Abstract:
Screening members, screening assemblies, methods for fabricating screening members and assemblies and methods for screening materials are provided for vibratory screening machines that incorporate the use of injection molded materials. Use of injection molded screen elements provide, inter alia, for: varying screening surface configurations; fast and relatively simple screen assembly fabrication; and a combination of outstanding screen assembly mechanical and electrical properties, including toughness, wear and chemical resistance. Embodiments of the present invention use a thermoplastic injection molded material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. Nos. 61/652,039 filed May 25, 2012, and 61/714,882 filed Oct. 17, 2012. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to material screening. More particularly, the present disclosure relates to screening members, screening assemblies, methods for fabricating screening members and assemblies and methods for screening materials. 
       BACKGROUND 
       [0003]    Material screening includes the use of vibratory screening machines. Vibratory screening machines provide the capability to excite an installed screen such that materials placed upon the screen may be separated to a desired level. Oversized materials are separated from undersized materials. Over time, screens wear and require replacement. As such, screens are designed to be replaceable. 
         [0004]    Replacement screen assemblies must be securely fastened to a vibratory screening machine and are subjected to large vibratory forces. Replacement screens may be attached to a vibratory screening machine by tensioning members, compression members or clamping members. 
         [0005]    Replacement screen assemblies are typically made of metal or a thermoset polymer. The material and configuration of the replacement screens are specific to a screening application. For example, due to their relative durability and capacity for fine screening, metal screens are frequently used for wet applications in the oil and gas industry. Traditional thermoset polymer type screens (e.g., molded polyurethane screens), however, are not as durable and would likely not withstand the rough conditions of such wet applications and are frequently utilized in dry applications, such as applications in the mining industry. 
         [0006]    Fabricating thermoset polymer type screens is relatively complicated, time consuming and prone to errors. Typical thermoset type polymer screens that are used with vibratory screening machines are fabricated by combining separate liquids (e.g., polyester, polyether and a curative) that chemically react and then allowing the mixture to cure over a period of time in a mold. When fabricating screens with fine openings, e.g., approximately 43 microns to approximately 100 microns, this process can be extremely difficult and time consuming. Indeed, to create fine openings in a screen, the channels in the molds that the liquid travels through have to be very small (e.g., on the order of 43 microns) and all too often the liquid does not reach all the cavities in the mold. As a result, complicated procedures are often implemented that require close attention to pressures and temperatures. Since a relatively large single screen (e.g., two feet by three feet or larger) is made in a mold, one flaw (e.g., a hole, i.e., a place where the liquid did not reach) will ruin the entire screen. Thermoset polymer screens are typically fabricated by molding an entire screen assembly structure as one large screening piece and the screen assembly may have openings ranging from approximately 43 microns to approximately 4000 microns in size. The screening surface of conventional thermoset polymer screens normally have a uniform flat configuration. 
         [0007]    Thermoset polymer screens are relatively flexible and are often secured to a vibratory screening machine using tensioning members that pull the side edges of the thermoset polymer screen away from each other and secure a bottom surface of the thermoset polymer screen against a surface of a vibratory screening machine. To prevent deformation when being tensioned, thermoset polymer assemblies may be molded with aramid fibers that run in the tensioning direction (see, e.g., U.S. Pat. No. 4,819,809). If a compression force were applied to the side edges of the typical thermoset polymer screens it would buckle or crimp, thereby rendering the screening surface relatively ineffective. 
         [0008]    In contrast to thermoset polymer screens, metal screens are rigid and may be compressed or tensioned onto a vibratory screening machine. Metal screen assemblies are often fabricated from multiple metal components. The manufacture of metal screen assemblies typically includes: fabricating a screening material, often three layers of a woven wire mesh; fabricating an apertured metal backing plate; and bonding the screening material to apertured metal backing plate. The layers of wire cloth may be finely woven with openings in the range of approximately 30 microns to approximately 4000 microns. The entire screening surface of conventional metal assemblies is normally a relatively uniform flat configuration or a relatively uniform corrugated configuration. 
         [0009]    Critical to screening performance of screen assemblies (thermoset polymer assemblies and metal type assemblies) for vibratory screening machines are the size of the openings in the screening surface, structural stability and durability of the screening surface, structural stability of the entire unit, chemical properties of the components of the unit and ability of the unit to perform in various temperatures and environments. Drawbacks to conventional metal assemblies include lack of structure stability and durability of the screening surface formed by the woven wire mesh layers, blinding (plugging of screening openings by particles) of the screening surface, weight of the overall structure, time and cost associated with the fabrication or purchase of each of the component members, and assembly time and costs. Because wire cloth is often outsourced by screen manufacturers, and is frequently purchased from weavers or wholesalers, quality control can be extremely difficult and there are frequently problems with wire cloth. Flawed wire cloth may result in screen performance problems and constant monitoring and testing is required. 
         [0010]    One of the biggest problems with conventional metal assemblies is blinding. A new metal screen may initially have a relatively large open screening area but over time, as the screen is exposed to particles, screening openings plug (i.e., blind) and the open screening area, and effectiveness of the screen itself, is reduced relatively quickly. For example, a 140 mesh screen assembly (having three layers of screen cloth) may have an initial open screening area of 20-24%. As the screen is used, however, the open screening area may be reduced by 50% or more. 
         [0011]    Conventional metal screen assemblies also lose large amounts of open screening area because of their construction, which includes adhesives, backing plates, plastic sheets bonding layers of wire cloth together, etc. 
         [0012]    Another major problem with conventional metal assemblies is screen life. Conventional metal assemblies don&#39;t typically fail because they get worn down but instead fail due to fatigue. That is, the wires of the woven wire cloth often actually break due to the up and down motion they are subject to during vibratory loading. 
         [0013]    Drawbacks to conventional thermoset polymer screens also include lack of structure stability and durability. Additional drawbacks include inability to withstand compression type loading and inability to withstand high temperatures (e.g., typically a thermoset polymer type screen will begin to fail or experience performance problems at temperatures above 130° F., especially screens with fine openings, e.g., approximately 43 microns to approximately 100 microns). Further, as discussed above, fabrication is complicated, time consuming and prone to errors. Also, the molds used to fabricate thermoset polymer screens are expensive and any flaw or the slightest damage thereto will ruin the entire mold and require replacement, which may result in costly downtime in the manufacturing process. 
         [0014]    Another drawback to both conventional metal and thermoset polymer screens is the limitation of screen surface configurations that are available. Existing screening surfaces are fabricated with relatively uniform opening sizes throughout and a relatively uniform surface configuration throughout, whether the screening surface is flat or undulating. 
         [0015]    The conventional polymer type screens referenced in U.S. Provisional Application No. 61/652,039 (also referred to therein as traditional polymer screens, existing polymer screens, typical polymer screens or simply polymer screens) refer to the conventional thermoset polymer screens described in U.S. Provisional Patent Application Ser. No. 61/714,882 and the conventional thermoset polymer screens described herein (also referred to herein and in U.S. Provisional Patent Application Ser. No. 61/714,882 as traditional thermoset polymer screens, existing thermoset polymer screens, typical thermoset polymer screens or simply thermoset screens). Accordingly, the conventional polymer type screens referenced in U.S. Provisional Application No. 61/652,039 are the same conventional thermoset polymer screens reference herein, and in U.S. Provisional Patent Application Ser. No. 61/714,882, and may be fabricated with extremely small screening openings (as described herein and in U.S. Provisional Patent Application Ser. No. 61/714,882) but have all the drawbacks (as described herein and in U.S. Provisional Patent Application Ser. No. 61/714,882) regarding conventional thermoset polymer screens, including lack of structural stability and durability, inability to withstand compression type loading, inability to withstand high temperatures and complicated, time consuming, error prone fabrication methods. 
         [0016]    There is a need for versatile and improved screening members, screening assemblies, methods for fabricating screening members and assemblies and methods for screening materials for vibratory screening machines that incorporate the use of injection molded materials (e.g., thermoplastics) having improved mechanical and chemical properties. 
       SUMMARY 
       [0017]    The present disclosure is an improvement over existing screen assemblies and methods for screening and fabricating screen assemblies and parts thereof. The present invention provides extremely versatile and improved screening members, screening assemblies, methods for fabricating screening members and assemblies and methods for screening materials for vibratory screening machines that incorporate the use of injection molded materials having improved properties, including mechanical and chemical properties. In certain embodiments of the present invention a thermoplastic is used as the injection molded material. The present invention is not limited to thermoplastic injection molded materials and in embodiments of the present invention other materials may be used that have similar mechanical and/or chemical properties. In embodiments of the present invention, multiple injection molded screen elements are securely attached to subgrid structures. The subgrids are fastened together to form the screen assembly structure, which has a screening surface including multiple screen elements. Use of injection molded screen elements with the various embodiments described herein provide, inter alia, for: varying screening surface configurations; fast and relatively simple screen assembly fabrication; and a combination of outstanding screen assembly mechanical, chemical and electrical properties, including toughness, wear and chemical resistance. 
         [0018]    Embodiments of the present invention include screen assemblies that are configured to have relatively large open screening areas while having structurally stable small screening openings for fine vibratory screening applications. In embodiments of the present invention, the screening openings are very small (e.g., as small as approximately 43 microns) and the screen elements are large enough (e.g., one inch by one inch, one inch by two inches, two inches by three inches, etc.) to make it practical to assemble a complete screen assembly screening surface (e.g., two feet by three feet, three feet by four feet, etc.). Fabricating small screening openings for fine screening applications requires injection molding very small structural members that actually form the screening openings. These structural members are injection molded to be formed integrally with the screen element structure. Importantly, the structural members are small enough (e.g., in certain applications they may be on the order of approximately 43 microns in screening surface width) to provide an effective overall open screening area and form part of the entire screen element structure that is large enough (e.g., two inches by three inches) to make it practical to assemble a relatively large complete screening surface (e.g., two feet by three feet) therefrom. 
         [0019]    In one embodiment of the present invention a thermoplastic material is injection molded to form screening elements. Previously thermoplastics have not been used with the fabrication of vibratory screens with fine size openings (e.g., approximately 43 microns to approximately 1000 microns) because it would be extremely difficult, if not impossible, to thermoplastic injection mold a single relatively large vibratory screening structure having fine openings and obtain the open screening area necessary for competitive performance in vibratory screening applications. 
         [0020]    According to an embodiment of the present disclosure, a screen assembly is provided that: is structurally stable and can be subjected to various loading conditions, including compression, tensioning and clamping; can withstand large vibrational forces; includes multiple injection molded screen elements that, due to their relatively small size, can be fabricated with extremely small opening sizes (having dimensions as small as approximately 43 microns); eliminates the need for wirecloth; is lightweight; is recyclable; is simple and easy to assemble; can be fabricated in multiple different configurations, including having various screen opening sizes throughout the screen and having various screening surface configurations, e.g., various combinations of flat and undulating sections; and can be fabricated with application-specific materials and nanomaterials. Still further, each screen assembly may be customized to a specific application and can be simply and easily fabricated with various opening sizes and configurations depending on the specifications provided by an end user. Embodiments of the present disclosure may be applied to various applications, including wet and dry applications and may be applied across various industries. The present invention is not limited to the oil and gas industry and the mining industry, it may be utilized in any industry that requires separation of materials using vibratory screenings machines, including pulp and paper, chemical, pharmaceuticals and others. 
         [0021]    In an example embodiment of the present invention, a screen assembly is provided that substantially improves screening of materials using a thermoplastic injection molded screen element. Multiple thermoplastic polymer injection molded screen elements are securely attached to subgrid structures. The subgrids are fastened together to form the screen assembly structure, which has a screening surface including multiple screen elements. Each screen element and each subgrid may have different shapes and configurations. Thermoplastic injection molding individual screen elements allows for precise fabrication of screening openings, which may have dimensions as small as approximately 43 microns. The grid framework may be substantially rigid and may provide durability against damage or deformation under the substantial vibratory load burdens it is subjected to when secured to a vibratory screening machine. Moreover, the subgrids, when assembled to form the complete screen assembly, are strong enough not only to withstand the vibratory loading, but also the forces required to secure the screen assembly to the vibratory screening machine, including large compression loads, tension loads and/or clamping loads. Still further, the openings in the subgrids structurally support the screen elements and transfer vibrations from the vibratory screening machine to the elements forming the screening openings thereby optimizing screening performance. The screen elements, subgrids and/or any other component of the screen assembly may include nanomaterials and/or glass fibers that, in addition to other benefits, provide durability and strength. 
         [0022]    According to an example embodiment of the present disclosure, a screen assembly is provided having a screen element including a screen element screening surface with a series of screening openings and a subgrid including multiple elongated structural members forming a grid framework having grid openings. The screen element spans at least one of the grid openings and is attached to a top surface of the subgrid. Multiple independent subgrids are secured together to form the screen assembly and the screen assembly has a continuous screen assembly screening surface having multiple screen element screening surfaces. The screen element includes substantially parallel end portions and substantially parallel side edge portions substantially perpendicular to the end portions. The screen element further includes a first screen element support member and a second screen element support member orthogonal to the first screen element support member. The first screen element support member extends between the end portions and is approximately parallel to the side edge portions. The second screen element support member extends between the side edge portions and is approximately parallel to the end portions. The screen element includes a first series reinforcement members substantially parallel to the side edge portions and a second series of reinforcement members substantially parallel to the end portions. The screen element screening surface includes screen surface elements forming the screening openings. The end portions, side edge portions, first and second support members and first and second series of reinforcement members structurally stabilize screen surface elements and screening openings. The screen element is formed as a single thermoplastic injection molded piece. 
