Viscosity selection for lubricants

[Inertially]

This is mainly in the context of miniature ball bearings.

I don't know where this goes, but this site seems to be one where it is more likely that people know what they're talking about. There doesn't seem to be a general lubrication subforum here, this section seems to be appropriate.


How is the appropriate oil viscosity determined for an application?

What are the consequences of using a lubricant that is too low or high in viscosity?

How is the appropriate lubricant fill determined?
For example, common lubricant fill for greased bearings is about 30% of free volume. Why 30%? Why not 5%, 10%, 20%?

The SKF lubrication selection app determined that a lubricant of about 10cst at operating temperature was appropriate for a miniature ball bearing.
Why 10cst? Why not 3 or 5cst? or 40cst?

The use of a higher viscosity lubricant increases the torque value (churn, heat, use energy). But what if you lower the lubricant fill (which seems to counteract what a high viscosity lubricant does) with a higher viscosity lubricant?

Higher lubricant fill with a lower viscosity lubricant VS a lower lubricant fill with a higher viscosity lubricant
Pros & Cons? In all or as many properties as possible (wear, lubricant life, torque, energy/heat... lubrication in general/detail)
The use of a lower lubricant viscosity vs oil plating with a higher viscosity lubricant?

As viscosity goes up, film strength goes up.
As RPMs go up, the lower lubricant viscosity required, why is this? Why are higher viscosity lubricants appropriate for slower moving (operating) bearings?

There's the factor of viscosity at start up.
Too much lubricant can mean churning and overheating.
Too little means poor lubrication in general..



Carrying away heat is also a reason to need plenty of oil, where there is an oil circulation system?

Would power steering fluid work well as a bearing lubricant or general lubricant? Why or why not (not just "it wasn't meant to be," in terms of its properties and composition)?
The description/features/properties on the package/label sound like it has the properties needed for a bearing lubricant.

Sometimes ATF is used in place of power steering fluid and vice versa.
And some seem to use ATF as a general lubricant.


How do I find out or what stores sell Mobil 1 Velocite No. 6 Spindle Oil?

What 10cst or lower oil @ 40C or lower would I be able to easily find/purchase that would work well ball bearings?
I think it would be a good idea to have EP additives for shock/impact loads..

What are the common EP additives (solid film lubricants?)

Graphite, Moly, Tungsten disulfide and...?
Is PTFE is an EP additive? Seems that Teflon has lower load carrying capacity.

 

[2oldtommy]

Welcome to BITOG! Your laundry list of questions could probably be answered by some of the engineering members here. (I am not one) The alternative would be to check other web sites for "Industrial Lubrication" . There is a lot to be learned here, spend some time and your knowledge of automotive lubrication will be increased immensely. FWIW--Oldtommy

 

[Tempest]

It would help a LOT if you were to post specifically what you want to do.

Look up elasto-hydrodynamic lubrication of bearings on the web and you will get answers. What you are asking is very complex.

I will answer one, however. You need a thinner oil at higher speeds because the hydrodynamic wedge is stronger as the shaft spins faster. This provides better protection to the parts.

 

[Shannow]

Lots of questions, as er tempest, need an application.

If I was doing small really fast stuff, I'd probably go to an oil mist lubrication system.

But don't know your application.

 

[Inertially]

I think many questions posted are concepts in general and don't need a specific application or target a specific application.

However, I'm interested in yo-yo bearings.

 

[XS650]

Try some online yo-yo bearing info sources. Since you haven't said what performance characteristics you are after, your questions still can't be given meaningful answers.

Which commercial yo-yo lubes do closer to what you want and how do you want to change that?

http://yoyowiki.org/wiki/Cleaning_a_Bearing#7._Lubricate_the_bearing

http://theyo.com/yoyo/showthread.php?t=26718

http://www.ehow.com/video_4411342_lubricate-yo_yo.html

You might be able to find two compatible oils, one very thin for low response and one at the thick end of yo-yo lube viscosities then mix them to get in-between characteristics if that is what you are looking for.

I would lean towards synthetic oils with a high viscosity index so performance characteristics didn't change as much as the bearing warmed up, but I don't know diddly about yo-yos and you might want the characteristics to change for all I know??

