Performance of porous refractory valve for liquid metals
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D. APELIAN,
AND
G. LANGFORD
An aggregate of nonwettable refractory particles can act as an off-on valve to control the flow of liquid metals. The performance of such a particle valve is evaluated experimentally and theoretically. The breakthrough pressure, PBR, which is the pressure differential required to initiate flow through the particle valve has been theoretically derived: PBR
= -10.928
[Yd-~] cos 0k
w h e r e YLV is the l i q u i d - v a p o r s u r f a c e t e n s i o n , d is the u n i f o r m p a r t i c l e d i a m e t e r , and 0}i is the a p p a r e n t a d v a n c i n g contact angle b e t w e e n the liquid and s o l i d . E x p e r i m e n t a l l y d e t e r m i n e d b r e a k t h r o u g h p r e s s u r e s for the Sn/A1203 and Hg/A1203 s y s t e m s a g r e e with and c o n f i r m the d e r i v e d e x p r e s s i o n . M e c h a n i s m s which m a y l e a d to p r e m a t u r e b r e a k t h r o u g h of the liquid t h r o u g h the v a l v e a r e : i) f a i l u r e due to d i r e c t i m p i n g e m e n t of liquid d r o p l e t s on the p a r t i c l e v a l v e , ii) f a i l u r e by a u g m e n t e d h y d r o s t a t i c p r e s s u r e c a u s e d by an impinging liquid d r o p l e t , and iii) f a i l u r e due to buoyancy f o r c e s a c t i n g on i n d i v i d u a l particles. Critical operating limits for each mechanism are given.
INTRODUCTION h quick r e l e a s e v a l v e for liquid m e t a l s has n u m e r o u s m e t a l l u r g i c a l a p p l i c a t i o n s and a d v a n t a g e s - i ) t r a n s f e r r i n g of liquid m e t a l b e t w e e n v e s s e l s without tilting, ii) pouring s l a g topped m e l t s without e n t r a p p i n g s l a g in the m e t a l , iii) i s o l a t i n g the m e l t f r o m the o r i f i c e in b o t t o m pour a t o m i z a t i o n p r o c e s s e s , and iv) f i l t e r i n g liquid m e t a l s . A p o r o u s r e f r a c t o r y v a l v e has b e e n s u c c e s s f u l l y u t i l i z e d in the diffusion s o l i d i f i c a t i o n (SD) p r o c e s s , 1 which is a method for c a s t i n g plain c a r bon s t e e l s at l o w e r t e m p e r a t u r e s than is p o s s i b l e v i a conventional c a s t i n g r o u t e s o r r h e o c a s t i n g . In the SD c a s t i n g p r o c e s s a liquid of high c a r b o n content (~3 pct C) is i n f i l t r a t e d into a bed of low c a r b o n s t e e l shot (~0.01 pct C). The liquid is i s o l a t e d f r o m the shot by an a g g r e g a t e o r bed of c o a r s e , nonwetting r e f r a c t o r y (A1203) b e a d s , h e r e a f t e r t e r m e d a p a r t i c l e v a l v e , (PV). F i g u r e 1 i l l u s t r a t e s the g e n e r a l a r r a n g e m e n t of the SD c a s t i n g p r o c e s s . B e c a u s e of the nonwetting n a t u r e of the liquid c a s t i r o n on A1203, the s u r f a c e t e n s i o n f o r c e s can p r e v e n t the liquid c a s t i r o n f r o m p e n e t r a t ing the A1203 PV. When m e l t t r a n s f e r is r e q u i r e d , a g a s p r e s s u r e is a
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