Metal transfer during vacuum consumable arc remelting
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An i n v e s t i g a t i o n was conducted to d e t e r m i n e how m e t a l is t r a n s f e r r e d d u r i n g v a c u u m c o n s u m a b l e a r c r e m e l t i n g . The t r a n s f e r mode was found to be dependent on a r c length for the e l e c t r o d e s i z e s (0.10 to 0.20 m d i a m ) and e l e c t r i c a l p a r a m e t e r s studied (1.9 to 3 kA and 25 V)o At s h o r t a r c lengths -0.1 m) the s p i k e s s e p a r a t e b e f o r e t o u c h i n g the anode. E x p e r i m e n t a l o b s e r v a t i o n s c o n c e r n i n g the c o a l e s c e n c e of m o l t e n m a t e r i a l at the cathode tip were made and they w e r e found to be in a g r e e m e n t with t h e o r i e s on liquid i n s t a b i l i t i e s . A r e v i e w of p e r t i n e n t l i t e r a t u r e c o n c e r n i n g v a c u u m a r c s was conducted and this along with g e n e r a l i n f o r m a t i o n on v a c u u m c o n s u m a b l e a r c r e m e l t i n g a r e i n c l u d e d as b a c k g r o u n d i n f o r m a t i o n .
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f i r s t known use of v a c u u m c o n s u m a b l e a r c r e m e l t i n g was d o c u m e n t e d by yon Bolton ~ in I905. A crude f o r m of the c u r r e n t p r o c e s s was used to m e l t and degas t a n t a l u m . However, the f i r s t w i d e s p r e a d d e v e l o p m e n t and use of v a c u u m c o n s u m a b l e a r c r e m e l t i n g o c c u r r e d a p p r o x i m a t e l y 25 y e a r s ago as a r e sult of d e m a n d s by e n g i n e e r s f o r a l l o y s c o n t a i n i n g r e active e l e m e n t s such as Ti, A1, Z r , and Nb (Cb). T h i s p r o c e s s is e s p e c i a l l y s u i t e d to the m i n i m i z a t i o n of m i c r o - and m a c r o s e g r e g a t i o n in t h e s e s u p e r a l l o y m a terials. Melting and s o l i d i f i c a t i o n a r e a c c o m p l i s h e d at low p r e s s u r e s , 0.133 to 1.3 • 104 P a (10 -s to 100 t o r r ) by m a i n t a i n i n g a d i r e c t c u r r e n t a r c b e t w e e n the e l e c t r o d e (cathode) and the m o l t e n pool atop an ingot (anode) and by cooling the ingot in a w a t e r cooled copper c r u c i b l e . The bulk c u r r e n t d e n s i t y at the cathode tip (electrode) f o r v a c u u m c o n s u m a b l e a r c r e m e l t i n g is low. U n d e r standard industrial processing, these current densit i e s range from 1.5 • 103 to 6.0 • l0 s A 9m-2 and cathode diameters range from 0.1 to 1.22 m. A labeled cut-away drawing of the lowerportion of the furnace located at Sandia Laboratories/Albuquerque is shown in Fig. I. As electrode material is melted by the arc it is transferred to the molten pool. Solidification starts within the molten pool at all locations where the temperature equals the liquidus temperature of the alloy being melted. Solidification is completed at the effective solidus temperature, usually at the melting point of one of the pure species or the peritectic or eutectic temperature as dictated by the equilibrium phase diagram. Little is published or understood
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