         [0023]    The screening openings may be rectangular, square, circular, and oval or any other shape. The screen surface elements may run parallel to the end portions and form the screening openings. The screen surface elements may also run perpendicular to the end portions and form the screen openings. Different combinations of rectangular, square, circular and oval screening openings (or other shapes) may be incorporated together and depending on the shape utilized may run parallel and/or perpendicular to the end portions. 
         [0024]    The screen surface elements may run parallel to the end portions and may be elongated members forming the screening openings. The screening openings may be elongated slots having a distance of approximately 43 microns to approximately 4000 microns between inner surfaces of adjacent screen surface elements. In certain embodiments, the screen openings may have a distance of approximately 70 microns to approximately 180 microns between inner surfaces of adjacent screen surface elements. 
         [0025]    In other embodiments, the screening openings may have a distance of approximately 43 microns to approximately 106 microns between inner surfaces of adjacent screen surface elements. In embodiments of the present invention, the screening openings may have a width and a length, the width may be about 0.043 mm to about 4 mm and the length may be about 0.086 mm to about 43 mm. In certain embodiments, the width to length ratio may be approximately 1:2 to approximately 1:1000. 
         [0026]    Multiple subgrids of varying sizes may be combined to form a screen assembly support structure for screen elements. Alternatively, a single subgrid may be thermoplastic injection molded, or otherwise constructed, to form the entire screen assembly support structure for multiple individual screen elements. 
         [0027]    In embodiments that use multiple subgrids, a first subgrid may include a first base member having a first fastener that mates with a second fastener of a second base member of a second subgrid, the first and second fasteners securing the first and second subgrids together. The first fastener may be a clip and the second fastener may be a clip aperture, wherein the clip snaps into the clip aperture and securely attaches the first and second subgrids together. 
         [0028]    The first and second screen element support members and the screen element end portions may include a screen element attachment arrangement configured to mate with a subgrid attachment arrangement. The subgrid attachment arrangement may include elongated attachment members and the screen element attachment arrangement may include attachment apertures that mate with the elongated attachment members securely attaching the screen element to the subgrid. A portion of the elongated attachment members may be configured to extend through the screen element attachment apertures and slightly above the screen element screening surface. The attachment apertures may include a tapered bore or may simply include an aperture without any tapering. The portion of the elongated attachment members above the screening element screening surface may be melted and may fill the tapered bore, fastening the screen element to the subgrid. Alternatively, the portion of the elongated attachment members that extends through and above the aperture in screening element screening surface may be melted such that it forms a bead on the screening element screening surface and fastens the screen element to the subgrid. 
         [0029]    The elongated structural members may include substantially parallel subgrid end members and substantially parallel subgrid side members substantially perpendicular to the subgrid end members. The elongated structural members may further include a first subgrid support member and a second subgrid support member orthogonal to the first subgrid support member. The first subgrid support member may extend between the subgrid end members and may be approximately parallel to the subgrid side members. The second subgrid support member may extend between the subgrid side members and may be approximately parallel to the subgrid end members, and substantially perpendicular to the subgrid edge members. 
         [0030]    The grid framework may include a first and a second grid framework forming a first and a second grid opening. The screen elements may include a first and a second screen element. The subgrid may have a ridge portion and a base portion. The first and second grid frameworks may include first and second angular surfaces that peak at the ridge portion and extend downwardly from the peak portion to the base portion. The first and second screen elements may span the first and second angular surfaces, respectively. 
         [0031]    According to an example embodiment of the present invention, a screen assembly is provided having a screen element including a screen element screening surface with a series of screening openings and a subgrid including multiple elongated structural members forming a grid framework having grid openings. The screen element spans at least one grid opening and is secured to a top surface of the subgrid. Multiple subgrids are secured together to form the screen assembly and the screen assembly has a continuous screen assembly screening surface comprised of multiple screen element screening surfaces. The screen element is a single thermoplastic injection molded piece. 
         [0032]    The screen element may include substantially parallel end portions and substantially parallel side edge portions substantially perpendicular to the end portions. The screen element may further include a first screen element support member and a second screen element support member orthogonal to the first screen element support member. The first screen element support member may extend between the end portions and may be approximately parallel to the side edge portions. The second screen element support member may extend between the side edge portions and may be approximately parallel to the end portions. The screen element may include a first series reinforcement members substantially parallel to the side edge portions and a second series of reinforcement members substantially parallel to the end portions. The screen element may include elongated screen surface elements running parallel to the end portions and forming the screening openings. The end portions, side edge portions, first and second support members, first and second series of reinforcement members may structurally stabilize the screen surface elements and the screening openings. 
         [0033]    The first and second series of reinforcement members may have a thickness less than a thickness of the end portions, side edge portions and the first and second screen element support members. The end portions and the side edge portions and the first and second screen element support members may form four rectangular areas. The first series of reinforcement members and the second series of reinforcement members may form multiple rectangular support grids within each of the four rectangular areas. The screening openings may have a width of approximately 43 microns to approximately 4000 microns between inner surfaces of each of the screen surface elements. In certain embodiments, the screening openings may have a width of approximately 70 microns to approximately 180 microns between inner surfaces of each of the screen surface elements. In other embodiments, the screening openings may have a width of approximately 43 microns to approximately 106 microns between inner surfaces of each of the screen surface elements. In embodiments of the present invention, the screening openings may have a width of about 0.043 mm to about 4 mm and length of about 0.086 mm to about 43 mm. In certain embodiments, the width to length ratio may be approximately 1:2 to approximately 1:1000. 
         [0000]    The screen elements may be flexible. 
         [0034]    The subgrid end members, the subgrid side members and the first and second subgrid support members may form eight rectangular grid openings. A first screen element may span four of the grid openings and a second screen element may span the other four openings. 
         [0035]    A central portion of the screening element screening surface may slightly flex when subject to a load. The subgrid may be substantially rigid. The subgrid may also be a single thermoplastic injection molded piece. At least one of the subgrid end members and the subgrid side members may include fasteners configured to mate with fasteners of other subgrids, which fasteners may be clips and clip apertures that snap into place and securely attach the subgrids together. 
         [0036]    The subgrid may include: substantially parallel triangular end pieces, triangular middle pieces substantially parallel to the triangular end pieces, a first and second mid support substantially perpendicular to the triangular end pieces and extending between the triangular end pieces, a first and second base support substantially perpendicular to the triangular end pieces and extending the between the triangular end pieces and a central ridge substantially perpendicular to the triangular end pieces and extending the between the triangular end pieces. A first edge of the triangular end pieces, the triangular middle pieces, and the first mid support, the first base support and the central ridge may form a first top surface of the subgrid having a first series of grid openings. A second edge of the triangular end pieces, the triangular middle pieces, and the second mid support, the second base support and the central ridge may form a second top surface of the subgrid having a second series of grid openings. The first top surface may slope down from the central ridge to the first base support and the second top surface may slope down from the central ridge to the second base support. A first and a second screen element may span the first series and second series of grid openings, respectively. The first edges of the triangular end pieces, the triangular middle pieces, the first mid support, the first base support and the central ridge may include a first subgrid attachment arrangement configured to securely mate with a first screen element attachment arrangement of the first screen element. The second edges of the triangular end pieces, the triangular middle pieces, the second mid support, the second base support and the central ridge may include a second subgrid attachment arrangement configured to securely mate with a second screen element attachment arrangement of the second screen element. The first and second subgrid attachment arrangements may include elongated attachment members and the first and second screen element attachment arrangements may include attachment apertures that mate with the elongated attachment members thereby securely attaching the first and second screen elements to the first and second subgrids, respectively. A portion of the elongated attachment members may extend through the screen element attachment apertures and slightly above a first and second screen element screening surface. 
         [0037]    The first and second screen elements each may include substantially parallel end portions and substantially parallel side edge portions substantially perpendicular to the end portions. The first and second screen elements may each include a first screen element support member and a second screen element support member orthogonal to the first screen element support member, the first screen element support member extending between the end portions and being approximately parallel to the side edge portions, the second screen element support member extending between the side edge portions and may be approximately parallel to the end portions. The first and second screen elements may each include a first series reinforcement members substantially parallel to the to the side edge portions and a second series of reinforcement members substantially parallel to the end portions. The first and second screen elements may each include elongated screen surface elements running parallel to the end portions and forming the screening openings. The end portions, side edge portions, first and second support members, first and second series of reinforcement members may structurally stabilize screen surface elements and screening openings. 
         [0038]    One of the first and second base supports may include fasteners that secure the multiple subgrids together, which fasteners may be clips and clip apertures that snap into place and securely attach subgrids together. 
         [0039]    The screen assembly may include a first, a second, a third and a fourth screen element. The first series of grid openings may be eight openings formed by the first edge of the triangular end pieces, the triangular middle pieces, and the first mid support, the first base support and the central ridge. The second series of grid openings may be eight openings formed by the second edge of the triangular end pieces, the triangular middle pieces, the second mid support, the second base support and the central ridge. The first screen element may span four of the grid openings of the first series of grid openings and the second screen element may span the other four openings of the first series of grid openings. The third screen element may span four of the grid openings of the second series of grid openings and the fourth screen element may span the other four openings of the second series of grid openings. A central portion of the first, second, third and fourth screening element screening surfaces may slightly flex when subject to a load. The subgrid may be substantially rigid and may be a single thermoplastic injection molded piece. 
         [0040]    According to an example embodiment of the present disclosure, a screen assembly is providing having a screen element including a screen element screening surface with screening openings and a subgrid including a grid framework with grid openings. The screen element spans the grid openings and is attached to a surface of the subgrid. Multiple subgrids are secured together to form the screen assembly and the screen assembly has a continuous screen assembly screening surface that includes multiple screen element screening surfaces. The screen element is a thermoplastic injection molded piece. 
         [0041]    The screen assembly may also include a first thermoplastic injection molded screen element and a second thermoplastic injection molded screen element and the grid framework may include a first and second grid framework forming a first grid opening and a second grid opening. The subgrid may include a ridge portion and a base portion, the first and second grid frameworks including first and second angular surfaces that peak at the ridge portion and extend downwardly from the peak portion to the base portion. The first and second screen elements may span the first and second angular surfaces, respectively. The first and second angular surfaces may include a subgrid attachment arrangement configured to securely mate with a screen element attachment arrangement. The subgrid attachment arrangement may include elongated attachment members and the screen element attachment arrangement may include apertures that mate with the elongated attachment members thereby securely attaching the screen elements to the subgrid. 
         [0042]    The subgrid may be substantially rigid and may be a single thermoplastic injection molded piece. A section of the base portion may include a first and a second fastener that secure the subgrid to a third and a fourth fastener of another subgrid. The first and third fasteners may be clips and the second and fourth fasteners may be clip apertures. The clips may snap into clip apertures and securely attach the subgrid and the another subgrid together. 
         [0043]    The subgrids may form a concave structure and the continuous screen assembly screening surface may be concave. The subgrids may form a flat structure and the continuous screen assembly screening surface may be flat. The subgrids may form a convex structure and the continuous screen assembly screening surface may be convex. 
         [0044]    The screen assembly may be configured to form a predetermined concave shape when subjected to a compression force by a compression assembly of a vibratory screening machine against at least one side member of the vibratory screen assembly when placed in the vibratory screening machine. The predetermined concave shape may be determined in accordance with a shape of a surface of the vibratory screening machine. The screen assembly may have a mating surface mating the screen assembly to a surface of the vibratory screening machine, which mating surface may be rubber, metal (e.g., steel, aluminum, etc.), a composite material, a plastic material or any other suitable material. The screen assembly may include a mating surface configured to interface with a mating surface of a vibratory screening machine such that the screen assembly is guided into a fixed position on the vibratory screening machine. The mating surface may be formed in a portion of at least one subgrid. The screen assembly mating surface may be a notch formed in a corner of the screen assembly or a notch formed approximately in the middle of a side edge of the screen assembly. The screen assembly may have an arched surface configured to mate with a concave surface of the vibratory screening machine. The screen assembly may have a substantially rigid structure that does not substantially deflect when secured to the vibratory screening machine. The screen assembly may include a screen assembly mating surface configured such that it forms a predetermined concave shape when subjected to a compression force by a member of a vibratory screening machine. The screen assembly mating surface may be shaped such that it interfaces with a mating surface of the vibratory screening machine such that the screen assembly may be guided into a predetermined location on the vibratory screening machine. The screen assembly may include a load bar attached to an edge surface of the subgrid of the screen assembly, the load bar may be configured to distribute a load across a surface of the screen assembly. The screen assembly may be configured to form a predetermined concave shape when subjected to a compression force by a compression member of a vibratory screening machine against the load bar of the vibratory screen assembly. The screen assembly may have a concave shape and may be configured to deflect and form a predetermined concave shape when subjected to a compression force by a member of a vibratory screening machine. 
