Mixing is a crucial unit operation in pharmaceuticals, involving the randomization of dissimilar particles to form mixtures, categorized as positive, negative, or neutral. Various mixing methods, including solid-solid, liquid-liquid, and semi-solid mixtures, are influenced by factors such as particle size, shape, and charge. Different types of mixers, including ribbon, sigma blade, and planetary mixers, serve specific purposes, with distinct advantages and disadvantages based on their design and functionality.

1. MIXIN
G

2. MIXIN
G
• Mixing may be definedas a unit operationthat tends
to
result in a randomization of dissimilar
particles within a system.
2

3. TYPES OF MIXTURES
• Positive mixtures - Positive mixtures are formed
from materials such as gases or miscible liquids
which mix spontaneously and irreversibly by
diffusion, and tend to approach a perfect mix.
• Negative mixtures- With negative mixtures
the components will tend to separate out. If this
occurs quickly, then energy must be continuously
input to keep the components adequately
dispersed, e.g. with a suspension formulation,
such as calamine lotion.
• Neutral mixtures - Neutral mixtures are said to be
static in behavior, i.e. the components have no
tendency to mix spontaneously or segregate
spontaneously once work has been input to mix
them. Examples of this type of mixture include
mixed powders, pastes and ointments
3

4. Application of
mixing
• Mixing is one of the most common pharmaceutical
operations. It is involved in preparation of many types of
formulations.
• Mixing of powders is done prior to filling in capsules,
sachets
and as dry powder inhalers.
• Blending of powders is required in the preparation of
talcum, tooth powders etc.
• Dry mixing of materials is required for direct
compression into
tablets.
• Mixing of miscible liquids is done to prepare linctuses
• Mixing of immiscible liquids is done to prepare
emulsions.
• Mixing is needed to prepare semi-solid dosage forms
such as
4

5. OBJECTIVES OF MIXING
• Simple physical Mixture: This may be simply
the production of a blend of two or more miscible
liquids or two or more uniformly divided solids.
• Physical Change: Mixing may aim at producing a
change that is physical as distinct from chemical, for
example the solution of a soluble substance.
• Dispersion: This includes the dispersion of two
immiscible liquids to form an emulsion or the
dispersion of a solid in a liquid to give a suspension or
paste.
• Promotion of Reaction: Mixing will usually
encourage (and control at the same time) a
chemical reaction, so ensuring uniform products.
5

6. Diff. between liquid and solid
mixing
Liquid Mixing Solid Mixing
Flow currents are responsible for
transporting unmixed material to
the mixing zone adjacent to
impeller
Flow currents are not possible
Truly homogenous liquid phase can
be observed
Product often consists of 2 or
more easily identifiable phases
Small sample size is sufficient to
study degree of mixing
Large sample size is required
Mixing requires low power Mixing requires high power
6

7. Types of
mixing
1. Solid-solid mixing
2. Liquid-liquid mixing
3. mixing of immiscible
liquids
4. Solid-liquid mixing
5. Semi solid mixing
7

8. Solid-solid
mixing
• This is the process in which two or more than two
solid substance are mixed in a mixer by continuous
movement of the particle.
• MECHANISM OF MIXING IN SOLIDS:
• convective mixing (macro mixing): In the case of
convective mixing material in the mixer is transported
from one location to another. Usually this type of
mixing is applied for free- flowing and coarse materials
• Shear mixing: Force of attraction are broken down so
that each particles moves on its own between region of
different composition.
• Diffusive mixing (micro mixing): Random motion of
particles within the powder bed thereby particle change
their position relative to one another
8

9. Degree of
mixing
• The mixedness or goodness of mixing of the
powder system is important because mixing
involves particles with different properties and
different ratios.
• A powder mixture can be visualized as shown in
the
slide.
9

10. IDEAL MIXING OR PERFECT MIXING
• Ideal degree of mixing is represented by a
chessboard with black and white squares
representing two components (equal quantities).
• It indicates that each particle of one component is
lying adjacent to a particle of another component.
• Such an arrangement is practically impossible to
achieve in any mixer.
• A random mixture is the one in which probability of
finding the particle of one component at any point
is equal to the proportion of that component in the
mixture
10

