Patent Publication Number: US-9885153-B2

Title: Device for forming an extended nip

Description:
The invention relates to an apparatus for forming an extended nip between a mating roll and a shoe roll for treating a material web, in particular a paper web, a board web, a tissue web, or any other fibrous web. 
     Apparatus of this type are used in particular in press sections and calendars. 
     DE 30 30 233 C3 discloses a wet press for dewatering fibrous webs, in which an elongated press zone is applied so as to substantially increase dewatering as compared with other press rolls. On account of a concave shape of the sliding face of the sliding shoe, an elongated press nip through which the fibrous web passes is formed between a mating roll and a rotating belt on which a sliding shoe bears from the inside. The rotating belt is held in a substantially roll-like shape by annular discs which are fastened to the end sides of the belt. The sliding shoe is fastened to a shoe base which is connected to a stationary yoke by way of a pressure cushion from an elastic material, for example plastics or rubber, and in relation to said yoke is guided in the direction of pressure by pins and transversely thereto is held in a form-fitting manner. Metal strips serve for fastening the pressure cushion to the shoe base and to the yoke. 
     The space which is enclosed by the pressure cushion is loadable via lines by a fluid, such that it is possible for the contact pressure of the sliding shoe on the mating roll to be varied. The pressure cushion here is disposed such that the resulting force applied by the pressure cushion on the sliding shoe in the running direction of the roll circumference runs through the second half of the formed press nip. As a result, a slow increase in pressure which thereafter at the end of the press zone rapidly decreases is caused, being advantageous for a dewatering operation. In order to be able to adjust different contact pressures across the roll width, the pressure cushion may be axially subdivided into zones. It is disadvantageous that the pressure cushion from an elastic material, for example plastics or rubber, is liable to wear. The cost advantages of pressure cushions as compared to more complex cylinder-type loading systems are therefore often lost on account of comparatively short maintenance intervals. 
     U.S. Pat. No. 4,713,147 discloses a wet press having an elongated press nip, in which two separate pressure cushions are provided for adjusting the line load along the length of the press zone of the press nip. Thereby, the shape of the pressure curve is better adjustable. However, the disadvantages mentioned above apply in a corresponding manner. 
     It is therefore an object of the invention to provide an apparatus for forming an extended nip according to the preamble of Claim  1 , in which the press shoe by way of a fluid-loadable pressure cushion as a contact pressure unit is pressable against the mating roll and the pressure cushion here operates with low wear. 
     This object is achieved by the features of Claim  1 . 
     By this means, an apparatus for forming an extended nip is provided, in which all frictional effects between a male form portion of the press shoe and the pressure cushion, on the one hand, and the groove-type chamber and the pressure cushion, on the other hand, are avoided. While avoiding stick-and-slip effects, the pressure cushion can be unfolded by the lateral guide of a rollable wall from a flat first profile to a higher second profile, by which a lifting movement of the press shoe is performed. The lifting movement enables displacement of the press shoe in relation to the roll shell and adjustment of a pressure in the extended nip. The pressure cushion is thus subject to substantially lower wear. 
     According to the invention the loading of the pressure cushion with fluid is a hind of inflating fluid loading, in which the rollable wall always forms a rolling fold which is maintained in all operational states. The rolling behaviour of the rollable wall enables guiding of a male form portion of the shoe, which extends in an axial manner along a shoe length which typically runs in a transverse manner to the machine direction (MD). 
     According to preferred exemplary embodiments, the pressure cushion is made from a flexible material which also configures the rollable wall having a rolling fold. Here, the male form portion of the press shoe between two axially extending rolling folds projects into the pressure cushion while sinking the latter. 
     It is furthermore advantageous that the pressure cushion is formed by a fluid-loadable flexible tube, the two material layers of said tube, which in the cross section are disposed on top of one another, are placed in a U-shape in the groove-type chamber in such a manner that the tube folds of the leg ends of the tube which is place in a U-shaped manner form the rollable wall. The rollable wall is then configured so as to be integral with the pressure cushion, as a result which a pressure cushion which can be readily and rapidly fitted is moreover achieved. Alternatively, a forming part having a rollable wall which is clamped at the end sides may be provided. 
     Furthermore, a several of pressure cushions can be provided longitudinally across shoe width in the machine direction, having assigned one male form portion of the press shoe, respectively. Setting of the line load along the press zone length of the extended nip is then variable. 
     In order for different contact pressures to be able to be set across the shoe length, that is to say across the roll width in a transverse direction to the machine direction, the pressure cushion may be axially subdivided into zones. Alternatively or additionally, the male form portion of the press shoe can plunge into the pressure cushion or pressure cushions by way of variably sized contact areas. Thus, peripheral loading or load relief of the press shoe is adjustable. Moreover, additional cylinder-type loading installations, by way of which the line load profile along the press zone in the extended nip may be varied, can also be provided. 
     Further refinements of the invention can be gathered from the following description and the dependent claims. 
    
