Abstract:
An underwater pelletizer for cutting extruded plastic into a flow of liquid is disclosed. The pelletizer includes a cutter hub ( 90 ) carrying at least one cutter blade ( 96 ), a cutter shaft ( 60 ) for rotationally driving the cutter hub, and a flexible torque converter ( 80 ) for connecting a motor to the cutter hub. In one embodiment, the torque converter has a first set of bushings ( 82 ) that is fastened to a face ( 98 ) of the cutter hub and a second set of bushings that is fastened to a face ( 64 ) of the cutter shaft. The disclosed pelletizer has a shaft extension ( 20 ) configured to engage a motor shaft, the shaft extension having an outer diameter having formed thereon a splined portion ( 38 ) and first ( 26 ) and second ( 28 ) sealing surfaces. A disclosed motor adaptor ( 40 ) has a seal surface ( 44 ). A water chamber plate ( 50 ) may also have a seal surface ( 52 ). A first mechanical seal ( 48 ) is illustratively configured to engage the first seal surface ( 26 ) of the shaft extension and the seal surface ( 44 ) of the motor adaptor. A second mechanical seal ( 49 ) is illustratively configured to engage the second seal surface ( 28 ) of the shaft extension and the seal surface ( 52 ) of the water chamber plate. Furthermore, a cutter shaft ( 60 ) has a splined bore ( 62 ) formed therein for engaging the splined portion ( 38 ) of the shaft extension.

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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. 
     In such a combined extruder and pelletizer assembly it is desirable to provide means for facilitating a smooth flow of the plastic material from the extruder to the die holes in the die. Also it is desirable to provide means for gaining easy access to the chamber for servicing the pelletizer, such as to replace worn cutting blades of the cutter assembly, to generally observe the formation of pellets by the rotating cutter assembly, and to clean the die. 
     It is also desirable to provide a long useful life for the cutting blades of the cutter assembly and die. That is to say, it is desirable to provide cutting blades that will last a long time. In addition, it is desirable to provide some means for automatically readjusting the position of the cutter assembly adjacent the die face as the space between the cutter assembly and the die face increases due to wear of the cutting blades. In this respect, it is desirable to keep the cutting blades juxtaposed to the die face to ensure clean cutting of the streams of plastic material into pellets. 
     U.S. Pat. No. 4,529,370 illustrates one example of a conventional underwater pelletizer. 
     Another example of a conventional underwater pelletizer is shown in U.S. Pat. No. 5,059,103. Some conventional components for pelletizers are shown in U.S. Pat. Nos. 4,621,996; 5,403,176; 5,624,688; and 6,332,765. 
     BRIEF SUMMARY OF THE INVENTION 
     An embodiment of an underwater pelletizer includes a flexible torque converter disc that engages a cutter hub having cutting blades and a cutter drive hub that is driven by a motor. The flexible torque converter disc accommodates misalignment between a motor shaft and a die face and maintains the cutting blades in contact with a die face during rotation. In a further refinement, mechanical seals are provided for a shaft extension to pass through a motor adaptor and a water chamber plate and provide for a high-pressure chamber. An access hole and a bore through the shaft extension permit a hub piston to be controlled by varying the pressure in the high pressure chamber in order to control the pressure of the cutting hub against the die face. In still another refinement, the water chamber has a water inlet and outlet arranged so that water pumped into the water chamber forms a vortex that rotates in the same direction as the rotation of the cutter hub. In a further refinement of this embodiment, the water chamber is fixedly attached to the motor adaptor and removably coupled to the die. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 ; 
         FIG. 3  is a side view of the cutting hub of  FIG. 1 ; 
         FIG. 4  is a top view of the cutting blade of  FIGS. 1-3 ; 
         FIG. 5  is an isometric view of the cutting blade of  FIGS. 1-4 ; 
         FIG. 6  is an assembled side view illustrating the water chamber housing of  FIG. 1  and associated water circulation equipment; 
         FIG. 7  is an assembled cross-sectional view of the underwater pelletizer of  FIGS. 1 and 6  that also illustrates automated clamping and pressure actuation components; 
         FIG. 8  is an exploded side view of the components of a cutter shaft assembly that includes a motor shaft extension, cutter shaft, hub piston, flexible disc coupling and cutter hub; 
         FIG. 9  is a frontal view of one embodiment of a flexible disc having four bushings and  FIG. 10  is a side view of the same embodiment; 
         FIGS. 11 and 12  are side and frontal views, respectively, of an embodiment of a cutter shaft; 
         FIGS. 13 and 14  are side and frontal views, respectively, of an embodiment of a shaft extension; 
         FIGS. 15 ,  16  and  17  are rear, side and frontal views, respectively, of an eight bladed embodiment of a cutter hub; 
         FIG. 18  is a side view of an embodiment of a piston for a diverter valve with grooves formed on a periphery of the piston. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     It is also desirable to provide for rapid cleaning of the cutting blades, die and water chamber, which must be cleared of excess extruded plastic in order to operate properly. Conventional underwater pelletizers provide for the plastic to be extruded through holes in the die face into a water chamber, where the plastic is cut by the cutting assembly. During start-up procedure the water chamber is flooded with plastic and it has to be manually removed by the operator. The water chamber is typically fixedly attached to the die and a motor adaptor with a water seal is removably coupled to the other end of the water chamber. 
