CA2320561C - Controllable variable magnetic field apparatus for flow control of molten steel in a casting mold - Google Patents

Abstract

An apparatus for providing a magnetic field in a casting mold to slow and redirect in a controllable fashion the flow of liquid steel exiting from a submerged entry nozzle into the casting mold uses selectable removable ferromagnetic and non-magnetic laminar elements stackable on the ends of core fingers in the vicinity of the poles of an electromagnetic yoke positioned adjacent the mold face. By selecting the type and location of the stackable elements on the ends of the fingers, one can modify the properties of the magnetic field permeating the interior of the mold. Optionally, independent field coils may be provided for energizing selected portions of the magnetic field core structure to provide further magnetic field control without having to remove and replace laminar elements.

Description

Y:\IP001\1111 CA\spec\spec 000924.wpd CONTROLLABLE VARIABLE MAGNETIC FIELD APPARATUS FOR FLOW
CONTROL OF MOLTEN STEEL IN A CASTING MOLD
Field of the Invention The present invention relates to a magnetic field apparatus for controlling the flow of molten steel in a casting mold, and more particularly to an apparatus for providing an adjustable magnetic field in a casting mold to impede and redirect in a controllable fashion the flow of liquid steel exiting from a submerged entry nozzle that discharges into the casting mold.
Background of the Invention It is known in the art of steelmaking to continuously cast molten steel using an oscillating mold, typically a water-cooled copper-faced mold having a straight or curved channel. The mold typically has a rectangular horizontal cross-sectional forming conduit as thick and wide as the slab to be cast. Liquid steel in the upper portion of the mold is cooled as it moves downward through the water-cooled mold, generating a steel shell as it passes through the mold before exiting the mold at the bottom.
The molten steel enters the mold from a tundish through an entry nozzle submerged in the liquid steel in the mold. The submerged entry nozzle is normally located generally centrally of the mold cross-section, and is provided with opposed exit ports that direct liquid steel generally horizontally outwardly toward the narrow sides of the mold. Some nozzles have a bottom port as well.
The flow of liquid steel out of the submerged entry nozzle varies in direction and velocity due to various external conditions (such as the ferrostatic head of steel above the nozzle, and steel chemistry). This can create disturbances in the steel flow that adversely affect both the surface quality and internal quality of the casting. These disturbances tend to generate undesired temperature imbalances that interfere with uniform solidification of the steel as it passes through the mold and downstream thereof, and also increase the tendency of the steel to incorporate unwanted inclusions from the mold powder/slag/impurities mixture at the meniscus of the liquid steel at the top of the mold. A conventional magnetic brake inhibits these disturbances by reducing the velocity of liquid steel emanating from the submerged entry nozzle, thereby tending to constrict the eddies and prevent them from reaching the end edges of the mold and the upper surface of the pool of liquid steel at the top of the mold.
A conventional magnetic brake includes a magnetic circuit energized by direct or slowly varying electric current passing through windings around an iron core forming part of the magnetic circuit. The magnetic circuit passes through the wide faces of the mold so as to provide a magnetic field through the interior of the mold. Normally, in a conventional magnetic brake, the magnetic circuit passes through the mold about mid-way along the longitudinal length of the mold and overlaps the point of entry of liquid steel into the mold from the submerged entry nozzle, but does not extend up to the top of the liquid steel pool nor down to the bottom of the mold.
Although the magnetic field in a conventional magnetic brake can be varied (by varying the amount of current flowing through the windings around the iron core of the magnetic circuit) there is, nevertheless, typically no fine control over the manner in which the magnetic field is applied. Such fine control would improve the ability to control the flow characteristics of the steel as it exits from the submerged entry nozzle, in the interest of generating uniform solidification of the shell of cast steel emerging from the mold and in the interest of reducing unwanted inclusion and non-uniform surface effects.

