Cylindrical filters and their manufacture

Abstract: A cylindrical filter is formed from a sheet of filter material which includes two connected layers of filter media. Opposed edges of the sheet are joined to form the cylinder by separating the media adjacent the edges and then sealing together the first of the separated layers followed by sealing the second separated layers with the first separated layers. The two seals are spaced inwardly of the edges and are spaced from one another. In this way, failure of one seal does not result in failure of the cylindrical filter.

Description: The invention relates to cylindrical filters and their manufacture. A cylindrical filter is customarily formed from a sheet of filter media joined along two opposed edges to form the cylinder. The media may be in the form of a plain sheet or the sheet may be corrugated, in which case the joined edges are the final corrugations. Such filters are not geometrically cylindrical because they may not be stable when unsupported and, when pleated, they have a corrugated surface. EP-A-0001407 shows such a filter and describes the filter as cylindrical or tubular. EP-A-0062867 also describes such a filter as cylindrical or tubular. GB-A-2101902 also describes such a filter as cylindrical or tubular. The term cylindrical as used in this specification is thus used in accordance with the accepted meaning in the art as referring to a sheet of filter material formed into a tube. The joint is customarily made by contacting the areas of the sheet adjacent the two edges and then forming a seal between these areas. In general, the overlap will be with the edges in register, particularly where the sheet is pleated. Such a sealed joint is acceptable where the sheet is formed from a single layer of filter media. It is, however, less satisfactory where the sheet is formed from two superimposed layers of media connected together. In this case, the possibility of a flow path through a single seal is increased. In EP-A-0001407 there is disclosed the joining of the edges of a sheet formed of two superimposed layers of media connected together and utilizing a channel strip for connecting the layers of media together. In US-A-3865919 a number of corrugations of a pleated sheet of filter material are bonded together and then provided with a tape or ribbon of adhesive in a space formed between the corrugations. The adhesive is melted to form a leak-proof seal. According to the first aspect of the invention, there is provided a method of forming a filter from a sheet of filter material including two layers of filter media by joining two opposed edges of the sheet to form a cylinder, the method comprising separating the layers of the filter media from each other from said opposed edges to form two separate layers, contacting a first layer associated with one edge with a first layer associated with the other edge, sealing said contacting layers together with a seal extending along the length of said edges at a position spaced inwardly of said edges, positioning the second layer associated with said one edge and the second layer associated with said other edge so that said second layers at least partially overlie the sealed first layers, and then forming a seal between said second layers to each other, with said second seal extending along the length of said edges at a position inwardly of said edges and spaced from said first mentioned seal. In this way, two separate seals are provided, which means that a failure of one seal need not result in a flow path between the edges. According to a second aspect of the invention, there is provided a cylindrical filter formed from a sheet of filter material and including two connected layers of filter media, two opposed edges of the sheet being joined to form said cylinder, the layers being separated along said edges, a first layer of one edge being sealed to a first layer of the other edge along the length of the edges by a first seal spaced inwardly of said edges and a second layer of said one edge being sealed to a second layer of the other edge along the length of said edges by a second seal spaced inwardly of said edges and spaced from said first mentioned seal, so forming a filter of circular cross-section. The following is a more detailed description of one embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a cross-sectional view of part of a cylindrical pleated filter formed from a sheet of filter material including two connected layers of filter media and joined at the final corrugations, Figure 2 is a diagrammatic view of a holder holding the ends of the pleated sheet shown in Figure 1 before joining and showing a first stage in the joining process, Figure 3 is a similar view to Figure 2, but showing a second stage in the joining process, Figure 4 is a similar view to Figure 1, but showing a second form of join between the final corrugations, Figure 5 is a similar view to Figure 1 but showing a sheet of filter media formed from three connected layers of media and three seals, the seals connecting two, four and six layers of media respectively, Figure 6 is a similar view to Figure 4 but showing a sheet of filter media formed from three connected layers of media and three seals, each seal connecting two of the layers, Figure 7 is a similar view to Figure 5 but showing only two seals, one seal connecting two layers and the other seal connecting all six layers, and Figure 8 is a similar view to Figure 6 but showing only two seals, one seal connecting two layers and the other seal connecting the remaining four layers. Referring first to Figure 1, the cylindrical filter is formed from a sheet of filter material having two layers of filter media 10,11 which overlie one another and which are connected to one another. These layers 10,11 are covered by upstream and downstream drainage material 12,13. The layers of filter media