Patent Publication Number: US-2005116074-A1

Title: Comminuter striker plate

Description:
FIELD OF THE INVENTION  
      This invention relates to various shredding, shearing, tearing, cutting and grinding devices which process small pieces of bulk materials, such as pieces of rubber tires, into crumb-sized particles.  
      The present invention more particularly relates to an apparatus for comminuting that is, performing a plurality of size reducing actions by a rotor mounted for rotation within a reduction chamber and, more particularly, to a striker plate carried by a rotor, preferably on lobes of the rotor, which cooperate with a stationary anvil which also preferably carries identical striker plates. The invention further relates to a configuration of an anvil to facilitate changing of striker members of the anvil.  
     BACKGROUND OF THE INVENTION  
      In general, a comminuter comprises a housing with a reducing chamber having an inlet for feeding material to the reducing chamber and an outlet for discharging material of reduced size. A rotor is arranged in the reducing chamber and is mounted on a horizontal drive shaft driven by a suitable motor. A plurality of striker plates are mounted along the periphery of the rotor radially of the rotor, and each has a striking surface or cutting edge oriented in the general direction of rotation of the rotor. The feed is caught between striker plates on the rotor and an anvil spaced from the striker plates. With revolution of the rotor, the feed pieces are sheared, cut, ground and the like to reduce their size. Preferably, the anvil also carries striker plates with cutting edges spaced from the cutting edges of the striker plates on the rotor.  
      Typical prior art heavy duty material reduction apparatus utilizing impact rotors of the type under consideration are disclosed in U.S. Pat. No. 5,402,948 Kaczmarek and U.S. Pat. No. 4,151,959 to Deister. These patents are illustrative of the prior art utilizing either a radially attached, axially or helically extending cutter bar or striker plate.  
      The Kaczmarek patent, for instance, illustrates a cutter bar extending axially on the surface of a rotating drum over the entire length of the drum. The cutter bar is shown with multiple removable cutting teeth-like striker plates mounted thereon for cutting in cooperation with cutting teeth-like striker plates carried on a stationary anvil. The Deister patent illustrates still another type of impact rotor comprised of a series of rotary discs with offset, radially extending lobes for mounting removable striker plates. A disadvantage in both these types of apparatus is that the cutter teeth or striker plates have a leading cutting edge subject to severe wear and deterioration. This is disadvantageous because it is necessary to completely remove the cutting edge wear component from the rotor or anvil in order to replace a cutting edge or to change or reverse the position of the cutter tooth or striker plate to present a new cutting edge. A disadvantage, particularly with heavy duty rotary hogs, is that this operation is expensive and time consuming. An associated disadvantage is that known cutter teeth and striker plates are expensive to manufacture and often are custom made for different positions on the rotor or anvil.  
     SUMMARY OF THE INVENTION  
      To at least partially overcome these disadvantages, the present invention provides an improved striker plate for a rotor or anvil in a comminuter used for the size reduction of feed material as by cutting, shearing, pulverizing and the like, most preferably, for comminuting rubber.  
      An object of the present invention is to provide an improved striker plate which is inexpensive and as well is adapted to be mounted in a manner which is easy to change and is cost effective.  
      Another object is to provide a configuration for an anvil in a comminuting apparatus which facilitates change of striker members of the anvil.  
      The present invention provides a striker plate carrying a cutting edge adapted for attachment to a rotor or an anvil of a size reducing apparatus.  
      The striker plates in accordance with the present invention are adapted for use to size reduce materials which are difficult to reduce such as multi-grade materials like rubber tires which comprise not only rubber but also steel and material cord. The striker plates provide cutting flexibility which reduces the impact force experienced by each cutting and allows the striker plates to strip coatings off of steel belted cord passing vertically between opposed cutting edges and to cut like material passing between opposed cutting edges and further to cut, shred, tear and grind various work materials.  
      In accordance with preferred embodiment of the invention, only one rotating grinding drum is employed and a stationary anvil carries striker plates with cutting edges on the drum housing. This is advantageous in that, if desired, close clearances may be established between the cutting edges on the striker plates on the rotor and cutting edges on the striker plates on the stator anvil such that the comminuting action may be primarily a cutting action although shearing, tearing, grinding, and ripping actions occur. Where the clearances between the cutting edges of the striker plates on the rotor and stator are smallest, the cutting edges co-act to shear material fed into the space therebetween.  
