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Significance and Use
4.1 The purpose of this guide is to report on the testing of, to discuss and compare the properties of, and to provide guidelines for the choice of lubricating greases for precision rolling element bearings (PREB). The PREB are, for the purposes of this guide, meant to include bearings of Annular Bearing Engineer's Committee (ABEC) 5 quality and above. This guide limits its scope to lubricating greases used in PREB.
4.2 The number of lubricating greases used in PREB increased dramatically from the early 1940s to the mid 1990s. In the beginning of this period, petroleum products were the only widely available base stocks. Later, synthetic base oils became available. They included synthetic hydrocarbons, esters, silicones, multiply alkylated cyclopentanes (MAC) and fluorinated materials, including perfluorinated ethers and the fluorosilicones. This broad spectrum of lubricant choices has led to the use of a large number of different lubricants in PREB applications. The U.S. Department of Defense, as a user of many PREB, has seen a significant increase in the logistics effort required to support the procurement and distribution of these items. In addition, as time has passed, some of the greases used in certain PREB are no longer available or require improved performances due to advanced bearing technology/requirements. This implies that replacement lubricating greases must be found, especially in this era of extending the lifetime of DoD assets, with the consequent and unprojected demand for sources of replacement parts.
4.3 One of the primary goals of this study was to take a broad spectrum of the lubricating greases used in PREB and do a comprehensive series of tests on them in order that their properties could be compared and, if necessary, potential replacement greases be identified. This study is also meant to be a design guide for choosing lubricating greases for future PREB applications. This guide represents a collective effort of many members of this community who span the spectrum from bearing manufacturers, original equipment manufactures (OEMs), grease manufacturers and suppliers, procurement specialists, and quality assurance representatives (QARs) from DoD and end users both inside and outside DoD.
4.4 It is strongly recommend that, prior to replacing a grease in a PREB, all of the existing grease should be removed from the bearing. Reactions may occur between incompatible greases resulting in severely degraded performance. When users have more than one type of grease in service, maintenance practices must be in place to avoid accidental mixing of greases. In addition, all fluids used specifically to prolong storage life of PREBs (preservatives) should be removed prior to lubricating the bearings. Reactions may occur which would degrade the grease.
4.5 The base oils, thickeners, and additives dictates grease performances. The properties of many base oils can be found in the previous study (Guide F2161). This study included a discussion of elastohydrodynamic lubrication theory.
1.1 This guide is a tool to aid in the choice of lubricating grease for precision rolling element bearing applications. The recommendations in this guide are not intended for general purpose bearing applications There are two areas where this guide should have the greatest impact: (1) when lubricating grease is being chosen for a new bearing application and (2) when grease for a bearing has to be replaced because the original grease specified for the bearing can no longer be obtained. The Report (see Section 5) contains a series of tests on a wide variety of greases commonly used in bearing applications to allow comparisons of those properties of the grease that the committee thought to be most important when making a choice of lubricating grease. Each test was performed by the same laboratory. This guide contains a listing of the properties of greases by base oil type, that is, ester, perfluoropolyether (PFPE), polyalphaolefin (PAO), and so forth. This organization is necessary since the operational requirements in a particular bearing application may limit the choice of grease to a particular base oil type and thickener due to its temperature stability, viscosity index or temperature-vapor pressure characteristics, etc. The guide provides data to assist the user in selecting replacement greases for those greases tested that are no longer available. The guide also includes a glossary of terms used in describing/discussing the lubrication of precision and instrument bearings.
1.2 The lubricating greases presented in this guide are commonly used in precision rolling element bearings (PREB). These greases were selected for the testing based on the grease survey obtained from DoD, OEM and grease manufactures and evaluated according to the test protocol that was designed by Subcommittee F34 on Tribology. This test protocol covers the essential requirements identified for precision bearing greases. The performance requirements of these greases are very unique. They are dictated by the performance expectations of precision bearings including high speed, low noise, extended life, and no contamination of surrounding components by the bearing’s lubricant system. To increase the reliability of test data, all tests were performed by a DoD laboratory and three independent testing laboratories. There were no grease manufacturer’s data imported except for base oil viscosity. Most of tests were performed by U.S. Army Tank–Automotive Research, Development and Engineering Center (TARDEC) and three independent laboratories, and the results were monitored by the Naval Research Laboratory (NRL). This continuity of testing should form a solid basis for comparing the properties of the multitude of lubricating greases tested by avoiding some of the variability introduced when greases are tested by different laboratories using different or even the “same” procedures. Additional test data will be considered for inclusion, provided the defined protocol is followed and the tests are performed by independent laboratories.
1.3 This study was a part of DoD Aging Aircraft Replacement Program and supported by Defense Logistic Agent (DLA) and Defense Supply Center Richmond (DSCR).2
1.4 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D217 Test Methods for Cone Penetration of Lubricating Grease
D972 Test Method for Evaporation Loss of Lubricating Greases and Oils
D1264 Test Method for Determining the Water Washout Characteristics of Lubricating Greases
D1742 Test Method for Oil Separation from Lubricating Grease During Storage
D1743 Test Method for Determining Corrosion Preventive Properties of Lubricating Greases
D1831 Test Method for Roll Stability of Lubricating Grease
D2265 Test Method for Dropping Point of Lubricating Grease Over Wide Temperature Range
D2266 Test Method for Wear Preventive Characteristics of Lubricating Grease (Four-Ball Method)
D2596 Test Method for Measurement of Extreme-Pressure Properties of Lubricating Grease (Four-Ball Method)
D3527 Test Method for Life Performance of Automotive Wheel Bearing Grease
D4048 Test Method for Detection of Copper Corrosion from Lubricating Grease
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4289 Test Method for Elastomer Compatibility of Lubricating Greases and Fluids
D4425 Test Method for Oil Separation from Lubricating Grease by Centrifuging (Koppers Method)
D4693 Test Method for Low-Temperature Torque of Grease-Lubricated Wheel Bearings
D5483 Test Method for Oxidation Induction Time of Lubricating Greases by Pressure Differential Scanning Calorimetry
E1131 Test Method for Compositional Analysis by Thermogravimetry
F2161 Guide for Instrument and Precision Bearing Lubricants--Part 1 Oils
F2488 Terminology for Rolling Element Bearings
Government DocumentsDoD-G-24508 Multipurpose Grease FederalStandardTestM Dirt Content of Grease MIL-G-21164 Molybdenum Disulfide Grease MIL-G-25537 Aircraft Helicopter Bearing Grease MIL-G-25760 Grease, Aircraft, Ball and Roller Bearing, Wide Temperature Range MIL-G-27617 Grease, Aircraft and Instrument, Fuel and Oxidizer Resistant MIL-L-15719 High Temperature Electrical Bearing Grease MIL-PRF-10924 Grease, Automotive and Artillery MIL-PRF-23827 Aircraft and instrument Grease MIL-PRF-81322 Aircraft Wide Temperature Range Grease MIL-PRF-83261 Aircraft Extreme Pressure
Industrial StandardsSKF Be-Quite Noise Test Method Available from SKF North American Technical Center, 46815 Port St., Plymouth, MI 48170. TA Rheometry Procedure for Steady Shear Flow Curve Available from TA Instruments Company, 109 Lukens Drive, New Castle, DE 19720-2765.
SAE StandardSAE-AMS-G-81937 Grease, Instrument, Ultra-Clean, Metric
ICS Number Code 75.100 (Lubricants, industrial oils and related products)
UNSPSC Code 15121900(Greases)