The Role of Bearing Lubrication
Bearing lubrication plays a very important role in function and life of rolling element bearings. The most important task of lubrication is to separate parts moving relative to one another in order to reduce friction and prevent wear.
A lubricant that is for specific operating conditions will provide a load bearing wear protective film. When the friction surfaces are separated by this film, the bearing is under ideal condition. In addition to providing this load bearing film, the lubricant should also allow for the dissipation of frictional heat thus preventing overheating of the bearing and deterioration of the lubricant and provide protection from moisture, corrosion, and the ingress of contaminants.
How to lubricate sealed-cartridge bearings
Tools for the lubrication: a sealed-cartridge bearing, a pick (you can use a nail or something sharp to replace it), and a vise.
Use the pick (or whatever you can use) to remove the seal. You can do it from the outside or the inside edge of the seal. Just try to be carefully to avoid poking a hole on the seal.
Gently pull the seal out. Get a big dab of grease out of grease gun with your finger, and pack it in the bearing as hard as you can.
After packing full grease all the way around, take the seal and put it back in place. Use your finger to press on the seal to tighten it on the bearing. Use the back side of the pick to pop the seal back in real well. In this way, your bearing will be much quieter.
The amount of grease is typically specified as a percentage, such as 30% fill. The percentage represents the actual grease volume compared to the free internal space within the bearing. In other words, if the internal space in the bearing is completely filled with grease with no voids, it would be 100% full. Manufacturers of bearings have different amounts that they would consider standard. This typically ranges from 20% to 40%. In small or miniature bearings grease fill amounts can be as little as 10%.