Filter cartridge end cap assembly and method of manufacture

Abstract: A filter cartridge 10 is provided with an end cap 14 and a lock ring 18 which capture a filter element 22 therebetween on assembly and which include projections 36,38 extending beyond the outer surfaces 30,34 of the end cap 14 and the lock ring 18. The application of heat to the projections 36,38 causes the material of the projections 36,38 to fuse together and provide a leak-proof seal between the end cap 14, the lock ring 18 and the filter material 22.

Description: Background of the Invention The present invention relates to filter cartridges for fluids and more particularly, to high surface area, replaceable filter cartridges for gas or liquid filtration applications. Efforts to increase the effective filter area while minimizing filtration unit size have led to a variety of filter arrangements in which a flat filter sheet is folded into a pleated structure. The pleated filter element is then assembled in a filter cartridge which provides support for the filter and the necessary structure for channeling the fluid to be filtered through the filter element. One such filter and filter cartridge is described in U.S.-A-4,842,739 In another prior art document, JP-A-58 81532 there is disclosed an end cap assembly for a tubular filter element comprising an end cap having an axis, an axially inner surface, an axially outer surface and an outer periphery connecting said axially inner and outer surfaces. The end cap is dimensioned such that a radially inner surface of the filter element may be drawn over the outer periphery of the end cap. A lock ring has an axis, an axially inner surface, an axially outer surface, and an inner peripheral surface connecting the axially inner and outer surfaces. The lock ring is sized to capture the filter element between the lock ring inner peripheral surface and the end cap outer periphery. This document is used to form the pre-characterising clause of the accompanying claim. According to JP-A-5881532 the filter cartridge end cap assembly is made of metal, but for lightness and cost it is desired to make the assembly of thermoplastic polymers. The invention provides a construction which allows the use of thermoplastic polymers without decreasing the structural integrity of the filter cartridge and the interface between the filter element and the filter cartridge to prevent leakage of the final assembly. Summary of the Invention According to the present invention there is provided an end cap assembly for a filter cartridge including a tubular filter element comprising: an end cap having an axis, a peripheral portion, said peripheral portion having an axially inner surface, an axially outer surface, and an outer peripheral surface connecting said axially inner and outer surfaces, said peripheral portion having dimensions such that an inner peripheral surface of said filter element may be drawn over said outer peripheral surface; a lock member having an axis, an axially inner surface, an axially outer surface and an inner peripheral surface connecting said axially inner and outer surfaces and sized to capture said filter element between said lock member inner peripheral surface and said end cap outer peripheral surface, characterised in that:- said lock member and said end cap are of thermoplastic polymers; the end cap additionally has an axially projecting portion extending a predetermined distance axially from the axially outer surface of the peripheral portion of the end cap and adjacent the outer peripheral portion of the end cap to form a high spot around said peripheral portion; the lock member additionally has an axially projecting portion to form a high spot extending substantially said predetermined distance axially from the axial outer surface (34) of the lock member and around and adjacent the inner peripheral surface of the lock member; whereby when said end cap axially outer surface and said lock member axially outer surface are axially aligned, said projecting portion high spots of said end cap and said lock member are axially substantially coextensive so that heat may be applied to said high spots of said end cap and said lock member after assembly of said lock member to said end cap to fuse said lock member to said end cap to provide a leak-proof seal therebetween. Brief Description of the Drawings The present invention will be more particularly described with respect to the accompanying drawings, wherein like numbers refer to like parts in the several views and wherein: Figure 1 is a perspective view of a filter cartridge of the present invention; Figure 2 is a partial, exploded cross-sectional view of the filter cartridge of Figure 1; Figure 3 is a partial, cross-sectional view of the filter cartridge of Figure 1 shown in an assembled configuration; and Figure 4 is a view identical to that shown in Figure 3, but after final heat fusing. Detailed Description of the Preferred Embodiment As shown in Figures 1-4, the subject of the present invention is a filter cartridge, generally indicated as 10, which includes a porous support tube 12, to which are connected two end caps 14 and two lock rings 18 which mate with the end caps 14 to capture opposite ends of a filter element 22 therebetween. An end cap 14 and a lock ring 18 form in combination an end cap assembly for the filter cartridge 10. Overlying the filter element 22 is a protective screen 24. The protective screen 24 and the support tube 12 prevent deformation of the filter element 22 in use. In operation, the