Abstract:
A method and machine for the manufacture of a fiber web, in particular of a tissue web or of a hygienic web, in which the fiber web is formed on a soft clothing with fine pores and the clothing is guided over a surface subject to suction and in which the fiber web is transferred from a soft clothing with fine pores directly onto a TAD wire of a TAD drying apparatus. An optimum quality of the respective final product is achieved with an energy effort which is as low as possible, in particular, the energy effort required with vacuum generation in the dewatering of the fiber web is reduced.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation of PCT application Ser. No. PCT/EP02/05807, entitled “METHOD AND MACHINE FOR THE PRODUCTION OF A FIBRE WEB”, filed May 27, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a method and to a machine for the manufacture of a fiber web, and, more particularly, to the manufacture of a tissue web or of a hygienic web.  
           [0004]    2. Description of the Related Art  
           [0005]    The use of so-called throughflow apparatuses or TAD drying apparatuses (TAD=through air drying) in paper making machines is known (see for example WO 97/03247, U.S. Pat. No. 4,036,684). The TAD units have previously made up a large part of the total costs of the respective paper making machines. The energy requirements for a TAD machine with a dual wire former is very high and, in particular, much higher than, for example, those for a crescent former. For example, approximately 12 vacuum pumps have thus been required up to now in one TAD machine in order to achieve the desired dry content and degree of cleansing.  
           [0006]    In a conventional TAD machine with, for example, a dual wire former, the web must be transferred from the forming zone to the TAD zone, with the desired dry content being able to lie on the web transfer, for example, in a range from approximately 22 to approximately 26.5%, depending on the basis weight. The web is then guided with this dry content, for example, to a wet suction box effecting a wet imprinting (wet molding) and then to the TAD drum. The named dry content has previously only been achieved, however, with a relatively high energy effort.  
           [0007]    What is needed in the art is an improved method and an improved machine with which an optimum quality of the respective final product can be achieved with an energy effort which is as low as possible. In particular the energy effort required in connection with the vacuum generation in the dewatering of the fiber web should be reduced in this process.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, a method for the manufacture of a fiber web, in particular of a tissue web or of a hygienic web, in which the fiber web is formed on a soft clothing with fine pores and the clothing is guided over a surface subject to suction and in which the fiber web is transferred from a soft clothing with fine pores directly onto a TAD wire of a TAD drying apparatus.  
           [0009]    An advantage of the present invention is that an optimum quality of the respective final product is achieved with an energy effort which is as low as possible, in particular, the energy effort required with vacuum generation in the dewatering of the fiber web is reduced.  
           [0010]    An optimum dry content gain results with minimum energy effort due to the combination of the surface subject to suction or of the vacuum generated there with the soft clothing with fine pores. When an appropriate soft clothing with fine pores is used, the capillary effect of the clothing can in particular be used for the web dewatering. The respective underpressure is thus supported and facilitated by this capillary effect. A lower number of vacuum pumps for the forming zone also results in view of the lower energy requirements. The dry content desired at the transfer to the TAD section is therefore achieved with a lower number of vacuum pumps in the forming zone. The transfer of the fiber web to the TAD wire preferably takes place after the surface subject to suction. The surface subject to suction is expedientiy curved. It is preferably formed by a suction guide roll, a shoe subject to suction or the like.  
           [0011]    In accordance with a preferred embodiment of the method in accordance with the invention, the fiber web is dewatered between two clothings which run together while forming a material inlet gap and are guided over a forming element such as a forming roll, with the fiber web being guided after the forming element, by the inner clothing coming into contact with it, to the surface subject to suction. Advantageously, in this process the outer clothing not coming into contact with the forming element can be formed by an endless fabric, preferably a water permeable endless fabric.  
           [0012]    The forming element can be formed by a solid forming roll or by a suction forming roll. In accordance with a preferred practical embodiment, the fiber web is wet molded on the TAD wire. The wet molding can take place at and/or after the web transfer position. It is advantageous, in certain cases for the two clothings to have a different running speed in order to produce a crepe effect acting on the fiber web.  
