By L. Audo, Ingenieur des Arts et Metiers, Works Director of the Paris-Orleans Railway Company.
[French Exchange Paper.]
“ Th ere w ill th erefo re be two th in gs to consider in e x p e rim e n ta l r e se a r c h : F ir s t ly , the a r t of o b ta in in g e x a c t fa c ts by rig o ro u s in v e stig a tio n : secon dly, the a r t c f ap p ly in g them by m eans o f ex p e rim e n tal re a so n in g , in order to establish know ledge o f the law s o f ph en om en a.”
Cl a u d e Be r n a r d.
O n “ O bservation an d E x p e rim e n t.”
T he m a n u f a c tu r e of h ig h -ten sile eastin g s p re se n te d difficulties a t a tim e w hich m ay he reg ard ed a s h a v in g preced ed th e w ar, w hen th e m ethods of in v e s tig a tio n av ailab le to fou n d ry m en w ere ra th e r c ru d e. M a n u fa c tu re was governed e n tire ly by em p iricism a n d o b serv atio n . The prod u ctio n of h ig h te n s ile m etals w as re s tric te d to a few 'firms who h a d a c q u ire d a w orld-w ide r e p u ta tio n which w as no d o u b t deserved, an d to th e special m etals em ployed, w hich w ere g en erally of B ritis h origin.
I n h is P a p e r p re se n te d to th e P a r is Congress in N ovem ber, 1925. M . V a rle t defined th ese special irons as fo llo w s: m etals m a n u fa c tu re d w ith cold b last, a t low p re ssu re , in sm all b la s t furnaces h e a te d by coke o r wood charcoal. T he m echanical p ro p e rtie s of such m etals, w hen su b jected to sim ila r te s ts, a re u n d en iab ly su p e rio r to those of iro n s m a n u f a c tu r e d in b last fu rn aces of larg e c a p a c ity w orked w ith h o t b la s t. These differ
ences c a n be ascribed only to th e m ethod of p re p a ra tio n , i t b ein g im possible a t p re s e n t to d e te r
m ine th e i r p recise cause.
N ev erth eless, th e p ro d u c tiv e cap a c ity of sm all b la s t fu rn a c e s is re s tric te d , w h ilst th e cost p rice of th e iro n o b ta in e d is h ig h . The difficulties of im p o rta tio n d u rin g th e w ar, an d la t e r th e re g re t
ta b le influence of th e ex ch an g e im pelled Con
tin e n ta l fo u n d ry m en to en d eav o u r to o b ta in hig h - ten sile c astin g s from th e p ro d u c ts of th e i r ow n c o u n tr y ’s soil.
T he m a n u f a c tu r e of sem i-steel p ro jectiles d u r in g th e w ar w as a first step to w ard s th e d esired re su lt. B u t even th e m a n u f a c tu r e of th ese w as a t t h a t tim e c a rr ie d o u t, fo r th e m o st p a r t , in a n e m p iric a l m a n n e r. T he scientific s tu d y of such m e ta l by M. P o rte v in , w ho h a s d e te rm in e d its s tr u c tu r a l c h a ra c te ris tic s , enabled its m a n u fa c tu re
Fi g. 1 .— Am e r ic a n Ty p e Lo c o m o t iv e Cy l i n d e r, We i g h t 7,260 l b s. Tw o Cy l i n d e r s f o r Ea c h En g i n e m a d e f r o m On e Pa t t e r n. Er e c t e d on t h e Ve r t ic a l Pla n o f Sy m m e t r y.
to be c a rrie d on m ethodically an d its uses to be ex ten d e d .
T h e lack oT hom ogeneity of sem i-steel m ade in th e c u p o la fo r d ir e c t c a stin g , how ever, does n o t p e rm it o f i'ts em plo y m en t fo r c a s tin g s su b jected to fric tio n , in p a r tic u la r for e n g in e c v lin d ers an d p isto n rin g s. T his d efect can be rem ed ied by a
p re lim in a ry p ig g in g . T his rem elted m etal will be m ade e ith e r in th e cupola by th e fo u n d e r him self or in th e e le c tric fu rn a c e by specialists.
