Abstract:
A tubular filter element and a device for producing the same for filtering fluids includes a filter mate. The facing ends of the filter mat are fixed in position by a connecting device which at least partially overlaps the filter mat.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a tubular filtering assembly for the filtration of fluids, including a filter mat. The ends of the filter mat join one another, and are affixed in their position by a connection device which at least partially overlaps the ends. The connection device formed of a thermally deformable plastic is welded together with the ends of the filter mat. The connection device is configured as a connection strip forming a clip element which is thrust onto the filter mat ends where it holds them together during the thermal welding process. Without any additional welding, the clip while in melted state is connected with the filter mat ends. 
     BACKGROUND OF THE INVENTION 
     Filtering assemblies serve for the filtration of liquids, for example, in the form of hydraulic power oil or solutions of that type, for example in the form of genuine suspensions, dispersions, emulsions or colloidal solutions. Such filtering assemblies have generally proven themselves reliable in use on account of their compact structure and their large filter surface. In order to guarantee that the fluid flow passes only through the proper filter medium, on the two end caps, the connection point of the two ends of the filter mat are adjacent to one another and adjacent to the seal, and are in the form of terminal webs or crosspieces to form one of the critical points which are to be closed off without leakage. 
     The known filtering assemblies available on the market today have a zigzag-folded or pleated filter mat composed of different filter materials for use under different circumstances. The filter mat is arranged around a solid support pipe arranged in the interior of the filtering assembly and provided with apertures. A fine-mesh wire netting encloses the filter mat to protect it from damage from the exterior. The netting is contiguous with and follows the folding path of the filter mat. In the case of the known filtering assembly, the connection point of the two filter mat ends, the same as the connection of the filter mat with the end caps, is attained by application of an adhesive layer, for example epoxy resin adhesive. Dependent upon the adhesive being used, considerable waiting time is required during the further processing or further use of the filtering assembly, until the adhesive following its gelling or cure time can be further processed and then placed under the stress of use and until it can be used again following its hardening time. 
     With one known tubular filtering assembly, disclosed in EP 0 695 211 B1, because of improved handling and an increased stress capacity, the filter mat is surrounded on its exterior by a metal mesh covering. The covering protects the filter mat with its small mesh width. In an adhesive layer, for example formed by a two-component adhesive, the components are embedded in one another and turned toward each other. The rounded-off end of the metal mesh covering holds the ends of the filter mat between them. A cradle-like metal clamp can be provided as further limitation for the adhesive layer. The ends of filter mat and metal mesh covering engage to produce the connection point. Also, with this solution, the gelling and hardening times of the adhesive being used are to be taken into consideration in the case of further processing of the filtering assembly. 
     Additionally, the use of adhesives in the connection device for the filter mat ends requires special devices to be arranged on the side of the device. Such special devices prevent undesired discharge of adhesive from the connection seam. The maintenance of such special devices is costly and provides another measure of the increased production costs. 
     A tubular filtering assembly of this type is disclosed in EP 0 001 407. The filter mat ends are welded with one another by means of a longitudinal seam clip configured as a connection device to avoid the use of the adhesive material and to avoid the manufacturing costs involved therewith. The free arms of the known clip are configured to be elastically flexible. They can be spread apart upon thrusting of the filter mat ends therein, and can exert, on these ends, the degree of pressure required for the fixing. At the point of the transition of the two free arms of the longitudinal seam clip, this clip forms a sort of shoulder. The free ends of the filter mat engage the shoulder and/or are limited in the direction of thrusting into the clip. The filter mat ends then terminate flush with one another and assume the definitive position required for production of the weld connection. The arrangement cannot lead to being damaged and discarded. However, particularly with highly stressed filtering assemblies, such a weld seam connection can tear apart and can lead to a breakdown of the filtering assembly or even to a hydraulic volume build-up, in which the resulting filtering assembly is worn down. 
     SUMMARY OF THE INVENTION 
     Objects of the present invention are to provide a tubular filtering assembly, as well as a device for the manufacture of such a tubular filtering assembly, which ensures a connection of the filter mat ends, and which simultaneously avoids the use of adhesives that cause considerable manufacturing outlay. The assembly of the present invention consequently leads to reduced manufacturing costs for functionally reliable connection points, even under highest stress. 
     The plastic clip, as part of the connection device and as a result of the thermal welding, includes an embossment along at least one of its two arms. The filter mat ends are welded with one another in sealed form. A particularly tight and permanent connection of the filter mat ends can be attained in this manner, even when these ends are to be subjected to very high fluid pressures during the filtration. The expensive and costly outlay for the gluing can be completely deleted. Since the welding process can be carried out in an extremely short time period with simultaneous application of the embossment for virtual completion of the manufacture, rational manufacture is possible without use of additional epoxy resin adhesives or the like. Also, no standing or gelling time is required and the element can be used immediately or can be further processed directly after manufacture. Since the device of the present invention for the manufacture of such a filtering assembly uses an ultrasonic welding device with a strip-shaped sonotrode or a strip-shaped anvil, provided with the embossing device for embossing that arm of the connection device, an energy-efficient and particularly favorable connection process is guaranteed. 
     In the case of one preferred embodiment of the filtering assembly of the present invention, the filter mat includes a plastic netting and/or a metal wire netting at least on the exterior periphery. Together with that netting, the plastic clip holding the filter mat ends together includes an embossment. This embossment engages in the web structure of the netting. A particularly secure and long-lasting connection between filter mat ends is guaranteed as a result of this arrangement. The embossment preferably has rectangular, particularly quadratic embossment structures, which preferably correspond to the relevant web structure of the netting. Thus the embossing, formed of welded plastic material, can engage in the open intermediate spaces in the netting structure, to guarantee a tight connection. Since the netting is formed of plastic material, the resulting netting material is connected by welding directly with the embossing material of the relevant embossment. 
     In another embodiment of the filtering assembly of the present invention, the connection device is formed of a polyamide or polyester material. With the resulting thermally deformable plastic, a good weld line can then be guaranteed. 
     In another preferred embodiment of the filtering assembly of the present invention, the filter mat is folded in zigzag shape and is of layered construction. The layers include at least one polyester material- and/or one fiberglass mat- and/or one paper material- and/or one melt-blown material, with one high-grade steel-polyester-mix netting or the plastic netting and/or the metal wire netting being provided. With this multiple-layer construction, a particularly excellent filtering result and adaptability of the filtering assembly can be attained for the relevant filtering purposes, without the filtering operation being impaired by the weld-seam connection of the relevant assembly. 
     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 a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIG. 1  is a perspective view of the filter mat with the connection clip, not welded, according to an embodiment of the present invention; 
         FIG. 2  is a partial, perspective view of the filter mat with connection clip of  FIG. 1 , not welded; 
         FIG. 3  is a partial end elevational view in section of the filtering assembly of  FIG. 1 ; 
         FIG. 4  is a perspective view of the main component parts of the device for the production of the weld connection according to an embodiment of the present invention; and 
         FIG. 5  is a partial perspective view of the weld seam construction by means of connection clip which can be produced by the device as in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The tubular filtering assembly is illustrated in a top end view in  FIG. 3 . This arrangement serves for filtration of fluids, and includes a zigzag—or pleat—folded filter mat  10 . Filter mat  10 , which is not shown in greater detail, is of a multiple-layer construction and can, for example, be of the following layer construction in sequence from the exterior into the interior:
         1. metal wire netting or plastic netting or plastic lattice construction with network structure,   2. polyester material,   3. fiberglass mat or melt-blown material,   4. fiberglass mat or melt-blown material,   5. paper material or polyester material,   6. high quality steel-polyester-mix netting, and   7. metal wire netting or cloth or plastic netting or cloth, or plastic lattice construction with network structure.       

     A metal support tube  12  is provided for support of filter mat  10  in the interior of the filtering assembly. Tube  12  is provided with fluid apertures, (not shown). The two ends  14  of filter mat  10  joined to one another extend at an acute angle relative to one another, and are of somewhat shorter length than the length of the adjacent folds of filter mat  10 . Depending upon the layer materials being used, tubular filter mat  10  is more or less flexible. The pleated filter strips can be laid one atop the other, as is shown in  FIGS. 1 and 4 , solely as an example. Support tube  12  consequently gives filter mat  10  a certain support and defines its position in the subsequently constructed filtering assembly. 
     A connection device, indicated in its entirety as  16 , fixes the ends  14  of filter mat  10  which are adjoining one another. Connection device  16 , as shown in the drawing, at least partially overlaps ends  14 . Connection device  16  is configured as a connection strip in the form of a clip  18 . When thrust on filter mat ends  14 , clip  18  holds these ends together throughout a thermal welding process. Without additional welding, clip  18  in melted state is connected non-detachably with filter mat ends  14 . Connection device  16  in the form of connection clip  18 , preferably is formed of a polyamide or polyester material which has excellent thermal welding properties. 
