Abstract:
A screen panel assembly is used with a screening machine. The screen panel assembly includes first and second generally planar screen panels and a coupling between the first and second screen panels that includes a compression clip jaw to temporarily secure the screen panels together. An overlap region between the first and second screen panels permits lifting of the second screen panel by a lifting force exerted upon the first screen panel while inhibiting the passage of material being screened between the two adjacent screen panels.

Description:
[0001]    This is a continuation in part of U.S. patent application Ser. No. 12/883,422, filed Sep. 16, 2010, which is in turn a continuation in part of U.S. patent application Ser. No. 12/261,117, filed Oct. 30, 2008. The application Ser. Nos. 12/883,422 and 12/261,117 applications are hereby incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to screening machines or separators of the type used to separate or classify mixtures of solid particles of different sizes. 
         [0003]    In screening machines or separators of the type described, a screen (which may be woven, an aperture plate or another design) is mounted and pre-tensioned in what is often called a “screen pane” or “screen deck” that includes a supporting peripheral frame around the perimeter of the screen. The terms “screening machine” and “separator” and respective derivatives thereof are herein used interchangeably. A main housing of the screening machine supports one more of the screen panels, as well as agitating structures that shake or vibrate the solids deposited on the screen panels. 
         [0004]    The screen panels are often removed from the screening machines for cleaning, replacement, readjustment or installation of a screen of a different mesh size or the like. In large commercial screening machines, the screen panels are inserted through and removed from a longitudinal end of the machine. In accordance with this movement of the screen panels, sufficient space must be devoted near the end of the machine, such that the generally horizontal screen panels may be inserted into and removed from the housing of the screening machine. Moreover, screen panels in large commercial screening machines tend to be relatively large, making their insertion and removal difficult or awkward at best, especially for a sole operator in tight working conditions. 
         [0005]    Many machines of this type are used to separate particulate material which, over time, often clogs or blocks the screen mesh. Commonly, an agitating mechanism is included in the machine to unblock the mesh by dislodging the clogging material. Often, the agitating mechanism is a number of balls captured by a ball tray and accessible to the screen mesh. In large commercial screening machines, the agitating structures may be also inserted and removed respectively through the end of the machine, as described above with respect to the screen panels, thereby presenting similar space requirements. Moreover, known agitating structures tend to be large and relatively heavy, making their insertion into and removal from the housing of the screening machine a particularly difficult and work-intensive task for the operators involved. 
         [0006]    It is evident, therefore, that a screening machine and screening machine components are needed that address these and other known problems associated with conventional screening machines. 
       SUMMARY OF THE INVENTION 
       [0007]    These and other shortcomings in the prior art have been addressed in various embodiments of this invention. In a first embodiment, a screen panel assembly is provided for use with a screening machine. The screen panel assembly includes first and second generally planar screen panels and a coupling between the screen panels. The coupling includes a projection from the first screen panel received in a receiving jaw of the second screen panel. The coupling further includes a resilient biasing member carried by either the projection or the receiving jaw, the resilient biasing member being compressed between the projection and the receiving jaw. 
         [0008]    In another embodiment, a screen panel is provided that is configured to be coupled with a like screen panel as part of a screen panel assembly. The screen panel includes a frame, a pre-tensioned screen supported on the frame, a receiving jaw on a leading end of the frame, and a projection on a trailing end of the frame opposite the leading end. The receiving jaw is configured to receive the projection of a like screen panel. The screen panel further includes a resilient biasing member carried by either the projection or the receiving jaw, the resilient biasing member being configured to be compressed between the receiving jaw and the projection of the like screen panel. 
         [0009]    In yet another embodiment, a screening machine is provided. The screening machine includes a main housing and a screen panel assembly having first and second generally planar screen panels. The screen panel assembly further includes a coupling between the screen panels configured to permit movement of the first and second screen panels by a force exerted upon the first screen panel. The coupling includes a projection from the first screen panel and a receiving jaw on the second screen panel configured to receive the projection. The coupling further includes a resilient biasing member carried by either the projection or the receiving jaw. The resilient biasing member is compressed between the projection and the receiving jaw. The coupling further includes an overlap region between the first and second screen panels engageable to thereby permit lifting of the second screen panel by a lifting force exerted upon the first screen panel. 
