Abstract:
Attachment apparatus by which a sifting screen is mounted to a tension rail of a shaker machine. The apparatus includes a portion of the sifting screen wherein a hem at the periphery thereof has a thickness smaller than that of an interior portion of the sifting screen. The hem portion further includes a wire cloth array which is cast in the hem portion. A shroud includes upper and lower segments which are folded back on each other. A hinge edge is thereby defined. Facing surfaces of the upper and lower segments of the shroud sandwich the hem portion of the sifting screen therebetween. Means are provided to inhibit movement of the facing surfaces across engaged surfaces of the hem portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part claiming priority of application Ser. No. 12/422,461, previously filed Apr. 13, 2009 under 35 U.S.C. §111(a). 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention deals broadly with large sifting apparatus used to size granular material as it is sifted by the apparatus. More narrowly, however, it is directed to screens, either the full sifting apparatus or modules thereof, used in classifying the granular material by size. A specific focus of the invention is structure employed to mount a screen to a mechanism for shaking the screen during the performance of the classification function. 
       BACKGROUND OF THE INVENTION 
       [0003]    Large aggregate sifting machinery for classifying material by size is well-known in the art. A number of problems are, however, prevalent with regard to such machinery. One problem is cost. Because of typically rapid deterioration, the useful life of an apparatus can be quite short. 
         [0004]    Another problem is clogging. Frequently, ambient dust can accumulate and fill holes through which the material to be classified passes. Depending upon various conditions such as moisture, obstruction of apertures can render such machinery at least temporarily non-operational. 
         [0005]    Another concern deals with transportability. Any number of components of such a sifting apparatus can be quite heavy, and such a machine can be rendered virtually immobile. 
         [0006]    A final issue which must be considered in the design of a sifting screen is the secure attachment and maintenance of a screen portion to a tension rail which circumscribes the location at which the screen portion is to be mounted. The screen portion must be securely attached and so maintained in order for the overall apparatus to function properly and securely. 
         [0007]    It is to these shortcomings and problems of the prior art that the present invention is directed. It is an improved sifting apparatus which addresses these problems and shortcomings. Because of the construction of an apparatus in accordance with the present invention, these shortcomings are overcome. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention is a sifting screen which includes a screen portion to be attached to a tension rail of a shaker apparatus. The screen portion, in turn, employs an apertured matrix defined by the intersection of segments which form the matrix. The matrix is made primarily of an elastomeric material having elastic properties that can allow the screen to operate under high tension without significant yield. A frame extends about at least a portion of the periphery of the matrix. The frame includes a plurality of hooks mounting the matrix of the screen portion to a shaker bed. With the matrix so disposed, the sifting screen can be used to sift a particular volume of material. The frame is shaped and sized relative to locations of attachment to the shaker bed. 
         [0009]    The matrix is afforded a degree of elasticity so that mounting of the screen portion to the shaker bed is accomplished by stretching and tensioning the matrix in such a way so as to form the screen over a bucker bar of the shaker bed. The screen portion is defined in part by a pair of opposite, generally arcuate, non-parallel edges, each of which has a relatively long radius of curvature. Mounting the screen portion to the shaker bed in a manner wherein alternate parallel edges carry mounting hooks causes the matrix surfaces to vibrate during sifting operations, wherein it generates a wave-like motion having longitudinal movement as well as surface vibration. Vibration of the matrix facilitates cleaning of the apparatus and does not permit specific particles and fine powder to accumulate. Consequent occluding of apertures in the screen portion is thereby obviated. 
         [0010]    It will be understood that, because of the elastic nature of the matrix, it can be folded for transportation. This enables the apparatus to be quite mobile. 
         [0011]    The hooks devised for mounting the matrix of the screen portion to a shaker bed are formed using a hem of the sifting screen portion. The hem is afforded a thickness smaller than that of an interior portion of the sifting screen. The hem can have a wire cloth array cast therein, but it will be understood that the hook can be formed even without using such an array. A shroud is formed by employment of a structure having upper and lower segments. Such segments are folded back upon each other to define a hinge, and wherein facing surfaces of the upper and lower segments define facing surfaces which sandwich the hem therebetween. The segments, it will be understood, pivot with respect to the hinge defined by manipulating the segments. Facing surfaces defined within the shroud sandwich the hem therebetween. 
