Abstract:
A grizzly screen apparatus has a screen of grizzly bars having first ends mounted in a transverse end member and second ends placed in a slotted comb member having alternating shallow and deep bed slots. The screen is rotatable about a transverse axis whereby the second ends of secondary grizzly bars in the deep bed slots are lowered relative to the second ends of grizzly bars in the shallow bed slots, resulting in simultaneous steepening of the screen and an increase of the interbar distance, to remove obstructing oversize objects from the screen. Each grizzly bar has a transverse lock bar at the first end which retains the grizzly bar within an aperture in the transverse end member without bolts or other fasteners. Obstructions on the grizzly screen may be cleared without the use of manually operated tools, and if desired, may be cleared by remote control.

Description:
“This is a divisional of application Ser. No. 08/690,478, filed Jul. 31, 1996.” 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to a screening apparatus for separating solid materials by size. More particularly, this invention pertains to an improved grizzly screen apparatus for separating rocks, concrete, asphalt and other objects by size. 
     A separation apparatus known as a “grizzly” or “grizzly screen” has been known for many years. Such screens comprise a series of strong, parallel, spaced apart bars that are used to separate large rocks and other debris from material of smaller size Such screens provide a relatively coarse size separation and are typically used to separate oversize rocks from smaller materials, such as in a gravel plant, a road construction project or quarry. 
     Typically, a grizzly screen will utilize parallel steel bars which are in a fixed position relative to each other and be spaced about 4-6 inches apart. Thus, the grizzly apparatus will separate rocks and other materials having a dimension greater than the bar spacing from smaller sized materials passing through the screen. 
     As unsorted debris is dropped onto the screen, objects which are smaller than the bar spacing slip between the bars into a receiving bin, flume, truck or conveyer. Objects larger than the bar spacing cannot slip between the bars and will roll and/or slide to the lower end of the screen and fall therefrom. The plane of the grizzly bars may vary depending upon the application, but is typically at an angle of about 20 degrees to encourage such rolling and sliding of the larger objects. 
     A major problem with grizzly screens is that objects having at least one dimension only slightly larger than the bar spacing tend to become jammed between the bars of the screen. These obstructions prevent or retard the discharge of subsequently encountered objects, and the screening capacity increasingly deteriorates. Often such jammed objects require manual removal from the screen using a crowbar, sledge hammer and the like. 
     It is known to manufacture a grizzly screen whose bars have tapered cross-sections wherein the bottom of each bar is narrower than the top, thus increasing the likelihood that objects passing downward through the screen will not become jammed between the bars This innovation does not, however, prevent all jamming of the screen and serious jamming problems still occur. 
     It is desirable to reduce the amount of manual contact which an operator must devote to the removal of jammed obstructures from the grizzly screen. Typically each removal effort requires the operator to remove four to six inch or larger rock from the bars with a heavy crowbar or sledge hammer, and any reduction of such manual clearing work decreases the risk of accident or injury. In addition, some materials sorted by the screen may be of a toxic nature, and it is desirable to reduce manual handling of and close operator exposure to such materials as much as possible. 
     Still a further shortcoming of existing grizzly screens is that the bars forming such screen are usually rigidly connected to the screen frame and require considerable effort and tools to remove or replace damaged or worn bars. It is desirable to provide a positive attachment apparatus for the screen bars which also allows easy removal and replacement of the bars without tools. 
     An object of the invention is an improved grizzly screening apparatus which effectively provides for rapid and easy removal of oversize materials which become jammed between the grizzly bars and obstruct the screen. 
     An additional object of the invention is a grizzly screening apparatus which has a reduced down time for dislodging obstructions from the screen. 
     A further object of this invention is a grizzly screening apparatus having a controllable movement whereby obstructions may be freed without manual intervention with tools. 
     Another object of the invention is a grizzly screening apparatus in which obstructing objects may be removed without significantly changing the separation or tolerance characteristic of the screen. 
     Another object of the invention is a grizzly screening apparatus in which worn or bent bars may be easily and quickly replaced with minimal use of tools. 