     The water seals provided in conventional underwater pelletizers are typically oil seals, which tend to break down if subjected to significant levels of water pressure. Breakdown of the seals leads to water entering the motor assembly, which can damage the motor and requires replacement of the seals. 
     Conventional water chambers have a water intake on one side of the chamber, e.g. the bottom, for inflow of water and an outlet on another side, e.g. the top, for outflow of water and pelletized material. The resulting flow of material is in one direction through the chamber. The cutting blade assembly rotates within the water chamber in approximately the same plain as the vector of the water flow through the chamber. Consequently, the blades of the cutting blade assembly rotate substantially with the water flow through half their rotation and against the water flow through the other half of their rotation. As a result, a significant amount of power is required to drive the cutting blade assembly against the flow of water in the water chamber. 
     Conventional blades used in conventional cutting blade assemblies typically have two sharpened cutting edges that engage the die face for cutting plastic as it is extruded. These blades are sharpened on opposing edges of a body of the blade, where the cutting edge is formed on opposing planar sides of the body so that the blade can be removed and reversed when one cutting edge has worn out. The conventional blades typically have two bolt holes for bolting the blade into the cutting blade assembly so that the blade does not rotate out of position under load when the cutting blade assembly is engaged and rotated against the die face. The conventional blades wear out after the two cutting edges are used up. 
       FIG. 1  is an exploded view of an exemplary embodiment of an improved underwater pelletizer. A motor  10  has a shaft  12  that engages shaft extension  20 . The shaft extension  20  passes through a motor adaptor  40  and water chamber plate  50  to engage cutter shaft  60 . A dual mechanical shaft seal assembly  48  is used to provide a seal between the shaft extension  20  and motor adaptor  40  at both a motor side and a water chamber plate side. Another mechanical seal engages water chamber plate  50  and provides a seal for shaft extension  20  between motor adaptor  40  and water chamber plate  50 . Shaft extension  20  also engages hub piston  70 , which engages pressure plate  92  of cutter hub  90 . 
     Water chamber housing  100  has a first open end  102  that is coupled to water chamber plate  50  such that cutter shaft  60  and cutter hub  90  are disposed within water chamber bore  104 . A second open end  106  of water chamber housing  100  is adapted to engage die ring  130  and driven rotor  140  removably couples thru the set of eccentrically guided pins with radial bearings water chamber housing  100  to die  150 . Die  150  is fixedly connected to die ring  130  on one side and to die clamp adaptor  160  on the other side, which engages clamp  180  for clamping die  150  to diverter valve  190 . Flow distributing insert  170  facilitates annular flow of plastic from diverter valve  190  to die  150 , where the plastic is extruded through holes in die face  152 . 
     The shaft extension  20  has a first bore  22  for engaging shaft  12  of motor  10 . A seal surface  26  is provided for seating a first mechanical shaft seal  48  against seal surface  44  of motor adaptor  40 . Another seal surface  28  is provided for seating second mechanical shaft seal  49  against seal surface  52  of water chamber plate  50 . When shaft extension  20  is assembled with motor adaptor  30  and water chamber plate  50  with mechanical shaft seals  48  and  49 , a high-pressure chamber  42  is formed with motor adaptor  40  and water chamber plate  50 , where the pressure in the high pressure chamber  42  may be controlled via pressure regulator  250  illustrated in  FIG. 7 . 