are of nylon. The sheet is corrugated to form two final corrugations 14,15, which both extend in the same direction and terminate at respective edges 16,17. In this description, the reference numerals 16,17 are used to distinguish generally one of the two edges being joined from the other and so are used to denote the opposed edges of both the sheet of filter material and the layers forming the sheet, since the edges of the layers together form the edges of the sheets. The sheet is formed into a cylinder in the following way. First, the downstream drainage material 13 is removed from the first media layer 10 inwardly of the edges 16,17 and along the length of the edges 16,17. The first and second media layers 10,11 and the upstream drainage material 12 are then separated from the edges 16,17 for the complete height of the final corrugations 14,15 and along the complete length of the final corrugations 14,15 to form three separate layers. The complete sheet with the separated edge layers is then mounted in the holder shown in Figure 2. This holder comprises a member 18 of T-shaped cross-section with the head 19 of the T movable so that the edges 20 of the head can engage with and disengage from respective supports 21. The width of the head is generally equal to twice the height of the corrugation of the completed sheet with which it is designed to be used. The penultimate folds 22 of the sheet prepared as described above, are arranged around the edges 20 of the head 19 of the member 18 and engaged with the supports 21. This ensures that the two edges 16,17 are parallel. The two separated first layers 10 are then brought together by manual manipulation, as seen in Figure 2, and these layers are then sealed together between heated jaws to form a seal extending parallel to the edges 16,17 and inwardly of the edges. The position and width of this seal are designated by the letter A in Figure 1 and it will be seen that the seal is adjacent the final folds. Referring next to Figure 3, the second layers are then positioned manually to overlie the joined first layers 10 so that the edges of all four layers 10,11 are in register. The layers 10,11 are then placed within jaws which form a second seal extending inwardly of the edges 16,17 parallel to said edges and spaced from the first seal A. This seal connnects together all four layers. The width and position of this seal are indicated by the letter B in Figure 1 and it will be seen that this seal is between the first seal A and the edges 16,17. Finally, the upstream drainage material 12 is re-assembled over the second layers 11. There is thus formed a pleated cylindrical filter in which the final corrugations are joined inwardly of their edges by two parallel but spaced seals A,B. If the seal B should fail in its central portion, the seal A will still remain. If the seal B should fail towards its outer edges, leaking material will still have to pass through the filter media. In addition, longitudinal strength is increased and there is an increase of strength in a cartridge in which the corrugated filter is incorporated. Six pleated cylindrical filters prepared as described above with reference to the drawings were tested in the following way. All six cartridges were placed in an autoclave at 140 o C for four periods of one hour each. All six cartridges were tested for forward flow before the four one hour cycles and after the four one hour cycles. The filters were tested water wet at 2.61 kpa (18 psi). An acceptable production limit for such forward flow is 10 ml/min and an acceptable limit in use is 22 ml/min. The results were as follows:- It will thus be seen that all filters remain well within the acceptable limits after autoclaving. This indicates that there has been no failure of the seals. It will be appreciated that the method of manufacture and construction described above need not be applied to pleated filters, it could be applied to filters in which no pleats are provided. Further, the join may not be with the two edges in register, it could be with the two edges overlapping. A second form of join is shown in Figure 4. Aspects of this join and the join described above with reference to Figures 1 to 3 are the same and these aspects will not be described in detail. In this second form of join, the first seal A is formed as described above with reference to Figures 1 to 3. However, after formation of this seal A, the portions of the first media layers 10 between the seal A and the edges 16,17 of the second media layers 11 are cut-away. Thus, when the second media layers 11 are positioned as shown in Figure 2, these layers 11 only partially overlie the first media layers 10 and portions of the second media layers 11 are in contact. The second seal B is formed between these contacting media layers 11, as shown in Figure 4. The upstream drainage material 12 is then re-assembled. It will be appreciated that filters having three or more media layers may be joined by either of the methods described above with reference to the drawings. In such cases, the media layers may all be separated and joined successively in pairs by spaced seals, so that there are as many seals as layers. This is shown in Figures 5 and 6 where parts common to Figures 1 and 4 and to Figures 5 and 6 will be given the same reference numerals and will not be described in detail. In these embodiments, the cylindrical filter is formed from a sheet of filter material having three layers of filter media 10,11,25 which overlie one another and are connected to one another. The layers of filter media 10,11,25 are of nylon. The sheet is corrugated to form two final corrugations 14,15, which both extend in the same direction and terminate at respective edges 16,17. The sheet of Figure 5 is formed into a cylinder in the way described above with reference to Figure 1 except that the third media layer 25 is also separated