         [0045]    A first set of the subgrids may be formed into center support frame assemblies having a first fastener arrangement. A second set of the subgrids may be formed into a first end support frame assembly having a second fastener arrangement. A third set of the subgrids may be formed into a second end support frame assembly having a third fastener arrangement. The first, second, and third fastener arrangements may secure the first and second end support frames to the center support assemblies. A side edge surface of the first end support frame assembly may form a first end of the screen assembly. A side edge surface of the second end support frame arrangement may form a second end of the screen assembly. An end surface of each of the first and second end support frame assemblies and center support frame assemblies may cumulatively form a first and a second side surface of the complete screen assembly. The first and second side surfaces of the screen assembly may be substantially parallel and the first and second end surfaces of the screen assembly may be substantially parallel and substantially perpendicular to the side surfaces of the screen assembly. The side surfaces of the screen assembly may include fasteners configured to engage at least one of a binder bar and a load distribution bar. The subgrids may include side surfaces such that when individual subgrids are secured together to form the first and second end support frame assemblies and the center support frame assembly that the first and second end support frame assemblies and the center support frame assembly each form a concave shape. The subgrids may include side surfaces shaped such that when individual subgrids are secured together to form the first and second end support frame assemblies and the center support frame assembly that the first and second end support frame assemblies and the center support frame assembly each form a convex shape. 
         [0046]    The screen elements may be affixed to the subgrids by at least one of a mechanical arrangement, an adhesive, heat staking and ultrasonic welding. 
         [0047]    According to an example embodiment of the present disclosure, a screen element is provided having: a screen element screening surface with screen surface elements forming a series of screening openings; a pair of substantially parallel end portions; a pair of substantially parallel side edge portions substantially perpendicular to the end portions; a first screen element support member; a second screen element support member orthogonal to the first screen element support member, the first screen element support member extending between the end portions and being approximately parallel to the side edge portions, the second screen element support member extending between the side edge portions and being approximately parallel to the end portions and substantially perpendicular to the side edge portions; a first series of reinforcement members substantially parallel to the side edge portions; and a second series of reinforcement members substantially parallel to the end portions. The screen surface elements run parallel to the end portions. The end portions, side edge portions, first and second support members, first and second series of reinforcement members structurally stabilize screen surface elements and screening openings, and the screen element is a single thermoplastic injection molded piece. 
         [0048]    According to an example embodiment of the present disclosure, a screen element is provided having a screen element screening surface with screen surface elements forming a series of screening openings; a pair of substantially parallel end portions; and a pair of substantially parallel side edge portions substantially perpendicular to the end portions. The screen element is a thermoplastic injection molded piece. 
         [0049]    The screen element may also have a first screen element support member; a second screen element support member orthogonal to the first screen element support member, the first screen element support member extending between the end portions and being approximately parallel to the side edge portions, the second screen element support member extending between the side edge portions and being approximately parallel to the end portions; a first series of reinforcement members substantially parallel to the side edge portions; and a second series of reinforcement members substantially parallel to the end portions. The screen surface elements may run parallel to the end portions. In certain embodiments, the screen surface elements may also be configured to run perpendicular to the end portions. The end portions, side edge portions, first and second support members, first and second series of reinforcement members may structurally stabilize screen surface elements and screening openings. 
         [0050]    The screen element may also have a screen element attachment arrangement molded integrally with the screen element and configured to mate with a subgrid attachment arrangement. Multiple subgrids may form a screen assembly and the screen assembly may have a continuous screen assembly screening surface that includes multiple screen element screening surfaces. 
         [0051]    According to an example embodiment of the present disclosure, a method for fabricating a screen assembly for screening materials is provided that includes: determining screen assembly performance specifications for the screen assembly; determining a screening opening requirement for a screen element based on the screen assembly performance specifications, the screen element including a screen element screening surface having screening openings; determining a screen configuration based on the screen assembly performance specifications, the screen configuration including having the screen elements arranged in at least one of flat configuration and a nonflat configuration; injection molding the screen elements with a thermoplastic material; fabricating a subgrid configured to support the screen elements, the subgrid having a grid framework with grid openings wherein at least one screen element spans at least one grid opening and is secured to a top surface of the subgrid, the top surface of each subgrid including at least one of a flat surface and a nonflat surface that receives the screen elements; attaching the screen elements to the subgrids; attaching multiple subgrid assemblies together to form end screen frames and center screen frames; attaching the end screen frames to the center screen frames to form a screen frame structure; attaching a first binder bar to a first end of the screen frame structure; and attaching a second binder bar to a second end of the screen frame structure to form the screen assembly, the screen assembly having a continuous screen assembly screening surface comprised of multiple screen element screening surfaces. 
         [0052]    The screen assembly performance specifications may include at least one of dimensions, material requirements, open screening area, cut point, and capacity requirements for a screening application. A handle may be attached to the binder bar. A tag may be attached to the binder bar, which tag may include a performance description of the screen assembly. At least one of the screen element and the subgrid may be a single thermoplastic injection molded piece. The thermoplastic material may include a nanomaterial. The subgrid may include at least one base member having fasteners that mate with fasteners of other base members of other subgrids and secure the subgrids together. The fasteners may be clips and clip apertures that snap into place and securely attach the subgrids together. 
         [0053]    According to an example embodiment of the present disclosure, a method for fabricating a screen assembly for screening materials is provided by injection molding a screen element with a thermoplastic material, the screen element including a screen element screening surface having screening openings; fabricating a subgrid that supports the screen element, the subgrid having a grid framework with grid openings, the screen element spanning at least one grid opening; securing the screen element to a top surface of the subgrid; and attaching multiple subgrid assemblies together to form the screen assembly, the screen assembly having a continuous screen assembly screening surface made of multiple screen element screening surfaces. The method may also include attaching a first binder bar to a first end of the screen assembly and attaching a second binder bar to a second end of the screen assembly. The first and second binder bars may bind the subgrids together. The binder bar may be configured to distribute a load across the first and second ends of the screen assembly. The thermoplastic material may include a nanomaterial. 
         [0054]    According to an example embodiment of the present disclosure, a method for screening a material is provided by attaching a screen assembly to a vibratory screening machine, the screen assembly including a screen element having a series of screening openings forming a screen element screening surface and a subgrid including multiple elongated structural members forming a grid framework having grid openings. Screen elements span grid openings and are secured to a top surface of the subgrid. Multiple subgrids are secured together to form the screen assembly. The screen assembly has a continuous screen assembly screening surface comprised of multiple screen element screening surfaces. The screen element is a single thermoplastic injection molded piece. The material is screened using the screen assembly. 
         [0055]    According to an example embodiment of the present disclosure, a method for screening a material is provided including attaching a screen assembly to a vibratory screening machine and forming a top screening surface of the screen assembly into a concave shape. The screen assembly includes a screen element having a series of screening openings forming a screen element screening surface and a subgrid including multiple elongated structural members forming a grid framework having grid openings. Screen elements span grid openings and are secured to a top surface of the subgrid. Multiple subgrids are secured together to form the screen assembly and the screen assembly has a continuous screen assembly screening surface comprised of multiple screen element screening surfaces. The screen element is a single thermoplastic injection molded piece. The material is screened using the screen assembly. 
         [0056]    Example embodiments of the present disclosure are described in more detail below with reference to the appended Figures. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0057]      FIG. 1  is an isometric view of a screen assembly, according to an exemplary embodiment of the present invention. 
           [0058]      FIG. 1A  is an enlarged view of a break out portion of the screen assembly shown in  FIG. 1 . 
           [0059]      FIG. 1B  is a bottom isometric view the screen assembly shown in  FIG. 1 . 
           [0060]      FIG. 2  is an isometric top view of a screen element, according to an exemplary embodiment of the present invention. 
           [0061]      FIG. 2A  is a top view of the screen element shown in  FIG. 2 . 
           [0062]      FIG. 2B  is a bottom isometric view of the screen element shown in  FIG. 2 . 
           [0063]      FIG. 2C  is a bottom view of the screen element shown in  FIG. 2 . 
           [0064]      FIG. 2D  is an enlarged top view of a break out portion of the screen element shown in  FIG. 2 . 
           [0065]      FIG. 3  is a top isometric view of an end subgrid, according to an exemplary embodiment of the present invention. 
           [0066]      FIG. 3A  is a bottom isometric view of the end subgrid shown in  FIG. 3 . 
           [0067]      FIG. 4  is a top isometric view of a center subgrid, according to an exemplary embodiment of the present invention. 
           [0068]      FIG. 4A  is a bottom isometric view of the center subgrid shown in  FIG. 4 . 
           [0069]      FIG. 5  is a top isometric view of a binder bar, according to an exemplary embodiment of the present invention. 
           [0070]      FIG. 5A  is a bottom isometric view of the binder bar shown in  FIG. 5 . 
           [0071]      FIG. 6  is an isometric view of a screen subassembly, according to an exemplary embodiment of the present invention. 
           [0072]      FIG. 6A  is an exploded view of the subassembly shown in  FIG. 6 . 
           [0073]      FIG. 7  is a top view of the screen assembly shown in  FIG. 1 . 
           [0074]      FIG. 7A  is an enlarged cross-section of Section A-A of the screen assembly shown in  FIG. 7 . 
           [0075]      FIG. 8  is a top isometric view of a screen assembly partially covered with screen elements, according to an exemplary embodiment of the present invention. 
           [0076]      FIG. 9  is an exploded isometric view of the screen assembly shown in  FIG. 1 . 
           [0077]      FIG. 10  is an exploded isometric view of an end subgrid showing screen elements prior to attachment to the end subgrid, according to an exemplary embodiment of the present invention. 
           [0078]      FIG. 10A  is an isometric view of the end subgrid shown in  FIG. 10  having the screen elements attached thereto. 
           [0079]      FIG. 10B  is a top view of the end subgrid shown in  FIG. 10A . 
           [0080]      FIG. 10C  is a cross-section of Section B-B of the end subgrid shown in  FIG. 10A . 
           [0081]      FIG. 11  is an exploded isometric view of a center subgrid showing screen elements prior to attachment to the center subgrid, according to an exemplary embodiment of the present invention. 
           [0082]      FIG. 11A  is an isometric view of the center subgrid shown in  FIG. 11  having the screen elements attached thereto. 
           [0083]      FIG. 12  is an isometric view of a vibratory screening machine having screen assemblies with concave screening surfaces installed thereon, according to an exemplary embodiment of the present invention. 
           [0084]      FIG. 12A  is an enlarged isometric view of the discharge end of the vibratory screening machine shown in  FIG. 12 . 
           [0085]      FIG. 12B  is a front view of the vibratory screening machine shown in  FIG. 12 . 
           [0086]      FIG. 13  is an isometric view of a vibratory screening machine with a single screening surface having screen assemblies with concave screening surfaces installed thereon, according to an exemplary embodiment of the present invention. 
           [0087]      FIG. 13A  is a front view of the vibratory screening machine shown in  FIG. 13 . 
           [0088]      FIG. 14  is a front view of a vibratory screening machine having two separate concave screening surfaces with preformed screen assemblies installed upon the vibratory screening machine, according to an exemplary embodiment of the present invention. 
           [0089]      FIG. 15  is a front view of a vibratory screening machine having a single screening surface with a preformed screen assembly installed upon the vibratory screening machine, according to an exemplary embodiment of the present invention. 
           [0090]      FIG. 16  is an isometric view of an end support frame subassembly, according to an exemplary embodiment of the present invention. 
           [0091]      FIG. 16A  is an exploded isometric view of the end support frame subassembly shown in  FIG. 16 . 
           [0092]      FIG. 17  is an isometric view of a center support frame subassembly, according to an exemplary embodiment of the present invention. 
           [0093]      FIG. 17A  is an exploded isometric view of the center support frame subassembly shown in  FIG. 17 . 
           [0094]      FIG. 18  is an exploded isometric view of a screen assembly, according to an exemplary embodiment of the present invention. 
           [0095]      FIG. 19  is a top isometric view of a flat screen assembly, according to an exemplary embodiment of the present invention. 
           [0096]      FIG. 20  is a top isometric view of a convex screen assembly, according to an exemplary embodiment of the present invention. 
           [0097]      FIG. 21  is an isometric view of a screen assembly having pyramidal shaped subgrids, according to an exemplary embodiment of the present invention. 
           [0098]      FIG. 21A  is an enlarged view of section D of the screen assembly shown in  FIG. 21 . 
           [0099]      FIG. 22  is a top isometric view of a pyramidal shaped end subgrid, according to an exemplary embodiment of the present invention. 
           [0100]      FIG. 22A  is a bottom isometric view of the pyramidal shaped end subgrid shown in  FIG. 22 . 
           [0101]      FIG. 23  is a top isometric view of a pyramidal shaped center subgrid, according to an exemplary embodiment of the present invention. 
           [0102]      FIG. 23A  is a bottom isometric view of the pyramidal shaped center subgrid shown in  FIG. 23 . 
           [0103]      FIG. 24  is an isometric view of a pyramidal shaped subassembly, according to an exemplary embodiment of the present invention. 
           [0104]      FIG. 24A  is an exploded isometric view of the pyramidal shaped subassembly shown in  FIG. 24 . 
