Abstract:
The invention relates to a method for refining cellulose fibers in aqueous suspension, using a plurality of refiner fillings having refining edges, of which one is operated on at least one stator and another is operated on at least one rotor, and the suspension to be refined is processed between the two refiner fillings. A partial flow of the suspension delivered to the outlet side flows back on the back side of the refiner filling on the stator side, and then flows through openings located between the refining edges of the refiner filling on the stator side, and again into the refining zone. This leads to particularly uniform and economical refining.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of PCT application No. PCT/EP2009/004739, entitled “METHOD FOR REFINING CELLULOSE FIBERS IN AQUEOUS SUSPENSION AND REFINER FILLING FOR PERFORMING THE SAME”, filed Jul. 1, 2009, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method for refining aqueous suspended cellulose fibers whereby these fibers are carried in an aqueous suspension between refiner fillings each of which are equipped on their face side with refining edges and which are located either on a rotor or a stator providing rotational movement relative to each other and which are pressed against each other, whereby mechanical refining is transferred onto the cellulose fibers and whereby suspension is delivered to the inlet side of refiner fillings and is then discharged again from outlet side of refiner fillings. 
         [0004]    2. Description of the Related Art 
         [0005]    It has been known for a long time that cellulose fibers, that is virgin cellulose fibers or waste paper fibers, are refined so that the subsequently produced paper has the desired characteristics, especially strength, formation and surface. Refining processes of the type considered here have utilized refining tools which are often equipped with bars referred to as blades and which can generally be screwed to the rotor or stator of the refiner. The refiner tools are generally referred to as fillings. The relevant machinery is known as refiners. The method may typically be accomplished by disk refiners or cone refiners. 
         [0006]    Refiner fillings for refining of cellulose fibers, utilizing refiner bars and grooves located between them are known for example from DE 20 2005 007 551 U1. 
         [0007]    DE 37 00 613 A1 describes disk refiners for processing of a fibrous suspension in paper production, whereby rotor and stator fittings are equipped with axially oriented openings. This divides the suspension which is to be refined into many axial partial flows, refines it and discharges it from the refiner. A similar principle is also employed in the method addressed in DE 10 2004 039 986 A1. 
         [0008]    What is needed in the art is a method of cellulose refining which would provide uniform and particularly economical refining, in other words one in which the desired technological refining changes are as uniform as possible on all fibers. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a method for refining aqueous suspended cellulose fibers whereby these fibers are carried in an aqueous suspension between refiner fillings each of which are equipped on their face side with refining edges and which are located either on a rotor or a stator providing rotational movement relative to each other and which are pressed against each other, whereby mechanical refining is transferred onto the cellulose fibers and whereby suspension is delivered to the inlet side of refiner fillings and is then discharged again from outlet side of refiner fillings, characterized in that a partial flow of suspension which was delivered to outlet side flows through at least one hollow chamber located on backside of stator-side refiner filling and then through openings which are located between refining edges of stator-side filling to refining edges of this refiner filling. 
         [0010]    The present invention further provides a refiner filling to implement the method described in the preceding paragraph, with an inlet side and an outlet side for suspension between which refiner edges suitable for refining suspension are located, characterized in that it has at least one, preferably several hydraulic connections between outlet side and refiner edges through which the suspension can get from outlet side to refiner edges. This refiner filling is especially suitable for the method of the present invention. 
