Types of Lubricants

Oil 

Oil is the basic lubricant for ball bearings, and NHBB offers both petroleum-based and synthetic oils such as diesters, silicone polymers and fluorinated compounds. In general, diesters have better low temperature properties, lower volatility and better temperature/viscosity characteristics than petroleum-based oils. Silicones and fluorinated compounds possess even lower volatility and wider temperature/viscosity properties.

Grease 

Grease consists of oil lubrication with added thickeners that prevent migration from the lubrication site, resulting in longer life. Grease is used in situations where frequent replenishment of the lubricant is undesirable or impossible. The operative properties of grease depend almost wholly on the choice of base oil. Other factors being equal, the use of grease instead of oil results in higher starting and running torque and can limit the bearing to lower speeds.

Solid film 

Solid film lubricants are any non-fluids used to prevent wear and reduce friction. They can range from simple sacrificial cages to graphite powder and ion sputtering. Each type must be engineered for the specific application. Solid film lubricants have definite advantages. They are very useful in areas of temperature extremes, vacuum, radiation, pressure, or harsh environments where conventional lubricants would fail. In addition, these lubricants do not deteriorate in storage.

Lubricant Specifications

Below is a table of commercial and military lubricants and their recommended uses. When ball bearings are ordered without a specified lubricant, it is the policy of NHBB to lubricate with MIL-PRF-6085 oil. Company standard lubricants are LO1 (Winsor Lube L-245X oil) per MIL-PRF-6085 and LG68 (Royco 27 grease) per MIL-PRF-23827. For nonstandard lubricants, please consult the factory to select an appropriate type.

The standard quantity of oil varies with bearing size, but is approximately one drop (3-6 mg) per bearing up to R-2 size and two drops (6-12 mg) for larger sizes. The standard quantity of grease is 25-35% of the bearing's internal free volume. For nonstandard applications, please consult the factory for specific lube fill recommendations.

Lubrication Methods

Centrifuging

Centrifuging an oil-lubricated bearing removes excess oil and leaves only a very thin film on all surfaces. This method is used on very low torque bearings and can be specified for critical applications.

Vacuum Impregnation

For ball bearings containing porous cages, vacuum impregnation forces lubricant into the pores, using the cage as an oil reservoir. When used with a greased bearing, this method prevents the cage material from leaching oil from the lubricant. Normally, the base oil of the grease is used in the cage to prevent incompatibility.

Grease Packing

Packing approximately 1/4 to 1/3 of a ball bearing's internal free volume with grease is one of the most common methods of lubrication. Grease quantity can be controlled by the use of special lubrication equipment.

Grease Plating

Grease plating consists of mixing a quantity of grease and solvent to the desired consistency, lubricating the bearing with this mixture, then evaporating the solvent at a moderate temperature, leaving a thin film of grease on raceways and balls.

Limiting Speed

No exact formula exists for calculating the maximum operating speed of a ball bearing. Sustained high speed performance is dependent on the specific properties of the bearing, shaft, housing and other components, as well as the application's specific operating conditions. The retainer is the feature of a ball bearing that most affects rotational speed, followed by tolerance grade and lubricant type and fill. The dimensional accuracy of mating components limits speeds, as does the application's maximum operating temperature. If properly installed and lubricated, high precision ball bearings will operate for long periods of time at high speeds.

After determining the lube-type and fill appropriate for the speed of the application (see table below), consult the table on the Cages page to select a suitable retainer, as it provides the maximum operating temperatures and speeds for each retainer type. To verify limiting speeds for unique operating conditions not covered here, and for full ball complement-type ball bearings, please consult the factory.

Speed Factor

The maximum usable operating speed of a grease lubricant is dependent on the type of base oil. The speed factor is a function of the bore of the bearing (d) in millimeters (mm) and the speed of the bearing (N) in revolutions per minute (rpm) where:

dN = d (bearing bore, mm) x N (rpm)

Table of Recommended Speed Limits (dN) for Grease with Select Base Oils