2. INTRODUCTION
• Mixing is defined as the process of thoroughly combining
different materials to achieve a homogenous mass. In most
cases, the mixture is a combination of dissimilar materials (such
as polyethylene pellets and black pigment to make trash bags)
using significant agitation. A mix can also be made with a
chemically homogenous material that requires uniform
distribution of its particles.
• Mixing basically done for solids. Solids and classified in to two
type:
– Non –Cohesive Solids: Solids which fall freely and
are easy to mix.
– Cohesive Solids: Solids which form lumps and need
a proper mixing
3. MIXERS FOR NON - COHESIVE
SOLIDS
• Non Cohesive mixers are for non-sticky solids which have a wide
variety free-flowing powders preferences to heavy pastes
options. Mixing could be carried out by agitation, tumbling,
centrifugal action and impact forces.
• Non-Cohesive solid mixers are of four types:
1. Internal Screw Mixer
2. Tumbling Mixer
3. Ribbon blender Mixer
4. Impact Wheels
5. • Internal screw mixture is made of carbon steel. Mixture casing is
vertical tank containing helical conveyers.
• Mixture inside Shaft is required its rotating in forward or
backward direction. And outside casing is fixed. It also consists of
a inlet and outlet valve.
• Helical shaft is connected with the motor which allows it to
rotate. Shaft is very close to the conical container which allows
effective mixing.
CONSTRUCTION OF INTERNAL SCREW MIXERS :
6. • It consists of a vertical vessel with a screw rotating to achieve the
circulation of material and secondly the elevation of material.
• This results in intermixing of solid grains as well as shear action to
the ones in contact with the screw or the walls of container.
• The feed enters from bottom usually with aim to nullify the gravity
factor which could escape the molecules without desired mixing.
• Two vessel shapes are normally used for this category, the
cylindrical and the conical
WORKING OF INTERNAL SCREW MIXERS :
7. • On the basis of screw movement, internal screw mixers are
further classified as:
– Type I: Conical shaped vessel, with a screw orbiting the centre
of axis of the vertical tank and also rotating around its own
axis.
– Type II: Conical shaped vessel, with a screw fixed at the centre
and rotating around its own axis, the conical tank is such
tapered that with increase in height the area swept increases.
– Type III: Cylindrical vessel with a screw in centre and rotating
around its own axis Internal screw mixers are normally used for
free-flowing grains and other light solids.
WORKING OF INTERNAL SCREW MIXERS :
(CONTINUED)
8. • Mixing and homogenization of powders, pastes and slurries
• Granulation or agglomeration of powders
• Addition or injection of liquids into dry powders
• Reaction under vacuum or pressure conditions
• Processing of powders under inert conditions
• Heating and cooling of powders
• Storage of non free flowing powders
• De aeration or densification of powders
• Homogenization of particle size and color
APPLICATION OF INTERNAL SCREW MIXERS :
9. TUMBLING MILL
Tumbling mills are used to mix different kind of powder materials of
required uniformity. They are also used for mixing the granules with
lubricant, binder or essence oil of flavors.
10. CONSTRUCTION OF TUMBLING MILL:
• Basic parts used are metallic vessels in which powder is
mixed, an electric motor for the rotation of the vessel, and
also baffles which helps in the mixing of the powders.
• A tumbler consists of a metallic enclosed vessel rotated on its
axis which causes the particles to mix of tumble over each
other onto the mixture surface.
• The mixing is done through the vessel by the baffles which are
present in the metallic vessel.
• To achieve the fast blending the ingredients are loaded top to
bottom instead of side to side. It is simple and very reliable. it is
made up of carbon steel or stainless steel.
• The mixed powder is discharged through butterfly or swivel
gate or pinch valve.
• The mixing of the powders can be achieved by slow rotation
either manually or with the help of the electric motor.
11. The feed is moved into the vessel be the hopper present in the
top of the vessel.
To achieve the fast blending the ingredients are loaded top to
bottom instead of side to side.
The metallic vessel which rotates either manually or with the
help of the electric motor.
In the rotation of the vessel the ingredients come over one
another and the function of mixing takes place.
For the mixing of the large bulk powders, the mixing of the
powder is done in the vessel of a suitable design along with the
baffles which gives a through mixing.
The rotation of the vessel should be slow so that the powder
does not remains stationary against the side the vessel held by
the centrifugal force but lifted by baffles and falls over
continuously.
WORKING OF TUMBLING MILL:
12. • Tumblers typically operate at speed of 5 – 25 rpm and have
capacities of 150 – 200 ft3. They can be filled to about 75% of
their maximum capacity.
• The most recent technology in tumbling mixing in bin blending.
In bin blending allows for ingredients to be a loaded, tumble –
blended, then stored or transported all in the same container.