      In one aspect, the present invention provides a striker plate for a rotatable rotor or stationary anvil of a rotary comminuting device comprising: 
          a striker plate having:     a first end face,     a second end face,     a rear face for attachment to a rotor or anvil,     a front face parallel the rear face,     a right cutting side face extending between the rear face and the front face on a right side thereof, and     a left cutting side face extending between the rear face and the front face on a left side thereof,     a right rear cutting edge formed at a juncture between the right side cutting face and the rear face,     a right front cutting edge formed at a juncture between the right side cutting face and the front face,     a left front cutting edge formed at a juncture between the left side cutting face and the front face,     a left rear cutting edge formed at a juncture between the left side cutting face and the rear face,     the right cutting side face comprising a plurality of identical planar right lands interspaced by a plurality of identical, parallel right grooves,     the right lands all lying in the same flat right land plane and each spaced from each adjacent right land by one of the right grooves, the right land plane disposed at a first angle to the rear face,     each right groove comprising a frusto-cylindrical surface of an angular extent not greater than 180 degrees about a respective groove axis extending at a second angle to the rear face,     each respective groove axis for all of the right grooves lying in a same right axis plane,     the left cutting side face comprising a plurality of identical planar left lands interspaced by a plurality of identical, parallel left grooves,     the left lands all lying in the same flat left land plane and each spaced from each adjacent left land by one of the left grooves, the left land plane disposed at the first angle to the rear face,     each left groove comprising a frusto-cylindrical surface of an angular extent not greater than 180 degrees about a respective groove axis extending at the second angle to the rear face,     each respective groove axis for all of the left grooves lying in a same left axis plane,     the right land plane parallel to the left land plane.        

      In another aspect the present invention provides a comminuting apparatus having: 
          a rotor for rotation about a horizontal axis relative to a stator,     the rotor having replaceable rotor striker plates secured thereto with a cutting side surface disposed radially outwardly from an outer most radial perimeter of the rotor,     the cutting side surface of the rotor having axially spaced rotor teeth with radially inwardly extending rotor grooves between adjacent rotor teeth,     a stationary anvil fixed to the stator radially outwardly of the rotor extending axially of the rotor and presenting replaceable anvil striker plates secured thereto with a cutting side surface disposed radially inwardly from an inner most radial perimeter of the stator towards the rotor,     the cutting side surface of the stator having axially spaced stator teeth with radially inwardly extending stator grooves between adjacent stator teeth,     the stator teeth alternating axially with the rotor teeth with each stator tooth disposed in a rotor groove spaced therefrom extending radially inwardly into the rotor groove radially inwardly of the radially outermost portions of the adjacent rotor teeth and with each rotor tooth disposed in a stator groove extending radially outwardly into the stator groove radially outwardly of the radially innermost portions of the adjacent stator teeth,     wherein at every axial point a radially extending gap is provided between the cutting side surface of the rotor striker plates and the cutting side surface of the stator striker plates,     the radially extending gap varying in radial extent over the axial extent of at least some of the stator grooves and rotor grooves.        