     In the drawings, the individual layers of filter mat  10  for simplicity are represented simply as layered unit  20 . In  FIGS. 2 and 5  the lattice-like metal wire netting arranged outermost on the mat is indicated with reference  22 . 
     As shown particularly in  FIGS. 1 and 2 , the plastic or connection clip  18  is thrust with its two free surrounding arms  24  onto the free ends  14  of filter mat  10 , and holds these parts together by means of its inherent elasticity. The two surrounding arms  24  of clip  18  are connected with one another by means of a curved connection piece or bight  26 . Connection piece  26 , because of the surrounding arms  24  extending in alignment with one another in this area, forms a definite contact for the free ends  14  of filter mat  10 . In this manner, it is guaranteed that the two ends  14  end at approximately the same point and are in definitive contact with one another for the welding process provided thereafter, to be described hereinafter. 
     Because of the inherent elasticity of clip  18 , these filter mat ends can be given a definite structural option in the area of the surrounding arms  24 , and at, but not in, the curved contact area of connection piece  26 . Plastic clip  18  is then optimized, so that the free thrust-on opening for filter mat ends  14  is maintained somewhat smaller than the width of the two filter mat ends  14  lying one over the other. Because of the plastic elasticity ratio of clip  18 , a pressing contact of free filter mat ends  14  with one another occurs. 
     A particularly cost-favorable feature for manufacture of clip  18  is that it is comparable with filter mat  10  in that the filter mat is formed of folded or pleated curvatures which are separate from one another, and thus, in turn end in a longitudinal clip  18 . To not impair the thrust-on capability of filter mat ends  14 , clip  18 , in the area of the free ends of the two surrounding arms  24 , is provided with a curved auxiliary feed device  28  inclined or angled outward toward the exterior. 
     Plastic clip  18  is thermally deformed during the welding process, and at that time, is provided with an embossment  30  (see  FIG. 5 ) corresponding essentially to the lattice-like structure of metal wire netting  22 . In other words, the thermally deformed plastic material of clip  18  penetrates into the open spaces within the wire lattice structure, so that a particularly tight connection is attained. That connection is still further sustained in that the layered unit  20 , which likewise is at least partially of plastic materials, is welded together with clip  18 . An ultrasonic welding process is preferably used for the welding of filter mat ends  14  together with connection device  16 . However, other thermal welding processes could also be used. As is shown especially in  FIG. 3 , the lengthwise ratios in any case in the area of the connection seam are selected so that connection device  16  as seen from a radial viewpoint ends along the radial exterior periphery of filter mat  10 . With clip  18  in a molten state, filter mat ends  14  are then embedded therein, so that a non-detachable permanent connection is extant for the subsequent filtration using filter mat  10  and/or using the filtering assembly. The aforementioned embossment  30  can occur along one surrounding arm  24  or along both surrounding arms  24 . 
     The ultrasonic welding device  32  with which the thermal welding process can be performed is shown in  FIG. 4 . The ultrasonic welding device includes a strip-like sonotrode  34  for the welding process. The sonotrode can be displaced in the direction of the arrow in  FIG. 4  from a starting position and moved in the direction toward the welding material in the form of longitudinal seam clip  18  during a welding process. For the welding process, filter mat  10  with its filter folds as shown in  FIG. 4  has one end lying atop the other. Then, the welding of filter mat ends  14  with clip  18  is undertaken, following the mounting of clip  18 . The resulting welding process can be simplified by auxiliary handling aids. However, it is also possible to manually feed filter mat  10  into welding device  32 . Following termination of the welding process, sonotrode  34  is raised again, and a weld seam construction is obtained as shown in  FIG. 5 . Filter mat  10  is then brought into tubular formation and is mounted on support tube  12  for the further manufacturing processes regarding the filtering assembly. 
     As a result of the welding process, the welded edge is sealed to prevent fiber migration, so that glass fibers, for example from the filter medium, are retained in filter mat  10 . Clip  18  is of such dimensions in relation to the plastic volume required that in any case the connection can be produced without additional welding. The filter mat of the present invention, as well as the device for the manufacture of such a filtering assembly, facilitate rational manufacture without use of connecting adhesive material, such as epoxy resin adhesive, so that there is no down time for the hardening of the adhesive. Also, the filter mat or the filtering assembly can be further processed directly following its manufacture. 
     While an embodiment has 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.