objectives, applications, factors affecting mixing, the difference between solid and liquid mixing, mechanism of mixing, double cone blender, twin shell blender, ribbon blender, sigma blade mixer, planetary mixer, propellers, turbines, paddles and silver son emulsifier

1. MIXING
Parag Jain
Assistant Professor
Chhattrapati Shivaji Institute
of Pharmacy
Durg, Chhattisgarh
Presented by

2. Mixing
Definition and objectives
Mixing equipment
Impellers for liquids
Mixers of dry powders
o Factors affecting mixing of solids
1. Tumbling mixers
2. Agitator mixers
3. Special mixers for powders
4. Entolator impact when mixer
5. Pneumatic mixer
6. V-type mixer
Mixers for semisolids
o Types of flow in semisolids
1. Beaters
2. Kneaders
3. Mixer-Extruders

3. Definition
It is the intermingling of two or more dissimilar portions
of materials resulting in attainment of a desired level of
uniformity ei-ther physically or chemically.
Perfect mixing:
It is that state in which any sample removed from the
mixture will have exactly the same composition as any
sample taken from any point of the mixture.

4. Random mixing:
It is the state in which there is a probability of finding the particles
of a given components the same at all points in the mixture and is
in the same ratio of components in the entire mixture.

5. • Objectives of mixing:
• Attainment of complete and mutual distribution of the
constituent materials.
• Increasing the contact surface thus promoting chemical and
physical reactions.
Mixing can be done for the following reasons:-
• When a solid is dissolved in a vehicle, a solution is obtained .
• When an insoluble solid is mixed with a vehicle, a
suspension is obtained.
• When a solid or liquid is mixed with a semisolid base, an
ointment or a suppository is produced.

6. Types of Mixtures
Mixtures may be classified as follows:
• 1. Positive mixtures
• 2. Negative mixtures
• 3. Neutral mixtures

7. 1. Positive mixtures
These types of mixtures are formed when two or more
than two gases or miscible liquids are mixed together by
means of diffusion process. In this case no energy is
required provided the time allowed for solution formation
is sufficient. These types of materials do not create any
problem in mixing.

8. 2. Negative mixtures
• These types of mixtures are formed when insoluble
solids are mixed with a vehicle to form a suspension or
when two immiscible liquids are mixed to form an
emulsion. These mixtures are more difficult to prepare
and require a higher degree of mixing with external
force as there is tendency of the components of these
mixtures separate out unless they are continuously
stirred.

9. 3. Neutral Mixtures
Many pharmaceutical products such as pastes,
ointments and mixed powders are the examples of
neutral mixtures. They are static in their behavior. The
components of such products do not have any tendency
to mix spontaneously but once mixed, they do not
separate out easily.

10. Mechanism of Mixing
In all type of mixers, mixing is achieved by applying one
or more of the following mechanisms: -
• Convective mixing – During convective mixing transfer
of groups of particles in bulk take place from one part
of powder bed to another. Convective mixing is
referred to as macromixing.

11. • Shear mixing – During shear mixing, shear forces are
created within the mass of the material by using
agitator arm or a blast of air.
• Diffusive mixing – During this mixing, the materials are
tilted so that the gravitational forces cause the upper
layers to slip and diffusion of individual particles take
place over newly developed surfaces. Diffusion is also
sometimes referred to as micromixing.

12. Rate of Mixing
• Mixing is the process of achieving uniform randomness
of the mixed components, which on subdivision to
individual doses contains the correct proportions of
each component which depends on the amount of
mixing done

13. Theory of mixing
• A significant aspect in mixing is to define when a
particular batch is mixed .This depends on the method
used for examining the samples and its accuracy, the
number and location of the samples and the desired
properties of the mixture. Diverse criteria like electrical
conductivity of the samples, specific gravity of the
samples, the amount of a key constituent in the
samples, the rate of solution of a soluble solid in the
samples etc.

