Regrease a bearing or leave it alone? 1

[dmalicky]

We make industrial machines used in a fairly dirty environment. We are debating whether or not to recommend regreasing for some pillow block bearings on our machines (SKF SYR series, 1 15/16" bore, with labyrinth seals). The bearings run 24/7/365 at ~3400rpm (thus the labyrinth seals) and L10 is ~20 years. From what we know, we can't count on regular or careful maintenance. I understand that improper regreasing (introducing dirt or overgreasing) can be worse than no regreasing at all. We'd like to know how long these bearings will probably last without *any* regreasing. If it is 5 years or more, we'll probably not recommend regreasing at all given the risks of improper greasing. My questions are:

1) Does anyone have an educated guess on the life of these bearings without regreasing?
2) Are there economical automatic lubricators that could dispense grease over 5 years?
3) Do labyrinth seals lose substantially grease more then rubber seals?
4) Any other suggestions?

Thanks,
David Malicky

 

[Hippo41]

Let me say from the start that I think SKF product is the best in the world.

However, I would not recommend running SY series inserts at that speed in a dirty environment and expect a long life. From experience (sewage presses and mining equipment in hot, dusty environments) I would suggest you look at using small bearing housings with double row ball bearings on tapered sleeves. For blind shafts use an end cap (thus halving any sealing problem) and then use steel labyrinth seals for through shafts.

As far as I know none of the auto,matic lub devices will purge over 5 years, probably 12 months max. Sounds like you need a proper centralised system.

If the loads on each bearing are know we could esti,mate bearing life. Knowing the system layout, one could calculate the hours between expected failure for the whole machine.

If you need anything else let me know.

Lester Milton
Telford, Shropshire, UK

 

[diamondjim]

With your duty cycles, you better
order a bearing with grease nipples.
I am amazed that your bearing company
would size this bearing for you under
those duty cycles and expect it to last
more than a few months without being
greased unless the loads are almost
non existant. You did not mention the
temperature range or the load.
Labyrinth seals do allow heat to escape.
I think overgreasing is better than
starving or withholding lubrication.

 

[dmalicky]

Thanks for the replies.

I didn't describe the environment very accurately: the bearings themselves are under a guard, so the only dirt they normally see is belt dust. But there is a *lot* of dirt outside the guard. So if the guard is removed (probably only for regreasing, or belt changes every 3 years) dirt will be introduced. So, if we recommend regreasing, we also are risking considerably more dirt introduction than just leaving them alone.

Oh, temp is ~room, and load is 900 lb, thus the L10 of 20 years (1 15/16" bore SYR). I selected the bearings; it was the only thing I could find that met the speed and life requirements.

On a similar application but with a 300lb load we have used tapered roller bearings (Dodge type K 2&quot, with rubber seals, at around 2800rpm (overspeed by a *lot* for that bearing, and they got hot, but it worked). Customers didn't regrease those and they typically lasted ok.

The SYR bearings (spherical rollers) were selected because we didn't think we could push the Dodge's to the higher speeds (up to 4500rpm, actually) since they are only rated to 2000rpm. The SYRs will go there, mostly due to the labyrinth seals.

My next questions are:
- Are spherical rollers much different than tapered rollers in their required regreasing intervals?
- I understand ball-bearings are need grease much less often than rollers -- is that correct?
- Who makes housed double/triple/quadruple-row ball bearings?

Thanks,
David Malicky