US3506059A - Method of continuous casting - Google Patents

Description

April 14, 1970 BURKART ET AL 3,506,059

METHOD OF CONTINUOUS CASTING Origin aI Filed Nov. 6, 1966 3 Sheets-Sheet 1 --:E, 53 O 2 O 40 5D I O :L :1: w ar- 0 d v| 76 (K 1, .5 X, 62 o Fmhl.

April 14, 1970 BURKART ErAL 3,506,059

METHOD OF commuous CASTING 3 SheetsSheet 2 Original Filed Nov. 6, 1966 INVENTORS (41.4 R. JOHN MBUEKHRT it April 14,1970 A. R. BURKART ETAL 3,

METHOD OF CONTINUOUS CASTING 3 Sheets-Sheet 3 Original Filed Nov. 6, 1966 INVENTORS 7am R 8 United States Patent 3,506,059 METHOD OF CONTINUOUS CASTING Alan R. Burkart, Shrewsbury, Mass., and John H. Mudge, Parma, Ohio, assignors to Aluminum Company of America, Pittsburgh Pa., a corporation of Pennsylvania Original application Nov. 6, 1966, Ser. No. 576,768. Divided and this application Nov. 21, 1968, Ser.

Int. (:1. B22d 11/10 US. Cl. 164-82 3 Claims ABSTRACT OF THE DISCLOSURE A continuous casting mechanism comprising a chill mold substantially defining the exterior transverse contiguous surface of a body, such as an ingot or billet, to be continuously cast and extracted therefrom; a heat insulating mold in unitary connection and communication in advance of said chill mold; a core or displacer disposable within and in spaced relationship to interior defining walls of both the chill and heat insulating molds; and the core or displacer contactable by molten metal supplied to the chill mold through the heat insulating mold being of heat insulating material. A method of continuous casting employing the aforesaid mechanism in which the heat insulating core or displacer extends into a molten metal crater defined by solidified exterior walls of a continuously cast ingot or billet.

This application is a division of parent application Ser. No. 576,768, filed Nov. 6, 1966.

This invention relates in general to new and improved apparatus and practices for the continuous casting of metals and alloys thereof, and is more particularly addressed to the production by continuous casting of mechanically and metallurgically sound aluminum and aluminum alloy ingots and billets for subsequent working in the production of wrought products therefrom. As herein and hereinafter employed, aluminum and aluminum alloys is intended to include aluminum metal and alloys containing at least 65 percent aluminum,

Conventional continuous casting has invariably followed the practice of introducing molten metal into one end of an open-ended relatively axially short chill mold while applying cooling media directly against the exterior of the chill mold in sufiicient amount to extract heatfrom the molten metal adjacent thereto to produce and define surrounding solidified walls and outer surfaces of an embryo ingot or billet of sufficient mechanical strength and thickness to support a molten phase or crater of generally cone or V-shape within the embryo ingot or billet as the same is continuously withdrawn from the exit or opposite end of the chill mold to that at which the molten metal is being continuously delivered. It has also been conventional practice to supply and apply cooling media directly against the exterior surfaces of emanating embryo ingots or billets discharged from the axially short chill molds employed in continuous casting practices in such quantity or amounts as to completely and substantially transversely solidify the initially interior molten phase of the embryo ingots or billets so cast in a plane some axially removed distance away from the discharge open end of the chill mold.

It has also been proposed in the published art addressed to continuous casting to additionally provide heat extracting means extending axially into the interior of the generally cone-shaped molten phase craters of embryo billets and ingots to promote internal heat extraction and acceleration of the rate of interior solidification of the molten phase within the craters of embryo ingots. Such published proposals have invariably recommended chilled cores or vessels of relatively high heat conductive materials extending into the molten phase craters of the embryo ingots or billets being continuously cast.

In contradistinction to prior art practices, the present invention is basically predicated upon the provision of heat insulating means, such as a core member, preferably axially displaceable, within the molten metal crater of continuously cast products, as well as mechanism and process steps for the manipulation and support thereof, which reacts to displace the molten metal within the crater and thermally controls the freezing rate thereof. The selection and use of a heat insulating means or core for the heretofore employed heat extracting chill core or vessel of the prior art, in combination with means for actuating the same during initiation and prior to completion of a continuous casting operation, has resulted in producing a substantially completely reversed isothermal freezing pattern within the interior molten metal craters of embryo continuously cast products. Phenomenal results have been observed from the substitution and use of the heat insulating core means of the invention and have been evidenced by an increase in the rate of production of continuously cast billets or ingots exhibiting mechanically and structurally sound fine-grained products. In addition, continuous casting in accordance with the invention of metallic alloy compositions, and particularly aluminum and similar alloys characterized by a tendency to produce exposed and sub-surface zones of depleted normal constituent or constituents under conventional continuous casting practice, has revealed a substantial decrease in the depth of such liquated Zones which is directly reflected in the depth of scalping required to provide acceptable continuously cast extrusion ingot and similar cast stock for subsequent work ng in the production of acceptable wrought products therefrom,

