US3349837A - Continuous casting apparatus with means supporting only outer portions of non-uniformingot - Google Patents

Description

Oct. 31, 1967 J- BRONDYKE ET AL 3,349,837

CONTINUOUS CASTING PPARATUS WITH MEANS SUPPORTING o OUTER PORTIONS 0F NON-UNIFORM INGOT Filed July 19, 1965 Kennefh Riv/7 BY United States Patent Ofilice 3,349,837 Patented Oct. 31, 1967 3,349,837 CONTINUOUS CASTING APPARATUS WITH MEANS SUPPORTING ONLY OUTER POR- TIONS OF NON-UNIFORM INGOT Kenneth J. Brondyke, Oakmont, and Richard T. Craig,

New Kensingtou, Pa., assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 19, 1965, Ser. No. 472,820 8 Claims. (Cl. 164-474) ABSTRACT OF THE DISCLOSURE In the continuous horizontal casting of large fiat metal ingots, e.g. having a cross section of 16 x 35 inches, the mold opening is concave across the top and bottom to allow for non-uniform shrinkage. The starting plug employed in initiating the run must correspond to the concave shape of the mold opening although the ingot, by the time it has emerged about a foot, has shrunk to its desired fiat configuration. The support means must be care fully aligned to prevent flexing of the ingot axis. If it is aligned with the lowermost portion of the concave mold opening so as to maintain mold alignment for the starting plug, the solidified ingot, when it reaches the support means, is out of alignment and tends to settle downwardly to the support means thereby flexing the ingot axis which, in turn, results in a serpentine appearance along the ingot length and necessitates excessive scalping and material waste. This difliculty is alleviated if the support means is arranged to support only the outermost portion of the ingot width, that is those portions of the ingot width where the concavities run-out does not ex ceed 50% of the total concavity run-out.

This invention relates to the continuous casting of metal ingots in horizontaly disposed open ended molds, and especially to casting ingots of the light metals, alu' minum and magnesium, together with their alloys.

Horizontal continuous casting of ingots has found commercial acceptance because of recognized advantages in certain respects over vertical continuous castings. In the horizontal casting under consideration here, molten metal is provided in a reservoir most often separated from an open ended horizontal mold by a partial barrier having an opening to conduct liquid metal from the reservoir to the drastically chilled mold from which the solidifying metal is continuously withdrawn in a horizontal direction. Means are provided for withdrawing and supporting the ingot emerging from the mold, and, accordingly, an endless belt, a series of rollers, or the like, is disposed to bear against the bottom surface of the ingot. The belt or other support can be powered to serve the dual functions of supporting and withdrawing the ingot.

When casting relatively large ingot, for instance having a cross-section of 16" in thickness by 35" in width, a size highly suitable for rolling into sheet, a non-uniform shrinkage pattern is observed across the ingot cross-section. Referring to FIGURE 1, an ingot 10 cast in a mold having a rectangular opening 12 will exhibit a concave surface condition 14 which necessitates removal of a large amount of metal to provide a flat ingot for hot rolling or the like. This non-uniform or disproportionate shrinkage or contraction in the vertical dimension is attributed to a non-uniform heat extraction condition in that more heat is extracted from the metal in the outer portions of the ingot width. To compensate for this condition, the bottom and top surfaces, and sometimes the side surfaces, of the mold opening are shaped to provide a concave wall configuration as shown in FIGURE 2.

As there shown, the ingot 10 is cast in a mold having concave inside top and bottom surfaces 20 to produce an ingot cross-section 12 which is substantially flat surfaced.

While the chilled mold is described as open ended, obviously the outlet of the mold is always closed against flow of molten metal. At the start of the casting run, a starting plug 74, as shown in FIGURE 3, of suitable size and configuration is used to close the mold outlet, generally by being inserted thereinto. The casting run is initiated by permitting molten metal to fill the mold and withdrawing the starting plug with the solidified, or partially solidified, ingot connected thereto. A'fter withdrawal of the starting plug, the mold outlet is closed to the flow of liquid metal by the solidified ingot metal.