         [0010]    In another embodiment, a method is provided for installing a screen panel assembly in a screening machine. The method includes positioning a first screen panel on an agitating structure of the screening machine so that a limiting tab on the first screen panel engages a flange on the agitating structure. The method further includes joining a second screen panel with the first screen panel to form the screen panel assembly. Engagement of the limiting tab on the first screen panel with the flange on the agitating structure prevents the first screen panel from moving when then the second screen panel is joined with the first screen panel. 
         [0011]    In embodiments having a screen panel assembly that is made up of two or more generally planar screen panels, insertion and removal of the screen panel assembly respectively into and out of the main housing of the screening machine is greatly facilitated. Similarly, in embodiments having an agitating structure that includes segmented co-planar trays, insertion and removal of the agitating structure in conjunction with the screen panels is likewise facilitated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a partially broken-away perspective view of a screen panel assembly being inserted into a screening machine in accordance with one embodiment of this invention; 
           [0014]      FIG. 2  is a partially broken-away perspective view of a pair of screen panels according to one embodiment of this invention; 
           [0015]      FIG. 3  is an enlarged partially broken-away cross-sectional view of the screen panels of  FIG. 2  taken along line  3 - 3  of  FIG. 2 ; 
           [0016]      FIG. 4  is an enlarged partially broken-away cross-sectional view of the screen panels of  FIG. 2  taken along line  4 - 4  of  FIG. 2 ; 
           [0017]      FIG. 5  is an enlarged partially broken-away and disassembled perspective view of the screen panels of  FIG. 2  taken along line  5 - 5  of  FIG. 2 ; 
           [0018]      FIG. 6  is an enlarged partially broken-away and assembled perspective view of the screen panels of  FIG. 2  taken along line  5 - 5  of  FIG. 2 ; 
           [0019]      FIG. 7  is an enlarged partially broken-away perspective view of the latching mechanism joining adjacent screen panels of one embodiment of this invention; 
           [0020]      FIG. 8  is a partially broken-away bottom perspective view of a pair of screen panels according to another embodiment of the invention; 
           [0021]      FIGS. 9A and 9B  are enlarged partially broken-away cross-sectional views of the interaction between the ledge, jaw, and compression clip of the screen panels of  FIG. 8 ; 
           [0022]      FIG. 10A  is a partially broken-away perspective view of a screen panel assembly being inserted into a screening machine in accordance with another embodiment of the invention; 
           [0023]      FIG. 10B  is a view like  FIG. 10A , and showing a trailing screen panel being brought into position relative to a leading screen panel; 
           [0024]      FIG. 10C  is an enlarged view showing the interaction between a limiting tab on the leading screen panel and a flange on a tray of an agitating structure; 
           [0025]      FIG. 10D  shows the leading and trailing screen panels being joined together; 
           [0026]      FIG. 10E  is an enlarged view and shows the screen panel assembly, including the joined leading and trailing screen panels, being lifted so the limiting tab on the leading screen panel clears the flange on the tray; 
           [0027]      FIG. 10F  shows a third screen panel being brought into position relative to the trailing screen panel; 
           [0028]      FIG. 10G  shows the third screen panel joined with the trailing screen panel, and the screen panel assembly being lifted so the limiting tab on the trailing screen panel clears the flange on the tray; 
           [0029]      FIG. 10H  shows the screen panel assembly aligned with and secured with the tray of the agitating structure; 
           [0030]      FIG. 10I  is taken along line  10 I- 10 I in  FIG. 10H , and shows a tongue extending from the flange on the tray of the agitating structure received in a lug spacing formed by the lug on the third screen panel; and 
           [0031]      FIG. 10J  shows the screen panel assembly and agitating structure installed in the screening machine. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    With reference to the figures, and more particularly to  FIG. 1 , a screening machine or separator  10  includes a main housing  12  having an access opening  14  located at a longitudinal end of the housing  12  for inserting and removing screening components such as a screen panel assembly  16  and an agitating structure  18  cooperating with the screen panel assembly  16  to segregate solids or other material (not shown) deposited on the screen panel assembly  16 . 
