OIL SAND CORES AND BINDERS

By Prof. A. Campion, F.I.C., and J. McEachen.

The use of oil a n d sim ila r b in d ers, alth o u g h of co m p arativ ely re c e n t in tro d u c tio n , is now th e ru le r a t h e r th a n th e exception, an d th e la rg e n um ber of com pounds o n th e m a r k e t is a n in d ic a tio n of th e m a g n itu d e of th e dem and fo r such h in d ers for d ry -san d cor os

I t m ay seem to some t h a t an apology is neces­

sa ry fo r d ealin g w ith th e su b ject a t th is d ate, before th e p re m ie r g a th e r in g of fo u n d ry m en in B rita in , b u t th e a u th o rs have fo r some consider­

able tim e been in v e s tig a tin g th e p ro p e rtie s o f a n u m b er of b in d ers u n d e r s ta n d a r d conditions, and have c a rrie d o u t a sy stem atic series of te s ts in th e la b o ra to ry an d th e fo u n d ry , an d th e y th o u g h t t h a t th e re su lts m ig h t be of in te re s t to fo u n d ry m en in g en eral, a n d p e rh a p s offer some suggestions fo r th e se ttin g u p of a s ta n d a rd o r s ta n d a rd s fo r core binders fo r d iffe re n t classes of w ork. I t c e rta in ly ap p e a rs desirable, in view of th e g r e a t v a ria tio n s found in th e p ro p e rtie s an d b eh a v io u r of th e m uch- ad v ertise d b in d ers, t h a t some m eans of com parison should become available.

The a u th o r s ’ ex p erien ce h as been t h a t m an y of th e m a te ria ls on th e m a rk e t show a m ark ed w a n t of u n ifo rm ity in consecutive c o n sig n m e n ts; m uch annoyance an d m any fa ilu re s h av e arise n from th is cause.

The sands best su ite d for use w ith m ost of th e m odern b in d ers a re them selves b o u d less; t h a t is, th e y a re fre e from clay o r, a t an y r a te , co n tain it in only very sm all a m o u n t. S ea sand is u sually recom m ended, b u t a clean riv e r san d answ ers equally well.

River Sand used as Basis.

The exp erim en ts to be described h av e all been c a rrie d o u t w ith a riv e r san d , as in th e fo u n d ry

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w ith w hich th e a u th o rs a re connected t h a t is th e only san d used in core m ak in g , a n d i t h a s been fo u n d to m eet all re q u ire m e n ts.

Jn th e p re p a r a tio n of th e core m ix tu r e s th e sand is first rid d led to rem ove la rg e p a rtic le s, pebbles, etc ., an d d ried . I t is th e n m ixed w ith th e b in d e r, m illed in a p an m ill fo r a d efin ite tim e, a n d finally passed to th e sand m ix er.

Sellers’ Instructions Defective.

T h e a u th o rs stro n g ly ad v o cate th e com plete d ry ­ ing of th e san d , as i t a d m its of a s ta n d a r d bond berng o b ta in e d by th e a d d itio n of a c o n s ta n t q u a n tity of w ater. I t is only in th is w ay t h a t uniform re su lts can be o b tain ed . T h ere is o ften considerable difficulty in o b ta in in g re g u la r u n ifo rm resu lts w ith some of th e com m ercial core b in d e rs on account of th e v ag u e in s tru c tio n s fo r use issued by th e su p p liers. F o r in sta n c e , t h e d ire c tio n s sen t o u t w ith one w ell-know n b ra n d s a y : “ I t is used d ilu te d in w a te r before b ein g m ix ed w ith th e sand, in p ro p o rtio n of one p a r t to th r e e o r fo u r of w a te r, 01 even up to six of w a te r w hen used w ith c o m p arativ ely d ry s a n d .” A n o th e r sa y s :

“ To one b u c k e t of m oistened sa n d ad d th re e - q u a rte rs to one p i n t .”

In th e first case, th e m ax im u m d ilu tio n is given when u sin g th e san d “ com paratively d r y ,” th u s in fe rrin g t h a t a c e rta in q u a n tity o f w a te r is neces­

sa ry ; b u t th e question is, how m uch w a te r, a n d w h a t a m o u n t of w a te r should be in th e san d w hen th e low er d ilu tio n is advised?

