Abstract:
A cutter hub and blade assembly supported and driven for rotational and axial movement in relation to the die face of a die plate in an underwater pelletizer including a positive control of such axial movement to obtain and maintain optimal axial position of the cutter hub and blades during the pelletizing operation and to minimize wear of 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 that extends through a driven hollow motor shaft. One end of the motion rod is connected with a hydraulic/pneumatic control and the other end of the rod is connected to a cutter hub holder that supports the cutter hub and blades for axial movement toward or away from the die face.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a complete utility application entitled to the priority and claiming the benefit of U.S. provisional application Ser. No. 60/378,660, filed May 9, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an underwater pelletizer and more specifically to a cutter hub and blade assembly supported and driven for rotational movement and axial movement in relation to the die face of a die plate in an underwater pelletizer. The supporting and driving arrangement for the cutter hub and blades 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 axial adjusted positions of the cutter hub and blades 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 a 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 rigidly connected to a cutter hub holder that supports the cutter hub and blades to move the cutter hub and blades toward and away from the die face. 
   2. Description of the Prior Art 
   Underwater pelletizers including a cutter hub holder supporting a cutter hub and blades associated with a die face in order to rotate the blades to cut strands of extruded polymer into pellets within a water box through which water is circulated to cool and harden the pellets and convey a slurry of pellets to an outlet in the water box are well known. Prior U.S. Pat. No. 6,332,765 issued Dec. 25, 2001 for Cutter Hub Holder discloses a cutter hub holder, cutter hub and blades biased toward the die plate by variable pressure through a resilient structure incorporated into supporting and driving engagement with the cutter hub and blades. The present invention comprises an improvement over the cutter hub holder disclosed in aforesaid U.S. Pat. No. 6,332,765 which, together with the prior art of record therein are incorporated herein by reference as if fully set forth herein. 
   In U.S. Pat. No. 6,332,765, the cutter hub holder is connected to and supports the cutter hub and blades and is drivingly connected to a motor shaft. The motor shaft extends through an electric motor and is hollow throughout its length. One end of the motor shaft is communicated with a stationary rotary transmission lead that is communicated with a source of fluid pressure through a pressure regulating valve. The hollow motor shaft includes a piston and piston rod moveable in the interior of the hollow motor shaft which defines a cylinder for the piston to move the piston and piston rod axially in relation to the motor shaft. The piston rod is connected to a cutter hub holder through a resilient device, such as a spring, to bias the cutter hub holder, cutter hub and blades thereon toward the die face. This structure provides an axial force to move the cutter hub and blades toward the die plate but does not provide any force to move the cutter hub and blades axially away from the die face. Further the prior art does not provide a mechanism for positively controlling the movement of the cutter hub and blades toward and away from the die plate. 
   SUMMARY OF THE INVENTION 
   This invention provides a positive control of the positions of a cutter hub and blades in relation to a face of an underwater pelletizer. 
   It is an object of the present invention to provide a control mechanism in which axial movement of the cutter hub and blades in relation to the die face is positively controlled in both directions of cutter blade adjustment axially in relation to the die face of a die plate in an underwater pelletizer. 
   Another object of the present invention is to provide a positive control of the relationship between the cutter hub and blades and the die face in an underwater pelletizer in which positive control of movement in both directions is provided by a hydraulic/pneumatic actuation system mechanically connected to the cutter hub through an elongated motion rod fixedly connected to the cutter hub holder that supports the cutter hub. 
   A further object of the present invention is to provide a positive control for the cutter hub and blades in accordance with the preceding object in which the motion rod connected to the cutter hub holder extends through a hollow motor shaft and rotatably connects to the piston rod of a double acting hydraulic actuated piston and cylinder assembly on the opposite side of the motor from the cutter hub and blades. The piston and cylinder assembly are associated with an air-oil pressure system that controls a closed hydraulic circuit that functions to move the motion rod, cutter hub, cutter hub holder and cutter blades in a positively controlled manner due to the incompressibility of the hydraulic fluid associated with the piston and cylinder and the economical use of air pressure directly on the closed hydraulic circuit. Lock positions of the motion rod, cutter hub holder, cutter hub and blades is obtained by a blocking valve positioned within the fluid circuits. 
