This article details the design, construction and operation of Sigma Mixer commonly used for mixing of high viscosity materials. The industrial applications for which Sigma Mixer is used are listed.
Media : Solid Powders, Dough, Viscous Paste
Mode of Operation : Batch Mixing
Design and Operation
Mixing Vessel - The sigma mixer consists of a W-shaped horizontal trough containing two sigma shape mixing blades rotating within.
Mixer Blades - The clearance between the external periphery of the blades and the internal wall of the mixing vessel is generally in the range of 2 – 3 mm. The clearance may be higher depending on the properties of the materials being mixed.The two blades are positioned tangentially or may overlap each other.
In the tangential blade sigma mixer, the blades rotate in the mixing vessel meeting tangentially. The front blade generally rotates faster than the rear blade. The ratio of rotation speeds depends on the application. Tangential blade design is user for mixing of viscous materials.
Video: Tangential Blade Sigma Mixer
In the overlapping blade sigma mixer, the blades overlap above the saddle of the mixing vessel. Both the blades rotate at the same speed. There is a faster interchange of material within the two compartments of the mixing vessel. Overlapping blades are used for materials such as carbon pastes, clay coatings, creams, and ointments.
Video: Overlapping Blade Sigma Mixer
Mixer Drive System - The sigma mixer is powered by a drive system comprising of a motor,gearbox, couplings. The front and the rear blade of the mixer may be connected through a pair of spur gears. Alternatively, each blade may be driven through an independent drive system.
Mixer Seal - The mixer shaft is provided with an appropriate sealing arrangement in the area where it exits the mixing vessel. The most common sealing arrangement consists of a stuffing box assembly. Mechanical seals can be used for critical applications, or when mixing is to be carried our under vacuum.
Material Charging and Discharging - Material is loaded in the mixer through the top cover. Discharge of material is generally through titling of the container assembly. Tilting arrangement could be manual, mechanical or through hydraulic operation. For materials which are flowable and have low viscosity, the mixer can be provided with one or two bottom discharge valves.
Heat Transfer - Sigma mixer are commonly provided with jackets for circulation of heating or cooling media.
Mixer Assembly - The mixer assembly comprising of the mixing vessel and the drive system are mounted on a supporting structure, base frame.
Video: Sigma Mixer- Design & Operation
The pair of sigma blades pass the vessel walls and each other at close clearances (2-3 mm), thereby causing repetitive stretching, folding, kneading of the viscous material, and thus resulting in homogenous mixing.
Mixing Mechanism : Convection Blending
Homogeneity of Mix: Up to 99%
Capacity: As the power required per unit volume is high, sigma mixers are most commonly designed for working capacities up to 2 m3. Mixer capacities may be increased upto 5 m3 depending on the required production capacities.
1. The sigma blade design can be replaced by masticator blade, spiral blade, naben blade and shredder blade design depending on extent of shear required, and based on properties of materials being mixed.
2. In some cases, a discharge screw may be provided in the lower portion of the mixing vessel. The material is directly extruded or discharged. This type of mixer is called as sigma mixer extruder.
Sigma mixers are best suited for mixing, kneading of highly viscous mass, sticky and dough like products. Sigma mixer is used for mixing of pastes, rubber, and heavy plastic masses. The following are some the application of the sigma mixer.
|Baking industry||Batter||Battery paste|
|Brake lining||Carbon black||Celluloid|
|Ceramic pastes||Ceramic powder||Chemical|
|Dry powder to wet phase mixing||Dyes||Explosives|
|Fiber glass||Floor coverings||Food dough|
|Food products||Greases||Greasy lnks|
|Gums and adhesives||Hot-melts||Inks,Colorants|
|Lead storage battery||Magnetic tape coatings||Master-batches|
|Mastics||Metal powder||Stiff paste|
|Plastics||Polishing pastes||Polyester compounds|
|PVC coatings||Resins||Rubber compounds|
|Sealing compounds||Silicone rubber||Silicone|
|Sludge||Slurries||Soap and detergent|
Unique Mixers & Furnaces Pvt Ltd
Contact Person: Mr Jayesh R Tekchandaney
Phone – +91-22-25801214/25822385
Website – www.uniquemixer.com