Patent Publication Number: US-6221214-B1

Title: Wet press and method for treating a fibrous material web

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 196 54 200.6 filed Dec. 23, 1996, the disclosure of which is expressly incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wet section of a machine for producing a fibrous material web, specifically a paper or a cardboard web, which includes at least one press unit that includes a nip through which the fibrous material web, which has been preformed in a web forming section, is guided. 
     The present invention also relates to a method for treating a fibrous material web in an elongated nip of a press section of a machine for producing a fibrous material web. The method includes preforming the fibrous material web in a forming section of the machine, guiding the fibrous material web, which has a dry matter content of approximately 15%, to at least one elongated nip and pressing the fibrous material web in at least one elongated nip. 
     2. Discussion of Background Information 
     The wet section of machines for producing a fibrous material web, particularly for producing either a paper or a cardboard web, occur after the web forming region and after the fibers have achieved a certain immobility gradient. Further drainage of the wet fibrous material web has, in the past, primarily been achieved by elements that essentially operate through the use of suction, such as, for example, particular foils, register rolls, suction boxes, suction rolls, or the like. Connecting this type of drainage to the machine incurs considerable expense, especially where, for example, the element requires a large amount of space or, for example, where generating the vacuum consumes an excessively large amount of costly energy. In addition, depending on the type of material, the drainage screen, which rubs over the mostly stationary drainage elements, may result in a relatively short screen service life. 
     In a wet section of the type discussed in EP-A-0 359 696, a press function is integrated into the screen region to eliminate a web pick-up point. The press point provided in the screen region includes a suction roll and an open roll. Either the relevant nip is not very hard, i.e. having a high linear force, or the nip is very short and soft, which can be attributed to a low linear force. Neither of these operations is suitable for removing the required quantity of water from the fibrous material web with the lowest possible pressure gradients when there are low dry matter contents, i.e. when the fibrous material web is still wet. 
     SUMMARY OF THE INVENTION 
     The present invention provides the ability to drain the pre-formed wet fibrous material web of a wet section of a machine while utilizing a minimal expenditure of energy, a small amount of space, and a correspondingly low operating cost. 
     The invention provides at least one long-nip press or elongated nip press, which is elongated in the web travel direction. The nip is positioned in a region or area where the dry matter content of the preformed fibrous material web coming into the nip is less than or equal to about 15%, and preferably, is less than or equal to about 12%. 
     The present invention may be used, for example, on gap formers, hybrid formers, fourdrinier wires, multistage fourdrinier wires, and/or the like. The nip length can be adapted to the respective types of production. Because the relevant press point is disposed closer to the headbox, the fibrous material web is warmer during pressing, which further increases the drainage capacity. In addition, lower screen wear is produced and the energy costs are clearly reduced. The pressing occurs in an extremely gentle fashion, wherein the progression of pressing power can be predetermined by a corresponding shoe embodiment (e.g. the length or shape or form of the shoe). 
     In fact, the pressure applied to the fibrous material web may increase in the traveling direction of the fibrous material web from approximately 1 bar to approximately 20 bars. Preferably, the pressure increases from about 1 bar to between about 5 and 10 bars. 
     At least one screen associated with the web forming zone is guided through the elongated nip. In particular industrial applications, it is advantageous to guide two screens associated with the web forming zone through the nip. 
     The fibrous material web, which is preformed in the web forming zone, can also be delivered to the nip by a water-absorbing belt. The fibrous material web is transferred onto the water-absorbing belt before the elongated nip. The water-absorbing belt can be, for example, a felt band, a screen belt, and/or a perforated belt. 
     Another embodiment of the invention provides for at least one belt being positioned on both sides of the fibrous material web and then being guided through the nip. The belts on either side of the fibrous material web are designed to be the same, i.e, symmetrical. 
     In this instance, starting from the fibrous material web, a support belt that supports the fibrous material web and is preferably comprised of fine woven cloth, a belt of porous woven cloth that serves to absorb and transport water, and a waterproof belt, are provided on each side of the web. In this instance, the support belt is preferably a felt band and/or screen belt. 