         [0011]    A considerable number of various refiner fillings has already been developed, which differ from each other in regard to blade width, number of blades and angle of blade edges relative to the radius. However, the inventive method contributes to a substantial improvement since it offers the possibility to direct the suspension flow so that an additional possibility of influence upon the refining effect provided by the refiner is created. In particular, the return flows inside the stator-side fillings are intensified. Already known fillings can here be used on the rotor side. The effect can be explained as follows: 
         [0012]    In a conventional blade type filling the grooves are to be considered as flow channels for the suspension. Here it can be assumed that due to the rotational movement of the rotor and the fibrous stock suspension which is carried along by it, a strong pressure build-up occurs from the inside radial areas to the outside radial areas. Similar action occurs also in rotary pumps, obviously in much stronger form. Because of this pressure differential a backflow of the suspension occurs from radially outside to radially inside in the non-rotating cavities of the stator which are provided according to the invention. This backflow may be influenced by selecting or changing the cross section of the flow-carrying surfaces. On the path which is being taken by the back-flowing suspension inside the cavities, a transfer can occur through the openings which are located between the refining edges of the stator-side refiner filling to the refiner edges of the opposite refiner filling. Since these return flows lead to a repeat of the refining processes, refining becomes more uniform which is of particular advantage, both technologically and economically. The inventive measures can strengthen this transfer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0014]    The invention is further explained with the assistance of and reference to schematic drawings: 
           [0015]      FIG. 1  shows the principle of the inventive method; 
           [0016]      FIG. 2  shows implementation of the method—in this example with a disk refiner; 
           [0017]      FIG. 3  shows an example of inventive refiner filling (section) viewed in direction of the back side; 
           [0018]      FIGS. 4-9  show details regarding the various embodiments of stator fillings; 
           [0019]      FIG. 10  shows a top view of one sector of usable rotor-side refiner filling; 
           [0020]      FIG. 11  shows additional forms for the openings in the stator refiner filling; and 
           [0021]      FIG. 12  shows implementation of the method with a cone refiner 
       
    
    
       [0022]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a schematic sketch of the suspension flows which occur when implementing the inventive method in a double disk refiner with one rotor  9  and two stators  8  and  8 ′. Suspension S which is to be refined is added in a central region of the double disk refiner, gets between rotor  9  and stators  8  and  8 ′ and is carried toward the outside where it is refined. As a result of the rotational movement a strong pressure buildup occurs on the path from infeed side  5  to outlet side  6 , in other words from radially inside to radially outside. The result is that a partial suspension flow S′ returns from radially outside to radially inside. Since stators  8  and  8 ′ are equipped with openings in radial direction, the suspension which flows back comes again into the refining zone. The refined portion S″ flows out of annulus  17  through a connection pipe. 
         [0024]    The arrows for the suspension flows are drawn with hollow tips in all drawings. 
         [0025]      FIG. 2  illustrates a schematically depicted section of a disk refiner suitable for the method. A refiner filling  1  is mounted on a stator  8  and a refiner filling  2  on a rotor  9  which are detachable by means of screws  12 . The rotor-side refiner fillings  2  are blade fillings which are equipped with refiner bars  7 . In the illustrated example suspension S which is to be refined is delivered to inlet side  5  of refiner fillings  1  and  2  through the center of stator  8 . This depiction shows an exaggeration of the distance between refiner fillings  1  and  2 . In operation it only amounts to a fraction of millimeters. Suspension S passes the conspiring refiner fillings  1  and  2 , emerges again on the outlet side, collects in annulus  17 , and a refined portion S″ leaves annulus  17  via an appropriate connection pipe. A partial flow S′ of the suspension flows through a hollow chamber  14  located on backside  11  of the stator-side refiner filling  1  and then through openings  15  which are located between refining edges  3  of stator-side refining fillings  1  to refining edges  3  of this refiner filling  1 . Such surfaces are considered to be refining edges which—in conspiring together with refining edge of an opposing filling (generally rotor with stator fillings)—transfer the refining effort to the fibers. Refining fillings  2  on the rotor side are equipped with refiner bars  7  which represent their refining edges. No return flow of suspension is generated on the backside of the rotor fillings. Rotor  9  is driven by a shaft  13 . Generally known means with which power is generated to press the two refiner fillings against each other are not illustrated. 
         [0026]      FIG. 3  illustrates a refiner filling  1  suitable for the method, shown in direction of backside  11  (see  FIG. 2 ). In order to support refining plate  12  which is equipped with openings  15  a support  10  is provided which can be welded, soldered or detachably connected with refining plate  12 . It may also form a single component with refining plate  12 , for example as shown in  FIG. 5 . Support  10  is open on its radial outer side, whereby the support elements are spoke-like, and are equipped with an enclosed ring on their radial inside. In between are hollow spaces  14 . The design is further clarified by the cross section of the side view in  FIG. 4 , whereby here refining plate  12  and support  10  consist of different components. Refining edges  3  are formed by the edges of openings  15 . 
