Abstract:
A screening apparatus ( 10 ) comprising a frame, a motor assembly ( 16 ) for vibrating the frame, at least one screen ( 20, 30 ) mounted on the frame for separating materials by size and at least one feed device ( 35 A,  35 B,  35 C,  35 D) provided for delivering a liquid onto said at least one screen ( 20, 30 ), said at least one feed device ( 35 A,  35 B,  35 C,  35 D) being adapted to deliver said liquid onto the at least one screen ( 20, 30 ) to define a laminar flow of liquid and entrained or suspended solid material over the at least one screen ( 20, 30 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a §371 international of International Patent Application No. PCT/EP2013/063976, filed Jul. 2, 2013, which claims the benefit of United Kingdom Patent Application No. GB 1211877.4, filed Jul. 4, 2012, both of which are hereby incorporated herein by reference in their entireties. 
     FIELD OF THE INVENTION 
     This invention relates to a screening apparatus. 
     BACKGROUND OF THE INVENTION 
     It is often desired to separate material by size, particularly in sand quarrying operations. It is known to provide a screening apparatus for such purpose, such apparatus typically comprising a frame or box, a motor assembly for vibrating the frame, a mesh screen mounted on the frame for separating materials by size and a feed device for delivering solid material, typically entrained or suspended in a flow of water, onto the screen, whereby fine solids, having a grain size smaller than the aperture size of the screen (known as undersize material), pass through the screen for collection/passage onto further processing steps, while solids having a grain size greater than the aperture size of the screen (known as oversize material) are conveyed over the screen to be collected from a downstream end of the screen. The feed device typically comprises a hopper or conveying device located above the screen whereby material to be screened, typically entrained or suspended in a flow of water, is dropped onto the upper surface of the screen. 
     The flow of water fluidizes the solid material, ensuring that the undersize and oversize materials are able to be separated efficiently while preventing the oversize material from clogging the screen. However, in known systems there is a tendency for the material to become dewatered while still on the screen due to the passage of water through the screen. Attempts have been made to alleviate this problem by spraying additional water onto the screen. However, such attempts result in increased water consumption and are generally not successful in re-fluidizing the solid material. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a screening apparatus comprising a frame, a motor assembly for vibrating the frame, at least one screen mounted on the frame for separating material by size and at least one feed device provided for delivering a liquid onto said at least one screen, said at least one feed device being adapted to deliver said liquid onto the at least one screen to define a laminar flow of liquid and entrained or suspended solid material over the at least one screen. 
     The or at least one of said at least one feed device, preferably an upstream most feed device, may be adapted to deliver a liquid having particles of solid material entrained or suspended therein onto said at least one screen. 
     Preferably said at least one feed device extends across the width of the at least one screen. 
     Said at least one feed device may comprise a chamber provided with at least one inlet for receiving a supply of liquid or a liquid having particles of solid material entrained or suspended therein and at least one outlet for delivering said liquid or liquid and solid mixture onto an upper surface of said at least one screen. Preferably said at least one outlet of the at least one feed device is provided adjacent the upper surface of the at least one screen to deliver said liquid onto the upper surface of the at least one screen in a direction substantially parallel to the upper surface of the at least one screen. Preferably said at least one outlet comprises an elongate slot through which said liquid is constrained to pass. Said elongate slot may be defined between upper and lower walls or lips located on either side of said slot, said upper and lower walls or lips constraining the liquid to flow out of the slot in a direction substantially parallel to the upper surface of the adjacent screen. At least respective portions of said upper and lower walls or lips may be arranged substantially parallel to one another. 
     Said at least one feed device may comprise a hollow box-like structure having a lower wall, an upper wall, a front wall, a rear wall and opposing end walls. In one embodiment said at least one outlet may be defined adjacent an upper end of the front wall. Alternatively said at least one outlet may be defined adjacent a lower end of the front wall. Preferably one of said upper and lower lips extends inwardly from said front wall towards said rear wall of the feed device. A distal edge portion of said lower lip and/or a distal edge portion of said upper lip may be inclined downwardly to redirect water passing out of said feed device into a direction substantially parallel to the upper surface of the adjacent screen. Preferably the lower lip of the at least one outlet is substantially contiguous with an upper surface of the adjacent screen. 
     In one embodiment said at least one outlet may be provided at or adjacent an upper region of the at least one feed device and said at least one inlet being provided at or adjacent a lower region of the feed device. Alternatively the at least one outlet may be provided at or adjacent a lower region of the feed device, said at least one inlet being provided at or adjacent an upper region of the feed device. 