           [0013]    The soft clothing with fine pores can in particular be formed by a felt, a capillary felt, a capillary membrane and/or the like. A coated wire, e.g. a wire with a foamed layer, and for example a felt with a foamed layer, can be used as the soft clothing with fine pores. In this case, the foam coating is preferably selected such that pores result in a range from approximately 3 to approximately 6 μm. The appropriate capillary effect is therefore used for the dewatering. The felt is provided with a special foam layer which gives the surface very small pores whose diameters can lie, for example, in the recited range from approximately 3 to approximately 6 μm. The air permeability of this felt is very low. The natural capillary effect is utilized for the dewatering of the web while it is in contact with the felt.  
           [0014]    At least one suction element arranged inside the loop of the TAD wire can be used for the wet molding. A pick-up element or suction element can, for example, be provided inside the loop of the TAD wire in the region of the web transfer position for the support of the web transfer.  
           [0015]    In accordance with an expedient practical embodiment, at least one suction element serving for the wet molding of the fiber web is provided inside the loop of the TAD wire in the region of the web transfer position and/or after the web transfer position. In accordance with a further advantageous embodiment of the method in accordance with the present invention, a shoe press is provided in the region of the web transfer position through which the fiber web is guided together with the soft clothing with fine pores and the TAD wire.  
           [0016]    Advantageously, in this process the length of the press nip of the shoe press considered in the web running direction can be selected larger than a value of approximately 80 mm, and preferably larger than or equal to approximately 85 mm, and in particular larger than or equal to approximately 120 mm. The shoe press can be designed such that a pressure profile results over the press nip length with a maximum pressing pressure which is smaller than or equal to a value of approximately 2.5 MPa, and in particular smaller than 2 MPa, with a press shoe length of larger than or equal to approximately 120 mm. A gentle pressing with a low pressing pressure is thus ensured and a larger dwell time or pressing time is secured due to the shoe length, whereby the molding effect is improved.  
           [0017]    The shoe press advantageously includes a shoe pressing unit, in particular a shoe press roll, and a wire roll cooperating with it and arranged inside the loop of the TAD wire. The pressing of the fiber web between the structured TAD wire and the soft clothing with fine pores effects the desired wet molding in this process. In this case, creping is not possible, i.e. there must not be any speed difference between the clothings.  
           [0018]    In specific cases, it is also advantageous for the fiber web to be wet molded both by way of the shoe press and by way of a suction element provided after it. Wet molding is therefore generally possible at different positions.  
           [0019]    In accordance with a preferred practical embodiment of the method in accordance with the present invention, a dewatering wire with zonally different wire permeability is used as the outer clothing not coming into contact with the forming element. In conjunction with the other method features, the advantage results therefrom of a higher water absorption speed of the fiber web, in particular of the tissue web or of the hygienic web.  
           [0020]    The fiber web is expediently transferred from the TAD wire onto a drying cylinder, in particular onto a Yankee cylinder, after the TAD drying. A shoe pressing unit, in particular a shoe press, which is preferably wrapped around by a soft felt or by a capillary felt and which includes a longitudinal shoe, can be provided in this process inside the loop of the TAD wire in the transfer region. A reliable and gentle transfer of the web is thus ensured in which it is avoided that the three-dimensional structure of the fiber web produced by the wet molding and by the TAD process, and thus the web quality such as in particular the water retention capability, the water absorption speed and/or the like, is again reduced. The respective web transfer can generally, however, also be ensured by a suction press roll, and in particular by a press roll not subject to suction.  
