Abstract:
A device for processing a continuous fiber web includes a membrane, a pressurized enclosure, a tension roll and a guide roll. The pressurized enclosure includes at least a first roll and defines an air press chamber. The first roll partially defines the air press chamber and carries the membrane. The tension roll also carries the membrane and is movable toward and away from the first roll. The guide roll further carries the membrane and is positioned between the first roll and the tension roll. The guide roll has opposite ends, at least one of which is pivotable toward and away from the first roll.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to paper-making machines, and, more particularly, to paper-making machines with an air press system. 
     2. Description of the Related Art 
     Press systems have long been relied upon to aid in the dewatering and in the forming of paper. Mechanical systems employing a series of rolls, shoes, etc. are the most common. More recently, development of air press systems has begun. 
     Semipermeable membranes have been used to convey paper webs since such membranes provide channels through which water may be conveyed away from a paper web. An example of such a membrane in the form of a laser drilled forming fabric is described in U.S. Pat. No. 5,837,102 (Graf), entitled “Perforated and Embossed Sheet Forming Fabric,” issued Nov. 17, 1998, which is assigned to the assignee of the present invention and herein incorporated by reference. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for processing a continuous fiber web that provides a guide roll for controlling a lateral position of the membrane on a fiber web roll and provides a tension roll for controlling a degree of slack and thus, conversely, an amount of tension in the membrane. 
     The invention comprises, in one form thereof, a device for processing a continuous fiber web that includes a membrane, a pressurized enclosure, a tension roll and a guide roll. The pressurized enclosure includes at least a first roll and defines an air press chamber. The air press chamber has a perimeter with the first roll partially defining that perimeter. Additionally, the first roll carries the membrane. The tension roll also carries the membrane and is movable toward and away from the first roll. The guide roll further carries the membrane and is positioned between the first roll and the tension roll. The guide roll has opposite ends, at least one of which is pivotable toward and away from the first roll. 
     An advantage of the present invention is that a longer membrane may be accommodated, thus promoting longer belt life by reducing the time spent in the nips by any given section of the membrane. 
     Another advantage is a centering mechanism is available that counteracts the tendency of the membrane to meander along the length of a fiber web roll. 
     Yet another advantage is that contact with and eventual loosening of the end seals of an air press belt run may be avoided by keeping the membrane generally centered. 
     A yet further advantage is that a seal at each nip between mating rolls is better maintained by using crown compensating rolls as the rolls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a schematic view of a first embodiment of an air press system of the present invention; 
     FIG. 2 is a schematic view of the membrane run shown in FIG. 1; 
     FIG. 3 is a schematic view of a second embodiment of a paper web processing unit of the present invention; and 
     FIG. 4 is a schematic view depicting an alternate embodiment of an upper felt transfer section shown in FIG.  3 . 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate 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 
     Referring now to the drawings, and more particularly to FIG. 1, there is shown an air press assembly  10  including a felt  12  for carrying a continuous fiber web  13 , a plurality of rolls  14 - 20 , a tension roll  22 , a guide roll  24 , and a membrane  26 . 
     Plurality of rolls  14 - 20  are arranged for cooperative rotation and include a first press roll  14 , a second press roll  16 , a first cap roll  18 , and a second cap roll  20 . First press roll  14  is opposed to and spaced apart from second press roll  16 , and first cap roll  18  is opposed to and spaced apart from second cap roll  20 . First cap roll  18  and second cap roll  20  each are positioned adjacent to and form roll nips  28 - 34 , respectively, with each of first press roll  14  and second press roll  16 . 
     First cap roll  18  is smaller in diameter than second cap roll  20 . By having such a relatively small diameter, first cap roll  18  may more easily create a sealing engagement with first press roll  14  and second press roll  16  at roll nips  30  and  32 , respectively. Forming such a sealing engagement is important when a pressurized fluid, such as compressed air, is injected (not shown) into a space  33  between rolls  14 - 20  of air press assembly  10 . The pressure created thereby may be selected depending on the specific application and, e.g., may be about 100 psig. 
