Abstract:
The present invention relates to a single shaft rotary grinder with an improved cutter and combination “comb” rotor and counter knife configuration for reducing film, fibrous material and other material which has a tendency to wrap around the rotor, rubber, solid plastics and wood. Reducing this type of material, such as plastic film, into small pieces has been problematic. This invention provides one or more comb shaped counter knives and a rotor having a plurality of geometrically shaped cutters mounted in a plurality of partial or full rows longitudinally along the rotor. The comb shaped counter knives and the rows of cutters work in cooperation to reduce film and other material into small pieces.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/325,621, filed Sep. 28, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a single shaft rotary grinder with an improved cutter and combination “comb” rotor and counter knife configuration for reducing film, fibrous material and other material which has a tendency to wrap around the rotor, rubber, solid plastics and wood. Reducing this type of material, such as plastic film, into small pieces has been problematic. This invention provides one or more comb shaped counter knives and a rotor having a plurality of geometrically shaped cutters mounted in a plurality of partial or full rows longitudinally along the rotor. The comb shaped counter knives and the rows of cutters work in cooperation to reduce film and other material into small pieces. 
     (b) Description of the Prior Art 
     U.S. Pat. No. 3,760,673, to Peterson, Jr. teaches an apparatus for dicing plastic sheet material, rather than film or fibrous material, in which a horizontal rotor has teeth on the periphery thereof which are in cutting relationship to the serrations on a stationary bed knife. The bed knife is tilted at an angle to the axis of the rotor. The rotor contains a series of straight knives which each contain a plurality of teeth which cooperate with the serrations on the stationary bed knife. The tilt of the bed knife causes the teeth of each rotor knife to first come into cutting engagement with the bed knife teeth at the left end of the bed knife and then to be brought into cutting engagement last with the teeth at the right end of the bed knife. 
     U.S. Pat. No. 3,186,277 to Brunner teaches an apparatus for cutting a strip of sheet material, rather than film or fibrous material, into separate particles which has a stationary bed knife having rectangular teeth and individual rectangular recesses between the teeth, a knife supporting rotor arranged axially parallel to the bed knife, and profiled knives on the rotor arranged in axially and angularly spaced relation with each cooperating with one of said recesses between the teeth of the stationary bed knife. The rotor also contains straight knives arranged in axially and angularly spaced relation which cooperate with the top of at least two teeth of the stationary bed knife. 
     U.S. Pat. No. 2,812,815 to Quinsey et al. teaches a method and apparatus for dicing a strip of sheet material, rather than film or fibrous material, into uniform sized and shaped pellets, both employing a bed knife with rectangular shaped teeth and a non-cylindrical rotor containing sets of fly knives, where each set of fly knives is comprised of a toothed knife with teeth complementary to the bed knife teeth and a cut off knife having a continuous linear cutting edge which cooperates with the front edge of the bed knife. 
     U.S. Pat. No. 1,874,902 to Clyne teaches a method of cutting sheets and a sheet cutting machine employing a cutter bar having substantially rectangular shaped teeth and rectangular shaped notches therebetween, all with cutting edges and a cutter with a plurality of rows of teeth with notches therebetween which correspond to the notches and teeth of the cutter bar During engagement, the cutter teeth do not fully engage the length of the notches on the cutter bar. Between each engagement of the row of teeth on the cutter with the cutter bar, the sheet to be cut is fed forward less than the length of a tooth on the cutter bar, thereby allowing only that portion of the sheet which has been fed past the edge of the cutter bar teeth and notches to be engaged by a row of teeth on the cutter bar. The size of the particle cut from the sheet is therefore controlled by how the material is fed towards the rotor. 
     Reducing product such as film utilizing the single shaft rotary grinders present in the field today is problematic. Film for products such as plastic bags, plastic wrapping, garbage bags and sandwich bags and fibrous material such as rope and string have increasingly been manufactured with qualities of reduced thickness (less than 0.0254 mm (0.001 inches)) and increased durability, which cause the product to be more difficult to reduce. A common problem arises when the product wraps around the rotor with the cutter poking through the product, rather than being reduced into smaller pieces. An additional problem is created when, due to wrapping, the diameter of the product build-up is increased to the point that rubbing occurs, generating heat which may cause melting or other damage to the grinder. Another problem occurs because the combination of rotor and screen, with specific screen hole sizes, is inefficient in controlling reduction of the product to a maximum size, thus adding frictional heat to the process. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a single shaft rotary grinder with an improved cutter and combination “comb” rotor and counter knife configuration for reducing film, fibrous material and other material which has a tendency to wrap around the rotor, rubber, solid plastics and wood. Reducing this type of material, such as thin plastic film, into small pieces has been problematic. In a first embodiment, this invention provides one or more comb shaped counter knives and a rotor having a plurality of geometrically shaped cutters mounted in a plurality of partial or full rows longitudinally along the rotor. The comb shaped counter knives and the rows of cutters work in cooperation to reduce film and other material into small pieces. 
     Rotary grinders are used to reduce material to a desired particle size for recycling and other purposes. The material to be shredded is placed in a hopper and a ram is used to drive the material toward one or more counter knives aligned in a row and a parallel rotor, the rotor having a plurality of cutters removably mounted thereon. When in use, the ram travels from its open position near the front end of the rotary grinder across the hopper floor towards the rotor, pushing material to be ground towards the rotor. As the rotor revolves about its shaft, the cutters on the rotor engage the material in the hopper, cutting or tearing pieces from the material and drawing the pieces downward towards the counter knives. The counter knives have teeth with cutting edges and interstices between the teeth. Counter knives commonly have “V” shaped teeth and “V” shaped interstices. The interstices are sized to receive the cutters, which commonly protrude from the rotor in a “V” shape, and the sizing of the interstices allows the cutters to pass in close proximity to the cutting edges of the teeth. 
