Abstract:
An expandable media filter structure is composed largely of biodegradable materials and is environmentally disposable. A plurality of pleated panels are interconnected at their edges so as to be collapsible for storage and shipping purposes but expandable for installation and use. A plurality of ribbons are ultrasonically welded to each of the panels edges, with the ribbon portions between edges being of substantially equal lengths, thereby maintaining equal spacing between the panel edges when the filter is in the expanded condition but allowing an each collapsing of the filter for storage. Forming a part of the nondisposable framework for support of the disposable filter are a pair of end plates which are C-shaped in cross section for slidably receiving an end panel of the media filter therein. The depth of the C-shaped channel is sufficient to allow a plurality of the unexpended pleats to be stored therein so that a single sized filter may be used for various sizes of cabinet openings. The end plates include a pair of slots formed near their ends for attachment to a nondisposable support structure. The nondisposable support structure includes a pair of molded plastic side caps that fit over the respective ends of the filter panels and the end plates. Each side cap has pair of flanges at its opposite ends which act to maintain the filter in its expanded condition when the end plates are placed in abutting position therewith. Each side cap also includes a boss which fits into a respective end plate slot to hold the end plates in their installed positions within the side caps.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to air filters and, more particularly, to expandable air filters for use in furnaces. 
     The use of disposable air filters in the air distribution system of a building has provided an efficient and economical method of removing undesirable particulate matter from the air. In its simplest form, a rectangular piece of filter media material is mounted in a cardboard framework, with the combination then being mounted in a filter cabinet or an air duct somewhere in the air distribution system. With a hot air furnace, it is common practice to place the filter in a filter cabinet just upstream of the fan so as to filter the return air as it enters the furnace from the return air duct. When the filter is spent, i.e. when it has collected a sufficient amount of particulate matter as to be considered “full”, then it is removed and replaced with a new filter. 
     One way to increase the surface area of a filter is to make it multi-dimensional, with a plurality of accordion-like pleats. Such a pleated media filter is thicker than a non pleated filter and therefore provides more active surface area, making it more effective and longer lasting. It can be rechargeable, i.e. cleanable, or disposable depending primarily on the type of material used for the filter media. A disposable material, however, tends to be less durable and strong, and many such materials will not be suitable for providing the necessary support structure that is necessary to secure and maintain the installed position of the disposable portion of the filter in the nondisposable support framework. Further, a homeowner should be able to simply and easily remove, replace and dispose of a dirty filter. 
     It would also be desirable for a serviceperson to have a single sized filter which can be used to accommodate various sizes of cabinet openings, such that his inventory can be substantially reduced to. Generally there are three sizes of filters that must be stocked and carried in order to meet the various installation requirements. 
     A pleated filter element may be selectively collapsed for storage and shipping purposes and then later expanded for installation and use. To accomplish this, it is necessary to provide some means to maintain the filter element in its expanded condition. It is also desirable to maintain substantially uniform spacing and angling of the pleats, and a comb-like, rigid framework has been used for that purpose. 
     It is therefore on object of the present invention to provide an improved furnace air filter and method of manufacture. That object and other features and advantages will become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings. 
     SUMMARY OF THE INVENTION 
     Briefly, in accordance with one aspect of the invention, a plurality of ribbons are placed on either side of the pleated filter element and are secured to the edges of the pleated panels with equal lengths of ribbon portions between the respective pleated panel edges such that, when the filter element is expanded, the expanded ribbon portions cause a uniform spacing and angling of the pleated panels to occur. An end plate is attached to each of the two end filter panels, and the ribbons are expanded and attached to the end plates. 
     In accordance with another aspect of the invention, the ribbons are secured to the pleated panel edges by way of ultrasonic welding. Such a process provides for an efficient, economical, and effective method of bonding the ribbons to the panel edges. 
     By yet another aspect of the invention, the filter element is maintained in its expanded condition by a pair of side caps which form the framework for, and to which the two end plates of the filter element are attached. The side caps each have a pair of spaced flanges over which the respective filter element end plates are stretched so as to maintain a minimum expanded length of the filter element, and a pair of bosses engage with corresponding slots in the end plates to hold them in their installed positions. 
