Abstract:
A granulator has a first coarse cutting stage operating at between 5 and 45 rotations per minute and a second fine cutting stage operating at two to ten times the speed of the first stage. Since granulate exiting the second stage is uniformly divided, the granulator operates independent of a screen. A first cutter stage has cutting segments having blades interspersed with deflector segments about a shaft. Rotation of the shaft urges the blades past a spaced stationary cutter.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/602,909 filed Jun. 23, 2000, now U.S. Pat. No. 6,450,427 which claims priority of U.S. Provisional Patent Application No. 60/140,875 filed Jun. 24, 1999, which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for granulating material and more particularly for granulating plastic and metal articles. 
     BACKGROUND OF THE INVENTION 
     Plastic granulators are used to fragmentize piece scrap or waste plastic material resulting from the production of various articles such that granulated pieces can be recycled into article production operations. Similarly, waste from molding processes are granulated prior to shipment and reprocessing. Efficient granulation requires that large quantities of scrap material be gravity fed into an apparatus and uniform compact granulate exit the apparatus. 
     One type of granulator uses a two-stage cutting process to successively coarse cut and granulate plastic. Often, a two-stage granulator requires the use of a screen prior to material discharge from the apparatus to assure granulate uniformity. U.S. Pat. Nos. 4,151,960; 4,377,261 and 5,402,948 are representative of two-stage granulators using a screen. Access to the screen is generally obtained by physically removing portions of the granulating apparatus resulting in operational downtime. Screen cleaning is periodically necessary to remove debris clogging the screen mesh. 
     Existing two-stage granulators often utilize more than two rotating shafts in order to operate a two-stage cutting process. U.S. Pat. No. 1,826,891; 4,750,678 and 5,143,307 are representative of two-stage granulators using more than two shafts. The synchronization in torque driving of interworking shafts requires comparatively complex gearing to adequately control the results in inefficient operation and both stages are not being taxed equally. 
     Existing two-stage granulators typically operate at speeds of between 50 and about 1000 rpms. Such high speed operation consumes considerable power, and presents unnecessary safety and maintenance demands on granulator operation. Thus, there exists a need for a two-stage granulator operating with two shafts at low speed and independent of screens. 
     Another type of granulator uses a single shaft having interspersed coarse cutters and fine cutters operating at about 30 rpm. U.S. Pat. No. 4,580,733 is representative of this design. The efficiency of such a single stage design is limited by the considerable torque needed to turn the unbalanced shaft and the limited throughput associated with fine cutters having to grind coarse material. Thus, there exists a need for a granulator cutter assembly that promotes uniform cutting torque and high throughput. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(   a ) is a fragmentary side view of a preferred embodiment of the present invention and  1 ( b ) is a cross-sectional view along the line A—A; 
         FIG. 2(   a ) is a side view of the two-stage cutting section of the embodiment depicted in  FIG. 1(   a ), and  2 ( b ) is a cross-sectional view along line B—B; 
         FIG. 3(   a ) is a perspective view of a first stage cutter assembly according to the present invention and  3 ( b ) is an exploded top view of the  FIG. 3(   a ) first stage cutter assembly; 
         FIG. 4  is a perspective view of another embodiment according to the present invention of a first stage cutter assembly depicting a tipped cutting blade; 
         FIGS. 5(   a )–( e ) are (a) perspective, (b) side, (c) end, and (d) magnified perspective views of a rotary cutter according to the present invention depicting a replaceable blade; and 
         FIG. 6(   a ) is an exploded view of a second stage cutter assembly according to the present invention and  6 ( b ) is a magnified side view of the second stage rotary cutter of  6 ( a ). 
     
    
    
     SUMMARY OF THE INVENTION 
     A granulator apparatus includes a first stage cutter mounted on a first shaft. A second stage cutter is mounted on a second shaft generally parallel to the first shaft and located to receive material after encountering the first stage cutter. A motor is coupled to the first and second shafts in order to rotate the first stage cutter at a rate between 5 and 50 rotations per minute and the second stage cutter at between two and ten times the rate of the first cutter. An exit aperture receives material having encountered the second stage cutter wherein a path is defined through said first and said second stage cutters and the exit aperture, the path being independent of a screen. 