     The material is further reduced as it is drawn between the cutters and the teeth of the counter knives. An optional screen placed after the rotor controls how finely the material will be ground. The screen has a plurality of openings of a specific size selected by the user. One grinder may have a plurality of rotor screens, each with a different size opening therethrough. A rotor screen with desired size openings is selected and positioned after the rotor. When the material is reduced to the appropriate size, it will pass through an opening in the screen into a conveying device. Reduced material which is too large to pass through the rotor screen openings and requires further reduction will be drawn by the action of the cutters back into the hopper area to be further reduced or will be further reduced by the action of the cutters as they abrade against material trapped between the screen and the cutters. After material passes through the screen and out of the rotary grinder, it may be passed through a granulator for further reduction, if required. 
     The comb shaped counter knives and rotor combination of the present invention has several advantages over other known counter knife and rotor combinations. First, the rectangularly shaped counter knife teeth and interstices form a comb shape along the length of the counter knife, and rectangularly shaped cutters aligned longitudinally form a comb shape row along the rotor, the rotor having a plurality of rows of cutters placed in this comb configuration. The combing action of the cutter and counter knife configuration and the “scissor” cutting action between the cutting edges of the cutter and the cutting edges of the counter knife teeth diminish the likelihood that film will wrap around the rotor. Second, the close spacing between the cutters and counter knives, combined with all cutters being arranged in partial or full longitudinal rows, increases the likelihood that particle size will have a length which approximates the distance between cutter rows and a width and depth that approximates the longitudinal and radial distance between the adjacent cutters. Third, the rows or partial rows of cutters engaging this film simultaneously clamp and hold the product “stretched,” so that the comb teeth can break the product, thus eliminating the requirement for extremely close tolerances between cutter and counter knife. Thus, product size may be controlled by the cutting action of the rotor rather than screen hole size. 
     In an alternate embodiment of the rotor, the rectangular cutters are arranged in at least pairs or partial rows randomly or staggered along the rotor body. As the rotor revolves, each cutter pair passes through a corresponding pair of interstices, thereby fully cooperating with one tooth and partially cooperating with two teeth of the counter knife. Cutting action is reduced from the first embodiment due to only partial engagement of two of the three teeth engaged. However, the cutter pair configuration randomly dispersed along the rotor body provides a more even feed of material to the screen and further minimizes the likelihood that the film will build up and pack together or clog the screen, as well as a more even torque requirement. 
     The preferred embodiment, which is a further alternate embodiment of the cutter, rotor and counter knife, generally hexagonally shaped cutters are arranged in a plurality of preferably partial rows along the rotor body. This embodiment provides one or more comb shaped counter knives which work in cooperation with the partial rows of cutters to reduce film into small pieces. The hexagonal shape of the cutters increases the cutting surfaces on the cutter and minimizes the amount of non-cutting surfaces on the counter knife and rotor while still maintaining the advantages of the combing action of the counter knife. The partial row of cutters configuration staggered along the rotor body provides a more even feed of material to the screen and reduces the amount of instantaneous torque required to power the rotor. In addition, the full cutting action of the cutter allows continuous cutting of solid plastic and rubber without encountering a non-cutting surface on the rotor. Another feature of this embodiment of the invention is that the cup shape of the cutters and the cutting action of the cutters on the face of a solid reduces the material before it reaches the counter knife. The cutter of this embodiment may also be arranged in pairs or full rows longitudinally along the rotor. 
     It is an object of the invention to create a combination “comb” rotor and counter knife configuration which reduces any material that tends to wrap around the rotor or which creates undesirable friction during the reducing process. Another object of the invention is to reduce or eliminate heat generated by friction during the cutting process, which will eliminate or reduce the need to utilize expensive methods of cooling the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the invention will be had upon reference to the following description in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a perspective view from the upper left side of a prior art rotary grinder, showing the outer frame of the grinder, a hopper, a ram in retracted position, and a motor which provides power to the rotor; 
         FIG. 2  is a cross-sectional view of a rotary grinder taken along the line  2 - 2  of  FIG. 1 , which has added thereto an embodiment of the rotor and counter knife combination of the present invention, the ram in a partially retracted position, a hopper, and a rotor screen positioned after the rotor; 
         FIG. 3  is a perspective view of the cutter shown in  FIG. 2 ; 
         FIG. 4  is a top view of the counter knife shown in  FIG. 2 , having a body, rectangularly shaped teeth, and rectangularly shaped interstices; 
         FIG. 5  is a partial perspective view from the upper left side of the rotary grinder of  FIG. 2 , with certain structures and the rotor removed for clarity, showing two counter knives installed in the grinder at an upward angle; 
         FIG. 6  is a partial perspective view of the rotary grinder of  FIG. 2 , showing the cutters mounted on the rotor in rows and the cutters passing through the interstices between the teeth of the counter knives; 
         FIG. 7  is an enlarged partial top view of the rotor and counter knives of  FIG. 2  working in cooperation, showing the tool holders to which the cutters are mounted passing through the interstices of the counter knives; 
         FIG. 8  is an enlarged partial perspective view of the rotor and counter knives of  FIG. 2  working in cooperation, showing the tool holders, cushioning plate, and cutters passing through the interstices of the counter knives; 
         FIG. 9  is a perspective view of an alternate embodiment of the rotor of the present invention, the rotor having cutters mounted in pairs and having cutter pairs randomly distributed along and around the rotor. 
