ASTM D4289 for elastomer compatibility of lubricating greases and fluids
4. Summary of Test Method
4.1 A prepared elastomer coupon is measured for initial hardness (Durometer A), density or relative density (to ensure that the coupon is within specified limits), and volume by water displacement. The coupon is immersed in test grease or fluid and aged for 70 h at either 100°C (for chloroprene and similar flex-resistant elastomers) or 150°C (for nitrile and similar heat-resistant elastomers) or at other conditions as required by the lubricant specification. The resulting changes in hardness and volume are determined.
5. Significance and Use
5.1 Measurement of the changes in the volume and hardness of an elastomer that occur from immersion in a lubricating grease or fluid provides a means for evaluating relative compatibility. Much of this test method was derived from procedures described in Test Method D471 and Federal Test Method 791C/3603.5. In contrast to these two test methods, which emphasize the evaluation of rubber and rubber-like compounds, Test Method D4289 was developed specifically to evaluate lubricating greases and fluids, especially those used in automotive applications, although the test method can be applied to lubricants used in industrial applications as well. Excepting the Shore Durometer A, this test method requires no specialized, rubber-testing equipment. Virtually all other equipment and supplies specified in the procedure are stock items in lubricants laboratories.
5.2 The volume and hardness-change values determined by this test method do not duplicate similar changes that occur in elastomeric seals under actual service conditions. However, they can be correlated in many instances. In one such instance, the volume-change values determined by the antecedent of this test method correlated (r(2) = 0.99) with those that occurred during a vehicle test. Because of wide variations in service conditions and differences in grease and elastomer formulations, correlations between the results obtained with this test method and particular applications should be determined on an individual basis.
5.3 When the optional Reference Elastomers AMS 3217/2B (acrylonitrile-butadiene, NBR-L) and AMS 3217/3A (chloroprene, CR) are used to evaluate compatibility, the results can be used to judge a service characteristic of lubricants. In this respect, this test method is useful for lubricant specifications (for example, Specification D4950). Similarly, this test method can be used in specifications for lubricating fluids as well.
5.4 With specifications requiring elastomers other than Reference Elastomers AMS 3217/2B or AMS 3217/3A, coupons cut from standard sheets (Practice D3182) should be used. When the preparation of such coupons is not feasible, or the lubricant specification requires the use of rubber products that do not have a suitable size or configuration for use in preparing coupons for testing (Practice D3183), this test method can be used as a guide for evaluating compatibility.
NOTE 4 - Inasmuch as the precision values apply only to the elastomers specified in Annex A1 of Test Method D4289, when a lubricant specification requires some other elastomer, the user and supplier of the lubricant should agree to the values of acceptable precision. Such values may or may not be the same as those of Test Method D4289. It is recommended that the agreed upon precision values be stated in the user's lubricant specification.
5.5 The results of this test method are most applicable to the use of lubricating greases and fluids in contact with elastomeric seals, boots, O-rings, and similar products, where the physical demands on the elastomer are not extreme. In critical applications where the lubricant will be in contact with rubber parts subject to severe flexing, extreme temperatures, or similar stresses, other rubber properties, such as tensile strength and elongation, should also be evaluated as they may be more indicative of the true compatibility characteristics.
6. Interferences
6.1 (Warning - Although greases and elastomers typically have long shelf lives, there is potential for change in time. Therefore, in order to ensure acceptable precision in this test method, neither test greases nor test elastomers should be more than approximately one year old.)
6.1.1 Before testing with reference elastomers stored for extended periods (approaching one year or more) or in an adverse environment (high ambient temperatures, solvent vapors, and so forth), the elastomers should be checked for conformance with the requirements in Table A1.1.
NOTE 5 - Experience has shown that storage conditions can affect the shelf life of the reference elastomers. Shelf life can be extended by storing elastomers in the dark in an inert atmosphere (such as a glass or metal, but not plastic, container, for example, vacuum desiccator, in which the air has been replaced by nonreactive gas (such as argon or nitrogen) at refrigerator temperatures. Elastomers should not be stored at temperatures lower than 5°C because of crystallinity and solubility changes that can affect test performance. Neither should they be stored at reduced pressures or in permeable containers or wrappers which could allow them to be affected by the normal atmosphere.
