EP0237558B1

EP0237558B1 - Method and apparatus for continuous casting

Info

Publication number: EP0237558B1
Application number: EP86905974A
Authority: EP
Inventors: Erik Allan Olsson
Original assignee: ERIK OLSSON AG
Current assignee: ERIK OLSSON AG
Priority date: 1985-09-13
Filing date: 1986-09-15
Publication date: 1992-01-22
Anticipated expiration: 2006-09-15
Also published as: SE8504252D0; BG80126A; SE8504252L; NO871949L; AU587867B2; AU6374786A; BR8606863A; JPS63500925A; ES2001785A6; SE464619B; SU1695822A3; PT83360B; PT83360A; CN86106731A; ATE71864T1; FI872097A0; DK241487D0; NO871949D0; KR870700426A; HUT43518A

Abstract

In a method of horizontal continuous casting with a horizontal or inclined mold (1), and heat treating the casting, which is at least partially solidified in the mold, the latter is supplied with melt (13) from a furnace or casting box preferably tippable about the center line of the mold, and via a casting pipe (2), the forward end of which projects into the mold opening. The mold (1) is movable in relation to the pipe (2) and is rotated continuously or stepwise in one direction or turned reciprocally about its center line. Bridging of solidified melt (13) between the pipe (2) and the casting skin (20) solidified in the mold (1) is prevented by a repelling electromagnetic force being caused to act in a substantially radial direction on the melt (13) flowing into the mold (1).

Description

The present invention relates to a method and an apparatus for continuous casting with a horizontal or inclined mold and in line hot working of the solidified casting, wherein melt is supplied into the mold opening from a casting box via a casting pipe having its forward end projecting and open out into the mold opening.
The object of the invention is to improve the reliability of the casting process, the quality of the casting and its surface finish, as well as to enable smoother casting progress and higher casting rates than is the case with the horizontal casting methods in the prior art.
According to conventional horizontal continuous casting methods, the mold is rigidly fastened to, and sealed against, the holding vessel from which the melt is fed to the mold, and which may be a casting box or a furnace, hereinafter designated "casting box". Between this and the mold there is a connection means such as a casting pipe or a casting nozzle, which is also sealingly joined to the mold. The latter is thus not able to move freely from the casting box, casting pipe or casting nozzle, resulting in the prevention of many functions regarded as absolutely necessary for a reliable casting sequence in continuous casting plants with vertical molds.
Among these functions may be mentioned the so-called mold oscillation, i.e. the vertical, reciprocal motion of the mold. This motion only has a short stroke of 5-20 mm in the withdrawal direction of the casting, with a rapid return to its upper position, this movement often being called "the stripping stroke". The mold is usually given a somewhat quicker movement than the casting for the movement in the withdrawal direction, this movement often being known as "negative strip", since the relative movement thus occurring counteracts the tendency of the melt to adhere to the walls of the mold. Since there is friction between the rapidly solidifying casting skin and the mold walls, any transverse cracks caused by tensional stresses, are compressed during the stripping stroke, these cracks then healing together. The thermally most loaded mold part is revealed at the stripping stroke, indeed for only a short time, but sufficiently long to allow effective lubrication and a certain thermal recovery of this mold part. In a vertical mold, the slag particles accompanying the melt are able to rise to the surface of the melt, where they can be skimmed off, or be compounded with so-called "casting powder", if such is used.
In contact with the surface of the melt, the slag and powder fuse and run down towards the meniscus between melt and mold wall. From here the fusion is pulled by the solidifying skin down through the mold to form a anti-friction layer between the skin and the mold wall. The slag particles that do not manage to float up to the surface distribute themselves rather uniformly over the cross section of the vertical casting.
The latter is not the case with horizontal casting according to methods used up to now. The slag particles float up in the casting and collect at its upper part. The rigid and sealing joint between mold and casting box or its casting pipe or casting nozzle allows neither the mold oscillation mentioned above nor lubrication of the mold walls, and accompanying advantages. There is a great risk that the brittle casting skin solidifying in the stationary, horizontal mold will be pulled off, since solidifying melt has a tendency to adhere to the casting pipe or nozzle or to the mold wall, due to the absence of lubrication agent or anti-friction coating.