      Further aspects and advantages of the present invention will be apparent from the accompanying drawing and description in which there is illustrated preferred embodiments of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Reference is made to the accompanying drawings in which:  
       FIG. 1  is a pictorial view of a comminuting apparatus in accordance with the first embodiment of this invention;  
       FIG. 2  is a schematic front view of the comminuting device shown in  FIG. 1 ;  
       FIG. 3  is a schematic right side view of the comminuting device shown in  FIG. 1 ;  
       FIG. 4  is a pictorial view of the reducing chamber and rotor of the comminuting device shown in  FIG. 1 ;  
       FIG. 5  is a schematic pictorial view of the rotor and stator shown in  FIG. 4  from the same angle of view as seen in  FIG. 4 ;  
       FIG. 6  is a schematic pictorial view showing the rotor and stator of  FIG. 4 , however, from an opposite side to that in  FIG. 5 ;  
       FIG. 7  is a top view of the rotor and stator of  FIG. 4  normal to the top surface of the stator anvil;  
       FIG. 8  is a schematic cross-sectional side view along section line  8 - 8 ′ of  FIG. 7 ;  
       FIG. 9  is an enlarged schematic cross-sectional side view of the anvil and radial edge of the rotor as seen in  FIG. 8 ;  
       FIG. 10  is a schematic pictorial view of the anvil of the stator of  FIG. 4  with a cover plate removed and schematically showing a single striking plate of the rotor;  
       FIG. 11  is a pictorial view of the radial outside of the stator anvil as seen in  FIG. 10 ;  
       FIG. 12  is a pictorial view of one rotor disc of the rotor in  FIG. 4 ;  
       FIG. 13  is a pictorial view of a preferred striker plate in accordance with the present invention as illustrated in FIGS.  1  to  12 ;  
       FIG. 14  is a top view of the striker plate of  FIG. 13 ;  
       FIG. 15  is a side view of the striker plate of  FIG. 13 ;  
       FIG. 16  is an end view of the striker plate of  FIG. 13 ;  
       FIG. 17  is a top view of a steel plate showing a method of manufacture of the striker plate of  FIG. 13 ;  
       FIG. 18  is a schematic top view illustrating two striker plates on the anvil and one striker plate on a segment of the rotor as seen in  FIG. 10 ;  
       FIG. 19  is an enlarged view of the top view of  FIG. 14  in the dotted semi-circular outline;  
       FIG. 20  is an enlarged view similar to  FIG. 19  but with the striker plates on the anvil displaced axially relative the striker plate on the rotor compared to that in  FIG. 19 ;  
       FIG. 21  is a top view similar to  FIG. 26  of opposed side edges of a stator striker plate and a rotor strike plate with symmetrical pyramidal teeth centered in corresponding grooves;  
       FIG. 22  is a top view the same as  FIG. 21  but with the teeth not centered in the grooves;  
       FIG. 23  schematically illustrates a portion of a striker plate as seen in top view in  FIG. 14 , as being shown to being manufactured by a milling process;  
       FIG. 24  is an end view similar to  FIG. 8  but of an arrangement including two stators at each end of a screen;  
       FIG. 25  is a cross-sectional view along section line A-A′ in  FIG. 24  showing a mechanism to locate the anvil striker plates axially;  
       FIG. 26  is an end view similar to  FIG. 16  but of a second embodiment of a striker plate in accordance with the invention;  
       FIG. 27  is an end view similar to  FIG. 16  but of a third embodiment of a striker plate in accordance with the invention; and  
       FIG. 28  is an end view similar to  FIG. 16  but of a fourth embodiment of a striker plate in accordance with the invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference is made to FIGS.  1  to  4  which show a first embodiment of a comminuting device  10  in accordance with the present invention. As best seen in  FIG. 4 , a rotor  12  is mounted within a stator  14  with the stator forming a reducing chamber  16 . The reducing chamber  16  is formed between a lower portion  18  of the stator and an upper hopper forming lid  20  which is shown in a closed position in FIGS.  1  to  3  and in an open position in  FIG. 4  to reveal notably the rotor  12  disposed for rotation about its horizontally extending shaft  22  and a stationary anvil  24  secured to the lower portion  18  of the stator  14 .  
      As is known, the shaft  22  of the rotor  12  is journalled in bearings  21  and  23  at either side as seen in  FIG. 2 . The shaft  22  is coupled to a motor  17  as preferably via connecting drive belts, not shown, disposed within belt drive housing  15 .  
      As is known, the reducing chamber  16  has a bottom surface comprising a screen, not shown other than as  130  in  FIG. 24 , which is disposed radially outwardly from the rotor  12  proximate thereto. Material to be sized reduced is introduced into an entrance chute  19  of the upper hopper lid  20 , drops down into the reducing chamber  16  where it becomes engaged between the rotor  12  and anvil  24  to be sized reduced and, hence, is moved down into the bottom of the reducing chamber  16  with sufficiently fine particles passing through the screen and down into a discharge duct  15 .  
