The benefit is claimed of U.S. Provisional Application Ser. No. 60/743,108, filed Jan. 9, 2006, which application is incorporated in its entirety by reference. 


   BACKGROUND 
   This invention relates generally to refiners for removing contaminants from fiber materials, such as recycled or recovered paper and packaging materials. In particular, the present invention relates to refiner stator plates and especially to the outer row of teeth on the stator plates. 
   Refiner plates are used for imparting mechanical work on fibrous material. Refiner plates having teeth (in contrast to plates having bars) are typically used in refiners which serve to deflake, disperge or mix fibrous materials with or without addition of chemicals. The refiner plates disclosed herein are generally applicable to all toothed plates for dispergers specifically and refiners in general. 
   Disperging is primarily used in de-inking systems to recover used paper and board for reuse as raw material for producing new paper or board. Disperging is used to detach ink from fiber, disperse and reduce ink and dirt particles to a favorable size for downstream removal, and reduce particles to sizes below visible detection. The disperger is also used to break down stickies, coating particles and wax (collectively referred to as “particles”) that are often in the fibrous material fed to refiner. The particles are removed from the fibers by the disperger become entrained in a suspension of fibrous material and liquid flowing through the refiner, and are removed from the suspension as the particles float or are washed out of the suspension. In addition, the disperger may be used to mechanically treat fibers to retain or improve fiber strength and mix bleaching chemicals with fibrous pulp. 
   There are typically two types of mechanical dispergers used on recycled fibrous material: kneeders and rotating discs. This disclosure focuses on disc-typed disperger plates that have toothed refiner stator plates. Disc-type dispergers are similar to pulp and chip refiners. A refiner disc typically has mounted thereon an annular plate or an array of plate segments arranged as a circular disc. In a disc-type disperger, pulp is fed to the center of the refiner using a feed screw and moves peripherally through the disperging zone, which is a gap between the rotating (rotor) disk and stationary (stator) disk, and the pulp is ejected from the disperging zone at the periphery of the discs. 
   The general configuration of a disc-type disperger is two circular discs facing each other with one disc (rotor) being rotated at speeds usually up to 1800 ppm, and potentially higher speeds. The other disc is stationary (stator). Alternatively, both discs may rotate in opposite directions. 
   On the face of each disc is mounted a plate having teeth (also referred to as pyramids) mounted in tangential rows. A plate may be a single annular plate or an annular array of plate segments. Each row of teeth is typically at a common radius from the center of the disc. The rows of rotor and stator teeth interleave when the rotor and stator discs are opposite each other in the refiner or disperger. The rows of rotor and stator teeth intersect a plane in the disperging zone that is between the discs. Channels are formed between the interleaved rows of teeth. The channels define the disperging zone between the discs. 
   The fibrous pulp flows alternatively between rotor and stator teeth as the pulp moves through successive rows of rotor and stator teeth. The pulp moves from the center inlet of the disc to a peripheral outlet at the outer circumference of the discs. As fibers pass from rotor teeth to stator teeth and vice-versa, the fibers are impacted as the rows of rotor teeth rotate between rows of stator teeth. The clearance between rotor and stator teeth is typically on the order of 1 to 12 mm (millimeters). The fibers are not cut by the impacts of the teeth, but are severely and alternately flexed. The impacts received by the fiber break the ink and toner particles off of the fiber and into smaller particles, and break the stickie particles off of the fibers. 
   Two types of plates are commonly used in disc-type dispergers: (1) a pyramidal design (also referred to as a tooth design) having an intermeshing toothed pattern, and (2) a refiner bar design. A novel pyramidal tooth design has been developed for a refiner plate and is disclosed herein. 
     FIGS. 1   a ,  1   b  and  1   c  show an exemplary pyramidal plate segment having a conventional tooth pattern. An enhanced exemplary pyramidal toothed plate segment is shown in commonly-owned U.S. patent application Publication No. 2005/0194482, entitled “Grooved Pyramid Disperger Plate.” For pyramidal plates, fiber stock is forced radially through small channels created between the teeth on opposite plates, as shown in  FIG. 1   c . Pulp fibers experience high shear, e.g., impacts, in their passage through dispergers caused by intense fiber-to-fiber and fiber-to-plate friction. 
   With reference to  FIGS. 1   a ,  1   b  and  1   c , the refiner or disperger  10  comprises disperger plates  14 ,  15  which are each securable to the face of one of the opposing disperger discs  12 ,  13 . The discs  12 ,  13 , only portions of which are shown in  FIG. 1   c , each have a center axis  19  about which they rotate, radii  32  and substantially circular peripheries. 
