Metal founding – Including means to directly apply magnetic force to work or... – By electromagnetic means
Reexamination Certificate
1999-10-18
2001-12-25
Elve, M. Alexandra (Department: 1725)
Metal founding
Including means to directly apply magnetic force to work or...
By electromagnetic means
C164S466000
Reexamination Certificate
active
06332493
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device with magnetic means, a magnetic brake which, in simultaneous casting of two strands by means of a continuous or semi-continuous casting process, is arranged for on the one hand braking a primary flow of hot melt which is introduced into a casting mold, made up of two sub-molds, and on the other hand controlling the secondary flow of melt which then arises in the non solidified parts of the strands in the sub-molds during the forming of the melt to strands.
The invention also relates to a device for simultaneous continuous or semi-continuous casting of two strands, comprising;
a chill mold, including a casting mold divided into two sub-molds, support beams arranged surrounding the casting mold, and chilling means for chilling the chill mold and the support beams, and to provide chilling agent to chill the melt during the casting, and
a magnetic brake for applying to the molten metal present in the chill mold at least one static or periodic low frequency magnetic field.
PRIOR ART
in continuous and semi-continuous casting processes for forming elongate castings, for continuously cast steel called strands, chill molds are used which are open at the both ends in the casting direction. The chill mold in the present application is understood to have both the casting mold in which the strand is formed, and support beams arranged around the mold, together with the chilling means which are provided for chilling the mold and the support beams, and to provide chilling agent for chilling the melt during the casting. The casting mold may consist of one or more parts, but is normally comprised of four chilled copper plates. The support beams comprise conduits in which chilling agent, preferably water, flows during the casting, and are normally referred to as water beams. The water beams are arranged surrounding the casting mold in good thermal contact with the mold in order to perform its double function of supporting and chilling the casting mold. The casting mold is fed with hot melt through a casting pipe which is submerged in the melt present in the casting mold—closed casting—or through a free tapping jet—open casting. In the casting mold, the hot melt is chilled and formed into a strand. The strand leaves the casting mold continuously and when leaving, it has a solidified skin which from a mechanical point of view is self-supporting, and a center of non-solidified melt. If the hot melt is allowed to flow into the casting mold in an uncontrolled manner, it will, due to its mechanical momentum, penetrate deep into the non solidified parts of the strand, which has a number of negative effects; undesired non-metallic particles present in the melt will penetrate deep into the melt and be trapped there, and furthermore the control of the temperature in the solidification front is rendered more difficult, and thus the control of the casting structure. From EP- 0 040 383, it is known to arrange means for generating a magnetic field adjacent to the casting mold for applying to the melt in the casting mold at least one static or periodic low frequency magnetic field. The magnetic field is applied to act over the melt in order to brake and split an incoming flow of hot melt, and to control the flow of melt in the non solidified parts of a strand which is being formed in the casting mold. Means for generating a magnetic field for the above purpose is at present referred to as a magnetic brake, or, when the magnets are electromagnets, an electromagnetic brake, EMBR. A magnetic brake is comprised of magnets and a magnetic feedback device, i.e. a yoke, which closes the magnetic circuit. Since the magnetic circuit is closed by means of said magnetic feedback device, the magnetic losses in the brake are reduced. The word magnet is, preferably, to be understood as an electromagnet, i.e. a coil which is fed with an electric current with a core of an electric conductor, but in some circumstances, permanent magnets may also be suitable. A brake comprising electromagnets is in the following referred to as an electromagnetic brake. In addition to the previously described qualitative improvements which are obtained when a static or periodic low frequency magnetic field, in the following referred to as a magnetic brake field, is applied to the melt by means of a brake, a number of manufacturing related advantages are achieved. The risk of melt re-melting and penetrating the solidified skin, with resulting long periods of down time in the manufacturing process is reduced, and it has in many cases shown to be possible to obtain an increase in the casting speed.
The chill mold is mounted and suspended in a framework. A vibrating table is arranged to vibrate the framework during casting in order to provide to the chill mold an oscillating motion, said oscillation preferably being in the casting direction. It is common for the electromagnetic brake to be mounted with the chill mold in the same framework, but the chill mold and the brake may be mounted in different frameworks, the latter being preferable when it is desirable to reduce the oscillating mass.
In order to increase production, in some casting plants a plurality of casting strands are formed in parallel. In parallel casting of large dimension strands, notably the casting of plate castings, commonly known as slabs, a rectangular casting mold is used, in which a partition is arranged to divide the casting mold into two sub-molds. Preferably the casting mold has the four conventional wall plates, arranged to constitute the long and short-sides of the casting mold, and at least one additional wall which is arranged as a partition in the casting mold between the sub-molds. In this way a plurality, preferably two slabs may be cast simultaneously in parallel in the same chill mold. This type of casting is commonly known as twin-casting. The partition is called T-wall, twin-wall, and each sub-mold is called T-mold. Each T-mold is provided with at least one hot flow of molten material, from which a casting strand is formed in the above described manner. When an electromagnetic brake, comprising a magnetic core with a width which essentially corresponds to the width of the long side of the original casting mold, is used to brake and subdivide these incoming flows, the magnetic fields which act in the respective sub-mold will be asymmetrical in relation to the incoming melt flow, as shown in FIG.
1
. Said asymmetry may under certain circumstances be unfavorable from a metallurgical point of view.
In order to avoid asymmetrical brake fields, it is known, for example, from the European patent EP 0 265 796, known to arrange a brake with a pole pair at each T-mold. The brake described in EP 0 265 796 generates a brake field in accordance with
FIG. 1
b
, which shifts polarity between the pole pairs. In order for this brake to generate a brake field which is symmetrical in both molds, the T-wall must be placed symmetrically between said pole pairs, and preferably in the center of the rectangular casting mold. In twin-casting, however, it is common to arrange the T-wall displaceably in relation to the center of the casting mold, to allow casting of strands of different sizes in the two T-molds. A brake according to
FIG. 1
a
or
3
a
is therefore unable to generate magnetic fields which are capable of acting symmetrically for different positions of the T-wall without providing the magnets with means for displacing the magnet poles sideways.
Preferably, each pole pair should be displaceable independent of the other pole pair. This requires a lot of space, which is normally not available adjacent to the chill mold. Further, magnetic leak flows between adjacent poles on the same side of the casting mold arise when trying to apply magnetic fields acting on a substantial portion of the width in the both submolds, due to their different polarity. Said leak flows may under certain circumstances disturb the flow in the sub-molds.
As an alternative, a brake is used with a pole width which is larger than the total width of
Hallefalt Magnus
Svahn Conny
Svensson Erik
ABB AB
Dykema Gossett PLLC
Elve M. Alexandra
Kerns Kevin P.
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