Abstract:
A blade ( 20 ) for wiping water from a sleeve ( 26 ) mounted on a press roll ( 14 ) in a paper making machine is adjustably mounted on the machine for movement toward and away from the sleeve ( 26 ). The wiper blade ( 20 ) is positionable against the surface of the sleeve ( 26 ) to wipe water therefrom adjacent and upstream from the nip between the sleeve ( 26 ) and a mating press roll ( 12 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to paper making machines and, more particularly, to press rolls employed in paper making machines and, most particularly, to an apparatus for removing water from the shoe press sleeve or belt in the press section of a paper making machine.  
         BACKGROUND OF THE INVENTION  
         [0002]    Paper, linerboard, and other sheet products produced from cellulose fibers are produced in a paper making machine by depositing an aqueous slurry of cellulose fiber containing various additives from a head box on a fabric screen to form a cellulose mat. Water is extracted from the slurry via vacuum boxes positioned below the fabric leaving a mat or sheet of cellulose fibers on the fabric. The mat is then transferred to a continuous press felt. The felt and mat are then run to a first pair of nip rolls, commonly referred to as a top press roll and a bottom press roll. Additional water is extracted from the mat as it passes between the top and bottom press rolls. A polyethylene sleeve or belt is mounted on one of the press rolls, typically the top press roll. Circumferential grooves are provided in the sleeve to allow the water being squeezed from the mat to travel laterally and thus extract it from the mat. Some of this water is removed from the grooves by the centrifugal force created by the spinning top press roll.  
           [0003]    However, it has been observed that water may still puddle ahead of the nip between the press rolls. The presence of this water detracts from the performance of the press rolls. It is therefore desirable to reduce or eliminate the puddling that occurs ahead of the nip between the press rolls. Heretofore, however, the origin of the water that puddles ahead of the nip and how to remove that water have not been fully understood.  
         SUMMARY OF THE INVENTION  
         [0004]    It has now been recognized that despite removal of water from the top press roll by centrifugal force, much water still remains on the surface of the rolls and particularly in the circumferential grooves in the sleeve. The present invention removes this water from the surface and the grooves by providing a means for wiping the surface of the grooved sleeve. This is accomplished with a top press roll wiper blade mounted in a bracket, which in turn is mounted on the paper making machine framework. The wiper blade has an edge that is positioned in contact with the surface of the sleeve upstream from the nip between the top and bottom press rolls. As the top press roll spins in the direction of the wiper blade and the nip, the wiper blade removes water from the surface of the sleeve and, moreover, removes water from the circumferential grooves in the sleeve. In a preferred form of the invention, the wiper blade is mounted for movement toward and away from the sleeve so as to allow for varying the pressure of the wiper blade on the sleeve and for retracting it from contact with the sleeve when it is not needed, or for repair or replacement. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0006]    [0006]FIG. 1 is a schematic view of top and bottom press rolls in a paper making machine along with a preferred form of the wiper blades constructed in accordance with the present invention;  
         [0007]    [0007]FIG. 2 is an enlarged side view of the wiper blade shown in FIG. 1;  
         [0008]    [0008]FIG. 3 is a top view of a segment of the wiper blade and mounting mechanism shown in FIG. 2; and  
         [0009]    [0009]FIG. 4 is an illustration of a top press roll, a wiper blade, and a trough constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]    Referring first to FIG. 1, the first set of press rolls  10  of a press section of a conventional paper making machine is shown in phantom. The press section of a conventional paper making machine may have more than one set of press rolls. The bottom press roll  12  is usually mounted on the paper making machine framework for rotation in a counterclockwise direction. The top press roll  14  is mounted for rotation in a clockwise direction. The top press roll is conventionally mounted so that it can be moved up and down, that is, toward and away, from the bottom press roll  12 . A felt  18  forming part of the press carries a mat of cellulose fibers between the nip  16  of the top and bottom press rolls. In this view, the paper mat is omitted for purposes of simplicity. The top press roll  14  normally carries a sleeve (shown in FIG. 2 as  26 ) that carries a plurality of circumferential grooves that assist in extracting water from the mat of cellulose fibers being run through the nip  16  between the rolls  12  and  14 . A wiper blade  20  constructed in accordance with the present invention is mounted on a blade mounting assembly  22 , in turn mounted on framework  24  of the paper making machine.  
         [0011]    Referring now to FIGS. 2 and 3, the blade  20  is positioned against the grooved sleeve  26  forming part of the top press roll  14 . The blade  20  itself is an elongated member that is at least the length of the sleeve  26 . A cross-sectional profile shows the blade coming to a sharp edge at the instance where it contacts the sleeve  26 . The opposite edge of the blade is fixed to the mounting assembly  22  as described further below. Although the blade is shown as a straight edge, in other embodiments the blade edge may be profiled to match the groove profile in the sleeve. For grooved sleeves, the blade edge would then be provided with protrusions to match the profile of the grooves. Groove profiles may be trapezoidal, square, U-shaped, or any other profile. It is also to be appreciated that other surface patterns besides grooves may be machined on the sleeve. For example, a drilled pattern sleeve can be used in place of a grooved sleeve. The blade assembly  22  has a first section  30  that is pivotally attached to a second section  32 . Opposing flanges  34  and  36  extend from the first and second sections  30  and  32 , respectively, and are coupled together by a pivot pin  38 . The axis of the pivot pin  38  is substantially parallel to the rotational axis of the top press roll  14 . The blade  20  is secured in the first section  30  of the bracket by conventional fasteners, such as bolts  40 . The second section  32  of the blade mounting assembly is affixed to an L-shaped bracket  42  by a conventional fastener  44  such as a bolt. The L-shaped bracket  42  has an upright arm  42   b  and a generally horizontal arm  42   a , which rests on a horizontal surface  46  forming part of the main framework  24  of the paper making machine. The L-shaped bracket  42  is mounted for movement toward and away from the press roll  14  in the direction of arrows  48 . A jack screw assembly  50  is employed to adjust the position of the L-shaped bracket relative to the top press roll  14 . The screw  50   a  is rotatably mounted in flange  52  attached to framework  24 . A threaded nut  50   b  is affixed to bracket  42 . A lock nut  53  is employed to lock the screw  50   a  to the nut  52   b . The jack screw mechanism provides a gross positioning of the blade mounting assembly  22  relative to the press roll  14 .  
