You're correct. The bearing has to "work harder" and the heat has
nowhere to go. Speeds son't have to be all that great.

On Sat, 11 Oct 2008 20:35:10 -0500, "Don Young"
wrote:


"Christopher Tidy" wrote in message
...
Gunner wrote:
On Fri, 10 Oct 2008 23:52:01 +0000, Christopher Tidy
wrote:


REMOVE Tom wrote:

On Fri, 10 Oct 2008 01:55:12 +0000, Christopher Tidy
wrote:



REMOVE Tom wrote:



Over lubrication is the primary cause of premature bearing failure.
Check out lube recommendations on the bearing or grease manufacturers
web site. Depending on the capacity of your grease gun usually a
couple of shots periodically will suffice.

Is that true? What damage does it do to the bearings? The worst I've
seen is for the excess grease to squirt out and make a mess.

Best wishes,

Chris


Grease is a great insulator - the rollers will push it out of their
path forming a wall which prevents it from dissipating the heat.

Surely this is only going to be a problem in bearings which run at tens
of thousands of rpm?

Best wishes,

Chris


Over greased bearings start heating up at 1500 rpm

I've sometimes seen two maximum speeds quoted on bearing data sheets: a
lower speed for grease lubrication and a higher speed for oil lubrication.
I guess the advantage of oil is that it can circulate and carry the heat
away, so it doesn't have to rely heavily on thermal conduction.

Best wishes,

Chris

I don't think thermal conduction is the culprit. I am pretty sure that the
friction from churning the higher viscosity lubricant raises the
temperature. It is an effect not commonly thought of but you can get an idea
by running a power paint stirrer in thick paint. Essentially all of the
power it takes to spin the stirrer is converted to heat. I had a "bush-hog"
gearbox overheat and ruin the seals because I had put in oil which was too
thick.

Don Young