Abstract:
A process for production of a filter element includes forming a cylinder by bending a flexible filter mat having a series of folds adjacent to one another at least in individual end areas on longitudinal end edges thereof such that the end areas overlap with end edges being aligned along a length of the cylinder, joining the end areas on an exterior of the cylinder along a junction seam, and reversing the cylinder inside out such that an annular filter element is formed with the junction seam on an interior thereof.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a division and claims for priority of U.S. patent application No. 10/522,682, filed Jan. 31, 2005 and entitled Filter Element and the Method for Production Thereof, the subject matter of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a filter element having a filter cylinder adjoining on its exterior a fluid-permeable support tube through which filter cylinder fluid to be filtered may flow. The filter element is made up of a filter mat web having a sequence of folds adjacent to each other at least in individual areas. The two ends of the filter mat web are joined to each other at a connecting point to form an annular element. The present invention also relates to a method for the production of such a filter element. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such filter elements are available on the market, and are widely used, for example, in hydraulic assemblies in branches of a system through which hydraulic fluids flow. The known filter elements are not entirely satisfactory with respect to their safety in operation and the beta value stability of decisive importance for filter output. With high fluid outputs in particular, the danger exists that deformation or damage may occur at the junction point at which the ends of the filter mat web are joined to form the annular element forming the filter cylinder as a result of the differential pressure of the fluid acting on the junction point. Such damage and/or deformation of the folds in the area of the junction point are identified by the common expression “fold bulging”. 
       SUMMARY OF THE INVENTION 
       [0004]    An object of the present invention is to provide a filter element with improved operating safety and beta value stability, even with high flow output. 
         [0005]    In a filter element, this object is basically attained by a method of producing a junction point to prevent bulging of the folds in the area of the junction point caused by the action of fluid flow. According to the present invention, special protective measures are taken at the point of junction of the filter mat web, which prevent bulging of the folds in this area. The desired improvement in operating safety is achieved even in the event of high flow output and correspondingly high fluid differential pressures in the area of the junction point. 
         [0006]    In one preferred exemplary embodiment, the configuration preventing bulging in the area of the junction point is formed by the folds of the filter mat web being joined to each other along their end edges. Such end edges face the interior of the annular element to be formed, so that both folds adjacent to each other at the junction point have their tops positioned on the exterior on the annular element and facing the support tube. In that the junction point, that is, the fusion seam or area of adhesion by which the annular element forming the filter cylinder is closed, is positioned in the interior on the filter cylinder, the junction point on both sides rests on the support tube by the adjacent folds. The tops of the folds are positioned on the exterior on the annular element. In this configuration, the junction point forms no point weak in resisting the active forces resulting from the differential pressure applied in operation. 
         [0007]    By preference, the filter mat web is in the form of a flexible mat structure of metal-free plastic-supported filter mats with connected ends of the filter mat web, so that a closed annular structure is formed and is effected by a fusion seam. To make simple and efficient production possible, the fusing process must be carried out on the exterior of the annular element, that is, with the junction point positioned on the exterior of the filter cylinder. With such positioning, the fusion seam would form a weak point of the filter cylinder during operation. 
         [0008]    To make allowance for this factor, provision is made by the present invention for an especially advantageous exemplary embodiment such that the dimensions determined for the flexible filter mat web are such that the annular element may be reversed after formation of an exterior fusion seam. The fusion seam is then positioned on the interior on the reversed annular element now ready for use. 
         [0009]    Despite the simplicity of the production method, that is, formation of a fusion seam on the exterior, the annular element forming the filter cylinder after reversal is protected as desired from bulges in the area of the fusion seam now positioned in the interior. 
         [0010]    In place of the protection from bulges resulting from the positioning of the junction point in the interior, or in addition to this protection, according to the present invention the configuration preventing bulging may have in the area of the junction point a retaining device with retaining elements. The retaining elements can overlap the folds of the annular element adjoining the junction point on both sides, on the side of the folds facing away from the junction point. Especially secure support of the folds in the area of the junction point is thereby ensured. 
