Screw Conveyor Capacity & Power (CEMA 350) Calculator
Calculate industrial screw conveyor volumetric and mass throughput, CEMA drive motor power (kW), empty friction drag, material conveying resistance, incline derating, and breakaway torque.
1. Conveyor Geometry & Drive Speed
2. Material Characteristics
Capacity & Drive Diagnostics
Power Requirement Breakdown
5 Fatal Engineering Traps in Screw Conveyor Design
1. Overfilling Abrasive Minerals Beyond 15%–30% Trough Loading
Specifying 45% trough loading for abrasive solids (limestone, crushed ores, foundry sand) completely submerges the intermediate hanger bearings beneath the moving material bed. Abrasive mineral fines work directly into the bearing journals, grinding through bronze or babbitt bushings in less than 300 operating hours and destroying the center drive pipe.
2. The Steep Incline Capacity Collapse (>15° Incline Back-Spill)
Operating a standard full-pitch screw conveyor on inclines exceeding 15° causes bulk solids to slip backward through the clearance gap between the screw flight and trough wall. Rather than advancing upward, material cascades backward, increasing power consumption while slashing net discharge capacity by up to 50%. Inclines >15° demand short-pitch flights (0.66× pitch) and close-clearance tubular housings.
3. Hanger Bearing Choking in Sticky & Fibrous Materials
Standard screw conveyors require intermediate hanger bearings every 3.0–3.6 meters to support shaft weight. When conveying cohesive municipal sludges, wet filter cakes, or fibrous products, material catches on the bearing hangers, building up an immovable brick-like plug that stalls the conveyor. Cohesive materials mandate shaftless screw conveyors with continuous UHMWPE liners.
4. Motor Burnout from Compacted Dead-Stop Breakaway Torque
When a screw conveyor trips or shuts down under full load, fine powders consolidate and pack tightly between the helical flights and trough bottom. Breaking this compacted plug on restart requires 250% to 350% of normal running full-load torque. Sizing standard general-purpose electric motors without NEMA Design C high-starting-torque windings or VFD torque boost trips circuit breakers instantly.
5. Center Pipe Sag & Trough Bottom Metal-to-Metal Gouging
Exceeding recommended unsupported conveyor spans without intermediate hanger bearings causes the rotating center pipe to sag under gravity and material load. The rotating outer edges of the steel helical flights plow directly into the bottom of the U-trough casing, gouging grooves through the trough metal, throwing sparks, and generating iron particle contamination in clean process products.
Governing CEMA 350 Equations & Mechanics
Standard full-pitch volumetric capacity is governed by screw cross-sectional displacement:
Cvol = π / 4 · [ Dscrew² - Dpipe² ] × Pitch × N × 60 × [ %TL / 100 ] × Kinc
Incline derating factor empirical formulation (CEMA 350):
Kinc ≈ cos(θ) - 0.015 · θ
CEMA Total Drive Shaft Power (Pshaft in kW):
Pshaft = Pempty + Pmaterial,horiz + Pelevation
Where:
P_empty=(L · N · F_d · F_b) / 100,000(kW)P_material,horiz=(C_vol · ρ_bulk · L · F_m) / (367,000 · 0.9)(kW)P_elevation=(Ṁ · L · sin(θ) · 9.81) / 3600(kW)T_running=(P_shaft × 9550) / N(N·m)T_breakaway=2.5 × T_running(N·m)