Abstract:
An improved pulper, mixer or defibering, rotor having a spar ring attached to a hub of the rotor with a series of curved vanes projecting from the spar ring. The curved vanes have a vane face and a trailing edge. The trailing edge may be unitary and integral with the vane, or may be segmented in combination with trailing edge portion provided on an underlying spar stub to which the vanes are attached. The hydrodynamic suction created by the trailing edge is enhanced by the addition of a dam at the vane tip end of the trailing edge zone. The vanes have a constant vane face angle relative to radians extending outward from the hub of the rotor. As a result of the constant vane face angle the pulp, or other materials, mixed by the vanes during rotation of the rotor are more consistently in contact with the vanes during rotation of the rotor. The vanes are also streamlined to reduce hydrodynamic drag especially at the vane tips where speed and therefore drag potential are at their highest levels. As a result, increased circulation and pumping effects with minimal power requirements are achieved. The vanes may be made of high wear resistant materials and are easily accessible for maintenance, repair or replacement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority benefit of U.S. Provisional Patent Application 60/440,532 filed Jan. 16, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     This invention relates to an improved pulper or mixer rotor with increased pumping and defibering capacities, reduced power requirements, easier maintenance and interchangeability of parts, and improved wear resistance.  
         [0004]     2. Description of Related Art  
         [0005]      FIG. 1  shows a conventional pulping, mixing, or defibering apparatus, which generally includes a vat, or tub,  10  formed of side wall  11  and bottom wall  12 . In the center of the bottom wall  12  is a perforated bed-plate  13 . The bed-plate  13  permits draining of pulped paper stock, for example, after a pulping operation is completed. A rotor  15  for circulating the paper stock, for example, or other material, is mounted on a hub  14  in the center of the bed-plate  13 . Supports  19  stabilize the pulping tub, or vat,  10 .  
         [0006]     The rotor  15  creates a mechanical shear and/or hydraulic shear effect on the pulp, or other material, being mixed. Mechanical shear, for example, is achieved by rotating the rotor  15  above the stationary bed-plate  13  so that the paper pulp stock, or other material, is agitated, and the fibers and liquids are approximately separated by being strained through the bed-plate  13  under the pressure applied by vanes  17  of the rotor  15 . Hydraulic shear, on the other hand, occurs by contacting the paper pulp fibers, for example, with other paper pulp fibers in the tub, or vat,  10  as a result of the turbulence, or flow pattern, generated by rotation of the rotor  15 . The rotor  15  is driven by gears that engage the hub  14 . A motor  22  powers the gears that are housed within gear housing  20 .  
         [0007]      FIG. 2  shows a conventional pulper rotor  15  with a series of straight vanes  17  extending beyond the outer circumference of a spar ring  16 . The straight vanes  17  tend to be fairly blunt and thick at a leading vane face  17   a , and tapers thinner at a trailing edge  17   b  of each vane  17 . One end of each vane  17  nearest the spar ring  16  joins an outer portion of the spar ring  16 . The portions where each vane  17  joins the spar ring  16  gradually tapers to form a gulley  17   c . These gulleys  17   c  are susceptible to cavitation wear from the turbulent flow of pulp, or other materials passing over the vanes  17  in the wake of the agitation generated by rotation of the rotor  15 .  