A lthough th e cost of th e final p ro d u c t is in creased by re m e ltin g in th e cupola, i't is possible to o b ta in h ig h -te n sile m etals a t a p racticab le price by th e em p lo y m en t of new m etal, even if of in d iffe re n t q u a lity (provided, of course, t h a t it does n o t c o n ta in th e in ju rio u s elem ents P a n d S i'n la rg e q u a n titie s ), la rg e r q u a n titie s of scrap , and steel s c ra p —• t h a t is to say, cheap p roducts. This steel m ay be of v ario u s o rig in s, m anganese steel b ein g excluded as, ow ing to th e presence of th a t
p IG 2.— Lo c o m o t iv e Tw in H .P . Cy l in d e r op t h e Peo a v o rt Ty p e, We i g h i n g 11,000 l b s. elem en t, th e re would be a risk of prod u cin g an a b n o rm al q u a n tity of cem en tite, w'hich would be p re ju d ic ia l to th e s tre n g th of th e castings and th e ir efficiency in service.
W hen th e a u th o r first in tro d u ced steel a t th e works of th e P a ris-O rle a n s R ailw ay, he used sp rin g steel d eriv ed from th e b roken leaves of th e sus
pension s p rin g s of vehicles. T his steel h as the follow ing c o m p o s itio n :—TO, 0.523; Si, 1.5; t t n , 0.6; P , 0.03; a n d S, 0.02 p e r c en t. T he sim ila rity of th is an aly sis, ex cep t as re g a rd s th e carbon, w ith t h a t of a good h e m a tite will be noticed.
These leaves a re ab o u t 15 mm. in th ic k n e ss an d have a m axim um len g tli of 20 cm.
H e th e n e x ten d e d th e use of steel to old riv e ts an d clip p in g s from sh e a rin g m ach in es—sm all pieces w hich a re easy to h an d le an d a re quickly m elted in th e cupola.
Fi g. 3 . — Lo c o m o t i v e L .P . Tw i n- Oy l i n d e r o f t h e Pa c i f i c Ty p e, We i g h t 1 2 , 2 1 0 l b s.
The p re p a r a tio n of th e re m e lte d m ix tu re s should provide, as f a r as possible, fo r all th e necessary a d d itio n s of ferro-alloys, so- t h a t th e re -m e ltin g m ay n o t n e c e ss ita te a n y m odification of th e charge. I n th e se tw o o p e ra tio n s a c c o u n t should be ta k e n of th e in flu en ce o f th e cu p o la on th e v ario u s elem en ts, each cupola b ein g , of course, th e su b je c t of special stu d y . T he use of fe r ro alloys w ith h ig h c o n te n ts w ill, of course, be avoided, as th e y a re g en e ra lly fria b le an d th e ir loss in m e ltin g is h ig h . These ferro -allo y s, m ore
over, p roduce ir r e g u la r p ro d u cts.
The, o b je c t of th e in tro d u c tio n of ste e l is, of course, to low er th e to ta l c arb o n c o n te n t an d to a d ju s t it to th e silicon c o n te n t so as to o b ta in th e p e a rlitic s tru c tu r e . I t is e v id e n t t h a t th e p ro d u ctio n of h ig h -te n sile m etals does n o t neces
129
s a rily im ply th e a d d itio n of steel, an d t h a t by th e use of special irons an d of well selected h e m a tite scrap th e o b je c t in view m ay be a tta in e d m ore d irectly .*
S em i-steel h a s been d escrib ed as a n “ artificial m e ta l.” B u t v ery m an y a rtic le s w hich one
F i g . 4 . — S h e a r i n g T e s t M a c h i n e ( F r e m o n t Ty p e) f o r S m a l l B a r s o f 5 . 6 4 m m . D i a m e t e r .
h a b itu a lly uses now adays a re m a n u fa c tu re d a r t i ficially, y e t one is p e rfe c tly satisfied w ith them . The m e ta l to be o b ta in e d , w h eth er m a n u factu red w ith o r w ith o u t accessories, should have a p e a rlitic
* See “ S tu d y on P erlitic M e ta l,” b y M. Le T h om as, Marine E n gin eer, “ Fon d erie M oderne,” F eb ruary, 1926.
