This document discusses comminution, or size reduction, which is the mechanical process of reducing the particle size of solids. It covers the reasons for size reduction in pharmaceutical applications, factors that affect the milling process, theories of comminution energy, and types of mills used. Size reduction increases surface area and can improve properties like solubility, dissolution rate, and bioavailability. The optimal particle size depends on factors like the material, moisture content, temperature, and feeding rate during milling. Particle size is determined using microscopy, sieving, sedimentation, or centrifugation.

2. COMMINUTION (SIZE
REDUCTION)
SAMIA GHANI
M.PHIL PHARMACEUTICS

3. TABLE OF CONTENTS
• REASONS FOR SIZE REDUCTION
• FACTORS AFFECTING SIZE REDUCTION
• PARTICLE SIZE DETERMINATION
• ENERGY MILLS (BALL MILL, ENDRUMER, EDGE RUMMER, DISINTEGRANT,
COLLOID MILL, HAMMER MILL, CUTTER MILL AND FLUID ENERGY MILL)

4. INTRODUCTION
• MILLING IS THE MECHANICAL PROCESS OF REDUCING THE PARTICLE SIZE OF
SOLIDS
• SYNONYMS: COMMINUTION, CRUSHING, DISINTEGRATION, DISPERSION,
GRINDING, PULVERIZATION
Cutting Compression Impaction Attrition

5. PURPOSE AND IMPORTANCE OF MILLING
• INCREASE SPECIFIC SURFACE (SURFACE AREA PER UNIT WEIGHT) OF THE SUBSTANCE,
IN GENERAL 10 FOLDS INCREASE IN SURFACE AREA IS GIVEN BY 10 FOLDS DECREASE
IN PARTICEL SIZE.
• IMPROVE DISSOLUTION AND THERAPEUTIC EFFICASY: MEDICINAL COMP. POSSESSING
LOW SOLUBILITY IN BODY FLUIDS, THEIR THERAPEUTIC EFFICIENCY AND DISSOLUTION
IS INCREASED DUE TO INCREASE IN AREA OF CONTACT BETWEEN SOLID AND
DISSOLVING FLUID. E.G. GRISEOFULVIN ORAL DOSAGE REGIMEN REDUCED TO HALF
DUE TO PARTICLE FINENESS. INHALATION PRODUCT PARTICLE SIZE DETERMINES
POSITION AND RETENTION IN BRONCHOPULMONARY SYSTEM.
• CONTROL OF PARTICLE SIZE AND SPECIFIC SURFACE INFLUENCES THE DURATION OF
ADEQUATE SERUM CONC., RHEOLOGY AND PRODUCT SYRINGEABILITY AS IN THE CASE
OF INTRAMUSCULAR SUSPENSION OF PROCAINE PENICILLIN G.
• EXTRACTION: EXTRACTION OR LEACHING FROM ANIMAL GLANDS (LIVER AND
PANCREAS) CAN BE FACILITATED BY COMMINUTION. TIME FOR EXTRACTION IS

6. • DRYING: MILLING INCREASES SURFACE AREA AND REDUCES THE DISTANCE
TRAVELLED BY MOISTURE WITHIN THE PARTICLE TO REACH OUTER SURFACE THUS
FACILITATES DRYING OF WET MASSES E.G. IN CASE OF MANUFACTURING OF
COMPRESSED TABLETS BY WET GRANULATION.
• FLOWABILITY: FLOW PROPERTIES AFFECTED BY PARTICLE SIZE AND SIZE
DISTRIBUTION. FREE FLOWING POWDERS IN HIGH SPEED FILLING EQUIPMENTS
AND TABLET PRESSES PRODUCE UNIFORM PRODUCT. FOR SUSPENSION OF HIGH
DISPERSE PHASE CONCENTRATION, REDUCTION IN PARTICLE SIZE RESULTS IN
INCREASED VISCOCITY.
• MIXING OR BLENDING: EASIER, GREATER DOSE UNIFORMITY, ARTIFICIALLY
COLOURED SOLID PHARMACEUTICALS ARE MILLED FOR UNIFORM DISTRIBUTION
OF COLOURING AGENT.
• FORMULATION: PROPER PARTICLE SIZE OF LUBRICANTS COATING THE SURFACE
OF GRANULATION OR POWDER IN CASE OF COMPRESSED TABLETS ALSO LARGELY
AFFECTS THE FORMULATION. SEDIMENTATION RATE IN CASE OF SUSPENSIONS
AND EMULSIONS IS GREATLY REDUCED BY REDUCING PARTICLE SIZE.

