Mixing is a general term that includes stirring, beating, blending, binding, creaming, whipping, and folding. In mixing, two or more ingredients are evenly dispersed in one another until they become one product.
3. INTRODUCTION
Mixing is defined as a process of thoroughly combining different materials to
produce a homogenous product.
Mixing fulfills many objectives such as simple combination of raw
ingredients, preparing suspensions, fine emulsions, dissolving components
etc.
4. Diagrammatic
representation of (A) a
perfect mix and (B) a
random mix.
A recently published
handbook on
industrial mixing
estimates the cost of
poor mixing to be as
high as US $ 100
million.
5. Objectives :
Mixing is a critical process.The quality
of final product depends upon the
nature of mixing .
Improper mixing lead to non
homogeneous products.
Proper mixing leads to decrease batch
cycle times and operational cost.
It also increase dissolution rate .
6. FACTORS AFFECTING
MIXING
1. Nature of product: For effective mixing particle surface should be
smooth.
2. Particle size: It is easier to mix powder of same particle size. Increasing
the difference in particle size will lead to segregation.
3. Particle shape: Particle should be spherical in shape to get a uniform
mixture.
4. Particle charge: some particle due to electrostatic charge exerts
attractive force which leads to separation.
5. Proportion of material: It is easier to mix powders if available in same
quantities
6. Viscosity: An increase in viscosity reduces the extent of mixing.
7. Temperature: Temperature also affects the mixing because viscosity
changes with increase in temperature.
8. Mixture volume: Mixing efficiency depends on mixture volume.
9. Agitator type: The shape, size, location and type of agitator also affect
affects the degree of mixing.
10.Mixing time: Mixing time is also very important for appropriate mixing.
7. MECHANISM OF MIXING
Mechanism of Solid Mixing:
1.Convective mixing, In which group of particles move from one
position to another. It also referred to as macromixing.
2.Shear mixing, In this, shearing force is created within the mass of
material by the use of a stirring arm or a burst of air.
3.Diffusive mixing, During this mixing, gravitational forces cause the
upper layers of material to slip and random motion of individual
particles take place on newly developed surfaces. Also known as micro
mixing.
8. Mechanism of Liquid Mixing:
•Bulk transport: It is the movement of large portion of material
from one location to another location. The movement is done by
rotating blades or paddles.
•Turbulent mixing: In this mixing is due to turbulence.
•Laminar mixing: It is define as one in which no turbulence
viscosity occurs.
•Molecular diffusion: The mechanism responsible for mixing at
molecular level is the diffusion resulting from thermal movement
of molecules.
11. SOLID MIXING EQUIPMENT:
1.Double cone blender:
Principle:the mixing occurs due
to tumbling motion.
Construction :All parts of the
equipment including the mixing tank
and blades are made of stainless steel.
The equipment consist of two cones
joined as a cylindrical section which
is rotated about an axis on the shaft.
The conical shape at both ends allows
uniform mixing and easy discharge.
12. Working:
The powder is filled up to two-thirds of the volume of the blender to ensure proper
mixing. The rate of rotation should be 30-100 revolutions per minute. On rotation, mixing
occurs due to tumbling motion. The product can be discharged from the bottom of the
equipment. The mixing tank can be slanted freely at the angle of 0° To 360° degrees for
discharging and cleaning purposes.
Advantages:
Easy to maintain and clean
There are no chances of clogging of material into comers
A large amount can be handled easily
It is efficient for mixing powders of different densities
Wear on equipment is little
Disadvantages:
Not suitable for fine particles
Not suitable for particles with greater particle size difference due to less shear
Pharmaceutical Application:
Double Cone Blender is efficient and versatile equipment for the homogeneous mixing of dry
powders and granules. Dry powder mixing for tablets and capsule formulations.
It can be used for pharmaceutical, food, chemical, and cosmetic products, etc.
13. V Cone Blender:
Principle: Mixing occurs by
to tumbling motion.
Construction:It consists
of an enclosed V-shaped vessel
that prevents any foreign
particle to enter into chamber. It
is made of either stainless steel
or transparent plastic. It
consists of a horizontal shaft
rotated about an axis causing
the particles within the mixer to
tumble over each other onto the
mixture surface. The charging
of material into the V-Blender is
through either of the two ends.
Batches from 20 kg to 1 tonne
can be loaded for mixing
depending upon the size of the
equipment
14. WORKING:
The material is loaded into the blender. The recommended fill-up volume for the
V-Blender is 50 to 60% of the total blender volume. On rotation, a tumbling
motion occurs. When the V-Blender tumbles, the material divides and
recombines continuously. The repetitive converging and diverging movement
between the material and the blender results in homogenous blending. The
product is collected from the bottom of V. Normal blend times are typically in the
range of 5 to 15 minutes depending on the properties of a material to be
blended.
Advantages of V Cone Blender:
•V-Blenders are therefore preferred when precise blend formulations are
required.
