Mixing

Mixing: Objectives, applications & factors affecting mixing,
Difference between solid and liquid mixing,
mechanism of solid mixing, liquids mixing and semisolids mixing.
Principles, Construction, Working, uses, Merits and Demerits of Double cone blender
Principles, Construction, Working, uses, Merits and Demerits of twin shell blender
Principles, Construction, Working, uses, Merits and Demerits of ribbon blender
Principles, Construction, Working, uses, Merits and Demerits of Sigma blade mixer
Principles, Construction, Working, uses, Merits and Demerits of planetary mixers
Principles, Construction, Working, uses, Merits and Demerits of Propellers
Principles, Construction, Working, uses, Merits and Demerits of Turbines
Principles, Construction, Working, uses, Merits and Demerits of Paddles
And
Principles, Construction, Working, uses, Merits and Demerits of Silverson Emulsifier.

1. U nit :3 Mixing

2. Mixing: Objectives, applications & factors affecting mixing, Difference between solid and liquid mixing, mechanism of solid mixing, liquids mixing and semisolids mixing. Principles, Construction, Working, uses, Merits and Demerits of Double cone blender Principles, Construction, Working, uses, Merits and Demerits of twin shell blender Principles, Construction, Working, uses, Merits and Demerits of ribbon blender Principles, Construction, Working, uses, Merits and Demerits of Sigma blade mixer Principles, Construction, Working, uses, Merits and Demerits of planetary mixers Principles, Construction, Working, uses, Merits and Demerits of Propellers Principles, Construction, Working, uses, Merits and Demerits of Turbines Principles, Construction, Working, uses, Merits and Demerits of Paddles And Principles, Construction, Working, uses, Merits and Demerits of Silverson Emulsifier.

3. U nit :3 Mixing Mixing is define as a process that leads to result in a randomization unrelated particles within a system. MIXING is defined as  the unit operation that combines two or more components together by agitation, shear or mixers .

4. U nit :3 Objectives Mixing  increases the homogeneity of a system by reducing non-uniformity or gradients in composition , properties or temperature Secondary objectives of mixing include control of rates of heat and mass transfer, reactions and structural changes. To obtained uniform composition of the mixed components. To enhance the physical and chemical reaction of mixed components. To improve the dissolution and diffusion of mixture. To get a true solution after a mixing two miscible liquids

5. U nit :3 Applications Mixing is one of the most common pharmaceutical Operations. It is involved in the preparation of many types formulation. Mixing is also an intermediate stage in the production of several dosage forms. Wet mixing in the granulation step in the production of tablets and capsules. Dry mixing of several ingredients ready for direct compassion as in tablets. Dry blending of powder in capsules , dry syrups and compounds powders

6. U nit :3 Factors affecting 1.Nature of the product 2. Particle size 3. Particle shape 4. Particle charge 5. Proportion of Material 6. Relative density 7. Viscosity 8. Surface tension of liquids 9. Temperature 10. Mixer volume 11. Agitator type 12. Speed/rpm of the impeller 13. Mixing time

7. U nit :3 Factors affecting 1.Nature of the product : For effective mixing, the particle surface should be smooth. The rough surface of one or more components leads to increase chances of entry of active substance into the pores of another ingredient and further affect mixing. 2. Particle size: It is easier to mix powders of the same particle size. Variation in particle size leads to improper mixing. Increasing the difference in particle size will lead to segregation (size separation) since small particles can fall through the voids between the larger particles 3. Particle shape: The particle should be spherical to achieve uniform mixing. 4. Particle charge: Some particles due to electrostatic charges exert an attractive force which leads to separation.

8. U nit :3 Factors affecting 5. Proportion of Material: It is easy to mix powders if available in equal quantities. But to mix small quantities of powders with large quantities of ingredients is a difficult process. 6. Relative Density: If the components have a different density, the denser material will sink through lighter material, the effect of which will depend on the relative positions of the matter in the mixer. 7. Viscosity: The mixing is also affected by the viscosity. An increase in viscosity reduces the extent of mixing. More viscous particles cause poor mixing. 8. Surface tension of liquids: The surface tension of the liquid is also an important factor affecting the mixing. High surface tension reduces the extent of mixing.

