ELECTRIC FURNACE PRACTICE

Preference of Founders for Acid Electric Steel for Castings.

Before discussing d etails of steel-m ak in g in electric furnaces, i t is a p p ro p ria te to re fe r to th e facto rs t h a t h av e recen tly re s u lte d in a re lativ ely sm all n um ber of u n its m ak in g basic electric steel for castings. T he p ercen tag e of such basic electric furnaces now being o p e ra te d is so sm all th a t th e a u th o r feels ju stified in confining his description«

of electric steel m eltin g , as now conducted, to t h a t perform ed w ith in an acid lin in g . P re lim in a ry to th ese discussions it should be ex p lain ed t h a t A m eri­

can p ra c tic e n a tu r a lly followed t h a t developed in E urope, in first em ploying basic linings.

A t r i a l fo r a reasonable p eriod convinced m any of th e pioneers in electric fu rn a c e o p e ra tio n for foundry use in th e S ta te s t h a t a basic slag an d th e super-refin em en t w hich it p erm its im pose a very serious h a n d ic a p on lin in g and roof, th ro u g h th e th in n a tu r e of th e ty p ical slag, a n d th e prolonged m ain te n a n c e of a v ery h ig h te m p e ra tu re , to which

• " T h e F o u n d ry ,” Septem ber, 1909, pages 33-34. “ Analysis of th e L ast P a r t of a Basic O pen-H earth H e a t,” by th e au th o r.

136

th e best o b ta in a b le re fra c to rie s a r e exposed. A n­

o th e r fa c to r of re a l consequence was th e in creased tim e re q u ire d for m ak in g a h e a t, an d th e b u rd e n t h a t im posed in a busy shop as com pared w ith th e very sa tis fa c to ry p o u rin g schedules p e rm itte d by c o n v e rte r o p eratio n s. I t m u st be rem em b ered t h a t m a n y elec tric steel fu rn a c e s in A m erican fo u n d ries h a d su p ersed ed c o n v e rte rs, th e u se of w hich was w ell-know n to m an y seeking a m ore sa tisfa c to ry u n it fo r m a k in g c a stin g s of th in sec­

tio n s, r e q u irin g h ig h flu id ity .

A bout th e tim e w hen excessive d a m ag e to re fra c to rie s, an d re ta rd e d p o u rin g o p e ra tio n s w ith th e i r re s u ltin g h a n d ic a p to m o u ld in g schedules dem anded th e serious c o n sid e ra tio n of th e A m eri­

can electric fu rn a c e p io n eers in th e fo u n d ry , a m ovem ent w as in s titu te d in th e S ta te s c ritic a lly to in v e s tig a te th e a c tu a l effects in steel of p h o sp h o ru s an d su lp h u r. T he sa tis fa c to ry u se fo r o rd n a n c e purposes of considerable ste e l m ade a b ro a d , con­

ta in in g re la tiv e ly h ig h p e rc e n ta g e s of pho sp h o ru s an d su lp h u r, h a d come to th e a tte n tio n of m an y A m erican m e ta llu rg ists . I t w as f e lt by m o st of these who w ere n o t biased, t h a t th e lim ita tio n s o rd in a rily im posed fo r s u lp h u r c o n te n t in steel a re th e re s u lt of su p p o sitio n —w hich is no co m p lim en t to th e m e ta llu rg ic a l profession. T he con v ictio n grew t h a t a steel w hich c a rrie s a rea so n a b ly h ig h p e rc e n ta g e of s u lp h u r p erfo rm s as s a tis f a c to r ily in service as one whose s u lp h u r c o n te n t is v e ry low.

A pplied to steel c a stin g m a n u fa c tu re , th e p e rc e n ­ ta g e of su lp h u r h as a n o th e r asp ect, r e la te d to re d ­ shortness. T his was g en erally fe lt to be p u re ly a m a n u fa c tu rin g a n d n o t a service problem . T he p re v a ilin g o p in io n in th e steel c a s tin g in d u s tr y to ­ day is t h a t a steel c astin g whose s u lp h u r c o n te n t is a ro u n d 0.015 p er cen t, w ill pro b ab ly g iv e no m ore s a tisfa c to ry re su lts u n d e r service c o n d itio n s of th e o rd in a ry e x a c tin g k in d th a n a sim ila r c a s tin g which h a s a s u lp h u r c o n te n t of 0.055 p e r c e n t, if all o th e r conditions a re equal.

