Abstract: A method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers and other high temperature crystallizing polymeric materials to crystallize the polymer pellets without subsequent heating. High velocity air or other inert gas is injected into the water and pellet slurry line to the dryer near the pelletizer exit. Air is injected into the slurry line at a velocity of from about 100 to about 175 m3/hour, or more. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the PET polymer pellets leave the dryer at a temperature sufficient to self-initiate crystallization within the pellets. A valve mechanism in the slurry line after the gas injection further regulates the pellet residence time and a vibrating conveyor after the dryer helps the pellets to achieve the desired level of crystallinity and to avoid agglomeration.

Abstract: An adjustable sectioned water flow guide stationarily mounted in the water box of an underwater pelletizer to adjust the flow of pressurized water through the water box in order to accommodate a range of variable process requirements, such as pellet size, water flow, water temperature, melt flow, etc., while preventing pellet distortion and die hole freezing. The length and surface configuration of the water flow guide may be readily adapted through selection of an appropriate number of grooved or ungrooved sections to optimize fluid flow for particular pelletizer applications.

Abstract: A cutter hub and blade assembly is supported and driven for rotational and axial movement in relation to the die face of a die plate in an underwater pelletizer. The supporting and driving arrangement includes a positive control of axial movement of the cutter hub and blades in relation to the die face as the cutter hub and blades are moved toward and away from the die face to obtain and maintain optimal axial position for the pelletizing operation and to minimize wear on the mechanical components involved. Positive control of the axial movement of the cutter hub and blades is obtained by a hydraulic/pneumatic actuation system controlling an elongated motion rod extending through a driven hollow motor shaft with one end of the motion rod connected with a hydraulic/pneumatic control and the other end being connected to a cutter hub holder that supports the cutter hub and blades to move the cutter hub and blades toward or away from the die face.