Principle
Table of Contents
The mechanism of action is shearing which is produced by intermeshing sigma-shaped blades. Sigma Blade Mixer belongs to the family of double arm kneader mixers.
Construction of Sigma Blade Mixer
It consists of two mixing blades, which shapes resemble the Greek letter sigma (∑), which 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.
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 speeds 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%.
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.
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.
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