Abstract:
Disclosed in this specification is a method for making a pleated filter cartridge by placing a pleated filter on a mold and adding a polymerizable potting compound to the inner cavity of the pleated filter. The potting compound is permitted to cover the portion of the upper surface of the mold that is encompassed by the pleats. The potting compound is selected to form a polyurethane after polymerization is complete.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a method and mold for making a pleated filter cartridge and more specifically to a method for making the molded bottom end cap of such a cartridge. 
     Conventional pleated filter cartridges include a pleated filter disposed between two molded end caps (i.e., a top end cap and bottom end cap). These pleated filters are used in a variety of applications, including removing particulates from gases in the food, pharmaceutical, and energy industries. During use, a gas (e.g. air) is passed over the surface of the pleated filter to trap particulates that may be present (e.g. dust, milk dust, coal dust, pollen, microorganisms including yeast, mold and bacteria). Initially, these particulates are entrapped on the surface of the pleated filter. Over time, the particulates may accumulate on the horizontally extending ledges of the molded bottom end cap. This accumulation can result either from particulate drift due to gravity or from the entrapped particles being dislodged during pulse jet cleaning. In certain applications, particulate accumulation on the horizontally extending ledges of the molded bottom end cap can impact the efficacy of the filtering process by reducing the available filtering area or increasing the risk of contamination or combustion. 
     It is difficult to produce quality pleated filter cartridges that do not have a horizontally extending ledge on their molded bottom end cap. The prior art method for producing such cartridges use two-part epoxy resins that have certain manufacturing challenges associated with them that inhibit their use on a commercial scale. 
     There is a need to provide an improved method for rapidly making pleated filter cartridges that do not have a horizontally extending ledge on their molded bottom end cap. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Disclosed in this specification is a method and mold for making a pleated filter cartridge by placing a pleated filter on a mold and adding a polymerizable potting compound to the inner cavity of the pleated filter. The potting compound is permitted to cover the portion of the upper surface of the mold that is encompassed by the pleats. The potting compound is selected to form a polyurethane bottom end cap after polymerization is complete. 
     An advantage that may be realized in the practice of some disclosed embodiments of the method is that polyurethanes usually cure more rapidly than two-part epoxy resins. This rapid curing minimizes permeation of the polyurethane through the pleated filter and minimizes the amount of polyurethane that leaks around the perimeter of the pleated filter, reducing or eliminating any horizontally extending ledges on the molded bottom end cap. Moreover, the molding process is sufficiently rapid to permit production of the pleated filter cartridges at speeds sufficient for commercial production. 
     In one exemplary embodiment, a method for making a pleated filter cartridge is disclosed. The method comprises the steps of placing the bottom end of a pleated filter on an elastomeric surface of the mold and applying a downward force to establish a seal. A polymerizable potting compound is added to the inner cavity and permitted to cover the portion of the elastomeric surface of the mold that is encompassed by the pleats including the spaces between the pleats that are part of the inner cavity. The potting compound is permitted to polymerize to form a polyurethane bottom end cap which is then removed from the mold. 
     In another exemplary embodiment, a mold for forming a bottom end cap of a pleated filter cartridge is disclosed, the mold comprising a base having a top surface with an elastomeric surface. 
     This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
         FIG. 1  is a top perspective view of an exemplary pleated filter cartridge; 
         FIG. 2  is bottom perspective view of the exemplary pleated filter cartridge of  FIG. 1  with a portion of the pleated filter cut away to illustrate the molded bottom end cap; 
         FIG. 3  is a bottom perspective view of a section of the molded bottom end cap; 
         FIG. 4  is a flow diagram for an exemplary method for making a pleated filter cartridge; 
         FIG. 5  is a cross-section of an exemplary mold for making a bottom end cap; 
         FIG. 6  is a depiction of the exemplary mold of  FIG. 5  in use; and 
         FIG. 7  is a perspective view of an exemplary molded top end cap of the pleated filter cartridge of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a top perspective view of an exemplary pleated filter cartridge  100 . Pleated filter cartridge  100  has an elongated pleated filter  102  which has a bottom end  104  and a top end  106 . The top end  106  of the pleated filter  102  has a top end cap  108 . An external support strap  110  encompasses the circumference of the pleated filter  102 , which can be formed of any suitable material. In one embodiment, the pleated filter  102  is formed of 260 gram per square meter spunbond nonwoven material made with bicomponent polyester fibers. Other suitable fiber materials include poly-p-phenylene sulfide (PPS), aramid, polytetrafluoroethylene (PTFE) or glass fibers. Non-woven constructs are also suitable. Examples of non-woven constructs include needle-punched felts, carded thermobonds, or hydroentangled webs. In one embodiment, these constructs are stiffened with resin or thermal heat calendaring. In another embodiment, an expanded PTFE (ePTFE) membrane is laminated into the pleated filter  102 . The bottom end  104  of the pleated filter  102  has a bottom end cap that is not visible from the perspective of  FIG. 1  but is visible in  FIG. 2 . 