     A screenless granulator apparatus is also disclosed which includes a first rotating cutting segment having a plurality of blades, the blades rotating against a stationary cutter. The first rotating cutting segment being mounted on a shaft. An angled gravity fed load bin is mounted above said first rotating cutting segment, the bin having a side wall terminating proximal to said stationary cutter and angled to promote travel of material through said bin along the side wall in preference to other wall components of the bin. 
     A method of granulating material includes the steps of shearing the material between a rotating blade of a first stage coarse cutter and a stationary first cutter to form coarsely divided granulate, wherein the blade rotates about a first shaft at a rate of between 10 and 20 rotations per minute. Thereafter, the coarsely divided granulate is sheared between a second blade of a rotating second stage cutter and a stationary second stage cutter to form finely divided granulate wherein the second stage rotating cutter rotates at a second rate greater than the first stage rotating cutter and the second rate is less than 60 rotations per minute. Finely divided granulate is then removed from the second stage cutter without said finely divided granulate contacting a screen. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As seen in  FIGS. 1 and 2 , the preferred embodiment of a granulator apparatus  10  for granulating waste plastic and sheet metal, includes a gravity fed loading bin  12 , a first coarse cutting stage  14  and a second fine cutting stage  16 . The granulator apparatus of the present invention as depicted in  FIGS. 1 and 2  are shown without cover panels, shields, stands or portions of the housing  13  in order to illustrate various operating components in features. The first cutting stage  14  is mounted about a first drive shaft  18 . Likewise, the second fine cutting stage  16  is mounted about a second parallel drive shaft  20 . Preferably, the first shaft  18  has a notch  35  in regions not enveloped by cutting segments  60  having rotating blades  34  to form material deflector segments  37 , as shown in  FIG. 1(   b ). Typical construction materials for a cutting stage according to the present invention include steel. Additionally, cutting surfaces are amenable to hardening procedures and coatings conventional to the art. 
     The material deflector segment  37  is characterized by having a cylindrical outer circumference save for a notch  35 . The notch  35  serves to catch partly cut material resting against the shaft  18  and deflect such material into the path of a cutting blade  34 . Furthermore, the notch  35  has been observed to nibble a fragment from plastic material, thereby providing some additional cutting capability. The outer circumference of a deflector segment  37  is optionally machined to include a plurality of the notch  35  to limit material accumulation between blades  34 . Preferably, one to six notches are formed in a deflector segment  37 . More preferably, two to six notches are present. Still more preferably, the notches are radially spaced about the shaft  18  to promote rotary balance. Thus, for example, two notches are formed in a diametric relationship on a deflector segment  37  as per  FIG. 1(   b ). It is appreciated that a deflector segment is also formed as a slip collar adapted to fit about a shaft, thereby facilitating deflector segment replacement. 
     The first drive shaft  18  and second drive shaft  20  are powered by a motor  22  by way of a transfer shaft  24  engaging gearing  26  such that the first stage  14  rotates at a lesser speed than the second stage. A motor having between ½ and 10 horsepower is sufficient for most usages, although it is appreciated that the present invention is amenable to scaling to a variety of sizes both smaller and larger. Gear reduction ratios from the motor  22  to the drive shaft are typically between 10:1 and 100:1. Preferably the ratio is between 20:1 and 60:1. It is appreciated that pulley, belt drives and other power transfer components are readily coupled in the motor  22  to drive shafts  18  and  20  as well as other apparatus components. Preferably, the first stage  14  rotates at between 5 and 50 rpms and the second stage  16  rotates at between two and ten times the speed of the first stage  14 . More preferably, the first stage rotates at between 10 and 20 rpms and the second stage  16  rotates at between two and four times the speed of the first stage  16 . Still more preferably, the second stage  16  rotates at less than 60 rpms. Further, it is preferred that the second stage  16  rotates counter to the first stage  14 . 
