By Horace J. Young, F.I.C., Member.
F o r in tro d u c tio n th e a u th o r wishes to explain those circu m stan ces u n d e r w hich th is n o te has heen w ritte n .
I t is know n now adays to m any people t h a t th e P e r lit process consists of a d efin ite fo u n d ry pro c e d u re co rre la te d w ith a n equally definite m etal
lu rg ic a l c o n tr o l; th e m oulds are h e a te d to a p re d e te rm in e d te m p e ra tu re to s u it th e m etal w ith w hich th e y a re to be filled, w hile th e m etal is con
tro lled to a p re -d e te rm in e d com position to s u it th e av e ra g e th ic k n e ss an d th e mass of th e c a stin g it is to occupy.
O bviously, an y one p o rtio n of th e process, as above described a n d as s e t o u t in th e p a te n t specifi
catio n s, can be m ade to re c ip ro c a te w ith th e o th er an d , th e re fo re , i t is possible to c a rry o u t th e m ethod a n d to a t t a i n th e d e sire d re s u lt in m ore th a n one m an n er. F o r in stan ce, one fo u n d ry may find i t co n v en ie n t to v a ry th e te m p e ra tu re of its m oulds an d to keep th e m e ta l c o n s ta n t; a n o th e r to use d iffe re n t m etals w h ilst using a sim ilar m o u ld -te m p e ra tu re th r o u g h o u t; w hilst a n o th e r m ay h av e such w ork as re n d e rs i t b e tte r to v ary b o th fa c to rs.
N o t long ago th e a u th o r, re a d in g a b o u t th is p ro cess in th e te c h n ic a l P ress, fo u n d i t difficult to ev a lu a te . M uch of th is difficulty w as due u n d o u b te d ly to a n e x tr a v a g a n t an d , in some in
stances, a n in a p p r o p ria te use of th e d escrip tio n
“ p e a r litic .” A v is it to th e C o n tin e n t, in th e e a rly p a r t of th is y e a r, gave o p p o rtu n ity fo r p e r
sonal in v e s tig a tio n in v ario u s fo u n d ries u sin g th e process a n d tu r n in g o u t all classes of w ork, lig h t, m edium o r heavy, as th e case m ig h t he.
T he final re m a rk o f th is p reface consists in say
in g t h a t th e process h as heen in o p eratio n in th e fo u n d rie s of th e N o rth E a s te r n M arin e E n g in e e r
in g C om pany fo r so sh o rt a p erio d as to m ake it im possible fo r th e a u th o r to include m any of th e
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o b serv atio n s m ade in those fo u n d rie s, b u t he has decided, n ev erth eless, to a d m it no n e m ad e else-1 w here an d n o t u n d e r h is su p erv isio n .
Of re c e n t y ears i t lias become recognised, from re s u lts o b ta in e d u n d e r service c o n d itio n s as well as those of m any research w orkers, t h a t grey cast irons c o n ta in in g li tt le silicon possess su p e rio r p ro p e rtie s to those of h ig h e r silicon ran g es. U n fo r
tu n a te ly , th e obstacles in th e way of using low- silicon m e ta l o fte n a re , fo r v ery m an y c astin g s m ad e u n d e r u su a l fo u n d ry c o n d itio n s, e n tir e ly p ro h ib itiv e . The u n re lia b ility o f o r d in a r y c a s t ir o n lies in t h e f a c t t h a t th e m e ta l has a v a ry in g
“ g r a in ” according to its section— a co m p licated
F i g . 1 .— Pe e l i t Ba b, c a s t i n . d i a s . Ge a p h i t e x 2 5 D I A S .
c a stin g is “ d iffe re n t all o v e r,” w h ilst a p la in one h a s a m etal “ c o re .” F o r in s ta n c e , an o rd in a ry te s t-b a r c a s tin g is d if fe re n t in t h e c e n tr e from w h a t i t is n e a r e r to th e o u ts id e . Also is i t recog
nised b ro ad ly t h a t g rey ir o n c o n ta in in g th e m a x i
m um a m o u n t possible of co m bined c a rb o n , w ith o u t fre e c e m e n tite , is th e b e s t fo rm in w hich an y one p a r t ic u l a r c a s t iro n c a n be— th is fo rm b e in g described as a ll-p e a rlitip .
