Engineering Reference

Miniature & Instrument Ball Bearings

Lubrication

Oil, grease, and dry film are the three main types of lubricants used in miniature & instrument ball bearings. Oil lubricants include petroleum and synthetic varieties. Selecting the most suitable lubricant is critical to achieving the full rated life of the bearing and optimal performance of the assembly, but choosing from the hundreds available can be an overwhelming task.  The charts published below list a small selection of lubricants we use regularly. They cover a wide range of temperatures, rotational speeds, load conditions, and assembly designs.  Please contact NHBB Precision Division's Applications Engineering department before making your final selection.


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 (Windsor 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.


 Lubricant Types

CodeBrand NameBasic TypeOperating Temp.Uses
L01Windsor L-245X (MIL-PRF-6085)
Fuchs Mineral Oil 
Synthetic oil-65 to +300 °FLight general purpose instrument oil
LO2Royco® 885 (MIL-PRF-6085)
Royal Lubricants
Synthetic oil -65 to +300 °F Light general purpose instrument oil
LY115Krytox® 143AC
Dupont 
Fluorinated oil-30 to +550 °F High temperature stability
Good lubricity properties
LY60CarnationMineral oil Consult factory High speed, FDA approved
LG20Beacon 325
EXXON Mobil 
Synthetic grease-65 to +250 °F General purpose grease
LG68Royco® 27 (MIL-PRF-23827)
Royal Lubricants 
Synthetic grease-100 to +275 °F  Corrosion resistance, heavy loads, high speed
LY17 Rheotemp® 500
NYE 
Synthetic (non-silicone) grease-65 to +350 °FSpecialty lube, high speed/high temp.
Inhibits oxidation, anti-wear protection
LY48Mobil 28 (MIL-PRF-81322)
EXXON Mobil
Synthetic hydrocarbon grease-65 to +350 °F Wide temperature range
Good low temperature torque
LY75SRI-2
Chevron
Mineral grease-20 to +350 °F Longer life under high speed/high temp.
Water/salt water resistance
LY101Krytox® 240AC (MIL-PRF-27617)
Dupont
Fluorinated grease-30 to +550 °F High temperature stability with good lubricity properties
LY121SRL
Kyodo
Synthetic grease-40 to +300 °FLow noise and low torque applications
LY328Braycote® Micronic® 601EF
Castrol® 
Perfluorinated polyether grease-112 to +400 °F Hostile chemical environment
Space applications
LY342Asonic GLY 32
Kluber
Synthetic hydrocarbon -58 to +284 °F Low noise, high speed
LY732Minebea 1473 (proprietary)
Minebea Co., Ltd. 
Synthetic hydrocarbon grease-20 to +350 °F Longer life under high speed/high temp.


Trademarks

Royco® is a registered trademark of Anderol Company.
Krytox® is a registered trademark of DuPont.
Braycote®, Micronic®, and Castrol® are registered trademarks of Castrol Limited.
Rheotemp® is a registered trademark of Nye Lubricants.


A Comparison of Oils and Base Fluids

Petroleum

Synthetic

Silicone

Perfluorinated Polyether

Excellent load carrying abilities

Moderate temperature range (–25 to +250 °F)

Greases with petroleum oil bases have high dN capability (recommended for light to heavy loads and moderate to high speeds)


Wide temperature range (–65 to +350 °F)

Resist oxidation

Less film strength than petroleum oils



Wide temperature range (–100 to +400 °F)

Less film strength than diesters

Tend to migrate


Wide temperature range (–112 to +400 °F)

Stable at high temperatures

Chemically inert

Low vapor pressure (10-9 Torr)




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

TYPEdNTEMPERATURE RANGE °F (°C)
Petroleum600,000-25 to +250 (-32 to +121)
Diester400,000-65 to +350 (-54 to +177)
Silicone200,000-100 to +400 (-73 to +204)
Perfluorinated polyether200,000-112 to +400 (-80 to +204)