         FIG. 10  is a perspective view of an alternate embodiment of the rotary grinder of the present invention, taken from the upper left side, showing the rotor and counter knife combination of the present embodiment; 
         FIG. 11  is a cross-sectional view of the rotor and counter knife combination of  FIG. 10  taken along the line  11 - 11  of  FIG. 10 ; 
         FIG. 12  is a perspective view, taken from the upper front side, of the cutter of  FIG. 10 ; 
         FIG. 13  is a front view of the cutter of  FIG. 10 ; 
         FIG. 14  is a back view of the cutter of  FIG. 10 ; 
         FIG. 15  is a perspective view of the counter-knife of  FIG. 10 , taken from the upper front side; 
         FIG. 16  is a partial perspective view of the rotary grinder of  FIG. 10 , showing the cutters mounted on the rotor in partial rows and a portion of the cutters passing through the interstices between the teeth of the counter knives; 
         FIG. 17  is an enlarged partial perspective view of the rotor of  FIG. 10  showing the tool holders and a cushioning plate and cutter mounted on a tool holder; 
         FIG. 18  is a perspective view of an alternative embodiment of a cutter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the Figures,  FIG. 1  shows a prior art rotary grinder  1  having a front end  2 , a back end  3 , a hopper  4 , a ram  5  in retracted position, a rotor  6  (not shown), at least one counter knife  7  (not shown), a plurality of cutters  8  and a motor  9  which provides power to the rotor  6 . 
       FIG. 2  shows a rotary grinder  10  similar to the rotary grinder  1  of  FIG. 1 , but containing an embodiment of the rotor  20  and counter knife  30  combination in the comb configuration of the present invention. The rotary grinder  10  of  FIG. 2  has a front end  12 ; a back end  14 ; a hopper  80  having a hopper front end  82 , a hopper back end  84 , a hopper floor  86 , and a trough  87  with an angled trough wall  88  in the hopper floor  86  at the hopper back end  84 ; a ram  92  shown in a partially retracted position towards the hopper front end  82 ; a rotor  20  mounted on a shaft  22  (see also,  FIG. 5 ) at the hopper back end  84 ; at least one counter knife  30  mounted on the angled trough wall  88 ; a filler plate  89  over the trough  87 ; and an optional rotor screen  90  positioned after the rotor  20 .  FIG. 2  also depicts the rotor  20  having tool attachments  24  integral to the rotor  20 , a slot  26  in the rotor  20  in front of each tool attachment  24 ; cutters  50  partially received in slots  26  and mounted to corresponding tool attachments  24 ; a cushioning plate  68  mounted between each cutter  50  and the corresponding tool attachment  24 ; and a groove  72  between adjacent tool attachments  24 . 
     As shown in  FIG. 2 , a counter knife  30  is mounted before the rotor  20  at the hopper back end  84  on the angled trough wall  88  (see  FIGS. 2 ,  5 ,  6 , and  8 ). A filler plate  89  may be placed over the trough  87  to prevent material to be reduced from accumulating in the trough  87 . A rotor screen  90 , whose use is optional, is shown positioned after and in close proximity to the rotor  20  to prevent or minimize the likelihood that large amounts of fully or partially reduced material will build up in the screen  90  and pack together or clog the screen openings. 
     As shown in  FIG. 3 , the cutter  50  of the present embodiment is rectangular and has a slightly concave front face  51  having a top edge  52 , a bottom edge  53 , a left edge  55  and a right edge  54 ; a back face  62  (not shown) having a generally flat surface; a threaded bore  49  for accepting a screw for mounting onto a tool attachment  24  extending from the back face  62  to the front face  51 ; a top portion  63 ; a bottom portion  64 ; and a top side  65 , a bottom side  66  (not shown), a right side  67  (not shown) and a left side  69 . The four edges of the front face  51 , namely top edge  52 , bottom edge  53 , right edge  54  and left edge  55 , are cutting edges. The top portion  63  and bottom portion  64  of the cutter  50  are generally mirror images, allowing the cutter  50  to be indexable such that, when the cutter is rotated 180 degrees, fresh cutting edges are revealed. While the present invention discloses two index positions, it is contemplated that the cutter  50  be indexable to a plurality of positions. Each cutter  50  is preferably made of hardened tool steel suitable to the application, but may be made of any suitable material. 