   A plate may or may not be segmented. A segmented plate is an annular array of plate segments typically mounted on a disperger disc. A non-segmented plate is a one-piece annular plate attached to a disperger disc. Plate segment  14  is for the rotor disc  12  and plate segment  15  is for the stator disc  13 . The rotor plate segments  14  are attached to the face of rotor disc  12  in an annular array to form a plate. The segments may be fastened to the disc by any convenient or conventional manner, such as by bolts (not shown) passing through bores  17 . The disperger plate segments  14 ,  15  are arranged side-by-side to form plates attached to the face of the each disc  12 ,  13 . 
   Each disperger plate segment  14 ,  15  has an inner edge  22  towards the center  19  of its attached disc and an outer edge  24  near the periphery of its disc. Each plate segment  14 ,  15  has, on its substrate face concentric rows  26  of pyramids or teeth  28 . The rotation of the rotor disc  12  and its plate segments  14  apply a centrifugal force to the refined material, e.g., fibers, that cause the material to move radially outward from the inner edge  22  to the outer edge  24  of the plates. The refined material predominantly move through the disperging zone channels  30  formed between adjacent teeth  28  of the opposing plate segments  14 ,  15 . The refined material flows radially out from the disperging zone into a casing  31  of the refiner  10 . 
   The concentric rows  26  are each at a common radial distance (see radii  32 ) from the disc center  19  and arranged to intermesh so as to allow the rotor and stator teeth  28  to intersect the plane between the discs. Fiber passing from the center of the stator to the periphery of the discs receive impacts as the rotor teeth  28  pass close to the stator teeth  28 . The channel clearance between the rotor teeth  28  and the stator teeth  28  is on the order of 1 to 12 mm so that the fibers are not cut or pinched, but are severely and alternately flexed as they pass in the channels between the teeth on the rotor disc  12  and the teeth on the stator disc  13 . Flexing the fiber breaks the ink and toner particles on the fibers into smaller particles and breaks off the stickie particles on the fibers. 
     FIGS. 2   a  and  2   b  show a top view and a side cross-sectional view, respectively, of a standard tooth geometry  34  used in the outer row of a stator plate. The tooth  34  has a pyramidal design consisting of strait sides  36  that taper to the top  38  of the tooth. The sides of the standard tooth  28  are each substantially parallel to a radial  32  of the plate. 
   A primary role of the disperger plate is to transfer energy pulses (impacts) to the fibers during their passage through the channels between the discs. The widely accepted toothed plate typically includes the square pyramidal tooth geometry with variations in edge length and tooth placement to achieve desired results. 
   Refiner material passing between the discs can be accelerated to a high velocity due to the centrifugal forces imparted by the rotor disc. Some of the refiner material exits the discs  12 ,  13  at a high velocity and are flung radially against the refiner casing  31 . The high velocity impacts of refiner material against the casing have caused abrasive wear and damaging cavitation to the casing. There is a long felt need for a means to reduce the wear and damage on refiner and disperger casing due and, particularly, to reduce the wear and damage caused by refiner material impacts against the casing. 
   BRIEF DESCRIPTION 
   This disclosure proposes a modified stator tooth geometry, such as an angled tooth, for the outermost row of a stator plate. The modified tooth geometry is intended to achieve a longer life of the casing by reducing impacts against the casing due to high velocity particles exiting the plates of the refiner. 
   A refiner stator plate has been developed having a plurality of concentric rows of teeth wherein an outer row is at or near an outer periphery of the plate segment. The teeth in the outer row include leading sidewalls, wherein the sidewalls are at an angle to radii of the plate segment. plate is preferably a stator plate for a disperger. The angle of the sidewalls of the outer row may be opposite to a direction of rotation of a rotor plate. The angle of the sidewalls is in a range of 10 to 60 degrees with respect to a radial, and preferably in a range of 15 to 45 degrees. The sidewalls may be planar, V-shaped having a straight radial inward surface and a slanted radial outward surface, or curved along their lengths. 
   Further, the angled sidewall of the teeth of the outer stator row are arranged to project normal (in other words, tangential) to a radial a distance at least equal to a gap between adjacent teeth of the outer stator row. In addition, the angled sidewall may include an angled wall portion and a radially aligned wall portion. Further, the outer row of teeth may have substantially perpendicular rear walls. 
