A fte r ex p ressin g h is th a n k s to M r. A. S. Beech fo r s u b m ittin g th e P a p e r, M. A udo p o in te d o u t t h a t th e c o n tro l of th e blow er o u g h t n o t to be con
fined exclusively to p re ssu re , b u t first a n d fo re
m ost to th e o u tp u t. T he cupola m ig h t be re g a rd e d as a n a p p a r a tu s fo r b u rn in g coke. S ta r ti n g from th is p rin c ip le i t was n ecessary to su p p ly i t w ith th e q u a n tity o f a ir n ecessary to effect * com bustion u n d e r th e b e st possible co n d itio n s, n am ely, w ith a m in im u m p ro d u c tio n of CO. T he p re ssu re w ould be th e re s u lta n t of th e fa c to rs o u tp u t a n d sections, th e l a t t e r of w hich should be c a lc u lated lib e ra lly . P ra c tic a l steps should be ta k e n to en su re t h a t th e p e n e tr a tio n of th e b la s t w as such t h a t th e e n tir e m ass of th e m a te ria ls fo rm in g th e ch arg e should be com pletely su b jected to th e a c tio n o f th e a ir.
I n a d d itio n to th e checks c a rrie d o u t d u r in g th e m e ltin g th e a u to m a tic o u tp u t m e te r w ould enable th e o x id a tio n , w hich w as in v a ria b ly caused if th e p re ssu re s only w ere co n tro lled , to' be su p p ressed
Fig. 12.
w hen th e m elt was finished. T he fu rn a c e , in fa c t, was e m p tied a t t h a t m o m en t. T he m a te ria ls offered b u t a feeble re s ista n c e to th e b la s t, a n d if a c o n s ta n t p re ssu re w ere re lie d u pon a c o n sid er
able excess of a ir was in tro d u c e d , w hich w as u n fa v o u ra b le to th e p ro d u c tio n of sound m e ta l. H e h a d th u s fo u n d t h a t w ith a n alm o st c o n s ta n t o u t
p u t th e m elt w as finished w ith a p re ssu re of only a few c e n tim e tre s.
Errors of the Frem ont Test.
T he very sim ple s ta n d a rd is a tio n of th e F re m o n t m achine in th e sh e a rin g t e s t p e rm itte d of re m a rk ably c o n c o rd a n t re s u lts b ein g o b ta in e d , n o tw ith s ta n d in g th e sm all sectio n of th e te s t piece. I t w as precisely th is sm all sectio n t h a t e n ab le d th e te s t to be re p e a te d a n d p e rm itte d of te s t pieces b ein g ta k e n fro m th e c a stin g s. I t w as th is l a t t e r m eth o d w hich en su red of th e m e ta l of th e c a stin g itse lf b ein g te s te d an d n o t th e m e ta l of th e m e lt as a whole.
T he te s t piece m ig h t be ta k e n e ith e r fro m th e c a stin g itse lf, o r fro m a te s t b a r o f th e sam e dim ensions as th e c a stin g s e n t fro m th e fo u n d ry w ith th e c a stin g a n d a tta c h e d to i t by its e n tir e section. T his m eth o d e n su red t h a t th e b a r should have a th e rm a l h isto ry absolutely id e n tic a l w ith t h a t of th e c a stin g . I t w as sufficient to p rovide for a t e s t b a r a t each p a r t of th e c a s tin g to be exam in ed in o rd e r to a s c e rta in th e p ro p e rtie s of th e c a stin g in all its p a rts .
T hus a locom otive c y lin d e r m ig h t be pro v id ed w ith th e follow ing te s t b a r s : —
(a) One in th e low er th i r d of th e cy lin d er body, 150 x 150 x 35 m m . (b) One in th e u p p e r th ir d of th e cy lin d er body, 150 x 150 x 35 m m ., a n d (c) one o n th e ste a m chest, 150 x 150 x 30 m m .
E ach te s t b a r was se p a ra te d m ech a n ically (w ith o u t shock) an d th e n saw n in to tw o p o rtio n s, one for b all te s ts a n d chem ical an aly sis, th e o th e r fo r b en d in g an d sh e a rin g te s t a n d m ic ro g ra p h ie a l ex a m in a tio n .
Difference Between Wear and Hardness.
I t h a d n ev er o ccu rred to th e a u th o r , M . A udo observed, to e sta b lish a c o rre la tio n betw een h a r d ness a n d w ear. H e re a re g r e tta b le confusion
e x iste d . The ball t e s t enabled th e d egree of homo
g e n e ity to be a s c e rta in e d ow ing to th e ease w ith w hich i t could be re p e a te d , as also th e m achining c a p a b ilitie s of c a stin g s. H e ag reed w ith M r. F . J . Cook in reco g n isin g t h a t in th e la t te r case a m a c h in in g , d rillin g o r tu r n in g te s t was excellent.
