Abstract:
A filtering flow box for receiving a supply of plastic pellets from a bottom-unloading tower silo and removing undesirable plastic strands (“angel hair”) from the pellets before they are processed for manufacturing. The box has an angled entry wall for laterally channeling pellets to an angled filter. The pellets pass through the filter and angel hair collects on the filter&#39;s upstream surface. The filter can be removed from the box at an angle having a vertical component for cleaning, thus allowing any pellets that have accumulated on top of the filter to fall back into the box.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a filter for sifting and channeling material flowing out of a bottom-unloading tower silo, and relates more particularly to a filtering flow box for receiving plastic pellets flowing from a bottom-unloading tower silo, sifting unwanted plastic strands (“angel hair”) out of the supply of pellets, and channeling the sifted pellets into vacuum feed lines for further processing. 
     2. Description of the Related Art 
     Plastic pellets comprise the raw material for many plastic articles of manufacture. Because of their small size and granular nature, such pellets are preferred for their ease of handling and processing. In order to convert plastic pellets into a form that is useable for fabrication, the pellets are melted down, and the resulting molten plastic is subsequently used in processes such as injection molding or blow molding. 
     Typically, plastic pellets are stored in bottom-unloading tower silos adjacent a processing facility. The pellets are conveyed into the processing facility through vacuum feed-lines when needed. One problem associated with plastic pellets is the formation of so-called “angel hair.” Angel hair is thin, elongated plastic strands that result from the unraveling of plastic pellets. During transportation and handling, it is common for a significant quantity of pellets to unravel and form angel hair. Angel hair is generally undesirable because they are not useful for processing, and therefore must be removed from a supply of pellets before use. 
     Traditionally, the problem of angel hair has been dealt with by mounting a filter box below the outlet of a bottom-unloading tower silo in which plastic pellets are stored. A filter box is generally rectangular in shape and has four side walls, an open top for receiving material, and an open bottom for dispensing material. The top of the box has a flange that is adapted to bolt directly to the edges of an opening on the bottom of the silo. Thus, all of the pellets that fall through the opening (outlet) of the silo must subsequently pass into the attached filter box before being used. 
     The conventional filter box has a narrow, horizontal slot formed in one of its side walls for accepting a flat, rectangular filter that is formed of slit and expanded metal. Brackets extend from the inner surfaces of the side walls for holding the filter in a perpendicular orientation relative to the flow of material through the box. As plastic pellets fall by gravity from the silo into the box, the pellets, which are slightly smaller than the apertures in the filter, are allowed to pass through the box while most of the angel hair is caught by the filter. 
     Over time, as angel hair accumulates on the upstream surface of the filter, the apertures of the filter become increasingly clogged and the throughput of pellets steadily decreases. Once the apertures are sufficiently blocked, pellets settle on top of the collected angel hair and cannot pass through. An operator must therefore periodically pull the filter out of the filter box and manually remove the accumulated angel hair from the filter&#39;s upstream surface. 
     A problem that is commonly associated with the procedure of removing and cleaning the filter of a traditional filter box is that a quantity of pellets that accumulate on top of a clogged filter tend to remain on the filter when it is removed from the box. Thus, as an operator pulls the filter out of the box, those remaining pellets roll off the top of the filter and fall to the ground or floor adjacent the operator, creating a mess and a potential slip hazard for the operator and others who may be in the area. Cleaning up the dropped pellets is a tedious and time consuming task. 
     Once the plastic pellets have been sifted through the filter box, they fall into a flow box that is mounted to the bottom of the filter box. The flow box is similar to the filter box in size and shape, but has a closed bottom. Vacuum feed-lines are connected to outlet ports formed in a side wall of the flow box. The feed lines remove pellets that accumulate in the box and convey them into an adjacent processing facility. 
     BRIEF SUMMARY OF THE INVENTION 
     It is a first purpose of the present invention to provide a filtering flow box having a filter that can be conveniently removed, cleaned, and replaced without creating a mess or a hazard. 
     It is a second purpose of the present invention to provide a filtering flow box that is compact and inexpensive. 
     It is a third purpose of the present invention to provide a filtering flow box having a filter that is less prone to clogging than those found in the prior art. 
