Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-01-31
2003-02-25
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S293000, C156S303100
Reexamination Certificate
active
06524411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an improved end-cap for pleated filter cartridges and a method of manufacturing such end-capped pleated filter cartridge. More particularly, the present invention relates to a pleated surface-type filter cartridge having an elastomeric end-cap which acts both as the end-cap for sealing the filter element and a gasket for providing a seal between the filter housing and the filter cartridge. The elastomeric end-cap of such pleated surface-type filter cartridge is bound to the filter element by means of a thermoset or thermoplastic adhesive.
2. Background of the Related Art
Filtration is the process of separating particles from a fluid suspension (liquid or gas) by use of a porous medium or by means of a medium possessing chemical properties, such as hydrophobicity, electrostatic charge, etc., which permit such medium to interact and hold the particles which are to be separated from the fluid while permitting the fluid to pass there through. In conventional filtration, the filter medium retains most of the suspended particles which are filtered on or within itself, but allows the fluid being filtered to pass through unimpeded. Flow across the filter medium is generally achieved by the application of a driving force, usually in the form of a static pressure difference across the filter, which may be generated, for example by external pressure applied upstream, a vacuum applied downstream, gravity, or other force. Fluid suspension separations are used extensively in the manufacture of polymer products, medicinals, mineral and metallurgical processing, petroleum refining, water purification, emissions control, and in beverage and food preparation.
Most conventional filters may be categorized into two broad categories of filters, surface-type filters and depth-type filters. In surface-type filters, particles larger than the pore size of the filter medium are stopped at the upstream surface of the filter. Solids form a filter cake on the surface of the filter medium, the cake itself forming a filter which clogs with time. In depth filtration, on the other hand, the filters are constructed of medium of sufficient thickness, relative to contaminant size, to filter throughout the full depth. Typically the filter medium has a distribution of pore sizes some greater than the particles to be removed, so that the particles can penetrate into the medium. The particles are mainly retained in the medium by means of direct interceptions and by adsorptive surface forces (molecular and electrostatic).
Filters are often fabricated into cartridges comprising filter media surrounding a tubular support and/or drainage core. Depth-type filtration cartridges are frequently fabricated from wound material, felts, some porous ceramics, sintered metal or metal fibers and bonded fibers. Surface-type filtration cartridges are frequently fabricated of fiber sheets. Surface-type filter cartridges may be resin impregnated paper, may be membranous, may comprise porous metal, plastic, or non-woven material and may be covered with a netting or cage to increase strength.
Generally as a fluid suspension is passed across filter media the pressure drop across the filter gradually increases. Such increase is generally due to collection of material on the filter media. An increasing pressure drop across the filter media translates into an increasing load on the means (such as a blower or pump) being employed to force the fluid across the filter media. A surface filter, therefore, must have a large enough area of filter media to minimize the rate of increase in pressure drop across the filter media.
In order to increase the surface area in a surface-type filter cartridge, pleated filter media have been developed. Pleated surface-type filters typically include cellulosic or synthetic filter media which are relatively thin (about 0.005 inch to about 0.030 inch in thickness) and are folded in an accordion-like fashion to produce a plurality of pleats. Each pleat is typically made up of a pair of rectangular panels, with fold lines separating the panels, the pleats and fold lines of the pleated filter usually running vertically. To help insure that the surface of the panels remain apart, and to provide even more surface area, the pleated surface-type filter may also be formed from corrugated material and/or have a substantially non-filtering material located on each side of the medium to act as a support and drainage layer. Typically, pleated surface-type filter media are formed from calendered melt-blown material, cellulose and/or paper.
A pleated surface-type filter cartridge, as many other filter cartridges, typically includes a pair of end-caps. The end-caps of a pleated surface-type filter cartridge span the filter media, with the pleats and fold lines normally running from one end-cap to the other end-cap. If corrugations are present, such corrugations generally run at right angles to the pleat tips, that is, parallel to the end-caps. The end-caps serve to prevent the fluid which is desired to be filtered, from circumventing passage through the filter media by, in the case of pleated surface-type filter cartridges, coursing along the fold lines of the pleats and directly exiting through the ends of the cartridge. The end-caps may be solid throughout, or may include an opening therein. Filter cartridges having one solid end-cap and an end-cap having an opening therein are referred to in the art as single open end filter cartridges, while filter cartridges having two end-caps with an opening therein are referred to as double open end cartridges. Pleated surface-type filter cartridge end-caps are typically made form metal (steel, stainless steel etc.), but also have been fabricated from non-elastomeric thermoplastic (such as polypropylene, polyester and polysulfone) and thermoset (such as plastisol, urethane, silicone, epoxy) material.
Various methods have been proposed for attaching an end-cap to a filter cartridge. In general, these methods may be classified into four major categories: potting, molding, thermal-welding and spin-welding.
Potting entails pre-forming the end-cap, filling the end-cap with an adhesive and inserting the filter element therein. Potting may also be performed by placing the adhesive on the surface of the filter element and pressing the filter element against the end-cap until the joint is set (this technique is also referred to as “bonding”). The adhesive is cured using a combination of heat and/or time.
In molding, the end-cap is molded directly onto the end of a filter element. The molding material is typically a thermoset polymer, such as plastisol, urethane, silicone and epoxy. The molded end-cap is then removed from the mold.
In thermal welding, a thermoplastic end-cap is heated to liquefy one surface of the end-cap and form molten plastic. One end of the filter element is then placed into the liquefied surface of the end-cap. When the end-cap solidifies once more, the filter element is securely joined to the end-cap.
In spin-welding, the end-cap and filter element are joined and placed in frictional contact with one another. Either the end-cap or filter element are then rotated with respect to the other so that heat is generated by frictional contact. The heat melts the surface of one or both to form a molten material at the interface of the two. When the rotation is stopped, the molten material solidifies to securely bond the end-cap to the filter element. Typically, one of the two members to be joined by spin welding is made of a thermoplastic resin. Spin-welding and thermal welding techniques are often referred to jointly as “heat bonding.”
Application of end-caps to pleated surface-type filter elements are associated with problems not generally seen with other types of filter elements, such as depth-type filter elements. Pleated surface-type filter elements suffer from an inherent lack of structural rigidity as compared to many other types of filter elements, and in particular suffer from a
Marcinczyk Daniel
Pulek John L.
Ball Michael W.
Cummings & Lockwood
CUNO Incorporated
Kilkenny Todd J.
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