         [0027]      FIG. 6  illustrates an example where refining edges  3 ′ are formed by refiner bars  7  which protrude from a refining plate  12 ′ which is equipped with openings  15 . This may offer advantages if a great number of refining edges  3 ′ are required. In addition, protruding refiner bars  7  may possibly be better protected against wear and tear. It is advantageous to then close off the grooves located between the refiner bars in radial direction toward the outside. 
         [0028]    Grinding plate  12 ″ in  FIG. 7  is not equipped with the hollow spaces  14  which are open toward outlet side  6 . These hollow spaces  14  are instead integral in stator  8 . Refining plate  12 ″ therefore represents refiner filling  1  which can be screw connected with stator  8 . 
         [0029]    Advantageous measures can be taken in order to take care of the flow of partial flow S′, especially in order to avoid troubling swirls and stagnation points. In particular, additional hydraulic guide elements and guide surfaces are to be provided for this purpose which, based on their shape, allow an as constant and an as loss free transportation of the suspension as possible from outlet side  6  to refining edges  3  or  3 ′. Several options which can be used individually, or in combination with each other, for this purpose are shown in  FIG. 8  and  FIG. 9 . Here, the radial outside of refining plate  12 ′″ is equipped with a rounded protruding turning element  18  which can also have an asymmetrical shape as shown in the detail in  FIG. 9 . In addition, hollow spaces  14  may be equipped with guide elements  19 ,  20 , and  21  which are aligned in a way so that the liquid flowing in hollow spaces  14  is rerouted to openings  15 . The transitions of hollow spaces  14  to openings  15  can be rounded with the assistance of guide surfaces  22 ,  23  and  24  in a way so that the flow can be diverted without a break. The depiction in  FIG. 8  shows a few examples, whereby the pitch (deviation opposite the radius) of openings  15  and their edges cannot be recognized. 
         [0030]    It must also be considered that a wear and tear zone  25  exists on the upper areas of refining edges  3  where possibly the flow caretaking measures would not be advantageous. 
         [0031]      FIG. 10  shows the section of a generally known refiner filling  2  which can be utilized on the rotor side when implementing the method. It contains a plurality of refiner bars  7  between which grooves  26  are located for the transport of suspension S from infeed side  5  to outlet side  6 . Refiner bars  7  are often combined into groups where they are positioned parallel to each other. In a favorable fabrication this would allow for a large number of refiner bars, located at a selectable angle of intersection with the radius. 
         [0032]    As shown in  FIG. 3  the shape of openings  15  which are located between the refining edges can be slotted, at an angle to the radius or precisely in radial direction.  FIG. 11  shows examples of additional forms such as round holes or polygons/squares. Variations in placement and size of openings  15  provide possibilities to influence the distribution of the return flow of the suspension. For example, openings which are located closer to the inside in radial direction can be larger in order to equalize lower pressure of the return flow in that location. 
         [0033]    The current invention not only improves refining with disk or double disk refiners, but also with cone refiners whereby the effect with a steep cone angle is greater than with a flat one.  FIG. 12  shows the method schematically utilizing a cone refiner where rotor  9  is truncated and carries the refiner filling on its circumference. The conspiring refiner filling is located at the periphery of the rotor and is connected with truncated stator  8 . Suspension S is carried in axial direction between the fillings from infeed side  5  to outlet side  6 . The steeper the cone, the greater the pressure build up which is being produced. It can be clearly seen that the refining fillings of stator  8  are provided with hollow spaces  14  and openings  15  in order to return a partial flow S′ from outlet side  6 . The illustration in  FIG. 12  is greatly simplified, is however sufficient to explain the principle of the invention with this example. 
         [0034]    The method can also be arranged so that in addition to the measures, in particular in combination with the measures described in the claims the flow cross section in grooves  26  of refiner filling  2  on the rotor side is changed by different groove width and/or depth. The groove width and/or groove depth therefore increases or decreases from the inside toward the outside. In particular this allows for the pressure build up through rotor  9  and thereby also the return flow in stator  8  to be influenced and to facilitate the transfer of return flow of suspension into the refining zone. 
         [0035]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.