CA2625569A1 - Method and apparatus for electromagnetic confinement of molten metal in horizontal casting systems - Google Patents

Abstract

The present invention provides an apparatus for strip casting of molten metal including a pair of casting rollers R1, R2, adapted to receive molten metal M
along a horizontal axis, wherein a vertical distance separating the pair of casting rollers defines a molding zone; and an electromagnetic edge containment apparatus 15 positioned on each side of the molding zone having an induction coil wound about a portion of a magnetic member to generate magnetic lines of force upon application of a current, wherein the poles of the magnetic member are positioned distal from to aligned to the planar sidewall of the casting rollers and the current provides magnetic lines of force perpendicular to said horizontal axis that contain the molten metal in contact to the casting rollers without substantially increasing the temperature of the molten metal.

Description

METHOD AND APPARATUS FOR ELECTROMAGNETIC CONFINEMENT OF
MOLTEN METAL IN HORIZONTAL CASTING SYSTEMS

Field of the Invention [0001] The present invention relates to the continuous casting of inetal strip, and more particularly, to the electromagnetic confinement of molten metal in a contlntioUs casting system.

Back~roitnd of the Invention [0002] Continuous casting of metals is performed in twin - roll casters and belt casters or coinbinations thereof. Methods are available for casting both in the horizontal and in the vertical direction. In particular, the steel industry has recently developed high speed twin roll strip casters which operate in the vertically down direction.

[00031 Up to the present, the mechanical edge dams have been employed to provide eontaimnent of the molten metal in the casting zone. Such devices have included the caterpillar type edge danls that move with the strip (as in the Hazelett casters) or fixed edge danis that are pressed against the surface of the rolls. The latter is used in the twin-roll steel strip casting industly. Such fixed mechanical edge dalns have a short service life as they get eroded by contact with the cold sidewall of the rolls. In addition, such mechanical edge dains provide sites for the forniation of skulls that have a tendency to be sheared off and thus enter the cast strip to render the inicrostructure nletallurgically undesirable. Caterpillar edge dains, while well proven for the thicker slab castings (10 - 25 nun tliick.), become ixnpractical for tliin strip casters or twin druin casters of the steel industry where the cross section to be contained changes sharply along the casting zone.

f0004] Electromagnetic edge dams have been elnployed in the prior art in the strip casting of inetals in vertical twin drum (roller) casting systeins.
Electroinagnetic edge dalns of a magtietic system type use a combination of a magnet assembly and an AC coil to generate confinement forces. Electromagnetic edge dams of an induction system type rely solely on an AC coil to generate the containment forces.

10005] The magnetic system electromagnetic edge dams use a magnetic meinber which coinprises a yoke or core connecting two pole faces disposed on eitlier side of the gap on which the molten metal is to be confined. The magnetic inember is made of a ferromagnetic material and is surrounded over a given length of the yoke by a coil carrying an AC current. The magnetic flux generated by the flow of the current into the coil is transmitted to the poles of the magnet through the yoke and establishes contaiiunent forces at the metal surface in the gap.

[0006] Typically, in magnetic systems, part of the magnetic member is covered with an electrically conductive shield to ininhnize leakage of flux in a direction away from the gap. Such magnetic confinement systems have the advantage that the confineinent cuxxent need not be as high as compared to those systems using solely an iiiduction coil. If a stronger inagnetic field is required, it can be achieved with the same current level by reducing the area of the pole faces to concentrate tlle field.
However, such systelns are not without disadvantages. For example, such systems typically have poor operating efficiency resulting from core losses and losses due to inagnetic hysterisis when an alternating magnetic field is applied to the magnetic material. Additionally, high teniperatLires are typically generated that need to be dissipated by cooling in order to prevent dainage to the nlagnetic system.

[0007] Induction confinement systenls typically einploy a shaped inductor positioned close to the gap in which the molten metal is to be contained. The AC
current flowing in the inductor generates induced currents as well as a tiine-va.lying magnetic field on the surface of the molten metal to be contained. The interaction between the current and the magnetic field provide containment forces. To improve efficiency, a magnetic menlber is built arotuld the inductor to focus the current to the inductor surface facing the molten tnetal. Induction coil systems are generally siinpler in design than magnetic systems. However, induction systems are disadvantageously limited in terins of the lnaximum metallostatic head that can be contained by the systezn. The lnaximum metallostatic head that can be supported in induction coil systems is Iimited, because induction coil systems reqtiire very high inductor currents to provide adequate contaimnent forces, wherein such high currents are accompanied by increased heat generation, which in tLirn hinders or slows the solidification process during casting.

[00081 Referring to Figure 1, in vertical twin roll casters, the molten znetal head against which containtnent must be provided tends to be very high. For typical operating condition, the metal head heiglxt Hl is about 65 1o the radius of the casting rolls. Therefore, electromagnetic edge dam apparatus used in vertical twin roll casters znust provide a magnetic field strong enough to contain a metal pool having a head height Hl that is 65% the raditts of the casting rolls. Such electroinagnetic edge dams have not been successfillly conimercialized for two reasons. First, the high current required to contain the inolten inetal pool creates standing waves on the top surface of the metal pool that are too large in magnitude for the casting process.
Second, the large electromagnetic forces needed to contain the molten inetal head formed atop vertical roller caster systems create indziction heating on the metal pool's sidewall, which interferes with the solidification process.

[0009] U.S. Patent No. 4,936,374 describes a vertical casting systenl and electromagnetic confznement apparatus having the disadvantages described above.
Further, U.S. Patent No. 4,936,374 describes casting rollers having a rim por.tion, in which the containnlent magnetic field is conducted through the rim portion of the casting roll. In addition to induction heating and wave generation, the riin portions of the casting rolls disclosed in U.S. Patent No. 4,936,374 produce a ridge in the cast product and therefore fail to provide a casting strip having uniforin sidewalls (edges).
The ridge formed in the casting strip produced using the apparatus and method disclosed in U.S. Patent No. 4,936,374 n-iust be machined prior to rolling of the casting strip. Additional machining disadvantageously adds to the cost of the production.

[0010] Accordingly, a need remains for a method of higll-speed continuous casting of metals and alloys, which achieves uniforinity in the cast strip surface, provides good molten metal containinent in the casting zone, and results in strip edges which can be rolled without needing to be machined by triiruning.

SuminM of the Invention [0011] The present invention overcomes the above-described obstacles and disadvantages by providing an electromagnetic confinement apparatus incorporated into a horizontal casting apparatus, wherein the positioning of the electromagnetic confinement apparatus and a magnetic field that is produced by an alternating current provides a cast metal strip having substantially uniform edges (sidevvalls).
The present invention fiirFller provides a inethod and apparatus for producing a cast inetal strip, wllich provides a means for adjusting the profile of the cast metal strip's sidewall.

