Size saperation introduction

Size saperation introduction

1. Size Se p aration L a r ge pie c es o f mat e r i al a r e usu a l l y e s timat e d visuall y , diff i cult i es aris i ng o n ly i n the e s t imation of p o w der s . siz e separ at i on i s a uni t op er at i on t h a t invol v e s t h e separa t i on of m i xt u r e of v eri ous siz e of par ti cle s into t w o or mo r e por ti on b y m eans of screenin g sur fa ce . a ls o know n as sie v ing , si ft ing , cl ass i fy in g or screening. Standa r ds fo r P o wders Standards f or p o w ders for pharmaceu t ic a l p urposes a r e l a id d o wn p rin c ipally i n the Indi an Pharmacopoe i a w h ich sta t es, that the deg r e e of coarseness or f i neness of a powder is diff e r en t iated and exp r essed b y t he si z e o f t he m e sh of the sieve th r ough w h ich the p o w d e r is able to pass.

2. Size Sep a r a tion T h e I P spec i fies f i v e g rades o f p o w d er and t he n u mber o f the si e ve th r ough w hich all the part i cles must pass. Grade of po w der Sieve th r ough w hich all part i cles must pass Coarse 10 Mode r ately coa r se 22 Modera t ely f ine 44 Fine 85 V ery fine 120

3. T h e I P specifies a s ec o nd, small e r si z e of si e ve for the c oarser p o w d ers b ut sta t es the not mo r e than 40 p er cent sha l l pass th r oug h . T h e r elev a nt grades of p o w d er and si e ve number a r e sh o wn in the tabl e : G r a d e of p o wder Sieve th r o u gh which all p a rticles must p a ss Sieve th r o u gh which n o t mo r e th a n 4 per cent of particles p a ss C o arse 10 44 Modera t ely coarse 22 60 Modera t ely f i ne 44 85 Fine 85 Not spec i f i ed V ery f i ne 120 Not spec i f i ed

4. Thus, the f ull defin i t i on of C oarse Pow d er is that : It is powder a l l the part i cles of which pass throu g h a No. 10 s i eve and not more than 40 percent through a No. 44 s i eve, th i s is usua l ly referred to as a 10 / 44 powder. O t her grades are expre s sed in a si m i l ar way.

5. T h e Indi an Pharmacopoe i a makes t w o sta t em e nts w i t h r e g ard to these `o f f i cial' grades of po w ders in practic e : It is r equi r ed that, when a p o w d e r is desc r ibed b y a numbe r , all part i cles must pass th r ough the spec i f i ed si e v e . When a ve g etab l e drug is being g r ound a n d si f ted, none must b e r ejec t ed. T h e r eason for this w i ll b e ap p a r ent if the charac t er o f a vege t a b le drug is compa r ed w i t h a chemic a l substanc e . T h e la t ter is a homogeneous ma t eri a l s o that, if a cert a in quanti t y , o f a powd e r is r equi r e d, a n excess may b e g r ou n d, a su f fic i ent amount of t h e desi r ed si z e range obtained b y si e v ing, and the oversi z e part i cles ( k no w n as ta i l i ngs) may b e discarde d . •

6. A veget a b l e dru g , h ow e ver, con s is t s o f a v a riety of ti s sues o f di f feren t degree s o f har dn es s , s o t h at s o fte r tissue s w il l b e grou nd f i r st and t a i l in g s o b t a ined b y si f t ing wil l c o n t ain a h i gher prop or ti o n o f th e harder ti s sues. In many ca s es, constit u e nts are not d i stribu t ed uniformly t h ro u gh v e g e t a ble tissue s ; fo r ex a mple, in d i gi t al i s th e g l yc o s i d e s are c o nc e n t ra t ed in t he mid-rib and v e in s . Hen c e, if t a ilings a re d i sca r ded whe n grinding and sift i ng th e drug , it is likel y tha t a h i gh prop o rtion o f t h e ac tive constit u e nts w il l b e lost.

7. In addi t io n to t he grades of p o w der spe c if i ed by t he B r it i sh Pharmaco p oei a , t he B r it i sh Pharmaceut i cal Cod ex det ails a f urther grade k n o w n as Ultr a -fi n e Po w de r . In t h is case, it is r equi r ed t hat t he ma x imum dimen sio n of at least 90 pe r c e nt of the p articl e s must be n ot g r eater t han 5 µm an d n o ne mu st be g r eater t han 50 µm. Det e rmina t io n of p a rticle si z e fo r t h is grade is car r ied ou t by a mic r o s cop i c meth o d.

