On heat transfer and liquid mixing in the continuous casting of steel
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C O N T I N U O U S c a s t i n g of s t e e l (and of other m e t a l s ) has gained w i d e s p r e a d p o p u l a r i t y in r e c e n t y e a r s due to its e c o n o m i c a d v a n t a g e s a s s o c i a t e d with i n c r e a s e d y i e l d s and the e l i m i n a t i o n of i n t e r m e d i a t e p r o c e s s i n g steps. A s c h e m a t i c d i a g r a m of the p r o c e s s is shown in Fig. 1. The t h e o r e t i c a l a n a l y s e s u n d e r t a k e n of the p r o c e s s up to the p r e s e n t were m a i n l y c o n c e r n e d with the dev e l o p m e n t of a n a l y t i c a l and n u m e r i c a l t e c h n i q u e s for r e l a t i n g the t h i c k n e s s of the solidified c r u s t to i n d e pendent v a r i a b l e s such a s axial d i s t a n c e along the mold, s u p e r h e a t , c a s t i n g speed, cooling r a t e s , and so forth. 1-3 As a r e s u l t of these i n v e s t i g a t i o n s the f a c t o r s d e t e r m i n i n g s o l i d i f i c a t i o n r a t e s in continuous c a s t i n g s y s t e m s a r e r e a s o n a b l y well u n d e r s t o o d , howe v e r , v i r t u a l l y no published i n f o r m a t i o n is a v a i l a b l e on the flow p a t t e r n s and velocity d i s t r i b u t i o n in the liquid pool of a continuous c a s t i n g unit. The knowledge of the b e h a v i o r of the liquid pool i s of c o n s i d e r able p r a c t i c a l i n t e r e s t a s the flow p a t t e r n may have a v e r y m a r k e d effect on the e v e n t u a l r e t e n t i o n of i m p u r i t i e s in the f i n i s h e d product. In continuous c a s t i n g the r e m o v a l of i m p u r i t i e s may be l e s s complete than in " s t a t i c " c a s t i n g o p e r a t i o n s and this p o s e s a l i m i t a t i o n of the quality and types of s t e e l s that a r e suitable for p r o c e s s i n g in this m a n n e r . The purpose of the p a p e r is to e x a m i n e the t e c h niques a v a i l a b l e for studying liquid phase flow patt e r n s in continuous c a s t i n g and to show how the i n f o r m a t i o n obtained on flow p a t t e r n s m a y be used for p r e dicting the i m p u r i t y content of the f i n i s h e d product. In c o n t r a s t to flow p a t t e r n s t u d i e s in c o n v e n t i o n a l c h e m i c a l e n g i n e e r i n g s y s t e m s , in this c a s e the p h y s i cal b o u n d a r i e s of the (liquid) phase u n d e r c o n s i d e r a tion a r e m a r k e d l y affected by the d y n a m i c s of the p r o c e s s itself. It follows that any c o n s i d e r a t i o n of flow p a t t e r n s has to be p r e c e d e d by the a n a l y s i s of the heat t r a n s f e r p r o c e s s so that the p h y s i c a l b o u n d a r i e s of the m o l t e n phase m a y be specified. J. SZEKELY is Professor of Chemical Engineering, State University of New York at Buffalo, Buffalo, NY. V. STANEK,on lease from Czechoslovak Academy of Sciences, Prague Czechoslovakia,is presently Postdoctoral Fellow, Department of Chemical Engineering,State University of
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