The invention relates to filters consisting of nets, including corrugations of the net to expand the active filtration surface in relation to a flat filter. Said corrugations are established in said net by fastening and shortening of woven, knitted, glued, welded or otherwise suitably inserted threads or fibres in the net.

Previously known, corrugated nets generally of the type shown for example by the Japanese patent specifications JP8226044 and JP8226045 suffer i.a. of the disadvantage that the corrugations are very flexible when load is exercised against the same, i.e. they fundamentally lack support over each corrugation along its entire extension except for the attachment points. This fact makes said known nets unsuitable to use for example in filtering context, where it is important that the corrugations are not likely to collapse under load, in particular where the loads in use are applied in more than one direction, for example, when filtration, separation and removal of paper pulp is performed by means of corrugated net filters.

The Japanese patent specification JP8226044 shows the use of multiple threads 4, which are located mutually parallel in the same plane, while the Japanese patent specification JP8226045 shows use of two threads 4 and 5, which are located mutually parallel but in different planes or levels. The first embodiment mentioned leaves the entire corrugation substantially free to move while the other embodiment fixates peaks and valleys mutually but leaves the flanks of the corrugations free and thus flexible when loaded.

The European patent 1732663 shows a corrugated net structure, intended for filtering purposes, i.e. intended for the same purpose as the present invention. This known net structure includes "a substantially even second surface " 16, consisting of mutually parallel shrink threads 13b directed in the same direction. This known embodiment lacks support for each corrugation in between the fixations of the valleys of the corrugations as well.

The aim of the present invention in relation to previously known techniques is to recognize a pleated (folded) filter net with increased filtering surface, to provide a stronger and more rigid filter net, to create a more stable attachment of the edges of the filter net, to provide stiffer and more stable corrugations or waveforms, to allow for variations in the shapes of the corrugations in different directions, for example, produce folds in the corrugations, to make available adjustment of the corrugated net, especially its backside, in relation to both flat and non flat supports, such as a filter sector with regular or irregular shape, to permit for example the creation of honeycomb or other kinds of active patterns in the corrugated filter net, and/or to create a support structure appropriately adapted in shape and strength to another support structure, like for example a filtrating and/or smooth surface.

The above aims and intentions are, at the filter net specified in the preamble of the description, solved according to the present invention such that the shortened threads are selected in a quantity of two or more and are directed in more than one direction. Especially useful are in one or more embodiments of the invention if the shortened threads are numbered more than three and are directed in a number of divergent directions more than two, and if several of said shortened threads have mutually different free lengths between successive attachment positions in said net.

Other objectives and further intentions with the invention are disclosed in more detail below by means of description of some

embodiments in connection with the attached drawings, of which Figure 1 shows in perspective view, seen obliquely from below, a net structure, which is provided with few, merely as an example chosen, shrinkable threads,

Figure 2a shows a perspective view of a corrugated net structure with a number of woven-in threads of differing free lengths between related attachment points in the net, Figure 2b shows the same embodiment as in Figure 2a but viewed from the side, Figure 3a shows a perspective view over a net structure with a number of woven-in threads having mutually deviating free lengths between related attachment points in the net but are directed in opposite directions to said threads shown in Figure 2a, Figure 3b shows the same embodiment as in Figure 3a but viewed from the side and Figure 4a shows in perspective view one embodiment aggregated according to Figures 2a and 3a, and Figure 4b shows the embodiment according to Figure 4a but viewed from the side.

The embodiment as shown in Figure 1 of the present invention includes a net 1 of a suitable, preferably but not necessarily polymeric material, such as polyester, polyethylene, polypropylene, polyethylene terephthalate, Nylon (Reg. Trademark), polyvinylidenfluoride, etc. Threads 2-4 are furthermore shown in Figure 1 , the number of which threads is selected in relation to the actual application and the load applied to the corrugation 5-7 and made by an appropriate material, for example by any of the above- mentioned materials, which threads 2-4 in Figure 1 have been drawn with dissimilar thicknesses to indicate that they if appropriate may have mutually different cross sections and/or might have been compressed mutually different and which threads all are directed in mutually different directions and are attached to varying levels of the corrugated net. Said threads 2-4 have, for example, before attached into the net 1 been prestretched and after

attachment into the net been treated so that they are compressed between the attachment locations in the net, whereby said corrugation 5-7 have been created. Said attachments of threads 2-4 in the net, for example, have been achieved by the per se known methods like woven-in, stitching-in, welding, gluing or by any other suitable method in one or more positions in the net.