filter cartridge 10 is supplied with a fluid to be filtered, either liquid or gas, through an end opening 26 of the support tube 12. The fluid flows through the filter element 22 and exits the filter cartridge 10 through the protective screen 24. The direction of flow may be reversed so that the fluid to be filtered enters the protective screen 24 and exits through the support tube 12. As shown in Figures 2-4, assembly of the filter cartridge is accomplished by stretching the filter element 22 over the outer circumference 28 of the end caps 14 so that the filter element extends past the outer surfaces 30 of the end caps 14. The lock rings 18 are then forced over the end caps 14 and the filter element 22 to capture the filter element 22 between the end caps 14 and the lock rings 18. It is preferred that the outer circumferences 28 of the end caps 14 and the inner annular surfaces 32 of the lock rings 18 be complimentarily tapered to facilitate assembly of the lock rings 18 to the end caps 14. The lock rings 18 are forced over the filter element 22 and the end caps 14 until the outer surfaces 34 of the lock rings 18 are aligned with the outer surfaces 30 of the end caps 14, as shown in Figure 3. Both the end caps 14 and the lock rings 18 are provided at their outer surfaces 30 and 34, respectively, with projections 36 and 38, again respectively, which extend equal distances beyond the outer surfaces 30 and 34 of the end caps 14 and the lock rings 18 when the lock rings 18 are assembled to the end caps 14. These projections 36 and 38 are included to provide material which is fused by the application of heat to seal the lock rings 18 to the end caps 14. After the lock rings 18 have been assembled to the end caps 14 in the manner shown in Figure 3, the filter element 22 extending beyond the extent of the projections 36 and 38 is preferably trimmed to the level of the projections 36 and 38 and heat is applied to melt the projections 36 and 38, and the filter element 22 therebetween, to fuse the materials comprising the projections 38 of the lock rings 18, the filter element 22 and the projections 36 of the end caps 14 to produce a seamless seal between the lock rings 18 and the end caps 14. A critical aspect of the design of the lock rings 18 and the end caps 14 is the provision of the projections 36 and 38. The projections 36 and 38 provide a quantity of material, when heated, which allows the material comprising the lock rings 18 and the end caps 14 to flow together with each other and the material comprising the filter element 22. The projections 36 and 38 provide a high spot on the end cap assembly which makes it considerably easier to contact the proper area with the source of heat and, because the projections 36 and 38 have a relatively small volume, the amount of heat required and the time of contact with the heat source is minimized, thus decreasing assembly cycle times and reducing the possibility of heat distortion of the end cap assemblies. Although the projections 36 and 38 are illustrated as being coextensive with the outer circumferences 28 of the end caps 14 and the inner annular surfaces 32 of the lock rings 18, neither positioning is necessary. The projections 36 and 38 may be spaced somewhat from the edges of the lock rings 18 or the end caps 14, so long as the projections 36 and 38 are located close enough to provide material to the joint of the lock rings 18 and the end caps 14 upon heating of the projections 36 and 38. It also is not necessary that the projections 36 and 38 have the cross-sectional shape illustrated. It is the volume of material included in the projections 36 and 38, not the shape in which this material is provided, which is important. The preferred method of applying heat to the the lock rings 18 and the end caps 14 is by use of a heated ring which is forced against the projections 36 and 38. Other methods of applying heat include ultrasonic welding or hot air or flame impingement. It has been found to be preferred to trim the filter element 22 extending beyond the projections 36 and 38 so that a neat appearance and a sound joint is produced, but this step may be omitted if the extension of the filter element is not too great. In order that proper fusing of the lock rings 18, the end caps 14 and the filter element 22 occurs, it is necessary that the material making up these elements be compatible and capable of fusing to each other. It is not necessary that the materials of these elements be identical, but merely that the various materials be capable of fusion. Thus the preferred material for the filter element is a thermoplastic material including, but not limited to polyolefins, polyamides, polyesters, polycarbonates and polysulfones. Preferably the identical thermoplastic material is used for the lock rings 18 and the end caps 14. It is possible to produce a filter cartridge 10 according to the present invention which uses a material for the filter element which will not fuse with the materials which comprise the end caps 14 or the lock rings 18, so long as the materials of the lock rings 18 and the end caps 14 are fusible with each other and can flow into and/or through the material of the filter element 22 to a degree sufficient to completely seal the joint between the lock rings 18 and the end caps 14. Although the filter cartridge and the end cap assemblies have been illustrated as having circular or cylindrical shapes. It is contemplated that any peripheral shape could be utilized, so long as the filter element is a continuous tube.