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A dded to th ese accepted facts is th e knowledge t h a t th e g r a p h ite should e x is t in am o u n ts below, sa,y, 2.5 p e r c e n t., an d t h a t th e dim ensions, shapes a n d d is trib u tio n of th e voids, p a rtly occupied by it, should be such as have been fo u n d to c h a r
a c te ris e those irons w hich have given th e b est se r
vice a n d e x h ib ite d su p e rio r physical p ro p ertie s.
In o th e r words, th ese voids should be sh o rt, th in , cu rly or n o d u la r, an d confined w ith in th e netw ork.
I n o rd e r to p re v e n t th is n o te from developing in to a discussion of m a tte r alread y proved and accepted by recognised a u th o ritie s, th e a u th o r has selected, fro m th e la rg e mass of evidenoe, only re m a fk s m ade by B ritis h w orkers which have
Fi g. 2 . — Pe r l i t Ba r, c a s t 1 j i n . d i a s. Gr a p h i t e x 75 d i a s.
a p p e a re d in those issues of Th e Fo u n d r y Tr a d e Jo u r n a l of th e d ates given in p a ren th esis.
H ilto n M ills (J u ly 5, 1923 and J u l y 19, 1923) w rite s :— “ The ten sile s tre n g th was u n d e r 8.0 to n s p e r sq. in. C arbon e stim a tio n s on th e te s t b a r showed : T o tal c arb o n , 4.20 p e r c en t. ; g ra p h ite , 3.40 p e r cen t. ; an d com bined carbon, 0 . 8 0
p e r c e n t.” F u r th e r , he w rite s : “ M y re a l
conten-122
tio n was, t h a t a h ig h p e a r lite c o n te n t was only of use w hen com bined w ith o th e r s t r u c tu r a l c h a r
acte ris tic s , th e chief of w hich is th e re q u is ite fine
ness of th e g ra p h itic c arb o n . A p e a rlite -g ra p h ite s tr u c tu r e is u n d o u b ted ly th e o n e to aim a t, for s tre n g th in o r d in a ry sa n d c a stin g s, b u t th e g r a p h ite m u st be th e r ig h t ty p e .”
J . Shaw (Dec. 6, 1923) w r o te :— “ T he essen tial c h a ra c c e n s tic s of h ig h -g ra d e c a s t iron m ay be said to be a fine d is trib u tio n of th e g ra p h ite , an d a p u rely p e a rlitic g ro u n d m a ss.”
Fi g. 3 . — Pe a r l i t e Ba r, c a s t 1 J i n . d i a s. Pe a r l i t e x 400 d i a s.
G. S. Bell an d C. H . A dam son (M ay 8, 1924) s t a t e : — “ I t is f a ir ly c e r ta in t h a t th e te n s ile s tre n g th v aries d ire c tly w ith th e closeness of th e s tru c tu r e s in a p a r tic u l a r co m p o sitio n .”
F . H . H u r r e n (M ay 22, 1924), d escrib in g th e m a n u f a c tu r e o f m o to r-ca r cy lin d ers, gives th e analyses of th r e e d iffe re n t p a r ts o f the sam e cylin der a n d r e m a r k s : “ T he figures a re ty p ic a l of m an y te s ts, a n d , as m ig h t be expected, th e only d ifference is in th e com bined carbon an d g ra p h ite c o n te n ts .”
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J . E . H u r s t (16-10-1924) says, in his P ap er e n title d “ N otes on P e a rlite O ast Iro n ” t h a t th e f a c t of P e r lit iro n being w h ite when cast in to a cold m ould “ a t once d iffe re n tia te s betw een an o rd in a ry cast iro n of a p e a rlite -g ra p h ite s tru c tu re a n d th e p ro d u c t now know n as p e a rlite cast iro n .”
F u r t h e r , he s ta te s f‘ I t is, g en erally speaking, well know n t h a t an all-p eai'litic s tru c tu r e is advisable fo r th e b est g en eral re s ista n c e to w ear.”
