Searching for ultra low friction bearing with 5/16" bore

[hydrobro]

Does anyone know where I can find a relatively inexpensive ulta-low friction ball bearing with 5/16" bore. My application demands really low friction under 10 rpm, room temperature environment. I have tried a skateboard bearing called Bones, Swiss Ceramic @ $15.00 each. The bearing is ok but my competitors are using bearings that have a 'rolling duration' of almost double the Bones bearing lubed lightly with triflo. It was suggested in another forum that I try using a self aligning bearing. Any additional suggestions or opinions?

 

[israelkk]

Ultra low is not a definition. You should define a torque number for starting and running torque if this is really important!! Usually this is a special request and it cost much more. What ABEC number (or equivalent) was your bearing? Who is the manufacturer? Skateboard bearings are not a reference. I have seen skateboard bearings claimed to be ABEC 5 (the lowest is ABEC 1) but I doubt it was really ABEC 5. Bearing can go up to ABEC 9. The higher the number the more precise the bearing but for a guarantied friction toque you need a special request.

 

[hydrobro]

The skateboard bearing is not ABEC rated. I am not experienced enough to give you a starting or running torque requirement. My application is basically a 36" diameter, 3/8" thick wooden wheel that is recieves about a 2 second pulse force from a 1 lb-in torque constant force spring. The spring force is applied when the wheel rotation is nearly stopped. Following the spring pulse, the wheel then freely rotates for as long as it can before it reverses rotation thus triggering the spring to give it another pulse. The bearing is at the center of the wheel and is mounted on a 5/16 carriage bolt. Would there be less friction using a cylindrical roller bearing?

 

[israelkk]

If you are located at the USA you can buy ABEC 5 skateboard bearings (at least they claim it is ABEC 5) at any BIG 5 sporting stores chain. Few years ago they sold 8 bearings for $16. Roller bearing doesn't have less friction.

 

[hydrobro]

I have heard from several people that an ABEC rating does not imply a degree of friction. I have tried bearings with ABEC 7 ratings that are less 'free wheeling' than a ABEC 3 bearing. Both bearings were without oil or grease. I understand that the ABEC rating simply defines the tolerances of the bearing's construction.

 

[caoimhin1]

ABEC precision ratings will have minimal affect on friction, particularly in applications as rough as a skateboard. This is just marketing from skateboard bearing suppliers and most bearing manufacturers are happy to play ball and boost their margins for ABEC 5 or P4 or whatever. These precision classes belong only in machine tool or printing applications, not in skateboards.
For your application I would suggest a standard deep groove ball bearing of the correct load rating, shields on both sides with a light grease, or without shields with a light oil. 628ZZ for example or its imperial equivalent. If load is minimal, go for the smallest section bearing possible (or maybe the heaviest, to act as a flywheel????) A cylindrical roller bearing will have a higher friction.

 

[hydrobro]

Thanks for the pointers, caoimhin1

You recommend without shields with light oil. I assume that shields add drag? Also, do have any thoughts on using a self aligning bearing. Will the double row of bearing balls add or reduce friction?

 

[caoimhin1]

No the shields won't add drag (just mass), but contact rubber seals would, hence the recommendation for shields. Double row self aligning would have a bit more friction, two points of contact versus one. Also, its self aligning, so depending on your set up you would need to use two of them, otherwise it will flap about. Polymer cage may help but most manufacturers use steel or cleated brass on the smaller sizes.

 

[hydrobro]

The ceramic bearing that I am curretly using has a removable nylon cage. It seems to me that the cage itself imparts friction since it snaps in and seperates the balls and inhibits the balls from freely rotating. If I'm correct is there any way to avoid this? Do I need a cage?

Also, the pasted quote below was on skf.com bearing site.
"Additionally, the self-aligning ball bearing has the lowest friction of all rolling bearings, which enables it to run cooler even at high speeds." That seems counter intuitive because more bearing balls means more friction. But maybe the increased # of balls spreads the bearing load of more point contacts?

 

[ischgl99]

You need the cage to keep the rolling elements separated, otherwise they will try to bunch up on one side and you will destroy the bearing in short order.

You can get full complement bearings that have more rolling elements and no cage, but the friction could be higher then the standard bearing.

 

[caoimhin1]

Interesting about the self aligning bearing. NSK agrees with you, heres a list of bearing friction coefficients:

http://www.jp.nsk.com/app01/en/catalog/index.cgi?pno=NSK_CAT_E728g_9

I'm amazed that cylindricals have a lower friction coefficient compared to deep groove ball bearings. Wonder why?

 

[hydrobro]

I have ordered some self-aligning bearings and may use in pairs to avoid wobble. But the doubling of the bearing will negate my friction savings, so we shall see. I have also ordered a 6 ball bearing - one less ball than all the other skateboard bearings I have tried. I have heard from some of the pros that the ceramic ball bearing have higher ABEC ratings (if they're rated), but the tighter tolerances can sometimes work against reducing friction, ie an ABEC 5 may be better than a ABEC 7 for longer 'roll out' durations.

 

[diskullman]

I'm assuming 8mm bore, like all skate bearings. Try Boca Bearing

Russell Giuliano

 

[hydrobro]

thanks diskullman.

I see on Boca's web site 2 possible 608 bearings:Ultra Seal or Ceramic Premium. Do you have a recommedation for a bearing with the least amount of friction at 5-8 rpm?

 

[unclesyd]

You might want to look at bearing torque for you application.

http://www.dynaroll.com/torque.asp

 

[Clyde38]

You might take a look at FAG's low friction "Generation C" bearings.

http://www.schaeffler.com/remotemedien/media/_shared_media/library/downloads/prk_de_en.pdf

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