           [0105]      FIG. 24B  is an exploded isometric view of a pyramidal shaped end subgrid showing screen elements prior to attachment to the pyramidal shaped end subgrid. 
           [0106]      FIG. 24C  is an isometric view of the pyramidal shaped end subgrid shown in  FIG. 24B  having the screen elements attached thereto. 
           [0107]      FIG. 24D  is an exploded isometric view of a pyramidal shaped center subgrid showing screen elements prior to attachment to the pyramidal shaped center subgrid, according to an exemplary embodiment of the present invention. 
           [0108]      FIG. 24E  is an isometric view of the pyramidal shaped center subgrid shown in  FIG. 24D  having the screen elements attached thereto. 
           [0109]      FIG. 25  is a top view of a screen assembly having pyramidal shaped subgrids, according to an exemplary embodiment of the present invention. 
           [0110]      FIG. 25A  is a cross-section view of Section C-C of the screen assembly shown in  FIG. 25 . 
           [0111]      FIG. 25B  is an enlarged view of Section C-C shown in  FIG. 25A . 
           [0112]      FIG. 26  is an exploded isometric view of a screen assembly having pyramidal shaped and flat subassemblies, according to an exemplary embodiment of the present invention. 
           [0113]      FIG. 27  is an isometric view of a vibratory screening machine with two screening surfaces having assemblies with concave screening surfaces installed thereon wherein the screen assemblies include pyramidal shaped and flat subassemblies, according to an exemplary embodiment of the present invention. 
           [0114]      FIG. 28  is a top isometric view of a screen assembly having pyramidal shaped and flat subgrids without screen elements, according to an exemplary embodiment of the present invention. 
           [0115]      FIG. 29  is a top isometric view of the screen assembly shown in  FIG. 28  where the subgrids are partially covered with screen elements. 
           [0116]      FIG. 30  is a front view of a vibratory screening machine with two screening surfaces having assemblies with concave screening surfaces installed thereon where the screen assemblies include pyramidal shaped and flat subgrids, according to an exemplary embodiment of the present invention. 
           [0117]      FIG. 31  is a front view of a vibratory screening machine with a single screen surface having an assembly with a concave screening surface installed thereon where the screen assembly includes pyramidal shaped and flat subgrids, according to an exemplary embodiment of the present invention. 
           [0118]      FIG. 32  is a front view of a vibratory screening machine with two screening surfaces having preformed screen assemblies with flat screening surfaces installed thereon where the screen assemblies include pyramidal shaped and flat subgrids, according to an exemplary embodiment of the present invention. 
           [0119]      FIG. 33  is a front view of a vibratory screening machine with a single screening surface having a preformed screen assembly with a flat screening surface installed thereon where the screen assembly includes pyramidal shaped and flat subgrids, according to an exemplary embodiment of the present invention. 
           [0120]      FIG. 34  is an isometric view of the end subgrid shown in  FIG. 3  having a single screen element partially attached thereto, according to an exemplary embodiment of the present invention. 
           [0121]      FIG. 35  is an enlarged view of break out Section E of the end subgrid shown in  FIG. 34 . 
           [0122]      FIG. 36  is an isometric view of a screen assembly having pyramidal shaped subgrids in a portion of the screen assembly, according to an exemplary embodiment of the present invention. 
           [0123]      FIG. 37  is a flow chart of a screen assembly fabrication, according to an exemplary embodiment of the present invention. 
           [0124]      FIG. 38  is a flow chart of a screen assembly fabrication, according to an exemplary embodiment of the present invention. 
           [0125]      FIG. 39  an isometric view of a vibratory screening machine having a single screen assembly with a flat screening surface installed thereon with a portion of the vibratory machine cut away showing the screen assembly, according to an exemplary embodiment of the present invention. 
           [0126]      FIG. 40  is an isometric top view of an individual screen element, according to an exemplary embodiment of the present invention. 
           [0127]      FIG. 40A  is an isometric top view of a screen element pyramid, according to an exemplary embodiment of the present invention. 
           [0128]      FIG. 40B  is an isometric top view of four of the screen element pyramids shown in  FIG. 40A . 
           [0129]      FIG. 40C  is an isometric top view of an inverted screen element pyramid, according to an exemplary embodiment of the present invention. 
           [0130]      FIG. 40D  is a front view of the screen element shown in  FIG. 40C . 
           [0131]      FIG. 40E  is an isometric top view of a screen element structure, according to an exemplary embodiment of the present invention. 
           [0132]      FIG. 40F  is a front view of the screen element structure shown in  FIG. 40E . 
           [0133]      FIGS. 41 to 43  are front cross-sectional profile views of screen elements, according to exemplary embodiments of the present invention. 
           [0134]      FIG. 44  is an isometric top view of a prescreening structure with prescreen assemblies according to an exemplary embodiment of the present invention. 
           [0135]      FIG. 44A  is an isometric top view of the prescreen assembly shown in  FIG. 44 , according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0136]    Like reference characters denote like parts in several drawings. 
         [0137]    Embodiments of the present invention provide a screen assembly that includes injection molded screen elements that are mated to a subgrid. Multiple subgrids are securely fastened to each other to form the vibratory screen assembly, which has a continuous screening surface and is configured for use on a vibratory screening machine. The entire screen assembly structure is configured to withstand rigorous loading conditions encountered when mounted and operated on a vibratory screening machine. Injection molded screen elements provide for many advantages in screen assembly manufacturing and vibratory screening applications. In certain embodiments of the present invention, screen elements are injection molded using a thermoplastic material. 
         [0138]    Embodiments of the present invention provide injection molded screen elements that are of a practical size and configuration for manufacture of vibratory screen assemblies and for use in vibratory screening applications. Several important considerations have been taken into account in the configuration of individual screen elements. Screen elements are provided that: are of an optimal size (large enough for efficient assembly of a complete screen assembly structure yet small enough to injection mold (micromold in certain embodiments) extremely small structures forming screening openings while avoiding freezing (i.e., material hardening in a mold before completely filling the mold)); have optimal open screening area (the structures forming the openings and supporting the openings are of a minimal size to increase the overall open area used for screening while maintaining, in certain embodiments, very small screening openings necessary to properly separate materials to a specified standard); have durability and strength, can operate in a variety of temperature ranges; are chemically resistant; are structural stable; are highly versatile in screen assembly manufacturing processes; and are configurable in customizable configurations for specific applications. 
         [0139]    Embodiments of the present invention provide screen elements that are fabricated using extremely precise injection molding. The larger the screen element the easier it is to assemble a complete vibratory screening assembly. Simply put, the fewer pieces there are to put together. However, the larger the screen element the more difficult it is to injection mold extremely small structures, i.e. the structures forming the screening openings. It is important to minimize the size of the structures forming the screening openings so as to maximize the number of screening openings on an individual screen element and thereby optimize the open screening area for the screening element and thus the overall screen assembly. In certain embodiments, screen elements are provided that are large enough (e.g., one inch by one inch, one inch by two inches, two inches by three inches, etc.) to make it practical to assemble a complete screen assembly screening surface (e.g., two feet by three feet, three feet by four feet, etc.). The relatively “small size” (e.g., one inch by one inch, one inch by two inches, two inches by three inches, etc.) is fairly large when micromolding extremely small structural members (e.g., structural members as small as 43 microns). The larger the size of the overall screen element and the smaller the size of the individual structural members forming the screening openings the more prone the injection molding process is to errors such as freezing. Thus, the size of the screen elements must be practical for screen assembly manufacture while at the same time small enough to eliminate problems such as freezing when micromolding extremely small structures. Sizes of screening elements may very based on the material being injection molded, the size of the screening openings required and the overall open screening area desired. 
         [0140]    Open screening area is a critical feature of vibratory screen assemblies. The average usable open screening area (i.e., actual open area after taking into account the structural steel of support members and bonding materials) for traditional 100 mesh to 200 mesh wire screen assemblies may be in the range of 16%. Specific embodiments of the present invention (e.g., screening assemblies with constructions described herein and having 100 mesh to 200 mesh screen openings) provide screen assemblies in the same range having a similar actual open screening areas. Traditional screens, however, blind fairly quickly in the field which results in the actual opening screening area being reduced fairly quickly. It is not uncommon for traditional metal screens to blind within the first 24 hours of use and to have the actual open screening area reduced by 50%. Traditional wire assemblies also frequently fail as a result of wires being subjected to vibratory forces which place bending loads of the wires. Injection molded screen assemblies, according to embodiments of the present invention, in contrast, are not subject to extensive blinding (thereby maintaining a relatively constant actual open screening area) and rarely fail because of the structural stability and configuration of the screen assembly, including the screen elements and subgrid structures. In fact, screen assemblies according to embodiments of the present invention have extremely long lives and may last for long periods of time under heaving loading. Screen assemblies according to the present invention have been tested for months under rigorous conditions with out failure or blinding whereas traditional wire assemblies were tested under the same conditions and blinded and failed within days. As more fully discussed herein, traditional thermoset type assemblies could not be used in such applications. 
         [0141]    In embodiments of the present invention a thermoplastic is used to injection mold screen elements. As opposed to thermoset type polymers, which frequently include liquid materials that chemically react and cure under temperature, use of thermoplastics is often simpler and may be provided, e.g., by melting a homogeneous material (often in the form of solid pellets) and then injection molding the melted material. Not only are the physical properties of thermoplastics optimal for vibratory screening applications but the use of thermoplastic liquids provides for easier manufacturing processes, especially when micromolding parts as described herein. The use of thermoplastic materials in the present invention provides for excellent flexure and bending fatigue strength and is ideal for parts subjected to intermittent heavy loading or constant heavy loading as is encountered with vibratory screens used on vibratory screening machines. Because vibratory screening machines are subject to motion, the low coefficient of friction of the thermoplastic injection molded materials provides for optimal wear characteristics. Indeed, the wear resistance of certain thermoplastics is superior to many metals. Further, use of thermoplastics as described herein provides an optimal material when making “snap-fits” due to its toughness and elongation characteristics. The use of thermoplastics in embodiments of the present invention also provides for resistance to stress cracking, aging and extreme weathering. The heat deflection temperature of thermoplastics is in the range of 200° F. With the addition of glass fibers, this will increase to approximately 250° F. to approximately 300° F. or greater and increase rigidity, as measured by Flexural Modulus, from approximately 400,000 PSI to over approximately 1,000,000 PSI. All of these properties are ideal for the environment encountered when using vibratory screens on vibratory screening machines under the demanding conditions encounter in the field. 
         [0142]      FIG. 1  illustrates a screen assembly  10  for use with vibratory screening machines. Screen assembly  10  is shown having multiple screen elements  16  (See, e.g., FIGS.  2  and  2 A- 2 D) mounted on subgrid structures. The subgrid structures include multiple independent end subgrid units  14  (See, e.g.,  FIG. 3 ) and multiple independent center subgrid units  18  (See, e.g.,  FIG. 4 ) that are secured together to form a grid framework having grid openings  50 . Each screen element  16  spans four grid openings  50 . Although screen element  16  is shown as a unit covering four grid openings, screen elements may be provided in larger or smaller sized units. For example, a screen element may be provided that is approximately one-fourth the size of screen element  16  such that it would span a single grid opening  50 . Alternatively, a screen element may be provided that is approximately twice the size of screen element  16  such that it would span all eight grid openings of subgrid  14  or  18 . Subgrids may also be provided in different sizes. For example, subgrid units may be provided that have two grid openings per unit or one large subgrid may be provided for the overall structure, i.e., a single subgrid structure for the entire screen assembly. In  FIG. 1 , multiple independent subgrids  14  and  18  are secured together to form the screen assembly  10 . Screen assembly  10  has a continuous screen assembly screening surface  11  that includes multiple screen element screening surfaces  13 . Each screen element  16  is a single thermoplastic injection molded piece. 
         [0143]      FIG. 1A  is an enlarged view of a portion of the screen assembly  10  having multiple end subgrids  14  and center subgrids  18 . As discussed below, the end subgrids  14  and center subgrids  18  may be secured together to form the screen assembly. Screen elements  16  are shown attached to the end subgrids  14  and center subgrids  18 . The size of the screen assembly may be altered by attaching more or less subgrids together to form the screen assembly. When installed in a vibratory screening machine, material may be fed onto the screen assembly  10 . See, e.g.,  FIGS. 12 ,  12 A,  12 B,  13 ,  13 A,  14  and  15 . Material smaller than the screen openings of the screen element  16 , passes through the openings in screening element  16  and through the grid openings  50  thereby separating the material from that which is too big to pass through the screen openings of the screen elements  16 . 
         [0144]      FIG. 1B  shows a bottom view of the screen assembly  10  such that the grid openings  50  may be seen below the screen elements. Binder bars  12  are attached to sides of the grid framework. Binder bars  12  may be attached to lock subassemblies together creating the grid framework. Binder bars  12  may include fasteners that attach to fasteners on side members  38  of subgrid units ( 14  and  18 ) or fasteners on base member  64  of pyramidal subgrid units ( 58  and  60 ). Binder bars  12  may be provided to increase the stability of the grid framework and may distribute compression loads if the screen assembly is mounted to a vibratory screening machine using compression, e.g., using compression assemblies as described in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. Binder bars may also be provided that include U-shaped members or finger receiving apertures, for undermount or overmount tensioning onto a vibratory screening machine, e.g., see mounting structures described in U.S. Pat. Nos. 5,332,101 and 6,669,027. The screen elements and subgrids are securely attached together, as described herein, such that, even under tensioning, the screen assembly screening surface and screen assembly maintain their structural integrity. 
