MALLEABLE CASTINGS - Proceedings of the Institution of British Foundrymen, Vol. 20 (1927-1928)

By W. T. Evans and A. E. Peace.

The p re p a ra tio n of a P a p e r on m alleable cast

ings to be p u t before E u ro p e a n fo u n d ry m en p re sen ts difficulties w hich would n o t arise if only one class of m a te ria l h a d to be co nsidered such as is th e only p ro d u c t of m alleable fo u n d rie s in A m erica, viz., b lack -h eart, in th e p ro d u c tio n of w hich th e a u th o rs a re now a c tiv e ly e n g a g e d . H av in g h a d ex p erien ce of b o th E u ro p e a n and A m erican m alleable i t is hoped to give some id ea of th e g en e ra l p ro d u ctio n of th e tw o v a rie tie s, as m an y fe a tu re s a re common to both.

I t is generally know n t h a t R e a u m u r comm enced th e p ro d u ctio n of m alleable c astin g s in E u ro p e som ewhere a b o u t th e y e a r 1722, an d t h a t B oyden, who e m ig ra te d to A m erica fro m E n g la n d , in a t

te m p tin g to m ake R e a u m u r m alleable w ith th e A m erican pig-irons, o b ta in e d re su lts, a b o u t 1826, which w ere th e fo u n d a tio n of th e p re s e n t black- h e a r t process. T he m a n u fa c tu re of c a stin g s by th is l a t te r process h as been in o p e ra tio n in E u ro p e fo r over 50 y ears, u sin g chiefly A m erican pig-irons, b u t now ex cellen t re s u lts a re being o b ta in e d by th e use of all B ritis h irons, w hich ' can be b o u g h t to as close specifications as A m eri

can irons p rovided th e p ig -iro n is o rd ered in la rg e enough q u a n titie s to enable m a n u f a c tu r e rs suc

cessfully to c o n tro l th e b u rd e n of th e ir b la s t furnaces.

T h ere can be no d o u b t t h a t m alleable castin g s in E u ro p e h av e been som eth in g of a bogey to th e en g in ee r, ow ing to a n o n -u n ifo rm ity of q u a lity , an d in p a r tic u la r w ith re g a rd to in d iffe re n t m a c h in a b ility w hich u n d e r p re se n t-d a y co n d itio n s is a m ost serious m a tte r , ow ing to th e expense of mass p ro d u ctio n to o lin g o p e ra tio n s. T his f a c t is em phasised by th e la te s t B .E .S .A . specification for m alleable which includes a clause to cover a m inim um speed fo r m ach in in g .

I n th is P a p e r th e a u th o rs w ill en d eav o u r to

convince e n g in ee rs an d users of m alleable c a s t

m a trix w ith , fre q u e n tly , fre e c e m e n tite , an d some free carbon nodules. (See m icro-graphs, F ig s. 1 an d 2.)

The f r a c tu r e of an n ealed b la c k -h e a rt is u n ifo rm ly black th ro u g h o u t e x c e p t fo r a slig h tly lig h te r a p p e a ra n c e on th e ex tre m e edge. T he s tru c tu r e is f e r r ite w ith ro u n d ed nodules of fre e

Fi g. 1 .— Ri m o p An n e a l e d Wh i t e- He a b t. Et c h e d x 5 0 .

carb o n (tem p er carbon) d is trib u te d th ro u g h o u t.

(F ig . 3.)

The B .E .S .A . specifications N os. 309 an d 310 in d ic a te th e physical p ro p e rtie s of th e tw o types, and a p o rtio n is h e re a b s tra c te d : —

Ultimate Tensile Strength W hite-heart Black-hea rt

(minimum) 20 tons. 2 0 tons.

Elongation in 2 in. (minimum) 5 per cent. 74 per cent.

Bend. Cold. Round 1 in. rad. 45 degrees. 90 degrees.

(minimum).

Maehineability. Approx. 90 ft. per 90 ft. per

min. min.

55 MANUFACTURE.

Air Furnace Melting for Black>heart.