     As shown in  FIGS. 2 ,  6  and  8 , a cutter  50  is removably mounted to each tool attachment  24 . The tool attachments  24  are preferably machined into and integral with the rotor  20 ; however, the tool attachments  24  may instead be welded or otherwise suitably attached or mounted to the rotor  20 . The rotor has a plurality of grooves  72  thereon between adjacent tool attachments  24  and which are between adjacent cutters  50  after they are mounted on the tool attachments  24 . The slot  26  in the rotor  20  in front of each tool attachment  24  partially receives a cutter  50  when it is removably mounted to that tool attachment  24 . For instance, the bottom portion  64  of a cutter  50  can be inserted into a slot  26  with the back face  62  towards the tool attachment  24  and the cutter bottom side  66  resting against the bottom of the slot  26 . In this configuration, the top portion  63  of the cutter  50  protrudes out of the slot  26  and functions as the working portion of the cutter  50 . When the cutting edges of the cutter top portion  63 , namely top edge  52 , the upper portion of left edge  55  and the upper portion of right edge  54 , are worn, the cutter  50  may be removed, rotated 180 degrees and remounted. In this configuration, the bottom portion  64  of the cutter  50  protrudes out of the slot  26  and functions as the working portion of the cutter  50 . When the cutting edges of the cutter bottom portion  64 , namely bottom edge  53 , the lower portion of left edge  55  and the lower portion of right edge  54 , are worn, the cutter  50  would then be removed and retooled or replaced with a new cutter  50 . 
     An optional cushioning plate  68  may be mounted between each cutter back face  62  and the corresponding tool attachment  24  in order to absorb shock and minimize or prevent damage to the tool attachment  24 . Each cushioning plate  68  is preferably made of a medium hard steel but may be made of any suitable material. 
     As best shown in  FIG. 4 , the counter knife  30  of the instant embodiment has a generally flat body  32 , a top  33 , a bottom  34  (not shown), a front  35 , a back  36 ; a plurality of teeth  40  extending laterally in the same plane as the body  32  from the front  35  of the body  32 . Each tooth  40  forms three sides of a rectangle, having a first tooth edge  42 , a second tooth edge  43  and a third tooth edge  44 . Each pair of adjacent teeth  40  defines an interstice  46  which is open on one side and whose three other sides form three sides of a rectangle defined by a third tooth edge  44 , an interstice edge  47 , and a first tooth edge  42 . These edges  42 ,  44 ,  47  which form the interstice  46  are each a cutting edge. When the rotor  20  and counter knife  30  are properly installed in the rotary grinder  10  and the rotor is rotating, the teeth  40  are designed to protrude into the groove  72  between adjacent cutters  50  as each of the adjacent cutters  50  are passing through the corresponding interstices  46  on the counter knife  30 . The combination of teeth  40  projecting from the counter knife body  32  with interstices  46  therebetween thereby form a comb configuration. 
     The second tooth edge  43  is preferably 16.002 mm (0.630 inches) in width but may be any suitable width as required by the application and the spacing between the cutters  50 . The interstices  46  between the teeth  40  are each preferably 41.173 mm (1.621 inches) in width but may be any suitable width as required by the width of the cutters  50  and the application. 
     The counter knife  30  is indexable, being symmetrical on its top  33  and bottom  34  sides, such that the counter knife  30  can be turned over to expose fresh cutting edges and remounted with its bottom  34  facing upward when the upper portions of the cutting edges  42 ,  44 ,  47  become dull. This allows the cutting edges  42 ,  44 ,  47  at the top  33  and bottom  34  sides of the counter knife  30  to be used before the edges  42 ,  44 ,  47  are resharpened. Each counter knife  30  is preferably made of hardened tool steel suitable to the application, but may be made of any suitable material. 
     As shown in  FIGS. 5 and 6 , a plurality of counter knives  30  may be installed adjacent each other in the rotary grinder  10 . The number of counter knives  30  employed, the length of the counter knife  30 , the number of fill and partial teeth  40  on the counter knife  30 , the length and width of the teeth  40  and the width of the interstices  46  are dependent upon the length and size of the rotor  20 , the number of cutters  50  employed longitudinally along the rotor  20 , the size of the cutters  50  and the positioning of the cutters  50  in relation to adjacent cutters  50 .  FIGS. 4 and 5  clearly show two counter knives  30  installed on the angled trough wall  88  in the floor  86  at the hopper back end  84 . The counter knives  30  are installed with their bottom  34  portions towards the floor of the trough  87  and with the front  35  portions of their bodies  32  and teeth  40  extending upward at an angle towards the rotor  20 . 
     As shown in  FIG. 6 , the tool attachments  24  on the rotor  20  may be arranged longitudinally in rows, and the cutters  50  are mounted to the tool attachments  24  so that the cutters  50  form a comb configuration with cutter rows  70 . Optionally, a cushioning plate  68  may be mounted between the tool attachment  24  and the cutter  50  as shown in FIGS.  2 , 6  and  8 . 
     As best shown in  FIG. 5 , the rotor  20  of the instant embodiment preferably has five rows  70  of cutters  50  arranged longitudinally along the rotor  20  body. However, the rotor  20  may contain a greater or lesser number of cutter rows  70 , and correspondingly a greater or lesser number of total cutters  50  on the rotor  20 . Cutters  50  immediately adjacent each other in a row  70  are preferably spaced 16.51 mm (0.650 inches) apart, but may be spaced apart any suitable distance as required by the application. Additionally, the number of cutters  50  per row  70  will be influenced by the length of the rotor  20 . For instance, a 106.68 cm (42 inch) rotor  20  may have five rows  70  of cutters  50 , with nineteen cutters  50  in each row  70 , for a total of ninety-five cutters  50  on the rotor  20 . The number of cutters  50  on each rotor  20  will influence the amount of horsepower required to power the rotor  20 . An increase in the number of cutters  50  present on the rotor  20  will increase the amount of horsepower required, and a decrease in the number of cutters  50  will decrease the amount of horsepower required. The total number of cutters  50  on the rotor  20  affects the total horsepower required. The total number of cutters  50  in a row  70  effects the instantaneous or peak torque required. Particle size produced by a single pass of a cutters  50  through an interstice  46  is regulated by the size of the cutter  50  and not the number of cutters  50  on the rotor  20  or in the row  70 . As best shown in  FIGS. 5 ,  6  and  8 , the counter knife  30  mounting is angled in order for the teeth  40  and interstices  46  to be in the same or slightly different plane as the cutters  50  when the cutters  50  enter the interstices  46 . 