[00121 In one en-ibodirnent of the present invention, the current applied through the electromagnetic confinement apparatus, as well as, the positioning of the electromagnetic confinement apparatus to the molding zone of the horizontal casting apparatus is selected to provide a cast metal strip having substantially uniform edges, in wliich the sidewall of the cast inetal strip edges may be substantially flat, or concave or convex in relation to the cast metal strip's centerline. The cast znetal strip's substantially uniforin edges allows for the cast nietal strip to be rolled without further machining. Broadly, one einbodiment of an apparatus of the present invention comprises:

(a) a pair of casting rollers adapted to receive niolten metal along a horizontal axis, wherein a vertical distance separating the pair of casting rollers defines a molding zone;

(b) an electromagnetic edge contaiinnent apparatus positioned on each side of the molding zone, coinprising an induction coil wound about a portion of a magnetic inember to generate niagnetic lines of force upon application of a current, wherein said magnetic member coinprises a first and second pole positioned distal from and aligned to a sidewall of said pair of casting rollers and the current provides magnetic lines of force perpendicular to said horizontal axis that contain the molten metal in contact to the casting rollers witll substantially no increase in temperature to the molten metal; and (c) a means for supplying the molten inetal to the molding zone along said horizontal axis from a tundish while ensuring said molten metal remains substantially non-oxidized, wllerein the tundish is separated fronl the molding zone by a distance to substantially eliminate wave generation within the tundish by the magnetic lines of force.

[00131 In another einbodiment of the apparatus of the present invention, a horizontal roller casting apparatus is provided in which containment of the metal through the apparatus is provided by the colnbination of a mechanical edge dain and an electromagnetic edge dam. Broadly, the inventive casting apparattis colnprises:

. (a) a pair of casting rollers adapted to receive molten metal along a horizontal axis, wherein a vertical distance separating the pair of castizig rollers defines a molding zone;
(b) a tip delivery structure positioned to supply the inolten metal to the znolding zone along said horizontal axis from a tundish w11ile ensuring said molten lnetal remains substantially non-oxidized; and (c) an edge containment apparatLis positioned on each side of the molding zone, said edge contaimnent apparatus comprising:
a mechanical edge dain positioned overlying at least an end portion of said tip delivery structure and partially extending towards said molding zone, and an electroinagnetic edge dam coinprises a first and second magnetic pole positioned distal from and aligned to a sidewall of said pair of casting rollers and overlying a portion of said mechanical edge dain partially extending towards said molding zone, wherein said electromagnetic edge dain provides magnetic lines of force perpendicular to said horizontal axis that contain the molten inetal in contact to the casting rollers.

[0014] In each einbodinlent, the vertical distance separating the horizontally disposed pair of casting rollers provides a nzetal head height that allows for contailunent of the molten metal by magnetic lines of force that are provided by an electromagnetic contaimnent device witllout a substantial increase in the teniperature of the molten metal. For the purposes of this disclosure, the terin "positioned distal frorn and aligned to a sidewall of said pair of casting rollers" is intended to denote that the poles of the electromagnetic edge dain do not extend towards the casting apparatuses centerline beyond a plane defined by the sidewall of the casting rollers, but are positioned within close enouph proximity to the castings roller's sidewall to provide a sufficient magnetic field to contain molten metal within the molding zone.
It is noted that the poles of the electromagnetic edge daxn inay be adjusted from adjacent to the casting rollers sidewall to any distance from the sidewall, so long as sufficient containment forces are provided by the poles to the molding zone.
In one embodiinent, the sidewall of the casting roller may be substantially planar.
The term "substantially planar" with respect to the casting roller's sidewall denotes that the casting roller does not incoiporate a lip portion. In one ernbodiznent, the electromagnetic lines of force are produced by an alternating current having a frequency ranging from 40 Hz to 10,000 Hz through the electromagnetic edge containment device.

100151 In another embodilnent of the present invention, a belt casting system is provided that employs electromagnetic edge contaimnent and produces a metal strip hdving substantially uniforin edges, wherein the substantially uniforin edges allows for the cast metal strip to be rolled without further machining. Broadly, the inventive belt casting systein for strip casting of molten metal coinprising:

(a) a pair of opposing endless metal belts, each of the pair of opposing endless metal belts passing over a roller and having a periphery substantially aligned to a periphery of the roller, said each of said opposing endless lnetal belts having a surface for accepting molten nietal, wherein a vertical diinension separating the pair of opposing endless metal belts defines a molding zone;

(b) an electromagnetic edge contailunent apparatus positioned on each side of the molduig zone comprising an induction coil wound about a portion of a magnetic member to generate magnetic lines of force upon application of a cuirent, wllerein the current provides magnetic lines of force that contain the inoltera metal within a width and in contact to at least a portion of said pair of opposing endless metal belts with substantially no increase in telnperature to the molten metal; and (c) a means for supplying said molten metal to the molding zone along a horizontal axis from a tundish, the tundish separated from said molding zone by a distance to substantially eliminate wave generation within the tundish by the inagnetic lines of force.

[0016] In another aspect of the present invention, a casting strip is provided that may be forined by the above casting apparatus. Broadly, the cast strip comprises:
(a) a first shell;

(b) a second shell; and (c) a central portion between said first shell and said second shell, said central portion coinprising grains having an equiaxed structure, wherein said cast metal strip has sidewall edges being substantially uniform.

[0017] In anotl2er aspect of the present invention, a lnethod is provided for casting a metal strip in which a magnetic field -is utilized to control the geometry of the metal strip's sidewall. Broadly, the inventive method comprises:

providing molten metal to ainolding zone along a horizontal axis;
containing said molten metal within said molding -zone witll a magnetic containment means; and casting said molten metal into a cast metal strip, wlierein sidewall geometry of said cast metal strip is configured by adjusting said nlagnetic contairunent means.

[00181 The magnetic field may be adjusted to provide a xnetal casting strip sidewall geoanetiy that is flat or is concave or convex relative to the centerline of the cast metal strip. In one embodiment, the inagnetic containlnent means may include an induction coil wound about a magnetic member to generate magnetic lines of force r.ipon application of a current. The magnetic nlember having a first and second magnetic pole positioned distal from to adjacent to the molding zone.

[0019] The niagnetic lines of force produced by the inagnetic containineiit ineans inay be adjusted by increasing or decreasing the current through the induction coil or by changing the positioning of the magnetic contairunent ineans relative to the inolding zone. Positioning the first and second magnetic poles of the lnagnetic contailunent means adjacent to the molding zone may produce a cast inetal strip having a concave sidewall and positioning the first and second magnetic poles of the magnetic containnnent zneans distal from the molding zone inay produce a cast metal strip having a convex sidewall.

Brief Description of the Drawings 100201 Figtire 1(side cross sectional view) is a scheinatic of a poi-tion of a vertical roller caster casting appratus depicting a molten metal head and a pair of rolls operated according to the prior art.

[0021] Figure 2a (side cross sectional view) is a schematic of one einbodiment of a llorizontal casting apparatus having electroinagnetic edge dains in accordance witli the present invention.

[0022] Figure 2b (side cross sectional view) depicts one embodiinent of a twin belt caster equipped with an electroinagnetic edge dain apparatus in accordance with the preSellt i11ve11tlon inveiltioll.

[0023] FigL2re 3 (side cross sectional view) depicts the lnolding zone of the inventive horizontal casting device. -[0024] Figure 4, depicts a table sulmnarizing the magnetic field density that is required to contain a molten pool of alulninum at different head heights.

[0025] Figure 5 depicts a plot of the magnetic field strength produced by aii electromagnetic contaiiunent device in accordance with the present invention at varying currents and distances wherein the distance is measured from the sidewall of the caster roll.