11. Factors affecting powder
mixing
• Particle size: It is easy to mix materials having the
same particle sizes. If there is variation in
particle sizes, separation may occur since the
small particles move downward through the
spaces between the bigger particles. As the
particle size increases, flow properties of the material
increases which facilitates mixing.
• Particle shape: Particles should be spherical in
shape for uniform mixing. If there is irregular
shape of the particles in a material, then they
become interconnected in such a way that their
separation is relatively difficult after mixing than if
the particle shape is regular.
12

12. Factors affecting powder
mixing
• Particle charge: If the particle has
some electrostatic charge that cause
attraction forces between particles, then
there are more chances of segregation or
separation.
• Nature of the particle: Particle
hardness, elasticity, porosity, texture are also
the factors that affect mixing phenomena
greatly.
• Relative Density: For uniform mixing,
the particles of the materials to be mixed
should have the same density
approximately. If the components are of
different density, the denser material will
sink through the lighter one and demixing
13

13. Factors affecting powder
mixing
• Proportion of materials: It is easy to
mix materials which are equal in proportion by
weight or volume (1:1). If there is a large
difference in the proportion of materials, then
mixing is done in the ascending order of their
weights.
• Presence of Moisture: Moisture present
in particles heap also affects mixing
phenomena. For example mixing of dry clay is
more rapid and efficient than wet mixing of
clay. In fact proper mixing requires specific
moisture content in bulk.
14

14. Classification of
mixers
15
Classificatio
n of
Mixers
Free
Flowing
Solids
V Cone
Blende
r
Double
Cone
Blender
Cohesive
Solids
Planetar
y
Mixer
Sigma
Blende
r

15. 16
Classification
of Mixers
Batch
Mixer
Double
Cone
Blender
Twin Shell
Blender
Ribbon
Blender Sigma
Blender
Planetary
Mixer
Continuous
Mixer
Barrel
Mixer
Zig-Zag
Mixer

16. Cylindrical
blenders
17

17. Cylindrical
blenders
• Tumblers or cylindrical blenders with no mixing blade
are meant for dry powders
• Equipment consists of a container of any geometric
form. Container is mounted on special roller so that
it can be rotated about any axis.
18

18. DOUBLE CONE
BLENDER:
• Principle: It consists of double cone mounted on
a rotating shaft.
• As the mixer rotates, the materials to be mixed
undergo a tumbling motion.
• Mixing takes place due to convective transport
and diffusion.
19

19. 20

20. Double Cone
Blender
• Construction: It consists of a container
in the shape of a double cone
mounted on a rotating shaft.
• Material loading and emptying is
done through the same port.
• The rate of rotation should be
optimum depending upon the
size, shape of the tumbler and
nature of the material to be mixed.
• The rate of rotation commonly ranges
from 30 -100 rpm.
21

21. Double Cone
Blender
• Working: The material
to
loaded approximately two-
third
be mixed is
of the
volume of the blender.
• The blender is allowed to rotate.
• The materials inside the mixer
undergo a tumbling motion.
• The particles of the materials are
displaced from one location to
another to enable mixing to occur
by convection and diffusion.
22

22. Double Cone
Blender
Uses:
• The mixer is good for mixing of free-
flowing granules/powders but
poor for cohesive/poorly flowing
powders because the shear forces
generated are usually insufficient
to break up any aggregates.
• A common use
is
lubricants,
glidants
in the
blending of or
disintegrants
wit
h
granules prior to
tableting.
23

23. Double Cone
Blender
Merits:
• The mixer is suitable for mixing of fragile
granules as there is minimum attrition
• It is available in large capacity
• It is easy to clean, load and unload
• It is easy to maintain
Demerits:
• It requires a high headspace for installation
• It is suitable only for mixing of free flowing and
granular materials
• It is not suitable for mixing of powders with
large differences in particle size distribution
because not enough shear is applied to the
materials.
24

24. V Cone
Blender
25

25. V-cone
blender
• It is V shaped and made up of stainless steel
or transparent plastic. Material is loaded through
either of shell hatches and emptying is normally
done through an apex port.
• The material is loaded approximately 50-60 % of the
total volume.
• Small models – 20 kg , rotate at 35 rpm Large models
– 1 ton, rotate at 15 rpm.
• As the blender rotates , the material undergoes
tumbling motion. When V is inverted, the material
splits into two portions. This process of dividing
and recombining continuously yields ordered mixing
by mechanical means
26