R e fe rrin g to o th e r p ro p e rtie s, he re m a rk s “ A
F i g . 4 . — P e r l i t B a r , c a s t l \ i n . d i a s . P e a r l i t e x 1 , 5 0 0 d i a s .
m ost im p o rta n t a d d itio n a l p o in t is t h a t th is high te n s ile s tr e n g th is secured w ith a com paratively low B rin ell h ard n ess. ” Pie goes on to say
“ W h ilst, b roadly sp eak in g , fo u n d ry m e ta llu rg ists a r e well aw are of th e influence of r a te of cooling on th e c o n stitu tio n of c a s t iro n , none of us has been aw are of th e f a c t t h a t th e r a t e of cooling could be modified in th e m a n n e r proposed in th e p e a rlitic cast-iro n process, an d for such modifica
tio n to be accom panied by such g ra tify in g re s u lts .” L a te r , he continues “ An all-p earlitic m a trix is th e b e st practice. I t is his experience
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w ith m an y c y lin d er problem s of re c e n t y ears t h a t th e low er th e silicon c o n te n t, th e b e tte r th e re s is t
ance to w ear u n d e r alm o st all co n d itio n s a p p e r
ta in in g in en g in e c y lin d er w ork, in c lu d in g in te rn a l-c o m b u stio n en g in e o r otherw ise. F ro m th ese p o in te of view th e p e a rlite cast-iro n s tr u c tu r e an d th e u n d e rly in g fe a tu re s o f th e L a n z p e a rlitic c a st iro n as defined, fully ju s tif y th e ir claim s re g a r d in g resistan ce to w ear. T h e d is
to r tio n of c a s t iro n u n d e r h e a t influences in th e e n g in e cy lin d er is a n o th e r com plex phenom enon
Fi g. 5 . — Pe r l i t Br a c k e t. Se c t i o n § i n . x 4 0 0 D I A S .
... i t is show n h ere, an d h as since been con
firm ed by o th e r in v e s tig a to rs , t h a t th e low er th e silicon c o n te n t th e g r e a te r th e re sista n c e of th e p e a rlite c o n s titu e n t to decom position u n d e r th ese circu m stan ces. I t is his o pinion t h a t a low silicon an d a n a ll-p e a rlitic c a s t iro n a re d e sira b le con
d itio n s to o b ta in th e b est re s ista n c e to d is to rtio n a risin g from th e above-m entioned ca u se s.” H e s ta te s “ I t will be q u ite c le a r from th e d efin itio n of p e a rlitic c a st iro n t h a t i t is in te n d e d to belong to th e class of iro n s w hich h av e been described as
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b o rd er-lin e com positions, an d we may expect th a t th is being th e case i t would be ex trem ely sensitive to th e effect of th e r a t e of c o o l i n g ...th e re is no sem blance of a n n e a lin g in th e process.”
P rof. C. H . Desch (8-1-1925) said “ T he best c a st iro n is likely to co n sist of a stro n g steel, con
ta in in g g r a p h ite cry stals of such sm all size and so g ro u p ed as to produce th e le a s t w eakening effect. T he to u g h e s t steel h a s th e com position of p e a r lite ... T here a re m an y reasons why cast iro n of close g ra in , w ith m in u te p articles of
Fi g. 6 . — Pb e i i t Br a c k e t, c a s t 1 £ i n. d i a s. Pe a r l i t e x 4 0 0 d i a s.
g ra p h ite held in a p e a rlitic ground-m ass, is d e sir
able, a p a r t from its s tre n g th an d m achining q u a litie s. Chem ical a tta c k , such as th e d estru c
tio n of acid ta n k s by su lp h u ric acid, is associated w ith a n open g ra in . . . he h a s m et w ith s tr ik in g in stan ces of th is actio n . S im ila r considera
tio n s ap p ly to irons which a re to be su b jected to high te m p e ra tu re s an d to th e action of oxidising gases. I t has been shown by C a rp e n te r and o th e rs t h a t ‘ grow th ’ only occurs in g ra p h itic
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iro n s a n d is p a rtic u la rly m ark ed in iro n s c o n ta in in g a h ig h p ro p o rtio n of silico n .”
