1. K. T. Jacob and J. M. Toguri: Met. Trans. B, 1978, vol. 9B, p. 301. 2. Z. Derriche and P. Perrot: Met. Trans. B, 1979, vol. 10B, pp. 297-98. 3. Z. Derriche and P. Pe[rot: Rev. ChirrL Miner., 1976, vol. 13, pp. 310-23. 4. E. V. Margulis and N. I. Kopylov: Russ. ,1. Inorg. Chem., 1964, vol. 9, p. 424. 5. A. E M. Warner, M. P. Roye and J. H. E. Jeffes: Trans. Inst. Mining Met., London, 1973, vol. 82, pp. C246-48. 6. E. N. Rodigina, K. Z. Gomelsky and V. F. Luginina: Russ. J. Phys. Chem, 1961, vol. 35, pp. 884-86. 7. K. K. Kelley: U. S. Bureau Mines Bull. 406, 1937. 8. M. Fredriksson, E. Rosen and L. Wittung, Chem. Scr., t977, voL 11, pp.32-36.

Discussion of "Electrochemical Determination of the Free Energy of Formation of SnO2"*

k,

9

180

160

I 800

I

I

i

900

i

i

1000

t 1100

~

I 1200

t

I 1300

I

I 1400

Tempecoture,K

S. S E E T H A R A M A N AND L . - I . S T A F F A N S S O N T h i s d i s c u s s i o n p e r t a i n s to t h e c o m p a r i s o n of t h e G i b b s e n e r g y of f o r m a t i o n of SnO2 r e p o r t e d b y B a m a n a r a y a n a n a n d B a r w i t h t h e r e s u l t s of a n u m b e r of s i m i lar measurements c a r r i e d o u t e a r l i e r 1-~ a n d w h i c h h a v e n o t b e e n r e f e r r e d to b y R a m a n a r a y a n a n a n d B a r , the latest among them being ours. 5 We used Ni-NiO as the reference electrode and there was no Pyrex seal separating the electrodes. O u r a t t e m p t s to u s e c h r o m e l w i r e s a s e l e c t r i c a l l e a d s in c o n t a c t w i t h m o l t e n t i n w e r e n o t s u c c e s s f u l a b o v e 1300 K d u e to s e r i o u s a t t a c k on t h e m a n d h e n c e we were forced to switch over to chromium cermet (Met a m i c 612, M o r g o n Co., U . K . ) e l e c t r o d e s w h i c h w e r e f o u n d to f u n c t i o n w e l l . T h e AG~n O v a l u e s r e p o r t e d b y R a m a n a r a y a n a n a n d B a r a g r e e we211 w i t h o u r r e s u l t s . B u t , a s t h e r e f e r e n c e e l e c t r o d e a s w e l l a s t h e s o u r c e of A G ~ f o r t h e r e f e r e n c e e l e c t r o d e a r e d i f f e r e n t f r o m o u r s , it w o u l d o n l y b e p r o p e r to ' c o n v e r t ' t h e i r e x p e r i m e n t a l d a t a to N i NiO reference electrode so that a meaningful comparison could be made. Hence their reported equation for the cell EMF: E (mY) = 624.4was recalculated the cell:

0 . 1 6 6 T (K) + 3.8

[11

u s i n g t h e e q u a t i o n f o r t h e E M F of

(-) Ni, NiO // ZrO~ - CaO//

0 . 0 7 0 4 6 T (K) + 0 . 1 9

[2]

v a l i d in t h e t e m p e r a t u r e r a n g e 924 to 1328 K. T h i s EMF expression has been recommended by Rapp and S h o r e s 7 a s t h e b e s t . T h e r e s u l t i n g e q u a t i o n of t h e E M F for the cell:

(-) Sn, SnO2//

ZrO2 - CaO//NiO,

Ni (+)

w i U then b e : E (mY) = 2 7 7 . 7 2 -

0 . 0 9 5 5 4 T (K) • 3 . 9 9 .

[3]

T h i s h a s b e e n i n c l u d e d in F i g , 1 t a k e n f r o m o u r p u b l i c a t i o n . 5 It c a n b e s e e n t h a t t h e a g r e e m e n t i s e x c e l l e n t . *T. A. RAMANARAYANAN and A. K. BAR: M e t . Trans. B, 1978, vol. 9B, pp. 485-86. S. SEETHARAMAN and L.-I. STAFFANSSON are Research Associate and Professor, respectively, Department of Theoretical Metallurgy, Royal Institute of Technology, S-100 44 Stockholm 70, Sweden. Discussion submitted December 281 1978. METALLURGICAL

