Sigma Blade
Mixer

(Z
Blade/Double blade/ Kneading Machine)

• It is an example of agitator mixers

• Its shape resemble the Greek letter sigma

• It uses 2 mixer blades

• Sigma blade mixer is a common form used to handle
semi-solids of plastic consistency

Principle – shear

Inter meshing of sigma blades creates high shear and kneading
action

Construction and
working

• It consists of
double tough shaped stationary bowl

• Two sigma shaped blades are fitted horizontally in each
tough of the bowl

• These blades are connected to a fixed speed drive

• Mixer is loaded from top and unloaded by tilting the
entire bowl

• The blades move at different speeds, one about twice than
the other, which allows movement of powder from sides to centers

• The material also moves top to downwards and gets sheared
between the blades and the wall of the tough resulting cascading action

• Perforated blades can be used to break lumps and
aggregates which creates high shear forces

• The final stage of mix represents an equilibrium state

Uses

• Used in the wet granulation process in the manufacture of
tablets, pill masses and ointments

• It is primarily used for liquid – solid mixing, although
it can be used for solid – solid mixing

Advantages

• Sigma blade mixer creates a minimum dead space during
mixing

• It has close tolerances between the blades and the sidewalls
as well as bottom of the mixer shell

Disadvantages

• Sigma blade mixer works at a fixed speed