     In accordance with the purposes of the present invention, there is provided a one-piece filtering flow box for removing angel hair from a supply of plastic pellets. The filtering flow box has a main housing with an open top. The housing has a floor, two side walls, a rear wall, and an entry wall. The entry wall extends outwardly from the floor at a preferred angle of 135 degrees. A removable filter is held intermediate the rear wall and the entry wall at a preferred angle of 45 degrees relative to the floor. The filter is formed of perpendicularly-interlacing cross members that define a plurality of rectangular apertures. As compared to the diamond-shaped apertures of traditional slit and expanded filters, the rectangular apertures offer a greater amount of open area through which plastic pellets may fit. The inventive filter thus provides greater throughput and clogs less frequently than traditional filters. 
     The filtering flow box has a flange that mounts to the outlet port of a bottom-unloading silo in the manner of a conventional filter box. When the box is in an operative orientation, the entry wall is positioned directly below the silo&#39;s outlet port. Thus, as plastic pellets are released from the silo, they fall by gravity onto the entry wall of the box and are subsequently channeled toward the removable filter. As the pellets fall through the apertures in the filter, angel hair collects on the filter&#39;s upstream surface. The filtered pellets are then collected by vacuum feed-lines that are connected to outlet ports in the rear wall of the box. 
     In order to remove the filter for cleaning, a cover located on top of the main housing adjacent the mounting flange is opened and the filter is slidably withdrawn. Because the filter is angled, any plastic pellets that had accumulated on the clogged upstream surface of the filter roll off the filter as it is pulled out of the housing. All of the pellets thus remain within the housing, thereby allowing the filter to be conveniently cleaned without creating a mess. 
     Additionally, the compact, one-piece construction of the filtering flow box requires less material to produce and requires less space than traditional, multi-piece filter and flow boxes. The filtering flow box can therefore be produced at a lower cost and can be used in a greater variety of application environments than traditional boxes. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating the preferred embodiment of the present invention. 
         FIG. 2  is a top view illustrating the preferred embodiment of the present invention shown in  FIG. 1 . 
         FIG. 3  is a right side view illustrating the preferred embodiment of the present invention shown in  FIG. 1 . 
         FIG. 4  is a right side view in section through the line  4 - 4  of  FIG. 2  illustrating the preferred embodiment of the present invention shown in  FIG. 1 . 
         FIG. 5  is a cut-away view illustrating a filter guide of the preferred embodiment of the present invention shown in  FIG. 1 . 
         FIG. 6  is a cut-away view illustrating a first alternative filter guide. 
         FIG. 7  is a cut-away view illustrating a second alternative filter guide. 
         FIG. 8  is a detail view illustrating the feed-line clamps of the preferred embodiment of the present invention shown in  FIG. 1 . 
     
    
    
     In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or terms similar thereto are often used. They are not limited to direct connection, but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-4  and  8 , the filtering flow box  10  has a main housing  12 , a mounting flange  14 , a removable filter  16 , two filter guides  18  and  20 , a filter cover assembly  22 , and two feed-line clamps  24  and  26 . All components of the box  10  are formed of stainless steel unless otherwise noted, although all other materials that are sufficiently rigid and durable, such as aluminum, iron, and various plastics and composites, are contemplated as will be understood by the person having ordinary skill. For the sake of convenience and clarity, terms such as “front,” “rear,” “top,” “bottom,” “up,” “down,” “inwardly,” “outwardly,” “lateral,” and “longitudinal” will be used herein to describe the relative placement and orientation of various components of the invention, all with respect to the geometry and orientation of the filtering flow box  10  as it appears in  FIG. 1  as mounted in an operable orientation. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
     Still referring to  FIGS. 1-4 , the main housing  12  is a box-shaped container having an open top. The housing  12  is defined by a floor  28 , a rear wall  30 , two side walls  32  and  34 , and an entry wall  36 . The floor  28  is rectangular in shape and preferably measures 10 inches square. The rear wall  30  extends perpendicularly upward from the rear edge of the floor  28  to a preferred height of 12 inches. The entry wall  36  extends upwardly and outwardly from the front edge of the floor  28  at a preferred angle of 135 degrees, although any angle in the range of about 120 degrees to about 150 degrees is contemplated. The entry wall  36  extends to a preferred height of 12 inches. The side walls  32  and  34  extend perpendicularly upward from the lateral edges of the floor  28  to a preferred height of 12 inches, and extend longitudinally forward and rearward to the lateral edges of the entry wall  36  and the rear wall  30 . The adjoining edges of the floor  28 , side walls  32  and  34 , entry wall  36 , and rear wall  30  are secured to one another by welds, although all other means for rigidly fastening the components to one another, such as with adhesives or fasteners, are contemplated. It is further contemplated that two or more of the walls  30 - 36 , or the floor  28  and one or more of the walls  30 - 36 , may be formed of a single piece of bent sheet-metal. 