•They are also well suited for applications where some ingredients may be as
low as five percent of the total blend size.
•Loading and unloading of material is easy
•Easy to clean
Disadvantage of V Cone Blender:
They require high headroom for installation and operation.
They are not suitable for blending particles of different sizes and densities.
There are chances of segregation of these particles at the time of discharge.
Pharmaceutical Applications:
V-Blenders are used for dry mixing. It provides efficient blending in a short time.
This blender is often used for pharmaceuticals. But not suited for very soft
powders or granules.
V-Blenders are generally used for Food products, Milk powder, Dry flavors.
Pesticides and Herbicides, Animal feed, Spice blends, Baby foods, and
Cosmetics
15. Ribbon Blender
Principle: The mechanism of mixing is shear which is transferred by
moving blades.
Construction of Ribbon Blender:A ribbon blender consists of a U-
shaped horizontal shell containing a helical double-ribbon agitator
that rotates inside. The shaft of the agitator is positioned in the center
of the trough on which the helical ribbons (also called spirals) are
welded. Since the ribbon stirrer consists of a set of internal and
external helical ribbons, it is also called a “double” helical ribbon
agitator. The counteracting blades are provided for high shear as well
as for breaking lumps or aggregates. The ribbon blenders are
powered by a drive system consisting of a motor, a gearbox, and
couplings.
16. Working of Ribbon Blender:
The materials are loaded into the blender, typically filling it between 40
and 70 percent of the total volume of the container. Ribbons are
allowed to rotate with the help of the drive system. During the blending
operation, one blade slowly moves the solids in one direction and the
other moves them rapidly in the opposite direction. As a result,
homogeneous blending is achieved in a short time. The mixing is
generally carried out in 15 to 20 minutes. After blending, the material is
discharged from a discharge spout located at the bottom of the trough.
Advantages of Ribbon Blender:
1.Ribbon blenders can be operated in
both batch and continuous modes.
2.High shear by baffles cause break
down of aggregates
Less headspace requirement
Disadvantages of Ribbon Blender:
1.It is practically difficult to obtain
100% discharge in the ribbon blender.
2.The movement of ribbons near the
vessel walls due to high shear and
compression can damage fragile
materials and cause attrition.
17. Semisolid Mixing Equipment
1.Sigma blade mixer
Principle: The mechanism of
action is shearing which is
produced by intermeshing
sigma-shaped blades.
Construction: It consists of two
mixing blades, which shapes
resemble the Greek letter sigma
, are fitted horizontally in each
trough of the bowl.
18. Working of Sigma Blade Mixer:
The powders (40 to 65 percent of the mixer’s total volumetric capacity) are
introduced from the top .The blades move at a different speed . which
includes a motor, gear reducer, couplings, gears, bearings, and seals. The
material moves up and down and shear occurs between the blades and the
wall. The equipment is also attached to the perforated blades to break lumps
and aggregates. The discharge of the material is either by tilting the mixing
vessel, through the bottom discharge valve, or a discharge screw. The
homogeneous mixture is obtained in 10 to 30 minutes.
Advantages:
During mixing, minimum dead space is created.
lumps and aggregates broken by perforated blades
Loss of volatile solvent during mixing can be prevented by closing the
chamber.
Disadvantages:
Both blades rotate at the same speed.
Applications of Sigma Blade Mixer:
The sigma blade mixer is a commonly used mixer for high viscosity
materials.
Sigma blade mixers are used for the wet granulation process in the
manufacture of tablets, pill masses, and ointments.
19. Planetray Mixers
Principle:
It works on the principle of shear
that develops between the
stationary wall and the rotating
blade. The blade is also used to
reduce the size. The planetary
blades rotate on their axis while
they travel around the center of the
mixing bowl which ensures
complete and effective
mixing.Planetary mixers are mostly
used in solid mixing and granulation
process.
Construction of Planetary Mixers:
It consists of a vertical bowl that
can be removed. The material can
be loaded into the mixer directly
loaded into the mixer bowl. The
mixer has two blades that rotate on
their axes when they orbit the
mixing container on a common
20. Working of Planetary Mixers:
The material to be mixed is loaded into a mixing bowl
or shell. The blades rotate on their axis when they
orbit the mixing bowl on a common axis. Therefore
there is no dead spot in the mixing and high shear is
applied for mixing. After mixing, the material is
discharged through a bottom valve, or by manual
scooping of the material from the bowl.
Advantages:
Simple construction, operation, and relatively lower
cost
No dead spot in the mixing
The rotation speed of blades can be varied
Used for the wet granulation process
High mixing efficiency
Disadvantage:
Require high power
Heat build-up within powder mix
21. Liquid Liquid Mixing
1.Propellers
Principle: the propeller mixer mainly
principle of shearing force.
Construction:
It consists of vessel and propeller.
A propeller has angled blades, which
cause the fluid to circulate in both an axial
and radial direction.
