Sigma Mixer Design-Construction-Applications Explained

Sigma Mixer is highly popular equipment used for efficiently mixing and kneading high viscosity materials with utmost ease. Since, sigma mixer comes from the double arm kneader mixer family. So, let’s take a quick look at the design and construction of double arm kneader mixers.

Design of Double Arm Sigma Mixer Kneader


Double arm Sigma Mixer kneader consist of two mixing blades which are positioned in a horizontal W shape. There is a wide array of blades made available such as masticator blade, sigma blade, spiral blade and nabbed blade to name a few. The gyratory motion of these blades takes place in two ways. One is peripheral motion to each other and the one other in which the blades inside the furrow can stretch outwards. The blades may operate at the same or different speeds while moving towards each other. The blades go over the container walls and each other at very close clearances of 2-3 mm which helps produce a homogenous mix.
The biggest benefit of such close clearances is high shearing action which easily reduces every single large size particle. A consistent particle size distribution can be achieved within a very short span of time which is as less as just 10 to 30 minutes. High homogeneity levels can be expected while using these mixers. You can expect upto 99 percent of homogeneity which is amazing in itself. These mixers also come with their variants such as double arm kneader mixer extruders and they are very much capable of handling highly viscous materials. Even materials with 10 million centiposes viscosity can be managed.

Energy Consumption

You must know that double arm kneader mixer’s energy consumption is quite high as opposed to other mixer types. It could be in the range of 45 to 75 kw for per m3 of mixture. The most commonly used double arm kneader mixer is sigma blade mixer which is the most sought after on account of variegated reasons.

Supporting tangential and oblique movement is necessary for the chemical in mixers that manage acid based products. The geometry of sigma blade has been designed in such a way that it can draw, shear, knead, coarse as well as fold the glutinous mass of the material. It becomes capable of doing so because of the blade manipulate which is just next to the trough. It may interest you that the twist angle of the blade can be adjusted according to the kind of shear you are looking for.

Operation of Sigma Blade Mixer

Now, let’s take a quick look at how sigma blade mixer operates. Material is loaded from the top of the container, but it is mostly just about 40 to 65 percent of the total volumetric capacity of the mixer. Heavy duty drive systems are in place to facilitate the rotation of blades.  These systems comprise a gearbox, motor, gears and couplings.

Usually the tip speed of a sigma mixer is kept to 60 metres/minute. The mixing process may take place either at room temperate or controlled temperature conditions. Provision of jackets is there for the circulation of hot or cold media which comes in handy to maintain the required temperature.  You can also equip the mixer with a discharge arrangement. The most commonly seen discharge arrangement is tilting discharge. Tilting arrangement of the container is designed for manual, motor or hydraulically operated arrangement.
For materials containing lower viscosity, a bottom discharge valve can be facilitated on the trough. It is flush with a mixer trough to keep at bay any sort of dead or unmixed pockets of material.

Applications of Sigma Mixer

Frankly speaking the list is pretty long. This mixer is considered quite ideal for sticky, gritty, and pasty slurries with high viscosity quotient. Here is a list of some of the many products which can be mixed in sigma mixer.

  • Biscuits
  • Adhesives
  • Ceramics
  • Chemicals
  • Chewing gum
  • Butyl rubber
  • Explosives
  • Crayon and lead used in pencils
  • Carbon pastes/sugar pastes
  • Confectionary products and some foods
  • Gaskets and gland packings
  • Hot-melts
  • Pharmaceuticals
  • Mould preparations
  • Erasers for pencils
  • Mastics
  • Fiberglass resin doughs
  • Plastics
  • Refractories
  • Silicon rubber
  • Soaps and detergents
  • Rubber solutions
  • Marzipan

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