     Shaft extension  20  also includes piston chamber  32  for receiving hub piston  70 . Piston chamber  32  is in communication with pressure access hole  36  via axial bore  34 . When assembled, pressure access hole  36  is in communication with high-pressure chamber  42  of motor adaptor  40  and hub piston  70  is seated in piston chamber  32 . Consequently, the axial force applied to pressure plate  92  of cutter hub  90  by hub piston  70  may be controlled by varying the pressure in high-pressure chamber  42  via pressure regulator  250  attached to pressure port  46 , as illustrated in  FIG. 7 . Thus, the axial pressure of cutter hub  90  against die face  152  is externally controllable during operation of the pelletizer. 
     Motor shaft extension  20  has a splined outer surface region  38  that, when assembled, engages splined bore  62  of cutter shaft  60 . Cutter shaft  60  has a flexible disc engagement face  64  that is formed to engage bushings  82  of flexible torque transmitting disc  80 . Cutter hub  90  also has a disc engagement face  98  that is formed to engage bushings  82  of flexible torque transmitting disc  80 . When assembled, rotary force generated by shaft  12  of motor  10  is transmitted through shaft extension  20  to cutter shaft  60  and from cutter shaft  60  through flexible torque transmitting disc  80  to cutter hub  90  in order to rotate the cutter blades  96  against die face  152  of die  150 . 
     Flexible torque transmitting disc  80  is a standard torque-transmitting device that is a generally available power transmission product frequently used in other power transmission applications. In the present embodiment, disc  80  is constructed of laminated sheets of stainless steel that permits approximately 5° of movement. The stainless steel prevents disc  80  from corroding due to contact with water in water chamber housing  100 . The flexibility of disc  80  permits it to accommodate both angular and parallel misalignment between motor shaft  12  and die  150 . Disc  80  transmits only rotary force from cutter shaft  60  to cutter hub  90  and transmits no axial force necessary to keep the blades  96  attached to the cutter hub  90  against die face  152 . 
     Note that the cutter hub  90 , cutter shaft  60 , blades  96 , flexible disc  80  and die  150  arrangement operates to maintain substantially consistent pressure of the blades against the die face  152 . This results in blades  96  self-sharpening as they rotate against the die face  152 . By avoiding uneven wear of the die face  152 , the present arrangement can extend the operational life of the die  150 . 
     As shown in  FIG. 1 , water chamber housing  100  has a water inlet opening  110 , a water outlet opening  112 , and a drain outlet  114 . The water inlet  110  and water outlet  112  are formed in the water chamber housing such that they are substantially parallel and adjacent to one another. When the pelletizer is assembled, the water inlet  110  and outlet  112  are arranged with respect to the rotation of cutter hub  90  so that a water vortex is formed within water chamber housing  100  that rotates in the same direction as cutter hub  90 . The resulting arrangement substantially reduces the amount of power required to rotate cutter hub  90  while cutting extruded plastic. It also results in improved pellet removal and reduces jamming. 
     In the pelletizer of  FIG. 1 , water chamber housing  100  is fixedly attached, e.g. bolted, to water chamber plate  50 , which is connected to motor adaptor  40 . In this embodiment, water chamber housing  100  is formed with an automatic clamp fitting for engaging die ring  130  via an automatic clamp rotor  140 , which is discussed in further detail below with regard to  FIG. 7 . When the pelletizer is assembled, water chamber housing  100  is fixedly attached to motor  10  and removably coupled to the die ring  130  and the die  150  via a clamping mechanism. 
     If an automated clamp mechanism is used in conjunction with a melt diverting valve and automatic water bypass system, then the start-up and shut-down process for the pelletizer can be fully automated. This arrangement substantially improves system efficiency and operator safety over manual procedure. 
     The embodiment of  FIG. 1  includes a die clamp adaptor  160  for fixed attachment to die  150 . The die  150  is then removably coupled to diverter valve  190  via quick clamp  180 . This arrangement permits that both the front and back of die  150  are rapidly accessible for maintenance and cleaning. 
