Patent Publication Number: US-8118977-B2

Title: Dryer section in a paper machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of PCT application No. PCT/EP2007/060295, entitled “DRYING SECTION OF A PAPER MACHINE”, filed Sep. 28, 2007, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a dryer section in a paper machine or in a cardboard machine or other machine for drying a moving web, especially a fibrous web. 
     2. Description of the Related Art 
     Dryer sections of this type are known in a plurality of design forms. See U.S. Pat. No. 6,365,004 B1, WO 2005/068713 A1, DE 10 2004 017 810 A1 and DE 10 2004 017 811 A1. 
     Known dryer sections are constructed as follows: they include a first row of dryer cylinders, and also a second row of dryer cylinders below the first row. The two rows generally progress parallel to each other and in horizontal direction. The dryer cylinders of one row are staggered relative to the dryer cylinders of the other row. All dryer cylinders are wrapped by a water vapor-permeable woven fabric belt, for example a dryer felt. The woven fabric belt represents a closed loop and rotates during the operation of the dryer section. At the same time the woven fabric belt carries the material web, for example a paper web which is to be dried. The web alternately is in direct contact with the surface area of a dryer cylinder and is enveloped by the fabric belt, while on the subsequent cylinder it lays freely on the fabric belt. 
     Frequently several dryer groups are provided. Viewed in direction of web travel these dryer groups are arranged in tandem. This has the advantage that a variety of influences can be exerted upon the web during the course of its travel through the entire dryer section. 
     The web is to be transferred from one dryer group to the subsequent one. The transfer may be accomplished such that the web is not exposed at any time and such that it is however sandwiched between the fabric belt of a first dryer group and the fabric belt of the subsequent second dryer group. 
     There are however also situations where the enclosed web transfer is not possible due to constructive or spatial reasons, so that the web must be transferred exposed and unsupported from one dryer group to the subsequent one. The web is subject to a certain tensile stress in longitudinal direction. In an exposed transfer one refers to exposed web segments. Exposed web segments are neuralgic locations, because of potential web breaks. 
     The danger of web breaks at exposed web segments depends on various factors. Papers having a high basis weight dry slower than papers which have a low basis weight. The dryer section in the paper machine however has only a certain drying capacity. This may be sufficient for papers having a low basis weight, however the tensile strength of such papers is also naturally lower. 
     It would therefore be desirable to adapt the drying capacity of the web to the prevailing conditions, thereby giving more consideration to different paper characteristics such as basis weight, tensile strength, etc. However, this is not possible. 
     What is needed in the art is to create a dryer section in a paper machine so that it is adaptable to varying requirements with regard to the web which is being processed, as well as to other influences. Exposed web segments should also be avoided. Ultimately, an existing dryer section should be able to be retrofitted accordingly. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for handling a moving material web, including: a treatment unit including a rotating conveyor belt which forms a closed loop and carries the material web; a second treatment unit with a second conveyor belt which also forms a closed loop, both treatment units being connected parallel relative to each other; a first switch-over for the transfer of the web from the first to the second conveyor belt; and a second switch-over unit for the transfer of the web from the second to the first conveyor belt. Accordingly, a second lower dryer group is provided in addition to the at least one first upper dryer group of a dryer section. This includes at least one dryer cylinder as well as a second vapor permeable fabric belt which forms a closed loop and wraps around the dryer cylinder or dryer cylinders respectively. Generally, several guide rollers will be provided. During operation of the dryer section the second fabric belt is driven in opposite direction to the direction of the first dryer group. 
     The most important characteristic consists in that measures are taken to bring the two fabric belts toward each other at two different locations in the web path. At the two transfer locations the two fabric belts progress in the same direction and at the same speed. The material web which is to be transferred is sandwiched between the two fabric belts over a brief period of time. Consequently there is no exposed web segment so that there is no danger of a web break. The two fabric belts—the one of the first upper dryer group, as well as the one of the second lower inventive dryer group—can however also be again directed away from each other. 
     The inventive additional dryer group is connected parallel to the conventional first dryer group. It serves so to speak as a by-pass. It may be connected or disconnected as required, depending upon the aforementioned requirements with regard of the web which is being processed. 
     It is not critical as to how the dryer groups—the conventional upper or the inventive lower—can be configured. For example, the first or the second dryer group may include an upper and a lower row of dryer cylinders. Both dryer groups may however also include an upper row of dryer cylinders and a lower row of suction rolls. Other additional dryer equipment is also feasible, for example infrared dryer sections, hot air drying equipment, and others. 
     It is also irrelevant whether the woven fabric belt of the inventive dryer group is brought to the fabric belt of the conventional dryer group, or vice versa. 
     One interesting configuration consists of an arrangement whereby the transfer locations are variable. For example, the upstream transfer location could be positioned at alternating locations. 
    
    
     
