Best bearing type for reciprocating motion?
Best bearing type for reciprocating motion?
(OP)
In general, is there a "best" bearing type to use for a shaft undergoing reciprocating motion (e.g. + and - 180 degrees of rotation, no continous rotation). My understanding is that most types of rolling element bearings will eventually develop "flat spots" on the rollers due to repetitive contact stresses. Would ball bearings be less susceptible, or more susceptible to wearing in this manner?
Thanks,
Ben T.
Thanks,
Ben T.





RE: Best bearing type for reciprocating motion?
Basically if each roller gets to perform one or more complete revolutions, and runs over the conact patch of its neighbour on every revolution you've covered most of the bases.
However if you were to restrict your angular motion to say +-90 degrees, then only half of the rollers would ever see any significant load, so your fatigue life would halve.
You could try some preload to even things up, but since it is the stress range that is the killer I can't see that helping much.
Would you consider a high pressure oil lubricated plain bearing?
Cheers
Greg Locock
RE: Best bearing type for reciprocating motion?
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RE: Best bearing type for reciprocating motion?
Relatively high loads (~1000-2000 lbs), very slow speed (<1 rpm). The question is would cylindrical or "needle" bearings provide better performance, because (in general) the load ratings are higher than similar sized ball bearings. I could maybe make an arguement that balls have the "ability" or at least the possibility, of rotating around to put the flat spot away from the line of contact.
Greg: so, provided the roller elements complete a full revolution, and travel over neighbor's contact patch, would you say the risk of Brinelling/flat spotting is minimized? I could envision a very small rolling element bearing (relative to shaft diameter) which could presumably satisfy the requirement with less than 90 degrees shaft rotation, or am I missing something? Seems like a pretty good design rule to use though, so thanks.
BTW, right after posting this, I "stumbled" (connotation of a bumbling idiot appropriate) over the "bearing design" forum. Probably should have posted there, sorry.
RE: Best bearing type for reciprocating motion?
At such low speed the grease may not get hot enough to flow properly in a roller or ball bearing.
RE: Best bearing type for reciprocating motion?
I agree with MintJulep that sort of load is usally taken in a plain bearing.
Cheers
Greg Locock
RE: Best bearing type for reciprocating motion?
RE: Best bearing type for reciprocating motion?
I don't think flooding a needle bearing will reduce its friction, in fact for optimum resistance we used to degrease ball bearings and just use CRC (we replaced them every day). If you want to use ball bearings you'll find self aligning bearings have the lowest friction usually, as they can accomodate shaft bending without generating side loads on the balls.
Cheers
Greg Locock
RE: Best bearing type for reciprocating motion?
Ball bearings = lighter loads, higher speeds
Roller Bearings = heaver loads, lower speeds.
The edict against short stroke motion with ball bearings primarilly has to do with greased bearings. Oil does not get to the short stroke area causing rapid metal to metal wear.
+/- 180 degrees is not short stroke. And if you put the bearing in a oil bath, lack of lubrication will not be a problem.
RE: Best bearing type for reciprocating motion?
Yoiks - unlubed roller bearings? How many cycles could you get doing that?
Hmm, good point about shaft bending, will have to include it in the mix of "things to look at".
RE: Best bearing type for reciprocating motion?
Cheers
Greg Locock
RE: Best bearing type for reciprocating motion?
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RE: Best bearing type for reciprocating motion?
RE: Best bearing type for reciprocating motion?
RE: Best bearing type for reciprocating motion?
Cheers
Greg Locock