A METHOD AND A DEVICE FOR CASTING IN A MOULD

Abstract: A method and a device, during casting of metal wherein a mould (11) which is open in both ends of the casting direction is supplied with a primary flow of melt, of controlling the flow of the melt in non-solidified portions of a cast strand (1) formed in the mould. Static or periodically low-frequency magnetic fields are generated and applied to act, at at least two levels (L1, L2) located one after the other in the casting direction, on the non-solidified portions of the cast strand while the cast strand is in the mould. At least one additional static or periodic low-frequency magnetic field is generated and applied to act, at at least one level (L3), on the non-solidified portions which remain in the cast strand while the cast strand is leaving the mould or immediately after the cast strand has left the mould.

Description: A method and a device for casting in a mould TECHNICAL FIELD The present invention relates to a method and device, during casting of metal in a mould, of controlling the flow of liquid metal in non-solidified portions of a cast strand which is formed in the mould. The flow is controlled by means of static or periodically low-frequency magnetic fields which are adapted to act at a plurality of levels located one after the other in the direction of casting. The mould is open in both ends of the direction of casting. A primary flow of liquid metal, melt, flowing into the mould is braked and secondary flows of liquid metal arisen in the non-solidified portions of a cast strand formed in the mould are controlled by means of the above-mentioned magnetic field arranged transversely of the casting direction. The invention is especially applicable to continuous casting in a chilled mould where an uncontrolled inflow of hot melt, containing slag particles or other non-metallic particles, and/or an uncontrolled secondary flow in the non-solidified portions of a cast strand, entail problems both from the points of view of quality and production engineering. BACKGROUND ART When a metal or a metal alloy, such as a steel, is cast in a mould, which is open in both ends of the casting direction, by means of a continuous or semi-continuous process, a melt is supplied to the mould by means of a free tapping jet, open casting, or through a casting tube, closed casting. When passing through the mould, a cast strand is formed by the melt being cooled. Before the cast strand leaves the mould, a cast strand has been formed, which at least comprises one solidi¬ fied self-supporting surface layer formed around the residual melt. An uncontrolled flow of metal in the non-solidified portions of the cast strand entails problems, both with respect to quality and production engineering. If an inflowing melt is allowed to flow into the melt in an uncontrolled manner, it will, because of its impulse, penetrate deep down into the non-solidified portions of the cast strand. This makes the separation of particles contained in the melt more difficult. These particles will then adhere to the solidi¬ fication front instead of being separated towards the upper surface. In addition, the self-supporting surface layer is weakened, which increases the risk of melt breaking through the surface layer formed in the mould. From, for example, European patent document EP 0 040 383, it is known to arrange one or more static or periodically low- frequency magnetic fields in the path of the melt in order to brake and split up the inflowing melt. Problems from the quality and production engineering points of view arise if hot melt, with or without non-metallic partic- les, is allowed, without being braked, to penetrate deep down into the non-solidified portions of the cast strand. If the secondary flows of hot melt rising towards the upper surface, the meniscus, become too weak, the meniscus runs the risk of freezing. If, instead, the upward flows become too strong, waves are formed on the upper surface as a result of the turbulence, which pulls down slag from the upper surface into the melt with ensuing quality problems. If the downward secondary flows are allowed to reach too deep down into the cast strand, the particles run the risk of adhering to the solidification front and remaining in the cast strand. One object of the invention is to suggest a method, by means of a plurality of static or periodically low-frequency magne¬ tic fields adapted to act at a plurality of levels arranged one after the other in the casting direction, of braking the primary flow of incoming hot melt and controlling secondary flows of melt arising in the non-solidified portions of a cast strand, such that a reliable and efficient control of these flows is obtained. Another object of the invention is to suggest a device for carrying out the invented method. SUMMARY OF THE INVENTION The flow of the melt in the non-solidified portions of a cast strand is controlled such that - the primary flow of hot melt arriving at the mould is braked and split up; - the circulation of melt in the non-solidified portions of a cast strand formed in the mould is controlled; - particles contained in the inflowing melt are separated, and - the supply of heat to the melt in the upper parts of the mould is controlled and a sufficient