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Underwater pelletizing unit
The underwater granulator is similar to the airflow granulator and the water spray granulator. The difference is that it has a steady stream of water flowing through the mold surface and in direct contact with the mold surface. The size of the pelletizing chamber is just enough to allow the pelletizing knife to rotate freely across the die surface without restricting the temperature of the water flow. The molten polymer is extruded from the die, and the rotating knife cuts the pellets. The pellets are taken out of the pelletizing chamber by the temperature-regulated water and enter the centrifugal dryer. In the dryer, the water is drained back to the storage tank, cooled and recycled; the pellets are passed through a centrifugal dryer to remove water.
The strip production line has low cost, simple operation and convenient cleaning. This has its advantages for colorant compounding, because the replacement of two batches of different colorants must thoroughly clean the equipment. However, the disadvantage of the method of making rods is that the cooling section takes up space, and its length is determined by the temperature requirements of the polymer.
Before being made into final products, most polymers must be blended and then pelletized to become marketable raw materials. What the granulator needs is proportional to the extrusion volume and exponential to the size of the filter screen. There are many different pelletizer designs, but all pelletizers can be divided into two categories: cold pelletizing system and die face hot pelletizing system. The main difference between the two is the time arrangement of the pelletizing process. The cold pelletizing system cuts pellets from the solidified polymer at the end of the process; while in the die face hot pelletizing system, pellets are cut when the molten polymer emerges from the die, and pellets are processed downstream cool down. Both cutting systems have their own advantages and disadvantages.