Stepwise withdrawal of the casting has been practised to counteract the above-mentioned deficiencies and disandvantages in horizontal casting. During the stationary period here the skin solidifying in the mold shall be given sufficient time to grow in thickness and strength without being subjected to tensional stresses, so that it will be better able to withstand them during the casting withdrawal step. To ensure that the skin always ruptures at the same place, and at the mold inlet end, a so-called breaker block is inserted at the junction between casting pipe and mold. The block usually has a smaller through passage than that of the mold, partly to reduce heat transfer at this place and partly thus to fix the position of the weakest section of the solidifying metal, i.e. the place of rupture. In spite of this block being made from very resistant material it is subject to heavy wear, and the consequent need of frequent replacement.
Since a lubricant or slide coating can not be used, a liner of a material providing less tendency to stickyness than conventional mold lining is sometimes used to reduce the adherence of the melt to the mold wall. Graphite is the material most used as lining, but it is worn rather quickly particularly on the underside of the mold, against which the casting skin is urged by its own weight, and is thus most subject to both mechanical and thermal stresses. This one-sided engagement in the mold naturally results in uneven heat dissipation along the periphery of the casting, apart from uneven mold wear, especially as the casting shrinks, causing an air gap between the upper side of the casting and the mold.
Several proposals to solve or avoid this problem have been published. However, none of them has come into practice.
EP-A 0 068 402 deals with the casting particularly of strands of a large transverse dimension. As the solidification time throughout the whole strand section is long, the casting speed must be low. As a result hereof the liquid metal flow through a tundish nozzle having the equal size as that of the mold opening would be very slow and consequently the freezing of a metal layer against the nozzle wall is unavoidable if no means against this are provided for. Therefore, this document proposes not only a reduction of the throughflow area of the ceramic tundish nozzle but also the use of an electro-magnetic force for a rapid flow of the molten metal forwards through the nozzle hole (towards the mold). The electro-magnetic force is accordingly directed longitudinally towards the mold and located in the ceramic nozzle. At the same time as the flowing speed through the nozzle is increased thereby preventing a freezing of the molten metal in the nozzle, the metal is prevented to leak out in the gap between the nozzle tip and the mold opening by applying an electro-magnetic force acting in this area in the casting direction. This is contrary to the present method in which the electro-magnetic force is directed radially for preventing a contact of the molten metal with and formation of a strand shell against the mold wall close to the nozzle tip inside the mold. The above is applicable also to EP-A 0 038 275 and EP-A 0 067 433, which describe methods of continuous casting using electro-magnetic force.
US-A 3,598,173 describes a machine with a mold which is rotatable in relation to the casting pipe. However, this machine would not be suited for industrial use especially not for metals having high melting temperatures. The strand shell would be ruptured at the passage from refractory material to the chill mold wall. The document does not learn how to solve this well known problem, i.e. how to succeed without rupturing the frail strand shell in its solidificating first phase.
The disadvantages mentioned above with horizontal casting methods used up to now are avoided in the present invention, and the advantages hereinbefore described in respect of casting with a vertical mold are regained. The method and apparatus in accordance with the present invention have the characterising features dislosed in the accompanying claims.
In the selection of current strength and frequency it will of course be necessary to take into account the wall thickness of the mold and its ability to let the electro-magnetic flux through, i.e. the electromagnetic permeability of the mold material. For the most usual metallic mold materials and thicknesses the frequency will usually be 60 Hz or less. If the need arises, which may be the case for larger casting dimensions, the electromagnetic permeability can be facilitated by the use of other, preferably non-metallic material, e.g. graphite, in the relevant mold part. This material can be formed into an insert in the mold, the wall of which is thinned off towards the inlet end.
In the rotation of a circular casting, the risk of longitudinal cracks is less, irrespective of the mold motion, if the meniscus, i.e. the line of contact between melt and mold wall, has a varying distance to the mold end or casting pipe mouth along the periphery of the casting. This relationship occurs automatically for a conductor loop arranged concentrically round the mold, since the static pressure of the metal in the mold is greater upwards than downwards, and this is the pressure acting against the uniformly distributed repelling force. However, this force acting on the melt, and thus the path of the contact line (meniscus) round the periphery may be varied with the aid of electromagnetic field properties known per se. The repelling force may thus be weakened or strengthened along desired areas by screens, asymmetric coils or welding another material into the conductor for a given distance such as to vary the current density.
