Stirrer

Abstract

A method for casting of metal. A mold is provided including two broad sides and two narrow sides. A molten metal is introduced into the mold. There is a meniscus at a top of the molten metal. Additional molten metal is supplied into the molten metal via a casting tube below the meniscus. At least one stirrer including an iron core and a coil applied around the iron core is arranged around the mold. A length of the iron core in relation to a length of the broad side of the mold is between 50% and 80% of the length of the broad side. An upper part of the iron core is positioned from 50 mm above to 195 mm below the surface of the meniscus. A magnetic field is applied to the molten metal with the at least one stirrer to stir the molten metal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional application of co-pending U.S. patent application Ser. No. 12 / 298,537 filed 27 Oct. 2008, and claims priority to Swedish patent application number 0600919-5 filed 25 Apr. 2006 and application Ser. No. 12 / 298,537 is the national phase under 35 U.S.C. §371 of PCT / SE2007 / 050269 filed 10 Apr. 2007.TECHNICAL FIELD[0002]The present invention relates to a device for continuous or semicontinuous casting of metals including a stirrer.BACKGROUND OF THE INVENTION AND PRIOR ART[0003]During continuous or semicontinuous casting, a molten metal is supplied to a casting mould, hereinafter designated mould, in which it is cooled and formed into an elongated strand. Depending on its cross-sectional dimensions, the strand is designated BILLET, BLOOM or SLAB. During the casting, a primary flow of hot, molten metal is supplied to the cooled mould, in which the metal is cooled and at least partially solidifies into an elongated...

AI Technical Summary

Benefits of technology

The solution achieves a consistent and low-turbulence metal flow, reducing inclusions and defects in the cast strand, while maintaining optimal heat supply and simplifying the installation process.

Problems solved by technology

This results in inclusions and irregularities in the finished, solidified cast strand.

If the hot metal flow is allowed to enter into the mould in an uncontrolled manner, the flow will penetrate deep into the cast strand, which probably will have a negative influence on the quality and productivity.

An uncontrolled hot metal flow in the cast strand may result in encapsulation of non-metallic particles and / or gas occlusions in the solidified strand, or cause casting defects in the inner structure of the cast strand.

A deep penetration of hot metal flow may also cause a partial remelting of the solidified surface structure so that the melt penetrates the surface layer below the mould, which causes severe disturbances in production and a long downtime for repair.

When the velocity of flow and hence the turbulence at the meniscus become too high, this leads to slag being drawn down from the casting powder and further down into the solidified strand, and results in an increased risk of cracking due to uneven shell growth.

On the other hand, when the velocity becomes too low at the meniscus, there is a risk of temperature differences arising, which may lead to local solidification at the meniscus with ensuing risks of cracking and of slag particles adhering under the shell that is solidifying at the meniscus.

In the region around the casting tube, there is a considerable risk of a local, unfavourable flow or stagnation of the melt arising, which leads to cracks being formed in the cast strand.

Further, the oscillating flow provides an unsymmetrical velocity downwards in the mould.

In certain situations, the velocity on one narrow side of the mould may become considerably higher than on the opposite narrow side, which results in a heavy downward transport of inclusions and gas bubbles with an ensuing deterioration of the quality of the cast object.

The dimension of the stirrer in relation to the broad side of the mould amounts to 0.4-0.7 times the dimension of the broad side of the mould (0.4-0.7)*b. This solution, however, is only intended to create stirring a certain distance down in the melt and does not completely solve the previously mentioned problems relating to velocity variations.

Images