Abstract:
A mobile material screening apparatus ( 100 ) for separating bulk particulate material into groups of particles of differing sizes comprises a support chassis ( 2 ), a horizontal screen box ( 3 ) housed within the support chassis ( 2 ) and an additional inclined pre-screening module ( 50 ) which is adapted to be demountably attached to the support chassis ( 2 ). The mobile screening apparatus ( 100 ) comprises five outputs. Foldable conveyors ( 7   a,    8, 9, 910, 920 ) can be deployed outwardly from and stowed inwardly against the material screening apparatus. The provision of an inclined pre-screening module ( 50 ) provides relief to the horizontal screen box ( 3 ) by first removing the larger sized particles from the bulk material which can be returned to a crusher for recycling and serves also to increase the total number of grades of material separated by the screening apparatus.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a material screening apparatus for separating bulk particulate material into groups of particles of differing sizes. 
       BACKGROUND ART 
       [0002]    A mobile screening apparatus is known whereby the material to be screened is fed via an apron feeder which receives and conveys said material onto a horizontal screen box with two decks, an upper deck where the largest particles are removed and a lower deck. Particles having a smaller size fall through the upper screen deck onto the lower screen deck below. At the lower screen deck, particles of the next largest size grouping are separated from the remaining smaller particulate matter which falls through the lower screen deck. 
         [0003]    Elongate conveyers, which are mounted to and extend away from the screening apparatus, convey the separated materials to three distinct and separate locations where they are deposited in stockpiles, according to particle grade. 
         [0004]    It is quite common to require five grades of material, namely a reject or oversized material and four different grades of screened material. This is achieved by using two screening apparatus together in series. 
         [0005]    It is therefore an object of all the present invention to alleviate the disadvantages associated with the prior art. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is more particularly defined in the appended claims which are incorporated in this description by reference. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0007]    The invention will hereinafter be more particularly described with reference to the accompanying drawings which show, by way of example only, the screening apparatus of the invention. 
     
    
     
       IN THE DRAWINGS 
         [0008]      FIG. 1  is a schematic side elevation of a screening apparatus of the prior art having a conventional apron feeder and shown in its operating mode; 
           [0009]      FIG. 2  is a schematic end elevation of a screening apparatus having a conventional apron feeder and shown in its operating mode; 
           [0010]      FIG. 3  is a schematic side elevation of a screening apparatus of the invention shown in its operating mode; 
           [0011]      FIG. 4  is a schematic side elevation of the screening apparatus of the invention shown in its stowed mode; 
           [0012]      FIG. 5   a  is a schematic plan view of a screening apparatus of the invention shown on-site and in its operating mode; 
           [0013]      FIG. 5   b  is a schematic plan view of a screening apparatus of the invention shown on-site and in an alternative operating mode; 
           [0014]      FIG. 6   a  is a schematic plan view of a preferred embodiment of a screening apparatus of the invention shown on-site and in its operating mode; 
           [0015]      FIG. 6   b  is a schematic plan view of the preferred embodiment of a screening apparatus of the invention shown on-site and in an alternative operating mode; 
           [0016]      FIGS. 7   a  and  7   b  are isometric illustrations of the preferred embodiment of a screening apparatus of the invention shown in its operating mode; 
           [0017]      FIG. 7   c  is a detailed illustration of the connection of a conveyor to the pre-screening module  50  when in a deployed position; 
           [0018]      FIG. 8   a  is an isometric illustration of the preferred embodiment of a screening apparatus of the invention shown in its stowed mode; 
           [0019]      FIG. 8   b  is a detailed illustration of the connection of a conveyor to the pre-screening module  50  when in a stowed position; 
           [0020]      FIG. 9   a  is a schematic illustration of a folding end conveyor of the preferred embodiment of a screening apparatus of the invention shown in an operating mode; 
           [0021]      FIG. 9   b  is a schematic illustration of the folding conveyor of the preferred embodiment of a screening apparatus of the invention shown in a stowed mode; 
           [0022]      FIG. 10   a  is an isometric illustration of a pre-screening module which comprises a telescopically movable upper conveyor and is shown in a deployed mode; 
           [0023]      FIG. 10   b  is an isometric illustration of a pre-screening module which comprises a telescopically movable upper conveyor and is shown in a stowed mode; and 
           [0024]      FIG. 10   c  is a detailed side elevation a pre-screening module which comprises a telescopically movable upper conveyor and is shown in a retracted mode. 