       FIGS. 2 and 3  show an exemplary embodiment of cutter hub  90  of  FIG. 1 .  FIG. 2  is a front view of the cutter hub from the perspective of the die face  152  that faces hub lid  94 .  FIG. 3  is a side view of the cutter hub. Cutter hub  90  includes multiple cutter blades  96 A-D arranged along a periphery of the cutter hub  90  and secured within slots formed in housing  210 , e.g. slot  214 C shown in  FIG. 3 . The slots are formed in housing  210  of cutter hub, and are wide enough to receive and hold securely a center portion  220  (shown in  FIGS. 4 and 5 ) of each cutting blade  96 .  FIG. 3  shows slot  214 C for mounting one of the blades  96 C of  FIG. 2 . A drilled and tapped bore  212 C is formed into housing  210  of hub  90  for insertion, in this example, of a conical tip set screw  216 C for aligning and securing blade  96 C within the housing  210  through screw hole  224  in the blade. 
       FIGS. 4 and 5  show an exemplary embodiment of cutting blades  96 A-D. Each cutting blade  96  is substantially symmetrical along two perpendicular axes A and B. A central portion  220  of cutting blade  96  is positioned along axis B and has a substantially rectangular cross-section for holding the blade securely within slot  214  in the cutting hub housing  210 . Each cutting blade has up to four cutting edges  222 A-D formed into it, where the cutting edges are formed proximally from the central portion and perpendicular to axis A. The cutting edges  222 A-D are formed on two opposing surfaces X and Y of blade  96 . Diametrically opposed cutting edges are formed on the same surface. For example, edges  222 A and  222 C are formed on planar surface Y and edges  222 B and  222 D are formed on planar surface X. The resulting cutting blade  96  may be removed from cutter hub  90  and rotated so that all four edges  222 A-D may be used for cutting before blade  96  is worn out. Removing and rotating blade  96  is accomplished by backing out set screw  216 , rotating and/or reversing blade  96 , and resetting set screw  216 . 
     In a preferred embodiment, a single securing hole  224  is formed at the intersection of axes A and B of blade  96 . The securing hole  224  is adapted to engage set screw  216  threaded through bore  212  in the cutter hub housing  210  that holds the cutting blade securely in place within cutter hub  90 . This arrangement results in the cutting blade being self-aligning within cutter hub  90 . The conical tip of set screw  216 , along with the alignment of screw hole  224  and bore hole  212  combine to align blade  96  within the housing  210 . 
       FIG. 6  is an assembled side view illustrating the water chamber housing  100  of  FIG. 1  fixedly coupled to motor adaptor  40  and motor  10  along with associated water circulation ports. Flow sight  230 , which allows water and pelletized material to be observed leaving water chamber housing  100 , is coupled to water outlet  112  via cam and groove coupling  236  and on top is coupled to hose fitting  232  via cam and groove coupling  234 , where hose fitting receives a water and pellet hose typically for transporting the resulting pelletized material to a pellet dryer. Water inlet  110  is coupled to hose fitting  238  via cam and groove coupling  237 , where hose fitting  238  receives a water supply line. Pneumatic valve  240  is coupled to drain outlet  114  and has a hose fitting  242  for receiving a hose for draining water chamber housing  100 . 
       FIG. 7  is an assembled cross-sectional view of the underwater pelletizer of  FIGS. 1 and 6  that also illustrates automated clamping and pressure actuation components. Motor  10  is secured to motor adaptor  40 , which is secured to water chamber plate  50 . Shaft extension  20  is coupled to motor shaft  12  and extends through high pressure chamber  42  formed within motor adaptor  40  along with shaft extension  20  and water chamber plate  50 . Mechanical shaft seal  48  forms a high pressure seal between shaft extension  20  and motor adaptor  40 . Mechanical shaft seal  49  forms a high pressure seal between shaft extension  20  and water chamber plate  50 . In one example, mechanical shaft seals  48  and  49  are ceramic and graphite disc seals actuated by a stainless steel spring, which are widely used in other equipment applications. 