In horizontal casting, it is essential that the bottom surface of the ingot emerging from the mold be aligned with the supporting surface of the belt or roller support, to avoid excessive deflection of the ingot as it reaches and is carried along the supporting surface. Any significant deflection here causes a repeating condition to occur in the freezing ingot which renders the ingot length somewhat wavy or serpentine. This, in turn, necessitates excessive metal removal to provide the non-wavy ingot surface required for subsequent fabrication such as hot rolling. In vertical casting, no such problem arises, since the ingot is principally supported on its end. However, in horizontal casting, a problem .in this respect is encountered in that while the center portion of the ingot undergoes a disproportionate shrinkage, desirably compensated for so that the ingot bottom surface is substantially flat before it reaches the support means, the starting plug maintains its convex protrusion. At the start of the casting run, the starting plug is positioned upon the support means and aligned with the bottom of the mold to facilitate insertion and withdrawal of the plug. However, the emerging flat bottomed ingot as it reaches the supporting means has undergone its disproportionate shrinkage and accordingly its bottom surface is disposed somewhat higher than the support means, by an amount equivalent to the concavity of the mold. This misalignment condition results in a wavy or serpentine characteristic along the ingot length caused by repetitive freezing ingot deflections downwardly to the support means.

The magnitude of the problem is dependent upon the size and shape of the ingot cross-section. The relatively large fiat ingot cross-sections highly suitable for hot rolling are the most susceptible. FOr instance, an ingot having a crosssection of 16" thick by 35" wide often requires a mold concavity approaching for the top and bottom surfaces to produce substantially flat corresponding ingot surfaces. The waviness resulting from the attendant /5". misalignment causes extremely costly metal waste when scalping to obtain flat surfaces to be hot rolled.

According to the invention, a unique solution to the problem has been found in that the wavy ingot condition caused by the alignment problem is alleviated by supporting only the outermost portions of the starting plug and ingot cross-sections. This solution offers the advantages of being inexpensive and readily provided for in existing facilities.

It is an object of the invention to provide an apparatus for continuously casting ingots, using a horizontally disposed chilled mold having surfaces allowing for nonuniform ingot shrinkage, to produce a substantially straight ingot length. Another object is to provide apparatus for the continuous casting of relatively flat surfaced ingots using a horizontally disposed, concave surfaced, chilled mold, the resulting ingot exhibiting a substantially straight, wave-free length.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter in this description and drawings in which:

FIG. 1 is a representation of a rectangular mold opening and the ingot cross-section obtained from it,

FIG. 2 is a representation of a concave mold opening and the rectangular ingot cross-section obtained from it,

FIG. 3 is an elevation, partially in cross-section, of a horizontal casting apparatus, and

FIG. 4 is an elevation in cross-section of an embodiment of the invention.

Suitable apparatus for continuous casting in a horizontally disposed mold is illustrated in FIG. 3 wherein molten metal reservoir 30 is provided on one side of an insulating barrier or closure 32. On the opposite side of the closure is a horizontally disposed mold 34 which is chilled by suitable cooling means such as water headers 36 provided with holes 38 to permit spraying water 40 against the surfaces of the mold and the ingot emerging therefrom. The arrangement shown in FIG. 3 is only schematic or representative in this respect. An opening 44 is provided in closure 32 for passage of liquid metal from the reservoir 30 to the chilled mold. The reservoir is enclosed by suitable insulating members 48, and the molten metal surface 31 is maintained at. a higher elevation than that of the emerging ingot, such that any liquid metal 51 within the mold 34 is under a positive liquid metal head. Within the mold, a relatively thin embryo ingot surface skin 50 is immediately formed by the liquid metal as it contacts the drastically chilled mold surface. This skin thickens as the ingot progresses outwardly from the mold. An ideal solidus line 52 is depicted for the center of the ingot width. The non-uniform shrinkage effect is not shown. As shown in FIG. 3, the ingot 60 may be solidified some time prior to reaching the support means which, in this case, consists of an endless belt 64 supported by belt rollers 66 and the belt support plate 68. The belt rollers 66 are about 20 to 25" in diameter and spaced about 6 to feet apart. The belt width is most often at least as wide as the ingot. The distance between the mold outlet and the initial contact between the belt and the ingot generally ranges from 10 to 30". If desired, some means such as overhead roller 70 may be provided to urge the ingot against the ingot support means to assure intimate ingot contact with the belt. The belt rollers 66 can be powered as by motor 67, so that the belt performs both the functions of supporting the ingot and withdrawing the ingot. The power transmission preferably includes a variable speed feature to allow for the different casting or ingot withdrawal speeds. Another advantage here is that when starting the casting run, the starting plug is best brought up to the desired casting speed somewhat gradually. Of course, rollers may be used in lieu of belts; the prime mover for ingot withdrawal may be something other than the support means, for instance hold down roller 70 may be driven by motor 71. Various schemes here will suggest themselves to those skilled in the art, although the powered belt shown in FIG. 3 has been found to perform quite reliably.