I n th e second case, th e use of m o isten ed sa n d is advised, b u t h e re a g a in o n e asks how m uch m ois­

tu r e should bo p re s e n t? I f th e sellers, as th e p a rtie s m ost in te re ste d , c a n n o t o r do n o t th in k i t desirab le to give m ore e x p lic it d irectio n s, how can th e av erag e fo u n d ry m a n be ex pected to o b ta in th e b est possible re su lts, unless he a d o p ts som e sy ste m a tic form o f te s tin g ?

I t w ould be v ery m uch m ore u sefu l to th e av erag e m oulder to h av e s ta te d th e p ro p e r q u a n tity of w a te r to be ad d ed to th e d ry san d , as he could easily m ak e th e a d d itio n an d o b ta in c o n s ta n t resu lts, o th erw ise he w ould guess a t th e q u a n tity , an d p ro b a b h m ak e several m ix in g s b efo re o b ta in ­ ing th e core Sand of th e r ig h t s tr e n g th a n d con­

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sistency for his p a r tic u la r re q u ire m e n ts, an d th e n t h a t would only hold good fo r th e p a r tic u la r b a tc h , an d in all p ro b a b ility on a n o th e r day th e san d would v a ry in m o istu re c o n te n t according to clim atic conditions, an d a re p e titio n of th e p ro ­ cess of guessing an d tr ia l w ould be necessary.

T he a lte rn a tiv e would be to d e te rm in e th e m ois­

t u r e in th e san d an d m easu re th e a m o u n t of w a te r a d d ed to th e m ix tu r e w h ich-gave th e b est results, an d use t h a t as a s ta n d a rd . I n p re p a r in g f u r th e r batch es i t w ould be necesary to r e p e a t th e mois­

tu r e d e te rm in a tio n a n d to c a lc u la te th e a m o u n t of w a te r re q u ire d to b rin g i t u p to th e sta n d a rd , fa c ilitie s fo r w hich a re n o t, u n fo r tu n a te ly , p re ­ sen tly av ailab le in all fo u n d rie s, a n d , even if th e y w ere, i t w ould occasion delay.

T h ere is a n o th e r g ro u n d of o b jectio n to such em p irical m ethods, an d t h a t is th e final re s u lt depends u p o n th e p e rs o n a lity of th e m oulder, core m a k e r o r san d m ix er, an d m ay v a ry w ith in very wide lim its , n o t only betw een d iffe re n t m en, b u t even in d ifferen t m ixings by th e sam e m an.

Valuation of a Core Mixture.

T he v alu e of a core m ix tu re depends u pon a n u m b er of facto rs, of w hich th e follow ing m ay be m e n tio n e d :— (1) T he cost of th e b in d in g a g e n t;

(2) th e fa c ility w ith w hich th e b in d e r can m ix w ith th e sand a n d p ro d u ce a th in c o atin g o v er each g r a i n ; (3) th e s tre n g th a n d ease w ith w hich th e m ix tu re can be h a n d le d in th e g reen s t a te ; (4) th e n u m b er of cores w hich can be m ade in a given tim e ; (5) th e m ethod a n d cost of d ry in g th e cores;

(6) th e v e n t a re a in th e finished c o re s ; (7) th e resistan ce of th e cores to m o is tu re ; (8) c h a ra c te r of th e su rfa c e of th e core w hich comes in c o n ta c t w ith th e m e t a l; (9) th e s tr e n g th of th e dried c o re ; (10) th e c h a ra c te r of th e h in d e r as re g a rd s th e fum es an d gases w hich it m ay give off d u rin g d ry in g an d when in c o n ta c t w ith m olten m e t a l ; (11) th e read in ess w ith w hich th e b u r n t core can he rem oved from th e casting.

Cost cf Core Binders.

As re g a rd s th e cost of th e b in d e r, th is depends not only upon th e a c tu a l price p e r cw t., b u t also upon th e a m o u n t of d ilu tio n i t can s ta n d , an d th e

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le n g th of tim e tile m ix tu r e r e ta in s its b in d in g p ro p e rtie s a f t e r m ixing. T he re a d in e ss a n d com­

p leteness w ith w hich i t m ixes w ith th e sa n d an d coats th e in d iv id u a l g ra in s is im p o rta n t, as upon it depends to a v ery la rg e e x te n t th e s tr e n g th of th e m ix tu r e b o th g reen an d d ry .

