Guide Bearing Grease Lubrication Temperature
Guide Bearing Grease Lubrication Temperature
(OP)
We have a grease lubricated journal bearing on a vertical shaft of an axial flow pump that demonstrates an unusual temperature cycle. The grease is injected every several hours into six equally spaced, helical grease grooves by a centralized system at high pressure. Each time grease is injected, the bearing temperature rises rapidly then slowly decays back towards equilibrium. Often it doesn't get there before the next grease cycle and temperature rises again.
There have been several theories passed around for the cause. One theory is that the double lip seals on the bearing are allowing the pressure to be maintained high while the grease leaks past the seals and this is causing a hydrostatic operation and higher load on the bearing. Other possibilities are whirl or grease churning (similar to in ball bearings). The pump is on a VFD and the phenomenon occurs at all speeds with average temperature proportional to speed. There is no real evidence the pump is anywhere near critical speed or 50% of critical speed (present best analysis is first harmonic is ~4 times maximum operating speed).
Question: is there a documented phenomenon for grease pressure causing temperature transients in a lightly loaded, vertical plain guide bearing? Any thoughts or references on the subject would be helpful. Thanks!
There have been several theories passed around for the cause. One theory is that the double lip seals on the bearing are allowing the pressure to be maintained high while the grease leaks past the seals and this is causing a hydrostatic operation and higher load on the bearing. Other possibilities are whirl or grease churning (similar to in ball bearings). The pump is on a VFD and the phenomenon occurs at all speeds with average temperature proportional to speed. There is no real evidence the pump is anywhere near critical speed or 50% of critical speed (present best analysis is first harmonic is ~4 times maximum operating speed).
Question: is there a documented phenomenon for grease pressure causing temperature transients in a lightly loaded, vertical plain guide bearing? Any thoughts or references on the subject would be helpful. Thanks!





RE: Guide Bearing Grease Lubrication Temperature
According to this link a temperature rise in a bearing can be expected after grease injection.
http://www.reliableplant.com/Read/25315/Tips-troub...
RE: Guide Bearing Grease Lubrication Temperature
RE: Guide Bearing Grease Lubrication Temperature
RE: Guide Bearing Grease Lubrication Temperature
RE: Guide Bearing Grease Lubrication Temperature
RE: Guide Bearing Grease Lubrication Temperature
RE: Guide Bearing Grease Lubrication Temperature
Are the seal lips oriented to:
- exlude water
- contain the grease?
Is the grease cavity:
- pressurized
- vented to atmosphere
- sealed to fend for itself
RE: Guide Bearing Grease Lubrication Temperature
1. It's a 6.625" shaft with a double lip seal on each end of the bearing. Both are Garlock Model 53 which has a published pressure rating of 7 psi.
2. Shaft RPM is 140-227 (on a VFD) and the grease supply system is an SKF Dual Line system. There are 6 grease injection ports into 6 helical grease grooves.
3. The seals are to exclude water as the bearing is on lower guide bearing of a vertical pump in a silty river environment (a hydroelectric facility to be exact)
4. The grease cavity is not vented to atmosphere. I'd say it is sealed to fend for itself and pressure is controlled by leakage past the seals.
5. The seals are tight enough that they have been observed to grind a fairly deep groove in the shaft.
Now that I see the 7 psi rating on the seals, it might imply a maximum and expected pressure of 14 psi. The L/D is ~2.3 so the bearing is long and the rated load of the bearing is only 29 psi so a 14 psi grease pressure would seem to me to be significant. It is a total loss system so I would expect it to be sensitive to any change in grease shear.
The lip seals appear to also be designed for oil retention and that may be the basis for the 7 psi rating. The lubricant in this case is NLGI 2 grease.
RE: Guide Bearing Grease Lubrication Temperature
1. The bearing is lightly loaded with a large surface area so that design pressure is 29 psi. Would a static grease pressure of 6-10 psi be enough to cause hydrostatic operation?
2. The bearing is flooded so I think a divergent cavitation region is expected. Does collapse or partial collapse of the vapor region seem likely given the pressure that can be built up?
Bottom line, is there a plausible explanation for the bearing temperature cycles that results from grease pressure transients caused by the lip seals?