     A plurality of baffles may be provided within the at least one feed device between the at least one inlet and the at least one outlet to ensure that any solid material entrained or suspended in the liquid passing through the feed device is evenly mixed and evenly distributed therein. Said plurality of baffles may be provided on one or more removable inserts to enable the baffles to be replaced in the event of wear. 
     The screening apparatus may comprise a first feed device for delivering a liquid, preferably having a solid material entrained or suspended therein, onto a first screen section mounted on said frame, at least one further feed device for delivering liquid onto at least one further screen section downstream of said first screen section. Said at least on further screen section may be arranged to received material to be screened from a downstream end of said first screen section. 
     The one or more screen sections may be adjustably mounted on the frame to permit adjustment of the angle of inclination of the or each screen section. 
     According to a further aspect of the present invention there is provided a feed box for a screening apparatus comprising a chamber provided with at least one inlet for receiving a supply of liquid or a liquid having particles of solid material entrained or suspended therein, and at least one outlet for delivering said liquid or liquid and solid mixture onto an upper surface of said at least one screen to define a laminar flow of liquid and entrained or suspended solid material over the at least one screen. 
     Preferably said at least one outlet comprises an elongate slot through which said liquid is constrained to pass. Said elongate slot may be defined between upper and lower walls or lips located on either side of said slot, said upper and lower walls or lips constraining the liquid to flow out of the slot in a direction substantially parallel to the upper surface of the adjacent screen. 
     These and other objects, advantages, purposes, and features of the present invention will become more apparent upon review of the following specification in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a screening apparatus in accordance with an embodiment of the present invention; 
         FIG. 2  is a longitudinal sectional perspective view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a longitudinal sectional view of the apparatus of  FIG. 1 ; 
         FIG. 4  is a detailed perspective view of the screen assembly of the apparatus of  FIG. 1  with the frame omitted for clarity; 
         FIG. 5  is a longitudinal sectional perspective view of the screen assembly of  FIG. 4 ; 
         FIG. 6  is a detailed sectional view through a portion of the screen assembly of  FIG. 4 ; 
         FIG. 7  is a sectional view through a modified embodiment of the feed device of the apparatus of  FIG. 1 ; 
         FIG. 8  is a sectional view through a further modified embodiment of the feed device; 
         FIG. 9  is a detailed sectional view through a further modified embodiment of the feed device; 
         FIG. 10  is a sectional view through a further modified embodiment of the feed device; 
         FIG. 11  is a sectional view through a further modified embodiment of the feed device; 
         FIG. 12  is a detailed sectional view through a portion of a screen assembly according to a further embodiment of the present invention; and 
         FIG. 13  is a detailed sectional view through a portion of a screen assembly according to a further embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in the drawings, a screening apparatus  10  in accordance with an embodiment of the present invention comprises a frame including a pair of side members  12 , 14  linked by a plurality transversely extending structural members. A motor assembly  16  is mounted between the side members  12 , 14  of the frame, the motor assembly  16  comprising a pair of eccentrically mounted motor driven rotors for vibrating the frame. 
     A pair of screen assemblies  20 , 30  are mounted between the side members  12 , 14  of the frame at longitudinally spaced locations along the frame, as will be described in more detail below. 
     Each screen assembly  20 , 30  comprising a pair of longitudinally spaced screen sections or decks  22 ,  24 ,  32 ,  34  mounted between the side members  12 , 14  of the frame, a respective feed box  35 A,  35 B,  35 C,  35 D being mounted immediately upstream of each screen section  22 ,  24 ,  32 ,  34  for feeding water onto the surface of the respective screen section to define a laminar flow of water over the surface of thereof. The upstream feed box  35 A, 35 C of each screen assembly  20 , 30  may be supplied with a mixture of water and particles of solid material to be screened, comprising a mixture of undersize and oversize material, said material being entrained or suspended within said water, such that the mixture is supplied onto the upstream screen section  22 , 32  of each screen assembly  20 , 30 . 
     Each feed box  35 A,  35 B,  35 C,  35 D comprises a hollow box-like member having a front wall  101 , a rear wall  102 , a pair of opposing end walls  103 , an upper wall  104  and a lower wall  105  (front and rear being defined in the sense of the normal direction of flow of material over each screen assembly  20 , 30 ). Each feed box  35 A,  35 B,  35 C,  35 D extends between the side members  12 , 14  of the frame such that the feed boxes define structural components of the frame. 
