FI63682C - FOER FARING FOER GJUTNING AV EN METALLSTAONG - Google Patents

Description

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Patent and ocean registration '' AmMun utb * d och uti. * Krtfun pubiicarad y '' (32) (33) (31) Pyydetty stuolksus — Bsflrd prlortMt 28.07.78 02.02.79, 07.02.79 Switzerland-Switzerland (CH), 813V78-0, 1029 / 79-7, 118U / 79-8

Proven-Styrkt J

(71) Concast AG, Tödistrasse 7, 8027 Zurich, Switzerland-Switzerland (CH) (72) Jan Lipton_, Wadenswil, Armin Thalmann, Uster, Axel-Ingo Haefeker,

Au-Wädenswil, Switzerland-Switzerland (CH), Carl-Äke Däcker, Oxelösund,

Sweden-Sweden (SE) (7 * 0 Leitzinger Oy (5M Method for casting a metal bar - Förfarande för gjutning av en metallstäng

The present invention relates to a metal forging process in which molten material is cast into a die, drawn into a rod having a flowable core, further cooled and a vortex flow into the flowable core is provided by at least one electromagnetic field device using a rod-induced stirrer.

The composition of the bar produced by the bar casting method depends, among other things, on the composition of the material and the casting temperature. When the casting temperature is only a few degrees Celsius above, a globulite and non-directional structure is formed, and when the casting temperature is above 15 ° C above the melting temperature, a columnar oriented structure is formed with strong and centrally positive melting of the particles. In practice, for casting technical reasons, it is necessary to cast at an overtemperature of more than 20 ° C. So many burdens are already being created; even in bar casting at temperatures, an ingot with an over-globulite, non-oriented structure is formed, the central melting of which is weak.

In steel bar casting, a method is known for achieving an improvement in the quality of the cast material 2,63682 by magnetic stirring of the molten material core by means of a more or less strong eddy current. These improvements have been achieved by using various methods to apply thrust to the molten material.

Steel contains alloying and additional elements, such as C, Si, Μη, P, S, etc., which, when stiffened, can cause melting and especially mutual melting. Such meltings as well as the crystal structure are known to depend on e.g. the temperature of the overtemperature. The purpose of the electromagnetic stirring, i.e. the eddy current provided, is to prevent such meltings. The stiffening structure should be influenced in such a way as to provide as large a zone as possible of a dense, non-oriented crystal structure. However, it has been shown that the vigorous movement of the molten material affects the stiffening region so that a so-called white ribbons. These white strips are negative melting phenomena that can have a detrimental effect on quality.

When casting ingots or billets, in order to improve both the surface and the inner quality, a method is known for rotating the molten material of a running core about the longitudinal axis of the rod by means of an electromagnetic device. In this case, the rotational movement is effected by an incomplete rotating field (three magnetic poles). Then, although a finer-grained structure is obtained, the formation of a large white band cannot be prevented.

Further known is a device having an electromagnetic device around a mold tube with three pairs of poles which cause a rotating core to rotate about the longitudinal axis of the rod. The rotationality of this rotational current produced by a perfect rotational field is insufficient. The mixing of the liquid steel is therefore incomplete because the uniform magnetic action on the molten material does not cause it any force transverse to the direction of the rod. This relatively low turbulence clearly leaves much to be desired in terms of the quality of the cast product, both in terms of surface and distribution of alloys and additives, as well as in terms of internal structure.

According to the known method, thrust forces are generated in the direction of the longitudinal axis of the rod by an electromagnetic exchange field, whereby the magnets passing around the rod are arranged between the pairs of rollers at the beginning of the casting. The flow along the drain provides a non-columnar structural range and prevents the occurrence of large-scale melting phenomena, especially central melting and white bands. Such a device requires too much space due to the large number of magnets, prevents the rod from cooling sufficiently, and is too expensive.

Another known ingot mold method has attempted to eliminate said white strips by also using an electromagnetic exchange field moved by two magnets facing each other on the longitudinal sides to provide thrust forces to the liquid steel. The purpose of these thrust forces is to act transversely to the longitudinal axis of the rod so as to provide a soft collision of the flow against the hardened wall so that this inverse flow remains within a limited range. This limited area of influence results in a dense, undirected crystal structure of the insufficient area. Furthermore, it has been found that with this method, the slotted strips can only be partially eliminated, so that due to these drawbacks, an optimal product cannot be obtained, which can have a negative effect on the quality of the rolled product, for example.