     A pressure regulator  250  (manual or electronic) is connected to supply port  46  and regulates the pressure in high-pressure chamber  42 . The pressure in high-pressure chamber  42 , in turn, affects the amount of force applied by hub piston  70  to pressure plate  92  of cutting hub  90  via pressure access hole  36  and axial bore  34 . By controlling the pressure in high pressure air chamber  42 , the amount of axial force applied by hub piston  70  to cutting hub  90  is controlled during pelletizer operation or blade lapping sequence. 
     Shaft extension  20  passes through water chamber plate  50  into water chamber  101  formed by water chamber housing  100 . Cutter shaft  60  is fitted onto shaft extension  20  and is coupled to cutting hub  90  through flexible disc  80 . The blades  96  of cutting hub  90  are pressed against the face of extrusion die  150  by hub piston  70 . When motor shaft  12  rotates, shaft extension  20  also rotates causing cutter shaft  60 , flexible disc  80  and cutting hub  90  to rotate in order to cut plastic extruded through holes in die  150 . 
     In the embodiment of  FIG. 7 , clamp  180  is a hinged quick clamp for engaging die clamp adaptor  160 , which is fastened to die  150 , and a clamp flange  192  of diverter valve  190 . An actuator  300  has a drive shaft  302  for rotationally driving driven gear  304 . Driven gear  304  engages rotor  140  fastened to water chamber housing  100  in order to open or close water chamber  101 . By automatically controlling actuator  300 , pressure regulator  250 , melt diverter valve  190  and a water bypass system start-up and shut-down of the pelletizer can be fully automated. 
     The water bypass system noted above diverts water from a hose connected to hose attachment  238  for water inlet  110  shown in  FIG. 6  to a hose connected to hose attachment  232  connected to water outlet  112 . This arrangement permits water chamber  100  to be automatically drained during a shut-down operation, but maintain the inertial flow of water in a water circulation system that attaches to hose attachments  232  and  238 . This allows the time required to service an interruption of operation to be reduced. 
       FIG. 8  is an exploded side view of the components of a cutter shaft assembly that includes shaft extension  20 , cutter shaft  60 , hub piston  70 , flexible disc  80  and cutter hub  90 . This expanded view illustrates o-rings  72  and  74  on hub piston  70 , which form a seal between hub piston  70  and piston chamber  32  of shaft extension  20 . As the pressure within high-pressure chamber  42  of  FIG. 7  is varied, hub piston  70  moves within piston chamber  32 . A retainer ring  76  seats into an end of shaft extension  20  and prevents hub piston  70  from being ejected from piston chamber  32 . 
     Also shown in  FIG. 8  are fasteners  84 A-C for securing flexible hub  80  to cutter shaft  60  and cutting hub  90 . In the embodiment shown, a pair of fasteners  84 A and  84 C secure disc  80  to drive shaft  60 . Another pair of fasteners, fastener  84 B and where the other fastener is obscured from view by fastener  84 B, secures disc  80  to cutting hub  90 . The fasteners are inserted through bushings on flexible disc  80  in an alternating fashion such that each pair of adjacent bushings on flexible disc  80  is secured to a different one of cutter shaft  60  and cutting hub  90 . This arrangement permits the disc to flex in order to accommodate misalignment between cutter shaft  60  and cutting hub  90 . 
       FIG. 8  also shows a retainer ring  66  that secures pressure plate  92  to cutter hub  90 . 
       FIG. 9  is a frontal view of one embodiment of flexible disc  80  having four bushings  82 A-D and  FIG. 10  is a side view of the same embodiment. As an example of securing flexible disc  80  in an alternating fashion, bushings  82 A and  82 C are secured to cutter shaft  60  and bushings  82 B and  82 D are coupled to cutter hub  90 . Other arrangements are possible, as are other embodiments where there are a larger number of bushings utilized. 