flow channel is achieved close to the meniscus, among other things to prevent the meniscus from freezing. At the same time, the flow in these upper parts of the non-solidified portions of the cast strand is limited so as not to become so strong that waves are formed on the upper surface of the melt. According to the invention, this is achieved by causing static or periodically low- frequency magnetic fields to act, at at least two levels located one after the other in the casting direction, on the non-solidified portions of the cast strand while it is in the mould, and by causing at least one static or periodic low- frequency magnetic field to act at at least one level on the non-solidified portions of the cast strand while the cast strand is leaving the mould or immediately after the cast strand has left the mould. The magnetic field is generated by means of magnetic-field generating devices, which may be in the form of permanent magnets and/or induction coils, supplied with current, with associated cores, and which are arranged adjacent two mould walls, located opposite to each other, to act across the inflowing melt. These magnetic-field generating devices, which may be in the form of permanent magnets or coils, supplied with current, with magnetic cores, will hereinafter in this application be referred to as magnets. In one embodiment, the magnets are adapted such that - at least one magnetic field is generated to act at a first level on the non-solidified portions of the cast strand in the upper part of the mould immediately downstream of the upper surface/the meniscus of the melt, and at a sufficient distance from the meniscus to ensure that upwardly-rising secondary flows are braked such that oscillations and the rate of flow of the melt are damped at the meniscus, while at the same time a channel with a limited and controlled flow of melt is main¬ tained adjacent to the meniscus, - at least one magnetic field is generated to act at a second level on the non-solidified portions of the cast strand in the mould downstream of the first magnetic field in the casting direction such that the incoming primary flow of melt is braked and split up into secondary flows, while - at least one magnetic field is generated to act at a third level on the non-solidified portions which remain in the cast strand while the cast strand is leaving the mould or immedia¬ tely after the cast strand has left the mould, whereby the depth of penetration of downwardly-directed secondary flows is reduced and the conditions for separation of the particles are improved. The static or periodically low-frequency magnetic fields are generated close to the mould by means of magnets, since the magnets are adapted to generate magnetic fields which, in a manner described above, act at at least three levels. The levels are arranged one after the other in the casting direc¬ tion to effectively brake and split up the primary flow of melt flowing into the mould and prevent the inflowing hot melt from penetrating, without being braked, deep down into the non-solidified portions, the sump, of the cast strand. At the same time, the magnetic fields control part of the hot melt to flow towards the upper surface such that a desirable con- trolled circulation of melt is obtained in the non-solidified portions of the cast strand. In a preferred embodiment of the invention, the magnets are adapted to generate magnetic fields at three levels. The levels are arranged one after the other in the casting direc¬ tion, and the magnetic field at the intermediate level is directed in the opposite direction to the magnetic fields at the two surrounding levels . In one embodiment of the invention, which is applicable to casting where melt is supplied to the mould through a casting tube, which with an arbitrary number of openings opens out into the melt, that is, downstream of the meniscus, the above- described braking and splitting up of the incoming primary flow as well as the control of the secondary flow are obtained by arranging the magnets such that : - at least one magnetic field is generated to act, at a first level, downstream of the meniscus and upstream of the above- mentioned openings of the casting tube, - at least one magnetic field is generated to act, at a second level, downstream of the above-mentioned openings of the cas¬ ting tube, and - at least one magnetic field is generated to act, at a third level, adjacent to the outlet end of the mould, or immediately downstream of this outlet end. The magnets are preferably arranged in magnetic circuits which are closed during casting. In addition to the magnets with associated magnetic poles and a static magnetic field, these magnetic circuits comprise a magnetic return path, preferably in the form of an external magnet yoke. This results in the necessary magnetic flux balance in the circuits. Of course, the magnets with associated poles, the magnetic fields and the yokes, may be arranged such that a magnetic flux balance is obtained for each mould half or for parts of a mould. The magnets are preferably adapted to generate two static or periodically low-frequency magnetic fields to act, at the same level, opposite to each other to jointly control the flow of melt over a cross section in the casting