The spray cooling system of an operating billet caster has been redesigned with the aim of reducing the formation of mid-way cracks. These cracks are caused by tensile strain which is generated at the solidification front when the surface temperature of the strand rebounds owing to a sharp reduction in surface heat extraction. The objective of the design, therefore, was to achieve a cooling system that would minimize surface temperature rebound of the strand as it passes from one cooling zone to the next. A computer program based on the explicit finite difference method has been used for the design work. The spray design was implemented on one strand of an operating continuous casting machine which produced 10.8 cm square billets. Transverse sections were cut from the test strand and sulfur printed, then compared to sulfur prints of sections taken from an adjacent strand of the same heat but with unmodified sprays. It was shown that with empirical adjustment, the redesigned spray system reduced the severity of mid-way cracks in over 80% of the heats. It was also found that the carbon content and cast structure have a profound effect on the cracking tendency, whereas, the Mn/S ratio (up to 30%) is less effective. Finally, a new design method for sprays has been proposed which may result in a better temperature distribution and may be easier to adjust to suit specific operating conditions. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate