Abstract:
A flexible press cover which has an additional strengthening element in at least one of its two end regions. As a result, in the end region, the tensile strength and the tensile rigidity in the circumferential direction are increased with respect to that hitherto known in such a way that it is no longer necessary to clamp the press cover end region in between two components. Instead, the press cover according to the present invention is suitable to be fixed to the outer circumferential surface of a rotatable supporting element belonging to the cover carrying disk without the aid of an outer ring, a clamping band, clamping filament or the like. In the most beneficial case, the arrangement for fixing the press cover to the aforementioned supporting element is completely free of any kind of fixing elements which would be associated with the cover outer surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation of PCT application No. PCT/EP02/07762, entitled “FLEXIBLE PRESS JACKET AND SHOE PRESS ROLL COMPRISING SUCH A FLEXIBLE PRESS JACKET”, filed Jul. 12, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a flexible press cover which is intended for a shoe press roll.  
           [0004]    2. Description of the Related Art  
           [0005]    A shoe press roll of this type is used for dewatering or calendering a moving fibrous web, in particular a paper or board web. The flexible press cover includes a plastic layer, preferably made of polyurethane and, as a strengthening element, a (“conventional”) reinforcement embedded in the plastic layer. The reinforcement can be formed as a woven fabric; however, preference is given to what is known as a laid fabric, which includes axially parallel longitudinal filaments and circumferential filaments wound in. The circumferential filaments can be wound into the plastic layer on the outer side of the longitudinal filaments (see EP 0330680=U.S. Pat. No. 5,134,010, PH 04378). However, the opposite arrangement is likewise possible (see WO 95/29293, Tamfelt).  
           [0006]    In relation to the prior art, reference is made to the following further documents:  
           [0007]    D1: DE 3546650 C2, (PH 04164A),  
           [0008]    D2: DE 29702362, (PH 10287),  
           [0009]    D3: DE 19633543 (PH 10368).  
           [0010]    As is known, a shoe press roll includes a stationary supporting element. Rotatably mounted on the latter are two cover carrying disks for the flexible press cover. In addition, there is arranged on the supporting element a radially displaceable press shoe, which is able to press the revolving press cover against an opposing roll in order to form a press nip extended in the web running direction. It is important that the press cover and the cover carrying disks, together with the supporting element, bound a closed, liquid-tight internal space.  
           [0011]    According to document D1, in order to achieve a liquid-tight connection between the press cover end region and one of the cover carrying disks, provision is made to bend over the end region radially inward and to press it against the outer end of the cover carrying disk with the aid of clamping elements.  
           [0012]    This arrangement has been tried and tested in practice. However, it is disadvantageous in that a large number of recesses has to be provided in the edge zone of the press cover, between which recesses tongues remain. In some cases, difficulties also arise in achieving the most exact circularity of the press cover.  
           [0013]    According to FIGS. 3 and 4 of document D2, attempts have been made to avoid the deformation of the press cover end region described in D1. Each of the two press cover end regions retains the normal cylindrical form, so that the production of recesses and tongues is dispensed with. Provision is made to clamp the cylindrical press cover end region in between an internal expandable (that is to say of enlargeable diameter) spreader ring and an outer ring. However, such an outer ring is frequently disruptive, since the replacement of a worn press cover by a new press cover is more awkward.  
           [0014]    According to FIGS. 2 to 4 of document D3, an annular circumferential groove is provided in the outer circumferential surface of a cover carrying disk, into which groove the annular region of the press cover is pressed, specifically by way of a clamping band or by way of a plurality of turns of a high-strength filament or by way of a shrinkage ring. If a covering provided in accordance with FIG. 1 at document D3 is left out, then there is no disruptive outer ring. Nevertheless, this known solution has not been able to gain acceptance in practice.  