TRANSACTIONS B

1. G. Petot-Ervas, R. Farhi, and C. Petot: J. Chem. Thermodyn., 1975, voI. 7, pp. 1131-36. 2. T. Palamutcu: Ph.D. Thesis, Imperial College of Science and Technology, London, 1970. 3. T. Oishi, T. Hiruma, and J. Moriyama: Nippon Ginzaku Gakkaishi, 1972, vol. 36, pp. 481-85. 4. Y. MatsusbAta and K. Goto: Thermodynamics L P. 111, IAEA, Vienna, 1966. 5. S. Seetharaman and L. -1. Staffansson: Scand. J. Metall., 1977, vol. 6, pp. 143-44. 6. G. G. Charette and S. N. Flengas: J. Electrochem. Soc., 1968, vol. 115, pp. 796-804. 7. R. A. Rapp and D. A. Shores: Techniques of Metals Research, R. F. Bunshah and R. A. Rapp, eds., Ph),sicochemicalMeasurements in Metals Research, vol. IV, Part 2, p. 159, lnterscience Pub., 1970. 8. T. N. Belford and C. B. Alcock: Trans. Faraday. Soc., 1965, vol. 61, pp. 443-53.

Heat Transfer Coefficient in Aluminum Alloy Die Casting S. HONG,

Cu20, Cu (+)

reported by Charette and Flengas, ~ viz.: E (mY) = 3 4 6 . 6 8 -

Fig. 1-EMF-Temperature plot for the galvanic cell ( - ) Sn, S n O z / / S o l i d electrolyte//NiO, Ni (+). 1) Belford and Alcock, 8 2) Petot-Ervas et al, l 3) Palamutcu, 2 4) Oishi et al, 4 5) Seetharaman and Staffansson: s o, 9 EMF values with two different types of cell arrangements, 6) Ramanarayanan and Bar.

D. G. BACKMAN,

AND

R. MEHRABIAN

The analysis of heat flow during the die casting process is difficuR owing to the multiplicity of complex physical phenomena occurring during the casting cycle. These phenomena include intricate metal flow during die filling, solidilication over a finite temperat u r e i n t e r v a l , c o n t r a c t i o n of t h e c a s t i n g d u r i n g c o o l ing, and the physical changes due to coatings and oxidation at the casting/die interface. In order to develop a n u n d e r s t a n d i n g of h e a t f l o w d u r i n g d i e c a s t i n g , a combined experimental and theoretical investigation S. HONG, formerly a Graduate Student at the University of Illinois at Urbana-Champaign is now with General Motors Technical Research Center. D. G. BACKMAN, formerly Assistant Professor in the Department of Mechanical and Industrial Engineering at the University of Illinois is now with General Electric, Lynn, Massachusetts. R. MEHRABIAN is Professor in the Department of Metallurgy and Mining Engineering and the Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 61801. Manuscript submitted May 26, 1978.

ISSN 0360-2141 / 79 / 0611-0299500.75 / 0 9 1979 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME

VOLUME 10B, JUNE 1979-299

775

J

J

0,111~1 - -

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MEASUREDDIE TEMPERATURES A 580 AI ALLOY INITIAL DiE TEMPERATURE-51O~K

MELTTEMPERArURE =

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r a

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/q,-o

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2-34-5--

2.54 x 1.27 x 2.54 x 6.35 x

lO-4m 10-3m 10-3m lO-3m

DEPTH OF T H E R M O C O U P L E S FROM DIE PARTING LINE: Fig. 1--Schematic of die cavity showing thermocouple locations.

