BACKGROUND OFTHEINVENTION

Filter units, which comprise a housing and a disposable filter cartridge sealingly engaged therein, are used for the filtration of fluids, such as compressed gases and liquids. The filter cartridge may comprise a single filter tube or comprise a plurality of coaxial, adjacent filter stages or tubes, to include a prefilter and/or a coalescing stage.

Typically, the ends of the filter tube or tubes of the filter cartridge contain end caps sealed to the filter tube ends by the use of potting compounds, such as thermosetting resins like epo.xy resins, plastisols or sealants like silicone rubber, as described, for example, in U.S. Patents

4,032,457 and 4,160,684 and British Patents 1,041,882 and 1,345,155.

One type of filter tube used in filter cartridges comprises a plurality of nonwoven, borosilicate glass fibers generally having an average diameter of 0.01 to 10 microns or more, the fibers formed into a self-gasketing, semirigid filter tube with a binder material. The filter tubes may be sealed in place by axial compression of the ends of the filter tubes against a flange surface. The binder material may comprise a hardenable compound; for example, a fluorocarbon, epoxy or silicone resin or inorganic silica material.

The use of potting compounds and sealants, to secure one or both end caps to filter tubes, often presents difficulties, where the fluid to be filtered may extract material from the potting compounds or sealants. Also the use of potting compounds and sealants requires an additional and often cumbersome and messy manufacturing step. Further, it is sometimes difficult to secure the desired degrees of adhesion between the material of the end cap and the potting compound and sealant. Thus, it is desirable to provide a filter cartridge with end caps, without the necessity of potting compounds and sealants to secure the end caps in a sealing relationship with the ends of the filter tubes.

Filter-tube adapters, for use in particular core-type, string-wound filters, have been suggested, which filter-tube adapters do not require the use of potting compounds and sealants (see U.S. Patent 3,868,325); however, such adapters are not satisfactory for semirigid, self-gasketing types ^' of filter tubes.

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SUMMARY OF THE INVENTION

The invention relates to filter cartridges and self-gasketing end caps employed with such filter cartridges. In particular, the invention also concerns a method of sealing self-gasketing filter tubes employing end caps, without the necessity of potting compounds and sealants.

An improved, disposable filter cartridge has been discovered containing a self-gasketing filter tube with end caps, and without the need for or use of potting compounds or sealants. The filter cartridge of the invention comprises a filter tube having a one and another end with end caps and having interior and exterior wall surfaces. The filter tube typically is a semirigid, self-supporting filter tube and may be composed of a plurality of inorganic or organic fibers usually with a binding agent, to form the fibers into a self-gasketing filter tube. It is essential that the filter tube be capable of being sealed by axial compression of the filter tube across the edge width of the ends of the filter tube, without substantially affecting the filtering capacity of the body of the filter tube. In one embodiment, the fibers are nonwoven fibers, such as glass like borosilicate glass fibers, or olefinic fibers like polypropylene or mixtures thereof, which contain a binding agent at the fiber crossover points, to form a self-gasketing filter tube.

The end cap of the invention provides for an end-cap seal at the one and/or the other ends of the filter tube to form the filter cartridge. The end cap comprises a body ring element having an annular surface, typically a flat surface which extends across the entire width of the end of the filter tube to be sealed, and at least one flange element, and more typically two flange elements. The flange elements extend downwardly from the body element, with the flange elements being in a close, contacting, support relationship with at least one wall surface, either interior or exterior, and preferably both wall surfaces of the filter tube. The end cap also includes one or more barb elements extending generally laterally from the ends of one or both of the flange elements, as desired. The barb elements are adapted to be biased ^' laterally, so as to be forced directly into the interior or exterior or both wall surfaces of the filter tube to be sealed. The barb element is so constructed, to engage frictionally the wall of the filter tube and to prevent the axially outward dislodgement of the barb elements, once in a sealing position.

Typically, the barb elements have a sharp point or edge extending laterally directly into the fibers of the tube wall surface and are designed, so that the barb elements cannot be withdrawn axially from the interior of the filter tube, without damage to the tube. The barb elements retain the interior, annular surface of the body ring element in position across the full edge width of the filter tube. The barb elements may be placed at the one end on a plurality of split ring or arcuate flange elements, and more typically are impaled in the interior wall surface of the filter tube.