     As shown in  FIGS. 6-8 , when the rotor  20  revolves on its shaft  22 , each cutter  50  passes at a small distance from the counter knife  30  through a corresponding interstice  46  located in the same vertical plane as the cutter  50 . Additionally, each tooth  40  located between two adjacent interstices  46  protrudes into the groove  72  between the two adjacent cutters  50  located in the same vertical plane as each of the two adjacent cutters  50  is passing through the corresponding one of the two adjacent interstices  46 , the tooth  40  protruding to within a small distance from the rotor  20 , which effectively “combs” the rotor  20 . As a cutter  50  passes through an interstice  46 , it is preferred that there is a first spacing  74  of 0.254 mm (0.010 inches), with a manufacturing tolerance of 0.127 mm (0.005 inches), between the third tooth edge  44  and the right edge  54  and between the first tooth edge  42  and the left edge  55 ; and a second spacing  76  of 0.127 mm (0.005 inches), with a manufacturing tolerance of 0.050 mm (0.002 inches), between the of cutter top edge  52  and the interstice edge  47 , although the first spacing  74  and second spacing  76  may be larger or smaller if required by the application. However, due to the temperature variation caused by the heat produced as the rotor  20  rotates and the resulting expansion of the rotor  20  in length, it would not be practical to reduce the first spacing  74  or second spacing  76  without employing a means to cool the rotor  20 . The first spacing  74  and second spacing  76  are also present when the cutter  50  is indexed 180 degrees to its second index position. 
     When the ram  92  pushes the film to be reduced into the revolving rotor  20 , each longitudinal cutter row  70  engages a portion of the film and drags it towards the counter knives  30 . As the cutters  50  move downward towards the counter knives  30 , film is stretched tight over adjacent cutters  50  along the cutter row  70 . As the cutter row  70  passes through the interstices  46 , the film is caught between the cutters  50  and the cutting edges  42 ,  44 ,  47  of the counter knife  30 . The corresponding tooth  40  projecting into the groove  72  between two adjacent cutters  50  over which film is stretched will puncture and tear the film as the cutters  50  pass through the interstices  46 . When the film wraps and/or becomes stretched between cutters  50 , the teeth  40  of the counter knife  30  “comb” the groove  72  between the cutters  50  and strip the film from its wrapped or stretched position. Additionally, when there is a sufficiently close spacing between each cutter  50  and the counter knife  30  (see  FIGS. 7 and 8 ) and/or layers of film have built up sufficiently on the cutters  50  to fill the gap between the cutter  50  and the counter knife  30 , further cutting action is provided by the scissor action between the two parallel sides  67 ,  69  and cutting edges  55 ,  54  of the cutter  50  and the corresponding cutting edges  42 ,  44  of adjacent teeth  40 . The close spacing between the cutters  50  and counter knives  30 , combined with all cutters  50  being arranged in partial  170  or full longitudinal rows  170 , increases the likelihood that particle size will have a length which approximates the distance between cutter rows  70 ,  170  and a width and depth that approximates the longitudinal and radial distance between the adjacent cutters  50 . 
       FIG. 9  shows an alternate embodiment of the rotor  120  of the present invention where pairs consisting of two adjacent tool attachments  124  are arranged in a staggered or random pattern longitudinally along the rotor  120  body. The tool attachments  124  are preferably machined into and integral with the rotor  120 ; however, the tool attachments  124  may instead be welded or otherwise suitably attached or mounted to the rotor  120 . This arrangement of tool attachments  124  in staggered or randomly placed pairs longitudinally along the rotor  120  with cutters  50  mounted thereon results in “cutter pairs”  170  such that two cutters  50  work in cooperation to cut the material to be reduced. 
     As in the first embodiment shown in  FIGS. 2-8 , a same cutter  50  is compatible with and may be used with the rotor  120  configuration of the present embodiment. The counter knife  30  of the first embodiment depicted in  FIG. 4  is also compatible with and may be used with the rotor  120  configuration of the present embodiment. The spacing between the cutters  50  comprising the cutter pairs  170  are the same spacing as between the cutters  50  comprising the cutter rows  70 , and the first spacing  74  and second spacing  76  between the counter knife  30  and the cutters  50  remain the same. 
     When the ram  92  pushes the film to be reduced into the revolving rotor  120 , each cutter pair  170  engages a portion of the film and drags it towards the counter knives  30 . As the cutter pair  170  rotates downward towards the counter knives  30 , film is stretched tight over the cutter pair  170 . As the cutter pair  170  passes through the corresponding interstices  46  on the counter knife  30 , the film is caught between the cutters  50  and the cutting surfaces of the counter knife  30 . The corresponding tooth  40  projecting into the groove  72  between the cutter pair  170  over which film is stretched will puncture and tear the film as the cutters  50  pass through the interstices  46 . When the film wraps and/or becomes stretched between the cutter pair  170 , the corresponding comb tooth of the counter knife  30  “combs” the groove  72  between the cutter pair  170  and strips the film from its wrapped or stretched position. The action of the cutter pair  170  in reducing the film is similar but not identical to the action of the cutter  50  row in the first embodiment. As the rotor  120  revolves, each cutter pair  170  passes through a corresponding pair of interstices  46 , thereby fully cooperating with one tooth and partially cooperating with two teeth  40  of the counter knife  30 . Cutting action is reduced from the first embodiment due to the only partial engagement of two of the three teeth  40  engaged. However, the cutter pair  170  configuration randomly dispersed along the rotor  120  body provides a more even feed of material to the screen and further minimizes the likelihood that the film will build up and pack together or clog the screen. 
