T h e second m eth o d of ex p ressin g th e fineness is by m ean s o f a figure, which m ay he called th e average fin en ess fig u re . T h is can he done in several ways. O ne, som etim es re f e rre d to as th e S c ra n to n m ethod, co n sists in m u ltip ly in g th e w eig h t of sa n d r e ta in e d on each sieve by th e m esh of th e n e x t c o arser sieve. T he sum of th ese p roduct^ is div id ed b y 100 a n d called th e a v e r
age fineness. T he o b jectio n to th is is t h a t sa n d s w hich differ m a rk ed ly in th e i r te x t u r e m ay give
Sp a c e d o n Lo g a r i t h m i c Co-o r d i n a t e s.
alm ost id e n tic a l fineness figures, as th e follow ing exam ples (T able I) ta k e n fro m a fo rth c o m in g P a p e r by M r. O. M. N e v in w ill show : —
T a b l e I .— Illustrating that similar fineness figures are given by totally different sands.
Mesh. No. 1. No. 2. No. 3.
6 0.0 0.10 1.10
12 . . .. 0.0 1.00 5.03
20 0.02 9.70 9.70
40 0.72 5.76 8.70
70 19.68 19.60 10.60
100 20.18 11.30 11.30
140 14.50 10.56 10.56
200 8.26 9.22 9.22
270 ... 9.46 13.50 13.50
270 (Pan) 11.40 11.00 12.01
Clay substance 16.70 9.14 9.14
Aver, fineness 98 98 98
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B e tte r re s u lts a re a p p a re n tly o b ta in e d if th e p e rc e n ta g e re ta in e d on each sieve a re divided by th e m esh size of t h a t sieve, a n d th e sum of th ese ta k e n , an d y e t th is second m ethod is n o t w ith o u t its objections. T he first one w orks b e st w ith coarse sa n d s a n d th e second w ith finer g rain ed ones.
O ne m ay, m oreover, question w h e th e r such an a v e ra g e fineness figure really shows as m uch as a curve, from w hich th e p e rcen tag e an d d is trib u tio n of th e d ifferen t sized g ra in s can be read a t a glance.
Fi g. 4 . — Cu m u l a t i v e Pe r c e n t a g e s w i t h Si e v e Op e n i n g s o n Lo g a r i t h m i c Co o r d i n a t e s.
M ost fo u n d ry m en , i t is th o u g h t, recognise th e v alue of a fineness te s t. T he te x tu r e of th e sand serves to in d ic a te th e v e n tin g q u a litie s of th e m a te ria l, as well as th e sm oothness of su rface finish w hich i t m ig h t produce, u n a id e d by any fa c in g m a te ria l, as well as th e ap p ro x im a te size of c a s tin g t h a t can be poured in it. I t is e x tre m e ly useful as one of th e te s ts to be applied in checking up new consignm ents of san d .
Grading Sands.
I n a re c e n t P a p e r before th e A m erican F o u n - d ry m e n ’s A ssociation, M r. C. M . iNevin has p re s en ted som e very su ggestive ideas on th e g ra d in g of sa n d s by m eans of th e fineness tests. H is views w orked o u t in connection w ith a stu d y of some 60 sam ples of A lbany sand. P lo ttin g all thoue of th e sam e p ro d u cers g ra d e on c o -o rd in ate p ap er, i t w as found t h a t th e y ag reed q u ite closely.
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T his p e rm itte d d ra w in g w h a t m ig h t be called an average curve. I f now o n e ith e r sid e of th is tw o o th e r cu rv es a re d raw n w hich in clu d e m ost of th e v a ria tio n s fro m th e a v erag e lin e, show n by th e san d s of t h a t g ra d e , a n d shade th e a re a betw een th ese tw o lines, i t gives w h a t N ev in suggests c allin g a n area curve. (F ig . 5, re p re
-Fig. 5 . — B y S h a d i n g t h e A r e a E n c l o s e d b y t h e D o t t e d L i n e s a n “ A r e a C u r v e ” f o r G r a d i n g S a n d s . A c t u a l l y i t i s No. 2 A l b a n y .
se n tin g th e a r e a cu rv e of No. 3, A lbany.) Such a re a cu rv es w ere c o n stru c te d fo r th e d ifferen t g ra d e s of A lbany san d . H a v in g th e n th e c u rv e p lo tte d , an y new sa n d fro m t h a t d is tr ic t c a n be fitte d in to its g ra d e . T his, of. course, re fe rs to te x tu re , an d n o t to an y o th e r p ro p e rtie s, a lth o u g h p e rm e a b ility is w ith in c e r ta in lim its m ore or less associated w ith te x tu re .
Now to ap p ly th e g ra d in g th e o ry a li tt le f u r th e r , le t it be supposed t h a t som e p ro d u c e r in a n o th e r te r r it o r y is sellin g a sa n d w hich he d esig n ates as No. 6 o r 3 F ., a n d y e t w hose fine
ness cu rv e fits nicely in th e a re a c u rv e of a N o. 1 A lbany. W hy should th is n o t be called a N o. 1 6and also? I n o th e r w ords, one m ig h t p ro b ab ly red u ce th ese d escrip tio n s to comm on te rm s, o r th e s a m e 1 lan g u ag e. T h e id e a seem s a tt r a c t iv e to m an y , a n d a su b -co m m ittee of th e A .F .A . has been re cen tly ap p o in te d to develop it , if pos
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sible. I f p ra c tic a b le , it is a ste p to w ard s th e developm ent of sa n d specifications, w hich m ay be given o u t by th e consum er to help th e producer to su p p ly him w ith w h a t he w ants.