F
s tru c tu r e . T his can be effected by a n a d ju s tm e n t of th e O an d Si c o n te n ts, w hich is a v ery easy o p e ra tio n in th e m a n u fa c tu re of steam cy lin d ers an d p isto n rin g s , c a stin g s in w hich th e thicknesses a re p ra c tic a lly re g u la r an d c o n s ta n t. I n a d d itio n
Fi g. 5 . — T r a n s v e r s e T e s t i n g M a c h i n e ( F r e m o n t T y p e ) f o r S m a l l B a r s o f 8 x 1 0 x 3 5 m m .
th e g r a p h ite laminae should be red u ced as fa r as possible, a n d th e a d ju s tm e n t of th e C an d Si c o n te n ts w ill he effected in such a m a n n e r t h a t th e final p ro d u c t w ill be less haa'd in re g a rd to th e rin g s th a n th e c y lin d ers. As th e se c a stin g s a re
c o n sta n tly in fric tio n a l c o n ta c t th e w ear will tak e place n o rm ally on th e rin g , a ty p e o f c a stin g , th e cost of w hich is re la tiv e ly low and which can be easily replaced.
I n o rd e r to o b ta in th is o rie n ta tio n o f th e B rin e ll num bers, acco u n t m u s t be ta k e n o f : (1) The f a c t t h a t th e th ick n ess of th e rin g s is
gener-Fi g. 6 .— Fr a c t u r e s f r o m Pis t o n Rin g Ir o n, a i l Ca s t f r o m t h e s a m e Ir o n. Ac tu a l Si z e.
ally less; (2) th e m ore r a p id cooling of these rin g s.
T he m ix tu r e fo r th e la t te r should th e re fo re be modified by slig h tly in c re a sin g th e C a n d Si con
te n ts , th e basis m etals b ein g s tric tly id en tical in both cases. On th e o th e r h an d , w hile o b tain in g th e p e a rlitic s tru c tu r e in th e rin g s, a relativ ely
f 2
h ig h g r a p h ite c o n te n t m ay be allowed ow ing to th e lu b r ic a tin g actio n of th is in g re d ie n t.
The follow ing is th e chem ical com position of th e m e ta ls ad o p ted by th e P a ris-O rle a n s R ailw ay C om pany: —
S te a m C ylin d ers.—TC, 3 .0; Si, 1.5; M n, 0.65;
P , 0 .2 ; an d S, 0.10 p e r c e n t. m ax.
P is to n B in g s .—TC, 3 .3; S i, 1.7; M n, 0.65; P , 0.2; a n d .9, 0.10 p e r c e n t. m ax.
Pi g. 6 .— C o n tin u ed .
The B rin e ll n u m b ers a p p ro x im a te to 230 in th e case o f th e c y lin d ers an d v a ry fro m 200 to 2 10 in t h a t of th e rin g s.
Melting.
T he m e ltin g of th e steel in th e ciupola som etim es occasions difficulties. I n o rd e r to overcom e th e m i t is desirab le to give th e m e ltin g a p p a ra tu s
some-w h a t special fe a tu re s, v iz : —A h e ig h t from h e a rth to t h r o a t r a t h e r g re a te r th a n t h a t generally a d o p te d ; a b o u t 6 tim es th e d ia m e te r of th e h e a rth m ay be t a k e n ; an d r e c ta n g u la r tu y e re s, wide b u t n o t very h ig h in o rd e r to p re v e n t o x id atio n . The to ta l section of tu y e re s is one q u a rte r of t h a t of th e cu p o la a t th e i r lev el; The a ir blown in should be re g u la te d by m eans of re g is te r in g a p p a ra tu s as f a r as possible. T he d iag ram s should be
com-F ig . *6.— C ontinued.
-pleted w ith all th e p a rtic u la rs w hich will enable th e fo u n d ry m an a g e r to exercise h is co n tro l over th e sm allest d etails.
The follow ing should be shown, fo r ex am p le:
T he tim e of s ta r tin g , in te n tio n a l or accidental sto p p ag es an d th e ir causes, th e te m p e ra tu re of th e m etal, th e n a tu r e of th e ch arg e (semi-steel, en g in e e rin g castin g s, e tc .), th e n um ber of
slag-g in slag-g s, th e p recise tim e of th ese slaslag-g slag-g in slag-g s, th e tim e of sto p p in g , e tc . T hus th ese d ia g ra m s m ay in f a c t serve as a d aily reco rd of th e w ork of th e fo u n d ry .
