T h is te s t involves co m p ac tin g th e g reen sand in a box m ould u n d e r specified conditions, then rem oving th e b a r fro m th e m ould an d d raw in g i t over th e edge of a p la te a t a given r a t e of speed. T he w eig h t of th e piece b re a k in g off v a rie s d ire c tly as th e s tre n g th of th e sand.* The b re a k in g o f th e b a r is d u e m ain ly to th e o p e ra tio n of forces of ten sio n , a n d w ith c a re i t is possible to g e t av erag e b reak s which do n o t v ary by m ore th a n 5 p e r c e n t, as specified in th e reco m m en d atio n s of th e sub-com m ittee. T he one p o in t to b e a r in m in d is t h a t th e size of th e piece w hich b reak s off of th e b a r depends p rim a rily (o th er th in g s equal) on th e s tre n g th of th e bond.
The te s t as a whole is sa tisfa c to ry , an d is being q u ite w idely used in d ifferen t fo u n d ries fo r con
tr o l w ork. The a p p a ra tu s req u ires m ore space th a n t h a t used fo r th e com pression or ten sile te s t, a n d w hen th e isand is too d ry th e re is considerable sh e a rin g in th e b a r, so t h a t th e tr u e s tre n g th is n o t o b ta in e d . I t m ig h t be said , however, th a t w hen th e san d g ets to t h a t co n d itio n i t is too dry to w ork in th e fo u n d ry .
Compression Test.
F o r th is purpose, th e san d is form ed in to a core, o b ta in e d by ra m m in g i t in a cylinder, broken in a s u ita b le m achine by com pression, th e re s u lts b ein g expressed in lbs. p e r sq. in ., or some o th er u n it. S ev eral ty p es of a p p a ra tu s a re now being tr ie d o u t in th e U n ite d S ta te s, a n d all seem capable of g iv in g good re su lts if p ro p erly m ade.
O ne p o in t to be considered is th e ra tio of d ia m e te r to h e ig h t of sa n d core te ste d , fo r cores of th e sam e sa n d in w hich th e r a tio of th ese tw o dim ensions v a ry do n o t alw ays give th e sam e compression s tr e n g th p e r sq u are inch.
A cy lin d er, 2 in. hig h an d 2 in. d ia ., yields a h ig h e r u n i t s tr e n g th th a n one w hich is I f in . high an d 1 | in . d ia ., th e com paction b ein g th e same.
F ro m th e v iew -point of m echanics of m a te ria ls, th e la t t e r m ay be m ore co rrectly p ro p o rtio n ed , b u t fro m th e s ta n d p o in t of p ra c tic a b ility th e fo rm er is
* T h e s tr e n g t h is re p r ese n te d b y th e w e ig h t o f th e p iec e b r e a k in g off. See A .F .A . p a m p h le t o n t e s t issu e d J u n e , 1934.
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ea sie r to m ake, because i t can be m oulded in th e ra m m e r used fo r th e p e rm e a b ility te s t, b u t even a f te r a s a tis fa c to ry com pression te s t h a s been m ade th e r e re m a in s some q u estio n as to w h e th e r i t is a n a p p ro p r ia te one fo r m e a s u rin g th e b o n d in g s tr e n g th of th e sa n d . T h ere seem s no d o u b t t h a t th e ch ief fa c to r w hich helps th e sa n d to re s is t a com pressive force is th e b ond s u r ro u n d in g th e g ra in s of sa n d , a n d hence i t is assum ed by some a t le a s t fo u n d ry m en a re re a lly m e a s u rin g th e b o n d in g s tre n g th .
T ests w hich h av e b een m ad e on th e sam e san d fo r com pression s tr e n g th , an d w ith th e A .F .A . b a r te s t, h av e in d ic a te d t h a t th e curves of th e tw o m ay r u n m ore o r less p a ra lle l, b u t t h a t w here b o th show a p eak the tw o peaks a re n o t alw ays in e x a c t a g reem en t. I n fa v o u r of th e com pression te s t is th e f a c t t h a t th e a p p a r a tu s re q u ire s li tt le space, a n d t h a t i t can be u sed on d r ie r san d s th a n th e b a r te s t can . W h e th e r i t is m ore d e lic a te th a n th e b a r te s t is a m a tte r of d isp u te .
Tensile Strength Test.
