Fan's Bearing

What's your drive configuration?

If axial force is important then deep grove ball bearings if axial force is small then spherical bearings.

Probably the deep groove bearing. The spherical ball bearing is compromised to allow for shaft misalignment, which can generally be avoided in a fan. If the fan is really a fan and not blower, then there will be some axial load that the deep grove bearing will handle better.

A further remark. The spherical ROLLER bearing has a higher radial capacity so that it has for same load a longer life expectancy but a reduced capability to take care of axial loads.

It is a suction fan with 17000m3/hr of capacity and running at 2965 RPM. Belt driven with a pulley ratio of 1:1 to the 55kW motor.

On what situation normally the fan will be having an axial load. Normally fan will be having more radial load than axial load due to its weight and centrifugal force action while rotating. Please correct me if I am wrong.

On what situation normally the fan will be having an axial load.

The reaction to airflow causes an axial load. It the fan's shaft is vertical then there is an axial load. Belt misalignment causes a slight axial load.

Centrifugal force does not, per se, cause an axial load, but imbalance does. Belt tension creates axial load.

1- The pulley, for instance, introduces as weight, a radial force loading both bearings, front and rear. Other sources can be due to dis-balance of the rotor + shaft + pulley. Other forces can come from uneven repartition of air channels. All those forces are in general NOT in same plane and some do rotate.

2- Axial forces can come from a pressure difference between the 2 rotor faces and from a direction change of air from axial input to radial outlet. If the belt has a slight angle it will also introduce an axial force proportional to its tension. A bad choice of bearings' type can also lead to axial forces.

If the fan draws air from both axial directions, and the belts are correctly aligned, the axial force should be very near zero. Use belt sheaves as large as possible (up to maximum allowable belt speed); this will minimize the radial load.