By C. C. BRISBOIS and A. E. C A R T W R IG H T (American Exchange Paper) T he energetic developm ent o f high-duty alloys
that has taken place during recent years, while being a tribute to the enterprise and ingenuity of the m etallurgist, has taxed considerably the resources of the foundrym an required to p ro duce castings em bodying the enhanced qualities implied by the results o f m etallurgical research.
T he foundry and m etallurgical technique re
quisite for the production o f sound, dense cast
ings in the m odern high-duty and alloyed irons, for exam ple, is m uch m ore exacting than that w hich was required in other days for the cast irons of the period. H igher pouring tem pera
tures are the general order, and dictate the use of m ore refractory m oulding sands. H igh liquid shrinkage and short freezing range o f the low- carbon high-strength grey irons, “ N i-Resist,”
“ N i-H ard ” and sim ilar alloys, dem and more generous feeding m easures than the grey-iron foundrym an was previously accustom ed to p ro vide.
A steadily increasing dem and for castings of these types o f alloys argues th at they are per
form ing satisfactory service. W hether m ethods o f producing them are universally such as to utilise to the fullest extent the m etallurgical im
provem ents th a t have been demonsitrated, is possibly debatable and a subject w orthy of co n sideration by those interested in their prom otion.
It is not sufficient that these m odern alloys should furnish some additional service value over that o f m aterial previously used; for true progress one m ust aim for the ultim ate properties pos
sible o f attainm ent from the alloy concerned.
T hat this attitude has been taken by pioneering producers of these alloys is certain; otherwise, regardless o f the im proved m etallurgical quali
ties and higher properties obtainable in test- bars, such m arked success, in com petition with other metals and m ethods o f fabrication, could not have so far been attained or m aintained.
It is recognised that discrepancy unavoidably exists between the m echanical properties o f sec
tions o f a casting and those obtained from a standard form o f test-bar, owing to the diverse structural characteristics, produced by differ
ences in cooling rates, occurring in the vary
ing designs o f castings. It is essential, however, that the foundrym an should take all precautions
against this discrepancy being widened by porous discontinuities produced by inadequate feeding In the authors’ experience, gating and feeding proportions m ay be such as to provide a
mini-F i g . 1.— B o t t o m P a r t s f o r t h e C a s t i n g s S h o w n i n F i g s . 3 a n d 4 .
m um or m axim um density in a casting, above the range where rejection, due to visible defects, occurs. M inute porosities resulting from m ini
m um feeding provision will usually be reflected in lowered strength and lessened resistance to wear, abrasion, cavitation and corrosion.
A num ber of variables are present when plan
ning the proportions and location o f gates and feeding heads for an unfam iliar design o f cast
ing. In foundries engaged in quantity repetition work, it is feasible to determ ine, on a trial basis,
the m ost effective an d econom ical m oulding extrem ely m iscellaneous jobbing foundry with w hich the authors are concerned. Experim ents alloys, including various tin bronzes, brasses, m anganese and alum inium bronzes, silicon bronze, nickel silvers, M onel, an d com m ercially pure nickel, as well as the alloyed irons m en
tioned above.
General Gating and Feeding Practice Consideration and transferring pouring directly into the riser, and (b) connecting the dow n-sprue w ith the m ethods used to increase feeding-head efficiency.
T he obvious m ethod o f dispensing w ith a separate in troductory gate and pouring directly and entirely through the feeding head is seldom
Existing References to Direct Pouring Methods D w yer1 illustrates and briefly describes a sys
tem o f direct pouring through a strainer-feed
ing head, attrib u tin g the original idea to an Italian foundry engineer, Brunelli. Ronceray*
likewise credits Brunelli w ith the initial recom the correct relative position fo r effective feed
ing. This process m ay be practicable under stand expected severe conditions. P ractical trials w ere m ade to determ ine the m ost efficient basic form of feeding heads to accentuate the expected advantages o f the m ethod o f direct head pouring.
C o-operative efforts o f the m etallurgist and practical foundrym an were, o f course, essential a t every stage of the experim ents. Critical com parative study of fractures and m etal
lurgical structures was a prim e m eans of evolving basic feeding-head designs. L aboratory and practical foundry tests of sands and bond
ing agents were o f im portance, as also were therm al tests indicating the relation between actual pouring tem peratures and the tem pera
ture of the m etal in the m ould at the end of pouring.
These data, considered along with freezing ranges of various alloys, indicated the im prove
m ents available by lowering the degree of super
heating of the m olten alloys necessary for
(2) A m oderate econom y in feeding m etal and gates, together w ith a large economy brought about by reduction in the num ber of defective castings.
(3) M uch lessened sensitivity to feeding head proportions fo r different casting designs and alloys o f different shrinkage charac
teristics; that is, the feeding head is generally of a size to com pensate for a range of shrinkage wider than that provided for by the m ore usual m ethods.