[0026] Figure 6 (side cross sectional views) depicts a sectional view taken along the lines 2-2 in Figure 2a, and illustrate the positioning of the electromagnetic edge dams in relationship to the sidewall of the roller casters.

[0027] Figures 7a-7d provide a sectional view of the electroinagnetic edge dain apparatus of the present invention illustrating the path of the inagnetic lines of force in relation to the roller casters of the horizontal roller caster casting apparatus.
[0028] Figures 8 a-c (side view) illustrate different pole face angles and orientations in accordance with the present invention.

[0029] Figure 9 illustrates an exeniplaly einbodiment of the present invention wherein a magnetic member has a split core design.

[00301 Figure 1 O illListrates all eXelnplary enlbodllnent of tlle present Inventlon wherein the magnetic member has a laminate design.

[0031] Figure 11 illustrates an exemplary elnbodiinent of the present invention wherein a mechanical edge dam'is used in conjunction with an electroinagnetic edge dam.

[0032] Figure 12 depicts a table summarizing the push of the electromagnetic edge dazn.

[0033] Figures 13 a-c are pictorial representations of sidewall of a casting strip.

[0034] FigLUes 14 a-b are photographic representations of the edges of the strip made with a high magnetic force in the electromagnetic dam.

[0035] Figure 15 is a pictorial representation of a casting strip having a flat edge profile (straight edge).

[0036] Figure 16 is a pictorial representation of -a castuzg strip following an 87% reduction (acceptable degree of edge cracking).

Detailed Description of Preferred Embodiments [0037] The present invention provides an electromagnetic edge dam that confines molten metal to the molding zone of a horizontally disposed roller casting or belt casting systein with a magnetic field that is produced by a lower AC
cLUrent than was previously possible. By providing sufficient electroniagnetic containinent means at lower AC currents, the present invention utilizes electromagnetic confinement without creating a substantial increase in the temperature of the molten metal or producing wave generation effects.

[00381 As discussed above, in prior vertical casting metllods with larger molten metal head height, larger magnetic forces are required in order to contain the greater pressure prodticed by the molten metal, wherein larger xnagnetic forces typically require higher currents that generate heat. For example, to contain molten aluminum against a 300 nun heigllt, as representative of typical vertical casting inethods, a rninimuln magnetic field intensity of 0.24 T would be needed. In the present invention, the inetal head height is kept low, as achieved by a horizontally disposed casting system, so that the required containinent can be met with relatively low magnetic field density. For exaxnple, a 50 inin head height in a horizontal casting apparatus consistent with the present invention requires a magnetic field density of only 0.055 T to contain molten aluininuin in the horizontal position while casting.
The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accoinpanying drawings, like and/or corresponding eleinents are referred to by like reference numbers.

[0039] RefeiTing to Figure 2a, in,.one embodiinent of the present invention, a horizontal roller casting apparatus 10 is provided having an electromagnetic edge daxn 15 positioned to provide magnetic lines of force to confine molten metal M
within the molding zone 20 of the apparatus 10, wherein the magnetic lines of force extend along a plane perpendicular to the plane on wllich the casting is drawn. The horizontal roller casting apparatus 10 is practiced using a pair of counter-rotating cooled rolls Rl and R2 rotating in the directions of the arrows Al and A2, respectively.
By the terin horizontal, it is meant to denote that the cast strip is produced along a horizontal plane, in which the horizontal plane is parallel to section line 2-2, or at an angle of plus or minus about 30 from the horizontal plane.

[0040] Referring to Figure 2b, in one embodiment of the present invention, a horizontal belt casting apparatus 10' is provided having an electromagnetic edge dani 15 positioned to provide magnetic lines of force to confine molten metal M
within the niolding zone 20 of the apparatus 10, wherein the lnagnetic lines of force extend along a plane perpendicular to the plane 2-2 on which the casting is drawn.
The horizontal belt casting apparatus 10' is practiced using a pair of counter-rotating belts B1 and B2 rotating in the directions of the arrows AI and A2, respectively. It is noted that although tlie following figures are directed towards the horizontal roller caster 10 depicted in Figure 2a, the following description is equally applicable to the horizontal belt caster 10' disclosed in Figure 2b with the exception that instead of the molten xnetal contacting'the roller casters Rl, R, the molten metal is contacting the counter-rotating belts B1, B2. It is further noted, that further differences between the horizontal roller casting apparatus 10 and the belt casting apparatus 10' in accordance witl-i the present invention are noted when relevant throughout the following portions of the specification.

[0041] Referring to Figure 3,lnolten metal M is transported to the molding zone 20 by a feed tip T, which may be made frozn a suitable ceramic material.
The feed tip T distributes molten inetal M in the direction of arrow B directly onto the casting rolls Rl and R2 rotating in the direction of the arrows Al and A2, respectively.' Gaps Gl and G2 between the feed tip T and the respective rolls Rl and R2 are maintained as sinall as possible to prevent molten metal from leaking out and to mininlize the exposure of the molten metal to the atmosphere. A suitable dimension of the gaps Gi and G2 is about 0.01 inch (0.25 nun). A plane L through the centerline .13 of the rolls R, and R2 passes throiigli a region of minimu.m clearance between the rolls RI and R2 referred to as the roll nip N.

[0042] The molten metal M delivered from the feeding tip T directly contacts the cooled rolls Rl and R2 at regions 18 and 19, respectively. Upon contact with the rolls RI and R2, the metal M begins to cool and solidify. The cooling metal produces an upper.shell 16 of solidified metal adjacent the roll RI and a lower shell 17 of solidified metal adjacent to the roll R2. The thickness of the shells 16 and increases as the metal M advances towards the nip N. Large dendrites 21 of solidified metal (not shown to scale) are produced at the interfaces between each of the upper and lower shells 16 and 17 and the molten inetal M. The large dendrites 21 are broken and dragged into a center portion 12 of the slower moving flow of the nlolten metal M and are carried in the direction of arrows C1 and C2.

[0043] The dragging action of the flow can cause the large dendrites 21 to be broken fi.irEher into smaller dendrites 22 (not shown to scale). In the central poi-tion 12 upstreain of the nip N, the metal M is senli-solid including a solid co7nponent including solidified small dendrites 22 and a molten metal component. The metal M
in the region 23 has a inushy consistency due in part to the dispersion of the snlall dendrites 22 therein. At the location of the nip N, sonie of the molten metal is squeezed backwards in a direction opposite to the arrows Ct and C2. The forward rotation of the rolls Rl and R2 at the nip N advances substantially only the solid portion of the metal (t11e upper and lower shells 16 and 17 and the small dendrites 22 in the central portion 12) while forcing molten lnetal in the central portion upstream from the nip N such that the metal is conlpletely solid as it leaves the point of tiie nip N.

[0044] Downstream of the nip N, the central portion 13 is a solid central layer 13 containing the small dendrites 22 sandwiclzed between the upper shell 16 and the lower shell 17. In the central layer 13, the small deindrites 22 may be about 20 to about 50 microns in size and have a generally equaixed (globular) shape, as opposed to having a colurnnar shape. The three layers of the upper and lower shells 16 and 17 and the solidified central layer 13.constitute a solid cast strip.