The reason for the above-mentioned lessening of the risk of longitudinal surface cracks is that for the "unsymmetrical" line of contact the growth of the skin does not only take place in the longitudinal direction but also around the periphery. For the contact line of a casting, where the line is inclined to an imaginary plane at right angles to the center line of the mold, the skin growth takes place in the approximate form of a helix. The shrinkage of the casting skin periphery due to the solidification of the melt against the mold wall is thus continuously compensated by a continuous supply of melt solidifying against the mold wall, the melt thus making up the shrinkage both peripherally and longitudinally, which does not customarily take place. The outer skin layer thus adjusts itself better to the periphery of the mold and is in engagement with the cooling mold wall for a longer distance than is otherwise the case. From this it follows that the gap between skin and wall will be less, and occur at a greater distance from the meniscus than otherwise is the case, simultaneously as the part of the casting given the worst cooling, due to the gap formation as the casting rotates, once again comes into contact with the cooling mold wall. In continuous casting according to conventional methods, the gap formation in the mold is a great disadvantage in that the almost absent cooling action of the mold caused by the gap formation results in inhibited growth of the skin and even reheating and weakening of it, with the frequent occurrence of cracks (bursting of the skin) and eruption of melt outside the mold as a result, especially with simultaneously increasing static pressure of the melt. Optimalisation of the mold length is attempted so as to avoid this, such that the casting can be cooled directly by spraying coolant over it as soon as possible. The above-mentioned risk and the need of rapid, direct cooling outside the mold does not occur when the casting is rotated, for easily understood reasons. The mold may therefore be made long and the risk of crack formation and eruption of melt outside the mold are completely obviated. The casting rate may therefore be increased such that availability of space longitudinally for cooling the casting right through will be the deciding factor for the casting rate, and not as previously the risk of eruption of melt outside the mold.
Due to repellance by the electromagnetic force of melt from the mold wall, a more uniform and effective distribution of anti-friction agent via one or more ducts in the casting pipe is also possible, particularly since this repellance results in an inclined casting skin edge. The mouth of the casting pipe may project into the space between pipe and melt. This projecting pipe part can contain supply and distribution ducts for the agent. When casting steel the agent may comprise a vegetable or mineral oil, a so-called casting powder or a metal with a considerably lower melting point than that of the cast metal, e.g. lead, vismuth, aluminium or other easily melted metal alloys. Metals heavier than the cast metal should be supplied through ducts in the lower part of the casting pipe, or along the part facing the downwardly moving part of the rotating mold, while metals lighter than the cast metal should be supplied to the upper part of the mold or to the upwardly moving part of it. This is to avoid a portion of the heavier metal sinking in the melt, or the reverse, which is that a portion of the lighter metal rises in the melt. The flank of the projecting casting pipe facing towards the rotational direction of the casting must be give a configuration, i.e. inclination in relation to an imaginary plane at right angles to the center line of the mold, such that the risk of the rotating skin being thrust in between the projecting casting pipe and the mold wall does not exist.
Particularly with horizontal casting, there is the risk of cavity formation at the center of the casting, as a result of to low a pressure in the still liquid core at the center of the casting, and which is not capable of breaking through the already solidified metal. An increase in pressure may be achieved by inclining the casting a few more degrees in the direction of casting, or by arranging an electromagnetic force acting on the casting skin or wall in the direction of casting. The magnetic field should be placed where the temperature of the casting is still over the curie point, and the conductor current strength and frequency adjusted to the solidified skin or wall thickness of the casting as well as the rotational speed thereof.
Casting tubular, or otherwise hollow castings can be accomplished in accordance with the invention by a still liquid core being prevented from filling out its surrounding skin with the aid of an electromagnetic force acting on the casting in the opposite direction to that of casting. The rotation of the casting guarantees a uniform skin or wall thickness as well as the central location of the hole. It is often an advantage to divide the electromagnetic field into two or more sections. The electric windings generating these sections are suitably mutually separated with respect to current strength and frequency, as well as being movable individually or all together along the casting.