It should be emphasized that the invention here is described only in connection with that said threads are attached to a net in one of its main directions, namely the warp direction, but it is of course also possible to provide the weft direction of the net with a number of attached and

compressed threads as described above. It is as well possible - if so desired or required - to provide said net 1 with threads running in a direction deviating from the warp and weft directions of said net 1 and besides that with substantially the same characteristics as mentioned above. In order to create corrugation 5-7 in a net 1 with at least

somewhat stiffened flanks, it is, in principle, required at least two shortened threads, for example 3 and 4, which are directed in mutually different directions. In relation to the stiffness desired or required of the corrugations 5- 7, the number of threads can be increased further to a large extent and the mutually directions thereof can vary widely.

Only as an example in Figure 1 , three threads 2-4 are shown, which have been given mutually different directions and are of divergent kinds and have different designs of anchorages in the net 1. Thread 2 runs as shown in Figure 1 woven-in about four stitches up from the left valley of corrugation 6 and then runs right past the right valley of the corrugation 6 without attachment to the mesh near the bottom of the right flank of

corrugation 7, and so on regularly. Thread 3 runs from the attachment to the left flank of corrugation 5 around a mesh with a free long length into the valley of corrugation 5 and then to the right flank of corrugation 6 almost in the middle thereof and fastened in this flank about 5 stitches and so on regularly. Thread 4 runs, contrary, from a high position on left flank of corrugation 5 to a somewhat higher position on the right flank of corrugation 5 and so on regularly. In addition to fact that the threads 2-4 as described above may have different dimensions in cross section and that they have mutually different free lengths and different attachment lengths in the net 1 , they can of course be composed of different kinds of materials with individual stretch and shrink features.

The free lengths of threads 2-4 between corrugations 5-7 can of course be varied widely as well as the numbers of wove-ins - or stich-ins - in the net 1 but in such ways are generated minor or major variations of the shapes of the corrugations 5-7. In other words, the corrugations 5-7 of the net 1 may be varied widely and thus be adapted to the different kinds of loads and load cases the net 1 is suitable for, either as a filter in itself or as a support for another filter, according to the present invention.

In this connection, it should also be mentioned that not only the upturned surfaces of corrugations 5-7 are stiffened and corrected and their shapes are affected by said threads 2-4 according to Figure 1 , but also the downturned side according to Figure 1 is significantly affected and could thereby, according to the present invention, also be adapted to a regular or irregular support.

According to the perspective view over a second, as an example chosen design in Figure 2a of the present invention, a number of six threads 8-13 is here chosen and used. Said threads 8-13 run in mutually different directions and are mutually differently attached to or fastened in the net 1. The threads are 8-13 in part drawn with lines having different thicknesses to indicate that they may also consist of different materials and/or be made of deviating cross sections. Figure 2b shows the net and the threads 8-13 in Figure 2a but viewed straight from the side, which view clearly illustrates the stable and steady right net flank formed by the different directions and deviating attachments of the threads 8-13 therein and the steady net valley formed to the right according to the figure. According to the perspective view over a third as an example chosen design according to Figure 3a of the present invention, a number of six threads 14-19 are used. Said threads 14-19 are all running in divergent directions in and are mutually advantageous differently attached to the net 1. The threads 14-19 are partly drawn with different thickness lines to indicate that they may consist of different materials and/or have different cross sections. Figure 3b shows the net and the threads 14-19 in Figure 3a but viewed straight from the side, said view clearly illustrates the stable and steady left net flank as formed by threads 14-19 having deviating directions and different attachments therein and the steady net valley formed to the left in the figure.

According to the perspective view over a third, as an example chosen design in Figure 4 of the present invention, a number of twelve threads 8-19 has been chosen and used. Said threads 8-19 all run in mutually different directions and are mutually advantageously attached in the net 1. The threads 8-19 are in part drawn with different thickness lines to indicate that they may consist of different materials and/or have different cross sections. Figure 4b shows the net and threads 8-19 in Figure 4a but viewed straight from the side, which view clearly illustrates the stable and steady net flanks created by the threads 8-19 running in deviating directions and differently attached and, thus, the steady net valleys which are formed to the left and to the right in the figure.

From the description above of some examples of different designs of the invention, it is with required clarity shown that the invention can be varied and adapted to a wide range of loading conditions and load variations far beyond what has hitherto been possible. The only relevant limits are the mesh size and cross-section of threads for the number and kind of threads used, ie. the smaller the mesh size used and the coarser the thread used in the net the less room there is for the compressed threads.