     It is also possible to provide a thick felt band and a waterproof belt, respectively, on each side of the web, starting from the fibrous material web. 
     However, it is also conceivable to provide a belt comprised of a fine woven cloth, a porous, coarse belt, and a waterproof belt, respectively, on each side of the web, starting from the fibrous material web. The belt comprised of fine woven cloth can, for example, be a screen belt. 
     In another suitable embodiment of the wet section according to the invention, at least one belt is on both sides of the fibrous material web and is respectively guided through the nip. The belts on either side of the fibrous material web are not the same, that is, they are asymmetrical. 
     For example, one asymmetrical belt design includes a felt band and a waterproof belt on one side of the web and a screen belt, a porous, coarse belt, and a waterproof belt provided on the other side of the web. 
     With an asymmetrical design like this, it is also possible, starting from the fibrous material web, to provide a waterproof belt on one side of the web and a screen belt, a porous, coarse belt, and a waterproof belt on the other side of the web. 
     In the embodiment, it is preferable to have an elongated nip formed between a rotating, flexible press belt, which is guided by at least one press shoe, and an opposing press face. Consequently the elongated nip can be formed, in particular, by a press shoe. 
     Because the pressing power exerted at low dry matter contents is relatively low, the region between the press shoe and the flexible press belt may be lubricated in a suitable fashion with water. As a result, there is also the possibility, in particular, of using the relevant press shoe in a continuous loop that is open on its end faces and to use an open system in which the shoe length can be relatively large. 
     According to one embodiment of the invention, the continuous loop formed by the rotating, flexible press belt may be open on its two end faces. 
     To form the first elongated nip that the web fibrous material web approaches, preferably, a press shoe is provided that includes a press face. The press face is at least substantially smooth on the jacket or flexible press belt side. In this instance, the woven cloths that travel through the nip may undergo less mechanical bending stress. Thus, the cloths or fabrics may be thicker and, thus, absorb more water. 
     Preferably, the wet section includes a headbox that is also supplied with dilution water. 
     According to one embodiment, the wet section is adapted to be used in combination with at least one other long-nip press or elongated nip press and a transfer zone where the fibrous material web is transferred to a dryer section. Preferably, the fibrous material web is guided so that, for the most part, a closed or continuous web guidance is produced. 
     According to one aspect of the invention, the first nip may be followed by at least one other nip, which can be a nip or an elongated nip. 
     To form a nip that is elongated in the web travel direction, a press belt may be provided that is guided by at least one press shoe. The press belt is further guided in an at least a substantially circular cylindrical fashion outside the shoe region and, thus, assumes the shape of a roll. 
     On the whole, the wet section according to the present invention produces lower screen wear. The energy costs are further minimized. Because the first press point is disposed closer to the headbox, the material cools less, which facilitates the drainage. The pressing is performed in an extremely gentle fashion, wherein the progression of pressing power can be predetermined by a corresponding shoe embodiment, such as, for example the length and shape of the shoe. In addition, the pressing is as volumetrically gentle as possible. 
     Another way to state the invention is a wet section of a machine for producing a fibrous material web including a web forming section that preforms the fibrous material web and at least one press that includes an elongated nip through which the fibrous material web is guided. At least one press and the elongated nip are elongated in a web travel direction. Further, the elongated nip is positioned in a region of the machine where the dry matter content of the fibrous material web, as it enters the elongated nip, is less than or equal to about 15%. 
     According to one aspect of the invention, the fibrous material web may be either a paper web or a cardboard web. 
     According to another aspect of the invention, the dry matter content of the fibrous material web may be less than or equal to about 12% as it enters the elongated nip. 
     Further, the fibrous material web may be transferred from the web forming section to a belt that delivers the fibrous material web to the elongated nip. 
     The wet section may include at least one screen belt that is associated with the web forming section. At least one screen belt may be guided through the elongated nip. 
     Further, the invention may include two screen belts, which are associated with the web forming section and are guided through the elongated nip. 
     According to one aspect of the invention, a water-absorbing belt may take the fibrous material web from the web forming section to the elongated nip. Further, the belt may be composed of either a felt band, a screen belt or a perforated belt. 
