ASTM D6185 for evaluating compatibility of binary mixtures of lubricating greases
ASTM D6185 standard practice for evaluating compatibility of binary mixtures of lubricating greases
7. Procedure
7.1 Either of two similar testing options can be used - the sequential testing protocol described in Option 1 (A1.1), or the concurrent testing protocol described in Option 2 (A1.2). Using Option 1, a 50:50 mixture and the two constituent greases are tested using three primary tests. If this mixture is found compatible, 10:90 and 90:10 mixtures are tested. Using Option 2, all mixtures (10:90, 50:50, and 90:10) and the two constituent greases are tested concurrently.

7.1.1 With either option, the test procedures (that is, dropping point, shear stability, or storage stability tests) can be run concurrently or sequentially in any order. The test procedures are presented in the order of the time required to run an individual test.

7.2 Preparation of Mixtures - Regardless of whether one or three mixtures of differing ratios are to be tested sequentially or concurrently, they shall be prepared in similar fashion.

7.2.1 Prepare a fresh 50:50 mixture of the two greases to be evaluated for compatibility. (For convenience, the neat, constituent greases are called A and B.) The amounts to be mixed shall be determined from the amount of grease required by the tests. Prepare at least 10 % more mixture than is actually needed for the tests. Do not prepare more than can be used immediately, that is no more than about 4 h should elapse between mixture preparation and the start of any test.

7.2.2 Weigh equal amounts +/-1 % of each neat grease and transfer to a hard, flat, impervious surface such as a glass or stainless steel plate. About a 400 mm-square surface is convenient.

7.2.3 With a suitable spatula, fold and blend the two greases into each other until a uniform blend is produced.

NOTE 2 - Caution: Great care should be taken to minimize the occlusion of air.

NOTE 3 - Warning: Do not use any other mixing equipment to prepare grease mixtures.

7.2.4 When 10:90 and 90:10 mixtures are to be tested, prepare fresh mixtures of these proportions in the same fashion. The weighing tolerance shall be +/-1 % of each neat grease.

7.3 Option 1 (see A1.1) - Use the primary test protocol to test the Constituent Greases A and B and the 50:50 mixture. If resources permit, the dropping points, shear stability, and storage stability tests can be run concurrently. Otherwise, any sequence of these tests can be used.

7.3.1 Dropping Point - Determine and record the dropping points as described in Test Method D566 or D2265.

7.3.1.1 Compare dropping point of the mixture with those of constituent greases. If the dropping point of the mixture is equal to or greater than that of either constituent grease, record as compatible or pass. If the dropping point of the mixture is less than the lower of the constituent greases by an amount equal to or less than repeatability of the test method (see 9.1.1 for repeatability values), record as a borderline compatible or borderline pass. If the dropping point of the mixture is less than the lower of the constituent greases by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.1.2 If the mixture is incompatible (fail), no further testing need be done. If the mixture is compatible or borderline compatible (pass or borderline pass), further tests are required. If not yet run, test the mixture and the neat greases for shear stability (100 000-stroke worked penetration) or high temperature storage stability, or both (7.3.2 and 7.3.3, respectively).

7.3.2 Shear Stability - Determine the 10 000-stroke worked penetrations as described in Test Methods D217.

7.3.2.1 Compare the 10 000-stroke worked penetration of the mixture with those of constituent greases. If the penetration of the mixture is equal to or between those of the constituent greases, record as compatible or pass. If the penetration of the mixture is less than the lower of the constituent grease or greater than the higher of the constituent grease by an amount equal to or less than repeatability of the test method (see 9.1.2), record as a borderline compatible or borderline pass. If the penetration of the mixture is less than the lower of the constituent grease or greater than the higher of the constituent grease by an amount greater than repeatability of the test method (see 9.1.2), record as incompatible or fail.

7.3.2.2 If the mixture is incompatible (fail), no further testing need be done. If the mixture is compatible or borderline compatible (pass or borderline pass), further tests are required. If not yet run, test the mixture and the neat greases for dropping or high temperature storage stability, or both (7.3.1 and 7.3.3, respectively.

7.3.3 High-Temperature Storage Stability - The following variation of Federal Test Method (FTM) 3467.1 shall be followed. Determine the 60-stroke penetrations of the neat, constituent greases and the blends. Test Methods D217 is preferred, but 1/2-scale equipment (Test Method D1403) may be substituted. One-quarter-scale equipment is considered generally unsuitable. Record the test method (Test Methods D217 or Test Method D1403) used.

NOTE 4 - Variations from FTM-3467.1 include oven requirements, sample containers, allowance of 1/2-scale measurements, and specified storage conditions.

NOTE 5 - According to Test Method D1403, 1/2-scale measurements are converted to full-scale values; the appropriate repeatability is applied as described.

7.3.3.1 Place test samples in worker cups or suitably sized glass or steel containers; loosely cap or cover with aluminum foil. Place containers on the wire shelf located about midway to upper third of the laboratory oven preheated to 120 +/-3°C. Maintain 120 +/-3°C for 70 +/-1/4 h.

7.3.3.2 Greases having low dropping points (less than 125°C); for example, hydrated calcium greases, cannot be tested under these conditions. When testing compatibility of such greases, the storage stability test shall be run at 75 +/-3°C for 1400 +/-4 h.

7.3.3.3 Remove samples from the oven and allow to cool. Determine 60-stroke worked penetration in accordance with Test Methods D217 (or Test Method D1403). Calculate change in 60-stroke worked penetrations.

7.3.3.4 Compare the change in 60-stroke worked penetration of the mixture with the penetration changes of the constituent greases. If the penetration change of the mixture is equal to or between those of the constituent greases, record as compatible or pass. If the penetration change of the mixture is less than that of the lower of the constituent grease or greater than that of the higher of the constituent grease by an amount equal to or less than repeatability of the test method (9.1.2), record as a borderline compatible or borderline pass. If the penetration change of the mixture is less than that of the lower of the constituent grease or greater than that of the higher of the constituent grease by an amount greater than repeatability of the test method (9.1.2), record as incompatible or fail.

7.3.3.5 If the mixture is incompatible (fail), no further testing need be done. If the mixture is compatible or borderline compatible (pass or borderline pass), further tests are required. If not yet run, test the mixture and the neat greases for dropping point or shear stability, or both (7.3.1 and 7.3.2, respectively).

7.4 If all the primary tests show the 50:50 mixture to be compatible, prepare 10:90 and 90:10 mixtures in a fashion similar to that described in 7.3.1-7.3.3. The weighing tolerance shall be +/-1 % of each neat grease.

7.5 Run these mixtures in the primary tests (7.3.1-7.3.3.4).

7.6 If all of the mixtures pass all three primary tests, the greases shall be reported as compatible. If any mixture fails any primary test, the greases shall be reported as incompatible (or borderline compatible if such is the case; see 7.3.3.4).

7.7 For greases determined to be compatible in primary testing, the user, or by agreement, the user and supplier, should determine whether additional testing is required. Depending on the criticality of the specification requirements, selection should be made from the secondary compatibility tests listed in Appendix X2.

7.8 Option 2 (see A1.2) - Follow the flowchart for Option 2 (A1.2) using the procedures described for sequential testing (7.3-7.3.3.5).

7.8.1 If all of the mixtures pass all three primary tests and the selected secondary tests, the greases shall be reported as compatible. If any mixture passes all primary tests but fails one or more secondary tests, the greases shall be reported as generally compatible but incompatible in certain applications. The failed tests shall be reported as well as the applications suggested by these tests.