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Significance and Use
The compatibility of greases can be important for users of grease-lubricated equipment. It is well known that the mixing of two greases can produce a substance markedly inferior to either of its constituent materials. One or more of the following can occur. A mixture of incompatible greases most often softens, sometimes excessively. Occasionally, it can harden. In extreme cases, the thickener and liquid lubricant will completely separate. Bleeding can be so severe that the mixed grease will run out of an operating bearing. Excessive syneresis can occur, forming pools of liquid lubricant separated from the grease. Dropping points can be reduced to the extent that grease or separated oil runs out of bearings at elevated operating temperatures. Such events can lead to catastrophic lubrication failures.
Because of such occurrences, equipment manufacturers recommend completely cleaning the grease from equipment before installing a different grease. Service recommendations for grease-lubricated equipment frequently specify the caveat–do not mix greases under any circumstances. Despite this admonition, grease mixing will occur and, at times, cannot be avoided. In such instances, it would be useful to know whether the mixing of two greases could lead to inadequate lubrication with disastrous consequences. Equipment users most often do not have the resources to evaluate grease compatibility and must rely on their suppliers. Mixing of greases is a highly imprudent practice. Grease and equipment manufacturers alike recognize such practices will occur despite all warnings to the contrary. Thus, both users and suppliers have a need to know the compatibility characteristics of the greases in question.
There are two approaches to evaluating the compatibility of grease mixtures. One is to determine whether such mixtures meet the same specification requirements as the constituent components. This approach is not addressed by this practice. Instead, this practice takes a specification-independent approach; it describes the evaluation of compatibility on a relative basis using specific test methods.
Three test methods are used because fewer are not sufficiently definitive. For example, in one study, using 100 000-stroke worked penetration for evaluation, 62 % of the mixtures were judged to be compatible. In a high-temperature storage stability study, covering a broader spectrum of grease types, only one-third of the mixtures were compatible. These studies used different criteria to judge compatibility.
Compatibility cannot be predicted with certainty from foreknowledge of grease composition. Generally, greases having the same or similar thickener types will be compatible. Uncommonly, even greases of the same type, although normally compatible when mixed, can be incompatible because of incompatible additive treatments. Thus, compatibility needs to be judged on a case-by-case basis.
Two constituent greases are blended in specific ratios. A 50:50 mixture simulates a ratio that might be experienced when one grease (Grease A) is installed in a bearing containing a previously installed, different grease (Grease B), and no attempt is made to flush out Grease B with Grease A. The 10:90 and 90:10 ratios are intended to simulate ratios that might occur when attempts are made to flush out Grease B with Grease A.
Note 1—Some companies evaluate 25:75 and 75:25 ratio mixtures instead of 10:90 and 90:10 ratio mixtures. But, the latter two ratios, which are prescribed by this practice, are considered more representative of the flushing practice described in 5.3.
Incompatibility is most often revealed by the evaluation of 50:50 mixtures. However, in some instances 50:50 mixtures are compatible and more dilute ratios are incompatible. (See Appendix X1 and Meade. )
Compatibility information can be used in product information literature supplied with specific greases. It can be used also in literature describing lubrication practices and equipment maintenance.
1.1 This practice covers a protocol for evaluating the compatibility of one or three binary mixtures of lubricating greases by comparing their properties or performance relative to those of the neat greases comprising the mixture.
1.2 Three properties are evaluated in a primary testing protocol using standard test methods: (1) dropping point by Test Method D566 (or Test Method D2265); (2) shear stability by Test Methods D217, 100 000–stroke worked penetration; and (3) storage stability at elevated-temperature by change in 60-stroke penetration (Test Method D217). For compatible mixtures (those passing all primary testing), a secondary (nonmandatory) testing scheme is suggested when circumstances indicate the need for additional testing.
1.3 Sequential or concurrent testing is continued until the first failure. If any mixture fails any of the primary tests, the greases are incompatible. If all mixtures pass the three primary tests, the greases are considered compatible.
1.4 This practice applies only to lubricating greases having characteristics suitable for evaluation by the suggested test methods. If the scope of a specific test method limits testing to those greases within a specified range of properties, greases outside that range cannot be tested for compatibility by that test method. An exception to this would be when the tested property of the neat, constituent greases is within the specified range, but the tested property of a mixture is outside the range because of incompatibility.
1.5 This practice does not purport to cover all test methods that could be employed.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and practices and determine the applicability of regulatory limitations prior to use. For specific safety information, see 7.2.3.
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
D566 Test Method for Dropping Point of Lubricating Grease
D972 Test Method for Evaporation Loss of Lubricating Greases and Oils
D1092 Test Method for Measuring Apparent Viscosity of Lubricating Greases
D1263 Test Method for Leakage Tendencies of Automotive Wheel Bearing Greases
D1264 Test Method for Determining the Water Washout Characteristics of Lubricating Greases
D1403 Test Methods for Cone Penetration of Lubricating Grease Using One-Quarter and One-Half Scale Cone Equipment
D1478 Test Method for Low-Temperature Torque of Ball Bearing Grease
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)
D2509 Test Method for Measurement of Load-Carrying Capacity of Lubricating Grease (Timken Method)
D2595 Test Method for Evaporation Loss of Lubricating Greases Over Wide-Temperature Range
D2596 Test Method for Measurement of Extreme-Pressure Properties of Lubricating Grease (Four-Ball Method)
D3336 Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures
D3337 Test Method for Determining Life and Torque of Lubricating Greases in Small Ball Bearings
D3527 Test Method for Life Performance of Automotive Wheel Bearing Grease
D4049 Test Method for Determining the Resistance of Lubricating Grease to Water Spray
D4170 Test Method for Fretting Wear Protection by Lubricating Greases
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4290 Test Method for Determining the Leakage Tendencies of Automotive Wheel Bearing Grease Under Accelerated Conditions
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
D4950 Classification and Specification for Automotive Service Greases
D5706 Test Method for Determining Extreme Pressure Properties of Lubricating Greases Using a High-Frequency, Linear-Oscillation (SRV) Test Machine
D5707 Test Method for Measuring Friction and Wear Properties of Lubricating Grease Using a High-Frequency, Linear-Oscillation (SRV) Test Machine
Federal StandardFederalTestMethod346 (Standard 791C), Storage Stability of Lubricating Grease Available from Standardization Documents Order Desk, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
ICS Number Code 75.100 (Lubricants, industrial oils and related products)
UNSPSC Code 15121902(Grease)
ASTM D6185-11, Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases, ASTM International, West Conshohocken, PA, 2011, www.astm.orgBack to Top