Attempts have been made by various prior workers in the field to provide some variation in the magnetic field applied through the mold. Representative such attempts are disclosed, for example, in U.S. Patent No. 5,404,933, issued 11 April 1995 to Andersson et. al. (the Andersson patent), and U.S. Patent No.
5,613,548 issued 25 March 1997 to Streubel et. al. (the Streubel patent). The Andersson patent discloses an apparatus for controlling the flow of molten metal by applying a static or periodic low-frequency magnetic field across the area through which the molten metal flows. The Streubel Patent discloses an apparatus that accomplishes a similar result by attaching partial cores to a principal core surrounded by an electrical core, thereby influencing the magnetic field applied.
Summary of the Invention The present invention is an improved version of the applicant's invention which is the subject of Canadian application serial no. 2,242,037 (Frank & Dorricott), filed 30 June 1998. The invention described in the '037 application and this present invention are both directed generally to an apparatus for providing a magnetic field for controlling the flow of molten steel inside a casting mold. Particularly, the apparatus is provided with a set of one or more pairs of magnetic poles each having a magnetic field core surrounded by a discrete coil for generating a magnetic field and means for reconfiguring the magnetic field so as to modify the flow characteristics of the molten steel exiting from a submerged entry nozzle in the mold. The magnetic field reconfiguration means include one or both of (1) at least one finger at the end of each core in proximity to the mold wherein each finger has removable laminar elements positioned in the magnetic circuit adjacent the mold face, and (2) discrete individually energizable coils in the magnetic circuit during the casting of molten steel. Magnetic field reconfiguration according to the first reconfiguration means is effected between casting runs, by increasing or decreasing the number of ferromagnetic laminar elements in each finger. Magnetic field reconfiguration according to the second reconfiguration means can be effected during or between casting runs, by varying the degree of energization of each individual coil so that the pattern of energized coils in the circuit is varied.
In accordance with one aspect of the present invention, there is provided a magnetic field generating apparatus having removable ferromagnetic and non-magnetic laminar elements for one or more of the fingers and means for varying the pattern of these elements such that a fine control of the magnetic field can be achieved. The varying of the element pattern is effected between casting runs. The apparatus is provided a pair of magnetic poles comprising at least a pair of magnetic field cores, each core being energized by at least one discrete coil located in the vicinity of a discrete opposed wide face of the mold. The cores are connected by a yoke so that the cores and the yoke together with the mold containing molten steel form a complete magnetic circuit. When the coils are energized, the magnetic field extends generally horizontally from one wide face of the mold to the other.
Each magnetic field core has a horizontal row of generally horizontally disposed closely packed "fingers" in proximity to the proximate wide face of the casting mold. (The term "fingers"
is used herein to identify a physically discrete projecting portion of the core adjacent the mold face, but it is to be understood that spaces between fingers are undesirable, although frequently necessary because of the need to accommodate opposed projections such as strengthening ribs on the surface of the mold.) The fingers protrude horizontally from the ends of their respective cores in two parallel, generally symmetrical arrays, each array abutting a respective face of the mold. (While the benefit of the invention as contemplated by the inventor is best obtained by having two generally identical matching arrays of fingers, one on either side of the mold, there may be circumstances in which the arrays are chosen not to be identical, or the fingers are provided on one side of the mold only.) The individual fingers in each array may abut one another, or some fingers may be slightly spaced apart so as to avoid interfering with other structural elements in the vicinity of the mold faces.
The fingers are comprised of removable ferromagnetic laminar elements and optionally spacers or non-magnetic laminar elements.
For each finger, these laminar elements are arrangeable in a vertically stacked array extending horizontally into proximity with the proximate wide mold face at a selected location. The fingers may comprise a lower horizontally projecting support, upon which the laminar elements may be stacked. For continuity of the magnetic circuit, each finger should be positioned as close as possible to the adjacent mold face. The local magnetic field in the molten steel in the casting mold near each finger (each selected location) may be varied independently of the local magnetic field in the molten steel in the casting mold near other fingers by varying the pattern of ferromagnetic and non-magnetic elements for each finger. Changing the element pattern is effected between casting runs as individual elements may have to be removed or added to each finger. The pattern may be varied by changing the number of elements in the finger, changing the proportion of magnetic to non-magnetic elements in the finger, or changing the dimensions of the elements in the finger. In this last approach, the elements may have differing widths and some may span the width of two or more fingers, or less than the width of a singer finger.
