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QSIMDO
10-07-2007, 10:44 AM
My experience with lubricating tapered roller bearings is probably like most others; greased & done with it for a lifetime of service.

I'm assuming a manual mill is pretty much the same?

Would you adopt a different regimen for our spindle running at higher speed?

Runner4404spd
10-07-2007, 10:49 PM
yes, but use less grease than a standard automotive tapered roller bearing. also make sure you use a high quality grease. i personally like synthetics for the spindle bearings.

NC Cams
10-08-2007, 06:23 AM
So called "greased for life" applications mean different things to different people.

Is "life" 2 years or 50 years?

Does "life" mean "life of the spindle" or "life of the greaee"?

These "lives" are definitely NOT one and the same.

When you have a bearing with a HUGE capacity (as in capacity to size ratio ala tapers),, it is not unusual to lube them with a sufficient quantity of grease and they will last perhaps the "life" of the part - cartridge syle wheel beainngs are a perfect example of this type of situation.

However, should the environment result in or alow for contamination of the lubricant, grease and component life will obviously be shortened. This sort of thing is intuitively obvious. Again, most cartridge wheel bearings fail due to grease contamination and not overload or fatigue.

However, what about cases where the lube is kept clean, and an adequate quantity is applied and you only run the lube at high speed? This situation results in a different phenomenon that varies from grease to grease.

As grease is worked at higher and higher speeds, more and more heat builds up in it. Depending on the base stock and the additives in the grease, over time, the grease will start to ozidize.

Most mineral based greases can tolerate temps that do not exceed 190-200F without appreciably breaking down. However, as grease temp reaches and exceeds 200-212F, grease oxidation and breakdown starts to occur. A runle of thumbe is that for every 10 deg you go above 210, you cut grease life in half. Synthetics are more heat resistant but they too have high temp "grease lives".

Hence, if the grease life of a normal, mineral lubed spindle was 400 hours, running it at 210F would cut GREASE life to about 200 hours. and down to a 100 hour GREASE life at 220F.

Again, grease life is NOT the same as bearing life but if/when the grease dies, the bearings usually die righ along with them.

I"ve seen many situations where the bearings would have easily survived had the grease not gotten overheated and cooked. Yet the bearings still got the "blame" for dying due to the failure of the grease.

Any smindle that will be continually run at/near the max rated speed should probably be treated to a more regular preventative maintenance regime (Ie: greasing and relubing). Otherwise, you may not achieve the maximum "mechanical life" out of the components.

If you do grease and run an application for a "life" of continuous high speed use, you'll be limited to the unpredictable life that the naturallly occuring ozidation that high speed grease milling creates.

We had a situation once that ate lifetime sealed spindle bearings like popcorn with greased bearings - from a load standpoint, the bearings were not heavily loaded but were contnually run at high pseeds (dyno spindle). BTW, the calculated "grease life" of the greased bearings didn't even reach that of the most conservative of calculations.

In desperation, we changed over to a more complex sump style oil splash lube. This allowed us to change/replenish the oil regularly and we never changed bearings again PROVIDING we changed oil once it started to color/ozidize.