         [0033]    With reference to  FIGS. 1-2 , the screen panel assembly  16  of this exemplary embodiment is in the form of a segmented assembly that includes a first, leading screen panel  20  and a second, trailing screen panel  22  that are substantially identical to and interchangeable with one another. It is contemplated that the screen panel assembly  16  may instead have any number of screen panels other than two including, without limitation, a single screen panel, and still fall within the scope of this invention. Each of the screen panels  20 ,  22  includes a pre-tensioned screen  24  supported about the respective perimeters of the screens by a frame  26  and further includes a top face  28  and an opposite bottom face  30 . The screen panels  20 ,  22  each have spaced longitudinal leading and trailing ends  32 ,  34  and spaced lateral sides  36  and are engageable with one another along adjacent ends to define an overlap a region  38 . The screen panels  20 ,  22  are generally symmetric about a longitudinal center line. 
         [0034]    The screen mesh material is pre-tensioned and mounted between the screen frame according to one embodiment of the screen panel according to this invention and secured to the frame via a cured or baked on enamel around the perimeter of the screen surface of the screen panel. Alternatively, epoxies or other materials may be utilized to secure the pre-tensioned screen material to the frame. 
         [0035]    The overlap region  38  includes a seal member  40  mounted to one of the screen panels and prevents or at least minimizes the likelihood of material deposited on the screen panels  20 ,  22  from falling onto the underlying agitating structure  18 . 
         [0036]    In this exemplary embodiment, the agitating structure  18  is in the form of a segmented tray assembly having multiple, generally coplanar trays  42  that are also engageable with one another through a tray coupling (not shown). Additional details of one embodiment of the agitating structure 16 are detailed in U.S. Published patent application No. 2010-0108579, which is incorporated herein by reference in its entirety. Each of the trays  42  in this exemplary embodiment is partitioned into several compartments  44  ( FIG. 1 ). Longitudinally extending lips  46  of each of the screen panels  20 ,  22  engage respective side walls  48  of the trays  42  and thereby determine a position of the screen panels  20 ,  22  relative to the trays  42  when these components are engaged with one another within the main housing  12  ( FIG. 1 ). Each of the longitudinal lips  46  extends only partially along the respective length of the associated screen panel  20 ,  22  to define a notch  50  between portions of the lips  46  and stopping elements in the form of first and second limiting tabs  52 ,  53 , which are situated on opposite sides of the notch  50  ( FIG. 10A ). 
         [0037]    Each tray  42  also includes a flange  54  projecting vertically adjacent the lips of the screen panels and a longitudinal, generally horizontal projection  56  ( FIG. 10A ). In the embodiment shown, the flange  54  extends substantially the entire width of the tray  42 . A generally horizontal tongue  55  extends from an upper region of the flange  54 . The tongue  55  optionally includes locating bores  57  configured to align with optional locating bores  59  on the panels  20 ,  22 , as will be described further below. 
         [0038]    Each of the individual trays  42  of the illustrated embodiment includes several compartments  44  that hold agitating elements that move and thereby vibrate the solids deposited on the screen panel assembly  16 . The agitating elements, although not shown, may for example and without limitation include balls made of metal, plastic or other suitable material and are held within the compartments  44 . The agitating elements are supported by a bottom support screen  45  and confined in the compartments  44  by partition walls  47  defining the compartments  44 . 
         [0039]    It is contemplated, however, that an alternative agitating structure may have other shapes and/or include any number of trays other than the two trays of this exemplary embodiment. Such alternatives include, without limitation, an agitating structure having a single tray rather than a segmented tray assembly. 