      The comminuting device in accordance with the present invention is particularly adapted for comminuting small chunks of feed material, notably small chunks of tires having steel belts and other material cores. The feed chunks are preferably tire material having outer dimensions of approximately three to four inches and the comminuter preferably reduces such input material to a relatively small mesh size, preferably, to form crumb rubber with a particle size of approximately one-sixteenth inch to five-eighths inch diameter and larger. The comminuting device in accordance with the present invention is, however, adapted for comminuting various other types of material.  
      As seen in FIGS.  4  to  7 , the preferred rotor  12  is of a segmented type comprising a plurality of rotor discs  26  which are keyed to the shaft  22  for rotation therewith. One disc  26  is illustrated in  FIG. 12 . Each rotor disc  26  carries a plurality of radially outwardly extending rotor lobes  28 . Each rotor lobe  28  provides a striker carrying face  30  for supporting a rotor striker plate  32 . As seen only in  FIG. 12 , each stator striker plate  32  is secured to the rotor lobe  28  by means of a pair of bolts  31  (one of which is shown) passing through bores through a clamp plate  34 , striker plate  32  and the rotor lobe  28  to engage threaded nuts  37  which are to engage a rear face  36  of the lobes. The nuts  37  are protected, in part, by being received within recessed channels  38  in the rear of the lobes  28 . The clamp plate  34  has a material deflecting outer surface  40  raised above forward surfaces  42  on which the heads  35  of the bolts  31  sit such that the heads  35  of the bolts  31  are received within channels  44  in the clamp plate  34  and are, at least to some extent, protected against wear. For ease of illustration, the bolt  31  and nut  33  are not shown other than on  FIG. 12 .  
      Preferably, openings  33  through the striker plate  32  through which the bolts  31  pass may be of a diameter larger than the diameter of the bolts  31  such that the striker plate  32  may be moved relative to the clamp plate  34  and, thus, the relative position on the striker plate  32  relative to the rotor lobe  28  may be suitably adjusted.  
      Reference is made to  FIGS. 5, 6 ,  9 ,  10  and  11  which illustrate the anvil  24  which comprises a number of components including an anvil base  46 , a latch rib member  48  and a wear bar  50  which are secured together so as to form, in combination, an anvil table upon which there is mounted a driven wedge  52  and a drive wedge  54 .  
      As best seen in  FIG. 9 , the driven wedge  54  has a striker carrying face  56  to which a anvil striker plate  58  is secured by bolts  60 . A cover plate  62  is secured via bolts  63  on top of the driven wedge  52  and anvil striker plate  58  to protect the bolts  60  from wear. Driven wedge  52  has a bottom surface  64  into which there is cut a keyway  66  which has a radial outward shoulder  68  which extends inwardly and radially outwardly.  
      The anvil table formed as a composite of the anvil base  46 , latch rib member  48  and wear bar member  50  together provide a flat planar table surface  72  upon which the bottom surface  64  of the driven wedge  52  mates and is slidable. A cam rib  70  carried on the latch rib member  48  extends upwardly into the keyway  66  in the driven wedge  52  and has a radially outer shoulder  71  extending radially outwardly and upwardly at an angle and complementary to the shoulder  68  on the driven wedge  52 .  
      The keyway  66  of the driven wedge  52  is of a radial extent greater than the radial extent of the cam rib  70 , such that, when the driven wedge  52  is slid along the table surface  72  radially outwardly, the radial innermost portions of the shoulder  68  on the driven wedge  52  are radially outward of the outer shoulder  71  of the cam rib  70  and the driven wedge  52  may then be removed in a direction normal to surface  72  for replacement by another driven wedge  52 .  
      The driven wedge  52  has an upper cam surface  74  which extends at an angle away from the table surface  72  and radially inwardly.  
      The drive wedge  54  has a complementary lower cam surface  76  to engage the upper cam surface  74 . The drive wedge  54  also has an outer cam surface  78  which slides upon an inner shoulder  80  of the anvil base  46 . A wedge stud  82  has one end secured in the drive wedge  54  and passes through the anvil base  46  to a nut  84  located underneath the anvil base  46  between vertical metal joists  85  supporting the anvil  24  to the remainder of the stator. The wedge bolts  82  extends parallel to the inner shoulder  80  of the anvil base  46 . By rotating the nut  84 , the drive wedge  46  can be moved towards the table surface  72  with the camming interaction of the outer cam surface  74  on the driven wedge  54  and the inner cam surface  56  of the drive wedge  54  urging the driven wedge  52  radially inwardly into a locked position in which its keyway  66  is urged radially into and is fixedly engaged on the cam rib  70 , against any movement whatsoever of the driven wedge  52 . As well, by loosening nut  84 , the drive wedge  54  can be moved to positions in which the driven wedge  52  is free to be removed from engagement on the keyway  66 .  