14. Classification of mixing equipments
S.No Type of mixer Name of the mixer Uses
1) Liquid-liquid
mixing
❖ Shaker mixers
❖Propeller mixers
❖ Paddle mixers
❖Turbine mixers
❖Sonic and ultrasonic devices
such as Rapisonic homogenizer
Used in the preparation of emulsions,
antacid suspensions, mixtures such as
anti-diarrhoeal bismuth-kaolin mixtures
etc.
Rapisonic homogenizer is
particulary used in the mixing of
immiscible liquids i.e. preparation of
emulsions.
2) Solid-solid
mixing
❖ Agitator mixers
❖ Tumbling mixers
❖Double-cone mixers
❖ V-blenders
Used for the mixing of dry powders.
3) Semi-solid mixing ❖ Agitator mixers like sigma
mixers and planetary mixers
❖Shear mixers like colloidal mills
and triple roller mills
These mixers are used for wet granulation
process in the manufacture of tablets, in
the production of ointments.
Sigma mixers can also be used for solid-
solid mixing.

15. Mixing equipment:
These are classified according to materials intended to be
mixed into:
1. Impellers for liquids
2. Mixers for powders
3. Mixers for semisolids or pastes.

16. I. Impellers for liquids
There are three types:
1- Paddle 2- Turbine 3- Propeller
The performance for impeller mixer depends on :
Creation of a current or stream of liquid which penetrate to
all point of mixing vessel or tank.
Turbulence movement to carry the current in all places of
the tank.

17. Types of flow in liquids:
1. Tangential flow (Rotational): the liquid flows as
circles around the impeller shaft.
2. Radial flow: flow of liquid in a direction to-ward the
walls of the tank verti-cal to the impeller shaft.
3. Axial or longitudinal flow: flow of liquid up and
down parallel to the impeller shaft
Shaft
Blade

18. Disadvantage of tangential flow:
If the tangential flow predominates, vortex forms also symmetry of
apparatus
(i.e. presence of shaft in center) leads to vortex formation.
Vortex Sever Vortex
Disadvantages of vortex:
1. No real mixing.
2. Settling of solid particles in the bottom and no dissolution
3. Air may be entrapped in solution causing degradation of oxdisable
materials.

19. Suppression of vortex:
To avoid vortex formation:
(1) In small tanks: Off-centering of the shaft or put the shaft inclined
Off centering of shaft Inclined shaft

20. (2) In large tanks: One use baffles on the wall or near to it
3) In very large tanks : The shaft is introduced from the side of the tank
in a horizontal position.

21. Types of impellers for mixing liquid dosage forms:
1- Paddles
Revolution 20 -120 (r.p.m)
The current are tangential and radial, there is no axial current.
The diameter of the shaft is 50 - 80 % of the di-ameter of mixing tank
Width of the blade is 1/6 - 1/10 its length.
It is suitable for mixing thin liquids having viscosity of about 1000
centi-poises.

22. Gate Paddle can be used for viscous liquids
Disadvantages:
1. It Cannot be used for liquids with viscosities more than 1000
centi-poises.
2. They are ineffective in suspending heavy solids because of absence
of axial flow.

23. 2- Turbines
Resemble paddles but the blades are more.
Revolution: 110 - 200 revolution/min.
Diameter of the shaft: 30 - 50% of the inside diameter of the container
Orientation of baffles and angles of blades

24. The blades may be straight, curved, vertical or pitched (inclined with angle
45°).
(Curved) (Pitched)
(Straight)
The currents in these turbines may be radial and tangential ( increasing
velocity cause increase in the radial current)
The turbine mixers are effective in mixing liquids with viscosities up to
100,000 centipoises.

25. 3- Propellers
a - Aircraft propeller b- Marine Propeller
Revolution: 400 - 1750 revolution / min.
Currents: Axial and tangential
Uses: They are used for suspending heavy solid particles to be kept
in suspension. Also they are suitable for rapid mixing of thin
liquids. They are not used for liquids having viscosities more than
5000 cen-tipoises (due to absence of radial flow)

26. Special mixers for liquids
Cone mixer:
Moves with higher speeds so give efficient mixing.

27. Disc impeller :Round discs of different configuration are mounted on
the rotating shaft to increase mixing efficiency.
In mixing of syrups , liquid dosage forms light suspensions in
pharmaceutical industry, one use the stainless steel steam jacktet mixing
tanks.