As it is generally desirable to have a generally uniform magnetic field across the entire transverse width of the array of fingers, fingers near the centre of the array may have fewer ferromagnetic laminar elements attached than do fingers at the periphery of the array, to compensate for the natural tendency of the magnetic field to be stronger in the centre. It may also be desirable to substitute non-magnetic laminar elements for ferromagnetic laminar elements in portions of the central fingers, or to provide spacers between selected successive ferromagnetic laminar elements, thereby creating air gaps in the magnetic field that serve essentially the same function as non magnetic laminar elements.
According to another aspect of the invention, there is provided a vertical stack of horizontally extending rows of cores for each mold face. Each row may have one or more cores, and each core may have one or more fingers. This creates a two-dimensional matrix of cores and fingers for each mold face that effectively extends control of the magnetic field in the vertical direction beyond the height of single core. Fine control of the matrix can be effected by controlling the magnetic field at each individual finger as described above, i.e. by selecting the layout of the ferromagnetic and non-magnetic laminar elements within each finger and/or by selecting the amount of ferromagnetic material in each element of each finger. Control of the magnetic field is also provided by the selective energization of the energizing coils of each core; for a matrix having cores extending in both the horizontal and vertical direction, the magnetic field distribution can be varied in both the horizontal and vertical direction. For configurations having only one coil per row, horizontal control can still be effected by varying the magnetic field at each finger by the varying the laminar element pattern therein.
Selectively energizing the coils to control the magnetic field distribution enables the operator to reconfigure the magnetic field during casting (in contrast to modifying the laminar element distribution by physically adding and removing laminar elements).
The magnetic field is created by a number of opposed pairs of magnetic field cores, each of which cores is energized by a discrete energizing coil. One core in each pair is located on one side of the wide face of the mold and its mating core on the other side of the mold directly opposite the first core. The terminal faces of each pair of opposed cores comprise poles of a component magnetic circuit, the overall magnetic circuit for the electromagnetic brake comprising the total of the component magnetic circuits. Each core is coupled within the magnetic circuit by an encircling yoke made from a magnetic material. A
discrete individually controllable electrical current may be passed through each coil. When the mold contains molten steel, a composite magnetic circuit is formed, each component of which passes through one core of one discrete pair of cores, the yoke, the other core of that pair of cores, and the adjacent selected portion of the mold and the molten steel contained therein, so that when the coils are energized, the magnetic field extends from one wide face of the mold to the other. The local magnetic field in any one of the selected portions of the mold may be varied by varying the electrical currents passing through the pairs of coils associated with the pairs of magnetic field cores near that selected portion of the mold, so as to modify flow characteristics of molten steel exiting from the submerged entry nozzle into the casting mold. As each component magnetic circuit pole is provided with a discrete energizing coil, each pole pair may be energized independently of the other pole pairs, thereby providing control of the local magnetic field in the molten steel in the casting mold during casting.
In this further aspect of the invention each coil preferably energizes a portion of the core associated with at least one discrete finger having removable ferromagnetic and non-magnetic laminar elements. Note that the array of pole pairs and counterpart array of energizing coils may desirably correspond to the array of fingers, but need not do so. The matrix may thus be configured to have a series of coils in both the vertical and horizontal dimensions, such that the magnetic field distribution can be varied both horizontally and vertically.
The cores, including at least some of the removable ferromagnetic laminar elements, and the yoke should be made of iron or an alloy chiefly composed of iron. The removable non-magnetic laminar elements may be made of a heat resistant ceramic material. The ferromagnetic and non-magnetic laminar elements may be stackable rectangular parallelepiped plates, and they may be of varying heights and widths. If desired, some of the laminar elements may be dimensioned to span more than one finger.
According to yet another aspect of the invention, there is provided means of varying the magnetic field by substituting selected portions of one or more of the cores (either a portion proximate to the laminar elements or at some other location within the core) with material which is ferromagnetic to an extent different from the material from which the un-substituted cores are made or non-magnetic, so as to alter the magnetic field in the casting mold as desired.
It is contemplated that a suitable selection of ferromagnetic and non-magnetic laminar elements in a matrix array immediately adjacent the mold face will accommodate the more major and persistent changes in steel characteristics (e. g., steel chemistry), while the use of the individually energizable coils (which may also be arranged in a matrix array adjacent the array of laminar elements) is intended to accommodate transient variations in the characteristics of the molten steel (e. g., ferrostatic head).
Brief Description of the Drawings In the drawings, which illustrate embodiments of the invention:
Figure 1 is a schematic bottom isometric view of an apparatus suitable for embodying a magnetic brake in conformity with the present invention.

