The working principle of mixing drum granulators is based on wet granulation (also known as tumble-growth, agitation, or non-pressure agglomeration), which utilizes motion combined with liquid binder to promote granule formation.

Mechanical Operation

The drum granulator operates through a mechanical drive system where the main motor drives belt and pulleys, transmitting power through a reducer to the drive shaft. Split gears installed on the drive shaft engage with large gears fixed on the drum body, causing the cylindrical drum to rotate. The drum is positioned at a slight angle (typically 2-5°) to facilitate material movement and granule discharge from the outlet.

Material Processing and Granule Formation

Initial Material Feeding: Raw materials enter the drum through the inlet via a conveyor system and achieve better mixing and granulation effects through the continuous rotation of the drum.

Tumbling Action: As the drum rotates, materials tumble within the cylinder, creating a rolling motion that is essential for granulation. This rolling action allows particles to roll against each other and against the drum’s interior sides.

Binder Introduction: At predetermined locations within the drum, liquid binder is introduced through a spray system. The binder can be introduced as atomized spray, steam, or droplets, depending on the specific application requirements.

Granule Development: The rolling action combined with the stickiness from the binder causes fine particles to collect together and form larger particles. These particles continue to pick up additional fines and binder as they tumble in the material bed, causing them to densify and develop additional layers through a phenomenon known as coalescence.

Granulation Methods

Wet Type Granulation: The drum can operate using wet granulation where steam and ammonia gas are admitted, or phosphoric acid, nitrogen solution, or phosphoric acid slurry are added to complete chemical reactions with heat supply within the cylinder.

Cold Granulation: Alternatively, the drum can perform cold granulation of compound materials using minimal moisture supplementation.

Centrifugal Force Action: The rotating cylinder generates centrifugal force that helps powders come together and form pellets. Under the action of extrusion pressure and rolling motion, powder materials transform into particles.

Critical Process Elements

Rolling Motion: Achieving proper rolling action in the material bed is crucial for adequate granulation, as particles must roll in a layering effect similar to rolling a snowball.

Pressure and Temperature: Materials are agglomerated into balls through the rotating movement of the cylinder, which generates extrusion pressure between particles at specific humidity and temperature conditions.

Spray System Design: The binder addition system is complex and influenced by factors such as how the binder is introduced, at what points in the drum it’s added, and the binder feed rate at each location.

This continuous process of tumbling, binder application, and particle coalescence transforms raw powdered materials into uniform granules through mechanical action and controlled moisture conditions.