           [0015]    What is needed in the art is a flexible press cover where the production of recesses and tongues in the press cover end region is superfluous, the mounting of the press cover end region on the respective cover carrying disk is easily achievable, the mounted press cover has good circularity and the outer circumferential surface of the press cover is free of fixing elements.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention provides a flexible press cover with the following requirements satisfied:  
           [0017]    a) the production of recesses and tongues in the press cover end region is superfluous;  
           [0018]    b) the mounting of the press cover end region on the respective cover carrying disk is able to be performed with the least possible effort; if the mounting operation is carried out within the papermaking machine, account must be taken of the fact that the mounting space which is available at the two roll ends is often very restricted;  
           [0019]    c) the most precise circularity of the finally mounted press cover should be achievable;  
           [0020]    d) the outer circumferential surface of the press cover should be free of fixing elements, for example outer rings.  
           [0021]    The present invention comprises, in one form thereof, a flexible press cover which has an additional strengthening element in at least one of its two end regions. As a result, in the end region, the tensile strength and the tensile rigidity in the circumferential direction are increased with respect to that hitherto known in such a way that it is no longer necessary to clamp the press cover end region in between two components. Instead, the press cover according to the present invention is suitable to be fixed to the outer circumferential surface of a rotatable supporting element belonging to the cover carrying disk without the aid of an outer ring, a clamping band, clamping filament or the like. In the most beneficial case, the arrangement for fixing the press cover to the aforementioned supporting element is completely free of any kind of fixing elements which would be associated with the cover outer surface.  
           [0022]    By virtue of the present invention, it is possible to achieve a number of advantages: the form of the press cover end region remains completely or at least approximately cylindrical. During the mounting of the press cover, deformation of the press cover end region is not necessary; the necessity of producing recesses and tongues is thus also dispensed with. The joining of the press cover end region to a radially outer part or region of the cover carrying disk can be carried out in the same way or at least in a very similar way as the joining of two metal components.  
           [0023]    Thus, the mounting of the press cover on the cover carrying disks can be carried out in a simpler way than hitherto known, namely with less effort, so that, if required, even an unpracticed person can be entrusted with the mounting work. A further important advantage is that no outer ring (rotating with the press cover) is required. Likewise, the clamping elements required in accordance with D1 are omitted; this makes it easier to work in restricted conditions of space within the papermaking machine.  
           [0024]    The press cover end region advantageously has a constant thickness, measured along axially parallel envelope lines. As a rule, on a finally mounted press cover, not only the outer circumferential surface but also the inner circumferential surface of the press cover end region (having the additional strengthening) are therefore cylindrical. However, a departure from this can be made if required. Specifically, it may be advantageous to design the inner circumferential surface of the press cover end region to be slightly conical, with an internal diameter which increases outward or inward. The fixing of the press cover end region to any kind of annular supporting element belonging to the cover carrying disk (or directly to the carrying disk) can be made easier hereby. In both cases, it can be advantageous to provide a supporting element of which the diameter can be enlarged, that is to say can be spread. However, the use of a non-spreadable ring is also possible, for example a mounting ring, which is inserted into a new press cover to be retrofitted outside the shoe press roll (see DE 101 38 527.7).  
           [0025]    The present invention can be applied in flexible press covers with different conventional reinforcements, in particular with woven fabric or laid fabric reinforcement. Different embodiments of the additional strengthening are also specified; this can be formed as an additional or strengthened reinforcement. As an alternative to this or in addition, materials with a modulus of elasticity that is higher in the circumferential direction can be used. One further possibility is for a strengthening ring to be integrated into at least one of the press cover end regions. The object of all these measures is to reduce the extensibility in the circumferential direction of the press cover end region as compared with that hitherto.  
           [0026]    Protection is also claimed for a complete shoe press roll having a flexible press cover formed in accordance with the present invention. In this case, at least one of the two cover carrying disks can be adapted in one way or another to the press cover end region formed in accordance with the present invention. Details are explained further below within the context of the figure description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    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:  
         [0028]    [0028]FIG. 1 is a partial longitudinal sectional view through a shoe press roll having an embodiment of a flexible press cover according to the present invention;  
         [0029]    [0029]FIG. 2 is a partial view of an embodiment of a spreader ring belonging to the shoe press roll according to the present invention;  
         [0030]    [0030]FIGS. 3-6 illustrate variants of FIG. 1 according to the present invention;  
         [0031]    [0031]FIGS. 7-13 illustrate various modifications of the press cover end region in longitudinal section according to the present invention;  
         [0032]    [0032]FIG. 14 illustrates an embodiment of the method of producing a press cover on the outer circumferential surface of a cast cylinder according to the present invention;  
         [0033]    [0033]FIG. 15 illustrates an embodiment of the press cover produced in accordance with FIG. 14 in the finally mounted state; and  
         [0034]    [0034]FIG. 16 illustrates a further variant of a shoe press roll having a flexible press cover according to the present invention. 
     
    
       [0035]    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  
       [0036]    Referring now to the drawings, and more particularly to FIG. 1, there is shown a shoe press roll, only one of the two end regions of flexible press cover  10  and its fixing to a rotatable cover carrying disk  20 . The latter is mounted in a known way on a supporting element, not visible, by way of a rolling contact bearing  21 . Likewise not illustrated is a press shoe, using which press cover  10  can be pressed against an opposing roll. These and further known details of a shoe press device can be seen, for example, from DE 19522761 (PH 10178).  
         [0037]    Press cover  10  is substantially composed of a plastic layer  30 , for example of polyurethane, with a conventional reinforcement embedded therein as a strengthening elements; the reinforcement includes, axially parallel longitudinal filaments  31  and circumferential filaments  32  wound thereon. The thickness d of press cover  10  is chosen such that grooves or blind holes  33  can be provided within the pressing zone P. In the end region E, press cover  10  has substantially the same thickness d as in pressing zone P. In end region E, as additional strengthening (that is to say in addition to conventional reinforcement  31 ,  32 ), additional circumferential filaments  34  of the highest possible tensile strength and tensile rigidity (high modulus of elasticity) are embedded in plastic layer  30 .  
         [0038]    According to the present invention, circumferential filaments  34  form an additional reinforcement, produced from high-strength plastic or metal filaments or wires. As compared with circumferential filaments  32  of the conventional reinforcement, the additional circumferential filaments or wires  34  can have a larger filament diameter and/or be formed from a material which has a higher tensile strength and, in particular, a higher modulus of elasticity (e.g. Kevlar). However, it is also possible to choose the same diameter and/or the same material for filaments  32  and  34 , preferably a material with a relatively high modulus of elasticity. In addition, the plastic layer can be formed from a material with an increased modulus of elasticity. Between end region E and pressing zone P, press cover  10  can have a zone of lower thickness, in order to increase its flexibility precisely where increased deformation takes place during operation.  
         [0039]    Cover carrying disk  20  includes an integrally molded collar  22  and an extension ring  23  screwed to the latter. Collar  22  and ring  23  engage around rolling contact bearing  21  and, on their outer side, bear an axially displaceable clamping ring, which is formed as an annular piston  24 . The three aforementioned components  22 ,  23  and  24  are shaped in such a way that an annular space  25 , to which a pressurized medium can be applied, is formed between them. As a result, annular piston  24  can be displaced outward hydraulically or pneumatically parallel to the roll axis. Sealing rings  26  are used to seal off the annular space  25 .  
         [0040]    In order to connect press cover  10  to cover carrying disk  20 , spreader ring  27  is provided. The latter has a cylindrical outer circumferential surface, provided with recesses if required, which engages in the cylindrical inner circumferential surface of the press cover end region E. Spreader ring  27  has a conical inner circumferential surface, which interacts with a conical outer circumferential surface of annular piston  24 . In the event of axial displacement of annular piston  24  (to the left in FIG. 1), spreader ring  27  (which bears axially on cover carrying disk  28 ) is widened, and therefore a secure, liquid-tight connection is made between press cover  10  and cover carrying disk  20 . By virtue of additional reinforcement  34 , an external clamping link is no longer required in the press cover end region.  
         [0041]    The axial displacement of annular piston  24  can also be carried out with the aid of screws (indicated at  28 ). Screws  28  of this type can also be used for the axial fixing of annular piston  24  after the annular piston has been displaced hydraulically or pneumatically. FIG. 2 shows spreader ring  27  from the outside. This ring is given its ability to spread by slots  29  machined in alternately from both sides, in which a highly elastic filler is provided, in order that the necessary hermetic sealing of the roll internal space is ensured.  
         [0042]    [0042]FIG. 3 differs from FIG. 1 in that, in end region E on press cover  10 ′, provision is made for bead  30 A projecting radially inward, which fits into a turned recess in spreader ring  27 ′. In this way, the accuracy of the axial fixing of press cover  10 ′ to carrying disk  20  is increased.  
         [0043]    Press cover  10 A of the exemplary embodiment illustrated in FIG. 4 is similar to that of FIG. 1; only length E′ of the press cover end region has been enlarged somewhat, corresponding to the greater axial length of spreader ring  27 A. Cover carrying disk  20 A again has collar  22 A to accommodate rolling contact bearing  21 . Between collar  22 A and spreader ring  27 A there is a simple clamping ring  24 A. The latter is displaced axially in the outward direction merely with the aid of screws  28 , enlarging the outer diameter of the spreader ring with its conical outer. circumferential surface, which interacts with a conical inner circumferential surface of spreader ring  27 A, in order to produce a secure connection to press cover  10 A. Integrally molded on spreader ring  27 A is collar  27 B, which again makes the accurate axial fixing of press cover to carrying disk  20 A easier.  
         [0044]    In a shoe press roll according to the present invention, both ends of the roll can be constructed in accordance with FIG. 1. Another possibility is for one end of a shoe press roll to be configured in accordance with FIG. 1 or FIG. 3, but, on the other hand, for the other end of the roll to be figured in accordance with FIG. 4 or in accordance with FIGS.  5  or  6  described below.  
         [0045]    Press cover  10 B of the exemplary embodiment illustrated in FIG. 5 differs from press cover  10 A of FIG. 4 only in the fact that the inner circumferential surface in the end region is not continuously cylindrical but is slightly conical a short distance from the outside, with an internal diameter that decreases from the outside toward the inside.  
         [0046]    This makes it easier to insert mounting ring  40 , which has a corresponding conical outer circumferential surface. The insertion of this ring  40  (and the fixing of the same in press cover  10 B, for example by way of adhesive) is preferably carried out outside the shoe press roll, that is to say before the removal of a press cover that has worn and is to be replaced. For fixing mounting ring  40  bearing press cover  10 B to cover carrying disk  20 B, the following is provided: the outer circumferential surface of cover carrying disk  20 B is offset at  41 . The inner circumferential surface of strengthening ring  40  has a corresponding offset, in the example illustrated, a relatively small internal diameter D being followed by a larger internal diameter in the axial direction from the inside to the outside. In this way, press cover  10 B, together with pre-mounted mounting ring  40 , can be pushed onto cover carrying disk  20 B in the direction of the arrow P over the entire (not illustrated) stationary supporting element. This is possible by virtue of the fact that the aforementioned relatively small internal diameter D of ring  40  is still somewhat larger than the external dimensions of the stationary supporting element, including the press shoe and further accessories. In order to screw ring  40  to cover carrying disk  20 B, the following is provided: bush  42  is rotatably mounted in a bore in cover carrying disk  20 B. Integrally molded at the inner end of bush  42  is a nose flange  43 ; a radial pin  44  is inserted into the outer end. In the illustrated position of bush  42 , the nose of nose flange  42  acts on the inner end of ring  40 . However, as a result of rotation of bush  42 , the nose permits the strengthening ring to pass when inserted in the direction of the arrow P. In order to fix mounting ring  40  (together with press cover  10 B) to cover carrying disk  20 B with the aid of the aforementioned nose flange  43 , a screw  28  is provided. A plurality of such arrangements are distributed over the circumference of cover carrying disk  20 B.  