     In accordance with still another aspect of the invention, the end plates, which form part of the disposable portion of the filter, are formed of a plurality of laminated layers which are adhesively bonded and compressed together into a U-shaped structure that provides the necessary strength and rigidity to support the expanded filter in its installed position. 
     By a further aspect of the invention, the end plates do not form an integral part of the of the disposable filter element and include hanger elements which permit the storage of unexpanded portions of the filter it, such that a single sized filter can be used for multiple sized openings, with the unneeded portions thereof being stored within the end plates. 
     In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded, perspective view of the filter structure in accordance with the present invention. 
     FIG. 3 is an exploded, perspective view of a portion of the filter structure in accordance with the present invention. 
     FIG. 2 is a sectional view of an side cap portion of the filter structure as seen along lines  2 — 2  of FIG.  1 . 
     FIG. 4 is a sectional view of a portion of the side cap with a filter element installed therein. 
     FIG. 5 is a sectional view of an alternative embodiment of a side cap portion of the filter structure. 
     FIG. 6 is a schematic illustration of an ultrasonic bonding process used in the manufacture of the filter structure in accordance with the present invention. 
     FIG. 7 is a partial perspective view of an end plate portion of the filter assembly in accordance with the present invention. 
     FIG. 8 is a partial perspective view of a modified embodiment of the end plate portion of the filter. 
     FIGS. 9 and 10 are schematic illustrations of the filter element as installed in a modified embodiment of the end plate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, an air filter structure is shown generally at  10  as comprising a media filter element  11 , a pair of end plates  12  and  13 , and a pair of side caps  14  and  16 . The side caps  14  and  16  are formed of a plastic material and are reusable, whereas the combination of the media filter element  11  and its associated end plates  12  and  13  are made of polypropylene and cardboard materials, respectively, and are intended to be disposable and replaceable at the time when the filter is considered to be “full” or “dirty”. 
     The side caps  14  and  16  are identical and comprise a substantially planer base element  17 , normally extending sidewalls  18  and  19 , and normally extending end walls  21  and  22 , the combination of which defines a cover for receiving one end of the filter element  11  as will be described hereinafter. As part of the base element  17  of each of the side caps  14  and  16 , of there are provided a pair of spaced handles or grips  23  and  24  which are molded into the base element  17  as shown. Also, on the outer surfaces of the end walls  21  and  22 , there are provided a pair of molded clearance ribs  26  and  27  which serve to reduce sliding friction when the filter assembly is being installed into its operating position within a duct or the like. 
     As shown in FIG.  1  and also in FIG. 2, the side caps  14  and  16  each include at each end thereof a pair of spacer flanges  28  extending normally from the base element  17  and a locking boss  29  on the inner side of the end walls  21  and  22 . Each of the spacer flanges  28  includes a beveled portion  31  angled inwardly from the wall,  21  and  22 , respectively, as shown in FIG.  2 . The spacer flanges  28  are designed to establish and maintain the proper expanse of the filter element  11  when it is installed into the unit in the expanded state, whereas the locking bosses  29  are provided to secure the filter element in its installed position within the side caps  16  and  17  as will be more clearly explained hereinafter. 
     Referring now to FIG. 3, the media filter  11  and its associated end plates  12  and  13  are shown in greater detail. The media filter  11  comprises a plurality of pleats  32 , with adjacent pleats  32  having their edges  33  integrally connect in accordion-like fashion so as to be collapsible into a tightly stacked condition for storage and shipping, or expandable into an open position as shown for installation and use. The one ends  34  of the various pleats  32  form a plane, and the other ends  36  of the pleats  32  form another plane. The pleats  32  are formed of a porous material which will readily allow the passage of air therethrough with little pressure drop while filtering out any solid particles that may be contained within the flowing air. The materials are preferably relatively inexpensive and biodegradable since this portion of the assembly is designed to be disposable. Any suitable material may be used, but a preferred material is polypropylene. 