     BRIEF SUMMARY OF THE INVENTION 
     A grizzly screening apparatus includes left and right side frame members which are interconnected by a transverse end member and at least one transverse crossbar fixed to the side frame members. Mounted on the frame and comprising a screen are a plurality of parallel solid metal, circular cross-section grizzly bars. Each grizzly bar has a first end which is pivotally held in a passageway in the transverse end member and so positioned therein as to prevent its unintended removal. The opposite, free ends of the grizzly bars interact with a stationary transverse comb member which comprises a vertically slotted horizontal member. The comb member has alternating deep bed and shallow bed slots into which the second ends of the grizzly bars are received. The grizzly screen is typically positioned above a receptacle such as a bin, flume, truck or conveyor. The screen is pivotable about a horizontal axis near its discharge end so that its transverse end member and the first ends of the grizzly bars attached thereto may be pivotally moved between a sorting position and a raised clearing position. 
     In the sorting position, where the screening operations are conducted, all of the grizzly bars have their second ends at about the same elevation, i.e. all grizzly bars are supported by at least one crossbar and are positioned near the upper ends of the slots of the comb member to about the same depth, in the comb member slots, regardless of the slot depth. In the raised clearing position, the second ends of some grizzly bars engage the shallow slot beds of the comb member while the second ends of other grizzly bars drop to a lower level in the deep slots. Thus, the second ends of the grizzly bars diverge from one another in elevation and spacing distance as the screen is pivoted upwardly to the clearing position. The second ends of the grizzly bars are held within the deep bed slots and shallow bed slots, and thus each bar moves in a vertical plane. As the screen moves from sorting to clearing position, the horizontal spacing between the adjacent grizzly bars remains essentially constant, while the actual spacing between bars increases as the second ends of the bars diverge as the angle of the screen with the horizontal is increased. 
     The pivot axis of the grizzly screen is so located toward the second ends of the grizzly bars that pivotal movement of the screen upwardly from a lower position results in engagement of some of the grizzly bars with the bottom of the shallow slots of the comb member, while alternate grizzly bars continue to drop to a lower level in the deep slots. As a result, the bars in the deep slots have their second ends lower than bars in the shallow slots, and the actual spacing between the second ends of adjacent bars increases. Because of this vertical bar movement and the accompanying increase in spacing, obstructions caught between the grizzly bars will come loose from the bars and roll or slide off the screen or pass through the screen, depending upon the size of the obstructing object. The increase in actual spacing is relatively small, so that the object rejection size or tolerance is not significantly changed. The simultaneous increase in slope and spacing of the grizzly bars results in enhanced rolling and sliding of obstructing materials from the screen, quickly and efficiently clearing objects from the screen. 
     The screen may be pivoted about the pivot axis by a hydraulic cylinder, electric motor or other device capable of lifting the screen. Any of these motive means may be equipped with a remote control device by which an operator may clear obstructions from the screen without leaving a front end loader or other vehicle. 
     The invention also includes a novel means for attaching the grizzly bars to the screen frame to provide positive retention of the bars, and to allow an operator to remove and quickly replace damaged or worn bars without tools. 
     These and other objects and advantages of the invention will be readily understood by reading the following description in conjunction with the accompanying figures of the drawings wherein like reference numerals have been applied to designate like elements throughout the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a left side view of a grizzly screen apparatus embodying the invention and shown in a sorting position over a receptacle; 
     FIG. 2 is a top view of the grizzly screen apparatus shown in FIG.  1  and taken from the direction of arrows  2 — 2  in FIG. 1; 
     FIG. 3 is a partial perspective side view of a grizzly bar retaining device associated with the grizzly screen apparatus and illustrating the manner in which grizzly bars are inserted in and retained by the screen frame; 
     FIG. 4 is a perspective side view of first embodiment of a grizzly bar comb member associated with the grizzly screen apparatus invention; 
     FIG. 5 is a perspective end view of a second embodiment of a comb member useable with the grizzly screen apparatus invention; 
     FIG. 6 is a partial diagrammatic front view of the grizzly bar comb member of FIG. 5, wherein the grizzly bars are in a position for screening; and 
     FIG. 7 is a partial diagrammatic front view of the grizzly bar comb member of FIG. 5, wherein the grizzly bars are in a screen clearing position. 
     FIG. 8 is a partial perspective view of a transverse end member embodying the invention and showing the configuration of slots that retain the grizzly bars. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, and particularly to FIGS. 1 and 2, an exemplary grizzly screen apparatus  10 , embodying the invention, is shown with a base  12  mounted on a receptacle  14 . The grizzly screen apparatus  10  includes a frame  16  in which a grizzly screen  18  is mounted. The frame  16  includes a left side member  20 , a right side member  22 , a transverse end member  24  fixed to and extending between the side members and one or more cross-arms  26  also extending between the side members and supporting the grizzly bars. A reinforcement member  35  extends between cross-arm  26  and end member  24 . The frame  16  is pivotable about a hinge means, here shown as hinge  28  having a transverse horizontal axis  30 , by a reversible controllable drive  32 , such as a pair of hydraulic cylinders  17  pivotally mounted between axis  11  on the base  12  and axis  13  on the frame  16 , with one such cylinder being positioned adjacent each side  20  and  22  of the frame  16 . 
