SIZE REDUCTION.pdf

PHARMACEUTICAL ENGINEERING

1. SIZEREDUCTION
MBS

2. Content
▶Sizereduction
▶Objectivesofsize reduction
▶Mechanismofsizereduction
▶Lawsgoverningofsizereduction
▶Hammermill
▶Ballmill
▶Edgerunnermill
▶End runnermill
▶Fluidenergy mill

3. Pharmaceuticalengineering
Itisconcernedwiththestudyofindustrial
pharmaceuticallyusefulproducts.
processinwhichrawmaterialarechangedinto
Sizereduction
Sizereductionisaprocessofreducinglargesolidunitmasses-vegetablesorchemicalsubstancesinto
smallunitmasses,coarseparticlesorfineparticles.Sizereductioniscommonlyemployedin
pharmaceuticalindustries.SizereductionprocessisalsoreferredtoasComminutionandGrinding.
WhentheparticlesizeofsolidsisreducedbymechanicalmeansitisknownasMilling.Thesizereduction
operationcanbedividedintotwomajorcategoriesdependingonwhetherthematerialisasolidora
liquid.Ifthematerialissolid,theprocessiscalledgrindingandcutting,ifitisliquid,emulsificationor
atomization.

4. Objectivesofsizereduction
▶Sizereductionleadstoincreaseofsurfacearea.
▶Pharmaceuticalcapsules,insufflations(i.e.powdersinhaleddirectlyintothelungs),
suppositoriesand ointmentsrequireparticlessizetobebelow60mmsize.
▶Toincrease the therapeuticeffectivenessofcertaindrugs byreducingtheparticlesize.
▶Sizereductionproducesparticlesinnarrowsizerange.Mixingofpowderswithnarrow
sizerangeiseasieranduniform .
▶Pharmaceuticalsuspensionsrequirefinerparticlesize.Itreduces rateofsedimentation.

5. Mechanismofsizereduction
▶Impact–thisinvolvehammerorbarathighspeed(hammermill).
▶Compression-particlecrushedb/wrollersbytheapplicationofforce(rollermill).
▶Cutting–thematerialcutbyasharp blade(cutter mill)
▶Attrition-arisingfromparticlesscrapingagainstoneanotherorrubbingaction(fluid
energymill).

6. Lawsgoverningsizereduction
▶Griffiththeory-The amountofforcetobeapplieddependsonthecracklength.
▶Kick'slaw-Workrequiredtoreducethesizeofagivenquantityofmaterialisconstant
forthesamereductionratioregardlessoftheoriginalsize.
▶Rittinger'slaw-Workeduse forparticulatesize reductionisdirectlyproportionaltothe
new surfaceproduced.
▶Bond'slaw-Workedusedtoreduceparticlesizeisproportionaltothesquarerootof
thediameteroftheparticleproduced.

7. FactorsaffectingSizeReduction
Selectionof mill-Itisrelatedto feed,milledproduct,safetyand economics
Factorsrelatedtonatureofrawmaterialsaffecting sizereduction
▶Hardness-Itiseasiertobreaksoftmaterialthanhardmaterials.Ex:Foriodinehammer
millisused.
▶Fibrous-Thesearetough innature.Asoft,tough materialhasmoredifficultythanahard,
brittlesubstance.Ex:Raowulfia,Ginger.Herecutterscanbeused.

8. ▶Elastic /Sticky-Becomesoftduringmilling.Ex:syntheticgums,waxes,resins.Low
melting substances should be chilled before milling. These are milled using hammer,
colloidorfluidenergymill.
▶Meltingpoint-Waxysubstances,fatsandoilsaresoftenedduringsizereductiondue
toheatgenerated.Thisisavoidedbycoolingthe millandthesubstance.
▶Hygroscopic-Certainsubstancesabsorbmoisturecontentrapidly.Thiswetmass
hampersthemillingprocess.Ex:Potassiumcarbonate.Closedsystemsuch asporcelain
ballmillisused.