9. U nit :3 Factors affecting 9. Temperature: The temperature also affects the mixing because the viscosity changes with the change of temperature. 10. Mixer volume: The volume of the mixing also affects the mixing phenomena. The blender volume should be such that overfilling should not be done as it decreases the mixing efficiency 11. Agitator type: The shape, size, location, and type of agitator also affect the degree of mixing achieved and the time required to mix specific components. 12. Speed/rpm of the impeller: The speed of the impeller affects the homogeneity of the mixing. As mixing at less rpm is more homogeneous than at a higher rpm.

10. U nit :3 Factors affecting 13. Mixing time: The mixing time is also very important for appropriate mixing. There is always an optimal mixing time for the specific conditions in which the mixing is taken place.

11. U nit :3 Difference

12. U nit :3 Mechanism In general mixing involves one or more of the following mechanisms: Convective Mixing: Convective mixing is a process of transferring groups of particles in bulk from one part of powder bed to another. It is also known as micro-mixing and is regarded as analogous to bulk transport. Depending on the type of mixer employed, convective mixing may occur by an inversion of the powder bed or by means of blades and paddles or by means of a revolving screw, or by any other method of moving a relatively large mass of material from one part of the powder bed to another.

13. U nit :3 Mechanism Shear Mixing: During this process, shear forces are created within the mass of material by using agitator arm or a blast of air. As a result of forces within the particulate mass slip and planes are set-up. Depending on the flow characteristics of the powder, these can occur singly or in such a way as to give rise to laminar flow. When shear occurs between regions of different composition and parallel to their interface, it reduces the scale of segregation by thinning the dissimilar layers. Shear that occurs in a direction normal to the interface of such layers is effective as it also reduces the scale of segregation..

14. U nit :3 Mechanism Diffusive mixing: Diffusive mixing is also known as micro mixing. In diffusive mixing, the materials are tilted to ensure that the upper layer slips and diffusion of individual particle take place at the new developed surfaces. This occurs when random motion of particles within a powder bed causes them to change position relative to one another. Such an exchange of positions by single particles results in a reduction of the intensity of segregation. Diffusive mixing occurs at the interfaces of dissimilar regions that undergo shearing and therefore it results from shear mixing. It may also be produced by any form of agitation that results in interparticulate motion.

15. U nit :3 Mechanism M mechanism of solid In solid mixing two different dimensions in the mixing process are convective mixing and intensive mixing. In convective mixing material in the mixer is transported from one location to another. This leads to less ordered state inside the mixer. The mixing components are distributed over the other components. With time the mixture becomes more random and after certain time the ultimate random state is reached. This type of mixing is observed for free-flowing and coarse solid materials. Physical properties of material that affects solid mixing are density, particle size and its distribution, wettability, stickiness and particle shape or roughness. Usually these factors contribute for the demixing of macromixed solids. If solids are in fine form with cohesive nature or if it is wet convective mixing is not enough to obtain random state. The relative strong inter-particle forces form lumps. The decrease in size of lump requires more intensive energy which is provided either as impact force or shear force.

16. U nit :3 Mechanism M echanism of liquid The liquid mixing occurs in two stages; first, localized mixing which applies sufficient shear to the particles of the fluid . second, a general movement sufficient to take all parts of the material through the shearing zone and to ensure a uniform final product. There are four essential mechanisms involved in liquid mixing as follows: Bulk Transport: Movement of a relatively large portion of material being mixed from one location in the system to another. Turbulent flow: It is characterized by the fluid having different instantaneous velocities at the same instant of time. The temporal and spatial velocity differences resulting from turbulence produce randomization of fluid particles. Laminar Flow: In this mechanism a streamline flow is encountered in highly viscous liquids.

17. U nit :3 Mechanism Molecular diffusion: It is a primary mechanism responsible for mixing at the molecular level which results from the thermal motion of molecules. It is governed by Fick's fist law of diffusion that describes concentration gradient across the system as: dm dt = − DA dc dx … (7.1) Where, dm dt = Rate of transport of mass across a surface area D = Diffusion co-efficient A = Area across which diffusion is occurring dc dx = Concentration gradient There is decrease in concentration gradient with time which approaches zero at completion. Liquid mixing as a process that can either be carried out batch to batch or can be a continuous one. Impellers, air-jets, fluid-jets and baffle mixers are the major types of mixing equipments used for batch mixing. Impellers operate using a combination of radial, axial and tangential flow. These might be classified into two further types, propellers and turbines, the former being used for low viscosity liquids while the latter for high viscosity liquids.