         [0008]      FIG. 3  shows that straight vanes  17  result in an angle of the leading edge of the vane face  17   a  varying relative to a radian r n , for example, projecting from the rotor hub  14  to the edge of the vane face  17   a . As seen in  FIG. 3 , for example, the angle of the vane face  17   a  at a location nearest the spar ring  16  is 43 degrees relative to a radian r 1  projecting from the rotor hub  14  to a first edge location of the vane face  17   a , whereas the angle of the same vane face  17   a  at an edge location furthest from the spar ring  16  is 30 degrees relative to a radian r2 similarly projecting from the rotor hub  14  to the edge of the vane face  17   a . As a result of the change in angle of the vane face  17   a , the vane face  17   a  strikes the pulp material, or other material being mixed, less consistently and with less mixing or agitation effect because the relative angle of the vane face  17   a  lessens as the vane  17  extends further from the spar ring  16 . That is to say, the pulp material, or other material being mixed by the vane  17  by striking the vane face  17   a , is less likely to be mixed with the same consistency or force by the straight vane  17  as the rotation of the rotor  15  occurs because the lessening relative angle of the vane face  17   a  encourages the materials being mixed to simply slide along the vane face  17   a  of each vane  17  and outward from the rotary path of the vanes  17 . Thus, the pulp, or other material being mixed, in conventional straight vane rotor systems tend to be ineffectively directed out of contact with the vane faces  17   a  and out of the rotary path of vanes  17 , resulting in a more time-consuming mixing of the materials being required in order to achieve a desired defibering, for example, effect. The additional mixing time due to the inefficiencies of straight vane rotors requires additional power consumption to operate the rotor until the desired defibering effect on the materials is achieved.  
         [0009]     Further, the bluntness of the leading edge of straight vane face  17   a  subjects the vane faces  17   a  to considerable wear as mixing of materials occurs. To compensate for the wear induced by the agitation of materials on the leading edge of straight vane faces  17   a , prefabricated wear plates are often separately welded onto the leading edge of the vanes  17 . Such straight vane face pulper rotors  15  with welded wear plates may be relatively easy to make, however, they tend to have some of the same inefficiencies at pumping materials in desired directions or capacities due, at least partially, to the changing relative angle of contact of each vane face  17   a  with the pulp, or materials, being mixed as discussed above. Further, the requirement of welding wear plates onto the vanes  17  limits the materials that can be used to those compatible with the underlying material chosen for the vane. Such compatibility requirements may limit the choice of vane materials to those that are generally not the most wear-resistant type materials in order for the wear plates to be successfully welded onto the vanes. Still further, because of the welding aspect of the wear plate, it is often required to change the entire vane, at least, even when only the wear plate is all that is worn.  
         [0010]     Moreover, straight vane face rotors can be difficult and economically inefficient to repair, replace or maintain. For example, often removal of the entire rotor is required in order to replace, repair or service just a vane or just a wear plate. The removal of an entire rotor may require additional personnel, and may result in significant inoperable time of the pulper, or mixer, in general.  
         [0011]     To address the inefficiencies of straight vane face rotors, booster vanes  18 , as shown in  FIG. 2 , are frequently used. Such booster vanes  18  are also typically welded to the top of the straight vanes  17  to add an additional material contacting face and to increase pumping efficiencies. The use of booster vanes  18  still does not render straight vane face rotors optimally efficient however, as the additional materials and production costs render such straight vane rotors  15  with booster vanes  18  more costly to manufacture. Further, even with booster vanes  18 , some materials are already directed away from the vanes  17 , in general, by the material&#39;s initial impact with the straight vane face  17   a  as discussed above. Such booster vanes  18  also require increased power requirements to achieve increased pumping capacities. Thus, any pumping efficiency added by the booster vanes  18  may well be offset by the added manufacturing and added operational costs incurred with straight vane rotors having booster vanes  18 . Further, the introduction of yet another additional part, represented by the booster vane  18 , increases the costs and time required for maintenance, repair and/or replacement, while still experiencing the inconvenience of having to remove the entire rotor  15  to perform such repair, replacement or maintenance functions. Further still, such booster vanes  18  result in the gulleys  17   c  being particularly susceptible to cavitation wear as a result of the increased turbulence of materials flowing in the wake of the booster vane  18  induced agitation of the pulp stock, or other material, being mixed.  