   A refiner or disperger has been developed comprising a rotor disc including a rotor plate including concentric rows of rotor teeth; a stator disc arranged opposite to the rotor disc in a disperger, wherein the stator disc includes a stator plate, wherein the stator plate includes concentric rows of stator teeth intermeshing with the rotor teeth and an outer row of the stator teeth include sidewalls angled in opposition to the rotation of the rotor disc so as to deflect particles flowing between the teeth of the outer row. 
   A method of refining pulp material between opposing discs in a refiner has been developed, the method comprising: feeding the pulp material to an inlet of at least one of the discs; rotating one disc with respect to the other disc while pulp material is moved between the discs due to centrifugal force; refining the pulp material by subjecting the material to impacts caused by rows of teeth on the rotating disc intermeshing with rows of teeth on the other disc; deflecting the pulp material as the material flows through an outer row of teeth on the other disc, wherein the outer row of discs comprise teeth having a sidewall angled to deflect pulp material moving radially between the teeth. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1(   a ) and  1 ( b ) are a front view and cross-sectional side view, respectively, of a toothed stator plate segment conventionally used in disc-type dispergers. 
       FIG. 1(   c ) is a side cross-sectional view of a stator and rotor disperger plates and discs with channels therebetween. 
       FIGS. 2   a  and  2   b  are a top down view and a side perspective view, respectively, of a conventional tooth geometry for the outer teeth row of stator disperger plate. 
       FIGS. 3   a  and  3   b  are a top down view and a side perspective view, respectively, of an angled tooth for the outer row of a stator disperger plate, wherein the sidewalls of the tooth are each angled with respect to a radius of the disc. 
       FIGS. 4   a  and  4   b  are a front plan view and a side cross-sectional view, respectively, of a disperging stator plate segment utilizing the angled tooth geometry for the outer row of teeth. 
       FIG. 5  is a top down perspective view of an alternative angled tooth geometry for an outer row of a stator plate. 
       FIG. 6  is a top down perspective view of another alternative angled tooth geometry for an outer row of a stator plate. 
   


   DETAILED DESCRIPTION 
   A novel arrangement of teeth for a toothed refiner stator plate has been developed in which the outer peripheral row of teeth are angled to deflect refiner material, e.g., pulp, moving through the disperging zone. The deflection reduces the velocity of refiner material particles that would otherwise move along a radial line at a high speed from between the refiner discs and into the casing. This novel arrangement of outer row stator teeth may be applied to any type of toothed refiner plate and especially disc-type dispergers. 
   The outer row of stator teeth are angled to control the feed of the pulp exiting the disperging zone and out from between the discs. In particular, the leading sidewall of the stator teeth in the outer row of teeth are angled to slant the teeth so as to deflect particles moving along a substantially radial line between the outer row of stator teeth. Deflecting refiner material reduces the velocity of the exiting refiner material and minimizes the impact of the refiner material on the walls of the refiner casing. 
   The angled outer row of stator teeth prevent pulp from following a direct radial path from the last row of stator teeth and into the casing where high velocity pulp can damage the casing wall. The angle of the outer row of stator teeth and the length of the angled portion of these teeth are selected such that the refiner material, e.g. pulp, passing through the disperging zone is deflected by the angled sidewalls of the last row of stator teeth. The outer row teeth are slanted, at least along a portion of the teeth, such that the slanted portion of the teeth project tangentially a distance at least equal to the gap between adjacent teeth. The deflection prevents refiner materials from being flung at high velocity radially from the discs and into the refiner casing. 
     FIGS. 3   a  and  3   b  show a top view and a side perspective view, respectively, of an angled stator tooth  40  where the sides of the tooth are angled with respect to a radial  32  of the disc center. The stator tooth  40  is preferably positioned at the outer row of the stator plate. One or both of the sidewalls  42  of the tooth  40  form an angle  44  with respect to a radius  18  of the disc. Further, the sidewalls  42  taper towards the top  46  of the tooth. The base  48  of the tooth is at the substrate of the plate. The front wall  50  of the tooth faces radially inward and the rear wall  52  of the tooth faces radially outward. The front and rear faces may each be aligned substantially tangent to the row and plate. The front wall may slope towards the top of the tooth. The rear wall, preferably, is generally perpendicular to the substrate of the plate. 