7. ADVANTAGES
• MIXING IS MORE UNIFORM IF THE INGREDIENTS ARE ROUGHLY THE SAME SIZE
• MILLING OF WET GRANULES CAN PROMOTE UNIFORM AND EFFICIENT DRYING
• INCREASED SURFACE AREA CAN IMPROVE DISSOLUTION RATE AND
BIOAVAILABILITY
• IMPROVE CONTENT UNIFORMITY OF DOSAGE UNIT

8. DISADVANTAGES
• EXCESSIVE HEAT GENERATION CAN LEAD TO DEGRADATION, CHANGE IN
POLYMORPHIC FORM IN CASE OF VOLATILE CONSTITUENTS
• INCREASE IN SURFACE ENERGY CAN LEAD TO AGGLOMERATION
• MAY RESULT IN EXCESSIVE PRODUCTION OF FINE OR OVERLY BROAD
PARTICLE SIZE DISTRIBUTION
• OXIDATION
• HYDROLYSIS

9. PHARMACEUTICAL APPLICATION
• SPECIFIC SURFACE (SURFACE AREA PER UNIT WEIGHT) INCREASED BY SIZE REDUCTION
WHICH AFFECT THERAPEUTIC EFFICIENCY OF MEDICAL SUBSTANCES SPECIALLY IF THE
MATERIAL HAVE LOW SOLUBILITY
• EXTRACTION.
• THERAPEUTIC ACTIVITY.
• RATE OF MIXING.
• DRYING.
• SMOOTH TEXTURE AND BETTER APPEARANCE.
• UNIFORMITY OF DOSAGE FORM ACHIEVED.
• LUBRICANT FUNCTION PROPERLY.
• DOSAGE FORM DEVELOPMENT SUCH AS AEROSOLS, EMULSION, SUSPENSION, TABLETS,
OINTMENTS, OPHTHALMIC PREPS.

10. THEORY OF COMMUNITION
• MECHANICAL BEHAVIOUR OF SOLIDS WHICH STRAINED UNDER STRESS AND
DEFORMED IS SHOWN IN STRESS-STRAIN CURVE

11. i. ELASTIC REGION
ii. YIELD POINT
iii. PLASTIC REGION
iv. FRACTURE POINT

12. Elastic
region
In it solids
shows
resistance
and go back
to its original
position.
It is a
reversible
state.
Plastic
deformation
A point where
solids break &
can’t resume
its original
position.
By applying
greater stress,
irreversible
state reached.
Area under
the curve
Represents
energy
fracture.
It is a
measure of
impact
strength of a
material.
Yield point
It is a
measure of a
resistance to
permanent
deformation.
At this state
stress- strain
curve
becomes
nonlinear.

13. • INITIAL LINEAR PORTION IS DEFINED BY HOOK’S LAW (STRESS IS DIRECTLY
PROPORTIONAL TO STRAIN) AND YOUNG’S MODULUS (SLOPE OF LINEAR
PROPORTION) EXPRESS THE STIFFNESS AND SOFTNESS OF SOLID IN DYNES PER
SQUARE CENTIMETERS.
• AT YIELD POINT (MEASURE OF RESISTANCE TO PERMANENT DEFORMATION)
STRESS-STRAIN CURVE BECAME NON-LINEAR.
• WHEN STRESS IS FURTHER INCREASED, RESULTS IN PLASTIC DEFORMATION
WHICH IS IRREVERSIBLE.
• WHEN SINGLE PARTICLE SUBJECTED TO SUDDEN IMPACT AND FRACTURE IT
YIELDS FEW RELATIVELY LARGE PARTICLES, NUMBER OF FINE PARTICLES AND
FEW OF INTERMEDIATE SIZE.
HOOKE’S LAW= STRESS Ἀ STRAIN

14. • MOST EFFICIENT MILLS USED NOW A DAYS PROVIDE ENERGY INPUT, OUT OF
WHICH 1% IS UTILIZED TO FRACTURE PARTICLE AND CREATE NEW SURFACE.
REST OF THE ENERGY IS DISSIPATED IN;
i. ELASTIC DEFORMATION OF UNFRACTURED PARTICLES
ii. TRANSPORT OF MATERIAL WITHIN THE MILLING CHAMBER
iii. FRICTION B/W PARTICLES
iv. FRICTION B/W PARTICLES AND MILL
v. HEAT
vi. VIBRATION AND NOISE
vii. INEFFICIENCY OF TRANSMISSION AND MOTOR

15. GRIFFITH THEORY
• CRYSTALS OF PURE SUBSTANCES HAVE INTERNAL WEAKNESSES DUE TO
MISSING ATOMS AND IONS IN THEIR LATTICE STRUCTURES AND FLAWS
ARISING FROM MECHANICAL OR THERMAL STRESS.
• GRIFFITH THEORY OF CRACKS AND FLAWS ASSUMES THAT “ALL SOLIDS
CONTAIN FLAWS OR MICROSCOPIC CRACK, WHICH INCREASE APPLIED FORCE
ACCORDING TO CRACK LENGTH AND FOCUS THE STRESS AT ATOMIC BOND
OF CRACK APEX.”
• IT CAN BE EXPRESSED AS;