As indicated earlier in this description, the ingot support surface of the belt must be aligned with the ingot as it reaches the belt to avoid causing the ingot deflection, but an alignment problem is encountered in that the bottom surfaces of the ingot and starting plug reach the support belt at different elevations. As also indicated earlier, the severity of the alignment problem in terms of ingot waviness, is related to the size and shape of the ingot cross-section. A relatively small symmetrical crosssection, such as a 6" square, poses a relatively minor problem in this respect, although a 6 thick by 30 wide section may have a misalignment equal to dimension x in FIGURE 2, of V1". Generally speaking, the misalignment between the emerging ingot and the support means is not critical so long as it is significantly less than A". However, as the condition approaches Ma" and increases,

such results in the ingot exhibiting a waviness condition which is considered excessive from a commercial standpoint. The simplest way to correlate the extent of misalignment with the apparatus employed is to consider the misalignment approximately equal to the total concavity dimension x, in FIG. 2, of the bottom surface of the mold opening and accordingly the invention will be described in this manner. Thus, the invention is concerned with the condition where mold bottom surface exhibits a substantial concavity, but more particularly where this concavity is A" or more, and especially where it is A" or greater, in which case the resulting ingot waviness can cause extremely costly metal scrap losses.

The solution to the alignment problem in accordance with the invention contemplates supporting both the starting plug and the -ingot connected thereto only at the outer portions of their respective widths. Such can be accomplished by the provision of two narrow belts in lieu of the single wide belt 64, or the positioning of two such belts upon an existing single belt. For instance, referring to FIG. 4, the substantially fiat-bottomed ingot 60 is supported only on the outer. portion of its width by narrow belts 65, as is also the starting plug 74. A practical limit in accordance with the invention is that the ingot and starting plug not be supported by more than that part of the outer width portion which corresponds to a maximum concavity run-out of of the total concavity. In a preferred embodiment, this value is further limited to a maximum of /8". Referring to FIG. 2, one side of the ingot is supported at any point between the outer edge 16 and point 18 which corresponds to a concavity run-out y of not more than 50%, or half, of x, or across this entire outer band, as by a belt or roller band of suitable width to support the side of the ingot from point 18 to point 16, the other side of the ingot width being similarly supported. Thus, restating the matter, each belt 65 supports the ingot and the starting plug 74 at the outer portion of their respective widths, the support provided thereby not extending inward, toward the center of the ingot width, beyond that portion of the ingot corresponding to a mold bottom surface run-out of 50% of the total concavity. As indicated above, it is preferred to further limit this value, y" in FIG. 2, to /s" maximum. The belt support plate 68 may be wide enough to support both belts or it can comprise two separate plates to provide separate support for each belt, although the former may be preferred in that it assures that the belts will describe a common plane. While extensive reference to supporting the ingot by an endless belt has been described, rollers or the like can also be used within the scope of the invention. In the event rollers are employed, bands may be positioned about their periphery to provide the same support in5 accordance with the invention as furnished by the belts 6 The dimensions of the belt cross-section can vary considerably in that any thickness which permits the starting plug bottom to clear the belt support plate 68 will suffice. However a thickness of to /1" has been found to be highly satisfactory in that it is of sufficient thickness to be used with molds having a bottom surface concavity of /2" which should include almost all ingot sizes of current commercial significance. A fabric and rubber composite belt of this thickness also generally exhibits sufiicient resiliency to compensate for the very minor shrinkage that does occur at the outer portions of the ingot width.