26. Advantages and
Disadvantages
Advantages of V cone blender
• If fragile granules are to be blended, twin shell
blender is suitable because of minimum attrition.
• They handle large capacities.
• Easy to clean , load, and unload.
• This equipment requires minimum maintenance.
Disadvantages of V cone blender
• Twin shell blender needs high headspace for
installation.
• It is not suitable for fine particulate system or
ingredients of large differences in the particle
size distribution, because not enough shear is
applied.
• If powders are free flowing, serial dilution is
27

27. DOUBLE CONE AND TWIN SHELL
BLENDER WITH AGITATION MIXING BLADE
28

28. DOUBLE CONE AND TWIN SHELL BLENDER
WITH AGITATION MIXING BLADE
• The double cone and v-cone blender
can be fitted with mixing blades for
agitation.
• These blenders are same as double
cone and v-cone blender in terms of
construction and working with the
added advantage of the presence of
agitator blade in them.
• Uses: These blenders are suitable
for mixing of not only dry
powders/granules but also for mixing
29

29. DOUBLE CONE AND TWIN SHELL BLENDER WITH
AGITATION MIXING BLADE
• Merits:
• Attachments of agitator blades
are beneficial for both wet and dry
mixing.
• Wide range of shearing force can
be applied with agitator bars
permitting the intimate mixing of
very fine as well as coarse powders.
• Serial dilution is not needed
when incorporating low-dose active
30

30. • Demerits:
• Attrition is large, size reduction of
friable particles results.
• Cleaning may be a problem,
because agitator assembly must be
removed and the packing should
be replaced for a product change
over.
• Potential packing (sealing) problems
may occur in these mixers.
31

31. Ribbon blender
• Principle: Mechanism of mixing is shear. Shear
is transferred by moving blades. High shear
rates are effective in breaking lumps and
aggregates. Convective mixing also occurs as
the powder bed is lifted and allowed to
cascade to the bottom of the container
32

32. Ribbo
n
33

33. Ribbon
Mixer
34

34. Ribbon Blender
Construction: It consists of
horizontal cylindrical trough usually
open at the top and fitted with helical
blades.
• The blades are mounted on a
shaft through the long axis of the tank
and are often of both right and left-hand
twist.
• The blades are connected to fixed
speed drive.
•
35

35. Ribbon Blender
• Working: During mixing the blades rotate at
fixed speeds.
• One blade moves the solids slowly in
one direction.
• At the same time the other blade quickly
turns the solids in opposite direction.
• The powders are lifted and allowed to cascade
to the bottom of the container with a
centrally located screw.
• After blending, the blend is discharged
from a discharge valve located at the
bottom of the trough.
36

36. Ribbon
Mixer
37

37. Ribbon
Mixer
• For mixing finely divided solids, wet solid mass,
sticky & plastic solids. It is used for liquid-solid & solid-
solid mixing
Advantages:
• High shear can be applied by using baffles, which
bring about a rubbing & break down aggregates.
Disadvantages:
• Shearing action is less than in planetary mixer.
• Dead spots are observed
• It is a poor mixer, because movement of particles is
2 –
dimensional
• Speed is fixed
38

38. Sigma Blade
Mixer
39

39. Sigma Blade
Mixer
• Principle: This robust mixer will deal
with stiff pastes and ointments and
depends for its action on the close
intermeshing of the two blades
which resemble the Greek
letter Ʃ in shape.
• The clearance between the blades and
the mixing trough is kept small by the
shape.
• Inter meshing of sigma blades creates
high shear and kneading action.
40

40. Sigma Blade
Mixer
Construction: It consists of double
trough shaped stationary bowl.
Two sigma shaped blades are
fitted horizontally in each trough of the
bowl.
These blades are connected to a fixed
speed drive.
Mixer is loaded from top and unloaded
by tilting the entire bowl.
41

41. Sigma Blade
Mixer
• Working: Powders are introduced from the top
of the trough.
• During blending, the two blades rotate at
different speeds, one usually about twice the
speed of the other, which allows movement
of powder from sides to centers.
• The material also moves top to downwards
and gets sheared between the blades and the
wall of the trough resulting in cascading action.
• The perforated blades helps to break lumps
and aggregates creating high shear forces.
• The final stage of mix represents an
equilibrium state.
42