Claims: An end cap assembly for a filter cartridge (10) including a tubular filter element (22) comprising: an end cap (14) having an axis, a peripheral portion, said peripheral portion having an axially inner surface, an axially outer surface (30), and an outer peripheral surface (28) connecting said axially inner and outer surfaces (30), said peripheral portion having dimensions such that an inner peripheral surface of said filter element (22) may be drawn over said outer peripheral surface (28); a lock member (18) having an axis, an axially inner surface, an axially outer surface (34) and an inner peripheral surface (32) connecting said axially inner and outer (34) surfaces and sized to capture said filter element (22) between said lock member inner peripheral surface (32) and said end cap outer peripheral surface (28), characterised in that:- said lock member (18) and said end cap (14) are of thermoplastic polymers; the end cap (14) additionally has an axially projecting portion (36) extending a predetermined distance axially from the axially outer surface (30) of the peripheral portion of the end cap and adjacent the outer peripheral portion of the end cap to form a high spot around said peripheral portion; the lock member (18) additionally has an axially projecting portion (38) to form a high spot extending substantially said predetermined distance axially from the axial outer surface (34) of the lock member and around and adjacent the inner peripheral surface (32) of the lock member; whereby when said end cap axially outer surface (30) and said lock member axially outer surface (34) are axially aligned, said projecting portion high spots of said end cap and said lock member are axially substantially coextensive so that heat may be applied to said high spots of said end cap (14) and said lock member (18) after assembly of said lock member (18) to said end cap (14) to fuse said lock member (18) to said end cap (14) to provide a leak-proof seal therebetween. An end cap assembly according to claim 1 wherein said axially projecting portion (36) of said end cap (14) is collinear with said end cap outer periphery (28). An end cap assembly according to claim 2 wherein said projecting portion (38) of said lock member (18) is collinear with said lock member inner peripheral surface (32). An end cap assembly according to claim 3 wherein said filter element (22), said lock member (18) and said end cap (14) are fusible. An end cap assembly according to claim 1 wherein said end cap outer periphery (28) and said lock member inner peripheral surface (32) are complementarily tapered to facilitate assembly. An end cap assembly according to claim 5 wherein said end cap periphery (28) and said lock member inner peripheral surface (32) are circular.

Inventors: STEPHAN GREGORY H C C O MINNES, TANG YUAN-MING C O MINNESOTA M, STEPHAN, GREGORY H.C. C/O MINNESOTA MIN.&MANUF.CO., TANG,YUAN-MING C/O MINNESOTA MIN. & MANUFACT. CO., Stephan, Gregory H.C. c/o Minnesota Min.&amp;Manuf.Co., Tang,Yuan-Ming c/o Minnesota Min. &amp; Manufact. Co.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1990
Main classification: B01D29
IPC codes: B01D29, B01D46, B01D27