Patent Publication Number: US-2009229082-A1

Title: Apparatus and method for dry forming of Fibrous Tissue

Description:
The present invention relates to an apparatus and a method for dry forming of fibrous tissue and comprising a suction box and a superjacent forming head with a forming wire fitted in between, on which the tissue is formed, in that the suction box has a suction area that sucks the fibres down towards the forming wire. 
     In the field of the dry forming technology the so-called beaching is a phenomenon that is known in the trade and that is undesirable. 
     The term beaching (in Danish termed “strandbred”) corresponds to the characteristic appearance that a fibrous tissue obtain. This appearance looks, most of all, like the pattern remained in the sand on a beach. 
     In concrete: there will be fibre material placed in a non-homogenously and non-uniformly distributed layer in the places, in which beaching will occur in the product. On the other hand, alternative types of non-homogenous material distributions, which cannot be characterized as beaching, do exist. However, a man skilled in the art will not be in doubt, when he sees beaching. 
     In the trade there is not complete clarity regarding the parameters that causes beaching in a product. Still, it is an unwanted phenomenon, and during several years many attempts have been made to reduce it. 
     One of the most essential parameters during the regulation is the intake air from the suction box, which sucks the fibres down towards the wire. The intake air from the suction box sucks the material from the forming head over the wire down to the forming wire. The material is caught by the perforated wire, while the intake air continues down into the suction box and further in a canal system. 
     During a normal process of dry forming, large air streams appear in the system. This is also the case in the air, being contained between the forming head and the wire over the suction box. The suction box is dimensioned and fitted in order to provide a essentially uniform suction, in manner ensuring that there also is provided a uniform air velocity and hence a uniform laying of fibre material in a homogenous tissue on the forming wire. 
     So far, the adjustment of intake air, which, substantially, has been provided through regulation of a suction ventilator and regulation of the actual suction box, has been intended to establish a suction, as uniform as possible, across the entire suction area. 
     The beaching that can be found in products does not necessarily appear in the entire suction area. Therefore, it is possible to find a product, in which beaching only appears in certain areas, for instance along one edge of the formed tissue. Even though it has not been possible to come up with a concrete explanation, within the trade, it is a prior assumption that beaching results from the disturbances that appear in the air stream across the suction box in the area, where beaching occur. Accordingly, by using the known adjustment methods, it has not been possible to reduce these disturbances that appear in the air stream and hence provide a homogeneous tissue without beaching. 
     U.S. Pat. No. 4,157,724, WO 0 029 668 and U.S. Pat. No. 4,353,686 describe examples of known solutions. These documents do not address any solution that makes it possible to provide a homogeneous tissue without beaching. 
     It is an object of the present invention to provide an apparatus and a method that makes it possible to remedy the drawbacks and reduce or totally eliminate beaching during dry forming of fibre tissue. 
     The objects of the present invention can be accomplished by a device as described introductory, which is characteristic in that, a pressure drop regulating means is fitted in the suction box, in a partly across the width of the forming wire extending sub-section of the suction area, in order to regulate the air stream and hence the turbulence that appears in said sub-section of the suction area of the suction box. 
     The method according to the invention is characteristic in that, a pressure drop regulation is provided in the suction box, in a partly across the width of the forming wire extending sub-section of the suction area, in order to regulate the air stream and hence the turbulence that appears in said sub-section of the suction area. 
     The solution in accordance with the present invention is based on the recognition, that beaching typically occurs in a sub-section of the suction area, and that a regulation parameter capable of regulating the air stream in such area, accordingly, is required. 
     By fitting a means, which can be applied to regulate the pressure drop in a sub-section of the suction area, is possible to regulate the air stream and hence the turbulence that appears in a sub-section of the suction area of the suction box. 
     It has, surprisingly, turned out to be possible to provide a significant beaching reduction in the formed fibrous tissue, through the application of a relatively simple solution. 
