Step 1: Calculate Required Throughput
Conveyor capacity depends on belt width, belt speed, material density, and trough angle. The volumetric capacity of a troughed belt:
A = cross-sectional area of material on belt (m²) — from manufacturer's tables for trough angle and belt width
v = belt speed (m/s)
ρ = bulk density of material (t/m³)
Belt speed guidelines by material type:
| Material | Max belt speed (m/s) | Reason for limit |
|---|---|---|
| Fine, dusty powders | 0.5–1.5 | Dust generation and spillage |
| Light unit loads | 1.0–2.0 | Discharge control |
| Grain, small aggregate | 2.5–4.0 | General; impact on scrapers |
| Coarse aggregate, ore | 3.5–5.0 | Impact and wear at load point |
| Lightweight, non-abrasive bulk | Up to 6.0 | Where dust and impact are not limiting |
Step 2: Calculate Effective Belt Tension
The effective tension (Te) is the net pulling force the drive must transmit to the belt:
Tf = friction component = f × L × g × (2mb + mi + mm)
Tg = gravity component = H × g × mm (positive for inclines, negative for declines)
Tm = material acceleration at loading = Q/3.6 × (v − v₀) where v₀ = initial material velocity
Where: f = friction factor (0.016–0.03 for well-maintained conveyors; up to 0.04 for high-drag environments); L = conveyor length (m); H = height change (m); mb, mi, mm = mass per metre of belt, idlers, and material respectively.
Step 3: Size the Drive Motor
Apply service factor of 1.15–1.25 for final motor selection
Add 5–10% for starting duty unless soft-starter or VFD is used
Worked example
100 m horizontal conveyor, 100 t/h of aggregate at 2.5 m/s. Belt mass = 12 kg/m, idler mass = 9 kg/m, material mass = 100,000/(3,600 × 2.5) = 11.1 kg/m. f = 0.022, g = 9.81.
Tf = 0.022 × 100 × 9.81 × (2 × 12 + 9 + 11.1) = 0.022 × 100 × 9.81 × 44.1 = 9,514 N
P = (9,514 × 2.5) / 1,000 = 23.8 kW. With service factor 1.15: select 30 kW motor (next standard size).
Maximum Belt Inclination
The maximum angle at which material stays on the belt depends on the material's angle of surcharge and the belt surface:
| Material | Max inclination |
|---|---|
| Sand, grain, loose aggregate | 12°–18° |
| Coal, fine ore | 15°–18° |
| Crushed stone, lumpy ore | 18°–20° |
| Unit loads on rubber-covered belt | Up to 25° with cleated belt |
Above these angles, material slides back during starting or belt deceleration. For higher inclinations, use cleated belts or switch to bucket elevators or pneumatic conveyors.