Abstract:
An air press for pressing a fiber web includes a plurality of rolls and a pair of end seal arrangements. Of the plurality of rolls, each pair of adjacent rolls forms a nip therebetween. Further, each roll has a pair of roll ends, the plurality of rolls together forming two sets of roll ends. Each end seal arrangement coacts with one set of roll ends, the plurality of rolls and the pair of end seal arrangements together defining an air press chamber having an air chamber pressure. Each end seal arrangement is composed of at least one roll seal, including a first roll seal, and an adjustable bias mechanism. Each roll seal forms a seal with at least one roll end, and one side of the first roll seal being exposed to the air chamber pressure. The adjustable bias mechanism is configured for controlling a position of each roll seal relative to a respective at least one roll end and for adjusting a seal force between the roll seal and the respective at least one roll end.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to air presses for a papermaking machine, and, more particularly, to end seal arrangements therefor.  
           [0003]    2. Description of the Related Art  
           [0004]    Effective water removal from a paper web is essential to the papermaking process. Various types of presses, using some combination of juxtaposed rolls, have been used for some time now for water removal. Such presses rely on the hydraulic pressure created at the nip between each pair of juxtaposed rolls through which the paper web travels in a given press configuration to drive water from the paper web.  
           [0005]    Various press have been developed which have attempted to add an element of a positive air pressure within the press assembly to more effectively force the water from the paper web. With respect to roll presses specifically, the rolls of the press have been configured to form a chamber with a positive air pressure being supplied therewithin.  
           [0006]    However, the effectiveness of a multi-roll air presses is limited by the degree to which the air chamber thereof can be sealed. The areas of the press where sealing becomes quite crucial are those areas where the paper web and the membrane(s) carrying it do not pass, as the web/membrane(s) combination inherently acts to seal the region of each nip through which it passes. Those regions of the air press through which the paper web/membrane(s) combination does not pass are the opposed lateral ends of each nip and the opposed chamber ends defined by the two sets of roll end associated with the air press. Consequently, an end seal mechanism is provided at each chamber end, each such mechanism having a seal member which contacts each of the roll ends associated with that particular chamber end.  
           [0007]    The ability of the end seal mechanism to efficiently seal a chamber is predicated on the application of a sufficient sealing force so that the seal member thereof maintains sealing contact with each of the roll ends of that chamber end. On the other hand, applying a force thereto that is greater than that needed to maintain a seal will cause the seal member to wear out quicker than is necessary.  
           [0008]    Additionally, current end seal mechanisms do not facilitate adjustments in the positioning thereof or in the force ultimately applied on the seal member thereof. With such systems, retraction of the end seal mechanisms for start-up and/or maintenance is not readily achieved. Additionally, it is difficult to optimize the forces applied to the seal member during start-up to initially achieve a sufficient seal therewith and yet promote a long life thereof.  
           [0009]    What is needed in the art is an end seal mechanism in which the sealing force applied to the seal member thereof can be readily adjusted in order to achieve sufficient sealing while minimizing the rate of wear of the seal member; and an end seal mechanism which permits adjustments in the positioning thereof and in the amount of force placed upon the seal member thereof during various operational stages.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides an end seal mechanism for an air press of a papermaking machine in which the force applied upon the end seal mechanism is independent of the air pressure inside the air press, the sealing force placed thereupon and the position thereof instead being controlled by an adjustable bias mechanism.  
           [0011]    The invention comprises, in one form thereof, an air press for pressing a fiber web, the air press including a plurality of rolls and a pair of end seal arrangements. Of the plurality of rolls, each pair of adjacent rolls forms a nip therebetween. Further, each roll has a pair of roll ends, the plurality of rolls together forming two sets of roll ends. Each end seal arrangement coacts with one set of roll ends, the plurality of rolls and the pair of end seal arrangements together defining an air press chamber having an air chamber pressure. Each end seal arrangement is composed of at least one roll seal, including a first roll seal, and an adjustable bias mechanism. Each roll seal forms a seal with at least one roll end, and one side of the first roll seal being exposed to the air chamber pressure. The adjustable bias mechanism is configured for controlling a position of each roll seal relative to a respective at least one roll end and for adjusting a seal force between the roll seal and the respective at least one roll end.  
