US2672665A - Casting metal - Google Patents

Description

March 23, 1954 o. M. GARDNER Erm.

2,672,665 CASTING METAL Filed March 13. 1950 INVENTOR OWEN A7. Gaza/vee.

Ausg/e7' J. J70/vf.

ATTORNEY Patented Mar. 23, 1954 CASTING METAL Owen M. Gardner,

Stone, Spokane, Wash minum & Chemical Calif., a corporation of Opportunity, and Albert J.

., assignors to Kaiser Alu- Corporation, Oakland. Delaware Application March 13, 1950, Serial No. 149,304 3 Claims. (Cl. 2,2-200.1)

This invention relates generally to the casting of light metals and alloys thereof. More particularly, the invention relates' to an improved method and apparatus for the continuous casting of ingots, billets and the like of light metals and alloys thereof.

In the continuous casting of metals, an openended mold, usually shallow and cast in light alloy, is provided and molten metal is continuously fed or poured into one end thereof (the top end in the case of a vertical mold), a supply of cooling uid, usually water,. is applied in a continuous manner to the outside surface of the mold to withdraw at least a part of the heat from the metal, and/or to the surfaces of the at least externally solidified casting as it emerges from the opposite'end of the mold (the bottom in the case of a vertical mold). The mold may be either horizontal or vertical but in the case of large castings, such as rolling ingots and extrusion billets, it is preferably vertical. The withdrawal of the ycasting is regulated at a desired rate, usually by means of amovable bottom for the mold, for, example, a platen of a hydraulic plunger which is lowered into a casting pit. The pouring rate for the molten. metal and the rate vof withdrawal of the solidified casting are correlatedto maintain'a substantially uniform or constant headlevel of metal ywithin the mold. The term head of the metal in the mold, that is, the distance from the plane of the lower periphery of the mold to the surface of the molten metal in the mold. The cross-sectional shape ofthe mold, and consequently the ingot orbillet may be ,practically any desired configuration, although usually it is square, rectangular, circular or elliptical; and in some cases, annular orY hollow where a mold core is employed. In the casting of large ingots or billets, the mold cross-section is in most cases angular and often elongated in one `direction, that is, of a shape having major and minor axes, for example, substantially rectangular.

- The method and apparatus for directly chilled (DC) continuous castingwhich are widely used in the casting of ingots and billets 'of light metal and light metal alloys, such as aluminum and its alloys, and to which this invention is particularly applicable are fully shown and described in U. S. Patent No. 2,301,027, dated'Nove'mber'B, 1942, issued in the name'of William T. Ennor. Y. A diiculty that has been frequently encounv-tered'in the 'continuous casting of'aluminum and indicates the depth 'ing of ingots7 billets and the aluminum alloy ingots, particularly those which contain edges or corners, for example, those which are substantially square or rectangular in cross-section, is the impairment of the ingot edges or end surfaces (in the case of elongated angular shapes) by so-called cold shuts. This occurrence of cold shuts is a phenomenon primarily restricted to the very narrow vertical area or line of contact between the molten metal and the inside periphery of the mold at the top of the molten surface, that is, at'the edge of the normal head level of the metal in the mold or the edge of the meniscus of the molten metal.

It has been determined that cold shuts occur when a non-uniform or excessive amount of heat is transferred from the molten metal or a portion of the molten metal through the mold in this critical area or plane, particularly at the edges or corners of the mold, for example, the end sections of the mold in the case of a mold of substantially rectangular cross-section. Such an excessive or non-uniform withdrawal of heat increases the surface tension and meniscus effect, which, in turn allows intermittent wetting of the mold surface by the molten metal with the result that freezing or solidiflcation takes place at points removed from the mold surface. Cold shuts are thus formed by this prefreezing of a portion of the metal.

Cold shuts may be induced by improper transfer of molten metal into the mold, such as permitting turbulence during pouring of the metal, or by excessively slow transfer or pouring. Also, cold shuts are occasioned by utilizing a pouring temperature which is too low. In addition, as indicated above, cooling the molten metal too rapidly and/or non-uniformly at or near the edge of the molten metal meniscus may result in cold shuts.

The first two above-named conditions favoring formation of cold shuts may be obviated by proper pouring technique and temperatures. It is with the last-named condition and the solution of the problem presented thereby that the present invention is primarily concerned.