9. HammerMill
▶Principle
Itoperatesontheprincipleofimpactbetweenrapidlymovinghammersmountedon
rotorandthestationarypowdermaterial.
▶Parts
Consistsofametalcasing,enclosingacentralshaft,towhich4ormoreswinging
hammersareattached.Lowerpartofcasingconsistsofascreen,throughwhich
materialcanpassandcollectedinasuitablereceiver.

10. Construction&Working
▶Ahammermillisessentiallyasteeldrumcontainingaverticalorhorizontalrotating
shaftordrumonwhichhammersaremounted.
▶Thehammersswingsontheendsorfixedtothecentralrotor.
▶Therotorisrotatesatahighspeedinsidethedrumwhilematerialisfedintoafeed
hopper.
▶Thematerialisputinto thehopperwhichisconnectedwiththe drum.
▶Thematerialispowderedtothedesiredsizeduetofastrotationofhammersandis
collectedunderthe screen
▶Thisaremainlyoperatedat1000to2500rpmforthereductionofthelargesized
particles.Highspeedrotoruses10000rpmspeed.

11. Uses
▶Brittlematerialis bestfracturedbyimpactfrom blunthammers.
▶Fibrousmaterialisbestreducedbycuttingedges

12. Advantages
▶Itisrapidin action,andiscapable ofgrindingmanydifferenttypesof materials.
▶Theyareeasytoinstallandoperate,theoperationiscontinuous.
▶Thereislittlecontaminationoftheproductwithmetalabraded fromthemillassurface
moveagainsteach other.
▶Theparticlesizeofthematerialto be reduced canbeeasilycontrolledbychangingthe
speedoftherotor,hammertype,shapeandsizeofthescreen.
Disadvantages
▶Heatbuildup duringmilling ismore,therefore,productdegradation ispossible.
▶Hammermillscannotbeemployedtomillsticky,fibrousandhardmaterials.
▶Thescreensmaygetclogged.

13. BallMill
▶Principle
Itoperatesontheprincipleofimpactandattritionbetweentherapidlymovingballsand
thepowdermaterial,bothenclosedinahollowcylinder.
▶Parts
Consistsofahollowcylindermountedonametallicframesuchthatitcanberotated
alongitslongitudinalaxis.Cylindercontainsballsoccupying30–50%ofmillvolume.
Weightofballisconstant;Sizedependsonthefeedquantityanddiameterofmill.

14. Working:
▶Atlowspeeds,theballrollovereachotherandattrition(rubbingaction)willbethepredominate
mode of action.
▶Thus,in theballmill,impactorattritionorbothareresponsibleforthesizereduction.
Advantages:
▶Itcanproduceveryfine powder.
▶Ballmillisusedforbothwetanddrygrindingprocesses.
▶Toxicsubstancescanbeground,asthecylinderisclosedsystem.
▶installation,operationandlabourcosts arelow.

15. Disadvantages:
▶Theball millis a verynoisymachine.
▶Ball millis aslowprocess.
▶Soft,fibrousmaterialcannotbemilledbyballmill.

16. USES–
▶Stainlesssteelarepreferredintheproductionofophthalmic&parentralproducts.
▶ballmillatlowspeedisusedformillingdyes,pigments&insecticides.

17. EDGERUNNER MILL
Principle
Thesizereductionisdonebycrushingduetoheavyweightofstone.
Construction
▶Itconsistof twoheavyrollersandmayweighseveraltons.
▶Theroller moveonabedwhichis madeupofgraniteorstone.
▶Eachrollerhasacentralshaftandrevolveonits axis.
▶The rollers aremountedonhorizontalshaftandmovearoundthebed

18. Working:
▶Thematerialtobegroundisplacedonthebedwiththehelpofthescrapperinsucha
waythatitcomesinthepathofthestonewheel.
▶Thesestonesrevolveonitsownaxisandatthesametimetravelaroundtheshallow
stonebed.
▶Thematerialis groundfordefiniteperiod.
▶Thepowderiscollectedand passedthroughasievetogetpowderofrequiredsize.