The s tre n g th of th e g reen m ix tu r e as i t d e te r­

m ines th e n u m b er of iro n s o r w ires a n d th e a m o u n t i f ram m in g necessary, especially in cores o f com­

p lic a te d shape or long sp an , a n d th o se w hich m u s t sta n d a considerable h e ig h t above th e p la te . I t is also an im p o rta n t fa c to r in d e te rm in in g th e n u m ­ b er of cores w hich can be m ad e in a g iv en tim e . The g re a te r th e g reen s tre n g th , th e e a sie r an d qu ick er can th e cores be m ade.

The a c tu a l o u tp u t of cores will, of course, d ep en d upon th e size, sh ap e an d n u m b er of irons necessary to en su re sufficient s tr e n g th fo r h a n d lin g in th e green sta te .

The m ix tu re s w hich h av e been tr ie d , th e a u th o rs place in th e follow ing o rd e r of m e r i t ; th e n u m b ers correspond to th o se in T able I . —

4, 5, 12, 6, 8, 9, 10, 7, 1, 2, 3, 11.

O il cores seldom stic k to th e box if p ro p e rly p re ­ p ared , a lth o u g h some m ix tu re s w hich c o n ta in gum s a n d sim ila r m a te ria ls, o r th o s e o f h ig h viscosity, h ave such a te n d en c y . N o. 11 was p a rtic u la rly bad in th is resp ect.

The m ethod of d ry in g th e cores u su a lly d epends upon th e ty p e of oven w ith w hich th e shop h a p p e n s to be equ ip p ed , b u t w h e re v e r possible ovens h e a te d by gas or h o t a ir are to be p re f e rre d ; th e y are n o t only clean er, b u t allow of a n e x a c t a d ju s t­

m e n t of te m p e ra tu re , a n d th is is a v e ry im p o r ta n t p o in t, as m any core m ix tu re s will o n ly give s a tis ­ fa c to ry re s u lts betw een som ew hat n a rro w lim its of te m p e ra tu re . T he b o n d in g by oil is d e p e n d e n t n o t on te m p e ra tu re alone, b u t also u pon o x id a tio n , ip th e sam e w ay as p a in t d ries an d h a rd e n s by o x id atio n of th e o i l ; th is m eans t h a t a c u r r e n t of a ir m u st pass th r o u g h th e oven in o rd e r to su p p ly th e a m o u n t of oxygen n ecessary fo r th e o x id a tio n of th e oil.

Drying Temperatures.

I t is fre q u e n tly s ta te d t h a t 450 to 500 deg. F . (230 to 260 deg. C.) is th e co rre c t te m p e r a tu r e for

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th e d ry in g of oil-sand cores, b u t th e a u th o rs, a fte r m any tr ia ls , have fo u n d t h a t b e tte r re s u lts are obtain ed if th e te m p e ra tu re is k e p t below 400 deg.

F . (205 deg. C.) an d in m ost cases 300 to 350 deg.

F . (150 to 175 deg. C.) gives th e best resu lts. The le n g th of tim e a t w hich th e cores should be m a in ­ ta in e d a t th e desired h e a t depends upon th e size of th e core, b u t in g en eral i t is p re fe ra b le to allow a m ore prolonged h e a tin g a t th e low er te m p e ra tu re th a n a s h o rte r tim e a t th e h ig h e r lim it. The a u th o r s ’ ex p erien ce h as been t h a t m o st of th e m a te ria ls a p p e a r to give w eaker an d less sa tis­

facto ry cores w hen b ak ed a t te m p e ra tu re s above 350 deg. F . (175 deg. C.), w hilst those w hich do n o t lose s tre n g th become less perm eable to gases ow ing to a deposition of fine m a te ria l in th e pores, th u s spoiling th e v e n tin g p ro p e rtie s.

Venting Properties.

I n th e case of sm all cores i t is seldom necessary to p u t in v en ts as m ost oil b in d ers give cores which are self-v en tin g , w h ilst in th e case of com plicated an d la rg e r cores th e n u m b e r an d size of v en ts re q u ire d is considerably less t h a n w ith o th e r b inders, due larg ely to th e u se of coarser sand which is p ra c tic a lly free from clay an d silt, and th e b u rn in g aw ay of th e b in d e r d u rin g c a stin g . The d e sid e ra tu m is to p roduce a core h a v in g th e la rg e st possible n a tu r a l v e n t a rea, an d th is is d ep en d en t upon th e size an d sh ap e of th e san d g ra in s, th e n a tu r e of th e bo n d in g m a te ria l used an d th e e x te n t to which it fills u p th e in tersp aces.

