Fans and blowers
Fans above 60 °C: what changes for bearings and grease
Standard fans are rated to about 60 °C. Above that, bearings, grease and the motor need extra attention.
The 60 °C line
Standard industrial fans work without modification up to about 60 °C of air temperature. Above that, heat travels along the shaft into the bearings and the motor, and the grease gets old faster.
What to check
- Grease: use a high-temperature grease, and shorten the relubrication interval. The interval roughly halves for every 15 °C above 70 °C at the bearing.
- Cooling: fit cooling wings or a finned slinger on the shaft so heat is thrown away before it reaches the housing.
- Clearance: choose a bearing with C3 internal clearance, because the inner ring runs hotter than the outer ring and the clearance shrinks.
- Motor: ask for extra motor cooling, and take particular care if the motor is on a variable-frequency drive, because it cools less at low speed.
- Locating bearing: put it on the cooler side so the shaft grows away from it.
Air density
Hot air is lighter. For the same speed, pressure and flow fall and the power drops. If the speed is raised to recover pressure, thrust and unbalance load rise with the square of speed.
Signs of trouble
- Grease darkening or leaking from the seals.
- A housing that is much hotter than the one at the other end.
- Rising vibration at running speed after the fan has run hot for a while.
Takeaway. Above about 60 °C, use high-temperature grease, shorten intervals, fit cooling and choose C3 clearance.
Put it to work in the tool