16. • WHERE;
• T IS TENSILE STRENGTH
• LAMBDA IS THE YOUNG’S MODULUS
• EPSILON IS THE SURFACE ENERGY OF THE WALL OF CRACK.
• C IS THE CRITICAL CRACK DEPTH REQUIRED FOR A FRACTURE

17. ENERGY OF COMMINUTION
• THE IMMEDIATE PURPOSE OF MILLING IS TO FORM CRACKS THAT SPREAD
THROUGH THE DEFORMED PARTICLES AT THE EXPENSE OF STRAIN ENERGY
AND PRODUCE FRACTURE.
• THE ENERGY WHICH IS EXPENDED IN PRODUCING NEW SURFACE IS:
• E IS ENERGY INPUT
• D1 IS DIAMETER OF MATERIAL FED TO THE MILL
• D2 IS DIAMETER OF PRODUCT DISCHARGED FROM THE MILL
• THE ENERGY REQUIRED TO REDUCE PARTICLE SIZE IS INVERSELY
PROPORTIONAL TO THE SIZE RAISED TO SOME POWER.

18. ENERGY OF COMMINUTION
• 3 LAWS ARE AS FOLLOWS WHICH EXPLAINS ENERGY FOR
COMMINUTION:
Kick’s law
Rittengir’s law
Bond’s law

19. KICK’S LAW
• IN 1885, KICK SUGGESTED THAT THE ENERGY
REQUIREMENT, E, FOR SIZE REDUCTION IS DIRECTLY
RELATED TO THE REDUCTION RATIO (D1/D2)
• WHERE; D1 AND D2 ARE THE DIAMETERS OF FEED MATERIAL
AND DISCHARGED PRODUCT, RESPECTIVELY
• CONSTANT “C” MAT BE REGARDED AS THE RECIPROCAL
EFFICIENCY COEFFICIENT
• “C=KKFC, WHERE; FC IS THE CRUSHING STRENGTH OF
MATERIAL AND KK IS KNOWN AS KICK’S CONSTANT
E= energy
D1= initial
diameter of
particle before
reduction
D2= final diameter
of particle after
reduction
C= constant; Kkfc
Kk=kick’s const
fc=force req. for
crushing

20. • IF N=1, THE GENERAL DIFFRENTIAL EQUATION REDUCES TO KICK’S EQUATION
• BASED ON KICK’S LAW, IF CERTAIN HORSEPOWER IS REQUIRED TO MILL A GIVEN
WEIGHT OF MATERIAL FROM 1000 TO 500 MICROMETER, SAME ENERGY WOULD BE
REQUIRED TO REDUCE THE SIZE FROM 500 TO 250 MICROMETER
• KICK’S PROPOSAL REPRESENTS ENERGY REQUIRED TO EFFECT ELASTIC
DEFORMATION BEFORE FRACTURE OCCURS
• KICK’S EQUATION ASSUMES THAT THE MATERIAL HAS FLAWS DISTRIBUTED
THROUGHOUT ITS INTERNAL STRUCTURE THAT ARE INDEPENDENT OF PARTICLE
VOLUME
• EXPERIMENTAL AND THEORATICAL VALUES APPLY BEST TO COARSE MILLING.

21. RITTINGER’S LAW
• IN 1867, VON RITTINGER PROPOSED THAT THE ENERGY REQUIRED FOR SIZE
REDUCTION IS DIRECTLY PROPORTIONAL TO THE INCREASE IN SPECIFIC
SURFACE AREA.
• WHERE; K1 DENOTES RELATIONSHIP BETWEEN PARTICLE SURFACE AND
DIAMETER.
• S1 AND S2 ARE SPECIFIC SURFACES BEFORE AND AFTER MILLING
RESPECTIVELY.

22. BOND’S LAW
• IN 1952, BOND SUGGESTED THAT “ENERGY REQUIRED FOR SIZE REDUCTION IS
INVERSELY PROPORTION TO SQUARE ROOT OF DIAMETER OF PRODUCT”
• WHERE; WT IS THE TOTAL WORK OF COMMINUTION IN KILOWATT HOURS PER
SHORT TON OF MILLED MATERIAL
• D2 KS THE SIZE IN MICROMETERS THROUGH WHICH 80% BY WEIGHT OF
MILLED PRODUCT WILL PASS.

23. MECHANISM OF COMMINUTION
• THERE ARE FOUR MAIN METHODS OF SIZE REDUCTION, INVOLVING DIFFERENT
MECHANISMS:
• CUTTING: IT INVOLVES APPLICATION OF FORCE OVER A VERY NARROW AREA OF MATERIAL
USING SHARP EDGE OF CUTTING DEVICE.
• COMPRESSION: IN COMPRESSION, THE MATERIAL IS GRIPPED BETWEEN THE TWO
SURFACES AND CRUSHED BY APPLICATION OF PRESSURE
• IMPACT: INVOLVE THE CONTACT OF MATERIAL WITH A FAST MOVING PART WHICH IMPARTS
SOME OF ITS KINETIC ENERGY TO THE MATERIAL. THIS CAUSES CREATION OF INTERNAL
STRESSES IN THE PARTICLE, THEREBY BREAKING IT.
• ATTRITION: THE MATERIAL IS SUBJECTED TO PRESSURE AS IN COMPRESSION BUT THE
SURFACES ARE MOVING RELATIVE TO EACH OTHER, RESULTING IN SHEAR FORCES WHICH
BREAK THE PARTICLES.

