Abstract:
A screening machine includes a vibratory carrier and a vibratory drive operatively coupled to the vibratory carrier for imparting vibratory motion thereto. The screening machine includes a screen assembly selectively coupled to the vibratory carrier so that the vibratory motion is transmitted to the screen assembly. A sealing mechanism including at least one rotary cam having a cam surface and at least one actuator being accessible to a user of said screening machine is coupled to the rotary cam. Actuation of the actuator to rotate the cam urges the screen assembly and the carrier into sealing engagement with a confronting surface of the screening machine. The screening machine further includes at least one stop positioned relative to the sealing mechanism to limit rotational movement of the rotary cam in at least one direction.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to screening machines of the type used to separate or classify mixtures of solid particles of different sizes. The invention also relates to screening machines of the type used for liquid/solid separations, i.e., for separating solid particles of specific sizes from a liquid in which they are carried. More particularly, the invention relates to a mechanism and method for sealing components within the screening machine. 
       BACKGROUND OF THE INVENTION 
       [0002]    In screening machines of the type described, a screen (which may be woven, an aperture plate or another design) is mounted in what is often called a “screen frame” or “screen deck” which includes a supporting peripheral frame around the perimeter of the screen. Typically associated with this screen frame are other material handling elements which are moved with the screen frame and form walls or partitions above or below the screen frame for containing the liquid and/or particulate materials adjacent to the screen and directing them to appropriate outlets. These elements may include a top cover and a pan beneath the screen frame. In the case of screening machines with multiple screens or deck units, spacer pans or frames are provided between the multiple screens. 
         [0003]    The screen frames are often removed from the screening machines for cleaning, replacement, readjustment or installation of a screen of a different mesh size or the like. The screen frame is releasably mounted to a carrier, frame, table or box to which vibratory motion is imparted, typically by one or more eccentric motors or other means of excitation. The carrier, frame, table or box is referred to herein as a “vibratory carrier”. The vibratory carrier may be moved in oscillatory, vibratory, gyratory, gyratory reciprocating, fully gyratory, rotary or another type of motion or combinations thereof, all of which are herein collectively referred to as “vibratory” motion or variations of that term. 
         [0004]    In large commercial screening machines, the weight of the various components including the screen assembly carried by the vibratory carrier, and the weight of the material being processed on the screen assembly may total several hundred pounds or more. This presents a very substantial inertial mass which resists the changes of motion applied thereto by the vibratory drive acting through the vibratory carrier. As a result of these inertial forces, a relative motion may exist between the vibratory carrier and the screen frame. Known screen frames and vibratory carriers are each constructed of metal which could result in significant noise, wear or damage due to the relative motion or rubbing action therebetween. The resulting impact forces between the screen frame and vibratory carrier significantly increase the stresses on the components and reduce their useful life. 
         [0005]    Reducing the metal-to-metal contact minimizes the wear on the various metal components and the noise associated with the operation of the screening machine. In some screening machines, a seal is provided between the screen frame and adjacent components such as other screen frames or the vibratory carrier. The seal prevents the escape of material from the screen frame and reduces the detrimental metal-to-metal contact between the screen frame and adjacent components. Certain screen frame designs may not be sealed or secured relative to the remainder of the screening machine, particularly in larger screening machines. This results in the above-described metal-to-metal contact between the screen frame and the remainder of the screening machine and prevents the screening of very fine material, such as sand or the like. The screen frames in known larger screening machines may be inserted and/or removed from the machine in a generally horizontal direction through an opening or slot at, for example, the head or foot end of the machine. This method of installation and removal of the screen frame is detrimental to known sealing arrangements because a seal which would engage the screen frame could be torn or damaged during the installation/removal and/or reinsertion of the screen frame. In other known screening machines, the screen frame may be inserted vertically, typically from the top of the machine. 
         [0006]    One known sealing mechanism for screening machines is disclosed in U.S. Pat. No. 5,226,546 which relates to a pneumatic seal that is inflated to raise up the screen frame for engagement with a seal. However, pneumatic systems by their very nature utilize a working fluid which may leak, thereby lowering the seal pressure. Furthermore, pneumatic systems require an air source at the machine location and traditionally are only used with the insertion/removal of the screen frame through the top of the machine in a generally vertical direction. Furthermore, screening machines with multiple screens and screen frames may require many or all of the screen frames to be removed for access to an individual screen frame. Furthermore, inspection of the resulting seal in pneumatic systems is not readily available. 