     Gravity fed loading bin  12  terminates within housing interior walls  28  which taper towards a coarse stationary cutter  32  and the rotating shaft  18  of the first cutting stage  14 . The first cutting stage  14  includes a plurality of rotating cutting segments  60 , each having blades  34  dispersed about the circumference of the first shaft  18 . The gravity fed loading bin  12  preferably has a side wall  50  terminating proximal to the stationary cutter  32  such that sprues and other material slide down the side wall  50  directly into the path of the blades  34  without encountering a ledge or region likely to be bridged by material within the bin  12 . The present invention overcomes the limitations associated with conventional right cylinder, cone or rectilinear bins which can readily be bridged by material lodging lengthwise across the bin opening. The side wall  50  promotes the linear feed of material into the blades  34  thereby lessening the likelihood of an obstruction in material feed. The side wall  50  is typically angled between 20° and 60° relative to vertical and the other side walls define a smaller angle than the side wall relative to vertical. Preferably, the opposing side wall  51  relative to side wall  50  defines a non-zero smaller angle than the side wall relative to vertical. A minimal clearance exists between the first stage stationary cutter  32  and a rotating blade  34  such that feed stock contacting the first stage  14  is rotated towards the first stationary cutter  32  resulting in shearing of the feed stock material between the first stage stationary cutter  32  and a blade  34 . Feed stock material that is pushed by a rotating blade  34  past stationary cutter  32  falls into a coarse granulate bin  36 . Preferably, the first stage  14  has a plurality of cutting segments  60 , each segment  60  having two blades  34 . More preferably, the two rotating blades are diametrically opposed with a concave trailing edge  39 , relative to the direction of rotation. 
     The coarse granulate bin  36  has walls  38  which taper towards an opening having a width suitable to allow insertion of a second stage stationary cutter  42  and the free rotation of the second cutting stage  16 . The second cutting stage  16  includes a plurality of cutter segments  60 ′, each having a plurality of rotating blades  44 . A clearance exists between the stationary cutter  42  and a rotating blade  44  such that feed stock contacting the second stage  16  is rotated towards the second stationary cutter  42  resulting in shearing of the feed stock material between the second stage stationary cutter  42  in a rotating blade  44 . Feed stock material that is pushed by a rotating blade  44  past stationary cutter  42  falls through a fine granulate exit aperture  46 . The fine granulate passing the exit aperture  46  and falling into a collection bin  52 . Optionally, a collector outlet tube  54  mounted at the base of the collection bin  52  facilitates automatic removal of granulate. The collector outlet tube  54  operating on a principle illustratively including suction, pressurized gaseous or liquid flow, or mechanical conveyance such as a screw or conveyor belt. Preferably, the second cutter stage  16  has more than three blades  44  per secondary cutting segment  60 ′. More preferably, the rotating blades  44  are angularly spaced at regular intervals about the secondary cutting segment  60 ′ and with a concave cutting edge  48 , as shown in  FIG. 2(   b ). Still more preferably, the concave cutting edge  48  is rotationally staggered relative to blades on proximal secondary cutting segments  60 ′,  FIG. 2(   b ). 
     Preferably, the interior housing walls  28  and coarse granulate bin walls  38  are integrated to form two opposing side sections  56  and  58  along the length of the coarse  14  and fine  16  rotating cutting stages. One integrated side section  56  containing the first stage stationary cutter  32 , while the other side section  58  contains the second stage stationary cutter  42 . More preferably, a side section according to the present invention is mounted on a hinge pin  30  to facilitate access to the rotating cutting stages  14  and  16 . 