T his h as ap p ealed to some, p a r tly because i t was th o u g h t m ore tr u th f u l ly to m easu re th e ty p e of fa ilu re o cc u rrin g in a g reen sa n d m ould, b u t th e t e s t itse lf does n o t th u s f a r seem to h av e been developed so t h a t i t is cap ab le o f b e in g u sed as re a d ily a n d w ith as li tt le p ra c tic e as th e com pression or b a r te s t. M ost of th e e x p e rim e n ts m ade fo r te n s ile s tre n g th h av e involved s h a p in g th e sa n d in to a b r iq u e tte sim ila r to t h a t u sed fo r te s tin g cem en t. Such a b riq u e tte , if m ad e of m o u ld in g san d , h a s b u t little s tr e n g th a n d re q u ire s th e m ost c a re fu l h a n d lin g , a n d h as n o t fo u n d m uch fa v o u r. A m odification re c e n tly described by W olf a n d G rubb* consists in ra m m in g th e san d in a core in sid e of a b rass c y lin d er. T his cy lin d er is div id ed h o rizo n tally , th e u p p e r a n d low er halves b ein g c a re fu lly fitte d , an d k e p t clam ped to g e th e r w hile th e cy lin d er is b ein g ram m ed w ith san d . T he low er end is th e n fa s te n e d to a base, th e clam ps rem oved, a n d te n s io n ap p lied to th e u p p e r h a lf. The force re q u ire d to p u ll th e sa n d c y lin d e r a p a r t is th u s m easu red . T his a p p a r a tu s is ingenious, an d is claim ed to be d elicate, b u t i t is
* A m erica n F o u n d r y m e n ’s A ss o c ia tio n , P r e p r in t N o . 430.
n o t y e t foolproof, an d in u n tr a in e d h a n d s m ig h t give re su lts of d o u b tfu l value.
Comparisons.
W h e th e r or n o t th e b ar, com pression an d ten sile te s ts all m easure th e sam e stress or n o t, th e re seems no d o u b t t h a t th e y all d e te rm in e th e s tre n g th developed by bon d in g m a te ria l in th e san d , an d t h a t is one fa c to r re q u ire d , e ith e r in stu d y in g new san d s or in daily fo u n d ry control.
I t is also tr u e t h a t all th re e of these te s ts are now in d a ily use in th e U n ite d S ta te s fo r control w ork, b ein g used fo r te s tin g e ith e r single sands or m ix tu re s. The first has been sta n d a rd is e d , th e o th ers re m a in to be.
Permeability.
I n view of th e im p o rtan ce of th is p ro p e rty , it is n o t su rp ris in g to find t h a t m any have developed a p p a ra tu s fo r te s tin g it. T h a t a n u m b er of d iffe re n t ty p es of a p p a ra tu s have been tr ie d in b o th A m erica a n d E u ro p e has been well b ro u g h t o u t in a P a p e r by T. C. A dam s p re se n te d to th e A m erican F o u n d ry m e n ’s A ssociation a t its M ilw aukee convention.*
One im p o rta n t fe a tu re stressed in th is P a p e r is t h a t w h ilst all th e d iffe re n t kinds of a p p a ra tu s d e te rm in e th e ease w ith w hich a ir can be forced th ro u g h san d , th e p e rm e a b ility as d eterm in ed is ra re ly expressed in term s of some common u n it, so t h a t th e figures o b ta in e d w ith one a p p a ra tu s c a n n o t be checked w ith those of a n o th er.
A dam s p o in ts o u t t h a t th e p erm eab ility a p p a r a tu s all fa ll in one of tw o m ain groups, as fo llo w s:— (1) Those w hich d eterm in e w ith th e aid of a p e rm e a b ility fo rm u la th e p erm eab ility of th e sa n d in some d efin ite u n its (usually cen tim etre- g ra m m e -m in u te u n its ), a n d (2) those which give th e p e rm e a b ility in some very a r b itr a r y u n it which depends on th e c o n stru c tio n of th e a p p a ra tu s .
All re s u lts fro m any a p p a ra tu s of group (1) are com parable. Those o b ta in e d by a p p a ra tu s of g ro u p (2) a re only com p arab le w hen each a p p a r a tu s m ade a f t e r a given design is s tric tly s ta n d ard ised , otherw ise th e re su lts m ay n o t be com
p a re d except w ith o th e r resu lts o b tain ed u pon th e one in d iv id u a l a p p a ra tu s .
* I n press.
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The S ub-C om m ittee oh T ests of th e A m erican F o u n d ry m e n ’s A ssociation has sp e n t considerable tim e on th e problem of p e rm e a b ility , a n d n o t only w ere a n u m b er of e x p e rim e n ts m ade to clear u p d o u b tfu l p o in ts, b u t sev eral pieces of e x p e ri
m e n ta l a p p a ra tu s w ere c o n stru c te d . A m ong th e fa c to rs in flu en cin g p e rm e a b ility , w hich m u s t be ta k e n in to c o n sid e ra tio n in d ev isin g a te s t, are g ra in siz e ; a m o u n t an d n a tu r e of b o n d ; q u a n tity of m o istu re in th e s a n d ; d eg ree of c o m p a c tio n ; h e ig h t of sa n d colum n th ro u g h w hich th e a ir is passing, an d pressu re.