       FIGS. 11 and 12  are side and frontal views, respectively, of an embodiment of cutter shaft  60 . Note that disc engagement face  64  that is formed to engage bushings  82  of flexible torque transmitting disc  80  includes, in one exemplary embodiment, threaded bores  362 A and  362 B for receiving fasteners  84 A and  84 C of  FIG. 8  for securing bushings  82 A and  82 C of flexible disc  80  to cutter shaft  60 . Also note recesses  364 A and  364 B, which accommodate fastener  84 B and another fastener that is obscured in  FIG. 8  for securing bushings  82 B and  82 D to cutting hub  90 . Note that recesses  364 A and  364 B are preferably sized larger than the heads of fastener  84 B to allow for flexion in disc  80 . Further note in  FIG. 12  the splined surface  366  of splined bore  62  for receiving splined outer surface region  38  of shaft extension  20  shown in  FIG. 14 . 
       FIGS. 13 and 14  are side and frontal views, respectively, of an embodiment of shaft extension  20 . As noted above, piston chamber  32  is in communication with pressure access hole  36  via axial bore  34  so that, when assembled, pressure access hole  36  is in communication with high-pressure chamber  42  of motor adaptor  40  shown in  FIG. 7 . Shaft extension  20  has a splined outer surface region  38  that, when assembled, engages splined bore  62  of cutter shaft  60 . 
     Piston chamber  32  is in communication with pressure access hole  36  via axial bore  34 , as further illustrated in  FIG. 7 . When assembled, as illustrated in  FIG. 7 , pressure access hole  36  is in communication with high-pressure chamber  42  of motor adaptor  40  and hub piston  70  is seated in piston chamber  32 . Consequently, the axial force applied to pressure plate  92  of cutter hub  90  by hub piston  70  may be controlled by varying the pressure in high-pressure chamber  42  via pressure supply port  46 . Thus, the axial pressure of cutter hub  90  against die face  152  is dynamically controllable during operation of the pelletizer or blade lapping sequence. p As shown in  FIG. 14 , shaft extension  20  has a splined outer surface region  38  that, when assembled, engages splined bore  62  of cutter shaft  60 , shown in  FIG. 12 . The splines of splined bore  62  may be formed by gear cutting or honing the interior surface of bore  62 , which results in a robust engagement of the shaft extension  20  to cutter shaft  60 . Seal surface  26 , shown in  FIGS. 13 and 14 , is provided for seating a mechanical shaft seal  48  against seal surface  44  of motor adaptor  40 , shown in  FIG. 1 . Another seal surface  28 , shown in  FIG. 13 , is provided for engaging second mechanical shaft seal against seal surface  52  of water chamber plate  50 , shown in  FIG. 1 . 
       FIGS. 15 ,  16  and  17  are rear, side and frontal views, respectively, of an eight bladed embodiment of a cutter hub  90 B.  FIG. 14  shows a disc engagement face  398  that is formed to engage bushings  82  of flexible torque transmitting disc  80 . In this embodiment, disc engagement face includes threaded bores  392 A and  392 B for receiving fastener  84 B and another fastener that is obscured in  FIG. 8  for securing bushings  82 B and  82 D to cutting hub  90 . Also note recesses  394 A and  394 B, which accommodate fasteners  84 A and  84 C of  FIG. 8  for securing bushings  82 A and  82 C of flexible disc  80  to cutter shaft  60 . Note that recesses  394 A and  394 B are preferably sized larger than the heads of fasteners  84 A and  84 C to allow for flexion in disc  80 . 
     Further note slot  414 A formed in the body of hub  390  for receiving a cutting blade, such as those discussed above. A threaded bore  412 A is formed at an angle and intersects slot  414 A so that a set screw can be used to secure the cutting blade in place within slot  414 A. Note that other configurations for cutter hub are possible, such as a six bladed embodiment. 
     In one embodiment, the diverter valve  190  shown in  FIGS. 1 and 6  has a piston  194  with peripheral grooves formed thereon, as shown in  FIG. 18 . In this embodiment, the grooves are approximately ⅛ of an inch wide and deep. Because the diverter valve piston  194  is typically subject to tight tolerances, e.g. thousandths of an inch, with the diverter valve housing  190 , the piston  194  is vulnerable to jamming due to contaminant particles, such as metal filings or wood splinters, that tend to jam conventional pistons. In this embodiment, the peripheral grooves trap the contaminant particles to prevent the particles from jamming the piston  194 . Also, molten plastic within the diverter valve  190  tends to solidify within the grooves and helps form a seal between the piston  194  and the diverter valve  190 . 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention