Abstract:
A device for producing plastic spirals for use in a machine for producing a fibrous web includes at least two rolls between which an adjustable roll nip is formed. The rolls have a shape which differs in at least one region from a cylinder shape and/or have a surface structure in at least one region on the surface thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of PCT application No. PCT/EP2013/071471, entitled “DEVICE AND METHOD FOR PRODUCING STRUCTURED PLASTIC YARNS, PLASTIC YARN AND SPIRAL FABRIC MADE FROM PLASTIC YARN”, filed Oct. 15, 2013, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention is directed to a device for producing plastic spirals, a method for producing plastic spirals using such a device, a plastic spiral thus produced, and a spiral fabric consisting of such plastic spirals. 
         [0004]    2. Description of the Related Art 
         [0005]    Textile clothing is found in a multitude of positions in machines for the production of fibrous web material, for example in paper or cardboard machines. In the forming section, the clothing facilitates sheet formation and dewatering; in the press section, absorption of water pressed from the fibrous web; in transfer positions, transfer into the next machine section; and in all sections it supports the fibrous web material. 
         [0006]    In the dryer section of a fibrous web machine, clothing—normally referred to as dryer fabric—in addition to supporting the fibrous web, serves to increase the drying efficiency and the energy efficiency of the dryer section. The dryer fabrics must be thin and, at the same time, dimensionally stable with low stretch, must not mark the fibrous material, not carry along air, provide optimal moisture removal, must have optimal sheet release characteristics, and ensure a uniform drying profile across the width of the fibrous web material. 
         [0007]    In particular, the last two characteristics are very strongly associated with the surface structure of the yarns forming the dryer fabric, whereas the characteristics of not marking the material and the high dimensional stability are also determinable through the cross sectional shape of the yarns. 
         [0008]    Among other arrangements, today&#39;s dryer fabrics consist of spiral structures wherein plastic spirals are formed from plastic yarns which are deposited overlapping adjacent next to one another in such a way that the individual spirals can be connected with pintle wires. The yarns used for this type of spiral fabric structures are either round or are already provided with a cross sectional shape that deviates from the round shape which can be, for example, flat-oval or approximately rectangular. 
         [0009]    A device to produce spirals from plastic yarns is known from WO09/130036 A1, comprising a winding device for the yarns which includes a guide rotatable around its axis, and having a forming body onto which the spirals are deposited by means of the winding device and from which they can be pulled. For the cross section of the respective yarn, a forming device that is rotatable with the winding device is assigned to the winding device. Accordingly, the produced spirals have a cross sectional shape that is determinable and can be adjusted to the aforementioned desirable characteristics of a dryer fabric. 
         [0010]    A disadvantage with the produced plastic spirals is that although a change in the cross-sectional shape of the wire is achieved, its surface, in particular on a microscopic scale, is not altered. This results in the dryer fabrics becoming dirty quickly and, as a result, cannot fulfill their tasks. Deteriorations are noted in sheet release, in the drying efficiency due to poorer moisture removal, and variable moisture cross profiles in the fibrous web material. 
         [0011]    What is needed in the art is a device and a method by which the yarns provided for the production of plastic spirals can be produced in a way that overcomes some of the known disadvantages of the prior art. 
       SUMMARY OF THE INVENTION 
       [0012]    The invention provides a device and method by which the yarns provided for the production of plastic spirals can be influenced during the manufacturing process not only in their cross sectional shape, but also in their surface structure. An accordingly formed and structured yarn and a spiral fabric can produced from the yarn. The plastic spirals that can be formed and structured in one simultaneous process step. This can occur by accordingly shaped rolls mounted in a roller bearing assembly that, in addition to a suitable shape for cross section deformation of the previously extruded yarns, have a surface design which embosses a structure into the yarn surface. 
         [0013]    The rolls can have a shape which differs, at least in regions, from a cylindrical shape and/or have a surface structure so that the surface design of the yarn can be discretionary in order to obtain the desired characteristics profile. 
         [0014]    In one embodiment, a shell surface of the rolls—at least in regions—has the shape of single, dual or multiple hyperboloid of revolution, of cones or tapers. This provides an easily realizable engineering adaptation of existing devices for the production of plastic spirals for spiral fabrics. 