The end cap may be molded integrally as one piece or be composed of one or more elements, and typically is formed from an inert, moldable resin or plastic material. The end cap also may include a means to retain a gasket on its upper surface, to permit the end cap to be placed in a sealing relationship with the inlet or outlet of the housing element in which the filter cartridge is to be employed. The end cap provides for the placing of one annular surface of the body ring element into a self-gasketing, sealing position, by the application and maintenance of an axial, compressive force by the body element against and across the entire edge width of the filter tube when placed in the housing, while the barb elements retain the body ring element in position on the filter ends and prevent outward movement of the end cap. The end cap with the filter tube avoids the necessity of the use of potting compounds and sealants; although, if desired, potting compounds and sealants also may be employed in combination with the filter cartridge of the invention.

In addition, the end cap of the filter cartridge also includes, optionally but desirably, means to prevent the rotary movement of the filter tube within the end cap, and, therefore, may include one or more antitwist prong elements extending downwardly from the interior, annular, facing surface of the body ring element into the outer edges of the filter tube, so as to prevent rotary movement between the end cap and the filter tube. Typically, the prongs may comprise sharp, conical-type prongs positioned generally and uniformly spaced perpendicularly downward from the body ring element and extending a short distance into the edge of the filter tube. Thus, the combination of the barb elements, to prevent withdrawal of the end cap and to maintain the end cap in an axially compressed position, and the antitwist prong elements, to prevent rotary movement, provides an improved, disposable filter cartridge.

The filter cartridge and end caps of the invention will be described for the purpose of illustration only in connection with particular embodiments; however, it is recognized that various changes, modifications and improvements may be made by those persons skilled in the art, all falling within the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic, sectional view of a filter unit including the filter cartridge of the invention;

Fig. 2 is a perspective, partially exploded and sectional view of the filter cartridge of the invention; and

Fig. 3 is an enlarged, fragmentary, sectional view of an end cap in a sealing position on the filter cartridge of the invention.

DESCRIPTION OF THE EMBODIMENTS

Fig. 1 is a schematic, sectional view of a filter unit 10 employing the filter cartridge of the invention, which includes a cylindrical-head housing element 12 and a bowl element 14, which may be transparent or nontransparent, threaded into or otherwise removably secured to the housing element 12. A filter cartridge 16, having end-cap elements 24 and 26, is secured within the bowl 14. The bowl 14 includes an annular knife edge 30, while the housing element 12 includes an inlet passageway 18 for the introduction of a fluid to be filtered into the interior of the filter cartridge 16, and an outlet 20 for the withdrawal of a filtered fluid from the bowl 14 of the unit 10, and an annular knife edge 28 on the housing element and about the inlet passageway 18. The bowl 14, optionally, includes a mechanical or automatic drain 22 for the removal of material from the bowl.

As illustrated, a fluid, such as a compressed gas like air or an inert gas like helium or a liquid, is introduced into inlet 18 and into the interior of the disposable filter cartridge 16, and passes through the walls thereof into the bowl 14 and to the outlet 20. The disposable filter cartridge is retained in a sealing relationship with the inlet passageway 18 through annular edges 28 and 30, which, on axial movement of the bowl 14, presses against a sealing gasket 56 on the top and bottom of the end caps 24 and 26. End caps 24 and 26 seal the filter tube 50 by axial compression across

the edge width of the top and bottom edges of the filter tube 50.

Fig. 2 is a schematic, partially exploded and sectional view of a filter cartridge 16 of the invention, wherein the filter cartridge 16, as illustrated, has an end cap 26 in a sealing position about one end of the filter cartridge 16 and the end cap 24 of the same construction as cap 26 in an exploded view. The end cap 24 comprises two molded resin elements, an interior insert 32 and an outer cap typically of polypropylene or other resin, but which, if desired, may be an integral, one-piece, molded end cap, which elements are adapted to be engaged frictionally and matingly, to form end caps 24 and 26 of the invention. Fig. 2 shows a flat, elastomeric, O-ring washer 56 which fits on the top, outer surface of the end cap insert 32, to form a seal, with the annular knife edge 28, in the filter unit 10. Of course, if desired, rather than employing the two end caps illustrated, a different end cap or means can be used to seal the bottom of the filter cartridge, or the end of the filter tube may be sealed directly by a self-gasketing technique against a flange surface. In the embodiment illustrated, both end caps are of the same construction and both are sealed with the housing element 12 and the bottom of bowl 14, by the use of knife edges 28 and 30 against gaskets 56. The outer cap insert has an annular, exterior flange 42 and comprises a body ring element 34 having annular inner 44 and outer flat surfaces, the outer surface adapted, with raised, annular flange 48, to provide a support surface for an elastomeric sealing gasket 56, while the inner, flat surface 44 has a width equal to the width of the filter tube edge and is adapted to be compressed axially across the full edge width of one or the other edge of the filter tube to be sealed. The inner cap insert 32 includes an annular flange element divided into a plurality of split-ring arcuate sections 36. These arcuate sections are flexible and constitute, for example, about 30- to 40-degree arcuate sections adapted to move laterally and biased outwardly. The flange elements 36 extend into a close, adjacent relationship with the interior wall surface of the filter tube 50 of the cartridge. The arcuate sections 36 have, at the one end thereof, frustoconical, arcuate, barb-like elements 38 extending laterally outwardly, with the outer edge thereof having a diameter greater than the internal diameter of the filter tube 50 to be sealed. The annular, exterior flange 42 fits and is adapted to be placed in a close, adjacent relationship with the exterior wall surface of the filter tube 50. The flat ring surface 44

