Grease & Dry Film Lubricants
The selection of lubricants is based on bearing materials, design, environment, and operating conditions. The following sections describe grease and dry film lubricants and list the most commonly used types.
|Type||Specification||Composition||Temperature Range||Use and Remarks|
|Grease, aircraft and instrument, gear, and actuator screw||MIL-PRF-23827||Lithium soap, ester oil, anti-rust and E.P. agents||-100° to +250°F||General purpose grease. Extreme pressure (E.P.) properties, good water resistance|
|Grease, MoS2, for high and low temperatures||MIL-G-21164||Same as MIL-PRF-23827, except 5% MoS2 added||-100° to +250°F||Similar to MIL-PRF-23827 but has added MoS2 for extra E.P. properties and anti-wear action under marginal lubrication conditions|
|Grease, Aircraft||MIL-PRF-81322||Synthetic oil and thickener||-65° to +350°F||High temperature grease|
Grease is an oil to which a metallic soap, synthetic filler, thickener, or a combination of these has been added to prevent oil migration from the lubrication site. The operative properties of grease depend almost wholly on the base oil.
Grease lubricants can be used on metal-to-metal spherical and rod end bearings such as a steel ball against a steel race, a steel ball against an aluminum bronze race, and a beryllium copper ball against a steel race.
The three most common grease lubricants used with NHBB bearings are shown above.
Grease-lubricated bearings are usually furnished with lubrication holes and grooves, and, in the case of rod ends, lubrication fittings for periodic relubrication. These bearings have a tendency to gall unless lubrication is very frequent and loads are reversing so that the grease is not squeezed out of the load area.
In applications with uni-directional loading, the grease will quickly be squeezed out of the bearing area. In these applications, dry film can be used. The use of PTFE also should be investigated.
NHBB grease lubricants are suitable for most airframe applications. If bearings will be required to operate in unusual conditions (for example, high vacuum, radiation, or near chemicals such as phosphate ester fluids or propellants), please consult the NHBB Applications Engineering Department before ordering.
The above illustrates a lubrication network that provides for lubricating both the ball/race and the ball/shaft (or pin) interfaces. Further, relubrication can be accomplished via the race housing or the ball shaft or pin. If relubrication is to be done via the race housing, and no lubrication is required in the ball bore, lube holes and I.D. lube groove in the ball may be omitted. Conversely, if relubrication is to be done via the shaft or pin, lube holes and O.D. groove in the race may be omitted.
Transverse Lube Groove
(lube groove size and depth exaggerated for clarity)
This is a transverse lube groove configuration for use on medium to large size spherical bearings in critical applications where lubrication demands are more extreme. The transverse grooves are machined into the cylindrical race blank prior to swaging. These bearings are often bushed with copper alloy sleeves, which in turn may incorporate transverse or equivalent lube groove patterns to provide for maximum possible lubrication.
Dry Film Lubricants
|Type||Specification||Lubricant||Binder||Temperature Range||Use and Remarks|
|Solid film, heat cured, corrosion inhibiting||MIL-L-46010 Type I||MoS2 (no graphite or powdered metals), and corrosion Inhibitors||Organic resins||-65° to +450°F||Good wear life. Used for most bearing applications other than extreme temperature situations.|
|Solid film, heat cured, corrosion inhibiting||MIL-L-46010 Type II||MoS2 (no graphite or powdered metals), and corrosion Inhibitors||Organic resins||-90° to +400°F||Similar to MIL-L-46010, TY I except that it will provide added corrosion protection to substrate. Must have phosphate coating pretreatment for effective use on steel.|
|Solid film, extreme environment||MIL-PRF-81329||MoS2 and other solid lubricants||Inorganic binders||-300° to +1200°F||To be used in extreme environments, i.e., vacuum, liquid oxygen, high temperatures. Wear life not as good as resin-bonded types.|
Dry film lubricants consist of MoS2 and small quantities of other materials such as graphite or powdered metals. These are bonded to the bearing race I.D., and often the ball O.D. and bore, by either organic resins or inorganic binders (phenolic, sodium silicate, or other glass compositions). Hardening or curing is achieved by baking at temperatures ranging from 300° to 1000°F depending upon the binding material.
NHBB can apply dry film lubricants to all metal-to-metal spherical and rod end bearings.
The three most common dry film lubricants used with NHBB bearings are shown in the table above. The advantages of dry film include good tenacity, low coefficient of friction (0.05 to 0.25), and resistance to high bearing pressure (up to 90000 psi on hard substrates). Dry film, however, is not as predictable as PTFE liners regarding wear characteristics.
NHBB dry film lubricated bearings are generally used in aircraft and engine applications in which extreme temperature conditions exist (-300° to +1200°F).
The graph below illustrates the difference in bearing life between dry filmed bearings and bearings that have not been lubricated.
Dry Film Lubricated vs. Non-Lubricated Bearings
Commonly Used Dry Films
|E/M® 967||-300° to +750°F|
|Lubeco M-390||MIL-L-46010, TY I||-65° to +500°F|
|Surf-Kote® LBO-1800-G||-65° to +1100°F|
|Molykote® 106||-321° to 450°F|
|Everlube® 811||MIL-PRF-81329||-300° to +1200°F|
|Vitrolube 1220||-400° to +700°F|
EVERLUBE® is a registered trademark of The Morgan Crucible Company PLC
E/M® is a registered trademark of the Morgan Crucible Company PLC
MOLYKOTE® is a registered trademark of Dow Corning Corporation
SURF-KOTE® is a registered trademark of Hohman Plating & Mfg. INC.