Figure 2 is a simplified schematic plan view of one magnetic pole of the apparatus of Figure 1 and an associated casting mold.
Figure 3 is a schematic end elevation section view of a finger of the magnetic pole of Figure 2 taken along the line 3-3 of Figure 2, illustrating a vertically stackable series of removable plates (laminar elements) in conformity with one aspect of the invention.
Figure 4 is a schematic side elevation section view of a finger of the magnetic pole of Figure 2 taken along the line 4-4 of Figure 2, and illustrating the vertically stackable series of removable plates seen also in Figure 3, in conformity with one aspect of the invention.
Figure 5 is a schematic side elevation section view of a finger of the magnetic pole of Figure 2 taken along the line 4-4 of Figure 2, and illustrating an alternative embodiment of the vertically stackable series of removable plates wherein the fixed end piece of the illustrated finger is replaced by a removable end piece.
Figure 6 is a schematic isometric view of one polar finger array of an embodiment of the present invention showing stackable laminar elements spanning more than one finger, in conformity with one aspect of the invention.
Figure 7 is a schematic plan view of one polar array of a multipole variant of an apparatus embodying the present invention, illustrating the multiple energizing coil feature of one aspect of the invention.
Figure 8 is a schematic isometric view of a multipolar array of a partial embodiment of a magnetic brake according to an embodiment of the invention that combines options illustrated in preceding figures.

