Description

A factorial designed matrix equipment (Taguchi Method) was set up to study conditions affecting the formation of pinholes. This experiment succeeded in identifying important factors needed to decrease billet surface pinholes on silicon killed high carbon heats, C> 0.45%. An interaction between mold oil flow rate and bellows shroud nitrogen line pressure was determined to be critical in producing zero pinhole billet etch tests. Currently, over 90% of all high carbon billets etch tests show zero pinholes. Just prior to the experiment, this number was 72%. A surprising subsequent decrease in billet surface bleeds was also realized.