The v e n t pores m u st be sufficiently fine to p re ­ v e n t th e in g ress of m etal, and g re a te r v e n tin g efficiency is o b ta in e d from a larg e n u m b er of sm all pores th a n from a sm aller n um ber of larg e ones, alth o u g h th e to ta l a re a be th e same.

Resistance to Moisture.

The resistan ce of th e cores to m o istu re is a p o in t of g r e a t im p o rtan ce in re g a rd to th e le n g th of tim e t h a t th e cores m ay be le f t in th e mould before castin g , a n d in connection w ith th e ir sto rag e B inders c o n ta in in g linseed or sim ila r oils of a d ry in g n a tu r e as an e ssen tial in g re d ie n t re s is t m o istu re to such an e x te n t t h a t th e boxes m ay be closed a long tim e before c a stin g w ith o u t fe a r of

o

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ill effects, an d m ay be p re p a r e d a n d sto re d a long tim e before use. Cores p re p a r e d w ith b in d ers 4 an d 5 a re e x cep tio n ally r e s is ta n t. C ores m ade

a b o u t a y e a r ago an d le ft ly in g a b o u t w ith o u t an y so rt of p ro te c tio n a re as good as w hen first m ade.

No. 1, w hich is linseed oil alone, is, o f course, also q u ite safe, p rovided th e b a k in g is done w ith p le n ty of a ir c u rr e n t, Nos. 6 a n d 9 a re p r e t t y good, Nos. 7 and 8 are inclined to d e te r io r a te a n d lose s tre n g th r a th e r quickly, w h ilst No. 3 w ill n o t keep m ore th a n a few h o u rs unless in a h o t cham ber.

Skin on Castings.

As re g a rd s th e c h a ra c te r of th e su rfa c e p re s e n te d to th e m etal an d th e re s u ltin g sk in on th e castin g s, th e r e has to be considered th e p o ro sity of th e core and its a b ility to pass th e gases a n d a ir d isplaced d u rin g p o u rin g , an d also th e ease w ith w hich th e b u r n t core leaves th e c a stin g . T he g ra d e of th e sand is an im p o r ta n t fa c to r in se c u rin g a close un ifo rm te x t u r e w ith fine pores. T h e cores of w hich te s ts a re g iv en h a v e all been p re p a r e d fro m sand of c o n sta n t g ra d e , an d an a v e ra g e o f g ra d in g analyses m ade d u rin g th e la s t 9 m o n th s is show n in A ppendix 1.

In some cases cores a re blackw ashed in o rd e r to im prove th e c a stin g skin an d m a k e t h e cores clean o u t m ore easily, b u t th e a u th o r s do n o t recom m end blackw ashing unless absolutely n e c e s s a ry ; p ro v id ed a su ita b le b in d e r a n d sa n d g ra d e a re u se d th e r e is no necessity to do so. Cores m ad e w ith N os. 4 a n d 5 b in d ers a re n o t blackw ashed an d p ro d u ce a v e ry fine skin on th e c astin g s a n d clean o u t exceedingly easily, b u t Nos. 3 an d 7 give cores w hich a re r a t h e r difficult to rem ove, a lth o u g h p ro d u c in g a good skin.

The s tre n g th of th e d rie d core is of th e g r e a te s t im p o rtan ce as affecting th e h a n d lin g a n d s e ttin g . This p ro p e rty h as h ith e rto been ju d g e d m erely by a p p e a ra n c e an d th e a m o u n t of h a n d lin g th e y w ill s ta n d w ith o u t b re a k a g e or p e rh a p s sc ra tc h in g w ith th e th u m b n a il; a n d com parison h a s been m erely q u a lita tiv e . The a u th o rs h a v e c a rrie d o u t a g r e a t n u m b er of te s ts of cores fo r tra n s v e rs e , te n s ile an d c ru sh in g s tre n g th , in o rd e r to t r y a n d a rr iv e a t re la tiv e v alu e of san d bo n d ed w ith d ifferen t m a te ria ls.

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