What types of bearing grease are there to choose from?

Proper lubrication is critical to bearing performance. It provides a thin film between the contact areas of the bearing to reduce friction, dissipate heat and inhibit corrosion on the balls and raceways. Bearing grease will affect maximum operating speed and temperature, torque levels, noise levels and ultimately bearing life. There are several options depending on the application.

Mineral or synthetic-based lubricants are the most commonly used lubricants and are designed for general and high-speed use. Fine filtered version for low noise applications. There are waterproof versions available, offering low or high temperature capabilities.

Silicone lubricants, commonly known as "silicone grease", have a wide temperature range and reduce viscosity as temperature changes. They also have good water resistance and are safe to use on most plastics. They are not suitable for high loads and speeds.

Perfluorinated lubricants, or PFPE lubricants, are non-flammable, compatible with oxygen, and highly resistant to many chemicals. They do not react with plastics or elastomers. Many have lower vapor pressures and are suitable for vacuum or clean room applications. Some can also withstand temperatures up to 300°C.

Dry lubricants are often specified where standard greases may cause contamination, such as in vacuum environments. Dry coatings such as molybdenum disulfide or tungsten disulfide are often polished onto the bearing's balls and raceways to allow for smooth operation and higher operating speeds than unlubricated bearings. These coatings are also resistant to water and dilute acids.

Grease Partial Grease on Bearings Grease is widely used in automotive parts to prevent rattling and squeaking. They are also used to give switches, sliders, threads and gears a "quality" feel. For the same reason, they are used, for example, in slow-rotating bearings in potentiometers.

Lubricant viscosity

Low viscosity oils and greases are used where low lubricity is required, such as sensitive instruments. For high load, high speed or vertical axis applications, higher viscosity lubricants can be specified. Low viscosity oils (or greases containing low viscosity base oils) are preferred for high speed applications because they generate less heat. Although greases generally provide greater resistance than oils, many modern low-torque greases can produce torque maps similar to some oils, especially if low-lubricant greases are used.

Most oils maintain good consistency over a wide temperature range and are easy to apply. For very low torque applications, a lightweight instrument oil should be specified. Using engine oil can increase operating speed, but because engine oil often cannot stay in place, continuous lubrication must be provided by oil spray, oil bath or oil mist, unless the speed is low or the rotation is short. Oil-containing phenolic or synthetic retainers made of materials with very low coefficients of friction do not require continuous external lubrication. These types of retainers are typically used on bearings operating at high speeds and low torque.

It's worth noting that too much grease can be bad for bearings. High grease fill means greater rolling resistance (higher torque), which may not be suitable for many applications, but worse still there is a risk of heat build-up. Free space inside the bearing is important to allow heat to dissipate away from the contact area between the balls and raceways. Therefore, unless the speed is very low, too much grease can cause premature failure. Standard padding is 25% - 35% of the interior space, but this may vary if required. For high-speed, low-torque applications, a smaller percentage may be specified, while for low-speed, high-load applications, a higher fill may be recommended.