(0045] The rolls Ri and R2 serve as heat siiiks for the heat of the molten metal M. In the present invention, heat is transferred froin the molten metal M to the rolls RI and R2 in a uniform manner to ensure uniformity in the surface of the cast strip.
Surfaces D1 and D2 of the respective rolls Ri and R2 may be made from a material of good thermal conductivity such as steel or copper or other metallic materials and are textured and include surface irregularities (not shown) whicli contact the nlolten lnetal M. The surface irregularities may serve to increase the heat transfer froin the surfaces D1 and D2. The rolls Rj and R2 may be coated with a material to enliance separation of the cast strip from the rolls Rl and R2 such as chromium or nickel. In a preferred eznbodiment, the rolls RI and R2, including surfaces D1 and D2, coinprise a ferroznagnetic material. In the einbodiments of the present invention, in which the rolls Rl and R2 do not conzprise a ferroinagnetic material, the casting surfaces DI, D2 of the roller as well as the roller's sidewall may be coated with a ferroznagnetic materials.

[0046] The control, maintenance and selection of the appropriate speed of the rolls RI and R2 may impact the operability of the present invention. The roll speed detennines the speed that the niolten metal M advances towards the nip N. If the speed is too slow, the large dendrites 21 will not experience sufficient forces to become entrained in the celitral portion 12 and break into the small dendrites 22.
Accordingly, the present invention is suited for operation at high speeds such as about 25 to about 400 feet per minute or about 100 to about 400 feet per minute or about 150 to about 300 feet per minute. The linear speed that molten aluminum is delivered to the rolls Rl and R2 may be less than the speed of tlie rolls RI
and R2 or about one quarter of the roll speed. High-speed continuous casting according to the present invention may be achievable in part because the textured surfaces Dt and D2 ensi.ire unifonn heat transfer from the molten metal M.

[0047J The roll separating force may be a parameter in practicing the present invention. The roll separating force is the force present between the rolls due to the presence of the strip within the roll gap. The roll force is particularly high wen the stip is being plastically deforined by the rolls during roll castiong. A
significant benefit of the present invention is that solid strip is not produced until the metal reaches the nip N. The thickness is deterlnined by the dimension of the nip N
between the rolls Ri and R2. The roll separating force may be sufficiently great to squeeze molten inetal upstream and away from the nip N. Excessive molten metal passing througli the nip N may cause the layers of the upper and lower shells 16 and 17 and the solid central portion 13 to fall away from each other and become niisaligned. Insufficient inolfien metal reaching the nip N causes the strip to form premati.irely as occurs in conventional roll casting processes. A prelnaturely formed strip 20 may be deformed by the rolls R1 and R2 and experience centerline segregation. Suitable roll separating forces are about 25 to about 300 pounds per inch of width cast or about 100 pounds per inch of width cast. In general, slower casting speeds may be needed when casting thicker gauge alunlinum alloy in order to remove the heat froin the tllick alloy. Unlike conventional roll casting, such slower casting speeds do not result in excessive roll separating forces in the present invention because fully solid aluminum strip is not produced upstream of the nip.

[0048] In. prior applications, roll separating force has been a limiting factor in producing low gauge aluminum alloy strip product but the present invention is not so limited because the roll separating forces are orders of niagnitude less than in conventional processes. Aluminuin alloy strip may be produced at thicknesses of about 0.1 incll or less at casting speeds of 25 to about 400 feet per minute.
Thicker gauge aluminum alloy strip nlay also be produced using the method of the present invention, for exainple at a tliickness of about 1/4 incll.

[0049] The aluininum alloy strip 20 continuously cast according to the present invention includes a first layer of an alumininn alloy and a second layer of the aluminum alloy (corresponding to the shells 16 and 17) witll an intermediate layer (tlle solidified central layer 13) therebetween. The grains in the aluminuzn alloy strip of the present invention are substantially undeforined because the force applied by the rolls is low (300 pounds per inch of width or less). The strip is not solid until it reaclzes the nip N; hence it is not hot rolled in the manner of conventional twin roll casting and does not receive typical therino-mechanical treatnlent. In the absence of conventional hot rolling in the caster, the grains in the strip 20, are substantially undeforined and retain their initial structure achieved upon solidification, i.e. an equiaxed structlire, such as globular.

[0050] Continuous casting of aluminiun alloys according to the present invention is achieved by initially selecting the desired dimension of the nip N
correspond'ulg to the desired gauge of the strip S. The speed of the rolls Ri and R2 may be increased to a desired production rate, or to a speed that is less than the speed at wllich the roll separating force increases to a level that indicates that plastic deforlna.tion of the casting strip is occurring between the rolls RI and R2.
Casting at the rates contemplated by the present invention (i.e. about 25 to about 400 feet per minute) solidifies the aluminuxn alloy strip about 1000 times faster than aluminum alloy cast as an ingot cast and improves the properties of the strip over alulninum alloys cast as an ingot.

[0051] The molten nletal M being delivered from the feed tip T is confined within the molding zone 20 by at least an electromagnetic edge daln 15 that is positioned to diiect magnetic lines of force perpendicular to the plane 2-2 on which the casting -is being drawn. In one embodiment, an electromagnetic edge dam 15 is positioned on each side of the casting apparatLis. In a preferred enibodiment, the molten metal M is confined within the molding zone 20 during casting by a mechanical edge.dam 55 in combination with an electromagnetic edge dain 15, wherein the mechanical edge dani 55 is positioned proximate to the feed tip T
and the electromagnetic edge dain 15 is positioned overlying the terminating end of the mechanical edge dain 55 and provides confinement forces along the entire length of the molding zone 20, as depicted in Figures 6 and 11.

[0052] The current and/or frequency utilized by the electromagnetic edge dam 15 to maintain the molten metal M within the molding zone 20 is substantially less than typically required in prior casting apparatuses using electromagnetic edge dazns.
In prior casting apparatus employing electroinagnetic edge dains, high magnetic force fields where required to contain the nzolten metal, which resulted in induction heating witliin the inolten metal that disadvantageously effected the solidification process. In the present invention, by reducing the magnitude of the required electromagnetic force, the current and/or ~iequency conducted through the electromagnetic edge dam is also reduced, which in turn advantageously reduces the incidence of induction heating on the sidewall of the molten metal in the molding zone.

[0053] Without wishing to be boLuld, but in the interest,of fitrtlier describing the present invention, applicants' believe that the reduction in the electromagnetic force that is requlred to contain the metal Wltllln the molding zone is related to the decreased head height 1-12 of the molten metal froni the feed tip T, as depicted in Figure 3, as opposed to the greater lieight H1 of the molten metal pool disposed atop the roller caster in prior vertical casting apparatuses, as depicted in Figure 1. As discussed above, the height H1 (or depth) of the molten pool atop the vertically disposed casting rollers is approxiYnately 65% the heigllt of the casting roller Rl, R2 and can range from 8 inches to 20 inches, as depicted in Figure 1. Referring to Figure 3, in the present invention, the height H2 of the molten metal as delivered from the tip feed T to the molding zone 20 can be on the order of about 1 inch, and in soine exainples may be further reduced to 0.5 inches. Hereafter, the difference in vertical location of the metal level in the tundish and that of the center of the strip being cast is referred to as a"inolten inetal head".