T he d esire to dispel su p p o sitio n an d to e s ta b ­ lish f a c t re su lte d in th e o rg a n isa tio n of a J o i n t C om m ittee on th e In v e s tig a tio n of P h o sp h o ru s a n d S u lp h u r in Steel. T he p ersonnel of th is com­

m itte e includes re p re se n ta tiv e s of all of th e im ­ p o r ta n t en g in e e rin g an d te c h n ic a l associations

whose in te re sts o u g h t to he cen tred in such a research. A p p ro p ria te ly , th e A m erican F o u n d ry - m en’s A ssociation has its d eleg ated re p re se n ta tiv e on th is J o i n t C om m ittee. D efinite co-operative steps th u s ta k e n to establish reliable d a ta seemed g re a tly to s tre n g th e n th e confidence of m any steel m akers in m etal c o n ta in in g norm al p e rc e n t­

ages of phosphorus and su lp h u r. The re s u lt was less im p o rtan ce assigned gen erally to th e a d m itte d su p e rio rity of th e basic electric fu rn a c e as com­

p a re d w ith th e acid, in d eliv erin g a p ro d u c t h av in g a very low c o n te n t both of phosphorus and su lp h u r.

E x p e rim e n ts in conversion of electric fu rn aces from basic to acid w ere ex trem ely sa tisfa c to ry , cam e p ro m p tly to th e notice of th e in d u s try a t larg e, an d w ere speedily followed by sim ilar tests, w ith subsequent definite decisions to em ploy acid linings. I n th e S ta te s it is n o t difficult in m ost localities to o b tain a t reasonable prices scrap of su itab le com position, which, when charged into th e acid electric fu rn a c e , w ith o u t any pig-iron, b u t w ith a no rm al p erc e n ta g e of th e fo u n d ry scrap locally produced, yields a m etal well w ithin th e lim ita tio n s for phosphorus an d su lp h u r in c u r­

r e n t specifications, and th e r e fo re below th e p e r­

centages generally believed to be h a rm fu l to steel in service.

The p re lim in a ry re p o r t of th e J o i n t C om m ittee on th e In v e stig a tio n s o f P hosphorus an d S u lp h u r in S teel, published in 1922, d ealin g w ith su lp h u r in c e rta in steels, has in no sense ten d ed to increase th e p re ju d ic e a g a in s t t h a t elem ent.*

Mistakes Attending Early Efforts.

I t was u n f o r tu n a te fo r th e desired e arly pro ­ gress in A m erica of elec tric steel-casting p ro d u c­

tion t h a t c e rta in ex p lo iters of th e e lec tric fu rn ace com bined w ith th e ir selling a rg u m e n ts th e claim t h a t th is m eltin g u n it was one t h a t could be depended upon re g u la rly to p ro d u ce good m etal simply by sw itching th e pow er on a ch arg e of ferro u s scrap. Some of th ese over-zealous p e r­

sons declared th e electric fu rn a c e to be a d a p ta b le to all classes of steel c a stin g s m a n u fa c tu re d , and

* “ Proceedings of th e .American Society for T esting M aterials,”

Vol. 22, Part. 1, pages 94 to 130 inclusive, “ Effect of Sulphur cp R iv et Steel,” by th e Jo in t Com m ittee referred to.

138

to be in effect a v e rita b le p a n a c e a fo r m ost of th e tro u b les common to ste e l-m a k in g in th e fo u n d ry . I n some in stan ces i t re q u ire d sa d ex p e rie n c e to d e m o n s tra te o th erw ise. F o u n d ry m e n le a rn e d t h a t good ju d g m e n t a n d scru p u lo u s c a r e a re re q u ire d of a successful e le c tric ste e l m e lte r. As th e n a tu r a l r e s u lt of e x a g g e ra te d claim s an d c a re ­ less an d in ex p erien ced m a n ip u la tio n , som e v e ry in fe rio r e lec tric steel w as m ad e in A m e ric a n fo u n d ries before t h e f a c t d aw ned on c re d u lo u s in d iv id u a ls t h a t so m eth in g m o re th a n “ tu r n in g on th e ju ic e ” is necessary. As a people, p e rh a p s we a re in clin ed to believe w h a t we a re to ld , a n d o fte n to liste n fo r w h a t we h a v e b een w ish in g to h e a r, in th e idealism w hich u n d o u b te d ly influences even o u r in d u s tria l a c tiv itie s . T his h a s m u ch to do w ith o u r re a d y d isp o sitio n to e x p e rim e n t w ith so m eth in g new. * To offset th is , h a p p ily , one seems to le a rn w ith reaso n ab le q u ickness fro m experience, an d th e re b y to d isco u n t th e fa n c ifu l sto ries t h a t o rig in a lly m a d e a v iv id im p ressio n . A m ericans in a n d o u t of th e fo u n d ry a re n o t p e r ­ p e tu a lly sold by a n id e a t h a t does n o t successfully b e a r th e s tr a in of h a rd ex p erien ce. O nce d is­

