Need Grease recommendation for 6,500 rpm bearing 4

[R Griffith]

Hello all,

This is my first post. I need tips for a bearing grease lubricant for a ball bearing application. I'll list the specs below.

Bearing ID: 80.00mm
Operating RPM: 6,500

 

[dvd]

oil mist lube system

 

[romke]

you should refer to the bearing manufacturer.

they all do recommend specific types of lubricants, depending om circumferential speed, temperature, type of load etc. if for the particular application "grease" is regarded as a suitable lubricant, also the composition of the grease itself becomes important: thickener type, base fluid viscosity and usable temperature range all play a major role in finding the optimal lubricant.

 

[3DDave]

I'm leaning to oil as well. I've had bad experiences with grease in bearings except for low surface speed devices. And even then I mostly wished that oil had been selected instead.

 

[badservo]

In addition to romke's answer, the volume of grease is also important. Too much grease will cause excessive heating.

 

[Tmoose]

The bearing manufacturer should have all the answers.

Way more specs are needed.

for instance, deep groove Ball bearing?

I'm guessing median diameter is 100 mm, so speed factors n ∙ dm = 650,000.
That is high speed, but achievable with "grease."
Precision machine tool spindles do it all the time.
But their bearings are VERY carefully made, and all the mating components require abutment runouts, seat concentricity and size to be accurate to 0.0001" .

At the very least Special high speed grease is needed.
starting page 24

https://www.klueber.com/ecomaXL/files/Lubrication_of_rolling_bearings_tips_and_advice.pdf

https://www.schaeffler.com/remoteme...chaeffler_2/tpi/downloads_8/tpi_176_de_en.pdf

 

[R Griffith]

Thank you all for your replies.

 

[romke]

generally speaking grease is a better lubricant then oil for most roller bearing applications, unless you need the lubricant to also function as a "coolant", about 90% of roller bearings used are grease lubricated. however, the optimal choice of lubricant can be quite complicated, as can be seen in the excellent publications mentioned by Tmoose. careful analysis of the operating conditions the bearing will encounter is a prerequisite for making the right choice and often a "special" type of grease may be needed.

not each and every lubricant supplier is able to supply all possible grease types. some of them have specialised on products for specific types of application. generally speaking the marketed greases fall in two categories. on the one hand greases that are truly "multipurpose" in the sense that they combine corrosion protection, mechanical stability, water resistance, load carrying capacity and oxidation stability at such a level that most applications can satisfactory be lubricated. over the years the "application envelope" has been enlarged including higher temperatures, longer relubrication intervals, better mechanical stability and higher water resistance. lithium and lithium/calcium based greases and most complex greases are examples of this grease types and may account for over 75% of the volume of grease sold.

the second category are the "special greases" - products that excel in some particular areas, and usually are not optimally formulated where other requirements are also important. in this group you will encounter "low noise" greases, high temperature greases, greases with special cold flow properties, resistance to various chemicals etc. a lot of them are based on less familiar thickener types and synthetic base fluids. they can help out where "multi purpose " greases are not good enough - at a price. some special greases may cost up to 500 times as much per unit of weight then standard "multi purpose" greases!

 

[tbuelna]

Tmoose pointed out a very important consideration regarding the relatively high dN of this bearing. If the plan is to use grease lubrication for a rolling element bearing operating at a dN >500k, it will require some method to keep the grease in place, such as a shield/seal/dam/etc. Most commercial elastomeric lip seals don't work well at surface speeds >4000 fpm, which might be the case with your application. A non-contacting bearing shield or housing dam will keep most of the grease around the bearing and won't produce any friction, but will still allow some small amount of lubricant to weep out.

Regarding a grease-lubed high dN bearing, the ratio of grease to internal bearing volume is important, as badservo noted. The Klueber technical manual linked by Tmoose has a good chart on page 12 showing that a bearing operating at a dN of ~600k should only be filled with grease to between 15-25% of its internal volume. This can involve some careful re-lubrication procedures. The old contaminated grease must first be removed from the bearing internal volume before adding the required amount of fresh grease. Not a simple thing to do properly with some bearing installations.