         [0040]    Referring to  FIGS. 1 and 2 , exemplary screen panels  20 ,  22  according to one embodiment of this invention are shown. Each screen panel  20 ,  22  is substantially identical to each other. The frame  26  of each screen panel includes the downwardly turned lip  46  extending longitudinally on each lateral side edge of the screen panel  20 ,  22 . The lip  46  includes the tabs  52 ,  53 . The tab  52  has a generally sloped leading edge  58  and a generally vertically oriented trailing edge  60  adjacent to the notch  50 . The tab  53  has a generally vertically oriented leading edge  61  adjacent to the notch  50  and opposite the trailing edge  60  of the tab  52  ( FIG. 10A ). 
         [0041]    The adjacent screen panels are joined together by a coupling  62  which in one embodiment includes one or more latching mechanisms  64 . One example of the latching mechanism  64  is shown particularly in  FIGS. 1 ,  2  and  7  is an over-center draw latch. One component of the latching mechanism  64  is a receiving hook  66  on the trailing end  34  of each screen panel  20 ,  22 . The receiving hook  66  projects from a base portion  68  and is mounted to the lip  46  via mechanical fasteners  70 , two of which are shown in  FIGS. 1 ,  2  and  7  as bolts, although other mounting mechanisms may be utilized. The base portion  68  is mounted via the bolts  70  to the lip  46  so that the hook  66  is juxtaposed to the adjacent, leading screen panel  20 . On the adjacent screen panel, a latch base  72  of the latching mechanism  64  is likewise mounted via a pair of mechanical fasteners  70  such as bolts to the downwardly turned lip  46 . A generally rectangular-shaped bail member  74  is pivotally coupled to a latch body  76  which is similarly pivotally coupled to the latch base  72  as is well known according to standard over-center draw latch design. Two latching mechanisms  64  are provided for each pair of adjacent screen panels  20 ,  22 , one on each opposite lateral side edge according to one embodiment of this invention. The latching mechanisms  64  draw the confronting adjacent longitudinal ends  32 ,  34  of the screen panels  20 ,  22  together. 
         [0042]    As shown in  FIGS. 1-7 , the leading longitudinal end  32  of each screen panel  20 ,  22  includes a contoured edge  78  with a generally linear central portion  80  bounded on each end by shoulder portions  82 . The contoured leading edge  78  of each screen panel  20 ,  22  is shaped and configured to mate with a contoured trailing edge  84  of each screen panel which includes a generally linear central portion  86  bounded on each end by jog portions  88 . Each jog  88  is configured to mate with the adjacent shoulder  82  of the adjacent screen panel. The leading and trailing contoured edges  78 ,  84  of the screen panels  20 ,  22  are positioned proximate the top face  28  of each screen panel. However, while the contoured leading edge  78  of each screen panel  20 ,  22  is at a distal end of the respective screen panel, the contoured trailing edge  84  of each screen panel is recessed relative to the distal edge of the screen panel such that a ledge  90  projects rearwardly beyond the trailing edge  84  at a recessed level relative to the top face  28  along a substantial portion of the trailing end  34  of the screen panel  20 ,  22 . 
         [0043]    The frame  26  of each screen panel  20 ,  22  along the leading end  32  thereof includes a hem  92  offset or recessed from the distal edge of the screen panel. The hem  92  includes a jaw  94  which presents an opening facing the leading end  32  of the screen panel  20 ,  22 . The jaw  94  is sized and configured to receive therein the ledge  90  along the trailing end  32  of the leading screen panel  20  so as to provide one aspect of the coupling  62  between the adjacent screen panels  20 ,  22 . The ledge  90  of the leading screen panel  20  mating with the hem  92  and jaw  94  of the trailing screen panel  22  provides an overlap portion  96  between the adjacent screen panels  20 ,  22  as shown particularly in  FIG. 4 . The cross-sectional view of  FIG. 4  shows the ledge  90  of the leading screen panel  20  seated within the jaw  94  of the trailing screen panel  22 . The seal member  40  is mounted along the contoured edge  84  of the trailing end  34  of the leading screen panel  20  atop the ledge  90 . When the adjacent screen panels  20 ,  22  are joined together, the seal member  40  is compressed between the contoured edges  78 ,  84  as shown in  FIGS. 3 and 4 . 
