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Pumping new grease into a bearing also helps flush away contamination. Many mounted bearings are designed to allow grease to enter the bearing cavity as close to the rolling elements as possible. As more grease is added, the old grease is pushed out of the seals if the seals are purgeable. The purged grease carries out contaminants and keeps dirt away from the seals. If you pump grease into the bearing until it purges out the seal, you probably have completely filled the bearing cavity.
Excess grease can increase operating temperature and may create enough pressure to blow the seal out. However, in low-speed or dirty conditions where contamination may easily enter the seals, filling a bearing with grease may help improve performance.
Application experience will dictate when the entire bearing cavity should be filled. If a bearing is making noise, internal damage has likely occurred. This increases over time, with the potential for catastrophic failure. Adding grease may provide temporary relief, but a noisy bearing should be closely monitored and replaced at the first opportunity. The root of the failure should also be investigated with either independent or manufacturer failure analysis.
Manufacturer analysis requires removal of the bearing as soon as possible to aid in a more accurate diagnosis of the problem. Greases do differ. Some may be incompatible because of the different thickeners soaps used. When two incompatible greases are mixed, they may thicken and harden or become thin and leak out of the bearing. For example, many electric motors use a polyurea thickener while some mounted ball bearings use lithium-complex thickeners.
These greases are borderline compatible, and depending on the actual makeup, may not work together. It's been my experience that you should never grease double shielded bearings. Any motors that we put double shielded bearings in, we remove and plug the grease zirk ports. I've also had situations involving bearings with grease ports in the outer race.
These bearings may have 1 shield, but should not have 2. The grease has to go somewhere. Typically the unshielded side of the bearing faces a grease cavity with a purge port.
Sorry to add to the confusion but as we here have thought for a long time a sealed bearing is sealead, a shielded bearing is shielded and not sealed so we beleive grease can escape and if it can escape then it should be replenished at a regular interval with the ability to purge the old grease out. Having said that, is there a bearing pro that can give us the proper definition of sealed and shielded.
Cause as always myths are not fact but that does not stop people from believing them. Hard facts from professionals are what we all require to do our job. Originally posted by lee David We have three deep well effluent pumps in which we replaced the upper plain bearing for a flanged SKF bearing.
The bearing is 2RS however the housing has a grease nipple fitted to which we fit a 6mm tube with a nipple at the assembly top plate.
The path of the grease is into the bearing and out through the rubber seals. I understand how greasing outside of 2RS bearings would not allow grease into the bearing.
In our case the force of the grease slightly distorts the seal but we know that fresh grease is arriving at the bearing. Regards Joe Mc Cormack. Lee, In answer to your question about sealed and shielded bearings. Sealed bearings typically have rubber seals on each side.
These seals make rubbing contact with the inner race, there is no gap. Everyone agrees that these can't be relubricated. They are normally only specified for harsh environments because the rubbing contact of the seals actually shortens bearing life, so they will not last as long as a shielded or open bearing in a good environment. Shielded bearings have metal or hard plastic shields on each side. The shields are affixed to the outer race and a small gap 10 mils exists between the shield and the inner race.
Shielded bearings were originally developed for use in dirty environments like coal plants, paper mills, etc None of the major bearing manufacturers recommend trying to grease sealed or shielded bearings. Motor manufacturers are mixed on the issue, with some recommending greasing and some not. My experience is that you can't get new grease into a shielded bearing. Membership Required We're sorry.
You must be signed in to continue. Sign In or Register. Are you sure you want to remove from your Block List? When you block a person, they can no longer invite you to a private message or post to your profile wall. The problem here is new grease entering an old, infrequently lubricated and overly lubricated bearing. As the new grease enters, it must make room, and in doing so, it pushes around the crusty remnants of grease past.
The oil from the thickener bled out slowly over time. Some of this oil entered the bearing race providing needed time-released lubrication. The principal contributors to a hard, crusty build-up in the bearing cavity are heat, long relube intervals, overlubrication too much grease and old bearings. There are other factors too, including grease quality, vibration, centrifugal forces, contamination, pressure and the relube procedure.
In addition to the thickener, hard particles are sometimes deposited along with the thickener forming a wall next to the bearing. These include wear particles, dirt, rust and manufacturing debris. For the new grease to reach the bearing core, it must break through this rock-like formation, creating a channel. Hydrostatic forces from a grease gun can reach levels exceeding 15, psi , kPa - more than enough pressure to send chunks of solids careening into the bearing track.
Imagine the new grease acting like an ice-breaker on a frozen river, mobilizing large blocks of ice as it moves. Sometimes fresh grease never reaches the bearing because of the wall-like barricade. Instead, it detours out the shaft seal or the vent port. The bearing is eventually starved to death. Large bearings especially large electric motor bearings are often lubricated through supply pipes line extensions from a grease fitting.
Hardened thickener, rust and other solids can build up in these pipes over time.
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