Underwater pelletizer

#This invention pertains to the field of underwater pelletizers, which are adapted to be mounted to the end of an extruder for cutting streams of plastic extruded through a die into pellets, which are carried away by water flow in a water chamber where the cutting takes place.

#Extruders for extruding plastic material from a molten stream of plastic material have been known and used for some time. One particular use of such an extruder is in connection with a pelletizer assembly, which is mounted to the end of the extruder. In such a combination of an extruder and a pelletizer, a die having a plurality of holes therein is mounted at the end of the extruder and at the entrance to the pelletizer assembly and forms part of both. The pelletizer then includes a rotating cutter assembly having cutting blades positioned adjacent the die face from which streams of molten plastic material flow. The rotating cutter assembly cuts the streams of plastic material into pellets of various sizes depending upon the extrusion flow rate through the holes in the die and the speed of rotation of the cutter assembly.

#Also, the flow of water through the chamber serves to carry the pellets away from the chamber.

#An exemplary embodiment is described below with respect to the following drawings, wherein:

#FIG. 1 is an exploded view showing individual components of an embodiment of a pelletizer with an automatic water chamber clamp;

#FIG. 2 is a front view of the cutting hub of FIG. 1;

#It is desirable to maintain the cutting blades of an underwater pelletizer in contact with a die face of an extrusion die in order to produce pellets of relatively uniform size and shape, as well as to avoid jamming the cutting blades with extruded plastic.

#One conventional cutting blade configuration present in devices produced by Gala Industries, Inc., includes a self-aligning cutting blade assembly that attaches to a motor shaft through a spherical coupling. The spherical coupling consists of a cut-away ball joint that is threaded for connection to a motor shaft. A pair of ball bearings and associated traces are used to implement a floating connection between the spherical coupling and the rest of the cutting blade assembly.

#As the shaft rotates about a rotational axis, the spherical coupling permits the cutting blade assembly to float, e.g. move with respect to the rotational axis, in order to compensate for misalignment between the shaft and the die. The movement of the spherical coupling maintains the cutting blades in contact with the die face. However, the spherical coupling is used to transmit axial force for forcing the cutting blade assembly against the die face and radial force for rotating the cutting blade assembly using the motor shaft. Consequently, a large amount of force is focused on the ball bearing traces and they are prone to rapid wearing.