[00541 The relationship between tlie height of the inolten metal head H2 and the magnetic field density required for containing inolten aluminuin at different head level's is best described tllrough the following equations. First, the pressure exterted by the molten metal head, which the magnetic field must contain within the molding zone 20 is calculated from:

p - PgH2 where p is is the magnetic pressure in Pa, p is the density of the metal, g is the acceleration of gravity and H2 is the height of the molten metal head. The pressure produced by the molten metal head in turn deterinines the strength of the magnetic field that inust be produced by electrornagnetic edge contaiiunent device 15 to contain the molten metal head witllin the molding zone 20. In the present 'invention, the height of the nlolten metal head H2 that is being horizontally delivered to the molding zone 20 by the feed tip T may be as low as 0.5 inches.
The pressure that is produced by the molten metal head of vaiying heigllt HZ, from the feed tip T of the present horizontal roller casting apparatus 10, was deterinined 19.

using the above equation and is listed in the Table depicted in Figure 4. To sulnmarize the pressure ranged from about 125 Pa for a metal head height H2 of approximately 0.5 inches (12.7 nnn) to abotit 2,492 Pa for a metal head height of approximately 10 inclles (254 mni).

[0055] The pressure required to contain the molten metal head H2 within the molding zone 20 is then used in the following equation to determine the required niagnetic field density (B):

p = B212 ga where p is the magnetic presstire in Pa (Pascals), B is the magnetic field density in T (Tesla) and o is the permeability of air (=4n xl0'7 H/ni).
Referring to Figure 4, from the above equation, it is calculated that for a relatively high molten metal head heigllt H, for feed tip T delivery of approximately 254 mnr (10 inch), the magnetic field density needed is 0.079 T (790 Gauss) and a molten metal head height H2 of approximately 12.7 min (0.5 inch), themagnetic field density needed is approximately 0.0177 T. As illustrated in Figure 4, reducing the molten metal head height H2 decreases the magnetic field density that is needed to contain the molten metal M within the molding zone 20. The magnetic field density required to contain metal head heights consistent with the present invention can be obtained with electromagnets at relatively low current levels. In one einbodiment, the electromagnetic edge daiil operates at approximately 2000 ampere turns (i.e. a coil of 10 ttirns drawing 200 A).

[0056] In another aspect of the present invention, the physical positioning of the electromagnetic edge dain, the molten metal head heigllt and the strength of the nlagnetic field can be varied to control the positioning of the edge of the molten metal within the molding zone with respect to the roller casters Ri, R2 sidewall. The strength of tlie magnetic field at different distances froin the face (edge) of the roller casters may be calculated by the following equation:

BL = ( o nI/1)/{(2D/H)sinh(L/1) + (w/1)cosh(L/l)}
where:
BL = magnetic field intensity at a distance L(in) in the gap from the roll face.

nI = coil turns and current.

w = roll gap 1= 4( , 8w/2) in which r = relative pernieability of steel caster roll (taken as 600), S= skin depth for steel (material of the caster roll), and w is the roll gap.

D = distance between electromagnet pole and the roll face.
H= height of magnet pole.

[0057] Referring to Figure 5, using the above equation, the magnetic field strength was calculated and plotted as a ftinction of the frequency of current (Hz) couducted tlirot,igh the electromagnetic edge daln 15, in which the distance at which the magnetic field strength was calculated ranged from 10 imn to 80 inm inward from the sidewall of steel casting rolls (reference line 1= 10 nun, reference line 2= 20 nun, reference line 3 = 30 in, reference line 4 = 40 intn, reference line 5=
60 mm, and reference line 6= 60 znin). In each of the calculations, the height (H) of the magnetic pole was set at 8 nun, the distance (D) between the electromagnetic pole and the roll face was set at 4 irun, and the roll gap (w) was set at 4 inin.
Additionally, reference lines where plotted to indicate the mininluni the field strength required to contain a metal head having a height H2 equal to 250 inin (reference line 7), 150 inm (reference line 8), 100 nnn (reference line 9), and 50 nun (reference line 11). The plot depicted in Figure 5 illustrates that the 0.079 T field density required for the 250 nun metal head 8 could be created by this electromagnet in distances as far as 20 mm into the roll gap.

[0058] The edge of the casting strip can therefore be contained inwards from the casting roll Rl, R2 face (sidewall), if desired, by increasing the current in the edge dam. It is noted that the field density decreases rapidly at longer distances from the roll face and only small metal head heights, on the order of 50 nun, can be contained in distances 40 trun or greater by the operation of this edge darn at 2000 amp turns.
The range of coiitaixunent can be extended fi.irther, if needed, by increasing the magnetomotive force (nI) on the edge dam. When increasing the electromagnetic force, due consideration need to be given to the heating effect of t11e edge dain.

[0059] It is fiirther noted that the plot depicted in Figtire 5 also illustrates that the electromagnetic edge dam as utilized in the present invention would operate effectively at any chosen frequency. The loss in magnetic field becomes noticeable only for operation at frequencies greater than 10 kHz.

[00601 In addition to the height of the molteil metal head and the magnetic field density, the positioning of the electromagnetic edge dain witll respect to casting rollers may also be adjusted to provide electromagnetic force lines to confine the nlolten metal M within the inolding zone 20. Referring to Figure 6, the electromagnetic edge dain 15 may be positioned wherein the poles of the magnetic member are aligned to the sidewalls 13 of the casting rollers Rl, R2. In one embodiment, the electroinagnetic edge dani may be positioned wherein the poles of the magnetic meznber are distal from tlie sidewalls of eacll casting roller RI, R2. In the einbodiments of the present invention in which a horizontal belt casting apparattis is employed as depicted in Figure 2a, the electromagnetic edge dazn 15 inay be positioned wherein each pole of the magnetic melnber is distal from to aligned to the adjacent sidewall of the casting belts Ba, B2. For the purposes of this disclosure the term "distal froin to aligned to the adjacent sidewall of the casting belts"
is intended to denote that the poles of the electromagnetic edge dam do not extend towards the casting apparatuses centerline beyond a plane defined by the sidewall of the casting belts, but are positioned within close enouph proximity to the sidewall of the castings belts to provide a sufficient magnetic field to contain molten metal within the molding zone.

[0061] The inventive electromagnetic edge dain will also perform in casters with rolls made froni a non-magnetic (non-ferromagnetic) material, such as copper.
However, when the rollers comprise a non-magnetic inaterial, the penetration of the magnetic field into the roll gap may be limited and thus contairunent will typically occur on a plaiie close to the end of of the rolls. It may be possible to obtain penetration into the gap by coating with a ferromagnetic material (such as iron, nickel or cobalt) the end faces and casting surfaces 200 of such rolls to the required depth of contaiznnent, as depicted in Figure 8d.

[0062] It is noted that prior casting apparatuses typically shape the magnetic poles of the electromagnetic devices and the casting rolls to focus the nlagnetic field towards the molding zone. In one exaniple, prior casting rollers employ lips extending froni the sidewall of each roller and may have fiirther included magnetic poles having a geometry corresponding to the extending lips of prior casting rollers.
Contraiy to prior casting apparatuses, the present invention does not require specially configured casting rollers to facilitate the focus of the magnetic field produced by the electromagnetic edge danl. In one embodiinent of the present invention, the sidewalls 113 of the casting rollers Rl, R2 may be substantially planar.
Further, the electromagnetic edge dam 15 of the present invention may be positioned so that the face of the electromagnetic edge containment device is aligned to the face of the casting roller's planar sidewall 113, wherein the electromagnetic edge dani 15 is in close proximity to the casting rollers Rl, R2. The electromagnetic edge dam 15 may also be positioned distal from the casting roller's sidewall 113. Regardless of the positioning of.the electroinagnetic edge dam 15, the electromagnetic edge dam 15 is positioned to provide sufficient electrolnagnetic force to contain the molten metal M
within the molding zone 20.