         [0015]    The surface structures of the rolls can be in the form of strips, ribs, grooves, or wavy lines. 
         [0016]    The strips, ribs, grooves or wavy lines can assume random positions between axially parallel to an axis of the rolls and parallel to a circumferential direction of the rolls. 
         [0017]    According to another embodiment of the invention, it may be provided that the surface structures are designed in the form of protrusions of various shapes, or recesses of various shapes. 
         [0018]    The surface structures may be distributed evenly or unequally over the surface of the rolls. 
         [0019]    According to another embodiment of the invention the surface structures may be designed as a macro-structure and/or a micro-structure. The macro-structure can have a size range of 0.9 mm to 0.9 μm. The micro-structure can have a size range of 0.9 μm to 0.01 μm. 
         [0020]    The depth of the surface structures can be 0.01 μm to 0.3 mm, such as 0.01 mm to 0.2 mm. 
         [0021]    The distance between two adjacent surface structures may be 0.1 μm to 0.9 mm, or 0.01 mm to 0.6 mm. 
         [0022]    The roughness in the region of the surface structure can be less than 0.3. 
         [0023]    A method for the production of plastic spirals by winding plastic yarn into individual spirals that are inserted into each other, overlapping in cross direction on a work surface and are merged with pintle wires into flat structure can provide that, after being wound, the spirals are deposited next to one another on the work surface and are engaged with each other on this work surface through a joining device and are respectively connected with one another by the pintle wires. The spirals are thereby produced by the at least one winding device and after thermal forming are placed—due to a movement of the joining device —besides a guide rail on the work surface. The respectively subsequent spirals are placed on the work surface between the guide rail and the spirals previously placed on the work surface due to the movement of their winding device and the joining device which is located downstream from it. The at least one previously placed spiral is moved in a transverse direction on the work surface through movement of the joining device by a measure of the overlap, and the respectively last placed spirals are respectively connected with each other by at least one inserted pintle wire, and the yarn is formed in a roller bearing assembly. The roller bearing assembly is designed with at least two rolls with a roll nip between them through which the yarn is guided and a change of the outside shape and/or surface of the yarn occurs. 
         [0024]    The change in the shape of the yarn can occur through an appropriate shape of the rolls mounted in the roller bearing assembly. 
         [0025]    The change to the surface of the yarn can occur through embossing of a surface structure that is provided on at least one of the rolls, at least partially, into the yarn. 
         [0026]    A plastic spiral for the use in dryer fabrics in the dryer section of a machine for the production of a fibrous web such as a paper or cardboard web can be produced according to the aforementioned method. The yarn forming the plastic spiral has a cross sectional shape deviating from a round shape and/or the yarn forming the plastic spiral has at least partial surface structuring. 
         [0027]    The surface structuring can be in the form of strips, ribs, grooves, wavy lines, protrusions of various shapes and/or recesses of various shapes. 
         [0028]    According to one embodiment of the invention, the strips, ribs, grooves or wavy lines can assume random positions between parallel to a direction of extension of the yarn and parallel to a circumferential direction of the yarn. 
         [0029]    The surface structures may be distributed evenly or unequally over the surface of the yarn. 
         [0030]    One embodiment of the invention provides that the surface structuring is done at least partially on one outside and/or on one inside of the plastic spiral after laying the yarn into the spiral shape. 
         [0031]    The surface of the plastic spiral can have a roughness of less than 0.3. 
         [0032]    A spiral fabric for use in a machine for the production of a fibrous web such as a paper or cardboard web, comprises a plurality of plastic spirals that are connected with one another by pintle wires. The plastic spirals are provided at least partially with a surface structuring which positively influences dirt resistance and sheet release characteristics of the spiral fabric, thus providing constant quality of the produced fibrous web. 
         [0033]    According to another embodiment of the invention, plastic spirals having different surface structures can be combined in unequal or equal sequences, whereby the sheet release characteristics can be significantly improved. 
