Equipment Introduction

The double-roller press granulator is a widely used solid material granulation equipment in industries such as chemical, fertilizer, pharmaceutical, food, and building materials, and is the core of the entire extrusion granulation production line. It is a room-temperature granulation device that forces materials into shape through mechanical pressure. Its design concept is to directly compress powder materials into granules with a certain strength without adding binders (or with very little addition). As an important granulation equipment, the double-roller granulator adopts a non-drying, room-temperature process, offering significant advantages in energy saving and improved production efficiency. Its core working principle is to extrude a properly proportioned mixture through a feeding mechanism into the gap between a pair of identical rotating extrusion rollers.

Under strong extrusion pressure, air inside the material is expelled, the interparticle spacing decreases, and the intermolecular forces increase, thus compressing the material into dense flakes or strips. As the rollers continue to rotate, the pressure on the material exhibits a specific changing pattern: when the straight line connecting the radii of the two rollers is horizontal, the pressure reaches its maximum value, typically reaching several megapascals or even higher, and then rapidly decreases. At this point, the formed material recovers due to its own elasticity, detaches from the roller surface under the action of the rebound force, and smoothly enters the next process. This granulation method fundamentally avoids the energy-consuming drying process in traditional wet granulation.

Equipment Composition and Structure

A double-roller press granulator generally consists of the following main parts:

Feeding System:Typically includes a hopper, metering device, and screw feeder, ensuring uniform and stable material feeding into the rollers.

Extrusion Rollers:The core component, usually a pair of opposing rotating rollers. Their surfaces may have molds or grooves to control particle shape and size.

Transmission System:Includes a motor, reducer, and various couplings to achieve synchronous and stable rotation of the rollers.

Pelletizing Chamber Shell:Supports the rollers and other components and prevents dust leakage.

Pellet Shaping and Sieving System:After initial extrusion molding, the pellets are often shaped and graded using a screen or vibrating screen.

Control System:Modern double-roller granulators are often equipped with a PLC control system, automatically adjusting various parameters to improve production efficiency and safety.

Working Principle of the Equipment

The double roller press granulator is a dry, high-pressure physical forming equipment. It requires no water, binder, or drying throughout the entire process. It achieves room-temperature granulation by forcing powder molecules to restructure, plastically deform, and tightly interlock under high mechanical pressure.

The core power source of the equipment comes from two sets of synchronously rotating, counter-rotating, high-pressure rollers. Pre-treated powdered material is uniformly and continuously fed into the two-roller interlocking extrusion zone by a forced feeding system. After entering the roller gap, the material is forced into the high-pressure forming zone as the rollers rotate. The grooves on the roller surface apply a gradient increasing extrusion stress (50–150 MPa) to the powder, completely expelling air from the material. The powder particles undergo a physical change from elastic compression to plastic yielding to tight molecular alignment.

Under ultra-high extrusion, the originally loose powder forms a dense, high-strength sheet or pillow-shaped blank through van der Waals forces, molecular adsorption forces, crystal bridging, and mechanical interlocking forces. After the material exits the high-pressure roller gap, the pressure is released instantly, and the billet detaches from the mold due to its own elasticity. It then enters the rear crushing and granulation mechanism, where it is uniformly cut and shaped into standard granules. Finally, it is graded by a vibrating screen. Qualified granules are output as finished products, while fine powder and unqualified large particles are automatically recycled for regranulation.

The entire molding process is a purely physical cold-state molding process that does not change the chemical composition of the material or damage its nutrients. It is the most stable and energy-efficient molding process for compound fertilizers, inorganic salts, mineral powders, and organic fertilizers.