     The grizzly screen  18  comprises a plurality, here shown as sixteen of generally parallel grizzly bars  34  having their first ends  36  supportively mounted in apertures  40  in the transverse end member  24 . 
     FIGS. 2,  4 ,  5  and  6  illustrate the plurality of slots of the comb member  46  that comprise a shallow bed slot  44   a  for receiving a primary grizzly bar  34   a  and a deep bed slot  44   b  for receiving a secondary grizzly bar  34   b . The shallow bed slot  44   a  is located on the comb member  46  adjacent to the deep bed slot  44   b . The shallow bed slot  44   a  has a length less than the length of the deep bed slot  44   b . Preferably, the shallow bed slot  44   a  length is at least half the length of the deep bed slot  44   b . The shallow bed slot  44   a  has a length at least as long as the width of the primary grizzly bar  34   a.    
     As shown in FIGS. 1 and 2, the second ends  38  of the grizzly bars  34  are positioned in slots  44   a  and slots  44   b  of a comb member  46 . As shown, the slots include alternating shallow bed slots  44   a  and deep bed slots  44   b  for adjacent pairs of grizzly bars where a first bar  34   a  and second bar  34   b  make up each such pair. The comb member  46  comprises a differential fulcrum for lowering the second ends  38   b  of second grizzly bars  34   b  relative to the second ends  38   b  of first grizzly bars  34   a , when the first ends  36  of the grizzly bars are raised by cylinders  17 , as the cylinders pivotally move the screen frame about axis  30 . The comb member  46  is shown in FIGS. 1 and 4 as a generally horizontal member attachable to the base  12  with fasteners such as bolts, not shown, passed through apertures  47 . It may alternatively be attached by welding or other means which will withstand the high forces placed thereon. 
     It should be understood that a primary series of grizzly bars, namely bars  34   a  move as a group when the frame  18  is raised and lowered and that the primary bars interact with shallow bed slots  44   a . Similarly a secondary series of grizzly bars, namely bars  34   b  also move as a group when the frame  18  is raised and lowered. These secondary bars  34   b  interact with deep bed slots  44   b . The screen is comprised of alternating primary and secondary bars  34   a  and  34   b , respectively, except at the center of the screen where two bars  34   a  are adjacent. 
     An alternate comb member  46   a  is shown in FIG.  5 . The comb member  46   a  is shown as being generally planar, with shallow bed and deep bed slots  44   a ,  44   b , respectively for holding primary and secondary grizzly bars  34   a ,  34   b , respectively. 
     The comb member  46  or  46   a  may be either planar or angled in any way which will intersect the grizzly bars  34 , providing a retention system when the screen is in sorting position and a differential fulcrum to separate the second ends  38   a ,  38   b  of the bars  34  when the frame is in its raised or clearing position. However, the use of the angled generally horizontal comb member  46  is preferred and generally has less tendency to prevent or retard rocks and the like from discharging from the screen  18 . 
     As shown in the drawings the comb member is preferably positioned so that the inner ends or beds  43   a  of shallow bed slots  44   a  are off-axis, i.e. are not coincident with pivot axis  30 . In addition, with the embodiment shown in FIG. 1, the distance  41   b  from the transverse end member  24  to the slot beds  43   a  should exceed the distance  41   a  from transverse end member  24  to the pivot axis  30 . Thus, as illustrated in FIGS. 4,  6  and  7 , the second ends  38   a ,  38   b  of the grizzly bars  34   a ,  34   b , respectively, will drop within slots  44   a ,  44   b , respectively, to engage the slot beds  43   a ,  43   b , respectively, and adjacent bars  34   a ,  34   b  will be differentially lowered as the frame  16  is raised. While the horizontal separation distance  54  (FIG. 6) between grizzly bars  34  remains substantially constant, the actual maximum separation distance  54   b  (FIG. 7) between adjacent bars  34  increases as bars  34   b  are lowered relative to bars  34   a . The actual maximum separation distance  54   b  between the centers of the bars is the product of the horizontal separation distance  54   a  between the centers of the bars and the secant of the angle  49 , where angle  49  is the angle shown in FIG. 7 between the plane  53  defined by the center lines of the grizzly bars  34   b  (or alternatively, bars  34   a ) and the longest line  55  connecting adjacent grizzly bars  34   a  and  34   b.    