         [0044]    Another aspect of the coupling  62  between the adjacent screen panels  20 ,  22  according to various embodiments of this invention are lugs  98  which extend from the ledge  90  along the trailing end  34  of the screen panel  20 . Two such lugs  98  are shown in the drawings. In particular, in  FIGS. 5 and 6 , one of the lugs  98  is shown as a folded under extension from the ledge  90 , and includes a lug arm  97  that is spaced from and extends under the ledge  90 , thereby forming a lug spacing  99  between the lug arm  97  and the ledge  90 . Each lug  98  is seated within a seat  100  formed in a gap of the hem  92  of the leading edge  32  of the trailing screen panel  22 . The seats  100  are particularly shown in  FIGS. 1 and 2  and are spaced across the width of the screen panel. The lug  98  positioned within the seat  100  is likewise shown in cross-sectional view of  FIG. 3 . The combination of the lugs  98  and the seats  100  on the adjacent mating ends  32 ,  34  of the screen panels  20 ,  22  helps to center the screen panels in a lateral direction relative to one another as well as providing an additional mechanism for coupling the panels. 
         [0045]    Another aspect of the coupling  62  between the adjacent screen panels  20 ,  22  according to various embodiments of this invention is shown in  FIGS. 8 ,  9 A, and  9 B and includes a plurality of resilient biasing members for joining the panels  20 ,  22 . In the embodiment shown, for example, the resilient biasing members are in the form of four compression clips  102  are disposed along the interface of the panels  20 ,  22  between the lateral sides  36 . The compression clips  102  encourage a tight fit between the ledge  90  of the leading screen panel  20  and the hem  92  and jaw  94  of the trailing screen panel  22 . In particular, each compression clip  102  includes portions that are resiliently moveable with respect to one another, such as pivotally moveable. 
         [0046]    As shown in  FIGS. 9A and 9B , the hem  92  (which includes the jaw  94 ) extends through a curved transition region  104  and terminates at a terminal end  106 . The jaw  94  includes an upper jaw portion  108  and a lower jaw portion  110 . A jaw opening  112  is formed between the upper and lower jaw portions  108 , no, and as described above, the opening  112  faces the leading end  32  of the screen panel  22 . Advantageously, the upper and lower jaw portions  108 , no are generally parallel with each other and with the top face  28  of the panel  22 . Because  FIGS. 8 ,  9 A, and  9 B depict features from the bottom of the panels  20 ,  22 , the lower jaw portion  110  is oriented above the upper jaw portion  108 , but this merely reflects the presentation of the drawings. 
         [0047]    The upper jaw portion  108  includes an upper surface  114  that is generally co-planar with the top face  28  of the screen panel  22 . The upper jaw portion  108  also includes a lower surface  116  which is generally opposite the upper surface  114  and partially defines the jaw opening  112 . The upper and lower surfaces  114 ,  116  are generally parallel with each other. 
         [0048]    The lower jaw portion  110  includes an upper surface  118  which is generally opposed from the lower surface  116  of the upper jaw portion  108  and partially defines the jaw opening  112 . The lower jaw portion  110  further includes a lower surface  120  which is generally opposite the upper surface  118 . The upper and lower surfaces  118 ,  120  are generally parallel with each other. 
         [0049]    The ledge  90 , which is received in the jaw opening  112  when the screen panels  20 ,  22  are joined together, generally includes an upper ledge surface  122  and a lower ledge surface  124  and terminates at a terminal end  126  which is generally away from the trailing edge  84 . The upper and lower ledge surfaces  122 ,  124  are generally parallel with each other and with the top face  28  of the screen panel  20 . 
