EP0237558A1

EP0237558A1 - Method and apparatus for continuous casting.

Info

Publication number: EP0237558A1
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: 1987-09-23
Anticipated expiration: 2006-09-15
Also published as: AU6374786A; BR8606863A; BG80126A; WO1987001632A1; KR870700426A; PT83360B; NO871949D0; ZA866963B; DE3683635D1; EP0237558B1; ES2001785A6; PT83360A; SU1695822A3; SE464619B; SE8504252L; AU587867B2; FI872097A0; NO871949L; SE8504252D0; FI872097A

Abstract

Dans un procédé de coulée horizontale en continu à l'aide d'un moule horizontal ou incliné (1), dans lequel on soumet à un traitement thermique la pièce coulée qui se solidifie au moins partiellement dans le moule, ce dernier est alimenté en bain de fusion (13) à partir d'un four ou d'un châssis basculant de préférance autour de la ligne centrale du moule, et via une conduite de coulée (2), dont l'extrémité avant fait saillie dans l'ouverture du moule. Le moule (1) est mobile par rapport à la conduite (2) et tourne en continu ou par pas dans un sens, ou effectue un mouvement de va-et-vient autour de sa ligne centrale. La formation de ponts de matières solidifiées (13) entre la conduite (2) et la croûte de moulage (20) solidifiée dans le moule (1) est empêchée par une force électromagnétique de répulsion agissant dans un sens essentiellement radial sur le bain de fusion (13) s'écoulant dans le moule.In a continuous horizontal casting process using a horizontal or inclined mold (1), in which the casting is subjected to a heat treatment which solidifies at least partially in the mold, the latter is supplied with bath from a furnace or a tilting frame preferably around the central line of the mold, and via a casting line (2), the front end of which projects into the opening of the mold . The mold (1) is movable relative to the pipe (2) and rotates continuously or in steps in one direction, or performs a back-and-forth movement around its central line. The formation of bridges of solidified materials (13) between the pipe (2) and the molding crust (20) solidified in the mold (1) is prevented by an electromagnetic repulsive force acting in an essentially radial direction on the melt. (13) flowing into the mold.

Description

Method and apparatus for continuous casting

The present invention relates to a continuous casting method with a horizontal or inclined mold, with subsequent treatment of the casting withdrawn from the mold, as well as an apparatus for carrying out the method. The object of the invention is to improve the re¬ liability 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, here¬ inafter 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 pre¬ vention 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 sec¬ tion 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, hori¬ zontal 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 un¬ even 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. he disadvantages mentioned above with horizontal casting methods used up to now are avoided in the present invention, and the advantages herinbeξore described in respect of casting with a vertical mold are regained. The method and apparatus in accordance with the present in¬ vention have the characterising features disclosed in the accompanying claims. In accordance with the present invention, the mold is given a continuous or stepwise rotational movement, or is reciprocally turned about its center line. By this means there is obtained a more uniform and improved .(intensified) cooling action along the periphery of the casting, since the casting is urged by its own weight against the under¬ side of the mold, this side being thus most stressed ther¬ mally and mechanically, but continually changing due to the .movement mentioned. In the casting of circular castings there will furthermore be a peripheral relative movement between the skin and the mold surface, which will contri¬ bute to reducing tensional stresses and thus reduce the risk of withdrawal cracks on withdrawing the casting, since stationary friction is no longer present due to the rotational movement of the mold. This rotational movement may possibly be coupled to the mold oscillation such that the mold is only turned in conjunction with the stripping stroke. This will give the stripping stroke a helical path. In addition, this mold motion affords the possi¬ bility of a simplified cooling system for the mold. The system otherwise used, a tubular mold with a surrounding cooling jacket having the task of uniformly distributing the flow and action of the cooling medium along the peri¬ phery of the casting, may now be exchanged for the simpler method of spraying the coolant on the mold, since its rotation answers for evening out the cooling action.. The mold motion may either be provided by a separate driving means or,, when the casting on withdrawal from the mold is also rotated (as will be described below) , with the aid of the friction present between, casting and mold wall. A relative movement between these surfaces or a stepwise or jerky rotation can then take place by braking the mold movement.

An oscillation, i.e. a reciprocatory movement, of the horizontal or inclined mold, additionally gives advantages put foreward above for the oscillation of a vertical mold. There is thus achieved more effective lubri¬ cation and thermal recovery in conjunction with the stripping stroke, as well as the compression and healing of any possible transverse cracks caused through using negative strip. The requirement for the effective lubri- cation and thermal recovery is,, however, that the most affected part, i.e. where the molten metal comes into contact with the mold wall before a skin has been formed. 5 i.e. in conjunction with the striping stroke, is main¬ tained free from melt, i.e. the melt continuously fed to the mold is kept out of contact with this part of the mold wall. From the publication DE 2 548 940 it is known to prevent, with the aid of the electromagnetic repelling action generated in a control conductor arranged along a joint and supplied with alternating current, the pene¬ tration by melt into the joint between two tubes, one of which may be movable, and could easily be a mold, while the other is a ceramic casting device through which melt is fed to the mold.