8. Sieve s fo r test Br i t i sh Standar d . p u rposes a r e the s u bject o f a Mos t o f t he sieves used a re o f the wire mesh typ e , the numbe r o f the sieve ind i cati n g the numbe r of meshes i nc l ude d i n a length o f 25 . 4 mm ( 1 in c h) i n each direc t i o n paralle l t o th e w i re s . Si e v e s

9. I t s h o ul d be n ot e d t ha t i t i s t he Th u s, a No. 1 sie v e h as 10 m es h e s p e r inch in e a c h dir e cti o n, but i t will be realiz e d that i f th e re were 10 wi r e s t her e w o ul d b e 9 m e shes onl y . T h e si mp l e state m e n t of th e numb e r of m es h e s p er uni t le ngt h is no t s uffici e nt , h o we v er, as t h e s ize of th e partic l e that w i ll pa s s th e sie ve will d e p e n d on othe r fa c tor s , principall y th e diam e ter of th e wi r e numb e r of m e sh es that is s p e c ifi e d wi r es. and no t t h e n um b e r of

10. Effect of w i r e di a meter on sieve mesh si z e.

11. STAN D ARDS FO R SIE V ES according to B. P . I t i s re q u i red that wi r e- m e sh sie v e s shall be m a de fro m w i r e o f u niform , cir c ul ar cr o s s - s e ctio n and for e a ch sieve th e followin g particular s are stated: N u m b e r o f S i e v e Thi s is th e numbe r o f meshes in a length of 25 .4 m m (1 in .) , in e a ch dir e ction, paralle l to th e wi r es.

12. N o m i nal S i z e o f A p e r t u re ( h o l e ) Thi s is t he distanc e betwe e n the wires, so that i t r epr e sents the length o f the side o f the s q uare apertur e. Nomi n al D i a m et e r o f the Wire Thi s dimens i o n and the numbe r o f me shes f o rm the basic standar d s fo r the sieve. Th e wire diamete r ha s b e en selec t ed to giv e a sui t ab l e aperture size, but also t o hav e suf f i cient strength to avoid disto rti o n .

13. Ap p roxi m ate Screeni n g Are a . Th i s s t andard e xpr e sses the area o f the m e shes as a percent a g e of the t o tal area o f the sieve. It is governe d b y the size o f wire use d fo r any parti c ula r sie v e numbe r and is k e p t wit h in the range 3 5 to 4 per cent . Th i s give s sui t able strength to the sieve, but leaves ade quat e area o f meshes sin c e these are o b v i ou s ly the use f u l area o f the siev e .

14. A p e r ture T o l er a nce A v e r age Som e var i ation i n t h e apert u re size is unavoid a bl e and th i s variati on , express e d as a p e rcentage, is known as the aperture t o lerance average. Th e term tolera nc e is use d i n engineer ing p r act i c e to mean the l i mits wit h in whi c h a part i c u lar quanti t y o r dimensi o n ca n b e al l owe d to vary a nd st i ll b e ac c eptab l e fo r the purpos e fo r wh i c h i t is require d.

15. Fi n er wires are l i k e ly t o b e subject to a gr e ater proport i ona l variati o n i n diamete r than c o ars e. f i n e me s he s canno t b e woven with the s a me accuracy as c o arse meshe s. Hence , t h e apertu r e toleran c e ave r age i s smal l er fo r sieves o f 5 o r 10 mesh than is the cas e fo r 30 mesh.

16. PERFO R ATED PL A T E SIEVES Sieve s ma y also b e made b y drill ing h o les i n m etal plate , s o that t hi s type w i ll hav e c i rcu l ar apertures as agai n st the square a p e r tures o f the wire mesh siev e. In gene r al, these sieves a re use d i n the larger sizes and ca n b e m ade with gr e ater a c c urac y t han w i re - mesh sieves, as susceptible to di st ortion w ell as be i n g less i n us e. Th i s type is c o mmonly use d also as screens i n impact mi l l s .

17. Usuall y , the ho l es are spaced with their centers arr a nge d at the a pice s o f equilateral triangles, so that all the apertures are equidistant A Per f orat ed plat e s i eve.