           [0021]    The machine in accordance with the present invention for the manufacture of a fiber web, in particular of a tissue web or of a hygienic web, is accordingly characterized in that the fiber web is formed on a soft clothing with fine pores and this clothing is guided over a surface subject to suction and in that the fiber web is transferred from a soft clothing with fine pores directly onto a TAD wire of a TAD drying apparatus.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    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:  
         [0023]    [0023]FIG. 1 is a schematic view of an embodiment of a machine for the manufacture of a fiber web according to the present invention;  
         [0024]    [0024]FIG. 2 is a schematic view of another embodiment of the machine according to the present invention with a shoe press arranged in the web transfer region; and  
         [0025]    [0025]FIG. 3 is a schematic view of another embodiment of the machine according to the present invention in which the web transfer from the TAD wire to the drying cylinder is supported by a shoe pressing unit.  
         [0026]    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  
       [0027]    Referring now to the drawings, and more particularly to FIG. 1, there is shown in a schematic partial representation a machine  10  for the manufacture of a fiber web  12  which can in particular be a paper web and preferably a tissue web or a hygienic web.  
         [0028]    Fiber web  12  is formed on a soft clothing  14  with fine pores in machine  10 . Clothing  14  is guided together with fiber web  12  formed thereon over a surface  16  subject to suction. Subsequent to this, fiber web  12  is transferred from soft clothing  14  with fine pores directly onto a TAD wire  18  of a TAD drying apparatus  20 .  
         [0029]    Fiber web  12  is therefore transferred from the same soft clothing  14  with fine pores directly onto TAD wire  18  on which it was formed. The transfer takes place in the web running direction L after surface  16  subject to suction. Surface  16  subject to suction is formed by a suction guide roll  22 .  
         [0030]    In the forming zone, fiber web  12  is dewatered between two clothings  14 ,  24  which run together while forming a material inlet gap and are guided over a forming element  28  such as in particular a forming roll. Fiber web  12  is guided after forming element  28 , by inner clothing  14  coming into contact with forming element  28 , to surface  16  subject to suction.  
         [0031]    Outer clothing  24  not coming into contact with forming element  28  can in particular be formed by an endless fabric, preferably a water permeable endless fabric. Forming element  28  can be formed by a solid forming roll or also by a suction forming roll.  
         [0032]    Fiber web  12  is wet molded on TAD wire  18 . The wet molding can generally take place at and/or after web transfer position I.  
         [0033]    In the present case, the two clothings  14 ,  24  have a different running speed in order to produce a crepe effect acting on fiber web  12 . Soft clothing  14  with fine pores can in particular be formed by a felt, a capillary felt, a capillary membrane and/or the like. In particular a felt with a foamed layer can thus be used as soft clothing  14  with fine pores. In this process, the foam coating can in particular be selected such that pores result in a range from approximately 3 to approximately 6 μm.  
         [0034]    At least one suction element arranged inside the loop of TAD wire  18  can be used for the wet molding. In the present case, only one such suction element  30  is used which is here provided, for example, after web transfer position I. Fiber web  20  is pulled toward TAD wire  18  by suction element  30  and thus wet molded.  
         [0035]    A pick-up element or suction element  32  is provided inside the loop of TAD wire  18  in the region of the web transfer position. The fiber suspension is introduced via a box head  34  into material inlet gap  26  formed between two clothings  14 ,  24 . Clothing  14  is conditioned by way of a so-called Uhle box  36 , i.e. a tube suction box, after the transfer of fiber web  12  to TAD wire  18 .  
         [0036]    Subsequent to suction element  30 , fiber web  12  is guided together with TAD wire  18  over a TAD drum  38  which, as can be recognized with reference to FIG. 1, is associated with a drying hood  40 .  
         [0037]    [0037]FIG. 2 shows in a schematic view a modified form of machine  10 . In this case, a shoe press  42  is provided in the region of web transfer position I through which fiber web  12  is guided together with soft clothing  14  with fine pores and TAD wire  18 .  