     In this way it was possible to inhibit the air stream in a sub-section of the suction area, by placing a pressure regulating means that covers the sub-section of the suction area. Accordingly, in a device or in a method, in which beaching occurs, it would be possible to mount a pressure drop regulating means, in a manner ensuring that enables regulation of the air stream in the specified sub-section. 
     According to a particular embodiment of the present invention, it is preferred that the means is adjustably mounted, substantially with spacious adjustment possibilities in three dimensions. This makes it possible to adjust the pressure drop regulating means according to the parameters of the formed fibrous tissue. 
     It has been shown that the beaching problems vary in a manner that depends upon the parameters of the formed fibrous tissue. Hence, beaching depends on the type of fibre being applied and the grammage being laid. 
     Thus, past experience has shown that, the pressure drop regulation according to the present invention is of particular advantage regarding production of products with grammage between 5 and 60 g/m 2 , preferably between 20 and 50 g/m 2 , because it has been shown that beaching problems particularly are associated with this kind of products. Furthermore, it has been shown that a greater degree of beaching occurs in products with short fibres than in products produced with long fibres. Therefore, the apparatus and method according to the present invention will be particular advantageous in the process of fibrous tissue production based on application of short fibres. 
     It is possible to adjust the air stream according to the formed product by adjusting the pressure drop regulating means. Alternatively, the apparatus can be equipped with replaceable pressure drop regulating means, so that a pressure drop regulating means adapted to a specific fibrous tissue is provided. 
     In order to achieve a self-cleaning effect, it is preferred that the means has a roughly smooth surface, in which the fibres cannot get stuck. Even though a smooth surface is preferred in order to provide the pressure drop regulating means, formed as a plate, which is mounted at the suction box, it would still, as an alternative, be possible to apply plates with more or less degree of perforation that enables a varied pressure drop regulation in the area, in which such plate or, alternatively, a mesh would be located. 
     It has turned out that the effect of the pressure drop regulating means, in particular, is beneficial in connection to devises, in which the forming head has at least one perforated rotating drum, in which fibres mixed with air enter the first end of the drum, which contains agents for fluidization of the fibres, and that the means is located in the suction area at said first end of the drum. In such forming head the fibres are feed from one side and the forming head will typically be subject to a circulating motion through an additional rotating drum, if the forming head contains two or more drums. In such construction it turns out, that the pressure drop regulating means has to be located at the first end of the drum, where the fibres are injected. In cases, in which more drums are applied, it would be at the first end or at the end of injection of the perforated rotating drum, which is located at the front end, as viewed in the feeding direction of the forming wire. 
     It is a prior assumption that the effect of the pressure drop regulating means, in such construction, has to be seen as an equalizing of the pressure drop caused by the fibres being laid on the forming wire, at a stage, when it is feed between the forming head and the suction box. During this feeding process early-stage fibrous tissue is formed. Accordingly, when the forming wire is feed into the suction area, the forming wire will contain no fibres, and a tissue with the desired grammage will be formed at the discharge point of the wire at the suction area. A dissimilar grammage will occur during the feeding process, when a sub-section transversely to the feeding direction of the forming wire is being considered. Normally, this can be balanced out by having more successive drums, in which the fibres are feed from one side or the other by turns. 
     In such forming heads with rotating drums, the plate would mainly be located in the area, which is call the first quadrant, that is at the feed-in end of the first rotating drum, which is provided in the forming head, as viewed in the feeding direction of the forming wire. It has emerged that this may inhibit the action of or completely eliminate beaching. 
     It is a prior assumption that the effect of the pressure drop regulating means established in order to equalize the pressure drop caused by the fibres being laid to the fibrous tissue, given that the early-stage forming of the fibrous tissue at the forming wire influences the uniform pressure drop, which normally is desired across the entire suction area. In that context it should be noted that a uniform air velocity normally is applied across the entire suction area, for example in the range between 5 and 6 m/s through the wire, and where no distribution variation of the air velocity, larger than plus/minus 0.1 m/s, normally, will occur across the suction area. 