   The slant (angle  44 ) of the outer row of stator teeth deflects refiner material as it passes through the outer row of stator teeth. The deflection is intended to slow the refiner material, pulp and entrained particles, as it leaves the channel between the disc and before the refiner material enters the casing of the disperger or refiner. By reducing the velocity of the refiner material, less damage is done to the casing as a result of refiner material hitting the casing. 
     FIGS. 4   a  and  4   b  are a font view and a side-cross-sectional view, respectively, of an exemplary stator plate  54  that is mounted on a disperger disc. The stator plate is opposite a rotor plate and a disperging zone is formed by the channels between the two opposing plates. The rotational direction (arrow  55 ) for the rotor plate is counter-clockwise (which appears clockwise from the view point of  FIG. 4   a  which shows a stator plate segment). 
   The stator disperger plate segment  54  includes rows  56 ,  58 ,  60 ,  62 ,  64  and  66  of teeth  68 . The inner teeth rows ( 56 ,  58 ,  60 ,  62  and  64 ) may have a pyramidal shape such as shown in  FIGS. 2   a  and  2   b . The sidewalls of the inner rows of teeth may be aligned with a radius of the disc, or may be slanted with respect to the radius. Similarly, the rotor plate (not shown) may have rows of teeth that interleave with the row of stator teeth, when the plates are arranged in the refiner. 
   The outer row  66  of stator teeth  40  have sidewall angles that are angled either in the same direction as or opposite to the rotation  55  of the rotor. It should make no difference to casing protection whether the last row of stator teeth are slanted towards or against the rotational direction. Slanting the outer row of stator teeth in a direction opposite to direction places the teeth in a “holdback” position, and slanting the teeth in the same direction of rotation is a “feeding position.” Further, the sidewall angle of the teeth  40  may be between 10 0  to 60 0 , and preferably in a range of 15 0  to 45 0 , with respect to a radial of the plate and disc. The angle ( 44  in  FIG. 3   a ) of the sidewalls of the last row  66  of stator teeth  40  is selected to deflect refiner material moving through the row and to allow the flow without too much obstruction. 
   The rear wall ( 52  in  FIG. 3   b ) extends to the outer periphery  24  of the stator plate. The sidewall of the teeth  40  are extended as a result of the rear wall being substantially normal to the substrate  72  of the stator plate  54 . Extending the sidewalls provides additional sidewall area to deflect the refiner material. The length and angle of the sidewall should be sufficient such that a fast moving particle cannot move along a radial through the gap between the teeth without hitting the sidewall of a tooth. Accordingly, the projection of the width of the sidewall along a tangential direction should be at least as wide as the gap between the teeth of the last stator row. 
   The sidewalls on both sides of the outer row stator teeth  40  preferably form the same angles with respect to radii. The leading sidewall (facing the rotational direction of the rotor) deflects pulp. The trailing sidewall is on the opposite side of the tooth and faces a leading sidewall of an adjacent stator tooth. Maintaining the same angles on both sides of the teeth ensures that the gap between teeth remains constant along the length of the teeth. Accordingly, the leading and trailing sidewalls of the stator tooth are preferably symmetrical. 
     FIG. 5  shows a top down perspective view of an alternative tooth  70  for the last row of the stator plate. The alternative tooth has a double angled sidewall  72  that includes a radial sidewall section  78  and an angled wall section  80 . The radial sidewall section  78  is substantially aligned with a radial of the stator plate. The angled wall section  80  is offset from a radial by an angle 10 to 60 degrees and preferably between 15 to 45 degrees. The length and angle of the angled sidewall  80  are arranged to deflect all refined material moving along a radial and between teeth in the last row of stator teeth. In particular, the tangential projection  81  of the length of the sidewall  80  spans the width of the gap between adjacent teeth in the last stator row. 
     FIG. 6  shows a top down perspective view of another alternative tooth  84  for the last row of the stator plate. The alternative tooth has a curved sidewall  86  that starts as a substantially radial sidewall section  88  and progressively turns to an angled wall section  90 . The inward radial sidewall section  88  is substantially aligned with a radial of the stator plate. The length and curvature of sidewall  86  are arranged to deflect all refined material moving along a radial and between teeth in the last row of stator teeth. In particular, the tangential projection of the length of the sidewall  86  should span the width of the gap between adjacent teeth in the last stator row. 
   While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
A refiner stator plate having concentric rows of teeth wherein an outer row is at or near an outer periphery of the plate, and the outer row teeth include leading sidewalls slanted to deflect high-velocity refining particles moving along a radial line between the plates.