     As shown in FIG. 2, various rock  48  or other objects having mixed sizes is dropped on the grizzly screen  18  and is separated thereby into (a) undersize materials  50  which pass downward in the spaces between the grizzly bars  34 , and (b) oversize rocks  52  which roll and slide down the grizzly bars  34  to be discharged from the second ends  38  of the grizzly bars, i.e. outside of the area covered by the screen  18 . 
     Referring now to FIG. 2, it has been found desirable to have primary grizzly bars  34   a  be longer than grizzly bars  34   b  so as to extend further outward from comb member  46  than the bars  34   b . Such an arrangement allows the operator of a front end loader to place his bucket below the extended bars  34   a  and raise the grizzly bars  34   a  by raising the bucket. Such a movement results in even greater separation between the second ends of the primary and secondary bars and allows the operator to dislodge the most stubbornly jammed obstructions from the screen. Desirable results are obtained when the primary bars  34   a  are about four inches longer than the secondary bars  34   b.    
     In FIG. 4, the grizzly screen  18  is shown in a raked or clearing position elevated above the normal operating or sorting position, shown in FIG. 1, in which sorting position all the grizzly bars  34   a ,  34   b  are parallel and substantially coplanar. Referring now to FIG. 1, the angle  58  of the upper edge  56  of base  12  with the horizontal is shown in FIG. 1 as approximately 23 degrees with the screen in the sorting position but may be between about 0 degrees, i.e. no slope and about 35 degrees depending upon the particular characteristics of the material to be sorted and the desired separation size. Typically, angle  58  is between about 15 and 30 degrees to provide the necessary gravitational force to move oversize materials  52  to the discharge ends, i.e. second ends  38  of the grizzly bars  34 . 
     As the screen is moved to the clearing position shown in FIG. 4, the angle between the screen and the base  12  increases, with the screen and bars preferably at an angle of about 75 degrees to the horizontal when the clearing position of FIG. 4 is reached. While an angle of about 75 degrees is preferred in order to permit a sufficient increase in inter-bar opening size and sufficient downward slope of the frame to release jammed obstructions from between the bars, it should be understood that the angle can be further increased or decreased by approximately 15 degrees to meet specific clearing conditions encountered at the work site. 
     The base  12  is formed to provide a sloped bed for the frame  16  and attached screen  18 . The base  12  is shown as having closed sides  62  and dimensionally fits atop the receptacle  14 . A downwardly directed opening  64  in the base  12  permits undersize material  50  to fall into the receptacle  14 . 
     The screen  18  is shown as comprising a plurality of parallel, solid metal grizzly bars  34 , each of which has a first end  36  retainably held by the transverse end member  24  in a way which permits bar  34  to move in a vertical plane about its first end  36  to some degree but prevents significant longitudinal or lateral movement of the bar. The grizzly bars  34  have a diameter W providing sufficient strength to prevent bending during the screening operations, and are spaced apart a distance  54  to define the desired separation size. 
     During screening operations, the grizzly bars  34  normally rest on the fixed transverse cross-arm(s)  26  and are also laterally restrained, being held in the slots  44   a  and the upper portions  42  (FIG. 5) of slots  44   b  of the comb member  46 . 
     Turning now to FIG. 3, each grizzly bar  34  is shown with a lock bar  82  affixed to the first end  36  thereof at a right angle with the bar axis  84 . The width X and thickness Z of the lock bar  82  are less than the grizzly bar diameter W, and the lock bar projects from the grizzly bar generally equally in opposite directions, having a typical overall length Y of about 1.2 to 2.0 times the grizzly bar diameter W. 
