Abstract:
A screening system with knocking devices includes a screen panel support, connector bars, knocking devices, and screen panels. The knocking devices are generally spherical-shaped balls held by elastic arms connected to the connector bars. When the screening system is activated by moving material onto the screen panels and vibrating the screen panel support, the knocking devices bounce around the undersurface of the screen panels and prevent the build-up or jamming of material blocking the openings in the screen panels. The knocking device and screen panels are separate so that when one of those elements becomes defective, the screening system can be fixed without replacing both elements.

Description:
This claims priority to U.S. Provisional Patent Application Ser. No. 61/034,532, filed Mar. 7, 2008 and hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the general field of screening systems and particularly to screening systems with a screen or sieve having openings and devices used to free the screen from material blocking or plugging the openings. 
     In mining and related fields, screening systems are used to separate fine pieces of material from larger pieces of material. These screening systems generally include some number of screen panels which sit on a framework of steel girders. When the steel girders are jostled and moved around, fine material on the screen panels drops through the openings in the screen and larger pieces of material bounce off the screens and off the sides of the screening system, where those larger pieces are collected for further processing. 
     In some screening applications fine material will begin sticking to the screen surface and build up to the point where fine material bridges over the openings in the screen. This bridging of fine material reduces the size of the openings in the screen (commonly referred to as blinding), which can get progressively worse over time. Once a sufficient percentage of the screen openings is blinded by bridged fine material, the screening system is too ineffective and must be shut down so that the screens can be removed or manually cleaned. This can frequently shut down an entire mining operation or plant, especially if the material being screened is damp or irregularly-shaped. 
     In addition to the problems with fine material bridging the openings, larger angular or irregular-shaped particles in the material can become lodged in the openings of the screen, blocking it much like blinding. This problem is widely referred to as plugging or pegging. The effects of plugging are very similar to those of blinding. 
     The mechanical action of a screening system causes some level of G-forces to be exerted on the screen panels. This mechanical action drives the screening process and helps avoid blinding or plugging of the screens, but the speed and stroke of the mechanical action must be within industry standards. If the screening system is running at maximum G-force (maximum referring to the state where an increase in speed will damage the screening system) and plugging or blinding still occurs, there needs to be some other mechanical means to vibrate or impact the screen and keep the screen surface clean. 
     Some of the screening system manufacturers have tried to solve this plugging and blinding problem with a design that incorporates steel wire baskets attached to the steel girders below every screen panel. These steel wire baskets contain rubber or urethane balls placed within the basket so that when the mechanical action of the screening system is activated, the balls bounce repeatedly off the steel wire baskets and into the bottom of the screen panels to help prevent blinding and plugging. These steel wire baskets wear out easily with abrasive materials being screened, and the frequent replacement of these baskets is time-consuming and expensive. These steel baskets also cannot be retrofitted to older screening systems, but can only be attached to newer screening systems designed to incorporate the baskets. 
     One design which attempted to solve the problems of the steel basket systems by attaching a beating device such as a plastic ball attached to rubberized arms connected to the frame of a screen panel is disclosed in U.S. Pat. No. 7,416,085. That system addressed many of the problems with the steel basket design, but attaching the beating device directly to the screen panel leads to different problems. New screen panels needed to be created to allow integration with the beating devices, and if one of the two elements is defective or broken, the entire screen panel and beating device unit must be replaced. 
     Consequently, it would be desirable to come up with a screening system which overcomes these and other problems with prior art systems and can knock loose build-ups of blinding and plugging material while being resilient to the abrasive materials typically screened with these machines. 
     SUMMARY OF THE INVENTION 
     This invention solves these and other problems with known screening systems. The invention in one embodiment is a screening system including a machine frame, girders, connectors, a screen panel, an elongated element, and a beater. The machine frame includes at least two girders, and the connectors are coupled to those girders. The screen panel includes at least one generally horizontal screen and a frame holding the screens. The frame of the screen panel is connected to adjacent connectors on opposite sides of the frame. The elongated element includes opposite ends attached to the adjacent connectors, and the elongated element holds the beater between these opposite ends. The beater consequently is located just below the screen panel, and during screening operations it knocks against the screens to free built-up particles of material lodged in openings of the screens. 