The width of the belts is not particularly critical although from the standpoint of commercial practice it is best to select a width and spacing combination compatible with as many ingot sizes as possible. This, of course, minimizes the extent of belt repositioning necessary when changing mold sizes. For instance, positioning two belts each 8" in width and A5" in thickness so as to provide a spacing or gap of about 24" between the belts will accommodate most ingots having widths ranging from 30 to 45". However, it is obvious that many deviations can be made to accommodate the individual circumstances posed by the particular continuous casting apparatus involved and those skilled in the art will have no trouble in utilizing the invention in their particular schemes. For instance, ingot size, composition and casting speed are among the predominate factors to be considered as will be appreciated by those skilled in the art.

In order to further illustrate the practice of the invenion, the following example will proceed. Ingots are horizontally cast of an aluminum base alloy having a nominal composition of 4.5 weight percent magnesium, the balance being aluminum and incidental impurities. The ingots have a predetermined cross-section of 16" in thickness by 39" in width with substantially fiat top and bottom surfaces and are intended to be used as stock in a hot rolling mill. The mold has an opening conforming to the crosssection of the ingot except that the top and bottom inner surfaces have a concavity of almost /2". Ingots are cast in an apparatus as generally illustrated in FIGURE 3 and described hereinbefore. A fiat belt is provided to Withdraw the ingot and an overhead hold down roller is employed to assure intimate contact therebetween. The support belt and the bottom surface of the mold are aligned to facilitate withdrawal of the staring plug which, by the way, has a cross-section substantially identical to that of the mold opening except for a small peripheral gap or clearance of, say, or M The starting plug is inserted ino the mold and molten metal is introduced into the molten metal reservoir and thence into the mold. Withdrawal of the starting plug is initiated immediately upon molten metal filling the mold in order to avoid massive freezing of the metal in the mold and reservoir which would then prevent a successful casting run. The ingot immediately adjacent to the starting plug conforms roughly to the convex section thereof, but after a short distance of about acquires very flat surfaces at the top and bottom. However, once this stable ingot configuration is achieved, the bottom surface of the ingot is disposed /2" above the support belt. This misalignment, unless compensated for as described herein, causes the ingot to defleet downwardly /2" to rest upon the belt. The deflection is permanent which causes the axis of the ingot between the mold and support belt to be inclined downwardly toward the belt. The ingot metal emerging subsequently must also deflect downwardly toward the support belt surface. This creates a series of waves or undulations along the length of the ingot. At the end of the casting run, it is required that surface imperfections be removed from the ingot in order to prepare the top and bottom surfaces for hot rolling. This may amount to a metal removal depth of only A", from the standpoint of the alloy segregation and other surface conditions which are intended to be cleaned up by this scalping operation. However, because of the serpentine-like undulations of up to /z" along the ingot length, this depth must be increased to M1 on both the top and bottom to assure a substantially straight piece with proper surfaces for hot rolling. In a run in which the ingot withdrawal belt is removed from the belt rollers and replaced with two separate belts, each in thickness and 8" in width, situated so as to bear against only the outermost 6" of the ingot and starting plug width, the belt surface is aligned with the predetermined flat-bottomed ingot plane. Casting is initiated as before, and here the flat-bottomed ingot misalignment is practically nil such that there are no significant deflections along the ingot length. This ingot can be prepared for hot rolling by the removal of only A" metal from the top and bottom surfaces as opposed to the previous practice of removing A. This savings in metal scrap is highly significant in a commercial operation.