direction of the cast strand. This can be achieved with magnets of opposite polari¬ ty, arranged in pairs, whereby the two magnets included in a pair may be arranged at the same mould side or at mould sides opposite to each other. The magnetic material included in the mould is preferably used as magnetic return path, whereby in many cases special magne- tic yokes are redundant in order to obtain magnetic circuits with magnetic flux balance. In one embodiment of the invention, the magnetic fields are generated, applied and controlled independently of each other. Likewise, the distribution of the strength and the propagation of the magnetic fields at the levels arranged across the cas¬ ting direction are controlled. This is achieved in a known way by varying the magnetic field strength, by using so-called pole plates of a magnetic material, and by changing the geo- metry of the pole. A change of the geometry of the pole may be achieved in a known manner by changing the distribution of magnetic material in a cross section of the permanent magnet or in the core of the coil supplied with current. According to one embodiment of the invention, one or more magnets are arranged, at one or a plurality of levels, to generate static or periodically low-frequency magnetic fields with a distribution such that they act across essentially the whole width of the cast strand formed in the mould, that is, across essentially the whole long side of the mould. This is achieved in a known way by arranging the magnets with poles which have a width which covers essentially the whole width of the cast strand formed in the mould, or by means of a pole plate arranged adjacent the magnets and the mould wall. In embodiments where pole plates are used, the pole plates extend preferably along the long sides of the mould. Behind the pole plates, one or a plurality of magnets may be arranged. By the pole plates, magnetic fields are brought together and/or distributed to generate and apply a static magnetic field to act between the pole plates over essentially the whole width of the cast strand formed in the mould. Furthermore, with the pole plates the conditions for adapting the magnetic field to variations in the dimensions of the blank, for example the width of slabs during slabs casting, are improved. In an especially advantageous embodiment of the invented device, the possibility of arranging static or periodically low-frequency magnetic fields to act, in accordance with the present invention, at three levels placed one after the other in the casting direction on the non-solidified portions of a cast strand is combined with a compact design. This is achieved by means of a device in which at least two three- legged essentially E-shaped cores are arranged close to two confronting mould walls. The E-shaped cores comprise magnets and are arranged with the back of the E-shaped core in parallel with the casting direction and with the free ends of the three legs directed towards the mould. The free ends of the legs of the three-legged cores thus constitute magnetic poles, which are arranged at three levels arranged one after the other in the casting direction. The magnetic pole at the intermediate level will have an opposite polarity relative to the magnetic poles at the two surrounding levels. The three- legged cores comprise one or more magnets and parts which are made of a magnetic material but do not constitute a magnet . Three different examples of alternative locations, designated A-E, E-B and E-C, of the magnets in the three-legged cores to achieve the pole distribution described above will now be described in more detail: E-A comprises two magnets placed in the two outer legs and oriented such that the two outer poles have the same polarity and consequently such that the intermediate central leg has an opposite polarity. E-B comprises, in the same way as A-E, two magnets which are placed on the back of the E-shaped core on respective sides of the central leg and facing each other with opposite poles; this results in a three-pole core with the desired pole distribution. E-C comprises only one magnet placed in the central leg which, in the same way as E-A and E-B, results in the desired pole distribution. In embodiments where a three-legged core, in accordance with the description in the foregoing, comprises at least two coils supplied with current, each of these may advantageously be supplied from an independent rectifier, whereby the strength of the magnetic fields as well as their direction and distri- bution between the poles are controlled. Flow is an inert phenomenon, with a time constant of 10 seconds or more, and therefore the strength and the direction of the static magnetic field may be advantageously adapted to vary in time, with a low frequency, to control the impulse of secondary flows arisen. By causing a number of magnetic fields to act at a plurality of levels located one after the other in the casting direction according to the invention, the desired control of the move- ments of the melt in the non-solidified portions of the cast strand is achieved. Improvements from the quality point of view are obtained by improving the separation of non-metallic particles and controlling the structure of the solidified metal. In addition, advantages from the production point of view are obtained since the risks of melting of the solidified surface layer or freezing of the upper surface of the melt are essentially eliminated, which is reflected in increased pro¬ ductivity in the plant as a result of improved availability and a higher casting rate. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 4 show embodiments of the invention applied to continuous casting. A number of static or periodically low- frequency magnetic fields are arranged one after the other in the casting direction in order to brake and split up, during casting, an incoming primary flow of hot melt which is supplied to the mould, and to control the flow in non- solidified portions of a cast strand. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiments of the invention which are shown in Figures 1 to 4, a primary flow of hot melt is supplied to a mould 11. The casting process according to the Figures is a so-called closed casting where melt is supplied to the mould through a casting tube 12. The invention may also be applied to so- called open casting when melt is supplied to the mould by means of a free tapping jet . During continuous and semicon- tinuous casting processes, at least one cast strand 1 is formed in the mould 11. The mould 11 is open in both ends of the casting direction. The mould 11 is preferably arranged in the form of a chilled copper mould 11. The casting tube 12 is arranged at its lower end with an arbitrary number of outlets 16, 16a, 16b directed in an arbitrary way. The outlets 16, 16a, 16b of the casting tube are preferably arranged centrally in the mould 11 to supply melt below the level where the meniscus 13 is located during steady state. To brake and split up the melt flowing into the mould 11 and prevent the primary flow of hot melt, which usually contains non-metallic partic¬ les, from penetrating deep down into the cast strand 1 and to control the flow in the non-solidified portions of the cast strand, static or periodically low-frequency magnetic fields are adapted to act on the non-solidified portions of the cast strand at least two levels LI, L2 located one after the other in the casting direction while the cast strand 1 is in the mould 11. According to the invention, magnets 15a, 15b, 150, 150a, 150b, 450a, 450b are adapted to generate at least one magnetic field to act at a first level LI. The first level LI is located close to the upper surface of the melt, the menis¬ cus 13, to ensure that upwardly-directed secondary flows do not give rise to too strong a turbulence and wave formation close to the upper surface 13. This reduces the risk of slag being pulled down from the meniscus 13 and into the melt and creates good conditions for separation of non-metallic par¬ ticles. To obtain a flow channel close to the meniscus 13 and hence to ensure a sufficient heat supply to the upper surface 13 of the melt and hence to prevent this from solidifying, however, it is required that this first level be located at a sufficient distance below the meniscus 13 so as not to elimi¬ nate this desired flow channel. # Downstream of this first level 11, magnets 25a, 25b, 250, 250a, 250b, 550a, 550b are arranged to generate one or more static or periodically low-frequency magnetic fields to act at a second level L2 on the non-solidified portions of a cast strand while the cast strand 1 is in the mould 11. Magnetic fields acting at this second level L2 are adapted to brake and split up the primary flow of incoming melt. Close to or immediately downstream of the outlet end 110 of the mould, magnets 35a, 35b, 350, 350a, 350b, 650a, 650b are arranged to generate additionally at least one static or periodic low-frequency magnetic field to act at a third level L3. Magnetic fields acting at this level L3 control the flow in the non-solidified portions which remain in the cast strand while the cast strand 1 is leaving the mould 11 or after the exit of the cast strand 1 from the mould 11. By applying mag¬ netic fields to act close to the exit of the cast strand from the mould 11, a reduction of the depth of penetration and an improved separation of non-metallic particles located in the melt are obtained. By the splitting up of the primary flow of melt, which prima¬ rily arises through the magnetic fields which act at a level L2 located downstream of the casting tube openings 16, 16a, 16b, secondary flows arise. These secondary flows are con¬ trolled - by arranging magnetic fields, according to the invention, to act at at least one level LI located between the openings 16, 16a, 16b of the casting tube and the meniscus 13 to brake upward secondary flows and control the flow of the melt close to the meniscus 13, and - by arranging magnetic fields to act at at least one level L3 located close to the lower outlet end 110 of the mould or immediately downstream thereof to act in the non-solidified portions which remain in the cast strand, while the cast strand is leaving the mould or after the exit of the cast strand from the mould. In this way, a controlled circulation of melt is obtained in the non-solidified portions of the cast strand 1, which means a good separation of any accompanying particles, a good control of the casting structure as well as good conditions