         [0145]    The screen assembly shown in  FIG. 1  is slightly concave, i.e., the bottom and top surfaces of the screen assembly have a slight curvature. Subgrids  14  and  18  are fabricated such that when they are assembled together this predetermined curvature is achieved. Alternatively, a screen assembly may be flat or convex (see, e.g.,  FIGS. 19 and 20 ). As shown in  FIGS. 12 ,  12 A,  13 , and  13 A, screen assembly  10  may be installed upon a vibratory screening machine having one or more screening surfaces. In one embodiment, screen assembly  10  may be installed upon a vibratory screening machine by placing screen assembly  10  on the vibratory screening machine such that the binder bars contact end or side members of the vibratory screening machine. Compression force is then applied to binder bar  12 . Binder bars  12  distribute the load from the compression force to the screen assembly. The screen assembly  10  may be configured such that it flexes and deforms into a predetermined concave shape when compression force is applied to binder bar  12 . The amount of deformation and range of concavity may vary according to use, compression forced applied, and shape of the bed support of the vibratory screening machine. Compressing screen assembly  10  into a concave shape when installed in a vibratory screening machine provides many benefits, e.g., easy and simple installation and removal, capturing and centering of materials to be screened, etc. Further benefits are enumerated in U.S. Pat. No. 7,578,394. Centering of material streams on screen assembly  10  prevents the material from exiting the screening surface and potentially contaminating previously segregated materials and/or creating maintenance concerns. For larger material flow volumes, screen assembly  10  may be placed in greater compression, thereby increasing the amount of arc of the screen assembly  10 . The greater the amount of arc in screen assembly  10  allows for greater retaining capability of material by screen assembly  10  and prevention of over spilling of material off edges of the screen assembly  10 . Screen assembly  10  may also be configured to deform into a convex shape under compression or remain substantially flat under compression or clamping. Incorporating binder bars  12  into the screen assembly  10  allows for a compression load from a vibratory screening machine to be distributed across the screen assembly  10 . Screen assembly  10  may include guide notches in the binder bars  12  to help guide the screen assembly  10  into place when installed upon a vibratory screening machine having guides. Alternatively, the screen assembly may be installed upon a vibratory screening machine without binder bars  12 . In the alternative embodiment, guide notches may be included in subgrid units. U.S. patent application Ser. No. 12/460,200 is incorporated herein by reference and any embodiments disclosed therein may be incorporated into embodiments of the present invention described herein. 
         [0146]      FIG. 2  shows a screen element  16  having substantially parallel screen element end portions  20  and substantially parallel screen element side portions  22  that are substantially perpendicular to the screen element end portions  20 . The screen element screening surface  13  includes surface elements  84  running parallel to the screen element end portions  20  and forming screening openings  86 . See  FIG. 2D . Surface elements  84  have a thickness T, which may vary depending on the screening application and configuration of the screening openings  86 . T may be, e.g., approximately 43 microns to approximately 100 microns depending on the open screening area desired and the width W of screening openings  86 . The screening openings  86  are elongated slots having a length L and a width W, which may be varied for a chosen configuration. The width may be a distance of approximately 43 microns to approximately 2000 microns between inner surfaces of each screen surface element  84 . The screening openings are not required to be rectangular but may be thermoplastic injection molded to any shape suitable to a particular screening application, including approximately square, circular and/or oval. For increased stability, the screen surface elements  84  may include integral fiber materials which may run substantially parallel to end portions  20 . The fiber may be an aramid fiber (or individual filaments thereof), a naturally occurring fiber or other material having a relatively high tensile strength. U.S. Pat. No. 4,819,809 and U.S. patent application Ser. No. 12/763,046 are incorporated herein by reference and, as appropriate, the embodiments disclosed therein may be incorporated into the screen assemblies disclosed herein. 
         [0147]    The screen element  16  may include attachment apertures  24  configured such that elongated attachment members  44  of a subgrid may pass through the attachment apertures  24 . The attachment apertures  24  may include a tapered bore that may be filled when a portion of the elongated attachment member  44  above the screening element screening surface is melted fastening screen element  16  to the subgrid. Alternatively, the attachment apertures  24  may be configured without a tapered bore allowing formation of a bead on the screening element screening surface when a portion of an elongated attachment member  44  above a screening element screening surface is melted fastening the screen element to the subgrid. Screen element  16  may be a single thermoplastic injection molded piece. Screen element  16  may also be multiple thermoplastic injection molded pieces, each configured to span one or more grid openings. Utilizing small thermoplastic injection molded screen elements  16 , which are attached to a grid framework as described herein, provides for substantial advantages over prior screen assemblies. Thermoplastic injection molding screen elements  16  allow for screening openings  86  to have widths W as small as approximately 43 microns. This allows for precise and effective screening. Arranging the screen elements  16  on subgrids, which may also be thermoplastic injection molded, allows for easy construction of complete screen assemblies with very fine screening openings. Arranging the screen elements  16  on subgrids also allows for substantial variations in overall size and/or configuration of the screen assembly  10 , which may be varied by including more or less subgrids or subgrids having different shapes. Moreover, a screen assembly may be constructed having a variety of screening opening sizes or a gradient of screening opening sizes simply by incorporating screen elements  16  with the different size screening openings onto subgrids and joining the subgrids in the desired configuration. 
         [0148]      FIG. 2B  and  FIG. 2C  show a bottom of the screen element  16  having a first screen element support member  28  extending between the end portions  20  and being substantially perpendicular to the end portions  20 .  FIG. 2B  also shows a second screen element support member  30  orthogonal to the first screen element support member  28  extending between the side edge portions  22  being approximately parallel to the end portions  20  and substantially perpendicular to the side portions  22 . The screen element may further include a first series reinforcement members  32  substantially parallel to the side edge portions  22  and a second series of reinforcement members  34  substantially parallel to the end portions  20 . The end portions  20 , the side edge portions  22 , the first screen element support member  28 , the second screen element support member  30 , the first series reinforcement members  32 , and the second series of reinforcement members  34  structurally stabilize the screen surface elements  84  and screening openings  86  during different loadings, including distribution of a compression force and/or vibratory loading conditions. 
         [0149]      FIG. 3  and  FIG. 3A  illustrate an end subgrid  14  unit. The end subgrid unit  14  includes parallel subgrid end members  36  and parallel subgrid side members  38  substantially perpendicular to the subgrid end members  36 . The end subgrid unit  14  has fasteners along one subgrid end member  36  and along the subgrid side members  38 . The fasteners may be clips  42  and clip apertures  40  such that multiple subgrid units  14  may be securely attached together. The subgrid units may be secured together along their respective side members  38  by passing the clip  42  into the clip aperture  40  until extended members of the clip  42  extend beyond clip aperture  40  and subgrid side member  38 . As the clip  42  is pushed into the clip aperture  40 , the clip&#39;s extended members will be forced together until a clipping portion of each extended member is beyond the subgrid side member  38  allowing the clipping portions to engage an interior portion of the subgrid side member  38 . When the clipping portions are engaged into the clip aperture, subgrid side members of two independent subgrids will be side by side and secured together. The subgrids may be separated by applying a force to the clip&#39;s extended members such that the extended members are moved together allowing for the clipping portions to pass out of the clip aperture. Alternatively, the clips  42  and clip apertures  40  may be used to secure subgrid end member  36  to a subgrid end member of another subgrid, such as a center subgrid ( FIG. 4 ). The end subgrid may have a subgrid end member  36  that does not have any fasteners. Although the fasteners shown in drawings are clips and clip apertures, alternative fasters and alternative forms of clips and apertures may be used, including other mechanical arrangements, adhesives, etc. 
         [0150]    Constructing the grid framework from subgrids, which may be substantially rigid, creates a strong and durable grid framework and screen assembly  10 . Screen assembly  10  is constructed so that it can withstand heavy loading without damage to the screening surface and supporting structure. For example, the pyramidal shaped grid frameworks shown in  FIGS. 22 and 23  provide a very strong pyramid base framework that supports individual screen elements capable of very fine screening, having screening openings as small as 43 microns. Unlike the pyramidal screen assembly embodiment of the present invention described herein, existing corrugated or pyramid type wire mesh screen assemblies are highly susceptible to damage and/or deformation under heavy loading. Thus, unlike current screens, the present invention provides for screen assemblies having very small and very precise screening openings while simultaneously providing substantial structural stability and resistance to damage thereby maintaining precision screening under a variety of load burdens. Constructing the grid framework from subgrids also allows for substantial variation in the size, shape, and/or configuration of the screen assembly by simply altering the number and/or type of subgrids used to construct the grid framework. 
         [0151]    End subgrid unit  14  includes a first subgrid support member  46  running parallel to subgrid side members  38  and a second subgrid support member  48  orthogonal to the first subgrid support member  46  and perpendicular to the subgrid side members  38 . Elongated attachment members  44  may be configured such that they mate with the screen element attachment apertures  24 . Screen element  16  may be secured to the subgrid  14  via mating the elongated attachment members  44  with screen element attachment apertures  24 . A portion of elongated attachment member  44  may extend slightly above the screen element screening surface when the screen element  16  is attached to the end subgrid  14 . The screen element attachment apertures  24  may include a tapered bore such that a portion of the elongated attachment members  44  extending above the screen element screening surface may be melted and fill the tapered bore. Alternatively, screen element attachment apertures  24  may be without a tapered bore and the portion of the elongated attachment members extending above the screening surface of the screening element  16  may be configured to form a bead on the screening surface when melted. See  FIGS. 34 and 35 . Once attached, the screen element  16  will span at least one grid opening  50 . Materials passing through the screening openings  86  will pass through grid opening  50 . The arrangement of elongated attachment members  44  and the corresponding arrangement of screen element attachment apertures  24  provide a guide for attachment of screen elements  16  to subgrids simplifying assembly of subgrids. The elongated attachment members  44  pass through the screen element attachment apertures  24  guiding the screen element into correct placement on the surface of the subgrid. Attachment via elongated attachment members  44  and screen element attachment apertures  24  further provides a secure attachment to the subgrid and strengthens the screening surface of the screen assembly  10 . 
         [0152]      FIG. 4  shows a center subgrid  18 . As shown in  FIG. 1  and  FIG. 1A , the center subgrid  18  may be incorporated into a screen assembly. The center subgrid  18  has clips  42  and clip apertures  40  on both subgrid end members  36 . The end subgrid  14  has clips  42  and clip apertures  40  on only one of two subgrid side members  36 . Center subgrids  18  may be secured to other subgrids on each of its subgrid end members and subgrid side members. 
         [0153]      FIG. 5  shows a top view of binder bar  12 .  FIG. 5A  shows a bottom view of binder bar  12 . Binder bars  12  include clips  42  and clip apertures  40  such that binder bar  12  may be clipped to a side of an assembly of screen panels (see  FIG. 9 ). As with subgrids, fasteners on the binder bar  12  are shown as clips and clip apertures but other fasteners may be utilized to engage fasteners of the subgrids. Handles may be attached to binder bars  12  (see, e.g.,  FIG. 7 ) which may simplify transportation and installation of a screen assembly. Tags and/or labels may also be attached to binder bars. As discussed above, binder bars  12  may increase the stability of the grid framework and may distribute compression loads of a vibratory screening machine if the screen assembly is placed under compression as shown in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. 
         [0154]    The screening members, screening assemblies and parts thereof, including connecting members/fasteners as described herein, may include nanomaterial dispersed therein for improved strength, durability and other benefits associated with the use of a particular nanomaterial or combination of different nanomaterials. Any suitable nanomaterial may be used, including, but not limited to nanotubes, nanofibers and/or elastomeric nanocomposites. The nanomaterial may be dispersed in the screening members and screening assemblies and parts thereof in varying percentages, depending on the desired properties of the end product. For example, specific percentages may be incorporated to increase member strength or to make a screening surface wear resistant. Use of a thermoplastic injection molded material having nanomaterials dispersed therein may provide for increased strength while using less material. Thus, structural members, include subgrid framework supports and screen element supporting members may be made smaller and stronger and/or lighter. This is particularly beneficial when fabricating relatively small individual components that are built into a complete screen assembly. Also, instead of producing individual subgrids that clip together, one large grid structure having nanomaterials dispersed therein, may be fabricated that is relatively light and strong. Individual screen elements, with or without nanomaterials, may then be attached to the single complete grid framework structure. Use of nanomaterials in a screen element will provide increased strength while reducing the weight and size of the element. This may be especially helpful when injection molding screen elements having extremely small openings as the openings are supported by the surrounding materials/members. Another advantage to incorporating nanomaterials into the screen elements is an improved screening surface that is durable and resistant to wear. Screen surfaces tend to wear out through heavy use and exposure to abrasive materials and use of a thermoplastic and/or a thermoplastic having abrasive resistant nanomaterials, provides for a screening surface with a long life. 