18. Simil ar standar d s a re la i d dow n with the appr o priate equivalent specifications for nom i na l width o f the br i d g e (dim e ns io n A plat e th i cknes s a n d i n the Figure ) whi c h c ont rol the strength o f t h e sieve i n the same way as wire diamete r i n wire mesh sieves.

19. M ateri a l s U s e d f o r S i e v e s Th e wir e sho u ld be of u n i f o r m , circu l ar cros s -se ctio n . T h e mater i al sho u ld hav e s u it a bl e st r ength to avoid disto r ti o n B e re s ista n t t o c o r r o s i on by a n y s ubst a nces that may be sif t e d.

20. M E TALS I r on wire Adv a ntage che a p, Disa d va ntage • R u sti n g • I r on cont a m i nation o f prod u cts

21. M E TALS  Co a ted Iron ( c oatin g with galvanizi ng or tin n ing ) . Adv a ntage Increases the pro t e c ti o n ag ainst cor r osi o n I n crease s t h e stre n gth Disa d va ntage Coating afte r m a n u f a ctu r e l e ad to some variat ion i n the m e s h size .

22. M E TALS  Copp er Adv a ntage Avo i di n g the ri s k o f iron cont a m i nation D i sa d vantage A s a s o f t m e t a l, m e sh e s can be disto r te d e a sily .

23. M E TALS Copper A ll o ys ( bras s and ph o sphor -bro n ze) Advan t ages Rese m ble copp e r i n p o s s e s sin g goo d resistanc e to cor r osi o n T h e ir stre n gt h i s greate r so t h at le s s r i sk o f the m e she s disto r ti o n .

24. M E TALS Stain l es s Steel Advantages Good resi s t a nc e t o corr osion Adequat e st r e n g t h T h e m o s t sui t able f or pha r m ac e utic a l purpose s . Disa dvantages E x pensive

25. NO N - M E TALS Used whe n all ri sk o f m e tall i c cont a m i nation be avoided . Used fo r s ieves wit h fin e m e s h e s , s i nce non -me tal f i ber s are stro n g e r than a m e tal wi r e o f simi l ar t h ick n es s .

26. NO N - M E TALS Ma terials of na tura l or i gin ( hair an d sil k ) , are us e d bu t synt h etic fib e r s ( nylon an d teryl e n e ) are m o r e su it a ble Advan t ages o f synt h eti c fib e rs Hav e m o re stre n gth and resi st a nc e to c o rro si on. can be extruded in all diameter s , so be enabl i ng mad e. a wide vari e ty of s i eve s to

27. S i e ving M e th o ds Si e ves shou l d be u s e d an d st or e d with car e, s i nce a s i ev e i s of l i t tl e value i f t h e meshe s b e c om e damag e d or di s tor te d. With t h e exc e pt i on of the sho u ld us e of never s i ev e s for gran u l a tion, ma t er i al t h rough a s i ev e . be fo r c e d Par t icle s, i f sm all enough , wi l l pas s t h rough a s i ev e ea si l y i f i t i s shak e n , t app e d , or brushe d .

28. I. ME C H A NIC A L SIEVING M E THODS Princip l e: B a se d o n method s as : Agita tion Brush the sieve Use centrifuga l force

29. 1. Agitatio n Methods Si e ves ma y be agita ted i n a n u mb e r of diffe r en t way s: O s c il l a t ion ( m o ve bac k and forth) The si e ve i s mo u n ted i n a frame t h at o s c i l l a t in g. Advan t ages Si m pl e m et h od Di s adv a n t ages The materia l m ay ro l l on t h e surfac e o f t h e s i ev e , and fibrous mater i als tend to “ bal l ”.

30. Vi brat ion The m e sh is vibra ted at high s p e e d, often b y an e l e c trical d evi c e. Advan t ages The rapid vibration i s i mparted to t h e par t icle s on t h e s i eve and t h e part icle s are le s s l i k e ly to “blind” t h e m e sh.

31. 2. Brushin g Methods A brush can be u s e d t o m ove t h e part icle s o n t h e surfac e of t h e s i ev e an d t o k e ep t h e m e sh e s c l ea r. A s i ngl e brush acro s s t h e diamete r of an ord i nary c i rcula r s i e ve, r o tating a bou t t h e m i d- point , is effe c tiv e; In larg e - s c ale pr o duction a horizonta l cy l indri cal s i e ve is empl oyed, with a s pira l bru s h rot a ting on t h e l o ngitudina l a x is of t h e s i ev e .