         [0047]    [0047]FIG. 6 shows a simplified alternative to FIG. 5. Mounting ring  40 ′ here has a smooth inner circumferential surface (without offset  41  shown in FIG. 5); in addition, bush  42  has been omitted. Mounting ring  40 ′ is screwed to cover carrying disk  20 ′ by way of simple studs  45 . In this design, however, a smaller internal diameter D′ of mounting ring  40 ′ will generally be needed than in FIG. 4. In order that, as the press cover is drawn in, mounting ring  40 ′ can nevertheless pass the stationary supporting element with its accessories, it may be necessary to arrange some of these accessories such that they can move on the supporting element; see the parallel patent application DE 101 38 527.7  
         [0048]    For fixing press cover  10 C to mounting ring  40 ′, the following is provided: the mounting ring has a conical outer circumferential surface that tapers in the outward direction. In addition, in press cover end region E″, circumferential filaments  32 A and/or  34 A are wound in with increased prestress, so that end region E″ likewise tapers conically in the outward direction. Press cover  10 C is fixed onto mounting ring  40 ′ in a manner similar to the fixing of a vehicle tire to its rim. The press cover design with circumferential filaments wound in under increased prestress can also be combined with a mounting ring whose outer circumferential surface is cylindrical.  
         [0049]    [0049]FIG. 7 shows press cover  11  which is modified with respect to FIG. 1 and whose conventional reinforcement (differing from FIG. 1) has axially parallel longitudinal filaments  35  arranged outside circumferential filaments  32  (corresponding to WO &#39;293). As additional reinforcement, circumferential filaments  36  are provided, which are preferably wound onto the reinforcement  32 ,  35  from the inside. As an alternative to this or in addition, in order to strengthen the press cover end region further, circumferential filaments  36 ′ which are wound onto the reinforcement  32 ,  35  from the outside can be provided.  
         [0050]    Press cover  12  illustrated in FIG. 8 has, as reinforcement, a woven fabric  37 . As additional reinforcement of the press cover end region, circumferential filaments  38  are provided, which are wound onto woven fabric  37  from the outside. Alternatively to this or additionally, circumferential filaments  38 ′ arranged radially on the inside can be provided.  
         [0051]    In the exemplary embodiments according to FIGS. 7 and 8, both press cover end regions can be designed identically. By contrast, the variant illustrated in FIG. 9 can be provided only at one of the two press cover ends. This results from the production method according to EP 0330680 (production of the press cover on the outer side of a cast cylinder). In detail, FIG. 9 shows a press cover  13  whose reinforcement  31 ,  32  corresponds to that of the press cover  10  illustrated in FIG. 1. The illustrated end region of press cover  13  has, in a way similar to FIG. 3, a thickening  30 A projecting radially inward. Located in this is an additional reinforcement, which can be formed as a woven fabric or (as illustrated) as a laid fabric, including axially parallel longitudinal filaments  39  and circumferential filaments  39 ′ wound thereon. In addition, a thickening (not illustrated) projecting radially outward can be provided, similar to that of FIG. 1 or  3 .  
         [0052]    [0052]FIG. 10 shows a press cover  50  according to the present invention whose end region has no thickening. Here, the additional strengthening is formed by circumferential filaments  32 ′ being wound more densely in the end region than circumferential filaments  32  located outside the end region. Circumferential filaments  32  and  32 ′ can include the same material. As an alternative to this, circumferential filaments  32 ′ can also be formed from a material with an increased modulus of elasticity. In addition, in the end region, plastic layer  30  can be produced from a material with an increased modulus of elasticity.  
         [0053]    FIGS.  11  to  15  show embodiments of the press cover according to the present invention in which a strengthening ring (of plastic or metal) is integrated into the end region of the press cover as additional strengthening. According to FIG. 11, the thickness d of the axially outer region  52  of strengthening ring  51  is substantially the same as or greater than the thickness of end region E of press cover  10  of FIG. 1. The axially inner region  53  is substantially thinner and overlaps the end of press cover  54 , initially produced in the conventional way (EP&#39;680), with its conventional reinforcement  31 ,  32 . Ring  51  is fixed by casting on an additional plastic layer  55  and winding in additional circumferential filaments  56  at the same time. Press cover  54  is fixed to the cover carrying disk in the same way as in FIGS.  1  or  4  or by way of screws which engage directly in strengthening ring  51  in the axial direction (see threaded hole  59 ).  