Detailed Description of the Invention A magnetic field apparatus embodying the present invention is generally indicated by numeral 10 in Figure 1. Apparatus 10 is comprised of two magnetic cores 12, each surrounded by a discrete coil 14. The cores 12 are connected together by a yoke leaving a gap 25 for a casting mold (not shown in Figure 1, but discussed below). In use, the casting mold and liquid steel in it complete a magnetic circuit including the yoke 15 and the 10 cores 12.
In operation, the mold is oriented vertically so that its opening is in the horizontal plane; for the sake of convenient reference, the description of the magnetic field apparatus will 15 be made with respect to the operational orientation of the mold.
On either side of the gap 25, the cores 12 are split into separate horizontally extending fingers, which are indicated generally by reference numeral 16. Ideally there would be no space between the fingers 16, and the fingers 16 would come into close proximity with the casting mold, so that with the mold in place receiving liquid steel, there would be two minimal gaps in the magnetic circuit.
Figure 1 illustrates a pair of discrete magnetic poles 11 each comprised of one core 12 surrounded by an associated coil 14 and ending in fingers 16. In Figure 2, one of the magnetic poles 11 of the apparatus 10 is shown close to one wide face of a casting mold 24 having a mold cavity 26 and a submerged entry nozzle 28. The end of the magnetic core 12 close to the casting mold 24 is split into several horizontally protruding fingers 16 which are shown in further detail in Figures 3 and 4. For ease of illustration, the end of the magnetic field core 12 close to the casting mold 24 is depicted in Figure 2 as being split into six fingers 16. As discussed above, the empty horizontal spacing between the fingers 16 could be eliminated where possible. The spacing is needed only when there are obstructions associated with the external water jacket and any other structural features (not shown) of the mold itself which must pass between the magnetic core 12 and the casting mold 24. One such possible structural feature is one or more strengthening ribs (not shown) that extend down the the wide faces of the mold. Such ribs can be accommodated by insetting the appropriate fingers relative to such ribs. By way of example, the centralmost pair of fingers is inset relative to the other fingers shown in Figure 1. In Figure 2, the schematically uniform spacing between the fingers 16 is shown for ease of illustration only.
The vertical position of the yoke relative to the mold is determined by the operator, taking into account factors such as the ferrostatic head of liquid steel above the submerged entry nozzle 28, the expected wear on the submerged entry nozzle 28, the size of the mold 26, and the chemical and physical properties of the steel.
In the embodiment illustrated in Figures 3 and 4, each finger 16 has a fixed lowermost end piece 20 which is an extension of the magnetic core 12. Each fixed end piece 20 is provided with bores 17 threaded for receiving bolts 18.
Removable upper end pieces (stackable laminar elements) 22 in the form of relatively small rectangular parallelepiped plates made from ferromagnetic or non-magnetic material, three of which are illustrated by way of example but not by way of limitation, are secured to the fixed lower end piece 20 using bolts 18, so as to build up a laminated structure having a selected amount of magnetic material. The amount and position of magnetic material in a particular finger 16 directly affects the structure and strength of the magnetic field in the casting mold 24 in the vicinity of that finger 16; decreasing the amount of magnetic material by substituting non-magnetic stackable elements for ferromagnetic stackable elements decreases the magnetic field locally. Note that the magnetic field in the casting mold 24 may be quickly and easily varied by selecting the number, type (usually, ferromagnetic or non-magnetic), and position of removable upper end pieces 22 for each finger 16 (as well as the current flow through any associated coil; see the discussion of Fig. 7 below) to produce the desired flow pattern in the molten steel.
Figure 5 shows an alternative embodiment of the structure of the finger 16 in Figures 3 and 4. Where the lower end piece 20 is an extension of the magnetic core 12, then the ferromagnetic properties of the lower end piece 20 will be the same as that of the magnetic core 12. However, it may be desirable to provide for a non-magnetic end piece at the bottom of a stack of laminar elements. This can be achieved by providing a removable, lower end piece 21 made from non-magnetic material, as shown in Figure 5. The removable lower end piece is provided with threaded bores 17 and attached to the core using bolts 18. Other bolts 18 are used to attach removable upper end pieces 22 to the removable lower end piece 21. The number of layers of removable upper end pieces 22 shown is merely an example, and should not be taken as a limitation of this embodiment. Optionally, removable, lower end piece 21 of each finger 16 can be ferromagnetic or non-magnetic, as required, in order to produce (as described above) the desired magnetic field in the casting mold 24 in the vicinity of each finger 16.
Figure 6 illustrates how the removable end pieces (stackable laminar elements) 22 may span horizontally more than one finger 16. In places where it is desirable to have a strong magnetic field, the gaps between the fingers 16 may be eliminated entirely by the use of removable upper end pieces 22 which are two or more times the width of a finger 16. Figure 6 shows this embodiment with removable lower end pieces 21, but fixed lower end pieces 20 could also be used. The bolts 18 holding the fingers 16 together are in the same position as in Figure 5. The particular arrangement shown is for illustrative purposes only. The laminar elements 21, 22 may be made of materials with varying degrees of ferromagnetic properties, depending on the magnetic field requirements.
Additional horizontal control over the magnetic field in a casting mold 24 may be achieved by use of more than one magnetic pole as illustrated in Figure 7. Reference numeral 30 in Figure 7 schematically indicates an exemplary five-pole system, wherein the poles 31 are horizontally spaced and each pole 31 terminates in a longitudinally (i.e. towards the mold) extending core 32 (only one core of each pole pair is shown in Figure 7). A
discrete energizing coil 34 is associated with each core 32, and, in this illustration, one finger 16 per core 32. The coils 34 are arranged in a manner such that no two adjacent coils are at the same longitudinal position on the cores 32 so as to avoid physical interference between coils associated with horizontally adjacent cores and so as to maintain minimal spacing between horizontally adjacent cores. More than one finger 16 per pole 31 may be provided if necessary. Figure 7 illustrates an idealized case in which there are no interfering obstructions.
However, for even better control it may be advantageous to use more than one finger per pole (preferably with no spacing between fingers) even in the absence of obstructions. Each finger 16 preferably has the structure illustrated in one of Figures 3, 4 or 5 and described above for the single pole case, namely, a fixed or removable lower end piece 20 or 21 to which replaceable upper end pieces 22 may be bolted to build up a laminated structure having a selected amount of magnetic material and non-magnetic material in selected locations.
By independently controlling electrical current passing through the coils 34, the configuration of the magnetic field in the casting mold 24 may be controlled as casting proceeds. For example, a selected replaceable upper end piece 22 on a selected finger may have been removed or replaced to produce a particular magnetic field emanating from the pole associated with that finger when the current passing through the coils 34 is set at a selected set of values, but during casting, a somewhat weaker magnetic field associated with that finger may become advantageous. A weaker magnetic field from that finger may then be obtained without stopping the casting process by reducing the current to the associated energizing coil 34. The particular changes to be made in the various energization currents for all the coils 34 may be determined empirically, and may be expected to depend upon such factors as the type of steel being cast, the dimensions of the mold 24, the temperature distribution of the molten steel in the mold 24, and the rate and the temperature at which molten steel is flowing into the mold 24 through the submerged entry nozzle 28.
Figure 8 shows an embodiment of the present invention in which the five-pole horizontal array 30 of Figure 7 is expanded in the vertical direction, creating a two-dimensional matrix of fingers for greater control over the magnetic field distribution.
The illustration shows five such five-pole arrays stacked vertically, resulting in a 25-pole matrix 40, each pole having one or more fingers. The coils 34 are arranged in a manner such that no two adjacent coils interfere with one another. Long bolts 19, which have a length approximately equal to the height of the 25-pole matrix 40, may be used in place of the shorter bolts 18 shown in previous illustrations. Removable lower end pieces 21 are shown by way of example only. The illustrated arrangement of the end pieces 21, 22 is merely one possible such arrangement, and is not intended to limit this embodiment of the invention.
It may be desirable to substitute one or more cores or selected portions of one or more cores (generally depicted in Figure 8 as 42) with material which is non-magnetic (or optionally, with material which is ferromagnetic to an extent different from the material used in the un-substituted cores), so as to alter the magnetic field that is applied across the molten steel within the casting mold 24, as desired.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto, since modifications may be made by those skilled in the applicable technologies, particularly in light of the foregoing description. The appended claims include within their ambit such modifications and variants of the exemplary embodiments of the invention described herein as would be apparent to those skilled in the applicable technologies.

Claims (23)

1. Apparatus for providing a magnetic field in molten steel passing from a submerged entry nozzle into and through a generally vertically oriented mold for continuously casting molten steel, the mold having a pair of opposed wide faces, said apparatus comprising:
a pair of magnetic field cores, each core of said pair located adjacent to a discrete opposed wide face of the mold and connected to the other core by a yoke so that a magnetic circuit is formed that passes through one of the cores in the pair, the yoke, the other one of the cores in the pair, and the mold containing molten steel, the pole of each said magnetic field core extending generally across the width of the adjacent wide face of the mold, each said pole being the termination of a generally horizontal array of discrete fingers in proximity to an adjacent wide face of the mold, each finger comprising a generally vertical stack of laminar elements, at least some of which laminar elements are removable and replaceable, and at least some of which laminar elements are made of non-magnetic material; and a pair of energizing coils through which electrical current may be passed to produce a magnetic field in molten steel in the casting mold, each coil being associated with one of said magnetic field core in the casting mold, whereby the magnetic field to be produced in molten steel in the casting mold when electrical current passes through the coils may be varied by the selection of the magnetic characteristics of the laminar elements stacked on each finger so as to modify flow characteristics of molten steel exiting the submerged entry nozzle in the casting mold.

2. Apparatus as defined in claim 1, wherein the laminar elements include elements made of ferromagnetic material.

3. Apparatus as defined in either claim 1 or claim 2, wherein at least one finger comprises a removable, lowermost projecting support, made of non-magnetic material, upon which laminar elements may be stacked.

4. Apparatus for providing a magnetic field in molten steel passing from a submerged entry nozzle into and through a generally vertically oriented mold for continuously casting molten steel, the mold having a pair of opposed wide faces, said apparatus comprising:
a plurality of pairs of magnetic field cores, each core in any said pair being located adjacent to a discrete opposed wide face of the mold and connected to the other core in such pair by a yoke so that for any said pair of cores, a magnetic circuit is formed that passes through one of the cores in the pair, the yoke, the other one of the cores in the pair, and the mold containing molten steel, the pole of each said magnetic field core extending generally across the width of the adjacent wide face of the mold, each said pole being the termination of a generally horizontal array of discrete fingers in proximity to an adjacent wide face of the mold, each finger comprising a generally vertical stack of laminar elements, at least some of which laminar elements are removable and replaceable; and a plurality of pairs of energizing coils through which electrical current may be passed to produce a magnetic field in molten steel in the casting mold, each coil being associated with a discrete one of said magnetic field cores, whereby the magnetic field to be produced in molten steel in the casting mold when electrical current passes through the coils may be varied by the selection of the magnetic characteristics of the laminar elements stacked on each finger so as to modify flow characteristics of molten steel exiting the submerged entry nozzle in the casting mold.