         [0007]    Known alternatives to pneumatic sealing systems for screening machines include mechanical clamps or locks located at a number of spaced locations on the sides of the machine. One example of this type of known mechanism is disclosed in U.S. Pat. No. 5,392,925. However, to clamp each of the screens in place, the user must progressively move along a first side of the machine tightening and adjusting each of the individual mechanism and then proceed to the opposite side of the machine and repeat the same procedure. This mode of operation is inefficient, time consuming and inconvenient for the user. Additionally, the user cannot easily inspect the resulting seal when going from clamp site to clamp site in such systems. Furthermore, the screen frames utilized in screening machines with known mechanical sealing mechanisms must be robust and heavy because they are supported at individual spaced locations by the clamps. 
         [0008]    U.S. Pat. No. 6,070,736 discloses a sealing mechanism including ramps having linear cam surfaces to bring a vibratory carrier respectively into and out of sealing engagement. A problem with the sealing mechanisms of this type may include the opportunity for a technician or user of the machine to advance the cam surface out of position thereby jamming the carrier into the machine. 
         [0009]    Therefore, it is apparent that there is a need for a sealing mechanism and method for screening machines which avoids metal-to-metal contact between the screen frame and adjacent components of the screening machine without the disadvantages associated with known pneumatic or mechanical sealing systems of the prior art. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with an embodiment of the invention, a screening machine includes a vibratory carrier and a vibratory drive operatively coupled to the carrier for imparting vibratory motion thereto. The screening machine includes a screen assembly having at least one screen mounted to a peripheral screen frame, which is selectively coupled to the carrier so that the vibratory motion is transmitted to the screen assembly. A sealing mechanism including at least one rotary cam having a cam surface and at least one actuator being accessible to a user of the screening machine is coupled to the rotary cam. 
         [0011]    Actuation of the actuator to rotate the cam urges the screen assembly and the carrier into sealing engagement with a confronting surface of the screening machine. The screening machine further includes at least one stop positioned relative to the sealing mechanism to limit rotational movement of the cam in at least one direction. 
         [0012]    The screening machine may include two rotary cams coupled to the actuator. Two stops may be positioned relative to the sealing mechanism to limit rotational movement of the cam in a clockwise direction and a counter-clockwise direction. The two stops may define a limiting cam which is coaxial with the rotary cam. 
         [0013]    At least one rotary cam may lie proximate a first edge on the peripheral screen frame and the screening machine may include a second rotary cam disposed proximate a second edge on the peripheral screen frame, which is disposed opposite the first edge. 
         [0014]    A screening machine in one embodiment includes at least one stop preventing rotation of the rotary cam beyond about 110° from a lowest vertical position of the screen assembly and the carrier. The stop prevents rotary motion of the rotary cam in one direction beyond a lowest vertical position of the screen assembly and the carrier. In another aspect of one embodiment, a cam has a surface portion adapted to permit rotary motion of the rotary cam beyond a highest vertical position of the screen assembly and the vibratory carrier. 
         [0015]    A screening machine according to this invention may include a rotary cam having a cam surface configured such that a tool driving the actuator is in a generally horizontal orientation when the screen assembly and the carrier reach a highest vertical position. The screening machine may further include a bracket, such that the at least one stop is integrally formed with the bracket. 
         [0016]    In another embodiment, a method of sealing a screen frame having a screen within a screening machine includes inserting the screen frame and screen within a vibratory carrier of the screening machine. The vibratory carrier imparts vibratory motion to the screen frame and the screen during use of the screening machine which includes a sealing member being positioned on a portion of the vibratory carrier. 
         [0017]    In another aspect of this embodiment, the method includes actuating a sealing mechanism having portions extending along a length of at least one side of the screen frame from an end of the screen frame. Such actuation is effected by rotating a rotary cam to urge the vibratory carrier and screen frame into and out of sealing engagement with corresponding portions of the screening machine. The method also includes rotating the rotary cam until a first stop is reached positioned to restrict rotational movement of the rotary cam in at least one direction. 