     Rolls  14 - 20  each can be one of a crown compensating, shoe, swimming, or piston type roll. Rolls  14 - 20  are preferably crown compensating rolls since crown compensating rolls are structured and arranged to prevent deflection at the center of the rolls. By preventing deflection at the center of the rolls, leakage between the rolls due to such deflection is likewise minimized, if not prevented. Such deflection, if not compensated for, can otherwise act as a significant leakage source at roll nips  28 - 34  since rolls  14 - 20  are usually 3 ft. to 40 ft. long and consequently may be prone to sagging. 
     In the preferred embodiment shown in the drawings, second cap roll  20  is a crown compensating roll. Crown compensating roll  20  has an outer roll surface  36 , and the section of outer roll surface  36  between roll nips  28  and  34  has been labeled as nip line  38 . Since second cap roll  20  is crown compensating, a seal may be maintained between outer roll surface  36  and membrane  26  along nip line  38 . This crown compensation helps counter the effect of gravity, which tends to cause second cap roll  20  to pull away from mating rolls  14  and  16 . This gravitational effect is not as critical for first cap roll  18 , which actually rests along its length upon rolls  14  and  16 . Broadly stated, it is preferable that at least the lowermost positioned roll within air press assembly  10  is crown compensated due to such gravitational effects. 
     Tension or stretch roll  22  is movable in a first direction  40  (shown schematically in FIG. 1) extending toward and away from plurality of rolls  14 - 20 . Such movement of tension roll  22  is generated by a first position controller  42  (FIG.  2 ). 
     Guide roll  24  is pivotable about an axis in first direction  40  and is movable in second direction  44  extending transverse to plurality of rolls  14 - 20 . Such movement of guide roll  24  is controlled by a second position controller  46 . 
     Guide roll  24  is shown to be cylindrical in the drawings. However, the outer longitudinal surface of guide roll  24  may be any one of cylindrical, convex, or concave, based upon necessary design criteria. 
     Second position controller  46  is operatively connected to a membrane position sensor (S)  47 . Membrane position sensor  47  detects a lateral position of membrane  26  upon second cap roll  20 . Membrane position sensor  47  may be any one of various types of position sensors, including, but not limited to, opto-electronic, inductive, mechanical, and sonic type sensors. 
     Membrane  26  is positioned so as to wrap around and be in movable contact with both second cap roll  20 , tension roll  22  and guide roll  24 . Membrane  26  is preferably semipermeable so that it conveys a certain amount of air into nip  28  between second cap roll  20  and first press roll  14 . As membrane  26  becomes compressed by rolls  14  and  20  at nip  28 , the air trapped within membrane  26  is forced outward and thereby pushes moisture into felt  12  carrying paper web  13 . Thus, membrane  26  and rolls  14  and  20  coact in a manner similar to a piston. An additional effect of this air compression is that it tends to force felt  12  and paper web  13  away from membrane  26  and onto first press roll  14 , opposing membrane  26 . This effect helps felt  12  and paper web  13  achieve the proper feed path upon entering air press assembly  10 . 
     Tension roll  22  is positionable in first direction  40  so as to maintain tension in membrane  26  and thereby avoid a slack run. A slack run of membrane  26  could damage both membrane  26  itself as well as fiber web  13 . 
     Additionally, guide roll  24  is stationed so as to be in coacting contact with membrane  26 . Preferably, guide roll  24  is in contact with inner membrane surface  48 . Alternatively, guide roll  24  instead contacts outer membrane surface  50  (shown in phantom in FIG.  1 ). 
     It is preferable to employ a membrane  26  of an increased length since an increased membrane length allows longer membrane life. The increased membrane life is possible since any given length of a longer membrane  26  would spend less time in roll nips  28 - 34  during a revolution of membrane  26  than the same given length of a shorter membrane. The increased length of membrane  26  is accommodated by the combined presence of tension roll  22  and guide roll  24 . Tension roll  22  and guide roll  24  in conjunction with second cap roll  20  can generate an extended path over which membrane  26  may travel. 
     During the operation of air press assembly  10 , fiber web  13  is fed into roll nip  28  and is conveyed along a section of first press roll  14  which faces second press roll  16  until reaching roll nip  30 . Upon reaching roll nip  30 , fiber web  13  is carried on a section of first cap roll  18  which generally faces away from plurality of rolls  14 - 20 . Once fiber web  13  enters roll nip  32 , fiber web  13  travels along a section of second press roll  16  which faces first press roll  14  and remains in contact therewith until after exiting through roll nip  34 . 