The ch arg es a re m ade in th e follow ing o rd e r : th e steel, th e p ig, th e sc ra p . T he fu rn a c e is lig h tly forced w ith 12 to 14 p er cen t, coke, th e
Fi g. 7 .— Fr a c t u r e s o f Ru n n e r s Ta k e n f r o m a St e a m Cy l i n d e r Ir o n. Al l h a v e b e e n Ca st FROM THE SAME IR O N . ACTUAL S lZ E .
b e st q u a lity being chosen. All th e s e c o n d itio n s b e in g observed, th e p re s su re of th e a ir blow n in will be a b o u t 35 to 40 cm. (14 to 16 ins.).
I n a d d itio n to th e fe a tu re s a lre a d y m e n tio n e d th e cupolas used by th e P a ris-O rle a n s R a ilw a y C om pany a re fu rn ish e d w ith receiv ers w ith a cap acity of 2-J- to n s. These enable th e m e ta l to
be p ro te c te d from th e re c a rb u ris in g action of th e coke, w hich is a p p reciab le in a n o rd in a ry cupola.
T hus in th is a p p a ra tu s th e re c a rb u ris a tio n is only 0.05 p e r cen t, w ith c arb o n c o n te n ts of 3.0 per c e n t. The receiv ers a re fu rn ish e d w ith an inspec
tio n hole e n a b lin g th e q u a n tity of m etal con tain ed in th e m to be a sc e rta in e d . T h e ir c a p a c ity of 2t to n s enables sm all an d m edium cylinders to be d raw n in a sin g le ta p p in g , a n d la rg e cylinders
Fi g. 7 . —C ontinued.
up to 5^ to n s in tw o ta p p in g s. U n d er fav o u r
ab le c o n d itio n s th e y h av e given G| to n s w ith o u t b o ttin g in.
T he p ro p o rtio n of steel to be used m u st obvi
ously v a ry according to th e basis m etals employed a n d th e th ick n ess of th e c a stin g s to be o b tain ed . T h e q u a n titie s of steel a re d ete rm in e d by the chem ical analyses of th ese basis m etals and of
th e final p ro d u c t re q u ire d , an d also by m icro- g ra p h ic a l e x a m in a tio n , w hich should show th e p e a rlitic s tru c tu r e .
Inspection Conditions.
The F re n c h railw ay com panies r e p a ir an d m a in t a i n th e ir p la n t in th e i r ow n w orks. O rd ers fo r new m a te ria l a re g e n e ra lly e n tr u s te d to p r iv a te
F ig . 7.— C o n tin u ed .
e n te rp ris e . T h e ir m a n u fa c tu re s , p a r tic u la r ly those of ste a m cylinders an d p is to n rin g s, th e re fo re cover a la rg e n u m b e r of ty p es, b u t on th e o th e r h a n d only a sm all n u m b er of c a stin g s to each ty p e . T h e te rm s o f in sp ectio n fo r th ese c a stin g s ap p ly to w ork ex ecu ted by p riv a te m a n u fa c tu re rs as well as to t h a t d o n e by th e w orks of th e com panies them selves. A t p re s e n t th e in sp ectio n te s ts a re as fo llo w s:
137 Steam Cylinders.
Shock te s t: h am m er 1 2kg. (26 lb .) ; te s t pieces of 40 by 40 by 200 mm. (1.5 b y 1.5 by 7.8 in s .);
d is ta n c e betw een k n ife su p p o rts 160 mm. (6.3 i n s .) ; first blow 30 cm. (11.8 i n s . ) ; successive increases 5 cm. (1.9 ins.) ; m in im u m r u p tu r e 50 cm. (19 ins.).
T ensile te s t: m in im u m r u p tu r e 18 kg. p e r sq.
mm. (11.4 to n s p e r sq. in .) on b a rs su ita b le for th e a v a ila b le m achines.