       FIG. 10  shows the preferred embodiment, which is an alternate embodiment of the rotary grinder  210  of the present invention containing an embodiment of the rotor  220  and counter knife  230  combination in the comb configuration of the present invention. The rotary grinder  210  of  FIG. 10  has a front end  212 ; a back end  214 ; a hopper  80  having a hopper front end  82 , a hopper back end  84 , a hopper floor  86 , and a trough  87  with an angled trough wall  88  in the hopper floor  86  at the hopper back end  84 ; a ram  92  in a retracted position (not shown); a rotor  220  mounted on a shaft  22  (see also,  FIG. 16 ) at the hopper back end  84 ; and at least one counter knife  230  (see  FIG. 16 ) mounted on the angled trough wall  88 .  FIG. 10  (and  FIG. 16 ) also depicts the rotor  220  having tool attachments  224  integral to the rotor  220 , a slot  26  in the rotor  220  in front of each tool attachment  224 ; cutters  250  partially received in slots  26  and mounted to corresponding tool attachments  224  ( FIG. 16  depicts only a partial complement of cutters  250  mounted on the rotor); a cushioning plate  268  mounted between each cutter  250  and the corresponding tool attachment  224 ; and a groove  272  between adjacent tool attachments  224 . A counter knife  230  is mounted before the rotor  220  at the hopper back end  84  on the angled trough wall  88  (see  FIGS. 11 and 16 ). A filler plate  89  may be placed over the trough  87  to prevent material to be reduced from accumulating in the trough  87 . 
     As shown in  FIGS. 12 and 13 , the cutter  250  of the preferred embodiment is generally hexagonal in shape and has six sides, namely top side  265 , upper left side  269 , lower left side  59 , bottom side  266 , lower right side  79 , and upper right side  267 , which form a generally hexagonal shape. However, it is contemplated that the number of sides could vary, which would affect the geometric shape of the cutter. The cutter  250  has a front face  251  which has a first concave surface  60  and a second concave surface  61  separated by a protruding edge  58 . The first concave surface  60  and second concave surface  61  on the front face  251  are approximately equivalent in size. It is contemplated that the front face  251  could have additional concave surfaces generally equivalent in size and separated by one or more additional protruding edges as needed. Sloping surfaces  94 ,  95  extends from outer edges  254 ,  255  towards said generally concave surfaces. The front face is framed by six outer edges, namely, top edge  252 , upper left edge  255 , lower left edge  56 , bottom edge  253 , lower right edge  57 , and upper right edge  254 . However, the number of outer edges could vary as the geometric shape of the cutter  250  varies. The seven edges of the front face  251 , namely, top edge  252 , upper left edge  255 , lower left edge  56 , bottom edge  253 , lower right edge  57 , upper right edge  254 , and protruding edge  58 , are cutting edges. 
     The protruding edge  58  is approximately parallel to the top edge  252  and to the bottom edge  253 ; however, the top edge  252  and the bottom edge  253  are in a first vertical plane, and the protruding edge  58  is in a second vertical plane. The top edge  252 , upper left edge  255 , protruding edge  58  and upper right edge  254  generally define a trapezoid; and the lower left edge  56 , bottom edge  253 , lower right edge  57  and protruding edge  58  also generally define a trapezoid. 
     The cutter  250  has a back face  262  having a generally flat surface ( FIG. 14 ); a top portion  263 ; and a bottom portion  264  separated on the front face  251  by protruding edge  58 . The back face  262  may contain a threaded bore  249  for accepting a screw for mounting onto a tool attachment  224 . The top portion  263  and bottom portion  264  of the cutter  250  are generally mirror images, allowing the cutter  250  to be indexable such that, when the cutter is rotated 180 degrees, fresh cutting edges are revealed. While the present invention discloses two index positions, it is contemplated that the cutter  250  be indexable to a plurality of positions. Each cutter  250  is preferably made of hardened tool steel suitable to the application, but may be made of any suitable material. 