for increased productivity. As will be clear from the figures, a continuous casting mould 11 usually comprises cooled mould plates 11a, lib, lie, lid, preferably water-cooled copper plates. The mould 11 is surrounded by water box beams which, in turn, are surrounded by a frame structure. The magnetic fields which act on the non-solidified portions of a cast strand formed in the mould are generated by magnets in the form of permanent magnets or coils supplied with direct current. The frame structure is provided with a magnetic return path 18a, 18b, 180, 180a, 180b, 280, 280a, 280b, 380, 380a, 380b, 480, 580, 680. Together with the magnets and the magnetic fields acting therebetween, the return paths form a magnetic circuit. Of course, the magnets, the magnetic fields and the return paths may be arranged such that circuits with magnetic flux balance are obtained for each mould half or for smaller parts of the mould 11. In embodiments where it is desired that the static magnetic fields 10 act over essentially the whole width of the cast strand 1 formed in the mould 11, the magnets 150, 250, 350, 450a, 450b, 450a, 550b, 650a, 650b, as shown in Figures 3 and 4, are arranged with a width which essentially corresponds to the width of the cast strand 1 formed in the mould 11, or the long side of the mould. Alternatively, this may be achieved by means of an embodiment of the invention shown in Figure 4. In this embodiment, pole plates 455, 555, 655 are arranged close to two confronting sides of the mould 11. The pole plates 455, 555, 655 are arranged so as to extend along the long sides of the mould 11. Behind the pole plates 455, 555, 655, one or more magnets 450a, 450b, 550a, 550b, 650a, 650b are arranged in the form of coils supplied with direct current, or permanent magnets. The fields from these magnets 15 are brought together and distri¬ buted to generate and apply a static or periodic low-frequency magnetic field which acts over essentially the width of the cast strand formed in the mould. To further improve the possibilities of controlling and dis¬ tributing the propagation and strength distribution of the magnetic fields 10 across the casting direction, the magnets 15 may be arranged with cores which are sectioned. These sections are arranged in the form of both magnetic and non¬ magnetic core elements which may be removed and the section be left open. The same core element may be reinserted in its previous place or be replaced by a core element with other magnetic properties to change the propagation and strength of the magnetic field. With magnets 15 in the form of induction coils supplied with direct current, the core of the coil is arranged with core elements according to the above. In this way, the possibilities of controlling the strength and propa- ga ion of a magnetic field generated by means of the induction coil are increased. With magnets in the form of permanent magnets, a pole core is arranged between the permanent magnet and the mould, the pole core comprising magnetic and non- magnetic core elements which are inserted, removed, or repla¬ ced to change a magnetic field generated by means of the per¬ manent magnet . By applying static magnetic fields one after the other in the casting direction according to the invention, and especially if these magnetic fields are controlled and distributed across the casting direction according to preferred embodiments of the invention, melt is prevented from penetrating down into the cast strand in an unbraked manner, while at the same time the flow of the melt in non-solidified portions of the cast strand is controlled. In this way it is ensured that - non-metallic particles contained in the inflowing melt are separated towards the upper surface, - the upper surface/the meniscus is supplied with a sufficient quantity of hot melt in order not to solidify, and that turbulence and wave formation at the meniscus are essentially avoided. To sum up, a better yield and a higher productivity are made possible by an improved control of the quantity of inclusions and the casting structure can be combined with an increased availability and a higher casting rate.

Claims: CLAIMS 1. A method of controlling the flow of the melt in non- solidified portions of a cast strand (1) which is formed by supplying and cooling at least one primary flow (20) of hot melt directly or through a casting tube (12) in a mould (11) which is open in both ends in the casting direction, wherein the incoming primary flow is braked and secondary flows arisen are controlled by means of a plurality of static or periodically low-frequency magnetic fields which are arranged, at a plurality of levels located one after the other in the casting direction, to act on the non-solidified portions of the cast strand, characterized . , in that the static or periodically low-frequency magnetic fields are generated and applied to act, at at least two levels (LI, L2) located one after the other in the casting direction, on the non-solidified portions of the cast strand while the cast strand is in the mould, and that at least one static or periodic low-frequency magnetic field is generated and applied to act, at at least one level (L3) , on the non- solidified portions which remain in the cast strand while the cast strand is leaving the mould or immediately after the cast strand has left the mould. 