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Screw conveyor capacity and power

Enter material, diameter, pitch, speed and length to see how much the screw conveys, whether speed is within the class limit and how much power the motor needs.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Pre-sizing
Material
Screw
Design

Horizontal screws and inclines up to 20°. Steeper or vertical screws need specific design (short pitch, high speed and choke feeding).

—Screw capacity at the entered speed
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Capacity versus speed

Capacity line at the class loading; the dashed line is design capacity and the vertical, the CEMA maximum speed.

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Power components (DIN 15262)

Power to move the material, to turn the empty screw and to lift the material, and power at the motor.

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Method, assumptions and references

Equations used

Capacity: Q = (π/4) · (D² − d²) · p · n · 60 · φ · ρ · C (Q in kg/h; D, d, p in m; n in rpm; φ = trough loading; C = incline factor)
Usual incline factor: C = 1.0 (0°), 0.9 (5°), 0.8 (10°), 0.7 (15°), 0.6 (20°); maximum speed from the CEMA 350 capacity table by class and diameter
Power (DIN 15262): P = P_H + P_N + P_St; P_H = Q · L · λ ÷ 367; P_N = D · L ÷ 20; P_St = Q · H ÷ 367 (P in kW, Q in t/h, L, H, D in m); P_motor = P ÷ η

Assumptions and limits

  • Standard single-pitch flight, no paddles or cut flights, steady feed and U-trough. Loadings and maximum speeds follow CEMA 350; λ coefficients follow DIN 15262 material groups.
  • Power is computed at design capacity. Starting with a full screw, material that sets when idle, special hanger bearings and flood feeding (feeder under a silo) are not included.

Standards and technical documents

  • CEMA Standard No. 350: Screw Conveyors for Bulk Materials
  • CEMA Standard No. 550: Classification and Definitions of Bulk Materials
  • DIN 15262:1983: Continuous conveyors — Screw conveyors for loose bulk materials — Principles of design
  • ISO 7119:1981: Continuous mechanical handling equipment for loose bulk materials — Screw conveyors — Design rules for drive power
  • Martin Sprocket & Gear: Screw Conveyor Catalog and Engineering Manual

U.S. regulations

  • ASME B20.1: Safety Standard for Conveyors and Related Equipment
  • OSHA 29 CFR 1910.212 (machine guarding) and 1910.147 (lockout/tagout)
  • OSHA 29 CFR 1910.272: grain handling facilities

Frequently asked questions

How do I calculate screw conveyor capacity?

Multiply the annular area (π/4 · (D² − d²)) by pitch, revolutions per hour, trough loading and bulk density. A 12 in screw with a 3.5 in pipe and full pitch moves 19.4 ft³/h per rpm at 45% loading, the value in the CEMA capacity table.

What is the maximum speed of a screw conveyor?

It depends on diameter and material class. Per CEMA 350, a 12 in screw runs up to 145 rpm with grain (45%), 90 rpm with mildly abrasive powders (30% A) and 45 rpm with abrasive materials (15%).

How is screw conveyor power calculated with DIN 15262?

Add three parts: material, Q · L · λ ÷ 367; empty screw, D · L ÷ 20; and lift, Q · H ÷ 367, with Q in t/h, lengths in m and power in kW. For 6 short tons per hour of lime over 40 ft with 6 ft of lift and λ = 4, that is about 1.25 hp at the shaft.

Why does an inclined screw carry less?

Material slips back over the flight. At 10° capacity drops to about 80% of horizontal and at 20° to 60%. Short pitch and higher speed recover part of the loss.