      In the preferred embodiment, each of the anvil base  46 , latch rib member  48 , wear bar  50  and driven wedge  52  comprise a unitary member which extends the entire axial extent of the anvil. The drive wedge  54  is illustrated as comprising four segments each controlled by two wedge bolts  82 .  
      It will be appreciated that in accordance with the present invention, the driven wedge  52  with its anvil striker plates  58  and cover plate  62  attached may be removed in its entirety as a unit and replaced by a similar replacement driven wedge  52 . The replacement driven wedge  52  may be properly set up and configured with new strike plates  58  and a cover plate  62  prior to assembly on the anvil. In this manner, all of the strike plates  58  on the anvil may be changed relatively quickly. Any new driven wedge  52  may have the striker plates  58  located thereon in a desired configuration and orientation prior to being secured to the anvil base  46 .  
      Reference is made to  FIG. 24  which illustrates an end view similar to  FIG. 8  but with a second stator  24  provided on the right-hand side of the rotor  26  such that two stators  24  are provided on each circumferential side of a screen  130  disposed below the rotor  26 . The two stators  24  are illustrated as identical. The right-hand side stator  24  is mounted for pivoting about a horizontal hinge pin  132  extending parallel the axis of rotor  26  such that for servicing of the right-hand stator  24 , the right-hand stator  24  can be swung from its use position shown in solid lines to a servicing position shown in dashed lines in which the stator  24  has its components, notably, its cover plates  62 , driven wedge  52  and drive wedge  54  on top of the anvil base  46  and accessible. For use, the right-hand stator  26  is locked in the use position.  
       FIG. 25  illustrates in a cross-section along section line A and A′ in  FIG. 24 , a mechanism for moving the driven wedge  32  to different axial positions relative to the anvil base  46 . A slide block  134  is received in a guideway  136  in the anvil base  46  constrained therein but for sliding parallel to the axis of the rotor as controlled and activated by a rotatable screw member  138  accessible via bore  140  in the end wall of the anvil base  46 . The slide block  134  carries a key  146  received in a keyway  142  in the driven wedge  52 . With the drive wedge  54  loosened sufficiently to permit axial sliding of the driven wedge  52  relative the anvil base  46 , by rotation of the screw member  138 , the driven wedge  52  may be moved axially as is advantageous to position the stator anvil plates  52  axially relative to the rotor striker plates  32 .  
      Reference is made to FIGS.  13  to  18  which illustrate a preferred striker plate  32  in accordance with the present invention and, as is illustrated in each of FIGS.  4  to  12 , is suitable for use both as a rotor striker plate  32  and a stator or anvil striker plate  58 . The striker plate  32  is an elongate, generally rectilinear member having a rear face  88 , a front face  90  parallel to the rear face, a right cutting side face  92  extending between the rear face  88  and the front face  90  on a right side thereof, a left cutting side face  94  extending between the rear face  88  and the front face  90  on a left-side thereof, a first end face  96  and a second end face  98 .  
      As best seen in  FIG. 16 , a right rear cutting edge  100  is formed at a juncture between the right side cutting face  92  and the rear face  88 . A right front cutting edge  102  is formed at a juncture between the right side cutting face  92  and the front face  90 . A left front cutting edge  104  is formed at a juncture between the left side cutting face  94  and the front face  90 . A left rear cutting edge  106  is formed at a juncture between the left side cutting face  94  and the rear face  88 .  