28. II. Mixers for dry powders
Purposes of dry powder mixing:
A. For preparation of multidose dry powder, e.g., effervescent salts or
antacids. So the constituents must be well mixed to give a uniform
dose.
B. Mixing of ingredients before compressed as tablets or filled into
capsules or for preparing any solid dosage form.

29. Scale of Scruting:
It is the smallest amount of a drug that can be mixed well .If the dose of
the drug in the mixture is less than the scale of scruting, the normal mixing
methods fail to attain efficient mixing.In this case geometric ,i.e., dilution
mixing must be adopted .
Mechanisms of Powder mixing:
During the mixing process of dry powder the particles may be subjected
to three types of forces :
1- Compression
2- Tensile force (Tension)
3- Shear(change in the positions of the mixture components)

30. In mixing of powder one need for application of shearing force to change
the position of particles and give efficient overall movement of particle.
Localized shear forces are applied as agitator or ribbon. This cause
overall movement of powder giving efficient mixing, but may cause
some sort of size reduction which would be undesirable.

31. Factors affecting mixing of solids:
1. Particle size:
The particle sizes must be nearly similar in all particles of
the mixture.
Increasing the difference in particle size will lead to
segregation (size separation), since small particles can fall
through the voids between the larger particles.
Constant movement of the mixer may lead to suspension of
fine parti-cles in air. So stop the mixer immediately or
remove the air.

32. 2- Density
The difference in densities among mixed particles will lead to
segregation. The heavy particles settle down while light ones
will rise up.
This is aggravated if the heavy particles are coarse and the light
particles are finer
So mixed particles would be equal in density to attain good
mixing.

33. 3- Electrostatic charges:
These charges are formed due to constant friction among the mixed
particles.
Similar charges repel particles from each others leading to
segregation.
This can be overcome by:
1. Stopping the mixing equipment. (no increase in time of
mixing)
2. Adding wetting agent or surface active agent which neutralize
similar developed charges on the particles
3. Adding some water and evaporate it after the mixing operation
is completed (if water do not affect stability of components)

34. Conditions to for good mixing
1. Capacity of mixer: the mixer must not be overfilled or low - filled.
Overfilling reduces the efficiency and do not allow sufficient space for
dilation of the powder. Overfilling prevents the movements of the powders.
2. Application of shear force to cause change of the position of powders so
give complete and efficient mixing.
3. Optimum time for mixing (determined by experience). Increasing the time
of mixing will cause segregation while decreasing the time of mixing will not
give complete mixing.
4. Light handling of powder to prevent segregation.
5. Mixer operates in three dimensions

35. Type of mixers for powder
I- Tumbling mixers:
Here, the movement of particles occurs by tilting the material beyond
angle of repose using gravity to impel flow

36. 1- Tumbling barrel or drum mixer :
• Consist of cylindrical vessel rotating on its horizontal axis. Gravity
impels flow.
• To increase the efficiency, put the mixer in-clined.
• It gives light movement so it is suitable for friable particles when.
Disadvantageous in low shear force

37. 2- Cubical - shaped blender
Mixing occurs by sliding of powder on its wall and gives
mixing in three dimensions if hanged from the corner.
Disadvantages:
1. Difficult in cleaning due to presence of different corners.
2. Sliding action causes abrasion of particles

38. 3- Double cone blender: Composed of two cones joined to short
cylindrical section. It is easily cleaned. It is charged by 50 % of its
capacity
by powder to ensure complete transfer of powder in the two cones.
Advantages:
1. No dead spots in mixing
2. It is easily cleaned,
3. It contains no corners.