was u n d e r t a k e n . By c o m p a r i n g the r e s u l t s of e x p e r i m e n t s and a c o m p u t e r s i m u l a t i o n it was p o s s i b l e to det e r m i n e the s u r f a c e heat t r a n s f e r coefficient, h, cont r o l l i n g heat flow a c r o s s the c a s t i n g / d i e i n t e r f a c e . A p p a r a t u s and P r o c e d u r e . Two s e r i e s of e x p e r i m e n t s w e r e conducted to a n a l y z e heat flow d u r i n g die c a s t i n g of A380 a l u m i n u m b a s e alloy.* T h e *Nominalcomposition:A1-3,5wt pct Cu-8.5wt pct Si-1.3wt pct Fe. e x p e r i m e n t s w e r e d e s i g n e d to d e t e r m i n e the i n f l u e n c e of die c a s t i n g v a r i a b l e s i n c l u d i n g p l u n g e r velocity, inj e c t i o n p r e s s u r e , m e l t t e m p e r a t u r e , and die s p r a y p r o c e d u r e on the t e m p e r a t u r e d i s t r i b u t i o n within the die. D u r i n g t h e s e e x p e r i m e n t s , m o l t e n A380 a l u m i n u m b a s e alloy was cast into a h o r i z o n t a l flat plate cavity, 1.59 • 10-s m thick, u s i n g a s i n g l e fan gating g e o m e t r y , F i g . 1. T h e die c a s t i n g m a c h i n e used was a 400 ton L e s t e r h o r i z o n t a l cold c h a m b e r m a c h i n e equipped with a u t o m a t i c c o n t r o l s to r e g u l a t e e a c h p o r t i o n of the c a s t i n g s e q u e n c e . T h e dies w e r e made f r o m H13 tool s t e e l . T h e a l u m i n u m alloy was m e l t e d in a n e l e c t r i c f u r n a c e c o n t r o l l e d to •176 The b u l k die t e m p e r a t u r e was m a i n t a i n e d and c o n t r o l l e d with four c a r t r i d g e h e a t e r s , each powered by a s e p a r a t e v a r i a c . Shot p i s t o n d i s p l a c e m e n t and v e l o c i t y and h y d r a u l i c p r e s s u r e w e r e m e a s u r e d v i a t r a n s d u c e r s on a h i g h - s p e e d stripchart recorder. The s t a t i o n a r y die half was fitted with six c h r o m e l / a l u m e l t h e r m o c o u p l e s which w e r e l o c a t e d at v a r i o u s depths b e n e a t h the m a t i n g s u r f a c e of the die. Two of the t h e r m o c o u p l e s were e l e c t r o n b e a m welded, n o m i n a l l y at the die s u r f a c e w h e r e a s the o t h e r four w e r e spot welded at v a r i o u s depths. T h e s e depths and t h e i r c o r r e s p o n d i n g l o c a t i o n s with r e s p e c t to the cavity s u r f a c e a r e shown i n F i g . 1. The t h e r m o c o u p l e output was r e c o r d e d u s i n g a f o u r - p e n , h i g h - s p e e d r e c o r d e r and two, t w o - p e n , s t r i p c h a r t r e c o r d e r s . Supp r e s s i o n was e m p l o y e d to r e c o r d the output y i e l d i n g m a x i m u m output s e n s i t i v i t y . D u r i n g the e x p e r i m e n t s , one v a r i a b l e was a l t e r e d at a t i m e and a p p r o x i m a t e l y four c a s t i n g s w e r e p r o d u c e d at each condition so that i n t r i n s i c v a r i a t i o n of the out300-VOLUME 10B, JUNE 1979

4703.OI

OI

1,0 TIME (s)

Fig. 2--Measured effect of metal temperature on die thermal behavior. put could be gaged. Two m e t a l p r e s s u r e s 8.75 X 10 7 and 17.5 • 107 N / m z, two m e l t t e m p e r a t u r e s , 878 and 960 K, and two ingate v e l o c i t i e s , 18.3 and 54.9 m / s , w e r e e m p l o y e d d u r i n g e x p e r i m e n t a t i o n . The c a s t i n g cycle was a p p r o x i m a t e l y 60 s. T h i s cycle t i m e was s e l e c t e d so that a n i d e n t i c a l t e m p e r a t u r e d i s t r i b u t i o n was p r e s e n t w i t h i n the die p r i o r to the p r o d u c t i o n of each c a s t i n g . Most c a s t i n g s w e r e p r o d u c e d without die s p r a y however, toward the c o m p l e t i o n of the e x p e r i m e n t s , an e n t i r e s e q u e n c e with s p r a y (Acheson No. 1163 diluted with w a t e r , 40 : 1 r a t i o ) was p r o d u c e d to u n c o v e r the effect of die l u b r i c a n t . The c o m p u t e r technique e m p l o y e d to a n a l y z e heat flow has b e e n d e s c r i b e d p r e v i o u s l y . ~ The p r o g r a m s o l v e s the one d i m e n s i o n a l heat flow e q u a t i o n w r i t t e n in finite d i f f e r e n c e f o r m u s i n g a n explicit method. The p r o g r a m i n c o r p o r a t e s s o l i d i f i c a t i o n over a finite t e m p e r a t u r e i n t e r v a l and has p r o v i s i o n to i n c o r p o r a t e r e s i s t a n c e to heat flow at the c a s t i n g / d i e i n t e r f a c e . One m a i n a s s u m p t i o n e m p l o y e d is that the die f i l l is i n s t a n t a n e o u s . T h e p r o g r a m output p r o v i d e s the t e m p e r a t u r e as a f u n c t i o n of time and p o s i t i o n in both the casting and the d i e . R e s u l t s . A p p r o x i m a t e l y 80 die c a s t i n g s w e r e made. Of the v a r i o u s p r o c e s s p a r a m e t e r s , only m e l t s u p e r heat had a d i s t i n g u i s h a b l e effect on m e a s u r e d t e m p e r a t u r e s within the die. No effect could be d i s c e r n e d 773