     The hexagonal shape of the cutters  250  of this embodiment increases the cutting surfaces on the cutter and minimizes the amount of non-cutting surfaces on the counter knife  230  and rotor  220  while maintaining the advantages of the combing action of the counter knife  230 . The preferably partial row  270  of cutters configuration staggered along the rotor  220  body provides a more even feed of material to the screen and reduces the amount of instantaneous torque required to power the rotor. These features also reduce the tendency of the cutters  250  to self-feed the material and minimizes the heat generated during the cutting process. The cutters  250  may also be arranged in full row  70  arranged longitudinally along the rotor  220  or in 
     pairs  170  in random or staggered arrangement along the rotor  220   
     As shown in  FIGS. 11 ,  16  and  17 , a cutter  250  is removably mounted to each tool attachment  224 . The tool attachments  224  are preferably machined into and integral with the rotor  220 ; however, the tool attachments  224  may instead be welded or otherwise suitably attached or mounted to the rotor  220 . The rotor has a plurality of grooves  272  thereon between adjacent tool attachments  224  and which are between adjacent cutters  250  after they are mounted on the tool attachments  224 . The slot  26  in the rotor  220  in front of each tool attachment  224  partially receives a cutter  250  when it is removably mounted to that tool attachment  224 . For instance, the bottom portion  264  of a cutter  250  can be inserted into a slot  26  with the back face  262  towards the tool attachment  224  and the cutter bottom side  66  resting against the bottom of the slot  26 . In this configuration, the top portion  263  of the cutter  250  protrudes out of the slot  26  and functions as the working portion of the cutter  250 . When the cutting edges of the cutter top portion  263 , namely top edge  252 , upper left edge  255 , upper right edge  254  and protruding edge  58 , are worn, the cutter  250  may be removed, rotated 180 degrees and remounted. In this configuration, the bottom portion  264  of the cutter  250  protrudes out of the slot  26  and functions as the working portion of the cutter  250 . When the cutting edges of the cutter bottom portion  264 , namely bottom edge  253 , lower left edge  56 , lower right edge  57  and protruding edge  58 , are worn, the cutter  250  would then be removed and retooled or replaced with a new cutter  250 . 
       FIG. 18  depicts a further embodiment of the cutter  350 . The cutter  350  of the present embodiment is generally hexagonal in shape. The cutter  350  has a top portion  363  and a bottom portion  364  separated by protruding edge  358 . The top portion is framed by top edge  352 , upper left edge  355  and upper right edge  354 . However, the number of outer edges could vary as the geometric shape of the cutter  350  varies. The four edges, namely, top edge  352 , upper left edge  355 , upper right edge  354 , and protruding edge  358 , are cutting edges. The bottom portion  364  is a plug which may be any shape and size which can be received by slot  26 . 
     As depicted in  FIG. 17 , an optional cushioning plate  268  may be mounted between the cutter back face  262  and corresponding tool attachment  224  in order to absorb shock and minimize or prevent damage to the tool attachment  224 . Each cushioning plate  268  is preferably made of a soft metal or metal alloy, such as soft steel, but may be made of any suitable material. 
     As best shown in  FIG. 15 , the counter knife  230  of the instant embodiment has a generally flat body  232 , a top  233 , a bottom  234  (not shown), a front  235 , a back  236 ; a plurality of modified “V” shaped teeth  240  extending laterally in the same plane as the body  232  from the front  235  of the body  232 . Each tooth  240  forms three sides of a modified V, having a first tooth edge  242 , a second tooth edge  243  and a third tooth edge  244 . Each pair of adjacent teeth  240  defines an interstice  246  which is open on one side and whose three other sides form a modified “V” which is anchored by an interstice edge  247 . A third tooth edge  244  and a first tooth edge  242  extend from the ends of the interstice edge  247  each at an angle of approximately 112.5 degrees. This angle may be varied to accommodate variations in the shape of the cutter  250 . The edges  247 ,  242 ,  244  which form the interstice  246  are each a cutting edge. When the rotor  220  and counter knife  230  are properly installed in the rotary grinder  210  and the rotor  220  is rotating, the teeth  240  are designed to protrude into the groove  272  between adjacent cutters  250  as each of the adjacent cutters  250  are passing through the corresponding interstices  246  on the counter knife  230 . The combination of teeth  240  projecting from the counter knife body  232  with interstices  246  therebetween thereby form a comb configuration. 
     The third tooth edge  244  is preferably less than 1.016 mm (0.040 inches) in width but may be any suitable width as required by the application and the spacing between the cutters  250 . The interstices  246  between the teeth  240  are each preferably 41.173 mm (1.621 inches) in width but may be any suitable width as required by the width of the cutters  250  and the application. The hexagonal shape of the cutters  250  increases the cutting surfaces on the cutter  250 , minimizes the amount of non-cutting surfaces  243  on the counter knife  240  and groove  272  while still maintaining the advantages of the combing action of the counter knife  240 . 
     The counter knife  230  is indexable, being symmetrical on its top  233  and bottom  234  sides, such that the counter knife  230  can be turned over to expose fresh cutting edges and remounted with its bottom  234  facing upward when the upper portions of the cutting edges  242 ,  244 ,  247  become dull. This allows the cutting edges  242 ,  244 ,  247  at the top  233  and bottom  234  sides of the counter knife  230  to be used before the edges  242 ,  244 ,  247  are resharpened. Each counter knife  230  is preferably made of hardened tool steel suitable to the application, but may be made of any suitable material. 
     As shown in  FIG. 16 , a plurality of counter knives  230  may be installed adjacent each other. The number of counter knives  230  employed, the length of the counter knife  230 , the number of full and partial teeth  240  on the counter knife  230 , the length and width of the teeth  240  and the width of the interstices  246  are dependent upon the length and size of the rotor  220 , the number of cutters  250  employed longitudinally along the rotor  220 , the size of the cutters  250  and the positioning of the cutters  250  in relation to adjacent cutters  250 .  FIG. 11  clearly shows a counter knife  230  installed on the angled trough wall  88 . The counter knife  230  is installed with its bottom  234  portion towards the floor of the trough  87  and with the front  235  portion of its body  232  and teeth  240  extending upward at an angle towards the rotor  220 . 