         [0011]    The retaining elements of the retaining device may be in the form of a retaining projections formed on the inside of the support tube and projecting radially inward. 
         [0012]    As an alternative, the retaining elements may be in the form of legs of a clamping element U-shaped in cross-section. The clamping element may be inserted onto the folds adjacent to the junction point of the annular element. 
         [0013]    Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]    Referring to the drawings which form a part of this disclosure: 
           [0015]      FIG. 1  is a top plan view of an annular element forming a filter element according to a first embodiment of the present invention, in the partly completed state, with a fusion seam formed on the annular element from the exterior and positioned on the exterior; 
           [0016]      FIG. 2  is a top plan view of the annular element of  FIG. 1  in a finished state, that is, with the fusion seam positioned on the interior after reversal; 
           [0017]      FIG. 3  is a perspective view of the annular element of  FIG. 2 ; 
           [0018]      FIG. 4  is a perspective view of the filter disk formed in the course of reversal of the annular element shown in  FIG. 1 ; 
           [0019]      FIG. 5  is a greatly enlarged, partial top plan view of a fold section of the annular element of  FIG. 2 , along with data indicating the dimensions; 
           [0020]      FIG. 6  is a top plan view in section of a filter element according to a second embodiment of the present invention; 
           [0021]      FIG. 7  is a perspective view of the support tube of the second embodiment shown in  FIG. 6 , without the filter cylinder being present in this support tube; and 
           [0022]      FIG. 8  is an exploded perspective exploded view of a filter element according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIGS. 1 to 5  illustrate a first exemplary embodiment of the filter element of the present invention, the conventionally configured support tube not being shown in these figures. The filter cylinder  1  is in the finished state enclosed in this support tube. In the form shown in  FIGS. 2 and 3 , it has been introduced into the support tube (not shown). During operation, filter fluid flows through the interior of the annular element indicated in  FIGS. 2 and 3 ; that is, the clean side of the filter device (not shown) having the filter element according to the present invention is situated on the exterior of the support tube enclosing the annular element  1 . 
         [0024]    As shown in the figures, the annular element  1  is in the form of a folded filter mat web joined at its two ends to form a closed ring. The junction point is configured as a fusion seam  5 . In the exemplary embodiments described, the filter mat web is in the form of a flexible mat structure possessing resilient properties. More precise, the mat structure is of metal-free plastic-supported filter mats fusible together by a fusion seam  5  extending longitudinally to produce the annular element  1 . 
         [0025]    By preference, a six-layer structure of the filter mat web is provided which has the following layers in sequence: an exterior support, a protective nonwoven layer, a prefilter layer, a main filter layer, a nonwoven support layer, and an interior support. A polyamide grid or a polyester fabric may be employed for the exterior support. A polyester material may be provided as the protective nonwoven layer. A glass fiber material, preferably in reduced form with respect to thickness and base weight, or a meltblown material may be employed for the filter layer. The main filter layer may analogously be a glass fiber material, which optionally is impregnated, or a meltblown material. A polyester or polyamide material may in turn be used as the support nonwoven layer, which may also be represented by a viscose nonwoven material or a polyamide with meltblown material. The interior support may, like the exterior support, be configured as a grid or fabric based on a polyamide or polyester basis. 
         [0026]    As shown in  FIGS. 1 to 4 , fusion seam  5  is displaced to the interior in the finished state shown in  FIGS. 2 and 3  by reversal of the annular element  1  from the initial state illustrated in  FIG. 1 , in which the fusion seam  5  is positioned on the exterior, that is to say, is in the form of a lengthwise seam made on the outside. While in the state shown in  FIG. 1 , with fusion seam  5  positioned on the exterior, on the outer edge of the annular element  1 , a gap  7  exists in the area where there is no contact between the tops  11  of the folds  9  immediately adjacent to and on both sides the fusion seam  5  and the enclosing support tube (not shown). In the state shown in  FIGS. 2 and 3  the tops  11  of the folds  9  immediately adjacent to the fusion seam  5  are positioned on the outside (see  FIG. 2 ) and accordingly are positioned adjacent on the support tube. 