18. U nit :3 Mechanism M echanism of Semi-Solid semi-solids form neutral mixtures having no tendency to segregate although sedimentation may occur. Three most commonly used semi solid mixers are: Sigma blade mixer: This mixer has two blades which operate in a mixing vessel which has a double trough shape. These blades moving at different speeds towards each other. It can be used for products like granulation of wet masses and ointments. Triple-roller mill: The triple roller has differential speed and narrow clearance between the rollers which develops a high shear over small volumes of semi-solid material. This type of mills are generally used to grind semisolids to achieve complete homogeneity in the material for example, ointments. Planetary mixers: This mixer has a mixing arm rotating about its own axis and also about a common axis usually at the centre of the mixing wheel. The blades attached to the arm provide the kneading action, while the narrow passage between the blades and the wall of the container provides shear

19. U nit :3 Classification Based on the Flow properties of the powder, appropriate mixing should be selected

20. U nit :3 Classification Classification of mixing Equipment's Nature of mixer Examples Mechanism Batch type Mortar pestle Trituration Tumbling mixers or Cylindrical mixers without mixing blade Double cone blender, v cone mixers without baffles cube blender Tumbling action Tumbling mixer with a mixing blade V cone blender with a mixing blade Double cone blender with a mixing blade Tumbling action as well as shearing with blade Static mixers Sigma blender Stationary shell and rotating blade Air Mixers Fluidised mixer Air supported blender Continuous type Zigzag type Rotating shell with rotating blade

21. U nit :3 Double cone blender Double Cone Blender is an  efficient and versatile machine for mixing of dry powders and granules homogeneously . All the contact parts are made of stainless steel. The effective volume for optimum homogeneity is between 35-70% of gross volume. The SLANT double cone design eliminates dead spots. The effective volume for optimum homogeneity is between 35-70% of gross volume. The SLANT double cone design eliminates dead spots which occasionally occur in conventional double cone mixer. It can be used for pharmaceutical, food, chemical, cosmetic products etc.

22. U nit :3 Double cone blender Primary Features The conical shape at both ends enables uniform mixing and easy discharge. The cone is statically balanced which protects the gear box and motor from any excessive load. Powder is loaded into the cone through a wide opening and discharged through a butterfly or a Slide valve. Depending upon the characteristic of the product, paddle type baffles can be provided on the shaft for better. Contact parts are made of SS 304 or SS 316. Flame proof electricals can be provided as optional. 'Slant' design (off center) CLIN CONE BLENDER. Dust free bin charging system ensures minimum material handling. Mixing, uniform blending and de-agglomeration.

23. U nit :3 Double cone blender

24. U nit :3 Double cone blender Advantages They handle large capacities. Easy to clean, load and unload. This equipment requires minimum maintenance. Disadvantages Double cone blender needs high headspace for installation. It is not suitable for fine partic ulate system or ingredients of large differences in the particles size distribution , because not enough shear is applied. If powder are free flowing , serial dilution is required for the addition of low dose active ingredients .

25. U nit :3 Twin shell blender Twin shell blender is made of either stainless steel or transparent plastic . Smaller models take a charge of 20Kg and rotate at 35 rpm. Large ones take a charge of about 1 tonne and rotate at 15 rpm. Material is loaded through either of the shell hatches . Emptying of the blend is normally done through an apex port. The material is loaded approximately 50 to 60 % of its total volume. As the blender rotates the material undergoes tumbling motion. When the V is inverted the material splits into two portions. This process of dividing and recombing continuously yields ordered mixing by mechanical means. The powder mass is converted clock wise so that no demixing due to density differences will occur. So that the material alternatively is collected in the bottom of the V.

26. U nit :3 Twin shell blender

27. U nit :3 Twin shell blender Advantages They handle large capacities. Easy to clean, load and unload. This equipment requires minimum maintenance. Disadvantages Twin Shell blender needs high headspace for installation. It is not suitable for fine partic ulate system or ingredients of large differences in the particles size distribution , because not enough shear is applied. If powder are free flowing , serial dilution is required for the addition of low dose active ingredients .

28. U nit :3 Ribbon blender Principle : The mechanism of mixing is shear. Shear is transferred to the powder bed by moving blades (ribbon shaped) in a fixed (non -movable) shell. 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. An equilibrium state of mixing can be achieved. Construction:

29. U nit :3 Ribbon blender Construction: A ribbon blender consists of a U-shaped horizontal trough or 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. They are generally powered by a 10 HP to 15 HP motor for 1000 kg of product mass to be blended. The specific power ranges from 3 to 12 kW/m² according to the products to be mixed.