         [0034]    The spiral fabrics according to the invention can be used in a multitude of locations in the paper machine, such as forming fabric or dryer fabric, but also as the base structure for a press felt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    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: 
           [0036]      FIG. 1  is a sectional view of a device for the production of plastic spirals according to the prior art; 
           [0037]      FIG. 2A  is a schematic view of an embodiment of a roller bearing assembly according to the present invention that can be used in the device shown in  FIG. 1 ; 
           [0038]      FIG. 2B  is a schematic view of another embodiment of a roller bearing assembly according to the present invention that can be used in the device shown in  FIG. 1 ; 
           [0039]      FIG. 3A  is a schematic view of a plastic spiral with a surface structure that can be produced using the devices shown in  FIGS. 1-2 ; 
           [0040]      FIG. 3B  is a schematic view of another plastic spiral with a surface structure that can be produced using the devices shown in  FIGS. 1-2 ; 
           [0041]      FIG. 3C  is a schematic view of yet another plastic spiral with a surface structure that can be produced using the devices shown in  FIGS. 1-2 ; and 
           [0042]      FIG. 4  is a schematic lateral view of an individual loop of a plastic spiral with embossed surface structures that can be produced according to the present invention. 
       
    
    
       [0043]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments 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 
       [0044]    Referring now to the drawings,  FIG. 1  shows a strongly schematized sectional view of a device  1  for producing plastic spirals for production of paper machine clothing, in particular spiral fabrics for use in the dryer section of a paper or cardboard machine according to the current state of the art. 
         [0045]    Such devices  1  are known so a detailed description of device  1  is omitted. The device is described only in regard to its invention-relevant components, in order to simplify understanding of the present invention. 
         [0046]    Device  1  include a housing  2  where a roller bearing assembly  3  is disposed. The roller bearing assembly includes a first roll  4  and a second roll  5  between which a roll nip  6  is formed. In roll nip  6 , an already deformed yarn  7  can be seen that has been transformed into a longitudinal oval cross sectional shape from an original approximately round cross sectional shape in which it, for example, exits an extruder that is not illustrated. 
         [0047]    First roll  4  is mounted adjustably in an adjustment device  8 , while second roll  5  is mounted stationary in housing  2 . The adjustment of the position and the drive of first roll  4  are possible via a drive  9  which is arranged suitably in housing  2 . 
         [0048]    Rolls  4  and  5  that are mounted in roller bearing assembly  3  are smooth and cylindrical according to the current state of the art. Deformation of yarn  7  therefore occurs only by moving first roll  4  closer to second roll  5  by reducing roll nip  6  and a corresponding displacement of the still deformable plastic material of yarn  7  toward the outside. 
         [0049]    The produced yarn  7  with altered cross section therefore has an altered cross section, but a smooth surface. Accordingly, the previously discussed properties of yarn  7 , or respectively of the dryer fabric produced from yarn  7 , are not satisfactory in regard to sheet release and dirt resistance. 
         [0050]    Remedial action can be provided by modification of rolls  4  and  5  that are mounted in roller bearing assembly  3 . Such modified rolls  24  and  25  are illustrated in  FIGS. 2A and 2B  according to the present invention. In order to maintain clarity, only rolls  24  and  25  respectively are shown in  FIGS. 2A and 2B , as well as yarn  7 . 
         [0051]    In  FIG. 2A , a combination is shown of a first roll  24  which has a double hyperbolic rotational shape with a second roll  25  which is cylindrical and which is provided with a surface structure  10 . 
         [0052]    First roll  24  imparts a macroscopic structure to yarn  7  which, in this case, can produce a groove  11  in the longitudinal direction of the yarn, whereas second roll  25  provides yarn  7  with surface structuring  12  which is imparted into the material of yarn  7  by pressing into surface structure  10  of roll  5 . 
         [0053]    Consequently, a yarn  7  is obtained which, on one top side and one bottom side can have differently designed surface shapes and structures. Depending on the orientation of yarn  7  in the subsequent plastic spiral, groove  11  can point inward or outward, and embossed surface structure  12  can point inward or outward. 
         [0054]      FIG. 4  shows an example of a single loop of a plastic spiral in whose upper region only a surface structuring  12  is visible, whereas yarn  7  may, for example, be provided with groove  11  on the outside (not visible in  FIG. 4 ). 
         [0055]    In  FIG. 2B , an additional embodiment of a roller bearing assembly  3  according to the present invention is shown, where both rolls  24  and  25  have a double hyperbolic rotational shape and accordingly impart a shape with grooves  11  onto the top and bottom side of yarn  7 . 
