CA2084206C - Sidewall containment of liquid metal with horizontal alternating magnetic fields - Google Patents
Sidewall containment of liquid metal with horizontal alternating magnetic fieldsInfo
- Publication number
- CA2084206C CA2084206C CA 2084206 CA2084206A CA2084206C CA 2084206 C CA2084206 C CA 2084206C CA 2084206 CA2084206 CA 2084206 CA 2084206 A CA2084206 A CA 2084206A CA 2084206 C CA2084206 C CA 2084206C
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- rim
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- Continuous Casting (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Coating With Molten Metal (AREA)
Abstract
An apparatus for confining molten metal (12) with a horizontal alternating magne tic field. In particular, this invention employs a magnet (24) that can produce a horizontal alternating magnetic field t o confine a molten metal (12) at the edges (30a, 30b) of parallel horizontal rollers (10a, 10b) as a solid metal sheet (18) is cast by counter-rotation of the rollers (10a, 10b).
Description
,~ .
2~20 6 SIDEWALL CONTAINMENT OF LI~UID METAL WITH HORIZONTAL ALTERNATING
MAGNETIC FIELDS
CONTRACTUAL ORIGIN OF THE INVENTION
The United States Government has rights in this invention under Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and the University of Chicago, operator of Argonne National Laboratory.
BACKGROUND OF THE INVENTION
This invention relates generally to the casting of metal sheets and is particularly directed to the ~
vertical casting of metal sheets between counter rotating rollers.
Steel making occupies a central economic role and represents a significant fraction of the energy con-sumption of many industrialized nations. The bulk of steel making operations involves the production of steel plate and sheet. Present steel mill practice typically produces thin steel sheets by pouring liquid steel into a mold, whereupon the liquid steel solidifies upon contact with the cold mold surface. The solidified SU8srlTuTE SHEEr WO 91/18696 2 ~ ~ ~ 2 o ~ PCI/US90/03243 _.
r ' . - 2 -steel leaves the mold either as an ingot or as a continuous slab after it is cooled typically by water circulating within the mold wall during a solidification process. In either case, the solid steel is relatively thick, e.g., 6 inches or greater, and must be subsequently processed to reduce the thickness to the desired value and to improve metallurgical properties.
The mold-formed steel is usually characterized by a surface roughened by defects, such as cold folds, lo liq~lation, hot tears and the like which result primarily from contact between the mold and the solidifying metallic shell. In addition, the steel ingot or sheet thus cast also frequently exhibits considerable alloy segregation in its surface zone due to the initial cooling of the metal surface from the direct application of a coolant. Subsequent fabrication steps, such as rolling, extruding, forging and the like, usually require the scalping of the ingot or sheet prior to working to remove both the surface defects as well as 20 the alloy deficient zone adjacent to its surface. These additional steps, of course, increase the comple~ity and e~pense of steel production.
Steel sheet thickness reduction is accomplished by a rolling mill which is very capital intensive and consumes large amounts of energy. The rolling process SUeSTlTUTE SHEET
WO91/1~96 2 0 8 4 2 0 6 PCT/US~/03~3 , - 3 -therefore contributes substant~ally to the cost of the steel sheet. In a typical installat~on, a 10 inch thick steel slab must be manipulated by at least ten rolling machines to reduce lts thickness. The rolling mill may extend as much as one-half mile and cost as much as SS00 milllon.
Compared to current practice, a large reduct~on in steel sheet total cost and in the energy required for its production could be achieved $f the sheets could be cast ~n near net shape, i.e. in shape and size closely appro%imating the final desired product. This would reduce the rolling mill operation and would result in a large savings in energy. There are several technologies currently under development which attempt to achieve these advantages by forming the steel sheets in the casti~ ~rocess.
One approach under consideration by the steel industry to reduce processing involves roller casting of sheets of steel. This method was originally con-ceived by ~. Bessemer over 100 years ago as describedin British patent nos. 11,317 (1847) and 49,053 ~1857) and a paper to the Iron and Steel Institute, U.R.
(October 1891). Th~s roller casting method produces steel sheets by pouring molten steel between counter rotatinq twin-rollers. The rollers are separated by a .~
20~4206 ~_ - 4 gap. Rotation of the rollers forces the molten metal through the gap between the rollers. Mechanical seals are necessary to contain the molten metal at the edges of the rollers. The rollers are made from a metal with high thermal conductivity, such as copper or copper alloys and water-cooled in order to solidify the skin of the molten metal before it leaves the gap between the rollers. The metal leaves the rollers in the form of a strip or sheet. This sheet can be further cooled by water or other suitable means via jets. This method has the drawback that the mechanical seals used to contain the molten metal at the roller edges are in physical contact with both the rotating rollers and molten metal and therefore subject to water, leaking, clogging, freezing and large thermal gradients. Furthermore, contact between the mechanical seals and the solidifying metal can cause irregularities along the edges of sheets cast in this manner thereby offsetting the advantages of the roller method.
Accordingly, of the present invention seeks to provide an improved method, apparatus and arrangement for casting thin metal sheets.
Further the present invention seeks to produce thin metal sheets which require little or no subsequent rolling after the sheet is cast.
The invention further seeks to provide for continuous roller casting of metal sheets.
Further still, this invention seeks to provide containment of a pool of molten metal between twin-roller casters, without sidewalls that make physical contact with the rollers and to prevent a pool of molten metal from flowing out the ends of ~ ~ 2~8420~
counter rotating rollers by means of a shaped horizontal alternating magnetic field.
Still further, this invention seeks to provide an electromagnetic stopper or seal that is capable of preventing or regulating the flow of a molten metal in a horizontal direction.
SUMMARY OF THE INVENTION
The present invention provides for confinement of molten metal with a horizontal alternating magnetic field. In particular, this invention employs a magnet that can produce a horizontal alternating magnetic field to confine a molten metal at the edges of parallel horizontal rollers as a solid metal sheet is cast by counter-rotation of the rollers.
The invention provides an apparatus for confining molten metal comprising containment means having an open side, a magnet capable of generating a mainly horizontal alternating magnetic field, the magnet located adjacent to the open side of the containment means whereby the field generated by the magnet is capable of inducing eddy currents in a thin layer at the surface of the molten metal which interact with the magnetic field producing a force that can contain the molten metal within the containment means. The magnet includes ma~netic poles located adjacent to the open side of the confinement means, a core connecting the poles, a coil encircling the core, the coil capable of being responsive to a current source, whereby an alternating magnetic field can be generated between the poles and parallel to the open side of the containment means so that a molten metal can be confined within the confinement means.
Another aspect of the invention comprehends an apparatus for ~.~.
' - 6 - 2~2~
confining molten metal comprising containment means having an open side comprising a pair of rollers, each of the rollers including a middle portion and a rim portion, wherein the rollers are parallel and adjacent to each other in a horizontal plane and further wherein the rollers are separated by a gap, whereby counter rotation of the rollers can force the flow of a molten metal between the gap between the rollers. A magnet is located adjacent to the open side of the containment means comprised of magnetic poles located adjacent to the open side of the containment means and extending axially into the ends of the rollers, a core connects the magnetic poles and a coil encircling the core, the coil capable of being responsive to a current source. An alternating magnetic field can be generated between the poles and parallel to the open side of the containment means so that a molten metal can be confined within the containment means. The middle portions of the rollers have a resistivity lower than the rim portions so that transmission of a magnetic field by the magnet through the middle portion is less than through the rim portion.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a cross sectional front view of the present invention.
Figure lb is a sectional view of a segment of the roller in Figure la.
Figure 2 is a view along section line 2 - 2' of Figure la.
Figure 3 is a view along section line 3 - 3' of Figure la.
Figure 4 is a cross sectional view of the core as depicted ~, along section line 4 - 4' of Figure 2.
WO9l/1~96 PCT/US90/03~3 _7_ 2 ~ ~2 0~
Figure 5 is a perspective view of the magnet and coil of one embodiment of this invention.
Figure 6 is a perspective view of another embodiment of the magnet and coil of this invention.
Figure 7 is a cross section of the yoke as depicted in Figure 6.
Figure 8 is a perspective view of another embodiment of the magnet core of this invention.
Figure 9 is a front sectional vertical front view of lo another embodiment of this invention.
Figure 10 is a vertical sectional front view of still another embodiment of the magnet of this invention and a sideview of the rollers.
Figure 11 is a horizontal sectional view of another embodiment of this invention.
Figure 12a is a front view of a portion of another embodiment of the roller rim of this invention.
Figure 12b is a top view of the embodiment of the roller rim of this invention as depicted in Figure 12a.
Figure 13a is a view of a portion of a roller showing another embodiment of the roller rim of this invention.
Figure 13b is a sectional view along line 13b-13b' of Figure 10.
Figure 14 is a side view of another embodiment of this invention.
SU~S I I I UTE SHEET
WO9l/1~96 PCT/US90/03~3 - 8 - _ Figure lSa is a side view of still another embodi-~Q ment of this invention.
Figure 15b is a horizontal view along line 15b-lSb' of Figure 15a.
DETAILED DESC~IPTION OF THE INVENTION
The present invention overcomes the problems of roller casting with a novel design which features electromagnetic containment of the liquid metal at the roller edges in place of mechanical seals thereby overcoming the problems associated with mechanical seals. The present invention provides a shaped hori-zontal alternating magnetic field to confine a pool of molten metal between the cylindrical surfaces of a pair of rollers as the molten metal is cast into a thin vertical sheet by counter rotation of the rollers which force the molten metal between them. The horizontal alternating magnetic field of the present invention can also be used to prevent or regulate the flow of molten metal from weirs or orifices of other geometries. The pressure, p, exerted by the molten pool of metal consists essentially of ferrostatic pressure Ph and pressure Pr induced by the rollers via the solidifying metal to be cast p s Ph + Pr . (1) The magnetic pressure, Pm, exerted by the hor-zontal alternating magnetic field, B, must balance the pressure WO91/1~96 ~ PCT/US90/03243 - _ 9 ~
from the top of the metal pool to the region where the shell of the metal has solidified sufficiently thick to withstand the pressure. The magnetic pressure is given by p = B2/ ~ (2) where the constant ~ O is the permeability of free space.
