

Greaseless ball bearings: A revolutionary spin - davidbarker
http://www.gizmag.com/greaseless-ball-bearings-coo-space-adb/37689/

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SwellJoe
Previous HN discussion:
[https://news.ycombinator.com/item?id=9588547](https://news.ycombinator.com/item?id=9588547)

~~~
mhb
Previous HN with no discussion:
[https://news.ycombinator.com/item?id=9575968](https://news.ycombinator.com/item?id=9575968)

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ridgeguy
This may limit the bearing's lifetime.

If everything else is done right (bearing mounted correctly, lubricated, no
dirt, correct loading, etc.), bearings ultimately fail due to high cycle
fatigue at the rolling element tracks on the races. Repeated flexing caused by
high Hertzian (contact) stress between ball and race makes tiny divots
fracture out of the race surface. Particle count goes up, more divots break
out...bearing fails.

The grooves they put in the races of these bearings will act as stress
concentrators and accelerate fatigue failure compared to ungrooved bearings.
Still, if low friction is more important in the application than long life,
this may be a useful new twist on rolling element bearings.

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po
In a greased bearing the problem is that the balls can touch each other
(causing sliding friction) and /or pack together on one side of the race
causing uneven load or the inner race to shift relative to the outer. The
solution is typically to put a cage in so they stay evenly spaced. This cage
can be metal or plastic and the balls can rub against it. The grease is mostly
used to lubricate the cage from the balls. The rolling resistance of the balls
on the race is very low as they aren't sliding across the race, but _are_
creating friction and wear when they touch the cage.

This system seems to work by allowing the bearings that are packed together to
touch briefly as they enter the divot causing them to space out afterward. I
guess it would perform similarly to an un-greased geared roller bearing?

I'm not sure if this will work well under load. Grease provides lubrication to
prevent pressure welding of the bearing to the race and it can also act as a
heat sink. Besides those, I would assume the main problem would be fatigue at
the site of the divot.

Still I think this is very clever.

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mcphage
So it acts like a stop sign—it slows traffic down, and then more evenly
spreads it out. Neat.

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drostie
The best part about all of this is if you follow the links to the Coo Space
web site and then mouseover the links: their web site is hosted on, of all
things, geocities.jp.

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JoeAltmaier
I wonder how this works under load. If a vibrating or asymmetrical load is on
the shaft (the normal condition for a bearing) then is the small
deceleration/acceleration effect still working to separate the balls?

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rwmj
Isn't another purpose of the grease to stop the ball bearings from rusting?

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JoeAltmaier
Don't they rust because of the water in the grease? So if the grease wears
away, it leaves the bearing damp?

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pjc50
Water and grease are textbook immiscible things. There isn't water in grease.
There may be water in the environment and there usually is in air, though.

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JoeAltmaier
Lithium grease is not resistant to water. And 'gear grease' has this
composition according to Wikipedia:

"Gear greases consist of rosin oil, thickened with lime and mixed with mineral
oil, with some percentage of water. "

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tenkabuto
If these truly experience "as little as 10 percent of the friction of a
regular ball bearing", I wonder how they'll change skateboarding.

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xd
Grease is needed to lubricate the balls so they are not in direct contact with
the races. Without grease the balls/races will fail rapidly when under load.
There is no _load_ on the cages so I fail to see how this development helps at
all.

~~~
xd
Thanks for the downvote. Obviously you do not agree with simple facts, but
just in case you think I'm making my point up:
[http://machinedesign.com/archive/proper-film-thickness-
key-b...](http://machinedesign.com/archive/proper-film-thickness-key-bearing-
survival)

Let me quote a key passage: "Engineers must check that films are sufficiently
thick so asperities — peaks of surface roughness between mating surfaces —
don't touch. Otherwise, bearings can rapidly wear and fail."