5. Apparatus as defined in claim 4, wherein the laminar elements include elements made of ferromagnetic material.

6. Apparatus as defined in claim 4, wherein the laminar elements include elements made of non-magnetic material.

7. Apparatus as defined in either of claim 5 or claim 6, wherein at least the fingers are arrayed in a matrix array extending both generally horizontally across the width of the mold and generally vertically over a central portion of the mold.

8. Apparatus as defined in claim 5, wherein one or more fingers comprises a lowermost projecting support upon which laminar elements may be vertically stacked.

9. Apparatus as defined in claim 8, wherein the lowermost projecting support is removable and is made of non-magnetic material.

10. Apparatus as defined in claim 5, wherein one or more of the magnetic field cores are made of non-magnetic material.

11. Apparatus as defined in claim 5, wherein selected portions of one or more of the magnetic field cores are made of non-magnetic material.

12. Apparatus for providing a magnetic field in molten steel passing from a submerged entry nozzle into and through a generally vertically oriented mold for continuously casting molten steel, the mold having a pair of opposed wide faces, said apparatus comprising:
a plurality of pairs of magnetic field cores, each core in any said pair being located adjacent to a discrete opposed wide face of the mold and connected to the other core in such pair by a yoke so that for any said pair of cores, a magnetic circuit is formed that passes through one of the cores in the pair, the yoke, the other one of the cores in the pair, and the mold containing molten steel, the pole of each said magnetic field core extending generally across the width of the adjacent wide face of the mold, each said pole being the termination of a generally horizontal array of discrete fingers in proximity to an adjacent wide face of the mold, each finger comprising a generally vertical stack of laminar elements, at least some of which laminar elements are removable and replaceable; and a plurality of pairs of energizing coils through which electrical current may be passed to produce a magnetic field in molten steel in the casting mold, each coil being associated with selected discrete portions of the magnetic field cores, whereby the magnetic field to be produced in molten steel in the casting mold when electrical current passes through the coils may be varied by the selection of the magnetic characteristics of the laminar elements stacked on each finger so as to modify flow characteristics of molten steel exiting the submerged entry nozzle in the casting mold.

13. Apparatus as defined in claim 12, wherein the laminar elements include elements made of ferromagnetic material.

14. Apparatus as defined in claim 13, wherein the laminar elements include elements made of non-magnetic material.

15. Apparatus as defined in claim 13, wherein the coils and discrete portions of the cores are arrayed in a generally horizontal array.

16. Apparatus as defined in claim 15, wherein the coils correspond to the fingers in a one-to-one relationship.

17. Apparatus as defined in claim 12, wherein the coils and discrete portions of the cores are arrayed in a matrix array extending both generally horizontally across the width of the mold and generally vertically over a central portion of the mold.

18. Apparatus as defined in claim 17, wherein the fingers are arrayed in a matrix array extending both generally horizontally across the width of the mold and generally vertically over a central portion of the mold, and the coils correspond to the fingers in a one-to-one relationship.

19. Apparatus as defined in claim 17, wherein one or more of the magnetic field cores or selected portions of one or more of the magnetic field cores are made of non-magnetic material.

20. Apparatus as defined in claim 18, wherein one or more of the magnetic field cores or selected portions of one or more of the magnetic field cores are made of non-magnetic material.

21. Apparatus as defined in claim 4, additionally including a plurality of discrete coils for individually energizing discrete portions of the cores.

22. Apparatus as defined in claim 21, wherein the coils and discrete portions of the cores are arrayed in a generally horizontal array.

23. Apparatus as defined in claim 22, wherein the coils correspond to the fingers in a one-to-one relationship.