Abstract:
The present invention provides a screen assembly having a base, a screen box having a screen medium and a pair of mutually opposed bearings, a shaft having a pair of eccentric journals that are rotatably supported in the respective pair of mutually opposed bearings, and at least one articulated suspension assembly having a first leg having a first torsion joint and a second torsion joint, a second leg having a third torsion joint and a fourth torsion joint, and a third leg having a first end pivotably secured to the second torsion joint and a second end pivotably secured to the third torsion joint, for pivotally interconnecting the screen box and the base to dampen vibrations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. Provisional Patent Application No. 60/815,403 entitled “Suspended Double Eccentric Screen,” filed on Jun. 21, 2006, which is hereby incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a screen assembly for separating materials and, more particularly, to a screen assembly that prevents the vibrations from reaching the structural support.  
       BACKGROUND OF THE INVENTION  
       [0003]     Screens are used in the aggregate business for separating rock, crushed rock, gravel, sand, and the like (herein referred to as “material”) into various sizes. Screens typically comprise one or more screen decks containing a perforated screening medium that acts as a sieve, through which the material is separated. A charge of material is deposited on the receiving end of the screen deck and, as the material is conveyed to the discharge end, smaller material falls through the openings, leaving the larger material retained on the screen deck.  
         [0004]     Screens generally use a vibrating mechanism to assist in the separation process, as well as in the conveyance of the material towards the discharge end. The assembly typically includes a screen box having a screen deck and a common frame. Generally, the screen box is vibrated by a vibrating mechanism that is coupled to the common frame. The vibratory motion promotes stratification in the material bed, bringing the smaller material down to the screening medium surface to pass through the openings.  
         [0005]     Vibrating mechanisms may be characterized by the form of the vibration and the number of bearings used in the mechanism. Vibrating mechanisms may produce motions that include circular, elliptical, and straight-line reciprocal movement. For example, a suspended double eccentric screen utilizes a counter weight on a shaft to vibrate the screen box, and consequently the screen deck, in a circle-throw motion. The material is propelled toward the discharge end by the motion of the vibrating mechanism.  
         [0006]     Typically, the screen box for a suspended double eccentric screen is isolated from the support structure by coil springs, rubber buffers, or shear rubber mounts. Such support systems are costly and require a great deal of space, which may restrict maintenance access. In addition, such mounts generally have a high tolerance in shear rates and do not sufficiently restrict lateral movements that can damage machinery components such as bearings and shafts. Further, conventional springs often break in corrosive environments and on overloading. Therefore, there is a need for a screen and support system that allows a more cost-effective design, is easier to maintain, requires less space, has a longer service life, and restricts lateral movements in the support system.  
         [0007]     Additional information will be set forth in the description that follows, which will be obvious in part from the description or may be learned by practice of the invention.  
       SUMMARY OF THE INVENTION  
       [0008]     A screen assembly for separating material according to particle size is provided. The screen assembly may have a base, a screen box having a screen medium and a pair of mutually opposed bearings, a shaft having a pair of eccentric journals that are rotatably supported in the respective pair of mutually opposed bearings. The shaft is rotatable about its axis to vibrate the screen box. At least one articulated suspension assembly having a first leg having a first torsion joint and a second torsion joint, a second leg having a third torsion joint and a fourth torsion joint, and a third leg having a first end pivotably secured to the second torsion joint and a second end pivotably secured to the third torsion joint, pivotally interconnects the screen box and the base so that the first torsion joint is pivotally secured to the screen box and the fourth torsion joint is pivotally secured to the base so that vibrations acting upon the screen box are dampened so that substantially no vibrational forces are transmitted to the base. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0009]     Operation of the invention may be better understood by reference to the following detailed description taken in connection with the following illustrations, wherein:  
         [0010]      FIG. 1  is a side view of a suspended double eccentric screen with an articulated suspension assembly.  
         [0011]      FIG. 2A  is an end view of the suspended double eccentric screen of  FIG. 1 .  
         [0012]      FIG. 2B  is top view of  FIG. 2A .  
         [0013]      FIG. 3  is a side perspective view of the suspended double eccentric screen with an articulated suspension assembly.  
         [0014]      FIG. 4  is a schematic view of an articulated suspension assembly in an embodiment of the present invention.  
         [0015]      FIG. 5  is a side view of the articulated suspension assembly in an embodiment of the present invention.  
         [0016]      FIG. 6  is a top and side perspective view of the articulated suspension assembly.  
         [0017]      FIG. 7A  is a partial view of a torsion joint in a first position in an embodiment of the present invention.  
         [0018]      FIG. 7B  is a sectional view of a torsion joint in a second position in an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     While the present invention is described with reference to the embodiments described herein, it should be clear that the present invention should not be limited to such embodiments. Therefore, the description of the embodiments herein is illustrative of the present invention and should not limit the scope of the invention as claimed.  
         [0020]     Reference will now be made in detail to the embodiments of the invention, as illustrated in the accompanying figures. Embodiments of a screen assembly  10  are shown in  FIGS. 1 through 7 . As shown in  FIG. 1 , the screen assembly  10  generally has a screen box  20 , a double eccentric shaft  30 , and an articulated suspension assembly  35 ,  40 .  
         [0021]     As shown in  FIG. 2A , the screen box  20  is a rigid frame having substantially vertical side walls  45 ,  50 . The side walls  45 ,  50  may be positioned substantially parallel to each other and may extend longitudinally along the screen assembly  10 . As shown in  FIG. 2A , a screen deck  25  extends between the side walls  45 ,  50  and longitudinally along the length of the screen assembly  10 . In one embodiment, the screen deck may extend substantially horizontally between the side walls  45 ,  50 . A screen medium  53  may be connected to and/or secured to the screen deck  25 . The screen deck  25  may be cambered to permit proper screen medium tensioning. The screen box  20  (or screen deck  25 ) may have components, such as buffer strips, to increase the life of the screen medium  53 . The screening medium  53 , such as woven cloth or perforated plates, contains a plurality of openings of predetermined sizes for screening material according to particle size. The screen medium  53  may define an array of sieve-like openings of a predetermined size for allowing material up to a predetermined size to pass through the screen medium  53 .  
         [0022]     It is understood that a plurality of screen decks  25  may be used in a stacked arrangement in the screen box  20 , one above the other, to separate material into multiple sizes. In one embodiment (not shown), a three-deck screen may be provided with an upper, middle, and lower screen deck, the upper screen deck having the largest openings, the middle screen deck having smaller openings, and the lower screen deck having the smallest openings. In such embodiments, the larger material is retained on the upper screen deck and removed from the screen deck at the upper discharge end. Likewise, the medium-sized material is retained on the middle screen deck and removed from the screen deck at the middle discharge end, the smaller size material is retained on the lower screen deck and removed from the screen deck at the lower discharge end, and the smallest material is deposited below the lower screen deck.  
         [0023]     As best shown in  FIG. 2A , the screen assembly  10  is provided with a shaft  30  for imparting vibrational movement to the screen box  20 . The shaft  30  may be double eccentric, meaning that journals  55 ,  60  are offset from the centerline of the shaft  30 . As shown in  FIG. 2A , journals  55  are positioned between journals  60  along shaft  30 . As shown in  FIG. 3 , a drive  63 , such as an electric motor, may be secured to either sidewall  45 ,  50 , or the base  80 . In some embodiments, the drive  63  may be coupled to the shaft  30  with a belt to rotate the shaft  30 .  
         [0024]     As shown in  FIG. 2A , the shaft  30  may be rotatably supported by bearings  65  and  70 . Bearings  65  are secured to the side walls  45 ,  50  and rotatably support the shaft  30  at journals  55 . Bearings  70  are positioned separate from screen box  20  and rotatably support the shaft  30  at outer journals  60 . It is understood that bearings  65 ,  70  may be spherical roller bearings having inner races fitted to the journals  55 ,  60  and outer races secured in housings, such as cast ductile iron bearing housings. Bearing seals may be provided to prevent grit or other foreign matter from reaching the bearings  65 ,  70 . Accordingly, bearings  65 ,  70  allow the shaft  30  to rotate in the bearings  65 ,  70  instead of sliding, so that the shaft  30  is not as inhibited by friction.  
         [0025]     One or more balance (or fly) wheels  75  may be provided on shaft  30  to balance the screen assembly  10 . In one embodiment, the balance wheels  75  may be positioned along the shaft  30  on either side of the screen box  20  to dynamically balance the screen assembly  10 . In one embodiment, as best shown in  FIG. 2A , the balance wheels  75  may be secured to each end of the shaft  30  between the bearings  65 ,  70 . The centrifugal force of the rotating balance wheels  75  creates the circular motion of screen box  20  and a circular motion of bearings  70 . To minimize the vibrations reaching the base  80 , the circular motion of the bearing  70  is offset 180 degrees from the circular motion of the screen box  20  by the opposite eccentricities of the shaft journals  55  and  60 . It is understood that the balance wheels  75  may be made from any material, such as steel, and may have adjustable weights so as to provide proper balancing.  
         [0026]     As best shown in  FIG. 1 , the screen box  20  is suspended by at least one articulated suspension assembly  35 . As shown in  FIGS. 1 and 2 B, suspension assembly  35  may be secured to brackets  82  that extend substantially perpendicularly outward from side walls  45 ,  50 . In addition, at least one suspension assembly  40  may be secured to bearing supports  83 , which are separate from the screen box  20 . The resulting configuration allows for free-floating action of the screen box  20  and permits the shaft  30  to find its natural center of rotation without placing strain or thrust on the bearings  65 ,  70 . As shown in  FIG. 1 , the articulated suspension assembly  35 ,  40  may be secured to a common base  80 . It is understood that in some embodiments, the base  80  may be a supporting structure  85 , such as the floor. Further, as shown in  FIG. 1 , the screen assembly  10  may be installed at an angle. In one embodiment, the screen assembly  10  may be installed at an angle of up to about 25 degrees.  
         [0027]      FIG. 4  shows a schematic view of one embodiment of the articulated suspension assemblies  35 ,  40 . The articulated suspension assemblies  35 ,  40  may have an assembly of arms (or legs)  107 , each arm  107  having torsion joints  108 ,  109  capable of dampening vibrations. The arms  107  may be interconnected via a linkage (or leg)  125  at the torsion joints  108 . In some embodiments, the arms  107  may be secured directly to machinery and the base  80  at torsion joints  109 . In other embodiments, the arms  107  may also be secured to top and bottom base members  100 ,  105  at the torsion joints  109 . Top and bottom base members  100 ,  105  provide convenient platforms for securing (and removing) suspension assemblies  35 ,  40  to machinery components. As shown in  FIG. 3 , brackets  82 ,  83 , may be secured to the top base member  100  and base  80  may be secured to the bottom base member  105 .  
         [0028]      FIGS. 5, 6  show an exterior side view of one embodiment of the articulated suspension assemblies  35 ,  40 . In such an embodiment, the torsion joints  108 ,  109  may have four rubber members  110  positioned about a core  115  such that the core  115  is not in contact with the joint housing (inside arm  107 ). In one embodiment, the core  115  may have a square shape. As illustrated in  FIG. 5 , the top base member  100  and bottom base member  105  are secured to the core  115  (of joints  109 ) with pins or bolts  120 . Linkage  125  may be secured to the core  115  (of joints  108 ) with one or more pins or bolts  120  to create an articulated linkage such that relative movement transferred from the screen box  20  and outside bearings  70  to base member  100  is dampened. It is understood that arms  107 , base members  100 ,  105 , and the core  115  may be made of any rigid material such as aluminum. In a preferred embodiment, the suspension assembly  35 ,  40  is of the type supplied by ROSTA AG, Hauptstrasse 58, CH-5502 Hunzenschwil, manufactured under the name ROSTA Type AB-D. It is understood, however, that the torsion joints  108 ,  109  should not be deemed as limited to any specific shape, type, or configuration. One of ordinary skill in the art will appreciate the use of various shapes, types, and configurations of torsion joints  108 ,  109 . Illustrative examples may include torsion springs, gas cylinders, and single elastomoric members with and without a core  115 .  
         [0029]     Turning now to the screen assembly  10 , an example of how to use the screen assembly  10  as illustrated in  FIGS. 1-7  is set forth below. A motor  63  coupled to shaft  30  may be energized to rotate the shaft  30 . Accordingly, the eccentric rotation of the shaft  30  vibrates the screen box  20 . The balance wheels  75  counterbalance the shaft  30  so as to generate the positive circle-throw motion of the screen box  20 , as well as the circular motion of the bearings  70 . Therefore, as material is fed at feed end  78  (as shown in  FIG. 3 ) and is placed upon the screen medium  53 , the vibration causes material smaller than the predetermined size to fall through the openings of the screen medium  53  so as to separate the smaller material from the larger material. The larger material is conveyed across the screen medium  53  by the circle-throw action and is discharged at a location separate from the discharge location of the smaller material. The circle-throw action makes it possible for the screen assembly  10  to both convey and screen the material in a continuous manner.  
         [0030]     The combination of the articulated suspension assemblies  35 ,  40  with a suspended eccentric screen provides an unique suspension system, which combines the functionality of springs, dampers, and bearings. As shown in  FIG. 4 , as vibration occurs, forces are applied collinearly to both ends of the suspension assemblies  35 ,  40 . In some embodiments, as shown in  FIGS. 4, 7A , and  7 B, the collinear forces are transferred via arms  107  to core  115  in torsion joints  108 ,  109 , thereby causing the core  115  to pivot and impart shear to the rubber inserts  110 . The resulting molecular friction within the rubber inserts  110  in turn creates reaction forces similar to a spring, thereby dampening the vibration.  
         [0031]     In addition, due to the free-floating configuration of the screen box  20  and the 180 degree offset of the journals  55 ,  60 , the dynamic reaction forces resulting from the circular motion of the screen box  20  are directionally opposite to the dynamic reaction forces of the bearings  70 . Therefore, the dynamic reaction forces acting on suspension assemblies  35 ,  40  cancel each other out, thereby allowing no substantial dynamic reaction forces to be transmitted from the base frame  80  to the supporting structure  85 .  
         [0032]     Accordingly, use of the articulated suspension assemblies  35 ,  40  with a suspended double eccentric screen box  20  provides spring rates with lower tolerances than those of shear rubber mounts and increases the accuracy of the suspension system, which in turn extends the life of machinery components such as the shaft  30  and bearings  65 ,  70 . The overall dimensions of the articulated arm suspension assemblies  35 ,  40  are smaller than the commonly-used shear rubber mounts, thereby decreasing the vertical clearance necessary to install the screen assembly  10 . Additionally, the top and bottom base members  100 ,  105  provide a less complicated design, allowing for easy installation and removal of the suspension assemblies  35 ,  40 .  
         [0033]     The invention has been described above and, obviously, modifications and alternations will occur to others upon the reading and understanding of this specification. The claims as follows are intended to include all modifications and alterations insofar, as they come within the scope of the claims or the equivalent thereof.