     This air velocity is governed by the use of the pressure drop regulating means in such a manner, that a more or less uniform air velocity is provided across the entire suction area, after the pressure drop regulation, so that it inhibits the influence of the different layer thickness of the fibres, which otherwise would be the cause of variation of the pressure drop, and hence the air velocity across the suction area. 
     Alternatively, forming heads without rotating drums would also have feeding/injection of fibres with different orientation. Even if attempts are made to provide the cloud of fibres in the forming as homogeneous as possible, it will also in this situation, turn out, that non-uniform fittings of the fibrous tissue may occur. Therefore, a pressure drop regulating means will be beneficial in such forming head as well. 
     Furthermore, it should be noted that the sub-area of the suction area, normally, is provided so it adjoins an edge of the suction area. In such a situation it is essential that the means is provided with a boundary, which is tight-fitting to the boundary of the suction area at the specified sub-section. Accordingly, no unfavourable air streams or special turbulences will occur at slits between the pressure drop regulating means and the boundary of the suction area. 
     The pressure drop regulating means may be provided as a plate that may have different forms. Thus, it is not restricted to be rectangular, and hence it may be formed differently. The plate may be provided as a plane plate or as a curved plate for provision of different pressure drop regulations across the entire suction area. 
    
    
     
       In the following the invention will be described in further detail with reference to the accompanying drawing, where 
         FIG. 1  shows a side view of an apparatus according to the invention, 
         FIG. 2  shows a view corresponding to  FIG. 1 , viewed from above and with certain parts omitted, 
         FIG. 3  shows an enlarged view of a detail of the apparatus shown in  FIG. 1 , 
         FIGS. 4 and 5  show a partial view illustrating different adjustment principles for the plate shown in  FIG. 1 , 
         FIG. 6  shows five alternative embodiments of the plate shown in  FIG. 1 , 
         FIG. 7  shows an adjustment option for the plate shown in  FIG. 1 , 
         FIG. 8  shows a further adjustment option for the plate shown in  FIG. 1 , 
         FIG. 9  shows an additional adjustment option for the plate shown in  FIG. 1 , 
         FIG. 10  shows a further embodiment for the profile of the plate shown in  FIG. 1 , 
         FIG. 11  shows an additional embodiment for the profile of the plate shown in  FIG. 1 , and 
         FIG. 12  shows a further embodiment for an apparatus according to the invention. 
     
    
    
     In the following description, identical or similar elements will be termed with the same reference designation in the different figures. Accordingly, all details will not be explained in every single figure/embodiment. 
     An embodiment for an apparatus according to the invention is shown in  FIGS. 1 and 2 . The apparatus comprises a forming head  1 , in which there is provided two rotating perforated drums  10 , each comprising spike rollers that produce agents for fluidization of fibres, which are feed into the drum as indicated by the arrow heads  12  and  13  in  FIG. 2 . The fibres can, in this way, be feed into the first end  14  of the two drums  10 . 
     There will, furthermore, be provided connections, which will bring about a circulating flow  15  of the fibres between the two drums  10 . Underneath the forming head  1  there is provided a forming wire  2 , on which a fibrous tissue  9  is formed, as the forming wire is moved in the direction of motion as indicated by an arrow head  16 . 
     The tissue  9  formed at the forming wire  2  will, due to the action of the suction box  4 , which defines a suction area  17  over the active opening of the suction box. According to the invention, a plate  6  is provided in a sub-section of the suction area  17 , where said plate  6  provides a pressure drop regulating means  3  in the specified sub-section, as indicated in  FIG. 2 . 
