Mechanism of alumina buildup in tundish nozzles during continuous casting of aluminum-killed steels
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C O N S T R I C T I O N of the l i q u i d - s t e e l p o u r i n g s t r e a m through tundish n o z z l e s p o s e s s e r i o u s p r o b l e m s in m a i n t a i n i n g a c o n s t a n t c a s t i n g s p e e d d u r i n g the c o n t i n uous c a s t i n g of a l u m i n u m - k i l l e d s t e e l s . This c o n s t r i c tion ts c a u s e d b y a buildup of m i c r o s c o p i c a l u m i n a p a r t i c l e s at the n o z z l e o r i f i c e , with the r e s u l t that n o z z l e s have to be changed often to m a i n t a i n a c o n s t a n t flow r a t e . If t h i s change is not m a d e , the buildup will c o n tinue until the n e t w o r k of fine a l u m i n a p a r t i c l e s g r o w s o v e r the e n t i r e c r o s s s e c t i o n and chokes the flow. D e s p i t e the f a c t that t h i s p r o b l e m h a s s e r i o u s l y inh i b i t e d the growth of continuous c a s t i n g of a l u m i n u m k i l l e d s t e e l , not much a t t e n t i o n h a s been f o c u s e d on r e s e a r c h to find the m e c h a n i s m of such buildup and t h e r e b y find a m e a n s to e l i m i n a t e it. Instead, a t t e m p t s have b e e n m a d e to c i r c u m v e n t the p r o b l e m b y a d d i n g a l u m i n u m w i r e o r m o l t e n a l u m i n u m to the liquid s t e e l in the m o l d o r b y u s i n g o v e r s i z e d n o z z l e s . D u r i n g r e cent y e a r s , s e v e r a l s t u d i e s , e s p e c i a l l y R u s s i a n , have a t t e m p t e d to a n a l y z e the m e c h a n i s m of the buildup of a l u m i n a i n c l u s i o n s in n o z z l e b o r e s . T h e r e a r e two m a j o r q u e s t i o n s to be a n s w e r e d : 1) What is the s o u r c e of the d e p o s i t i n g p a r t i c l e s ? 2) Why do t h e s e p a r t i c l e s d e p o s i t a t the n o z z l e - b o r e site? Although s e v e r a l r e s e a r c h e r s have opinions c o n c e r n ing the s o u r c e of the a l u m i n a p a r t i c l e s , no one has m a d e much a t t e m p t to d e t e r m i n e why the p a r t i c l e s d e p o s i t at the b o r e .
S. N. SINGH is Senior Research Engineer, United States Steel Corporation, Monroeville, Pa. 15146. Manuscript submitted March 14, 1974. METALLURGICAL TRANSACTIONS
Snow and Shea ~ f i r s t noted that t u n d i s h - n o z z l e c o n s t r i c t i o n was c a u s e d by the buildup of a l u m i n a p a r t i c l e s . D u d e r s t a d t , I y e n g a r , and M a t e s a 2 r e c e n t l y publ i s h e d a work on the e x a m i n a t i o n of t u n d i s h - n o z z l e b l o c k a g e and a t t e m p t s to c i r c u m v e n t it. Although t h e s e a u t h o r s p r e s e n t e d v e r y u s e f u l i n f o r m a t i o n , t h e y did not a t t e m p t to s t u d y the m e c h a n i s m of the buildup of a l u m i n a p a r t i c l e s in the n o z z l e o r i f i c e . A d e t a i l e d l i t e r a t u r e s e a r c h on the c o n s t r i c t i o n of the p o u r i n g s t r e a m through tundish n o z z l e s y i e l d e d f o u r m a j o r v
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