     The mounting flange  14  is preferably a flat, rectangular body having four sides  38 ,  40 ,  42 , and  44  that define a central inlet port  46 . The outer edge of the flange  14  preferably measures 16 inches square and the inner edge of the flange  14  (i.e., the outer edge of the inlet port  46 ) preferably measures 10 inches square. The flange  14  is rigidly mounted to the top of the main housing  10  with the inner front edge of the flange  14  being welded to the top edge of the entry wall  36  and the inner lateral edges of the flange  14  being welded to the top edges of the side walls  32  and  34 . Thus, the front side  38  of the mounting flange  14  extends forward from the top edge of the entry wall  36 , the lateral sides  40  and  42  of the flange  14  extend laterally outwardly from the top edges of the side walls  32  and  34 , and the rear side  44  of the flange extends laterally across and between the side walls  32  and  34 . 
     Referring now to  FIGS. 1 and 2 , the mounting flange  14  has a series of mounting apertures  48  formed through it. The apertures  48  are preferably spaced evenly about the flange  14  and are configured to allow the flange  14  to be fastened to a conventional silo outlet port. When the filtering flow box  10  is in an operative position below a silo, for example, the top surface of the mounting flange  14  flatly abuts a conventional receiving flange extending from the silo&#39;s outlet port. Each of the mounting apertures  48  is aligned with an aperture in the receiving flange, and a removable fastener, such as a bolt, is threaded through each pair of aligned apertures and is secured with a nut. Alternatively, it is contemplated that the mounting apertures  48  may be omitted, and that the flange  14  can be mounted to a silo outlet port by any other suitable means, such as by clamping or welding. 
     Referring to  FIGS. 1 ,  2 , and  4 , the removable filter  16  is preferably a planar, rectangular body having a border element  50  (see  FIG. 5 ) that frames, and that is rigidly affixed to, a screen element  52 . The outer edge of the border element  50  preferably measures 10 inches square, and the inner edge of the border element preferably measures 9 inches square. The border element  50  has a lip  54  extending perpendicularly from its top edge for allowing an operator to easily grip the filter  16  and to rigidify the filter  16 . 
     The screen element  52  is formed of a conventional metal screen having a plurality of perpendicularly-interlacing cross-members that define a plurality of rectangular filter apertures  56 . Each of the filter apertures  56  preferably measures ¾ inches square for allowing plastic pellets of a standard size (e.g., one-quarter inch) to pass through while at the same time allowing the filter  16  to effectively catch and retain strands of angel hair on its upstream surface. Although it is preferred that the screen element  52  be formed of interlacing cross-members, it is contemplated that any other filter means, such as slit and expanded sheet metal or drilled sheet metal, can alternatively be used. 
     Referring now to  FIGS. 1 ,  4 , and  5 , each of the filter guides  18  and  20  (filter guide  20  is not shown, but is a mirror image of guide  18 ) is preferably formed of an elongated upstream bracket  58  and an elongated downstream bracket  60 . The brackets  58  and  60  are mounted to the interior surfaces of the side walls  32  and  34  in a parallel orientation. Each bracket  58  and  60  is L-shaped with planar mounting portions  62  and  63  and planar retaining portions  64  and  65 . The mounting portions  62  and  63  flatly abut, and are welded to, the interior surface of the side wall  34 . The retaining portions  64  and  65  of the brackets extend perpendicularly from their respective mounting portions  62  and  63  into the main housing  12 , with the retaining portion  64  of the upstream bracket  58  facing the retaining portion  65  of the downstream bracket  60 . The brackets  58  and  60  are spaced apart from one another to form an elongated retaining channel  66  therebetween. The width of the channel  66  is slightly greater than the thickness of the border element  50  of the filter  16 , thus allowing the filter  16  to slidably engage the channel  66 . The channel  66  extends from the entry wall  36  at a preferred angle of 45 degrees relative to the floor  28  (thus 90 degrees to the entry wall  36 ), although any angle in the range of about 30 degrees to about 60 degrees is contemplated. Thus, when the removable filter  16  is in an operative position within the main housing  12 , a lateral edge of the border element  50  seats within the retaining channel  66  and the bottom edge of the border element  50  seats against the entry wall  36 . 