   A still further object of the present invention is to provide a positively controlled cutter hub for effectively controlling movement of the cutter hub and blades in both directions in relation to the die face of a die plate in an underwater pelletizer in which the structure enables assembly and disassembly of the cutter hub and cutter hub holder, the drive structure for the cutter hub holder and the elongated motion rod connected to the cutter hub holder at one end and rotatably connected to the piston in the hydraulic cylinder in closed hydraulic circuit at its other end, with the hollow shaft guidingly supporting said motion rod during its axial movement. 
   Still another object of the present invention is to provide a positive control axial movement of the blades of an underwater pelletizer in accordance with the preceding objects in which the motion rod connected to the pelletizer blade hub holder is moved axially forward toward the die face as well as axially backwards away from the die face and rotates with the hollow motor shaft of the pelletizer motor in order to isolate any torsional forces created by operation of the motor during pellet cutting. This assembly eliminates the need for a cylindrical or barrel piston, piston rod and spring assembly in the motor shaft, thus reducing the number of mechanical components and providing direct mechanical connection between the motion rod and the cutter hub holder, cutter hub and cutter blades. 
   Yet another object of the present invention is to provide a positive control for the cutter hub and blades of an underwater pelletizer in which the closed circuit hydraulic double acting cylinder and piston connected to the motion rod has both ends of the cylinder connected to an air-oil actuator through independent stop valves which serve to hold the pelletizing blades in their position once operating pressure has been reached so as to insure a uniform pellet shape. Each air-oil actuator is communicated with a source of air pressure through a proportional valve. The air pressure is translated to a hydraulic fluid pressure in the air-oil actuator for positively controlling movement and position of the piston in the hydraulic cylinder. The piston rod extending from the piston is directly connected to the rotatably driven motion rod which in turn is directly connected to the cutter hub holder, cutter hub and cutter blades all of which are moved axially in both axial directions in unison with the piston in the double acting hydraulic cylinder. 
   Yet a further object of the present invention is to provide a positive control for a cutter hub and cutter blades in an underwater pelletizer for movement in both axial directions in relation to a die face by utilizing the elongated motion rod extending through the hollow motor shaft and rotatably connected to a piston of a double acting hydraulic cylinder at an end of the rod opposite to the cutter hub and blades with the end of the motion rod adjacent the cutter hub being threadedly engaged with the cutter hub holder which is threadedly engaged with the cutter hub to enable easy assembly and disassembly of the components. A lock screw is preferably threaded into the cutter hub holder and engaged with the threaded end of the motion rod to lock the cutter hub holder in nonrotative relation to the motion rod to assure continuous engagement between the motion rod and cutter hub holder but yet enabling easy disassembly by removing the lock screw and threadedly uncoupling the cutter hub holder from the motion rod. 
   An additional object of this invention to be specifically enumerated herein is to provide an underwater pelletizer with positively controlled cutter hub in accordance with the preceding objects and which will conform to conventional forms of manufacture, be of simple construction and easy to use so as to provide a device that will be economically feasible, long lasting and relatively trouble free in operation. 
   These together with other objects and advantages which will become subsequently apparent reside in the details of construct 8 on and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numeral refer to like parts throughout. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view of an underwater pelletizer, partly in section, illustrating the structural details and relationships of the components of the positive control of the cutter hub and cutter blades in accordance with the present invention. 
       FIG. 2  is a perspective view, partly in section, illustrating the cutter hub holder drivingly connected to the motor shaft and the motion rod extending through the cutter hub holder with the end of the motion rod threadedly engaged with the interior of the end of the cutter hub holder that is threaded into the cutter hub, in accordance with the present invention. 
       FIG. 3  is a partially exploded perspective view illustrating the relationship of the cutter hub holder, cutter hub with blades and a lock screw that threadedly engages the internal threads in the cutter hub holder and locks the motion rod against rotation in relation to the cutter hub by contact with the end of the motion rod, in accordance with the present invention. 