         [0050]    The compression clips  102  are compressed between the ledge  90  and the jaw  94  when the ledge is inserted into the jaw opening  112 . Each compression clip  102 , one of which is shown in  FIGS. 9A and 9B , has a generally U-shaped body that includes a first wing  128  and a second wing  130 . The wings  128 ,  130  are connected through a generally curved junction region  132 . The clip  102  is resiliently deformable and the wings  128 ,  130  tend to resist being deformed or deflected either toward or away from each other. 
         [0051]    In the embodiment shown, the clip  102  is carried by the lower jaw portion  110  and extends into the jaw opening  112 . In particular, the first wing  128  of the clip  102  is secured to the lower surface  120  of the lower jaw portion  110  and the junction region  132  is generally adjacent the terminal end  106  of the hem  92 . The second wing  130  of the clip  102  extends into the jaw opening  112  between the upper surface  118  of the lower jaw portion no and the lower surface  116  of the upper jaw portion  108 . As shown, the second wing  130  is generally adjacent the upper surface  118  of the lower jaw portion no near the terminal end  106 , and extends somewhat an angle from the terminal end  106  in the direction of the curved region  104  and the upper jaw portion  108 . As further shown, the first wing  128  is secured to the lower jaw portion no while the second wing  130  is free and generally unsecured in the jaw opening  112 . 
         [0052]    When the panels  20 ,  22  are joined, this aspect of the coupling  62  is made when the ledge  90  of the leading screen panel  20  is inserted into the jaw opening  112  of the trailing screen panel  22  and engages the clip  102 . In particular, as the ledge  90  is inserted into the jaw opening  112  toward the curved region  104  of the hem  92 , the terminal end  126  of the ledge  90  enters the jaw opening  112  and the ledge  90  contacts the second wing  130  of the clip  102 . Further insertion of the ledge  90  causes the second wing  130  to deflect generally toward the first wing  128  and the lower jaw portion  110 , as shown in  FIG. 9A . The clip  102  is thereby compressed between the ledge  90  and the jaw  94 . The clip  102  tends to resist this deflection and the second wing  130  resiliently biases the ledge  90  into contact with the jaw  94 . In particular, the clip  102  presses against the lower ledge surface  124  of the ledge  90 . This presses the upper ledge surface  122  of the ledge  90  against the lower surface  116  of the upper jaw portion  108 . The close engagement of the surfaces  116 ,  122  provides a further seal that inhibits material leakage through the connection of the ledge  90  and the jaw  94 . Thereby, the ledge  90  is held captive in the jaw  94  and the clip  102  encourages a tight fit between the ledge  90  and the jaw  94 . 
         [0053]    The ledge  90  can be removed from the hem  92  and the jaw  94  to break this aspect of the coupling  62 . When the ledge  90  is thus removed, as shown in  FIG. 9B , the clip  102  restores to its previous condition, with the second wing  130  being free and deflecting back toward the upper jaw portion  108 . Advantageously, by securing the first wing  128  of the clip  102  to the lower surface  120  of the lower jaw portion  110 , this point of securement is out of the way of the jaw  94  and is not disturbed when the ledge  90  is inserted into or removed from the jaw  94 . 
         [0054]    While the embodiment shown includes resilient biasing members in the form of generally U-shaped clips  102  that are carried by the lower jaw portion  110 , other shapes and configurations are also possible. For example, the resilient biasing member could be in the form of a generally planar leaf spring where one end is attached to the upper surface  118  of the lower jaw portion  110  and the other end is free and extends in the jaw opening  112  toward the upper jaw portion  108 . Further, the resilient biasing member could be carried by the upper jaw portion  108 . Further still, the resilient biasing member could be carried by the ledge  90  on either the upper ledge surface  122  or the lower ledge surface  124 . In addition, while the embodiment shown includes resilient biasing members as well as latching mechanisms  64  and lugs  98 /seats  100 , a screen panel assembly could be constructed having only resilient biasing members, and none of or any of latching mechanisms  64  and lugs  98 /seats  100 . 