         [0155]      FIG. 6  shows a subassembly  15  of a row of subgrid units.  FIG. 6A  is an exploded view of the subassembly in  FIG. 6  showing individual subgrids and direction of attachment to each other. The subassembly includes two end subgrid units  14  and three center subgrid units  18 . The end subgrid units  14  form the ends of the subassembly while the center subgrid units  18  are used to join the two end subgrid units  14  via connections between the clips  42  and clip apertures  40 . The subgrid units shown in  FIG. 6  are shown with attached screen elements  16 . By fabricating the screen assembly from subgrids and into the subassembly, each subgrid may be constructed to a chosen specification and the screen assembly may be constructed from multiple subgrids in a configuration required for the screening application. The screen assembly may be quickly and simply assembled and will have precise screening capabilities and substantial stability under load pressures. Because of the structure configuration of the grid framework and screen elements  16 , the configuration of multiple individual screen elements forming the screening surface of the screen assembly  10  and the fact that the screen elements  16  are thermoplastic injection molded, the openings in screen elements  16  are relatively stable and maintain their opening sizes for optimal screening under various loading conditions, including compression loads and concavity deflections and tensioning. 
         [0156]      FIG. 7  shows a screen assembly  10  with binder bars  12  having handles attached to the binder bars  12 . The screen assembly is made up of multiple subgrid units secured to each other. The subgrid units have screen elements  16  attached to their top surfaces.  FIG. 7A  is a cross-section of Section A-A of  FIG. 7  showing individual subgrids secured to screen elements forming a screening surface. As reflected in  FIG. 7A , the subgrids may have subgrid support members  48  configured such that screen assembly has a slightly concave shape when the subgrid support members  48  are fastened to each other via clips  42  and clip apertures  40 . Because the screen assembly is constructed with a slightly concave shape it may be configured to deform to a desired concavity upon application of a compression load without having to guide the screen assembly into a concave shape. Alternatively, the subgrids may be configured to create a slightly convex screen assembly or a substantially flat screen assembly. 
         [0157]      FIG. 8  is a top isometric view of a screen assembly partially covered with screen elements  16 . This figure shows end subgrid units  14  and center subgrid units  18  secured to form a screen assembly. The screening surface may be completed by attaching screen elements  16  to the uncovered subgrid units shown in the figure. Screen elements  16  may be attached to individual subgrids prior to construction of the grid framework or attached to subgrids after subgrids have been fastened to each other into the grid framework. 
         [0158]      FIG. 9  is an exploded isometric view of the screen assembly shown in  FIG. 1 . This figure shows eleven subassemblies being secured to each other via clips and clip apertures along subgrid end members of subgrid units in each subassembly. Each subassembly has two end subgrid units  14  and three center subgrid units  18 . Binder bars  12  are clipped at each side of the assembly. Different size screen assemblies may be created using different numbers of subassemblies or different numbers of center subgrid units in each subassembly. An assembled screen assembly has a continuous screen assembly screening surface made up of multiple screen element screening surfaces. 
         [0159]      FIGS. 10 and 10A  illustrate attachment of screen elements  16  to end subgrid unit  14 , according to an exemplary embodiment of the present invention. Screen elements  16  may be aligned with end subgrid unit  14  via the elongated attachment members  44  and the screen element attachment apertures  24  such that the elongated attachment members  44  pass through the screen element attachment apertures  24  and extend slightly beyond the screen element screening surface. The elongated attachment members  44  may be melted to fill the tapered bores of the screen element attachment apertures  24  or, alternatively, to form beads upon the screen element screening surface, securing the screen element  16  to the subgrid unit  14 . Attachment via elongated attachment members  44  and screen element attachment apertures  24  is only one embodiment of the present invention. Alternatively, screen element  16  may be secured to end subgrid unit  14  via adhesive, fasteners and fastener apertures, etc. Although shown having two screen elements for each subgrid, the present invention includes alternate configurations of one screen element per subgrid, multiple screen elements per subgrid, one screen element per subgrid opening, or having a single screen element cover multiple subgrids. The end subgrid  14  may be substantially rigid and may be formed as a single thermoplastic injection molded piece. 
         [0160]      FIG. 10B  is a top view of the end subgrid unit shown in  FIG. 10A  with screen elements  16  secured to the end subgrid.  FIG. 10C  is an enlarged cross-section of Section B-B of the end subgrid unit in  FIG. 10B . Screen element  16  is placed upon the end subgrid unit such that elongated attachment member  44  passes through the attachment aperture and beyond a screening surface of the screen element. The portion of the elongated attachment member  44  passing through the attachment aperture and beyond the screening surface of the screen element may be melted to attach the screen element  16  to the end subgrid unit as described above. 
         [0161]      FIG. 11  and  FIG. 11A  illustrate attachment of screen elements  16  to center subgrid unit  18 , according to an exemplary embodiment of the present invention. Screen elements  16  may be aligned with center subgrid unit  18  via the elongated attachment members  44  and the screen element attachment apertures  24  such that the elongated attachment members  44  pass through the screen element attachment apertures  24  and extend slightly beyond the screen element screening surface. The elongated attachment members  44  may be melted to fill the tapered bores of the screen element attachment apertures  24  or, alternatively, to form beads upon the screen element screening surface, securing the screen element  16  to center subgrid unit  18 . Attachment via elongated attachment members  44  and screen element attachment apertures  24  is only one embodiment of the present invention. Alternatively, screen element  16  may be secured to center subgrid unit  14  via adhesive, fasteners and fastener apertures, etc. Although shown having two screen elements for each subgrid, the present invention includes alternate configurations of one screen element per subgrid, one screen element per subgrid opening, multiple screen elements per subgrid, or having a single screen element cover multiple subgrid units. The center subgrid unit  18  may be substantially rigid and may be a single thermoplastic injection molded piece. 
         [0162]      FIGS. 12 and 12A  show screen assemblies  10  installed on a vibratory screening machine having two screening surfaces. The vibratory screening machine may have compression assemblies on side members of the vibratory screening machine, as shown in U.S. Pat. No. 7,578,394. A compression force may be applied to a binder bar or a side member of the screen assembly such that the screen assembly deflects downward into a concave shape. A bottom side of the screen assembly may mate with a screen assembly mating surface of the vibratory screening machine as shown in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. The vibratory screening machine may include a center wall member configured to receive a binder bar of a side member of the screen assembly opposite of the side member of the screen assembly receiving compression. The center wall member may be angled such that a compression force against the screen assembly deflects the screen assembly downward. The screen assembly may be installed in the vibratory screening machine such that it is configured to receive material for screening. The screen assembly may include guide notches configured to mate with guides of the vibratory screening machine such that the screen assembly may be guided into place during installation and may include guide assembly configurations as shown in U.S. patent application Ser. No. 12/460,200. 
         [0163]      FIG. 12B  is a front view of the vibratory screening machine shown in  FIG. 12 .  FIG. 12B  shows screen assemblies  10  installed upon the vibratory screening machine with compression applied to deflect the screen assemblies downward into a concave shape. Alternatively, the screen assembly may be preformed in a predetermined concave shape without compression force. 
         [0164]      FIGS. 13 and 13A  show installations of screen assembly  10  in a vibratory screening machine having a single screening surface. The vibratory screening machine may have a compression assembly on a side member of the vibratory screening machine. Screen assembly  10  may be placed into the vibratory screening machine as shown. A compression force may be applied to a binder bar or side member of the screen assembly such that the screen assembly deflects downward into a concave shape. A bottom side of the screen assembly may mate with a screen assembly mating surface of the vibratory screening machine as shown in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. The vibratory screening machine may include a side member wall opposite of the compression assembly configured to receive a binder bar or a side member of the screen assembly. The side member wall may be angled such that a compression force against the screen assembly deflects the screen assembly downward. The screen assembly may be installed in the vibratory screening machine such that it is configured to receive material for screening. The screen assembly may include guide notches configured to mate with guides of the vibratory screening machine such that the screen assembly may be guided into place during installation. 
         [0165]      FIG. 14  is a front view of screen assemblies  52  installed upon a vibratory screening machine having two screening surfaces, according to an exemplary embodiment of the present invention. Screen assembly  52  is an alternate embodiment where the screen assembly has been preformed to fit into the vibratory screening machine without applying a load to the screen assembly, i.e., screen assembly  52  includes a bottom portion  52 A that is formed such that it mates with a bed  83  of the vibratory screening machine. The bottom portion  52 A may be formed integrally with screen assembly  52  or maybe a separate piece. Screen assembly  52  includes similar features as screen assembly  10 , including subgrids and screen elements but also includes bottom portion  52 A that allows it to fit onto bed  83  without being compressed into a concave shape. A screening surface of screen assembly  52  may be substantially flat, concave or convex. Screen assembly  52  may be held into place by applying a compression force to a side member of screen assembly  52 . A bottom portion of screen assembly  52  may be preformed to mate with any type of mating surface of a vibratory screening machine. 
         [0166]      FIG. 15  is a front view of screen assembly  53  installed upon a vibratory screening machine having a single screening surface, according to an exemplary embodiment of the present invention. Screen assembly  53  has similar features of screen assembly  52  described above, including a bottom portion  53 A that is formed such that it mates with a bed  87  of the vibratory screening machine. 
         [0167]      FIG. 16  shows an end support frame subassembly and  FIG. 16A  shows an exploded view of the end support frame subassembly shown in  FIG. 16 . The end support frame subassembly shown in  FIG. 16  incorporates eleven end subgrid units  14 . 
         [0168]    Alternate configurations having more or less end subgrid units may be utilized. The end subgrid units  14  are secured to each other via clips  42  and clip apertures  40  along side members of the end subgrid units  14 .  FIG. 16A  shows attachment of individual end subgrid units such that the end support frame subassembly is created. As shown, the end support frame subassembly is covered in screen elements  16 . Alternatively, the end support frame subassembly may be constructed from end subgrids prior to attachment of screen elements or partially from pre-covered subgrid units and partially from uncovered subgrid units. 
         [0169]      FIG. 17  shows a center support frame assembly and  FIG. 17A  shows an exploded view of the center support frame subassembly shown in  FIG. 17 . The center support frame assembly shown in  FIG. 17  incorporates eleven center subgrid units  18 . Alternate configurations having more or less center subgrid units may be utilized. The center subgrid units  18  are secured to each other via clips  42  and clip apertures  40  along side members of the center subgrid units  18 .  FIG. 17A  shows attachment of individual center subgrid units such that the center support frame subassembly is created. As shown, the center support frame subassembly is covered in screen elements  16 . Alternatively, the center support frame subassembly may be constructed from center subgrids prior to attachment of screen elements or partially from pre-covered subgrid units and partially from uncovered subgrid units. 
         [0170]      FIG. 18  shows an exploded view of a screen assembly having three center support frame subassemblies and two end support frame subassemblies. The support frame assemblies are secured to each other via the clips  42  and clip apertures  40  on the subgrid end members. Each center subgrid unit is attached to two other subgrid units via end members. End members  36  of end subgrid units having no clips  42  or clip apertures  40  form the end edges of the screen assembly. The screen assembly may be made with more or less center support frames subassemblies or larger or smaller frame subassemblies. Binder bars may be added to side edges of the screen assembly. As shown, the screen assembly has screen elements installed upon the subgrid units prior to assembly. Alternatively, screen elements  16  may be installed after all or a portion of assembly. 
         [0171]      FIG. 19  illustrates an alternative embodiment of the present disclosure where screen assembly  54  is substantially flat. Screen assembly  54  may be flexible such that it can be deformed into a concave or convex shape or may be substantially rigid. Screen assembly  54  may be used with a flat screening surface. See  FIG. 39 . As shown, screen assembly  54  has binder bars  12  attached to side portions of the screen assembly  54 . Screen assembly  54  may be configured with the various embodiments of the grid structures and screen elements described herein. 
         [0172]      FIG. 20  illustrates an alternative embodiment of the present disclosure wherein screen assembly  56  is convex. Screen assembly  56  may be flexible such that it can be deformed into a more convex shape or may be substantially rigid. As shown, screen assembly  56  has binder bars  12  attached to side portions of the screen assembly. Screen assembly  56  may be configured with the various embodiments of the grid structures and screen elements described herein. 
         [0173]      FIGS. 21 and 21A  show an alternative embodiment of the present disclosure incorporating pyramidal shaped subgrid units. A screen assembly is shown with binder bars  12  attached. The screen assembly incorporates center and end subgrid units  14  and  18  and center and end pyramidal shaped subgrid units  58  and  60 . By incorporating the pyramidal shaped subgrid units  58  and  60  into the screen assembly, an increased screening surface may be achieved. Additionally, material being screened may be controlled and directed. The screen assembly may be concave, convex, or flat. The screen assembly may be flexible and may be deformed into a concave or convex shape upon the application of a compression force. The screen assembly may include guide notches capable of mating with guide mating surfaces on a vibratory screening machine. Different configurations of subgrid units and pyramid subgrid units may be employed which may increase or decrease an amount of screening surface area and flow characteristics of the material being processed. Unlike mesh screens or similar technology, which may incorporate corrugations or other manipulations to increase surface area, the screen assembly shown is supported by the grid framework, which may be substantially rigid and capable of withstanding substantial loads without damage or destruction. Under heavy material flows, traditional screen assemblies with corrugated screening surfaces are frequently flattened or damaged by the weight of the material, thereby impacting the performance and reducing the screening surface area of such screen assemblies. The screen assemblies disclosed herein are difficult to damage because of the strength of the grid framework, and the benefits of increased surface area provided by incorporating pyramidal shaped subgrids may be maintained under substantial loads. 