While the invention has been described with particular reference to a preferred embodiment and practice, it is to be understood that the claims are intended to embrace other embodiments and practices as fall within the true spirit of the invention.

What is claimed is:

1. An apparatus for the continuous casting of a metal ingot comprising a horizontally disposed open ended mold, the inside surface of the bottom mold wall exhibiting a concavity of at least A3" to compensate for non uniform ingot contraction in the vertical dimension, a starting plug having a cross-section to substantially match that of the mold opening such that it may be positioned within the mold opening to substantially close the same, means for withdrawing said starting plug and the ingot connected thereto from the mold and for supporting only the outer portions of the widths of the starting plug and the connected ingot corresponding to those outer portions of the mold width having a maximum concavity runout of 50% of the total concavity run-out.

2. An apparatus for the continuous casting of a metal ingot comprising a horizontally disposed open ended mold, the inside surface of the bottom mold wall exhibiting a concavity of at least A1" to compensate for nonuniform ingot contraction in the vertical dimension, a starting plug having a cross-section to substantially match that of the mold opening such that it may be positioned within the mold opening to substantially close the same, means for withdrawing said starting plug and the ingot connected thereto from the mold and for supporting only the outer portions of the widths of the starting plug and the connected ingot corresponding to those outer portions of the mold width having a maximum concavity run-out of 50% of the total cavity run-out, but not to exceed /8 3. The apparatus according to claim 2 wherein the supporting means comprises one or more endless belts.

4. The apparatus according to claim 2 wherein the supporting means comprises two endless belts each positioned to support one side of the ingot width.

5. The apparatus according to claim 2 wherein common means are provided for withdrawal and for support of the starting plug and ingot.

6. The apparatus according to claim 2 wherein separate means are provided for withdrawal and for support of the ingot and starting plug.

7. The apparatus according to claim 2 wherein common means provided for withdrawal and for support of the starting plug and ingot are integral.

8. The apparatus according to claim 2 wherein separate means are provided for withdrawal and for support of the ingot and starting plug.

References Cited UNITED STATES PATENTS 944,668 12/1909 Douteui 22-57.2 2,121,280 6/1938 Bell 2257.2 2,890,560 6/1959 Nigelli et al. 19834 3,250,376 5/1966 Griner et al. 19835 FOREIGN PATENTS 200,324 11/ 1955 Australia.

531,090 10/ 1956 Canada.

WILLIAM J. STEPHENSON, Primary Examiner. R. D. BALDWIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,349 ,837 October 31 1967 Kenneth J. Brondyke et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 lines 58 and 72 for "5/6", each occurrence read 5/8 column 6 lines 43 and 46 for the claim reference numeral "2", each occurrence, read l line 50 before "provided" insert are Signed and sealed this 26th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Ir.

Attesting Officer

Claims (1)

1. AN APPARATUS FOR THE CONTINUOUS CASTING OF A METAL INGOT COMPRISING A HORIZONTALLY DISPOSED OPEN ENDED MOLD, THE INSIDE SURFACE OF THE BOTTOM MOLD WALL EXHIBITING A CONCAVITY OF AT LEAST 1/8 TO COMPENSATE FOR NONUNIFORM INGOT CONTRACTION IN THE VERTICAL DIMENSION, A STARTING PLUG HAVING A CROSS-SECTION TO SUBSTANTIALLY MATCH THAT OF THE MOLD OPENING SUCH THAT IT MAY BE POSITIONED WITHIN THE MOLD OPENING TO SUBSTANTIALLY CLOSE THE SAME, MEANS FOR WITHDRAWING SAID STARTING PLUG AND THE INGOT CONNECTED THERETO FROM THE MOLD AND FOR SUPPORTING ONLY THE OUTER PORTIONS OF THE WIDTHS OF THE STARTING PLUG AND THE CONNECTED INGOT CORRESPONDING TO THOSE OUTER PORTIONS OF THE MOLD WIDTH HAVING A MAXIMUM CONCAVITY RUNOUT OF 50% OF THE TOTAL CONCAVITY RUN-OUT.

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