Friction forces between mould and strand shell during billet casting

During continuous casting processes lubrication between mould and strand shell is very important for reaching and maintaining a good surface quality of both the as-cast strand and the finished product. The lubrication is influenced by the properties of the mould powder but also by the friction forces caused by the periodic movements of mould and the descending strand shell. In the present research measurements were carried out to investigate the friction forces during 150 mm sq. billet casting of different steel grades using mould powder or granules and submerged entry nozzles. The friction forces reached values up to 6 kN. Since friction forces are depending on upward and downward movements within the mould-strand-system, the evaluation of a rheogram shows the typical change of pressure and tension. Maximum friction forces arise during the positive strip time of the rising mould, introducing tensions and cracks in the as-cast strand. On the other hand lowest frictions forces are generated by the descending mould within the negative strip time leading to the healing of faults in the as-cast strand. These industrial experiments indicate a correlation between friction forces and surface quality of as-cast strands.