[0063] The positioning of the edge dams 15 may be dependent on the current or frequency utilized in the edge dam. For exaniple, lower currents may provide lower magnitude electrolnagnetic force line and therefore be more likely to require that the edge dam 15 be positioned in closer proxiunity to the molding zone 20. The higher the current conducted through the electromagnetic edge dain the greater the inagnitude of the electromagnetic force lines and hence the father away the electromagnetic edge dams may be positioned from the molding zone.

[0064] Referring to Figures 7a-7c, in one einbodiment, the positioning of the electroinagnetic edge dain 15 and the inagnitude of the electromagnetic force lines are selected to fornl a substaiitially flat sidewall (Figure 7a), a convex sidewall (Figure 7b), or concave sidewall (Figure 7c) in the inolten inetal M witllin the molding zone 20. In one exaxnple, a current of 2200 Ainp/turns produces a casting strip having a concave sidewall; a current of 1200 .Axnp/turns produces a casting strip having a substantially flat or straigllt sidewall; aiid a current of on the order of 1200 .Amp/turns produces casting strip having a substantially convex sidewall. It is noted that the above exainples are provided for illustrative purposes only and are not intended to limit the present invention, as any current is applicable to the present invention, so long as the current provides suffzcient contaimneilt forces to the molding zone 20 and does not result in excessive induction heating. In some of the prefelred-einbodiments of the present invention, in which the casting strip's sidewall is concave or convex, the curvahire of the sidewall may be defined by a radius that is approximately half the lnolten head height.

[00651 In another embodiment, the electromagnetic edge dam 15 may be configured to provide molten metal within the inolding zone having a convex sidewall relative to the centerline of the molten metal M within the molding zone 20.
Preferably, the sidewall of the nlolteli metal within tlle molding zone is substantially aligned to the planar surface of the roller casters, as depicted in Figures 8a and 8c.
Alternatively, the electromagnetic edge dam 15 may be configured to project magnetic lines of force beyond the sidewall 113 of the casting rollers, wherein the inolten metal is confined interior to the edge of the roller casters, as depicted in.
Figures 8b and 8d.

[0066] The electromagnetic edge dain's 15 structure is illustrated in detail in Figure 8a, representing a sectional view of the edge danl apparatus 15 illustrated in Figure 2a. In the preferred embodinlent of the invention, the electromagnetic edge dam 15 is a magnet type of confinement system and includes a generally C-shaped magnetic meinber. The magnetic member 30 thus includes a core 32 having an upper arln or pole 34 and a lower arm or pole 36 extending therefrom to define a generally C-shaped cross section. The core 32, includes an induction coil winding 38 coinprising a coil wound about the core 32 of the magnetic meinber 30 to establish an induction coil. Thus, the winding is composed of a plurality of conductors wotuld about the core 32 of the magnetic member 30. The core wind'ulgs 3 8 about the core 32 ean be, i.nade of solid metal such as copper wire.

[0067] Still referring to Figure 8a, the upper arzn 34 terininates in a pole face 42 where as the lower arm 36 tertninates in a pole face 44, respectively, with the molten metal M being maintained therebetween. The pole faces 42 and 44 thus define the surface from which the magnetic lines of force generated by the magnetic element 30 with its induction coil 38 pass froin one of the pole faces 42 to the other pole face 44, as illustrated by the magnetic lines of force 48.

[0068] Figures 9a-9c illustirate different pole face 44 angles and orientations in accordance with the present invention. It will be appreciated by those skilled in the art that as the inter-pole-face gap 43 increases, the strength of the field across the gap decreases. Figure 9a illustrates a cross section of a lnagnetic znember 30 wherein the pole faces 42 and 44 have a negative angle relative to the ver-tical plane substantially perpendicular to the plane on which the casting is being drawn. Tlie negative angle nieans that the inter-pole-face gap 43 is less at the outside edge of each pole than at the inside edge of each pole face. As a result, the containment forces created by the inagnetic member shown in Figure 9c are stronger at the outside edge of each pole face than at the inside edge of each pole face. Figure 9b illustrates a cross section of a magnetic meinber 30 wherein the pole faces 42 and 44 have no angle relative to the vertical plane substantially perpendicular to the plane on which the casting is being drawn. The zero angle means that the inter-pole-face gap 43 is the saine at the inside edge of each pole face and the otitside edge of each pole face. As a result, the magnetic field created by the magnetic member shown in Figure 9b is relatively uniforin across each pole face. Figure 9c ilh.istrates a cross section of a inagnetic member 30 having pole faces 42 and 44 that are parallel in pc-u-t and not parallel in part. The inside region of the pole faces 42 and 44 have a negative angle relative to the horizontal.

[0069] In one embodinient of the present invention, the magnetic member 30 is forined from a ferromagnetic material such as silicon steel, and can be formed from a solid piece of such ferroinagnetic material. Alternatively, the nlagiietic meinber 30 can be formed frozn znultiple ferromagnetic materials, such as the split core design depicted in Figure 10. In another embodiment, the magnetic member 30 can be fornled frolll a series of lanlnlated ele111ents lnachlned a11d seCLlred together using 111echalllcal 111ealls, a11 adhesive or like ffieans to yield the desired confl.guratloll, as depicted in Figure 11. In many instances, the use of such laininates is preferable, because laminates may serve to more uniformly distribute tlle flux lines in the magnetic member and reduce loss due to saturation of the magnetic meinber. In addition, for a magnetic lnember made of laminated ferromagnetic material, tlie electrical energy dissipated as heat is also more evenly distributed atld more easily removed, particularly where the adhesive einployed to hold the laminate elements together has good thermal conductivity.

[00701 Referring back to Figures 8a-8d, siirrounding the magnetic inember 30 is an outer shield 50, whicll is preferably made of a material, and most preferably a metal, having structural rigidity and extreinely high electrical and-thernlal conductivities. Preferably, the outer shield 50 is fabricated of copper, although other metals such as silver and gold can likewise be used. The high electrical conductivity of the outer shield 50 aids in containing the magnetic lines of force within the xnagnetic ineznber while the good tliermal conductivity aids in the dissipation of heat from the overall apparatus. As will be appreciated by those skilled in the art, the outer shield 50 may be provided with cooling chamlels therein or brazed tLibes thereon to distribute cooling fluid tllrough or at the surface of the outer shield to fixrther aid in the reinoval of heat generated by the electromagnetic field. For exainple, an inlet.can be employed to pass a cooling fluid tllrough the outer shield for removal from a discharge port wllen additional cooling capability is required. Thus, the cooling fluid can be passed through a conduit within the outer shield to remove heat generated by the electromagnetic field.

