Abstract:
A waste water filter screen assembly that has a substantially open foot section to promote more efficient flow through. The rotating grid is generally free hanging. The present invention further provides a drive assembly with square, high friction drive drums mounted on the drive shaft. The present invention further provides idler roller assemblies mounted for guiding the rotating grid adjacent the filter screen assembly head. The open foot section, drive assembly and idler roller assembly are useable with filter grids of both the link element type and the panel type.

Description:
BACKGROUND  
         [0001]    Difficulties are encountered in practice in the treatment of contaminated water flows such as sewage prior to fine filtration, due to the presence of heavy and generally untreatable objects such as rags, string, plastic bags, and the like. Wastewater treatment plants typically utilize some type of screening equipment to remove harmful debris contained in the waste stream flow. Screening equipment is often utilized in the headworks section of the plant, and is the first area to come in contact with the waste stream. The screens are typically made from corrosion resistant materials such as 304 or 316 stainless steel, plastics or other synthetic materials. In order to protect the downstream equipment and processes, screening equipment is designed and incorporated in a plant to remove a large majority of debris before it comes into contact with any downstream equipment. If such items are not removed, proper and adequate treatment of the liquid does not result, and blockage of ducts and channels may occur.  
           [0002]    There are many different screening equipment designs. A screening device is known comprising a continuously movable endless conveyor loop formed of a series of interconnected link pieces each having a lifting hook on which material to be screened is collected during movement through the contaminated water flow. Fine screens of this nature are typically defined by the size of the screen openings, which can be from as small as a quarter inch to one-half inch. These units can also be sized to have clear openings as large as 2 inches or more, but typically are not. The screen openings are designed to address both the horizontal and vertical limiting dimensions. The horizontal dimension is the small dimension and definition of the continuous belt, for example, one-quarter inch. The vertical dimension is typically significantly larger (approx. 4 in. or 6 in.) and is tied to the length of individual elements and the interconnected driving links and support shafts or pivot rods.  
           [0003]    Another type of screening device is a panel type filter screen assembly. The panel type filter screen units generally include a plurality of filter panels and an endless chain operationally connected to the filter panels to move the filter panels through the water or wastewater while following a guided path in the structural frame of the filter screen. Typical panel type filter screen units utilize a plurality of filter panels that are fabricated of metal such as steel or stainless steel or other non-corrosive material. Such a panel typically consists of a large number of metal bars  2  spaced from and generally parallel to one another and welded vertically to a metal panel frame  4 . The filter panel assemblies are operationally attached to the drive system, such as to an endless chain, and movement of the chain in turn moves the filter panel assemblies along a guided path within the structural frame of the screen filter apparatus  10 .  
           [0004]    An illustrative screen filter apparatus  10  is shown in FIGS.  1 - 3 . Referring first to FIG. 1, it will there be seen that a waste material filtering apparatus  10  of the prior art generally includes a frame  11 , a plurality of pipe spreaders  13 , a drive motor  15  connected to a drive sprocket assembly  22  by a drive belt or chain  23 , shown in phantom lines, and a rotating screen assembly  17  driven by the sprocket assembly. Referring to FIG. 2, the apparatus  10  sits in a channel  21  within which flows a stream of water containing solid waste.  
           [0005]    The rotating grid assembly  17  is a link type grid that includes a plurality of vertically disposed, laterally spaced apart link members  12  that are disposed in articulated relation to one another. The trailing end of each link  12  has an integral horizontally-extending part  16  that helps hold and lift solid matter from the stream as the screen segments travel upwardly on the upstream side of the machine. Means are provided at the discharge end of the apparatus for dumping the matter so lifted into a solid waste collection container.  
           [0006]    The opposite ends of each link  12  is mounted on a shaft  31 ,  33 . The trailing end of each link  12  is the aforementioned horizontally-extending member  16  that helps hold and lift solid matter from the water stream as the links rotate, as is perhaps best understood by observing the links at the lower left corner of FIG. 1. The uppermost or leading end of each link is denoted  18 . Plural directional arrows, collectively denoted  19 , show the path of travel followed by the links as the machine operates. The orientation of machine  10  in a channel of water is shown in FIG. 2. The concrete channel is denoted  21 . In this particular example, there are about twenty five upstanding screen segments disposed in equidistantly spaced lateral relation to one another, each screen segment being formed by a group of articulated link members  12 .  
