Screw Conveyor Flow Rate Calculation

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Screw Conveyor Flow Rate Calculator
Common sizes: 6, 9, 12, 16, 20, 24 inches
Standard pitch usually equals diameter
Grain ~45, Sand ~100, Cement ~90
15% (Abrasive/Heavy) 30% (Avg. Industrial) 45% (Free Flowing/Light) 95% (Feeder Application)
0 for horizontal. Efficiency drops with incline.
Volumetric Flow Rate: 0 ft³/hr
Mass Flow Rate (lbs): 0 lbs/hr
Capacity (Tons): 0 TPH
Conveying Speed: 0 ft/min

How to Calculate Screw Conveyor Capacity

Determining the flow rate of a screw conveyor is essential for properly sizing equipment in bulk material handling operations. Whether you are moving grain, cement, sand, or chemical powders, the capacity calculation relies on the geometry of the screw, the rotation speed, and the characteristics of the material.

The Flow Rate Formula

The standard industry formula (based on CEMA standards) for calculating the capacity of a screw conveyor is:

C = 60 × (π/4) × (D² – d²) × P × N × F × e

However, for most practical estimations, we simplify this to the volumetric displacement multiplied by efficiency factors:

  • N (RPM): The speed at which the screw shaft rotates.
  • Cross-Sectional Area: Determined by the screw diameter.
  • Pitch (P): The distance the material moves forward in one revolution (usually equal to the diameter in "standard pitch" screws).
  • Trough Loading (F): The percentage of the trough cross-section occupied by material.
  • Incline Factor: A reduction coefficient applied when the conveyor operates at an angle.

Understanding Trough Loading (%)

Not all screw conveyors run full. In fact, overloading a screw can lead to bearing failure or motor stalls. The loading percentage is chosen based on the material type:

Material Type Recommended Loading Examples
Abrasive / Heavy 15% Silica sand, fly ash, cement clinker
Average Industrial 30% Coal, limestone, sawdust
Light / Free-Flowing 45% Grain, malt, dry plastic pellets

Effect of Incline on Flow Rate

Gravity works against the flow of material when a screw conveyor is inclined. As the angle of inclination increases, the conveying efficiency drops significantly because material tends to tumble back over the screw flights. A standard rule of thumb is:

  • 0° – 10°: Minimal loss (approx 95-100% efficiency).
  • 10° – 20°: Noticeable loss (approx 80-90% efficiency).
  • 20° – 30°: Significant loss (approx 60-70% efficiency).
  • > 45°: Requires specialized vertical screw designs.

Using This Calculator

To use the Screw Conveyor Flow Rate Calculator above, input the Screw Diameter and Pitch in inches. If you are unsure of the pitch, standard screws usually have a pitch equal to their diameter (e.g., a 12-inch screw has a 12-inch pitch). Enter the RPM and the Material Density to get the mass flow rate in Tons Per Hour (TPH).

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