When thin-walled castings, e.g. tubes, are to be cast, it is simpler to incline the mold and casting upwards in the casting direction. The level of the melt or its length inside the casting skin is then allowed to determine the tube thickness, which will be uniform, due to the rotation and uniform cooling of the casting. Should a casting box which is in communication with the mold and tippable about the center line thereof be used, the melt level or its length inside the skin may be decided by the tipping angle of the box and thus the melt level in it. Otherwise the flow of melt to the mold must be controlled by other methods, e.g. by a stopper and coupling bash inserted in the box, a gate in the casting pipe between box and mold or by electromagnetic control of the melt flow through the pipe. Where there are two or multi-line machines with a common casting box, one of the latter solutions will be applicable, since a box tippable about the center line of the mold can not be used. Advance of the tube thus formed is suitably arranged using inclined rolls, which may optionally have a machining function also, similar to the one in conventional tube production methods.
The invention will now be described with reference to the accompanying drawings on which

FIG 1 illustrates an apparatus in accordance with the invention in a side view and partially longitudinal section.
FIG 1A is a cross section along the line A - A in FIG 1,
FIG 1B is a cross section along the line B - B in FIG 1,
FIG 2 illustrates an apparatus in accordance with the invention in a side view and partially longitudinal section.
FIG 3 is a longitudinal section of a detail in a inventive apparatus,
FIG 4 illustrates an apparatus in accordance with the invention in a side view,
FIG 5 is a plan of the apparatus according to FIG 4, and
FIGs 6-8 illustrate means for further processing in the apparatus according to FIGs 4 and 5.

A simple embodiment is illustrated in FIG 1 of a mold 1, freely movable in relation to a casting pipe 2 and cooled by sprayed-on liquid 4. The mold comprises a simple tube, suitable of a material having good conductivity, e.g. copper, and is supported by rollers 5,6. These are provided with flanges 7, which mate with a groove 8 milled into the tube. The mold tube 1 is thus positionally fixed longitudinally, while being able to expand freely in this direction. The tube 1 is provided with a chainwheel 9 at its discharge end for rotation or turning (i.e. rotation through less than 360^o). The chainwheel is driven by a motor via a sprocket 11 and chain 10. The motor is suitably reversible and with variable speed. The drive means 12 for the sprocket 11 can be configurated in several conventional ways.
A conductor means 14 usually in the form of a coil is placed around the inlet end of the mold 1. The mold consists of a non-magnetic metal, e.g. coppar. The conductor 14 is energized with an alternating electric current with appropriate strength and frequency for being able to induce sufficient electro-magnetic flux energy for permeating the mold wall and generating required eddy currents intensity in the molten metal 13 in front of the inlet tube 2 that opens out in the mold opening. According to physical laws a repelling force is, thus, established acting on the molten metal and directed perpendicular to the electro-magnetic field and, thus, also to the mold wall. Consequently, the molten metal is pushed away from the chilling mold wall in the action area of the electro-magnetic field, i.e. just in front of the inlet tube tip. Consequently the molten metal is prevented from solidifying against the mold wall along this area whereby a bridge of solidified metal between the inlet tube 2 and the strand shell 20 solidifying at a longer distance from the inlet tube cannot be formed. As a consequence the mold can be rotated around its centerline or longitudinally oscillated or both at the same time as well. When the mold 1 is oscillated the inlet tube tip shall open out into the mold opening (i.e. the tube boring 2' opens out inside the mold) at a distance from the mold edge that is at least so long as the length of the mold stroke length. The gap between the inlet tube tip and the mold wall should preferably not be bigger than the molten metal at a power interruption is prevented from leaking out but big enough to allow the mentioned mold motions. This allowance may be bigger than what is usual because the mold wall is always chilled by sprayed-in cooling fluids into the gap between inductor coil 14 and the mold walls 1 so that the molten metal will solidify at once upon contact with the mold wall. It is conceivable to use direct current for achievidng the same repelling effect when the molten metal flows across the electro-magnetic field, but as this is not always the case, e.g. at temporary stops of the strand widthdrawal, an alternating current brings about a better reliability.
The effective repelling power depends not only on the current strength and frequency but also on the electro-magnetic permeability of the mold material. Therefore, copper is an appropriate mold material in as much as it has got heat conductivity- In order to facilitate the permeation of the electro-magnetic field the mold has been made so thin walled as possible within the conductor area.