         [0055]    With reference to  FIGS. 10A-10J , the functionality of the limiting tabs  52 ,  53  of the screen panels is described in further detail. In particular, the limiting tabs  52 ,  53  provide structure for interfacing with the agitating structure  18  to enhance joining multiple screen panels (such as screen panels  20 ,  22 ) into a screen panel assembly  16 . The limiting tabs  52 ,  53  also provide structure for interfacing with the agitating structure  18  to enhance disassembly a screen panel assembly  16  into separate screen panels. 
         [0056]      FIG. 10A  shows the screen panel  20  being moved into position relative to the tray  42  of the agitating structure  18 . The tray  42  is already partially received in the access opening  14  in the main housing  12  of the screening machine  10 . The leading screen panel  20  is positioned above the tray  42  so that the screen panel  20  can be lowered onto the side walls of the tray  42 , with the leading end  32  nearer the access opening than the trailing end  34 . The screen panel  20  may be moved toward the access opening  14 , with the lip  46  of the screen panel riding on the flange  54  of the tray  42 . Continued movement of the screen panel  20  toward the access opening  14  causes the sloped leading edge  58  to come into engagement with the flange  54 , thereby lifting the screen panel  20  relative to the tray  42  before the screen panel  20  drops when the flange  54  enters the notch  50  ( FIGS. 10B and 10C ). A small amount of further movement of the screen panel  20  toward the access opening  14  brings the leading edge  61  of the tab  53  into contact with the flange  54 , which tends to inhibit further movement of the screen panel  20  toward the access opening  14  ( FIGS. 10B and 10C ). 
         [0057]    With continued reference to  FIG. 10B , the trailing screen panel  22  can be moved into position relative to the leading screen panel  20  for joining the screen panels  20 ,  22  together. As shown in  FIG. 10D , the trailing screen panel  22  can be pushed into engagement with the leading screen panel  20 , and the coupling  62  between the screen panels  20 ,  22  can be established. For example, the jaw  94  of the trailing screen panel  22  can be pushed onto the ledge  90  of the leading screen panel  20 , and the compression clips can hold the ledge  90  in the jaw  94 . Also, the lugs  98  of the leading screen panel  20  can be seated in the seats  100  of the trailing screen panel  22 . In addition, the latching mechanisms  64  can be used to secure the first and second screen panels  20 ,  22 . 
         [0058]    As the trailing screen panel  22  is pushed together with the leading screen panel  20 , the engagement of the limiting tab  53  with the flange  54  prevents the screen panels  20 ,  22  from moving. This facilitates joining the screen panels  20 ,  22 . 
         [0059]    As shown in  FIG. 10E , once the trailing screen panel  22  is joined with the leading screen panel  20 , the screen panel assembly  16  is lifted and moved forward in the direction of the access opening  14 . In particular, lifting the trailing screen panel  22  causes the leading screen panel  20  to be lifted, and the two screen panels  20 ,  22  can be manipulated and moved at the same time. The assembly  16  is lifted so the limiting tab  53  of the leading screen panel  20  clears the flange  54  of the tray  42 , as indicated by the arrow in  FIG. 10E . The screen panel assembly  16  can be moved into the access opening  14 . 
         [0060]      FIG. 10F  shows a third screen panel  23  being brought into position relative to the trailing screen panel  22  for joining therewith and incorporation into the screen panel assembly  16 . The third screen panel  23  is substantially identical to and interchangeable with the screen panels  20 ,  22 . The trailing screen panel  22  is situated so that its second limiting tab  53  engages the flange  54 , as discussed above for the leading screen panel  20 . The third screen panel  23  is brought into engagement and joined with the trailing screen panel  22  in a similar manner as discussed above for the leading and trailing screen panels  20 ,  22 . 
         [0061]    Once the third screen panel  23  is coupled with the trailing screen panel  22 , it becomes part of the screen panel assembly  16 . The screen panel assembly  16  is then lifted so that the limiting tab  53  of the trailing screen panel  22  clears the flange  54  of the tray, and the assembly  16  can be moved further into the access opening  14  ( FIG. 10G ). 