A. C am pion {22-1-1925) in a P a p e r u pon th e facto rs in flu en cin g th e s tre n g th of c a st iro n said
‘1 The ideal c a s tin g -te m p e ra tu re w ould h e such t h a t th e m ould could be com pletely filled, w hilst all c o n s titu e n ts of th e iro n a re com pletely in so lution, a n d t h a t th e y should begin to s e p a r a te im m ed iately t h e r e a f t e r .” H e describes s u ita b le cooling c o n d itio n s as re s u ltin g in “ no rm al c ry s ta llis a tio n p rio r to th e s a tu r a tio n p o in t of th e
Fi g. 7 . — P e r l i t Bu s h. C a s t i n g T H IC K N E S S , 1 J I N . G R A P H IT E X 2 5 D IA S .
c arb id e being reach ed . O bjectionable g ra p h ite g ro w th is th u c p re v e n te d , an d a .m echanically sound s tr u c tu r e is o b ta in e d .”
P ro f. T. T u rn e r (29-1-1925) com m enting upon th e L an z process said “ H e w as in te re s te d to h e a r th e figure of 4 p er c e n t, as th e to ta l of silicon an d carbon. H e was rem in d ed o f so m eth in g t h a t h ap p en ed fo rty y e a rs ago w hen he m ^de e x p e ri
m en ts on silicon in c a st iro n , an d -when th e b a r
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w hich gay© th e b est re s u lt in a series co n tain ed a b o u t 2.2 p e r cen t, carbon an d 1.8 p e r cent, silic o n .” F u r th e r , he s ta te d ‘‘ The im p o rtan ce was d e m o n stra te d of fine-grained g r a p h i t e ...
in o th e r w ords, i t w as desirab le to produce i t in a sm all flake an d alm ost g ra n u la r c o n d itio n .”
“ H e was p leased ,” he sa id , “ to feel t h a t they could, by th e a p p lic a tio n of know ledge now w ithin th e i r reach , e n su re m a te ria l of a h ig h q u a lity and of a u n ifo rm c h a ra c te r, m a te ria l which could be d ep en d ed upon to re s ist shock, to give good w ear,
Fi g. 8 . — Pe r l i t Bu s h. Ca s t i n g T H IC K N E S S l j I N . X 400 D IA S .
to give sm ooth ru n n in g su rfaces, an d w hich would n o t creep or grow u n d u ly w hen i t was exposed to h ig h te m p e r a tu r e .”
A. L ogan (19-2-1925) said “ S lig h t changes of u ltim a te com position will p roduce d ra s tic changes in s tr u c tu r a l com position. T he re te n tio n of a li tt le over 0.2 p er c e n t, m ore carbon in th e com
bined s ta te , fo r in s ta n c e , w ould be sufficient to ta k e u p th e w hole of th e free fe r rite , an d th e m a trix w ould th e n be com pletely p e a rlitic .” H e calc u lated t h a t 0.50 p er cen t, of combined carbon form s 59.52 p e r cent, of p e a rlite by w eig h t or
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54.60 p e r cen t, by volum e, a n d c o n tin u e d “ I t follows t h a t th e stro n g e s t iro n s a re th o se w hich co n tain a m in im u m a m o u n t of g r a p h ite in th e m oat finely div id ed fo rm a n d p re fe ra b ly g ro u p e d ,’ a n d h a v in g in a d d itio n , a com pletely p e a rlitic m a trix w ith o n ly a sm all a m o u n t of phosphide e u te c tic p re s e n t. ”
H a v in g g iv en th e above referen ces, th e a u th o r th in k s i t un n ecessary f u r th e r to lab o u r th e p o in t involved th e re in .
Fi g. 9 . — Pe r l i t Ir o n. Ph o s p h i d e Ne t w o r k x 2 5 b i a s.