Mechanism or apparatus, exemplary but in no sense limiting the new and improved continuous casting practice of the invention, is hereinafter descr bed in conjunction with the following illustrations, in which:

FIG. 1 represents the molten metal charging end plan View of a continuous casting mechanism illustrating one form of mechanical structure capable of permitting practice of the invention;

FIG. 2 represents a cross-sectional elevation taken on the plane 22 of FIG. 1 at the beginning of a casting operation; and

FIG. 3 represents a cross-sectional elevation taken on the plane 33 of FIG. 1 at some subsequent period during the continuous casting operation.

Explanatory of the aforesaid illustrations and following description, it is to be understood that the vertical disposition and generally right cylindrical trace or outline of the casting apparatus and ingot continuously produced thereby are not limiting factors, but are merely representative of mechanism and practice of the invention.

Referring now to the aforesaid generally stated practice and description of the invention, a conventional open ended axially short chill mold 10, constructed from a relatively highly efficient heat conducting chill-inducing material, such as graphite or alumimun, is outwardly flanged or otherwise configurated at its entry end at 12 in direct communicating continuation with an openended non-chilling high heat resistant and heat insulating laterally enclosing mold section 14. The commercial material known as Marinite (heat insulating asbestossilica composition) has been successfully employed for the mold section 14. Other commercially available nonchilling heat resistant materials however, such as fire brick or the like, commonly employed for lining elevated temperature metallurgical furnaces, may be substituted for the Marinite portion of mold section 14.

The mold section 14 may be a one-piece structure, but it has been found structurally and economically desirable to construct the same from abutting heat insulating plate members orlaminae 16 exteriorly enclosed Within a protective steel supporting frame or shell 18 unitarily secured to the entrance end flange 12 of the chill mold 10. The shell 18 surrounding, confining and supporting the non-chilling heat insulating mold section 14, is preferably of generally channel shape in longitudinal cross-section and is provided with an outwardly directed terminal entry flange 20 which serves as a support for connection thereto of a steel or other metallic base plate or ring 22 in unitary seourement to the flange 20 as by means of a peripheral line of bolts 26 (FIG. 1). A pressure plate or ring 28 is also preferably provided within the entry end to the exterior shell 18 in bearing contact against the heat insulating plate or lamina 16 therewithin adjacent the flange 20, and manually adjustable pressure screws 36- (FIGS. 1 and 3), threadedly engaged within the stationary base plate or ring 22, bear and exert pressure at their free ends against the ring 28 and insure unitary compact assembly of the plates or laminae 16 within the shell 18 of the nonchilling heat insulating mold section 14.

Oppositely disposed steel or similar brackets or standards 32 are secured to the outer exposed face of the base plate or ring 22, as by bolts 34 (FIG. 1), and parallel spacer rods 36, preferably at least two, each carrying paired clamping nuts 38 and 40 on the opposite threaded ends thereof, provide a unitary appendage or superstructure incorporating the aforesaid standards 32 in rigid association with the base ring 22.

A cross shaft 42 is rotatably supported in aligned bearing openings in the brackets or standards 32 and axially centrally supports a pinion 44 splined thereon and secured by a set screw, or the like, to insure meshing engagement with a rack 46 to be later described. Positive and accurate disposition of the cross shaft 42 between the standards 32 is maintained and insured by the set screwsecured collars 48 mounted on thecross shaft 42 in abutting engagement against the inwardly facing surfaces of the standards 32. A manipulating hand wheel 50 (FIGS. 1 and 2) is secured to an outboard extension of the cross shaft 42 which incorporates a disc 52 having an aperture 54 (FIG. 2) through the thickness thereof in concentrical alignability with any one of a series of like apertures 56 (FIGS. 2 and 3) extending through the thickness of the standard 32 adjacent but spaced inboard therefrom. Reference to FIG. 2 will reveal that an angular locking pin or key bar 58 is employable in extended disposition through the aperture 54 into any selected aperture 56 to positively lock the hand wheel 50, cross shaft 42 and pinion 44 against relative movement in respect to the axially aligned mold sections 10 and 14.