       FIG. 3(   a ) is a perspective view of a first stage cutter assembly according to the present invention and  FIG. 3(   b ) is an exploded top view of the  FIG. 3(   a ) first stage cutter assembly. A coarse stationary cutter  332  is positioned relative to a first cutting stage  314 . The first cutting stage  314  capable of free rotation around a shaft  318 . The first cutting stage  314  includes at least one cutter segment  360  adjacent to at least one deflector segment  370  mounted about a shaft  318 . The shaft  318  has a bearing race  372  to allow free rotation of the shaft  318 . Additionally, a low friction washer  374  is provided to prevent wear through contact with a stationary mounting housing (not shown) and further to prevent material from becoming lodged in a clearance gap. A cutter segment  360  includes a plurality of rotating blades  334  dispersed about the circumference of the cutter segment  360 . The cutting edge  380  is particularly well suited for shearing soft or brittle polymers illustratively including polyvinyl chloride, acrylonitrile-butadiene-styrene copolymers (ABS), nylon, and polyethylene. It is appreciated that the cutter segment  360  and/or the deflector segment  570  is optionally integral to the rotating shaft  318 . A clearance between the stationary cutter  332  and a blade  334  is between 0.5/1000 and ½ inch. Preferably, for the granulation of thermoplastic materials, the clearance is between 2/1000 and 4/1000 of an inch. The clearance between the deflector segments  370  and the stationary cutter  332  is between 1/1000 and ½ inch. Preferably, the clearance between a deflector segment  370  and a stationary cutter  332  for the granulation of thermoplastics is between 3/1000 and 5/1000 of an inch. 
       FIG. 3(   a ) and  FIG. 3(   b ) show an embodiment of the present invention which includes a plurality of cutter segments  360 , the blades  334  of each cutter segment  360  are staggered relative to the other cutter segments to lessen differences in rotational torque of the first cutting stage  314 . Thus, in the embodiment depicted in  FIGS. 3(   a ) and  3 ( b ), the four cutter segments  360  sequentially pass the stationary cutter  332  such that only one cutting edge  80  at any given time during first cutter stage rotation is actively cutting material. Preferably, cutting segments and stationary cutters according to the present invention are constructed from a material having a Rockwell hardness of between 56 and 58. More preferably, the cutter segments  360  and stationary cutter are both constructed of D2 or CPM steel. 
     As shown in  FIGS. 3(   a ) and  3 ( b ), the cutting segments  360  each have two blades  334  diametrically opposed. Preferably, the trailing edge  362  of a blade  334  is concave in the operational cutting rotational direction. The deflector segments  370  have a cylindrical outer circumference and a notch  335 . Preferably, there are approximately an equal number of notches  335  as there are blades  334  on the adjacent segment and a notch  335  is concave in the direction of rotation. More preferably, a notch  335  in a deflector segment  370  is rotationally staggered relative to an adjacent blade  334 . Most preferably, a notch  335  leads an adjacent cutting blade by an angle of between 0.3 and 0.6 times the angular displacement between blades on an adjacent cutting segment. For example, in the embodiment depicted in  FIG. 3  where two blades are spaced apart by 180° on a cutting segment  360 , then the most preferred location for a notch  335  is between 54° and 108° in front of a blade. It is appreciated that while the embodiments of the present invention depicted herein that contain a plurality of cutter segments are shown as having an equal number of blades on all cutting segments, optionally cutting segments of a first stage cutter having varying numbers of blades. Thus, cutter segments having two blades are readily used in conjunction with cutter segments having more than two blades. 
     Another embodiment of a first cutting stage according to the present invention is depicted in  FIG. 4 . Five cutting segments  460  are staggered from one another to create a sequential cutting motion from distal to central portions of a cutting stage  414 . Each cutting segment  460  has two cutting blades  434 . A cutting blade  434  has a concave trailing edge  439 . A rearward angled cutting edge  480  is characterized by having a leading tip  482  adapted to secure material as the remainder of the rearward angled cutting edge  480  and the trailing edge  439  drive the material towards a stationary cutter  432 . The scissor-like cutting action of cutting blade  434  is particularly well suited for shearing of high strength—high flexural modulus materials illustratively including polycarbonates, LEXANs (Du Pont), liquid crystal polymers, polystyrene, polyacrylics, and thermoplastic elastomers. It is appreciated that any number of modifications to the tipped leading edge are readily made illustratively including multiple tips, serrations, and a tip extending the full length of the leading edge  480 . 