         [0012]    If desired, means can be employed to inhibit movement of the facing surfaces across the hem portion. Such structure can take the form of a patch of expanded metal welded to each of the facing surfaces opposite one another. The expanded metal patches can have, defined therein, apertures, the edges of which include burrs. Such burrs, when the shroud upper and lower segments are pivoted about the hinge and brought into contact with the hem portion, dig into the hem. 
         [0013]    The shroud, when facing surfaces of the segments sandwich the hem portion therebetween, can be bent to define an angle. The angle is a function of the cross-section of the tension rail to which the sifting screen is to be attached. That is, the hook will be bent to an angle appropriate for securely attaching the sifting screen to the tension rail. 
         [0014]    The invention is thus an improved sifting screen apparatus. 
         [0015]    More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, appended claims and accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a top plan view of the screen portion of a sifting screen mechanism in accordance with the present invention; 
           [0017]      FIG. 2  is a side sectional view of a sifting screen as cast; 
           [0018]      FIG. 3  is a view similar to  FIG. 2  but with a hem portion flattened to a lesser thickness; 
           [0019]      FIG. 4  is a view similar to  FIGS. 2 and 3  illustrating attachment of a shroud structure; 
           [0020]      FIG. 5  is a view similar to  FIGS. 2-4  illustrating the bending of the shroud to attain an attachment configuration; and 
           [0021]      FIG. 6  is a top plan view illustrating an alternative, modular embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to the drawing figures wherein like reference numerals denote like elements throughout the several views,  FIG. 1  illustrates a sifting screen  10  in accordance with the present invention. The screen  10  includes a screen portion  12  formed by an apertured matrix  14 . The matrix  14  is formed from an elastomeric material. Typically, the matrix  14  is homogeneously elastomeric being formed of a material such as polyurethane, rubber or another polymer which, when tensioned, has a low yield with a targeted modulus of elasticity. The elastic nature of the matrix  14  is for a purpose discussed hereinafter. The matrix  14  is formed by a multiplicity of intersecting, elastic segments  26  of material. The intersecting segments  26  thereby define a multiplicity of apertures  18  through which a granular-like material can pass during a sifting operation of the screen  10 . 
         [0023]    The overall sifting screen  10  is typically substantially rectangular in shape, but it can assume other geometric configurations. It is defined by a pair of opposite, substantially linear edges  22  which extend parallel to, and on opposite sides of, a central axis  20 . Further, edges  24  of the sifting screen are defined by slightly outwardly bowed portions. The arcuate, bowed edges have a relatively large radius of curvature. Consequently, the bowing is relatively slight. 
         [0024]    Lateral edges  22  further provide frame sections  16 . These sections  16  would, it is intended, mount a plurality of hook members  28  as best seen in  FIGS. 2-5 . Hook members  28  are, typically, of a type and design as known in the prior art. They can be mounted along the generally parallel, lateral edges  22  of sifting screen  10 . They can be spaced at appropriate intervals for cooperative engagement with corresponding locations on a shaker bed (not shown). 
         [0025]      FIG. 2  shows a wire screen as cast. The particular screen illustrated utilizes a peripheral network of wires  30  running through the matrix. Typically, such a network is a continuation of such a network running through the matrix of the sifting screen  10 . 
         [0026]      FIG. 3  illustrates the segment of the cast material with a hem  32  thinner than the rest of the screen. It will be understood that the specific dimensions of the structure will vary depending upon the dimensions and parameters of the overall apparatus being used. For example, in one application, the width of the hem  32  can be made to extend approximately two feet to three feet. The thickness of the thinned hem  32 , in such an application, would be approximately three inches. 