_ includes a plurality of generally equally spaced, antitwist, conical-type prong elements 46 extending perpendicularly, downwardly from the surface 44.

The filter cartridge 16 illustrated is an inside-outside, flow-type filter cartridge 16, which includes an outer, semirigid, self-supporting, self-gasketing filter tube 50 which may be sealed by full-edge-width axial compression of the one or the other end of the filter tube 50, by compression of the fibers adjacent and about the peripheral ends 54, without substantially affecting the filtering capacity or position of the body of the filter tube 50. In one embodiment, the filter tube comprises a plurality of nonwoven, borosilicate glass fibers having an average diameter of 0.03 to 8 microns, and bonded together by an inert binding material, such as a fluorocarbon or silicone resin. The filter cartridge 16 includes an internal, prefilter layer 52 typically composed of a plurality of nonwoven, relatively coarse fibers, such as polypropylene glass fibers, adjacent the interior wall surface of the filter tube 50.

Fig. 3 is a schematic, enlarged, fragmentary, sectional illustration of the end cap 24 in a sealing position in the filter cartridge 16. As illustrated, the inner flat surface 44 of the end cap ring is placed in an axially compressive sealing position, to compress the glass fibers of the filter tube 50 about the edge 54, so as to place the surface 44 in a fluid-sealing relationship across the full edge width of the end of the filter tube 50. The surface need not be wholly flat and may contain or include ridges, but merely may constitute a surface which exerts a sufficient force in the housing to provide a seal. The outer flange 42 extends along the exterior wall surface of the filter tube 50, while the inner flange 36 extends along the interior wall surface of the filter tube 50. The barb elements 38 extend directly into the interior wall surface of the nonwoven filter tube 50, and frictionally retain the surface 44 in position and prevent axial, outward movement or dislodgement of the end cap 24. The barb elements 38 have a sharp edge, to penetrate the wall surface, and are biased outwardly, to penetrate directly the fiber wall surface of the tube 50, with the flat edge of the frustoconical barb elements extending upwardly, to prevent further movement. The peripheral compression and seal of the glass fibers of the filter tube 50 are schematically illustrated by the higher-density, generally uniform shading adjacent the surface 44. The antitwist prong 46 is embedded into the edge 54 of the tube 50, generally less than the

elements 36 and 42, but sufficient to prevent rotary movement of the end cap on the filter tube 50. The prefilter layer 52, generally greater in width and loosely formed, is not secured by the end cap 24.

In operation, the end cap 24 may be placed in position, firstly, by placing the exterior end cap ring over the end 54 of the filter tube 50 and, thereafter, axially forcing the interior end cap insert 32 into the internal opening of the end cap ring and to snap-fit into place, so that compressive sealing of the edge 54 by surface 44 and penetrating of the wall surface, by barb elements 38, of the filter tube occur. If desired, the end cap 24 can be an integrally molded ring or be preformed by the combination of the exterior and interior inserts, and, thereafter, the preformed end cap 24 is axially forced into the end of the filter tube 50. If desired, a single, annular flange, either exterior or interior, may be used, but preferably spaced-apart, inner and outer flanges are desirable for appearance, sealing and the structural integrity of the filter cartridge.

In operation and structure, forcing the end caps 24 and 26 downwardly over and across the full edge width of the filter tube typically provides a fluid-tight end seal across the end cap, depending of course on the amount of force used; however, even if the desired degree of self-gasketing compression sealing is not fully accomplished, the axial force on the gasket 50 of the end caps 24 and 26 by the knife edges 28 and 30 through the screw-on bowl, or other means, such as tie rods of holding the filter cartridge, provides or completes the axial sealing force. The end caps 24 and 26 can move axially, slightly downwardly into a more effective sealing position with additional axial force, but cannot be withdrawn due to bias slope of the barb elements.

The use of the end caps 24 and 26 obviates the necessity of employing potting compounds and sealants, to seal the end caps, and provides a rapid, simple and easy method to provide a disposable filter cartridge.