         [0038]    The length of press nip  44  of shoe press  42  considered in the web running direction L can expediently be selected to be larger than a value of approximately 80 mm, and preferably larger than or equal to approximately 85 mm, and in particular larger than or equal to approximately 120 mm. The shoe press can in particular be designed such that a pressure profile results over the press nip length with a maximum pressing pressure which is smaller than or equal to a value of approximately 2.5 MPa and in particular smaller than 2 MPa with a press shoe length of larger than or equal to approximately 120 mm. In this manner, a gentle pressing with a low pressing pressure is thus ensured and a larger dwell time and pressing time is secured due to the corresponding shoe length, whereby the molding effect is improved. Wet molding can therefore also already take place in the region of web transfer position I. In addition, suction element  30  likewise serving for the wet molding (see also FIG. 1) can also again be provided after this web transfer position I, but this is not mandatory in the present case.  
         [0039]    Wet molding can therefore generally take place in each case in the region of web transfer position I or after web transfer position I or such wet molding can take place both in the region of web transfer position I and after web transfer position I.  
         [0040]    Shoe press  42  includes a shoe pressing unit  46 , in particular a shoe press roll, and, in the embodiment of FIG. 2, a suction roll or suction press on roll  48  cooperating with it and arranged inside the loop of TAD wire  18 . In the present case, the two clothings  14 ,  18  have the same speed, i.e. wet creping does not take place here. In another respect, this embodiment can, for example, have the same design as that of FIG. 1. Parts corresponding to one another have been associated with the same reference numerals.  
         [0041]    [0041]FIG. 3 shows in a schematic view of another embodiment of machine  10  whose forming zone and TAD zone are again designed at least substantially in the manner shown in FIG. 1, with again all modifications also being conceivable here. These forming zones, including all mentioned modifications, can thus also be designed such as was described in connection with the embodiment in accordance with FIG. 2. Elements corresponding to one another have been associated with the same reference numerals.  
         [0042]    Moreover, outer clothing  24  not coming into contact with forming element  28  can be formed by a dewatering wire with zonally different wire permeability, which in particular brings about the advantage of a higher water absorption speed of fiber web  12 . As can be recognized with reference to FIG. 3, fiber web  12  is transferred from the TAD wire  18  onto a drying cylinder  50 , in particular onto a Yankee cylinder, after the TAD drying. In the present case, a shoe pressing unit  54 , which can again preferably be a shoe press roll, which is preferably wrapped around by a soft felt or by a capillary felt  52  and includes a long shoe, is provided inside the loop of TAD wire  18  in web transfer region II. However, a suction press roll (SPW) or a press roll can also generally be provided in web transfer region II, for example. A hot air hood  56  is associated with drying cylinder  50 . Web  12  is finally wound up to form a winding roll  58 .  
         [0043]    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.  
       Reference Symbol List  
       [0044]    [0044] 10  machine  
         [0045]    [0045] 12  fiber web  
         [0046]    [0046] 14  soft clothing with fine pores  
         [0047]    [0047] 16  surface subject to suction, suction guide roll  
         [0048]    [0048] 18  TAD wire  
         [0049]    [0049] 20  TAD drying apparatus  
         [0050]    [0050] 22  suction guide roll  
         [0051]    [0051] 24  outer clothing  
         [0052]    [0052] 26  material inlet gap  
         [0053]    [0053] 28  forming element  
         [0054]    [0054] 30  suction element  
         [0055]    [0055] 32  pick-up or suction element  
         [0056]    [0056] 34  box head  
         [0057]    [0057] 36  Uhle box (tube suction box)  
         [0058]    [0058] 38  TAD drum  
         [0059]    [0059] 40  drying hood  
         [0060]    [0060] 42  shoe press  
         [0061]    [0061] 44  press nip  
         [0062]    [0062] 46  show pressing unit  
         [0063]    [0063] 48  suction roll or suction press-on roll  
         [0064]    [0064] 50  drying cylinder, Yankee cylinder  
         [0065]    [0065] 52  soft felt, capillary felt  
         [0066]    [0066] 54  shoe pressing unit  
         [0067]    [0067] 56  hot air hood  
         [0068]    [0068] 58  winding roll  
         [0069]    L web running direction  
         [0070]    I web transfer section  
         [0071]    II web transfer region