The removal of solid particles from molten aluminum in the spinning nozzle inert flotation process
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p r o c e s s which was i n t r o d u c e d r e c e n t l y to the a l u m i n u m i n d u s t r y as an a l t e r n a t e method to c h l o r i n e fluxing and to m o l t e n m e t a l f i l t e r i n g . 3 This nonpolluting metal refining process utilizes an i n e r t gas, v e r y s m a l l a m o u n t s of h a l i d e s and v i g o r o u s s t i r r i n g of the m e t a l for p u r i f y i n g a l u m i n u m a l l o y s f r o m d i s s o l v e d h y d r o g e n and f r o m solid n o n m e t a l l i c i m p u r i t i e s . Most of the n a t u r a l p r o c e s s e s p r o m o t e d in this p r o c e s s a r e not c h e m i c a l in n a t u r e ; t h e r e f o r e , the f a m i l i a r e x p r e s s i o n of " f l u x i n g " has b e e n abandoned i n f a v o r of " r e f i n i n g . " One of t h e s e n a t u r a l p r o c e s s e s , the flotation of solid p a r t i c l e s f r o m m o l t e n a l u m i n u m a l l o y s , has b e e n chosen for the s u b j e c t of this r e p o r t b e c a u s e the c o n c l u s i o n s d e r i v e d f r o m t h e o r y on the b e h a v i o r of s o l i d p a r t i c l e s i n a s t i r r e d and bubbled a l u m i n u m m e l t w e r e c o n s i d e r e d f u n d a m e n t a l enough to d e s e r v e both p r a c t i c a l and theoretical interest.
OBJECTIVES AND LIMITATIONS A q u a n t i t a t i v e t r e a t m e n t of p a r t i c l e flotation n e c e s s i t a t e s the d e f i n i t i o n of a p h y s i c a l s y s t e m i n r e f e r e n c e to both t i m e and s p a c e . T h i s s y s t e m has b e e n defined for the p u r p o s e of p r e s e n t i n v e s t i g a t i o n as the a c t u a l SNIF r e f i n i n g s y s t e m c h a r a c t e r i z e d by the t y p i c a l o p e r a t i n g data as shown in T a b l e I. T h e o b j e c t i v e of the i n v e s t i g a t i o n was to d e r i v e a n s w e r s to the following q u e s t i o n s : a) What i s the r a t e of p a r t i c l e r e m o v a l u n d e r t h e s e p r o c e s s conditions ? b) What is the s m a l l e s t p a r t i c l e s i z e c a t e g o r y which can be r e a c h e d and e l i m i n a t e d f r o m a l u m i n u m by flot a t i o n d u r i n g the a v a i l a b l e r e s i d e n c e t i m e of the m e t a l i n the r e f i n i n g f u r n a c e ? The c h a r a c t e r i s t i c o p e r a t i n g p a r a m e t e r s of the SNIF p r o c e s s w e r e s e l e c t e d by d e s i g n to c o n f o r m with the p r a c t i c a l l i m i t a t i o n s e x i s t i n g in t o d a y ' s cast h o u s e s . The s i z e of the f u r n a c e r e p r e s e n t s a c o m p r o m i s e b e t w e e n the d e s i r e d m e t a l t r e a t m e n t r a t e and the s p a c e a v a i l a b l e on the c a s t i n g floor. C o n s i d e r ing that the m e t a l r a t e t h r o u g h an i n - l i n e r e f i n i n g s y s t e m is d i c t a t e d by the c a s t i n g speed which i s r e l a t i v e l y high in m u l t i p l e D.C. ingot c a s t i n g , while s p a c e is u s u a l l y s c a r c e , the r e s t r a i n t
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