V a ria tio n in th ese fa c to rs b rin g s a b o u t v a r i a tio n in p e rm e a b ility . The r a t e of flow of a ir th ro u g h a san d is p ro p o rtio n a l to th e p ressu re c au sin g th is flow. I t is also p ro p o rtio n a l to th e a re a of th e c y lin d er, a n d in v ersely p ro p o rtio n a l to its le n g th . T h is m ay serve to e x p la in w hy th e T est C om m ittee recom m ended t h a t th e sa n d be ram m ed in a core of u n ifo rm d ia m e te r, h e ig h t an d com paction.
W ith such a s ta n d a r d core of sa n d th e p re ssu re re q u ire d to p ass th e a ir th ro u g h can he d e te rm in e d a n d th e tim e re q u ire d fo r a g iv en volum e of a ir to p e rm e a te th e sa n d n o te d . R esu lt« w hich a re c om parable w ith th o se o b ta in e d on o th e r a p p a ra tu s w here p re s su re a re th u s g iven, a n d tim e c a n he m easu red , p ro v id ed th e sa n d oore is p re p a re d in th e sam e m a n n e r.
T h e o rig in a l a p p a ra tu s recom m ended by th e c o m m ittee was esse n tia lly t h a t used a t th e B u re a u of S ta n d a rd s . T his, w hile a c c u ra te , w as n o t suffi
c ie n tly ru g g ed , com pact, o r r a p id fo r fo u n d ry use, p i d so' th e c o m m itte e , a f t e r tr y in g o u t sev eral d iffe re n t ty p es, finally evolved th e sm all p o rta b le one which it has been recom m ended an d described in th e special p a m p h le t a lre a d y re f e rre d to . I t is c o n stru c te d e n tire ly of brass, w ith th e excep tio n o.f th e tw o sh o rt legs o f th e m an o m eter tu b e . I t is also a c c u ra te w hen used as a s ta n d a rd a p p a ra tu s , an d th e special orifices fo r r a p id w ork add g re a tly to lits u tility . A lth o u g h th is a p p a r a tu s was recom m ended n o t o v e r e ig h t m o n th s ago, th e r e a re now betw een fifty an d six ty of th e m in use fo r fo u n d r y oontrol w o rk in th e U n ite d S ta te s .
T h ere m a y be o th e r ty p e s of p e rm e a b ility a p p a r a tu s devised, e ith e r in A m erica o<r E u ro p e,
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b u t th e w r ite r w ishes to u rg e t h a t th e y be con
s tru c te d an d m a n ip u la te d so t h a t th e y give com
p a ra b le re s u lts . (Some of those described in E u ro p e a n m ag az in es can be easily a d ju s te d to give th e sam e re s u lts as th e A .F .A . model.
Base Permeability.
T h is m ay be a new te r m to m any, and need e x p la n a tio n . I t has been fo u n d , fo r exam ple, t h a t a given san d w ith coarse g ra in , b u t a p p re c ia b le clay su b stan ce, m ay give a re la tiv e ly low -perm eahility w hen te s te d by itse lf. I f now th e clay su b stan ce is w ashed o u t of th e sand a n d th e d ry p e rm e a b ility of th e g ra in d eterm in ed alone, i t m ay be fo u n d to he considerable. T his is th e base p erm eab ility . As s ta te d by D ie te r t in a P a p e r previously re fe rre d to , “ The base p e rm e a b ility is of u tm o st im p o rtan ce, fo r i t com
p a re s th e p e rm e a b ility of all san d s u n d er lik e con.
d itio n s. Some high-clay sands are dense, due to th e a m o u n t of clay th e y co n tain . I f n a tu r a l p e rm e a b ility is th e only th in g considered, one w ould class th e se sands as closing-up sands for h eap -san d , w hile in re a lity th e y m ay h av e a ve<ry o pen g ra in -s tru c tu re , w hich would he shown in th e base p e rm e a b ility re a d in g . W hen th e clay- c o n te n t of th is san d is red u ced by m ix in g i t in to th e h e a p , its open g ra in -s tru c tu re would a c t as an o p en er. All new san d p laced in a h eap-sand will be b ro u g h t to som e p re d e te rm in e d olay-oontent by s a n d co n tro l. I n o rd e r to d e te rm in e w h a t th e v ario u s new san d s w ill do to a heap -san d th ey should h av e th e i r base p e rm e a b ility d e te rm in e d .”