P erl it iro n possesses som e u n iq u e p ro p e rtie s, one of w hich is p roved b y th e sim plest p ra c tic a l te s t, nam ely, t h a t one o f tr y in g to b re a k i t w ith a h am m er. R ecently th e a u th o r c a s t a sm all b ra c k e t of P e r lit iro n , its dim ensions bein g a b o u t 9 in.
long, 6 in. w ide an d v a ry in g in section from th re e - q u a rte rs to an inch a n d a q u a r te r . T h e c a s tin g was a poor one a n d a la b o u re r p re d ic te d t h a t he could b re a k i t w ith a ta p of his h am m er. U lti
m ately , tw o m en s tru c k i t fo rty tim e s w ith 20-lb.
sledges an d th e c a stin g re m a in s u n b ro k e n . The s tr u c tu r e of th e m etal in th e j- in . sectio n a n d in th e 1^-in. section is shown in F ig s. 5 a n d 6
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respectively. The m agnification in each case is 400 d iam eters an d c lea rly in d ic a te s th e fineness of th e lamallse, th e a ll-p e a rlitic m a trix an d th e fine g ra p h ite spaces w ith some n o d u la r ones.
All p ro p erly -m ad e P e r l it iro n ex h ib its th is re m a rk a b le re s ista n c e to im p act, a n d th e foundry w orkers a re a sto n ish ed by it . A p ra c tic a l te s t of th is n a tu r e is m ore convincing, p erh ap s, to th e en g in e e r an d th e fo u n d ry m a n th a n ab stru se re s u lts d ep en d in g fre q u e n tly upon p a rtic u la r con
d itio n s. I t w ould a p p e a r to he ir re fu ta b le proof t h a t a new a n d b e tte r c a s t iro n has been dis
covered. W h en one a tte m p ts to visualise th e reasons u n d e rly in g th e b eh av io u r of th e iro n when su b je c te d to th is p a r tic u la r te s t, i t becomes e v id e n t t h a t th e m e ta l w ill he su p e rio r in o th e r d ire c tio n s also. F o r in sta n c e , th e size, shape and d is trib u tio n of th e voids, p a r tly filled w ith g ra p h ite , w ill he su p e rio r to those in o rd in a ry cast i r o n ; th e m a trix w ill be a t its b est in all sections, a n d th e g rain -size w ill be m ore u n ifo rm and fav o u rab le. T h a t th ese p red ictio n s are tr u e in fa c t a p p e a rs to be e v id e n t fro m th e m icro stru c
tu r e of th e P e r lit m e ta l. F ig s. 1 an d 2 show th e g r a p h ite in a b a r c a s t in . d ia ., w h ilst th e p e a rlite in th e sam e b a r is so fine t h a t m uch of i t is unresolved by a m agnification of 400 d iam eters, as seen in F ig . 3, w hilst a t th e high pow er of 1,500 d iam eters th e lamellae e x h ib it a b e a u tifu lly fine te x tu r e , as seen in F ig . 4. S im ilar re s u lts a re to be observed in F ig s. 7 an d 8, which re p re s e n t a bush, 24 in . long, 14J in . outside d ia m e te r, an d 1 | in . th ic k . I n all cases th e B rinell h ard n ess h as been low, betw een 175 an d 185 being th e ru le . The n etw o rk is good, as shown in F ig . 9.
Of course, th e p h o to g rap h s given in th is note [represent th e in itia l re s u lts of th e w ork in its very early stag es, an d i t is to be expected, th e re fo re , t h a t m uch b e tt e r re su lts w ill be o b tain ab le as c o n tro l an d ex p erience a re a tta in e d . O u tsta n d in g is th e f a c t t h a t , by th is process, can be produced c a stin g s, of t h e th in n e s t sections if necessary, of low-silicon iro n , w hich will be p e a rlitic th ro u g h o u t an d h av e g ra p h ite voids an d p e a rlitic m a trix of su p e rio r ty p e s to th o s e fo u n d in o rd in a ry cast iro n , nam ely, th e h ig h e r silicon m etal su ita b le fo r cold-m ould p ra c tic e .
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By reason of th e i r b e in g little o r no ch illin g effect upon th e m e ta l w hen i t m eets th e h o t m ould su rfaces, th e re w ill he no chilled shell form ed, a n d , m oreover, i t is n o t u n re a so n a b le to su g g e st t h a t th e r e is a “ h e s ita tio n ” d u rin g w hich e v e ry th in g has a chance to “ level u p .” T his conception enables one to a p p re c ia te t h a t m uch m ay h a p p e n to e x p la in th e absence of core a n d th e presence of a n a ll-p e a rlitic s tr u c tu r e th r o u g h o u t an in tr i c a te c a s tin g m ade in th is m a n n e r. E ith e r h o t or cold sa n d is a v ery poor co n d u cto r of h e a t, an d , even th o u g h th e above-m entioned “ h e s ita tio n ” m ay e x is t a t or a b o u t th e fre e z in g p o in t, it does n o t follow t h a t th e m e ta l w ill pass th ro u g h its p e a rlitic ra n g e so slowly as i t w ould do in a cold m ould (u sin g a h ig h e r silicon m etal)'.
