Abstract:
A pair of refiner members comprises respective refiner bars which cooperate to refine pulp. At least one the refiner bars extends in a spiral pattern for imparting a screw-like pumping action to the pulp. The refiner bars of the cooperating refiner members have different pitch to produce a differential pumping action and increase crossovers between the refiner members in order to improve refining. A sinuous curvature can also be introduced in the spiral pattern to further increase crossovers between the refiner members.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements in apparatuses for refining pulp and to a method for the refining of pulp. 
     2. Description of the Prior Art 
     Pulp refiners of the type comprising a pair of refiner members having opposed facing refining surfaces defining a gap therebetween for receiving a material to be refined are well known in the art. 
     For instance, U.S. Pat. No. 4,874,136 issued on Oct. 17, 1989 to Applicant discloses a pulp refiner comprising a pair of cooperating refiner members having identical plain spiral refining edges. The spiral refining edges face each other and have many intersections, characterized as crossovers. The discs are normally driven at equal rotary speeds but in opposite directions. As a result, a locus of any such crossover moves straight along a stationary line as a radius. 
     Although such cooperating spiral patterns have been found suitable in that they apply a smooth, low-audible, screw-like, sliding-pinching action to the material to be refined, thereby reducing wear of and power consumption, it has been found that when both plain spiral patterns pump outward, the flow is strong but the refining is weak, leaving a deficiency problem for some grades of pulp. 
     SUMMARY OF THE INVENTION 
     It is therefore an aim of the present invention to improve pulp refining using spiral refining patterns. 
     It is also an aim of the present invention to increase crossovers and hydraulic shear. in a refining zone. 
     Therefore, in accordance with the present invention, there is provided a pair of cooperating refiner members having opposed facing refining surfaces defining a gap therebetween for receiving a material to be refined, each said refining surface being formed with alternating grooves and lands, the lands of one refining surface intersecting the lands of the other refining surface to form crossovers therewith, wherein at least one of said refiner member is rotatable, and wherein said grooves and lands defined in said at least one refiner member extend in a continuous spiral pattern of at least one revolution for providing a screw-like pumping action on the material when said at least one refiner member is rotated, said continuous spiral pattern of said at least one refiner member being different from a refining pattern of the other cooperating refiner member to provide additional crossovers and increased hydraulic shear between said refining surfaces compared to refiner members having similar patterns of grooves and lands. 
     In accordance with a further general aspect of the present invention, there is provided a pair of cooperating refiner members, at least one of said refiner member being rotatable and having a sinuous spiral refining pattern defined thereon in order to increase an area of crossovers between said refiner members. 
     In accordance with a further general aspect of the present invention, there is provided a method of refining material, comprising the steps of: providing a pair of refining surfaces having different refining patterns, operating said refining surfaces by rotating at least one of said refining surfaces to impart a screw-like pumping and pinching action to the material to be refined, and introducing the material to be refined between said refining surfaces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: 
     FIG. 1 is a diagrammatic, exploded view of a pair of cooperating refiner discs having different opposed refining surfaces in accordance with a first embodiment of the present invention; 
     FIG. 2 is a diagrammatic, superposed view of the refiner discs of FIG. 1 showing the work-edge intersections thereof; 
     FIG. 3 is a diagrammatic, superposed view of a pair of cooperating refiner discs having different pitch and different spiral directions in accordance with a second embodiment of the present invention; 
     FIG. 4 is a diagrammatic, superposed view of a plain spiral refining pattern and a sinuous spiral refining pattern, the patterns having different pitch but same spiral direction in accordance with a third embodiment of the present invention; 
     FIG. 5 is a diagrammatic, superposed view of a plain spiral refining pattern and a sinuous spiral refining pattern, the patterns having different pitch and spiral directions in accordance with another embodiment of the present invention; 
     FIG. 6 is a diagrammatic, superposed view of a pair of sinuous spiral refining patterns having same pitch and same hand in accordance with a further embodiment of the present invention; and 
     FIG. 7 is a diagrammatic, superposed view of a cooperating pair of different refining patterns in accordance with a further general embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a pair of cooperating refiner discs  10  and  12  adapted to be mounted in a facing relationship on a common axis normal to the disc plane. The material to be refined is received in an adjustable gap  13  defined between the refiner discs  10  and  12 . The refiner discs  10  and  12  are provided with respective opposed working surfaces  14  and  16  adapted to be disposed face-to-face to cooperate in refining the material introduced therebetween. In operation, one of the disc  10  and  12  may remain stationary while the other rotates or, alternatively, both discs  10  and  12  can be rotated in opposite hand directions or at different speeds so as to create shear planes that serves to refine material while the same flows from a central port (not shown) to the periphery of the refiner discs  10  and  12 . 