from the edges 16,17 for the complete height of the final corrugations 14,15 and along the complete length of the final corrugations 14,15 to form six separate layers. The layers 10,11 are joined as described above with reference to the drawings. The two separated third layers 25 are then brought together by manual manipulation, and these layers are then sealed together between heated jaws to form a seal extending parallel to the edges 16,17 and inwardly of the edges. The position and width of this seal are designated by the letter C in Figure 5 and it will be seen that the seal is adjacent the final folds, and closer to the edges 16,17 than the previously formed seals A,B. Finally, the upstream drainage material 12 is re-assembled over the third layers 25. There is thus formed a pleated cylindrical filter in which the final corrugations are joined inwardly of their edges by three parallel but spaced seals A,B,C. If the seal C should fail in its central portion, the seals A and B will still remain. If the seal C should fail towards its outer edges, leaking material will still have to pass through the filter media. In addition, longitudinal strength is increased and there is an increase of strength in a cartridge in which the corrugated filter is incorporated. The second form of join is shown in Figure 6. Aspects of this join and the join described above with reference to Figures 1 to 3 and 5 are the same and these aspects will not be described in detail. In this second form of join, the first seal A and the second seal B are formed as described above with reference to Figure 5. However, after formation of the second seal B, the portions of the second media layers 11 between the seal B and the edges 16,17 are cut-away. Thus, when the third media layers 25 are positioned as shown in Figure 6, these layers 25 only partially overlie the first and second media layers 10,11 and portions of the third media layers 25 are in contact. The third seal C is formed between these contacting media layers 25, as shown in Figure 6. Alternatively, two layers (or more where there are four or more layers) of each edge may be joined together so that there are less seals than layers. This is shown in Figures 7 and 8 where parts common to Figures 1 to 6 and to Figures 7 and 8 will be given the same reference numerals and will not be described in detail. In Figure 7, the third media layer 25 is not separated from the second media layer 11 and the edges 16,17 of these two layers 11,25 are sealed together as one, as described above with reference to Figures 2 and 3. There are thus only two seals A,B, with the same seal A connecting two inner media layers 10, and the other seal B connecting all six media layers 10,11,25. In Figure 8, the third media layer 25 is not separated from the second media layer 11 and the edges 16,17 of these two layers are sealed together as one, as described above with reference to Figure 4. There are only two seals A,B with the inner seal connecting the two inner media layers 10, and the outer seal connecting the remaining four media layers 11,25.

Claims: A method of forming a filter from a sheet of filter material including two connected layers of filter media (10,11) by joining opposed edges (16,17) of the sheet to form a cylinder, characterised in that the layers of the filter media (10,11) are separated from each other from said opposed edges (16,17) to form two separate layers, contacting a first layer (10) associated with one edge (16) with a first layer (10) associated with the other edge (17), sealing said contacting layers (10) together with a seal (A) extending along the length of said edges (16,17) at a position spaced inwardly of said edges, positioning the second layer (11) associated with one edge (16) and the second layer (11) associated with the other edge (17) so that said second layers at least partially overlie the sealed first layers (10), and then forming a seal (B) between said second layers (11), with the second seal (B) extending along the length of said edges at a position inwardly of said edges (16,17) and spaced from said first mentioned seal (A). A method according to claim 1 characterised in that the first layers (10) are contacted with the respective edges (16,17) thereof in register, so that a layer (10) of one media of one edge (16) is first sealed to a layer (10) of the same media of the other edge (17) with said first-mentioned seal (A) and then the layers (11) of the other media of the two edges (16,17) are sealed with said second seal (B). A method according to claim 2 characterised in that portions of the first layers (10) between the first-mentioned seal (A) and the associated edges (16,17) are removed after said sealing step, so that when the second layers (11) are positioned to overlie said sealed first layers (10), portions of the second layers (11) adjacent the associated edges (16,17) are in contact, the second seal (B) being between said contacting portions. A method according to claim 2 characterised in that when the second layers (11) are positioned to at least partially overlie the first layers (10), the edges (16,17) of the first and second layers (10,11) are in register, so that the second seal (B) seals together the two first and second layers (10,11) so sealing together the second layers (11). A method according to claim 3 or claim 4 characterised in that the sheet is corrugated with the seals (A,B) being formed between final corrugations of the sheet, the first seal (A) being between downstream filter media (10) and the second seal (B) being between the upstream filter media (11). A method according to any one of claims 1 to 5 characterised in that the sheet is provided with a surface drainage (12,13) material on both surfaces thereof, the method including removing the drainage materials (12,13) from said edges (16,17) before sealing. A method according to any one