         [0054]    [0054]FIG. 12 differs from FIG. 11 in that strengthening ring  51 A is thinner in its axially outer region than the thickness d of the finished press cover end region, and in that it is sheathed over its entire length by the additional plastic layer  55 A with additional circumferential filaments  56 .  
         [0055]    [0055]FIG. 13 shows the end region of a press cover  60  produced in accordance with WO &#39;293 with strengthening ring  61 . Illustrated schematically is a cast cylinder  62  with its inner circumferential surface  63 . Firstly, during the production of the press cover  60 , strengthening ring  61  fixed to cast cylinder  62  and is used to clamp the longitudinal filaments  64  on. Plastic layer  65  is then cast, circumferential filaments  66  simultaneously being wound from the inside onto longitudinal filaments  64  and strengthening ring  61 . In order to fix press cover  60  to a cover carrying disk (not illustrated), strengthening ring  61  has flange  67  projecting radially inward. Alternatively, flange  68  projecting radially outward could be provided.  
         [0056]    [0056]FIG. 14 shows the production method of a press cover  70  with strengthening rings and  71  and  72 . The production method similar to that of EP &#39;680, with a cast cylinder  73  on whose circumferential outer surface the production takes place. Differing from EP &#39;680, instead of clamping rings, strengthening rings  71  and  72  are provided, which are used initially to clamp longitudinal filaments  74  on and which, after plastic layer  75  has been cast on and circumferential filaments  76  have simultaneously been wound on, remain a constituent part of press cover  70 . The secure fixing of strengthening rings  71  and  72  in press cover  70  is achieved by the longitudinal filaments  74  (as disclosed by EP &#39;680) being drawn in a meandering fashion through strengthening rings  71 ,  72  and then being tensioned, additionally by the fact that circumferential filaments  76  are wound onto the strengthening rings with a certain prestress. FIG. 14 also shows how casting nozzle  77  moves from one end of cast cylinder  73  to the other during the casting operation, while the cylinder rotates at the same time.  
         [0057]    One strengthening ring  71  has flange  71   a  projecting radially inward, which bears on one end of cast cylinder  73 . The other strengthening ring  72  has flange  72   a  projecting radially outward, in which clamping screws  78  engage in order to tension longitudinal filaments  74 .  
         [0058]    [0058]FIG. 15 shows the press cover  70  produced in accordance with FIG. 14 in the finished state mounted on cover carrying disks  79  and  80 . In this case, flanges  71   a  and  72   a  are used for fixing the press cover to the carrying disks, in each case with the aid of screws  81 ,  82 . Each of the two strengthening rings  71 ,  72  is centered on an outer circumferential surface of its cover carrying disk. In order to make it easier to draw in press cover  70  in the axial direction (arrow P), the diameter of the outer circumferential surface of carrying disk  79  on the left (in FIG. 15) is smaller than that of the right-hand carrying disk  80 . Accordingly, cast cylinder  73  in FIG. 14 is offset slightly at  83 .  
         [0059]    In the case of press cover  14  illustrated in FIG. 16 (whose conventional reinforcement is not illustrated), additional strengthening is formed as an end section  16  of the press cover which is folded inward (or turned over). Additional reinforcement  15  is provided therein. As FIG. 16 shows, the inner circumferential surface of the inwardly folded end section  16  is conical with an internal diameter increasing in the inward direction. As a result, press cover  14  is fixed to cover carrying disks  20 C and  20 D in a manner similar to the fixing of a vehicle tire to a rim. One press cover end section preferably rests directly on cover carrying disk  20 D, which has a corresponding conical outer circumferential surface. The other end section rests on clamping ring  17 , which likewise has a corresponding conical outer circumferential surface and which can be displaced in an axially parallel manner on cover carrying disk  20 C. A plurality of ring segments  18  can be inserted into cover carrying disk  20 C in the radial direction from the outside to the inside. Through said segments there extend screws  19 , using which the press cover end section can be clamped in between clamping ring  17  and ring segments  18 .  
         [0060]    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.