Bearing lubrication for high performance

Correct lubrication is critical to bearing performance. Whether you are working with ball bearings, sealed bearings or high-speed applications, selecting the right lubricant helps prevent bearing failure, reduce friction, manage heat and extend bearing life.

For more information on our standard oils and greases, please see our LUBRICANT TABLES

 

Why bearing lubrication matters

Lubrication creates a thin film between the contact surfaces of a bearing, reducing friction, dissipating heat and protecting against corrosion. The choice of lubricant will affect maximum running speed and temperature, torque level and noise level. Ultimately, it determines the efficiency and lifespan of your rolling elements.

 

Types of lubricants

There are a range of options depending on the application. Most bearing lubricants are based on either mineral oil or synthetic fluids. Each has specific properties suitable for different operating conditions, including high temperature, high loads or environments requiring low noise. Common types include:

Silicon lubricants have wide temperature ranges and change viscosity less with temperature. They also have good water-resistance and are safe to use with most plastics. They are not suitable for high loads and speeds.

Perfluorinated lubricants or PFPE lubricants are non-flammable, oxygen compatible and highly resistant to many chemicals. They do not react with plastics or elastomers. Many have low vapour pressure and are suitable for vacuum or clean-room applications while some can withstand temperatures of over 300°C.

Dry lubricants are used where standard lubricants may cause contamination such as vacuum environments. Popular materials such as molybdenum disulphide or tungsten disulphide may be burnished or sputtered on to the balls and raceways to give smooth operation and higher running speeds than unlubricated bearings.

Solid polymer lubricants consist of a synthetic polymer impregnated with lubricating oil which fills most of the internal space of the bearing. This type of lubricant is often used in sealed bearings in dusty environments or where lubricant leakage cannot be tolerated such as clean environments and vertical shaft applications. Solid lubricants have excellent water resistance and will withstand regular wash-downs. They will also tolerate high vibration and high centrifugal force.

Dampening greases are widely used in automotive parts to prevents rattles and squeaks. They are also used to give a “quality” feel to switches, slides, threads and gears. They can be used in slow rotating bearings in, for example, potentiometers for the same reason.

Food grade lubricants are required for the food and beverage industries to conform with strict hygiene regulations. H1 approved lubricants are required for bearings were there may be incidental contact with food and H2 approved greases are used where there is no contact. These greases are also designed to be highly resistant to being washed out by cleaning processes.

 

Understanding lubricant viscosity

Low viscosity oils and greases are used where low rolling resistance is required such as sensitive instruments. Higher viscosity lubricants may be specified for high load or vertical shaft applications. Low viscosity oils (or greases with low viscosity base oils) are preferred for high-speed applications as they generate less heat.

Although greases often provide much greater resistance than oils, many modern low torque greases can produce torque figures that are similar to some oils, particularly where a low grease fill is used.

Oils

Most oils maintain their consistency well over a wide temperature range and are easy to apply. For very low torque applications, a light instrument oil may be specified. Higher running speeds are possible with oil but, as it tends not to stay in place, continuous lubrication must be applied by oil jet, oil bath or oil mist unless speeds are low or rotation is for short periods.

An oil-impregnated phenolic retainer or a synthetic retainer made from a material with a very low coefficient of friction such as Torlon do not need continuous external lubrication. These types of retainer are often used in high speed, low torque dental bearings.

Greases

Greases are lubricating oils combined with thickeners to ensure they remain in place within 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.

Surprisingly, excessive grease can be detrimental to a bearing's performance. Overfilling increases rolling resistance (and thus torque), which may be unsuitable for many applications. More critically, it can lead to heat build-up, potentially causing premature failure. The free space inside a bearing is important to allow the heat to radiate away from the contact area between balls and raceway.

As a result, too much grease can lead to premature failure unless speeds are low. The standard fill is 25 per cent to 35 per cent of the internal space but this may be varied if required. A smaller percentage may be specified for a high speed, low torque application while a much higher fill may be advisable for a low speed, high load application.

 

Grease speed rating and DN values

Greases are rated for speed using "DN" values, calculated as: Speed (rpm) x [(Bearing ID + Bearing OD) / 2]

Assume a bearing rotates at 20,000 rpm. The bearing ID is 8mm and the OD is 22mm. The above formula produces a DN of 300,000 so the grease should be rated above this figure. Many modern greases are suitable for high speeds with some rated at 1 million DN or more.

 

Selecting the right lubricant for bearings

Selecting the right lubricant requires a thorough understanding of the application’s types, properties and operating conditions. Whether you need lubricating oil for high-speed precision equipment, high temperature grease for sealed systems or a dry lubricant for contamination-sensitive areas, choosing the correct lubricant helps prevent wear, minimise friction and avoid bearing failure.

Still unsure which lubricant suits your needs? Get in touch with our specialist bearing and lubrication team today by emailing sales@smbbearings.com or fill in the contact form.