Fine Material Screw Washers are especially useful if the application requires more retention time in order to hydrate materials. McLanahan has designed its Fine Material Screw Washers with a longer screw shaft to provide a longer dry deck area, resulting in a drier product discharge. If an application calls for a greater level of dewatering, then they are often placed in series with a Dewatering Screen.
To achieve the desired results with a Fine Material Screw Washer, sand or other fine material is directed to the feed box in the baffle plate. Coarser, heavier materials sink to the bottom of the box, while finer waste fractions are carried by the up-current of water to the surface and overflow the weirs.
The heavier material that has sunk to the bottom is conveyed up an 18-degree slope toward the discharge end. The rolling and tumbling of the material releases fines and lightweight fractions into suspension; it also mildly scrubs superficial clays from the sand/mineral surfaces. As the material is conveyed toward the discharge end, the water begins to separate from the material. McLanahan has designed an extra-long dry deck area, providing maximum dewatering of material. A channel is provided opposite the conveying side to allow water to drain from the material and return to the pool area.
As with any McLanahan design, safety is key. Fine Material Screw Washers have fewer moving parts, especially when compared to similar equipment such as bucket wheel desanders. When equipped with an optional top protective cover, access into the machine is virtually eliminated.