19. Advantages
▶Does notrequireattentionduringoperation.
Disadvantages
▶Morespacethanothermill,Contamination,Timeconsuming,Notuseforsticky
materials.
Uses
▶Grindingtoughmaterialtofinepowder.

20. fig.ofedgerunnermill-

22. ENDRUNNERMILL
Principle
Sizereductionisdonebycrushingduetoheavyweightofsteelpestle.Shearingstressisalsoinvolved
duringmovementofmortar andpestle.
Construction
▶Itisconsideredasmechanicalmortar pestle.
▶Itconsistof asteelmortarwhichisfixed toaplate.
▶Theconstructionofmortarisconnectedtohorizontalshaftbearingapulleysotheplatewithmortarcan
berotatedathighspeed.
▶Thepestleisdumb-bell shapedandbottomofpestleisflat.
▶Constructionofpestleisdoneinsucha waythatitcanberaisedfrommortarfor cleaningandemptying

23. Working
▶Thematerialtobegroundisplacedinthemortar.Themortarrevolvesatahighspeed.The
revolvingmortarcausesthepestle to revolveduringthisprocess,sizereductionisachieved.
Advantages
▶Endrunnermillprovidesmoderatelyfinepowderandoperatessuccessfullywithfibrous
materials,bark,woodsfruits,leaves,etc.Wetgrindingwithveryviscousmaterialsuchas
ointmentsandpasteisalsopossible
Disadvantages
▶Notsuitableforunbrokenor slightlybrokenconditionofdrug.

24. Uses:
▶Useforfinegrinding.

25. FluidEnergyMill
Principle
Itoperatesonthe principleofimpactandattrition.
Parts
▶Consistsofaloopof pipewithdiameter20-200mm.Theoverallheightofthepipeis2m.
▶Inletforfeedandaseriesofnozzlesforair,inertgas.Outletwithclassifierwhichpreventsthe
particlestopassuntiltheybecomesufficientlyfine.

26. Construction
▶It consistsofaloopof pipe,whichhas adiameterof 20to200mm,dependingonthe
overallheightof theloop,whichmaybeuptoabout2m.
▶Thereisaninletforthefeedandaseriesofnozzlesfortheinletof airor aninertgas.
▶Italso hasanoutletwitha classifierwhichallowthe airto escapebutpreventstheparticles
topassuntiltheybecomesufficientlyfine.

27. Working
▶Theairorinertgasisintroducedwithaveryhighpressurethroughthenozzles.Solids
areintroducedintoairsteamthroughinlet.duetohighdegreeofturbulence,impactand
attritionalforcesoccursbetweentheparticles.Thefineparticlesarecollectedthrougha
classifier.Fluidenergymillreducestheparticlesto1to20micron.Togetaveryfine
powder,evenuptofivemicron,thematerialispretreatedtoreducetheparticlesizeto
theorderof100meshandthenpassedthroughfluidenergymill.
Uses
▶Themillisusedtogrindheatsensitivematerialtofinepowder.
▶Themillisusedto grindthosedrugsinwhichhighdegreeofpurityisrequired.

28. Advantages
▶Themillisusedtogrind the materialtofinepowder.
▶Theparticlesizeofpowdercanbecontrolledduetothe useof a classifier.
▶Thereis nowearofthe millandhencethere isnocontaminationofthe product.
▶Itisusefulforgrindingheatsensitivesubstances suchassulphonamides,vitaminsandantibiotics.
Disadvantages
▶Tendencyofformingaggregatesoragglomeratesaftermilling.
▶Generationofamorphouscontentduetohighenergyimpact.
▶Formationofultra-fineparticles
▶Highenergyconsumption.