Ribbon blender is the best choice for most of the blending operations due to its versatility and economy. It is based on a proven agitator construction providing a triple mixing action for fast and effective blending.
Principle
Ribbon blender mixer works on the principle of shear. The ribbon-shaped moving blades transfer the shearing force to the powder bed contained in the non-movable fixed shell. High shear rates effectively breakdown the lumps and aggregates. Convective mixing also occurs as the powder bed Is lifted and fell at the bottom of the container. An equilibrium state of mixing is attained.
Construction
Ribbon blender consist of a non-movable horizontal cylindrical shell which is open at the top for material loading. However, a lid is provided to close the shell at the time of mixing. It is held in position by two helical movable blades mounted on the same shaft through the long axis of the shell. The blades have right and left hand twists, and are connected to a fixed speed drive. The outlet for discharging material is present at the bottom.
Working
The materials to be mixed are fed from the opening provided at the top of the shell. After loading the body is closed with a lid because dry blending may produce dust and wet granulation may evaporate the granulating solution.
The fixed speed drive makes the ribbon blades to rotate. One blade slowly moves the material in one direction and the second blade quickly moves it in opposite direction. Centrally located vertical screw lifts the materials and cascades them at the bottom of the container (this is the tumbling action). The counteracting blades create a high shearing force which effectively breakdown the solid lumps or aggregates. The materials are moved from one end to another by the helical blades. An equilibrium state is attained in the final stage of mixing. The operating conditions can affect the steady state and the mixing quality. The product blend is unloaded from the opening provided at the bottom.
uses
Ribbon blender has the following uses:
1) It is used to mix finely divided solids, wet solid mass, sticky and plastic solids.
2) It easily mixed the materials of uniform mixing size and density.
3) It is suitable for liquid-solid and solid-solid mixing.
Merits
Ribbon blender has the following merits:
1) By using perforated baffles, high shear can be applied which breaks down the aggregates.
2) It requires less space for installation.
Demerits
Ribbon blender has the following demerits:
1) It involves two-dimensional movement of particles, thus is not preferred in some cases.
2) Its shearing action is comparatively less than some other mixers.
3) Dead spot (unmixed areas) are observed during mixing.
4) It is having a fixed speed drive.
Sigma blade mixer is a commonly used mixer for high viscosity materials. It provides a wide range in the capacities of the mixers ranging from 5-2500 liters.
principle
Sigma blade mixer works on the principle of shearing and convective action. The sigma-shaped blades inter-mesh and create high shear and kneading actions. Convective mixing occurs as the material is cascaded.
Construction
Sigma blade mixer consist of the following parts:
1) An open trough, with almost semi-cylindrical bottom.
2) Two double armed sigma-shaped blades placed horizontally and parallelly at the bottom of the mixing trough. These blades provide through mixing by rotating at varying speeds in opposite direction, enabling the transfer of product from one blade to another and also from one end to other end.
Working
The materials to be mixed are fed from the top of the container body. After loading the body is closed with a lid because dry blending may produce dust and wet granulation may evaporate the granulating solution.
The sigma blades are made to rotate with the help of the fixed speed drive. The blades move at different speeds (one moves twice the speed of other), resulting in lateral pulling of the material. The blades turn towards each other, thus the materials moves from the sides to the center of the bowl. The material further moves from the top to downwards and then sheared between the blades and the container walls.in this way, convective and shear action can be achieved. The perforated blades breakdown the lumps and aggregates, thus creating high shear forces. An equilibrium state is attained in the final stage of mixing. The operating conditions can affect the steady state and the mixing equipment quality. The container is tilted with the help of a rack-and-pinion drive so that the product blend can be discharged working capacity.
Uses
Sigma blade mixer has the following uses:
1) It is used in the process of wet granulation for manufacturing pill masses, ointments, and tablets.
2) It is suitable for kneading of high viscous and mixing of sticky and dough like products highly viscous mass sticky.
3) It is used for liquid-solid and solid-solid mixing.
4) It is used for mixing rubber, pastes, heavy plastic masses etc stainless steel.
5) Certain industries like food, rubber, pharmaceutical, and chemical industries also employ such mixers for several purposes.
Merits
Sigma mixer blade has the following merits:
1) Minimum dead spaces are observed during mixing.
2) A close tolerance exists between the blades, the sidewalls, and bottom of the mixer shell.
Demerit
It operates at a stationary speed.
Objectives
The main objectives for carrying out the process of mixing are as follows:
1) In chemical industries, chemical reaction enhancement uses mixing and kneading to continue a reaction appropriately which require a close contact among reacting substances.
2) Simple physical mixtures of two or more miscible liquids, homogeneously divided solids, etc. can be obtained by mixing.
3) Physical changes are carried out by mixing such as from a supersaturated solution crystals are formed outer ribbons viscous materials.
4) Achieving dispersion is also an objective of mixing in which two or more immiscible liquids and one or more liquids with finely divided solids to produce a quasi-homogeneous substance.
During the tablet and capsule manufacturing, wet mixing elements blades is done in the granulation stage.
For easy compression of tablets, various components are mixed by dry mixing.
For capsules manufacturing, pellets are formed mixer extruders.
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