           [0012]    In another form, the present invention comprises a method of achieving an end seal in an air press for pressing a paper web. The method includes a series of steps, the first of which is providing a plurality of rolls, each pair of adjacent rolls forming a nip therebetween. Each roll has a pair of roll ends, the plurality of rolls together forming two sets of roll ends. An end seal arrangement is positioned adjacent a respective set of roll ends, the plurality of rolls and the respectively positioned end seal arrangements together defining an air press chamber having an air chamber pressure. Each end seal arrangement is composed of at least one roll seal, including a first roll seal, and an adjustable bias mechanism. Each roll seal forms a seal with at least one roll end, and one side of the first roll seal being exposed to the air chamber pressure. The adjustable bias mechanism is configured for controlling a position of each roll seal relative to a respective at least one roll end and for adjusting a seal force between the roll seal and the respective at least one roll end. The seal force provided by the adjustable bias mechanism is increased to seat the set of roll ends within the end seal arrangement. Then, the seal force provided by the adjustable bias mechanism is decreased upon seating of the set of roll ends within the end seal arrangement. Finally, a substantially constant low net force is maintained on each roll seal upon the seating and during operation of the air press, the substantially constant low net force being maintained using the adjustable bias mechanism.  
           [0013]    an end seal mechanism in which the sealing force applied to the seal member thereof can be readily adjusted in order to achieve sufficient sealing while minimizing the rate of wear of the seal member; and an end seal mechanism which permits adjustments in the positioning thereof and in the amount of force placed upon the seal member thereof during various operational stages.  
           [0014]    An advantage of the present invention is the seal force applied to the seal member of the end seal mechanism can be readily adjusted in order to achieve sufficient sealing while minimizing the rate of wear of the seal member.  
           [0015]    Another advantage is the end seal mechanism permits adjustments in the positioning thereof and in the amount of force placed upon the seal member thereof during various operational stages, thereby facilitating the optimization of both the forces applied to the seal member during start-up to initially achieve a sufficient seal therewith and the force needed to promote a long life thereof  
           [0016]    Yet another advantage is that the end seal mechanism can be designed so that the total force applied on a seal member is independent of the air chamber pressure in the air press and thus not subject to potential fluctuations in the air chamber pressure.  
           [0017]    An even further advantage is that biasing springs can be eliminated from the design of the end seal mechanism due to the presence of the adjustable bias mechanism. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    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:  
         [0019]    [0019]FIG. 1 is a schematic, side view of an embodiment of a papermaking machine of the present invention;  
         [0020]    [0020]FIG. 2 is a schematic, partially-sectioned, fragmentary view of the end seal arrangement of FIG. 1; and  
         [0021]    [0021]FIG. 3 is a schematic, partially-sectioned, fragmentary view of another embodiment of an end seal arrangement which can be employed in the papermaking machine shown in FIG. 1.  
         [0022]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the invention, in one form, 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 papermaking machine  10  for processing a paper web  12  which generally includes an air press assembly  14  and a plurality of conveyor rolls  16 .  
         [0024]    Air press assembly  14  is constituted of a plurality of press rolls  18  juxtaposed with one another so as to define a plurality of nips  20  therebetween and an air chamber  22  thereamongst. Contacting a set of end faces  24  of press rolls  18  is an end seal arrangement  26  for closing off what would otherwise be an open end of air chamber  22 .  
         [0025]    End seal arrangement  26  is composed of a piston holder  28  (FIG. 2), a seal piston  30 , a seal holder  32 , at least a first seal member  34  and an adjustable bias mechanism  36 . Each end seal arrangement  26 , by closing off an open end of air chamber  22 , further defines air chamber  22 , air chamber  22  having an air chamber pressure associated therewith. Piston holder  28 , seal piston  30 , seal holder  32  and first seal member  34 , by each specifically helping to define the boundary of air chamber  22 , are all exposed to the air chamber pressure.  
         [0026]    Piston holder  28  acts as an outer structural member for end seal arrangement  26 . Piston holder  28  has a holder side wall  38  within which seal piston  30  is movably mounted. A gasket  40  is provided in seal piston  30  adjacent holder side wall  38  to ensure sealing contact therebetween. Seal piston  30  is movably mounted within piston holder  28  so to facilitate both the positioning of and the adjustment of a biasing force B applied on at least first seal member  34 .  
         [0027]    Seal holder  32  extends from seal piston  30  opposite piston holder  28  and holds at least first seal member  34  therein. Seal holder  32  may either be integral with seal piston  30 , as shown in FIG. 2, or attached thereto. First seal member  34  is configured for directly contacting and sealing with end faces  24 . If only first seal member  34  is employed, first seal member  34  would advantageously made of a hard seal material and would be bonded directly to seal holder  32 , in addition to being exposed to air chamber  22 .  