25. FACTORS AFFECTING MILLING
• NATURE OF MATERIAL
• MOISTURE CONTENT
• TEMPERATURE
• PARTICLE SHAPE
• POLYMORPHISM
• FEEDING RATE

26. NATURE OF MATERIAL
• MATERIAL MAY BE HARD, INTERMEDIATE AND SOFT
• PHYSICAL NATURE OF MATERIAL DETERMINES PROCESS OF COMMINUTION
• HARD MATERIAL (IODINE, PUMICE) ARE ABRASIVE AND CAUSE RAPID WEAR OF
MILL PARTS IMMEDIATELY INVOLVED IN SIZE REDUCTION
• FIBROUS MATERIAL (GLYCYRRHIZA, RAUWOLFIA) CANNOT BE CRUSHED BY
PRESSURE OR IMPACT AND MUST BE CUT.
• FRIABLE MATERIAL (DRIED FILTER CAKE, SUCROSE) TEND TO FRACTURE
ALONG WELL DEFINED PLANES AND MAY BE MILLED BY ATTRITION, IMPACT OR
COMPRESSION.

27. MOISTURE CONTENT
• PRESENCE OF MORE THAN 5% MOISTURE HINDERS COMMINUTION AND OFTEN
PRODUCES STICKY MASS UPON MILLING. THIS EFFECT IS PRONOUNCED WITH FINE
MATERIALS RATHER WITH LARGE PARTICLES.
• WATER CONC IF MORE THAN 50%, THE MASS BECOMES SLURRY OR FLUID
SUSPENSION. THE PROCESS IS THAN A WET MILLING PROCESSWHICH AIDS IN SIZE
REDUCTION. INCREASE IN MOISTURE REDUCES MILLING RATE TO PARTICULAR
SIZE.
• DRUGS POSSESSING WATER OF CRYSTALLIZATION LIBERATE WATER AT LOW
TEMPERATURE CAUSING MILL CLOGGING E.G. GLAUBER’S SALT.
• HYGROSCOPIC MATERIALS RAPIDLY ABSROBS MIOSTURE TO THE EXTENT THAT
WET MASS STICKS AND CLOGS THE MILL E.G. CALCIUM CHLORIDE.

28. TEMPERATURE
• HEAT DURING MILLING SOFTENS AND MELTS THE MATERIAL WITH LOW MP.
• SYNTHETIC GUMS, WAXES AND RESINS BECOME SOFT AND PLASTIC
• HEAT SENSITIVE DRUGS MY BE DEGRADED OR EVEN CHARRED
• PIGMENTS CHANGE THEIR COLOR IF HEAT IS EXCESSIVE DURING MILLING E.G.
OCHER AND SIENNA
• UNSTABLE COMPOUNDS AND ALMOST ANY FINELY POWDERED MATERIALS
MAUPY IGNITE AND EXPLODE IF THEIR TEMP IS HIGH.

29. PARTICLE SHAPE
• AN IMPACT MILL PRODUCES SHARP IRREGULAR PARTICLES, WHICH MAY NOT
FLOW READILY.
• WHEN SPECIFICATION DEMAND A MILLED PRODUCT THAT WILL FLOW FREELY,
IT WOULD BE BETTER TO USE AN ATTRITION MILL, WHICH PRODUCES FREE
FLOWING SPHERICAL PRTICLES.

30. POLYMORPHISM
• MILLING MAY ALTER THE CRYSTALLINE STRUCTURE AND CAUSE CHEMICAL
CHANGES IN SOME MATERIALS.
• WET MILLING MAY BE USEFUL IN PRODUCING A SUSPENSION THAT CONTAINS A
METASTABLE FORM OF MATERIAL CAUSING CRYSTAL GROWTH AND CAKING. E.G IN
CASE OF CORTISONE ACETATE CRYSTALS.
• STARCH AMYLOSE AND AMYLOPECTIN MAY BE BROKE. DOWN TO A WIDE
MOLECULAR WEIGHT RANGE BY A VIBRATORY MILL
• POWDERED POVIDONE BREAKS DOWN INTO LOWER MOLECULAR WEIGHT
POLYMERS DURING BALL MILLING.