         [0027]    While in the state shown in  FIG. 1  and at the differential pressure prevailing during operation, the danger of bulging exists in the area of the fusion seam  5 . Fusion seam  5  may be moved radially outward by pressure forces, with tensile forces active on the fusion seam  5  tending to tear the seam open. In the reverse state illustrated in  FIGS. 2 and 3 , no bulging result of radial movement of the fusion seam  5  is possible, since the adjacent fold top  11  is supported. The fusion seam  5  is also not subject to load application in the form of forces of pressure tending to effect separation. 
         [0028]      FIGS. 4 and 5  illustrate the configuration and determination of the dimensions of the filter mat web forming the annular element  1 , that is, a configuration permitting reversal of the annular element. The maximum length of the annular element permitting reversal, if it is in the form of a flexible fold structure, depends on the number of folds, the height of the folds, the strength of the mat structure, and the thickness of the folds of the annular element.  FIG. 4  illustrates the exterior and interior diameters of the disk element  13  which are temporarily obtained in the course of reversal of the annular element  1 .  FIG. 5  illustrates determination of the dimensions of the folds  9  with respect both to strength of the material and to the fold size. 
         [0029]    The maximum length of the annular element may be determined as follows on the basis of the parameters entered in  FIGS. 4 and 5 , wherein
   F ANZ =number of folds   F H =height of fold   F D =thickness of fold   M=strength of material of mat structure   L M =extended length of filter web   L Mmax =maximum extended length of filter web   D amax =maximum external diameter of filter disk   D i =internal diameter of filter disk   L max =maximum length of filter cylinder   
 
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         [0039]      FIGS. 6 and 7  illustrate a second exemplary embodiment of the filter element according to the present invention. Unlike the preceding example, the support tube  15  enclosing the filter cylinder is shown. This support tube  15  is shown separately in  FIG. 7 , that is, without the filter cylinder inserted. As is clearly shown in  FIG. 7 , the support tube  15 , which is of transfer-molded plastic, has on the exterior, which in a filter device of the present invention adjoins the clean side, has strips  17  extending longitudinally, strips  17  are connected by webs  19  forming annular elements between which are apertures  21  defining fluid passages. As shown in  FIG. 6 , when a filter cylinder has been inserted into the support tube  15 , the area adjacent to and on both sides of the fusion seam  5  is secured by a retaining device. The retaining device projections  23  and  25  overlap the folds of the annular element adjacent to the fusion seam, on both sides of the fusion seam and on the sides of those folds facing away from the fusion seam  5  (see  FIG. 6 ). 
         [0040]    As shown in  FIG. 7  in particular, the retaining projections  23  and  25  are integrally molded on the inside of the support tube  15 . Retaining projection  23  is configured to extend along and through a strip  17  of the support element. The divided retaining projections  25  are provided on the other side between which are interstices  27  corresponding to the apertures  21  forming the fluid passages. With the enclosure of the area of the fusion seam  5  formed by the retaining projections  23  and  25 , effective protection is obtained from the danger of bulging in the area of the junction point. 
         [0041]      FIG. 8  shows a third exemplary embodiment of the present invention having a support tube  15  without interior retaining projections  23  and  25 . In place of the enclosure of the area of the junction point, that is, the fusion seam  5 , this exemplary embodiment provides a retaining device having a metal clamping element  31 . The clamping element is U-shaped in cross-section, and may be positioned by insertion on the sides of the adjacent folds facing away from the fusion seam  5 . The retaining action essentially corresponds to that of the retaining projections  23  and  25  of the second exemplary embodiment. 
         [0042]    In addition, in the example shown in  FIG. 8 , the annular element  1  has been reversed to assume the state shown in  FIG. 2 . The fusion seam  5  is then positioned in the interior and the tops of the folds adjoining this seam are supported directly by the support tube  15 . Consequently, this exemplary embodiment is protected in two ways from bulging in the area of the fusion seam  5 . 
         [0043]    While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.