illusioned, th e y go seriously in to th e b u sin ess of d ig g in g th e ir w ay o u t. A ccordingly, by stag es, steel fo u n d ry m en in th e S ta te s le a rn e d how to m ake good steel in th e e lec tric fu rn a c e , a n d w here econom ically to em ploy th is m eth o d of m e ltin g .

Electric Steel M elting.

T he d eg ree of e d u c a tio n t h a t h as been a tt a in e d by A m erican fo u n d ry m en in e lec tric m e ltin g is, of course, v a ria b le . In f o rm a tio n y e t to be le a rn e d by all en g ag ed in th e a r t is co n sid erab le. M an y im p o rta n t fa c ts h av e been estab lish ed , a n d h av e been th e m eans of re g u la tin g c e r ta in m a jo r d e ta ils of p ra c tic e w ith slig h t v a ria tio n s .

T he fu rn a c e design itself n a tu r a lly h a s received m uch stu d y by m e ta llu rg ists a n d by e le c tric a l en g in ee rs. . R eferen ce in th is P a p e r w ill be con­

fined to th e a rc ty p e of fu rn a c e , becau se of th e p ra c tic a l u n a n im ity of o p in io n fa v o u rin g i t in th e S ta te s as com pared w ith th e in d u c tio n f u r ­ nace. O pinions n a tu r a lly differ re g a r d in g th e k in d of a rc fu rn a c e found b e st to em ploy. I t is n o t th e p ro p e r fu n ctio n of th e w rite r to ad v o cate th e use of an y p a r tic u la r m ake of fu rn a c e nor

139

indeed, is it seientiiic for anyone to form a p jsi- tiv e o pinion w ith o u t o p p o rtu n ity definitely to a sc e rta in th e re su lts achieved from d ifferen t types of furnaces.

The elec tric fu rn a c e as commonly found in A m erican steel fo u n d ries has an electrically- tilte d c irc u la r shell, an d has th re e electrodes p ie rc in g th e roof. P re fe re n c e fo r th e m a te ria l in th ese electrodes is a b o u t equally d iv id ed as betw een g ra p h ite an d carbon. T he use of econom isers fo r th e electrodes in A m erica is uncom m on. T he w rite r does n o t know o f any steel fo u n d ry in th e S ta te s w here th e electrodes a re m ade an d bak ed from th e h e a t produced by th e fu rn a c e itself, as is th e case to some e x te n t in E u ro p e. As in d ic a te d previously, th e lin in g of th e ty p ic a l fu rn a c e is an acid one, an d is generally form ed from silica brick, or from g a n is te r ram m ed in to place. M ost of th e roofs are of silica b rick , o r a com bination of th ese and special silica shapes, th ro u g h w hich th e electrodes pass.

A ra te d cap acity of th r e e n e t to n s to re p re se n t th e m etal-ch arg e is m ost fav o u red in th e S ta te s fo r fo u n d ry o p e ra tio n s. T his is due largely to th e n a tu r e of th e w ork fo r which electric steel is m ost su itab le. A fa c to r of im p o rtan ce is th a t of th e tim e re q u ire d for m ak in g a h e a t, in re la ­ tio n to th e d e sira b ility of h a v in g th e m etal delivered w ith o u t long in te rv a ls to th e m oulding floor. A m erican foundrym en realise th e economy of a u n it of fa irly la rg e m e ltin g cap acity , when considered solely from th e s ta n d p o in t of fuel con­

sum ed. I n th e selection of fu rn aces v a ry in g from

1 to 6 to n s in ca p a c ity th e m a tte r of pow er con­

su m ption has th e re fo re been given ca re fu l con­

sid e ra tio n . M any of those who form erly in stalled fu rn aces ra te d below 2 tons an d above 4 to n s would p robably to -d ay p re fe r 3-ton u n its, in th e lig h t of th e ir exp erien ce an d t h a t of o th e rs w ith whom th e y have exchanged d a ta .

