Pelletizers - Thermoplastic polymers, elastomers and additives

In water ring pelletizers (WRPs), molten polymer flows in multiple orifices arranged in a circular pattern on a matrix plate and cut into particles as it emerges from the face of the matrix. The cut is made by a series of rotating blades that are also arranged in a circular pattern. The face of the die is made of hardened metal, so wear occurs mainly on the knives. The pressure is applied hydraulically to the cutting assembly to ensure adequate contact with the face of the die. WRPs produce granules that are rounded but flat (lenticular). As the polymer exits the holes of the die and is cut with the rotating blades, the resulting lenticules are thrown outward into a water ring that is tangentially fed to the cutting chamber. The water cools the granules and transports them to a bucket of water for further cooling and transport to a centrifugal dryer operating in the manner already described. The water is returned to a tempering and filtration system and recycled to the granulation process. The WRP is the most compact of the three main granulation processes and provides a degree of automation. The process is particularly unsuitable for sticky or high-heat materials. There are also capacity limitations compared to the UWP. Water ring pelletizers, due to their lower production capacity and their limitation to materials with high resistance to melting, are recommended mainly for charged polymers, for recycling and recovery.

In "Spaghetti" granulation, the polymer is cut into granules after it has cooled and solidified. By its nature, this system is operated in line with extrusion. The molten polymer is dosed in one strand. The strands enter a bath or canal, where they are cooled, then dried with an irrigation unit or an air knife, and finally introduced in a granulator, where they are cut into cylindrical granules. A disadvantage of this pellet form is that the flat ends of the cylinders can stick together and cause a bridge. After cutting, the granules fall into a vibrator, which oversizes the granules or agglomerates and removes any dust. The process is particularly unsuitable for soave materials such as elastomers. "Spaghetti" granulation can process virtually any polymer and can be used for the full range of applications, including mineral filled and fiberglass polymers.

As with other granulation systems, the cooling water in the UWP is supplied by a process water unit, which tempers the water, that is, mixes hot and cold water to ensure a constant temperature, and filters the dust and water. the fines.

The underwater pelletizer can process virtually any polymer and can be used for the full range of applications, including composition, hot melts, TPE, mineral charge masterbatches, polymerization, recycling and recovery, can not be used with fiberglass.