Symptom: You’re suffering repeated failures of grease-lubricated bearings in vertically mounted equipment, such as pumps, electric motors, mixers and so on, especially in equipment that was originally designed for horizontal operation. The downtime is getting serious enough that management is starting to pay attention. When inspecting the bearings during an overhaul, shiny bearing raceways, surface distress and spalling are evident. What’s happening?
Answer: There may be a lubrication problem. Gravity forces grease to flow down through the bearing, and leaks out of the arrangement. In vertical applications, grease with a higher consistency (e.g., NLGI 3) may be preferred to better retain the grease in the bearing. Due to the possible upward pumping effect of the bearing itself, grease with a lower consistency may be appropriate as well, provided it has high mechanical stability.
The suggested relubrication interval for vertical applications is half the interval required for a similar horizontal arrangement. After inspection of grease condition, the interval may be decreased or increased. Even better: Regrease continuously, with the desired grease quantity spread over the relubrication interval. Relubricate (e.g. via grease fitting) above the bearing. The use of a seal or grease retention shield is a prerequisite to prevent leakage. Operating temperatures and vibration also have a great effect on relubrication intervals.
Moral: For grease-lubricated bearings that are mounted on vertical shafts, special attention is needed in grease selection, relubrication procedures and perhaps even sealing. For the right selection and intervals, consult the advisory programs LubeSelect and LuBase on @ptitudeXchange.com.
LubeSelect for SKF greases is an online selection tool that includes all SKF lubricants and can be used for free after registration.