T he a ir fu rn a c e s used have capacities ra n g in g fro m 5 to 30 to n s an d ty p ic a l fu rn aces are illus

tr a te d in F ig s. 4 an d 5. The fu rn aces are lined w ith good-quality firebricks which have to stand

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te m p e ra tu re s aro u n d 1,600 deg. C., an d resist th e a c tio n of a slig h tly oxidising slag. A l u m i n o u s

b ricks excel in w ith s ta n d in g th e high te m p e ra tu re s a n d erosion, b u t e x h ib it unwelcome sp allin g pro p en sities, ow ing to th e ra p id cooling of th e f u r nace when a h e a t is ta k e n off an d a n o th e r one ch arg ed . T able 1 shows th e life of various bricks

in th e w alls. , „ . . ,,

S ilica san d is gen erally used for m ak in g th e b o tto m of th e b a th , b u t firebrick bottom s have been ad o p te d in some cases w ith success. lh e a d v a n ta g e of th e l a t te r ty p e of bottom is

saving of fuel re q u ire d to f r i t or b u rn a bottom in. A sand bottom w ill la s t ab o u t 8 or 9 h eats, w hereas a brick bottom w ith care m ay ru n to

Fi g. 3 . — An n e a l e d Bl a c k- He a r t. Et c h e d x 5 0 . Ta b l e I .— Life of Various Refractories in A ir Furnace

Walls Using Pulverised Fuel.

Analysis. Firebrick

Good Quality. Aluminous

Brick.

SiO, 63.90 47.62

TiO, 1 .1 2 3.80

Fe/ ) 3 2 .2 0 1.34

a l o3 29.73 44.58

MgO 0.46 0.25

CaO 0.8S _{1 .1 0}

Alkalies 1.71 1.31

Melting Point 1700 0. 1780"C.

Life Average Number

of Heats. 13 17

I

Conditions Influencing the Life of Refractories.

One of th e ch ief fa c to rs w hich d e te rm in e s th e life of re fra c to rie s is th e velocity of th e flam e passin g th ro u g h th e fu rn a c e , an d w ith fu rn a c e s

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Fi g. ü. Ha n d-11 i r e d Ai r Fu r n a c e. 6 To n s

w orking on pulverised fu el th e secondary a ir should n o t be a d m itte d to th e fu rn ace a t a pres

su re above 2 oz. B u rn e rs an d pipe lines are designed of sufficient a re a to supply th e correct volum e of a ir a t th is low p ressure. D ry coal and low velocity a re th e first essentials for th e suc

cessful a p p lic a tio n of pulverised coal.

W ith hand-fired fu rn aces a ir is a d m itte d below th e fire g ra te in such q u a n titie s as p a rtia lly to b u rn th e coal w ith a d is tilla tio n of th e volatile

2 0 To n s Ca p a c i t y.

p ro d u cts, an d pass in to th e fu rn ace w h at is v ir tu a lly a low -grade p roducer gas. The secondary a ir, w hich is a d m itte d th ro u g h tu y eres in th e roof, effects com bustion of th is gas in th e furnace.

T he p ressu re of th e p rim a ry a ir u n d e r th e fire

b a rs m u s t be so re g u la te d as n o t to blow any of th e sm all coal over th e f r o n t b ridge on to th e b a th . T his h a p p e n in g , usually term ed “ thro w in g

Ca p a c it y.

ashes ” increases th e carb o n c o n te n t of th e b ath a n d is o ften caused by u sin g fria b le coals.

The Bath.

I t will be observed from F ig s . 4 an d 5 t h a t th e roof is b u ilt w ith a s t r a ig h t ta p e r from b u rn e rs o r firebox to b rid g e. T he b a th of m e ta l m ay be from 5 to 9 in . in d e p th a t th e d eep est p a r t (lower tap h o le), d e p en d in g on th e c a p a c ity of th e f u r n a c e : too d eep a b a th le n g th e n s th e tim e r e quired to o b ta in th e necessary c a stin g te m p e ra tu re . Tapholes are usually p u t in a t tw o levels, th e low er to d ra in th e b a th an d th e h ig h e r one to ta k e oft th e • h o tte s t m e ta l first. These holes a re b e tte r m ade w ith a special b rick , such as is show n in F ig . 6. F ro zen tap h o les can be easily opened o u t w ith an oxygen to r c h ; t h a t is, a le n g th o f iro n p ip in g 4 in . d ia . coupled to an oxygen cy lin d er, gas b ein g d eliv ered a t ab o u t 30 lbs. p re ssu re .

