How to use Screw Conveyor Capacity& Drive Power Sizing Calculator
- Enter Conveyed bulk material type and adjust the options as needed.
- Run the tool and inspect its results, evidence and limitations.
- Copy or download the result, then verify it against the actual website, source data or business records.
Try a concrete example
Conveying dry grain/wheat (bulk density 0.75 t/m³, CEMA material friction factor 1.2) at target capacity 25.0 t/h (33.3 m³/h) over L=15.0m at a 10° incline (incline derating factor 0.80): using a Ø250 mm (10-inch) screw with 45% trough loading and standard pitch (P=250 mm). CEMA kinematic calculations yield required rotational speed of 117 RPM (below maximum 170 RPM limit). Drive power comprises 0.16 kW empty friction, 1.23 kW material horizontal push, and 0.18 kW gravity lift, totaling 1.56 kW shaft power. Factoring drive efficiency recommends a 3.0 kW (4.0 HP) gearmotor for steady continuous duty.
How to interpret results
Screw conveyors (augers) transport powders and granular solids in grain handling, chemical mixing, and cement plants. Primary design constraints are trough loading percentage and critical speed limit. Excess trough loading submerges hanger bearings in abrasive grit, causing rapid seizure. Excessive speed generates centrifugal forces that pin bulk solids against casing walls, halting axial transport. This tool sizes conveyors per CEMA 350 standards.
Frequently asked questions
What is screw conveyor trough loading and why is it restricted to 15%-45%?
Trough loading is the percentage of U-trough cross-sectional area occupied by material. Conveyors cannot operate 100% full; overfilling causes bulk solids to rotate with flights instead of advancing axially. Crucially, intermediate hanger bearings (spaced every ~3m) must remain above the material bed. Submerged bearings suffer catastrophic grit ingestion and seizure. CEMA limits loading to 15% for heavy abrasives, 30% for standard powders, and 45% for light materials.
Why is there a maximum RPM limit for screw conveyors and what happens if exceeded?
Axial conveyance relies on gravity and casing friction overcoming tangential flight drag. Above critical speed, centrifugal force exceeds gravitational force, pinning solids to casing walls and throwing them in chaotic circular flight. Forward throughput drops precipitously, particles degrade, and flight wear skyrockets. CEMA specifies maximum safe speeds (e.g. ≤ 70-80 RPM for Ø250 mm).
How does incline conveying impact capacity and required drive power?
As incline angle θ increases, gravity causes bulk solids to slip backward through flight clearances, degrading volumetric efficiency. Under CEMA derating: at 10° incline, capacity drops to ~85%; at 15°, to ~70%; at 20°, to ~60%. Beyond 30°, standard pitch flights fail (requiring tubular casings and short pitch flights). Furthermore, gravitational lift requires additional motor power (P_lift = Q · g · H).
When should a shaftless screw conveyor be selected over a conventional shafted screw?
Shafted conveyors weld helical flights to a central steel pipe, offering high torsional rigidity across long spans with hanger bearings. Shaftless conveyors eliminate the center pipe and hanger bearings, using a cold-formed heavy-duty alloy spiral resting on wear liners (such as UHMW-PE). Shaftless designs prevent clogging and are the premier choice for dewatered sludge, stringy municipal waste, and sticky bulk materials.