     The transverse end member  24  is shown as a rigid metal part of the frame  16  and may include a reinforcement member such as channel  24   a . The transverse end member  24  has a generally flat front  66 , a generally flat top  68 , and a generally arcuate transition portion  69  between the front and top. The transverse end member  24  has a plurality of inverted L or dogleg-shaped keyhole apertures  40  on its front  66  and transition portion  69 , one for each grizzly bar. As best shown in FIG. 8, each of the keyhole apertures  40  is shown with a vertical portion  70  which has a width A slightly larger than the grizzly bar diameter W, and a height B. The width A of the vertical portion  70  is preferably between about 1.01 and 1.2 times the grizzly bar diameter W and is sized so that the grizzly bar  34  may be moved freely up and down within the vertical portion  70  during insertion and removal. A “dogleg” slot  78  projects at about a right angle (either left or right) from the upper portion  76  of each keyhole aperture  40 . The width D of slot  78  is less than the grizzly bar diameter W but may be greater than the lock bar width X, or alternatively greater than the lock bar thickness Z. The length C of the dogleg slot  78  is preferably slightly greater than one-half of the lock bar length Y plus one-half of the grizzly bar diameter W, so that when the grizzly bar  34  is at the upper portion  76  and the grizzly bar is rotated clockwise about its axis  84  in direction  92  (FIG. 3) toward the dogleg slot  78 , the upper end of the lock bar  82  will pass through the dogleg slot  78 . 
     In the shown embodiment, the width D of slot  78  is greater than the lock bar thickness Z. The length C of the dogleg slot  78  added to the width A of the vertical portion  70  equals the length  79  of the keyhole aperture  40 . 
     Because of the slope of the grizzly bars  34 , during operation gravitational forces tend to maintain the grizzly bars in the steepest angle which can be achieved, i.e. parallel to the “fall line”, and prevent axial movement of the bars away from the transverse end member  24 . Thus, a grizzly bar  34  cannot be simply pulled from the keyhole aperture  40  or released by vibration, heavy loads and the like which are common to grizzly screening operations. Nevertheless, the grizzly bar  34  is easily and quickly removed from the transverse end member  24  by a particular coordinated movement of the bar. No bolts or other fasteners need to be removed. The dogleg slot  78  may project either to the right (as shown) or to the left of the vertical portion  70  of the keyhole aperture  40 . 
     Referring now to FIG. 3, to install a grizzly bar  34  in an aperture  40 , the operator first places the bar  34 , such as the left-most bar in FIG. 3, in an orientation generally parallel to but slightly above the plane of the screen  18 , with the lock bar  82  in the shown generally upright orientation. The grizzly bar is then lowered into vertical portion  70  of the aperture, keeping the lock bar  82  lateral to and confronting the dogleg slot  78 . When the grizzly bar nests in the curved bottom of the portion  70  of the slot, the operator rotates the grizzly bar clockwise about the bar axis  84  as illustrated by the center grizzly bar in FIG. 3 to allow the lock bar  82  to be rotated through the dogleg slot  78  and into the chamber between transverse end member  24  and channel  24   a . Finally the operator pulls the grizzly bar axially toward the comb member  46  or  46   a  to position the lock bar  82  against the rear face of surface  66  as illustrated by the right bar in FIG. 3, and thereby locks the grizzly bar into its operating position. The second end  38  of the grizzly bar is then aligned in an appropriate slot of the comb member  46  or  46   a . The bars may be easily removed and replaced by reversing this procedure. 
     In one typical application, the grizzly screen apparatus  10  may be set up for screening soil contaminated with toxic substances. Upwardly projecting shields  94  may be attached to two or three sides of the frame  16  to confine toxic materials to specific areas. A front-end loader may be used to excavate the contaminated soil and dump it on the grizzly screen  18 . Undersize materials  50  passing through the spaces  54  between the bars  34  fall into a bin or truck for transport to a treatment/disposal site. Large rocks or other oversize materials  52  are discharged separately for special handling. Any materials which do not pass through the screen  18  and which clog the screen are handled by manually actuating or remotely controlling the hydraulic cylinders  17  to lift the screen  18  to the clearing position, causing the obstructing objects to either pass through the screen or be discharged from the second ends  38  of the grizzly bars  34 . The hydraulic system is then manually actuated or remotely actuated to lower the screen  18  to the lower sorting position for continued screening. Remote control systems for hydraulic cylinders and the like are well known in the art. 
     The invention solves numerous problems presented by the prior art by combining the use of both angular elevation and changing of spacing of the grizzly bars  34 . First, an effective apparatus for clearing obstructions from the screen is achieved. Secondly, control of the clearing process may be done by remote control and without manual tools. Thirdly, the grizzly bars are attached without bolts, screws or other fasteners, and may be installed and removed easily and quickly. Downtime is minimized. A single operator in a front-end loader may control the entire operation without leaving the vehicle. The reduction in manual clearing operations enhances safety. 
     It is anticipated that various changes and modifications may be made in the structure, arrangement, operation and method of construction of the grizzly screening apparatus disclosed herein without departing from the spirit and scope of the invention as defined in the following claims.