Charging Operations and Fuel Ratios.

W hen c h a rg in g a fu rn a c e tw o o r th r e e b u n g s are rem oved a t th e f r o n t a n d a t th e b ack of th e fu rn a c e . T he scrap a n d sp ru e a re first ch arg ed an d levelled dow n, follow ing w ith th e p ig -iro n an d steel s c r a p ; th e bu n g s a re rep laced an d lu te d up.

W ith han d -fired fu rn a c e s u sin g a h a rd b itu m in o u s coal a r a t io of iro n to fu el o f 2.25 m ay be o b ta in e d w ith good p r a c tic e ; th is should be associated w ith a m e ltin g speed of 30 m ins. p e r to n . W hen m e ltin g w ith p u lv erised coal, ra tio s of 2.50 to 1 m ay be o b ta in e d u n d e r good co n d itio n s, an d th e m e ltin g speed is im proved up to 2 0 m ins.

per to n . M uch b e tte r tim es a n d ra tio s th a n th ese a re o b ta in e d in A m erican p ra c tic e , 3.0 to 1 b ein g comm on, an d th e a u th o rs h av e seen h e a ts m ade w ith a 4.0 to 1 ra tio . T h ere seem s no d o u b t t h a t th e se ex cellen t figures a re o b ta in e d by reaso n of m ore easily d rie d fuel. T he com position of s u i t

able A m erican an d E n g lish coals is com pared in T able I I I .

I n connection w ith fu el ra tio s i t should be borne in m ind t h a t th ey vary considerably w ith th e size of th e h e a ts w hich can be m elted , w hich fa c to r is d e te rm in e d by th e class of c a stin g s being produced, as one d a y a sin g le la rg e h e a t m ay be r u n and

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h e a ts p o u red , w ith a n a g g re g a te to n n a g e of a p p ro x im a te ly 1 0 0 ,0 0 0 to n s, only six fa ile d to pro d u ce s a tis fa c to ry m a te ria l fo r a n n e a lin g , one has to a d m it t h a t th is p ra c tic e is p e rh a p s e q u al to th e m ore scientific m ethods so m uch ad v o cated .

Recording Data.

R e g u la rly rec o rd in g th e d e ta ils of fu rn a c e w ork

in g is very useful. F ig . 9 (pp. 80-81) shows th e re corded d a ta on one m o n th ’s o p e ra tio n o f a fu rn a c e .

Fi g. 7 .— Se c t i o n Th r o u g h Te s t Pi e c e Co r e. Sc a l e 1 / 3 .

As S a n d P a re su b je c t to li tt le v a ria tio n , only TC, Si an d M n a re e n te re d . I t w ill be seen t h a t th e in fo rm a tio n sum m arised includes w eig h t of ch arg e, tim e of m e ltin g , w eig h t of fu el used an d m e ltin g ra tio , a d d itio n s m ade, n u m b er of te s ts ta k e n , im p o r t a n t re p a irs a n d th e fu r n a c e m a n ’s check num ber.

Adjustments to Composition.

T h e n u m b er o f te s ts, an d th e a p p e a ra n c e of th e fra c tu re s , to g e th e r w ith th e a n a ly tic a l an d o th e r d a ta from th e p a r tic u la r m ix tu r e a n d previous h e a ts on th e fu rn a c e in q u estio n , enable those in ch a rg e of th e m e ltin g o p e ra tio n s to decide w h eth er

an d in th e o th e r case, h ig h , say 1.25 p e r c en t.

Low g ra d e ferro -silico n , w ith a Si c o n te n t of a b o u t 1 0 p e r c e n t., is also som etim es c h a rg e d in sm all q u a n titie s . I t m ig h t be m e n tio n e d h e re t h a t th e chrom ium c o n te n t of all ra w m a te ria ls m u s t be low, as i t h a s a very serio u s effect on g ra p h itis a tio n , as re f e rre d to la te r .

