TABLE OF CONTENTS Direct strip casting is a much simpler process than the more conventional continuous casting routes since a number of secondary processing stages are minimised or eliminated completely (Figures 3.23 and 3.24). However, DSC involves high casting speeds and, due to thickness constraints associated with the process, there is reduced scope to modify the as-cast microstructure and improve strip quality. To ensure that a strip caster operates efficiently, a well-controlled casting process is of paramount importance.
The TRC process is an established mode of strip casting for steel and aluminium and is under development for magnesium and other metals. The process of strip formation by TRC is extremely rapid and, for the case of steel, the time for the outer shell of the as-cast strip to thicken to 0.2 mm is of the order ~ 0.02s with complete solidification occurring in less than a second. Therefore, process control technology must be highly sophisticated and include an automated starting procedure, a precise level control at the meniscus of the pool, methods to monitor and control the strip thickness, roll separation force and thermal roll expansion (Legrand et al. 1997). Because any change to one or more parameters in the operating procedure must activate rapid changes to various other process parameters, these variables are controlled concurrently by a feed-back, feed-forward type of strategy. For example, if the pool height in the mould of a twin roll caster is suddenly increased, the...