P o r o s i ty : h y d ra u lic te s t a t a p re ssu re equal to t h a t of th e w orking p re ssu re of th e boiler in creased by 1 kg. in th e case of h ig h pressure c y lin d ers; a t a u n ifo rm pressure of 10 kg. (22 lbs.) in th e case of low p re ssu re cylinders.
Piston Rings.
Sh o ck t e s t : id e n tic a l w ith t h a t used for th e cylinders. Tensile t e s t : id e n tic a l w ith t h a t used fo r th e cy lin d ers. T ransverse t e s t : a rin g m ach in ed on its fo u r faces to 26 by 15 mm . (1.0 by 0.59 in s.) is opened by tw o saw -cuts g iving an o p en in g of 25 m m . (0.98 in s.). T he segm ent th u s o b ta in e d is susp en d ed to a fixed p o in t, th e cen tre of th e o pening coinciding w ith th e h o rizo n tal d ia m e te r. T ension is e x e rte d v ertically by the successive a d d itio n of w eights a rra n g e d on a
p la te u n til r u p t u r e ta k e s place.
The c h a ra c te ris tic s re q u ire d are given in the follow ing ta b le : —
E x tern al diam eter of th e finished
rings.
Breakin g load. Opening a t breaking point.
Minimum. Average. Minimum. Average.
348 135 140 75 100
368 128 133 85 113
388 120 128 95 125
408 110 115 100 130
428 105 110 105 135
448 100 105 115 145
468 95 100 120 150
488 90 95 130 160
508 87 92 140 170
528 85 90 150 180
548 82 86 165 195
568 78 82 180 210
F ro m th e p o in t of view of c h a ra c te ris in g th e m e ta ls fo r c y lin d ers an d p is to n rin g s, th e te s ts
Fi g. 8 . — Te s t Sa m p l e f o r Me t a l f o r St e a m Cy l i n d e r s.
N o te th e sim ila rity of grain in th e tw o different sectio n s t h e sm aller of w hich (25 m m .) w a s a tta ch ed at right a n g les
t o th e larger (55 m m .). T w o -th ird s a ctu a l size.
such as h av e been described c a n n o t in d i
c a te very clea rly th e a c tu a l m ech an ical p ro p e rtie s
139
Fi g. 9 a . — Pi s t o n Rin g Ik o n (1 ) Ce m e n t i t e, (2) Li g h t Re f l e c t io n s f r o m t h e Gr a p h it e x 7C 0 .
of th e p ro d u c ts c a st. H e re th e shock te s t h as no significance, w hile th e ten sile te s t, as M.
P o rte v in h as p o in te d o u t, is fre q u e n tly im p a ire d by e rro rs.
A few m o n th s ago th e a u th o r h a d reco u rse t o ' th e te s ts recom m ended by th e A ssociation T ech
n iq u e F ra n ç a is e de F o n d e rie , viz., tr a n s v e rs e a n d sh e a rin g te s ts on sm all b ars. To th e se w ere added th e h a rd n e s s te s t, w hich is in d isp en sab le in d e te r m in in g th e p ro p e rtie s of c a stin g s su b ject to fric tio n .
T he te s t b a rs a re ta k e n as t e s t pieces p o u red w ith th e castin g s, th e ir dim ensions b ein g id e n tic a l w ith th o se of th e c a stin g s, so t h a t th e b ars an d ca stin g s m ay b o th h a v e th e sam e “ th e rm a l h is to ry .”
The tra n s v e rs e te s t c a rrie d o u t on th e F ré m o n t m achine, w hich re g is te rs th e curves, is m ost valuable in ex a m in in g m e ta ls d esigned fo r p isto n rin g s, ow ing to th e po ssib ility of s tu d y in g these curves a n d th e ease w ith w hich th e te s t can be re p e a te d .
T he te s ts m a d e by th e P a ris-O rfe a n s R ailw ay C om pany ap p lied to a la rg e n u m b e r of cases, so as to find sim ple form ulae c o n n e c tin g th e old te s ts a n d th e new . T h is was fo r th e p u rp o se of a t once im p a rtin g th e re s u lts o b ta in e d to p riv a te fo u n d ry m en w ith o u t th e i r re q u irin g to c a rry o u t them selves th e le n g th y rese a rc h w ork involved.
