The invention relates to portable screen systems.
Previously, it has been known to provide portable screen systems for separating fine material from coarse material wherein the frame of the unit is lowered flush onto preferably flat level ground, and material to be processed which overflows beyond side ends of the screen builds up along end sides of the unit. A set of wheels are made movable relative to the frame from an operative position for transporting the apparatus to an inoperative position for resting the frame flush on the ground. Such a unit is shown, for example, in U.S. Pat. Nos. 4,197,194, Des. 263,836, 4,237,000, and 4,256,572.
There are significant disadvantages with such a system. If the ground onto which the frame is rested in flush fashion is not level and/or bumpy and undulating, the vibrating screen will not be level side-to-side, and the material placed on the vibrating screen will be inefficiently processed and tend to shift more to one side of the screen than the other and thus be unevenly distributed. Accordingly, with the aforementioned unit, the ground on which the frame is positioned in flush manner should be level and not bumpy or undulating.
A further disadvantage is that during operation of the aforementioned unit, overflow material to the sides of the unit builds up around the wheels and the side walls and can interfere with removal of the unit from the site due to such build-up of overflow material. Also, build-up of material where the frame sits flush on the ground may impede removal during freezing weather if such material were to freeze and trap the frame.
Another disadvantage of the above described unit is that if the frame resting on the ground settles unevenly during operation, the unit may become tilted, particularly if a rock was in contact with one small portion of the frame.