[0071] The electromagnetic edge dam employed in the practice of the present inventioxi also includes an inner shield 56 dinzensioned to fit witllin the C-shaped configuration of the nlagnetic nlelnber 30. The iiuier shield 561ikewise serves to contain the magnetic lines of force generated by the coil 38 of the magnetic member 30, insuring that the magnetic lines of force are maintained within the magnetic meinber 30. In addition, it is also possible, and some times desirable, to include within the inner shield conduit ineans for the passage of a cooling fluid tl-ierethrough where it is desired to increase the ability to dissipate heat from the magnet.
It is also possible to do away with the inrier shield; especially so when using grain oriented silicon steellaininates wllere the field lines prefer to flow within the laminates.

[0072] The path of the magnetic field of the pesent invention is indicated in Figures 8a thortiglz 8d. In Figure 8a, magnetic field flows from one pole of the edge dam to the other in a plane essentially parallel to the side faces of the rolls. It is applicable to metallic rolls which are non-ferroinagnetic (such as copper).
The field creates the containinent forces on the end faces of the rolls. Figure 8b illustrates the case when the field penetrates into the gap and contains the molten metal inwards from the roll faces. This will be the case for ferromagnetic rolls and strong fields. It can also be acliieved by the application of a feiromagnetic coating 200 of sufficient depth to the end faces and end of the casting surface of a non-ferxomagnetic roll material, as depicted in Figure 8d.

[0073] In designing the electromagnetic contaimnent apparatus employed in the practice of this invention, a nuYnber of different tecbniques can be used in dissipating heat generated by the electromagnetic field. As shown in Figure 8c, the windings 40 inay be fonned of an annular conductor having a central opening 41 extending tlierethrough. Thus, cooled water can be passed through the central opening of the windings 40 to aid in the dissipation of heat generated by the electromagnetic field. As shown in Figure 12, the core 30 may also be equipped witll a cooling conduit 47 extending therethrougli; in that way, a cooling fluid can be passed tlirough the cooling conduit 47 to aid in the dissipation of heat generated by the electromagnetic field.

[0074] Figure 12 illustrates one preferred embodiment of the present invention, wherein a mechanical edge dain 55 is used in conjunction with an electromagnetic edge dam 15 having a magnetic nzeniber 30. The magnetic znember 30 is preceded by the mechanical edge ciam 55. The mechanical edge dam 55 shown should ideally have a cerailiic-less surface and comprise magnetic material to reduce the reluctance at the mouth of the molding zone. A ceramic material inay also be used to inake Ynechanical edge dam 55 if process conditions preclude the use of a metallic material. In one embodiment of the present invention, the mechanical edge danz 55 is positioned to ensure that the molten metal is contained witllin the casting apparatus while being delivered from the tundish H to the feed tip T. Once the molten metal M reaches the feed tip T, containtnent forces are provided by the electroli'lagnetic edge dam 15. In this arrangement, the seivice life of the mechanical edge dain 55 is increased by the electromagnetic edge dani 15, since the electromagnetic edge dam 15 is positioned in the most hostile portion of the casting apparatus.

[0075] The followhlg ea.amples are provided to fiirtlier illustrate the present invention and delnonstrate some advantages that arise therefrom. It is not intended that the invention be liunited to the specific exainples disclosed.

[0076] Aluminum strip was cast in accordance with the present invention using a caster with steel rolls. The strip was then metallograpliically tested to confirln the effect of the electromagnetic force on the molten metal witllin tlie molding zone.

Test specimens were forined using a horizontal roller caster and a combination of electrolliagnetic and nlechanical edge dains consistent witll the present disclosure.
Casting strips of three different thicknesses (2.44 nun, 2.291xun, and 2.16 inln) were then cast operating the electroinagnetic edge dam at 2180 A turns. Sanlples were then cut from the edges of the strips and were prepared for metallographic examination. It was observed that the center part of the casting strip vvas pushed inwards as compared to the outer surfaces of the strip, as shown in Figures 14a and 14b. This observation confirms the confinement effect of the electromagnetic edge dam during casting, since the central portion of the strip is the last to solidify.

[0077] The depth of the confinement effect into the roll gap was estimated by first measuring the width of the casting strip at room temperature, wherein the width of the casting strip was approximately 400.5 ixun. From this measurement, the width of the strip within the inolding zolie can be estimated as 406 rnnl by adding the contraction that occurred during solidification and cooling to room tenlperature.
[0078] Taking into account that the width of the casting roll is approximately 432 nun, it is evident that the magnetic field pushed the molten center of the casting strip a distance of approximately 13 mm (13 nu11= (432(width of roller caster) -406)/2) from the casting roll face on each side of the casting roll. More specifically, by subtracting the calculated widtli of the casting strip in the molding zone from the width of the casting roller the total displaceinent produced by the electromagnetic edge dains is calculated. The amount of displaceinent produced by a single edge dam is calculated by the nunlber of edge dains ernployed, which in this experiinent consisted of two electromagnetic edge danis positioned at opposing ends of the casting rollers.

[0079] SinZilar electroinagnetic push effects were observed for all three different strip tliiclaless (strip gauge), as suirunarized in the Table depicted in Figure 13. The degree of magnetic push was measured as the depth of the center portion of the strip with respect to the edges. The magnetic push was somewhat higher for thinner gauge strip, since the narrower roll gap would create a higher field density at any given distance. It is believed that the difference in the lnagnetic push between the two sides (drive side and operator side) of the caster rolls, as summarized in Figure 13, is attributed to variations in the location of the electroinagnets and the mechanical edge dains.

[0080] The edge profile of the as-cast strip was checked for operation at different inagnetoinotive force levels in the electromagnet. The edge profile obtained at 2180 A ttirn operation shown in Figure 14 were considered unsuitable for subseqtient rolling of the strip unless the edges were trinuned prior to rolling. In order to provide cast strip having edge profiles suitable for rolling without additional machining, the inagnetomotive force of the electroinagnet was reduced to decrease the push on the central portion of the castiilg strip so that the edge profile of the strip would be flat or slightly convex.

[0081] A flat edge profile was obtained in the casting strip at a current level of 180 A (or 1620 A turns) being applied to the electrolnagnet. To obtain a flat edge profile, the magnetic field should be selected to jtist offset the pressure produced by the molten metal in the molding zone, which is produced by the metal head with a minor contribtition small roll presstire. Referring to Figure 15, the edge of the casting strip made under these conditions was flat and highly straigllt indicating that it could be rolled without trimining the edges of the casting strip or other additional macllining.

10082] This strip was rolled in-line successfi.illy through four stands of rolling mills. The casting strip was rolled fronl a 2.7 null (0.107 inch) as-cast tl-iickness to a thickness of approximatelyl 0.36 mm (0.014 inch), which corresponded to an 87 %
reduction in thickness. Referring to Figure 16, the sheet made by this method showed only minor cracks at the edges, wliicll could be removed by triinining prior to coiling.

[0083] Following proper adjusttnent of the electromagnetic edge dam, high quality edges are obtained in the as-cast strip which perinits rolling to higli reduction ratios saving materials and ixnproving the efficiency of the process.

[0084] While the present invention has been particularly shown and described witll respect to preferred enlbodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forins and details described and illustrated, but fall within the scope of the appended claims.

