Abstract:
A screen panel has a pre-tensioned screen with a polished metal plate mounted to the top of the frame to eliminate all the exposed surface areas of epoxy which secures the screen to the screen panel frame. The metal plate also provides an edge against which a silicone bead may be seated to provide a much cleaner and finished looking panel which is anticipated to meet the standards set forth by the USDA. Additionally, the spatial positioning of the plate atop the screen material and screen frame allows for a clean and smooth transition across the components and one which may accept a finished bead of silicon or other material for reducing and/or eliminating sites for mold growth or other containments thereby enhancing the ability to clean and sterilize the screen panel for the processing of various materials.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to screening machines of the type used to separate or classify mixtures of particles of different sizes. More particularly, the invention relates to an improved screen panel for use within such a screening machine. 
     In screening machines of the type described, a screen (which may be woven, an aperture plate or another design) is mounted in what is often called a “screen frame” or “screen deck” which includes a supporting peripheral frame around the perimeter of the screen. Some screens are tensioned when they are installed in the screening machine and other screens are pre-tensioned in a frame prior to being installed in the machine. Typically associated with the screen deck are additional material handling elements that are moved with the screen and form walls or partitions above or below the screen for containing the liquid and/or particulate materials adjacent to the screen and directing them to appropriate outlets. These elements may comprise a top cover and a pan beneath the screen deck. In the case of screening machines with multiple screens or deck units, spacer pans or frames are provided between the multiple screens. 
     The screens are often removed from the screening machines for cleaning, replacement, readjustment, or installation of a screen of a different mesh size or the like. The screen is releasably mounted to a carrier, table or box to which vibratory motion is imparted, typically by one or more eccentric motors or other means of excitation. The carrier, table or box is referred to herein as a “vibratory carrier”. The vibratory carrier may be moved in oscillatory, vibratory, gyratory, gyratory reciprocating, fully gyratory, rotary or another type of motion or combinations thereof, all of which are herein collectively referred to as “vibratory” motion or variations of that term. 
     Screening machines of this type are used to separate or classify a wide variety of materials. Some of the materials which are processed in these screening machines are subject to various governmental regulations and/or other requirements during the handling and processing of the materials. These requirements and regulations often include cleanliness and sanitary standards for certification under the United States Department of Agriculture (USDA) regulations. USDA certification would then allow use of such a screening machine in the production and processing of protein products such as whey powder, milk powder, cheese, etc. The processing and handling of these and other types of products require USDA certification. 
     One challenge to satisfying the USDA certification standards for screen panels and screening machines has been a pre-tensioned screen panel that could meet the performance aspects of a standard screen panels as well as meet the cleanliness standards set by the USDA. Existing pre-tensioned screen panels typically have wire tensioned over a tubular frame and fastened to the frame using a Food and Drug Administration (FDA) approved epoxy. A bead of silicone may be located between the edge of the tubular frame and the wire interface to act as a damper to prevent wire fatigue. Various problems with such a screen panel design for satisfying the USDA requirements include the fact that the epoxy creates bubbles during the curing process and thereby create pores in which bacteria may collect and grow. Moreover, the epoxy interface with the screen panel components is often uncontrolled and does not have a clean appearance thereby creating more sites for potential mold growth. Additionally, when the epoxy presses through the screen wire, it creates fingers, or a series of protrusions that can either break off into the product being screened or create a cavity for bacteria to collect and grow. 
     SUMMARY OF THE INVENTION 
     The above-described and other problems with prior art screening machines and associated screen panels have been resolved by this invention. Screening machines and screen panels according to various embodiments of this invention utilize a perforate screen assembly engaging the machine frame, and a driver imparting vibratory motion to the screen assembly, the machine frame and screen assembly designed to hold particulate matter to be screened. The screening machine also includes a first outlet which discharges a first portion of the particulate matter that remains on top of the screen assembly and a second outlet which discharges a second portion of the particulate matter that passes through the screen assembly. 