           [0007]    The conventional assembly pattern of links is best understood in connection with FIG. 3. The links  12  of the prior art rotating screen are typically assembled in the following pattern. The trailing and leading ends  16 ,  18 , respectively, of a link  12   a  are slipped onto a pair of contiguous shafts  31 ,  33 , with the same procedure repeated about the remaining alternating shafts  31 ,  33  of the screen assembly  17 . The trailing end of the next link  12   b  is then slid onto shaft  31  and the leading end of that link is slid onto shaft  33 . The alternating pattern is then followed as links are placed on all of the shafts  31 ,  33 . Spacers  20  are then added to each shaft, and the same pattern of assembly is repeated to construct a screen assembly  17  of a desired width. The alternating nature of the links  12   a ,  12   b  connects the links into a continuous loop.  
           [0008]    The rotating grid assembly  17  is generally a large structure that is directly driven by the sprocket drive assembly  22  and is under significant tension. The sprocket assembly  22  generally includes a plurality of laterally spaced apart motor-driven sprocket segments. The sprocket segments are positioned in offset relation to the individual links  12  so that as the links  12  pass there over, the sprocket segments enter into the spaces between the links  12 . Such a sprocket drive assembly  22  is subject to jamming because the apparatus performs well only when the sprocket segments are perfectly or almost perfectly aligned with respect to each contiguous set of links. In order to establish such perfect alignment, the spacers between the sprockets must be manufactured to very tight tolerances. However, a single drive shaft may include from 10 to 150 or more spacers. Any inaccuracy in the individual spacer tolerances is accumulated across the shaft to create a total inaccuracy that is often unacceptable. Even when the sprocket segments and links  12  are in their respective ideal relative positions, the sprocket segments rub against their contiguous links  12  in alternating succession, displacing each link about one-sixteenth of an inch per rub. More particularly, the links are displaced in a first direction in a first rub, and are displaced in an opposite direction during a second rub. Due to the rubbing and alternating displacement of the links, the sprocket segments and links  12  eventually become misaligned and collide with one another. This bends the links  12 , damages the sprocket segments, and prevents further rotation of the rotating screens until the apparatus has been disassembled and new links  12  and sprocket segments installed. The repair procedure typically requires the grid assembly to be dismantled to expose the drive shaft and sprockets for repair or the entire assembly must be removed and returned to a shop for repair.  
           [0009]    To define the path of the screen assembly  17 , the prior art system includes sliding wear bars  40  to define the path of the screen loop adjacent the top of the filter assembly  10  and inner and outer guide rails  42 ,  44  and a bottom guide  46  are provided adjacent the bottom of the assembly  10  to track the screen assembly  17 . The wear bars  40  are subject to significant wear from the continuous travel of the links  12  there over. The internal positioning of the wear bars  40  make them difficult to maintain and replace. Additionally, the wear bars  40  cause wear and additional frictional load on the screen assembly  17 . The guide rails  42 ,  44  and bottom guide  46  are also subject to wear. Additionally, since these components  42 - 46  are in the fluid stream, they act as a point of debris build-up. The built up debris negatively effects flow throughput. Additionally, grit, sand and the like trapped between the guides  42 ,  44  and  46  and the screen assembly  17  acts to accelerate wear on the screen assembly  17 . The limited accessibility makes component replacement and debris flushing difficult.  
         SUMMARY  
         [0010]    The present invention provides a waste water filter assembly that has a substantially open foot section to promote efficient flow through. The filter screen is generally free hanging with spaced apart guide rails and a wear bar defining the filter path extents, but not confining the filter screen grid. The present invention further provides a drive assembly with square, high friction drive drums mounted on a drive shaft. Each side of the drum is provided with a high friction material, for example, high friction brake pad lining. The present invention further provides idler roller assemblies mounted for guiding the filter screen adjacent the filter assembly head. Each roller preferably includes replaceable split roller wheels with non-lubricated bushings that align with and contact respective guide link sections on the screen loop. Each roller is preferably free-wheeling and independent of the other roller wheels of the assembly. The rollers are preferably sized slightly larger toward the outer edges of the screen to maintain proper tracking of the screen loop. The open foot assembly, drive assembly and idler roller assembly are useable with filter grids of both the link element type and the panel type. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a side elevational view of a prior art waste material filter assembly;  
         [0012]    [0012]FIG. 2 is a front elevational view of the filter assembly of FIG. 1 disposed in a channel for carrying waste water;  
         [0013]    [0013]FIG. 3 is an exploded perspective view showing the assembly of the prior art filter assembly;  
         [0014]    [0014]FIG. 4 is a side elevational view of a waste water filter assembly in accordance with the present invention with the filter screen cleaning grid omitted;  
         [0015]    [0015]FIGS. 5 and 6 are partial elevational views of the filter assembly in accordance with the present invention with the filter screen properly tensioned (FIG. 5) and in need of tensioning (FIG. 6);  
