Ribbon blender - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes

Ribbon blender

Principle

Mechanism of mixing is shear

Shear is transferred by moving blades. High shear rates are effective in breaking lumps and aggregates. Convective mixing also occurs as the powder bed is lifted and allowed to cascade to the bottom of the container. An equilibrium state of mixing can be achieved.

Construction

• Consists of horizontal cylindrical trough usually open at the top. It is fitted with two helical blades, which are mounted on the same shaft through the long axis of the trough.

• Blades have both right and left hand twists.

• Blades are connected to fixed speed drive.

• It can be loaded by top loading and emptying is done through bottom port.

Working

• Through fixed speed drive, ribbons are allowed to rotate.

• Helical blades moves powders from one end to another.

• One blade moves material in one direction and other moves opposite.

• Close open trough to avoid dusting during dry blending.

• Due to high shear it effectively breaking up lumps and agglomerates.

• Once equilibrium achieved, powder mixture discharge from the bottom

Uses

• Used for mixing of finely divided solids, wet solid mass, and plastic solids

• Uniform size and density materials can be easily mixed

• Used for solid – solid and liquid – solid mixing

Advantages of ribbon blender

• High shear can be applied by using perforated baffles, which bring about a rubbing and breakdown aggregates

• Headroom requires less space

Disadvantages of ribbon blender

• It is a poor mixer, because movement of particles is two dimensional..

• Shearing action is less than in planetary mixer

• Dead spots are observed in the mixer, though they are minimum

• It has fixed speed drive