31. FEEDING RATE
• IF SLOW, POWDER DISCHARGED READILY, AMOUNT OF FINE PARTICLES MINIMIZED.
• CHOKE FED AT FAST RATE, MATERIAL IN MILLING CHAMBER FOR LONGER TIME AS ITS
DISCHARGED IS IMPEDED BY MASS OF MATERIAL. GREATER PARTICLE SIZE REDUCTION BUT
REDUCES MILL CAPACITY AND INCREASED POWER CONSUMPTION.
• RATE OF DISCHARGE IS EQUAL TO RATE OF FEED WHICH IS SUCH THAT THE MILLING PARTS
CAN OPERATE MOST EFFECTIVELY.
• MILLS DESIGNED FOR PHARMACEUTICAL OPERATIONS ARE DESIGNED SO THAT FORCE OF
GRAVITY IS SUFFICIENT TO GIVE FREE DISCHARGE GENERALLY FROM THE BOTTOM OF THE
MILL.
• FOR ULTRAFINE GRINDING, FORCE OF GRAVITY IS REPLACED BY A FLUID CARRIER.
• POWDER IS REMOVED FROM THE FLUID BY CYCLONE SEPERATORS OR BAG FILTERS.

32. PARTICLE SIZE DETERMINATION
• DETERMINING THE NUMBER OF PARTICLES- MICROSCOPY
• DETERMINING THE WEIGHT OF PARTICLES- SIEVING, SEDIMENTATION,
CENTRIFUGATION, ELUTRIATION.
• DETERMINING VOLUME OF PARTICLES- COULTER COUNTER
• DETERMINING LIGHT SCATTERING BY PARTICLES- DYNAMIC AND LASER LIGHT
SCATTERING

33. • MANY METHODS AVAILABLE FOR DETERMINING PARTICLE SIZE SUCH AS
OPTICAL MICROSCOPY, SIEVING, SEDIMENTATION AND PARTICLE VOLUME
MEASUREMENT.
1. OPTICAL MICROSCOPY (RANGE: 0.2-100 ΜM).
2. SIEVING (RANGE: 40-9500 ΜM).
3. SEDIMENTATION (RANGE: 0.08-300 ΜM).
4. PARTICLE VOLUME MEASUREMENT (RANGE: 0.5-300 ΜM).

34. A GUIDE TO RANGE OF PARTICLE SIZES
APPLICABLE TO EACH METHOD

35. MICROSCOPY
• MOST DIRECT METHOD FOR SIZE DISTRIBUTION MEASUREMENT.
• ITS LOWER LIMIT OF APPLICATION IS DETERMINED BY THE RESOLVING POWER OF
A LENS, IF SIZE IS CLOSE TO THE WAVELENGTH OF LIGHT SOURCE THAN PARTICLE
CAN NOT BE RESOLVED.
• WITH SPECIAL LENSES AND ULTRAVIOLET LIGHT, THE LOWER LIMIT MAY BE
EXTENDED TO 0.1 MICRON.
• IN ULTRAMICROSCOPE, THE RESOLUTION IS IMPROVED BY USE OF DARK FIELD
ILLUMINATION, ITS SIZE RANGE IS FROM 0.01 TO 0.2 MICROMETER.
• PHTOMICROGRAPHS, PROJECTIONS AND AUTOMATIC SCANNERS HAVE BEEN USED
TO LESSEN THE OPERATOR FATIGUE.

37. SIEVING
• MOST WIDELY USED BECAUSE IT IS INEXPENSIVE, SIMPLE AND RAPID WITH LITTLE
VARIATION BETWEEN OPERATORS.
• CONSISTS OF A PAN WITH A BOTTOM OF WIRE CLOTH WITH SQUARE OPENINGS.
• IN US, TWO STANDARDS OF SIEVE ARE USED;
• TYLER STANDARD SCALE: BASED ON THE SIZE OF OPENING IN A WIRE CLOTH
HAVING 200 OPENINGS PER LINEAR INCH, I.E. 200 INCH
• THE UNITED STATE STANDARD SCALE PROPOSED BY NATIONAL BUREAU OF
STANDARDS.
• PROCEDURE INVOLVES MECHANICAL SHAKING OF A SAMPLE THROUGH A SERIES
OF SUCCESSIVELY SMALLER SIEVES AND THE WEIGHING OF SAMPLE PORTION
RETAINED ON EACH SIEVE.

39. • TYPE OF MOTION INFLUENCES SIEVING, VIN
• VIBRATORY MOTION IS MOST EFFICINET, FOLLOWED SUCCESSIVELY BY SIDE-
TAP MOTION, BOTTOM-TAP MOTION, ROTARY MOTION WITH TAP.
• IMPORTANT FACTORS: TIME OF SIEVING, POWDER LOAD, TYPE OF MOTION.