         [0012]     As with the inefficiencies experienced by the changing angle of the vane face relative to the series of radians r n  projecting from the rotor hub  14 , straight vanes  17  also have a varying intersection angle relative to the underlying bedplate  13  of the conventional pulper rotor  15 . The interface of the pulp stock, or other material, agitated by the vanes  17  of the rotor  15  and pressed downward toward the bedplate  13  results in the desired defibering, for example, of the pulp, or other materials, as the liquefied matter passes, as if strained, through apertures  13   a  of the bedplate  13  (see  FIG. 4 ). Thus, because the intersection angle of the vanes  17 , relative to the bedplate  13 , changes as the vanes  17  extend across the bedplate  13 , the pressure imposed upon the pulp stock, or other material, from the vanes  17  is not consistently applied to the materials from the inner diameter to the outer diameter of the bedplate  13 . As a result, defibering efficiency is less than optimal.  
         [0013]     The inefficiencies of such straight vane rotors with respect to pumping and defibering inefficiencies, even with booster vanes, and the susceptibility of straight vane rotors to high wear zones and maintenance, repair or replacement inconveniences, pose problems the improved pulper, or mixer rotor, as set forth herein, is designed to help overcome. Further the power consumption inefficiencies of straight vane rotors may be minimized by the improved pulper, or mixer rotor described herein which helps eliminate the need for such booster vanes, and performs similar mixing of materials in less time, while requiring less power.  
       SUMMARY OF THE INVENTION  
       [0014]     This invention provides an improved pulper, mixer or defibering, rotor having a spar ring attached to a hub of the rotor with a series of curved vanes projecting from the spar ring. The curved vanes have a constant vane face angle relative to radians immediately adjacent one another and extending outward from the hub of the rotor. As a result of the constant relative vane face angle, the pulp, or materials, mixed by the vanes of the rotor are more consistently in contact with the vanes during rotation of the rotor. Thus, booster vanes are not required. As a result, increased circulation and pumping effects with minimal power requirements are achieved.  
         [0015]     This invention separately provides a series of curved vanes having vane faces with substantially similar, or preferably equal, surface volumes. As a result of the substantially similar, or preferably equal, vane face surface volumes, the paper pulp stock, or other materials, being mixed by the vanes in the pulper tub, or vat, remains in contact with the vane face of each vane for a prolonged period as circulation occurs.  
         [0016]     This invention separately provides the series of curved vanes projecting from the spar ring as separately attachable to the spar ring via spar stubs. The spar stubs are made of a high strength material integral with the spar ring, whereas the separably attachable vanes are made with a highly wear-resistant material. As a result of the separably attachable nature of the vanes to the spar stubs, maintenance is easier as the vanes may be repaired or replaced without requiring removal of the entire rotor. Further because the vanes are separably attached, rather than welded, a greater variety of highly wear-resistant materials are available to form the vanes. As a result of the high strength spar ring and spar stubs, the need for additionally welded wear plates and/or booster vanes are not required, thus minimizing weight and power consumption. As a result of the highly wear-resistant material, the circulation and pumping effectiveness of the vanes and rotor continue longer, reducing the need for repair or replacement. As a further result of the separably attachable vanes, the opportunity to change configurations of the vanes to meet changing customer needs is also more readily available.  
         [0017]     This invention separately provides vanes having an endplate feature that improve the tip suction pulse effect, which recirculates the paper pulp stock, or other material, more easily in the pulper tub, or vat, until the desired defibering, for example, is achieved.  