     The working surfaces  14  and  16  of the refiner discs  10  and  12  each include a series of alternating grooves and lands extending in a continuous spiral pattern of at least one revolution. As diagrammatically illustrated in FIGS. 1 and 2, the working surfaces  14  and  16  thus includes respective plain spiral refining edges  18  and  20  extending continuously and uninterruptedly in a spiral pattern from respective first points  22  and  24  generally centrally of the discs  10  and  12  to respective second points  26  and  28  at the periphery of the discs  10  and  12 . 
     As opposed to conventional pairs of cooperating spiral patterned discs which have the same pitch, i.e. the same distance between lands, the cooperating discs  10  and  12  are formed with spirals of different pitch. Indeed, as best seen in FIG. 1, the spiral of disc  12  has a smaller pitch than that of the spiral of disc  10  and, thus, the spiral of disc  12  has a higher number of turns or revolutions. By using a pair of refiner discs having refining spiral patterns of different pitch, the refining action on the material fed therebetween can be improved, as will be seen hereinafter. 
     As seen in FIG. 2, the discs  10  and  12 , which face one another, have refining edge intersections characterized as “crossovers”. It has been found that by increasing the number of crossovers, for instance, by using cooperating facing spirals of different pitch, improved refining can be achieved. 
     According to the embodiment illustrated in FIGS. 1 and 2, the spirals of the discs  10  and  12  are manufactured with the same hand, i.e. the same direction of spiral, and in view of their facing relationship, the spirals thus extend in opposite directions when they are projected in a plane parallel to the working surfaces  14  and  16 , as seen in FIG.  2 . The discs  10  and  12  are rotated in counter-directions at a same speed, as indicated by arrows  30  and  32  in FIG.  2 . Each disc  10 ,  12  is rotated in a direction opposite to the direction of the spiral thereof so as to provide an outward screw pump action on the material to be refined, thereby forcing the same outwardly towards the periphery of the discs  10  and  12 . Accordingly, both discs  10  and  12  pump outward but at a different rate because of the different pitch of the spiral patterns thereof. The pumping differential causes hydraulic shear which improves refining of material. 
     FIG. 3 illustrates another embodiment of the present invention wherein a pair of cooperating discs  40  and  42  are provided with respective spiral refining edges  44  and  46  of different pitches and opposite hands. The differential in pitch forms more crossovers than when the discs have equal pitches. The discs  40  and  42  are rotated at a same speed in counter-directions, as indicated by arrows  48  and  49 . The rotation hand (direction of rotation) of the disc of lesser pitch, namely disc  42 , is the same as the spiral hand thereof and, thus, disc  42  pumps inward. The rotation hand of disc  40  is opposite to its spiral hand and, thus, disc  40  pumps outward. Since the pitch of disc  40  is greater than the pitch of disc  42 , the outward pumping will exceed the inward pumping, thereby creating high shear on the material discharged at the periphery of the discs  40  and  42 . The resulting additional crossovers and shear increases the refining action produced on the material to be refined. 
