Screw Conveyor Sizing Calculator: Capacity, Speed and Drive Power by the Handbook Method
The capacity, recommended speed and drive power of a screw conveyor for a given material and throughput.
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How this calculator works
A screw conveyor pushes material along a trough as the screw turns. Each turn moves one pitch length of the flighted section, and only the share of the trough cross-section that is filled (the trough loading) carries material. The capacity is the volume per turn times the speed times that loading, reduced when the conveyor slopes upward.
The drive power has two parts: the power to turn the screw and move the material along, and the power to lift it on a slope. The handbook relation uses a size factor for the screw diameter and a material factor for how hard the material is to move. Fast screws wear quickly, so there is a recommended maximum speed for each class of material.
Formulas used
- C = 60\,\frac{\pi}{4}(D^2 - d^2)\,P\,N\,\psi\,K
- hp = 10^{-6}\,(A L N + C W L F)
- P_l = \dot m\,g\,L\,\sin\theta
Worked example
With the default numbers in the calculator above:
- Volume carried per revolution at full trough: 21.38 L per revolution (304.8 mm pitch)
- Capacity factor for the angle: 1
- Capacity at this speed and loading: 23.09 m³/h (27.71 t/h)
- Share of the capacity your throughput uses: 50.53 percent (11.67 m³/h needed)
- Speed needed to carry that throughput: 30.32 rev/min
- Recommended maximum speed for the material group: 77.14 rev/min
- Power to turn the empty screw and move the material: 1.308 kW (A = 171, F = 1.4)
- Power to lift the material on the slope: 0 kW
- Power at the head shaft: 1.308 kW
- Motor power after the drive losses: 1.454 kW (next standard motor 1.5 kW)
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
What trough loading should I use?
About 45 percent for light, free-flowing material, 30 percent for lumpy or fine material and 15 percent for abrasive or difficult material. Take the figure from the screw maker.
Does the power include the slope?
Yes. The material lifting power is added for a conveyor above horizontal. The capacity also falls with the slope: about 10 percent at 10 degrees and 78 percent at 35 degrees.
Is this enough to order a motor?
No. It gives a good first estimate. Starting torque, bearings, flight type and the drive service factor must be confirmed with the screw maker.
Related calculators
Further reading: Standard Handbook of Engineering Calculations (screw conveyor power input and capacity); manufacturer screw conveyor data.
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