Properties of the Hard Iron.

F ig . 10 shows a m ic ro g ra p h of th e h a r d iro n p roduced. I t w ill be seen t h a t i t co n sists of ap p ro x im a te ly 75 p e r cen t, p e a r lite a n d 25 p e r cen t, fre e c e m e n tite ; th e d e n d ritic s t r u c tu r e is u su al for all w hite iro n s. A re m a rk a b le f e a tu r e of th is low -carbon w h ite iro n is its te n s ile s tr e n g th , which is a b o u t 30 to n s p e r sq. in . I t is i n t e r e s tin g to record t h a t i t is fa irly easily m ach in ed , a n d h as a Scleroscope n u m b e r of 45 to 48, e q u al to a B rin e ll of 300 to 350. I t w ill w ith s ta n d considerable ro u g h u sag e, as i t is n o t n e a rly so b r ittle as th e o rd in a ry h ig h e r-c a rb o n w h ite iro n s.

I t h as been used w ith success fo r c a stin g s w hich w ould o therw ise h av e to be c a s t in chilled m oulds.

T his m a te ria l is re g u la rly b ein g m a ch in ed to fine lim its, an d sm all a d d itio n s of m a n g an e se, in th e form of 80 p e r c en t, ferro -m a n g a n e se , to th e la d le when p o u rin g im prove its m a c h in in g q u a litie s, w ith litt le ch an g e in th e an aly sis.

Melting for W hite-heart.

T he m e ltin g of iro n fo r w h ite -h e a rt is u su ally c a rrie d o u t in th e cupola. T h is is by f a r th e qu ick est an d c h eap est m e ltin g m ed iu m to p roduce m alleable castin g s. A lth o u g h th is w ould seem to show considerable sav in g com pared w ith a ir fu rn a c e p ra c tic e , th e com position of th e m e ta l c a n n o t be co n tro lled to such fine lim its.

B ro ad ly sp eak in g , an y cupola s u ita b le fo r m e lt

in g g rey iro n w ill be s a tis f a c to r y fo r m alleable.

As th e m e ta l re q u ire d m u s t be low in Si an d P , a n d is alw ays h ig h in S, i t w ill be re a d ily seen t h a t i t m u s t be h ighly s u p e rh e a te d to o b ta in th e life necessary successfully to p o u r th e lig h t classes of c a stin g s m ade. I t is e ss e n tia l to use good coke, an d ch arg e som ew hat la r g e r q u a n titie s th a n is u su a l in cupola p ra c tic e . T he cost of fuel p e r to n

Fxa.10.—UnannealedBlaok-Heaiit. Etchedx50. Fig. 11.—UnannealedWhite-Heaht. Etched

of good c a stin g s is very m uch m ore th a n is th e case w ith g rey iro n , as in a d d itio n to th e p o o rer fu el r a tio , th e p e rc e n ta g e of feeders a n d ru n n e rs is from two to th re e tim es g re a te r.

A p a r t from th e g r e a te r fu e l co n su m p tio n , th e re does n o t a p p e a r to be u n a n im ity on th e d e ta ils of cupola w o rk in g fo r m alleable. H ig h e r b la s t p ressu res a re fa v o u re d by some, b u t th e r e is no d o u b t t h a t th is should be gov ern ed by th e d ia m e te r of th e cupola a n d th e d isp o sitio n an d a re a o f th e tu y e re s. T he e s s e n tia l re q u ire m e n t is h o t, clean iro n , an d an y p ra c tic e w hich fulfils th is w ith r e g u la r ity m ay be considered good.

Use of Refined Irons.