       FIGS. 5(   a )–( d ) depict another embodiment of a cutting stage according to the present invention having a replaceable leading edge and particularly well suited for granulating bulk material such as toilet seats, door panels, bumpers and the like. According to this embodiment, a cutting segment  560  is mounted about a shaft  518 . The cutting segment  560  has a notch  585 . The base of the notch  585  terminates in a recess  586  adapted to receive a blade  534 . Preferably, the blade  534  is secured in the recess  586  with a threaded fastener  588 . Optionally, the threads within the blade  534  adapted to engage the threaded fastener  588  extend through the blade face  587 . Preferably, the blade face  587  is concave in the direction of rotation. While an open aperture in the cutting blade face  587  will harmlessly collect material through use, it is appreciated that a cap (not shown) may be inserted into the blade face  587 . Preferably, such a cap has a pointed tip extending from the blade face  587  to facilitate gripping of material. A stationary cutter (not shown) is designed to have an edge complementary to the side view edge  590 . Preferably, the blades  534  are sequentially staggered on adjacent cutting segments  560  with an overlap such that a preceding blade holds material for a blade to cut, thereby lessening bumping. More preferably, each cutting segment  560  has a plurality of blades  534 .  FIG. 5(   e ) depicts an alternative embodiment of a bulk material cutter blade  534 . A rectilinear cross sectional cutter blade  534 ′. The blade  534 ′ is divided into a first cutting surface  580  and a set back second cutting surface  584 . Preferably, the first and second cutting surfaces are concave in the direction of rotation. A stationary cutter (not shown) complementary to the cutter blade cross section is utilized to create a complete cutting stage according to the present invention. Other numbered elements of  FIG. 5(   e ) correspond to the description thereof in conjunction with  FIGS. 5(   a )–( d ). Optionally, deflector segments are interspersed among the cutting segments  560 . 
     It is appreciated that a first stage cutter as depicted in  FIGS. 1–5  is readily adapted to be used without a second stage, or screen for the granulation of thermoplastics, thermoplastic elastomers such as SANTOPRENE, and thermoresins. 
     A second stage cutter  616  is depicted in  FIGS. 6(   a ) and ( b ). A secondary cutting stage  616  includes a plurality of secondary cutter segments  660  and complementary stationary cutter  642 . Each secondary cutter segment  660  has a plurality of blades  644  spread radially about the segment. A clearance exists between a stationary cutter  642  and a rotating blade  644 . The clearance typically being from 1/1000 to ⅛ of an inch. Preferably, the cutting edge  645  of the blade  644  is concave. More preferably, the cutting edge  645  and the trailing edge  662  of blade  644  are concave. 
     Blades  644  of adjacent cutting segments  660  are preferably staggered radially from one another to lessen radial torque differences upon rotation of the second cutting stage  616 . More preferably, blades  644  of adjacent cutting segments are staggered to produce a terminal to center sequential cutting sequence. As with reference to  FIG. 3(   b ), a shaft  620  as shown in  FIG. 6(   a ) includes a bearing race  672 . Preferably, cutting segments and stationary cutters according to the present invention are constructed from a material having a Rockwell hardness of between 56 and 58. More preferably, cutting segments  660  and a stationary cutter  642  are constructed of D2 or CPM steel. 
     Various modifications of the present invention in addition to those shown and described herein will be apparent to those skilled in the art from the above description. Such modifications are also intended to follow from the scope of the appended claims. 
     All patents or other publications cited herein are incorporated by reference to the full extent as if each individual patent or other publication was individually incorporated by reference.