A cradle type housing is supported by the transverse spacer rods 36 and is constructed in the form of spaced side rails or frame members 60 provided with extending locating pins 62 projecting into registering apertures in the rods 36 (FIG. 2). The projecting ends of the pins 62 may be threaded for receiving nuts (not shown or essential in the vertical arrangement of the casting equipment illustrated in the appended drawings) which would permit rigid unitary assembly of the cradle on the spacer rods 36. The side members 60 of the cradle type housing are rigidly tied together in the plane of their outermost stirfaces remote to their supporting spacer rods 36 by means of a cross bar or plate 64, which supports or carries a bronze anti-friction edge bearing plate 66 in rubbing contact against a surface of the aforementioned rack 46 opposite or remote to the pinion 44 (FIG. 3). It will be manifest from the mechanism thus far described that rotation of the cross shaft 42, by manipulating the hand Wheel 50, will impart reciprocal motion or translation of the rack bar 46.

FIGS. 2 and 3 best illustrate essential structure in regard to the practice and advantages attributable to the 4 present invention, Therein it will be observed that a generally cylindrical or box-shaped vessel, herein called a core member or displacer and identified in its entirety by reference numeral 68, has been unitarily aind rigidly secured to the end of a unitary extension of the rack bar 46 remote to the pinion 44 engaging therewith.

The heat insulating core or displacer 68 is concentrically or centrally disposed in respect to the common longitudinal axis of the chill mold 10 and attached heat insulating mold section 14 by proper adjustment and secured location of the cross shaft 42 and pinion 44 carried thereby in their relation to the plane and axis of rectilinear movement of the rack bar 46 in mesh with the pinion 44. I

In addition, the heat insulating core or displacer preferably and generally comprises a hollow steel or other structural metal member provided with opposite end and intermediate transverse plate or reinforcing baflle members 70, 72 and 74, respectively, secured as by welding, or the like, to interior surface areas forming an uninterrupted side wall, or side walls, of the drum or boxshaped shell of the displacer 68. The rack bar 46 is rigidly secured to the displacer 68 and is preferably cross-sectionally reduced in its unitary extension beyond the rack teeth thereof, extended through registering complementary apertures in one opposite end and intermediate plate members 72 and 74 (FIGS. 2 and 3), Where welded or other mechanical attachment is made therewith. Also, guide and snubbing rods 76, secured to the end plate member 72 and projecting outwardly therefrom, are provided for guiding extension through aligned apertures in the spacer rods or bars 36 and carry adjustable nuts 78 (FIG. 2) at their outer threaded end extrernities to limit the extent of axial translation of the displacer 68 within the integrated mold sections 10 and 14.

The cardinal structural feature and touchstone of suc= cess of the invention turns on the provision of a nonchilling heat resistance and substantially high heat insulating exposed surface liner or exterior wall for the core member or displacer 68. This requirement has been satisfactorily met by providing an end plate or disc 80- 0f Marinite, or similar non-chilling heat insulating material, secured to the adjacent end plate of the displacer 68 in any suitable manner, such as by the central exteriorly manipulated tap bolt 82. A washer 84 is recommended under the head of the tap bolt 82 to distribute the clamping pressure exerted thereby between the central raised bearing or stepped area of the plate and outwardly directed surface of end plate 70 of the interior shell of the displacer 68 in abutting contact therewith.

The end plate 80 is preferably selected to project laterally or overhang beyond the interior uninterrupted side wall or walls of the core member or displacer 68 to provide abutting contact against an exposed or outer non-chilling heat insulating side Wall 86 surrounding the interior wall or walls thereof which supports a pressureapplying and assembly ring or plate 83 of steel, or the like, remote to the end plate 80. The plate 88 is preferably engaged by the free ends of bolts 90 in adjustable pressure-exerting threaded engagement in an outwardly extending flange 92 in unitary attachment to the side wall of the displacer shell 68 to thus provide unitary assembly of the heat insulative exterior side and end surfaces of the centrally disposed displacer 68 of the invention. Thermocouples 94- (FIG. 2), or similar temperature sensing and/ or measuring devices, have been provided in at least three axially separated planes parallel to the transverse plane of the end plate 80 of the displacer 68, whereby thermal conditions within the mold have been determined.

In the preferred practice and operation of the continuous casting mechanism of this invention thus far described, a conventional translatory end closing chill block or plate 102 is disposed within the otherwise open discharge end of the chill mold 10 in sealing relationship thereto, as indicated in broken line construction in FIG. 2, and with the displacer 68 either completely oppositely axially withdrawn from the insulated mold section 14, or in conservation of space is disposed axially intermediate the length of the same, as indicated in FIG. 2 and herein termed the preferred starting position or location thereof, molten metal to be cast is delivered through the open end of mold section 14 remote to the chill mold from a suitable source of reservoir, as by means of one or more delivery troughs 96, to fill the chill mold 10 above the broken line position of the end closing plate 102 (FIG. 2) to a level within the insulated mold section 14 controlled by the delivery trough or troughs 96.

