ON LINE MONITORING OF MOLD-SHELL INTERACTION DURING CONTINUOUS-CASTING OF STEEL BILLETS

Industrial trials involving billet casting moulds instrumented with th ermocouples, load cells, and linear variable differential transducers have been conducted at four companies to study mould lubrication (oil) , heat transfer, and billet surface quality for the development of an 'intelligent mould'. The mould taper at the meniscus has been found to influence mould behaviour profoundly, Shallow tapers, of the order of 0.4-0.8% m(-1), gave rise to high copper tube temperatures, in excess of the boiling range of the lubricating oil weeping down the hot face , the boiling point of water flowing past the cold face, and the softe ning temperature of DHP copper. The need for mould thermocouples close to the meniscus to sense mould behaviour as a critical input to the i ntelligent mould was clearly demonstrated. Measurements of the mould o scillation cycle revealed problems at three of the companies and the n eed for the intelligent mould to possess an on line maintenance assess ment capability, as well as the ability to monitor billet quality on l ine. A technique to evaluate the mechanical interaction between the mo uld and the strand quantitatively has also been elucidated based on th e negative strip time and response of load cells.