       FIG. 4  is an exploded group perspective view, with portions in section, illustrating further association of the motor shaft, pelletizer shaft, the driving connection between the shafts, the motion rod and the relationship to the cutter hub holder and cutter hub with the lock screw positioned for threaded engagement with the end of the cutter hub holder in accordance with the present invention. 
       FIG. 5  is a perspective view partially in section illustrating the spline structure of the cutter hub holder and the relationship between the lock screw, the cutter hub holder and the end of the motion rod in accordance with the present invention. 
       FIG. 6  is a schematic elevational view of the double acting hydraulic cylinder and piston illustrating fluid pressure on the piston in both axial directions in accordance with the present invention. 
       FIG. 7  is a schematic diagram of the closed hydraulic fluid circuit and the pneumatic circuit for controlling flow in the hydraulic circuit in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although only one preferred embodiment of the invention is explained in detail, it is to be understood that the embodiment is given by way of illustration only. It is not intended that the invention be limited in its scope to the details of constructions and arrangement of components set forth in the following description or illustrated in the drawings. Also, in describing the preferred embodiment, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
   An underwater pelletizer constructed in accordance with the present invention is generally designated by reference numeral  10  in  FIG. 1 . The pelletizer  10  includes a rotatable cutter hub  12  supporting a plurality of cutter blades  14  associated with the die face of a die plate  16  through which molten polymer or other extrudable material is extruded through extrusion orifices in the die plate, and the cutter blades  14  cut the strands exiting the die face into pellets. A water box generally designated by reference numeral  20  includes an interior  22  having a water inlet  24  and a water and pellet slurry outlet  26  in opposed relation thereto. Water passing through the water box interior  22  cools and solidifies the molten plastic or extrudate as the strands are cut into pellets and entrains the pellets into the water flow for discharge through the outlet  26 . The above described structure is a conventional underwater pelletizer such as that disclosed in U.S. Pat. No. 6,332,765. The water box  20  includes a tapered flange  28  abutingly engaging a flange  30  mounted on the end of a motor  50  by fastening bolts  32 . The flanges  28  and  30  have oppositely slanted peripheral edge portions for engagement by a two part channel shaped clamp  34  to enable assembly and disassembly of the water box in relation to the motor mounted flange  30  in a conventional manner. 
   As illustrated in  FIG. 3 , the cutter hub  12  includes a centrally disposed internally threaded opening  38  which screw threadably receives a male threaded, reduced diameter end portion  40  of a cutter hub holder  42 . As illustrated in  FIG. 2 , the cutter hub holder  42  is slidingly and drivingly connected to an intermediary  44  by a slidable spline drive connection  46  in the form of longitudinal grooves and ridges in a manner similar to that disclosed in U.S. Pat. No. 6,332,765. The intermediary  44  includes a longitudinal recess  47  of larger diameter than the portion of intermediary which engages with the cutter hub holder  42  for receiving a motor shaft  48  which extends through the center of the electric drive motor  50 . The intermediary  44  is drivingly connected to the motor shaft  48  by set screws  52  or similar fastening devices. The structure of the motor shaft  48 , intermediary  44  and cutter hub holder  42  are the same as disclosed in the aforesaid U.S. Pat. No. 6,332,765. 
   As illustrated in  FIGS. 2–4 , the motor shaft  48  is hollow and includes an elongated one piece motion rod  54  extending completely through the motor shaft  48  and the motor  50 . The motion rod  54  includes a reduced diameter threaded end  56  which is screw threadedly engaged with an internally threaded end portion  58  of the cutter hub holder  42 . The reduced end  56  of motion shaft  54  has a screw driver receiving kerf  57  therein to enable assembly and disassembly of motion rod  54  and cutter hub holder  42 . The reduced threaded end  56  on rod  54  defines a shoulder  60  which abuts an inner shoulder  62  at the inner end of the internally threaded portion  58  of the end of the cutter hub holder to thereby screw threadedly connect the threaded end  56  of the motion rod  54  to the interior of the cutter hub holder  42 . A lock screw  64  is threaded into the internally threaded end portion  58  of the cutter hub holder  42  into abutting engagement with the end of the motion rod  54  to provide a locking action between the external threads on the motion rod  54  and the internal threads  58  in the end of the cutter hub holder  42 . The holder  42  is threaded into the cutter hub  12  by external threads  40  engaging the internal threads  38  in the cutter hub  12 . 