         [0027]      FIG. 4  illustrates a shroud  33  having upper and lower segments, bent about a hinge portion, sandwiching the hem of the sifting screen therebetween. In order to effect a more secure capturing of the hem by the shroud, a patch of expanded metal  35  is shown as being secured to the facing surfaces of the shroud  33 . These expanded metal patches  35  would, typically, be welded to the upper and lower segments  40 ,  42  of the shroud. It will be understood, however, that any method of affixation would be appropriate. 
         [0028]    The expanded metal patches  35 , it is envisioned, have a plurality of apertures formed therein. The edges of the apertures include burrs (not shown). The burrs, when the shroud upper and lower segments  40 ,  42  are pivoted about the hinge  46  and brought into contact with the hem portion  32 , dig into the hem. It is contemplated that the apertures would be generally diamond-shaped to give significant holding. 
         [0029]    Referring to  FIG. 5 , it will be seen that the shroud  33  is bent back upon itself to form means for attaching the sifting screen to the tension rail to which it is to be mounted. That figure illustrates a portion of a tension rail  48  having an apex  50  which defines an angle measuring approximately 45 degrees. Consequently, the degree of bend of the shroud  33  will be approximately that same measure. 
         [0030]    As previously discussed, the screen portion and matrix  14  thereof are elastomeric in nature. The degree of this attribute afforded to the matrix  14  is a calculated figure which will enable the matrix  14  to be both stretched for mounting and appropriately tensioned to facilitate optimum operation of the sifting screen  10 . 
         [0031]    The bowing of forward and rearward edges  24  enables the sifting screen  10 , in operation, to not only vibrate to accomplish sifting of a granular material placed on an upper side thereof. Further, in view of the tensioning of the bowed edges  24 , longitudinal movement of the media along the screen portion will also be enabled. This results from the generation of a wave-like motion during sifting operations. When the screen is in tension along the A-A′ axis, the entire screen is subject to linear tension, for the most part, from one hook to another. This force tends to draw the screen sides  24  inward toward each other during operation at a high sifting motion and will display a vertical surface vibration with a wave-like profile perpendicular to the A-A′ plane. This phenomenon cannot be displayed in a rigid structure such as woven or welded wire screen or flat modular screen. 
         [0032]    As will be best seen in  FIGS. 2-5 , the apertures  18  employed in the matrix  14  are, it is intended, defined by tapered walls  30 , an aperture  18  having a smaller area at the top thereof than at the bottom. 
         [0033]    A sifting screen  10  thus structured is enabled to solve problems of the prior art. While the material forming the matrix  14  is not as strong as a more rigid material, it is more elastic and vibrant which allows for a high number of operating hours. It is also significantly less expensive. Consequently, the cost per time unit of operational life achieved is more desirable. 
         [0034]    Further, the sifting screen  10  in accordance with the present invention serves to optimize sifting operations. Because of the shape of apertures  18 , occluding is deterred. Occlusion is, however, also deterred by the vibration and longitudinal movement of the media being sifted. These motions, since they occur in unison, do not cause deformation of the screen opening, thus keeping the grading very much within the desired mix. In contrast, with thin wire, when vibrating, the opening gets bigger and the larger particles will go through causing an off spec material. 
         [0035]    The invention also facilitates transportability of the sifting screen  10 . The elastomeric materials used in manufacturing the matrix  14  tend to be considerably lighter than other materials used on sifting screens in the prior art and are foldable. 
         [0036]    A further embodiment of the invention (illustrated in  FIG. 6 ) is one which employs modular elements  34  wherein each can be stretched and mounted on a small modular frame  36 . The modular frames  36 , in turn, are fixed on a large flat frame  38 . While such an embodiment adds to the complexity of the apparatus, greater versatility is achieved. The modular elements  34 , when they are stretched along their edges, seal the edge of the overall apparatus along tension rails. Further, they also create the longitudinal motion previously discussed so that the screen assembly will vibrate up and down and move in a wave-like profile. 
         [0037]      FIG. 6  illustrates a large flat frame  38  capable of receiving multiple modular elements  34 . It will be understood that, while only one such element  34  is illustrated, that figure illustrates multiple other loci  40  at which small modular elements  34  could be attached. 
         [0038]    It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.