When the conductor coil is concentrically placed around the mold as in FIG. 1, the strand shell start to solidify width an upwards increased distance from the inlet tube tip (2) because the metallostatic pressure is decreasing upwards. The tail end of the solidifying strand shell 20 is indicated with 20' in FIG. 1. This configuration is favourable with respect to strand shell growth in particular as mentioned before. As the distance between the conductor and the molten metal plays a role for the magnetic field strength end, accordingly, the repelling force as well, the inclination of the tail end of the strand shell can abe altered by changing the distance of the conductor to the mold wall over its circumference, but the same can be achieved by inserting shields on desirable places. An antifriction agent that reduces the tendency of metal to stick by the mold wall as well as the friction between the solidified strand shell and mold wall is supplied through the pipe 16. By the rotation of the mold, the agent will be well distributed over the mold circumference.
The conductor arrangement 14 being acting as an inductor for the electro-magnetic field consists usually of from each other isolated turns of a watercooled tube. For facilitating the electro-magnetic flux around the coil turns and for preventing stray current, the conductor tubes are surrounded by a U-formed laminated iron yoke open at the mold side. These details are not shown in FIG. 1.
The rollers 5, 6 for mold tube rotation/turning and the sprocket 11 width its drive are arranged in a frame to a base plate 17. When oscillation, i.e. longitudinal reciprocatory movement is desired for the rotating/turning mold tube, the base plate can be carried by wheels, wheel segment or, as illustrated in the FIG, by needle bearing pads 18. These provide low friction for the reciprocatory movements of the mold and its driving means.
This movement can take place using an eccentric, cam or a cylinder-piston means 19, which may either be hydraulic or pneumatic. As mentioned earlier, what is important here is that in the mold movement in the casting direction the skin 20 formed on the casting in the mold is subjected to a pressure in its longitudinal direction, thus to press together any transverse ruptures occurridng during the stripping stroke.
A stepping motor can be used for a stepping movement of the mold, or a system built up together with the mold oscillation, the mold than being rotated one step at the stripping stroke. A certain amount of peripheral negative strip may be used here, i.e. the mold is turned back a small amount, e.g. by spring action in the means providing the turning movement.
When very narrow or differently dimensioned castings are to be produced, it is suitable to use roller rings instead of allowing the mold to be supported directly by the rollers, different mold sizes can then be inserted in the roller ring.
When a single mold is fed from a casting box, which may optionally be heated, it is advantageous to make the box tippable, with the center line of the mold as turning axis. In addition the box should be displaceable in the transverse and longitudinal directions of the mold. An arrangement for raising and lowering it is also desirable, taking into account position adjustment of the casting pipe of the box in relation to the mold opening.
The casting pipe may include an inner wear-resistant refractory material such as zirconium oxide, alumina with over 90% A1 0 , magnesite etc. If the inner tube is wound with a electric resistance wire, an effective barrier against heat transfer is obtained.
A peripheral negative strip may be used to advantage when the mold is rotated stepwise. Possible transverse cracks can then be pressed together and be healed up. With chain or belt transmission this can be readily arranged so that the non-driven transmission part is pressed in, e.g. by a jockey wheel, a certain amount of counter movement then taking place.
FIG 2 is a schematic side view of a casting, partially in vertical section, in a multi-line casting plant for manufacturing hollow castings, e.g. tubes with desired wall thickness, hollow shaft or hollow blanks for machining etc. The casting box 24 is common to all the molds 21 and castings 20 sloping upwards in the casting direction, where the castings may have different dimensions. The lateral spacing of the molds and castings is assumed to be unalterable, and therefore the spacing of the casting pipes 22 mounted on the box and projecting into the molds must also be constant, i.e. unaffected by any expansion of the plate casing 24 round the box due to heat. For this reason the casing has been provided with a cooling jacket between each pipe.
The casting box is placed on a slide 27, displaceable in the longitudinal direction of the castings by cylinder-piston means 26, the slide being a part of a carriage 28, displaceable transverse this direction. This arrangement allows rapid exchange of an emptied casting box.
