Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1993-07-09
1995-04-11
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164502, B22D 2702
Patent
active
054049334
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and a device for controlling the flow of liquid metal in non-solidified portions of a cast strand by means of static magnetic fields arranged adjacent to a mould used for forming the metal into a cast strand. Liquid metal--molten metal--flowing into the mould is slowed down and the flow of liquid metal in the non-solidified portions of a cast strand is controlled by controlling and distributing the propagation and intensity of the magnetic field, particles accompanying the molten metal thus being separated and floating up to the surface.
The invention is especially applicable to continuous casting in a chilled mould in which an uncontrolled inflow of hot molten metal containing slag particles or other nonmetallic particles, and/or an uncontrolled secondary flow, entail problems both from the point of view of quality and production technique.
BACKGROUND ART
In continuous casting, hot molten metal flows directly or through a casting tube into a mould. In the mould the molten metal is cooled and a solidified, self-supporting surface layer is formed before the strand, the blank, leaves the mould. If inflowing molten metal is allowed to flow into the mould in an uncontrolled manner, it will penetrate, due to its impulse, deep down into the non-solidified portions of the strand. This renders difficult the separation of particles trapped in the molten metal, which adhere to the solidification front instead of being separated to the upper surface. In addition, the self-supporting surface layer is weakened, which increases the risk of molten metal breaking through the surface layer formed in the mould.
From, for example, Swedish patent SE 436 251, it is known to arrange one or several static or periodic low-frequency magnetic fields in the path of the molten metal to brake and split up the inflowing molten metal. The magnetic fields are generated by means of magnetic poles, permanent magnets or induction coils supplied with direct current, and are arranged to act across the inflowing molten metal. The magnetic poles are arranged close to two opposite mould walls. However, the solution according to the above does not take into account any changes and non-symmetry in the flow configuration. Changes and non-symmetry in the flow configuration occur not only because of changed mould dimensions and non-symmetrical location of the casting tubes, but also by, for example, erosion and clogging which disturbs the flow out of the casting tube.
A non-symmetrical flow configuration entails great problems with regard to quality and production engineering: For example, hot molten metal, with or without non-metallic particles, may penetrate without being braked deep down into the non-solidified parts of the strand with ensuing quality problems. The upward flows of hot molten metal towards the upper surface, the meniscus, may become too weak, resulting in a risk of the meniscus freezing. If, instead, the upward flows become too strong, wave formation arises on the upper surface as a result of the turbulence, which pulls down slag from the upper surface into the molten metal with ensuing quality problems.
SUMMARY OF THE INVENTION
According to the invention, the flow of the molten metal in non-solidified portions of a strand is controlled in the casting of metal in which at least one strand--slab, bloom or billet--is formed in a mould which is downwardly open and which, directly or through a casting tube, is supplied with at least one primary flow of hot, inflowing molten metal, by means of at least one static or periodic, low-frequency magnetic field. The static magnetic field is generated close to the mould by means of magnetic poles, permanent magnets or coils supplied with direct current. The mentioned static magnetic field is applied to act with a maximum magnetic field strength in the mould exceeding 1000 Gauss. It acts in the path of the inflowing molten metal to brake and split up the primary flow of molten metal flowing into the mould and thus prevent inflowing hot mol
Andersson Erland
Eriksson Jan-Erik
Kollberg Sten
Tallback Gote
Asea Brown Boveri AB
Lin Kuang Y.
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