         [0018]     These and other features and advantages of this invention area described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Various exemplary embodiments of the systems and methods of this invention will be described in detail with reference to the following figures, wherein:  
         [0020]      FIG. 1  illustrates a conventional pulper;  
         [0021]      FIG. 2  illustrates a conventional straight vane faced rotor with booster vanes;  
         [0022]      FIG. 3  illustrates a vane face angle of a conventional straight vane faced rotor relative to a radian originating from a rotor hub;  
         [0023]      FIG. 4  illustrates an improved rotor mounted above a perforated bed-plate according to at least one exemplary embodiment of the invention;  
         [0024]      FIG. 5  illustrates a bottom view of an exemplary embodiment of an improved rotor according to the invention;  
         [0025]      FIG. 6  illustrates another embodiment showing a different mounting of the vane to a spar ring;  
         [0026]      FIG. 7  illustrates an exemplary embodiment of a single vane according to the invention;  
         [0027]      FIG. 8  illustrates a vane face angle of the improved rotor referred to in  FIG. 4  relative to a radian originating from the rotor hub;  
         [0028]      FIG. 9  illustrates another exemplary embodiment of a spar stub and vane according to the invention;  
         [0029]      FIG. 10  is a schematic view of a composite vane in accordance with another embodiment of the invention; and  
         [0030]      FIG. 11  is a schematic view of another vane structure. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0031]     The conventional pulper tub, or vat,  10  shown in  FIG. 1  shows generally the type of pulper tub, or vat,  10  with which the various exemplary embodiments of the improved pulper, mixing or defibering, rotor  35  of the invention described herein is intended to be used. Accordingly, like numerals are used, where possible, in describing the various exemplary embodiments of the invention when referring to features translatable with those of the conventional pulper of  FIG. 1 .  
         [0032]      FIG. 4  shows one exemplary embodiment of the improved pulper, mixer or defibering, rotor  35  of the invention. The pulper, mixer or defibering, rotor  35  includes a spar ring  36  that supports a plurality of vanes  37 . The vanes  37  extend generally radially outwardly from the spar ring  36  towards an outer circumference of the perforated bed-plate  13 . The spar ring  36  is mounted about a hub  14  at the center of the bed-plate  13 . The pulper, mixer or defibering, rotor  35  may be driven by a conventional gearing and motor  22  combination, as generally depicted in  FIG. 1 . Rotation of the vanes  37  of the pulper, mixer or defibering, rotor causes paper pulp stock, for example, or other material, to circulate in the tub, or vat,  10 . The circulation of the stock, or other materials, helps achieve the hydraulic shearing effect among the circulating stock, or other materials, as well as the mechanical shearing effect on the stock, or other materials, via the interaction of the rotating vanes  37  against the stationary bed-plate  13  at a bottom of the pulper tub, or vat,  10 . Once the fibers of the paper pulp stock, or other material, are sufficiently broken down, or defibered, for example, the materials pass through apertures  13   a  of the bed-plate  13 .  
         [0033]      FIG. 5  illustrates the underside of an exemplary embodiment of the pulper, mixer or defibering, rotor  35 . The vanes  37  are demountably attachable to spar stubs  38  extending from the spar ring  36 . The spar stubs  38  may be made integrally with the spar ring  36  as shown in  FIG. 5 . Alternatively, the spar stubs  38  may be separably attached, for example welded, to the spar ring  36  as shown in  FIG. 4 . In any event, the spar stubs  38  project, at designated intervals, from an outer circumference of the spar ring  36 . The spar stubs  38  may be made of the same material as the spar ring  36 , or of a different material, in order to provide similar strength and a high degree stability between the spar stubs  38  and spar ring  36 .  
         [0034]     The spar stubs  38 , of the exemplary embodiment shown in  FIG. 5 , include attachment devices  39  for securing the vanes  37  to the spar stubs  38 . The attachment devices may be any of screws, rivets, projections, or other such structures for securing the vanes  37  to the spar stubs  38 . It is noted that those skilled in the art may fashion other coupling arrangements besides the projection/spar stubs  38  that may be received in female grooves or the like shown. For example, the vanes  37  could be designed to have male projections on their i.d. ends adapted for receipt in female concavities provided in appropriate locations on the spar ring  36 . One such alternative coupling design is shown in  FIG. 6 . Here, specifically configured female slots  100  are provided around the periphery of spar ring  36 . Mating male ends  102  of the vanes  37  are snugly fitted in the slots and the joint can be further secured by bolts or the like (not shown) that would be inserted through registered bores  104 ,  106  placed respectively in the female and male parts, and corresponding apertures  108  of the clamp ring  110 . A rotor cap  112  is attached over the assembly to secure to the clamp ring.  