       
    
    
       [0025]    Referring initially to  FIG. 1  and  FIG. 2 , a mobile screening apparatus  1  of the prior art comprises a chassis  2  mounted on tracks  2   a,  a horizontal screen box  3  having an upper screen deck  3   a  and a lower screen deck  3   b,  a catwalk  6 , conveyors  7 ,  8 ,  9 , a rear mount  10  and an apron feeder  11 . 
         [0026]    Bulk material to be screened is fed via apron feeder  11  to the upper screen deck  3   a  of horizontal screen box  3  which separates the largest particles. Movement of the screen propagates the large particles remaining on the screen surface towards conveyor  7  which conveys them away from the screening apparatus  1  to a remote heap  95 , as shown in  FIG. 5   a.  All particles that are not screened off at this initial stage fall downwardly through upper upper screen deck  3   a  onto the lower screen deck  3   b  of the horizontal screen box  3 . At lower screen deck  3   b,  particles of the next largest size grouping are separated from the remaining smaller particulate matter which falls through the screen. The particles which are retained by lower screen deck  3   b  are removed from the screening apparatus  1  via conveyor  8  which conveys them to a remote heap  96 , as shown in  FIG. 5   a.  The remaining particles which are sieved off from lower screen deck  3   b  fall downwardly and are transferred via either a chute or a conveyor (not shown) to conveyor  9  which further conveys them to remote heap  97 , as shown in  FIG. 5   a.    
         [0027]    Referring now to  FIG. 3 , the mobile screening apparatus  100  of the invention is shown in its operating configuration. Components of the apparatus indicated by reference numerals  2  through to  10  are common with those of the prior art screening apparatus  1  shown in  FIG. 1  and  FIG. 2 . The mobile screening apparatus  100  of the invention further comprises a pre-screening module indicated generally by the reference numeral  50 . 
         [0028]    The pre-screening module  50  comprises an upper conveyor  51 , a lower conveyor  52 , an inclined two-deck screen box  53 , a mounting bracket  54 , a dual acting folding ram  55  and a dual acting lifting ram  56 . The two-deck inclined screen box  53  further comprises an upper inclined screen  57 , a lower inclined screen (not shown) and upper and lower chutes  58 ,  59 , respectively. 
         [0029]    Pre-screening module  50  is pivotally mounted to the screening apparatus  100  via mounting bracket  54  which is adapted to fit onto rear mount  10  such that the module  50  can revert from an inclined operational position as shown in  FIG. 3  to a horizontal stowed position as shown in  FIG. 4  upon actuation of dual acting lift ram  56  which extends from the rear of the chassis  2  at mounting point  60  to the uppermost portion of the two-deck screen box  53 . With the dual acting lifting ram  56  extended the pre-screening module  50  is tilted about rear mount  10  such that the pre-screening module  50  can operate at various inclined angles. In an operational position, extension of dual acting folding ram  55  deploys upper conveyor  51  which thereby rises above two-deck screen box  53 . 
         [0030]    Referring to  FIG. 3  and  FIG. 5   a,  the operation of the mobile screening apparatus  100  will be described as follows: 
         [0031]    Bulk material, which may be in the form of quarried rocks, stones, gravel, coal, ash or particulate minerals, is transferred from a crusher  90  or transportation means onto the upper conveyor  51  of pre-screening module  50 . The bulk material is conveyed upwardly by inclined conveyor  51  until it reaches the uppermost point of the conveyor. At the apex of the conveyor&#39;s  51  travel, the bulk material drops into the top portion of the two-deck screen box  53  before travelling downwardly over upper inclined screen  57  where at a first screening stage the largest particles are separated from the bulk material. 
