Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Reexamination Certificate
2000-08-31
2002-10-15
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
C164S471000, C164S507000, C164S443000
Reexamination Certificate
active
06463995
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a device for continuous or semi-continuous casting of metal or metal alloys into an elongated strand, where the strand is cast using a device comprising a cooled continuous casting mold and an inductive coil arranged at the top end of the mold. The coil is supplied with a high frequency alternating current from a power supply. The invented device exhibits low induced power losses.
BACKGROUND ART
During continuous or semi-continuous casting of metals and metal alloys, a hot metal melt is supplied to a cooled continuous casting mold, i.e. a mold which is open in both ends in the casting direction. The mold is typically water-cooled and surrounded and supported by a supportive back-up structure. Typically the back-up structure comprises a plurality of support beams or back-up plates provided with internal cavities or channels for a coolant such as water. Melt is supplied to the mold where the metal is solidified and a cast strand is formed as it is passed through the mold. A cast strand leaving the mold, comprises a solidified, self-supporting surface layer or shell around a residual melt. Generally it can be said that conditions of initial solidification is critical for both quality and productivity. A lubricant is typically supplied to the upper surface of the melt in the mold. The lubricant serves many purposes, amongst others it will prevent the skin of the cast strand first developed from sticking to the mold wall. Normal adherence between oscillation show as so called oscillation marks. Should the solidified skin stick or adhere more severely to the mold it will show as severe surface defects and in some cases as ripping of the first solidified skin. For large dimension strands of steel the lubricant is predominantly a so-called mold powder comprising glass or glass forming compounds that is melted by the heat at the meniscus. The mold powder is often continuously added to the upper surface of the melt in the mold during casting, as an essentially solid, free flowing particulate powder. The composition of a mold powder is customized. Thereby the powder will melt at a desired rate and lubrication will be provided at the desired rate to ensure lubrication. A too thick layer of lubricant between mold and cast strand will also effect the solidification conditions and surface quality in an undesired way, thus the thermal conditions at the meniscus need to be controlled. For smaller strands and for non-ferrous metals oil, typically vegetable oil, or grease is used as lubricant. Irrespective of what type of mold lubricant is used it should preferably be fed into the interface cast strand/mold at an even rate sufficient to form a thin uniform film in the interface to avoid surface defects originating from adherence between mold and strand. A too thick film might cause uneven surface and disturbs the thermal situation.
Heat losses and overall thermal conditions at the meniscus are predominantly controlled by the secondary flow that is developed in the mold. The use of inductive HF heaters for influencing the thermal situation at the top end is discussed in e.g. U.S. Pat. No. 5,375,648 and in earlier not yet published Swedish Patent Application No. SE-A-9703892-1. High thermal losses are compensated by a supply of heat to the upper surface, either by a controlled upward flow of hot melt or by a heater, otherwise the meniscus can start to solidify. Such a solidification will severely disturb the casting process and destroy the quality of the cast product in most aspects.
A high frequency inductive heater arranged at the top end of a continuous casting mold will provide means to improve the temperature control at the upper surface of the melt, the meniscus, and the same time generate compressive forces acting to separate the melt and the mold, thereby reducing the risk for sticking, reducing oscillation mark and in general provide improved conditions for mold lubrication. This technique, which today often is referred to as electromagnetic casting, EMC, for an improved lubrication and thus improved surfaces is primarily attributed to the compressive forces acting to separate the melt from the mold. The inductive heater or coil may be of single-phase or poly-phase design. Preferably a high-frequency magnetic alternating field is applied. Typically the inductive coil is supplied with an alternating current having a base frequency of 50 Hz or more, preferably, at least when a mold assembled from four mold plates are used, with an alternating current having a base frequency of 150-1000 Hz. Most preferred for large size slab molds is an alternating current having a base frequency of about 200 Hz. The compressive forces, generated by the high frequency magnetic field, reduce the pressure between the mold wall and the melt, whereby the conditions for lubrication are significantly improved. Surface quality of the cast strand is improved and the casting speed can be increased without risking the surface quality. Oscillation is primarily applied to ensure that the cast strand leaves the mold. As the compressive forces act to separate the melt from the mold they will minimize any contact between the melt and mold during initial solidification of the skin and improve the feed of lubricant hereby further improving the surface quality of the cast strand. Thus the use of an inductive coil supplied with a high frequency alternating current and arranged at the meniscus is believed to provide a means to substantially improve surface quality, internal structure, cleanliness and also productivity. However, it has been noted that the induced power losses are high. The typical mold for casting large size slabs comprises a mold with four mold plates made in copper or a copper alloy. These mold plates are backed by a supporting back-up structure of plates and/or beams. The beams comprises internal channels or cavities for a coolant such as water and it is known to use stainless steel in this back-up structure to reduce the inductive power losses, but they are still substantial. For example has an EMC device for a continuous casting mold for casting of large size slabs with a dimension of 2000×250 mm and using a frequency of about 200 Hz or more in operation shown that only about 20 to 30% of the total active power is induced in the melt, while about 3 to 10% is induced in the Cu mold, about 15 to 25% is lost in the coil and about 50% is induced in the mold support beams or the part of the mold support system which normally is called backup plates. The back-up plates in the example were made of stainless steel and comprised internal cooling channels for flowing water or other suitable coolant. The total active power required to obtain the desired compressive forces acting to separate the melt and the mold were in the example calculated to be about 3400 kW when a alternating current with a frequency of 200 Hz was used, wherein the following power distribution was calculated;
about 800 kW induced in the melt,
about 250 kW induced in the Cu mold,
about 1700 kW induced in the stainless steel back-up plates, and
about 650 kW generated in the coil.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a device for continuous casting of metal strand, wherein the conditions for the initial solidification of the case metal in the mold are improved and in particular the conditions for mold lubrication is improved by the use of an EMC that exhibit low induced power losses. In particular, it is an object of the present invention to provide a device where the power induced in the mold support beams, back-up plates is substantially reduced. The continuous casting device according to the present invention shall ensure good and controlled thermal, flow, lubrication and overall conditions at the top end of the mold, thus attaining considerable improvements with respect to quality and productivity.
DESCRIPTION OF THE INVENTION
A device for continuous or semi-continuous casting of metal typically comprises;
a cooled continuous casting mold assembly,
means for
Kroon Tord
Lehman Anders
Svensson Erik
ABB AB
Dunn Tom
Gossett PLLC Dykema
Lin I.-H.
LandOfFree
Device for casting of metal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for casting of metal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for casting of metal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2936139