     The upstream bracket  58  extends from the entry wall  36  to a point adjacent the top edge of the side wall  34 . The downstream bracket  60  extends from a point that is preferably spaced ½ inch from the entry wall  36  to a point adjacent the top edge of the side wall  34 , thus leaving a gap  68  between the bottom of the downstream bracket  60  and the entry wall  36 . A series of semi-circular notches  70  are formed in the retaining portion  64  of the downstream bracket  60 . The gap  68  and the notches  70  prevent the accumulation of pellets in the retaining channel  66  when the filter  16  is not present, and also allow pellets to exit the channel  66  when the filter  16  is inserted. For example, when the filter  16  is removed for cleaning, plastic pellets are allowed to accumulate in the housing  12 . As the pellets pile vertically over the guide  18 , the channel  66  may become filled with pellets. When the operator pushes the filter  16  back into channel  66 , the gap  68  and the notches  70  provide outlets for the pellets in the channel  66  to escape, thus allowing the filter  16  to be inserted with minimal resistance. 
     Although it is preferred that the filter guides  18  and  20  be formed of brackets like those described above, it is contemplated that any suitable retaining means can be used to slidably hold the filter  16  in place. For example, the brackets  58  and  60  may be replaced by a series of flat, rectangular tabs  72  (as shown in  FIG. 6 ). Alternatively, the brackets  58  and  60  may be replaced by a series of round pins  74  (as shown in  FIG. 7 ). It is further contemplated that the upstream portion of each filter guide may be structurally different than the downstream portion of the guide. For example, an embodiment of the invention is contemplated wherein the upstream portion of each filter guide is formed of a bracket similar to the upstream bracket  58  shown in  FIG. 5 , and wherein the downstream portion of each guide is formed of a series of round pins like those shown in  FIG. 7 . Regardless of the type, or types, of filter guides that are incorporated in a particular embodiment, it is preferred that the downstream portion of each guide have a means for allowing accumulated plastic pellets to escape the retaining channel, such as the gap  68  and notches  70  shown in  FIG. 5 , the spaces between the tabs  72  shown in  FIG. 6 , or the spaces between the pins  74  shown in  FIG. 7 . 
     Referring now to  FIGS. 1-4 , the filter cover assembly  22  is defined by a cover plate  76  that is pivotably mounted to a mounting plate  78  by a hinge  80 . The mounting plate  78  is a planar, rectangular body that is rigidly mounted to the top of the main housing  12 . The front edge of the plate  78  abuts the rear edge of the mounting flange  14  and the lateral edges of the plate  78  are welded to the top edges of the side walls  32  and  34 . The rear edge of the mounting plate  78 , along with the top edges of the side walls  32  and  34  and the top edge of the rear wall  30 , define a filter access port  82  in the top of the main housing  12 . The tops of the filter guides  18  and  20  are located directly below the access port  82  (see  FIG. 4 ), thus allowing the removable filter  16  to be conveniently inserted into, and withdrawn from, the guides  18  and  20  through the port  82 . 
     The cover plate  76  is a substantially planar, rectangular body having downwardly-bent lateral edges for fitting over, and completely covering, the filter access port  82 . The hinge  80  is welded to the top surface of the cover plate  76  and is fastened to the mounting plate  78  by a series of removable fasteners  84 . The removable fasteners  84  are preferably conventional nut and bolt combinations, although it is contemplated that any other means of mounting the hinge  80  to the mounting plate  78 , such as by welding or with adhesives, may alternatively be used. The cover plate  76  may thus be rotated about the axis of the hinge  80  between a closed position (as shown in  FIG. 3 ) and an open position (as shown in  FIG. 4 ). When the filter  16  is not being accessed, the cover plate  76  should be kept in the closed position for preventing external elements, such as water and debris, from entering the main housing  12 . Conventional draw-latches  86  and  88  are preferably mounted adjacent the top edges of the side walls  32  and  34  for releasably engaging locking apertures  90  and  92  that are formed in the downwardly-bent portions of the cover plate  76 , thereby allowing the cover plate  76  to be locked in the closed position. 