         [0174]    A pyramidal shaped end subgrid  58  is illustrated in  FIG. 22  and  FIG. 22A . Pyramidal shaped end subgrid  58  includes a first and a second grid framework forming first and second sloped surface grid openings  74 . Pyramidal shaped end subgrid  58  includes a ridge portion  66 , subgrid side members/base members  64 , and first and second angular surfaces  70  and  72 , respectively, that peak at ridge portion  66  and extend downwardly to side member  64 . Pyramidal shaped subgrids  58  and  60  have triangular end members  62  and triangular middle support members  76 . Angles shown for first and second angular surface  70  and  72  are exemplary only. Different angles may be employed to increase or decrease surface area of screening surface. Pyramidal shaped end subgrid  58  has fasteners along side members  64  and at least one triangle end member  62 . The fasteners may be clips  42  and clip apertures  40  such that multiple subgrid units  58  may be secured together. Alternatively, the clips  42  and clip apertures  40  may be used to secure pyramidal shaped end subgrid  58  to end subgrid  14 , center subgrid  18 , or pyramidal shaped center subgrid  60 . Elongated attachment members  44  may be configured on first and second sloped surfaces  70  and  72  such that they mate with the screen element attachment apertures  24 . Screen element  16  may be secured to pyramidal shaped end subgrid  58  via mating elongated attachment members  44  with the screen element attachment apertures  24 . A portion of the elongated attachment member  44  may extend slightly above the screen element screening surface when the screen element  16  is attached to pyramidal shaped end subgrid  58 . The screen element attachment apertures  24  may include a tapered bore such that a portion of the elongated attachment members  44  extending above the screen element screening surface may be melted and fill the tapered bore. Alternatively, the screen element attachment apertures  24  may be without a tapered bore and the portion of the elongated attachment members extending above the screening surface of the screening element  16  may be melted to form a bead on the screening surface. Once attached, screen element  16  may span first  74  and second sloped grid openings. Materials passing through the screening openings  86  will pass through the first  74  and second grid openings. 
         [0175]    A pyramidal shaped center subgrid  60  is illustrated in  FIG. 23  and  FIG. 23A . Pyramidal shaped center subgrid  60  includes a first and a second grid framework forming a first and second sloped surface grid opening,  74 . Pyramidal shaped center subgrid  60  includes a ridge portion  66 , a subgrid side members/base members  64 , and first and second angular surfaces  70  and  72  that peak at the ridge portion  66  and extend downwardly to the side member  64 . Pyramidal shaped center subgrid  60  has triangular end members  62  and triangular middle members  76 . Angles shown for first and second angular surface  70  and  72  are exemplary only. Different angles may be employed to increase or decrease surface area of screening surface. The pyramidal shaped center subgrid  60  has fasteners along side members  64  and both triangle end members  62 . The fasters may be clips  42  and clip apertures  40  such that multiple pyramidal shaped center subgrids  60  may be secured together. Alternatively, the clips  42  and clip apertures  40  may be used to secure pyramidal shaped center subgrid  60  to end subgrid  14 , center subgrid  18 , or pyramidal shaped end subgrid  58 . Elongated attachment members  44  may be configured on first and second sloped surfaces  70  and  72  such that they mate with the screen element attachment apertures  24 . Screen element  16  may be secured to pyramidal shaped center subgrid  60  via mating elongated attachment members  44  with the screen element attachment apertures  24 . A portion of the elongated attachment member  44  may extend slightly above the screen element screening surface when the screen element  16  is attached to pyramidal shaped center subgrid  60 . The screen element attachment apertures  24  may include a tapered bore such that the portion of the elongated attachment members  44  extending above the screen element screening surface may be melted and fill the tapered bore. Alternatively, the screen element attachment apertures  24  may be without a tapered bore and the portion of the elongated attachment members extending above the screening surface of the screening element  16  may be melted to form a bead on the screening surface. Once attached, screen element  16  will span sloped grid opening  74 . Materials passing through the screening openings  86  will pass through the grid opening  74 . While pyramid and flat shaped grid structures are shown, it will be appreciated that various shaped subgrids and corresponding screen elements may be fabricated in accordance with the present disclosure. 
         [0176]      FIG. 24  shows a subassembly of a row of pyramidal shaped subgrid units.  FIG. 24A  is an exploded view of the subassembly in  FIG. 24  showing the individual pyramidal shaped subgrids and direction of attachment. The subassembly includes two pyramidal shaped end subgrids  58  and three pyramidal shaped center subgrids  60 . The pyramidal shaped end subgrids  58  form ends of the subassembly while pyramidal shaped center subgrids  60  are used to join the two end subgrids  58  via connections between the clips  42  and clip apertures  40 . The pyramidal subgrids shown in  FIG. 24  are shown with attached screen elements  16 . Alternatively, the subassembly may be constructed from subgrids prior to attachment of screen elements or partially from pre-covered pyramidal shaped subgrid units and partially from uncovered pyramidal shaped subgrid units. 
         [0177]      FIGS. 24B and 24C  illustrate attachment of screen elements  16  to pyramidal shaped end subgrid  58 , according to an exemplary embodiment of the present invention. Screen elements  16  may be aligned with pyramidal shaped end subgrid  58  via elongated attachment members  44  and screen element attachment apertures  24  such that the elongated attachment members  44  pass through the screen element attachment apertures  24  may extend slightly beyond the screen element screening surface. The portion of elongated attachment members  44  extending beyond screen element screening surface may be melted to fill tapered bores of the screen element attachment apertures  24  or, alternatively, to form beads upon the screen element screening surface, securing the screen element  16  to pyramidal shaped subgrid  58 . Attachment via elongated attachment members  44  and screen element attachment apertures  24  is only one embodiment of the present invention. Alternatively, screen element  16  may be secured to pyramidal shaped end subgrid  58  via adhesive, fasteners and fastener apertures, etc. Although shown having four screen elements for each pyramidal shaped end subgrid  58 , the present invention includes alternate configurations of two screen elements per pyramidal shaped end subgrid  58 , multiple screen elements per pyramidal shaped end subgrid  58 , or having a single screen element cover a sloped surface of multiple pyramidal shaped subgrid units. Pyramidal shaped end subgrid  58  may be substantially rigid and may be a single thermoplastic injection molded piece. 
         [0178]      FIGS. 24D and 24E  illustrate attachment of screen elements  16  to pyramidal shaped center subgrid  60 , according to an exemplary embodiment of the present invention. Screen elements  16  may be aligned with pyramidal shaped center subgrid  60  via elongated attachment members  44  and screen element attachment apertures  24  such that the elongated attachment members  44  may pass through the screen element attachment apertures  24  and may extend slightly beyond the screen element screening surface. The portion of the elongated attachment members  44  extending beyond screen element screening surface may be melted to fill tapered bores of the screen element attachment apertures  24  or, alternatively, to form beads upon the screen element screening surface, securing the screen element  16  to pyramidal shaped subgrid unit  60 . Attachment via elongated attachment members  44  and screen element attachment apertures  24  is only one embodiment of the present invention. Alternatively, screen element  16  may be secured to pyramidal shaped center subgrid  60  via adhesive, fasteners and fastener apertures, etc. Although shown having four screen elements for each pyramidal shaped center subgrid  60 , the present invention includes alternate configurations of two screen elements per pyramidal shaped center subgrid  60 , multiple screen elements per pyramidal shaped center subgrid  60 , or having a single screen element cover a sloped surface of multiple pyramidal shaped subgrids. Pyramidal shaped center subgrid  60  may be substantially rigid and may be a single thermoplastic injection molded piece. While pyramid and flat shaped grid structures are shown, it will be appreciated that various shaped subgrids and corresponding screen elements may be fabricated in accordance with the present disclosure. 
         [0179]      FIG. 25  is a top view of a screen assembly  80  having pyramidal shaped subgrids. As shown, the screen assembly  80  is formed from screen subassemblies attached to each other alternating from flat subassemblies to pyramidal shaped subassemblies. Alternatively, pyramidal shaped subassemblies may be attached to each other or less or more pyramidal shaped subassemblies may be used.  FIG. 25A  is a cross-section of Section C-C of the screen assembly shown in  FIG. 25 . As shown, the screen assembly has five rows of pyramidal shaped subgrid units and six rows of flat subgrids, with the rows of flat subgrid units in between each row of the pyramidal shaped subgrids. Binder bars  12  are attached to the screen assembly. Any combination of flat subgrid rows and pyramidal shaped subgrid rows may be utilized.  FIG. 25B  is a larger view of the cross-section shown in  FIG. 25A . In  FIG. 25B , attachment of each subgrid to another subgrid and/or binder bar  12  is visible via clips and clip apertures. 
         [0180]      FIG. 26  is an exploded isometric view of a screen assembly having pyramidal shaped subgrid units. This figure shows eleven subassemblies being secured to each other via clips and clip apertures along subgrid side members of subgrid units in each subassembly. Each flat subassembly has two end subgrids  14  and three center subgrids  18 . Each pyramidal shaped subassembly has two pyramidal shaped end subgrids  58  and three pyramidal shaped center subgrids  60 . Binder bars  12  are fastened at each end of the assembly. Different size screen assemblies may be created using different numbers of subassemblies or different numbers of center subgrid units. Screening surface area may be increased by incorporating more pyramidal shaped subassemblies or decreased by incorporating more flat assemblies. An assembled screen assembly has a continuous screen assembly screening surface made up of multiple screen element screening surfaces. 
         [0181]      FIG. 27  shows installation of screen assemblies  80  upon a vibratory screening machine having two screening surfaces.  FIG. 30  is a front view of the vibratory machine shown in  FIG. 27 . The vibratory screening machine may have compression assemblies on side members of the vibratory screening machine. The screen assemblies may be placed into the vibratory screening machine as shown. A compression force may be applied to a side member of the screen assembly such that the screen assembly deflects downward into a concave shape. A bottom side of the screen assembly may mate with a screen assembly mating surface of the vibratory screening machine as shown in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. The vibratory screening machine may include a center wall member configured to receive a side member of the screen assembly opposite of the side member of the screen assembly receiving compression. The center wall member may be angled such that a compression force against the screen assembly deflects the screen assembly downward. The screen assembly may be installed in the vibratory screening machine such that it is configured to receive material for screening. The screen assembly may include guide notches configured to mate with guides of the vibratory screening machine such that the screen assembly may be guided into place during installation. 
         [0182]      FIG. 28  shows an isometric view of a screen assembly having pyramidal shaped subgrids where screen elements have not been attached. The screen assembly shown in  FIG. 28  is slightly concave, however, the screen assembly may be more concave, convex or flat. The screen assembly may be made from multiple subassemblies, which may be any combination of flat subassemblies and pyramidal shaped subassemblies. As shown, eleven subassemblies are included, however, more or less subassemblies may be included. The screen assembly is shown without screen elements  16 . The subgrids may be assembled together before or after attachment of screen elements to subgrids or any combination of subgrids having attached screen elements and subgrids without screen elements may be fastened together.  FIG. 29  shows the screen assembly of  FIG. 28  partially covered in screen elements. Pyramidal shaped subassemblies include pyramidal shaped end subgrids  58  and pyramidal shaped center subgrids  60 . Flat subassemblies include flat end subgrids  14  and flat center subgrids  18 . The subgrid units may be secured to each other via clips and clip apertures. 
         [0183]      FIG. 31  shows installation of screen assembly  81  in a vibratory screening machine having a single screening surface, according to an exemplary embodiment of the present invention. Screen assembly  81  is similar in configuration to screen assembly  80  but includes additional pyramid and flat assemblies. The vibratory screening machine may have a compression assembly on a side member of the vibratory screening machine. Screen assembly  81  may be placed into the vibratory screening machine as shown. A compression force may be applied to a side member of screen assembly  81  such that screen assembly  81  deflects downward into a concave shape. A bottom side of the screen assembly may mate with a screen assembly mating surface of the vibratory screening machine as shown in U.S. Pat. No. 7,578,394 and U.S. patent application Ser. No. 12/460,200. The vibratory screening machine may include a side member wall opposite of the compression assembly configured to receive a side member of the screen assembly. The side member wall may be angled such that a compression force against the screen assembly deflects the screen assembly downward. The screen assembly may be installed in the vibratory screening machine such that it is configured to receive material for screening. The screen assembly may include guide notches configured to mate with guides of the vibratory screening machine such that the screen assembly may be guided into place during installation. 