         [0028]    In the embodiment shown in FIG. 2, a further second seal member  42  is provided between and bonded to each of first seal member  34  and seal holder  32 . First and second seal members  34 ,  42  can be considered roll seals as each seals with end faces  24  of press rolls  18 . In this instance where two roll seals are employed, second seal member  42  is advantageously made of a hard seal material, while first seal member  34  is favorably made of a soft seal material. The soft seal material deforms to form an efficient seal interface between end seal arrangement  26  and corresponding end faces  24 . Meanwhile, a hard seal material offers increased stiffness and wear resistance in comparison to a soft seal material. It is thus favorable for at least one of first and second seal members  34 ,  42  to be made of a hard seal material in order to ensure sufficient seal stability and to minimize the rate at which seal wear occurs, as that wear rate is set by the hardest seal material present and in contact with each end face  24 . First and second seal members  34 ,  42  may advantageously be made of a carbon fiber (CF) composite and/or polytetrafluoroethylene (PTFE) (commonly known by its trade name “Teflon®”), respectively.  
         [0029]    First seal member  34  and, if present, second seal member  42  are sized and configured to maintain a separation distance  44  between each end face  24  and seal holder  32  to avoid wearing of seal holder  32 . As such, the time between seal member changes is dictated by the wear time needed to cause separation distance  44  to reach zero.  
         [0030]    In the embodiment of FIG. 2, first seal member  34  and second seal member  42  together define a seal boundary  48 , seal boundary  48  encompassing a pressurized seal area  50  (schematically shown) therewithin. Similarly, inner holder face  52  of holder side wall  38  bounds and thereby defines a pressurized piston area  54  (schematically shown). Since, in the embodiment shown in FIG. 2, pressurized seal area  50  is approximately equal to pressurized piston area  54 , the pressures are balanced throughout seal boundary  48 , advantageously resulting in essentially no net chamber seal force F being applied upon first seal member  34  and/or second seal member  42 , regardless of the air chamber pressure. Under balanced pressure conditions, chamber seal force F is independent of the air chamber pressure.  
         [0031]    In the embodiment of FIG. 2, both seal boundary  48  and holder side wall  38  define a similar dog-bone shape (FIG. 1). It is contemplated that those shapes could differ (e.g., seal boundary  48  could define a dog-bone shape and holder side wall  38 , a circle) as long as the areas encompassed thereby were essentially the same.  
         [0032]    By achieving no net chamber seal force F regardless of air chamber pressure, the risk is avoided of underloading first seal member  34  and/or second seal member  42  in the case of a drop in air chamber pressure and of thus inviting possible leakage and/or slow seal breakage. Likewise, the risk of overloading first seal member  34  and/or second seal member  42  in the case of a rise in air chamber pressure and thus wearing out first seal member  34  and/or second seal member  42  at an even greater rate is also avoided when pressures are balanced. If, for example, pressurized piston area  54  were instead greater than pressurized seal area  50 , chamber seal force F would exist on first seal member  34  and/or second seal member  42  due to the air chamber pressure, chamber seal force F increasing with increasing air chamber pressure. In certain instances, it may prove desirable to have pressurized piston area  54  be slightly greater than pressurized seal area  50  so that a small chamber seal force F and, thus, a sealing function would exist in all operational situations.  
         [0033]    Adjustable bias mechanism  36  is configured for controlling a position of first seal member  34  and, if present, second seal member  42  relative to a respective set of end faces  24  and for providing a biasing force B between each of first seal member  34  and second seal member  42 , if present, and respective end faces  24 . Adjustable bias mechanism  36  is capable of generating the smallest possible biasing force B needed to create a suitable seal between each of first seal member  34  and second seal member  42 , if present, and respective end faces  24 . It is advantageous to apply the smallest possible biasing force B needed to create a suitable seal as seal wear can be minimized thereby.  
         [0034]    Adjustable bias mechanism  36  is advantageously capable of ensuring that first seal member  34  and second seal member  42 , if present, are engaged when air chamber  22  is pressurized; retracting end seal arrangement  26  for startup and maintenance; and regulating biasing force B such that biasing force B is increased during seal break in and decreased once seated to maximize seal life. The ability to retract end seal arrangement  26  when nips  20  are being closed avoids the possibility of first seal member  34  and/or second seal member  42  being broken by end faces  24  catching thereon. Further, since biasing force B is independent of chamber seal force F, even if chamber seal force F is not zero, end seal arrangement  26  can be closed and loaded independently of air chamber pressure. As a result of such independence, such a design can advantageously eliminate the need for springs in the end seal arrangement.  