DIE TEMPERATURESAT VAFIIOUSDEPTHS A 380 AI ALLOY MELTTEMPERATURE- B78~ INITIAL DIE TEMPERATURE-5bO ~ K

/ ~ ~m Q

I

/

- - -

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TIME (s)

Fig. 3--Comparison of computer simulated and measured die thermal behavior. METALLURGICALTRANSACTIONSB

by v a r y i n g e i t h e r the m e t a l p r e s s u r e or the ingate v e l o c i t y . The m e a s u r e d die t e m p e r a t u r e s d u r i n g c a s t ing of A380 a l u m i n u m alloy when the dies w e r e at an i n i t i a l t e m p e r a t u r e of 510 K is shown in F i g . 2. Two s e t s of four c u r v e s a r e shown for m e l t t e m p e r a t u r e s of 960 and 878 K, r e s p e c t i v e l y . When the m e l t t e m p e r a t u r e was 960 K, the peak die s u r f a c e t e m p e r a t u r e was 758 K o c c u r r i n g at a t i m e of a p p r o x i m a t e l y 0.1 s. F o r m e t a l cast at lower s u p e r h e a t , 878 K, the peak t e m p e r a t u r e was 743, 15 K c o l d e r . However, the d i f f e r e n c e in s u p e r h e a t does not a p p e a r to a l t e r the t i m e at which the p e a k t e m p e r a t u r e s w e r e a c h i e v e d . In addition, at long t i m e s , g r e a t e r than 2.0 s, the effect of s u p e r h e a t a p p e a r s to be n e g l i g i b l e . At the other t h e r m o c o u p l e l o c a t i o n s , the s a m e type of b e h a v i o r was o b s e r v e d . The t i m e at which peak t e m p e r a t u r e s were r e c o r d e d was not a l t e r e d by s u p e r heat although an i n c r e a s e in s u p e r h e a t of 82 K r e s u l t e d in a n i n c r e a s e in t e m p e r a t u r e of a p p r o x i m a t e l y 15 to 20 K. Both of the t e m p e r a t u r e d i s t r i b u t i o n s d e s c r i b e d above and plotted in F i g . 2 were s i m u l a t e d u s i n g the c o m p u t e r p r o g r a m in o r d e r to d e t e r m i n e the v a l u e of the s u r f a c e heat t r a n s f e r coefficient, h, at the c a s t i n g / d i e i n t e r f a c e . The r e s u l t s a r e shown in Fig. 3. I n o r d e r to obtain a g r e e m e n t b e t w e e n the m e a s u r e d t e m p e r a t u r e s and the calculated t e m p e r a t u r e s , an h

METALLURGICALTRANSACTIONSB

value of 7.94 • 104 W / m 2 9 K was e m p l o y e d . T h e a g r e e m e n t b e t w e e n the two c u r v e s , shown in F i g . 3 u s i n g this v a l u e of h, is good, p a r t i c u l a r l y c o n s i d e r i n g that the t i m e axis is l o g a r i t h m i c and the a p p a r e n t d e v i a tion in the two c u r v e s at a g i v e n t h e r m o c o u p l e location for t i m e s l e s s than 0.1 s is on the o r d e r of app r o x i m a t e l y 50 m s . The s m a l l d i s c r e p a n c y is a t t r i buted to,a c o m b i n a t i o n of t h r e e f a c t o r s . F i r s t , the holes for the t h e r m o c o u p l e w e r e d r i l l e d f r o m the b a c k side of the die r e s u l t i n g i n a s m a l l e r r o r in m e a s u r e d t h e r m o c o u p l e location. Second, each t h e r m o c o u p l e has a finite r e s p o n s e t i m e . L a s t l y , the line width of the t h e r m o e o u p l ~ t r a c e is e q u i v a l e n t to a t i m e of a p p r o x i m a t e l y 20 m i l l i s e c o n d s i n d i c a t i n g that s m a l l i n a c c u r a c i e s i n data t r a n s f e r r a l a r e likely. In g e n e r a l , for the conditions Studied, the value of h was in the r a n g e 7.9• 104 to 8.7• 104W/m 2 "K. This work was sponsored by the Army Materials and Mechanics Research Center, Watertown, Massachusetts. Technical assistance by Mr. Michael Kaufman is gratefully acknowledged.

1. D. G. Backman,R. Mehrabian,and M. C. Flemings:Met. Trans. B, 1977,voL 8B, p. 471.

VOLUME 16B, JUNE t979-301