Can someone explain the different types of fan bearings?

[BehindEnemyLines]

I've seen ball-bearing, sleeve bearing, hydro bearing, etc...what do all these things mean? And which one is supposed to be quieter?

 

[GalvanizedYankee]

What little I know.

Sleeve bearings are made of sintered bronze, bronze being an alloy of brass & tin. Sinter is a powder of metal.
The sinter in formed into the desired shape under high pressure then heated close to it's melting point to bind
the grains of powdered metal. Solid lubricants, like graphite, are added to the matrix before the forming.
Generally no machining is required for housing or shaft fit.

Some sleeved fans are "rifle drilled". This would mean that the housing was put together and the bushings(sleeves)
were reamed at the same time, This would give better alignment for the shaft. It just might have been that they had a bunch of tight bushings and had to ream them

There are three basic types of ball bearings, low speed, medium speed & high speed. The higher the speed rating the
looser the fit. High speed ball bearings tend to be noisy.

Some fans have one of each. A ball bearing at the fan blade end and a sleeve bearing at the back.
I would think this is a working compromise between cost, noise & service life.

Panaflow goes into some detail at their site about why it's bushings are so good. From what I've read on line they
are not what they use to be. They are made in China now and the QC is not like Nippon's.

EDIT: My comment on Panaflow is based on what has been recently posted on silentpcreview's forums.
Rifled bushings are a "good thing", that comment was in jest. But manufactures do take steps to compensate for errors in a production run, then sell it as excellence in engineering. They are just fans after all.


EDIT: SP errors