   The spline coupling  46  enables the cutter hub holder  42  to elongate or shorten as determined by movement of the motion rod  54 . The lock screw  64  enable assembly and disassembly of the cutter hub holder  42  from the motion rod  54  and locks the cutter hub holder and cutter hub fixedly but detachably to the motion rod  54 . 
   Turning back to  FIG. 1 , the motor  50  includes a housing extension  66  which is supported from the motor  50  by elongated bolts  68 . Housing extension  66  is closed at its remote end by an end plate that supports a double acting hydraulic cylinder  72  outwardly thereof, preferably within a rear enclosure  74 . The motion rod  54  which extends through the motor drive shaft  48  is provided with a rotary coupling  76  in the interior of the housing extension  66 . A bracket  77  supports the coupling  76  and a thrust bearing  78 . The hydraulic cylinder  72  includes a piston  83  and piston rod  84  connected with the coupling  76  to rotatably connect the motion rod  54  to non-rotatable piston rod  84 .  FIG. 7  illustrates the function of the double acting hydraulic cylinder  72  to transmit forward or backward motion forces to the piston  83 , and through piston rod  84  and thrust bearing  78 , to motion rod  54  and thus to the pelletizer cutter hub and blades. 
   More specifically, the double acting motion cylinder  72  generates the pressure for advancing or withdrawing the blades as triggered by the control system illustrated in  FIG. 7 . The control system provides hydraulic fluid pressure that is incompressible to the cylinder  72  on opposite sides of the piston  83  as shown in  FIG. 6  to move the piston rod  84  and thus the motion rod  54  in opposite directions, moving the cutter hub and blades either towards or away from the die face. Hydraulic fluid is supplied to opposite ends of the cylinder  72  by hydraulic fluid pressure lines  85  and  86  each of which includes a pressure gauge  88 . The hydraulic line  84  provides for forward motion of the piston  83  and motion rod  54 , and the hydraulic line  86  provides backward motion of the piston  83  and motion rod  54 . Each of the hydraulic lines  85  and  86  is also provided with a stop valve  90  which is connected to one end of an air-oil actuator  92  which includes a cylinder  94  having the fluid pressure lines  85  and  86  connected to one end of the cylinder  94  and an air supply line  96  connected to an outer end of a cylinder  94 . Each air supply line  96  is provided with a proportional valve  98  communicated with an air supply  100  through a pressure amplifier or amplifiers  102  depending upon the air pressure supply. 
   The air-oil system includes two pressure circuits that can be controlled independently from one another including a blade forward pressure circuit and a blade back pressure circuit. In the blade forward pressure circuit the pelletizing pressure is controlled by a proportional valve to automatically insure the optimum pelletizing pressure in each operating phase. The generated pneumatic blade forward pressure is translated into a fluid pressure in an air-oil actuator and this incompressible fluid pressure then acts on the piston side of the double acting cylinder to move the blade forward or toward the die plate. 
   The blade back pressure circuit provides a backward motion or pressure which is also set by a proportional valve and translated into a fluid pressure in an air-oil actuator to act on the side of the piston to move the blades backwards or away from the die plate. Thus, the two variables providing fluid pressure on opposite sides of the piston insures an optimum positioning of the pelletizer blades and avoiding any unnecessary blade wear. The stop valves in the control circuits serve to hold the pelletizing blades in their position after start up of the pelletizer and proper operating pressure has been reached so as to insure a uniform pellet shape. 
   The positive controlled movement of the cutter hub and blades enables control of the forces acting on the blades and the die plate in all operating stages to reduce wear of the pelletizing blades and die face. The double acting motion cylinder  72  generates pressure for advancing or withdrawing the blades with the pressure being transmitted to the cutter hub holder and thus to the cutter hub blades by the motion rod  54  which is fixed to the cutter hub holder and passes through and rotates with the hollow motor shaft. 
   The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.