Claims (31)

1. An apparatus for strip casting of molten metal coinprising:

(a) a pair of casting rollers adapted to receive molten metal along a horizontal axis, wherein a vertical distance separating the pair of casting rollers defines a molding zone;
(b) an electromagnetic edge containment apparatus positioned on each side of the molding zone, coinprising an induction coil wound about a portion of a magnetic member to generate magnetic lines of force upon application of a current, wherein said magnetic member comprises a first and second pole positioned distal from and aligned with a sidewall of said pair of casting rollers and the current provides magnetic lines of force perpendicular to said horizontal axis that contain the molten metal in contact with the casting rollers with substantially no increase in temperature to the molten metal; and (c) a means for supplying the molten metal to the molding zone along said horizontal axis from a tundish, while ensuring said molten metal remains substantially non-oxidized, wherein the tundish is separated from the molding zone by a distance to substantially eliminate wave generation within the tundish by the magnetic lines of force.

2. The apparatus of Claim 1 wherein said current comprises an alternating current having a frequency ranging from 40 Hz to 10,000 Hz.

3. The apparatus of Claim 1 wherein said current comprises less than 2,000 amp/turns.

4. The apparatus of Claim 1 which includes shield means positioned about the magnetic member.

5. The apparatus of Claim 1, wherein the magnetic member has a generally C-shaped configuration, including a core portion and parallel poles integral with and extending therefrom.

6. The apparatus of Claim 5, wherein the induction coil is wound about the core of the magnetic member, in which the induction coil is coiled from 1 to 100 times around the magnetic member.

7. The apparatus of Claim 1, wherein the vertical distance separating the pair of casting rollers provides a metal head height that allows for containment of the molten metal between the casting rollers by the magnetic lines of force at said current without a substantial increase in temperature of the molten metal resulting from the magnetic lines of force.

8. The apparatus of Claim 1, wherein the vertical distance separating the pair of casting rollers is less than 1.0".

9. The apparatus of Claim 1, wherein the magnetic member is positioned to the molding zone to position the magnetic lines of force to produce a convex sidewall, a concave sidewall, or a substantially flat sidewall to the molten metal within the molding zone.

10. The apparatus of Claim 1, wherein the magnetic member is formed of a ferromagnetic material from a stack of bonded or mechanically linked laminates or the magnetic member is formed from a solid core of ferromagnetic material.

11. The apparatus of Claim 1, wherein said pair of casting rollers comprises a ferromagnetic material, non-ferromagnetic material, or a non-ferromagnetic material that is at least coated with a ferromagnetic material on at least casting surfaces and said sidewalls of said pair of casting rollers.

12. The apparatus of Claim 1, wherein said sidewall of said pair of casting rollers is substantially planar.

13. An apparatus for strip casting of molten metal comprising:

(a) a pair of opposing endless metal belts, each of the pair of opposing endless metal belts passing over a roller and having a periphery substantially aligned to a sidewall of the roller, said each of said opposing endless metal belts having a surface for accepting molten metal, wherein a vertical dimension separation the pair of opposing endless metal belts defines a molding zone;

(b) an electromagnetic edge containment apparatus positioned on each side of the molding zone comprising an induction coil wound about a portion of a magnetic member to generate magnetic lines of force upon application of a current, wherein the current provides magnetic lines of force that contain the molten metal within a width and in contact to at least a portion of said pair of opposing endless metal belts with substantially no increase in temperature to the molten metal; and (c) a means for supplying said molten metal to the molding zone along a horizontal axis from a tundish, the tundish separated from said molding zone by a distance to substantially eliminate wave generation within the tundish by the magnetic lines of force.

14. The apparatus of Claim 13, wherein the magnetic member comprises an upper pole and a lower pole, the induction coil wound about a portion of the magnetic member to generate magnetic lines of force passing from one of the upper and lower poles to the other, with the magnetic member being positioned such that the upper and lower poles direct magnetic lines of force establish containment forces at the edges of the pair of opposing endless metal belts to contain the molten metal therebetween.

15. The apparatus of Claim 13, wherein the vertical distance separating the pair of opposing endless metal belts provides a metal head height that allows for containment of the molten metal between the pair of opposing endless metal belts by the magnetic lines of force at said current without a substantially increase in temperature of the molten metal resulting from the magnetic lines of force.

16. The apparatus of Claim 13, wherein the minimum vertical distance separating the pair of opposing endless metal belts, at the nip of the caster, ranges from about 0.025" to 0.25".

17. The apparatus of Claim 13, wherein the magnetic member is positioned to the molding zone to position the magnetic lines of force to produce a convex sidewall, concave sidewall or substantially flat sidewall to the molten metal within the molding zone.

18. A cast metal strip comprising:
a first shell;

a second shell; and a central portion between said first shell and said second shell, said central portion comprising grains having an equiaxed structure, wherein said cast metal strip has sidewall edges being substantially uniform.

19. The cast metal strip of Claim 18 wherein said first shell is an upper shell and said second shell is a lower shell.

20. The cast metal strip of Claim 18, wherein said cast metal strip may be rolled without machining said sidewall edges.

21. The cast metal strip of Claim 18 comprising aluminum and other light metals such as magnesium and zinc.

22. The cast metal strip of Claim 18, wherein said equiaxed structure is substantially globular.

23. A casting apparatus comprising:

(a) a pair of casting rollers adapted to receive molten metal along a horizontal axis, wherein a vertical distance separating the pair of casting rollers defines a molding zone;

(b) a tip delivery structure positioned to supply the molten metal to the molding zone along said horizontal axis from a tundish while ensuring said molten metal remains substantially non-oxidized; and (c) an edge containment apparatus positioned on each side of the molding zone, said edge containment apparatus comprising:

a mechanical edge dam positioned overlying at least an end portion of said tip delivery structure and partially extending towards said molding zone, and an electromagnetic edge dam comprises a first and second magnetic pole positioned distal from and aligned to a sidewall of said pair of casting rollers and overlying a portion of said mechanical edge dam partially extending towards said molding zone, wherein said electromagnetic edge dain provides magnetic lines of force perpendicular to said horizontal axis that contain the molten metal in contact to the casting rollers.

24. The casting apparatus of Claim 23 wherein said tip delivery structure has a length that substantially eliminates wave generation within the tundish by the magnetic lines of force.

25. The casting apparatus of Claim 24 wherein said electromagnetic edge dain comprises an induction coil wound about a magnetic member to generate magnetic lines of force upon application of a current.

26. The casting apparatus of Claim 25 wherein said current provides magnetic lines of force that contain the molten metal in contact to the casting rollers with substantially no increase in temperature to the molten metal.

27. A method of forming a cast metal strip comprising providing molten metal to a molding zone along a horizontal axis;
containing said molten metal within said molding zone with a magnetic containment means; and casting said molten metal into a cast metal strip, wherein sidewall geometry of said cast metal strip is configured by adjusting said magnetic containment means.

28. The method of Claim 27 wherein said sidewall geometry is flat or is concave or convex relative to a centerline portion of said cast metal strip.

29. The method of Claim 28 wherein said magnetic containment means comprises an induction coil wound about a magnetic member to generate magnetic lines of force upon application of a current, said magnetic member having a first and second magnetic pole positioned distal from to adjacent to said molding zone.

30. The method of Claim 29 wherein said adjusting said magnetic containment means comprises increasing or decreasing said current through said induction coil.

31. The method of Claim 29 wherein said adjusting said magnetic containment means comprises moving said first and second magnetic poles adjacent to or distal from said molding zone.