Working principle: In a dispersion where solid powder coexists with liquid and is mainly composed of solid phase, the self bonding performance of the dispersion material is utilized. Through external forces such as extrusion pressure, gravity, centrifugal force, airflow impulse, etc., the basic particles in the solid phase in the material adhere to each other and increase through the interface of the liquid, forming a group of particles with a certain shape and relatively uniform particle size. This is the common mechanism of wet granulation.

Main features: coexistence of solid and liquid phases (for materials with low softening points, the moisture content is extremely low or no moisture content, but the granulation process causes softening or melting of the material to form coexistence of solid and liquid phases); The basic particles in the solid phase have no plastic deformation; ⑶ The granular materials after granulation generally need to be dried, and materials with lower softening points need to be cooled.

For materials without self-adhesion or with poor self-adhesion, a few amount of binder or solvent that can dissolve the solid phase without affecting the product quality index can be added during granulation to facilitate granulation or increase the particle strength of the granulation product.

Based on the mechanism and characteristics of wet granulation, combined with physical properties, process, and product usage requirements, a typical wet granulation complete process includes: material pre-treatment operation, granulation operation, and post-treatment operation.

Preprocessing operation: The main purpose of this process is to adjust the material status to meet the needs of subsequent granulation processes. The operation includes regulating and controlling water content and mixing or kneading. For selecting extrusion granulation, mixing and kneading are particularly important for the efficiency and quality of granulation. For multi-component composite materials, a multi-channel proportional quantitative batching system should also be included before the mixing process.

Granulation operation: Multiple granulation processes such as extrusion and agglomeration can be selected according to different requirement. The main forms of extrusion granulation include spiral extrusion, flat die/ring die extrusion, and counter tooth extrusion. The main forms of agglomeration granulation include drum granulation, disc granulation, high-speed stirring tooth granulation, etc.

Post processing operations: mainly including rounding, drying or cooling. Moisture containing materials often require drying operations after granulation, while low softening point materials may require rapid cooling treatment.