FRICTION FACTOR (F) (f)

The friction factor f is the lumped-parameter coefficient that DIN 22101 (and ISO 5048) use to express the main motion resistance of a belt conveyor. It captures everything that rolls or rubs along the carry and return runs: idler bearing friction, idler seal drag, belt indentation rolling resistance (the hysteretic loss as the belt bulges into and recovers from each idler contact), and the energy lost agitating the bulk material as it flexes over each idler.

Typical f values: 0.018 for clean, modern, well-aligned overland conveyors with low-rolling-resistance covers; 0.020 for normal industrial conveyors in good condition; 0.022–0.025 for older or dusty installations; 0.028–0.030 for short, dirty or poorly maintained belts. DIN 22101 recommends 0.020 as the default starting value for new designs, with an adjustment based on belt speed, ambient temperature, expected fouling and the specific cover compound. For high-efficiency long-haul belts, suppliers tune the cover compound to achieve f < 0.012 — measurable savings of 30 % on installed motor power.

Because main resistance is the dominant term on long horizontal belts, a 10 % error in f translates almost directly into a 10 % error in Te and installed motor power. For this reason, large overland projects often perform a measured belt-pull test at commissioning to verify the assumed f against reality. The measured value is then locked into the as-built design package so future expansions, speed upgrades or cargo changes can be re-rated against a known baseline.