ARRANGEMENT IN STEEL MANUFACTURING BY MEANS OF INDUCTIVE STIRRING

Abstract: An arrangement for steel making with inductive stirring of the steel melt in a steel melt container. It is desirable for the various parts of the steel melt to be forced up to the surface, while at the same time being mixed, in order to be exposed there to as large an area as possible. This task has been solved by the inductive stirring producing at least one magnetic field which acts in the lower part of the steel melt and which there, substantially in the horizontal plane, drives the steel melt to rotate in a certain direction, and by the inductive stirring producing at least one further magnetic field which acts in the upper part of the steel melt and which there, substantially in the opposite direction, drives the steel melt.

Description: Arrangement in steel manufacturing by means of inductive stirring . The present invention relates to an arrangement for steel making in a container for molten steel with inductive stirring * "C of the molten steel. In the manufacture of quality steel, different steel qualities 5 require different metallurgical measures while simultaneously stirring and mixing the molten steel. It has long been known that a so-called inductive stirrer, located on the outside of the steel melt container, may cause the steel melt to rotate while being influenced by the magnetic field created by the in 10 tive stirrer. Known applications comprises one or more induct stirrers, which however primarily cause the steel melt in its entirely to rotate rather than to be mixed. Since the metal¬ lurgical penetrations in most cases occur at the surface of th steel melt, it would be desirable - in addition to achieving 15 improved mixing - for the various parts of the steel melt to be forced up to the surface, while at the same time being mixe in order to be exposed there to as large an area as possible. Such a movement pattern of the steel melt would provide more uniform steel qualities in a shorter process time, which in tu 20 would result in a direct reduction of the cost of production. As examples of measures which are taken on the surface of the steel melt may be mentioned heating, dehydrogenation under vacuum, desulphurizing by means of lime, carbon combustion by means of oxygen, and supplying alloying materials. 25 The invention aims to provide a solution to the above-mentione problems and other problems associated therewith and is charac terized in that the inductive stirring is adapted to be brough * ~ about by at least two substantially horizontally acting induc¬ tive stirrers, located at different levels of the steel melt, 30 the stirring direction of one stirrer thus being substantially opposite to that of the other stirrer. By means of the invention, a stirring is achieved in which the different parts of the steel melt, while being simultaneously mixed, are forced up to the surface in order to be exposed at the surface to as large an area as possible. This has been solved by the inductive stirring producing at least one magne- tic field which acts in the lower part of the steel melt and which there, substantially in the horizontal plane, drives the steel melt to rotate in a certain direction, and by the induc¬ tive stirring producing at least one further magnetic field which acts in the upper part of the steel melt and which there, substantially in the opposite direction, drives the steel melt. In a preferred embodiment of the invention, the stirring is given greater force and/or speed in the lower parts of the stee melt container than in the upper parts. The ideal condition would then be to have the highest speed of rotation at the bottom of the steel melt container and the lowest at the surfac of the steel melt. At different levels of the steel melt - and while at the same time the layers of the steel melt are twisted in relation to each other - the steel melt will be pressed from the centre of rotation and outwards towards the walls of the steel melt conta and there, while being at the same time rotated, be pressed further up towards the surface of the steel melt and then, from all directions, float inwards towards the centre of rotation and be sucked down there, and then again, at different levels, be pressed out towards the walls of the steel melt container. Where necessary, a slag layer may also be broken up and be splashed with steel melt by reducing the counteracting effect of the upper inductive stirrer and/or increasing the driving effect of the lower inductive stirrer, which leads to a major depression on the surface of the steel melt and thus enables splashing and breaking-up. The stirrers may be powered with different frequencies, for example a lower frequency for the upper stirrer, which then achieves a longer depth of penetration in that part of the mel The frequency range may be from very low values up o mains frequency (0.1-60 Hz). The invention will be exemplified in greater detail with ref ¬ erence to the accompanying drawing, wherein Figure 1 shows a ladle with two multi-phase, electromagnetic, horizontal stirrers and Figure 2 shows the configuration of flow in the ladle. Figure 1 shows a ladle 1 for molten steel with an upper (2) and a lower (3) stirrer. The stirrers provide a mutually substan- tially opposite travelling field (see 21 and 22). Possibly, the lower stirrer 3 is also given a greater power so that the magnetic field from this stirrer is more powerful than the fiel from the upper stirrer 2. It is also possible to stir with a greater speed in the lower parts than in the upper parts. In order to achieve this, the upper stirrer 2 may have a lower frequency. However, this will result in a greater depth of penetration for the field from the stirrer supplied with lower frequency. Of course it is also possible to supply the stirrers with the same frequency, however with greater power in the other one. Figure 2 shows two thick arrows 2 and 3, which symbolically show the mutually opposite directions of stirring, i.e. arrow 2 shows the upper magnetic field acting on the steel melt and arrow 3 shows the lower magnetic field acting on the steel mel The arrows 4 in the middle of Figure 2 illustrate the speeds of rotation diminishing in an upward direction, and the small arrows 5 show the superimposed movements of the melt. It is thus clear that the different parts of the melt are force up to the surface while at the same time being mixed. The arrangement according to the invention can be varied in ma ways within the -scope of the appended claims.

Claims: CLAIMS 1. Arrangement for steel making in a container for molten steel with inductive stirring of the molten steel, c h a r a c t e r i z e d in that the inductive stirring is adapted to be accomplished by at least two substantially hori¬ zontally acting inductive stirrers located at different levels of the steel melt, the stirring direction for one of the stirr¬ ers being substantially opposite to that for the other stirrer. 2. Arrangement according to claim 1, c h a r a c t e r i z e in that the stirring force and/or the rate of stirring for the lower stirrer is/are greater than for the upper stirrer. 3. Arrangement according to claim 1 and possibly claim 2, c h a r a c t e r i z e d in that the power of the magnetic fields from the respective stirrers may be varied and/or that the stirring direction may be reversed. 4. Arrangement according to one or more of the preceding claims, c h a r a c t e r i z e d in that the frequency for one of the stirrers is lower than for the other stirrer.

Inventors: BERKESTAD KARL-ERIK, BERKESTAD, KARL-ERIK
Applicants: ASEA AB
Application year: 1987
Main classification: F27D23
IPC codes: B01F13, C21C7, F27B14, F27D3, F27D23, H05B6