The melt 23 in the box 24 communicates via the pipes 22 with each mold 21, which is thus filled to a level corresponding to the melt level in the box 23. The length of the melt core within the solidified casting skin, and thereby the length along which the skin grows in thickness, is thus dependent on the melt level in the box 23. Rapid exchange of the box 24 requires the same inclination of all casting pipes, molds and castings in FIG 2, but the height of them in relation to a selected melt level in the box can be varied from casting to casting, if so desired, and the dimension of the molds and castings may also be varied one from the other. When these parameters have been decided, the desired wall thickness of each casting may now be determined by selecting the appropriate withdrawal and casting rates, these being set by the respective speeds of the driving rolls 29. Continuous withdrawal of the casting with its skin 20' from the mold has been enabled in accordance with the present invention by an electromagnetic field with a repelling action on the melt in the mold having been arranged, and which prevents bridging over between melt solidified on the casting pipe and the skin solidified in the mold.
The electromagnetic field is generated by the conductor 30 being passed through by a high-strength current and placed level with the pipe about the mold 21. This location is necessary so that the flow of melt through the casting pipe 22 will not be disturbed, or quite simply prevented, as would be the case if only penetration of melt into the gap between mold and pipe were prevented according to SE 417 484. This method can be used in certain cases in combination with the present invention, however, which will be explained more closely below.
The drive rolls are inclined in relation to the center line of the casting to give the hollow casting 20, and thereby the solidified casting skin 20 in the mold 21 a rotational movement. If the rotational speed of the skin is made sufficiently large in relation to the rate of withdrawal of the casting, the thickness of the skin formed, i.e. the wall thickness of the casting, will be the same all the way around the periphery. If optional resetting of this arrangement is desired, the drive means of the casting may be placed on swive lable base plates, with the aid of which the inclination of the rolls and thus the rotational speed of the casting in relation to its rate of withdrawal may be changed. In this case it is of course simplest to have all the rolls either horizontal or vertical, and not transverse, as illustrated in FIG 2.
The rotation or turning of the mold is performed by a drive means, and according to FIG 2, this includes a motor 31 with an operable clutch 32, a chain transmission 33 and a chainwheel rigidly mounted on the mold tube. In certain cases, rotation of the mold 21 occurring due to its friction against the rotating casting 20 being withdrawn is sufficient. Here the mold drive means may be cut out by disengaging the clutch 32. A braking means may be arranged for periodically breaking or stopping this movement, such means working on a clutch half, for example, and being enabled or disabled by an electromagnet.
The casting may be cut into desired lengths by conventional methods. However, a rotating casting affords several possibilities of shaping heat working, some examples of which are given later on in this description.
The withdrawal means for the casting 20 may be optionally implemented so that a certain amount of heat working, e.g. to given dimensions or shaping of the casting, can be performed, but a forging machine arranged after the drive rolls may also be a rational solution in the process of continuously producing bar stock. The tools required for such operations are naturally made from material suitable for heat working, and are cooled with a suitable medium where necessary.
Of course, the working operations mentioned above may also be applied in horizontal continuous casting apparatus for solid bars, possibly after the casting has been given suitable dimensions by rolls, as illustrated in figs 6 and 7.
The horizontal casting, cast according to FIG 1, can be rotated or turned, similar to the hollow one upwardly inclined in its transport direction according to FIG 2. Particularly in the horizontal casting of steel and other metals difficult to melt, where the still unsolidified melt in the interior of the casting will be elongate and sharply pointed, there will often be cavities and porousness in the central zone of the casting. The explanation of this is that more or less periodical bridgings of chrystallised melt to in front of the core tip, before the center of the casting as solidified completely. Another reason is certainly the decreasing visosity of the more and more tapering melt core in the interior of the casting as a consequence of successive lowering of temperature and separation on to chrystallisation cores. The static pressure in the melt at the tip is too weak for melt to be urged forward to fill the cavities resulting from solidification shrinkages. Some success has been obtained in improving the interior structure of the casting by using electro-magnetic agitation of the melt in the core tip. However, the tendency to have faults in the center may be reduced by a certain amount of downward inclination of the casting reducing the static pressure in the core tips together with the rotation of the casting.