Accordingly, it is a primary object and purpose of the invention to improve the surface qualities of continuously cast light metalsand alloys thereof by eliminating the formation of cold shuts. l y p Another object is to provide an improved method and apparatus for the continuous castlike of light metals and light metal alloys.,.A further object is to provide an improved method and apparatus for formation-of cold shuts.

3 the directly chilled (DC) continuous casting of aluminum and aluminum alloys susceptible to the formation of cold shuts to eliminate the same.

A more specific object is to provide an improved method of regulating heat transfer and an improved mold construction therefor in the directly chilled T(2130)' continuous casting Vingots and bil-lets of aluminum and aluminum alloys to eliminate formation of cold shuts in the metal during casting. These and other objects and advantages of this invention will be apparent from the following detailed description thereof It has been discoveredfth'atformation: of cold shuts during continuous -castingof light metals and alloys thereof is substantially*-completely eliminated by regulating the withdrawal ortransefer of heat from the metal through or to thefmold in a manner such that cooling 'of the molten metal is substantially retarded and solidicationvis prevented at the edge ofthe meniscus thereof or around \the periphery\ of. `the normal -headlevel ofthe metal. obects ofthe invention and the process-thereof It-has further been found that-the vmay bef suitably accomplished 4and performed by theprovision of a casting mold having-a ther- Armally insulating-material disposed in close convtac-:twvvi-th or adherent to the inside surface of the -mold extending longitudinally throughout the I -areaof-the mold surface which contacts the edge of the-metallmeniscus orl the periphery of the molten metal atnormalhead level.

The insulatingmaterial placed either around the` entire peripheryl of the mold surface at the xrindica-tedareaoronly on the surfaces of the end sections-of the-mold prevents contactl of the molten metalV and the mold surface and thus revtardsthetransfer or withdrawal of heat from-the metal. I `Solidincation `cannot 'take placein this areaA since the metal remains above the melting i point, orhighest-eutectic point. Initial solidicav tion thusis forced toA occur belowthel edgesof the metal meniscus, that is,vbelow the metal level in `ther-mold: where 'heat-is rapidly extracted, and vtherefore, thefreezing is notinluenced by surface tension andmeniscus eflectasfin` the: case whereim'olten metal-mold oontactfoccurs= at' the` metal levelor top surface which frequently results in The insulator 'retains suicient heat in the molten metal to preclude any prefreezing,thereby eliminating lformation of deep-coldfshuts.4

- In its foregoing. genericy aspect; the invention is applicable to continuous casting ofingots vofa v variety of shapes, but particularly to ingotsvhaving `somewhat angular configurations,K that is, in-

cluding edges or corners,si'nce thel cold shut prob- -1em-` appears to be particularly manifest in' the 1 edge qualities ofA such ingots.` The Athermally insulating material in such case may be disposed or applied aroundV the entireinside periphery of the -moldwithin the above-defined critical longitudi- The invention contemplates the use of a Wide variety of high temperature insulating materials, which in some instances may be directly applied to the inside surface of the mold and adherent thereto, while in other cases the material may be merely held in close contact with the mold surfadeby suspens-ion fro'fr tlietdp' of lt'l'ie mold or in some' other suitablemanner.

Among the various materials particularly suit- `v-alole as high temperature insulators may be mentioned a fibrous material, such as asbestos, felted V o`r`i` the form of paper, and secured to the mold i wall'lby a suitable adhesive, such as a cement or l mold-greasefsuitably resistant to high tempera- Because-of the excellent results, economy e'aseofapplication, the foregoing insulatoris-preferred.

Also, a high temperature cement may be appl-idto the critical area of the mold wall to eiectively retard withdrawal of heat through the mold shell. vA particularly `suitable cement is one having a refractory base or ifi-ller 'of=glas'si1bers; a binder of an 'appropriateA syntheticrubber1 such as Buma-S, or Bu'na-N, -andan *evaporative* solvent, s'u'ch as methyle'ethylrv ketone'.

In the above specific examples of high itemtures.

Vperature insulating.-materials, they constitute upon application a yrelatively'thin orlthick` lining or' coating for the mold ar'ea affected.

A-further suitable high 'temperature'insulator Wasfound to be aref-ractory Acoated metal', such as, limes-coated steel-wires suspended fromlthe'top of the mold shell and held inclose contactwith the mold surface.

