1. TOPIC : Mixers for Non - Cohesive Solids
SAL COLLEGE OF ENGINEERING Department of Chemical Engineering ALA MECHANICAL OPERATIONS
( )
TOPIC : Mixers for Non - Cohesive Solids
YASHRAJ JADEJA ( )
SANDIP KOLADIYA ( )
MANAS DOSHI ( )
MILAN DONGA ( )
FACULTY:
GREESHMA NAIR

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
intoduction
MECHANICAL OPERATIONS- ALA
April 28, 2017

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:
Internal Screw Mixer
Tumbling Mixer
Ribbon blender Mixer
Impact Wheels
MECHANICAL OPERATIONS- ALA
April 28, 2017

4. Mixers for Non - Cohesive Solids INTERNAL SCREW MIXERS
MECHANICAL OPERATIONS- ALA
April 28, 2017

5. CONSTRUCTION OF INTERNAL SCREW MIXERS :
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

6. WORKING OF INTERNAL SCREW MIXERS :
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
MECHANICAL OPERATIONS- ALA
April 28, 2017

7. WORKING OF INTERNAL SCREW MIXERS : (CONTINUED)
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

8. APPLICATION OF INTERNAL SCREW MIXERS :
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
MECHANICAL OPERATIONS- ALA
April 28, 2017

9. Mixers for Non - Cohesive Solids 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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

11. WORKING OF TUMBLING MILL:
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

12. WORKING OF TUMBLING MILL: (CONTINUED)
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

13. APPLICATIONS OF TUMBLING MILL:
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

14. Mixers for Non - Cohesive Solids 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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

15. CONSTRUCTION OF RIBBON BLENDERS :
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

16. WORKING OF RIBBON BLENDERS :c
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

17. WORKING OF RIBBON BLENDERS : (CONTINUED)
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

18. APPLICATIONS OF RIBBON BLENDERS :
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

19. Mixers for Non – Cohesive Solids IMPACT WHEELS
MECHANICAL OPERATIONS- ALA
April 28, 2017

20. 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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

21. WORKING OF IMPACT WHEELS :
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.
MECHANICAL OPERATIONS- ALA
April 28, 2017

22. WORKING OF IMPACT WHEELS : (CONTINUED)
A 14 inches disk turns at 1750 rpm for easy problems and for hard it turn at 3500 rpm.
For a good results the primix 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 porwders
MECHANICAL OPERATIONS- ALA
April 28, 2017

23. MECHANICAL OPERATIONS- ALA
April 28, 2017