Calculate screw-conveyor mass and volumetric flow from geometry, loading, density, and speed, or reverse-solve the RPM required for a target throughput.
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Screw Conveyor Flow Rate Formula
This calculator estimates mass and volume flow using net annular area, pitch, speed, an effective fill fraction, bulk density, and a capacity reduction factor. Its effective fill fraction is applied to the net annular area; manufacturer trough-loading percentages may use a different geometric convention. Use the manufacturer’s capacity tables and recommended loading and speed for equipment selection.
Mass flow (kg/h) = 60 × (π / 4) × (D² − d²) × pitch × RPM × fill fraction × density × capacity factor.
Mass flow (lb/h) = mass flow (kg/h) / 0.45359237.
- Mass flow (kg/h) = mass flow rate in kilograms per hour
- Mass flow (lb/h) = mass flow rate in pounds per hour
- D = screw outside diameter, converted to meters
- d = shaft diameter, converted to meters
- Pitch = screw pitch, converted to meters
- RPM = screw speed in revolutions per minute
- Fill fraction = fill factor or loading ratio, from 0 to 1
- Density = bulk density, converted to kg/m³
- Capacity factor = inclination factor, from 0 to 1
The term (D² − d²) removes the shaft area from the screw cross section. The pitch and RPM determine how much material is advanced per minute. The effective fill factor reduces the modeled full annular volume; it does not establish the actual loaded portion or measured throughput. Bulk density converts volume flow into mass flow. The inclination factor reduces capacity for upward conveying. The optional capacity factor defaults to 1.0 for a horizontal geometric estimate. For an incline, enter an applicable manufacturer or test-derived reduction factor; angle alone does not determine capacity.
Fill and Capacity Factors
Obtain loading and reduction factors for the specific bulk material and conveyor. Manufacturer trough-loading recommendations commonly use discrete loading classes such as 15%, 30%, or 45%; those percentages are not automatically equivalent to this model’s net-annular-area fill. The tables below preserve the existing illustrative assumptions, not validated design recommendations.
| Material behavior | Illustrative effective fill factor | Notes |
|---|---|---|
| Free-flowing, non-abrasive material | 0.30 to 0.45 | Often used for grains, pellets, and similar materials |
| Moderately flowing bulk solids | 0.20 to 0.35 | Good starting range for many powders and granules |
| Abrasive, sluggish, or irregular material | 0.10 to 0.25 | Lower loading helps reduce overload and wear |
| Illustrative case | Illustrative capacity factor | Capacity effect |
|---|---|---|
| Horizontal | 1.00 | No inclination reduction |
| Example A (no rated angle) | 0.85 to 0.95 | Small capacity reduction |
| Example B (no rated angle) | 0.65 to 0.85 | Noticeable reduction |
| Example C (no rated angle) | 0.35 to 0.65 | Large reduction, material behavior becomes more important |
Example Calculations
Example 1: Horizontal conveyor in metric units
Given:
- Screw diameter: 0.30 m
- Shaft diameter: 0.05 m
- Pitch: 0.30 m
- Speed: 60 RPM
- Fill factor: 0.30
- Bulk density: 800 kg/m³
- Inclination factor: 1.00
Calculation:
Mass flow ≈ 60 × (π / 4) × (0.30² − 0.05²) × 0.30 × 60 × 0.30 × 800 × 1.00 ≈ 17,812.8 kg/h.
The estimated flow rate is 17,812.8 kg/hr.
Example 2: Imperial inputs with lb/hr output
Given:
- Screw diameter: 12 in
- Shaft diameter: 2 in
- Pitch: 12 in
- Speed: 45 RPM
- Fill factor: 0.25
- Bulk density: 50 lb/ft³
- Inclination factor: 0.80
After unit conversion, the estimated mass flow is about 9,351.6 kg/hr, which is about 20,616.7 lb/hr.
FAQ
What fill factor should you use?
Use the actual loading ratio if you know it. If you are estimating, choose a lower fill factor for abrasive, sticky, sluggish, or irregular materials. Choose a higher fill factor only for free-flowing materials and conveyors designed to carry that loading safely. Enter the effective fill as a percentage from 0 to 100. Zero fill produces zero forward flow; in the speed inverse, zero fill gives either an impossible positive target or a nonunique zero target. Do not use a suggested range as an equipment safety rating.
Why does shaft diameter reduce the flow rate?
The shaft occupies part of the screw cross section, so that area cannot carry material. The calculator accounts for this by using D² − d². A larger shaft leaves less open conveying area and lowers the calculated capacity.
Is the result exact for every material?
No. The result is an estimate based on geometry, speed, loading, density, and inclination. Real flow can change because of material slip, particle size, moisture, aeration, screw clearance, inlet conditions, and discharge restrictions. For design work, compare the result with manufacturer data and material test data when possible.