         [0032]    The inclination of the screen box  53  assists in the separation of and removal of the large particles which then exit the rear of the screen box  53  via upper chute  58  before being transferred by mobile wheeled stockpiler  91  to a heap  94  as shown in  FIG. 5   a.  In an alternative arrangement, shown in  FIG. 5   b,  the large particles that exit upper chute  58  may be fed via mobile-wheeled stockpiler  92  back to a crushing device  90   a  which can reprocess the particles before returning the recycled material via a conveyor to the inclined screen  57  for re-screening. 
         [0033]    The remaining bulk material falls through the upper inclined screen  57  onto a lower inclined screen below (not shown) for a second screening stage whereby particles in the next largest size range are separated from the bulk material. Particles which are unable to pass through the lower inclined screen exit the rear of the screen box  53  via chute  59  and are then transported by mobile wheeled stockpiler  92  to a heap  93  as shown in  FIG. 5   a.    
         [0034]    The bulk material which has passed through both upper  57  and lower inclined screens falls onto continuously moving lower inclined conveyor  52  which elevates to the upper screen deck  3   a  of horizontal screen box  3  on the main mobile screening apparatus  1  for further screening as described previously. 
         [0035]    Referring to  FIGS. 7   a,    7   b  and  FIG. 8   a,  in a preferred embodiment of the mobile screening apparatus of the invention, pre-screening module  50  is provided with a deploying mechanism that raises the module from a horizontal stowed position ( FIG. 8   a ) to an inclined operational position ( FIGS. 7   a  and  7   b ) using lifts  61  that extend from mounting point  62  on chassis  2  to the rear of pre-screening module  50 . Raising lifts  61 , which are actuated by hydraulic lifting rams  61   a,  causes pre-screening module  50  to tilt upwardly about rear mount  10  such that the pre-screening module  50  can operate at various inclined angles. Upon tilting the pre-screening module  50 , lifts  61  also serve to pull said module rearwards along a plurality of rollers (not shown) provided on module support structure  200  so that the upper end of lower inclined conveyor  52  is retained in relative proximity to upper conveyor  5  (shown without conveyor belt) of the horizontal screen box  3  provided on the main mobile screening apparatus  100  as shown in  FIGS. 7   a  and  7   b . Pre-screening module  50  is also provided with a plurality of damping springs  201  which are required for the vibration function of the apparatus and also help absorb the impact of heavy bulk material being loaded onto said module and damp the vibrational forces imparted by the module during the initial sequence of pre-screening. 
         [0036]    Referring to  FIGS. 7   a,    7   b  and  FIGS. 6   a,    6   b,  in the preferred embodiment, pre-screening module  50  is integrally provided with hanging conveyors  910  and  920  (shown without conveyor belts) which obviate the need for separate mobile wheeled stockpilers to transport the pre-screened bulk particulate material from the module  50 . Conveyor  910 , which extends further than conveyor  920 , is deployed obliquely from the support structure  200  of pre-screening module  50  such that the largest particles separated from the bulk material may either be conveyed to a separate heap  94  ( FIG. 6   a ) or be fed back to a crushing device  90   a  ( FIG. 6   b ) where they can be reprocessed before being returning as recycled material via a conveyor to the pre-screening module  50  for re-screening. 