     According to yet another aspect of the invention, there may be at least two belts which sandwiching the fibrous material web. The two belts may be composed of the same material and at least one of the two belts may be guided through the elongated nip. 
     According to yet another aspect of the invention, the belts may include at least one support belt and at least one waterproof belt. Further, the invention may include at least two support belts, each supporting the fibrous material web on both sides of the fibrous material web. Further, the invention may include two waterproof belts, each waterproof belt associating with a corresponding support belt. 
     It is possible that at least one support belt may be composed of a porous, fine woven cloth or a felt belt, or a screen belt. 
     According to one aspect of the invention, at least one support belt may be composed of at least one thick felt band and the waterproof belt may be composed of at least one waterproof belt. At least one felt band may associate with a corresponding waterproof belt and this combination may be provide don on both sides of the fibrous pulp sheet. 
     It is possible for the belt combination to include at least one fine woven cloth belt, at least one porous course belt and at least one waterproof belt. Both sides of the fibrous material web, moreover, may be provided with this combination of belts. 
     It is possible, moreover, for the fine woven cloth belt to be composed of a screen belt. 
     Further, according to yet another aspect of the invention, the fibrous material web may include a first side and second side that is positioned opposite the first side. The first side may be associated with at least one belt and the second side may be associated with at least one belt. The belt or belts that are associated with the first side of the fibrous material web may be a different combination of belts that is associated with the second side of the fibrous material web. Further, at least one belt associated with the first side and at least one belt associated with the second side may be guided through the elongated nip. 
     It is possible, moreover, for at least one belt associated with the first side of the fibrous material web to be composed of a felt band and/or a waterproof belt and at least one belt associated with the second side of the fibrous material web to be composed of a screen belt, a porous, coarse belt and a waterproof belt. 
     It is possible, moreover for the first side of the fibrous material web to be provided with a waterproof belt and the second side of the fibrous material web to be provided with a screen belt, a porous course belt and a waterproof belt. 
     The wet section may further include a rotating flexible press belt and at least one press shoe that guides the rotating flexible press belt. Further, the elongated nip may be formed between the rotating flexible press belt and an opposing face. 
     The region between at least one press shoe and the rotating flexible press belt may be lubricated with water. 
     It is possible, moreover, for the rotating flexible press belt to form a continuous loop that includes two end faces. The continuous loop, moreover, may be open on the two end faces. 
     The wet section may further include a shoe press that is positioned adjacent the elongated nip. The press shoe may include a press face, and the press face may be substantially smooth on the side of the flexible press belt or jacket side. 
     The wet section may also be associated with a headbox that supplies the fibrous material pulp and dilution water. 
     It if further possible that the wet section may be adapted for use in combination with at least one additional elongated nip and a transfer zone, where the fibrous material web is transferred to a dryer section of the machine. The fibrous material web is, preferably, guided so that a substantially continuous web guidance is produced. 
     Another way to state the invention is a wet section of a machine for producing a fibrous material web that includes a web forming section to form the fibrous material web and at least one press section that includes at least one elongated nip through which the fibrous material web is guided. At least one press and at least one elongated nip are elongated in a web travel direction. 
     According to another aspect of the invention, the fibrous material web may be either a paper web or a cardboard web. 
     Further, the dry matter content of the fibrous material web may be less than or equal to about 15% as it enters a first at least one elongated nip or it may be less than or equal to about 12% as it enters a first at least one elongated nip. 
     According to another aspect of the invention, the wet section may be positioned between the web forming section and a dryer section. 
     Further, the wet section may be associated with at least one belt to transport the fibrous material web. It is possible for the belt to be screen belt or a felt belt. Moreover, it is possible to have two sets of belts sandwiching the fibrous material web. 
     The sets of belts may be composed of water absorbent material or water impermeable materials. 
     Further, the two sets of belts may be composed of either a different profile of belts or a substantially identical profile of belts. 
     The present invention also includes a method for treating a fibrous material web in a wet section of a machine for producing the fibrous material web. The wet section includes at least one press, which includes an elongated nip. At least one press and the elongated nip are, moreover, elongated in a web travel direction and the elongated nip is positioned in a region of the machine where the dry matter content of the fibrous material web as it enters the elongated nip is less than or equal to about 15%. The method includes preforming the fibrous material web in a forming section of the machine, guiding the fibrous material web to the at least one elongated nip and pressing the fibrous material web in at least one elongated nip elongated nip. 
