Mould fluxes play an important part in continuous casting. They must lubricate the steel shel and provide the right level of horizontal heat transfer in order to avoid both longitudinal cracking and sticker breakouts. Powder consumption (Q_s in kg flux/m~2 of mould) is a measure of the lubrication supplied by the mould flux. Plant data for billet - , bloom-, slab-and thin slab- casting from steelworks all over the world have been analysed. It is shown that Q_s is a sensitive function of the parameter, R (ratio of surface area/volume of the mould) which is a function of the mould dimensions. The melting rate of the flux must satisfy the demand for molten slag and it is shown that the hierarchy of the parameter (percent C/R) is in the order of slabs and thin slabs>blooms>billets. The horizontal heat transfer is controlled by the thickness and the crystallinity of the solid slag film in the mould/strand gap. The thickness of the slag film is partially determined by the reak (or solidification) temperature; plots of recommended break temperature as functions of viscosity and casting speed are given for the optimum casting of different steel grades.
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