       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 illustrates the referred to subject with connected additional dryer group; and 
         FIG. 2  illustrates the referred to subject with disconnected additional dryer group; 
         FIG. 3  shows another embodiment of the present invention with connected additional dryer group. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, 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, the conventional dryer section is always on top. It comprises two dryer groups—one dryer group  1  and one dryer group  2 . The dryer group  1  includes dryer cylinders whereby the dryer cylinders  3  through  8  are visible. A stabilizer roll  27  with a stabilizer box  28  is located between the dryer cylinders  7  and  8 . The second dryer group  2  also includes dryer cylinders whereby the dryer cylinders  9  through  11  are visible. In addition, a suction roll  13  is part of the second dryer group  2 , and several guide rollers are part of both dryer groups  1 ,  2 . 
     The dryer group  1  includes a dryer fabric  15 , and the dryer group  2  includes a dryer fabric  16 . 
     The inventive dryer group  17  is located below the two dryer groups  1  and  2 . This is arranged predominantly in the basement of the paper machine. It includes one dryer cylinder  18 , in addition one dryer fabric  19 , as well as one dryer fabric  20 . 
     The two dryer fabrics  19  and  20  wrap around numerous guide rollers  21 , in addition two pivoting guide rollers  22 ,  23 . 
     In addition the dryer group  1  includes a cut-off device  25 , and the dryer group  2  includes a web tear sensor  26  which controls the cut-off device  25 . 
     The web which is to be dried travels into the dryer group  1 —as seen in the drawing—from right to left. See arrow on stabilizer roll  27 . At the drying cylinder  3  the web is held sandwiched between the surface area of the cylinder and the dryer fabric  15 . At the dryer cylinder  4  it is outside, and the dryer fabric  15  is located between the surface area of the dryer cylinder  4  and the web. 
     At the dryer cylinder  5  the paper web is again located between the surface area of said cylinder and the dryer fabric  15 , and so on. 
     The stabilizing roll  27  is a suction roll with a bored roll sleeve and with a suction connection. Likewise, the areas which are in contact with the dryer fabric  15  are equipped with perforations. The surfaces of the stabilizing box  28  which are in contact with the web are also perforated, and a suction unit is also allocated to the stabilizing box  28 . In the configuration according to  FIG. 1  where the inventive additional dryer group  17  is connected, neither the stabilizing roll  27  nor the stabilizing box  28  are equipped with suction. The web which is on the outside of the stabilizing roll  27  is now admitted from the dryer fabric  15  onto the dryer fabric  19  of the dryer group  17 . Dryer fabric  19  glides over the first stabilizing elements  24 . Then the dryer fabric  19  with the web on it arrives at the dryer cylinder  18 . There it is enveloped between the surface area of the dryer cylinder  18  and the second dryer fabric  20 , as well as the first dryer fabric  19 . 
     After traveling around the dryer cylinder  18  the web travels over the second group of stabilizing elements  24 . At the pivoting guide roller  23  it is transferred to the dryer fabric  16  of the dryer group  2 . In this area the dryer fabric  16  glides over an additional stabilizing box  29 . This, again, is equipped with perforated gliding surfaces. In the example according to  FIG. 1  it is equipped with suction, so that the web is transferred positively from the dryer fabric  19  to the dryer fabric  16 . 
     The two stabilizing boxes  28  and  29  are positioned longitudinally—see the perforated lines. The two components of the aforementioned stabilizing boxes  28  and  29  can therefore be supplied independently from each other with suction. 
     The individual stabilizing elements  24 —the ones depicted on the right, as well as those on the left—can be supplied at different levels of suction. For example, the lower one of the stabilizing elements  24  depicted on the right is operated at a higher vacuum in the configuration according to  FIG. 1 . Its function is to reduce the dragged along air volume in the clothing. Another option is to use a steam blow box in this area. 
     The guide roll  22  and the stabilizing elements  24  depicted on the right are structurally connected with each other. These aforementioned components—guide roller  22  and the associated stabilizing elements  24 —can be pivoted together, so that they assume either the closed configuration depicted in  FIG. 1 , or the open configuration depicted in  FIG. 2 . 
     The same applies to the pivoted guide roller  23  with the stabilizing elements  24  depicted on the left. 
     The invention has general application, and not only for the dryer section of a paper machine. 
     The invention may generally be utilized in an apparatus for the treatment of a moving material web. The apparatus includes a first treatment unit including a conveyor belt which forms a closed loop and carries the material web. 
     According to the current invention a second treatment unit is provided which includes a second conveyor belt which also forms a closed loop. In addition, the two treatment units are parallel connected. Finally, a first switch-over is provided with which the material web can be transferred from the first to the second conveyor belt and a second switch-over with which the material web can be transferred back from the second conveyor belt to the first conveyor belt (see, for example,  FIG. 3 ). 
     One could refer to this as a kind of bypass shifting arrangement. 
     One interesting deviation from the basic concept consists in that the upstream transfer location for the transfer from the first conveyor belt (dryer fabric) to the second conveyor belt (dryer fabric) can be freely selected. 
     In the illustrated design example this variation consists in that the guide roller  22  can be pivoted not only between the dryer cylinder  6  and the stabilizing roll  27 , but also (in addition) at a different location, for example in the area of the dryer cylinder  4 . 
     The same applies to the pivoted guide roller  23 . 
     In general one would strive to keep the distance between the two pivoted guide rollers  22 ,  23  as small as possible, relative to the path of the web between the two transfer locations. In the configuration according to  FIG. 1  everything belonging to the upper dryer group  1  and  2  is not used for drying. 
     In the illustrated design example the “switch-over”, in other words the transfer location from the two upper dryer groups to the lower inventive additional dryer group, is located on top. However, this could also be reversed. The transfer locations could therefore also be located on the lower dryer group. 
     It is understood that the lower dryer group may include more than only one single dryer cylinder. 
     COMPONENT IDENTIFICATION 
     
         
           1  Dryer group 
           2  Dryer group 
           3  to  8  Dryer cylinder 
           9  to  11  Dryer cylinder 
           13  Suction roll 
           14  Guide rollers 
           15  Dryer fabric 
           16  Dryer fabric 
           17  Dryer group 
           18  Dryer cylinder 
           19  Dryer fabric 
           20  Dryer fabric 
           21  Guide rollers 
           22  Pivoted guide roll 
           23  Pivoted guide roll 
           24  Stabilizing element 
           25  Cut-off device 
           26  Tear sensor 
           27  Stabilizing roll 
           28  Stabilizing box 
           29  Stabilizing box 
       
    
     While this invention has been described with respect to at least one embodiment, 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.