         [0037]    With reference to  FIGS. 7   a,    7   b  and  8   a,  hanging conveyors  910 ,  920 , (shown without conveyor belts), each comprise a beam  930  that is connected to a universal joint  931  which is rotatably mounted to the support structure  200  of pre-screening module  50 . Support spars  932 , which are rotatably attached to at one end to support structure  200  by means of pivotal hinges  932   a  connect via pivotal joints  932   b  to mounting members  930   a  provided on beams  930 . Pivotal hinges  932   a  are vertically and horizontally offset from universal joints  931 . Hydraulic rams  933  act upon support spars  932  such that when said rams are retracted, conveyors  910 ,  930  are deployed outwardly from mobile screening apparatus  100  as shown in  FIGS. 7   a,    7   b  and  7   c.  Upon extension of hydraulic ram  933   s , support spars are each rotated about a plane as determined by pivotal hinges  932   a  and beams  930  are in turn moved substantially in the direction of rotation of the support spar and are thus moved inwardly towards the pre-screening module  50  and are simultaneously revolved about universal joints  931  so that the stockpilers  910 ,  920  are stowed substantially parallel to and vertically against, mobile screening apparatus  100  as shown in  FIGS. 8   a  and  8   b,  respectively. Flexible linkages  934  which may comprise chains, cables or other suitable means extend between beams  930  and the module support structure  200  to provide additional support to the outwardly extended conveyors  910 ,  920  and to locate the conveyor in the optimum working position with the head drum  950  of the conveyor in a horizontal position. Further support may be provided to the conveyors by means of separately detachable rigid support spars  940  which can be connected between beams  930  and the module support structure  200  as shown in  FIGS. 10   a  and  10   c.  Detailed illustrations showing the connection of a conveyor ( 910 ) to pre-screening module  50  together with the associated linkages in deployed and stowed positions are provided in  FIGS. 7   c  and  8   b,  respectively. 
         [0038]    Conveyors  8  and  9 , located on opposing sides of mobile screening apparatus  100  and shown without conveyor belts in place, each comprise a beam  930  that is connected to a universal joint  935  which is rotatably mounted to chassis member  936 . Support spars  937 ,  938  which extend upwardly from universal joints  937   a  and  938   a  attach to the underside of beam  930 . An hydraulic ram  939  acts on a single support spar of the respective conveyors  8 ,  9  such that extension of said ram causes said support spar to move the conveyors  8 , 9  outwardly from a stowed position ( FIG. 8   a ) to a deployed position ( FIGS. 7   a,    7   b  and  7   c ). The provision of rotatably mounted universal joints  931  and  935  enables the respective conveyors  910 ,  920  and  8 , 9  to reside within the confines of catwalk  6  and rest flat against the sides of mobile screening apparatus  100  thereby minimising its overall dimensions while in a stowed transportation mode. 
         [0039]    With reference to  FIG. 9   a  and  FIG. 9   b,  to further minimise the overall dimensions of mobile screening apparatus  100 , in the preferred embodiment end conveyor  7   a,  which is shown without a conveyor belt in place, is of two-part construction and is provided with a folding mechanism indicated generally by reference numeral  70  which enables the conveyor to fold back on itself. Folding mechanism  70  comprises hydraulic rams  71 ,  72 , spaced apart lever assembly members  73 , linkage arms  73   a  and support posts  74 ,  75 . Lever assembly members  73  each comprise a substantially L-shaped member having a first limb  73   b  and second limb  73   c.  Hydraulic rams  71 ,  72  each extend upwardly from brackets mounted on opposing edges of the rear of mobile screening apparatus  100  and connect at their respective ends to the respective ends of opposing first limbs  73   b  of lever assembly members  73  at pivot points  730 . The respective second limbs  73   c  of lever assembly members  73  are pivotably coupled to the respective sides of the upper portion of conveyor  7   a  at pivot points  76 . Linkage arms  73   a,  are each pivotally connected between a lever assembly member  73  at a position proximate the intersection of first limb  73   b  and second limb  73   c  and extend upwardly towards a support post  74 ,  75  to which they are pivotally connected by means of fulcrums  77 . This arrangement enables folding mechanism  70  to rotate about support posts  74 ,  75 , upon actuation of hydraulic rams  71 , 72 . From a deployed position ( FIGS. 7 and 9   a ) stowing of conveyor  7   a  ( FIGS. 8 and 9   b ) is facilitated by the extension of hydraulic rams  71 ,  72  which causes folding mechanism  70  to revolve upwardly about fulcrums  77  provided on support posts  74 ,  75 , which in turn induces the rotation of the upper portion of conveyor  7   a  about hinges  78  which link said upper portion to the lower portion of conveyor  7   a.  