     Further, the dry matter content of the fibrous material web may be less than or equal to about 12% as it enters the elongated nip. 
     Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be further described in the detailed description which follows, in reference to the noted drawing by way of non-limiting example of a preferred embodiment of the present invention, and wherein: 
     FIG. 1 is a schematic side view of an embodiment of a wet section with a nip that is elongated in the web travel direction and is positioned between two press shoe rolls; 
     FIG. 2 is a schematic side view of another embodiment of a wet section with a nip that is elongated in the web travel direction and is embodied between a press shoe roll and a suction roll; 
     FIG. 3 is a schematic side view of another embodiment of a wet section with a nip that is elongated in the web travel direction and is embodied between a forming roll and a press shoe roll; 
     FIG. 4 is a schematic side view of another embodiment of a wet section with a headbox that is additionally supplied with dilution water, 
     FIG. 5 shows another embodiment, with a separate press shoe before the pick-up in the press section; and 
     FIG. 6 represents an example of a belt arrangement employed with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for the fundamental understanding of the invention, the description taken with the drawing figure making apparent to those skilled in the art how the invention may be embodied in practice. 
     FIG. 1 shows, in a schematic side view, shows an embodiment of a wet section of a machine for producing a fibrous material web, in particular a paper and/or cardboard web. 
     In this wet section, a web forming zone, which includes two convergent screens or sieves or belts  12 ,  14  is furnished with at least one fibrous suspension flow by a headbox  16 . The headbox  16  is only briefly indicated by an arrow. In this connection, the lower screen  12  is guided around a forming roll  18 . 
     The wet section includes a long-nip or elongated nip press  20  with a nip that is elongated in the web travel direction L and is formed between two shoe press rolls  22 ,  24 . A belt  26  is guided around the lower shoe press roll  22  and a second belt  28  is guided around the upper shoe press roll  24 . The belts  26 ,  28  can be, for example, a screen belt or a felt belt or band. An example of such a belt arrangement is shown in FIG.  6 . While FIG. 6 illustrates that the composition of each belt  26  and  28  are symmetrical, as noted above, the composition of the belts  26  and  28  may differ from one another. 
     The nip formed by the elongated nip or the long-nip press  20  is disposed in a region where the dry matter content of the preformed fibrous material web  10  coming into the nip is less than or equal to about 15% and, preferably, is less than or equal to about 12%. 
     As can be seen in FIG. 1, only the lower screen  12 , of the two screens  12 ,  14  that are associated with the web forming zone, is guided through the nip of the long-nip press  20 . 
     The two shoe press rolls  22  and  24  each include a flexible press belt or jacket  32  guided by a shoe press  30 . The region between the shoe presses  30  and the flexible press belt  32  is lubricated with water. In addition, the shoe presses  30  in the current instance each have a press face that is at least substantially smooth on the jacket side or the flexible press belt side. 
     The wet section is provided in combination with two other presses  34 ,  36 , of which the one, namely the press  34 , is a long-nip or an elongated nip press, and a transfer zone  38  for a transfer of the fibrous material web  10  into the dryer section (not shown). The fibrous material web  10  is guided so that, for the most part, a continuous web guidance is achieved. 
     In the current instance, the two other presses  34 ,  36  include a central deflection compensation roll  40  that has a smooth roll jacket surface, i.e. the roll jacket is closed. The two other presses further include another shoe press roll  42  and another press roll  44 . The central, smooth deflection compensation roll  40  takes over the fibrous material web  10  directly from the lower screen  12 . 
     FIG. 2 is a schematic side view diagram of another embodiment of a wet section. This wet section also includes a nip that is elongated in the web travel direction. In this instance, the elongated nip is formed between a shoe press roll  46  and a suction roll  48 . The correspondingly obtained long-nip press  50  is in turn provided in a region in which the dry matter content of the preformed fibrous material web coming into the nip is less than or equal to 15% and is preferably less than or equal to 12%. As can be further inferred from FIG. 2, only the lower screen  12  of the two screens  12 ,  14  associated with the web forming zone is guided through the nip of the long-nip press  50  (compare to FIG.  1 ). The web forming zone in the region of the forming roll is constructed in the same manner as in the embodiment of FIG.  1 . 