Thanks for the interesting question.

and

 

[Inertially]

Yeah, yo-yo websites do not have reliable information, as with most skate websites, most of the information are guesses by 14 year olds who consider themselves experts but have not done their research.

I thought asking here, the information presented would be more credible.

The popular play style current is unresponsive, with very low torque bearing requirements, as free spinning a bearing as possible.
Many players use a bearing without any lubrication.

I wonder how much a yo-yo bearing really heats up to though?
And if dry-film lubricants would be suitable.

And the chances of the oil or grease's viscosity being too high and the balls skidding.
Both viscosity and lubricant fill seem to affect that.

 

[XS650]

Originally Posted By: Inertially
Yeah, yo-yo websites do not have reliable information, as with most skate websites, most of the information are guesses by 14 year olds who consider themselves experts but have not done their research.

I thought asking here, the information presented would be more credible.


It will be once people get dialed in on what characteristics are desired. Not being a yo-yo(er) I would have guessed that minimum friction was one of the most important things, but from reading the 14 year olds and thinking about it some, it isn't always.

Something to consider is that motorcycle fork oil is available in very low viscosities and easier to get than very thin industrial lubes. You might get some 3 weight and 20 weight MC fork oil from the same company and experiment to find what ratio you like best.

I don't think you need to be concerned about going as thin as SAE 3 fork oil, it isn't like the bearings are in a heavily loaded machine.

You also don't need much oil in them, just enough that the balls roll through it when the bearing is spinning. Less is more if you are trying to minimize friction, not so when you are trying to increase response. Since those bearings have shields instead of seals, you also don't want to fill them too full or it will leak out and make a mess in additional to adding resistance.

Here is one company that has SAE 2.5 through SAE 30 weight fork oils. Fork oils may not be ideal for your application because they have lots of additives to counter the terrible sliding friction in forks. Until someone comes up with something better, they are a good starting point because of the wide viscosity range available and the ease of finding them online and in MC shops. You will have the best luck in looking in off road and sport bike shops.

 

[XS650]

Originally Posted By: Inertially

Many players use a bearing without any lubrication.

I wonder how much a yo-yo bearing really heats up to though?
And if dry-film lubricants would be suitable.

And the chances of the oil or grease's viscosity being too high and the balls skidding.
Both viscosity and lubricant fill seem to affect that.



My impression is that ball bearings handle dirt better with some lube. Yo-yo bearings aren't sealed, just shielded so dust and fine crud gets in. It seems like a dry bearing, dry film lubed or not would give inconsistent results. What do the 14 year olds say?

Even if the do have acne, they have experience so I wouldn't totally disregard what they say, just apply a lot of acne cream to their comments and filter them

With the drastically varying loads, even if the bearings do slide a bit, I would just ignore that problem whether it's real or not. They won't be sliding all the time, maybe a bit when the load approaches zero.

 

[Tempest]

I would give a look at Corrosion X "Speed X". I use their Aviation product for a general purpose spray and it is impressive, though I've not used the Speed X.

The man that formulates their oils used to work for a major oil company and is very good at what he does.

 

[Inertially]

Quote:
I don't think you need to be concerned about going as thin as SAE 3 fork oil, it isn't like the bearings are in a heavily loaded machine.


SAE 3 is for heavy loads? Thought higher weights are for higher loads.

--

How can they be serious about selling a lubricant without even listing any of its specifications like viscosity?

Didn't answer my e-mail on it either.
Though I don't plan on buying any of it.

 

[APStore]

Has anyone considered a high speed grease? If the bearing is not sealed, grease would provide a barrier for condensation and grit getting in as well as lubricate well in bearing with a couple thousand RPM. Not sure how much of a shock load whipping a yo-yo down is, but may provide that type of protection also. Same grease used in small high speed electric motor bearings.

What kind of speed does a performance yo-yo spin at?

 

[APStore]

Originally Posted By: Shannow

If I was doing small really fast stuff, I'd probably go to an oil mist lubrication system.


A yo-yo with an oil mist system would be sweet. ha ha ha!