Coolant, such as water or the like, is'supplied against the exterior of the chill mold 10 from a perforated manifold 98 in amount sufficient to extract heat from the molten metal so charged within the mold sections 10 and 14 to freeze an embryo ingot 100 defined by a laterally enclosing and supporting shell within the axial length of the chill mold 10 and an enclosing end wall contiguous therewith in contact with the end plate 102, and characterized by having a substantially central liquid crater phase of non-solidified metal extending axially into the mold section 14, where the metal charge remains liquid.

Translation of the end plate 102 out of sealing relationship within the chill mold 10 to some axially removed position thereof disclosed in full line construction in FIG. 2, under uninterrupted regulated delivery of molten metal to the insulated mold section 14 and controlled coolant supplied against the chill mold 10 and now exposed frozen shell of the embryo ingot 100, is representative of conventional continuous casting practice.

Preferred practice of the instant invention is initiated in the otherwise conventional continuous casting practice above described by translating the displacer 68 axially through the molten phase crater of the embryo ingot 100 to a position illustrated in FIG. 3, which is representative of its location during continuous casting in accordance with the preferred practice of the invention. It will be understood and observed in this respect, and particularly on comparison of the curvilinear solidus contour lines 104 and 106 of FIGS. 2 and 3, respectively, that the molten metal craters and solidus contour lines defining the same are radically changed in response to translatory movement of the displacer 68 to the position occupied thereby in FIG. 3, wherein it now extends axially through the insulated mold section 14 into the chill mold 10 a distance substantially equal to half the axial length of the chill mold 10.

Presence and use of the core member or displacer 68, as hereinabove described, has provided a substantially reduced or narrow feed channel 108 defined in transverse cross-sectional area between the interior wall of heat insulating mold 14 and outwardly directed heat insulating wall of the displacer 68 both in advance of and within the chill mold 10 (FIG. 3), as compared to the respective enclosing transverse cross-sectional areas of the mold sections 10 and 14 in the absence of the displacer 68, and it is this reduced transverse cross-sectional area of feed channel 108, coupled with the thermally insulated walls of the insulating mold 14 and core member or displacer 68 forming the feed channel, that has resulted in the increase in casting rate heretofore referred to.

Testing of a mechanism as hereinabove described, the appended illustrations of which are scaled down representations of an apparatus employed in the continuous casting of twenty-five inch diameter 2214 aluminum alloy ingots, established a casting rate of double that for the same ingot composition and same mechanism without incorporating the core member or displacer 68. The nominal composition of 2214 aluminum alloy on a percent by weight basis is 0.8 silicon, 4.4 copper, 0.8 manganese, 0.4 magnesium and the balance aluminum.

It will be observed that the solidus contour line 106 (FIG. 3) substantially approaches or follows the general configuration of the exposed end of the displacer heat insulating immersed end block '80, as compared to that of the deeper crater defined in FIG. 2 by the solidus contour line 104. It will also be observed that the feed channel 108 may be slightly enlarged in transverse crosssection as it enters the embryo ingot, at 110 (FIG. 3), in substantially the transverse plane of the contacting interface formed between the chill mold 10 and heat insulating mold 14. It is the expressed belief herein that the initially delivered elevated temperature molten metal charge within the feed channel 108 is subjected to maximum drastic chilling and heat extraction in substantial coincidence with the enlarged cross-sectional feed area 110 and that the so chilled molten metal contactingly follows the contour of the heat insulating displacer block to provide a uniformly falling temperature gradient from the center to the outer surfaces of the ingot being cast.

A twenty-five inch diameter 2214 aluminum alloy ingot so continuously cast was found to be mechanically and structurally sound; exhibiting a fine grain structure and a decreased depth of surface and sub-surface liquated zones; and was substantially free from cold shuts, all of which characteristics can be attributed to a more uniform and directional heat extraction transversely across the width, or normal to the common longitudinal axis of the molds 10 and 14, of the continuously cast products, produced in accordance with the invention, substantially within the axial length of the chill mold 10 thereof. The foreshortened axial length of the molten metal phase within the crater of FIG. 3 also points to the fact that the temperature of the molten metal in a transverse plane across the crater is more uniform and that solidification takes place appreciably more uniformly inwardly towards the center of the so-cast products than has been the case in the longer cone-shaped craters heretofore experienced in conventional continuous casting processes illustrated, at least in degree, in FIG. 2.

