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The detection of mould-strand interaction employing load cells in the continuous casting of billets Brendzy, J. Lorraine


Instrumentation of the mould with load cells and linear variable displacement transducers was completed to evaluate mould-strand interaction in a continuous casting machine for steel billets. A plant trial was conducted in which several lubricants were tested at four rates. Three carbon grades were cast under similar mould lubricating conditions. In the analysis of the accumulated data, correlation between the mould loading as determined by the load cell signals and the oscillation cycle as indicated by the linear variable displacement transducers was achieved. The load cell data indicated that there are two modes of strand-mould interaction occurring during each oscillation cycle. During the positive-strip period, lubrication conditions and carbon content were observed to affect the loading of the mould but during the negative-strip period, the effects of lubrication and carbon are masked due to the mould bearing down on the strand. During the period which the mould travels downward faster than the strand, the load cell response indicated a smooth decrease in mould loading. It is also shown that the minimum load reached is related with changes in casting speed: as casting speed decreases, the mould attempts to overtake the strand to a greater extent than when the casting speed is higher. The result is a greater decompression of the load cell when casting speeds are slower. This finding supports a proposed mechanism for the formation of oscillation marks in billets. It is shown that different lubricants produce different loading responses and that a reduction in flow rate causes increases in load on the mould during upstroke. A theoretical analysis employing a fluid flow model has also been undertaken to determine the presence of lubricant at the meniscus during an oscillation cycle. The results from this analysis indicates that lubricant reaches the meniscus generally during the downstroke and that replenishment of lubricant at the meniscus does not occur during the upstroke leaving only residual lubricant to provide lubrication at the mould-strand interlace. This finding suggests that two modes of lubrication may operate: hydrodynamic lubrication occurring when lubricant is present at the meniscus and boundary layer or solid layer lubrication operating when bulk lubricant does not reach the meniscus region. From the load cell response, binding was evident which was correlated with the presence of depressions found on the surface of examined billets.

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