30. U nit :3 Ribbon blender The area where the shaft exits the container is envisaged with a Sealing arrangement to ensure that the material does not move from the container to the outside. The material is charged into the mixer usually by feed hoppers. It is also equipped with a bottom discharge spout

31. U nit :3 Ribbon blender Working: The materials to be blended 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. Particle size and bulk density have the strongest influence on the mixing efficiency of the ribbon mixer. Ingredients having a similar particle size and bulk densities tend to mix faster than the ingredients with a variation of these attributes.

32. U nit :3 Ribbon blender Advantages of Ribbon Blender: Ribbon blenders can be operated in both batch and continuous modes. High shear by baffles cause break down of aggregates Less headspace requirement Disadvantages of Ribbon Blender: It is practically difficult to obtain 100% discharge in the ribbon blender. Higher clearance between the external periphery of the outer ribbon and the container may result in unmixed or dead spots. The movement of ribbons near the vessel walls due to high shear and compression can damage fragile materials and cause attrition.

33. U nit :3 Ribbon blender Pharmaceutical applications: A ribbon blender is used for blending large volumes of dry solids, wet solid mass, bulk drugs, chemicals, and cosmetic powders.

34. U nit :3 Sigma blade mixer Principle: The mechanism of action is shearing which is produced by intermeshing sigma-shaped blades. It belongs to the family of double arm kneader mixers. Construction: It consists of two mixing blades, which shapes resemble the Greek letter sigma (∑), are fitted horizontally in each trough of the bowl. The clearance between the blades and the vessel walls is low ( ~ 2 mm) The low clearances produce high shear.

35. U nit :3 Sigma blade mixer Working of Sigma Blade Mixer: The powders (40 to 65 percent of the mixer’s total volumetric capacity) are introduced from the top of the trough. The entire process is carried out in a closed enclosure because the dust can be released. The blades move at a different speed using the drive system. 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 of the trough. 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. Mixing homogeneity up to 99%.

36. U nit :3 Sigma blade mixer 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: The power consumption in double arm kneader mixers is very high compared to other types of mixers and can range from 45 to 75 kW/m of mix material. Both blades rotate at the same speed.

37. U nit :3 Sigma blade mixer 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. It is primarily used for solid-liquid mixing and also for solid-solid mixing.

38. U nit :3 Planetary mixers 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.

39. U nit :3 Planetary mixers Construction of Planetary Mixers: It consists of a vertical cylindrical shell or bowl that can be removed. The shell or bowl is covered and may be provided with nozzles, a liquid spray arrangement viewing ports. The material can be loaded into the mixer either through the nozzles on the top cover, or 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 axis. The mixing Blade is mounted at the top of the shell. The drive system consists of a motor and a gearbox that drives the planetary head. Each planetary blade is generally driven by gears that rotate due to the movement of the planetary head.

40. U nit :3 Planetary mixers 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.

41. U nit :3 Planetary mixers 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

42. U nit :3 Silverson Emulsifier Silverson mixer emulsifier produces intense shearing force and turbulence by the use of high-speed rotors. This turbulence causes the liquids to pass through fine interstices formed by closely placed perforated metal sheets. Circulation of material takes place through the head by the suction produced in the inlet at the bottom of the head. Circulation of the material ensures the rapid breakdown of the dispersed liquid into smaller globules.

43. U nit :3 Silverson Emulsifier Construction of Silverson Mixer Emulsifier: The construction of a Silverson emulsifier is shown in the Figure. It consists of long supporting columns connected to a motor which give support to the head. The central portion contains a shaft, one end of which is connected to the motor and the other end is connected to the head. The head carries turbine blades. The blades are surrounded by a mesh, which is further enclosed by a cover having openings.

44. U nit :3 Silverson Emulsifier Working of Silverson Mixer Emulsifier: 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 blades at a very high speed. This creates a pressure difference. As a result, liquids are sucked into the head from the center of the base and subjected to intense mixing action. Centrifugal forces expel the contents of the head with great force through the mesh and onto the cover (Figure). 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 the rapid breakdown of the bigger globules into smaller globules. Uses: Silverson mixer is used for the preparation of emulsions and creams of fine particle size.

45. U nit :3 Silverson Emulsifier Advantages: Silverson mixer is available in different sizes to handle liquids ranging from a few milliliters to several thousand liters. It can be used for batch operations. It is also used for continuous operation by incorporating into a pipeline, through which the immiscible liquids flow. Disadvantage: Occasionally, there is a chance of clogging of the pores of the mesh.

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