The working principle of a double roller granulator is based on dry extrusion granulation, which compresses powdered materials into dense granules through mechanical pressure without requiring water or heat. The process involves several sequential steps that transform loose powder into uniform, solid pellets.

Material Feeding and Initial Processing

The granulation process begins when raw materials are fed into the granulator’s top hopper. The powdered materials, which must have a moisture content of less than 10-20%, move toward the two roller shafts due to gravity. Before reaching the compression zone, the materials undergo pre-treatment processes such as degassing and spiral preloading to prepare them for optimal compression.

Compression and Extrusion Process

The core of the working principle centers on the compression mechanism between two counter-rotating rollers. When the motor drives the belt pulley through a speed reducer, both the driving shaft and passive shaft operate synchronously. As the materials pass between the two relatively rotating roller shafts, they experience extreme squeezing force that causes plastic deformation and compresses them into dense, hard flakes or sheets.

The extrusion process serves multiple critical functions:

1. Squeezes air between particles out
2. Brings particles close enough to generate attractive forces like van der Waals forces, adsorption forces, and crystal bridges
3. Creates molecular attraction that binds particles together without chemical additives

Sheet Formation and Breaking

After compression, the material forms dense sheets or “cakes” that exit the roller gap. The roller surfaces often contain grooves or specific patterns that help shape the material during compression and determine the final granule shape. These compressed sheets then move to a crushing chamber where they are broken down into individual granules by stirring shafts or crushing devices.

Granule Formation and Screening

The final step involves crushing the flake material into uniform particles. A pair of stirring shafts breaks down the pressed fertilizer cake into individual granular particles. To ensure quality and uniformity, the system includes screening equipment that only allows properly sized granules to pass through, while oversized or undersized particles are returned for reprocessing.