When tested symmetrically with phase-acting thrusts whose thrust travels perpendicular to the longitudinal axis of the rod, which thrust is provided by a stirrer arranged on the other side of the ingot, the sands show white strips and a wide dendritic strip, which means a cast steel grade.

It is an object of the present invention to provide a method for obtaining optimal bar quality. In particular, it would be appropriate to provide an adequate zone for a denser non-directional crystal structure. The cast material should have no white stripes and not to mention melting, especially with respect to central melting.

The solution to this problem is achieved according to the invention in such a way that the eddy current is provided by different thrust forces acting on the molten material, acting asymmetrically in the fields.

Surprisingly, it has been found that a vortex flow of 4 63682 has been achieved with different forces acting on the molten material inside the fields that, despite the high overtemperature, there are practically no white bands in the sand and a desired zone of larger, more compacted orientation.

Depending on the given casting parameters, according to a preferred application of the method, a pushing direction running in a straight line to the molten material parallel to or transverse to the longitudinal axis of the bar can be provided in a linear manner with different pushing forces acting within the fields. Higher bar thicknesses, using a pushing effect transverse to the direction of travel of the bar, thus reduce the space requirement in the direction of travel of the bar to provide a sufficiently long mixing power.

In another way, in ingot and preform molds, a pushing direction of the molten material extending arcuately with respect to the longitudinal axis of the rod is provided within the fields by differently acting pushing forces. By using this procedure in a mold, in addition to a better internal structure, the surface of the rod can be improved.

In order to provide different thrust forces, in another embodiment of the invention, the coil of the second stage can be acted upon with a different current with respect to the coil of at least one other stage. Preferably, these differences in currents are in the range of 10 to 25%. Of course, thrust forces acting in different ways can be obtained by forming the steps in a geometrically different way.

Surprisingly, it has been found that the eddy current becomes stronger if, according to a further feature of the invention, the weaker thrust of the second stage is made to act before the stronger thrust of the next stage in the direction of movement.

At the start of casting, a certain amount of time elapses before the liquid core can be circulated. In order to then achieve the desired vortex flow, a further feature of the invention further adjusts the phase asymmetry from almost zero to a predetermined maximum value. Thus, it can be achieved that the metallurgical properties of the upstream rod section are also desired.

In the method according to the invention, according to the

II

5 63682 weaves, in addition to the force acting in the mixing direction, a transverse force pulsating between zero and maximum. This additional force further enhances the turbulence when, in accordance with a feature of the invention, by adjusting the direction of travel of the fields asymmetrically, the force acting on the stage, perpendicular to the surface of the mixer, is affected by the agitator surface turned towards the rod.

In this way, a further improvement in quality can be achieved, especially when using a single-sided mixer.

Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

Figure 1 shows a mixing device with a straight line in the direction of push and intended for carrying out the method in an arc device.

Figure 2 shows a sand view of a section of a ingot with the running core of the ingot mixed with a transfer field acting transversely to the rod.

Figure 3 shows the distribution of sulfur along the line III-III in Figure 2.

Figure 4 shows a sandal view of a section of a ingot with the running core of the ingot mixed according to the invention.

Figure 5 shows the distribution of sulfur along the line V-V in Figure 4.

Figure 6 shows a sectional view of an ingot or ingot mold with a stirrer providing an arcuate thrust direction.

In Fig. 1, reference numeral 1 shows a cooled, bent and oscillating die for casting a ingot of running steel from a crucible (not shown) down to a casting tube extending into the die 1. The rod 2 with a running core 3 formed in the mold 1 is guided and supported on the curved rod track 4 following the mold 1 by means of rollers 5. The radius of the tank track 4 is 10 meters. Injection nozzles 6 are arranged between the rollers 5 to further cool the rod 2. The operating direction 7 pulls and directs the rod.

63682

About 5 meters below the mold head, a stirrer is arranged, which is a known interchangeable field structure 10 and which is arranged inside the bar track 4. Between the magnets 10 and the inner surface of the rod 2, rollers 5 'are placed, which are of antimagnetic material, for example stainless steel. The magnet 10 is built in two phases. Three-phase magnets can also be used. The thrust forces produced by the mixer act transversely to the longitudinal axis of the rod.

The size of the ingots cast with the described device was 1550 mm x 270 mm. The drawing speed was about 0.55 m / min. Both phases were supplied with a voltage of 200 V at a frequency of 2 Hz and an intensity of about 100 Aj, i.e. they were affected symmetrically. Figure 2 shows a sand pattern of steel cast at an overtemperature of 29 ° C; the steel contained 0.15% C, 0.025% S and other common additives, and the usual mixing procedure was used. The sand image shows a relatively thin edge zone 20 with a victorious globulite structure. Bounded by this zone is zone 21, the structure of which is columnar with dendrites directed towards the center. Zone 21 is followed by zone 22, which has a non-directional crystalline structure and forms a white band. This strip may consist of a single piece, as indicated by reference numeral 22, or may be divided into several strips 23, 24, 25. The zone 22 is followed by a zone 26, the crystal structure of which is dense and non-directional, and which terminates in a central fusion 27.