     As it appears from  FIG. 2 , the plate  6  is provided in the sub-section of the suction area, which is located under the first end  14  of the first drum  10 , as viewed in the feeding direction  16  of the forming wire  2 . In  FIG. 3  an enlarged view of the pressure drop regulating means  3  is shown. As seen here, the plate  6  is attached to the suction box  4  by means of a fixed hinge member  5  at one side. The plate  6  is at the other side supported by a length-adjustable bar  8  that is attached to the plate by means of a mounting  7  and that is attached to the suction box by means of another mounting  7 ′. 
     As it appears from  FIG. 4 , there is provided an adjustable connection rod  8  at each end of the plate  6 . In this way the plate can be tilted transversely, as it appears from  FIG. 4  and the side view illustrated in  FIG. 5 . Thus, it is possible to adjust the plate  6 , so that it covers different sub-sections of the suction area  17 . 
     It should be noted that the plate  6 , as illustrated in  FIGS. 4 and 5 , not is placed at its edges  18 ,  19  lying true against the edges  20 ,  21 , as shown in  FIG. 2 . However, between the edges  18 ,  19  of the plate there would be provided tightenings for the edges  20 ,  21 , which define the boundary of the suction area. Accordingly, no unintentional air streams that could cause turbulence in said areas will occur. 
       FIG. 6  illustrates various designs for the plate  6 . There is, accordingly, illustrated a plate  6 ′ with a straight edge  22  at the front. A plate  6 ″ with a front edge  23  cut inclined at the front. A plate  6 ′″ with a convex side edge  24  in front. A plate  6 ″″ with a concave side edge  25  in front, and a plate  6 ′″″ with a saw-toothed edge  26  in front. 
     Other designs than the ones shown would be possible. 
       FIG. 7  illustrates an embodiment, in which the plate  6  is being adjusted about a hinged point  5 , as the length-adjustable bar is being lengthened or shortened, in such a manner that the plate  6  is being rotated upwards or downwards, as indicated at the arrow head  27 . 
       FIG. 8  illustrates a further embodiment, in which the plate is provided by component parts, so that it can be length-adjusted, as indicated by the arrow head  28 . In this situation, the plate is connected to a hinged point, and the length-adjustable connection rod  8  can be maintained at constant length or it could be lengthened as well.  FIG. 9  illustrates a situation, in which the plate  6  is displaced by adjusting the mounting in the fixed hinge member  5 . In this way, a hinge can be height-adjustable or alternatively it is possible to provide more hinged points, in between which the plate  6  can be connected. 
       FIG. 10  illustrates an alternative embodiment for a plate  6 . As seen here, the plate  6  is provided with a curved edge area  29  in front. The edge area  29  may have other curvatures than the one shown and it may for instance also be manufactured with several rectilinear plate sections provided along bend lines, so that a edged edge area is formed in place of the circular edge area  29  illustrated in  FIG. 10 . 
       FIG. 11  illustrates a further embodiment for the plate  6 . Here it is shown that the plate is designed with a circular profile  30  that extends across the entire plate. The curve form  30  may be single-buckled or double-buckled. 
       FIG. 12  shows an illustration corresponding to  FIG. 2 . In here there is shown another embodiment for an apparatus according to the invention with a forming head  31 , in which there is provided a feeding for fibres, as indicated by the arrow head  32 . In this embodiment the forming head is not provided with drums, as indicated above. The bottom in such forming head may be provided with a mesh with transverse drums or with so-called impellers that coat a mesh at the bottom of a forming head. Such means are, however, left out in the drawing for the sake of clarity. Also in this embodiment a pressure drop regulating means  3  covering a sub-section of the suction area  17  is provided. 
     Above is shown embodiments for an apparatus according to the invention. These embodiments are shown as non-limiting examples. Thus, it should particularly be noted that the forming head may have another design than the one shown with perforated rotating drums  10 . The suction box may, as well, be constructed with other designs than the funnel-shaped opening against the active suction area. Accordingly, there may be provided a direct opening into the suction box, wherein a sub-section of such suction area is installed with a pressure drop regulating means.