         [0035]    In the embodiment shown in FIG. 2, adjustable bias mechanism  36  includes an air cylinder  56  and an air cylinder shaft  58 . Air cylinder  56  may either be mounted outside of piston holder  28  (as shown in FIG. 2) or inside thereof (not shown). Air cylinder shaft  58  is selectively driven by air cylinder  56  and operably connects air cylinder  56  with seal piston  30 . If air cylinder  56  is mounted outside of piston holder  28  with air cylinder shaft  58  accordingly extending therethrough, appropriate seals (not shown) are advantageously provided between air cylinder shaft  58  and piston holder  28  to minimize leakage therebetween.  
         [0036]    In operation, end seal arrangement  26  is positioned adjacent a set of end faces  24  of press rolls  18 . Air cylinder  56  of adjustable biasing mechanism  36  is first used to apply an increased biasing force B during break in of first and second seal members  34 ,  42 . Biasing force B is then decreased once seated to a minimum force needed to maintain a sufficient seal between end faces  24  and first and second seal members  34 ,  42  to maximize seal life thereof.  
         [0037]    End seal arrangement  60 , shown in FIG. 3, is a second embodiment of the end seal arrangement of the present invention. End seal arrangement  60  is composed of a piston holder  62 , a seal piston  64 , a seal holder  66 , a first seal member  68 , a second seal member  70  (optional in the same manner as the first embodiment, requiring first seal member  68  to be bonded directly to seal holder  66  if not used) and an adjustable bias mechanism  72 . Each end seal arrangement  60 , by closing off an open end of air chamber  22 , further defines air chamber  22 , air chamber  22  having an air chamber pressure associated therewith. Piston holder  62 , seal piston  64 , seal holder  66  and first seal member  68 , by each specifically helping to define the boundary of air chamber  22 , are all exposed to the air chamber pressure.  
         [0038]    Only those features which differ from those of the first embodiment will be discussed in detail with respect to this second embodiment.  
         [0039]    Piston holder  62 , seal piston  64  and o-rings  74  together define adjustable bias mechanism  72 . Adjustable bias mechanism  72  has an adjustable biasing pressure therein, a net biasing force B 1  produced thereby being a function of the difference between the biasing pressure therein and the atmospheric pressure outside of end seal arrangement  60 . In a manner similar to that for the first embodiment, piston holder  62  encompasses a pressurized piston area  76 , and the combination of first and second seal members  68 ,  70  bounds and thereby defines pressurized seal area  78 , and pressurized piston area  76  is essentially equal to pressurized seal area  78 , thereby producing no net chamber seal force F 1 .  
         [0040]    As such, the only net force placed on first and second seal members  68 ,  70  is one generated by adjustable bias mechanism  72 , i.e., biasing force F 1 . Thus, if the biasing pressure is equal to atmospheric pressure, biasing force B 1  is equal to zero, resulting in no downward force on first and second seal members  68 ,  70 . However, a biasing pressure in excess of atmospheric produces a positive biasing force B 1 , resulting in a downward force on first and second seal members  68 ,  70 . Conversely, first and second seal members  68 ,  70  can be retracted from end faces  24  by applying a less than atmospheric pressure (e.g., a vacuum) within adjustable bias mechanism  72 .  
         [0041]    Other features of the second embodiment which differ from the first are apparent in FIG. 3. Seal holder  66  is separate from seal piston  64  and is attached thereto via a holder attachment mechanism  80  (e.g., a bolt or screw). Using a separate seal holder  66  eases seal member replacement but introduces the requirement of attaining a sufficient seal between seal holder  66  and seal piston  64 .  
         [0042]    Both lateral and vertical movement of seal piston  64  relative to piston holder  62  is limited by piston attachment mechanism  82  (e.g., a bolt or other attachment pin). Piston attachment mechanism  82  extends through seal piston  64  and is mounted in piston holder  62 . Piston attachment mechanism  82  is supplied with a head  84 , head  84  acting as a vertical movement stop for seal piston  64 .  
         [0043]    Additionally, an indicator light  86  (e.g. an LED) is provided on head  84  to act as a visual indicator of a gap and thus a potential leak site between end faces  24  and end seal arrangement  60 . Such an indicator light  86  could also be advantageously employed within the first embodiment.  
         [0044]    Operation of end seal arrangement  60  is similar to that of end seal arrangement  26  with the exception of using a variable biasing pressure within adjustable bias mechanism  72  to produce the desired biasing force B 1 .  
         [0045]    While this invention has been described as having a preferred design, 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.