Some electrical characteristics of a DC electroslag unit
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T H E function of the s l a g in an e l e c t r o s l a g unit g e n e r a l l y has b e e n r e g a r d e d to be twofold: to a c t as a c h e m i c a l r e a c t a n t and a l s o a s the h e a t g e n e r a t i n g and heat t r a n s f e r m e d i u m . T h e p u r p o s e of t h i s p a p e r is to e x a m i n e the way in which the e l e c t r i c a l c i r c u i t r y of an e l e c t r o s l a g unit m a y a f f e c t the l a t t e r f u n c t i o n s and t h e r e b y affect the m e t a l l u r g i c a l c h a r a c t e r i s t i c s of the p r o c e s s . P r e v i o u s w o r k e r s 1'2 have i n d i c a t e d that the c i r c u i t r y of an ESR unit can a f f e c t the o p e r a t i n g e f f i c i e n c y , the ingot m a c r o s t r u c t u r e and c o m p o s i t i o n . M a x i m o v i t c h I r e p o r t s that the o p e r a t i o n of a " l i v e " m o ld , F i g . 1, can c a u s e a r c i n g b e t w e e n the s l a g and m o l d wall and c o n s e q u e n t l y up to 20 pct r e c t i f i c a t i o n of an ac o p e r a t i n g c u r r e n t . He a l s o i n d i c a t e s m o l d puncture can r e s u l t if excessive arcing occurs. Whittaker 2 reports a differe n c e in d e s u l f u r i z a t i o n of a s t e e l m e l t in dc o p e r a t i o n depending on wh e t h e r or not the m o l d is i s o l a t e d f r o m the ingot b as e. T h i s e f f e c t i s not found 2 for a s i m i l a r m e l t in 60 Hz ac o p e r a t i o n . The d e s c r i p t i v e a c c o u n t s of the ESR p r o c e s s 3-5 all a s s u m e that the s l a g skin f o r m e d around the ingot c o n s t i t u t e s a p e r f e c t e l e c t r i c a l i n s u l a t o r but a r e e q u i v o c a l as to w h e t h e r or not the skin e x i s t s b e t w e e n the liquid slag and the m o l d wall. T h e f o r m the s l a g skin t a k e s u n d e r v a r i o u s c o n d i t i o n s has b e e n d i s c u s s e d , 6 and it i s e v i d e n t that the c o m p o s i t i o n , t h i c k n e s s , t e m p e r a t u r e , and continuity of this skin will c o n t r o l the e l e c t r i c a l p o t e n ti a l of the m o l d . T h e e l e c t r i c a l r e s i s t i v i t y of the slag skin i s a function of t e m p e r a t u r e but h a s b e e n e s t i m a t e d 11 to be a p p r o x i m a t e l y 10 ~2/sq c m u n d e r n o r m a l ESR o p e r a t i n g c o n d i tions. T h i s would give a total e l e c t r o d e - m o l d r e s i s t a n c e of 0.2 ~ , in the g e o m e t r y of the ESR unit in the p r e s e n t study. Although the r e s i s t a n c e c a l c u l a t e d is l a r g e c o m p a r e d with the r e s i s t a n c e of the liquid s l a g , it is s m a l l enough to put an " i s o l a t e d " m o l d at a stable pot en t i al i n t e r m e d i a t e b e t w e e n the e l e c t r o d e and the ingot. It would be much m o r e difficult to c a l c u l a t e the r e s i s t a n c e of the skin b e t w e e n the m o l d wall and the s o l i d i f y i n g ingot, as the ingot s h r i n k a g e c a u s e s the skin to c r a c k or d e f o
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