Underwater granulator is similar to air flow granulator and water jet granulator, except that it has a smooth water flow through the mold surface and is 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 face without restricting the water flow temperature. The molten polymer is extruded from a die, the pellets are cut by a rotary knife, and the pellets are carried out of the pelletizing chamber by tempered water into a centrifugal dryer. In the dryer, the water is drained back to the holding tank, cooled and recycled; the pellets are passed through a centrifugal dryer to remove the water.

strip material production line cost is not high, easy to operate, and easy to clean. This has advantages for colorant compounding, since the replacement of two batches of different colorings necessitates thorough cleaning of the equipment. However, a disadvantage of the strip-making process is the space occupied by the cooling section, the length of which is determined by the temperature requirements of the polymer.

Most polymers must be compounded and pelletized into marketable raw materials before they are made into final products. The required amount of the granulator is proportional to the amount of extrusion and exponentially related to the size of the filter screen. There are many different pelletizer designs, but all pelletizers can be divided into two main categories: cold pelletizing systems and die face hot pelletizing systems. The main difference between the two is the timing of the pelletizing process. Cold pelletizing system, at the end of the processing process from the solidified polymer pelletizing; and in the mold surface hot pelletizing system, when the molten polymer from the die appears when the pelletizing, and the pellets are cooled downstream. Both pelletizing systems have their own advantages and disadvantages.