39. 4- Twin -shell or V -shaped mixer: It gives more efficient and
more precise mixing due to high shearing force

40. Factors for good mixing in tumbling mixers:
1. Capacity of the mixer must not more than 50% of its capacity.
2. Optimum time of mixing.
3. Optimum speed of the mixer ,increasing the speed causes adhesion
of powder on the walls of the mixer.
4. Light handling of the powders to minimize size reduction.
5. The method of charging the powders in the tumbling mixers is
important: The materials must not be placed in layers. If placed in
layers, mixing will affect the upper layer only. So, materials are pre-
mixed or put side - by - side and mixing starts immediately.

41. Advantages of tumbling mixers:
1. They are mild equipment (not aggressive).Thus they are suitable
for friable materials.
2. They are preferable when different particle sizes and densities
powders are to be mixed due to repeated reversal of direction of
flow.
3. If some mixers trough contains an arm which rotates to transmit
shearing action to parti-cles representing an advantage.

42. II. Agitators mixers:
In these mixers, shear is applied by means of agitating
ribbon force.
Example : Ribbon blender

43. Ribbon blender:
There is an outer spiral ribbon to move the materials in one direction
and an inner spiral ribbon to move materials in the opposite direction.
The outer ribbon must have a fairly close clearance with the wall so no
material remains in the bottom surface.
It is used for blending of materials (or powders) tend to aggregate or
don't flow freely.
Dry Mixer

44. Disadvantages:
1. It is not precise .
2. Consumption of powder is more than that in tumbling.
3. Grinding of materials may occur.
4. It is not used for fragile particles

45. 3- Special Mixers for Powder
1.Impact wheel mixer.
2. Pneumatic mixer.

46. • This is based on rotating a disc or a wheel 20-68 cm in diameter,
rotate 1750 - 3500 revolution / min.
• The materials are feed from above in the center of the disc. The shear
force developed cause continuous powder mixing.
• The particles of powder are then ejected by the centrifugal force
from the disc periphery onto the walls of a conical tank which gives
the mix-ture a spiral movement towards the bottom
4. Entolator impact wheel mixer:

47. 4- Pneumatic mixer: (Airmix mixer)
Here, the driving force is the com-pressed air
which is introduced through nozzles present at
the lower part. These nozzles are arranged in a
man-ner that escaped air stream in a vertical
mo-tion gives a chance for powder to settle.

48. Evaluation of a blend of powder after mixing :
1.The sample mixture is taken and evaluated by:
2. Microscopic Counting if particles are different in shape.
3. Analytical techniques for the drug and other components in the
mixture
4. Screen analysis of the mixture, if the powder mixture is different in
size.

49. V- Type mixer:
It has two motors :One for rotating the shell and
the baffled shaft in opposite direction.
Advantages of the V-type mixer:
1. It is efficient in mixing
2. It has no dead spot
3. It has variable speed rotation
4. Easily cleaned
the other for rotating

50. Types of mixers for semisolids and pasts: There are four classes of
equipment:
(1) Beaters (2) Kneaders
(3) Mixer extruders (4) Mixing rolls.

51. 1. Beaters:
These are similar in principle to the agitator mixers for powders
and liquids, but are more heavily built to handle materials of
greater consistency. The agitator arms are designed to give a
pulling and kneading action, and the shape and the movement of
these arms are such that there are no "dead spots" in the mixing
vessel. An example of such mixers is the Hobart's Mixer shown in
the following Figure
Hobart's Mixer: (a) The mixer (b)
Planetary motion.

52. 2. Kneaders:
Kneading involves squashing the material flat, folding
it over on itself, and squashing it once more. Most
kneading machines also tear the mass of material apart
and shear it be between a moving arm and a stationary
surface.
Double-Arm Mixer

53. Blades of various designs as those shown in the following Figure are
available for several kneading purposes:
Blades of Various Designs: (a) Sigma blade (b) double-naben blade,
(c) Dispersion Blade.