Size of the propeller is small and many
increases up to 0.5meters depending on
size of tank.
22. Working:
The liquids to be mixed are transferred to the mixing vessel through pumping.
When propeller is started a vortex is formed due to centrifugal force to the
liquid by the propeller blades, This action causes liquid bulk to back-up
around the sides of the vessel and create a depression at the center around
the shaft. As the speed of rotation is increased air may be sucked into the
fluid by the formation of a vortex. The vortex formation is suppressed to
considerable levels by fitting baffles in vertical position into the vessel.
Vertical propeller mixer consists of three blades of suitable size depending
upon the diameter of vessel. Propellers are mounted on the impeller shaft
inclined at an angle to the vessel axis to improve the mixing. It provide good
blending capability in small batches of low to medium viscosity liquids
23. Advantages: (i) Propellers are used
when high mixing capability is required.
(ii) They are effective in mixing gas-liquid
dispersions at laboratory scale.
(iii) Propellers increases the homogeneity of
materials,
(iv) Can be used in two different patterns for
drying and pressing
Disadvantages:
(i) Propellers are not effective with liquids of
viscosity greater than For example, glycerin
and castor oil.
(ii) Need to be operated at high speed to
avoid solid settlings in reactor vessels.
24. Turbine mixer
Principle :
A turbine mixer is a mechanical device that is used in
mixing different type of liquids. The turbine mixer
works mainly on the principle of shearing action.
Construction:
1.Turbine consists of number of blades attached to
the circular disk.
2.The blades used in the mixture are of various
types: flat blades, disk-type flat blades, inclined
blades, curved blades, arrow headed blades, and
so on.
3.The diameter of turbine varies from 30 to 50
percentage of the diameter of vessel.
4 As compared to propeller turbines rotates at lower
speed
25. Merits of Turbine Mixer: Turbines give greater
shearing force than propeller.
Therefore, turbines are suitable for emulsification.
Demerits of Turbine Mixer: Turbines have less
pumping rate.
Uses of Turbine Mixer: 1.A turbine mixer suitable
for viscous fluids (7.0 pascal-second).
2. Turbines used for thin paste and emulsification.
3. Turbines can also be used to handle slurries with 60
percentage solids. Mainly used for semisolid materials.
26. PADDLES
Principle of Paddles:
Paddles consist of two long flat
blades attached vertically to a
shaft. IT rotates at low speed.
Paddle mixer is suitable to mix
viscous liquids or semisolids.
Construction of Paddles:
1.Blades used in this mixer are
dished or hemispherical in shape.
2.The diameter of paddle is 50-80
percentage of inside diameter of
vessel.
27. Working of Paddles: Paddles push liquid radially and
tangentially. There is no axial movement of flow during
mixing.
Merits of Paddles:
Vortex formation is not possible.
It has low speed.
Mixing efficiency is better.
No dead spots and deposited solids.
Demerits of Paddles:
Here suspension mixing is poor.
Baffled tanks are required.
28. SILVERSON EMULSIFIER
Principle of Silverson
Emulsifier: The silverson homogenizer
works on the principle that the large
globules in a course emulsion are broken in
to smaller globules by intensive shearing
forces and turbulence by high speed rotors
Construction of Silverson
Emulsifier: It consists of emulsifier
head.
The emulsifier head consist of a number of
turbine blades.
The blades are surrounded by mesh which
is enclosed by cover having perforations.
The blades are rotated by using electric
motor fitted at the top.
There is also one shaft whose one end is
connected to motor and other end is
connected to head
29. Working of Silverson Emulsifier:
The emulsifier head is dipped in to the vessel containing immiscible liquids.
When the motor is started, shaft rotates the head.
Therefore, turbines blades also rotate at very high speed.
The liquids are sucked trough the fine holes.
This is followed by intense hydraulic shear.
The oil is reduced in to globules quickly resulting in a homogenous uniform
product.
Then the fine emulsion emerge trough opening of cover.
Merits of Silverson Emulsifier:
Fast and efficient.
They are used to get a fine droplet or particle size (2-5 microns).
Process efficiency is good.
Low operating cost.
Demerits of Silverson Emulsifier:
Chance of chocking of pores of mesh.
Uses of Silverson Emulsifier:
Used in preparation of creams, ointments, pharmaceutical suspension and
emulsion of fine particle size.
30. Refrence
C. V. S. Subramanyam, T. J. Setty, S. Suresh,
and K. V Devi, ” Vallabh prakashan, Delhi,
vol. 9, pp. 70–120, 286-318, 2005.
L. Lachman, H. A. Lieberman, and J. L.
Kanig, The theory and practice of industrial
pharmacy. Lea & Febiger, pp. 3–30, 89-107,
2009.
J. P. Remington, Remington: The science
and practice of pharmacy, vol. 1. Lippincott
Williams & Wilkins, pp. 453–757, 2013
Wikipidea
Epg pathshala video lecture and notes.
Pv book of pharmaceutical engineering.