32. 3 . Centrifuga l Methods Use a ver t ic al c yl i ndri c al s i ev e with a high speed roto r ins id e t h e c yl i nder , s o t h at part icle s are t h row n out w ards by c e n trifuga l forc e . The curr e nt of a i r cr e a ted by t h e m ove me n t he l p s s i ev i n g. Espe c ially i s us e fu l with very fin e powd e r s .

33. Industria l m ethods o f pa r t i c l e size separati o n based o n sedimentation o r o n elutr i ati o n . W et siev i n g is more eff i c i ent than the dry process, be c ause pa rt i c l es a re suspende d passin g easily t h rough t he r eadily and with l ess sieve bl ind i n g o f the meshes. II. WE T S I E VING ME TH O DS ( FLUI D C L A S SI F ICA T IO N )

34. A su s pe n sion o f the sol id s in a flu id , most c om m only wat er, is pla c ed in a tank and allowed to stand fo r a su i table tim e. Th e uppe r layer is then remov e d , givin g a s ingle separation, o r the su s pe n sion m a y be c ollect e d as a numb er o f fra c tions by ar r anging fo r the pum p in l et to rem a in j u st b e low the su rfa c e. Th e su s pe n sion pumpe d ou t will then c ontain successively c oarse r particles. SE D IMEN T A TION ME T HO D S 1. Sedimentation T ank

35. A d vant a ges Simpl e process D i s a dvant a ges • A bat c h proces s on l y It does no t giv e a c l ean spl i t o f pa rt i c l e sizes be c ause s om e sma l l pa rt i c l es wi l l b e near the b ot t om o f the tank at the b eginning o f the pr o ces s and so w i ll b e re move d with the c o arse pa rt i c l e s.

36. 2 . Conti n uou s Sed i me n t a t i on Tank C o ntinuou s sedim e ntati o n tank

37. Part i c l es e n t e r i n g t h e t a n k wi l l be ac t ed up o n by a fo r c e that ca n b e divide d in t o two components : Hori z o ntal componen t du e t o t h e flo w o f t h e f l ui d t h at car r i es the par t i cl e forward Ver t ical componen t du e t o g r avi t y, w hi c h cau s es t h e par t i cl e t o fal l t o wards the bot t o m o f the t a n k .

38. T h e latter will d e pe n d o n St o k es' law, s o that the veloci t y of fal l is pr o porti o na l t o t h e di a m eter. Th u s, particl e s will se t tle to th e fl o o r of t h e t a n k at a p o int that d e p e n d s on p a r t icle size, th e c oar s est partic l es b e ing n e a rest t o t h e i nle t a n d th e fi n est n e arest to th e outle t.

39. I n some t a n ks, par t i t i on s a r e a r r a nged en a bling par t i cul a r size fr a ct i o n s to o n t h e flo o r, b e col l ec t ed cont i n u o us l y. I n o t he r t a n k s, t h e f low i s a r r a nge d so t h at onl y coa r se par t i cl e s will se t t l e out , f i n e p a r t i cl e s be i ng car r i ed t hr o ug h t o the overfl o w an d col l ec t ed e l s e w her e by sed i m e nta t ion o r fi l t r a t io n .

40. Ad v antag e s • S i mple • Inex p ensive • Continuou s i n op e rat i on • Gives a c l ean se p arat i o n of par t i c l es in t o many size fract ions as required .

41. 3. Cyclon e Separator T h e cycl on e s eparat or c o nsis t s of a cyli n dr i c al ve s s el wi t h a c o nical b a se T h e r otator y f l ow wi t h in th e cyclo n e c a us e s t h e p art icle s t o be a c ted o n by cen t r ifuga l fo rce, s olids b ei n g t hro w n o u t to the walls, t h e n fall i n g t o t h e c o n ical b a se and ou t t hro u g h t h e s o l ids dis c harg e. Cyclone sep a rat o r

42. T h e sus p ens i on i s in t roduced tangential l y vel o city , so at fai rly high tha t a r o t ary movement tak e s the ves s el, and re move d fro m a at the t o p . plac e within the f l ui d is centra l out let

43. Th e sepa r a to r i s s t i ll a fo r m of sed i m e nta t i on , b u t wi t h c e nt r i fu g al for c e use d ins t ead o f the g r avi t a t ional force . H e nce , d epend i n g o n t h e f l ui d veloc i t y , the c y clon e c a n b e us ed t o sepa r a t e all par t i cl e s o r t o r e m o ve onl y c oar ser par t i cl e s a n d al l o w f i n e par t i cl e s t o be ca rr i e d th r oug h wi t h th e flu i d . C y clone s ca n be u sed wi t h l i quid m ost s u sp e ns i o n s o f so l i d s , b u t t he com m o n app l ica t ion i s wi t h su sp e nsi on s o f a sol i d i n a gas , usuall y ai r .