         [0062]      FIG. 10H  shows the screen panel assembly  16  substantially aligned with the tray  42  so that the locating bores  57  on the tongue  55  of the tray  42  are aligned with the locating bores  59  of the third screen panel  23 . In that configuration, the limiting tabs  52 ,  53  of the third screen panel  23  are forward of the flange  54 . 
         [0063]    In addition, and as shown in  FIG. 10I , the screen panel assembly  16  is secured to the tray  42  through the third screen panel  23 . Particularly, the lugs  98  of the third screen panel  23  receive and engage the tongue  55  which extends from the flange  54  of the tray  42 . The tongue  55  is received in the lug spacing  99  between the lug arm  97  and the ledge  90 , and engages with the lug arm  97  to form a tight fit between the lugs  98  and the tongue  55 . 
         [0064]    Thereby, the screen panel assembly  16  and the agitating structure  18  are secured together and may be moved as a single piece and further inserted into the access opening  14 , as shown in  FIG. 10J . The main housing  12  includes locating brackets  140  formed near the access opening  14 . The locating brackets  140  include locating bores  142 , and the locating bores  57 ,  59  of the third screen panel  23  and the tray  42  can be moved into alignment with the locating bores  142  ( FIG. 10J ). A fastener  144  can be inserted into the locating bores  142 ,  57 ,  59  to secure the screen panel assembly  16 , the agitating structure  18 , and the main housing  12  together. 
         [0065]    The screen panel assembly  16  and the agitating structure  18  can be removed from the screening machine  10 , and separated from each other by reversing the above-described steps. While  FIGS. 10A-10J  show the installation of the screen panel assembly  16  and the agitating structure in the screening machine  10 , it will be appreciated that reference may be made to those figures for understanding the following description of the removal. 
         [0066]    If fasteners  144  are situated in the locating bores  142 ,  57 ,  59 , the fasteners  144  can be removed. The screen panel assembly  16  and the agitating structure  18 , which may be secured together through the engagement of the lugs  98  on the third screen panel  23  with the tongue  55  on the tray  42 , can be moved somewhat out of the main housing  12  through the access opening  14 . The connection can be broken between the lugs  98  on the third screen panel  23  and the tongue  55  by moving either the tray  42  or the screen panel assembly  16  so that the tongue  55  is removed from the lug spacing  99 . Thereby, the screen panel assembly  16  is disconnected from the agitating structure  18 . 
         [0067]    The screen panel assembly  16  can then be moved further out of the access opening  14 . In particular, the screen panel assembly  16  is moved until the flange  54  goes into the notch  50  on the trailing screen panel  22  (not shown). A small amount of further movement of the screen panel assembly  16  away from the access opening  14  brings the trailing edge  60  of the tab  52  on the trailing screen panel  22  into contact with the flange  54 . This tends to inhibit further movement of the trailing screen panel  22  away from the access opening  14 . With the trailing screen panel  22  being prevented from further movement, the third screen panel  23  can be separated from the trailing screen panel  22 . With the third screen panel  23  removed from the screen panel assembly  16 , the screen panel assembly  16  (which then includes the leading and trailing screen panels  20 ,  22 ) can be further removed and disassembled. 
         [0068]    The screen panel assembly  16  is lifted so that the tab  52  of the trailing screen panel  22  clears the flange  54  of the tray  52 , and the screen panel assembly  16  is moved further out of the access opening  14 . The screen panel assembly  16  is moved until the flange  54  goes into the notch  50  on the leading screen panel  20 . 
         [0069]    Then, the trailing screen panel  22  can be separated from the leading screen panel  20  in a similar manner as described above for separating the third screen panel  23 . Finally, the leading screen panel  20  can be removed from the tray  42  and separated completely from the agitating structure  18 . 
         [0070]    From the above disclosure of the general principles of this invention and the preceding detailed description of at least one embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.