41. SEDIMENTATION
• USED OVER A SIZE RANGE OF 1 TO 200 MICROMETER TO OBTAIN SIZE-WEIGHT DISTRIBUTION CURVE AND TO
PERMIT CALCULATION OF PARTICLE SIZE.
• EXPRESSED BY STOKE’S EQUATION:
• DSTOKES IS EFFECTIVE OR STOKE’S DIAMETER
• ᵞ IS THE VISCOSITY OF DISPERSION FLUID.
• X/T IS THE RATIO OF SEDIMENTATION OR DISTANCE OF FALL X IN TIME T
• G= GRAVITATIONAL CONSTANT.
• Ρ-Ρ◦ ARE THE DENSITIES OF PARTICLE AND MEDIUM RESPECTIVELY.

42. • APPLICABLE TO FREE SPHERES THAT ARE FALLING AT A CONSTANT RATE.
• ANDREASEN PIPET METHOD IS THE SIMPLEST MEANS OF INCREMENTAL
PARTICLE SIZE ANALYSIS.
• LARGER PARTICLES SETTLE FASTER.

43. ANDREASEN METHOD
1% suspension
of the powder in
a suitable liquid
placed in
pipette.
At given time
intervals from
the centre 10ml
sample
withdrawn
without
disturbing
suspension
After drying
weigh the
particles &
measure
particle
diameter by
stokes
equation

46. CYCLONE SEPARATOR
THIS METHOD IS USED FOR SUSPENSIONS SUSPENDED IN GAS
OR AIR.
From inlet fluid
enters
Rotary motion
occurs due to
pressure and size
reduced
Solids sediment at
bottom
CYCLONE
SEPARATOR

47. CENTRIFUGATION
• WHEN PARTICLES ARE SMALLER, NORMAL SEDIMENTATION METHODS ARE
VERY SLOW AND FACTORS SUCH AS BROWNIAN MOVEMENT INTERFERES
WITH THE RESULTS.
• THIS CAN BE OVERCOME BY APPLYING THE SAME BASIC PRINCIPLES, BUT
UTILIZING CENTRIFUGAL FORCE INSTEAD OF GRAVITATIONAL FORCE, WHERE
SETTLING VELOCITIES CAN BE INCREASED GREATLY.

48. ELUTRIATION
• PROCEDURE IN WHICH FLUID MOVES IN A DIRECTION OPPOSITE TO THE
SEDIMENTATION MOVEMENT, SO THAT IN THE GRAVITATIONAL PROCESS E.G.
THE PARTICLES MOVES VERTICALLY UPWARDS.
• VELOCITY OF THE FLUID IS LESS THAN SETTLING VELOCITY

49. MILLING EQUIPMENTS
MILLING EQUIPMENT CLASSIFIED ACCORDING TO THE SIZE
OF THE MILLED PRODUCT:
• COARSE
• INTERMEDIATE
• FINE
Coarse milling produces particles larger than 20-
mesh
It produces particles from 200 to 20-mesh
Fine milling produces particles smaller than 200-mesh

50. SELECTION OF A MILL FOR SIZE REDUCTION
• Product specification
• Capacity of a mill
• Speed
• Versatility of mill
• Dust control mechanism
• Sanitation
• Auxiliary equipments
• Labor cost
• Space occupied

51. TYPES OF MILL
Open type mill
• Product for single cycling
purpose
Closed type mill
• For recycling purpose

52. PARTS OF A MILL
Feeding
zone/chute
Grinding
zone/chute
Discharge
zone/chute

53. MILLING TECHNIQUES
Temperature Moisture
content
Pre
treatment
Subse quant
treatment
Dual
process
Special
atmosphere

54. CONTI…
Special
atmosphere
Hygroscopic material
milled in a closed
system supplied with
dehumidified air.
Thermo labile,
oxidizable materials
should be milled in a
closed system with an
inert atmosphere of
CO2 or NO2.
Temperature
control
There should be a
controlled temperature
because heat may
raise the temp. of a
material.
So to prevent this,
milling chamber
should be cooled by
cooling jacket or a
heat exchanger.
Dual
process
Sometimes
simultaneously two
process occur in a
time for example,
milling-mixing or
milling-drying.
For example, if hot gas
is circulated through a
mill, the mill can be
used to comminute &
dry moist solids
simultaneously.

55. Pretreatment
• The feed should be of the proper size & enter at a fairly
uniform rate.
• For e.g, pretreatment of fibrous materials with high pressure
rolls or cutters facilitates comminution.
Subsequent
treatment
• If extreme control of size is required the it is necessary to
recycle the larger particles.
• By simple screening, Air separator element are required.
Wet & dry
milling
• Dry milling is recommended if the product undergoes physical or
chemical change in water. Grinding aids facilitate size reduction. In
certain cases addition of salts for e.g, ammonium salts are useful.
• Wet milling is useful but flocculation restricts the lower limit approx
10microns. Wet grinding eliminates dust hazard & done in low speed
mills. Silicates & phosphates are useful dispersing agent in wet
grinding.