     Concurrent with the feeding of fiber web  13  through plurality of rolls  14 - 20 , membrane  26  is conveyed around second cap roll  20  and tension roll  22  and against guide roll  24 . Membrane  26  interacts with fiber web  13  at roll nips  28  and  34 . 
     During operation, membrane  26  has a tendency to meander back and forth along the length of second cap roll  20 . In fact, use of a longer membrane as per this invention tends to magnify the effect of the natural tendency of a membrane to oscillate laterally along a roll through multiple membrane cyclings. This tendency is offset by sensing a position of membrane  26  using membrane position sensor  47  and, as necessary, adjusting the pivot angle of guide roll  24  using second position controller  46  to counteract the tendency to meander and thereby generally laterally center membrane  26  on second cap roll  20 . Guide roll  24  may further be moved in second direction  44  by second position controller  46 , for example, to optimize the membrane centering capability thereof or to ease a changeover of membrane  26 . 
     A second embodiment of the present invention, shown in FIG. 3, depicts a schematic system view of a paper web processing unit  60 . Paper web processing unit  60  includes an upper felt run  62 , a lower felt run  64 , an air press assembly  66 , and a transfer device  68 . 
     Upper felt run  62  includes an upper felt  70  and a plurality of rolls  72 - 82 . At least one of rolls  72 - 82  is mounted to a drive shaft (not shown) in order to power movement of upper felt  70  in first travel direction  84  through upper felt run  62 . In the embodiment shown in FIG. 3, roll  74  is a guide roll movable about pivot direction  86 , while roll  78  is a stretcher roll movable in second direction  88 , which is essentially equivalent to second direction  44  in the first embodiment. Roll  82  is a pick-up roll, also movable in second direction  88 . 
     Alternatively associated with upper felt run  62  adjacent to pick-up roll  82  is a transfer box  90 , shown in FIG.  4 . Transfer box  90  applies a vacuum to paper web  92  and lower felt  94  to ensure that paper web  92  remains on lower felt  94  and is not transferred upward along with upper felt  70  by pick-up roll  82  after upper felt  70 , paper web  92  and lower felt  94  have passed through and beyond air press assembly  66 . 
     Lower felt run  64  includes a lower felt  94 , plurality of rolls  96 - 106 , cleaning showers  108 , Uhle boxes  110  and lube showers  112 . 
     Rolls  96 - 106  include at least one roll which is mounted to a drive shaft (not shown) in order to power movement of lower felt  70  in second travel direction  114  through lower felt run  64 . In the embodiment shown in FIG. 3, roll  98  is a guide roll movable in pivot direction  116 , and roll  104  is a guide roll movable in pivot direction  118 . Roll  102  is a tension roll movable in second direction  88 . 
     Cleaning showers  108 , Uhle boxes  110 , and lube showers  112  are provided to maintain lower felt  94 . Cleaning showers  108  rinse out of lower felt  94  residual paper fibers and chemicals which may remain from a previous paper web transfer cycle. Uhle boxes  110  condition lower felt  94  between transfer cycles. Lube showers  112  are used to keep lower felt  94  lubricated when paper web processing unit  60  is not in a production mode. 
     Transfer device  68  includes a suction pick-up roll  120  and a transfer membrane  122 . Transfer device  68  is positioned downstream from air press assembly  66  and is configured for moving paper web  92 , now densified upon passing through air press assembly  66 , onto a next part of the paper-making process. 
     Air press assembly  66  is as substantially described previously in relation to the first embodiment shown in FIGS. 1 and 2. Air press assembly  66  includes rolls  124 - 134  and membrane  136 , which correspond and function similar to rolls  14 - 24  and membrane  26 . 
     During operation of paper web processing unit  60 , paper web  92  is introduced between upper felt  70  and lower felt  94  at web entry point  138 . Paper web  92  is then conveyed along with upper felt  70  and lower felt  94  through air press assembly  66 , where paper web  92  is densified. Upon exiting air press assembly  66 , upper felt  70  is directed away from paper web  92  and lower felt  94  at roll  82 . At the next proceeding station downstream of air press assembly  66 , densified paper web  92  is suctioned off of lower felt  94  by suction pick-up roll  120  and transported to a next part of the paper-making process by transfer membrane  122 . Lower felt  94  continues on through lower felt run  64 . 
     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.