An example is illustrated in FIG 3 of a plant where mold unit and casting are inclined in the direction of casting. It is also shown here how the mold tube 21 can be rotated or turned in a cooling jacket 40 of approximately the same kind as used in vertical casting. The electromagnetic inductor 41 is built into the jacket 40, which is made from a magnetic material, or is at least provided with welded-in strips of such material, to prevent leaking eddy currents from heating the jacket. The annular yoke 42, consisting of laminated plates, serves to facilitate and amplify the electromagnetic flux round the conductor. When a large dimension is cast, a means according to SE 417 484 may be used together with the means 41, 42 of the present invention. The laminated ring 44 between the electric conductor 43 and the casting pipe 45, 46 prevents the electromagnetic, substantially radially directed forces from closing in and disturbing the flow of the melt 23 through the casting pipe 45, 46.
In order to prevent the melt from sticking to the mold wall, should there be unintentional skew between casting pipe and mold, the outer forward surface of the pipe 45 has been made somewhat convex (at the arrow A), the conductor 43 disposed around the pipe may now be supplied with a current at a higher frequency than the current supplied to the one around the mold, since there is no electrically conductive material between melt and conductor. The electromagnetic repelling force is indeed lower for higher current frequency, but the heat generated in the melt will be greater, which assists in preventing adherence of solidified melt on the pipe and bridging of solidified melt between it and the skin solidified in the mold in the area where the action of the electromagnetic inductor arranged outside the mold ceases.
This arrangement can be advantageous when the casting is cut by a stationary cutter and when the inductor 41 is supplied with direct current. As a result of casting movement needing to be stopped and movement of the melt substantially ceasing during the cutting operation, the action of the repelling force from the d.c. inductor 41 ceases. Melt bridging between casting pipe 45 and skin 20' can consequently occur at 45', since the action of the a.c. conductor 43 is maintained. Melt is thus prevented from penetrating into the gap between mold wall and pipe at 45',simultaneously as the skin has managed to grow in thickness and strength during its period of no movement, and can thus withstand the extra tensional stress to which it is subjected when advance of the casting (withdrawal of the mold) takes place once again. Static friction is greater than sliding friction, as is well known.
FIG 4 - 8 illustrate as examples a survey of some different applications of an apparatus in accordance with the invention, FIG 4 illustrating the casting machine itself as seen from one side, and FIG 5 from above. The casting 21, produced and rotating in this machine is cut to desired casting lengths in the usual way, using a blowtorch 51 in FIGS 4 and 5, or is alternatively taken directly into a roll stand or forging machine.
In FIG 6 a planetary rolling mill has been utilised, and is characterised by a plurality of tapering rolls 67 being driven planetarily round the casting 21, which is thus given the desired dimension. If so desired, the rotating casting can be given a surface treatment, such as a hot grinding descaling process or working by one or more scraper tools arranged along the casting. A heating or heat equalisation stretch may also be desirable.
When the casting rotates, the planetary rolling mill illustrated in FIG 5 may optionally be exchanged for, or supplemented by, stationray rotating rolls 68 (FIG 7), thus making driving of the rollers considerably more simplified compared with the mill drive. Although the schematic figures merely show one pair of mutually opposingly directed rolls nipping the casting round its periphery, three or more rolls are used to avoid breaking up or cavity formation in the center of the casting. Of course, if so desired, the rolling equipment may be exchanged for holding equipment.
The advantage with direct rolling of the rotating casting is inter alia that different casting dimensions can be achieved for one and the same casting dimension, even during the course of one casting procedure, by setting the roll nip to the desired amount.
The rolled-down casting 21, still rotating and without being cut, can then, possibly after passage through a further heating or heat equalisation stretch (unillustrated), be taken to a conventional mill, e.g. for the production of reinforcing bars or wire. Rotation of the casting must be stopped for this purpose. According to FIG 8, this takes place by the rotating roll leader 69 taking the casting in circular form 70 into the rotating drum 71, from which the casting is taken out tangentially to the rolling mill 72 for further rolling or shaping. Possibly necessary, unillustrated equipment for temperature adjustment can be arranged in the drum.