      Each of the left and right cutting side faces  92  and  94  comprise a plurality of identical lands  108  interspaced by a plurality of identical parallel grooves  110 . As schematically seen in  FIGS. 14 and 16 , the lands  108  of each side face all lie in the same flat land plane  109 . Each land  108  is spaced from an adjacent land by one of the grooves  110 . Each groove comprises a frusto-cylindrical surface about a groove axis  111  extending at an angle to the front and rear faces  88  and  90 . The groove axes  111  for all of the grooves  110  in the same side face of the striker plate to lie in the same axis plane  112  which is parallel to the land plane  109  in which the lands  108  on that side face lie. The lands  110  preferably have an axial extent in the range of 0.1 to 1.9 times the radius of the grooves, more preferably, 0.25 to 1.0 times, more preferably, 0.3 to 0.6 times and, preferably, about 0.5 times.  
       FIG. 17  shows a metal plate from which a number of striker plates  32  are made in accordance with a first preferred process for manufacture.  FIG. 17  shows a top view of a portion of a flat sheet of metal  114  of uniform thickness equal to that of a desired striker plate  32  and having parallel front and rear surfaces. The surface  116  of the sheet which is shown is to become one of the rear face  88  or front face  90  for a striking plate  32 .  
      A plurality of circular groove forming bores  120  are drilled through the sheet  114  from the surface  116 . The bores  120  are preferably each disposed about an axis normal to the surface  116  of the sheet  114 . In each row, the bores  120  have their axis spaced an equal distance from the axis of an adjacent bore. A plurality of locating bores  33  are also drilled through the sheet  114  suitably spaced between the rows of bores  120 .  
      After forming all of the bores  120  in one row, the sheet is then cut along side cut lines  122  normal to the surface of the sheet along a side cut line  124  in which the axis of the bores  120  lie, thus, effectively splitting each bore  120  in half.  
      The sheet is also cut along end cut lines  126  preferably perpendicular to the side cut line  124  and with the end cut lines  126  being intermediate the axis of adjacent bores  12 . As a result, from a flat planar sheet of metal, individual striker plates  32  are formed. Each individual striker plate is preferably heat treated so as to provide increased hardness to its various cutting edges.  
      A second preferred process for manufacture of a striker plate  32  having the configuration shown in  FIG. 13  is schematically illustrated in  FIG. 23 . As seen in  FIG. 23 , a plate of metal is cut into rectangular blocks after which the grooves  100  are cut into each side face as with a milling machine or router-like machine which removes material located within a circular extent of a rotating cutting head or bit. By selection of the diameter of the cutting head  4 , the extent to which the milling head cuts inwardly from the side face, the depth of grooves  100  may be selected. Varying diameter grooves  100  are schematically shown by dashed lines.  
      A preferred striker plate  32  having the configuration described above can be manufactured relatively inexpensively using conventional metal drilling and cutting techniques.  
      Reference is made to  FIGS. 9, 10 ,  18  and  19  which illustrate the preferred relative positions that a striker plate  32  on the rotor  12  will assume as it passes by striker plates  58  on the stator. As best seen in  FIGS. 13, 18  and  19 , the lands  108  effectively form the radial outermost point of a tooth  150  for a striker plate. As best illustrated in  FIGS. 18 and 19 , a striker plate  32  on the rotor is disposed with its teeth  150  disposed in the grooves  110  of the striker plates  58  on the stator anvil and each tooth  150  on the striker plates  58  of the stator anvil are disposed within grooves  110  of the striker plate  32  of the rotor. In the preferred configuration, the teeth  150  and grooves  110  not only are arranged in an alternating pattern along the axial extent of the rotor and anvil but, as well, each of the teeth  150  extends radially into the groove  110  of an opposed striking plate.  
      The opposed striking plates  32  and  58  do not engage each other but rather are spaced from each other with a gap therebetween. In the preferred embodiment as illustrated, a gap which separates the cutting edges of one striker plate from the cutting edges of an opposed striker plate, as measured in a purely radial direction relative to the rotor  12  will vary as such gap is measured in a radial direction at different axial points or locations along the cutting edges. Thus, as seen in  FIG. 19 , a radial gap  152  may be measured at radially extending lines “a” to “i” spaced axially between the center of one tooth  150  and the center of an adjacent second tooth  150 . The extent of the radial gap between the two cutting edges indicated as  102  and  104  varies at the different axial locations. As well, axially extending lines indicated as “k”, “l” and “m” extending parallel the axis of the rotor  12 , measure the axial gap  154  between the radially overlapping portions of the teeth  150  and grooves  110  and shows the extent of the axial gap between the two cutting surfaces  102  and  104  also varies at different radial locations.  