The formulae estab lish ed by th e ra ilw a y com
p any a re obviously of p a r tic u la r in t e r e s t in con
n ectio n w ith its ow n m a n u fa c tu re s . I t m u s t be rem em bered t h a t th e re la tio n s in q u estio n a re influenced by th e chem ical com position o f th e m etals em ployed, th e r a t e of cooling, e tc . These formulae a r e as fo llo w
s:—-Tensile stre n g th = 0 .9 1 6 shearing stren g th — 1.2.
Shearing stren g th = ( A X 0 .2 3 ) — 25.
Manufacture.
A. S te a m C y lin d e rs.— C o n tra ry to th e m eth o d g en e ra lly ad o p ted in G re a t B r it a in , w here c y lin d ers a re c a s t on th e flat, in F r a n c e a n d B elgium th e y are c a s t v e rtic a lly . W ith re g a r d to th e m o u ld in g , m en tio n will only be by w ay of re m in d e r of th e d iffe re n t processes em ployed :
(1.) B y a n o rd in a ry p a tt e r n h a v in g loose side
142
lig h tly “ w a s h e d ” in case of a c c id en tal boiling.
I t will be fo u n d t h a t v e rtic a l c a stin g fa c ilita te s th e e lim in atio n of possible blow-holes.
Piston Rings.
T he ta n g e n tia l c a stin g of cy lin d rical w ork, w h eth er by bottom c a s tin g alone o r by bottom c a stin g w ith a r e tu r n g a te , h as long been recom m ended in connection w ith p is to n rin g s. I t s p u r pose, acco rd in g to those who ad v o cate it , is to p roduce in th e m ould a r o ta r y m ovem ent of th e m etal w hich helps to loosen t h e slag along th e w alls. I f th is m ovem ent could be effected over
th e e n ti r e h e ig h t of th e c a stin g a n d d u rin g th e e n tir e d u ra tio n of p o u rin g , b o tto m c a stin g would u n d o u b ted ly fulfil its p u rp o se an d w ould be d e sir
able.
U n fo rtu n a te ly , th is is n o t th e case. T he r o ta r y m ovem ent is p ro d u ced effectively a t th e b eg in n in g of th e filling, b u t i t ta k e s place o n ly in th e d ra g , a n d becomes pro g ressiv ely feeb ler to w ard s th e s u rfa c e of th e liq u id , c easin g a t a h e ig h t of 10 to 15 cm. As th e h o tt e s t m e ta l is a t th e m iddle circu m feren ce i t b re a k s th e u p p e r film of cooler
Fi g. 9 b .— S t e a m C y l i n d e r x 4 50.
m e ta l, an d b rin g s an y slag t h a t m ay have form ed down o n to th e walls.
W ith to p p o u rin g by filtra tio n th e a u th o r has o b ta in e d ex c e lle n t re su lts, a n d h as ado p ted it g e n e ra lly fo r c y lin d e r w ork.
The p isto n rin g s a re p o u red open by m eans of a b asin placed a s trid e th e cope an d th e core.
T he low er p a r t of th e basin is p ierced w ith 15 mm.
(0.59 in .) holes, th e i r n um ber v a ry in g w ith th e w eig h t of th e c a stin g to be poured. The filling is done a t a speed of 220 lbs. in 15 seconds, t h a t is to say, quickly.
F i g . 9 c .— S t e a m C y l i n d e r I r o n x 450.
T h is r a t e of p o u rin g is th e re s u lt of tw o facts w hich a re re a d ily observable in connection w ith th e filling of open m o u ld s :— (1) The presence in th e liq u id m e ta l of an ascen d in g m ovem ent pro
ceeding -from th e w alls of th e m ould to th e cen
t r a l s tre a m , w hich m ovem ent ca rrie s th e im p u ri
tie s to w a rd s it. T h is is th e sam e phenom enon w hich all h av e observed on th e su rfa c e of a ladle
fu l of h o t m e ta l; (2) th e p ro d u ctio n , ow ing to th e ra p id fall, of a d is tu rb a n c e fa v o u rin g th e fre e in g of th e s e im p u ritie s.
C e rta in a u th o rs h av e recom m ended le arn ed for
mulae fo r th e p u rp o se of d e te rm in in g th e ra te