According to FIGS 4 and 5, casting is performed from a ladle 54 provided with a sliding gate 52 and casting pipe 53. In gate, and therewith the flow of melt to the casting vox 24, may suitably be automatically regulatable in respect of the filling level in the box. The latter is tippable about the center line of the mold 20 and casting with the aid of a piston-cylinder means 55, suitably automatically regulated in respect of the melt level in the box 24. To enable rapid exchange of the box when it has become worn for one that has been freshly prepared, these are each placed on a carriage 56 which is movable transverse the casting direction. To enable this movement, the casting box 24, which has its casting pipe 22 projecting into the mold opening, must be moved in the longitudinal direction of the mold. The box is therefore placed on a slide 57, which can be rapidly moved from its position during casting with the aid of the piston-cylinder means 58. The previously described electromagnetic inductor around the foreward end of the tube mold 20 is denoted by the numeral 59. Since the mold rotates, uniform cooling can be achieved by direct spraying of water 60. The rotation or turning of the mold is performed by the drive means 61, and longitudinal oscillation by the cylinder 62. Secondary cooling is denoted by 63 and the support rolls for the rotating casting 21 by 64. Along the casting there is a travelling means 65 for electromagnetically acting on the melt at the center of the casting. The inclined rolls 66 for roational advance of the casting 21 have been shown as lying in different planes, but if it is desired to have rotation adjustable in relation to the advancing rate, they should preferably be placed such that they only engage against the casting from two directions, in order to obtain a simpler drive, which has already been mentioned in connection with FIG 2. For the sake of clarity, drive equipment for the rolls has not been shown in the FIG. This can be performed in different conventional ways. The advancing rate can, of course, be made automatically regulatable in respect of the position of the liquid core tip, which may be sensed by such as supersonic methods. Since the repelling force exercised by the electromagnetic inductor 59 must always be somewhat greater than the static pressure prevailing in the lower part of the mold, it is suitable to introduce here, as well, the automatic regulation of current strength and/or frequency of the current supplied to the inductor in relation to the indicated melt level in the casting box.
The entire operational sequence in a plant like the one described above can be automated using conventional regulation and automating equipment, resulting in the need for a minimum of staff. There is a great advantage in that such a plant can be erected at ground level, resulting in large savings in building costs. Conveying, intermediate storage and heating costs, which otherwise constitute a large part of the cost of the finished product are also reduced.

Claims

A method of continuous casting with a horizontal or inclined mold (21) and in line hot working of the solidified casting (20), wherein melt (23) is supplied into the mold opening from a casting box (24) via a casting pipe (27) having its forward end projecting and open out into the mold opening, characterized by the combination of a repelling electro-magnetic force caused to act close to and in front of the casting pipe tip in a substantially radial direction to the melt (23) flowing into the mold (21) with the fact that the casting (20) is given a rotational movement about its outer line as it is withdrawn from the mold (21).
Method as claimed in claim 1, the mold (21) movable in relation to the casting pipe (22), characterized in that the mold is rotated with another speed and/or direction than the casting.
Method as claimed in claim 2, characterized in that the mold (21) is oscillated in its longitudinal direction.
Method as claimed in claim 1 or 2, characterized in that the repelling force is caused to operate unevenly along the periphery of the melt (22) flowing into the mold (21).
Method as claimed in any one of claims 1 - 4, characterized in that at least a part of the forward end of the casting pipe (22) projects into the part cleared from melt (23) by the electromagnetic repelling force, said projecting part of the pipe being provided with one or more ducts for supplying anti-friction agent to the mold surface, the flank of the projecting part opposite to the direction of rotation of the casting being given a shape such that the risk of an already solidified casting skin being thrust, due to its rotation, into the gap between the casting pipe and the mold wall is reduced.
An apparatus for carrying out the method according to any one of claims 1 - 5 and including a casting box (24) with a casting pipe (22) fastened to it for transferring melt (23) from the box, a cooled mold (21), discharge and conveying rolls (29) for the casting (20) in the mold, and a secondary cooling stretch between the discharge or conveying rolls and the mold, having cooling pipes provided with spraying nozzles (60) and support rollers (64), characterized by an inductor supplied from an energy source is placed outside the mold and drive means (66) for rotation of the casting (20) at its withdrawal from the mold (21).
Apparatus according to claim 6, the mold (21) being movably mounted for its rotation, characterized by means (9 - 11) for breaking or driving the mold (21) in its rotational movement.