The ferrostatic pressure Ph exerted by the molten pool of metal increases linearly with increasing down-ward distance h from the surface of the pool Ph = 9~ h (3) where ~ is the density of the metal and g is the acceler-ation of gravity. The magnetic field required to con-tain the ferrostatic pressure can be found by equating the magnetic and ferrostatic pressure, B = (2~ o g ~ h)l/2 = khl/2 (4 For casting steel k is approximately 4~0 if h is measured in cm and B in gauss.
The roller induced pressure Pr depends on the pro-perties of the metal being cast, the roller diameter and speed and the thickness of the metal strip or sheet being cast. In case of steel sheets, it is estimated that Pr can be many times larger than the hydrostatic pressure Ph-The frequency of the alternating magnetic fieldchosen is as low as practicable consistent with the WO91/18696 PCT/US90/03~3 ~Q distance between the rollers and the distance between the end of the rollers, typically between 39 Hz and 16,000 Hz.
Figure la depicts a cross sectional view of the roller casting arrangement of the present invention. A
pair of rollers lOa and lOb (referred to collectively as rollers 10) are parallel and adjacent to each other and lie in a horizontal plane so that a molten metal 12 can be contained between them above the point where the lo rollers are closest together. Rollers 10 are separated by a gap, d (shown in Figure 2). Counter rotation of rollers lOa and lOb (in the direction shown by the arrows lla and llb), operating with gravity, forces the molten metal 12 to flow through the gap d between the rollers 10 and out the bottom.
Magnetic poles 16a and 16b located on both sides of the gap d between rollers lOa and lOb generate an alternating magnetic field which exerts an electromagnetic inward force that prevents the molten liquid 12 from flowing out the sides at the edges of the rollers lOa and lOb. Throughout this application references will be made to confinement at one end of a pair of rollers. It should be understood that confinement of molten metal between a pair of counter rotating rollers as provided by the present invention will be used at both ends of the pair of rollers.
SU~STIT~ITE SHE~T
WO91/1~96 ~ 0 ~ 4 ~ ~ ~ PCT/US90/03243 Rollers 10 include a cooling means to cool and thereby solidify the molten metal by conduction as it passes between rollers 10. Referring to Figure lb, the cooling means may comprise a plurality of circulating water-cooled channels 13 located inside the surface wall of the roller. Referring again to Figure la, after emerging from rollers 10, the metal has solidified into a sheet 18 hav~ng a thickness equal to the gap, d, between the rollers 10. Jets 22 located below the 10 rollers further cool the cast metal sheet by spraying a coolant (such as water or air) on it. The cast metal sheet is guided, supported and carried away from the rollers by mechanical guides 23.
Referring to Figure 2, there is depicted a hori-zontal sectional view of the invention along section line 2-2' of Figure la. Figure 2 depicts the arrange-ment of magnetic poles with respect to the rollers.
Rollers lOa and lOb are separated by a gap, d, through which the metal being cast 18 can pass. Magnet 24 is 20 comprised of a yoke 26 and poles 16a and 16b. Coils 28a and 28b wind around the magnet. Coils 28a and 28b carry an electric current supplied by an alternating current source thereby magnetizing the magnet 24 and inducing a magnetic field between poles 16a and 16b.
The major portions of magnetic poles 16a and 16b are WO91/1~96 PCT/US90/03243 ., located inside the outer edges 30a and 30b of the rollers. The magnetic pol~s 16a and 16b are stationary and radially separated from the rollers lOa and lOb by a space clearance large enough to allow free rotat~on of the rollers 10. The poles 16 extend axially into the ends of the rollers 10 a short d~stance.
The cylindr~cal surfaces of rollers 10 have a middle middle portion 32 which comes in contact with the molten metal. The middle portions 32 are constructed of a materlal which has high thermal conductivity so that a cooling means, used in conjunction with the rollers, can remove heat from the molten metal thereby facilit-ating the casting process. In the present embodiment, the cooling means used in conjunction with the rollers comprises water cooled channels 13 in the interior of rollers 10 as shown in Figure lb. In this embodiment, the middle portions 32 of rollers 10 are made of copper alloy.
The rollers 10 also have outer rims 34a and 34b which form extensions of middle portions 32 of rollers 10. Rims 34 are located in the area between the mag-netic poles 16. Poles 16 generate a magnetic field that penetrates through the rims 34 of rollers 10 in this embodiment. Therefore, for this embodiment rims 34 must be made of a material suitable for the transmis-WO91/18696 2 ~ PCT/US90/03243 s~on of a magnetic field. In this embodiment of the present invention, the rims are made of stainless steel.
The resistivity of stainless steel (approximately 75 micro-ohm-cm at room temperature) matches reasonably the resistivity of molten steel ~approximately 140 micro-ohm-cm); therefore, the horizontal magnetic flux can penetrate both metals. ~ue to eddy currents in the molten metal, the field decays exponentially as the axial distance, z, from the edge of the pool increases.
Therefore, a magnet force Fl at the pool edge is larger than the oppositely directed force F2 further into the pool, as shown in Figure 3, resulting in a net containing force F
F = 1~ oJzl 3 ~B dz. (5) As a result, the molten metal can be contained between the rollers.
Referring again to Figure 2, the edges 30 of rollers 10 are curved and tapered on their interior portions to accomodate the magnetic poles 16. Likewise poles 16 generally conform in shape to the exterior portion of the rollers 10. Shield 33 encloses yoke 26 and portions of poles 16 except ~or the pole ends.
Yoke 26 may be made of a laminated core. Shield 33 encloses the core 26 without forming an electrically WO91/18696 PCT/US90/03~3 ili:9 shorted turn as ~llustrated by Figure 4. The shield 33 may be formed by two U-channels 33a and 33b made from copper sheets and insulated from each other by at least one gap 35. Shield 33 should be made of a material with low resistivity to prevent transmission of a mag-netic field by means of eddy current shielding and thereby serve to reduce flux leakage, enhance shaping the magnetic field and improve circuit efficiency.
Shield 33 may also serve as a heat shield for the mag-net and may be water cooled for th~s purpose. A materialwith low resistivity and high thermal conductivity, such as copper or copper alloy, is ideal for use as shield 33.
Referring to Figure 3, there is depicted a hor$-zontal cross section of the present invention as viewed along section line 3-3' of Figure la. Figure 3 depicts a section between the rollers at a point dispiaced vertically from the horizontal axes of the rollers 10.
Figure 3 shows containment of the molten metal 12 by the rollers 10 and the interaction of magnetic field, B, and eddy currents i. Figure 3 depicts rollers 10 having middle portion 32 and rims 34. Also shown in Figure 3 is the magnet 24 having a yoke 26, poles 16 coil 28 and shield 33.
Figure 3 also depicts molten metal 12 retained between the ends of rollers 10 by the magnet field, B
WO9l/18696 2 ~ PCT/US90/03243 (shown as the dashed lines), between poles 16. The magnetic field, 8, causes eddy currents, ~, in the molten metal, indicated by arrow heads out oE the page and arrow ta$1s into the page, and a resultant electro-magnetic force, F, directed toward the interior of the pool to contain the molten metal. The containment forces, F, are due to the interaction of the horizontal field, B, with the eddy currents, i, in the molten metal, induced in the molten metal by the magnetic f~eld, B.
In the present invention, a number of different magnet and coil geometries can be employed to adapt to particular requirements of the casting process. Figure 5 is an perspective view of the magnet 24 and coil 28 as depicted in Figures 1-4. The magnet has laminated yoke 26 and po es 16a and 16b. The poles 16 are arced in shape and may conform to the shape of the interior portions of rollers 10. The coil compr.ses a coil pair 28a and 28b which encircle laminated core portions 40a and 40b of magnet 24. Coils 28 are connected to an alternating current supply 36 which prov-des an alter-na-ting current, Is, which energizes the magnet 24. The pair of coils may be connected in ser~es to the current source or in parallel depending upon design considerations.
For simplicity, the eddy current shield around the magnet ~s not shown.
WO91/18696 PCT/US90/03~3 ~ - 16 -~, Another embodiment of the magnet and coil is depicted in Figure 6. In this embodiment, the magnet 42 has a square shaped core 44 connecting poles 46a and 46b. Poles 46a and 46b in this embodiment have shaped pole faces 48a and 48b but squared off backs 50 to con-form to the square shape of the core 44. As illustrated by the cutaway view of pole 46b, an insulated copper shield 51 encloses the core to reduce leakaqe flux. A
gap 52 in the shield 51 prevents the shield from being a shorted turn around the magnet core. Coil 60 encircles core 44 and shield 51. In this embodiment, the coil 60 is a single layer coil instead of a coil pair as in the previous embodiment. Coil 60 is connected to a alter-nating current supply 36 which provides an alternating current, Is~ whtch energizes the magnet 42. The leakage flux could be reduced further by also enclosing the coil 60 with a copper shield 53a and 53b as depicted in Figure 7. This additional shield 53a and 53b would reduce the cross sectional area available in the air space for the leakage flux around the coil windings and thereby reduce such leakage flux. In still another embodiment, the inner shield 51 could be deleted and the core and coil assembly enclosed by only an outer shield 53. --Figure 8 depicts another varia_ion of the magnet used in the present invention. In this embodiment, WO91/18696 2 ~ 8 ~ 2 ~ ~ PCT/US90/03~3 magnet 54 has a generally truncated trapezoidal shaped core with rectangular flat arms 55 connecting the trapezoidal yoke 56 to the poles 57a and 57b. Similar to the magnet design in Figure 5, this magnet may have the advantage of being simpler to construct.