Once the hydraulic rams reach their maximum extension, the upper portion of conveyor  7   a  will have revolved about hinges  78  such that said upper portion of conveyor  7   a  will be inverted and resting on top of the upper deck of the screening apparatus as shown in  FIGS. 8   a  and  9   b.  From a stowed position, deployment of conveyor  7   a  is effected by the retraction of hydraulic rams  71 , 71  causes folding mechanism  70  to revolve downwardly about support posts  74 ,  75 . The use of such a folding mechanism  70  on conveyor  7   a  enables the overall length and height of the mobile screening apparatus  100  while in a transportation mode to be advantageously minimised. Furthermore, the provision of a such a hydraulically operated folding mechanism  70  on the underside of conveyor  7   a  provides additional robust support to said conveyor which is particularly advantageous when the mobile screening apparatus  100  is operating with a conventional apron feeder in place (i.e. in place of pre-screening module  50 ) and whereby the heaviest of the screened material will be conveyed by this particular conveyor. 
         [0040]    To further minimise the overall length of a mobile screening apparatus  100 , in a further embodiment the pre-screening module  50  may be provided with an upper conveyor  51   a  which is telescopically movable along its longitudinal axis enabling it to revert from an in-use extended position to a contacted transport position as shown in  FIGS. 10   a  and  10   b , respectively. Telescopically movable upper conveyor  51   a  comprises an upper portion  51   c  and a lower portion  51   b , wherein the lower portion  51   b  is linearly extensible relative the upper portion  51   c  to which it is slidably attached. A plurality of rams  80  which extend between each side of the pre-screening module support structure  200  and the respective sides of lower portion  51   b  enable said lower portion to move upwardly and downwardly along the side rails  51   d  of upper portion  51   c.  Upon retraction of the rams  80  the lower portion  51   b  is telescopically extended into its operating position as shown in  FIG. 10   a . Further retraction of the rams  80  causes the telescopically movable conveyor  51   a  to be raised above the upper inclined screen  57  by means of connecting arms  51   e  which are pivotably connected between hinged brackets  51   f  provided on the module support structure  200  and lifting bar  51   g  on upper portion  51   c.  Hinged brackets  51   f  also act as a stop (as shown in  FIG. 10   c ) against the travel of arms  51   e  thus retaining the telescopically movable conveyor  51   a  at a correct working height above the upper inclined screen  57 . Movable mounting means provided on the module support structure support the underside of telescopically movable conveyor  51   a  during use and enable said conveyor to slide smoothly between operating and transport positions. By way of example of a suitable movable mounting means, rollers  81  are shown in the figures. 
         [0041]    Following the initial sequence of pre-screening, the particulate material subsequently presented to the main screening apparatus  1  is of a finer consistency than would otherwise be the case associated with the prior art from one machine. Furthermore, the provision of a pre-screening module having a two-deck screen box increases the versatility of the mobile screening apparatus which is able to provide at least two additional grades of screened material while still maintaining its mobility. 
         [0042]    The material screening apparatus has a number of unique features:
   a folding mechanism for on board conveyors   five-way split output for different grades of materials   combined horizontal and inclined pre-screening module are mounted on the same chassis   oversize material is taken off at the front conveyor and fed back to a crusher rather than being fed right through the apparatus   the entire apparatus can easily be moved with a transport mode so that the weight, height and width of the apparatus are within the maximum requirements of the TÜV transport specifications and no special permit is required transport the apparatus   the pre-screening module can be removed from, or installed on, the apparatus depending on the usage requirements in any given situation.   
 
         [0049]    It is thought that the present invention and its advantages will be understood from the foregoing description and it will be understood that the invention is not limited to the specific details described therein, which are given by way of example only and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.