         [0035]      FIG. 7  illustrates an exemplary embodiment of a vane  37 . The vane  37  is separably attachable to the spar stubs by attachment devices  40  corresponding to the attachment devices of the spar stubs. Each vane  37  includes a vane face  37   a  on the leading edge, a trailing edge  37   b  and a spar stub mounting surface  37   c . The vane face  37   a  is provided with a designated vane height h1. The vane height h1 at the vane face  37   a  tapers to a vane height h2 at the trailing edge  37   b  of the vane  37 . The pitch angle of the vane face  37   a  is preferably constant, for example at 30°, to provide a desired pressure to the paper pulp stock, or other materials, being mixed by contact with the vane face  37   a  of the vane  37  upon rotation. The vane  37  may be slid onto the spar stub  38  (see  FIG. 5 ) in order to align the spar stub mounting surface  37   c  of the vane  37  so that the corresponding attachment devices are aligned to secure the vane  37  to the spar stub  38 , and the innermost vane surface  37   d  abuts the spar ring  36  ( FIG. 4 ). The outermost vane surface  37   e  of the vane  37  is generally curved from the vane face  37   a  to the trailing edge  37   b . The interface of the trailing edge  37   b  and outermost vane surface  37   e  of the vane  37  provides a lifting effect that sucks fiber off from the stock, or other materials, being mixed by rotation of the rotor  35 . Note also in  FIG. 7  that the trailing edge of the vane comprises a curved edge  116  radiused downwardly toward the bed-plate surface. This too helps to provide a suction pulse that cleans the bed-plate. Further protruding end dam member  114  is provided along the o.d. extremity of the trailing edge. The end dam doesn&#39;t allow flow to “leak” off the end of the rotor; thereby improving suction and bed-plate cleaning across the entire swept area.  
         [0036]      FIG. 8  shows generally, according to the various exemplary embodiments of the invention, a configuration of the vanes  37  mounted to the spar ring  36  by attachment devices  40 . The vanes  37  are mounted such that the angle between the vane face  37   a  and a radian r 1  extending from the center of the hub  14  towards the outermost circumference of the spar ring  36  is substantially the same as the angle between the vane face  37   a  and any other radian, for example r 2 , similarly extending from the center of the hub  14  and toward the outermost circumference of the spar ring  36  or the outermost vane surface  37   e . By substantially the same we mean that the difference in vane face surface to intersecting radian angle for any two points along the vane face surface should not exceed greater than about 10°. By controlling the angle of the vane face  37   a  relative to the spar ring  36 , more constant contact of the paper pulp stock, or other materials, being mixed is achieved upon rotation of the rotor  35  and vanes  37 . Further, because the vanes  37  may be separably attached to the spar ring  36  by mounting to the spar stubs  38  ( FIG. 5 ), the vanes  37  may be made of a greater variety of materials, such as ceramics, urethanes, or other highly wear resistant and durable materials that previous straight vane faced rotors, for example, were not able to be made of.  
         [0037]     Of course, it should be appreciated that the angles of each of the vane faces  37   a  are not limited to uniformity, rather, the angle of the vane face  37   a  of each vane may be varied to accomplish the desired contact with the stock, or other materials, being mixed. Likewise, the contour or shape of the vanes  37  may be varied even though mounted on the same spar ring  36 , such that one vane  37  may be smooth, and another vane  37  may be toothed, for example, or otherwise not smooth, in order to achieve different pulping, mixing or defibering, actions. Similarly, vanes  37  of different lengths may be mounted on the same spar ring  36  to achieve different pulping, mixing or defibering, actions as well.  