44. 4 . Mechan i ca l Air C lassifier M e chani ca l air separati o n methods us e sim i lar principle s to the cy c l o n e separ a t o r, but the air moveme n t i s o b t a ined b y m eans o f a rotat i n g dis c and vane s , and separation is improved b y the u s e o f stat ionar y vanes.

45. By c o ntr o l l i n g t h e se van e s and the s p e e d of r otatio n , i t is p o ssible to vary th e size at which separation o c c urs . T h e m e t h od i s u s e d i n c o njun ctio n and re t urn for furt h er s ize with mills to s e parate ove r si z e reductio n . particl e s

46. E L U TRI A TION M E TH O DS Elutri ati o n d e p e n d s o n t he move m ent of a fluid ag a in s t the di rectio n o f s e di m e nt ati o n o f the particle s . Fo r th e gr a vitational s y s t e m , t he apparatus c o n sists si mpl y of a vertical c olu mn w i th ne ar th e bottom a n in l et for th e su s p ensi o n , an o utlet at the base for c oa r s e partic le s, overf l ow ne ar th e t op and fine particle s . and an for f l u id Flu i d a n d fine p a rtic l es Suspens i on Co arse par t icles

47. O n e c o l u mn wi l l giv e a single s e paratio n into t wo fra c tions, but i t m u st be re m e m b er e d that this will n ot g i ve a clean c ut , s in c e there i s a velocity gradi e n t a c ross th e tube, resulti n g i n t h e s e p aration of particl e s of differ e n t si z es a c c ordi n g to t h e d i s t ance from th e wall . Elutri ati o n Flu i d a n d fine p a rtic l es Suspension Co arse p a r ticles

48. I f more t ha n o n e f raction i s re q uire d , a numb er of tub e s of increa s ing area of cr o s s -s e c tion can be c o n ne ct e d in series. With t h e s a m e overal l flo w - rate, th e v e l o ci t y will d e c r e a se i n su cce e d i n g t ube s a s the area of cross - sec t io n i ncre a s e s, g i vin g a numb er of fra c tion s . Mul ti -stage elutr i ator (1) to ( 4) a r e frac t ions of dec r eas i ng part i cle si z e

49. Advant a ges Th e proces s is c ontin u o us. Th e sepa r ation is quicke r than wi t h sed i mentation D isadva n tages T h e s u s p e n sion ha s to sometimes be undesi rabl e. be dil ute; w hi c h may

50. APPLIC A TIONS OF SEDIME N T A TION AN D ELUTR I A TION B o th metho d s ar e u s e d for si m i lar purp o se s, us u al ly foll o wi n g a size r ed u ction proc e s s , with the o bject o f s ep a rat i ng ov e rsize p a rt i cles , w h ich m a y b e r eturn e d f or further grin d in g , use d for o ther pur p os e s , o r d iscarded ac c ording to the circumstances .

51. W ith liquids ; t he te c hn i qu e s ar e a ppl i ca ble to inso l uble s olid s , s uch as ka olin or ch alk, w hich a r e oft e n s u b j ec t e d t o w e t grinding f ollo w e d by sedimentation or elutriation w ith w ate r . W ith ga s e s , the m eth o ds ar e ap plic a ble to f i ner solids t hat w ould se p arate t o o slo w ly i n li q uids, to w at er- so lu ble su b s t a nc e s , or where d r y proce ss i n g is requ i re d. T h us, a c y c l one or mechanical air separa t or is o f ten incor p orat e d in circ u i t w ith a ba l l mi l l or h am m er mi l l to se p arate and return ov e rsi z e particles.

52. S u spen d e d TRISO f ue l p a rticle s in the ho p pe r for se par a tion and individual transport

53. Cros s -sec t ion diagr a m of hopper sho w ing pl a cemen t of pneu m atic transf er line and selecte d sensor s for p a rticular TRISO f ue l a p plication