How to Calculate Screw Conveyor Capacity and Power Requirements
Screw conveyors are widely used in industries for transporting bulk materials horizontally, vertically, or at an incline. Proper calculation ensures efficient operation and prevents equipment failure. Below is a step-by-step guide to determining screw conveyor capacity and power requirements.
1. Calculating Screw Conveyor Capacity
The capacity (Q) of a screw conveyor depends on screw diameter, pitch, rotational speed, and material characteristics. The formula is:
\[ Q = 60 \times \frac{\pi}{4} \times D^2 \times p \times n \times \psi \times \gamma \]
Where:
- Q = Capacity (tons/hour)
- D = Screw diameter (meters)
- p = Pitch (meters, usually equal to screw diameter for standard conveyors)
- n = Rotational speed (rpm)
- ψ = Filling coefficient (typically 0.15–0.45 depending on material flowability)
- γ = Bulk density of material (tons/m³)
For example, if a conveyor has a 0.3m diameter screw rotating at 50 rpm with a pitch of 0.3m and transports cement (γ = 1.5 tons/m³), assuming ψ = 0.3:
\[ Q = 60 \times \frac{\pi}{4} \times 0.3^2 \times 0.3 \times 50 \times 0.3 \times 1.5 ≈ 9.55 \, tons/hour\]
2. Determining Required Motor Power
The power requirement depends on conveyor length, material friction, inclination angle, and capacity:
\[ P = P_h + P_f + P_{st} \, (\text{kW}) \]
Where:
- P_h = Power needed for horizontal transport (\(P_h = Q × L × f × g / 3600\))
- P_f = Power lost due to friction (\(P_f = Q × H × g / 3600\))
- P_st= Additional power for startup (~20% extra)
Variables:
- L = Conveyor length (meters)
- f= Friction coefficient (~1–4 depending on material abrasiveness)
- H= Lift height if