Hot Bearings

My first thought was seal friction, but ZZ denotes shields rather than contact seals. Any idea how fast the bearing is turning and the approximate axial load? Thats enough information, making an assumption on rolling friction, to make a SWAG on how much heat you could expect to be generated.

If the bearing doesn't get too hot to touch after an extended run, I wouldn't be too concerned. Just pay attention to any noises that might warn of an impending failure. What have you got to lose, besides $10 worth of bearings?

Ned Simmons

RPM is directly off the 3phase motor, I assume it's 1725 it sure dosen't look like it's spinning at 3450... Axial load is hard to estimate... its the spring force from the other split sheave pully, pulling the big assed 1.5 inch wide V-belt tight. My big concern was that after about 10 mins of running I could just barley touch the hottest of the 2 bearings.. meaning I could keep my finger on it, but it was pretty damn hot, a lot hotter than I'd expect...The one with the sheave as a heat sink was moderatly warm...

I assume that the C3 means these are class 3 bearings so that means they are a bit closer tollerance than is really needed, but that's what the bearing shop had soo.. and yeah they cost me 12 bucks.. :-) I plan on running it for short periods 10 or 15 mins, and let things calm down and *hope* things run in and get better... and that'll be OK in the short term.. when it blew I was making some 1/4 inch clevis pins.. but shortly I'm gonn be doing some reasonably heavy work, I've got ten 6 inch diam cast iron wheels to machine for my new locomotive and I sure as shit don't wanna blow the drive again when I'm cutting those.. and IIRC it's about 10 or 15 mins for any of the steps to machine these, 4 or 5 steps (face back, face front, cut tread, profile flange, drill hole).. last time I did a set of drivers it was a 2 day's work.. that's stretch to a wheel a day if I could only do 15mins per hour... :-(

--.- Dave

It sounds to me like something is wrong. I would give a call to the bearing house and ask them about it. Ball bearings are there to resist friction and the only place that heat is coming from is friction. I doubt things are going to get any better the longer you run.

There might be a lack of lube.

[replace bearings]

The old bearings failed and the new ones are hot; is every shaft straight? A bent shaft could be straightened, slightly, by its bearings, but only by overstressing them.

Flame straightening or application of a lead hammer might be your fix.

If you can keep your finger on it, the bearing is probably not more than

130F or so. That may shorten the life of the grease a bit, but is far below the temp where you need to worry about the bearing itself.

I just ran a quick calculation on friction, assuming the bearing is loaded to about 10% of it's rated load. It wouldn't be unreasonable to expect the friction to result in up to 20 watts of heat, which would get that little bearing pretty warm without a heat sink.

C3 refers to the internal clearance, or looseness, of the bearing, which is independent of the accuracy. C3 is standard. The ABEC-1 in the number is the accuracy class.

I noticed a note in the table on bearing rolling friction I looked at that said the friction in new or freshly greased bearings can be as much as 5x that of a greased bearing after it's been run, so I think your approach is sound. And I learned something as well. The 20 watts above assumes the high end for a freshly greased bearing.

Ned Simmons

Thanks for running some numbers Ned, and the hint about friction on new bearings can be 5x, that's certianly an eye opener.

FWIW I figure that the reason the outter bearing was toast is that it jut ran hot because of no heat sink, and after 25+ years lost all it's lubrication.

--.- Dave

FYI this is pretty much a self centering rig... The bearing that's getting hot is being pressed on by 2 hydraulic plungers, one on either edge of the bearing (well, a small housing holding the bearing), the plungers are connected to the same reservoir so they essentially equilize the load. Yes old bearing failed, after 25+ years... I don't think it owed me any thing :-)

--.- Dave

Be aware that the 2Z (or ZZ) sealing you got on your BB insted of the 2RS will lose the grease __much__ quicker than 25 years.

Nick

You have fitted a deep groove bearing. Would a better job be done by an angular contact bearing?

Mark Rand RTFM

Sealed bearings dont always indicated lubricated bearings..unfortunately. Ive seem more than my fair share of unlubed bearings that were supposed to be lubed..sigh

Got some PB Blaster? if so..spritz the ZZ bearings really well and see if they cool down after equal run time. ZZ bearings have (usually) enough gap to allow thin lube to get in, yet keep out the spooge, unlike rubber seals.

On the other hand..I did a pair of spindle bearings Thursday...$400 for the pair..and they are noisey..hummm..more noisey than I like, when running. The customer watched each and every step of the operation..so he knows I didnt screw up anything. We are hoping they will run in..but if not..he is out for another set of bearings and Im out at least 8 hours of labor to do it again under warranty.

