calculation examples for screw conveyor

Screw Conveyor Calculation Examples in the Aggregate Industry

Screw conveyors are essential in the aggregate and sand production industry, widely used for transporting bulk materials such as crushed stone, sand, and gravel. Proper design and calculation ensure efficient operation and minimize wear. Below are key calculation examples to determine capacity, power, and speed for screw conveyors in aggregate applications.

1. Capacity Calculation

The volumetric capacity (Q) of a screw conveyor is calculated as:
\[ Q = 60 \times \frac{\pi}{4} \times D^2 \times p \times n \times \psi \times C \]
Where:

  • D = Screw diameter (m)
  • p = Pitch (usually 0.8–1.0 times D)
  • n = Rotational speed (rpm)
  • ψ = Loading efficiency (typically 15–40% for aggregates)
  • C = Material factor (e.g., 0.7 for sand, 0.5 for crushed stone)

    • Example:
    For a 0.3m diameter screw moving sand (C=0.7) at 50 rpm with 30% loading:
    \[ Q = 60 \times \frac{\pi}{4} \times 0.3^2 \times 0.25 \times 50 \times 0.3 \times 0.7 ≈ 11.1 \, \text{m³/h} \]

    2. Power Requirement


    The drive power (P) depends on material resistance and conveyor length:
    \[ P = \frac{Q \times L \times \lambda \times g}{367} \]
    Where:

  • L = Conveyor length (m)
  • λ = Friction coefficient (1.5–4 for aggregates)
  • g = Gravity (9.81 m/s²)

Example:
A 10m conveyor handling 11.1 m³/h sand (λ=2.5):
\[ P = \frac{11.1 \times 10 \times 2.5 \times 9.81}{367} ≈ 7.4 \, \text{kW} \]

3. Speed Selection


Optimal speed avoids material degradation. For abrasives like granite, limit to 20–40 rpm; for sand, up to 60 rpm.

FAQ

Q: How to reduce wear in screw conveyors?
A: Use hardened flights, limit speed, and ensure proper alignment.

Q: Can screw conveyors handle wet aggregates?
A: Yes, but consider steeper inclines and corrosion-resistant materials.

Engineering Case

A quarry in Texas upgraded its sand handling with a 0.4m screw conveyor (15m length, 35 rpm). Calculations ensured 20 m³/h capacity with a 10 kW motor, reducing blockages by 30%.

By applying these principles, aggregate producers can optimize screw conveyor systems for durability and efficiency.

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