         [0016]    [0016]FIG. 7 is a sectional view taken along the line  7 - 7  in FIG. 4;  
         [0017]    [0017]FIG. 8 is a front elevational view taken along the line  8 - 8  in FIG. 4 with one of the side plates removed;  
         [0018]    [0018]FIG. 9 is a sectional view taken along the line  9 - 9  in FIG. 4;  
         [0019]    [0019]FIG. 10 is a sectional view taken along the line  10 - 10  in FIG. 9;  
         [0020]    [0020]FIG. 11 is a sectional view taken along the line  11 - 11  in FIG. 10;  
         [0021]    [0021]FIG. 12 is a partial schematic illustration of the preferred head section of the filter assembly in accordance with the present invention;  
         [0022]    [0022]FIG. 13 is a sectional view taken along the line  13 - 13  in FIG. 12;  
         [0023]    [0023]FIG. 14 is a side elevational view of the preferred drive shaft;  
         [0024]    [0024]FIG. 15 is a front elevational view taken along the line  15 - 15  in FIG. 13;  
         [0025]    [0025]FIG. 16 is a schematic illustration of the filter screen rotating grid positioned about the preferred drive drum assembly of the present invention;  
         [0026]    [0026]FIG. 17 is a side elevational view, with half of the assembly in section, of a preferred idler roller assembly of the present invention;  
         [0027]    [0027]FIG. 18 is a front elevational view of a preferred idler roller assembly of the present invention;  
         [0028]    [0028]FIG. 19 is a side elevational view of a preferred idler roller of the present invention;  
         [0029]    [0029]FIG. 20 is a front elevational view of the idler roller wheel of FIG. 19. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The present invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and “rearward”, is used in the following description for relative descriptive clarity only and is not intended to be limiting.  
         [0031]    The preferred waste water filter screen assembly  100  of the present invention is shown in FIGS.  4 - 18 . Referring to FIGS. 4 and 5, the filter screen assembly  100  generally includes a frame assembly  110  in which a fine filter rotating grid  130  (see FIG. 5) travels. The rotating grid  130  may be a link type grid or a panel type grid. The rotating grid  130  is driven by a drive assembly  190  adjacent the filter screen assembly head  180 . Idler roller assemblies  220  are provided to guide the rotating grid  130  through the filter screen assembly head  180 . Water travels in the direction of the arrow A in FIG. 4 and passes through the rotating grid  130  in the foot section  140  of the filter screen assembly  100 .  
         [0032]    The preferred embodiment of the foot section  140  is shown in FIGS.  4 - 11 . The foot section  140  includes an open area  142  through which the water travels. The open area  142  is defined by thin side walls  144  and  146  and a bottom plate  148 . Removable side plates  150  and seal members  152  seal the side walls  144  and  146  to the water channel. However, removal of the side plates  150  and seal members  152  allows easy access to the internal components. The rotating grid  130  travels between spaced apart inner and outer guide members. In the preferred embodiment, the guide members are defined by outer guide rails  160  and an inner semi-circular wear bar  166 . The guide rails  160  defining the outer extent of the grid  130  travel path and the inner wear bar  166  defining the inner extent of the grid  130  travel path.  
         [0033]    The rotating grid  130  does not ride on the guide rails  160  and the inner wear bar  166 . Instead, the guide rails  160  and wear bar  166  only define the extents of the rotating grid path, with the rotating grid  130  preferably hanging substantially freely between the guide rails  160  and bar  166  as shown in FIG. 5. The rotating grid  130  has a thickness T and the guide rails  160  and bar  166  are spaced a distance D that is substantially greater than the thickness T. The distance D is preferably approximately twice the thickness T. As such, in operation the grid  130  is generally not in contact with the guide rails  160 , as shown in FIG. 5. In the event the rotating grid  130  sags, stretches or is otherwise misaligned, see FIG. 6, the grid  130  is be supported by the guide rails  160  until the grid  130  is repositioned to the desired operating position. The filter screen assembly  100  preferably includes an adjustment mechanism  154  that allows the grid  130  to be lifted to the desired operating position. As can be seen from the figures, the foot section  140  is free of side guide rails that define a specific travel track for the rotating grid  130 .  
         [0034]    Referring to FIGS.  9 - 11 , the guide rails  160  are preferably positioned at spaced apart locations that are to align with guide portions of the rotating grid  130 . Each guide rail  160  includes an arcuate planar surface  162  supported on a support member  164  extending between the bottom plate  148  and a rear support bar  165 . The planar surfaces  162  are preferably manufactured from stainless steel and are removable to allow easy maintenance and replacement. Water and grit are free to pass through the open area  142  and do not get caught between the grid  130  and the guide rails  160 . The relatively small cross-sectional area and the spacing of the guide rails  160  allows grit and smaller debris to easily travel past the rails  160  without any build-up. An adjustable dual influent brush  168  is positioned along the bottom plate  148  to prevent larger debris from passing past the grid  130 . Larger debris contacts the brush  168  and is directed upward where it is picked up and removed by the grid  130 . The brush  168  is right within the open area  142  so it is easily accessible, cleanable and replaceable.  