         [0012]    The entire blade assembly and captive blade extend the entire length of the top press roll  14 . Only one end portion of the blade  20  and mounting assembly  22  is shown in FIG. 3. Several of the jack screw mechanisms  50  are placed at intervals along the length of the blade mounting assembly. In a preferred installation, it is preferred that the blade  20  be mounted less than about 90 degrees from the nip  16  of the top press roll  14 .  
         [0013]    The blade mounting assembly  22  also has a pair of bladders  54  and  56  mounted between the first and second sections  30  and  32  and above and below the pivot pin  38 . The bladders are coextensive in length with the blade mounting assembly  22 . Selective inflation of the bladders  54  and  56  allows the first section  30  to be pivoted to and fro so that the blade  20  can be moved toward and away from contact with the surface of the sleeve  26  and so that variable pressure can be applied by the leading edge blade of the wiper blade  20  against the surface of the sleeve  26 . In other embodiments, the bladders  54  and  56  can be replaced with other equally suitable biasing devices, including leaf or coil springs. In a preferred embodiment, the blade mounting assembly is constructed so as to allow movement of the blade toward and away from the surface of the sleeve  26  of the top press roll  14  from one to two inches. The blade load may be adjusted so that loads on the order of 0.2 pounds per linear inch (PLI) (36 grams per cm) can be applied by the blade against the surface of the press roll sleeve  26 .  
         [0014]    In a preferred embodiment, the sleeve  26  of the top press roll is preferably comprised of polyethylene. The grooves in the sleeve  26  are conventionally machined into the surface of the polyethylene. It is also preferred that the blade  20  also be made of polyethylene. Thus, when the blade is brought into contact with the press roll sleeve  26 , a minimum of frictional wear is created. Without the wiper blade of the present invention, the sleeve appears to be free of water. However, when the blade is positioned against the sleeve, substantial amounts of water are removed. Measurements have shown that on the order of an additional 66 gallons of water per minute are removed from a sleeve in the press section of a paper making machine running at an overall output of 58 tons per hour of paper. This results in substantial overall energy savings in the paper making process because the amount of water that is removed from the sleeve is not required to be evaporated from the fiber mat at a later stage.  
         [0015]    Referring now to FIG. 4, one embodiment of the present invention is illustrated, whereby a trough  50  is located below the blade  20 . The trough has a lower base  56  surrounded by peripheral walls  58 , thus forming a collection basin for water that may run off from the outboard side of the blade  20 . The water is indicated by arrows  52 . The trough  50  has sufficient width to also collect water that may run off from the inboard side of the blade  20 , said water run off being indicated by arrow  54 . Lengthwise, the trough  50  is at least as long as the blade  20 . The trough  50  has sufficient volume to contain the expected water collection from the sleeve surface  26  and the sleeve grooves  26   a . The trough  50  is inclined, meaning that one end of the trough is at a higher relative position than its opposite and lower end. At the lower end, a pipe  60 , or other suitable conduit, may be connected to channel away the collected water from the roll. The trough  50  may be positioned at any location below the blade  20 . However, in one embodiment, the trough is located below the machine framework  24 . In this manner, any water that is collected from the sleeve  26  and the sleeve grooves  26   a  may be captured and discarded from the process.  
         [0016]    The invention may be incorporated into any paper making process that produces paperboard, linerboard, and/or any other sheet products produced from cellulose fibers that are formed into a fiber mat. The process includes depositing an aqueous slurry of cellulose fiber containing various additives from a head box onto a fabric screen to form a cellulose fiber mat. Water is extracted from the slurry via vacuum boxes positioned below the fabric screen leaving a fiber mat or fiber sheet of cellulose fibers on the fabric. Paper making machines having a press roll system often include more than one pair of nip rolls. After forming, the fiber mat or sheet is then transferred to a continuous press felt. The felt and the mat are run through the press roll system to a first pair of nip rolls. The nip rolls are also referred to as a top press roll and a bottom press roll. As mentioned previously, the press roll system can include a plurality of pairs of nip rolls. Water is further extracted from the fiber mat or sheet as it passes between the pairs of top and bottom press rolls. The present invention can be incorporated into any one top or bottom press roll or both and in one or more pairs of press rolls in the press roll system. Any roll that is provided with a surface patterned sleeve can be modified to incorporate the wiper blade in accordance with the present invention. The water is removed from the fiber mat or sheet by the wiper blade assembly in accordance with the invention, thus producing a fiber mat of reduced water content before further processing, meaning less water than would ordinarily be expected will need to be evaporated from the fiber mat or sheet.  
         [0017]    While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. For example, one of ordinary skill will recognize that, alternatively or in addition, a grooved sleeve can be mounted on the bottom press roll. A wiper blade constructed in accordance with the present invention can be positioned to contact such a sleeve upstream from the nip and remove water from the sleeve so positioned.