Figure 3 shows a quantitative analysis of the sulfur content along line III-III in Figure 2. The coordinate shows the sulfur content in percent and the abscissa the ingot thickness. It can be seen from the diagram that the sulfur content in the white strips (zones 23, 24, 25) is significantly reduced.

Figure 4 shows a sandal view of a section of a ingot mixed by the method according to the invention. The dimensions of the ingot, the quality of the steel, the drawing speed, the direction and frequency of the thrusts were the same as those shown in connection with Fig. 2. The overtemperature was 43 ° C. The current was 830 A for the second phase and 1000 A for the second phase. The second phase is thus powered by a current about 20% stronger than the other, i.e. the phases of the electromagnetic fields are asymmetrical. The sand image again shows zone 31, which is profitably glo-bulitic. Related to this follows zone 32 with dendrites directed to the center of ingot 63682 7. Associated with zone 32 is a poorly formed zone 33 having a non-oriented crystal structure. In the center of Harko there is a zone 34, which is also a non-oriented crystal structure, which, however, is finer and denser than the corresponding one in Fig. 2.

Figure 5 shows a quantitative analysis of the sulfur distribution along the line V-V in Figure 4. It appears from the analysis that by mixing the flowable core with the method according to the invention and the vortex flow thus generated, a relatively even sulfur distribution is obtained. As well as a non-positive middle melt such as a negative molten earth in zone 32 no longer occurs for the most part; moreover, there are only insignificant white stripes.

With the described asymmetry, the thrust forces having a different direction of thrust on the molten material, i.e. a continuous frequency-dependent variation between a stronger and a weaker thrust, substantially increase the turbulence in the flow of the flowing core. Intermittent alternation of a weaker thrust before a stronger thrust, i.e., arranging 830 A-loaded phases before 1000 A phases, results in an intermittently pulsating thrust in the direction of action of the alternating field resulting in an increase in turbulence.

On the basis of the sand pictures, it has been shown that in practical casting operations a substantially longer time interval is required in order to achieve a qualitatively sound casting structure, if an asymmetrical procedure is used at the initial stage instead of the almost symmetrical operation of the mixer. Namely, in order to achieve the desired turbulence in the molten material, it is first necessary to form the flow guides connected to the rod core, the so-called flow rollers, into which additional vorticity is then integrated by an asymmetrical method due to the difference in thrust forces of both stages. This is manifested in practice by the fact that when casting begins until sufficient flow in the rod mass is achieved, mixing begins with only a small current difference in each stage, e.g. 1000 A is fed to stage 1 and almost 1000 A to stage 2. The required flow is generated, i.e. when the flow core is caused eddy rotation, said asymmetric power is turned on. In this way, the first, lower quality part of the ingot can be significantly shortened.

8 63682

Furthermore, it has been found that the direction of travel of the exchange field also has a significant effect on the quality of the casting. When mixed, for example, transversely to the rod in a straight line, it can run from the side of the ingot from left to right or vice versa. The mixer may be arranged on one or both wide sides. The asymmetry generates a transverse force acting mainly perpendicular to the main motion components and also perpendicular to the direction of traction of the rod. If desired, by adjusting the direction of pushing of the fields, the force acting perpendicular to the surface of the mixer should be made to act by the surface of the mixer facing the rod. With certain casting parameters, its direction of action can be rotated 180 °, i.e. from the center of the rod to its surface.

By cooperating with another, opposite mixer, e.g. in the case of thick ingots, the mixers can advantageously be connected so that their alternating fields run opposite each other, whereby the transverse force of both the second and second alternating fields is directed to the center of the rod.

The denser non-oriented crystal structure obtained by the described method as well as the insignificant white strips give substantially better properties to the rolled products when the ingot is rolled. In addition, the device requires little space to achieve optimal eddy flow.

