Patent ID: 8505738

Claim:
A mobile material screening apparatus for separating bulk particulate material into groups of particles of differing sizes, the apparatus comprising: a support chassis; a horizontal screen box apparatus, the screen box mounted on the support chassis and having an upper screen deck and a lower screen deck; the mobile screening apparatus further comprising an additional pre-screening module, which is slideably connected to, and supported on, mounting means provided on the support chassis, the pre-screening module having an upper inclined screen and a lower inclined screen wherein the pre-screening module is provided with an upper conveyor and lower conveyor, the upper and lower conveyors being arranged parallel to the upper inclined screen and a lower inclined screen, the upper conveyor being adapted to convey material to the pre-screening module screens and the lower conveyor being adapted to transfer material from the pre-screening module to the horizontal screen box apparatus; the screening apparatus further comprising at least one lifting ram that extends from the support chassis to the pre-screening module, the at least one lifting ram operable to move the pre-screening module between a horizontal stowed position and an operational position in which the angle of inclination of the pre-screening module is altered to thereby tilt the pre-screening module relative to the horizontal screen box, and, when the pre-screening module is being moved from the stowed position to the tilted operational position, the at least one lifting ram is further operable to simultaneously pull the pre-screening module along a plurality of rollers on the support chassis to a position above the horizontal screen box so that the particulate material is conveyed from the lower inclined conveyor to the pre-screening module to the horizontal screen box, and, whereby the provision of the horizontal screen box and the pre-screening module provides five different grades of material as output from the mobile screening apparatus, including reject unscreened material and four different grades of screened material.