       FIG. 2  shows a bottom perspective view of the exemplary pleated filter cartridge  100  of  FIG. 1  with a portion of the pleated filter  102  cut away to illustrate the molded bottom end cap  200 . The molded bottom end cap  200  is formed from a polyurethane, which is present between the pleats  202  of pleated filter  102  within the confines of pleated filter  102 . The polyurethane molded bottom end cap  200  does not extend outside of the perimeter of the pleated filter  102 . 
       FIG. 3  is a bottom perspective view of a section of the molded bottom end cap  200 , illustrating pleated filter  102  circumscribed by pleats  202 . The jagged circumference of pleats  202  defines the perimeter of the inner cavity  610  (see  FIG. 6 ) of the pleated filter  102 . The polyurethane bottom end cap  200  covers the inner cavity  610  of the pleated filter  102 , including those portions of the inner cavity  610  between the pleats  202 . The spaces  302  between the pleats  202 , which are not part of the inner cavity  610 , are free of polyurethane. 
       FIG. 4  is a flow diagram for an exemplary method  400  for making a pleated filter cartridge  100 . In step  402 , filter media is cut to a predetermined size, folded to form pleats, encircled to form a cylinder, and seam sealed to create a pleated filter  102 . In step  404 , an internal support core  604  (see  FIG. 6 ) is inserted into inner cavity  610  of pleated filter  102  to provide structural integrity to the pleated filter  102 . A variety of support cores may be used provided they do not block the potting compound  600  used to form the molded bottom end cap  200  from flowing between the pleats  202 . In one embodiment, the support core  604  is a wire frame and the potting compound  600  passes between the frame. In another embodiment, the support core  604  is a cylindrical tube with passages for passing the potting compound  600  between pleats  202 . 
     In step  406 , external support strap  110  is formed. In one embodiment, the external support strap  110  is formed by extrusion. The external support strap  110  circumscribes the outer diameter of the pleated filter  102  and holds the pleated filter  102  against the support core  604 . In step  408 , the bottom end  104  of the pleated filter  102  is inserted into a mold  500 .  FIG. 5  is a cross-section of an exemplary mold  500  for making a bottom end cap  200 . The mold  500  has a circular base  502  and a vertical sidewall  504  that may be formed from any suitable material (e.g., aluminum). The mold  500  also includes a circular elastomeric surface  506 . 
     In step  409 , after the pleated filter  102  has been inserted into the mold  500 , a downward force  606  is applied to the top end  106  of the pleated filter  102  that causes the bottom end  104  of the pleated filter  102  to impinge into the elastomeric surface  506 , which has a minimal Shore hardness. In one embodiment, the Shore A hardness is between 0 and 20. In another embodiment, the Shore 00 hardness is between 10 and 60. In one embodiment, the applied downward force  606  is of sufficient magnitude to cause the elastomeric surface  506  to be deformed to form a liquid-tight seal. In one embodiment, the downward force can be applied manually, while in another embodiment, the downward force can be applied by a plate powered by hydraulics. 
     In step  410 , a polymerizable potting compound  600  is added to inner cavity  610 . The components of the potting compound  600  are selected such that, after polymerization, a polyurethane is formed. In one embodiment, the potting compound  600  includes an isocyanate monomer and a hydroxyl monomer. In one such embodiment, a soft polyurethane is formed by selecting a flexible, difunctional hydroxyl monomer such as polyethylene glycol (PEG). The polyurethane may be a thermoplastic or thermoset polyurethane. Examples of suitable thermoset polyurethanes include material 1384A available from MCPU Polymer Engineering LLC (Pittsburg, Kans.). Examples of suitable thermoplastic polyurethanes include the Pellethane brand polymers from Lubrizol (Wickliffe, Ohio). In one embodiment, the Shore A hardness of the cured polyurethane molded bottom end cap is between 20 and 80. In another embodiment, the Shore A hardness is greater than 80. In certain embodiments, the potting compound  600  includes a cross-linking agent. 