of claims 1 to 6 characterised in that the sheet of filter material has three or more connected layers of filter media the or at least one of the layers additional to said first and second layers being maintained connected to the first or second layers during said method. A method according to any one of claims 1 to 6 characterised in that the sheet of filter material has three or more connected layers of filter media, the or at least one of the layers additional to said first and second layers (10,11) being separated from said opposed edges (16,17) to form a further separate layer (25), the further separate layers being positioned so that said layers at least partially overlie the sealed first and second layers (10,11) and then a seal (C) being formed between said further layers. A cylindrical filter comprising a sheet of filter material including at least first and second layers (10,11) of filter media, each having first and second edges (16,17), wherein a portion of the first layer (10) near the first edge (16) and a portion of the first layer (10) near the second edge (17) are sealed by a first seal (A) spaced inwardly of and extending along the length of the edges (16,17) and a portion of the second layer (11) near the first edge (16) and a portion of the second layer (11) near the second edge (17) are sealed by a second seal (B) spaced inwardly of and extending along the length of the edges (16,17) and spaced from the first seal. A filter according to claim 9 wherein the first and second edges (16,17) of each layer (10,11) are in register and a portion of the first layer (10) near the first edge (16) is sealed to a portion of the first layer (10) near the second edge (17) by said first seal (A) and the portions of the second layer (11) near the first and second edges (16,17) are sealed by the second seal (B). A filter according to claim 10 wherein the registered edges (16,17) of the first layer (10) are spaced from the registered edges (16,17) of the second layer (11) so that the portions of the second layer (11) are in contact, the second seal (B) being between said contacting portions. A filter according to claim 10 wherein the edges (16,17) of the second layer (11) are in register with the edges (16,17) of the first layer (10) so that the second seal (B) seals together the first and second layers (10,11). A filter according to claim 10 wherein the second seal (B) is positioned between the first seal (A) and the registered edges (16,17) of the second layer (11). A filter according to claim 10 wherein the sheet of filter material is corrugated with the seals being formed between final corrugations (14,15) of the sheet. A filter according to claim 14 wherein the first seal (A) is adjacent the final corrugations (14,15). A filter according to claim 10 wherein the first layer (10) is downstream from the second layer (11). A filter according to claim 10 wherein the sheet of filter material includes a layer of surface drainage material (12,13) on both surfaces thereof. A filter according to claim 17 wherein the layers of surface drainage material (12,13) are not sealed to the layers of filter media. A filter according to claim 9 wherein the layers of filter media include nylon. A cylindrical filter according to claim 9 further comprising a third layer (25) of filter media, having first and second edges (16,17); wherein a portion of the third layer (25) near the first edge (16) and a portion of the third layer (25) near the second edge (17) are sealed by a third seal (C) which is spaced inwardly of and extends along the length of the edges (16,17) and is spaced from the first and second seals (A,B). A filter according to claim 20 wherein the edges (16,17) of the first layer (10), the edges (16,17) of the second layer (11) and the edges (16,17) of the third layer (25) are in register so that the second seal (B) seals together the first and second layers (10,11) and the third seal (C) seals together the first, second and third layers (10,11,25). A filter according to claim 20 wherein the edges (16,17) of the first layer (10) are spaced from the edges (16,17) of the second layer (11) so that the portions of the second layer (11) are in contact, said second seal (B) contacting portions of the second layer and wherein the edges (16,17) of the second layer (11) are spaced from the edges (16,17) of the third layer (25) so that the portions of the third layer (25) are in contact, said third seal (C) sealing the contacting portions of the third layer (25). A cylindrical filter according to claim 9 further comprising a third layer (25) of filter media, having first and second edges (16,17); wherein portions of the second layer (11) and third layer (25) near the first edge (16) of each layer (11,25) and portions of the second layer (11) and third layer (25) near the second edge (17) of each layer (11,25) are sealed by a second seal (B) which is spaced inwardly of and extends along the length of the edges (16,17) and is spaced from the first seal (A). A filter according to claim 23 wherein the second seal (B) is positioned between said first seal (A) and the edges (16,17) of the second and third layers (11,25). A filter according to claim 23 wherein the edges (16,17) of the first layer (10), the edges (16,17) of the second layer (11) and the edges (16,17) of the third layer (25) are in register so that the second seal (B) seals together the first, second and third layers (10,11,25). A filter according to claim 23 wherein the edges (16,17) of the first layer (10) are spaced from the edges (16,17) of the second and third layers (11,25), the second seal (B) sealing the contacting portions of the second layer (11) and sealing together the second and the third layers (11,25).

Inventors: GRIMES MICHAEL, GRIMES, MICHAEL
Applicants: PALL CORP, PALL CORPORATION
Application year: 1991
Main classification: B01D27
IPC codes: B01D29, B01D46