I n th e in d u s try w ith w hich we a re concerned th e re m ay be said to be p ra c tic a lly no c h a rg in g of m olten m etal. G enerally th e scrap is shovelled in to th e c h a rg in g door ju s t as tr a n s p o rte d from the stock y ard . I n some cases chutes a re con­

s tru c te d , in to w hich th e charges a re loaded. T he pro ced u re is to in tro d u c e th e open end o f th is

140

c h u te into th e doorw ay, an d to lif t th e o th e r en d by m eans o f a cra n e , so as to slid e th e scrap ch arg e in to th e b a th , a t a co n sid erab le sav in g of tim e in c h a rg in g . I n a sm all p ro p o rtio n of f u r ­ naces in th e S ta te s th e fu rn a c e roof is of th e t i l t ­ ing ty p e , in te n d e d n o t only fo r th e q u ick in tr o ­ d u ctio n of th e ch arg e, b u t th e p re h e a tin g of th e sam e, g en erally by m eans o f fuel-oil in a su p p le­

m e n ta ry vessel. T he c h a rg e re d -h o t, b u t n o t m elted, is d u m p ed in to th e fu rn a c e , w ith re s u ltin g economy in pow er co n su m p tio n , a n d a lessen in g of m e ltin g tim e re q u ire d in th e fu r n a c e itself.

T h ere a re r a t h e r w ide v a rie tie s of v o lta g e s a n d power in -p u ts fo r w hich a u x ilia r y e le c tric a l e q u ip ­ m e n t is p rovided, in e lec tric steel fo u n d rie s in th e S ta te s . W hile m an y tra n s fo r m e rs in s ta lle d in th e p io n e e rin g d ays w ere of in a d e q u a te p ro p o r­

tio n s an d u n su ita b le d esig n fo r f a s t w ork in m e lt­

ing an d fo r flexibility in v o lta g e c o n tro l, re c e n t opinion seems to fa v o u r a f a ir ly h ig h v o ltag e (fro m 140 to 180) in m e ltin g dow n, a n d a low er voltage (a ro u n d 120 to 130) fo r th e final o p e ra ­ tion. Some fo u n d ry m en h av e re c e n tly p ro v id e d tra n s fo rm e rs p e rm ittin g by th e u se of m an y ta p s a very flexible a rr a n g e m e n t as to v o lta g e . T his was done p a rtly in o rd e r to a s c e rta in w h a t v o lt­

ages a re b est to em ploy a f t e r th o ro u g h ly tr y in g those covered by a w ide ra n g e .

W ith cold charges, 3-ton acid fu rn a c e s w ill fr e ­ q u en tly deliver, as th e r e s u lt of a fu ll ch a rg e , u n d e r conditions of n o rm al in p u t a n d v o ltag e, very h o t low -carbon steel s u ita b le fo r ru n n in g sections of | in ., on a p ow er co n su m p tio n t h a t will av erag e a b o u t 650 kw .-h. p e r n e t to n of charge. U n d e r sim ila r co n d itio n s, w hen th e ch arg e is p re h e a te d b u t n o t a c tu a lly m elted , such a fu rn a c e will pro b ab ly a v e ra g e 550 k w .-h. p e r n e t to n of charge. A fa c to r w hich h a s m u ch to do w ith such pow er co n sum ption, a n d o n e w hich is of widely d iffering n a tu r e in th e S ta te s , is t h a t of tig h tly -sealed openings fo r c h a rg in g an d ta p p in g . W hen th e se a rc w ater-cooled to p re v e n t w arp in g an d re s u ltin g a ir leak a g e, th e th e r m a l efficiency of th e fu rn a c e is g re a tly in c re a se d . Those who h a v e in s ta lle d such w ater-co o lin g devices feel well re p a id fo r h a v in g done so.

P robably a n o th e r a d v a n ta g e lies in th e su p erio rity of th e m e ta l th u s pro d u ced th ro u g h

141

th e m uch m are effective control in th e adm ission of oxygen to th e b a th .

