Fans and blowers
Why fan bearings fail early: unbalance, build-up and belt pull
Three loads dominate fan bearing life. How to tell them apart and what to do about each.
Three loads
A fan bearing sees the weight of the impeller, the unbalance force left in it, and (on belt-driven fans) the belt pull. Of the three, unbalance is the one that changes with time, because dust and wear change the balance.
How to tell them apart
| Symptom | Likely load | First check |
|---|---|---|
| Vibration at running speed rising slowly | Build-up on the impeller | Inspect and clean the blades |
| Sudden jump in vibration | Lost balance weight or blade damage | Stop and inspect the impeller |
| High temperature at the sheave-side bearing | Belt tension too high | Measure belt tension and sheave alignment |
| Spalling on one bearing only | Overhung impeller load | Check which side is nearer the impeller |
| Smeared bands on a bearing | Too little load | Check the minimum load at running speed |
What damage you will see
- Fatigue spalling on the raceway of the impeller-side bearing: the overhung load working over time.
- Fretting marks under a sleeve or hub: a loose fit under a flexing shaft.
- Smearing on a lightly loaded bearing at the other end.
What to do
- Clean and rebalance the impeller as part of routine maintenance, and rebalance after every repair.
- Set belt tension and alignment to the drive maker's value.
- Recalculate the bearing loads if the impeller, the speed or the pressure changes. The Worked templates in the Load Calculator do this.
Takeaway. On a fan, trend vibration at running speed. A slow rise is build-up, a jump is damage.
Put it to work in the tool