System for controlling cutter hub position in underfluid pelletizer

Abstract

A cutter hub position control device for consistent blade adjustment in an underfluid pelletizer is provided in connection with a motion rod attached to the pelletizer cutter hub and extending through a hollow shaft of the pelletizer motor. The cutter hub position control device can be collinear, transaxial or in a plane parallel to the axis of the motion rod to which it is attached. Adjustment of the cutter hub position control device is automated through use of feedback control mechanisms.

1 . An underwater pelletizer comprising:
 an extruder for extruding a polymer through an extrusion die having a cutting face;   a water box with transport fluid flowing therethrough for receiving the extruded polymer;   a cutter hub with a plurality of cutting blades driven by a hollow drive shaft having a motion control rod passing therethrough;   a position control device for said cutter hub operatively coupled to said motion control rod for linearly moving said motion control rod within said drive shaft to position the cutter hub and blades axially toward and away from the cutting face of the die; and   a controller for providing automated feedback to said cutter hub position control device based on at least one parameter selected from the group consisting of forces of the extruded polymer, transport fluid flow rate, and rotation of the cutter hub itself such that the cutter hub with attached cutter blades is consistently and reproducibly positioned against the cutting face to form uniform pellets from an extruded material.   
     
     
         2 . The pelletizer according to  claim 1  wherein the cutter hub position control device is collinear with the motion rod through the hollow drive shaft. 
     
     
         3 . The pelletizer according to  claim 1  wherein a longitudinal axis of the cutter hub position control device is in a plane parallel to that of the motion rod through the hollow drive shaft, said position control device being drivingly attached to the motion rod. 
     
     
         4 . The pelletizer according to  claim 3 , wherein the cutter hub position control device is drivingly attached to the motion rod using a driving mechanism of said cutter hub position control device that is drivingly connected to a driven mechanism attached to the motion rod utilizing at least one of a chain and a belt. 
     
     
         5 . The pelletizer according to  claim 4  wherein the driving mechanism and driven mechanism include at least one of a sheave, a pulley, and a sprocket. 
     
     
         6 . The pelletizer according to  claim 4  wherein the driving mechanism is connected to the driven mechanism by a belt that is chemical resistant and slip-resistant. 
     
     
         7 . The pelletizer according to  claim 1  wherein a longitudinal axis of the cutter hub position control device is transaxial to the motion rod and the hollow drive shaft and is drivingly attached to the motion rod. 
     
     
         8 . The pelletizer according to  claim 7  wherein the cutter hub position control device is drivingly attached to the motion rod using a driving mechanism on the cutter hub position control device that is drivingly connected to a driven mechanism attached to the motion rod utilizing a belt. 
     
     
         9 . The pelletizer according to  claim 8  wherein the driving mechanism and driven mechanism include at least one of a sheave, a pulley, a sprocket, and a gear. 
     
     
         10 . The pelletizer according to  claim 9  wherein the driving mechanism and driven mechanism include at least two gears that can intermesh in at least one of a transaxial and a coplanar manner. 
     
     
         11 . The pelletizer according to  claim 10  wherein the driving mechanism and driven mechanism are drivingly coupled to one another by a belt. 
     
     
         12 . The pelletizer according to  claim 1  wherein the cutter hub position control device is in a plane different from that of the motion control rod and further comprising a manual control device attached collinearly with the motion rod. 
     
     
         13 . The pelletizer according to  claim 1  wherein the cutter hub position control device includes a stepper motor, a microstepper motor or a servo motor. 
     
     
         14 . The pelletizer according to  claim 13  wherein the cutter hub position control device includes a servo motor utilizing combinations of alternating current and direct current. 
     
     
         15 . The pelletizer according to  claim 1  wherein said controller includes a programmable logic controller. 
     
     
         16 . The pelletizer according to  claim 15  wherein the cutter hub position control device receives feedback relating to at least one of torque, amperage, linear distance, degrees of rotation, vibration, and conductivity. 
     
     
         17 . The pelletizer according to  claim 15  wherein the cutter hub position control device receives feedback from at least one of an encoder, a resolver, a synchro, a rotary transformer, a Hall device, and a tachometer. 
     
     
         18 . The pelletizer according to  claim 1  wherein the cutter hub position control device is configured to convert rotary motion to linear motion through at least one of a linear screw and a linear actuator. 
     
     
         19 . An underwater pelletizer comprising:
 a die having a die face;   a hollow drive shaft operably connected to a pelletizer drive motor;   a motion control rod linearly movable within said hollow drive shaft, said hollow drive shaft and said motion control rod being received within a pelletizer housing;   a cutter hub having at least one blade attached thereto, said cutter hub being engaged with one end of said motion control rod; and   a cutter hub position control device positioned in a plane different from that of the motion control rod and located outside of said pelletizer housing for adjusting a linear position of said motion rod within said drive shaft to move the cutter hub and blade toward and away from said die face, said control device initiating movement of said motion rod in response to input received from a feedback mechanism indicating said cutter hub and blade to be outside a range of values set by said feedback mechanism.   
     
     
         20 . The pelletizer according to  claim 19  wherein a longitudinal axis of the cutter hub position control device is in a plane parallel to that of the motion rod through the hollow drive shaft, said rotary cutter hub position control device being drivingly attached to the motion rod. 
     
     
         21 . The pelletizer according to  claim 19  wherein a longitudinal axis of the cutter hub position control device is transaxial to the motion rod and the hollow drive shaft and is drivingly attached to the motion rod. 
     
     
         22 . A method of controlling cutter blades relative to the cutting face of a die plate in an underwater pelletizer having a cutter hub and blades coupled to a motor-driven hollow drive shaft through which a motion control rod extends, said motion control rod being linearly movable within said drive shaft to move the cutter hub and blades axially toward and away from the cutting face of the die, said method comprising:
 moving the cutter hub away from the die face to a first position based upon a position of the motion control rod, said first position defining a home position and a feedback lower limit;   moving the cutter hub toward the die plate to a second position using the motion control rod until the blades are against the die face, said second position defining a feedback upper limit;   starting the pelletizer and setting a time period;   operating the pelletizer until the time period has elapsed; and   invoking a feedback mechanism and adjusting a position of the cutter hub and blades with respect to the die face based on input received from said feedback mechanism.   
     
     
         23 . The method as set forth in  claim 22 , wherein said step of adjusting includes maintaining the position of the cutter and blades against the die face within a range of values determined by the feedback mechanism and between the feedback upper and lower limits.