     Attached to the edges  33 , on each side of the pleats  32  are a plurality of flexible spacer elements  37  which are connected to the edges  33  of the pleats  32  so as to allow a collapsing of the media filter element  11  for storage and transport, and for the maintenance of a proper spacing of the pleats  32  when the filter element in  11  is in its expanded condition. That is, the spacer elements  37  are so attached to the pleat edges  33  that when the spacer elements  37  are in their expanded condition, the pleat edges  33  are uniformly spaced from their associated adjacent pleat edges  33 , and when the filter element  11  is collapsed, the spacer elements portions between the pleat edges  33  will go slack and not interfere with the collapsing of the filter element  11 . The spacer elements  37  can be of any flexible material but are preferably in the form of a strand, string, ribbon, or the like, that can be readily and securely affixed to the pleat edges  33  to accomplish the spacing function intended. For purposes of description, the spacer elements  37  are shown as ribbons. A preferred material is one which is relatively inexpensive, of reasonable strength and durability, and is biodegradable, as this is part of the disposable portion of the structure. 
     The manner in which the spacer elements are affixed to the pleat edges  33  may vary in accordance with the needs and facilities of the manufacture. One approach would be to use an adhesive, while another would be to stitch the elements together. A preferred approach is to use ultrasonic bonding for that purpose as will be described more fully hereinafter. 
     The number and location of the spacer elements  37  may also be varied in accordance with the needs and desires of the manufacturer. Although the filter element  11  is shown with three equispaced elements on each side of the filter element  11 , that number and location may be increased or decreased as desired. However, in order to accommodate ease in installation, it is preferable to have at least one spacer elements  37  on each side of the filter element  11 . In addition to attaching the spacer elements to the pleat edges  33 , it is also desirable, for purposes of durability, to attach the spacer element overhangs  38  at each end of the spacer elements  37  to the outer side of the respective end pleats  41  and  42  as shown in FIG.  3 . 
     Continuing with the description of FIG. 3, the end plates  12  and  13  are identical and are generally U.-shaped in form, having a body element  43  and two normally extending side elements  44  and  46 . Formed in each end of the body  43  is a slot  47  which is used for securing the filter element  11  in its installed position within the side caps as will be more fully described hereinafter. Although the end plates  12  and  13  may be formed of a molded plastic material, or the like, a preferred material is cardboard because of its relatively low-cost and biodegradability. The use of such material for this purpose, however, poses certain problems which were solved in a manner to be described more fully hereinafter. 
     The end plates  12  and  13  are part of the disposable filter structure  10  and as such are securely fastened to the respective end pleats  41  and  42  by an adhesive or the like. That is, the entire outer side  39  of each of the end pleats  41  and  42  are preferably glued to the inner sides of the respective body elements  43  of the end plates  12  and  13 . In doing so, the spacer element overhangs  38  are also captured between the two elements to thereby provide a durable union which remains together for the life of the filter structure  10 . The end plates  12  and  13 , with their side elements, therefore serve to encase the collapsed media during storage and shipment and to facilitate and maintain expansion of the media during installation and operation. 
     Having described both the disposable filter portion, i.e. the filter structure  10  as shown in FIG. 1, and the reusable side caps  14  and  16  into which they are installed, the manner in which the disposable portion is installed within the side caps will now be described as shown in FIG.  4 . To install a disposable filter element, a collapsed filter structure  10  is removed from its packaging and expanded to a fully open position, with the spacer elements  37  being extended to their full-lengths. When the filter structure  10  is in its fully expanded condition, the separation of the end plates  12  and  13  should be such that they should be able to be easily installed in the space between the spacer flange  28  and end wall  21  or  22 . That is, the side elements  44  and  46  of each of the end plates  12  and  13  should slide over the beveled portion  31  and onto the spacer flange  28  as shown in FIG.  4 . When in the fully installed position, the body element  43  will be fully engaged with the inner side of the end wall  21 , such that the boss  29  slips into the slot  47  to secure the filter structure  10  within the side cap. In this position, the pleat ends  34  and  36  are captured in an interference fit within the boxlike structure of the side caps  14  and  16  to form a composite sealed unit which can now be installed in its desired position within a duct or the like. When the filter becomes dirty, the entire assembly can be removed to replace the disposable filter structure  10 . Removal can be easily accomplished by slightly compressing the end plates  12  and  13  together so as to disengage the boss  29  from the slot  47  and allow the filter structure  10  to be removed from the side caps  14  and  16 . 