Opti-mum'results are obtained by disposingathe insulating material on the' 'mold surface to 'extend from' any transverse plane' abovethenarrowlarea or plane' ofthe molten' meta'lmeniscu's or normal -head level of the metalin the-moldlto ai transverse plane about one-'half inch below thelnarrowatea or plane of 'the meniscus. Alternatively'stated,

the lower'edge of the*msulator--preferablyfshould f substantially more than* five-:eighties Tot-fan?? inch below the area loftheedgaof the metalmeni'scus.

being necessary only to avoidi an undue' retardationin solidification;whichg'if excessive; would affectthe'quauty ofthe casting.

drawings, which 'are' not to beconstrud asf tation thereof, iii which:

Figure Bis' averti-zs'ala section-fofa-fmoldlad metaly ingot' 'formingtheeirr within@ tlii'tiial insulator;

Figure 4' a verticalisctionffi a-moldand'irigot forming' therein- 'showingiiarifasbstos liningldisposed according to the invention;

Figure 5":is a verticalfsctionof aimoldfand yingot forming therein showing: a coating'fofliig-h temperature cement at lfthe"critical araon'- the mo1d;-an`d l Figure 6J a Y=fragrnentary vertical y"secizi'o'n, partly in side elevation, of a mold showing-retractory coated wires asthethermal yins-ulaautori Referringfnow to Fiel-Ir 3-,- it may 'balsem-that the line of contact of the periphery of the molten metal meniscus and the mold wall. The casting 4 consisting of a skin of solid metal of a certain thickness depending on cooling and lowering rates emerges from the bottom of the mold with a crater of molten metal 2 in the interior extending vertically from the normal head level of the metal to the point at which the temperature of the ingot is below the lowest melting eutectic of the alloy.

Although this method of rapidly extracting,

heat from the metal is necessary to produce sound castings, the rapid cooling at the metal leve1 or meniscus was found to result in cold shuts, particularly on the curved end surfaces of the ingots, and particularly in the casting of the softer more ductile aluminum alloys or commercially pure aluminum, having little or no positively added alloying constituents, for example, aluminum alloys designated as 2S, commercially pure aluminum, and 3S aluminum containing manganeseon the order of 1%. The formation of these discontinuities, as set forth above, was induced by excessive heat extraction from the region near the edge of meniscus, indicated at a in the drawing.

Referring to Figure 1, the preferred embodiment of the invention is shown wherein the insulating material 6 is disposed only on the curved end sections, including the edges Vor corners. It was observed that with molds of substantially elongated angular cross section, for example, substantially rectangular, as shown in Figure l, the occurrence of cold shuts on the ingot predominated at the end sections or edges. as opposed to the straight sided intermediate section. Thus,

shuts Was substantially eliminated by employing the embodiment of Figure 1.

In Figure 2, a substantially square mold 3 is shown, and, in this case, the insulating material B is placed around the entire inside periphery of the mold to eliminate cold shuts.

Figures 4 and 5 illustrate the use of two different insulating materials, namely, an asbestos paper lining 6a adhesively secured to the mold surface, and a high temperature resistant cement 6b, respectively. It may be seen that as the molten metal 2 contacts the asbestos 6a or the cement 6b, the insulating material is wetted by the metal and a concave meniscus I results. Heat extraction from the metal through the mold is substantially retarded including the narrow region marked b and solidication is prevented from occurring in this meniscus region. Solidication can only initially occur below the lower edge of the insulator which is located, as shown in the drawings, about one-half to about veeighths of an inch below the meniscus edge or head level of the metal.

Figure 6 shows in fragmentary vertical section partly in side elevation, that embodiment wherein lime-coated steel wires 1 suspended at 8 from the top of the mold 3 act this case, also the lower ends of the wires are disposed about one-half to ve-eighths of an inch below the meniscus edge. The Wires are spaced one from the other, illustrating that the insulating surface may be discontinuous as well as continuous to accomplish the desired result. The

' spacing ofthe wires may shuts. A eutectic alloy and be varied, the drawing being intended to show about 10 wires to the inch. It is to be noted, however, that the invention also contemplates a continuous sheet of refractory coated metal as the insulator.

The elimination of cold shuts may be satisfactorily attained by the use of any high temperature insulating material resistant to temperatures of the order of 12007.11. or ,such temperature as must be employed with the particular metal being cast, and which material is not adversely affected by contact with the molten metal and which will not adversely affect the metal. Accordingly, it is to` be understood that the invention is not limited to the preferred embodiments of materials illustrated in the drawings.