54. 3- Mixer-Extruders:
The operation of a mixer-extruder depends essentially upon cutting
and folding the material in a mixing chamber by means of special
blades, and extruding It through a die, thereby subjecting the
material to additional shear.
Mixer-extruders continuously mix materials that are difficult to mix
such as clays and thermoplastics.
An example of such mixers is the "Roto-feed Mixer" shown in the
following figure.
Roto-feed mixer

55. 4. The Mixing Rolls:
In mixing rolls, the materials subjected to intense shear by passing
between smooth metal rolls turning at different speeds. By repeated
passage between such rolls, solid additives can be thoroughly
distributed into pasty or plastic materials.
An example of such mixing rolls is the "Triple-Roll Mill".

56. Mixers for semi-solids
Mixers for semi-solids may be divided into:
• 1) Agitator mixers –
• Sigma mixers and planetary mixers.
• 2) Shear mixers -
• Colloidal mill

57. 1) Agitator mixers
• These are similar in principle to the agitator mixers
used for liquids and for powders, indeed the planetary
motion mixer is often used for semi-solids. Mixers
designed specifically for semi-solids are usually of
heavier construction to handle materials of greater
consistency.
Sigma mixer :-
• Sigma mixer contains mixing element (Blades) of Sigma
type two in numbers which contra rotates inward to
achieve end to end circulation and thorough and uniform
mixing at close or specified clearance with the container .
The mixed product can be easily discharged by tilting the
container by hand lever manually either by system of gears
manually operated or motorized.

58. Uses of sigma mixers:-
• sigma mixers are used for wet granulation process in the
manufacture of tablets, pill masses and ointments. It is
primarily used for solid-liquid mixing although it can be
used for solid-solid mixing also.
Advantages :-
• Sigma blade mixer creates a minimum dead space during
mixing. There is close tolerance between the blades and
the sidewalls as well as the bottom of the mixer shell.
Disadvantage:-
• Sigma mixers work at a fixed speed.

59. Sigma blade mixer

60. Planetary mixers
• Planetary mixers are used for mixing and beating for
viscous and pasty materials, the planetary mixer is still
often used for basic operations of mixing and blending in
pharmaceutical industry. Figure 10-a and 10-b shows
planetary mixer and its different blade attachment.
Uses of planetary mixers: -
• Low speeds are used for dry blending and faster speeds
for the kneading action required in wet granulation.
Advantage:-
• Planetary mixers work at varying speeds. This is more
useful for wet granulation and is advantageous over sigma
mixers.

61. • Disadvantages
• 1. Planetary mixers require high power.
• 2. Mechanical heat is built up within the powder
mix.
• 3. Use is limited to batch work only

62. 2) Shear mixers
Machines designed for size reduction can be used for
mixing e.g. roller mills but although the shear forces are
good, the general mixing efficiency is poor. Rotary forms
may be used and the colloid mill has a stator and a rotor
with conical working surfaces. The rotor works at a speed
of the order of 3000 to 15000 r.p.m. and the clearance
can be adjusted between 50 and 500 micrometers.

63. Colloid Mill
• The colloid mill is useful for milling, dispersing, homogenizing and
breaking down of agglomerates in the manufacture of food pastes,
emulsions, coatings, ointments, creams, pulps, grease, etc.
Rotational speed of the rotor varies from 3,000-20,000 r.p.m. with
the spacing between the rotor and stator capable of very fine
adjustment varying from 0.001 inch to 0.005 inch depending on the
size of the equipment.
Advantages :-
• Extremely fine particle distribution through optimal shear force.
• High capacity with minimal space requirements.
• Rapid ha ndling and easy cleaning.
• Virtually unlimited application due to highly flexible homogenization
system.

64. Colloid Mill

65. Website: www.probecell.com Email: probecellinfo@gmail.com
Ph: 7415211131
Office: Smriti Nagar, Bhilai, Chhattisgarh - 490020
https://youtube.com/c/ParagJainthunderpassionate https://www.facebook.com/thesisresearchwriting
Research article Review article Thesis Synopsis PhD Title Research guidance