       FIGS. 18 and 19  illustrate a condition in which each tooth  150  is centered axially relative to its opposing groove  110 . This is not necessary and it is to be appreciated that insofar as a tooth  150  may not be axially centered in a groove  110  but offset axially to one side, then there will be an increased variance of the radial gap  152  and axial gap  154 .  
      Reference is made to  FIG. 20  which shows a top view identical to that in  FIG. 19  but with teeth  150  not axially centered in each groove. Thus, as seen in  FIG. 20 , the radial gap  152  is greater on the left-hand side of each tooth  150  of the rotor striker plate  32  than on the right-hand side. As well, the axial gap  154  is also greater on the left-hand side of each tooth  150  of the rotor striker plate  32  than on the right-hand side.  
      In addition to the radial gap  152  and axial gap  154  being greater on the left-hand side, the cross-sectional area representing the gap, as seen in plan view normal the front surface, is greater on the left-hand side. The extent to which the radial and axial gaps may differ on each side of a tooth can be adjusted as, for example, by movement of the stator striker plates  58  axially parallel the axis of the rotor relative to the rotor. In the embodiment illustrated in  FIG. 25 , such axial movement is permitted by rotating adjusting screw  138 . Adjusting the axial position of the striker plate on the anvil and rotor can change the nature of the resultant materials from the comminuter as to size, size distribution and rubber/metal separation.  
      Having the extent of the gap between the cutting edges vary is believed to be preferred so as to assist in cutting, shearing and tearing of the materials to be comminuted particularly in the case of rubber tire feed materials which may have metal, such as bands, therein. It is believed that portions of the metal may be caught or sheared between smaller gap regions while rubber about the metal may effectively be caught, compressed drawn and pulled from the metal where the rubber is caught in gaps of different radial one and/or axial dimension and overall size and shape.  
      Reference is made to  FIGS. 21 and 22  which schematically illustrate opposing surfaces of anvil striker plate  58  and rotor striker plates  32  which have identical alternating frusto-pyramidal teeth  150  and grooves  110 .  FIG. 21  illustrates a configuration with the teeth  150  and grooves  110  with the teeth  150  centered in the grooves and constant axial gaps between the teeth  150  and grooves.  FIG. 22  illustrates a preferred arrangement in accordance with the present invention wherein the symmetrical teeth  150  are not centered in the symmetrical grooves  110  but are displaced axially relative a rotor such that the axial gaps on the right-hand side of each tooth  150  are greater than that on the left-hand side. Improved pinching and tearing is believed to occur with the embodiment of  FIG. 22  over that of  FIG. 21 .  
      In accordance with the present invention, it is preferred that the striker plates  32  used on the rotor  12  and the striker plates  58  used on the anvil are identical modular striker plates. In the preferred embodiment, each striker plate  32  carried on the rotor  12  is preferably offset so as to overlap with two identical striker plates  58  on the anvil. This, of course, is not necessary but preferred.  
      Each of the rotor discs  26  are illustrated as carrying six lobes  28 . Preferably, the individual rotor discs  26  forming the rotor  12  may be identical but are keyed to the shaft  22  at different angular orientations such that preferably only one of the striker plates  32  on the rotor  12  are to pass adjacent the anvil  24  at any one moment.  
      The modular striker plates of the preferred orientation as illustrated in  FIG. 13  are conveniently to be selected of a size such that one striker plate  22  covers the entire axial extent width of a rotor disc  26 . In any event, the rotor discs  28  may be selected to have an axial extent to represent an integral number of the length of the cutting side face of the identical striker discs. In the preferred embodiment, the rotor  12  is illustrated as having ten rotor discs  28  and thus having an axial length equal to that of ten rotor discs  32 . The anvil  24  is illustrated as carrying eleven stator striker plates  58  each axially offset about 50% relative to the striker plates  32  on the rotor discs  24 .  
