| Summary: | 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. === Applied Science, Faculty of === Materials Engineering, Department of === Graduate
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