     An inlet  36  is provided in one or both end walls  103  of each feed box adjacent the lower wall  105  thereof, whereby water, or a mixture of particles of solid material entrained or suspended in water in the case of each upstream feed box  35 A, 35 C, may be fed into the respective feed box. Alternatively the at least one inlet may be provided in the lower wall  105  of the feed box, or where the at least one outlet is provided adjacent the lower wall  105 , the at least one inlet may be provided in the upper wall  104  of the feed box. 
     In the embodiment shown in  FIGS. 1 to 6 , an outlet slot  38  of defined in the front wall  101  of each feed box  35 A,  35 B,  35 C,  35 D adjacent the upper wall thereof for delivering water onto the adjacent screen section. Each outlet slot  38  is defined by a pair of vertically spaced lips, comprising an upper lip  40  defined by the upper wall  104  of the respective feed box and a lower lip  42  defined by an upper portion of the front wall  101  of the respective feed box extending rearwardly and inwardly from the front wall  101  towards the rear wall  102  of the respective feed box. The upper and lower lips  40 , 42  are shaped and angled to direct water onto the upper surface of the adjacent screen section in a laminar and even flow across the width of the respective screen section. 
     As can be seen from  FIG. 6 , one or both of the lips  40 , 42 , or at least a terminal edge thereof, are angled downwardly and the lower lip  42  is arranged to lie contiguous with the upper surface  44  of the adjacent screen section such that the water exits the outlet slot  38  parallel to the surface of the adjacent screen section. One or both of the upper and lower lips may be adjustable, or incorporate adjustable or deformable portions, to enable adjustment of the flow of water through the outlet  138 . 
     At least one baffle may be defined within at least each upstream feed box  35 A, 35 C to restrict the flow of water through the feed box, generating mixing and evenly distributing the solid material within the water in the feed box and ensuring that any particles of solid material entrained or suspended in the water are evenly spread across the width of the respective screen section as the mixture leaves the outlet slot  38  of the feed box. 
     Each feed box may be associated with vibration generating means for maximising agitation of the material passing through the feed box to maintain any particles of solid material, such as sand, in suspension. 
     Each feed box  35 A,  35 B,  35 C,  35 D may comprise a trough like body  50  defining a structural member of the frame and having end plates  52 , at least one of which is provided with a water inlet  36 . In the embodiment shown in  FIG. 6 , a first insert member  54  is insertable into the bottom of the body  50  of the feed box and an upper insert member  56 , having lip portions  40 , 42  defining said outlet slot  38 , is insertable into the body  50  of the feed box to rest on top of the first insert member  54 . Apertures  58  are provided in the base of the upper insert member  56  such that the upper insert member  56  defines said baffle arrangement within the feed box. 
     In an alternative embodiment, shown in  FIG. 7 , a plurality of insert members  62 ,  64 ,  66 ,  68  are provided to be received within the body  60  of the respective feed box, the base of each inert member having apertures  69  formed therein such that the insert members define said convoluted baffle arrangement within the respective feed box. 
     The baffle plates may not be required and a single insert member  72 , as shown in  FIG. 8 , may be located within the body  70  of the feed box, said insert member  72  having lip portions defining said outlet slot  38 . In the embodiment shown in  FIG. 8 , only an upper lip  40  may be provided, where such is sufficient for dispensing water and/or a water and solids mixture onto the upper surface of the adjacent screen section to define a laminar flow of water across the screen section to entrain any solid material present into said flow of water. It is envisaged that the solid material may be applied onto the screen section from above to be entrained into the flow of water on the screen. However, it is preferred that the solid material to be screened be passed into the feed box entrained in a flow of water to ensure that the solid material is evenly distributed within the flow of water as it leaves the feed box and is passed onto the adjacent screen section. 
     As discussed above, each screen assembly  20 , 30  comprises an upstream screen section  22 , 32  and a respective downstream screen section  24 , 34 , each screen section having a respective feed box  35 A,  35 B,  35 C,  35 D at an upstream side thereof for delivering a laminar flow of water onto the respective screen section. The upstream feed box  35 A, 35 C of each screen assembly  20 , 30  may be supplied with a mixture of water and particles of solid material entrained or suspended therein, comprising a mixture of oversize and undersize material. Such mixture is delivered onto the upper surface of the upstream screen section  22 , 32 , such that undersize material passes through the screen section  22 , 32  to be collected therebelow while oversize material flows over the screen section  22 , 32  and passes onto the respective adjacent downstream screen section  24 , 24 . A flow of water is delivered from the downstream feed box  35 B, 35 D of each screen assembly  20 , 30  onto the respective downstream screen section  24 , 34  to fluidize the particles of solid material passing onto the respective downstream screen section  24 , 34  from the respective upstream screen section  22 , 32  and to ensure that the mixture flows evenly across the surface of the respective downstream screen section  24 , 34  to ensure efficient separation of oversize and undersize material on the respective downstream screen section  24 , 34 . Finally oversize material is delivered to a collection region at the downstream end of the respective downstream screen section  24 , 34  of each screen assembly  20 , 30 , oversize material from the upstream screen assembly  20  passing through a gap  80  defined between the upstream  20  and downstream  30  screen assemblies. 