     In some embodiments, the connectors are connector bars and include a cross section including a top knob, a bottom knob, and a central rectangular section which creates opposing side surfaces of the connector bar. The top knob is designed to hold the screen panel in place, and the screen panel frame has concave opposing side edges to engage the top knob. The opposing side surfaces of the connector bar have notches at various intervals, and the ends of the elongated element are designed to fit in these notches. The ends and notches can be any shape which allows the elongated element to be removably attached to adjacent connector bars, but one embodiment includes dovetail-shaped ends and notches. The screen panel and beater can each be made of resilient plastic material to help these parts last longer before failure. 
     The invention also includes a method of constructing the screening system described above. The method includes hammering the bottom knob of the connector bar into girders which make up the machine frame. The elongated element is then attached to the notches in adjacent connector bars. The final step is to hammer the screen panel onto the top knob portion of the adjacent connector bars. Once completed, the beater and elongated element engage the screen panel. 
     The invention further includes a method of screening material to remove fine particles of material from larger or course particles of material using a screening system as described above and including a machine frame, connector bars, a screen panel, an elongated element, and a beater. The method includes delivering material made of fine and course pieces onto the screen panel, followed by actuating the machine frame with vibratory or shaking movement to shake the connector bars and screen panel. This vibratory or shaking motion of the connector bars actuates the elongated element, causing the beater to bounce against the underside of the screen panel to remove built-up material on the screen panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objectives and features of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an exploded perspective view of one embodiment of a screening system according to this invention; 
         FIG. 2  is a perspective view of the screening system of  FIG. 1  in operating position; 
         FIG. 3  is a cross-sectional view taken along line  3 - 3  of the screening system of  FIG. 2  illustrating the movement of a knocking device; 
         FIG. 4  is a perspective view of an alternative embodiment of a knocking device according to this invention; 
         FIG. 4A  is a cross-sectional view taken along line  4 A- 4 A of  FIG. 4 ; and 
         FIG. 4B  is a view similar to  FIG. 4A  of a further alternative embodiment of a knocking device according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One exemplary embodiment demonstrating various features and aspects of a screening system  10  according to this invention is shown in  FIGS. 1-3 . The screening system  10  of this invention includes a support member in the form of a girder or the like  12  coupled to a vibrating machine, connectors  18 , knocking devices  28 , and screen panels  36 , only one of which is shown. While one exemplary screening system  10  is shown and described herein, it will be readily appreciated that this invention is not limited to any particular screening system. 
     As shown in  FIG. 1 , the screen panel support  12  is made from a framework of girders  14 . Each girder  14  has a generally tubular cross-sectional configuration with an opening  16  on a top surface of the girder  14 . A connector  18 , which in one embodiment is a bar and is referred to as a “nokin bar,” is hammered into the opening  16  of each girder  14  of the machine frame  12 . The connector  18  may be a rigid bar with a cross-section most easily shown in  FIG. 3 . The cross-section of the connector bar  18  includes a central rectangular section  20 , a top knob  22  which is typically rounded and integral with the central rectangular section  20 , and a bottom knob  24  adapted to fit within the opening  16  to hold the connector bar  18  in place with respect to the girder  14 . At regular intervals down the length of the connector bar  18 , openings or grooves  26  are formed in the central rectangular section  20  of the connector bar  18 . The connector  18  according to this invention may be of another configuration or design. 
     The knocking device  28  is designed to couple to the connectors  18  using these grooves  26 . The knocking device  28  includes a beater  30 , which is surrounded by and connected to a pair of elastic arms  32 . The distal end  34  of each arm  32  is configured to fit in the grooves  26  of the connector  18 . The ends  34  and grooves  26  are shown in the drawings as dovetail-shaped, but it will be appreciated that alternative shapes of the ends  34  and grooves  26  are possible as well as other techniques for coupling the knocking device  28  to the connectors  18 . For example, an alternative embodiment of the knocking device according to this invention is shown in  FIGS. 4-4B . The knocking devices  28  shown in  FIGS. 4-4B  include opposing and laterally projecting tabs  35  on each of the ends  34 . Moreover, inserts  37  are embedded in each end  34  to increase the strength of the device  28  and minimize the likelihood that the end  34  would break or rupture from the arm  32 . The insert  37  may also have tabs  39  ( FIG. 4B ) and be metal or of another material and configured in the shape shown in  FIG. 4A ,  FIG. 4B  or another shape according to this invention. The beater  30  is any kind of plastic or resilient material that can impact the screen panels  36  to jar loose materials stuck on the screen panel, and may be a plastic ball or sphere as shown in  FIGS. 1-4 . The arms  32  are any kind of elastic and resilient material, as they act like a rubber band between the connectors  18  and the beater  30 . In one embodiment, the ends  34 , arms  32  and beater are integrally molded urethane, polyurethane or another material of 60, 75, 82 or 90 durometer or another design. 
     The screen panel  36  includes a plurality of screens  38  with openings to sieve through fine and course material, and a panel frame  40  surrounding and holding the screens  38 . The screens  38  and panel frame  40  are usually made out of polyurethane plastic, but other materials can be used. The screens  38  and panel frame  40  may be connected by gluing, welding, or casting, or the screens  38  and panel frame  40  could be formed integral with one another. The panel frame  40  projects downwardly from the screens  38  at each side  42  of the panel frame  40 . As shown most clearly in  FIG. 1 , the opposing side walls  42  are shaped as a rounded cavity. These opposing side walls  42  are thus adapted to mate with the rounded top knob  22  of the connector  18 . As shown in  FIG. 3 , within these opposing side walls  42  is the undersurface  44  of the screen panel  36  which is contacted by the beater  30  during operation of the screening system  10 . 
     The construction of the embodiment of a screening system  10  shown in  FIGS. 1-3  is as follows. Once the screen panel support  12  is assembled, the bottom knob  24  of each connector  18  is knocked or hammered into the opening  16  in the associated girder  14 . The knocking devices  28  can then be added to the system  10  by fitting the ends  34  into the grooves  26  as illustrated by the phantom lines in  FIG. 1 . Then a screen panel  36  with side walls  42  in the shape of a round cavity can be knocked or hammered into place between the top knobs  22  of adjacent spaced connectors  18 . The reason the connector  18  is commonly referred to as a “nokin bar” as referenced above is because the screen panels  36  are knocked into place between the connector bars  18 . Once all of these steps have been completed, the assembly of the screening system  10  is complete as shown in  FIG. 2 . 
     After construction, the screening system  10  of  FIGS. 1-3  operates as follows. First, a mechanical agitator or other control system imparts vibration or shaking motion to the screen panel support  12 . As the girders  14  move, the connector bars  18  and screen panels  36  also vibrate, and the screen panel  36  shakes fine material atop the screen through the openings of the screen  38  while retaining larger and more course pieces of material atop the screen  38 . The shaking of the connector bars  18  leads the beater  30  to elastically bounce into contact with the undersurface  44  of the screen panel  36  as shown by arrow  46  and the phantom representation of  FIG. 3 . The beaters can move transversely, longitudinally, and/or diagonally relative to the screen  38 . The repeated impact by the beater  30  breaks up blinding material and dislodges plugging materials from reducing the opening size in the screen  38 . Consequently, the screening system  10  can operate for longer periods of time than the prior art before a screen panel  36  has to be removed for cleaning the plugging and blinding materials from the openings, even in damp environments. 
     The embodiments shown in  FIGS. 1-4B  of a screening system  10  has another benefit over prior art systems. Connecting the knocking devices  28  to the connector bars  18  instead of directly to the screen panels  36  or screen panel frames  40  leads to easier installation and replacement. In case the elastic arms  32  or beater  30  becomes defective over the course of screening, the original screen panel  36  does not need to be replaced but instead can be knocked back on the connector bars  18  once a replacement knocking device  28  is placed in the system  10 . While this invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, each inventor does not intend to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative methods and apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit of the inventor&#39;s general inventive concept. The scope of the invention itself should only be defined by the appended claims.