     FIG. 5 shows an alternative embodiment of an side cap  17  wherein, on the outer side thereof, an extended edge is molded around entire perimeter and is seen as a pair of border ribs  48  and  49  which are integrally molded at the respective ends of the side cap  17 . The purpose of the ribs  48  and  49  are to extend the depth of the filter assembly to fit a deeper cabinet. In this way, a single filter size may be used in cabinets of various depths by simply changing the side caps, with the side caps selected having ribs  48  and  49  which are of the appropriate length to extend across the depth of the cabinet. 
     As mentioned hereinabove, the spacer elements  37  are secured to the pleat edges  33  by way of an ultrasonic bonding process. That process will now be described with reference to FIG. 6. A conveyor belt or continuous chain  51  with a sawtooth form corresponding to the size and shape of the pleated filter material is provided as shown, with motor drive means (not shown) to cause it to rotate in a clockwise direction. A first ultrasonic welder  52  is provided on the upper side of the conveyor belt, and a first backup device  53  is provided below the conveyor belt, opposite the welder  52 . This welder is used to ultrasonically bond the spacer elements  37  to the upper side of the media filter material as it passes through the welding apparatus. Similarly, a second ultrasonic welder  54  located below the conveyor belt, and a second backup device  56 , located above the conveyor belt, are used to ultrasonically bond the spacer element  37  to the opposite side of the media filter material. 
     As a first step in the process, the filter media goes through a laminating process wherein a wire mesh support is attached to one side thereof, with the combination then going through a pleating machine to form pleats to the desired depth. This is a common process in the manufacture of pleated filters. The pleated media  11  is then fed into the welding apparatus from the left side thereof, in an expanded condition, as shown. As it proceeds along the conveyor belt, the ribbons which act as spacer elements  37  are then introduced on each side of the media as shown. Thus, an upper ribbon  57  coming off of a spool  58  is extended along the upper side of the expanded pleated material, and a lower ribbon  59  coming off of a spool  61  is extended along the lower side of the expanded pleated material. As the edges of the pleated material, with its overlaid ribbon, pass through the welding apparatus, the two welders operate to ultrasonically weld the ribbon to each edge of the media material. This is accomplished on the upper side, for example, by the backup device  53  being pneumatically raised to a position directly below the peak or edge of the pleated material to provide support thereof, and the welder  52  being pneumatically lowered to momentarily engage the ribbon and press it against the edge of the pleated material. During engagement, the welder  52  causes ultrasonic vibrations within both the ribbon and the pleated material, thereby causing both of them to heat up and bond to each other. The backup device  53  is then retracted, the welder is raised slightly, and in the pleated material is advanced to the next edge so that in the process can be repeated. Meanwhile, the same process is occurring at the other (lower) side of the media material by the welder  54  and backup device  56 . The result is a pleated material being delivered at the right side of the welding apparatus, with ribbons  57  and  59  being attached to each edge thereof so as to thereby establish a uniform maximum spacing of the pleats when in the expanded condition. That expanded filter material can then be cut to the desired length, attached to end plates at either end thereof, and then be collapsed for storage and shipping. 
     Whereas the process as just described was applied to bond a single ribbon on each side of the media material, it will be understood that the same process can be extended to simultaneously weld a plurality of ribbons on each side of the media material. Also, even though the process as described includes the steps of expanding the media and extending the ribbon across the expanded edges, it is also possible to present the pleated material in a collapsed or partially collapsed condition for the welding process. This approach would require a similar collapsing of the ribbon in order to obtain the proper spacing relationship with the pleat edges, but may allow the simultaneous welding of a plurality of edges with a single welder. 