     Although it is preferred that the cover plate  76  be pivotably mounted relative to the main housing  12 , it is contemplated that the hinge  80  and the mounting plate  78  may be omitted, and that the cover plate  76  may be completely removable from the main housing  12 . It is further contemplated that the entire filter cover assembly  22  may be omitted, and that the filter access port  82  can be left open. 
     Referring now to  FIGS. 3 ,  4 , and  8 , two circular feed-line ports  94  and  96  are formed in the bottom of the rear wall  30 . Vacuum feed-lines  98  and  100  engage the ports  94  and  96  in a conventional manner for drawing filtered plastic pellets out of the main housing  12 . Feed-line clamps  24  and  26  are provided for holding the feed-lines  98  and  100  in secure engagement with the ports  94  and  96 . 
     Each of the feed-line clamps  24  and  26  has a U-shaped retaining bracket  106  and  108  and a cooperative U-shaped retaining collar  110  and  112  having threaded ends. The retaining brackets  106  and  108  are welded to the exterior surface of the rear wall  30  adjacent the feed-line ports  94  and  96 . Each of the brackets  106  and  108  has a pair of apertures  114  and  116  formed in its bottom surface for receiving the threaded ends of its cooperating retaining collar  110  and  112 , and each threaded end is secured on the bottom side of the bracket by a nut  118 ,  120 ,  122 , and  124 . As the nuts  118 - 124  are tightened, the clamps  24  and  26  tighten around their respective feed-lines  98  and  100 , thus preventing the lines  98  and  100  from becoming disengaged from the ports  94  and  96 . Although the feed-line clamps  24  and  26  are the preferred means for securing the vacuum feed lines  98  and  100 , all other means for securing the lines, such as by conventional, tubular feed-line sleeves, are contemplated. 
     Although the filtering flow box  10  is shown as having two feed-line ports  94  and  96  and two feed-line clamps  24  and  26 , it is contemplated that the box  10  may have as many or as few ports and clamps as are necessary to accommodate the number of feed-lines present in a particular instance. It is further contemplated that the feed-line ports  94  and  96  and clamps  24  and  26  can alternatively be located on either of the side walls  32  and  34  or on the floor  28 . 
     During typical operation, the filtering flow box  10  is mounted to a bottom-unloading tower silo with the entry wall  36  positioned directly below the outlet port of the silo and with the filter access port  82  positioned laterally adjacent the outlet port. As plastic pellets and angel hair fall from the outlet port through the inlet port  46  and onto the entry wall  36 , they roll and slide down the wall  36  toward the removable filter  16 . Initially, the pellets and angel hair engage the bottom portion of the filter  16 . After the bottom portion of the filter  16  becomes clogged, the incoming pellets and angel hair will accumulate against the clogged area and will begin to pile vertically. As the pellets and hair pile up, they engage more elevated areas of the filter  16 . As those elevated areas of the filter  16  become clogged, the pellets will pile still higher, thus clogging the filter  16  from bottom to top. 
     After the filter  16  is substantially clogged and the throughput of pellets becomes sufficiently diminished, an operator unlocks the draw latches  86  and  88  and pivots the cover plate  76  to the open position. The operator then grasps the lip  54  of the filter  16  and withdraws the filter  16  from the guides  18  and  20 . As the filter  16  slides out of the box at an angle, the pellets that had accumulated on the filter&#39;s clogged surface will roll and slide by gravity off the filter, thus remaining in the housing  12 . After the accumulated angel hair has been removed from the upstream surface of the filter  16 , the operator reinserts the edges of the filter  16  into the guides  18  and  20  and slides the filter  16  back into the housing  12 . The operator then pivots the cover plate  76  back to the closed position and secures the draw latches  86  and  88 . 
     Many components of the filtering flow box  10  have been described above as having a particular size and/or shape. It is contemplated, however, that these components can have any other size or shape, as long as the same general spatial relationships and fitment constraints as those described above are adhered to. For example, the side walls  32  and  34  can alternatively extend away from one another as they extend upwardly from the floor, thereby requiring the entry wall  36 , the filter  16 , and the rear wall  30  to be trapezoidal in shape. In another example, the filter apertures  56  can be made larger or smaller for accommodating different sizes of plastic pellets. Still further, and more broadly, the dimensions of some or all of the filtering flow box  10  components may be varied to accommodate larger or smaller silos, or to accommodate greater or lesser amounts of material throughput. 
     This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.