         [0056]    First roll  24  moreover has a surface structure  10  which is shark skin like. This produces a corresponding surface structuring  12  on yarn  7  which provides excellent characteristics in regard to dirt and water resistance, as well as to flow properties of air and water. Such effects (for example the so-called Lotus-effect) are known from nature and are used in many ways technologically. 
         [0057]    There are hardly any limits in regard to the shape of rolls  24  and  25  and to the arrangements of their surface structures  10 . Any combination of single, double or multiple hyperboloids of revolution, as well as combinations of conical, cylindrical or optional other geometrical shapes are possible. 
         [0058]    Surface structures  10  can be in the form of strips, ribs, grooves or wavy lines and can assume positions parallel, tilted or diagonal relative to the roll axis, as far as to the circumferential direction of the rolls. Protrusions in any discretionary shape or recesses in any discretionary shape, even or uneven, can be distributed at least over regions over the surface of rolls  24 ,  25 . Several surface structures  10  may also be combined on one of the rolls  24 ,  25 . Moreover, it is possible to combine, for example, the rotational hyperbolic shape with a surface structure  10 . 
         [0059]    Dimensioning of surface structures  10  can thereby be divided into a macro- and a micro-structuring which can be used individually or in combination with each other. The macrostructure may have a size range of 0.9 μm to 0.9 mm, whereas the microstructure can have a size range of 0.01 μm to 0.9 μm. 
         [0060]    The depth of surface structures  10  can be 0.01 μm to 0.3 mm or 0.01 mm to 0.2 mm. A distance between two adjacent surface structures  10  can be 0.1 μm to 0.9 mm or 0.01 mm to 0.6 mm. 
         [0061]    The roughness in the region of surface structures  10  can be less than 0.3 so that the surface roughness of yarns  7  is also less than 0.3. 
         [0062]    Suitable limiting elements (not illustrated) in roll nip  6  can limit the width of squeezed yarn  7  and produce an almost rectangular cross sectional shape. By structuring these limiting elements, the sides of yarn  7  can also undergo targeted structuring. 
         [0063]      FIGS. 3A ,  3 B and  3 C illustrate examples of several plastic spirals  13  which together form a dryer fabric  14 . Plastic spirals  13  are held together in a generally known manner by pintle wires  15 . 
         [0064]    As shown in  FIG. 3A , the plastic spirals  13  can each be provided with an embossed groove  11 , as well as an overlaid surface structuring  12 . 
         [0065]    As shown in  FIG. 3B , the plastic spirals  13  can all be provided with a diagonally progressing groove-type surface structuring  12 . 
         [0066]    As shown in  FIG. 3C , a combination of two differently arranged plastic spirals  13  can be arranged always alternating. Spiral fabrics of this type can be produced in one work cycle wherein several spiral producing units are operated with different embossing units. 
         [0067]    As already mentioned,  FIG. 4  illustrates a single loop of a plastic spiral  13  which can be used in a dryer fabric  14  for a paper or cardboard machine which is provided in the upper region on its inside and in the lower region on its outside with a surface structuring  12 , as previously described. The diverse arrangement of surface structuring  12  may have a variety of consequences in regard to the performance of plastic spiral  13  or, respectively, subsequently in the dryer fabric. An improved dirt resistance on the inside of plastic spiral  13  results in greater uniform drying efficiency, since the open volume of the dryer fabric still remains intact even after prolonged use. Exterior surface structures  12  can improve the sheet release characteristics, in particular if differently structured plastic spirals  13  alternate with each other, as illustrated in  FIG. 3C . 
         [0068]    Different structuring can be provided on the outside and on the inside of plastic spiral  13 , thereby being able to achieve different characteristics. Transverse structuring of the inside simplifies insertion of pintle wires  15 , whereas with other suitable structuring the fixation of filler wires can be favored. At the same time, a modification can be provided on the outside that is different from the structuring on the inside, for example, with the objective to influence the sheet release characteristics or to reduce the contamination susceptibility. 
         [0069]    Utilization of described plastic spirals  13  is possible in almost any paper machine clothing, such as dryer fabrics and former fabrics. Use as base structure for press felts is also conceivable and possible. 
         [0070]    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.