42. Sigma blade
mixer
43

43. Sigma Blade
Mixer
Uses: The mixer is used in the
wet granulation process in the
manufacture of tablets, pill masses and
ointments.
It is primarily used for liquid – solid
mixing, although it can be used for
solid – solid mixing.
It is ideal for mixing, kneading of
highly viscous mass, sticky and
dough like products.
44

44. Sigma Blade
Mixer
• Merits:
• Sigma blade mixer creates a
minimum dead space during
mixing.
• It has close tolerances between the
blades and the sidewalls as well as
bottom of the mixer shell.
• Demerits:
• Sigma blade mixer works at a fixed
speed.
45

45. Planetary
mixer
Principle
• Mechanism of mixing is shear. Shear is applied
between moving blade and stationary wall. Mixing
arm moves around its own axis and around the
central axis so that it reaches every spot of the vessel.
The plates in the blades are sloped so that powder
makes an upward movement to achieve tumbling
action also.
Construction:
Consists of vertical cylinder shell which can be
removed. The blade is mounted from the top of the
bowl. Mixing shaft is driven by planetary gear and it
is normally built with variable speed drive.
46

46. 47

47. • Working: The mixing blade is set off centre and is
carried on a rotating arm.
• It therefore travels round the circumference of the
rotating bowl while simultaneously rotating around its
axis.
• is therefore a double rotation similar to that of a
spinning planet around the sun-hence the name.
• The blade tears the mass apart and shear is applied
between the moving blade and its stationary wall.
• The plates in the blade are sloped so that the powder
makes an upward movement.
• Thus the tumbling motion is also achieved.
• Since the speed of the blade can be changed, initially
the blade is allowed to move at slow speed for pre-
mixing and finally at increased speed for active
mixing.
• The mixer is designed so that the blade covers all the
volume of the mixer.
48

48. • Uses: Planetary mixer is a very efficient mixer and can
break down agglomerates rapidly producing precise
blends. Low speeds are used for dry blending and fast
for wet granulation.
• Merits:
• In this mixer, the speed of rotation can be varied at
will. It is more useful for wet granulation process as
compared to sigma blade and ribbon blender.
• Demerits:
• Mechanical heat is buildup within the powder mix.
• It requires high power.
• It has limited size and is useful for batch work only.
49

49. Planetary
Mixer
50

50. MIXING OF MISCIBLE LIQUID
AND SUSPENSION
• Mobile liquids with a low viscosity are
easily mixed with each other.
• Similarly, solid particles are
readily suspended in mobile liquids,
although the particles are likely to
settle rapidly when mixing is
discontinued.
• Viscous liquids are more difficult to stir
and mix, but they reduce the
sedimentation rate of suspended
51

51. LIQUID
MIXING
• The mechanism of mixing can be classified into
four classes .
• Bulk transport
• Turbulent
• Laminar mixing
• Molecular diffusion
52

52. Mechanism of mixing in
liquids
• Bulk Transport: Bulk transport involves the movement
of a relatively large amount of material from one
position in the mixing equipment to another.
• Turbulent Mixing: Turbulent mixing arises from
the haphazard movement of molecules when forced
to move in a turbulent manner. The constant changes
in speed and direction of movement means that
induced turbulence is a highly effective mechanism for
mixing.
• Laminar Mixing: It is the mixing of two dissimilar
liquids through laminar flow, i.e., the applied shear
stretches the interphase between them. In this
mechanism, layers fold back upon themselves.
• Molecular Diffusion: It is the mixing at molecular level
in which molecules diffuse due to thermal motion.
53

53. FACTORS INFLUENCING LIQUID MIXING
• Viscosity: Mixing is affected by viscosity of
the liquids. More the viscosity of the liquids
more will be the difficult to proper mixing.
• Miscibility of the liquids: It is easier to mix
a mixture of miscible liquids than immiscible
ones.
• Surface tension of liquids: surface tension
of liquid is also an important factor that effects
mixing. High surface tension reduces extent of
mixing.
• Temperature: Temperature also affects mixing
as viscosity changes with the change in
54

54. FACTORS INFLUENCING LIQUID MIXING
• Mixer volume: Mixer volume also
affects mixing phenomena.
Mixer volume should be such that
over filling should not be done as it
decreases efficiency of mixing and
mostly material can’t be mixed
thoroughly.
• Mixing
time:
important
for
mixing timeis also
very proper
mixing. There is
always an optimum mixing time for
specific conditions in which mixing is
taken place.
55