     One aspect of this invention is the screen assembly including a screen panel having a generally planar screening surface. In various embodiments, the screen panel of this invention utilizes a pre-tensioned screen with a polished metal plate glued to the top of the frame to eliminate all the exposed surface areas of epoxy which secures the screen to the screen panel frame. The metal plate also provides an edge against which a silicone, epoxy or other material bead is seated to provide a much cleaner and finished looking panel which is anticipated to meet the standards set forth by the USDA. Additionally, the spatial positioning of the plate atop the screen material and screen frame allows for a clean and smooth transition across the components and one which may accept a finished bead of silicon or other material for reducing and/or eliminating sites for mold growth or other containments thereby enhancing the ability to clean and sterilize the screen panel for the processing of various materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objectives and features of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an exemplary screen panel according to one embodiment of this invention; 
         FIG. 2  is a top plan view of the screen panel of  FIG. 1 ; 
         FIG. 3A  is a cross-sectional view of the screen panel of  FIGS. 1-2  taken along line  3 C- 3 C of  FIG. 2  with the components in a disassembled arrangement; 
         FIG. 3B  is a view similar to  FIG. 3A  with the components assembled and a seal bead added; and 
         FIG. 3C  is a view similar to  FIG. 3B  with the seal bead in a finished configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an exemplary embodiment of a screen panel  10  according to this invention is shown. The screen panel  10  maybe used in a screening machine, many types of which are sold commercially by Rotex Global LLC of Cincinnati, Ohio, the assignee of this invention. However, this invention is not limited to any particular type of screening machine design or application and the machine disclosed herein is for illustrative purposes. Exemplary screening machines are disclosed in U.S. Pat. Nos. 8,522,981; 8,261,915; 6,763,948; 6,073,979; and 6,070,736, each of which is hereby incorporated by reference in its entirety. 
     Within a screening chamber of the screening machine, one or more screen panels  10  are each mounted to receive the material being screened from a feed chute at the head end of the screening machine. The screen panels  10  are mounted on slightly sloping planes (approximately 4 degrees) with the head end thereof being slightly elevated relative to a foot end so that during the screening process the material advances, in part by gravity, over the screen panels  10  toward a discharge end of the machine. Even though the screen panels  10  of the screening machine may be on a slightly sloping plane, to provide a reference for the purposes of clarity herein, these components will be considered to be generally horizontal and the direction perpendicular or orthogonal to the screen panels  10  will generally be referred to as a vertical orientation or direction. The direction of travel of the material being screened from the head end to a discharge end across the screen panels  10  is referred to as the longitudinal direction and the perpendicular orientation extending from side to side on the screen panels  10  is a lateral direction. 
     Accordingly, as the material to be screened is deposited from the inlet port onto the screen panels  10 , the vibratory motion of the screening machine advances the material longitudinally across the top of the screen panels  10  of the toward the discharge end. Appropriately sized and configured material passes through the screen panels  10 . The screen panels  10  may include a fine mesh screen material  12  through which material passes for collection and discharge. Certain material may also pass through an upper screen panel  10  and is deposited on a lower screen panel  10 . Therefore, the lower screen panels  10  may be included to provide an additional separating mechanism for the appropriately sized particles to pass through for collection in a lower pan (not shown). 
     The unacceptably sized particles remain atop the upper screen panels  10  and fall off the terminal edge thereof into a collection basin for discharge through an outlet (not shown). The acceptably sized particles that pass through both the upper and lower screen panels  10  are collected in a lower pan and discharged through an outlet (not shown) located at the discharge end of the machine. 
     Referring to  FIGS. 1-3C , one embodiment of the screen panel  10  includes a generally perforated mesh screen material  12  making a screening surface  14 . The mesh screen material  12  includes a number of intersecting longitudinal threads or wires  16  and lateral threads or wires  18  which are oriented orthogonally to each other to provide appropriately sized and configured openings  20  in the screening surface  14  to prevent or allow the passage of material. The screen panel  10  includes a generally rigid peripheral frame  22  extending around at least a portion of the screening surface  14 . A cross-sectional profile of the frame  22  may have a generally rectangular configuration and provide the frame  22  with a tubular construction as shown in  FIGS. 3A-3C . The tubular frame  22  may be aluminum or any other material appropriate for the design parameters of the screen panel  10 . The screen material  12  of various embodiments of this invention is pre-tensioned on the frame  22  as distinguished from screen panels in which the screen material is otherwise stretched and locked onto a separate frame assembly. 
     The mesh screen material  12  may be bonded or adhered to the frame  22  by an epoxy  24  as shown in  FIGS. 3A-3C . As it may be appreciated by those in the art, the epoxy  24  is initially a flowable material and oozes or migrates between the threads or wires  16 ,  18  of the screen material  12  prior to the epoxy  24  curing or setting up. Normally such an arrangement is appropriate to bond the screen material  12  to the frame  22  for many applications. However, as noted above, the epoxy  24  filtering through the screen material  12  often provides for an irregular surface and one which has many available sites for mold growth and the like and creates fingers of excess epoxy dangling from the frame or screen material. According to various embodiments of this invention, a plate  26  is positioned atop the frame  22 , epoxy  24  and adjacent portions of the screen material to provide a smooth, clean and cavity free surface to this portion of the screen panel  10 . In various embodiments, the plate  26  may have a generally frame-like configuration with a central opening to expose the screening surface  14  of the screen panel  10 . 
