ASTM D6185 for evaluating compatibility of binary mixtures of lubricating greases
ASTM D6185 standard practice for evaluating compatibility of binary mixtures of lubricating greases
1. Scope
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 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.

2. Referenced Documents
2.1 ASTM Standards:
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 Water Washout Characteristics of Lubricating Greases
D1403 Test Method 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 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)
D2509 Test Method for Measurement of Load-Carrying Capacity of Lubricating Greases (Timken Method)
D2595 Test Method for Evaporation Loss of Lubricating Greases over WideTemperature 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 Grease
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4290 Test Method for Determining the Leakage Tendencies of Automotive Wheel Bearing Greases 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

2.2 Federal Standard:
Federal Test Method Standard 791C, Method 3467.1, Storage Stability of Lubricating Grease

3. Terminology
3.1 Definitions:
3.1.1 bleed (bleeding), n - of lubricating greases, the separation of a liquid lubricant from a lubricating grease for any cause.

3.1.2 lubricant, n - any material interposed between two surfaces that reduces the friction or wear between them.

3.1.3 lubricating grease, n - a semifluid to solid product of a dispersion of a thickener in a liquid lubricant.

3.1.3.1 Discussion - The dispersion of the thickener forms a two-phase system and immobilizes the liquid lubricant by surface tension and other physical forces. Other ingredients imparting special properties are often included.

3.1.4 spatulate, v - to mix or blend by spreading and folding with a flat thin, usually metal, tool.

3.1.5 syneresis, n - of lubricating greases, the separation of liquid lubricant from a lubricating grease due to shrinkage or rearrangement of the structure.

3.1.5.1 Discussion - Syneresis is a form of bleeding caused by physical or chemical changes of the thickness. Separation of free oil or the formation of cracks that occur in lubricating greases during storage in containers is most often due to syneresis.

3.1.6 thickener, n - in a lubricating grease, a substance composed of finely divided particles dispersed in a liquid lubricant to form the product's structure.

3.1.6.1 Discussion - The thickener can be fibers (such as various metallic soaps) or plates or spheres (such as certain non-stop thickeners) which are insoluble or, at most, only very slightly soluble in the liquid lubricant. The general requirements are that the solid particles be extremely small, uniformly dispersed, and capable of forming a relatively stable, gel-like structure with the liquid lubricant.

3.2 Definitions of Terms Specific to This Standard:
3.2.1 compatibility, n - of lubricating greases, the characteristic of lubricating greases to be mixed together without significant degradation of properties or performance.

3.2.1.1 Discussion - When a mixture of two greases has properties or performance significantly inferior to both of the neat, constituent greases, then the two greases are incompatible. If the properties are inferior to those of one neat grease but not inferior to those of the other, then such is not necessarily considered an indication of incompatibility. To be considered significantly inferior, the property of the mixture would be worse than the poorer of the two neat greases by an amount exceeding the repeatability of the test method used to evaluate the property (see pass and fail). Incompatibility most often is manifested by a degradation in physical properties rather than in chemical properties, although, occurrence of the latter is not unknown.

3.2.2 borderline compatibility, n - of lubricating greases, the characteristic of lubricating greases to be mixed together with only slight degradation of properties or performance.

3.2.2.1 Discussion - Slight degradation means that the properties or performance of the mixture is poorer than those of the two neat greases but by an amount less than the repeatability of the test method used to evaluate the property. (See borderline pass).

3.2.3 primary compatibility tests, n - of lubricating greases, those test methods employed first to evaluate compatibility

3.2.3.1 Discussion - The test methods considered the most significant in the evaluation of grease compatibility, insofar as they provide the most information with the least expenditure of testing resources, include tests for dropping point, consistency (usually softening) after shearing conditions, and consistency change after storage at elevated temperatures.

3.2.4 secondary compatibility tests, n - of lubricating greases, those test methods used to evaluate compatibility when the primary compatibility tests are insufficient or inconclusive.

3.2.4.1 Discussion - Such tests are driven by the critical features of a given application. For example, if the application subjects the grease to water contamination, water washout or water spray-off tests and, perhaps, corrosion tests would be used for additional evaluation. Secondary compatibility tests are suggested, but not required, by this practice.

3.2.5 pass, n - in compatibility testing of grease mixtures, a test result that is equal to or better than that of the poorer of the two constituent greases.

3.2.6 borderline pass, n - in compatibility testing of grease mixtures, a test result that is inferior to that of the poorer of the two constituent greases by an amount not exceeding the repeatability of the test method used for the evaluation.

3.2.6.1 Discussion - Borderline pass, borderline fail, borderline compatible, and borderline incompatible are synonymous terms.

3.2.7 fail, n - in compatibility testing of grease mixtures, a test result that is inferior to that of the poorer of the two constituent greases by an amount exceeding the repeatability of the test method used for the evaluation.

3.2.8 50:50 mixture, n - a uniform blend of 50 mass % of each of two component greases.

3.2.9 10:90 mixture, n - a uniform blend of 10 mass % of one grease with 90 mass % of a second grease.

3.2.10 90:10 mixture, n - a uniform blend of 90 mass % of one grease with 10 mass % of a second grease.