     Having generally described the end plates  12  and  13  in design and function, the specific design structure will now be described with reference to end plate  13  as shown in FIG.  7 . As will be seen, the end plates are constructed of a plurality of layers  62  of a natural fibrous material such as paperboard or cardboard, with the layers  62  being laminated by bonding and compressing at high pressures the individual layers into the final U-shaped form to provide a rigid, strong and durable structure that will withstand the demands of intended use. A suitable structure has been found to result from the use of 6-10 layers of approximately 0.015 in. thickness paperboard that are adhesively bonded together with a water-based glue. The outer layer may have a clay coating in order to obtain a low-cost, high contrast, white surface for the printing of instructions and other information. 
     Such a laminated construction of the end plates provides the strength and rigidity to prevent sagging of the unsupported middle portion thereof, and its shape retention capability facilitates the easy insertion into and locking into place within the side caps as described hereinabove. At the same time, it is sufficiently flexible to allow it to be pushed in to unlatch it from the side caps for purposes of replacement. The natural materials from which it is made are biodegradable and therefore easily disposable. 
     Referring now to FIG. 8 an alternative embodiment of the end plate is shown at  63  to include a body element  64 , side elements  66  and  67 , and hangar elements  68  and  69  to form a C-shaped element. A slot  71  is formed in the body element  64 , at each end thereof, in the same way as described hereinabove with respect to end plates  12  and  13 . However, here the end plate  63  does not form an integral part of the disposable filter assembly but is rather a nondisposable part that is used not only to support the disposable media filter element  11  but also to selectively provide a storage container for portions thereof in order to accommodate the needs of an installer in meeting the requirements of multiple sized openings. This will be more clearly seen with reference to FIGS. 9 &amp; 10. 
     If a service person can carry a single filter size for installation in various sized cabinets, he can reduce his inventory to save space and money. That is, filters for residential use are generally of one of three sizes: 16×25 in., 20×25 in., or 24×25 in. If a service person can carry only the 24×25 in. filter and use them for all installations, it will be to his benefit. The present design of the end plate  63  will allow this to occur. Referring to FIGS. 9 &amp; 10, a single media filter element  11 , having dimensions of 24×25 in., for example, is used in its entirety for installation in a 24×25 in. opening as shown in FIG. 10, and is partially used in a 16×25 in. opening as shown in FIG. 9, with the remaining unused portion being stored in the end plates  63  as shown. 
     The disposable filter  11  includes no integral end plates but only the plurality of folded pleats as described hereinabove. Such a filter is installed into the two end plates by simply inserting the end panels into the respective end plates and sliding them in. This is shown in FIG. 10 wherein only a single end panel is captured within the respective end plates  63 , with the hangar elements  68  and  69  providing the necessary support to maintain the filter in its expanded condition when the end plates  63  are installed into the side caps as described hereinabove. In the FIG. 9 installation, wherein the opening is only 16×25 in., a portion of the pleats  72  remain in their collapsed condition and are collectively installed into the end plates as shown. Similarly, for use in an opening of 16×20 in., a smaller portion of the pleats  72  would remain in their collapsed condition and be inserted into the end plates  63 . In each case, however, the operative, expanded portion of the filter element  11  would be fully expanded as shown. 
     Since the C-shaped end plates  63  are designed for re-use, they are preferably composed of a more robust material. Whereas it may be possible to form the C-shaped element in a laminated material as described hereinabove, a molded plastic or a light metal material is preferred. Further, it may take various forms and still provide the same function. For example, the hangar elements  68  and  69  do not need to be continuous along the lengths of the end plates  63  as shown, but only need to provide support at various points along the length and can therefore be discontinuous or simply be a plurality of brackets attached to the side elements  66  and  67 . Also, whereas the end plates  63  have been shown and described as open-ended to facilitate the easy insertion of the end pleats therein, they may be closed to provide greater strength, with the end pleats then being installed in another manner such as by installing one edge of the pleat and then flexing the pleat in order to install the other edge thereof.