         [0018]    The invention may also include rotating the rotary cam to urge the vibratory carrier and screen frame out of sealing engagement with corresponding portions of the screening machine to engage a second stop positioned to restrict movement of the rotary cam in a direction beyond a lowest height of the vibratory carrier and screen frame. 
         [0019]    Advantageously, by including at least one rotary cam having at least one stop to prevent rotational motion thereof, the screening machine described herein has a sealing mechanism that effectively seals the screen frame without damaging it or adjacent components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and other objectives and advantages will become readily apparent to those of ordinary skill in the art from the following description of embodiments of the invention and from the drawings in which: 
           [0021]      FIG. 1  is a perspective view of an exemplary screening machine; 
           [0022]      FIG. 2  is an enlarged elevation view of one embodiment of a sealing mechanism of the screening machine of  FIG. 1 ; 
           [0023]      FIG. 3  is a view similar to that of  FIG. 2  showing a point in the rotation of a cam of the sealing mechanism of  FIG. 2 ; 
           [0024]      FIG. 4  is a view similar to those of  FIGS. 2-3  showing a subsequent point in the rotation of the cam of  FIG. 3 ; 
           [0025]      FIG. 5  is a perspective view of a rotational cam assembly and actuator according to one embodiment of the sealing mechanism of  FIGS. 2-4 ; 
           [0026]      FIG. 6  is an elevation view of an exemplary embodiment of a primary cam of the sealing mechanism of  FIGS. 2-5 ; 
           [0027]      FIG. 7  is an elevational view of another exemplary embodiment of a primary cam of the sealing mechanism of  FIGS. 2-5 ; and 
           [0028]      FIG. 8  is a perspective view of a bracket according to one embodiment of the sealing mechanism of  FIGS. 2-5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    With reference to  FIG. 1 , an exemplary embodiment of a screening machine  10  in which this invention may be used is shown. Screening machines of many types are sold commercially by Rotex, Inc. of Cincinnati, Ohio, the assignee of this invention. However, this invention is not limited to any particular type of screening machine design or component and the machine and associated components depicted and disclosed herein are shown for illustrative purposes. 
         [0030]    The screening machine  10  includes an inlet port  12  near an inlet section  14  proximate a head end  16  of the machine  10 . The screening machine  10  may also include a top cover  18  in any one of a variety of forms. Particulate or other material to be screened is fed into the inlet port  12  from a hopper (not shown) for screening and processing by the machine  10 . 
         [0031]    The screening machine  10  is supported structurally by a base frame  20  including beams  22  connected together by laterally oriented struts  24  on each end of the screening machine  10 . The screening machine  10  includes an electric motor  26  coupled to a drive weight (not shown) to impart an oscillatory, vibratory, gyratory, gyratory reciprocating, fully gyratory, other motion or combinations thereof (herein collectively referred to as “vibratory” motion or variations of that term) to at least the head end  16 . 
         [0032]    Within a screening chamber of the screening machine  10 , one or more screen assemblies  28  are each mounted in combination to form one or more screen decks  30  to receive the material being screened from the inlet port  12  at the head end  16  of the machine  10 . The screen assemblies respectively include screen panels  28 , which are mounted on slightly sloping planes (about 4°) with the head end thereof being slightly elevated relative to a foot end so that during the screening process the material advances, in part by gravity, over the screen panels  28  toward the foot or discharge end  32  of the machine  10 . Even though the screen panels  28  of the screening machine  10  may be on a slightly sloping plane, to provide a reference for the purposes of clarity herein, these components will be considered to be generally horizontal and the direction perpendicular or orthogonal to the screen panels  28  will generally be referred to as a vertical orientation, direction or attitude. The direction of travel of the material being screened from the head end to the foot end across the screen panels  28  is referred to as the longitudinal direction and the perpendicular orientation extending from side to side on the screen panels is a lateral direction. 