     FIG. 4 illustrates another embodiment of the present invention wherein a pair of cooperating refiner discs  50  and  52  are respectively provided with a plain spiral refining edge  54  and a sinuous spiral refining edge  56 , the plain spiral edge  54  and the sinuous spiral edge  56  being of different pitch but same hands. As explained hereinbefore, the differential pitch provides additional crossovers. Furthermore, the sinuous shape of the refiner edge also contributes to provide additional crossovers. As seen in FIG. 4, pockets  60  are formed between the plain spiral edge  54  and the sinuous spiral edge  56 . The ever-changing shapes of the pockets  60  produce an increased number of crossovers and increased shear, which both contribute to improve the refining. 
     The discs  50  and  52  are rotated at a same speed but in opposite directions, as depicted by arrows  58  and  59 . Both discs  50  and  52  pump outward. The differential in pitch causes the disc having the greater pitch, i.e. disc  52 , to pump more than disc  50  which has a smaller pitch. Hydraulic shear is thereby further increased as compared to conventional discs having equal pitches. 
     FIG. 5 represents the mating of a plain spiral refining edge  72  of a disc  70  with a sinuous spiral refining edge  76  of a companion disc  74 , the discs  70  and  74  being rotated at a same speed in opposite directions, as indicated by arrows  78  and  79 , respectively. The spiral refining edges  72  and  76  have different pitch and opposite hands. The sinuous spiral pumps outward while the plain spiral pump inwards. The increased number of crossovers caused by the differential in pitch and the sinuous nature of the spiral  76  both contribute to improve the refining. The increased shear resulting from the pumping differential also contributes to improve the refining. 
     FIG. 6 illustrates a further embodiment of the present invention wherein a pair of refiner discs  80  and  82  having respective sinuous spiral refining edges  84  and  86  cooperate to refine a material fed therebetween. The discs are rotated at a same speed in opposite directions, as indicated by arrows  88  and  89 . The spiral edges  84  and  86  have the same pitch and same hand. Both discs  80  and  82  pump outward at a same rate. However, the refining on the material is improved because of the increased number of crossovers resulting from the sinuous nature of the refining edges  84  and  86 . Moreover, the sinuous spiral refining edges  84  and  86  create pockets  87  which contribute to increase the shear action of the material to be refined, thereby further improving the refining. 
     FIG. 7 illustrates the mating of a plain spiral refining edge  90  of a disc  92  with portions of conventional refiner patterns  94  of a companion disc  96 . The number of crossovers is greater than what is obtained for plain spirals of equal pitch in an equal size apparatus. The discs  92  and  96  are rotated at a same speed in opposite directions, as indicated by arrows  98  and  99 , respectively. The hydraulic shear between the outward flow caused by the centrifugal action of the disc  96  on the material and the inward flow generated by the disc  92  is increased as compared to crossovers and shear using plain spiral of equal pitch. Refining, therefore is improved. 
     In operation, the refining edges act as dams. Therefore, the material advances at the speed of land advance, like a screw conveyor, with material being conveyed mainly in the grooves between the lands. The passage of one work surface against the other maintains a turbulence on the material in the grooves. A lesser amount of material is conveyed during its advance while pinched in the crossovers. Spiral crossovers are much longer than crossovers of conventional refining patterns, whereby spiral crossovers tend to roll material in their pinch rather than to hammer and chop the material. Therefore, the spiral improves the refining by retaining fiber length. 
     Other combinations would be apparent to an artisan. For example, one need not have a rotary pattern on both sides of a refining zone, stationary patterns being common. Using a stator, the rotor must do all the pumping, the flow thereby being less than when two rotors pump outward. A change in pitch from right to left hand may be seen as a change from positive pitch to negative pitch. A zero pitch could be represented by a circle which, of course, could not pump. Thus a stationary pattern, i.e. a stator, could have any chosen pitch, either positive or negative, including a zero pitch. 
     Finally, it is pointed out that the spiral principle according to the present invention, besides being utilized as a plate or disc, can be utilized as a cone.