I n a n o th e r connection he also ag reed t h a t n e ith e r th e w ear of th e p isto n rin g n o r of th e cylinder should be s o u g h t fo r, b u t r a t h e r th e w ear of th a t one of th e tw o c astin g s th e cost p ric e of w hich was low er. T h is d id n o t m ean t h a t h e recom m ended a so ft rin g . On th e c o n tr a r y ; th e B rin ell num bers he h a d g iv en (200 to 210) 'd e m o n s tra te d th is.
W h a t, he ask ed , w as th e p a r t played by th e r in g in th e cy lin d e r? (1) To en su re a good fit betw een th e tw o faces of th e p isto n —th e p ro p e rty of e la s tic ity a s c e rta in e d by th e tra n sv e rs e te s t (m easu rem en t of th e loads a n d deflections, d eterm i
n a tio n o f th e coefficient of e la stic ity ). (2) To p re v e n t a b ra siv e a c tio n on th e c y lin d e r; hence th e n ecessity fo r fre e carbon, w hich was a lu b ric a tin g elem en t, a n d , o n th e o th e r h a n d , th e necessity of a v o id in g h a r d c o n stitu e n ts (cem entite and s te a d ite ).
F o r seg m en ts M r. Cook p re fe rre d a m e ta l id en tic a l w ith th e w h ite m etals, viz., h a rd crystals en
cased in a s o ft c o n s titu e n t. H e (M. Audo) was not convinced t h a t th is view was co rrect. A w hite alloy was a n in tim a te m ix tu re o f h a rd an d so ft c ry stals, th e p u rp o se of th e fo rm er being to su p p o rt a lo ad w hich was generally high an d to resist w ear, w hile th e so ft c o n s titu e n t enabled th e h ard c ry s ta ls to dispose them selves su itab ly in its mass, w hile conform ing to th e sh ap e of th e ro ta tin g cham ber, its e lf co nsisting of a hom ogeneous m etal of g r e a t h a rd n e ss. T he s o ft cry stals were more su b je c t to w ear th a n th e h a rd , as a re su lt of which d epressions of 5 o r 6 m icrons, in which th e lu b ri
c a n t was d ep o sited , w ere produced on th e surface of th e m e ta l. Could an id e n tic a l phenom enon be looked fo r in th e c y lin d er if th e pressure of th e seg m en ts w ere w eak a n d th e tw o m etals in co n tac t w ere p ra c tic a lly id e n tic a l? Could i t be supposed t h a t th e v ery h a rd c e m e n tite cry stals would a rr a n g e them selves in th e p e a rlitic mass, which was its e lf h a rd (A = 200 to 260), acoording to t h e fineness of th e lamellae, m erely u n d e r th e
in-G
Fig. 12.
Huence of th e low load due to th e e la stic ity of th e se g m en t? M ig h t i t n o t be concluded, on th e o th e r h a n d , th a t , as th e p e a rlite w as w orn because it was less h a rd , th e p a rtic le s of cem e n tite would p re s e n t th e i r sh a rp edges a n d a ccelerate th e w ear as ra p id ly as a n equal n u m b er of small high-speed steel tools w ould do?
M . A udo r e g r e tte d t h a t he w as u n ab le to reply definitely re g a rd in g th e d istan ces tra v e lle d , and th e w ear an d te a r in service, an d t h a t he person
ally could n o t give an y o th e r figures th a n those he h a d q u o ted , w hich, how ever, he reg ard ed as sa tis
fa c to ry . H e allu d ed to th e w earin g te s ts carried o u t by M M . B. B uffet an d A. R oeder, q u o tin g th e follow ing figures : —
D ry tests.
Number of alterations per minute .. 110
Area of contact .. .. .. 58.75 sq. cm.
Pressure per sq. cm. .. .. .. 293 gm.
Loss of w eight:
Cylinder metal . . .. 10 gm. in 4 days.
Pearlitic cast-iron .. .. 7 gm. in 4 weeks Influence of the Cooling Conditions.
T he divergences in d ic a te d in th e carbon an d the silicon c o n te n ts w ere d u e : (1) To th e differences in th ic k n e ss of th e tw o cylinder castin g s (in th e body), v iz., 35 to 40 m m ., an d of th e segm ents 25 to 30 m m .; (2) to th e differences of te m p e ra tu re of th e m oulds a t th e m om ent of castin g , due to th e differences in m ass of th e m oulds and th e h e a t losses by ra d ia tio n betw een th e tim e of leaving th e d ry in g stove a n d c a s t in g ; an d (3) to th e differences in th e r a t e of h e a t exchange due to th e ra tio betw een th e mass of th e castin g s an d th e mass of th e m oulds.