         [0184]      FIG. 32  is a front view of screen assemblies  82  installed upon a vibratory screening machine having two screening surfaces, according to an exemplary embodiment of the present invention. Screen assembly  82  is an alternate embodiment where the screen assembly has been preformed to fit into the vibratory screening machine without applying a load to the screen assembly, i.e., screen assembly  82  includes a bottom portion  82 A that is formed such that it mates with a bed  83  of the vibratory screening machine. The bottom portion  82 A may be formed integrally with screen assembly  82  or it may be a separate piece. Screen assembly  82  includes similar features as screen assembly  80 , including subgrids and screen elements but also includes bottom portion  82 A that allows it to fit onto bed  83  without being compressed into a concave shape. A screening surface of screen assembly  82  may be substantially flat, concave or convex. Screen assembly  82  may be held into place by applying a compression force to a side member of screen assembly  82  or may simply be held in place. A bottom portion of screen assembly  82  may be preformed to mate with any type of mating surface of a vibratory screening machine. 
         [0185]      FIG. 33  is a front view of screen assembly  85  installed upon a vibratory screening machine having a single screening surface, according to an exemplary embodiment of the present invention. Screen assembly  85  is an alternate embodiment where the screen assembly has been preformed to fit into the vibratory screening machine without applying a load to the screen assembly i.e., screen assembly  85  includes a bottom portion  85 A that is formed such that it mates with a bed  87  of the vibratory screening machine. The bottom portion  85 A may be formed integrally with screen assembly  85  or it may be a separate piece. Screen assembly  85  includes similar features as screen assembly  80 , including subgrids and screen elements but also includes bottom portion  85 A that allows it to fit onto bed  87  without being compressed into a concave shape. A screening surface of screen assembly  85  may be substantially flat, concave or convex. Screen assembly  85  may be held into place by applying a compression force to a side member of screen assembly  85  or may simply be held in place. A bottom portion of screen assembly  85  may be preformed to mate with any type of mating surface of a vibratory screening machine. 
         [0186]      FIG. 34  is an isometric view of the end subgrid shown in  FIG. 3  having a single screen element partially attached thereto.  FIG. 35  is an enlarged view of break out section E of the end subgrid shown in  FIG. 34 . In  FIGS. 34 and 35 , screen element  16  is partially attached to end subgrid  38 . Screen element  16  is aligned with subgrid  38  via elongated attachment members  44  and screen element attachment apertures  24  such that the elongated attachment members  44  pass through the screen element attachment apertures  24  and extend slightly beyond the screen element screening surface. As shown along the end edge portion of screen element  16 , the portions of the elongated attachment members  44  extending beyond screen element screening surface are melted to form beads upon the screen element screening surface, securing the screen element  16  to end subgrid unit  38 . 
         [0187]      FIG. 36  shows a slightly concave screen assembly  91  having pyramidal shaped subgrids incorporated into a portion of screen assembly  91  according to an exemplary embodiment of the present invention. A screening surface of the screen assembly may be substantially flat, concave or convex. The screen assembly  91  may be configured to deflect to a predetermined shape under a compression force. The screen assembly  91 , as shown in  FIG. 36 , incorporates pyramidal shaped subgrids in the portion of the screen assembly installed nearest the inflow of material on the vibratory screening machine. The portion incorporating the pyramidal shaped subgrids allows for increased screening surface area and directed material flow. A portion of the screen assembly installed nearest a discharge end of the vibratory screening machine incorporates flat subgrids. On the flat portion, an area may be provided such that material may be allowed to dry and/or cake on the screen assembly. Various combinations of flat and pyramidal subgrids may be included in the screen assembly depending on the configuration desired and/or the particular screening application. Further, vibratory screening machines that use multiple screen assemblies may have individual screen assemblies with varying configurations designed for use together on specific applications. For example, screen assembly  91  may be used with other screen assemblies such that it is positioned near the discharge end of a vibratory screening machine such that it provides for caking and/or drying of a material. 
         [0188]      FIG. 37  is a flow chart showing steps to fabricate a screen assembly, according to an exemplary embodiment of the present invention. As shown in  FIG. 37 , a screen fabricator may receive screen assembly performance specifications for the screen assembly. The specifications may include at least one of a material requirement, open screening area, capacity and a cut point for a screen assembly. The fabricator may then determine a screening opening requirement (shape and size) for a screen element as described herein. The fabricator may then determine a screen configuration (e.g., size of assembly, shape and configuration of screening surface, etc.). For example, the fabricator may have the screen elements arranged in at least one of a flat configuration and a nonflat configuration. A flat configuration may be constructed from center subgrids  18  and end subgrids  14 . A nonflat configuration may include at least a portion of pyramidal shaped center subgrids  60  and/or pyramidal shaped end subgrids  58 . Screen elements may be injection molded. Subgrid units may also be injection molded but are not required to be injection molded. Screen elements and subgrids may include a nanomaterial, as described herein, dispersed within. After both screen elements and subgrid units have been created, screen elements may be attached to subgrid units. The screen elements and subgrids may be attached together using connection materials having a nanomaterial dispersed within. Multiple subgrid units may be attached together forming support frames. Center support frames are formed from center subgrids and end support frames are formed from end subgrids. Pyramidal shaped support frames may be created from pyramidal shaped subgrid units. Support frames may be attached such that center support frames are in a center portion of the screen assembly and end support frames are on an end portion of the screen assembly. Binder bars may be attached to the screen assembly. Different screening surface areas may be accomplished by altering the number of pyramidal shaped subgrids incorporated into the screen assembly. Alternatively, screen elements may be attached to subgrid units after attachment of multiple subgrids together or after attachment of multiple support frames together. Instead of multiple independent subgrids that are attached together to form a single unit, one subgrid structure may be fabricated that is the desired size of the screen assembly. Individual screen elements may then be attached to the one subgrid structure. 
         [0189]      FIG. 38  is a flow chart showing steps to fabricate a screen assembly, according to an exemplary embodiment of the present invention. A thermoplastic screen element may be injection molded. Subgrids may be fabricated such that they are configured to receive the screen elements. Screen elements may be attached to subgrids and multiple subgrid assemblies may be attached, forming a screening surface. Alternatively, the subgrids may be attached to each other prior to attachment of screen elements. 
         [0190]    In another exemplary embodiment, a method for screening a material is provided, including attaching a screen assembly to a vibratory screening machine and forming a top screening surface of the screen assembly into a concave shape, wherein the screen assembly includes a screen element having a series of screening openings forming a screen element screening surface and a subgrid including multiple elongated structural members forming a grid framework having grid openings. The screen elements span grid openings and are secured to a top surface of the subgrid. Multiple subgrids are secured together to form the screen assembly and the screen assembly has a continuous screen assembly screening surface comprised of multiple screen element screening surfaces. The screen element is a single thermoplastic injection molded piece. 
         [0191]      FIG. 39  is an isometric view of a vibratory screening machine having a single screen assembly  89  with a flat screening surface installed thereon with a portion of the vibratory machine cut away showing the screen assembly. Screen assembly  89  is a single unit that includes a subgrid structure and screen elements as described herein. The subgrid structure may be one single unit or may be multiple subgrids attached together. While screen assembly  89  is shown as a generally flat type assembly, it may be convex or concave and may be configured to be deformed into a concave shape from a compression assembly or the like. It may also be configured to be tensioned from above or below or may be configured in another manner for attachment to different types of vibratory screening machines. While the embodiment of the screen assembly shown covers the entire screening bed of the vibratory screening machine, screen assembly  89  may also be configured in any shape or size desired and may cover only a portion of the screening bed. 
         [0192]      FIG. 40  is an isometric view of a screen element  99  according to an exemplary embodiment of the present invention. Screen element  99  is substantially triangular in shape. Screen element  99  is a single thermoplastic injection molded piece and has similar features (including screening opening sizes) as screen element  16  as described herein. Alternatively, the screen element may be rectangular, circular, triangular, square, etc. Any shape may be used for the screen element and any shape may be used for the subgrid as long as the subgrid has grid openings that correspond to the shapes of the screen elements. 
         [0193]      FIGS. 40A and 40B  show screen element structure  101 , which may be a subgrid type structure, with screen elements  99  attached thereto forming a pyramid shape. In an alternative embodiment the complete pyramid structure of screen element structure  101  may be thermoplastic injection molded as a single screen element having a pyramid shape. In the configuration shown, the screen element structure has four triangular screen element screening surfaces. The bases of two of the triangular screening surfaces begin at the two side members of the screen element and the bases of the other two triangular screening surfaces begin at the two end members of the screen element. The screening surfaces all slope upward to a center point above the screen element end members and side members. The angle of the sloped screening surfaces may be varied. Screen element structure  101  (or alternatively single screen element pyramids) may be attached to a subgrid structure as described herein. 
         [0194]      FIGS. 40C and 40D  show a screen element structures  105  with screen elements  99  attached and having a pyramidal shape dropping below side members and edge members of the screen element structure  105 . Alternatively, the entire pyramid may be thermoplastic injection molded as a single pyramid shaped screen element. In the configuration shown, individual screen elements  99  form four triangular screening surfaces. The bases of two of the triangular screening surfaces begin at the two side members of the screen element and the bases of the other two triangular screening surfaces begin at the two end members of the screen element. The screening surfaces all slope downward to a center point below the screen element end members and side members. The angle of the sloped screening surfaces may be varied. Screen element structure  105  (or alternatively single screen element pyramids) may be attached to a subgrid structure as described herein. 
         [0195]      FIGS. 40E and 40F  show a screen element structure  107  having multiple pyramidal shapes dropping below and rising above the side members and edge members of screen element structure  107 . Each pyramid includes four individual screen elements  99  but may also be formed as single screen element pyramid. In the configuration shown, each screen element has sixteen triangular screening surfaces forming four separate pyramidal screening surfaces. The pyramidal screening surfaces may slope above or below the screen element end members and side members. Screen element structure  107  (or alternatively single screen element pyramids) may be attached to a subgrid structure as described herein.  FIGS. 40 through 40F  are exemplary only as to the variations that may be used for the screen elements and screen element support structures. 
         [0196]      FIGS. 41 to 43  show cross-sectional profile views of exemplary embodiments of thermoplastic injection molded screen element surface structures that may be incorporated into the various embodiments of the present invention discussed herein. The screen element is not limited to the shapes and configurations identified herein. Because the screen element is thermoplastic injection molded, multiple variations may be easily fabricated and incorporated into the various exemplary embodiments discussed herein. 
         [0197]      FIG. 44  shows a prescreen structure  200  for use with vibratory screening machines. Prescreen structure  200  includes a support frame  300  that is partially covered with individual prescreen assemblies  210 . Prescreen assemblies  210  are shown having multiple prescreen elements  216  mounted on prescreen subgrids  218 . Although, prescreen assemblies  210  are shown including six prescreen subgrids  218  secured together, various numbers and types of subgrids may be secured together to form various shapes and sizes of prescreen assemblies  210 . The prescreen assemblies  210  are fastened to support frame  300  and form a continuous prescreening surface  213 . Prescreen structure  200  may be mounted over a primary screening surface. Prescreen assemblies  210 , prescreen elements  216  and the prescreen subgrids  218  may include any of the features of the various embodiments of screen assemblies, screen elements and subgrid structures described herein and may configured to be mounted on prescreen support frame  300 , which may have various forms and configurations suitable for prescreening applications. Prescreen structure  200 , prescreen assemblies  210 , prescreen elements  216  and the prescreen subgrids  218  may be configured to be incorporated into the prescreening technologies (e.g., compatible with the mounting structures and screen configurations) described in U.S. patent application Ser. No. 12/051,658. 
         [0198]      FIG. 44A  shows an enlarged view of prescreen assembly  210 . 
         [0199]    The embodiments of the present invention described herein, including screening members and screening assemblies, may be configured for use with various different vibratory screening machines and parts thereof, including machines designed for wet and dry applications, machines having multi-tiered decks and/or multiple screening baskets, and machines having various screen attachment arrangements such as tensioning mechanisms (under and overmount), compression mechanisms, clamping mechanisms, magnetic mechanisms, etc. For example, the screen assemblies described in the present disclosure may be configured to be mounted on the vibratory screening machines described in U.S. Pat. Nos. 7,578,394; 5,332,101; 6,669,027; 6,431,366; and 6,820,748. Indeed, the screen assemblies described herein may include: side portions or binder bars including U-shaped members configured to receive overmount type tensioning members, e.g., as described in U.S. Pat. No. 5,332,101; side portions or binder bars including finger receiving apertures configured to receive undermount type tensioning, e.g., as described in U.S. Pat. No. 6,669,027; side members or binder bars for compression loading, e.g., as described in U.S. Pat. No. 7,578,394; or may be configured for attachment and loading on multi-tiered machines, e.g., such as the machines described in U.S. Pat. No. 6,431,366. The screen assemblies and/or screening elements may also be configured to include features described in U.S. patent application Ser. Nos. 12/460,200, including the guide assembly technologies described therein and preformed panel technologies described therein. Still further, the screen assemblies and screening elements may be configured to be incorporated into the prescreening technologies (e.g., compatible with the mounting structures and screen configurations) described in U.S. patent application Ser. No. 12/051,658. U.S. Pat. Nos. 7,578,394; 5,332,101; 4,882,054; 4,857,176; 6,669,027; 7,228,971; 6,431,366; and 6,820,748 and U.S. patent application Ser. Nos. 12/460,200 and 12/051,658, which, along with their related patent families and applications, and the patents and patent applications referenced in these documents, are expressly incorporated herein by reference hereto. 
         [0200]    In the foregoing, example embodiments are described. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope hereof. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.