         [0033]    In the embodiment of the screening machine  10  shown in  FIG. 1 , upper and lower screen decks  30   a,b  each include four screen panels  28  mounted generally coplanar with each other in the associated screen deck  30   a,b . Accordingly, as the material to be screened is deposited from the inlet port  12  onto the upper screen deck  30   a , the vibratory motion of the screening machine  10  advances the material longitudinally across the top of the screen panels  28  of the upper screen deck  30   a  toward the foot end  32 . Appropriately sized and configured material passes through the upper screen deck  30   a  and falls onto the lower screen deck  30   b . The screen panels  28  of the upper screen deck  30   a  may include a fine mesh screen material  34  adjacent the inlet port  12  through which dust and other fine particulate matter passes for collection and discharge. Certain material also passes through the upper screen deck  30   a  and is deposited on the lower screen deck  30   b . Therefore, the lower screen deck  30   b  is included to provide an additional separating mechanism for the appropriately sized particles to pass through the second lower screen deck  30   b  for collection in the lower pan (not shown) and discharge through an outlet or exit section  36 . 
         [0034]    The unacceptably sized particles remain atop the first upper screen deck  30   a  and fall off the terminal edge thereof into a collection basin (not shown) for discharge through the outlet section  36 . Material that passes through the upper screen deck  30   a  and remains atop the lower screen deck  30   b  falls off the terminal edge thereof and into the collection basin for discharge through a reject port (not shown). The discharge and reject ports are separated by a baffle (not shown) to keep the classified particles separate from one another. 
         [0035]    With continued reference to  FIG. 1 , one or more doors  38  are each pivotally connected by a hinge  40  to a lateral side  42  of the screening machine  10 . When opened, the doors  38  provide access for insertion and removal in the lateral direction of the screen panels  28 . It will be appreciated that although one side  42  of the screening machine  10  is shown in  FIG. 1 , additional doors on the opposite side of the screening machine  10  may also be provided. The screen panels  28  may be inserted laterally or perpendicularly to the longitudinal direction of travel of the material being screened in the screening machine  10  from the head end  16  to the foot end  32  of the machine  10 . 
         [0036]    With reference to  FIGS. 1-2 , when the screen panel  28  is inserted into the screening machine  10 , it is supported on a vibratory carrier  44 . In one embodiment, the vibratory carrier  44  may include a ball tray  46  capturing a number of balls or other agitation producing members (not shown) which repeatedly impact the screen panel  28  to dislodge particulate material that might accumulate on the screen material  34  and inhibit occlusion of the screen material  34  as is well known in the art. 
         [0037]    One embodiment of the screen panel  28  includes a generally perforated mesh screen material  34  including a number of intersecting longitudinal and lateral threads, wires or strings which are oriented orthogonally to each other to provide appropriately sized and configured openings in the mesh screen material  34  to prevent/permit the passage particulate material therethrough. The screen panel  28  includes a generally rigid perimeter frame  54  having a leading side edge  56  opposite from a trailing side edge  58 . 
         [0038]    With continued reference to  FIGS. 1-2 , the leading side edge  56  of the screen panel frame  54  may be inserted laterally into the screening machine  10  while a user or operator grasps the trailing side edge  58  for manipulation. In particular, a downwardly turned elongate handle  60  is formed on the trailing side edge  58  of the screen panel  28 . In one embodiment, the handle  60  is oriented about 90° relative to the plane of the screen panel  28  and provides a convenient and easy access for the user or technician to grasp or manipulate the screen panel  28 . Additionally, the handle  60  or adjacent surfaces of the screen panel frame  54  provide a convenient location for identifying indicia and labels indicating various service parameters, design characteristics and other aspects of the screen panel  28 . 
         [0039]    One or more tabs  62  each located proximate a head end  64  or a tail end  66  of the screen frame  54  are located along the trailing side edge  58  of the frame. The tabs  62  are each oriented about 90° relative to the plane of the screen panel  28  and along with the handle  60  provide a convenient location for the user or technician to grasp and manipulate the screen panel frame. Likewise, upon insertion of the screen panel  28  into the screening machine  10 , the tabs  62  and handle  60  provide a detent when juxtaposed against the vibratory carrier  44  for proper orientation and location of the screen panel  28  in the screening machine  10 . 
         [0040]    With continued reference to  FIGS. 1-2 , in another aspect of the illustrated embodiment of the screen panel  28  and associated frame  54 , beveled edges or lips  68  extend along the longitudinal head end  64  and/or foot end  66  of the screen panel frame  54 . Each lip  68  is oriented about 45° relative to the upper surface or plane of the screen panel  28  and extends substantially along the entire width of the frame  54 . While the lips  68  are shown along both the longitudinal head and foot ends  64 ,  66  of the screen panel frame  54 , one of ordinary skill in the art will readily appreciate that the lip  68  may be provided at neither, either or both of the head and foot ends  64 ,  66 . 