Error in the Correlative Formula.
M. A udo d ire c te d a tte n tio n to th e re s tric te d lim its w ith in w hich th e formulae given w ere valid.
H e sa id t h a t th e y h a d been d raw n up m erely for th e p u rp o se of in fo rm in g th e su p p liers of th e Com
p a n y a t once in case th e F re m o n t te s ts w ere to be ap p lied a t th e in sp ectio n o f th e castings, so as to m ake i t un n ecessary fo r th e m to c a rry o u t long a n d costly research es fo r th e sam e purpose.
G 2
Effects of Slight Changes in Composition.
T he com positions he h a d specified w ere th o se a t p re s e n t in use. No p ra c tic a l m a n , how ever, w ould im ag in e t h a t th e y could he o b ta in e d m a th e m a tic a lly in th e cupola. These com positions w ere av erag es, a n d special efforts w ere now b ein g m a d e to o b ta in divergences of c o n te n t in th e d iffe re n t elem ents in p ro p o rtio n to th e differences of speed
in cooling, as a lre a d y e x p lain ed , a n d w ith th e v ery d efin ite o b je c t of o b ta in in g th e p e a rlitic s tr u c tu r e in th e v a rio u s p a rts . T he feeble re c a r b u ris a tio n he h a d in d ic a te d was d u e to th e presence o f cupola receiv ers, w hich e n ab le d th e liq u id m e ta l to be w ith d ra w n ra p id ly from c o n ta c t w ith th e liq u id coke. T h is re c a rb u ris a tio n w as fu lly 0.05 p e r c en t, of to t a l carb o n p e r 3 p e r c e n t, of th e ch a rg e .
H e d id n o t give th e process of m a n u fa c tu re as a b so lu te. H e h a d m erely described i t in th e belief t h a t i t m ig h t pro v e p ro fitab le. W ith re g a rd to th e com positions a d o p te d th e y w ere th e r e s u l t : (1) Of th e s tu d y of th e v a rio u s fa c to rs affecting th e m ech a n ical p ro p e rtie s o f c a st iro n in g e n e r a l; (2) of a n e x a m in a tio n o f th e cooling conditions o f th e c a stin g s concerned, according to th e m ethod of m a n u f a c tu r e a d o p te d ; a n d (3) of an ex am in atio n of th e re s u lts o b ta in e d in service—re su lts which h a d been specified in his P a p e r an d which a p p e a re d to h im sa tisfa c to ry .
The lim its o f his p re s e n t n o te w ere too re s tric te d to en ab le him to go in to th e question of th e influence of th e v a rio u s elem ents co n tain ed in c a st iro n of d iffe re n t ty p es on th e ir m echanical p ro p e rtie s . H e would th e re fo re beg h is read ers t o r e f e r to th e stu d ie s a lre a d y m ade on th e sub
je c t, a n d m ore p a rtic u la rly to th e very in te re s tin g co m m u n icatio n of M . P o rte v in in M arch, 1927. t T h ere th e y w ould find a n acco u n t of th e tran sv erse s tr e n g th a n d th e v alu e of th e deflections, p ro p e r
tie s w hich w ere o f suprem e im p o rtan ce in th e m a n u f a c tu r e of p isto n rin g s.
W ith re g a r d to th e phosphorus co n ten t, an d in re p ly to M r. W . H . Poole, he sta te d t h a t he ad o p ted 0.2 p e r c e n t, (som etim es 0.3 p e r cen t.) in p lace of 0.6 to 0.8 p e r c e n t., ow ing to th e possi
b ility o f th e fo rm a tio n of s te a d ite (phosphorus e u te c tic ), a h a r d a n d b r ittle c o n stitu e n t, th e a b ra siv e p ro p e rtie s of w hich w ere com parable w ith those of cem e n tite. P ho sp h o ru s te n d e d , m oreover, to d im in ish th e d efo rm atio n cap acity on ru p tu re . H e r e g r e tte d t h a t he was u n ab le to give p a r tic u la r s on th e su b je c t of c e n trifu g a l castin g . H e considered, how ever, t h a t th is m ethod of m an u fa c tu re o u g h t to give excellent re su lts. H e wished to th a n k h is B ritis h colleagues fo r th e in te re s t th e y h a d been good enough to show in h is P a p e r, a n d tr u s te d research es o f a m ore ex h au stiv e n a tu r e w ould be c a rrie d o u t o n th e su b je c t of wear.
t See B u lle tin de l ’A sso cia tio n T echnique F rançaise de F o n d erie, M arch, 1927.
ON THE EFFECT OF NICKEL AND CHROMIUM ON