In the example shown, different thrust forces are achieved by using coils with different currents. But these different thrust forces can also be achieved by forming the phases with different geometries, e.g. the coil speeds. Alternating field magnets can also be arranged so that different thrust forces act in the direction of the longitudinal axis of the rod or diagonally against it. Instead of one exchange field acting on one side of the rod, an additional exchange field on the other side of the rod can be used. For rods with long running cores, more than one exchange field can be used in the longitudinal direction of the rod. The vortex flow can also be caused to the mold, in which case the flow is preferably kept such that it does not affect the liquid surface, so that no negative effects occur with respect to the surface of the rod. The described asymmetry can also be achieved by the interaction of several mixer segments in the same mixer using a different phase load or 9 63682 geometric design.

Fig. 6 illustrates the use of the method according to the invention in an ingot mold, in which the arcuate pushing direction causes the molten material to rotate about the longitudinal axis of the rod. Reference numeral 51 is a sectional view of a mold. It consists of a mold tube 52 which is copper and a mold shell 53. A radiator jacket 54 is arranged around the tube 52. Coolant water flows between the mold 52 and the radiator jacket 54. Inside the mold 52, a partially stiffened rod 60 with a flowable core 61 is seen. This rod 60 is pulled from the mold in a known manner and further cooled.

Magnetic terminals 70, 71, 72, 73 are provided on each side of the radiator jacket 54, each of which is provided with a coil 74, 75, 76, 77.

These magnetic poles are cooled by coolant water between the radiator jacket 54 and the mold jacket 53. The coils 74, 75, 76, 77 are connected so as to generate an alternating field. These magnetic poles form an agitator that induces an electromagnetic field in the rod. According to the casting parameters, the first stage is fed with a current 10 to 25% stronger than the second, subsequent stage. For a block of 100 x 100 mm, coils 74 and 76 are loaded with a frequency of 50 Hz and a voltage of 50 V and a force of 400 A, and coils 75 and 7j are loaded with a force of 320 A. The exchange field causes different pushing forces on the running steel, which, based on the arrangement of the magnetic poles described, cause a rotational movement in the molten material. If a deeper penetration of the mixing effect or a lower mixing speed is desired, the frequency is reduced accordingly, especially in the case of a large wall thickness of the mold tube.

Of course, the connection can also be selected so that the magnetic flux flows between the pole pairs 70, 72 and 71, 73, respectively, and the magnetic field is thus used to provide a rotational movement. In this case, the spool pair 70, 72, for example 400 A, and the pole pairs 71, 73 320 A are affected.

In the case of larger ingot or billet sizes, the number of poles can be increased. Instead of an asymmetrical current load on the coils, different acting thrusts can be provided by different acting thrusts of the phases, e.g. different rotational currents or different formation of pole irons, such as changing the cross-sectional shape and size of the iron core and / or pole axis direction, etc.

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An asymmetrical current load and a variable geometric shape can also be combined. The last example shown illustrates mixing * with an arcuate pushing motion in a mold. However, this mixing can also take place in the secondary cooling zone. Instead of an arcuate pushing direction, a straight-line pushing movement in the longitudinal direction of the bar can also be used in the mold.

The method according to the invention can be used in all types of bar casting devices with a through-mold, also in devices for casting support profiles and for metals other than iron. Rods with long liquid cores can be operated with several mixers simultaneously.

Claims (9)

11 63682 A method for casting a metal rod, wherein the molten material is cast, cooked, the resulting rod having a fluid core is withdrawn, further controlled and cooled, and at least one agitator inducing an electromagnetic field into the rod produces a vortex flow in the fluid core, characterized in that is provided by various thrust forces acting on the molten material, caused by the asymmetry of the field phases. Method according to Claim 1, characterized in that in the fields, a pushing direction extending in a straight line to the molten material is provided in the direction of the transverse axis of the rod or transversely to it. Method according to Claim 1, characterized in that in the fields, a pushing direction for the molten material extending arcuately about the longitudinal axis of the rod is provided by different acting pushing forces. Method according to one of Claims 1 to 3, characterized in that the coil of one phase is loaded with respect to the coil of at least one second phase in the field at different currents. A method according to claim 4, characterized in that the second stage coil is loaded with a current 10 to 25% higher than the second stage coil. Method according to one of Claims 1 to 3, characterized in that the thrust forces acting differently are obtained by forming the steps geometrically differently. Method according to one of Claims 1 to 6, characterized in that the weaker thrust of the second stage acts before the stronger thrust of the next stage in the direction of thrust. Method according to one of Claims 1 to 7, characterized in that the asymmetry of the phases during the initial phase is adjusted from almost zero to a predetermined maximum value. 12 6 36 82 Method according to Claim 2 or 6, characterized in that the force acting perpendicular to the surface of the mixer, caused by the asymmetry of the phases, acts on the rod-side surface of the mixer by adjusting the direction of push of the fields.