Density of Sand.
I n an y te s t w here th e san d has to be com pacted i t is reoognised t h a t a v a ry in g d eg ree of com paction w ill ' affect th e results.
T hus, w ith a given san d an d a given m o istu re con
t e n t increased com paction w ill te n d to in crease th e s tr e n g th as m easu red by th e m ethods re fe rre d to above, an d decrease th e p erm eab ility . R ecogni
tio n of th is h a s been m ad e by th e sub-com m ittee, an d th e fo rce of com paction used in th e several te s ts is t h a t w hich give® a body h a v in g th e same deg ree of d e n s ity as th e av erag e m ould.
E x p e rim e n ts m a d e on d ifferen t sands w hen com
p a c te d in cylinders show t h a t u n ifo rm com paction
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is n o t o b ta in e d fro m th e to p to b o tto m o f th e core in all oases. T h u s, in th e p e rm e a b ility te s ts as recom m ended by th e A .F .A . th e core of san d m ade w ith th e ra m m e r is m a d e 2-in. h ig h , because it gives fa irly u n ifo rm co m p ac tio n th r o u g h o u t its le n g th . A core, say , 4-in. h ig h , if ra m m e d all a t once, iwould n o t show u n ifo rm com paction. To overcom e th is difficulty as m uch as possible, D ie te r t h as su g g ested th e use of “ double-end- ra m m in g ,” as i t is called. T h is is do n e by h a v in g a m ovable ra m m e r slid in g in to th e c y lin d e r from below. T o p r e v e n t th e cy lin d er from slid in g down over it , a hole is d rille d in th e ra m m e r f o r a p in . T his holds th e c y lin d e r in p lace u n ti l th e san d is p u t in i t . T h e u p p e r ra m m e r is th e n le t down in to th e u p p e r e n d of th e c y lin d e r, a n d th e p in is w ith d ra w n before th e s lid in g w eig h t on ro d of u p p e r ra m m e r is d ro p p ed . As a r e s u lt of th is e q u al ra m m in g fo rces a r e ap p lied to b o th en d s of th e sa n d specim en d u rin g th e ra m m in g o p e ra tio n , a n d m ore u n ifo rm com paction re s u lts .
Optimum Water Content.
I t is p ro b ab ly w idely reco g n ised by now t h a t th e p e rm e a b ility an d b o n d in g s tr e n g th v a ry w ith th e a m o u n t of m o istu re w hich t h e sa n d c o n ta in s, a n d t h a t th e q u a n tity o f m o is tu re w hich gives th e m axim um d ev elo p m en t fo r e ith e r t h e b o n d in g s tr e n g th o r p e rm e a b ility is called th e o p tim u m w a te r c o n te n t. T h e re fo re c u rv e s can be p lo tte d show ing th e p e rm e a b ility a n d b o n d in g s tr e n g th fo r d iffe re n t p e rcen tag es of m o istu re . I n all o f th e sa n d s firs t te s te d a t th e C o rn ell U n iv e rs ity san d la b o ra to ry i t w as n o ticed t h a t th e cu rv es fo r b o th p ro p e rtie s showed a w ell-developed p eak w ith in t h e m o is tu re r a n g e a t w hich th e sa n d could be w orked. As m o re a n d m o re sa n d s w ere te s te d , how ever, i t w as' fo u n d t h a t th e r e seem ed to be m a n y ex cep tio n s to th is.
F ig . 6 shows t h e p e rm e a b ility a n d bon d in g s tr e n g th curves of over 200 sa n d s te s te d w ith in th e m o istu re r a n g e a t w hich th e y w ere w orkable.
T hese h av e been d iv id ed in to th r e e classes, of w hich th e u p p e r p a ir of curves in each case m ay he ta k e n as t h e t y p e : —
I n Class I th e peaks of th e cu rv es a g re e ; in Olaes I I th e p e rm e a b ility p eak P oocurs a t a lower
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m o istu re c o n te n t th a n t h a t of th e bond te s t c u rv e B ; an d in C lass I I I th e p o sitio n of th e p e a k s is reversed. I t w ill be observed t h a t in sev eral oases no p eak is show n, due probably to th e f a c t t h a t i t is developed w hen th e san d is too w e t o r to o d ry to be w orkable. The reason fo r th is is ev id e n tly to be so u g h t fo r in th e q u a n tity an d n a tu r e of th e clay su b stan ce p re s e n t, a n d has been discussed a t some le n g th in a P a p e r on “ The