Eddy current response to metallic solidification in one dimension
- PDF / 466,463 Bytes
- 5 Pages / 583 x 777.28 pts Page_size
- 14 Downloads / 253 Views
INTRODUCTION
THE aim of this investigation is to d e v e l o p a t e c h nique which can without mechanical interference annl y r i c a l l y m o n i t o r m a c r o s c o p i c solidification p h e n o m e n a of p u r e m e t a l s and a l l o y s in m o l d s of l a b o r a t o r y and i n d u s t r i a l d i m e n s i o n s .1 Such a p r o c e d u r e w o u l d a l l o w d i r e c t s t u d i e s of solidification p r o c e s s e s and p r o v i d e a b a s i s f o r p r o c e s s c o n t r o l ,z Eddy c u r r e n t t e s t i n g h a s b e e n a v a i l a b l e f o r f i f t y y e a r s3-s and a n a l y t ical a p p l i c a t i o n s of the d a t a f o r n o n d e s t r u c t i v e t e s t i n g have b e e n e m p l o y e d m o s t n o t a b l y t h r o u g h the e f f o r t s of H. Libby6 and C . D o d d .7"~ In this p a p e r , the eddy c u r r e n t r e s p o n s e to solidification of s i m p l e m e t a l s y s t e m s w i t h i n a m e t a l l i c mold will b e c o n s i d e r e d by m o d e l l i n g o n e - d i m e n s i o n a l solidification g e o m e t r i e s . S i n c e a u n i q u e - i n v e r s e s o l u t i o n does not e x i s t , the eddy c u r r e n t p r o b l e m is m o s t c o n v e n i e n t l y h a n d l e d f o r a s p e c i f i c g e o m e t r y r a t h e r than in g e n e r a l . T h e p h e n o m e n a to be e x a m i n e d a r e the eddy c u r r e n t r e s p o n s e s to p h a s e f o r m a t i o n , solid-liquid i n t e r f a c e p o s i t i o n , and t e m p e r a t u r e w i t h i n a p u r e s i n g l e p h a s e m e t a l l i c s y s t e m that is solidifying o r m e l t i n g . Such p r o p e r t i e s as m u s h y z o n e t h i c k n e s s , i n c l u s i o n , t h e r m a l g r a d i e n t s and d e n d r i t i c a r m s p a c i n g a r e also c o n t r i b u t i o n s to d e t e c t e d eddy c u r r e n t s i g n a l s but will not be a s u b j e c t of this p a p e r . EDDY CURRENT SIGNALS Eddy c u r r e n t m e a s u r e m e n t s of m e t a l l i c c o n d u c t i v i t y c h a n g e s r e q u i r e an a n a l y s i s of low f r e q u e n c y e l e c t r o magnetic radiation reflected from a conductor. Inform a t i o n a b o u t the s p a t i a l conductivity v a r i a t i o n s w i t h i n the mold and m e l t is c o n t a i n e d in the m a g n i t u d e and p h a s e d i f f e r e n c e s b e t w e e n the i n c i d e n t and the r e f l e c t e d s i g n a l . T h e i n d u c t i o n coil w h i c h p r o d u c e s the i n c i d e n t e l e c t r o m a g n e t i c r a d i a t i o n is also u s e d to d e tect the e l e c t r i c f i e l d , E ( x , t), a s s o c i a t e d with the r e f l e c t e d s i g n a l . This e l e c t r i c f i e l d is c o l i n e a r with the i n d u c e d eddy c u r r e n t s and is r e p r e s e n t a t i v e of the bulk p r o p e r t i e s w i t h i n the test p i e c e . A m o r e c o n v e ient v a r i a b l e , the v e c t o r p o t e n t i a l , A-(x, t), will b e u s e d to d e s c r i b e the c h a r a c t e r i s t i c s of the
Data Loading...