2. A method according to claim 1, characterized in that - at least one magnetic field is adapted to act at a first level (LI) immediately downstream of the upper surface/the meniscus (13) of the melt and at a sufficient distance from the meniscus to ensure that upwardly-rising secondary flows are braked such that oscillations and the rate of flow of the melt are damped at the meniscus while at the same time a controlled flow of melt is maintained at the meniscus, - at least one magnetic field is adapted to act at a second level (L2) downstream of the first level such that the incoming primary flow of melt is braked and split up into secondary flows, and - at least one magnetic field is adapted, at a third level (L3) close to the outlet end (110) of the mould or immediately downstream of said outlet end, to act on the non-solidified portions which remain in the cast strand when the cast strand leaves the mould or immediately after the cast strand has left the mould, whereby the depth of penetration of downwardly- directed secondary flows is reduced and separation of partic¬ les accompanying the melt is improved. 3. A method according to claim 1 or claim 2, characterized in that when a primary flow of melt is supplied to the mould (11) by means of at least one casting tube (12) with one or more openings (16, 16a, 16b) which open out into the melt below the meniscus (13), - at least one magnetic field is adapted to,act at a first level (LI) on non-solidified particles of the cast strand downstream of the meniscus and upstream of said casting tube openings, - at least one magnetic field is adapted to act at a second level (L2) on non-solidified particles of the cast strand downstream of said casting tube openings, and - at least one magnetic field is adapted to act at a third level (L3) on the remaining non-solidified portions of the cast strand close to the outlet end of the mould or immediately downstream of said outlet end. 4. A method according to one or more of the preceding claims, characterized in that, at one or more of said levels (LI, L2, L3) , a magnetic field is arranged and distributed to act over essentially the whole width of the cast strand (1) formed in the mould. 5. A method according to claim 4, characterized in that, at one or more of said levels (LI, L2, L3) , a pole plate (455, 555, 655) is arranged close to the wall of the mould (11a, lib, lie, lid) and at least one magnetic pole (450a, 450b, 550a, 550b, 650a, 650b) such that said magnetic field is distributed to act over essentially the whole width of the cast strand (1) formed in the mould. 6. A method according to one or more of claims 1 to 3, characterized in that, at one or more of said levels (LI, L2, L3) , two or more static or periodically low-frequency magnetic fields are arranged and distributed to jointly act over a cross section in the casting direction of the cast stand. 7. A method according to claim 6, characterized in that, at one or more of said levels (LI, L2, L3) , two static or periodically low-frequency magnetic fields, which are directed opposite to each other, are arranged to jointly act over a cross section in the casting direction of the cast stand. 8. A method according to one or more of the preceding claims, characterized in that said magnetic fields, arranged at at least three levels in the casting direction (LI, L2, L3) , are arranged with an intermediate magnetic field (L2) which is directed opposite to both of the immediately surrounding magnetic fields (LI, L3) in the casting direction. 9. A method according to one or more of claims 1 to 6, characterized in that said magnetic fields are generated, applied and controlled independently of each other. 10. A device for controlling the flow of the melt in non- solidified portions of a cast strand (1) which is formed by supplying and cooling at least one primary flow (20) of hot melt directly or through a casting tube (12) in a mould (11) which is open in both ends in the casting direction, wherein magnets (15) in the form of permanent magnets and/or coils supplied by direct current, are arranged to generate, at a plurality of levels located one after the other in the cas¬ ting direction, static or periodically low-frequency magne¬ tic fields to act on the non-solidified portions of the cast strand, thus braking and splitting up the primary flow of melt flowing into the mould and controlling secondary flows arisen, characterized in that said magnets close to the mould are adapted to generate magnetic fields which at at least two levels (LI, L2) act on the non-solidified portions of a cast strand while the cast strand is in the mould, and that magnetic poles are arranged close to or immediately downstream of the outlet end of the mould in order to gene- rate magnetic fields which at at east one level (L3) act on the non-solidified portions which remain in a cast strand while the cast strand is leaving the mould or immediately after the cast strand has left the mould. 