Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/420189
AGGREGATES MANAGER December 2014 16 1) A slurry of solids and water is fed downward onto a steeply inclined screen surface to achieve rapid drainage. 2) A pool of water forms in the valley as solids build up on the inclined surface that moves material upward toward the discharge end. 3) Counter rotating motors create a linear motion that moves solids uphill while water drains through the screen media. 4) e uphill slope of the screen surface along with a discharge weir creates a deep bed that acts as a filter medium, allowing retention of much finer solids than the screen media aperture openings. Dewatered sand moves over the end weir and discharges as a drip-free product. Studies have shown that the key to dewatering screen perfor- mance is droplet formation at the underside of the screen me- dia. Essentially, the upward acceleration and amplitude of the linear action must draw (force) the water to the boom of the cake through what is best described as a tortuous capillary type path formed by the nested grains of sand and then through the apertures to form droplets before the downward stroke, other- wise the water may well migrate back into the cake. European studies have shown there are specific combina- tions of amplitude and speed that are the most suitable for dewatering fine mineral particulates. e most common that is currently in use is 900 to 1,200 rpm and a 1/4- to 3/8-inch stroke. Claims of across the board 10-percent moisture of the output product should be ignored; however, claims of 12 to 15 percent for C-33 sand all day are completely possible. For fines recovery, producers can expect it to be more like 20 to 25 per- cent moisture. Essentially, you will achieve, at a minimum, 10 percent points drier material than in a single-gravity machine like a bucket-wheel or screw. Screen media can be as varied as the applications where High amplitude motion at relatively low frequency is most effective at removing interstitial water from a granular mass. Amplitude and acceleration must combine to force the water out of capillaries in the bed. EQUIPMENT MANAGEMENT Inside the dewatering screen, a slurry of solids and water is fed into the screen. As solids move up the slope of the screen and over the end weir, water drains through the screen media.