         [0041]    With reference to  FIGS. 2-4 , the screening machine  10  includes a sealing mechanism which will now be described. One example of a sealing mechanism is disclosed in U.S. patent application Ser. No. 11/382,353, filed May 6, 2006, and hereby incorporated by reference. The downwardly turned bevel lips  68  along the head and foot ends  64 ,  66  of the screen panel frames  54  are supported by a similarly inclined face  70  of the vibratory carrier  44  as shown in  FIG. 2 . A compressible seal member  72  lies juxtaposed to the terminal edge  74  of the lip  68  and is mounted in the carrier  44 . Likewise, a lower surface of the screen panel frame  54  is supported along a similarly configured profile of the carrier  44  as shown in  FIG. 2 . 
         [0042]    The sealing mechanism also includes a bracket  76  that cooperates with a rotational cam assembly  78  sitting thereon and which supports the carrier  44 . The rotation of the cam assembly  78  is accomplished by an actuator  80  accessible to the operator or technician when the door  38  of the screening machine  10  is open. The screening machine  10  also includes a downwardly depending channel  82  initially spaced from the bevel lip  68  of the screen frame  54  as shown in  FIG. 2 . 
         [0043]    With continued reference to  FIGS. 2-4 , upon rotation in the direction of arrow A (i.e., clockwise) of the actuator  80 , the cam assembly  78  is rotated, thereby raising the carrier  44  and screen panel  28  supported thereon upwardly into sealing engagement with an upper portion  84  of the screen deck  30   a , b as shown in  FIG. 3 . As the carrier  44  supporting the screen panel  28  is raised, a face  86  of the channel  82  is juxtaposed against the bevel lip  68  of the screen panel frame  54  and the seal member  72  is compressed against the channel  82 . As a result, the upper portion  84  of the screen deck  30   a, b  and upper surface of the screen panel frame  54  are sealed to prevent and inhibit the discharge of material being screened. In another aspect of this embodiment, the orientation of the seal member  72  is generally parallel with the lateral direction in which the screen panel  28  is inserted and removed respectively into and from the machine  10 . 
         [0044]    While the exemplary embodiment of  FIGS. 2-4  is depicted having a vibratory carrier  44  and screen panel frame  54  capable of sealing engagement with an upper portion of a deck  30   a, b , persons of ordinary skill in the art will readily appreciate that, alternatively, the vibratory carrier  44  and screen panel frame  54  or any other part of the screen assembly may be capable of sealing engagement with any other suitably chosen part of the screening machine  10 , such as, for example, a fixed support frame. 
         [0045]    With reference to  FIG. 5 , the actuator  80  in this exemplary embodiment includes a conventional bolt  79  having a hex head  81  and a threaded body section  83 . The actuator  80  further includes a locking nut  85  threadably engaged with the threaded body section  83  and a conventional serrated washer  87  that receives the threaded body section therethrough. The threaded section  83  is threadably engaged within a correspondingly threaded aperture  89  in the rotational cam assembly  78  such that the washer  87  lies between the locking nut  85  and the threaded aperture  89 . The actuator  80  cooperates with the cam assembly  78  and bracket  76 , as described below. 
         [0046]    The rotational cam assembly  78  includes a limiting cam go and a primary cam  92 , both disposed generally proximate the trailing side edge  58  and both rotational about an axis  94 , as well as a shaft  95  supporting both cams go,  92  and extending in the direction of the head and foot ends  64 ,  66  of the screen panel frame  54 . The rotational cam assembly  78  may further include a secondary cam  96  supported by the shaft  95 , disposed generally proximate the leading side edge  56  of the screen panel frame  54 , and generally similar in profile to the primary cam  92 . A protrusion  93  may be also present extending from the secondary cam  96  and engageable with a slot (not shown) in the screening machine  10  to facilitate rotation of the secondary cam  96  about the axis  94 . As such, the leading and trailing side edges  56 ,  58  of the screen panel frame  54  may be lifted in unison as the actuator  80  is rotated, thereby maintaining the screen panel  28  generally horizontal during raising and lowering thereof. 