11. A device according to claim 10, characterized by - magnets (15a, 15b, 150, 150a, 150b, 450a, 450b) arranged immediately downstream of the upper surface/the meniscus (13) of the melt and at a sufficient distance from the meniscus to generate at least one magnetic field which acts at a first level (LI) and brakes upwardly-rising secondary flows, damps oscillations and the rate of flow of the melt at the meniscus while at the same time maintaining a controlled flow of melt at the meniscus, - magnets (25a, 25b, 250, 250a, 250b, 550a, 550b) arranged downstream of the first level to generate at least one mag¬ netic field which acts at a second level (L2) in the mould and brakes the incoming flow of melt and splits it up into secondary flows, and - magnets (35a, 35b, 350, 350a, 350b, 650a, 650b) arranged close to the outlet end (110) of the mould or immediately downstream of the outlet end to generate at least one mag¬ netic field which at a third level (L3) acts on the non- solidified portions which remain in a cast strand while the cast strand is leaving the mould or immediately after the cast strand has left the mould. 12. A device according to claim 10 or claim 11, characterized in that, when a primary flow of melt is supplied to the mould (11) by means of at least one casting tube (12) with one or more casting tube openings (16, 16a, 16b) arranged under the meniscus, - magnets (15a, 15b, 150, 150a, 150b, 450a, 450b) are arranged close to the mould to generate at least one magne- tic field to act downstream of the meniscus and upstream of said casting tube openings, - magnets (25a, 25b, 250, 250a, 250b, 550a, 550b) are arranged close to the mould to generate at least one magne- tic field to act downstream of said casting tube openings, and - magnets (35a, 35b, 350, 350a, 350b, 650a, 650b) are arranged close to the mould to generate at least one magne¬ tic field to act on the remaining non-solidified portions of the cast strand close to the outlet end of the mould or immediately downstream of said outlet end. 13. A method according to any of claims 8 to 12, characterized in that, at one or more of said levels (LI, L2, L3), pole plates (455, 555, 655) are arranged along the two long sides (11a, lie) of the mould and with an extent across the casting direction sufficient to generate a magnetic field to act over essentially the whole width of a cast strand (1) formed in the mould. 14. A method according to any of claims 8 to 12, characterized in that, at one or more of said levels (LI, L2, L3), magnets (15a, 15b, 25a, 25b, 35a, 35b, 150, 150a, 150b, 250, 250a, 250b, 350, 350a, 350b, 450a, 450b, 550a, 550b, 650a, 650b) are arranged in the form of permanent magnets which have an extent across the casting direction sufficient to generate a static magnetic field to act over essentially the whole width of a cast strand formed in the mould. 15. A method according to any of claims 8 to 12, characterized in that, at one or more of said levels (LI, L2, L3), magnetic poles (15a, 15b, 25a, 25b, 35a, 35b, 150, 150a, 150b, 250, 250a, 250b, 350, 350a, 350b, 450a, 450b, 550a, 550b, 650a, 650b) are arranged in the form of coils, supplied with current, with cores which have an extent across the casting direction sufficient to distribute a static or periodic low-frequency magnetic field to act over essentially the whole width of a cast strand formed in the mould. 16. A method according to any of claims 8 to 12, characterized in that, at one or more of said levels (LI, L2, L3), at least two magnets (150a, 150b, 250a, 250b, 350a, 350b) are arranged and that said two magnets are of opposite polarities to generate at said level two static or periodi¬ cally low-frequency magnetic fields directed opposite to each other. 17. A method according to any of claims 8 to 16, characterized in that magnets (15a, 15b, 25a , 25b, 35a, 35b, 150, 150a, 150b, 250, 250a, 250b, 350, 350a, 350b, 450a, 450b, 550a, 550b, 650a, 650b) are arranged at at least three levels, arranged one after the other in the casting direction, and that the magnets (25a, 25b, 250, 250a, 250b, 550a, 550b) at the intermediate level (L2) are arranged with reversed pola¬ rity relative to the magnets (15a, 15b, 35a, 35b, 150, 150a, 150b, 350, 350a, 350b, 450a, 450b, 650a, 650b) at the imme¬ diately surrounding levels (LI, L3) to generate a magnetic field at the intermediate level (L2) which is directed oppo¬ site to the magnetic fields at the immediately surrounding levels (LI, L3) . 18. A method according to claim 17, characterized in that at least two three-legged, essentially E-shaped cores are arranged close to two confronting mould sides and that said E- shaped cores comprise magnets, that the back of the E-shaped core is arranged parallel to the casting direction and that the free ends of the three legs of the core are directed towards the mould and constitute magnetic poles (15a, 15b, 25a, 25b, 35a, 35b, 150, 150a, 150b, 250, 250a, 250b, 350, 350a, 350b, 450a, 450b, 550a, 550b, 650a, 650b) arranged at three levels (LI, L2, L3), placed one after the other in the casting direction, the magnetic pole at the intermediate level (L2) having a polarity opposite to that of the two surrounding levels (LI, L3) .

Inventors: ERIKSSON JAN ERIK, LEHMAN ANDERS, ERIKSSON, JAN, ERIK, LEHMAN, ANDERS
Applicants: ASEA BROWN BOVERI, ERIKSSON JAN ERIK, LEHMAN ANDERS, ASEA BROWN BOVERI AB, ERIKSSON, JAN, ERIK, LEHMAN, ANDERS
Application year: 1996
Main classification: B22D11
IPC codes: B22D11, B22D27