56. MANUAL METHODS FOR SIZE REDUCTION
Triturat
ion
• In pestle and mortar
Lavigat
ion
• Few drops of liquid used i.e, insoluble in a material
• For example in ointments
Pulveri
zation
• A process in which solvent evaporated after mixing.
• For example, camphor in alcohol & iodine in ether.

57. INDUSTRIAL METHODS FOR SIZE
REDUCTION
Industrial methods
Cutter mill
Roller mill
hammer
mill
Ball mill
Fluid
energy mill
Colloid mill
stone mill

58. CUTTER MILL
Feeding of a
material
Shaft move
Through
knives cutting
occurs
Based on cutting mechanism
Stationary and rotating blades are attached to mill and
Desired size screen are attached at bottom
Material fed through hopper and size reduction takes
Place by blades.
Coare powder is obtained by through this mill
Used for fibrous, crude animal and vegetable drugs

59. CONTI...
• USED TO OBTAIN COARCE PATICLES SUCH AS ROOTS AND PEELS BEFORE
THEIR EXTRACTION
• USED FOR CRUDE ANIMAL AND VEGETABLE DRUG
• LIMITATIONS
• NOT USED FOR FRIABLE MATERIAL
• FED SIZE SHOULD BE LESS THAN 1 INCH THICK AND SHOULD NOT EXCEED
LENGTH OF CUTTING KNIFE
• MATERIAL IS PRE-MILLED AND IS USUALLY SUSPENDED IN A STREAM OF AIR OR
LIQUID, WHEN FED TO THE MILL

60. ROLLER MILL
Feeding of
the particles
Due to speed
& gap b/w
rollers
Size
reduction
occurs
ROLLER MILL

61. • WORKS ON PRINCIPLE OF ATTRITION
• CONSISTS OF TWO METALLIC ROLLS WITH ADJUSTABLE GAP BETWEEN THEM
BY WHICH REDUCTION IS ADJUSTED
• MATERIAL IS FED THROUGH HOPPER

62. HAMMER MILL
Feeding
of particle
Hammers
move
Size
reduced

63. • WORKS ON PRINCIPLE OF IMPACTION
• CONSIST OF CENTRAL SHAFT ATTACHED TO IT ARE NUMBER OF HAMMERS IN
STEEL CASE.
• WHEN SHAFT IS ROTATED, HAMMERS SWING IN RADIAL POSITION
• SCREEN OF DESIRED SIZE IS FITTED AT BOTTOM
• MATERIAL IS FED THROUGH HOPPER AND SIZE EDUCTION TAKES PLACE BY
IMPACTION OF HAMMERS.

64. CONTI…
• MERITS OF A HAMMER MILL:
a) RAPID IN ACTION.
b) EASY AND SIMPLE TO INSTALL AND OPERATE.
c) DIFFERENT TYPES OF MATERIAL WE CAN GRIND FOR EXAMPLE LEAVES, BARKS ETC.
d) NO CHANCES OF CONTAMINATION.
e) PRODUCT OBTAINED 4 TO 325-MESH.
f) PARTICLE SIZE CAN BE CONTROLLED BY SPEED ADJUSTMENT, HAMMER AND SCREEN
• DEMERITS OF A HAMMER MILL:
a) SPEED MAY BE TOO HIGH THAT CAN PRODUCE HEAT.

65. BALL MILL
Feeding of a
particle in a
single container
Due to friction
b/w ball &
medium
Size reduction occurs
Schematic diagram of a ball mill

66. CONTI...
• WORKS ON PRINCIPLE OF IMPACTION AND ATTRITION
• CONSISTS OF CYLINDRICAL CONTAINER FILLED WITH NUMBER OF BALLS MADE
UP OF STEEL, BALLS ACT AS GRINDERS. BALL SIZE DETERMINED PARTICLE
SIZE. CYLINDRICAL CONTAINER IS ROTATED AT SLOW SPEED.
• MATERIAL US FED TROUGH HOPPER AND TH MOVING BALLS REDUCES THE
SIZE OF MATERIAL.

67. CONTI…
• ADVANTAGES OF BALL MILL:
a) PRODUCT SIZE OBTAINED 20 TO 200-MESH.
b) EASY AND SIMPL TO OPERATE, CLEAN AND ECONOMICAL
c) FOR WIDE VARIETY OF MATERIALS EITHER WET OR DRY.
d) USED IN COMPLETELY CLOSED FORM SO SUITABLE FOR
TOXIC MATERIALS
• DEMERITS:
a) NOISE PRODUCTION
b) NOT FOR ABRASIVE MATERIAL
c) NOT APPLICABLE FOR SOFT MATERIALS

68. EDGE RUNNER MILL OR CHILEAN MILL OR
STONE MILL
Through hopper
feeding of a
particle
Due to gap
between revolving
& stationary stone
Product obtained
(for coarse
powders)