The surfaces on either side of the gap will naturally be cleared of melt, as will be seen from FIG 5 in the publication. However, when the mold, oscillates, there is a risk that the joint or gap between the two parts will be too large in the mold movement in. the casting direction, thus permitting melt to leak out. In order to prevent such a situation when the mold oscillates, it is safer to allow the forward end of the casting pipe to come into the mold by a length at least corresponding to the stroke of the oscillatory motion. The electric conductor providing the repelling force must consequently be placed outside the mold. 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 flax 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, pre¬ ferably 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 shrink¬ age 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 shrink- age 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 en¬ gagement 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 dis¬ advantage in that the almost absent cooling action of the

5 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

10. 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 5 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

20 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 5 distribution of anti-friction agent via one or more ducts in the casting pipe is possible, particularly since this repellance results in an inclined casting skin edge. The mouth of the casting pipe may project into the space bet¬ ween pipe and melt. This projecting pipe part can contain 0 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. 5 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, suitably 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°) . The chainwheel is driven by a motor via a sprocket 11 and chain 10. The motor is suit¬ ably reversible and with variable speed. The drive means 12 for the sprocket 11 can be configurated in several conventional ways.

A conductor means supplied with alternating current is placed round the gap joint 14.and the mold tube. The purpose of this is to prevent, melt penetrating into the spalt joint, which is the space between the tube 1 and a casting pipe or casting nozzle 2 fastened to the unillust- rated casting box or furnace and through which melt is supplied to the tube 1. The alternating electromagnetic field generated in the conductor induces alternating currents in the melt. The result of this arrangement is that there is a repelling force directed towards and at right angles to the conductor and its surrounding electromagnetic field. This force urges the melt away from the gap and the sur¬ face of the mold tube within the zone of action of the electromagnetic field. It is conceivable to use an electro-magnetic field generated by direct current, since it is known that currents of the same character are gene¬ rated if a non-magnetic substance, i.e. a melt in this case, moves within a magnetic field such that it cuts the field. However, it is uncertain whether the movement in the melt in the mold closest to the vicinity of the casting pipe adjacent the mold wall is sufficiently great. In any case, this is not so when there is an interruption in casting, which may occur knowingly, i.e. when it is desived to part the casting when it is stationary. For this reason alternating current has been chosen here, at a frequency suited to the magnetic permeability of an inter¬ mediate mold wall. The repelling action of the field on the melt is dependent on the electromagnetic permeability of any intermediate material, and its thickness. The distance to the conductor also plays a decisive role. The thickness of the mold wall has therefore been reduced in this part of the mold tube (at the arrow 15) . An anti-friction agent, which does not reduce the tendency of the melt to adhere to the tube wall, but reduces the friction between the. tube wall and the casting skin solidifying against it. This agent is supplied through a pipe 16. The location of this pipe around the mold tube or the casting pipe/nozzle should be appropriate to the agent used, as already de¬ scribed above. Metering out the agent may performed by an advancing screw in the extension of the illustrated pipe 16.

The rollers 5,6 for mold tube rotation/turning and the sprocket 11 with its drive are arranged in a frame to a base plate 17. When oscillation, i.e. longitudinal reci- procatory 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 occurring 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 then 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-resis¬ tant 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-rdriven 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, dis- placeable 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 5 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, 10. howe-ver, 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 15 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 0 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 5 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 0 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 5 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 unsolidi- fied 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 ex- planation 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 cast¬ ing 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 taper¬ ing 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 roll¬ ing mill Illustrated in FIG 5 may optionally be ex¬ changed 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 cast¬ ing 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. Accord¬ ing 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 ex¬ change 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 electromagnet',c 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

1. A method of continuous casting with a horizontal or inclined mold, and heat treating the at least partially solidified casting in the mold, wherein the melt is supplied to the mold from a furnace or casting box tippable about the center line of the mold and via a casting pipe having its forward end projecting into the mold opening, characterized in that bridging of solidified melt between the pipe and the casting skin solidified in the mold is prevented by a repelling electromagnetic force being caused to act in a substantially radial direction to the melt flowing into the mold.

2. Method as claimed in claim 1, characterized in that the mold is movable in relation to the casting * pipe, and is rotated continuously or stepwise in one direction or is turned reciprocally about its center line.

3. Method as claimed in claim 2, characterized in that the casting is given a rotation movement as it is withdrawn from the mold.

4. Method as claimed in claim 2, characterized in that the mold is oscillated in its longitudinal direction.

5. Method as claimed in any one of the preceding claims, characterized in that the repelling force is caused to operate unevenly along the periphery of the melt flowing into the mold.

6. Method as claimed in any one of the preceding claims, characterized in that the tip of the casting pipe, which is fastened to the furnace or casting box, opens out into the mold opening.

