Conveyor idler (roller) load and impact calculator
Load on the most-loaded carrying and return roller from pitch, belt and material load, with service factors — and the impact load in the loading zone.
Result
How it works
Each carrying idler set supports the belt and material over one pitch. The centre roller of a troughed set takes the largest share, and duty, environment and lump size raise the load further. The result is compared with the load capacity in your roller catalogue.
This calculator follows the method published in Rulmeca’s technical information. The factor values in the drop-downs are Rulmeca’s published values; shock and speed factors and the roller capacity come from your roller maker.
Formula
Carrying set: Ca = ao × (qb + IV / (3.6 v)) × g Dynamic: Ca1 = Ca × Fd × Fs × Fm; most-loaded roller ca = Ca1 × Fp Return set: Cr = au × qb × g; Cr1 = Cr × Fs × Fm × Fv; cr = Cr1 × Fp Impact (fine material): Hc = Hf + Hv sin²γ; pi ≈ IV √Hc / 8 [kgf]; pic = Fp × pi g = 9.81 m/s²; 1 daN = 10 N
| Symbol | Meaning | Unit |
|---|---|---|
| ao, au | Carrying and return idler pitch | m |
| qb | Belt mass per metre | kg/m |
| IV | Capacity | t/h |
| v | Belt speed | m/s |
| Fp | Participation factor of the most-loaded roller | — |
| Fs, Fm | Service (hours per day) and environment factors | — |
| Fd, Fv | Shock (lump size) and speed factors | — |
Worked example
Inputs: Carrying idler pitch ao = 1.2 m; Return idler pitch au = 3 m; Belt mass qb = 9.9 kg/m; Capacity IV = 1000 t/h; Belt speed v = 2.3 m/s; Carrying set — Fp = 0.65 ; Return set — Fp = 1 ; Hours per day — Fs = 1.1 ; Environment — Fm = 1 ; Shock factor Fd = 1.03 ratio; Return speed factor Fv = 0.97 ratio; Roller diameter = 108 mm; Roller load capacity (catalogue) = daN; Impact: fall height Hf = 1.5 m; Impact: Hv = 0 m; Impact: chute angle γ = 0 °.
- qG = 1000 / (3.6 × 2.3) = 120.8 kg/m
- Ca = 1.2 × (9.9 + 120.8) × 9.81 = 153.8 daN
- Ca1 = Ca × 1.03 × 1.1 × 1.0 = 174.3 daN; ca = Ca1 × 0.65 = 113.3 daN
- Cr = 3.0 × 9.9 × 9.81 = 29.1 daN; Cr1 = Cr × 1.1 × 1.0 × 0.97 = 31.1 daN
- Impact at Hc 1.5 m: pi = 1000 × √1.5 / 8 = 153 kgf; pic = 100 kgf
- Matches the Rulmeca worked example within rounding (Ca 153.8, Ca1 174.2, ca 113.2, Cr 29.2, Cr1 31.2 daN).
Assumptions and limits
- Factor values follow Rulmeca’s roller-rating convention. Other roller makers rate capacity on their own basis — use their method with their catalogue.
- Compare the most-loaded roller with the catalogue capacity for the right diameter, length, speed and bearing life.
- The impact estimate is for fine, uniform material. Large lumps need the roller maker’s lump method. Use about half the normal pitch and impact rollers or garlands in the loading zone.
- Belt mass qb comes from the belt maker’s data sheet.
Screening estimate, not a design approval. Verify measured inputs, current standards, manufacturer limits and site procedures before purchasing, cutting or installation. Isolate and lock out equipment before any hands-on measurement.
Questions
Why does the centre roller carry more?
In a troughed set the material sits mostly over the centre roll; Rulmeca’s participation factor for a 30° 3-roll set is 0.65 of the set load.
What pitch should the loading zone have?
About half the normal carrying pitch or less, with impact rollers or garlands.
Source notes
- Rulmeca, Rollers and Components for Bulk Handling, Technical Information pp.40–47 (carrying and return set loads, participation factor Tab.17, service Tab.18, environment Tab.19, shock Tab.20, speed Tab.21; loading-zone impact). Method used with credit; tables summarised, not reproduced.
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