     In an alternative embodiment, illustrated in  FIG. 9 , the feed box  135  may be effectively inverted, so that that water, and any solid material entrained therein, enters an upper region of the feed box  135  via one or more inlets  136  located in an upper region of the feed box  135 , the water/solids mixture passing out of the feed box onto an upper surface of an adjacent screen section  122  via an elongate outlet slot  138  defined along a lower region of the feed box between lip portions  140 , 142 . The upper lip  142  extends substantially parallel to the lower wall  140  of the feed box and to the upper surface of the screen section  122  to direct the flow of water to define a laminar flow across the screen section. An inner portion  144  of the upper lip  142  extends inwardly from the front wall of the feed box towards the rear wall thereof. By providing the inlet  136  of the feed box  135  adjacent an upper region thereof and the outlet  138  adjacent a lower region, any tendency for solid material to settle out in the feed box  135  is avoided. 
     As with the previous embodiments, inserts  154 , 156  are located within the body  150  of the feed box  135 , the inserts  154 , 156  having apertures  169  to define a convoluted flow path through the feed box to ensure that solid material is evenly distributed within the water exiting the feed box. 
     As shown in  FIG. 10 , in a further embodiment, the baffle plates may form part of a single component  254  located within the body  250  of each feed box  235 , rather than being formed by numerous insert members. 
     In the embodiment shown in  FIG. 10 , water (within which may be entrained particles of solid material) may be fed into the feed box  235  via an inlet  236  in a bottom wall  205  of the feed box. Alternatively, as illustrated in  FIG. 11 , the inlet  336  may be formed in a rear wall  302  of the body  350  of the feed box  335 . 
     Where it is desired to add further water to the material downstream of an upstream screen section, the screen box may be modified to receive material from the upstream screen section and mix such material with a flow of water, optionally with additional solid material entrained therein. 
     An example of such modified embodiment is shown in  FIG. 12 , wherein an inlet slot  439  is formed in the rear wall  402  of the feed box  435 , adjacent the upper wall  404 , said inlet slot  439  communicating with a mixing region  460 , defining a convoluted or curved path through the interior of the body  450  of the feed box  435 , upstream of the outlet slot  438 , such that the material entering the inlet slot  439  from a downstream end of the upstream screen section  422  mixes with and is entrained into the flow of water passing through the body  450  of the screen box  435  in the mixing region  460  before passing out of the screen box  435  onto the downstream screen section  424  via the outlet slot  438 . The water flow path through the feed box  435  between the baffles defines a narrowed slot like neck region  451  upstream of said mixing region  460  such that water flows into the mixing region  460  in a blade like jet, ensuring that the particles of solid material are entrained into the flow of water, before passing through the convoluted or “S” shaped mixing region  460  and out of the narrow outlet slot  438 , ensuring that the particles of sold material are evenly distributed in the laminar flow of water passing onto the downstream screen section  424 . 
     A further embodiment is illustrated in  FIG. 13 , wherein the inlet and outlet slots  538 , 539  and mixing region  560  are provided at a lower end of the body  550  of the feed box  535 , a water inlet  536  being defined in an upper wall  504  of the feed box  535 . As with the embodiment shown in  FIG. 12 , a narrowed slot like neck region  551  is defined between the baffles within the body  550  of the feed box  535  so that water passes into the mixing region  560  as a blade like jet to entrain the solid material into the flow of water, before passing through the convoluted or “S” shaped mixing region  560  and out of the outlet slot  538  to ensure even mixing of the solid material into the flow of water. 
     The feed box of the screen apparatus in accordance with the present invention ensures thorough mixing of the solids material in the water flowing over the surface of the screen and maintains the fluidized state of the solid material, ensuring reliable and efficient operation of the screen apparatus while minimising water consumption. The provision of a laminar flow of water and entrained/suspended solids across the surface of the screen enhances the efficiency of the screening process. 
     The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention. Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims, as interpreted according the principles of patent law, including the doctrine of equivalents.