Italian bearings..never again

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

I seem to recall that at least one manufacturer used "C3" to indicate a variation in the clearance, either tighter or looser. So your bearings might actually have inadequate clearance.

I have been amazed at the many numbers, letters, and symbols used by different manufacturers to indicate variations in bearings. Some seem to be consistent but many are not.

Don Young

So the fricken circlip popped out again yesteday afternoon.. and took out a small chunk of what was left of the really thin cast iron with it... SHIT.. what now... After thinking all night I decided the best fix was gonn be to

*pin* this thing in place by drilling and tapping through the Delrin coverd shaft that this sits in.. this is gonna be tricky the, disk is only about .300 thick, I've gott hit it pretty much in the center and I wanted to use some #10 set screws I have, so there ain't much room for error... Oh and just to complicate things the fixed sheave/shaft is pretty firmly attached to the motor shaft, soaking what I could in Kroil and heating with a lamp wouldn't get it loose so I decide I'd have to do this in place by fricken hand... so I measured with a depth gauge and made a drill guide and a tap guide... wedged the whole thing and went at it.. sumbitch if it didn't all work out as planned... :-)

So on to the bearing part of this... ONE of the original bearings wasn't in that bad of shape, I just originally figured since I was there I'd replace them both, so.... when I reassembled it all I decide I'd stick the old good bearing on the outside where I'm getting the most heat, It's easy enough to get at if I need to replace ..... guess what.... It gets just as hot as the replacment bearing... :-)....

I figure what's happening here is that since this is ALL axial load all the balls are always carrying force, not a %50 (or so) duty cycle like if it was radial in one direction, and this bearing has virtually NO heat sink... it's a 2 inch bearing hung on the end of a 3/8 rod with a small carrier and that it's...

--.- Dave

I kinda doubt that all two bearings get hot. Because if it is that way, the construction is crap or you missed something when you reassembled it. On a shaft with axial load, only one BB (of the type you are using) can take axial load. The other one has to be movable axial. If both BBs are fixed on the axle and outside, there IS something wrong. And you won't fix it by replacing BBs over and over again.

Nick

Um.. Nick,

First I'm not willy nilly replacing bearings.... I HAD to take it all down again because the original problem resurfaced, (or didn't you read that well enough?)..

Second off, trust me I haven't "missed" anything is reassembly...

Third off, I guess you don't have a good enough picture of what's going on... and how both bearings are essentialy on oppisite ends of a hydraulic slave so both bearings beraing receive exactly the same force.. simple eh?

I do agree with you, I think the original design has a flaw in it.. there is essentially no heat sink of any kind on the outer bearing, so any heat it generates has no place to go... And please don't tell me bearing don't get hot.... they do, friction IS a fact of life...

--.- Dave

So everything is OK. And the bearings don't get hot, no need to replace them, no C-ring popping out ...

Oh! Or maybe they gave you the wrong bearings. Or they need some adjustment.

A bearing that needs cooling is sick in most cases. Either due to a defect or a wrong construction or a wrong bearing-type. Then if it needs cooling, it is stupid to have a grease-filled one, because this is the very first place to reduce friction. Didn't they give you a 2Z, albeit the original was a 2RS? Now what sealant type could keep oil? A RS or a Z? After that, if it still needs cooling, there's got to be a _real_ reason for making the construction that way. A real reason might be a high-speed-spindle or something else running well above the specs of that bearing, not without contacting the manufacturer. But then, it does have some active cooling.

I'm sorry that I wanted to help you.

Nick

Hi Dave,

Ever since you mentioned that the hot bearing has very little mass/heat sink around it I have been wondering if you can add your own heat sink.

Without a picture of your assembly though I am just guessing if this is a possibility or not.

Just curious, musing out loud...

Most bearings don't get hot unless they are overloaded, out of line, low on lub, to small for the job or run at a very high speed... Don't believe me ??? Just start feeling machine bearings next time your around machinery ... I've allways checked running machines to see if any problem pop up...

Obviously you have never laid a hand on your front wheel bearings after a loooong drive.

Bad example - Disc brakes get rather hot in normal operation, and the rotor heats the hub through conduction to a point well past where the bearings alone would get it.

Now if you're talking trailer wheel bearings (no brakes), those you check by hand, they don't get very warm from normal use and they have the hub and wheel to conduct away that little bit of heat. If they're notably hot to the touch, there most likely is a problem.

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