(4) G enerally lower requisite pouring tem peratures for all alloys, with corresponding less necessity for excessive superheating of the m olten alloy. T he last is an especially attractive feature from the m etallurgical
Fi g. 3.— Di e s Be f o r e Fe t t l i n g.
optim um results. Intelligent revision of m ould
ing technique to suit the conditions, economical planning o f existing equipm ent, and the addi
tion of a m inim um of new essentials, persever
ance in overcom ing various m inor obstacles, and, no t least, tact in obtaining the co-operation of the conservative m oulder in efficiently hand
ling the less usual m aterials and methods, were all m atters requiring careful attention.
Advantages Obtainable by Direct Riser Pouring
It was increasingly dem onstrated that, properly applied, the principle o f direct riser pouring was capable of providing the following advantages : —
(1) M uch enhanced effectiveness o f feeding by having the feeding head filled last with hottest m etal, and m aintenance of feeding head tem perature by virtue of the head being covered with a heated strainer core.
standpoint where those alloys m ost susceptible to oxidation or gas absorption beyond their melting point are concerned.
Design o f Direct-Pour Feeding Head The basic design of feeding head chosen was that o f a straight-sided, round-shouldered, short
necked bottle. The total height and diam eter are variable, according to the size of section to be fed and the alloy concerned. T he follow ing principles of proportion are adhered to as closely as possible: —
(1) The diam eter o f the base (neck) of the feeding head adjoining the casting should be not less than one-half the full diam eter o f the head.
(2) The full diam eter o f the feeding head should be continued dow nw ard to a point as near the casting as is consistent w ith m ain
taining a sufficient m ould strength a t the junction.
T he im portance o f an efficient feeding head pro p o rtio n and the general adaptability o f a few sizes and shapes were considered sufficient to w arra n t m aking and m aintaining a store o f p a t
terns. T he riser p attern decided upon is handed to the m oulder along w ith the casting pattern. This elim inates uncertainties due to any m isunderstanding on the m oulder’s p a rt as to the required feeding provision. Som e o f these p atterns are m ade o f w ood; others are cast hollow in scrap alum inium . P lain cylin
drical o r square extensions are provided fo r varying height, and a coreprint is provided for seating the strainer core used in all direct-pour heads. F o r heavy solid w ork having flat backs, such as die-blocks, the round bottle-shaped
bronzes, a n atu ral sand w ould be sufficiently resistant to the pouring conditions. A fairly open sand is desirable (preferably one w ith a grain fineness n um ber o f 80 to 120 an d with high perm eability, a sand corresponding to A .F .A . coarse N o. 3 o r fine N o. 4), and the m ould should be well treated with a graphite wash to obtain good surface quality. In personal practice, the au th o rs lean generally tow ard sand o f high perm eability rath e r than use o f a vent w ire on a less open sand.
Synthetic Sand
T he synthetic sand m ixture chosen fo r direct riser pouring consists o f a pure white silica sand bonded w ith 10 to 12 per cent, bentonite.
F i g . 4 .— F i n i s h e d D i e s M a d e o f N i c k e l - C h r o m i u m I r o n .
feeding head, unm odified in shape, is used.
V arying casting designs, position and shape of cores, reinforcing bars in flask equipm ent, etc., frequently m ake necessary m odification o f the actual shape o f feeding heads. T he p ro p o r
tional dim ensions are, however, adhered to as closely as possible.
M ost o f the earlier experim ents were carried o u t w ith dry-sand m oulding. This procedure was follow ed because the m ore expensive re
jections concerned this type of w ork; th a t is, fairly large castings of relatively heavy sections, an d also because ordinary green-sand m ould surfaces do no t satisfactorily resist the im pact o f m olten m etal falling from a height. I t was found desirable to use a synthetic sand fo r the higher m elting point alloys, such as nickel alloys and alloyed irons. T h e fac t th a t this sand is constantly available is the m ain reason that o ther alloys, perhaps n o t strictly requiring such a highly refractory sand, happen to have been cast in it. It is quite likely that, l o t ordinary
T he heap sand gradually has been built up over a period o f two years by p rep a ra tio n o f a facing sand including ab o u t 20 per cent, of new silica sand. W hen no increase in the quantity of heap sand is required, it is usual to prepare a facing sand from 100 per cent, heap sand, 1 per cent, bentonite being added.
Cereal Binders
T he addition o f 2 to 5 per cent, cereal binder is m ade to the facing sand. This com bats the tendency tow ards surface drying an d crum b
ling generally associated w ith synthetic sands.
T he cereal binder is very efficient in m aintain
ing plasticity w ithout leaving behind undesir
able fine m aterial o f bond destroying qualities w hen it burns out, a difficulty som etim es ex
perienced w hen using, fo r exam ple, coal dust.
Mechanical Analyses
T he sand, as will be seen from the m echanical analyses o f T able I, is very resistant to grain changes and to reduction to fine m aterial. Sand
losses are confined to average burning-out of bond and to relatively sm all am ounts o f sand adhering to castings going to the fettling shop.
The quantity of w ater used throughout is about 10 per cent. A typical analysis of new silica sand and, fo r com parison, analyses of facing sand and heap sand are given in T able I. The analyses of T able I are of new silica as re
ceived, and o f facing and backing sand after bonding m aterial had been w ashed out.
Working Characteristics
The sand m ixture is no t readily w orkable for hand ram m ing of moulds. All m oulds m ade of this sand are ram m ed with an air ram m er. The sand m ixture is rather sticky, and difficulty at first was experienced in w ithdraw ing the pattern, but this was overcom e by spraying the pattern with a light fuel-oil before the m ould was ramm ed.
■ Ta b l e I .— Com parison of M echanical A n alyses of N ew
S ilica , Facing and H eap Sands.
R etained on.
N ew silica, per cent.
Facing sand, per cent.
Heap sand, per cent.
Mesh.
N o. 6 N il N il N il
N o. 12 N il N il N il
No. 20 2 .7 2 .9 2 .6
N o. 30 2 1 .5 17 .6 14.1
No. 40 2 7 .6 2 1 .6 1 9 .4
No. 50 2 5 .6 14 .8 1 6 .5
N o. 70 14.1 1 1 .4 1 3 .2
N o. 100 6 .1 8 .4 1 0 .4
No. 140 1 .4 4 .5 3 .6
N o. 200 0 .3 3 .2 3 .4
N o. 270 0 .2 2 .2 2 .1
Pan 0 .5 3 .5 4 .3
N otw ithstanding the coarse grade of sand used, a very fine surface is obtained on cast
ings when the m ould surface is protected by a wash of the following m ixture applied by air-spray before the m oulds are dried : —
Plum bago ... 15 quarts.
G lutrine . . . ' ... 1 quart.
D iluted w ith w ater to 24 deg. Be.
Strainer cores perform the very im portant function o f providing clean m etal to the moulds and are used in the to p o f the feeding heads.
These cores are m ade of a strong oil-sand m ix
ture and in standard diam eters ranging from 2 to 10 in. They vary in thickness from \ to H in. as the diam eter o f the core increases.
The num ber and size of the holes in the strainer cores vary according to the job, generally from 4 to 12 holes o f 1 to Î in. diam eter being used. Except w hen it is required to avoid striking a centrally-located core, the gate holes are arranged near the centre o f the strainer
Fi g. 5 .— Co i l- Wi r e An n e a l in g Po t Sh o w i n g Ga t in g Ar r a n g e m e n t s.
be noted here that, owing to restrictions of space and sand handling and preparing equip
m ent, the am ount of bentonite used is rather larger than would be necessary w ithout these lim itations.
Figs. 1 to 13 will serve to give a fair idea of the m ethod of application of direct head pouring m ethods and to exemplify the variety of designs for which it has been found useful.
A brief description of each follow s: —
Fig. 1 illustrates the bottom parts of moulds for the dies of Figs. 3 and 4. T he vents appearing at one end of each m ould are n o t to be m istaken for ingates. Fig. 2 shows the
E core. Care is exercised in all cases to avoid metal striking directly on the protruding sand section at the riser-casting junction.
F o r the past two years, direct riser pouring has been successfully adapted to Sandslinger m oulding and m uch of the w ork previously made in dry sand has been transferred to the Sandslinger. The sand m ixture, both heap sand and facing sand, used for Sandslinger practice, is identical with that described fo r dry-sand m oulding, w ith the exception o f m oisture con
tent, which is controlled in this case between 4 and 6 per cent. A ll this w ork is skin-dried with a portable fuel-oil torch. It should
closed m oulds fo r the sam e dies w ith strainer cores in place, and Fig. 3 the dies before fettling.
Fig. 4 illustrates a group o f feeding head- poured dies of high-tensile nickel-chrom ium iron having a tensile strength o f 25 tons per sq. in. T he Brinell hardness num ber o f the 1.2-in. dia. transverse b ar was 278, while th a t o f the die sections varied only from 269 to 278 on any p art o f the 4- to 6-in. cross- section of these dies, indicating a very satis
factory density th ro u g h o u t the casting. Inci
dentally, the surface o f these dies was obtained suitable fo r easy file-finishing as-cast, dem on
strating the adequacy of m oulding technique and m aterials.
oil refinery castings in “ N i-Resist ” (austenitic nickel-copper-chrom ium cast iron); Fig. 12 a group of solid and cored bushings in M onel metal; and Fig. 13 a com m ercially-pure nickel pum p-casing, direct-head poured; the small im
peller at the left has conventional gating.
