precision bearing lubrication

there are speed limits that bearings can run at depending on the lubricant used. Grease tends to create viscous drag when the speeds get above a certain point and that point depends on the size of the bearing as well. For high speed, ususally starting at approximately 3000 and and up, you want to use a light oil, and that oil viscosity will decrease the higher the speed. All that is required of the oil is to keep a hydro-dynamic wedge between the rolling elements and the races. Think of a boat in water, the faster the boat goes the less water it needs to run in as it planes on top. If the water is thicker, it would take more power to go through and maintain the plane. There are calculations that show the viscosity required, as well as the volumes of oil to apply the bearings.

That is where an automated system can apply a very small amount of lube often to maintain the film needed without causing the viscous drag that can cause heat and wear if too much is applied.

Here is a couple of articles on high speed bearings:

http://www.machinerylubrication.com/article_detail.asp?...earing%20Lubrication

http://www.plantservices.com/articles/2002/4.html

Hi Dean,
i am impressed with your veiw but my exactly point is there are greases with low viscosity base oil which shoud not create drag having dmn factor above 125000 for example kluber nbu15 or rocol sapphire hi speed with fine quality thickner specially designed for high speed cnc precision bearings. will it be suitable to apply the grease in bearings which are oil lubricated at the same time

I would be interested in learning more about these kinds of products. My limited experience with grease and high speed bearings has not been good. Most of the customers I deal with do not have these kinds of products available to them and when someone greases high speed bearings they just grab what is on the shelf and inevitably cause them to fail within weeks. I have been installing air/oil systems onto these types of bearings with great success. I've been able to help improve the life from as low as 4-6 weeks, to more than 3-1/2 years and counting. Other benifits seen when switching from an oilmist style of system are they have noticed a substanial drop in bearing temperature as well, in part because the air/oil system does not heat the oil up to atomize it as an oilmist system does.

If you have any info or links to the grease products you mentioned I'd be interested in looking at it.

Thanks

Dean.

All high speed spindles I know of on CNC's that are 10,000> are all oil lubed mostly ISO 15 grade.

Changeing to a grease is a bad idea if unit was oil which I think thay all are. Heat from grease will cause bearing wear/oxidation not to mention relubication problems.

Even if grease has a good amount of oil bleed it may work but why risk an exspensive spindle pak rebuild.

Part of why modern spindles have oil is the ability to cool and be filtered of debris something grease will not allow.

Cool running spindles will hold tolerence better the whole idea I think.

bruce CLS

quote:

Originally posted by amit:
Hi,
sorry for my folly question but i want to know that in cnc high speed spindle bearings
10000 rpm lubricated by servospin thin oil.
willitbe correct to lubricate the bearings with
a grease claims life lasting in the same bearing which are oil lubricated at the same
time in order to provide maximum protection.

Cost-cutting grease lubrication for high-speed bearings

Greases put fewer demands on bearing design than oils. In the past, greases were only able to meet speed factors up to 1.3 million in high-speed applications like milling, grinding, turning and boring spindles, while at speeds exceeding this value oil-air lubrication had to be used. The new high-speed lubricating greases allow speed factors as high as 2.3 million. Owing to its consistency it is suitable for both horizontally and vertically mounted machine tool spindles. Oil-air lubrication can now be replaced by grease lubrication in many cases, thus reducing equipment and handling costs.
Lowering bearing temperatures during operation is another advantage of the new greases. Consequently, the service life is extended. Lifetime lubrication or longer re-lubrication intervals ensure considerable cost savings. Furthermore, reduced temperatures in high-speed bearings allow optimized machine design contributing to an even higher manufacturing quality. Apart from machine tools, the new lubricating grease is also suitable for high-speed bearings in power tools or electric motors.--ALSO SEE: www.lubricationventblock.com