Operation of the continuous casting method and mechanism hereinabove described can be terminated by interrupting molten metal delivery to the insulating mold section 14, withdrawing the displacer 68 out of physical contact with remaining molten metal in the crater of the product being cast, and continuing axial extraction of the cast product 100, while preferably maintaining continuous coolant flow against the chill mold 10 and product until the molten metal crater is completely solidified, at which time the coolant flow can be interrupted and the product 100 removed from the casting apparatus of the invention.

Having thus described and explained one embodiment of apparatus and method of continuous casting employing the same, it will be understood by those skilled in the art to which the invention is addressed, that other embodiments of the invention may be practiced, as hereinafter defined in the appended claims.

What is claimed is:

1. Continuous casting of ingots from molten metals comprising the steps:

(a) continuously supplying molten metal to the inlet end of an openended chill mold, temporarily closed at its opposite end,

(b) chilling the so-supplied molten metal through the walls of the chill mold and the temporary end closure therefor to create an embryo ingot in the form of a shell comprising contiguous solidified exterior side walls and a solidified end wall contiguous therewith in abutment against the temporary end closure and having an interior molten metal phase crater supported within said shell,

(c) positioning a heat insulating core member axially within the molten metal phase crater in lateral and axial end clearance spaced relationship to the solidified side and end walls of the embryo ingot shell,

(d) continuously withdrawing the temporary end closure and initial embryo ingot shell in abutment therewith while continuously feeding molten metal between the core member and chill mold, and

(e) continuously supplying coolant against the chill mold in sufficient quantity to insure progressive creation of the embryo ingot shell and solidification of the molten metal crater therewithin adjacent and out of contact with the heat insulating core member and chill mold under continuous extraction of a continuously cast ingot from the chill mold.

2. Continuous casting of ingots from molten aluminum comprising the steps:

(a) continuously supplying molten aluminum to the inlet end of an open-ended chill mold, temporarily closed at its opposite end,

(b) chilling said so-supplied molten aluminum through the walls of the chill mold and the temporary end closure therefor to create an embryo ingot in the form of a frozen shell comprising contiguous solidified exterior side walls and a solidified end wall contiguous therewith in abutment against the temporary end closure and having an interior molten aluminum phase crater supported Within said shell,

(c) providing a heat insulating core member in axial extension within the molten aluminum phase crater in lateral and axial clearance spaced relationship to the solidified side and end Walls of the embryo ingot shell,

(d) continuously withdrawing the temporary end closure and initial embryo ingot shell in abutment therewith while continuously supplying molten aluminum between the core member and chill mold, and

(e) continuously supplying coolant against the chill mold in sufficient quantity to insure progressive creation of the embryo ingot shell and solidification of the molten aluminum crater therewithin adjacent and out of contact with the heat insulating core member and chill mold under continuous extraction of a continuously cast aluminum ingot from the chill mold.

3. Continuous casting of ingots from molten aluminum comprising the steps:

(a) continuously supplying molten aluminum through an inlet to a heat insulating mold section supported adjacent and in continuity with an open-ended chill mold, temporarily closed at its end remote to the heat insulating mold section, in sufiicient quantity to fill the cross-section of said chill mold,

(b) extracting heat from the so-supplied molten aluminum through the walls of said chill mold and the temporary end closure therefor to create an embryo ingot in the form of contiguous solidified exterior side walls and a solidified end wall contiguous therewith in a'butment against the temporary end closure and having an interior molten aluminum crater supported within said shell,

(c) advancing a heat insulating displacer axially from the heat insulating mold section into the chill mold into the molten aluminum crater thereof in lateral and axial end spaced relationship to the solidified side and end walls of the embryo ingot shell, heat insulating mold section and chill mold,

(d) maintaining the aforesaid axial location of the displacer,

(e) continuously withdrawing the temporary end closure and initial embryo ingot shell in abutment therewith while continuously supplying molten aluminum between the displacer, heat insulating mold section and chill mold, and

(f) applying coolant against the exterior side wall of the chill mold in suflicient quantity to insure progressive creation of the embryo ingot shell and solidification of the molten metal crater thereof adjacent the displacer and chill mold under continuous withdrawal of an aluminum ingot from the chill mold.

References Cited UNITED STATES PATENTS 3,381,741 5/1968 Gardner 164-82 X 3,409,068 11/1968 Yearley et al 164-85 FOREIGN PATENTS 860,243 12/1952 Germany. 969,019 4/1958 Germany. 750,131 6/ 1956 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl. X.R. 164-89

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