     From the belt  28  guided via the central suction roll  48 , the fibrous material web  10  is taken over by another central roll  54  disposed between the suction roll  48  and another press roll  52  so that after the elongated nip of the long-nip press  50 , two additional nips are produced before the fibrous material web  10  is supplied to the drier section. 
     In a schematic side view, FIG. 3 shows another embodiment of a wet section with a nip that is elongated in the web travel direction. In this instance, the elongated nip is formed between a forming roll  56  and a shoe press roll  22  around which, in turn, a belt  26  is guided. A lower screen  12  associated with the web forming zone is guided around the forming roll  56 . The headbox  16  supplies the incoming side of the nip. The nip is formed between the lower screen  12  and the forming roll  56 , including at least one fibrous suspension flow so that the fibrous material web is produced between the lower screen  12  and the forming roll  56 . 
     In FIG. 3, the forming roll includes pneumatically loaded blades  13  that remove the water which permeates the lower screen  12 . Further, the pneumatically loaded blades  13  create, between the lower screen  12  and the forming roll  56 , pressure pulsations in the suspension which improves the quality of the finished paper. The water collection receptacle  15  collects the drainage from the forming web. 
     From the forming roll  56 , the fibrous material web is eventually taken over by a felt belt  60  guided around a suction roll  58 . The fibrous material web may then be taken to other nips, which can, in turn, be formed by at least one long-nip press. 
     In the embodiment shown in FIG. 3, the first long-nip press  62  that includes a shoe press  22  is provided in the region of the forming roll  56 , wherein the relevant elongated nip is formed between this forming roll  56  and the shoe press roll  22 . Also in this instance, the long-nip press is again disposed in a region where the dry matter content of the preformed fibrous material web coming into the relevant nip is less than or equal to about 15% and, preferably, is less than or equal to about 12%. 
     FIG. 4 is a schematic side view of another embodiment of a wet press that includes a headbox  16  that is also supplied with dilution water. 
     In one instance, the forming roll  18  is disposed in the loop of the upper screen  14 , while the lower screen  12  is guided by this forming roll  18  around which the screen  14  winds. After the forming roll  18 , the screen  12  is guided around a suction roll  64  to then supply the preformed fibrous material web  10  to the first elongated nip formed by the long-nip press  20 . 
     Otherwise, this embodiment according to FIG. 4 has essentially the same structure as the wet section shown in FIG.  1 . Therefore, in this case as well, only the lower screen  12  of the two screens  12 ,  14  that are associated with the web forming zone is guided through the first elongated nip. Here, too, the relevant nip that is elongated in the web travel direction is again positioned in a region where the dry matter content of the preformed fibrous material web coming into the nip is less than or equal to about 15% and, preferably, is less than or equal to about 12%. 
     FIG. 5 shows another embodiment of the present invention that includes a separate shoe press  66  before being guided to a suction box and at least one long nip shoe press in the press section of machine. 
     It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to a preferred embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and the spirit of the invention in its aspects. Although the invention has been described herein with reference to particular means, methods, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 
     Reference Numeral List 
       10  fibrous material web 
       12  screen 
       13  pneumatically loaded blades 
       15  water collection receptacle 
       14  screen 
       16  headbox 
       18  forming roll 
       20  elongated nip press 
       22  shoe press roll 
       24  shoe press roll 
       26  belt 
       28  belt 
       30  shoe press 
       32  flexible press belt 
       34  elongated nip press 
       36  press 
       38  transfer zone 
       40  deflection compensation roll 
       42  shoe press roll 
       44  press roll 
       46  shoe press roll 
       48  suction roll 
       50  elongated nip press 
       52  press roll 
       54  central roll 
       56  forming roll 
       58  suction roll 
       60  felt 
       62  elongated nip press 
       64  suction roll 
       66  shoe press