         [0047]    In another aspect of this embodiment, the locking nut  85  permits locking of the angular position of the primary cam  92  and thereby the corresponding positions of the carrier  44  and screen panel  28  with respect to the screening machine  10 . Persons of ordinary skill in the art will readily appreciate that, alternatively, the sealing mechanism may include any other type of fastener or structure capable of providing the locking functionality of locking nut  85 , or even include no locking fastener or device at all. 
         [0048]    With continued reference to  FIG. 5 , the primary cam  92  includes a profile defined by serially disposed arcuate and flat surfaces  98  such that rotation of the actuator  80  in a specified direction results in raising and lowering of the screen panel  28  and subsequent sealing thereof and of the carrier  44  against the surface  84  of the screen deck  30   a, b , as described above. 
         [0049]    In one embodiment, the surfaces  98  may be configured as shown in  FIG. 2 , wherein clockwise rotation of the actuator  80  results in raising of the carrier  44  and screen panel  28 , while counter-clockwise rotation lowers these two components. Persons of ordinary skill in the art will appreciate the fact that the surfaces  98  may be configured such that, alternatively, clockwise rotation lowers the carrier  44  and screen panel  28  while a counter-clockwise rotation raises them. The surfaces  98  may be further configured such that different rising rates (i.e., increase in height of the carrier  44  and screen panel  28 ) are achieved corresponding to a given angular rotation of the primary cam  92 . For example, and without limitation, the surfaces  98  may be configured to yield a higher rising rate in rotations between about 0° and about 60° from a the lowest position of the carrier  44  and screen panel  28  than the rising rate during the subsequent about 30°. 
         [0050]    In another exemplary embodiment, the configuration of the surfaces  98  of the primary cam  92  may be designed such that the carrier  44  and screen panel  28  reach their maximum height when a wrench or the like tool driving the actuator  80  is in a generally horizontal position, thereby facilitating the application of torque by the operator to seal the carrier  44  and screen panel  28  against the surface  84  on the upper screen deck  30   a, b  or any other suitably chosen portion of the machine  10 , as explained above. Moreover, the surfaces  98  may be configured such that the seal  72  and associated components are neither damaged nor compromised with any rotational motion of the primary cam  92 , thereby extending the service life of the seal  72  while maintaining effective sealing and associated screening operations. 
         [0051]    While the above exemplary configurations of the surfaces  98  describe them as contemplated configurations for the primary cam  92 , persons of ordinary skill in the art will readily appreciate that the same are also applicable to the secondary cam  96 , if present. 
         [0052]    With reference to  FIGS. 2-5 , the cam assembly  78  includes a limiting cam go coaxial with the primary cam  92 . The limiting cam go includes serially disposed surfaces  100  which may or may not be configured to match corresponding surfaces  98  on the primary cam  92 . In one embodiment, the surfaces  100  may be configured such that the limiting cam go simply “floats” over (i.e., does not make contact with) the surfaces against which the primary cam  92  moves. The limiting cam go includes one or more limiting surfaces  102 ,  104  such that rotation in at least one direction (i.e. clockwise or counter-clockwise) is limited when one of such surfaces  102 ,  104  engages a stop block, to be described below. In the illustrative embodiment of  FIGS. 2-5 , the limiting cam go includes two limiting surfaces  102 ,  104  such that rotation of the primary cam  92  is limited in both, clockwise and counter-clockwise directions. 
         [0053]    The clockwise limiting surface  102  is circumferentially disposed on the limiting cam go such that clockwise rotation is prevented beyond a point that may lead to damage to the primary and secondary cams  92 ,  96 , screen panel frame  54 , carrier  44 , seal  72  or other components of the screening machine  10 . In one exemplary embodiment, the clockwise limiting surface  102  may be configured such that it maximizes rotation of the cam at about 110° from the lowest position of the carrier  44  and screen panel  28 . 
         [0054]    Similarly, the counter-clockwise limiting surface  104  is circumferentially disposed on the limiting cam go such that counter-clockwise rotation is prevented beyond a desired position. In one exemplary embodiment, the counter-clockwise limiting surface  104  may be configured such that the primary cam  92  cannot rotate counter-clockwise from the lowest position of the carrier  44  and screen panel  28 . 