P ig -iro n s a re confined to h e m a tite q u a lity as th e m axim um phosphorus c o n te n t perm issib le is 0 . 2 0

p e r cen t. These iro n s a re u su ally of th e w h ite a n d m o ttled g rad es, b u t v a ry co n sid erab ly in com

position. T he follow ing shows th e ra n g e c o v e re d :—T .C ., 3.00 to 3.80-, S i, 0.40 to 1.20;

M n, 0.10 to .70; S , 0.15 to 0.45; a n d P , u p to 0.10 p e r cen t. I n a d d itio n refin ed iro n s are' largely used. T he n a tu r e of th e re fin e m e n t is som ew hat obscure b u t a p p e a rs, a t an y r a t e in m an y cases, to co n sist of re m e ltin g th e o rd in a ry h e m a tite irons in th e cupola w ith th e a d d itio n of steel in a n a tte m p t to low er th e c arb o n con

te n t. Some refined iro n s a re now m ad e w hich have been co nsiderably d esu lp h u rised , an d w hen used w ith c a re th ese a re v e ry beneficial. The ex p erien ce of m an y w orkers te n d s to show t h a t th e “ r e f in e d ” iro n s p ro d u ce b e tte r m alleab le c a stin g s th a n th e o rd in a ry g rad es.

T he p ig is m ix ed w ith th e shop s c r a p w hich, as in d ic a te d p reviously, is sufficient to su p p ly ab o u t 50 p e r c en t, of th e ch arg e. T h e a n n e a le d scrap is used by m an y fo u n d e rs to a s lig h t e x te n t, w hile o th e rs condem n it . I t seems t h a t w ith good p ra c tic e sm all q u a n titie s can be used successfully, b u t th e c o n tin u e d use of a m o u n ts above 5 p er c en t, of th e ch a rg e pro d u ces m e ta l w ith sh o rt life.

T he losses on m e ltin g v a ry co nsiderably w ith th e cu p o la p ra c tic e ad o p ted a n d th e p ig -iro n s used. T h e to ta l-c a rb o n shows li t t le ch an g e, a lth o u g h g en e ra lly th e tendency is to w ard s a

Fig. 12.—GreytoWhiteFractureinUnannealedBlack-HeartCasting.

slig h t loss. The Si loss m ay ru n from 0.15 to 0.25

P rim a rily th e fo u n d e r h as to produce th e cast

in g from m a te ria l which will sa tisfa c to rily anneal or h is efforts are useless. To achieve th is i t is necessary to p o u r th e m oulds w ith irons of a low- silico n -co n ten t an d in th e case of b lack -h eart w ith a low to ta l-c a rb o n c o n te n t both of w hich shorten th e freezin g ra n g e . W ith w h ite -h e a rt th e T.C.

m ay be much h ig h er, b u t th e low silicon, to g e th e r w ith th e very m uch h ig h e r S. will b rin g ab o u t som ew hat sim ilar co n d itio n s of freezing. T here

fo re, th e r e m u s t be a high degree of su p e rh e a t in th e m e ta l as p o u red . T his high c astin g te m p e ra tu r e , sh o rt freezin g ra n g e , h ig h liquid an d solid c o n tra c tio n are a set of c o n d itio n s which m ake th e p ro d u c tio n of c astin g s of uneven an d th in sections a n y th in g b u t an easy proposition. B u t in th e face of th is , good, reliable, sound castings a re m ade as w ill be acknow ledged from th e d a ta show n of m a c h in a b ility to be p resen ted la te r in th is P a p e r

I t w ill be seen t h a t to overcom e these special co n d itio n s, th e fo u n d e r can n o t ad o p t grey-iron fo u n d ry p ra c tic e of ru n n in g a so fter m ix tu re for th e lig h t w ork, ow ing to th e fa c t t h a t an iron w hich would give a w h ite f r a c tu re in sections of

Ta b l e IV.— Analyses of Metal from a 1 2-ton heat on pul

verised coal-fired, air furnace taken at ten-minute intervals during running out.

No. 1. No. 2. No. 3. No. 4. No. 5. No. 6.

T.C. .. 2.46 2.42 2.38 2.33 2.30 2.28

Si .. 0.938 0.938 0.938 0.938 0.938 0.938

Mn .. 0.309 0.305 0.299 0.296 0.286 0.253

Ta b l eV.— Analyses of Metal from a 5-ton heat on a hand- fired air furnace taken at five-minute intervals during

running out.

No. 1. No. 2. No. 3. No. 4. No. 5.