Also i t h as to be rem em bered t h a t th e voids, p a r tly filled b y g ra p h ite , m ay he gaseous.
In d eed , th e i r sh ap e an d size m ay he d e te rm in e d by gas influence in th e first place. T h erefo re, th e su p e rio r voids fo u n d in P e r lit iro n , as co m p ared w ith those in grey iro n c a st in cold m oulds, m ay be d u e to th e h o t m ould n o t c a u sin g th e p re c ip i
ta t io n of th e se gases a t th e sam e p e rio d or to th e sam e degree.
T he a u th o r m akes no p re s u m p tio n of u n d e r s ta n d in g th e m echanism of th e P e r l it process. H e feels t h a t it is likely to th ro w lig h t u p o n m an y p o in ts w hich h av e been p u zzlin g fo u n d ry m e ta l
lu rg ists in conneotion w ith g rey iro n m e ta llu rg y ; in an y case i t opens o u t a new field of re se a rc h an d of m a n u f a c tu r e a b o u t w hich, a t th e m om ent, th e r e is li tt le d a ta to w ork u p o n ; all t h a t is know n is t h a t th e iro n is d iffe re n t from an d b e tt e r th a n o rd in a ry c a s t iro n of h ig h e r silicon c o n te n t, an d t h a t i t conform s w ith th e o p in io n s of scientific observers as to w h a t good c a s t iro n should be w ere i t possible, as i t now is in th is process, to m a k e i t m ore u n ifo rm ly alik e th r o u g h o u t a n y one ca stin g .
T he a u th o r wishes to express his sin cere th a n k s to M r. Sum m ers H u n te r an d to th e N o rth - E a s te rn M a rin e E n g in e e rin g C om pany fo r allow ing th is note, d escrib in g h is im pressions an d ex periences in connection w ith th e s ta r tin g - u p of th e P e r l it process in th e ir fo u n d ries to he p re s e n te d to th is m eeting.
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by th e A m erican s was t h a t all iro n w as u n d e r a p e rlitic c o n d itio n a n d all th e y w a n te d to do was to fix i t so t h a t i t co u ld he realise d a n d m a in ta in e d in t h a t c o n d itio n . P e rso n a lly , he h a d h a d evidence o f fo u n d ries p ro d u c in g c a stin g s t h a t reached 24 to 27 to n s te n sile . I n th e s e fo u n d rie s th e y h a d been doin g t h a t s o r t o f th i n g fo r some years. T h e y w ere p o u rin g th e i r c a stin g s in cold m oulds an d p ro d u c in g m a te ria l a t o r a b o u t th e sam e cost as o rd in a ry g rey iro n . T h e A m eri
can , by k eep in g a v e ry c a re fu l c o n tro l o v er chem ical an aly sis, w as c o n v e rtin g h is fo u n d ry in to a la b o ra to ry m ore th a n we in th is c o u n tr y could ever hope to do. I n A m erica th e y w ere a p p ro a c h in g th is q u estio n fro m th e fla t r a t e of p ro d u c tio n , a n d th e y w ere lo o k in g to th e tr e a tm e n t o f th e m e ta l to en su re t h a t , in th e m a in , i t w as d e a lt
can , by k eep in g a v e ry c a re fu l c o n tro l o v er chem ical an aly sis, w as c o n v e rtin g h is fo u n d ry in to a la b o ra to ry m ore th a n we in th is c o u n tr y could ever hope to do. I n A m erica th e y w ere a p p ro a c h in g th is q u estio n fro m th e fla t r a t e of p ro d u c tio n , a n d th e y w ere lo o k in g to th e tr e a tm e n t o f th e m e ta l to en su re t h a t , in th e m a in , i t w as d e a lt