     The plate  26  is adhered to the frame  22  and screen material by the epoxy  24  and conceals the epoxy  24  thereby eliminating epoxy fingers and sites for mold growth which would otherwise be presented. In various embodiments, the plate  26  may be stainless steel or another material which is readily susceptible to being cleaned, sterilized or otherwise prepared in accordance with applicable USDA regulations for the screening or processing of various food and other products. The plate  26  may be polished and may be an FDA approved material having a specified micro-finish consistent with such standards. 
     Unlike prior screen panels, the screen panel  10  of this invention presents a smooth clean upper surface atop the screen frame  22  and the epoxy  24  or other material securing the screen material  12  to the frame  22  is not exposed to offer sites for mold growth and the like. The plate  26  may be commensurate with the upper profile of the screen frame  22  as shown generally in  FIG. 1 . In other embodiments, the plate  26  covers the entire peripheral edge of the screen material  12  adhered to the screen frame  22 . The plate  26  eliminates exposed epoxy on the finished screen panel  10  and is adhered to the frame  22  by the epoxy  24 . As such, the tubular frame  22  with the screen material  12  and plate  26  adhered thereto form a single-piece screen panel  10  assembly. 
     As shown in  FIGS. 3B-3C , a bead  28  of epoxy or other material may be added to the perimeter edge of the plate  26 . The bead  28  may be trimmed via grinding, polishing or another technique to provide a smooth transition from the edge of the plate  26  to the outer face of the frame  22  as shown in  FIG. 3C . The bead  28  may be trimmed after it is cured or hardened or prior to curing and hardening. The outer and/or inner perimeter edge of the plate  26  may be offset D 1 , D 2  from the associated edge of the frame  22  so as to provide a seat  30  into which the silicone bead  28  resides and offer a cleaner and finished profile to the screen panel  10  and one which does not harbor mold or other contamination sites as in other designs. 
     With prior screen panel designs, a bead of epoxy and a bead of silicone are applied onto the tubular frame and the frame is pressed up into the pre-tensioned screen material causing the two beads to protrude through the wires of the screen material creating fingers of excess material. With embodiments of this invention, one or more beads of epoxy  24  can be placed onto the tubular frame  22  and the frame  22  pressed into the pre-tensioned screen material  12 . Then the plate  26  is placed on top of the screen material  12  and frame  22  and clamped thereto to hold in place. Next, tape may be laid on top of the screen material  12  offset from the inside border of the plate  26 . Then a bead  32  of silicone caulk is laid in the offset seat  30  and wiped with a finger across the caulk to force the caulk into the space between the tubular frame  22  and the plate  26 . The bead of caulk may be any appropriate material for the application, construction and environment of the screen panel  10 . The tape is then pulled off. In various embodiments of this invention, the plate  26  has a slightly smaller outer dimension and a slightly larger inner dimension creating offsets D 1  and D 2  relative to the associated edges of the frame  22  as shown in  FIG. 3B . Therefore, when the silicone  32  is pressed through the screen material  12  with an operator&#39;s finger, the tubular frame  22  acts as a backing and prevents fingers of epoxy or silicone caulk being created on the backside of the screen panel  10 . The silicone underneath the screen material  12  may line up with a top bead of silicone on top of the screen material thereby filling any voids or crevices. 
     In one embodiment of this invention, epoxy is used to seal along all the outside edges of the plate  26  and silicone is used along all the inside edges of the plate  26 . The plate  26  covers the epoxy  24  for attaching the screen material  12  to the frame  22  which often contains any bubbles in the epoxy, but the outside edge of the plate  26  may be filled with a small bead of epoxy where the bubbles can be managed and the epoxy ground smooth. 
     The screen panel  10  may be manufactured by a variety of processes, including stretching the mesh screen material  12  to put longitudinal wires  16  and lateral wires  18  in tension, robotically applying epoxies or adhesives, curing with ultraviolet light for about 30 seconds, and trimming or grinding off any excess wire  16 ,  18 . In some embodiments, the silicone bead can be installed on the perimeter where the ends of wires  16 ,  18  are exposed. In another embodiment, the screen panel  10  can be manufactured by dipping the frame  22  in epoxy  24  and pressing the mesh screen material  12  and plate  26  onto the frame  22  with a heat press. 
     The screen panel  10  of the current embodiment has several advantages over conventional screen panels, including for example the elimination of sites in which mold or other containments may be located so as to offer a screen panel  10  which is capable of meeting or exceeding standards set forth by the USDA and others for the processing of food related and other materials. 
     From the above disclosure of the general principles of this invention and the preceding detailed description of at least one embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.