70. CONTI...
• CONSISTS OF ONE OR TWO HEAVY METAL OR GRANITE ROLLERS MOUNTED ON A
HORIZONTAL SHIFT AND TURNED ROUND A CENTRAL VERTICAL SHIFT ON A BED OF
STEEL OR GRANITE.
• STONES MAY VARY FROM 0.5 TO 2.5 M IN DIAMETER, THE LARGE SIZE WEIGHING
UPTO ABOUT 6 TONNES
• MATERIAL TO BE GROUNDED IS KEPT IN THE PATH OF THE RUNNER BY SCRAPPERS
• REDUCTION MECHANISM IS CRUSHING BY THE WEIGHT OF THE STONE (ATTRITION)
BUT MORE TO FRICTION BETWEEN SURFACES OF CONTACT BETWEEN RUNNERS
AND BED STONE.
• ALTHOUGH THESE ARE LARGELY REPLACED BY SOPHISTICATED MACHINES BUT
STILL IN USE FOR REDUCING EXTREMELY TOUGH AND FIBROUS
MATERIALS_ROOTS AND BARKS

71. CONTI...
• ADVANTAGES
• PRODUCES FINE PARTICLES
• REQUIRE LESS ATTENTION DURING MILLING OPERATION.
• DISADVANTAGES
• NOT SUITABLE FOR SIZE REDUCTION OF STICKY MATERIAL
• MACHINE NOISE LEADS TO NOISE POLLUTION.

72. COLLOID MILL
Through hopper
feeding occurs
Rotar & stator.
Due to gaps b/w
rotar & stator
Size reduction

73. CONTI…
• MERITS:
• SIZE REDUCTION IS CARRIED OUT IN THE PRESENCE OF LIQUID
• USEFUL FOR COLLOIDS, EMULSION, SUSPENSION.
• LOTIONS AND OINTMENTS.
• LESS THAN 1UM SIZE CAN BE OBTAINED.
• DEMERITS:
a) IT IS NOT USED TO PROCESS DRY MATERIALS.

74. • IT WORKS ON THE PRINCIPLE OF SHEARING
• CONSIST OF CONICAL ROTOR AND STATOR AND THE DISTANCE BETWEEN
THEM IS ADJUSTED BETWEEN 0.005 TO 0.075CM.
• ROTOR IS CONNECTED TO HIGH SPEED MOTOR WHICH CAN REVOLVE AT A
SPEED 3000 TO 20000 RPM
• MATERIAL IS FEED TO HOPPER AND SIZE REDUCTION TAKES PLACE WHEN
MATERIAL MOVES THROUGH ROTOR AND STATOR

75. END-RUNNER MILL
• CONSISTS OF WEIGHTED PESTLE MOUNTED ECCENTRICALLY IN A CERAMIC
GRANITE OR METAL MORTAR WHICH IS ROTATED BY A MOTOR.
• PESTLE ROTATES BY FRICTION AND IS FREE TO RISE AND FALL IN MORTAR SO THAT
ITS GRINDING ACTION INVOLVES BOTH IMPACTION AND SHEAR.
• THE MATERIAL BEING CRUSHED AND RUBBED BETWEEN IT AND THE ROTATING
MORTAR.
• SPRING-LOADED SCRAPPERS ENSURE THAT MATERIAL IS CONSTANTLY RETURNED
TO THE GRINDING AREA.
• AT THE END OF OPERATION THE PESTLE CAN BE SOUND CLEAR OF THE MORTAR
TO FACILITATE EMPTYING AND CLEANING.

76. • ADVANTAGES.
• THESE MILLS PROVIDE MODERATELY FINE POWDERS AND OPERATES
SUCCESSFULLY WITH FIBROUS MATERIALS, BARKS, WOODS, FRUITS, LEAVES
ETC
• WET GRINDING WITH VERY VISCOUS MATERIAL SUCH AS OINTMENT AND
PASTE IS POSSIBLE.

78. FLUID ENERGY MILL
Through
nozzles
fluid or
inert gas
passed
By
pressure
particles
strike with
this fluid
Reduction
of particle
size
occurs

79. • ALSO CALLED JET MILL, ULTRAFINE GRINDING MILL OR MICROFIBER
• WORKS ON PRINCIPLE OF IMPACTION AND ATTRITION
• FLUID (USUALLY AIR) IS PASSED THROUGH NOZZLE AT HIGH PRESSURE WHICH
WILL MOVE MATERIALS WITH TURBULENCE AT HIGH VELOCITY
• COARSE PARTICLES ARE FED INTO MILL AND TURBULENCE CAUSES IMPACT
AND ATTRITION TO PRODUCE FINE PARTICLES.

80. CONTI…
• MERITS:
a) NO MOVING PART SO NO NOISE PRODUCTION.
b) NO HEAT GENERATION.
c) SUITABLE FOR THERMO LABILE COMPOUNDS.
d) LESS THAN 5UM PARTICLE SIZE OBTAINED.
e) NO CONTAMINATION DUE TO ABRASION
f) DOESNOT CONTAIN ANY MOVING PARTS