      The preferred striker plate  32  has its rear face  88  parallel to its front face  90 . As well, it has its first end face  96  parallel to its second end face  98 . As well, it has the lands of its right side face  92  and its left side face  94  parallel to each other and normal to the rear face  88  and front face  90  and normal to the first end  96  and second end  98 . An advantage of this configuration is that each striker plate, therefore, has four identical cutting edges  100 ,  102 ,  104  and  106  and can be oriented and used on the rotor  12  or anvil  24  in one of four separate positions optimizing the length of time that a striker plate can be used.  
       FIG. 26  illustrates a second embodiment of a striker plate  132  within the scope of the present invention in which the lands  108  on each side face of the plate are not perpendicular to the rear face  88  and front face  90  but rather are disposed at an angle thereto as, for example, in the range of between 90° and 40°. The lands  110  on each side face being disposed in parallel land planes  109 . With such a configuration, striker plates  132  can be used in one of two different orientations. Each striker plate is preferably symmetrical about a central longitudinal plane passing through the bit so that it may be easily removed, rotated 180° and remounted. The striker plate configuration is adaptable for use with most designs of rotors having radial lobes for that purpose. Each striker plate is mounted to project forwardly and presents a cutting edge and face which is preferably inclined forwardly from the front face of the rotor to present an aggressive rake angle with the radial line through the axis of the rotor in the direction of rotation of the rotor. Identical cutting edges are provided as  102  and  106 . In the embodiments of  FIG. 26 , the axis  112  of each of the grooves  110  is indicated as lying in an axis plane  112  which is parallel to the land plane  109 .  
       FIG. 27  shows an end view of a fourth embodiment of a striker plate  232  in which the left and right side faces  92  and  94  are not parallel but are disposed to have their lands  108  in land planes  109  at the same angle to the rear face  90 . Identical cutting edges are provided as  100  and  106 .  
       FIG. 28  illustrates an end view of a third embodiment of a striker plate  332  in which the axes of the grooves  110  are disposed in an axis plane  112  which is not parallel the land plane  109 . Such a striker plate as illustrated in  FIG. 22  is intended for use in one of two orientations. When setting up the striker plates on the rotor and anvils, it is important to arrange them so that there is no interference. However, having the axes of the grooves  110  extend in an axis plane  112  not parallel the land plane  109  can provide for the gap between the side faces of opposing striker plates to vary as any two plates move circumferentially past each other through different angular positions.  
      As seen in  FIG. 9 , each of the rotor striker plates  32  may be oriented such that a center line  120  between the rear face  88  and the front face  90  of each striker plate on the rotor being disposed along a radius of the rotor  12 . Similarly, the anvil striker plates  58  carried on the anvil  24  may also be located such that a center line between its rear face  88  and front face  90  is disposed along a radius of the rotor  12 . This is not necessary and either of the striker plates may be canted or raked as to be at an angle to a radius to the rotor.  
      The striker plates are shown as being mounted to directly engage the rotor  12  or to directly engage the driven wedge  52 . This is not necessary and other intermediate mounting devices may be disposed between the striker plate and the rotor or the slider block as may be of assistance, for example, to facilitate removal of each striker plate from the rotor block or anvil, or to provide desired rake angles. The striker plate may be part of a striker plate assembly with the cutting edge portion carried as an insert to a striker carrier in a manner as described in U.S. Pat. No. 5,950,945 to Schaller.  
      The preferred striker plates as illustrated in  FIG. 13  may be machined using conventional computerized control boring and cutting machines at relatively low cost. Having identical modular striker plates for all locations on the rotor and for all locations on the anvil reduces the need to have increased inventory.  
      Nevertheless, rather than have individual modular striker plates  58  on the anvil, it is possible to have one or more striker plates of longer length than the striker plates provided on the rotor disc. Either single or multiple replaceable striker plates may be used for any particular rotor or anvil.  
      Preferred striker plates in accordance with the present invention may be made from flat planar sheet metal merely by forming circular bores and straight flat cuts. The illustrated embodiments show both sides of a striker plate  32  being the same. This is not necessary and, for example, the lands on one side may be offset 50% from the lands on the other side.  
      While the invention has been described with reference to preferred embodiments, many variations and modifications will now occur to persons skilled in the art. For a definition of the invention, reference is made to the following claims.