A further modification to the magnet is depicted in Figure 9. In Figure 9, a molten liquid 12 is being cast into a sheet 18 between rollers lO. As in the previous embodiments, magnet poles 59a and 59b confine the molten metal at the edges of the rollers lO. In this embodiment, the magnetic poles 59 are adjustable in position. The poles 59a and 59b can be slanted and moved to be closer to or further away from the roller rims. This feature enables adjustment of the magnetic field. As depicted in Figure 9, the upper parts of the poles 59 have been moved further away from the roller rims as compared to the bottom part of the poles. As shown by the dashed lines representing the magnetic field B in Figure 9, with the top ends of poles 59 further apart, the magnetic field can be made relatively stronger near the lower end and weaker at the higher end as compared to the pole configuration shown in Figure la. This adjustability can be utilized for casting metal sheets of different thickness where different forces of confinement may be necessary.
SUB~ ~ EET
WO9l/18696 PCT/US90/03243 Figure 10 shows still another variation of the G~
magnet in the present invention. This variation offers the most fle~ibility of any of the designs shown so far. (Figure 10 depicts just one magnet pole; it should be understood that 'an identical pole would be positioned opposite this pole in the other roller.) In Figure 10, each magnet pole is divided into three discreet separate magnetic elements 61a, 61b, and 61c. Each of these elements is an independent magnet comprising cores 62, excitation coils 63, and eddy-current-shields 33, which enclose their respective coils and cores, except for an air gap which prevents the shields f rom becoming a shorted turn such as dep-cted in Figures 4 or 7. Magnetic element 61a contains the upper portion of the sidewall of the molten metal pool 12, element 61b contains the center of the pool sidewail and element 61c contains the lower portion of the pool sidewall.
In this embod~ment, each individual discreet mag-netic element is individually controlled and provided with individual currents, Isa, Isb, and IsC~ These three magnetic elements may be energized from a single alternating current power source 64 or from three ind~vidual power sources. W~th a single power source, two variable reactors would be connected in series with the coils of two of the three magnetic elements in order that the magnetic f~elds of the three magnetic WO91~18696 ~ PCT/US90/03243 elements can be adjusted independently; the time constant (L/R) of the reactors is designed to be the same as the time constant of the magnets in order that the flux generated by the three independent magnets is in phase. With three independent power sources, care must be taken that the three sources have the correct phase relation. Because each element can be individually adjusted there is provided a high degree of adjustability for the total magnetic field as well.
lo This adjustability can be utilized to optimize operation under varying conditions, such as with different sheet thicknesses, different molten metals or alloys, different temperature conditions, start-up and shut-down.
Feedback loops can utilize sensors 65 to monitor the position of the upper, middle and lower portions of the electromagnetically contained sidewall. Any deviation from a present position will produce an error signal which, after suitable amplification, will change the power supplied to the respective magnetic elements in order to restore the preset containment position of the respective sidewall portion. These sensors may take the form of discreet beams (rays) that are transmitted parallel to the sidewall from one side and detected by a receiver on the other side (the beam being interrupted when the sidewall moves closer to the magnet).
Alternately, the sensors may take the form of SUEtSTITU ~ E ~- ET
WO 91/18696 ~ PCT/US90/03243 '~
discreet beams that are transmitted normal to the side-wall and their reflection from the surface of the side-wall being detected by a receiver and used to determine the posltion of the sidewall. The sensors ~ay take the form of variable capacitors where the monitored sidewall portion is one electrode of the capacitor and the other is a suitable electrode mounted a fixed distance and in parallel to the sidewall. In a still further alternative, the sensor may take the form of an impedance measurement of the magnet excitation which changes with the flux linkage between the magnet and the liquid metal of the respective sidewall portion.
A st~ll further embodiment of the magnet desisn is depicted on Figure ll. Figure ll depicts a horizontal sectional view of one end of one roller pair. In this embodiment the pole assemblies 66a and 66b are hoop-shaped and contained inside and attached to the rollers lOa and lOb behind rims 34a and 34b, respectively.
Accordingly, poles 66 will rotate with rims 34 and rollers lO. Port~on 68 of shield 69 is located between core sections 72a and 72b and close to the area where the casting takes place. Poles 66a and 66b are circular and made of a ferromagnetic material. The coil 60 magnetizes yoke 70 and magnet a-rms 72a and 72b as in the previous embodiments. Eddy current shields 69 and 79 confine the magnetic flux to the yoke 70, magnet WO91/18696 ~ ~ ~ 4 ~ ~ ~ PCT/US90/03243 arms 72 and poles 66 (reducing leakage flux) as described earlier. Shields 69 and 79 may also incorporate heat shielding or cooling means to protect the coil or the magnet. Poles 66a and 66b though separated from magnet arms 72a and 72b and rotating with rollers lOa and lOb, are magnetized by the~r close proximity to arms 72a and 72b via relatively small gaps 74a and 74b. This embodi-ment has the advantage that the poles can be located as close together as physically possible, i.e. inside the rims. This design simplifies the shape of the magnet yoke and permits the use of different magnet yokes and coils when the assembly of rollers 10 and poles 66 is used to cast different thicknesses of metal sheets.
Casting sheets, i.e. 0.4~ thick would utilize a more powerful magnet assembly than casting 0.04~ thick metal sheets.
As described previously and shown in ~ sures 2, 3, and 11, the magnetic f~eld penetrates through the outer rim portion of the rollers to confine the molten metal.
The present invention can also be practiced without a special rim portion provided a suitable material is used for the rollers, such as a ceramic, which enables penetration by a magnetic field without generating eddy - currents in the roller. However, in the preferred embodiment, use of a r~m portion on the rollers provides WO91/18696 PCT/US90/03~3 for shaping the maqnetic fie]d by establishing a well defined transition from the area of a high magnetic flux near the edge of the roller to an area of low magnetic flux further away from the roller's edge. Shaping the magnetic field in this manner provides the advantages of better control of the magnetic field that contains the sidewall of the molten pool of metal.
The present invention provides for shaping the magnetic field by using a material with a low resistivity, such as copper or copper alloy, for the main portion of the roller and a material with a higher resistivity for the rim portion. The copper or copper alloy used for the main portion will effectively prevent penetration of the magnetic field (except for a small negligible skin layer on the surface) and will, at the same time, cool the molten metal efficiently causing it to solidify.
In the rim portion of the roller, it is essential to allow penetration of the magnetic field to confine the sidewall of the molten metal between the two roller surfaces. The present invention includes several different embodiments of the rim portion designed to allow penetration of the magnetic field. In one embodiment, this is accomplished by connecting a rim made of a material with a much higher resistivity, such as stainless steel, to the edges of the copper rollers.
SUE~STITUTE SHEET
WO91/18696 - 23 - $ ~ ;~i ~ PCT/US90/03~3 , , Figures 2, 3 and 11 depict stainless steel rims 34 of this type. The stainless steel rims may be connected to the copper rollers by brazing, bolting or other suitable methods. In addition to allowing penetration of the magnetic field, the stainless steel rims provide a smooth surface for the casting surface in case the molten metal encroaches on the rim.
Another embodiment of the rim portion is depicted in Figures 12a and 12b. The roller 80 is made of a low o resistivity material such as copper. At the edges around the circumference of the rollers are a plurality of slots 82 all the way through the roller. The slots 82 extend a short distance, s, in the axial direction of the roller. The slots 82 permit the magnetic flux in the edge portion, or rims of the rollers, defined by the slots. Although the slots can be left empty, it is preferred that the slots be filled with a material of relatively high resistivity such as ceramic or stainless steel, which is insulated from the sides of the slots, or filled with a material of high magnetic permeability. Alternatively, the slot can be filled with laminations of high permeability metal which are insulated from each other and from the sides of the slots. Leaving the slots empty would require that the magnetic field is shaped such that the molten metal is kept away from the slots at all times. Filling the slots provides a smooth surface in case the molten metal encroaches on part of the rim during the casting process. Slot dimensions can be determined based upon the application. An advantage of the slotted copper SUB~i 111 ~JTg; SHEET
WO9l/1~96 PCT/US90/03~3 rim design is that it features a low reluctance path for the magnetic flux, i.e. the slots, filled with highly permeable material or with air, thereby enabling a high frequency alternating magnetic field. For example, whereas the roller design with stainless steel rims can operate at relatively low frequencies, e.g. up to 500 Hz, the roller design with slotted rims can operate with a much wider frequency range, e.g. up to at least 16 kHz.
Other embodiments of the rim portion are shown in Figures 13a and 13b. Figure 13b is a horizontal cross section along line 13b-13b~ of figure 10. The water-cooled rollers 10 are made of high thermal conductivity material such as copper. At the edges and around the circumference of the rollers are one or more hoop-shaped extensions 91 of rollers 10. Arranged between these hoop-shaped extensions 91 are similar hoop-shaped members 92 made of copper. These hoops, 91 and 92, are insulated from each other and mounted to the rollers 10 with bolts 93. The bolts 93 are insulated from the hoops to prevent electrical contact between the individual hoops and between the hoops and the roller.
The hoop-shaped extensions 91 serve the same purpose as the slots 82 in the previous embodiment, i.e. to transmit the magnetic field to the confinement region.
Extensions 91 can be made of similar materials as slots 82. Extensions 91 can be SUB~ ~ JTE S~IEET
WO91/1~96 2 Q ~ 4 2 ~ 6 ~ ; PCT/US90/03~3 made of an ~nsulating material, such as ceram~c, having a high resist~vity and relatively low permeability and, therefore, no eddy currents. Extensions 91 can be made of a non-magnetic, high res~stiYely metal, such as stainless steel, wh~ch also has relat~vely low perme-ab~1ity, but has h~gher thermal conductivity than ceramic. Alternately, extensions 91 can be made of a magnetic material, such as silicon steel, which has high magnetic permeabiltty and reasonable thermal conductivity. With a high permeability material the hoop-shaped extensions themselves become magnetized.
Thin insulated laminations of a ferromagnetic material could be used. W~th hoop-shaped extens~ons of stainless steel or ferromagnetic material, each hoop should be insulated from adjacent copper hoops. The alternating flux emanating from the magnet pole penetrates the roller through the hoops 91 and through the skin depth of the copper hoops 92. A portion of this flux ~nduces eddy currents in the molten metal 12 between the rollers.
The interaction between the flux and the eddy currents in the molten metal contains the sidewall of the molten metal pool between the rollers as described before.
The thickness of the hoop-shaped extensions 91, the - number of hoop-shaped extensions, the hoop-shaped extension material, and the magnet are designed to contain the sidewalls of the molten pool between the rollers. W~th the hoop-shaped extension made from highly permeable magnetic material, the electromagnetic conta~nment circult is most efficient. ~n this case the reluctance of the magnetic circuit is mainly deter-mined by the reluctance of the molten metal 12 and by the small air gap, 94, between hoops 91 and magnet pole 61c; all other designs have much larger air gaps and resultant larger leakage flux.
Another embodiment of this invention is shown in Figure 14. This embodiment of the invention may be used where conditions are such that the edge of the cast metal sheet is not fully solidified by the time it exits from between the rollers. This condition may occur for a number of reasons dictated by the casting process, such as the need for high magnetic fields of relatively high frequency resulting in large eddy current heating of the edges of the metal being cast, insufficient cooling effect of the rollers near the edges, thick cast sheet dimensions, or a combination of these or other factors. Figure 14 depicts the rollers 10 and molten metal 12 a5 in previous embodiments.
Figure 14 also shows poles 95a and 95b which extend below the center line of rollers 10. Th~s has the effect of also extending the magnetic field below the center l~ne of the rollers thereby extending the e~ec-tromagnetic containment of the edges.
WO9l/18696 PCT/US90/03~3 aos42~
Wheel induced forces on the liquid edge of the metal sheet vanish when the sheet leaves the rollers. Only gravitational forces act on the still molten edges which may be cooled by gas flow or by water spray. The magnetic forces between poles 95 decrease as the sheet moves further from the rollers; this is compatible with the solidifying edge as the sheet moves down. However, if the edge of the sheet is not quite solid near the end of the magnetic field between poles 95, further confinement of the still molten edges of the sheet can be provided by supplemental magnet with poles 96a and 96b which extend the magnetic field well below rollers 10 until the metal sheet is sufficiently hard enough to be supported by mechanical guides 23.
Another embodiment of this invention is depicted in Figures 15a and 15b. This embodiment presents a combination of a magnetic and mechanical means to contain a molten metal at the edges of a roller casting system. As mentioned above, the problem of using mechanical seals to contain a molten metal at the edges of counter-rotating casting rollers was that the mi~ture of the molten and solidifying metal in combination with the rotation of the rollers would clog up around the mechanical seals. As described above, the present invention shows how a magnetic field can be used to contain the sidewalls of the molten metal. The present SUBSTITUTE S~
WO91/18696 PCT/US90/03~3 embodiment uses both a mechanical seal and a magnet~'c field to advantage. As in previous embodiments, rolLers 10 and poles 16 contaln a molten metal 12. The present embodiment also includes a mechanical dam 100 positioned between poles 16a and 16b. Mechanical dam 100 is shaped so that it will contain the molten metal in that area wbere there is lit~le likelihood of clogging or deforming the cast sheet, i.e. away from the solidifying effects of the rollers. As depicted in Figures 15a and lSb, mechanical dam 100 is spaced away from rollers 10.
It is in the areas close to rollers 10 that the metal is solidifying and where the likelihood o~ clogging is greatest. Magnetic confinement with the poles 16 is used to confine the molten and solidifying metal in the gaps between the mechanical dam 100 and rollers 10.
Mechanical dam 100 may be made of a ferromagnetic material 101 so that it provides a low reluctance path for the flux between the poles 16. The side of the dam facing the molten metal pool may be made of a layer of high temperature ceramic 102 covering a water cooled heat shield 103 in front of the high permeability material which may be made from steel laminations or from high temperature ferrite. This embodiment has the advantage of requiring less energy than the previous embodiments because the magnetic field along the molten metal extends only over the gaps between the rollers 16 and WO91/18696 2 ~ ~ 4 2 ~ ~ PCT/US90/03243 ~_ - 29 -mechanical dam 100. Also, because the volume of the molten metal contained by the magnetic field is sma;ler, there is less heating of the molten metal due to eddy currents. Various mechanical dam shapes can be designed for shaping flux density suitable for different castinq requirements.
MAGNETIC FIELDS
CONTRACTUAL ORIGIN OF THE INVENTION
The United States Government has rights in this invention under Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and the University of Chicago, operator of Argonne National Laboratory.
BACKGROUND OF THE INVENTION
This invention relates generally to the casting of metal sheets and is particularly directed to the ~
vertical casting of metal sheets between counter rotating rollers.
Steel making occupies a central economic role and represents a significant fraction of the energy con-sumption of many industrialized nations. The bulk of steel making operations involves the production of steel plate and sheet. Present steel mill practice typically produces thin steel sheets by pouring liquid steel into a mold, whereupon the liquid steel solidifies upon contact with the cold mold surface. The solidified SU8srlTuTE SHEEr WO 91/18696 2 ~ ~ ~ 2 o ~ PCI/US90/03243 _.
r ' . - 2 -steel leaves the mold either as an ingot or as a continuous slab after it is cooled typically by water circulating within the mold wall during a solidification process. In either case, the solid steel is relatively thick, e.g., 6 inches or greater, and must be subsequently processed to reduce the thickness to the desired value and to improve metallurgical properties.
The mold-formed steel is usually characterized by a surface roughened by defects, such as cold folds, lo liq~lation, hot tears and the like which result primarily from contact between the mold and the solidifying metallic shell. In addition, the steel ingot or sheet thus cast also frequently exhibits considerable alloy segregation in its surface zone due to the initial cooling of the metal surface from the direct application of a coolant. Subsequent fabrication steps, such as rolling, extruding, forging and the like, usually require the scalping of the ingot or sheet prior to working to remove both the surface defects as well as 20 the alloy deficient zone adjacent to its surface. These additional steps, of course, increase the comple~ity and e~pense of steel production.
Steel sheet thickness reduction is accomplished by a rolling mill which is very capital intensive and consumes large amounts of energy. The rolling process SUeSTlTUTE SHEET
WO91/1~96 2 0 8 4 2 0 6 PCT/US~/03~3 , - 3 -therefore contributes substant~ally to the cost of the steel sheet. In a typical installat~on, a 10 inch thick steel slab must be manipulated by at least ten rolling machines to reduce lts thickness. The rolling mill may extend as much as one-half mile and cost as much as SS00 milllon.
Compared to current practice, a large reduct~on in steel sheet total cost and in the energy required for its production could be achieved $f the sheets could be cast ~n near net shape, i.e. in shape and size closely appro%imating the final desired product. This would reduce the rolling mill operation and would result in a large savings in energy. There are several technologies currently under development which attempt to achieve these advantages by forming the steel sheets in the casti~ ~rocess.
One approach under consideration by the steel industry to reduce processing involves roller casting of sheets of steel. This method was originally con-ceived by ~. Bessemer over 100 years ago as describedin British patent nos. 11,317 (1847) and 49,053 ~1857) and a paper to the Iron and Steel Institute, U.R.
(October 1891). Th~s roller casting method produces steel sheets by pouring molten steel between counter rotatinq twin-rollers. The rollers are separated by a .~
20~4206 ~_ - 4 gap. Rotation of the rollers forces the molten metal through the gap between the rollers. Mechanical seals are necessary to contain the molten metal at the edges of the rollers. The rollers are made from a metal with high thermal conductivity, such as copper or copper alloys and water-cooled in order to solidify the skin of the molten metal before it leaves the gap between the rollers. The metal leaves the rollers in the form of a strip or sheet. This sheet can be further cooled by water or other suitable means via jets. This method has the drawback that the mechanical seals used to contain the molten metal at the roller edges are in physical contact with both the rotating rollers and molten metal and therefore subject to water, leaking, clogging, freezing and large thermal gradients. Furthermore, contact between the mechanical seals and the solidifying metal can cause irregularities along the edges of sheets cast in this manner thereby offsetting the advantages of the roller method.
Accordingly, of the present invention seeks to provide an improved method, apparatus and arrangement for casting thin metal sheets.
Further the present invention seeks to produce thin metal sheets which require little or no subsequent rolling after the sheet is cast.
The invention further seeks to provide for continuous roller casting of metal sheets.
Further still, this invention seeks to provide containment of a pool of molten metal between twin-roller casters, without sidewalls that make physical contact with the rollers and to prevent a pool of molten metal from flowing out the ends of ~ ~ 2~8420~
counter rotating rollers by means of a shaped horizontal alternating magnetic field.
Still further, this invention seeks to provide an electromagnetic stopper or seal that is capable of preventing or regulating the flow of a molten metal in a horizontal direction.
SUMMARY OF THE INVENTION
The present invention provides for confinement of molten metal with a horizontal alternating magnetic field. In particular, this invention employs a magnet that can produce a horizontal alternating magnetic field to confine a molten metal at the edges of parallel horizontal rollers as a solid metal sheet is cast by counter-rotation of the rollers.
The invention provides an apparatus for confining molten metal comprising containment means having an open side, a magnet capable of generating a mainly horizontal alternating magnetic field, the magnet located adjacent to the open side of the containment means whereby the field generated by the magnet is capable of inducing eddy currents in a thin layer at the surface of the molten metal which interact with the magnetic field producing a force that can contain the molten metal within the containment means. The magnet includes ma~netic poles located adjacent to the open side of the confinement means, a core connecting the poles, a coil encircling the core, the coil capable of being responsive to a current source, whereby an alternating magnetic field can be generated between the poles and parallel to the open side of the containment means so that a molten metal can be confined within the confinement means.
Another aspect of the invention comprehends an apparatus for ~.~.
' - 6 - 2~2~
confining molten metal comprising containment means having an open side comprising a pair of rollers, each of the rollers including a middle portion and a rim portion, wherein the rollers are parallel and adjacent to each other in a horizontal plane and further wherein the rollers are separated by a gap, whereby counter rotation of the rollers can force the flow of a molten metal between the gap between the rollers. A magnet is located adjacent to the open side of the containment means comprised of magnetic poles located adjacent to the open side of the containment means and extending axially into the ends of the rollers, a core connects the magnetic poles and a coil encircling the core, the coil capable of being responsive to a current source. An alternating magnetic field can be generated between the poles and parallel to the open side of the containment means so that a molten metal can be confined within the containment means. The middle portions of the rollers have a resistivity lower than the rim portions so that transmission of a magnetic field by the magnet through the middle portion is less than through the rim portion.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a cross sectional front view of the present invention.
Figure lb is a sectional view of a segment of the roller in Figure la.
Figure 2 is a view along section line 2 - 2' of Figure la.
Figure 3 is a view along section line 3 - 3' of Figure la.
Figure 4 is a cross sectional view of the core as depicted ~, along section line 4 - 4' of Figure 2.
WO9l/1~96 PCT/US90/03~3 _7_ 2 ~ ~2 0~
Figure 5 is a perspective view of the magnet and coil of one embodiment of this invention.
Figure 6 is a perspective view of another embodiment of the magnet and coil of this invention.
Figure 7 is a cross section of the yoke as depicted in Figure 6.
Figure 8 is a perspective view of another embodiment of the magnet core of this invention.
Figure 9 is a front sectional vertical front view of lo another embodiment of this invention.
Figure 10 is a vertical sectional front view of still another embodiment of the magnet of this invention and a sideview of the rollers.
Figure 11 is a horizontal sectional view of another embodiment of this invention.
Figure 12a is a front view of a portion of another embodiment of the roller rim of this invention.
Figure 12b is a top view of the embodiment of the roller rim of this invention as depicted in Figure 12a.
Figure 13a is a view of a portion of a roller showing another embodiment of the roller rim of this invention.
Figure 13b is a sectional view along line 13b-13b' of Figure 10.
Figure 14 is a side view of another embodiment of this invention.
SU~S I I I UTE SHEET
WO9l/1~96 PCT/US90/03~3 - 8 - _ Figure lSa is a side view of still another embodi-~Q ment of this invention.
Figure 15b is a horizontal view along line 15b-lSb' of Figure 15a.
DETAILED DESC~IPTION OF THE INVENTION
The present invention overcomes the problems of roller casting with a novel design which features electromagnetic containment of the liquid metal at the roller edges in place of mechanical seals thereby overcoming the problems associated with mechanical seals. The present invention provides a shaped hori-zontal alternating magnetic field to confine a pool of molten metal between the cylindrical surfaces of a pair of rollers as the molten metal is cast into a thin vertical sheet by counter rotation of the rollers which force the molten metal between them. The horizontal alternating magnetic field of the present invention can also be used to prevent or regulate the flow of molten metal from weirs or orifices of other geometries. The pressure, p, exerted by the molten pool of metal consists essentially of ferrostatic pressure Ph and pressure Pr induced by the rollers via the solidifying metal to be cast p s Ph + Pr . (1) The magnetic pressure, Pm, exerted by the hor-zontal alternating magnetic field, B, must balance the pressure WO91/1~96 ~ PCT/US90/03243 - _ 9 ~
from the top of the metal pool to the region where the shell of the metal has solidified sufficiently thick to withstand the pressure. The magnetic pressure is given by p = B2/ ~ (2) where the constant ~ O is the permeability of free space.
The ferrostatic pressure Ph exerted by the molten pool of metal increases linearly with increasing down-ward distance h from the surface of the pool Ph = 9~ h (3) where ~ is the density of the metal and g is the acceler-ation of gravity. The magnetic field required to con-tain the ferrostatic pressure can be found by equating the magnetic and ferrostatic pressure, B = (2~ o g ~ h)l/2 = khl/2 (4 For casting steel k is approximately 4~0 if h is measured in cm and B in gauss.
The roller induced pressure Pr depends on the pro-perties of the metal being cast, the roller diameter and speed and the thickness of the metal strip or sheet being cast. In case of steel sheets, it is estimated that Pr can be many times larger than the hydrostatic pressure Ph-The frequency of the alternating magnetic fieldchosen is as low as practicable consistent with the WO91/18696 PCT/US90/03~3 ~Q distance between the rollers and the distance between the end of the rollers, typically between 39 Hz and 16,000 Hz.
Figure la depicts a cross sectional view of the roller casting arrangement of the present invention. A
pair of rollers lOa and lOb (referred to collectively as rollers 10) are parallel and adjacent to each other and lie in a horizontal plane so that a molten metal 12 can be contained between them above the point where the lo rollers are closest together. Rollers 10 are separated by a gap, d (shown in Figure 2). Counter rotation of rollers lOa and lOb (in the direction shown by the arrows lla and llb), operating with gravity, forces the molten metal 12 to flow through the gap d between the rollers 10 and out the bottom.
Magnetic poles 16a and 16b located on both sides of the gap d between rollers lOa and lOb generate an alternating magnetic field which exerts an electromagnetic inward force that prevents the molten liquid 12 from flowing out the sides at the edges of the rollers lOa and lOb. Throughout this application references will be made to confinement at one end of a pair of rollers. It should be understood that confinement of molten metal between a pair of counter rotating rollers as provided by the present invention will be used at both ends of the pair of rollers.
SU~STIT~ITE SHE~T
WO91/1~96 ~ 0 ~ 4 ~ ~ ~ PCT/US90/03243 Rollers 10 include a cooling means to cool and thereby solidify the molten metal by conduction as it passes between rollers 10. Referring to Figure lb, the cooling means may comprise a plurality of circulating water-cooled channels 13 located inside the surface wall of the roller. Referring again to Figure la, after emerging from rollers 10, the metal has solidified into a sheet 18 hav~ng a thickness equal to the gap, d, between the rollers 10. Jets 22 located below the 10 rollers further cool the cast metal sheet by spraying a coolant (such as water or air) on it. The cast metal sheet is guided, supported and carried away from the rollers by mechanical guides 23.
Referring to Figure 2, there is depicted a hori-zontal sectional view of the invention along section line 2-2' of Figure la. Figure 2 depicts the arrange-ment of magnetic poles with respect to the rollers.
Rollers lOa and lOb are separated by a gap, d, through which the metal being cast 18 can pass. Magnet 24 is 20 comprised of a yoke 26 and poles 16a and 16b. Coils 28a and 28b wind around the magnet. Coils 28a and 28b carry an electric current supplied by an alternating current source thereby magnetizing the magnet 24 and inducing a magnetic field between poles 16a and 16b.
The major portions of magnetic poles 16a and 16b are WO91/1~96 PCT/US90/03243 ., located inside the outer edges 30a and 30b of the rollers. The magnetic pol~s 16a and 16b are stationary and radially separated from the rollers lOa and lOb by a space clearance large enough to allow free rotat~on of the rollers 10. The poles 16 extend axially into the ends of the rollers 10 a short d~stance.
The cylindr~cal surfaces of rollers 10 have a middle middle portion 32 which comes in contact with the molten metal. The middle portions 32 are constructed of a materlal which has high thermal conductivity so that a cooling means, used in conjunction with the rollers, can remove heat from the molten metal thereby facilit-ating the casting process. In the present embodiment, the cooling means used in conjunction with the rollers comprises water cooled channels 13 in the interior of rollers 10 as shown in Figure lb. In this embodiment, the middle portions 32 of rollers 10 are made of copper alloy.
The rollers 10 also have outer rims 34a and 34b which form extensions of middle portions 32 of rollers 10. Rims 34 are located in the area between the mag-netic poles 16. Poles 16 generate a magnetic field that penetrates through the rims 34 of rollers 10 in this embodiment. Therefore, for this embodiment rims 34 must be made of a material suitable for the transmis-WO91/18696 2 ~ PCT/US90/03243 s~on of a magnetic field. In this embodiment of the present invention, the rims are made of stainless steel.
The resistivity of stainless steel (approximately 75 micro-ohm-cm at room temperature) matches reasonably the resistivity of molten steel ~approximately 140 micro-ohm-cm); therefore, the horizontal magnetic flux can penetrate both metals. ~ue to eddy currents in the molten metal, the field decays exponentially as the axial distance, z, from the edge of the pool increases.
Therefore, a magnet force Fl at the pool edge is larger than the oppositely directed force F2 further into the pool, as shown in Figure 3, resulting in a net containing force F
F = 1~ oJzl 3 ~B dz. (5) As a result, the molten metal can be contained between the rollers.
Referring again to Figure 2, the edges 30 of rollers 10 are curved and tapered on their interior portions to accomodate the magnetic poles 16. Likewise poles 16 generally conform in shape to the exterior portion of the rollers 10. Shield 33 encloses yoke 26 and portions of poles 16 except ~or the pole ends.
Yoke 26 may be made of a laminated core. Shield 33 encloses the core 26 without forming an electrically WO91/18696 PCT/US90/03~3 ili:9 shorted turn as ~llustrated by Figure 4. The shield 33 may be formed by two U-channels 33a and 33b made from copper sheets and insulated from each other by at least one gap 35. Shield 33 should be made of a material with low resistivity to prevent transmission of a mag-netic field by means of eddy current shielding and thereby serve to reduce flux leakage, enhance shaping the magnetic field and improve circuit efficiency.
Shield 33 may also serve as a heat shield for the mag-net and may be water cooled for th~s purpose. A materialwith low resistivity and high thermal conductivity, such as copper or copper alloy, is ideal for use as shield 33.
Referring to Figure 3, there is depicted a hor$-zontal cross section of the present invention as viewed along section line 3-3' of Figure la. Figure 3 depicts a section between the rollers at a point dispiaced vertically from the horizontal axes of the rollers 10.
Figure 3 shows containment of the molten metal 12 by the rollers 10 and the interaction of magnetic field, B, and eddy currents i. Figure 3 depicts rollers 10 having middle portion 32 and rims 34. Also shown in Figure 3 is the magnet 24 having a yoke 26, poles 16 coil 28 and shield 33.
Figure 3 also depicts molten metal 12 retained between the ends of rollers 10 by the magnet field, B
WO9l/18696 2 ~ PCT/US90/03243 (shown as the dashed lines), between poles 16. The magnetic field, 8, causes eddy currents, ~, in the molten metal, indicated by arrow heads out oE the page and arrow ta$1s into the page, and a resultant electro-magnetic force, F, directed toward the interior of the pool to contain the molten metal. The containment forces, F, are due to the interaction of the horizontal field, B, with the eddy currents, i, in the molten metal, induced in the molten metal by the magnetic f~eld, B.
In the present invention, a number of different magnet and coil geometries can be employed to adapt to particular requirements of the casting process. Figure 5 is an perspective view of the magnet 24 and coil 28 as depicted in Figures 1-4. The magnet has laminated yoke 26 and po es 16a and 16b. The poles 16 are arced in shape and may conform to the shape of the interior portions of rollers 10. The coil compr.ses a coil pair 28a and 28b which encircle laminated core portions 40a and 40b of magnet 24. Coils 28 are connected to an alternating current supply 36 which prov-des an alter-na-ting current, Is, which energizes the magnet 24. The pair of coils may be connected in ser~es to the current source or in parallel depending upon design considerations.
For simplicity, the eddy current shield around the magnet ~s not shown.
WO91/18696 PCT/US90/03~3 ~ - 16 -~, Another embodiment of the magnet and coil is depicted in Figure 6. In this embodiment, the magnet 42 has a square shaped core 44 connecting poles 46a and 46b. Poles 46a and 46b in this embodiment have shaped pole faces 48a and 48b but squared off backs 50 to con-form to the square shape of the core 44. As illustrated by the cutaway view of pole 46b, an insulated copper shield 51 encloses the core to reduce leakaqe flux. A
gap 52 in the shield 51 prevents the shield from being a shorted turn around the magnet core. Coil 60 encircles core 44 and shield 51. In this embodiment, the coil 60 is a single layer coil instead of a coil pair as in the previous embodiment. Coil 60 is connected to a alter-nating current supply 36 which provides an alternating current, Is~ whtch energizes the magnet 42. The leakage flux could be reduced further by also enclosing the coil 60 with a copper shield 53a and 53b as depicted in Figure 7. This additional shield 53a and 53b would reduce the cross sectional area available in the air space for the leakage flux around the coil windings and thereby reduce such leakage flux. In still another embodiment, the inner shield 51 could be deleted and the core and coil assembly enclosed by only an outer shield 53. --Figure 8 depicts another varia_ion of the magnet used in the present invention. In this embodiment, WO91/18696 2 ~ 8 ~ 2 ~ ~ PCT/US90/03~3 magnet 54 has a generally truncated trapezoidal shaped core with rectangular flat arms 55 connecting the trapezoidal yoke 56 to the poles 57a and 57b. Similar to the magnet design in Figure 5, this magnet may have the advantage of being simpler to construct.
A further modification to the magnet is depicted in Figure 9. In Figure 9, a molten liquid 12 is being cast into a sheet 18 between rollers lO. As in the previous embodiments, magnet poles 59a and 59b confine the molten metal at the edges of the rollers lO. In this embodiment, the magnetic poles 59 are adjustable in position. The poles 59a and 59b can be slanted and moved to be closer to or further away from the roller rims. This feature enables adjustment of the magnetic field. As depicted in Figure 9, the upper parts of the poles 59 have been moved further away from the roller rims as compared to the bottom part of the poles. As shown by the dashed lines representing the magnetic field B in Figure 9, with the top ends of poles 59 further apart, the magnetic field can be made relatively stronger near the lower end and weaker at the higher end as compared to the pole configuration shown in Figure la. This adjustability can be utilized for casting metal sheets of different thickness where different forces of confinement may be necessary.
SUB~ ~ EET
WO9l/18696 PCT/US90/03243 Figure 10 shows still another variation of the G~
magnet in the present invention. This variation offers the most fle~ibility of any of the designs shown so far. (Figure 10 depicts just one magnet pole; it should be understood that 'an identical pole would be positioned opposite this pole in the other roller.) In Figure 10, each magnet pole is divided into three discreet separate magnetic elements 61a, 61b, and 61c. Each of these elements is an independent magnet comprising cores 62, excitation coils 63, and eddy-current-shields 33, which enclose their respective coils and cores, except for an air gap which prevents the shields f rom becoming a shorted turn such as dep-cted in Figures 4 or 7. Magnetic element 61a contains the upper portion of the sidewall of the molten metal pool 12, element 61b contains the center of the pool sidewail and element 61c contains the lower portion of the pool sidewall.
In this embod~ment, each individual discreet mag-netic element is individually controlled and provided with individual currents, Isa, Isb, and IsC~ These three magnetic elements may be energized from a single alternating current power source 64 or from three ind~vidual power sources. W~th a single power source, two variable reactors would be connected in series with the coils of two of the three magnetic elements in order that the magnetic f~elds of the three magnetic WO91~18696 ~ PCT/US90/03243 elements can be adjusted independently; the time constant (L/R) of the reactors is designed to be the same as the time constant of the magnets in order that the flux generated by the three independent magnets is in phase. With three independent power sources, care must be taken that the three sources have the correct phase relation. Because each element can be individually adjusted there is provided a high degree of adjustability for the total magnetic field as well.
lo This adjustability can be utilized to optimize operation under varying conditions, such as with different sheet thicknesses, different molten metals or alloys, different temperature conditions, start-up and shut-down.
Feedback loops can utilize sensors 65 to monitor the position of the upper, middle and lower portions of the electromagnetically contained sidewall. Any deviation from a present position will produce an error signal which, after suitable amplification, will change the power supplied to the respective magnetic elements in order to restore the preset containment position of the respective sidewall portion. These sensors may take the form of discreet beams (rays) that are transmitted parallel to the sidewall from one side and detected by a receiver on the other side (the beam being interrupted when the sidewall moves closer to the magnet).
Alternately, the sensors may take the form of SUEtSTITU ~ E ~- ET
WO 91/18696 ~ PCT/US90/03243 '~
discreet beams that are transmitted normal to the side-wall and their reflection from the surface of the side-wall being detected by a receiver and used to determine the posltion of the sidewall. The sensors ~ay take the form of variable capacitors where the monitored sidewall portion is one electrode of the capacitor and the other is a suitable electrode mounted a fixed distance and in parallel to the sidewall. In a still further alternative, the sensor may take the form of an impedance measurement of the magnet excitation which changes with the flux linkage between the magnet and the liquid metal of the respective sidewall portion.
A st~ll further embodiment of the magnet desisn is depicted on Figure ll. Figure ll depicts a horizontal sectional view of one end of one roller pair. In this embodiment the pole assemblies 66a and 66b are hoop-shaped and contained inside and attached to the rollers lOa and lOb behind rims 34a and 34b, respectively.
Accordingly, poles 66 will rotate with rims 34 and rollers lO. Port~on 68 of shield 69 is located between core sections 72a and 72b and close to the area where the casting takes place. Poles 66a and 66b are circular and made of a ferromagnetic material. The coil 60 magnetizes yoke 70 and magnet a-rms 72a and 72b as in the previous embodiments. Eddy current shields 69 and 79 confine the magnetic flux to the yoke 70, magnet WO91/18696 ~ ~ ~ 4 ~ ~ ~ PCT/US90/03243 arms 72 and poles 66 (reducing leakage flux) as described earlier. Shields 69 and 79 may also incorporate heat shielding or cooling means to protect the coil or the magnet. Poles 66a and 66b though separated from magnet arms 72a and 72b and rotating with rollers lOa and lOb, are magnetized by the~r close proximity to arms 72a and 72b via relatively small gaps 74a and 74b. This embodi-ment has the advantage that the poles can be located as close together as physically possible, i.e. inside the rims. This design simplifies the shape of the magnet yoke and permits the use of different magnet yokes and coils when the assembly of rollers 10 and poles 66 is used to cast different thicknesses of metal sheets.
Casting sheets, i.e. 0.4~ thick would utilize a more powerful magnet assembly than casting 0.04~ thick metal sheets.
As described previously and shown in ~ sures 2, 3, and 11, the magnetic f~eld penetrates through the outer rim portion of the rollers to confine the molten metal.
The present invention can also be practiced without a special rim portion provided a suitable material is used for the rollers, such as a ceramic, which enables penetration by a magnetic field without generating eddy - currents in the roller. However, in the preferred embodiment, use of a r~m portion on the rollers provides WO91/18696 PCT/US90/03~3 for shaping the maqnetic fie]d by establishing a well defined transition from the area of a high magnetic flux near the edge of the roller to an area of low magnetic flux further away from the roller's edge. Shaping the magnetic field in this manner provides the advantages of better control of the magnetic field that contains the sidewall of the molten pool of metal.
The present invention provides for shaping the magnetic field by using a material with a low resistivity, such as copper or copper alloy, for the main portion of the roller and a material with a higher resistivity for the rim portion. The copper or copper alloy used for the main portion will effectively prevent penetration of the magnetic field (except for a small negligible skin layer on the surface) and will, at the same time, cool the molten metal efficiently causing it to solidify.
In the rim portion of the roller, it is essential to allow penetration of the magnetic field to confine the sidewall of the molten metal between the two roller surfaces. The present invention includes several different embodiments of the rim portion designed to allow penetration of the magnetic field. In one embodiment, this is accomplished by connecting a rim made of a material with a much higher resistivity, such as stainless steel, to the edges of the copper rollers.
SUE~STITUTE SHEET
WO91/18696 - 23 - $ ~ ;~i ~ PCT/US90/03~3 , , Figures 2, 3 and 11 depict stainless steel rims 34 of this type. The stainless steel rims may be connected to the copper rollers by brazing, bolting or other suitable methods. In addition to allowing penetration of the magnetic field, the stainless steel rims provide a smooth surface for the casting surface in case the molten metal encroaches on the rim.
Another embodiment of the rim portion is depicted in Figures 12a and 12b. The roller 80 is made of a low o resistivity material such as copper. At the edges around the circumference of the rollers are a plurality of slots 82 all the way through the roller. The slots 82 extend a short distance, s, in the axial direction of the roller. The slots 82 permit the magnetic flux in the edge portion, or rims of the rollers, defined by the slots. Although the slots can be left empty, it is preferred that the slots be filled with a material of relatively high resistivity such as ceramic or stainless steel, which is insulated from the sides of the slots, or filled with a material of high magnetic permeability. Alternatively, the slot can be filled with laminations of high permeability metal which are insulated from each other and from the sides of the slots. Leaving the slots empty would require that the magnetic field is shaped such that the molten metal is kept away from the slots at all times. Filling the slots provides a smooth surface in case the molten metal encroaches on part of the rim during the casting process. Slot dimensions can be determined based upon the application. An advantage of the slotted copper SUB~i 111 ~JTg; SHEET
WO9l/1~96 PCT/US90/03~3 rim design is that it features a low reluctance path for the magnetic flux, i.e. the slots, filled with highly permeable material or with air, thereby enabling a high frequency alternating magnetic field. For example, whereas the roller design with stainless steel rims can operate at relatively low frequencies, e.g. up to 500 Hz, the roller design with slotted rims can operate with a much wider frequency range, e.g. up to at least 16 kHz.
Other embodiments of the rim portion are shown in Figures 13a and 13b. Figure 13b is a horizontal cross section along line 13b-13b~ of figure 10. The water-cooled rollers 10 are made of high thermal conductivity material such as copper. At the edges and around the circumference of the rollers are one or more hoop-shaped extensions 91 of rollers 10. Arranged between these hoop-shaped extensions 91 are similar hoop-shaped members 92 made of copper. These hoops, 91 and 92, are insulated from each other and mounted to the rollers 10 with bolts 93. The bolts 93 are insulated from the hoops to prevent electrical contact between the individual hoops and between the hoops and the roller.
The hoop-shaped extensions 91 serve the same purpose as the slots 82 in the previous embodiment, i.e. to transmit the magnetic field to the confinement region.
Extensions 91 can be made of similar materials as slots 82. Extensions 91 can be SUB~ ~ JTE S~IEET
WO91/1~96 2 Q ~ 4 2 ~ 6 ~ ; PCT/US90/03~3 made of an ~nsulating material, such as ceram~c, having a high resist~vity and relatively low permeability and, therefore, no eddy currents. Extensions 91 can be made of a non-magnetic, high res~stiYely metal, such as stainless steel, wh~ch also has relat~vely low perme-ab~1ity, but has h~gher thermal conductivity than ceramic. Alternately, extensions 91 can be made of a magnetic material, such as silicon steel, which has high magnetic permeabiltty and reasonable thermal conductivity. With a high permeability material the hoop-shaped extensions themselves become magnetized.
Thin insulated laminations of a ferromagnetic material could be used. W~th hoop-shaped extens~ons of stainless steel or ferromagnetic material, each hoop should be insulated from adjacent copper hoops. The alternating flux emanating from the magnet pole penetrates the roller through the hoops 91 and through the skin depth of the copper hoops 92. A portion of this flux ~nduces eddy currents in the molten metal 12 between the rollers.
The interaction between the flux and the eddy currents in the molten metal contains the sidewall of the molten metal pool between the rollers as described before.
The thickness of the hoop-shaped extensions 91, the - number of hoop-shaped extensions, the hoop-shaped extension material, and the magnet are designed to contain the sidewalls of the molten pool between the rollers. W~th the hoop-shaped extension made from highly permeable magnetic material, the electromagnetic conta~nment circult is most efficient. ~n this case the reluctance of the magnetic circuit is mainly deter-mined by the reluctance of the molten metal 12 and by the small air gap, 94, between hoops 91 and magnet pole 61c; all other designs have much larger air gaps and resultant larger leakage flux.
Another embodiment of this invention is shown in Figure 14. This embodiment of the invention may be used where conditions are such that the edge of the cast metal sheet is not fully solidified by the time it exits from between the rollers. This condition may occur for a number of reasons dictated by the casting process, such as the need for high magnetic fields of relatively high frequency resulting in large eddy current heating of the edges of the metal being cast, insufficient cooling effect of the rollers near the edges, thick cast sheet dimensions, or a combination of these or other factors. Figure 14 depicts the rollers 10 and molten metal 12 a5 in previous embodiments.
Figure 14 also shows poles 95a and 95b which extend below the center line of rollers 10. Th~s has the effect of also extending the magnetic field below the center l~ne of the rollers thereby extending the e~ec-tromagnetic containment of the edges.
WO9l/18696 PCT/US90/03~3 aos42~
Wheel induced forces on the liquid edge of the metal sheet vanish when the sheet leaves the rollers. Only gravitational forces act on the still molten edges which may be cooled by gas flow or by water spray. The magnetic forces between poles 95 decrease as the sheet moves further from the rollers; this is compatible with the solidifying edge as the sheet moves down. However, if the edge of the sheet is not quite solid near the end of the magnetic field between poles 95, further confinement of the still molten edges of the sheet can be provided by supplemental magnet with poles 96a and 96b which extend the magnetic field well below rollers 10 until the metal sheet is sufficiently hard enough to be supported by mechanical guides 23.
Another embodiment of this invention is depicted in Figures 15a and 15b. This embodiment presents a combination of a magnetic and mechanical means to contain a molten metal at the edges of a roller casting system. As mentioned above, the problem of using mechanical seals to contain a molten metal at the edges of counter-rotating casting rollers was that the mi~ture of the molten and solidifying metal in combination with the rotation of the rollers would clog up around the mechanical seals. As described above, the present invention shows how a magnetic field can be used to contain the sidewalls of the molten metal. The present SUBSTITUTE S~
WO91/18696 PCT/US90/03~3 embodiment uses both a mechanical seal and a magnet~'c field to advantage. As in previous embodiments, rolLers 10 and poles 16 contaln a molten metal 12. The present embodiment also includes a mechanical dam 100 positioned between poles 16a and 16b. Mechanical dam 100 is shaped so that it will contain the molten metal in that area wbere there is lit~le likelihood of clogging or deforming the cast sheet, i.e. away from the solidifying effects of the rollers. As depicted in Figures 15a and lSb, mechanical dam 100 is spaced away from rollers 10.
It is in the areas close to rollers 10 that the metal is solidifying and where the likelihood o~ clogging is greatest. Magnetic confinement with the poles 16 is used to confine the molten and solidifying metal in the gaps between the mechanical dam 100 and rollers 10.
Mechanical dam 100 may be made of a ferromagnetic material 101 so that it provides a low reluctance path for the flux between the poles 16. The side of the dam facing the molten metal pool may be made of a layer of high temperature ceramic 102 covering a water cooled heat shield 103 in front of the high permeability material which may be made from steel laminations or from high temperature ferrite. This embodiment has the advantage of requiring less energy than the previous embodiments because the magnetic field along the molten metal extends only over the gaps between the rollers 16 and WO91/18696 2 ~ ~ 4 2 ~ ~ PCT/US90/03243 ~_ - 29 -mechanical dam 100. Also, because the volume of the molten metal contained by the magnetic field is sma;ler, there is less heating of the molten metal due to eddy currents. Various mechanical dam shapes can be designed for shaping flux density suitable for different castinq requirements.
Claims (43)
1. An apparatus for confining molten metal comprising:
containment means having an open side;
a magnet capable of generating a mainly horizontal alternating magnetic field, said magnet located adjacent to the open side of said containment means whereby the field generated by said magnet is capable of inducing eddy currents in a thin layer at the surface of the molten metal which interact with the magnetic field producing a force that can contain the molten metal within said containment means;
wherein said magnet includes:
magnetic poles located adjacent to the open side of said confinement means;
a core connecting said poles;
a coil encircling said core, said coil capable of being responsive to a current source;
whereby an alternating magnetic field can be generated between said poles and parallel to the open side of said containment means so that a molten metal can be confined within said confinement means.
containment means having an open side;
a magnet capable of generating a mainly horizontal alternating magnetic field, said magnet located adjacent to the open side of said containment means whereby the field generated by said magnet is capable of inducing eddy currents in a thin layer at the surface of the molten metal which interact with the magnetic field producing a force that can contain the molten metal within said containment means;
wherein said magnet includes:
magnetic poles located adjacent to the open side of said confinement means;
a core connecting said poles;
a coil encircling said core, said coil capable of being responsive to a current source;
whereby an alternating magnetic field can be generated between said poles and parallel to the open side of said containment means so that a molten metal can be confined within said confinement means.
2. The apparatus of claim 1 in which said containment means comprises:
a pair of rollers parallel and adjacent to each other in a horizontal plane and further wherein said rollers are separated by a gap;
whereby counter rotation of said rollers can force the flow of a molten metal between the gap between said rollers.
a pair of rollers parallel and adjacent to each other in a horizontal plane and further wherein said rollers are separated by a gap;
whereby counter rotation of said rollers can force the flow of a molten metal between the gap between said rollers.
3. The apparatus of claim 2 in which said magnetic poles extend axially into the ends of said pair of rollers.
4. An apparatus for confining molten metal comprising:
containment means having an open side comprising a pair of rollers each of said rollers including a middle portion and a rim portion, wherein said rollers are parallel and adjacent to each other in a horizontal plane and further wherein said rollers are separated by a gap, whereby counter rotation of said rollers can force the flow of a molten metal between said gap between said rollers, a magnet located adjacent to said open side of said containment means comprised of magnetic poles located adjacent to said open side of said containment means and extending axially into the ends of said rollers, a core connecting said magnetic poles, a coil encircling said core, said coil capable of being responsive to a current source, whereby an alternating magnetic field can be generated between said poles and parallel to said open side of said containment means so that a molten metal can be confined within said containment means, in which said middle portions of said rollers have a resistivity lower than said rim portions so thattransmission of a magnetic field by said magnet through said middle portion is less than through said rim portion.
containment means having an open side comprising a pair of rollers each of said rollers including a middle portion and a rim portion, wherein said rollers are parallel and adjacent to each other in a horizontal plane and further wherein said rollers are separated by a gap, whereby counter rotation of said rollers can force the flow of a molten metal between said gap between said rollers, a magnet located adjacent to said open side of said containment means comprised of magnetic poles located adjacent to said open side of said containment means and extending axially into the ends of said rollers, a core connecting said magnetic poles, a coil encircling said core, said coil capable of being responsive to a current source, whereby an alternating magnetic field can be generated between said poles and parallel to said open side of said containment means so that a molten metal can be confined within said containment means, in which said middle portions of said rollers have a resistivity lower than said rim portions so thattransmission of a magnetic field by said magnet through said middle portion is less than through said rim portion.
5. The apparatus of claim 4 in which said rim portions of said rollers are between said magnetic poles.
6. The apparatus of claim 5 including:
roller cooling means for cooling the surfaces of said rollers whereby molten metal coming in contact with said rollers will tend to solidify.
roller cooling means for cooling the surfaces of said rollers whereby molten metal coming in contact with said rollers will tend to solidify.
7. The apparatus of claim 6 in which said middle portions of said rollers have surfaces of copper or a copper-alloy.
8. The apparatus of claim 6 in which said rim portions of said rollers are stainless steel.
9. The apparatus of claim 6 in which said rim portions of said rollers have slots spaced around the circumference of said rim portion, said slots having lower reluctance to alternating magnetic flux than said middle portion of said rollers so that said magnet can generate a magnetic field between said rim portion.
10. The apparatus of claim 9 in which said slots are filled with a ceramic.
11. The apparatus of claim 9 in which said slots contain a high resistivity metal, said high resistivity metal being insulated from the sides, of said slots.
12. The apparatus of claim 11 in which said slots contain stainless steel.
13. The apparatus of claim 9 in which said slots are filled with laminations of a high permeability metal, said laminations being insulated from each other and from the sides of said slots whereby the high permeability metal contained in said slots is capable of being magnetized by said magnets.
14. The apparatus of claim 6 in which said rim portions are comprised of a plurality of rim hoops of a material having lower reluctance to alternating magnetic flux than said middle portion of said rollers, each of said plurality of rim hoops separated from an adjacent rim hoop by a hoop of material having higher reluctance to alternating magnetic flux.
15. The apparatus of claim 14 in which said plurality of rim hoops are made of ceramic.
16. The apparatus of claim 14 in which said plurality of rim hoops are made of a high resistivity metal, said plurality of rim hoops being insulated from adjacent hoops and said middle portion.
17. The apparatus of claim 16 in which said plurality of rim hoops are made of stainless steel.
18. The apparatus of claim 14 in which said plurality of rim hoops are made of a high permeability metal, said plurality of rim hoops being insulated from adjacent hoops and said middle portion whereby the high permeability metal is capable of being magnetized by said magnet.
19. The apparatus of claim 6 in which said magnetic poles are adjustable whereby the shape of the magnetic field between said magnetic poles can be varied.
20. The apparatus of claim 6 in which said magnetic poles are movable whereby the shape of the magnetic field between said magnetic poles can be varied.
21. The apparatus of claim 6 in which said magnetic poles are comprised of a plurality of isolated segments each of said plurality of isolated segments beingindependently adjustable as to magnetic field strength whereby the shape of the entire magnetic field between said magnetic poles can be varied.
22. The apparatus of claim 19 including a sensor means constructed and adapted to monitor the dimensions or position of a metal pool being cast between said rollers.
23. The apparatus of claim 22 in which the field strength of said magnetic poles is adjustable in response to said sensor means.
24. The apparatus of claim 6 in which said magnetic poles are hoop shaped and rigidly affixed to the interiors of said rollers inside said rims and further wherein said magnetic poles are aligned in proximity with but do not touch said core so that said magnetic poles can be magnetized by said core.
25. The apparatus of claim 6 in which said core is trapezoidal in shape.
26. The apparatus of claim 6 in which said core is square in shape.
27. The apparatus of claim 6 in which said coil is comprised of a pair of coils encircling said core on extensions which connect to said magnetic poles.
28. The apparatus of claim 1 including a first eddy current shield enclosing said core except for a gap to prevent said first eddy current shield from being a shorted turn.
29. The apparatus of claim 28 in which said first eddy current shield is made of a low resistivity metal.
30. The apparatus of claim 29 in which said first eddy current shield is made of a metal selected from a group consisting of copper, copper alloy, and aluminum.
31. The apparatus of claim 6 including a second eddy current shield enclosing said core and said coil except for a gap to prevent said second eddy current shield from being a shorted turn.
32. The apparatus of claim 31 in which said second eddy current shield is made of a low resistivity metal.
33. The apparatus of claim 32 in which said second eddy current shield is made of a metal selected from a group consisting of copper, copper alloy, and aluminum.
34. The apparatus of claim 6 including a first eddy current shield enclosing said core and said coil except for a gap to prevent said first eddy current shield from being a shorted turn.
35. The apparatus of claim 28 or 31 in which said eddy current shield also includes a cooling means.
36. The apparatus of claim 8 including:
a dam located between said magnetic poles and separated from said rollers;
whereby said dam in cooperation with a magnetic field between said magnetic poles can confine a molten metal between said rollers.
a dam located between said magnetic poles and separated from said rollers;
whereby said dam in cooperation with a magnetic field between said magnetic poles can confine a molten metal between said rollers.
37. The apparatus of claim 36 in which said dam is made of a ferromagnetic material.
38. The apparatus of claim 37 including a layer of high temperature ceramic attached to said dam on the side of said dam on which molten metal can be retained.
39. The apparatus of claim 38 including a liquid-cooled heat shield located between said dam and said layer of high temperature ceramic.
40. The apparatus of claim 6 including:
a supplemental magnet having poles on either side of the gap between said rollers;
whereby said supplemental magnet can cooperate with said magnet to confine a molten metal between said poles of said magnet and said supplemental magnet.
a supplemental magnet having poles on either side of the gap between said rollers;
whereby said supplemental magnet can cooperate with said magnet to confine a molten metal between said poles of said magnet and said supplemental magnet.
41. The apparatus of claim 6 including:
a sheet cooling means located below said rollers, said sheet cooling means capable of cooling a sheet of cast metal as the sheet passes out from said rollers.
a sheet cooling means located below said rollers, said sheet cooling means capable of cooling a sheet of cast metal as the sheet passes out from said rollers.
42. The apparatus of claim 6 in which said alternating magnetic field operates between 30 Hz and 16,000 Hz.
43. The apparatus of claim 6 including guide means located below said rollers, said guide means capable of supporting a cast metal sheet leaving said rollers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2084206 CA2084206C (en) | 1990-06-07 | 1990-06-07 | Sidewall containment of liquid metal with horizontal alternating magnetic fields |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2084206 CA2084206C (en) | 1990-06-07 | 1990-06-07 | Sidewall containment of liquid metal with horizontal alternating magnetic fields |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2084206A1 CA2084206A1 (en) | 1991-12-08 |
| CA2084206C true CA2084206C (en) | 1999-03-30 |
Family
ID=4150770
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2084206 Expired - Fee Related CA2084206C (en) | 1990-06-07 | 1990-06-07 | Sidewall containment of liquid metal with horizontal alternating magnetic fields |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2084206C (en) |
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1990
- 1990-06-07 CA CA 2084206 patent/CA2084206C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2084206A1 (en) | 1991-12-08 |
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