Although the invention is generally applicable to light metals and alloys thereof and in particular to aluminum and aluminum alloys, the character of the metal being cast also has an iniiuence on the tendency toward formation of cold an alloy which contains an intermetallic phase has less tendency to form cold shuts than the unalloyed metal or intermediate alloys of either the homogeneous or heterogeneous types. In the case of aluminum and aluminum alloys, the strong heat-treatable types have less tendency to formv cold shuts than do the common (non heat-treatable) alloys under similar casting conditions. Accordingly, the invention finds particular application in the casting of the softer, more ductile aluminum alloys, such as 2S and 3S, referred to above.

A specic illustration of the application of the invention follows. In producing hot rolling ingots, smooth ingot edges are essential to minimize side trim on the rolled sheet. In attempting to produce satisfactory edges on 3S ingots, a high temperature pouring practice was adapted which produced 3S ingots having edges satisfactory in minimizing edge cracks encountered on hot rolling. However, this practice increased susceptibility of 3S ingot to cracking during casting. Excessive cracking led to adoption of lower pouring temperatures, and this deviation was immediately reflected in poorer edge quality of the 3S ingots due to cold shuts, which, in turn necessitated excessive side trimming of the hot rolled sheet.

To eliminate formation of cold shuts and thereby improve ingot edge quality, an asbestos paper insulating liner was adhesively secured to the inside surface of the mold with mold grease at the end sections thereof and extending longitudinally from above the normal head level t0 about one-half to five-eighths inch below normal head level.

The 3S ingot produced with the insulator at the mold edges using lower pouring temperatures (hot holding temperature of 13501380 F.) had smooth glassy edges which resulted in a minimum side trim of hot rolled sheet. A saving of one to one and one-half inches side trim was accomplished thus increasing hot line metal recovery by at least 3 percent.

Although the invention is described with particular reference to continuous casting of aluminum and aluminum alloys, it is not intended to limit the same to this particular metal or type of casting, as the invention is applicable to other metals and other types of casting where similar problems are encountered.

What is claimed is:

1. In the continuous casting of ingots of light metals and alloys thereof in open-ended molds semanas #whereintheingot cross#sectio'rx is 5vof substantially angular configurationincluding corners yorend surfaces, f molten metal l is continuously fed into -the mold to maintain a molten'V metal level therein, a portion 'offthe' heat is withdrawn to initially solidify the peripheral portions-of the rmetal in contact with the xno1d==shell,`v and the partially solidified castinglis continuously withdrawn fromthe mold, the inlprovernent"ofy elim- 1 inat'ing cold. shuts at the corners vor `end` surfaces `of the ingot, which comprises, -retardingf'the extraction of heat -fromthe molten metal atthe corners or end surfaces bythermally insulating 'such portions of 4.the metal from contact with the mold at the molten metal -level to 4prevent initial solidication of the metal "where -the cause initial solidicationof-the peripheral portions of the metal by direct contact of the molten` metal'with' the mold not substantiallyless than about 1/2 inch norsubstantially more thanv 5/8 inch below the molten metal level.

.2. In the continuous casting of aluminum and `aluminum alloys vinlopen-ended molds wherein .theV ingot is of elongated cross-section including corners and end surfaces, 'molten metal is continuously fed. into the mold to maintain a `molten metal level-therein, a portion offthe heat -is withdrawn to initially solidify the vperipheral portions of the metal in contact Withfthe'xnold shell,

and the partiallysolidied casting is continuously Withdrawn from'the mold, the improve- `ment ofeliminating cold shuts'atlthe-'corners or '-\--end surfaces of ftheingot; Which'comprisesgre- "tardingthe extraction of heatfrom the molten metalvv only at the corners and end surfaces of 'the mold by thermally insulating only'the corresponding-portions ofthe metal from'contact Y withthe mold at the molten metal level to pre- `"vent initial solidification of the'metal where the molten metal meniscus exists, and 'thereafter rapidly-'extracting heat yfrom the molten metal .molten metal miniscus exista-and thereafter-rapidly'extracting heat rfrom thev molten metal to to cause initial solidiflcation of the peripheral -portions of the metal by direct contact ofthe `rriolten-metal with the mold not substantially less thanfabout 1/, inch below the molten metal level.

Y 3. A process `according to claim 2 inWhich the molten metal is thermally insulated at the corners or end surfaces with Van asbestos material.

' OWEN M. GARDNER.

ALBERT J. STONE.

References Cited in the file of `thispatent yUNITED STATES PATENTS

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