FR2620360A1 - METHOD AND DEVICE FOR ELECTROMAGNETIC STIRRING OF FUSION BATHS IN A CONTINUOUS CASTING MOLD - Google Patents

Abstract

The invention relates to a method and a device for electromagnetic stirring of molten baths in a continuous casting mold, according to which forces are induced in the molten mass, by establishing a magnetic field, which cause it to rotate in horizontal planes. . The device according to the invention consists of a coil device 4 surrounding the continuous casting mold 1 in a horizontal plane and adjustable in height relative to the continuous casting mold 1, which is equipped with a pole switch to modify the direction of rotation of the current and, where appropriate, a frequency converter. Application to continuous casting.

Description

1i 2620360

  METHOD AND DEVICE FOR AGITATING THE CTRCM ALTITUDE OF FUSION BATHS

IN A CASTING MOLD CONTINUES.

  The invention relates to a method and an electromagnetic stirring device

  melting baths in a continuous casting mold in which a magnetic force is introduced which puts the rotating mass into

  horizontal plans. Thanks to this provision, we must erase the power of

  dendritic structure and the formation of shrinkage and

  gregations in the casting bath.

  By electromagnetic stirring in the continuous casting mold, there is often a strong and undesirable bath movement in the area of its area. When casting slag with a dip tube, a

  Excessive movement of the surface area of the bath can lead to the following pheno-

lowing:

  - inclusions of slag in the melt.

  - insufficient lubrication between the bath and the mold by cracking

the area of the bath.

  - oxygen absorption from the atmosphere.

- heavy wear of the dip tube.

  The present invention aims to create a method and a device which

  keep a calm surface for the bath, while stirring

  the melt in the continuous casting mold for the indicated purpose

  above, in the area of agitation - that is, the area in the

  what is the solidification? We had not thought so far about

  such a possibility because it seemed inevitable that a movement of rota -

  melt in the mold produces effects up to the level of

  the surface of the bath and also mixes this area turbulently.

  The invention proposes a solution to this problem which makes it possible to maintain a calm bath surface despite intense agitation in the stirring zone

in the continuous casting mold.

  This object is achieved, in accordance with the invention, by virtue of the fact that

  current in the coil device which turns the melt into

2 2620360

  rotation is alternated periodically, the cycle being chosen in such a way

  that the surface of the bath remains stationary while the molten mass is

  agitated in the planes below the surface of the bath. Preferably, the half cycle time is set between 1 and 4 seconds, with a pause of about 0.5 seconds between the current conducting cycles. Note that it is known in itself to change the direction of the current in the case

  electromyagnetic agitation of the liquid crater inside the guiding

  bath casting in the continuous casting of steel slabs. Thus, German Patent DE-A-24 01 145 describes such a method for avoiding secondary white bands and secondary dendrites. The cycle time after

  which the direction of the current is changed is, according to this document, from 5 to 30 seconds.

  onds. No provision is provided for preventing a movement of the

bath surface.

  If, with the means indicated previously alone, it is not possible,

  Due to the intense stirring of the molten mass in the stirring zone in the continuous casting mold, the regulation of an immobile bath surface, an advantageous embodiment of the method according to the invention proposes that the height of the coils creating the magnetic field is set in relation to the bath surface of the melt in the continuous casting mold according to the magnitudes (field strength, frequency) characteristics of the magnetic field and the parameters influencing the rotation of the melt, in particular viscosity of the

  melt, geometry and mold material, so that

  bath face remains motionless during agitation. The following practical solutions are therefore used to carry out the process according to the invention:

  1. periodic change of the direction of the current.

  2. periodic change in direction of current and conduction

current in the coils.

  3. periodic change in current conduction of the electromagnetic field

  in connection with a height adjustment of the device

  electric coil on the continuous casting mold.

3-620360

  With the means indicated, the aim of shaking

  tensed a molten metal mass in a continuous casting mold in

  the stirring zone while still leaving the surface of the bath.

  An embodiment of the device according to the invention for producing

  an electromagnetic magnetic field in the area of a casting mold

  tinue is shown schematically in the drawing, thanks to which one can implement the method according to the invention. FIG. 1 represents a view in

  longitudinal section and Figure 2 a cross-sectional view.

  A coil device 4 is mounted around the continuous casting mold 1 into which the plunger tube 2 opens, through which the molten mass 3 arrives.

  in the continuous casting mold 1. The coil device 4 for stirring

  Electromagnetic distribution of the molten mass 3 in the continuous casting mold 1 is adjustable in height relative thereto. The coil device 4

  consists of six coils 5 arranged regularly distributed over the

  of the mold 1, which are mounted around magnetic poles 6 which

  7. The coil device 4 is coupled to a poles caimutator and, in this case, a short circuit ring 7 is surrounded by a metal jacket 8.

  if necessary, to a frequency converter (not shown).

  Example 1 A copper continuous casting mold with a wall thickness of 10 mm is surrounded by a rotating stirring coil having the following dimensions: inner diameter of 515 mm, outer diameter of 870 mm and height of

  490 mm, which is mounted at a height of about 200 mm below the

  face of the melt bath in the continuous casting mold. The flow

  in the coil is set to 400 A and the frequency to 6 Hz.

  in each direction lasts 3 s with a pause of 0.5 s between

sions of sense of current.

4 2620360

Claims (4)

REVENICATICNS   1.- Electromanagnetic stirring process of fusion baths in a mold   continuous casting, which is induced in the melt, in   a magnetic field, forces which rotate it in horizontal planes, characterized in that the current conduction to the coils creating the magnetic chaup is alternated according to a cycle such that the surface of the bath remains motionless.   2. Method according to claim 1, characterized in that the duration   cycle is set between 1 and 4 s.   3. A method according to claim 1 or 2, characterized in that the height of the coil device creating the magnetic field is adjusted relative to the bath surface of the melt in the casting mold   continues according to the quantities (intensity of the cart, frequency)   characteristics of the magnetic field and the parameters influencing the rotation of the melt, in particular the viscosity of the melt, geometry   mold material, so that the surface of the bath remains immovable bile during agitation.   4.- Device for creating an electramagnetic chanp in the region of a continuous casting mold for carrying out the method according to one of   Claims 1 to 3, characterized in that it consists of a   coil device (4) surrounding the continuous casting mold (1) in a horizontal plane and adjustable in height with respect to the continuous casting mold (1), which is equipped with a poles switch to change the direction of rotation of the current and, where appropriate, a frequency converter.