    
     
       The invention will be explained in more detail below by using the exemplary embodiments illustrated in the appended figures, in which: 
         FIG. 1 a    shows schematically an apparatus for forming an extended nip, having a shoe roller according to a first exemplary embodiment, in the cross section and in a partial manner; 
         FIG. 1 b    shows schematically an apparatus for forming an extended nip, having a shoe roll according to a second exemplary embodiment, in the cross section and in a partial manner; 
         FIG. 2 a    shows schematically the apparatus according to  FIG. 1 a   , having a pressure cushion at a higher profile; 
         FIG. 2 b    shows schematically the apparatus according to  FIG. 2 a   , for a third exemplary embodiment; 
         FIG. 2 c    shows schematically a flat first profile and a higher second profile of a pressure cushion; 
         FIG. 3 a    shows schematically the apparatus according to  FIG. 2 a   , for a fourth exemplary embodiment; 
         FIG. 3 b    shows schematically the apparatus according to  FIG. 2 a   , for a fifth exemplary embodiment; 
         FIG. 3 c    shows schematically the apparatus according to  FIG. 2 a   , for a sixth exemplary embodiment; 
         FIG. 4  shows schematically an apparatus for forming an extended nip, having a shoe roll according to the first exemplary embodiment, having a connector installation for fluid loading, in the longitudinal section and in a partial manner; 
         FIG. 5  shows schematically an apparatus for forming an extended nip, having a shoe roll according to the first exemplary embodiment, having another connector installation for fluid loading, in the longitudinal section and in a partial manner; 
         FIG. 6  shows schematically the apparatus according to  FIG. 2 a   , for a seventh exemplary embodiment; 
         FIG. 7 a    and  FIG. 8 a    show male form portions which taper off in the end region; 
         FIGS. 7 b  to 7 d    and  FIGS. 8 b  to 8 d    show different line load curves along a press zone in the extended nip. 
     
    
    