In utilising these m ethods of direct pouring into feeding heads over a four-year period, some lim itations in their applicability have, naturally, com e to light in various form s and degrees.
T he m ore im p o rtan t o f these lim itations are described and some notes of caution included, based on personal experiences.
A n attem pt was m ade to produce the M onel centrifuge casting illustrated in Figs. 14 to 17, by m eans o f a single direct-poured feeding head
Fi g. 6 .— Sl u d g e Pu m p Ca s t i n g s i n Ni- Ha r d.
Fig. 5 illustrates the m ethod used to produce a coil-wire annealing pot in a heat-resisting nickel-chrom ium cast iron. It is also typical of the procedure fo r m oderate wall-size bush
ings. Fig. 6 shows a group o f direct-head poured sludge pum p parts in N i-H ard (mar- tensitic white iron), and Fig. 7 a refrigeration pum p th a t had been a constant source of heavy loss due to leakers when gated by other methods. The internal design is com plicated with a b ru p t changes o f section. T he direct- p our heads adm it m etal dropping directly on the com plicated oil-sand core, which adequately resists this severity.
Fig. 8 is a tw o-ton bushing w ith 6-in. wall in high-tensile nickel-chrom ium iron using two bottle-design direct-pour heads. Steel ingot m oulds have been produced satisfactorily in rike m anner. Fig. 9 shows a valve section in high-tensile alloyed iron, and Fig. 10 large gears in high-tensile iron, using unm odified bottle heads for casting. Fig. 11 shows some
on the hub. T he casting was o f difficult design and dim ensions an d the result, by this m ethod, was serious cracking in one arm and outer section, caused by too long m aintenance o f high tem perature in the hub by the pouring head.
The authors were recom m ended, from an o u t
side source, to m ould the centrifuge as show n in Fig. 14, w ith the hub extension dow n in the drag and surrounded with external chills. Chills also w ere to be placed u nder the outside rim.
A separate gate entering the hub was to be used, the rem ains o f which are visible in the picture.
Between the arm s a loose m ixture o f sawdust, sand, and ashes was ram m ed and as soon as it was deem ed safe after pouring, the cope was lifted and the hub and arm s freed. H ow ever, the result was very sim ilar to th a t o f the first effort in regard to strain cracks.
Follow ing this experience, it was decided to adopt a rather radical procedure for a third trial.
It is thought th a t this procedure, in view o f the result obtained, m ay be o f interest an d assis
tance to others faced with a sim ilar problem . A skeleton insert o f the design shown at the bottom o f Fig. 15 was cast in Monel. The m ould for the m ain casting was designed with
against possible, though doubtless lessened, con
traction strains in the arms.
The casting so produced was apparently per
fectly sound and satisfactory. As will be seen,, the only points at which an exam ination of the effects of the inserts was possible were the sup
porting prints in the hub and on each arm.
Figs. 16 and 17 show this casting before clean
ing, and the protruding ends of the insert are visible. Each protrusion was examined m inutely; chipping, grinding, filing and subse
quent m achining failed to reveal the outline of the insert below the surface so treated.
T he use of internal chills has been criticised by some authorities; Batty,5 for example, refers to their being “ potentially dangerous as
iso-Fi g. 7 .— Re f r ig e r a t i o n Pu m p Ca s t in g Wi t h “ Bo t t l e ” Fe e d in g He a d s.
gating shown in the two upper sketches of Fig. 15. T he skeleton, after thorough cleaning by sand blasting, was placed in the m ould as indicated in the diagram , the extensions on the bottom and arm s of the insert being firmly bedded in the m ain sand mould.
The relative section sizes were such as to leave at least from ^ to 1 in. between the insert and every p art o f the adjacent m ould wall and core, with the exception of the supporting points. It was considered that the insert would so
func-Fi g. 8.— Tw o- To n Bu s h i n g Ma d e i n Ni- Cr Ca s t Ir o n Us i n g “ Bo t t l e ” Di r e c t- Po u r He a d s.
tion as to accelerate cooling in its locality, that it would either com pletely m elt into the mass o f molten M onel or, on the other hand, if it retained its form , would act as a reinforcem ent
Fi g. 9 .— Va l v e Se c t io n in Hi g h- Du t y Al l o y Ir o n.
lated foreign bodies in what should be a hom o
geneous structure.” T he authors do not agree wholeheartedly w ith this view, believing that, in com m on with m any other foundry p ro
geneous structure.” T he authors do not agree wholeheartedly w ith this view, believing that, in com m on with m any other foundry p ro