Spinning bearings with air

[tornitore45]

The street wisdom is "never spin bearing with compressed air"
Why?
I suppose it may run the RPM way above specs, but that depends on the way one holds the nozzle respect the bearing.

Is easy enough to control the RPM to be wheel below spec while cleaning a bearing that feels gritty. Drown it in kerosene and spin it gently.

[GlennW]

For one thing, slide that ball bearing onto your finger and spin it up to about 10,000 rpm and have it seize.

You'll have an unpleasant experience!

[John Hasler]

I think that the assumption is that you will spin it as fast as you can get it to go, dry.

[tornitore45]

For one thing, slide that ball bearing onto your finger and spin it up to about 10,000 rpm and have it seize.

An how did you learned that, Glenn?

One reason for always question rules. What may be true for a 4 ounces bearing may may not apply to a 10 grams or a 9 pound bearing (not likely to be be fingered)

Seem like the rule refer to playing rather then trying to accomplish something useful minding the limitation.

[earlgo]

In keeping with that, NEVER spin up a "fidget spinner" with air. The plastic hoops cannot hold the weights after a certain rpm. Disaster may ensue. My buddy tried it but fortunately he quit before anything happened.
I know no-one here would ever try this at home.
--earlgo

[choprboy]

The street wisdom is "never spin bearing with compressed air"
Why?

I would guess that the reason is that you are blowing contamination into, and oil/grease out of, the bearing race, thereby shorting the life of a new bearing about to be installed. But yeah, cleaning an old gritty bearing I don't think its going to make any difference. After initial cleaning, multiple washes with clean solvent and then a good oil/regrease is probably better.

[STRR]

The reason you are not supposed to spin bearings with air it two-fold. First: You have NO lubrication on a freshly cleaned bearing. High rpm with no lube spells short life of the bearing. Second: As said earlier, it's easy to exceed the rated speed of the bearing.

When cleaning and drying the bearing, it's ok to use air and spin the bearing at LOW rpm. Just don't let it whiz into outer space without lubrication.

Good Luck,
Terry

[NP317]

Thought:
Spinning an unloaded bearing is different than spinning a loaded bearing.
Overspeed at zero load is far less likely to cause a problem, than with a load.
~RN

[John Hasler]

I'm not sure that's true. With no preload the balls and the outer race have some freedom to rattle and clatter in that turbulent air stream rather than roll smoothly.

[4gsr]

According to some of my old bearing manuals, spinning the bearings dry with compressed air will scratch the races and the bearing balls. I've always held on to the bearing and let the bearing rotate slowly while blowing out with air. Lubricate the baring with light oil afterwards so rust bunny's don't start appearing until ready for assembly or packing with grease. Remember, air will have some traces of moisture in it, this will kill a bearing real quick. Another thing you can do after cleaning is dip it in clean fresh Naphtha and let dry. KenS.

[EOsteam]

My aircraft mechanic friend is zealous about air and spinning a bearing. He claims that it doesn’t take much movement with a dry bearing to cause damage. After cleaning in solvent they will blow the bearing out but restrict any moment in the bearing. He said that is standard practice in the aircraft repair industry. He won’t even let me spin a bearing by hand unless it has been repacked with grease.

[pete]

Personally I think there's some sound logic behind not spinning up a dry bearing to high rpms. I've worked with multiple and highly experienced mill wrights and mechanics in the past who all seem to think it's a bad idea for various and multiple reasons that have already been mentioned. I've also craned in some extremely large bearings for mine site personnel and a few outside contractors. One thing in common with all of those crews is how gently each bearing is handled at every step even when weighing 200 - over 1,000 lbs. A bearings lubrication either grease or oil should provide a slight cushion between the hardened balls or rollers and the hardened race. I once saw a comment on a bearing manufacturers website, SKF maybe? that stated brinelling of the bearing internals can start on precision bearings with as little as 4 ft. lbs of shock load. Once a bearing is even slightly damaged they will start to fail early. Since so many think it's a bad idea, then being cautious and not doing so seems like the best practice to me since there's no benefits of running them up to a high rpm anyway. Blowing them clear of any solvent at low rpms and then immediately oiling or repacking I'm guessing shouldn't causes any problems.

Washing out and then air drying a bearing after a flush with Naptha/White Gas should be fine. However I learned the hard way that leaving parts submerged in it for up to a week is a real bad idea. I left an expensive 3 jaw soaking in it for about a week and found it covered in surface rust when I got back to it.