Miniature & Instrument Ball Bearings
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 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 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 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.
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.
|Code||Brand Name||Basic Type||Operating Temp.||Uses|
|L01||Windsor L-245X (MIL-PRF-6085)|
Fuchs Mineral Oil
|Synthetic oil||-65 to +300 °F||Light general purpose instrument oil|
|LO2||Royco® 885 (MIL-PRF-6085)|
|Synthetic oil||-65 to +300 °F||Light general purpose instrument oil|
|Fluorinated oil||-30 to +550 °F||High temperature stability|
Good lubricity properties
|LY60||Carnation||Mineral oil||Consult factory||High speed, FDA approved|
|Synthetic grease||-65 to +250 °F||General purpose grease|
|LG68||Royco® 27 (MIL-PRF-23827)|
|Synthetic grease||-100 to +275 °F||Corrosion resistance, heavy loads, high speed|
|LY48||Mobil 28 (MIL-PRF-81322)|
|Synthetic hydrocarbon grease||-65 to +350 °F||Wide temperature range|
Good low temperature torque
|Mineral grease||-20 to +350 °F||Longer life under high speed/high temp.|
Water/salt water resistance
|LY101||Krytox® 240AC (MIL-PRF-27617)|
|Fluorinated grease||-30 to +550 °F||High temperature stability with good lubricity properties|
|Synthetic grease||-40 to +300 °F||Low noise and low torque applications|
|LY328||Braycote® Micronic® 601EF|
|Perfluorinated polyether grease||-112 to +400 °F||Hostile chemical environment|
|LY342||Asonic GLY 32|
|Synthetic hydrocarbon||-58 to +284 °F||Low noise, high speed|
|LY732||Minebea 1473 (proprietary)|
Minebea Co., Ltd.
|Synthetic hydrocarbon grease||-20 to +350 °F||Longer life under high speed/high temp.|
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
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)
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
Low vapor pressure (10-9 Torr)
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.
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.
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 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.
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.
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
|TYPE||dN||TEMPERATURE RANGE °F (°C)|
|Petroleum||600,000||-25 to +250 (-32 to +121)|
|Diester||400,000||-65 to +350 (-54 to +177)|
|Silicone||200,000||-100 to +400 (-73 to +204)|
|Perfluorinated polyether||200,000||-112 to +400 (-80 to +204)|