• The advantages of this technology are the elimination of a
transfer step from blender to container and the elimination of a
cleaning step between different batches.
• Since the process is all occurring within one container, force
that could potentially cause segregation of the mixture is also
greatly reduced.
WORKING OF TUMBLING MILL:
(CONTINUED)
13. • Used for the mixing powder, Granule, lubricant additive, binder,
essence oil of flavor of western medicine, Chinese medicine and
health food.
• It is also used chemical – technical industry, drug and dye works,
Food and luxury food industry as well as textile and leather
industry.
APPLICATIONS OF TUMBLING MILL:
14. RIBBON BLENDERS
Ribbon blenders are used for mixing the powders, paste mixing and
also for heating and cooling. Shear mixing and gentle mixing are done
by ribbon mixers.
15. • A ribbon blender consists of a U-shaped horizontal trough
containing a double helical ribbon agitator that rotates within.
• The agitator's shaft is positioned in the centre of the trough and
has welded spokes on which the helical ribbons (also known as
spirals) are welded.
• Since the ribbon agitator consists of a set of inner and outer
helical ribbons, it is referred to as a “double” helical ribbon
agitator.
• The gap between the ribbon’s outer edge and the internal wall of
the container ranges from 3 to 6 mm depending on the
application.
CONSTRUCTION OF RIBBON BLENDERS :
16. • The charging of material in the blender is generally through
nozzles or feed-hoppers mounted on the top cover of the blender.
• The inlet cover also provides maintenance and cleaning access to
the inside of the blender.
• An external jacket can also be provided on the blender container
for applications which require heating or cooling of product
material
• The materials to be blended are loaded into the blender, typically
filling it to between 40 and 70 percent of the total volume of the
container.
• A spray pipe for adding liquids can be mounted above the
ribbons.
• For materials that tend to form agglomerates during mixing, high
speed choppers can be provided for disintegration of the
agglomerates.
WORKING OF RIBBON BLENDERS :c
17. • During the blending operation, the outer ribbons of the agitator
move the material from the ends to the center while the inner
ribbons move the material from the center to ends. Radial
movement is achieved because of the rotational motion of the
ribbons.
• After blending, the material is discharged from a discharge valve
located at the bottom of the trough. The discharge can be fitted
with any of various valves. Ribbon blenders can be designed for
multiple discharge ports. Unlike tumbling blenders where 100%
discharge of material is achieved by gravity, in a ribbon blender the
material is discharged by rotation of the ribbon agitator.
• An alternate design to the ribbon agitator is the paddle agitator
which can handle fragile material. The paddle agitator is composed
of both forward and reverse paddles in place of the ribbon. The
paddles are positioned to move the material in opposing lateral
directions as well as in a radial direction.
WORKING OF RIBBON BLENDERS :
(CONTINUED)
18. The following are the applications of the Ribbon Blender:
– Blending large volumes of dry solids.
– Dry powder to wet phase mixing.
– Mixing of bulk drugs, chemicals, and cosmetic powders.
– Dry Blending of capsule formulations.
– Lubrication of dry granules in large quantity.
– Heating, cooling, and drying of materials.
– Coating solid particles with small amounts of liquids to produce
formulations.
Materials commonly blended in the ribbon blender are as follows:
– Abrasives, Engineered plastic resins, Pesticides and herbicides,
Animal feeds, Epoxy resins, Pet foods, Bakery premixes, Carbon
black.
APPLICATIONS OF RIBBON BLENDERS :
19. CONSTRUCTION OF IMPACT WHEELS
• Impact wheels has a stationary shell which is made of thick
steel, the impact wheel rotor is at the center of shell which
collects the feed from the inlet and then vigorously mixes the
material.
• Due to rotation of wheel the material mixes and some times gets
grinded.
• Impact wheel contains the hammer connected to the wheel.
IMPACT WHEELS
20. • Fine, light powder blended continuously by spreading them out
in a thin layer under centrifugal action.
• A premix of the several dry ingredients is fed continuously near
the center of a high speed spinning disk.
• The disk of 10 to 27 inches in diameter, which throw throw it
outward into a stationary casing.
• The intense shearing force acting on the powder during there
travel.
• The premix is dropped onto a horizontal double rotor.
• Rotor carrying short vertical pins near its periphery to increase
the mixing effective ness.
WORKING OF IMPACT WHEELS :
21. • A 14 inches disk turns at 1750 rpm for easy problems and for
hard it turn at 3500 rpm.
• For a good results the premix fed to an impact wheel must be
fairly uniform.
• There is almost no hold-up of material in the mixer and no
chance for recombining material
• Recombined material passed through with that which is
entering.
• Impact wheels blend 1 to 25 tons/hr of light free- flowing
powders
WORKING OF IMPACT WHEELS :
(CONTINUED)
