ACID OPEN-HEARTH PRACTICE

E x p la n a tio n a lre a d y m ade re g a r d in g th e p r e f e r ­ ence in th e m iddle w est fo r th e basic o p e n -h e a rth fu rn a c e fo r fo u n d ry uses a u to m a tic a lly su g g ests some idea of th e opposite choice in th e e a s te rn section, w here th e acid o p e n -h e a rth fu rn a c e .s stro n g ly fav o u red f o r m an y classes of c a s tin g s re g u la rly p ro d u ced . These in clu d e p a r t s fo r w hich m etal c o n ta in in g a m inim um of oxides a n d m a x i­

m um h om ogeneity is d esirab le. A m ongst such classes of c astin g s a re rolls fo r m ills; a n d la rg e c astin g s sub seq u en tly m ach in ed fo r a p p lic a tio n , to locom otives a n d o th e r e q u ip m e n t, w here s lig h t blem ishes a re h ig h ly o b jectio n ab le, a n d w here blow ­ holes of v ery sm all a re a a re serio u s in possible consequences. T he m a n u f a c tu r e of c a stin g s in th ese classes h a s 'b e e n c o n tin u o u s an d p ro g re ssiv e in th e e a s te rn sta te s , w here i t h a s b een chiefly c e n tra lise d —q u ite n a tu r a lly becau se of g r e a te r p ro x im ity to places of co n su m p tio n o r a p p lic a tio n of such c a stin g s.

T he castin g s in th e classes j u s t re f e rre d to a re in th e m ain of la r g e r section th a n th o se m ade in those basic o p e n -h e a rth fo u n d rie s t h a t a r e g e n e ra lly re fe rre d to as “ ra ilro a d sp ecialty s h o p s ,” w here a n o rm al section is fro m f to | in ., p ro v id in g in m any cases a s a f e ty -f a c to r r a n g in g u p to 8, o n a purposely-assum ed low e la stic v alu e. G iven an e q u ality of g en e ra l p ro p o rtio n s a p a r t from section, a steel c a stin g 8 f t. long, of in tr ic a te sh ap e, is m ore liable to crack in cooling a f te r p o u rin g , an d th e re fo re needs a low er su lp h u r c o n te n t, if its sec­

tio n s a re f in . th ic k , th a n if th ese a re 3 in . th ic k . I t is such co n sid eratio n s a s th is t h a t s u s ta in th e choice of c e rta in fo u n d rie s fo r acid ste e l, w here m axim um su scep tib ility to red -sh o rtn ess does n o t a tte n d ty p ic a l designs of c a stin g s, a n d w here m e ta l m ade w ith th e le a s t possible o x id a tio n is d esirab le . T he a u th o r believes th e r e can be n o so u n d m e ta l­

lu rg ic a l o r com m ercial a rg u m e n t successfully ad v an ced a g a in s t th e p referen ces t h a t h av e gen erally governed th e selection of acid an d b asic b ottom for o p en -h e a rth fo u n d ry o p e ra tio n s in

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A m erica. C onsidering th e d esirable fe a tu re s of the castings as delivered, th e consum er of each class of o p e n -h e a rth p ro d u c t doubtless generally receives th e a rtic le which will give him th e most s a tisfa c to ry service t h a t could be ren d ered from m etal m ade in e ith e r k in d of o p en -h earth furnace.

The o rd in a ry m etal-ch arg e of th e acid open- h e a rth fu rn a c e used for fo u n d ry o p eratio n s in th e S ta te s co n tain s less p ig -iro n th a n in th e case of th e basic fu rn a c e used for castin g s. P robably an average p e rc e n ta g e of p ig -iro n charg ed in such acid o p e ra tio n is betw een 1 2 p e r c en t, an d 20 p er cent., when th e desired o u tp u t is to be reasonably low in carbon, o r u n d e r 0.30 p er cen t. As th e desired carbon c o n te n t o f th e finished m etal increases, the pro p o rtio n of p ig-iron used in th e c h a rg e is raised . The p rin c ip a l reason fo r u sin g in acid p ra c tic e a sm aller p ro p o rtio n of p ig-iron in th e charge lies in th e lesser e x te n t o f th e o x id a tio n t h a t occurs in th a t fu rn ace. The a u th o r’s experience confirms th e objection on th e p a r t of m any basic an d acid m elters to th e delivery of m etal from th e fu rn ace spout, which h as m elted dead s o f t,” w ith a very low carbon c o n te n t which h as to be increased by carbon ad d itio n s. T ro u b le from sh rin k ag e cracks is believed by man}’ to follow a very dead “ m elt­