         [0038]     Certain advantages of the various exemplary embodiments of the rotor  35  using the separably mounted vanes  37  of the invention versus standard, or conventional, rotors may occur. For example, the various exemplary embodiments of the rotor  35  and vanes  37  will achieve the same thrust (Th) using significantly less horsepower (hp) than standard, or conventional, rotors. As a result, not only will more stock, or other materials, be in contact with the vane face  37   a  of the vanes  37 , as described with reference to  FIG. 7 , for example, but the efficiency of the pulping, mixing or defibering will be increased as well while less power will be used as evidenced by higher thrust/horsepower ratios (Th/hp) than conventional designs. Additionally, a greater volume, or quantity, of stock, or other materials, may be pulped, mixed or defibered per unit time (sec) as would be evidenced by the quantity to time ratio (Q).  
         [0039]     Thus, not only are the various exemplary embodiments of the separably attached vanes more efficient, they also are more durable and wear resistant due to the choice of materials available to comprise each vane  37 . Moreover, even were replacement or repair of the vanes  37  required, such replacement or repair is relatively easy as the rotor  35  may be left in the pulper tub, or vat,  10 , for example, whereas prior art conventional rotors require the complete removal of the rotor in order to work only on the vanes, or other vane related components, for example.  
         [0040]      FIG. 9  illustrates another exemplary embodiment of the vanes  47  according to the invention. The vanes  47 , according to the exemplary embodiment shown in  FIG. 10  differ from the vanes  37  shown in  FIG. 7 , which illustrate vanes  37  having a continuous trailing edge  37   b  extending from the innermost vane surface  37   d  to the outermost vane surface  37   e  and integral with each vane  37 . As a result, the vanes  37  are mounted by sliding over the spar stubs  38 , in a generally perpendicular direction relative to the spar ring  36 , towards the spar ring  36 . The exemplary embodiment of the vanes  47  shown in  FIG. 9 , on the other hand, provides spar stubs  48  joined at one end to the spar ring  36  and having an outer end  48   a  opposite the spar ring  36 . Each spar stub includes a first trailing edge portion  48   b  extending from the spar ring  36  to an outer end  48   a  of the spar stub  48 .  
         [0041]     A vane  47  having a vane face  47   a  and a second trailing edge portion  47   b  is slidingly mounted over each spar stub  48 , in a generally lateral direction relative to the spar ring  36 , such that the first trailing edge portion  48   b  of the spar stub  48 , and the second trailing edge portion  47   b  of the vane  47 , are immediately adjacent one another to form the equivalent of the unified trailing edge  37   b  of the exemplary embodiment described with reference to  FIG. 7  above. Once aligned appropriately over the spar stub  48 , the vane  47  is attached to the spar stub  48  in a manner as described with reference to the exemplary embodiments discussed above.  
         [0042]     The vanes  47  of the exemplary embodiment illustrated in  FIG. 9  have vane faces  47   a  of a constant pitch angle such that the stock, or other materials, being mixed are more readily contacted by the vane face  47   a  as the rotor  35  and vanes  47  rotate. Likewise, the vane  47  tapers from a height h1 at the vane face  47   a  to a height h2 at the combined trailing edge formed of first trailing edge portion  48   b  and second trailing edge portion  47   b.    
         [0043]     The vanes  47  thus provide similar advantages to those described with reference to the exemplary embodiments discussed above. Such advantages include the greater choice of materials to form the vanes  47 , more flexibility in the arrangement of vanes  47  on the spar ring  36 , greater contact area and contact time of the materials being mixed with the vane face  47   a , decreased power requirements, and easier accessibility for maintenance and repair of the vanes  47 .  
