There are three common types of bearings: ball bearing, hydraulic bearing, and sleeve bearing.
Sleeve bearing is made of porous metal that can absorb and retain lubricating oil. The lubricant filled between the blade shaft and sleeve acts as a drag reducer. Generally, the lifetime of sleeve bearing is 8000-10000 hours. It is suitable for a fan with medium or low speed.
Advantages: low price, low noise, suitable for intermittent use.
Disadvantages: high wear rate, short service life.
Advantages: Long service life, suitable for the fans with higher rotation speed.
Disadvantages: high price, high noise level caused by rolling of metal beads.
Advantages: low noise, longer life than sleeve bearing.
Disadvantages: more expensive than sleeve type.