     The liquid-tight seal formed between the bottom end  104  of the pleated filter  102  and the elastomeric surface  506  at step  409  prevents the potting compound  600  from leaking outside of the inner cavity  610  of the pleated filter  102 . In certain embodiments, the composition of the elastomeric surface  506  is selected to function as a release agent to facilitate removal of the pleated filter cartridge  100  and molded bottom end cap  200  after the polyurethane has cured in step  410 . A spraying agent can also be used to facilitate removal of the pleated filter cartridge  100  after curing. Examples of suitable elastomers for the elastomeric surface  506  include silicone elastomers. In the embodiment depicted in  FIG. 5 , the elastomeric surface  506  is held in place by a ledge  508  inserted into a groove in the vertical sidewall  504 . The elastomeric surface  506  of the mold  500  includes a bump  510  that has a bump width  512 . In one embodiment, the bump width  512  is at least 50% of the magnitude of the mold inner diameter  514 . In another embodiment, the bump width  512  is at least 75% of the magnitude of the mold inner diameter  514 . In yet another embodiment, the bump width  512  is at least 85% the magnitude of the mold inner diameter  514 . The bump  510  serves several functions, one of which is to guide the polymerizable potting compound  600  toward the pleats  202  in step  410 . In one embodiment, the bump  510  is circular and has a height that is at a maximum at the center of the bump  510  and gradually diminishes in height as the distance from its center increases (i.e. near the edges of the bump  510 ). The bump  510  may be centered with respect to the support core  604  during step  410 . This shape facilitates the flow of the potting compound  600  to the areas between the pleats  202  during step  410 . Additionally, the presence of the bump  510  diminishes the amount of potting compound  600  needed to create the molded bottom end cap  200 , which speeds the curing process. 
     In  FIG. 6 , which is a is a depiction of the exemplary mold  500  of  FIG. 5  in use, a window  608  is shown in the pleated filter  102  to aid in the illustration of the inner cavity  610  of the pleated filter  102 . The potting compound  600  is injected into the inner cavity  610  of the pleated filter using nozzle  602  and thereafter permitted to cover the portion of the elastomeric surface  506  that is circumscribed by pleats  202 . A sufficient volume of the potting compound  600  is used to fill the inner cavity  610  of the pleated filter  102  to a pre-determined depth. For example in one embodiment, the potting compound  600  fills a depth of about 0.5 cm to about 10 cm and all sub-ranges therebetween. 
     The potting compound  600  is permitted to polymerize to form a polyurethane bottom end cap  200 . Advantageously, polyurethanes polymerize rapidly compared to other conventional polymers (e.g. two-part epoxy resins which typically require several hours to cure). Accordingly, many processing problems are obviated by using polyurethanes. For example, diffusion of the potting compound  600  through the pleated filter  102 , as well as wetting of the pleated filter  102  through wicking action, is minimized due to the rapid polymerization of polyurethanes. The rapid polymerization of polyurethanes also minimizes leakage of the resin outside of the portion circumscribed by the pleats  202 . In one embodiment, the resulting polyurethane has a Shore A hardness between 20 and 80. Polyurethanes with a Shore A hardness outside of the range of 20 to 80 may also be used. Once the polyurethane has finished curing, the pleated filter  102  is removed from the mold  500 . 
     In step  412 , a second mold (not shown) is filled with a polymerizable resin. In one embodiment, this polymerizable resin is a potting compound  600 . In another embodiment, the polymerizable resin has a composition that is different than the composition of potting compound  600 . During step  414 , the top end  106  of the pleated filter  102  is inserted into this second mold and is removed after a specified cure time. In this fashion, top end cap  108  is formed.  FIG. 7  is a perspective view of an exemplary molded top end cap  108  of the pleated filter cartridge  100  of  FIG. 1 . The shape and configuration of the molded top end cap  108  varies according to the design of a specific cartridge. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.