     As shown in  FIG. 1 a    and  FIG. 2 a   , the invention according to a first exemplary embodiment relates to an apparatus for forming an extended nip  1  between a mating roll  2  and a shoe roll  3  for treating a material web. The material web is in particular a paper web, a board web, a tissue web, or any other fibrous web. 
     The shoe roll  3  comprises a carrier  4  and a flexible roll shell  5  which is rotatable about the carrier  4 . The carrier  4  is preferably configured as a stationary yoke. The roll shell  5  in the region of the extended nip  1  is supported on a head face  7  of a press shoe  6  which is guided on the carrier  4 . The press shoe  6  for generating a pressure by way of at least one fluid-loadable pressure chamber, presently, according to the first exemplary embodiment, the pressure chambers  8 ,  9 , is movably supported on the carrier  4 . 
     The pressure chamber  8 ,  9  is configured as a pressure cushion  10  on which the press shoe  6  by way of the rear side is supported in a planar manner, wherein the pressure cushion  10  is placed in a groove-type chamber  11 . 
     The press shoe  6  on the rear side has at least one male form portion  12  or a base, respectively, which for performing lifting movements projects into at least one pressure cushion  10  which can be sunk. To this end, the pressure cushion  10  is supported in a guiding manner by way of a pressure-cushion side wall, which forms a rollable wall  13 , on the groove-type chamber  11 . This can be achieved by the pressure cushion  10  being made from a flexible material. 
     The rollable wall  13  forms a rolling fold  14  between the male form portion  12  of the press shoe  6  and an inner side wall  15  of the grove-type chamber  11 . The rolling behaviour of the rollable wall  13  determines a lifting length in the lifting direction. Preferably, a clear height H of the groove-type chamber  11  should be at least half of the lifting movement of the press shoe  6  in the direction of pressure X, as is clarified in  FIG. 2   c.    
     A spacing Y between the male form portion  12  of the press shoe  6  and the inner side wall  15  of the groove-type chamber  11  is selected such that the rollable wall  13  during displacement of the male form portion  12  in the lifting direction is pressed against the inner side wall  15  of the groove-type chamber  11 . 
     A substantial advantage of the pressure cushion  10  also lies in that the compression surface of the pressure cushion  10  which acts on the male form portion  12  is independent of the lifting movements, as is shown in  FIG. 1 a    in conjunction with  FIG. 2   a.    
     As a pressure cushion  10 , a fluid-loadable flexible tube  16  is preferably placed in the axially extending groove-type chamber  11 . The two material layers  17 ,  18 , of the tube  16 , which in the cross section are disposed on top of one another, are placed in a U-shape in the groove-type chamber  11  in such a manner that the tube folds of the leg ends of the tube which is placed in a U-shaped manner form the rollable wall  13 . The male form portion  12 , which is engaged for lifting with the pressure cushion  10 , while performing lifting movements is enclosed by the tube  16  in a U-shaped cross-sectional manner. 
     The tube  16  preferably consists of a fibre-reinforced plastic material or of a fibre-reinforced rubber compound. The rollable wall  13  is then configured so as to be integral with the tube  16 . 
     The press shoe  6  is brought into contact with the mating roll  2  or a mating element and pressed there against by way of at least one pressure, and when two pressure cushions  10  are provided according to  FIG. 2 a   , by way of two pressures P 1  and P 2 , in the tubes  16 . For contacting thereon, the tube  16  rolls upward in its receptacle, presently the chamber  11 . The pressures P 1  and P 2  can be set independently of one another. In this way, different pressure profiles can be set in the extended nip  1 . 
     As an alternative to a tube, the pressure cushion  10  can be formed by a flexible shaped piece  19 , which at the end side is clamped to fixing points  20 , as is shown in  FIG. 2   b.    
     According to  FIG. 1 b    the press shoe  6  can be embodied in a divided manner. This enables the press shoe  6  to be constructed from layers  21 ,  22  of different materials. These layers  21 ,  22  in relation to one another can be guided in the machine direction (MD), for example by means of fitting keys  23  or screws. Due to differences in temperature, the layer  21  can bend in relation to the layer  22 . The layers  21 ,  22  can be freely displaceable in the machine cross direction (CD). The same may apply to the male form portions  12  below the press shoe  6 . 
     As is shown in the described  FIG. 1 a   ,  FIG. 1 b   ,  FIG. 2 a   , and  FIG. 2 b   , the press shoe  6  in the machine direction (MD) can have at least two male form portions  12  which extend transversely to the machine direction in a spaced-apart manner and which are in each case assigned one groove-type chamber  11  having a pressure cushion  10  placed therein. Pressure loading of the several pressure cushions  10  is preferably performed in a variable manner. 
       FIG. 3 a    shows an exemplary embodiment having three pressure cushions  10  made from U-shaped inlaid tubes  16 , for example. The press shoe  6  then can be pressed against the mating roll  2  or a mating element, respectively, by way of three male form portions  12 . The pressure P 2  then is a primary operating pressure, for example, while the pressures P 1  and P 3  are pressures used for MD profiling. 
     As is shown in  FIG. 3 b    and  FIG. 3 c   , the press shoe  6  can be pressed only by way of one male form portion  12  having an assigned pressure cushion  10 , presently formed by a tube  16 .  FIG. 3 b    shows that the press shoe  6  here is connected to the carrier  4  and in relation to the latter is guided in the direction of pressure X by pins  31  and in a transverse manner thereto is held by mountings  32 . This applies in a corresponding manner to the previously described exemplary embodiments. 
     As is shown in  FIG. 4  and  FIG. 5  in the machine cross direction (CD), the axially extending tube  16  at the end side can have a lateral connector  27  for fluid loading  24 . According to  FIG. 4 , this connector  27  is configured so as to be round, for example. Furthermore, a support element  25 , which prevents force acting from the free tube end onto the press shoe  6 , can be provided. According to  FIG. 5 , the lateral connector  27  is configured so as to be, for example, rectangular or U-shaped, like the tube  16  below the press shoe  6 . The opposite end of the tube  16  can in each case be configured in a corresponding manner. 
     As is finally shown in  FIG. 6 , the male form portion  12  across the shoe length, that is to say in the machine cross direction (CD), can plunge into the respective pressure cushion  10  by way of variably sized bearing faces  26 . The bearing face  26  of a male form portion  12  at the peripheries can be smaller than in the centre. 
       FIG. 7 b    to  FIG. 7 d    in an exemplary manner show for a male form portion  12  ( FIG. 7 a   ) in the machine cross direction (CD) the line forces in the press zone of the press shoe  6  resulting therefrom. The comparatively small bearing faces  26  on the peripheral side lead to lower line loads in the peripheral region of the press shoe  6  than in the central region. The reduction in the effective thrust face can be 25%, for example, as is shown in  FIG. 6 . 
     The male form portion  12  having a comparatively small bearing face  26  can be assigned a separate force component F 1 , F 2  for increasing a localized press force. The point of attack of these additional force components F 1 , F 2  preferably lies between the exemplary two male form portions  12 , as is clarified in  FIG. 6  in conjunction with  FIG. 7 a   . As is shown in  FIG. 7 c   , using these additional force components a line load without the effect of the pressure cushion/pressure cushions  10  can only be adjusted in the peripheral region. As is shown in  FIG. 7 d   , the peripheral load relief according to  FIG. 7 b    can be compensated for across the shoe length by the additional force components F 1  and F 2  on the identical line load. 
     As is shown in  FIG. 8 b    to  FIG. 8 d   , the additional force components F 1  and F 2  can apply such additional pressures as is clarified in  FIG. 8 c    so that despite the comparatively small bearing faces  26  the line loads for such a male form portion  12  according to  FIG. 8 a    at the peripheral side are higher than in a central region. 
     In the case of all exemplary embodiments a cloth  28  can be placed as wear protection between the head face  7  of the press shoe  6  and the roll shell  5 , as is illustrated in an exemplary manner in  FIG. 3 c   . This cloth  28  is preferably thermally resistant and can be composed of a material comparable to that of the roll shell  5 . 
     The apparatus described above may find use as a wet press or a calender.