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 Method8201;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 28201;=8201;0.99) with those that occurred during a vehicle test.7 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 3217/2C (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 3217/2C 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.
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.