     As shown in  FIG. 16 , the tool attachments  224  on the rotor  220  may be arranged longitudinally in a series of partial rows in a staggered arrangement, and the cutters  250  are mounted to the tool attachments  224  so that the cutters  250  form a comb configuration with the partial cutter rows  270 . 
     As best shown in  FIGS. 11 and 16 , the rotor  220  of the instant embodiment preferably has five sets of partial cutter rows  270  arranged in a staggered arrangement longitudinally along the rotor  220  body. However, the rotor  220  may contain a greater or lesser number of sets of partial cutter rows  270 , and correspondingly a greater or lesser number of total cutters  250  on the rotor  220 . Cutters  250  immediately adjacent each other in a partial cutter rows  270  are preferably spaced 1.016 mm (0.040 inches) apart, but may be spaced apart any suitable distance as required by the application. Additionally, the number of cutters  250  per set of partial cutter rows  270  will be influenced by the length of the rotor  220 . The number of cutters  250  on each rotor  220  will influence the amount of horsepower required to power the rotor  220 . An increase in the number of cutters  250  present on the rotor  220  will increase the amount of horsepower required, and a decrease in the number of cutters  250  will decrease the amount of horsepower required. The partial row of cutters configuration staggered along the rotor body provides a more even feed of material to the screen and reduces the amount of horsepower required to power the rotor. 
     As shown in  FIG. 16 , when the rotor  220  revolves on its shaft  22 , each cutter  250  passes at a small distance from the counter knife  230  through a corresponding interstice  246  located in the same vertical plane as the cutter  250 . At its smallest width, the groove  272  between the two adjacent cutters  250  is preferably 1.016 mm (0.040 inches). Additionally, each tooth  240  located between two adjacent interstices  246  protrudes into the groove  272  between the two adjacent cutters  250  located in the same vertical plane as each of the two adjacent cutters  250  is passing through the corresponding one of the two adjacent interstices  246 , the tooth  240  protruding to within a small distance from the rotor  220 , which effectively “combs” the rotor  220 . 
     As a cutter  250  passes through an interstice  246 , it is preferred that there is a first spacing  74  of 0.254 mm (0.010 inches), with an additional manufacturing tolerance of 0.127 mm (0.005 inches), between the third tooth edge  244  and the right edge  54  and between the first tooth edge  242  and the left edge  55 ; and a second spacing  76  of 0.127 mm (0.005 inches), with an additional manufacturing tolerance of 0.050 mm (0.002 inches), between the of cutter top edge  252  and the interstice edge  247 , although the first spacing  74  and second spacing  76  may be larger or smaller if required by the application. However, due to the temperature variation caused by the heat produced as the rotor  220  rotates and the resulting expansion of the rotor  220  in length, it would not be practical to reduce the first spacing  74  or second spacing  76  without employing a means to cool the rotor  220 . The first spacing  74  and second spacing  76  are also present when the cutter  250  is indexed 180 degrees to its second index position. 
     When the ram  92  pushes the film to be reduced into the revolving rotor  220 , each cutter  250  in a set of partial cutter rows  270  engages a portion of the film. The cutting edges  252 ,  255 ,  56 ,  253 ,  57 ,  254 ,  58  and concave surface  60 ,  61  of the working portion of the cutter  250  cooperate to cut and scoop out portion of the film. As the cutters  250  move downward towards the counter knives  230 , the cutting edges  252 ,  255 ,  56 ,  253 ,  57 ,  254 ,  58  on the working portion of the cutter cut through the film while the concave surface  60 ,  61  on the working portion of the cutter and the downward action of the cutter  250  act to scoop out a generally trapezoidally shaped portion of film and transport it towards the counter knives  230 . After a cutter  250  passes through the counter knife  230  the scooped portion of plastic is expelled from the cutter  250  as it reaches toward the bottom arc of its rotation. The cutters  250  also engage and drag uncut portions of film towards the counter knives  230 . As the partial cutter row  270  passes through the interstices  246 , any film caught outside the concave surfaces  60 ,  61  of the cutter  250  is either cut between the cutter  250  and the cutting edges  242 ,  244 ,  247  of the counter knife  230  or punctured and torn by the corresponding tooth  240  projecting into the groove  272  between two adjacent cutters  250  over which film is stretched as the cutters  250  pass through the interstices  246 . When the film wraps and/or becomes stretched between cutters  250 , the teeth  240  of the counter knife  230  “comb” the groove  272  between the cutters  250  and strip the film from its wrapped or stretched position. Additionally, when there is a sufficiently close spacing between each cutter  250  and the counter knife  230  (see  FIG. 16 ) and/or layers of film have built up sufficiently on the cutters  250  to fill the gap between the cutter  250  and the counter knife  230 , further cutting action is provided by the scissor action between the sides  267 ,  269 ,  79 ,  59  and cutting edges  255 ,  254 ,  56 ,  57  of the cutter  250  and the corresponding cutting edges  242 ,  244  of adjacent teeth  240 . 
     In addition to reduction of film, the scooping action of the cutting edges  252 ,  255 ,  56 ,  253 ,  57 ,  254 ,  58  and the concave surfaces  60 ,  61  of the cutter  250  have proven useful in reducing solid plastics and reducing rubber into smaller particles. Furthermore, the scooping action of the cutters  250  controls the maximum size of the reduced material, which eliminates or reduces the need for a screen placed after the rotor  220 . Smaller sized cutter  250  will result in an even smaller particle size. 
     The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention.