES PATENTS 10 2,242,350 Eldred May 20, 1941 2,405,355 Harrison Aug. 6, 1946 2,651,821 Chadwick et al Sept. 1-5, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0- 2,955,334 October ll 1960 Verne Pul sifer It is hereby certified that error appears in the printed specification of the above 11 umbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 40 for "suitable" read me substantial column 6,, line 59, for "'contactnig" read contacting =9 Signed and sealed this llth day of April 1961e (SEAL) Attest: E N S W- SW D ARTHUR W, CROCKER Attesting Oficer Acting Commissioner of Patents