Pelletizing is a method of agglomeration, or particle size enlargement, in which material fines are processed into pellets or granules. Pelletizing is used throughout a multitude of industries to process thousands of materials from difficult to handle powders and fines, into easy to handle pellets.

With many benefits and a highly customizable process, pelletizing has become a staple in many industries, with new applications for this valuable process constantly on the rise. 
 

The underwater pelletizer (UWP) is a die-face pelletizer. This means that molten polymer is cut into pellets as it exits the die holes, which are arranged in a circular pattern in a round die. The crucial difference from the water-ring pelletizer (also a die-face pelletizer) is that the cutting chamber is completely filled with process water so that the polymer drops are immersed in water as they exit the die holes. Because of forces that minimize surface tension, each drop takes on a spherical shape, which is unique to UWPs.

Underwater pelletizer is mainly used for processing polymers or thermoplastics with a very high melt flow index. The melt came out of the platen and was scraped off by the blade of the granulator. The whole process takes place underwater. In the centrifuge, the particles are separated from the treated water and dried.
 

In water ring pelletizers (WRPs), as in UWPs, molten polymer flows into multiple holes arranged in a circular pattern in a die plate and is cut into pellets as it emerges from the die face. The cutting is accomplished by a series of rotating knives that are also arranged in a circular pattern. The die face is made of hardened metal, so that wear takes place mainly in the knives. The pressure is hydraulically applied to the cutting assembly to ensure proper contact with the die face.

Water ring pelletizer is mainly used for thermoplastics with higher viscosity. The melt leaves through the wear-resistant template and is shot down by the pelletizer blades. The precipitate cooled in the water ring is washed away, dried in a centrifuge, and discharged. By adjusting the blade pressure, the pelletizer blade can provide a longer service life; replacement is convenient and fast.

In strand pelletizing, the polymer is cut into pellets after it has cooled and solidified. By its nature, this system is operated in-line with extrusion. The molten polymer is metered into a strand die that is much like a sheet dies except that the material exits the die through multiple holes, each forming a strand of the polymer. The strands enter a water bath or trough, where they are cooled, then are dried by a de-watering unit or air knife, and finally are fed into a strand pelletizer, where they are cut into cylindrical pellets. A disadvantage of this pellet shape is that the flat ends of the cylinders can stick together and cause bridging.

Strand pelletizing is mainly used for low viscosity melts. The melt comes out of the steel strand nozzle, is cooled in a water bath, dried by a fan, and cut to the required length in a granulator. The result is cylindrical dust-free particles with excellent mixing properties.
 

The air pelletizer was designed to use air to cool and convey the pellets and thus eliminate any need to dry the pellets. At the same time, the system benefits from the thermal insulation, resulting in a uniform cut and easy conveying of the pellets from the "cool" cutting surface, without generating chains or agglomerates.

Air cooling pelletizer is mainly designed for online applications that do not use water. The melt leaves through the wear-resistant template and is shot down by the pelletizer blades. The particles are carried away in the airflow and cooling.