         [0035]    The preferred drive shaft assembly  190  of the present invention is shown in FIGS.  12 - 16 . The drive shaft assembly  190  includes a drive shaft  192  driven by a motor (not shown) or the like. The shaft  192  is mounted in an external bearing assembly  194  that allows for easy removal of the drive shaft  192 . As seen in FIG. 14, the shaft  192  preferably has end key slots  193  for engaging the shaft  192  with the bearing assembly  194  and a center key slot  195 . A plurality of drive drums  196  are mounted on the shaft  192 . Each drum  196  has a square frame  198  mounted on the drive shaft  192 , via set screws  197  received in the center key slot  195 , for rotation therewith. Each side of the frame  198  is provided with a high friction material pad  200 , for example, high friction brake pad lining. The drums pads  200  preferably have a contact length approximately equal to the distance between adjacent screen guide links (not shown) such that the high friction pad  200  contacts almost all of the filter elements  12  in that grid section. The weight of the rotating grid  130  allows the friction between the drum pads  200  and the filter elements  12  to drive the rotating grid  130 . Any misalignment between the filter elements  12  is absorbed by the friction pads  200  such that proper grid  130  driving is maintained even if the filter elements  12  are misaligned.  
         [0036]    Referring to FIGS. 12 and 17, a preferred embodiment of the idler roller assembly  220  is shown. The idler roller assembly  220  comprises a shaft  222  mounted between a pair of roller support members  240 . The illustrated shaft  222  has a center roller  228  and a pair of end rollers  230 . Each roller wheel  228 ,  230  aligns with and contacts a respective guide link (not shown) on the rotating grid  130 . The number, and positioning of the rollers  228 ,  230  can be adjusted to meet the requirements of a given filter screen assembly  100 . Each roller  228 ,  230  is a solid cylinder with a center hole for positioning on the shaft  222 . The rollers  228 ,  230  may be press fit, keyed, welded or otherwise secured to the shaft  222 . The rollers  228 ,  230  are preferably sized such that the outer rollers  230  are slightly larger to maintain proper tracking of the rotating grid  130 , but may have various configurations.  
         [0037]    The shaft  222  is a hollow tube with a smooth surface roll sleeve  230  press fit in each end thereof. Set holes  224  extend through the shaft  222  and sleeves  226  at each end of the shaft  222 . The roll sleeves  226  are configured to receive and rotate with a support shaft  242  extending from each support member  240 . Each support shaft  242  has set bores  243  configured to align with the set holes  224  such that set screws (not shown) journal the shaft  222  to the support shafts  242 . Each support shaft  242  extends through a hole  147  in a respective side wall  144 ,  146  of the filter screen assembly  100 . The support shaft  242  is received in a bushing  246  that allows smooth rotation of the support shaft  242 . The bushing  246  is preferably manufactured from a synthetic material, for example, Acetron GP. The bushing  246  is supported in a sleeve  248  secured between a mounting plate  244  and an end cap  250 . The shaft  222  can easily be removed for maintenance or replacement by simply releasing the set screws and removing the support assemblies  240  which are external and easily removed.  
         [0038]    An alternate embodiment of the idler roller assembly  220 ′ is shown in FIGS.  18 - 20 . The roller assembly  220 ′ includes a shaft  322  mounted in external roller bearings  324  that allow rotating of the shaft  322  if necessary and for easy removal of the idler roller assembly  220 ′. A plurality of roller supports  326  are mounted on the shaft  322  for support of roller wheels  328 . Each roller wheel  328  preferably includes a replaceable split steel roller wheel  334  with an internal non-metallic bushing  336 . Each roller wheel  328  aligns with and contacts a respective guide link (not shown) on the rotating grid  130 . The roller wheels  328  are preferably secured between opposed plates  330 ,  332  to create a confined path for the roller wheel  328  and to add rigidity. The roller wheels  328  are preferably sized such that the outer roller wheels  328 ′ are slightly larger to maintain proper tracking of the rotating grid  130 . The idler nature of the independent roller wheels  328  of the roller assembly  220  significantly reduces the frictional load on the rotating grid  130  and allows each guide link grid path to act independently of one another regardless of accumulated tolerances throughout the grid.