55. Mixing equipment
• A system for batch mixing
commonly consists of two
primary components:
 A tank or other container suitable to
hold the material being mixed and
 A means of supplying energy to the
system so as to bring about rapid
mixing.
56

56. 57

57. Mixing
equipment
• The mixing device is called impeller,
which is mounted with the help of
shaft. The shaft is driven by a motor.
• Three
main
namely-
• Propeller
• Turbine
and
• Paddles
types of impeller are
used
58

58. Flow pattern during mixing
• The movement of the liquid at any point in the vessel
will have three velocity components which are as
follows:
• Radial component, acting in a direction vertical to
the impeller shaft. Excessive radial movement
will take materials to the container wall, whence
they fall to the bottom and may rotate as a mass
beneath the impeller.
59

59. Flow pattern during
mixing
• A longitudinal or axial component acting parallel to
the impeller shaft. Adequate longitudinal pattern is
best used to generate strong vertical currents
particularly when suspending solids are present in a
liquid.
60

60. Flow pattern during
mixing
• A tangential component acting in a direction
that is tangent to the circle of rotation round
the impeller shaft.
61

61. Flow pattern during mixing
62

62. Mixing
devices
63

63. Propellers
64

64. Propeller
s
• It consists of number of blades,
generally 3 bladed design is most
common for liquids.
• Blades may be right or left
handed depending upon the slant of
their blades.
• Two or more propellers are used for
deep tank.
• Size of propeller is small and
may increased up to 0.5 metres
depending upon the size of the tank.
•
65

65. Propeller
s
Uses:
The propeller will perform most
mixing duties with liquids when used
correctly.
It is the best unit when strong
vertical currents are required as in
suspension of solids in a liquid.
It is not normally suitable when
considerable shear is needed as in
emulsification.
66

66. Propeller
s
Merits:
• Used when high mixing capacity is required.
• Effective for liquids which have maximum
viscosity of 2.0 pascals. sec or slurry up to 10%
solids of fine mesh size.
• Effective gas-liquid dispersion is possible
at laboratory scale.
Demerits:
• Propellers are not normally effective with
liquids of viscosity greater than 5
pascal.second, such as glycerin castor oil, etc.,
67

67. 68
Propeller Mixing Process

68. Turbine
s
•
A turbine mixer may be used for
more viscous liquids.
•A turbine consists of a circular disc
to which a number of short vertical
blades are attached.
•Blades may be straight or curved.
•The diameter of the turbine ranges
from 30-50% of the diameter of the
vessel.
•The turbines impeller is rotated at a
lower speed than the propellers (50-
200rpm).
69

69. 70

70. Flat blade
turbine
Pitched blade
turbine
71
Most turbine impellers have flat blades
and cause the liquid to move rapidly in
a radial direction.

71. turbine
s
Uses:
 Turbine mixers are satisfactory
with mobile liquids, but, because
of the greater shearing effects they
can deal with more viscous
liquids than the propeller mixers.
 The turbines are particularly
suitable for preparing emulsions.
72

72. Turbine
s
73
Turbine

73. Turbines
Merits:
• Turbines give greater shearing forces than propellers
and is suitable for emulsification.
• Effective for high viscous solutions.
• They can handle slurries with 60% solids.
• Turbines are suitable for liquids of large volume and
high viscosity, if the tank is baffled.
Demerits:
• The standard turbine mixer is less suitable than
propellers for suspending heavy solids because of
absence of vertical flow.
74

74. Paddle
s
• A paddle consists of a central hub with long
flat blades attached to it vertically.
• Two blades or four blades are common.
• Sometimes the blades are pitched and may
be dished or hemispherical in shape and
have a large surface area in relation to the
tank in which they are used.
• Paddles rotates at a low speed of 100 rpm.
• They push the liquid radially and tangentially
• In deep tanks several paddles are attached
one above the other on the same shaft.
75

75. 76
Hemispherical Paddle
Flat Blade Paddle

76. Paddle
s
Uses: Paddles are used in the
manufacture of antacid suspensions,
antidiarrheal mixtures such as
bismuth-kaolin.
Merits:

Vortex
paddl
e
mixin
g.
formation is not
possible with impellers
because of low speed
Demerits:
 Mixing of the suspension is poor
therefore baffled tanks are required.
77

77. Vortex
formation
• A strong circulatory flow pattern
sometimes manifests into formation
of a vortex near the impeller shaft .
78

78. VORTEX FORMATION
Vortex can be formed when:
 Shaft is placed symmetrically in the
tank. Blades in the turbines are
arranged perpendicular to the central
shaft.
At high impeller speeds
 In unbaffled Containers
79
Vortex formation reduces mixing intensity by reducing
velocity of the impeller relative to the surrounding
fluid

79. 80
Prevention of Vortex Formation
Off-Centre Inclined Side-entry Push-pull
Baffled Container

80. Mixing of immiscible
Liquids
Mixing of immiscible liquids is carried
in pharmacy mainly in the
manufacturing of emulsions.
The
equipment
emulsion
is
used
calle
d
for preparing
the
emulsifier
or
homogenizer.
Silverson mixer, colloid mill and
rapisonic homogenizers are
suitable for emulsification.
81

81. 82
SILVERSON MIXER-HOMOGENIZER

82. Silverson Mixer-Emulsifier
Principle:
• It produces intense shearing forces
and turbulence by use of high speed rotors.
• The emulsifier head is dipped in the mixture
of immiscible liquids.
• The liquid mixture is sucked inside
the emulsifying head due to suction and is
dispersed in the form of fine globules when
acted upon by the turbine blade and
issued through the perforations from the
head.
83

83. SILVERSON HOMOGENIZER
CONSTRUCTION:
• It consists of long supporting columns and a
central portion.
• The central portion consists of a shaft which is
connected
to motor at one end and other to the emulsifying
head.
• The emulsifying head carries turbine blades.
• The blades are surroundedby a mesh, which is
further enclosed by a cover having openings.
84

84. SILVERSON HOMOGENIZER
• Working: The emulsifier head is placed in the
vessel containing immiscible liquids (or coarse
emulsion) in such a way that it should get completely
dipped in the liquid. When the motor is started,
the central rotating shaft rotates the head, which in
turn rotates turbine blade at a very high speed. This
creates a pressure difference. As a result, liquids are
sucked into the emulsifier head from the center of the
base and subjected to intense mixing action.
Centrifugal force expel the contents of the head with
great force through the mesh and onto the cover. As
a result a fine emulsion emerges through the
openings of the outer cover. The intake and
expulsion of the mixture set up a pattern of
circulation to ensure rapid breakdown of the bigger
globules into smaller ones.
85

85. Silverson mixer -
Emulsifier
 Uses: Used for the preparation of emulsions and
creams of fine particle size.
 Advantages: Silverson mixer is available in different
sizes to handle the liquids ranging from a few
milliliters to several thousand liters.
• Can be used for batch operations as well as
for continuous operations by incorporating into a
pipeline, through which the immiscible liquids flow.
 Disadvantages: Occasionally, there is a chance
is clogging of pores of the mesh
86

86. Silverson
Emulsifier
87

87. Semi-Solid
Mixing
• Semi solids dosage forms include ointments,
pastes, creams, jellies, etc., while mixing such dosage
forms, the material must be brought to the agitator
or the agitator must move the material throughout
the mixer.
The following mixers are helpful for mixing:
• Agitator mixers: e.g.:- Sigma mixers and Planetary
mixer.
• Shear mixers: e.g.:- Triple roller mill and Colloidal mill.
88

88. Mixing of semi-
solids
• The problems that arise during the mixing of
semisolids (ointments and pastes) stem from the
fact that, unlike powders and liquids, semisolids will
not flow easily. Material that finds its way to 'dead'
spots will remain there. For this reason, suitable
mixers must have rotating elements with narrow
clearances between themselves and the mixing
vessel wall and they must produce a high degree of
shear mixing, as diffusion and convection cannot occur.
The forces required for efficient mixing are high and
consumption of power is also high. Hence the
equipment must be rugged
constructed to
exhibit
dilatant
tolerate
propert
y
these forces. Some
semisolids i.e.,
viscosity increases with
increase in shear rates. Therefore, mixing must be
done at lower speeds. The speed must be changed
accordingly to thixotropic, plastic and pseudo plastic
materials.
89

89. Colloid
Mill
90

90. Triple Roller
Mill
91