Bearing Lubrication Selection

Bearing lubrication is an essential element of bearing selection. Proper lubricant can reduce friction, prevent bearing wear, protect bearing surfaces from corrosion, and carry away excess heat from bearing operation. PQB® Bearings selects only bearing approved and tested oils and greases for our variety of lubricant options. Bearings operate on a very thin film of lubricant which must be maintained, or replaced, to ensure that maximum bearing life is achieved. Proper selection, application, and maintenance are vital in maximizing bearing life. Using the proper lubrication in the bearing will reduce friction and wear. This is achieved by creating a hydrodynamic film of appropriate thickness and strength to support the load while separating the balls from the raceway.

Bearing lubrication prevents against metal to metal contact. It also minimizes retainer wear by reducing friction. Proper lubricant will conduct heat away from the bearing. Operational conditions such as temperature, loads, speed, torque, and environment determine the lube appropriate for the application. Oils are used where low bearing friction torque is a primary concern. Grease may provide longer operating life and resist lubricant loss due to centrifugal forces at higher speeds. Dry film lubricants are often appropriate for vacuum environments or other conditions where wet lube is not an option. PQB® Bearings offers bearing lubrication in grease form, oil lubricants, and solid dry film lubricants.

Correct lubrication is critical to bearing performance. It provides a thin film between the contact areas in a bearing to reduce friction, dissipate heat and inhibit corrosion on balls and raceways. The lubricant will affect maximum running speed and temperature, torque level, noise level and, ultimately, bearing life.

Lubricants are available for a whole range of applications

Silicon lubricants have wide temperature ranges and change viscosity less with temperature. They also have good water-resistance and are sfe to use with most plastics but are unsuitable for high loads and speeds.

Perfluorinated lubricants withstand temperatures of up to 300°C and are resistant to most chemicals. They do not react with plastics or elastomers.

Mineral or synthetic based lubricants are designed for general and high speed use.

Low viscosity oils and greases are used where low lubricant resistance is required but higher viscosity lubricants may be specified for high load applications. Although greases are usually thought to be stiffer than oils, many modern low torque greases can even produce similar torque figures to some of the instrument oils.

• Oils – maintain their consistency well over a wide temperature range and are easy to apply. For very low torque applications, a light instrument oil should be specified. Higher running speeds are possible with oil but the obvious drawback with oil is the fact that it tends not to stay in place.

For anything other than very low speeds, continuous lubrication through oil mist, oil jet or oil bath is normally necessary. An exception to this is the use of a retainer (cage) that can be impregnated with oil such as the phenolic retainer. Perfluorinated oils can offer improved performance at slightly higher speeds as they don’t migrate (run out) as easily.

• Greases – are simply oils mixed with a thickener to so that they stay inside the bearing. Greases are generally more suitable for heavy loads and have the obvious advantage of giving constant lubrication over a long period without maintenance.

Finely filtered greases are used for low noise applications.

Lithium based greases are multipurpose, often low torque and high speed and widely used.

Polyurea thickened greases have very good water resistance and a wide temperature range.

Aluminium complex greases have excellent resistance to water washout.

USDA approved non toxic food grade greases are required in food processing environments. H1 grade lubricats are needed where incidental contact with food is possible and H2 where food contact is not possible. These greases have excellent resistance to water washout.

PTFE thickened greases can withstand very high temperatures.

Surprisingly, too much grease can be bad for a bearing. A high fill will mean greater rolling resistance (higher torque) which may not be suitable for many applications but worse still is the risk of heat build-up. The free space inside a bearing is important in allowing the heat to radiate away from contact area between balls and raceway. As a result, too much grease can lead to premature failure. The standard fill is 25% – 35% of the internal space but this may be varied if required. A smaller percentage may be specified for low torque, low load applications while a much higher fill may be advisable for a high load application provided the speed is low.

• Dry Lubricants – are used primarily in vacuum applications or where standard lubricants are unsuitable. We use graphite based dry lubricants and also molybdenum disulfide for its hardwearing and low friction properties and the fact that it is insoluble in water and dilute acids. It is also effective within a wide temperature range of -180 to +300C. By burnishing the balls and raceways of a bearing, friction is reduced allowing higher speeds than with dry bearings. This also gives improved performance in vacuum applications.

We stock many different lubricants but for more information on our standard oils and greases, please see the following our LUBRICANT TABLES.

Standard Oils

Standard Greases