T.C. .. 2.46 2.41 2.36 2.32 2.31

Si 0.906 0.906 0.896 0.890 0.890

Mn 0.326 0.317 0.302 0.299 0.299

f in . th ick n ess, m ay show m uch free carbon in sections of 1 in . or over. I t is necessary to com

prom ise. As all c a stin g s c a n n o t be m ade of one

Fig. 13a.—SprayofCastings, showing" Spinning” Feeder.

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M uch sav in g of fu el can be effected by th e use of special in s u la tin g m a te ria l in th e c o n stru c tio n of th e oven doors, such as d iam a ta c e o u s bricks.

I t is Usual fo r th e w alls an d back of th e oven to

Fi g. 1 3c.— Au t o m o b il e Ca s t i n g. No t e t h e Si e v e Ru n n e r.

be sufficiently th ic k , or else fo r th e ovens to be co n stru c te d in b a tte rie s , so t h a t th e r e is li tt le loss of h e a t in c u rre d in th is d ire c tio n . T he doors, how ever, h a v in g to he rem oved fo r each a n n e a l a re m ad e as lig h t as possible, a n d r e s u lt in a very g r e a t loss of h e a t, unless th e p re c a u tio n , m

en-tio n e d above, is ta k e n . I n a d d itio n , such in su la tio n red u ces th e r a t e of cooling, w hich is a very d esirab le fe a tu re , p a rtic u la rly in th e case of black- h e a r t, as w ill be d e a lt w ith la te r in a discussion

Fi g. 1 3d.— Au t o m o b i l e Ca s t i n g, s h o w i n g Fe e d e b s o n Jo i n t a n d Ti e s.

on th e th e o ry of a n n e a lin g . I t m ay be p o in ted o u t t h a t w here oven doors a re b u ilt up anew each tim e , th e d iam ataceo u s b ricks a re too soft a n d firable to w ith s ta n d th e ro u g h usage.

S m all p la n ts u su ally p ack a n d u n p a c k th e ir c a stin g s in sid e th e oven. T his n ecessitates th e

oven te m p e ra tu re being low enough to en ab le m en to w ork a n d h a n d le th e c a stin g s a n d p o ts before th e oven can be e m p tie d , an d re c h a rg e d fo r th e n e x t a n n eal. W ith m odernised an d la r g e r p la n ts ,

Fi g. 1 3e.— Au t o m o b i l e Ca s t i n g. No t e t h e Fe e d e r s o n Jo i n t d o n o t Co m e Th r o u g h.

th e p o ts a re pack ed in sta c k s o u ts id e th e ovens, a n d a re ch arg ed w ith a special tr u c k . T h is shows a d ire c t sa v in g in tim e of d eliv ery a n d in th e fu el co n su m p tio n , as i t is possible to d ra w ovens a t fa irly h ig h te m p e ra tu re s a n d re c h a rg e in a few hours.

Annealing Pans.

A n n ealin g p a n s a re m ade of w hite c a st iron, s im ila r in com position to th e w h ite -h e a rt h a rd cast

in g s. T he u se fu l life of th ese p an s m ay he

pro-Fi g. 1 3f.— Au t o m o b i l e Ca s t i n g. No t e t h e Ti e o n Fl a n g e.

longed by th e a d d itio n of chrom ium from about

0 . 2 0 to 0.60 p e r c e n t., an d good re su lts have been o b ta in e d by u sin g m e ta l w ith m an g an ese increased to a b o u t 1.25 p e r c en t. N ickel-chrom e p an s, w hilst g iv in g fro m 5 to 10 tim es th e life of th e h e m a tite iro n p an s, a re p ro h ib itiv e in p rice, as to prove econom ical th e y w ould be re q u ire d to give some

2 0 0 tim es th e life o f th e o rd in a ry pans.

B la c k -h e a rt c a stin g s are packed in th e p an s w ith a n in e r t m a te ria l such as cru sh ed slag , w hich is used to su p p o rt th e c astin g s a n d p re v e n t u n d u e

W dokumencie Proceedings of the Institution of British Foundrymen, Vol. 20 (1927-1928) (Stron 62-98)