Aggregate Washing Sand Screw 2D — Counter-Current Wash & Dewater

Screw & Feed

Screw rotation speed 9 rpm

Feed rate 60 t/h

Wash water flow 50 m³/h

Live Readouts

Running — steady state

Poor washClean

Clean sand output

0 t/h

Fines removed

0 t/h

Residence time

0 s

Product moisture

Trough status

Nominal

How it works

A sand screw washer conveys wet, clay-contaminated sand up an inclined trough with a slow-turning helical auger. The lower end of the trough sits below a water bath fed near the discharge — water flows downhill while sand is carried uphill, a true counter-current arrangement. Light clay and silt fines stay suspended and are carried backwards by the water to overflow at the low end (the "overflow launder"), while denser sand sinks and rides the screw flights up and out above the waterline.

conveyor speed  v ∝ screw rpm × pitch
residence time  t_wash = L_wash / v          (more rpm → shorter wash time)
wash efficiency = 1 − exp(−(t_wash/τ) × (Q_water/Q_sand)/ratio0)
dewater time    t_dry  = L_incline / v       (time spent above waterline)
moisture%       = moistMin + (moistMax−moistMin) × exp(−t_dry/τ_d)

Too fast a screw — short residence time in the wash zone and short drainage time above the waterline: fines stay stuck to the sand and the discharged product is wetter.
Too slow a screw — thorough washing and good dewatering, but throughput drops below the feed rate and the trough backs up (overload).
More wash water — dilutes the slurry and lifts more fines into suspension per unit time, improving wash efficiency at any given rpm, at the cost of a wetter, higher-volume overflow.
Higher feed rate — more sand per unit of water and per unit of screw capacity, so wash efficiency falls unless rpm or water flow are increased to match.

Real-world relevance: this counter-current screw-washing/dewatering step is standard in aggregate and silica-sand processing — it is a distinct unit operation from vibrating-screen size classification, which sorts particles by size rather than washing fines off a single size fraction.

Raw / muddy sand Washed / clean sand Clay & silt fines

Wash Efficiency & Moisture vs. Time