         [0055]    With reference to  FIGS. 6-7 , two illustrative embodiments of the primary cams  92   a ,  92   b  are depicted. These cams respectively include a notch  93   a ,  93   b  that receives the shaft  95  as well as an outer surface profile  99   a ,  99   b . The configuration and design of each of the outer surface profiles  99   a ,  99   b  are suitably chosen to carry out functions such as those described above to determine, for example, the extent of any rotational motion of the primary cam  92   a ,  92   b  beyond a maximum height reached by the carrier  44  and screen panel  28 . 
         [0056]    With reference to  FIG. 6 , the outer surface profile  99   a  of the exemplary primary cam  92   a  includes respective top and bottom surface portions  101   a ,  102   a . The top and bottom portions  101   a ,  102   a  are relative flattened such that relative motion of the carrier  44  and screen frame  28  with respect to the screening machine  10  levels out. More particularly, rotational motion of the primary cam  92   a  beyond a final position such as one corresponding to a maximum or minimum height of the carrier  44  and screen panel  28  yields little or no substantial change in position. Such configuration signals an operator that a maximum or minimum height of the carrier  44  and screen panel  28  has been reached. 
         [0057]    With reference to  FIG. 7 , the outer surface profile  99   b  of the exemplary primary cam  92   b  includes respective top and bottom surface portions  101   b ,  102   b . The top and bottom portions  101   b ,  102   b  are relative peaked such that an operator is made aware of the fact that a maximum or minimum height of the carrier  44  and screen panel  28  has been reached and passed. In another advantageous aspect of this embodiment, the peaks  103  of the top and bottom portions  101   b ,  102   b  provide locks that may make the locking nut  85  redundant. More particularly, once rotation of the primary cam  92   b  in a first direction is such that a peak  103  has been reached and passed, inadvertent rotation in a second, opposite direction is not likely to occur. This is because a relatively large torque is required to rotate the primary cam  92  in the second direction past a corresponding peak  103 . 
         [0058]    With reference to  FIG. 8 , and as mentioned above, the sealing mechanism includes a bracket  76  mounted on a screen deck  30   a, b , and includes a wall  104  defining a notch  106 . The wall  104  and notch  106  are disposed to support the cam assembly  78  and allow access to the actuator  80 . In the illustrative embodiment of  FIG. 8 , the wall  104  and notch  106  are disposed such that a portion of the threaded body section  83  of the bolt  79  is received therein, for example, between the locking nut  85  and the serrated washer  87 . 
         [0059]    The bracket  76  includes a bottom plate  108  adapted to receive motion of the primary cam  92  along the surfaces  98  in ways well known to those of ordinary skill in the art. A stop block  110  is mounted on the bottom plate and provides a surface engageable against the limiting surfaces  102 ,  104  to prevent further rotational motion of the primary cam  92 , as explained above. The dimensions and shape of the stop block  110  are such that suitable engagement is made possible against either or both of the limiting surfaces  102 ,  104  while permitting rotational movement of the primary cam  92 . To that end, the stop block  110  may be integrally formed with or coupled to the wall  104  and/or the bottom plate  108  such that no extraneous surfaces such as welding points extend beyond the volume occupied by the stop block  110  and interfere with the motion of the primary cam  92 . 
         [0060]    With continued reference to  FIG. 8 , the stop block  110 , wall  104 , and bottom plate  108  are made of materials suitable to support the cam assembly  78  while resisting a force applied against it when any of the limiting surfaces  102 ,  104  engage the stop block  110 . For example, and without limitation, the stop block  110 , wall  104  and bottom plate  108  may be made of metal such as steel and further be integrally formed from one of several known casting processes known to those of ordinary skill in the art. 
         [0061]    While the above description describes an embodiment including one bracket  76 , persons of ordinary skill in the art will readily appreciate that in the case of embodiments including a secondary cam  96  ( FIG. 5 ), a secondary bracket (not shown) similar to the bracket  76  may be disposed on the screening machine  10  to be in cooperating relationship with the secondary cam  96 . 
         [0062]    Accordingly, many further embodiments, applications and modifications of the invention will become readily apparent to those of ordinary skill in the art without departing from the scope of the invention and the inventors intend to be bound only by the claims appended hereto.