dow n.” T he a d d itio n to very so ft m etal in an o p en -h earth fu rn a c e of a considerable a m o u n t of carbon in some form o th e r th a n t h a t in pig-iron is th o u g h t by m any to be u n sa tisfa c to ry in results, excepting those of th e o rd in a ry chem ical analysis of the finished m etal. Such analysis alone a p p a re n tly leaves n o th in g to be desired. S teel is steel, and chem ical analysis is som ething else, h ighly im por­

ta n t, b u t lim ited , in its sphere of usefulness. T here are a few fo u n d ries in th e S ta te s in localities w here pig-iron is n o t locally a v a ila b le and is tra n s p o rte d a t very high cost. Som e of these p la n ts use a very much sm aller p ro p o rtio n of p ig -iro n in th e ch a rg e th a n is ty p ic a l of th e in d u s try as a whole. Indeed, c e rta in of th ese fo u n d ries h av e m ade considerable tonnages of steel w ith o u t th e use of any p ig-iron in th e charge. W h e th e r th e physical te s ts of th is m etal a re in all respects as sa tisfa c to ry as those from m etal c o n ta in in g a fa ir p ro p o rtio n of pig- iron, th e w rite r does n o t know. H e v en tu res th e

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opinion, a t least, t h a t h o t cracks, o th e r c o n d itio n s being equal, a re m ore p re v a le n t w here such “ pig- less ” steel is m ade.

Specification of Compositions.

T h e com position of th e steel pro d u ced in th e acid o p e n -h e a rth fu rn a c e is fre q u e n tly less fixed th a n i t is in th e basic o p e n -h e a rth fu rn a c e , due to th e la rg e r v a rie ty of steels re q u ire d by th e t r a d e served re g u la rly by acid steel m ak ers. T h ere is a p referen ce fo r m ost classes o f w ork m a d e fro m e ith e r acid o r basic steel m elted by an y process, for physical p ro p e rtie s t h a t ju s tif y a carb o n co n ­ te n t close to 0.25 p e r cen t. H ow ever, th e ra n g e u p w ard for special acid o p e n -h e a rth c a s tin g s is considerable, re a c h in g a t tim e s 1.50 p e r c e n t., as in th e case of roll steel. T he m an g an e se c o n te n t will p robably a v erag e 0.G5 p e r c e n t., o r slig h tly below t h a t ty p ic a l of basic p ra c tic e . T he p e r­

cen ta g e o'f silicon in th e acid steel is o fte n a tr ifle lower th a n t h a t g en erally re g a rd e d as d e sira b le fo r th e basic o p e n -h e a rth m e ta l w hich ju s tifie s e x tr a sa fe g u a rd s fo r d e o x id a tio n , a n d is n o t f a r fro m 0.25 p e r c e n t. T he p e rc e n ta g e o f s u lp h u r in acid o p e n -h e a rth steel is g en erally betw een 0.035 a n d 0.040 p e r c e n t., w hile th e p e rc e n ta g e o f phos­

p ho ru s av erag es a b o u t 0.045 p e r c en t. A ll of th ese ty p ical p e rcen tag es r e la te to th e g e n e ra l r u n of work p ro d u ced in th e acid o p e n -h e a rth fo u n d rie s, an d do n o t o b ta in in th e cases of sp ecial m e ta l m ade in considerable to n n a g e s by some such p la n ts . Because of th e n a tu r e of th e d em an d serv ed by acid o p e n -h e a rth fo u n d ries, th e r e is m o re alloy steel produced in them th a n in basic open h e a rth s . C om binations c o n ta in in g v ario u s p e rc e n ta g e s of nickel, chrom ium , v a n a d iu m , m olybdenum an d m anganese a re q u ite comm on.

T he u su a l tim e for m ak in g an acid o p e n -h e a rth h e a t in th e A m erican steel fo u n d ry is p ro b ab ly five a n d one-half h o u rs when some k in d of a c h a r g ­ ing m achine is used, and ab o u t seven h o u rs w hen th e ch arg e is in tro d u ced w ith o u t m ech an ical m eans.

P ro b ab ly n a tu r a l gas is th e fa s te s t m e ltin g fu e l, o th e r co n d itio n s being equal. C e rta in ly p ro d u c e r- gas is slower th a n fuel-oil, which is now th e m ost widely used fo u n d ry o p en -h e a rth fuel. T he co n ­ sum ption of fuel-oil p e r ton ch a rg e d g en e ra lly

ran g es betw een 45 an d 55 gallons, according to th e ty p e of fu rn a c e , in u n its of o rd in a ry ca p a c ity (from 15 to 25 to n s).

METALLURGICAL CONSIDERATIONS REGARDING