Vibratory Tests for Fineness.
Every' in d u s try has its sh o rt-c u t m ethods for m a k in g c e rta in te s ts, and th e fo u n d ry in d u s try is no exception. In d eed , as m any know , a descrip
tio n of some was re c e n tly p re se n te d before th e F re n c h F o u n d ry m e n ’s Congress.* I n th e U n ited S ta te s some a tte n tio n has been a ttra c te d to w hat is know n as th e S m ith V ib ra to ry T est, an d , as some r a t h e r s tro n g claim s have been m ade fo r th is m ethod, i t m ay n o t be o u t of place to devote a few w ords to it.
B riefly s ta te d , a mass of sand an d w a te r are sh ak en th o ro u g h ly by h a n d in a te s t tu b e or b o ttle a b o u t 6 in. h ig h and 1 in. d iam eter. T he suspension is th e n placed on a v ib ra to r fo r half an h o u r, w hereupon th e g ra in s of differen t sizes se ttle to th e b o tto m of th e tu b e, th e coarsest on t h e b o tto m an d th e finest on th e top, p re s e n tin g a b e a u tifu l series of layers. T he thickness of th ese is m easu red by m eans of a scale, th u s o b ta in in g th e p e rc e n ta g e of th e several grades. The la y e r of finest m a te ria l is classed as bond. M r.1 S m ith h as so u g h t to show t h a t th is one sim ple t e s t m ay ta k e th e plaoe of all th e s ta n d a rd ones u sed in fo u n d ry co n tro l, b u t th is does n o t ap p e a r to be th e case, as th e follow ing com parisons ta k e n from a P a p e r by D ie te r t on fo u n d ry control will show.
‘'N e a r l y all sa n d showed a la rg e r a m o u n t of clay substance. A p a r t of th e bond m easured in th e v ib ra to ry te s t is p a n m a te ria l. T he p er
c e n ta g e o f bond as show n by v ib ra to ry te s t does n o t en ab le one to e s tim a te th e p e rm e a b ility or s tr e n g th of th e san d . The s ta n d a rd p erm eab ility an d s t r e n g th te s ts can be m ade mu oh quicker t h a n th e v ib ra to ry te s t .” W here th e sam e sand m ix tu r e is b e in g used from d a y to day, th e v ib r a to ry te s t will give a n ap p ro x im a te idea of w h e th e r i t is ru n n in g u n ifo rm o r not.
* P r o c éd é d ’B tu d e e x p é r im e n ta le d es S a b les d e F o n d erie, Ame C o ngres d e F o n d erie, P a ri» , N o v em b er, 1924.
Fineness and Permeability.
O bserv atio n s th u s f a r m ade -indicate, of pourse, t h a t a g e n e ra l re la tio n ex ists betw een te x t u r e an d p e rm e a b ility , b u t i t is o n ly a v ery g e n e ra l one. I f we could c a lc u la te th e p e rm e a b ility from th e fineness, i t w ould be very c o n v e n ie n t. T hus f a r no one h as su g g ested a • s a tis f a c to r y m eth o d , a n d i t seem s d o u b tfu l w h eth er i t can be done.
Bonding Strength.
This all m u st a d m it is a v ery im p o r ta n t p ro p e rty of m o u ld in g san d s, an d co n seq u en tly one fo r w hich th e r e should be a s a tis fa c to ry m ean s of m easu rem en t. A ny te s t devised to m easure th e bon d in g s tre n g th should be sim ple, ra p id , and reiquire on ly easily o p e ra te d an d ru g g ed a p p a ra tu s . I t is safe to assum e t h a t th e te s t fo r b o n d in g s tr e n g th an d t h a t fo r p e rm e a b ility , to be re f e rre d to la te r, h av e th u s f a r received m ore a tte n tio n a n d h av e h a d m ore lab o u r bestow ed u p o n th em th a n a n y o th e r la b o ra to ry in v e s tig a tio n m ethods.
I t is n o t th e w r ite r ’s in te n tio n a t th e p re s e n t to discuss th e n a tu r e of th e bond. I t s presence is acknow ledged, a n d t h a t i t plays a v ita l rôle in s tre n g th e n in g th e sand an d h o ld in g i t to g e th e r in th e m ould is a d m itte d , as well as a ss istin g i t to re s is t th e d iffe re n t forces w hich te n d to d is
r u p t i t before, an d even d u rin g th e process of filling th e m ould.
T h e re s till a p p e a rs to be som e d ifference of o p in io n as to w h a t forces a re o p e ra tiv e in d is
ru p tin g th e san d , t h a t is, w h e th e r th e y are ten sile, com pression, o r s h e a rin g forces, o r a co m b in atio n of th e se , w hich one of th e se th e bond te s t should m easu re, o r w h eth er th e y a re so re la te d to each o th e r t h a t an y form of t e s t w hich m easures th e s tre n g th of th e bond m ay be used.
T h ere a re in th e U n ite d S ta te s th r e e ty p e s of te s t w hich h a v e been recom m ended fo r d e te r
m in in g th e b o n d in g s tr e n g th of g reen san d s, viz. :
— (1) T he b a r te s t w hich h a s b een sta n d a rd is e d by th e A .F .A . ; (2) a com pression te s t, a n d (3) a te n sile te s t. T he la s t tw o are now u n d e r in v e s tig a tio n by th e su b -co m m ittee on te s ts, an d recom m enda
tio n s m ay, no doubt,, be ex pected in th e not- d is ta n t fu tu re .
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