I t is alm ost th e u n iv ersal p ra c tic e in acid steel m eltin g in A m erican fo u n d ries using th e electric fu rn a c e to use no p ig -iro n in th e charge, ex cep t when fa irly high carb o n steel is to be m ade. E ven th e n in m an y cases carbon is su p p lied freq u en tly by im m ersing electrodes in th e b a th , o r by a d d in g broken p o rtio n s of electrodes carefu lly w eighed.

I f th e th eo ry held by m an y o p e n -h e a rth m elters is co rrect, t h a t a c e rta in a m o u n t of carbon con­

ta in e d in th e o rig in a l m etallic c h a rg e is desirable, one m ay ask if th e sam e co ndition does n o t apply to elec tric m eltin g , and, if n o t, w h a t reason exists fo r th e difference? The a u th o r does n o t presum e to give th e c o rre c t e x p la n a tio n . T he co n tin u al presence of carbon v ap o u r e m a n a tin g from th e ends of th e electrodes m ay have som ething to do w ith th is.

The a d d itio n of silicon to th e m etal in an acid electric fu rn a c e in th e S ta te s is g en erally by m eans of cold 50 p e r cen t, ferro-silicon, in tro d u ced in to th e b a th a few m in u te s before ta p p in g . T here a re some fo u n d rie s w here i t is believed b e tte r re su lts a re o b ta in e d by re d u c tio n of th e silicon from th e silica, fo r which p u rp o se th e sc a t­

te r in g of a n th r a c ite coal o v er th e slag seems to be an aid in th e re a c tio n on th e lin in g produced by th e slag. F lo o r-tests p oured a t fre q u e n t in te r­

vals before ta p p in g re g u la te th e q u a n tity of ferro- silicon ad d itio n s.

T here is n o th in g t h a t would p robably be sig n i­

ficant to B ritis h fo u n d ry m en in a stu d y of A m erican electric fu rn a c e p ra c tic e , so f a r as it relates to m anganese a d d itio n s fo r t h a t p a rtic u la r practice. M anganese ad d itio n s, as in o p en -h earth p ractice, a re in th e form of 80 p e r cen t, fe rro ­ m anganese, a re usually added cold, g en erally in th e la rg e ladle, and in a m in o rity of cases in th e b a th . C om m ents re g a rd in g such ad d itio n s, m ade in th e section devoted to o p e n -h e a rth m elting, apply w ith equal force to th e p ra c tic e now being considered.

E ith e r as th e m e ta l is ta p p e d from th e fu rn a c e into th e la rg e ladle, o r as i t is sh an k ed fro m th e la rg e lad le to p o ts fo r h a n d p o u rin g , electric steel receives alu m in iu m a d d itio n s of r a th e r varv-

in g am ounts, according to th e ideas held by in d i­

142

v id u a ls ; also acco rd in g to th e n a tu r e of th e c a st­

ings b ein g m ade. Such steel used fo r c a stin g s to be v ery th o ro u g h ly m ach in ed , w hich m u s t show n o t th e s lig h te s t evidence of “ p in -h o les,” as sm all blow-holes a re te rm e d , g e n e ra lly receives a slig h tly la r g e r a lu m in iu m a d d itio n th a n does o th e r steel. T he a u th o r believes th is sa fe g u a rd h a s been em ployed o fte n w ith o u t d u e r e g a r d fo r physical p ro p e rtie s. F u r t h e r com m ents r e g a r d ­ ing a lu m in iu m a d d itio n s a re u n n ecessary in view of prev io u s re m a rk s o n th is s u b je c t as r e la te d to o p e n -h e a rth p ra c tic e . I t m ay a p p ro p r ia te ly be s ta te d t h a t th e a u th o r ’s o b jectio n to h ig h a lu ­ m in iu m a d d itio n s ap p lies irre sp e c tiv e of th e m ethod used fo r m e ltin g .

P ro d u c in g m e ta l by m eans of th e e le c tric a rc fo r steel c astin g s len d s itself to a la rg e v a r ie ty of flexible d e ta ils a cco rd in g to th e id eas o f th e d esig n er, th e ju d g m e n t of th e fo u n d ry m a n , th e class of w ork p ro d u ced , an d th e local co n d itio n s.

P ro d u c in g m e ta l by m eans of th e e le c tric a rc fo r steel c astin g s len d s itself to a la rg e v a r ie ty of flexible d e ta ils a cco rd in g to th e id eas o f th e d esig n er, th e ju d g m e n t of th e fo u n d ry m a n , th e class of w ork p ro d u ced , an d th e local co n d itio n s.