7. Method as claimed in any one of the preceding claims, characterized in that at least a part of the forward end of the casting pipe projects into the part cleared from melt 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 cast- ing skin being thrust, due to its rotation, into the gap between the casting pipe and the mold wall is reduced.

8. Method as claimed in claim 3, characterized in that upstream of the casting advance drive means there is exercised an electromagnetic force substantially in the casting direction and. on the still liquid metal core to prevent the melt from entirely filling the cast¬ ing when the casting skin or wall has reached a desired thickness, so that a tubular casting is formed.

9. Method as claimed in any one of the preceding claims, characterized in that the casting is worked to . the desired cross section by tapering rolls, possibly after the casting has passed a temperature equalising stretch.

10. Method as claimed in claim 9,. characterized in that the tapering rolls rotate planetarily about the casting, possibly after the casting has passed a temperature equalizing stretch.

11. Method as claimed in claim 9, characterized in that the tapering rolls are stationary.

12. Method as claimed in claim 3 or claim 10 in as much as these are subordinate to claim 3, characterized in that, with the aid of a leader means rotating with the casting, the rotational movement of the casting is converted to a helical movement discharging the casting tangentially.

13. Method as claimed in any one of the preceding claims, characterized in that the mold and casting are downwardly inclined in the casting direction to increase the static pressure in the liquid tip.

14. Method as claimed in any one of the preceding claims, characterized in that the mold or casting are upwardly inclined in the casting direction, and in that the level or length of the melt not yet solidified inside the casting skin is adjusted to the desired wall thickness of the tubular casting thus formed.

15. Method as claimed in any one of the preceding claims, characterized in that the desired static pressure in the mold is maintained by the casting box or furnace being tipped about a centre coincident with the center line of the mold, and in that the degree of this tipping is controlled according as the value of the inductive resistance in the conductor surrounding the mold and providing the electromagnetic repelling force.

16. Method as claimed in any one of the preceding claims, characterized in that the melt is fed into the mold from means under vacuum.

17. Apparatus for carrying out the method according to any one of the preceding claims, and including: a) a casting box with a casting pipe fastened to it for transferring melt from the box to a mold, b) a horizontal or inclined, cooled mold, 6) discharge and conveying rolls for the casting cast in the mold, d) a secondary cooling stretch between the discharge or conveying rolls and the mold, having cooling pipes provided with spraying nozzles and also support rollers, e) a parting device for the casting, possibly placed such that the casting has first been heat-treated, characterized in that the mold is movably mounted for its rotation or partial rotation (turning) and longitudinal oscillation, in that an inductor supplied from an energy sources is placed outside the mold in the vicinity of the input end of the mold, and in that there are drive means for the mold movements.

18. Apparatus as claimed in claim 17, characterized in that a casting box is mounted on a slide and a carriage for rapid exchange of one casting box for another.

19. Apparatus as claimed in claim 17 or 18, characterized in that the drive means for mold rotation or turning is regulatable and disconnectable from the mold.

20. Apparatus as claimed in any one of claim 17 - 19, characterized in that the mold comprises a simple metal tube, which is cooled by spraying it with water.

21. Apparatus as claimed in any one of claims 17 -

20, characterized in that the mold is inserted in a cooling jacket and sealed against it such that the mold tube can be rotated or turned and be allowed to expand as a result of being heated.

22. Apparatus as claimed in any one of claims 17 -

21 , characterized in that the forward end of the casting pipe projecting into the mold opening has a shape such that a part of its wall projects into the space cleared from melt by the action of the electromagnetic inductor surrounding the mold, and in that the casting skin solidified against the mold wall is not urged into the gap between this pipe part and the mold wall when the casting is rotated or turned during its withdrawal.

23. Apparatus as claimed in claim 22, characterized in that a friction reducing agent is supplied to the mold wall via one or more ducts in or on the projecting casting pipe part.

24. Apparatus as claimed in any one of claims 17 - 23, characterized in that the discharge or conveying rolls are disposed at an angle inclined to the casting, thus to cause a rotational withdrawal or conveying movement in the casting.

25. Apparatus as claimed in claim 24, characterized in that the discharge or conveying rolls are mounted in swivellable stands, which allow an alteration of the angle between rolls and casting, and accordingly an alteration in the relationship between casting rotational movement and conveying speed of the casting.

26. Apparatus as claimed in any one of claims 17 - 25, characterized in that a planetary rolling mill is arranged after the discharge and conveying rolls for rolling the casting down to the desired dimension.

27. Apparatus as claimed in any one of claims 17 - 25, characterized in that rolling equipment is arranged after the discharge and conveying rolls, and comprises one or more sets of at least three driven rolls, stationarily located round the rotationally moving cast¬ ing and urged against it for its reduction rolling to the desired dimension.

28. Apparatus as claimed in any one of claims 17 -

27, characterized by a means for inhibiting the rotational movement of the casting and comprising a curved leader rotating in a manner corresponding to that of the casting and delivering the casting in a circular form.