         [0044]     An alternative vane structure is shown in  FIG. 10 . Here, the face  37   a  of the vane comprises a wear plate  118  made of a hard metal that is, for example, investment cast to the desired shape. The trailing body section  214  of the vane may be formed from a filler/bonding material. As shown, spar stub  38  is partially in phantom and includes a male mounting end  116  adapted for reception in a female recess or the like in the spar ring (not shown). The body section  214  may hold the face plate and spar stub  38  together and provide the required hydraulic profile. Body section  214  may be composed of an urethane/epoxy but could also be a bi-metal cast process.  
         [0045]      FIG. 11  illustrates another unique aspect of the invention. Here, the id. surface of the vane is shown at  140  with the o.d. surface depicted as  142 . One inner length of the vane shown at  150  is shorter than an outer vane length shown at  152 . The vane length in this embodiment increases progressively from inner vane location toward outer vane location. In operation, this vane length/section increases as the peripheral shield of the vane location increases to improve performance and reduce drag.  
         [0046]     It is apparent that the vane member shown in  FIG. 11  is streamlined to enhance operational performance. The vane member is adapted for radial disposition on a hub or the like in a pulp and paper apparatus. The vane member is rotatable around a central axis that extends through the hub and the vane has an inner-end adapted for positioning adjacent to the hub at an opposing outer edge at an outer radially directed extremity of the vane. The vane comprises a leading edge  190  and a trailing edge  192 . The vane lengths are shown at  150  and  152  and they are defined as the distance between the leading edge and the trailing edge at given points along a continuum  160  that extends in the radial direction from the inner-end of the vane to the outer-end. In accordance with this aspect of the invention, the vane length increases as one proceeds along the continuum from the inner-end to the outer-end.  
         [0047]     In operation, with any of the exemplary embodiments of the improved pulper, or mixer, rotor  35  described herein, including the spar ring  36 , spar stubs  38  or  48 , and vanes  37  or  47 , paper pulp stock, or other material, is placed into the pulper tub, or vat,  10 . The motor  22  is then operated to drive the gear  20 . The gear  20  engages the hub  14 , to which rotor  35  is mounted. The rotation of the rotor  35  therefore causes the vanes  37  or  47  to rotate in a direction such that the vane face  37   a  or  47   a  contacts the stock, or materials, initially. As rotation of the rotor  35  and vanes  37   a  or  47   a  occurs, more consistent contact of the stock, or materials, with the vane face  37   a  or  47   a  is maintained resulting in increased agitation and mixing of the materials. In addition, the trailing edge  37   b , or the combined first trailing edge portion  48   b  of the spar stub  48  with the second trailing edge portion  47   b  of the vane, helps lift fibers, for example, from the stock, or materials, being mixed such that defibering is achieved. The defibered materials, for example, are then passed through the apertures  13   a  ( FIG. 4 ) in the bed-plate  13  underlying the rotor  35  at the bottom of the tub, or vat,  10 .  
         [0048]     In summary, one aspect of the invention is directed toward the combination of demountable vane members that are adapted to be mounted over and carried by the spar stubs with the spar stubs being fixed to the annular spar ring by welding or the like. The demountable vanes may be composed of any one or more of a variety of wear resistant materials such as for example, wear resistant initial such as “stellite”, cast cobalt alloys, polyurethanes, even ceramic materials.  
         [0049]     In another aspect of the invention, each of the leading surfaces of the vanes presents a substantially constant angle relative to at least two radians that extend from the rotor axis to any two points located along that leading cage. By “substantially constant”, we mean that this angle should not vary by more than about 10°. It is generally desirable than this angle, as measured between the axis and to a point or tangent along the leading edge should be between about 10° to about 60°, preferably about 300 to about 40°. In many cases, it will be advantageous if each of the vanes (and their corresponding leading edges) possesses this same leading edge angle.  
         [0050]     While the invention has been described with reference to the exemplary embodiments set forth herein, it should be appreciated that other alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the preferred embodiments of this invention, as set forth above, are intended to be illustrative only, and not limiting. Various changes can be made without departing from the spirit and scope of this invention.