Process of choking of a slide valve channel in teeming of bearing steels

Abstract

It is known that in teeming of alloy constructional and high-alloy steels skull formation in the channel of a slide valve leads to a reduction in teeming rate, poorer ingot quality, and premature wear of the refractories caused by required burning out of the channel with oxygen.The configuration of the channel cross section, the length of hold of steel in the ladle, and preheating of the ladle before tapping of the heat are of great significance for normal teeming. It has also been established [1][2][3] that replacement of magnesia refractories with high alumina ones with lower thermal conductivity [4] causes a reduction in choking and skull formation in the slide valve channel.Experience in the service of slide valves has shown that, in addition to rational selection of refractory parts, no small role in the process of skull formation in teeming of steels containing components with a high affinity for oxygen is played by selection of the material of the packing which fills the cavity of the ladle nozzle to prevent premature entry of metal into the channel and solidification of it in contact with the plates.At the moment of opening of the valve the packing in the form of refractory powder material pours out of the channel and the molten metal freely flows from the ladle without the use of oxygen lancing.In steel plants various forms of materials (coke fines, chamotte, staurolite, nepheline ore, etc.) excluding burning through of the channel before the start of teeming are used as the packing of the nozzle [5][6][7].Investigation of the composition and structure of the skull on the surface of the teeming channel in relation to the refractory and nozzle channel packing used is significant in searching for methods of reducing choking of the channel and the nonmetallic inclusion content in the steel, especially in repeated use of slide valve refractory parts. However, until the present, thorough investigations have not been made in this direction.During teeming of steel from steel teeming ladles through slide valves accumulation in the lower portion of the collector-nozzle of a skull formed on the inner surface of the channel in the form of hanging icicles increasing with throttling of the stream, with movements from one bottom pouring assembly to another, and also with failure of the forming edge of the teeming channel is characteristic. With dropping into the ingot this skull increases the nonmetallic inclusion content [8] and reduces the qual• of the metal.