ASTM D4289 for elastomer compatibility of lubricating greases and fluids
1. Scope
1.1 This test method evaluates the compatibility of lubricating greases and fluids with coupons cut from standard elastomer sheets (Practice D3182) or, optionally, from SAE Specification AMS 3217/2B (NBR-L) and AMS 3217/3A (CR) sheets. Compatibility is evaluated by determining the changes in volume and Durometer A hardness that occur when elastomer coupons are totally immersed in a lubricant sample for 70 h at either 100 or 150°C or as required by the lubricant specification.

1.1.1 Some lubricant specifications may require different test conditions, such as longer durations or lower or higher temperatures. In such instances, the repeatability and reproducibility values stated in Section 12 do not apply, and the user and supplier should agree on acceptable limits of precision.

NOTE 1 - The scope of this test method now includes the evaluation of the elastomer compatibility of both lubricating fluids and greases. Testing of fluids was not included in Test Method D4289–95 and earlier versions.

1.2 This test method can also be used as a guide to evaluate the compatibility of greases with rubber products not in standard sheet form (Practice D3183).

1.3 The values stated in SI and Durometer A units shall be regarded as the standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 8.4-8.6.

2. Referenced Documents
2.1 ASTM Standards:
D217 Test Methods for Cone Penetration of Lubricating Grease
D297 Test Methods for Rubber Products - Chemical Analysis
D412 Test Methods for Vulcanized Rubber and Thermo-plastic Elastomers - Tension
D471 Test Method for Rubber Property - Effect of Liquids
D1193 Specification for Reagent Water
D2240 Test Method for Rubber Property - Durometer Hardness
D3182 Practice for Rubber - Materials, Equipment, and Procedures for Mixing Standard Compounds and Preparing Standard Vulcanized Sheets
D3183 Practice for Rubber - Preparation of Pieces for Test Purposes from Products
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4950 Classification of and Specification for Automotive Service Greases

2.2 Federal Standard:
Federal Test Method Standard 791C, Method 3603.5, Swelling of Synthetic Rubbers

2.3 U.S. Air Force Specification:
539 Specification Bulletin for Standard Elastomer Stocks

2.4 SAE Standards:
AMS 3217A Standard Elastomer Stocks - Test Slabs
AMS 3217/2B Test Slabs, Acrylonitrile Butadiene (NBR-L) - Low Acrylonitrile, 65 - 75
AMS 3217/3A Test Slabs, Chloroprene (CR) - 65 - 75

NOTE 2 - USAF Specification Bulletin 539 was specified in Test Method D4289-94 and earlier versions. This specification is obsolete and has been replaced by SAE Standard AMS 3217A. USAF-539 NBR-L has been replaced by SAE AMS 3217/2B (NBR-L), which is virtually identical. USAF-539 CR has been replaced by the similar, but not identical, SAE AMS 3217/3A (CR). Elastomer sheets prepared to this latter specification are not known or expected to provide test results identical with those of the USAF Specification 539 counterpart.

NOTE 3 - With respect to elastomer AMS 3217/2A, the elastomer specification has been superseded by AMS 3217/2B. Per SAE, the elastomers are identical, however, the synthetic lubricant immersion fluid used to reference the elastomer has been exchanged from ARM-200 to AMS 3021. Reference fluid AMS 3021 better represents current market aviation fluids.

3. Terminology
3.1 Definitions:
3.1.1 elastomer, n - a natural or synthetic polymer having the rubber-like property of substantially recovering its size and shape after removal of a deforming force.

3.1.2 hardness, n - of an elastomer, the resistance to deformation or indentation.

3.1.2.1 Discussion - In this test method the hardness of an elastomer is measured with a Shore Durometer A (see Test Method D2240).

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

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

3.1.4.1 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.

3.1.5 relative density, n - the ratio of the density of a material at temperature, t1, to the density of water at a reference temperature, t2.

3.1.5.1 Discussion - In this test method relative density is determined with the temperature of the elastomer and water being equal and within the range from 20 to 25°C, and the temperature correction for the density of water is not applied. The term, relative density, replaces the synonymous, deprecated term, specific gravity, used in some earlier editions of this test method.

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-soap 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 coupon, n - a test piece of specified dimensions cut from standard elastomer sheets.

3.3 Symbols:
3.3.1 Symbols used in the calculation of hardness change (see Eq 1 in 10.1):
DH = hardness change, Durometer A units,
Hi = initial hardness, Durometer A units,
Hf = final hardness, Durometer A units.

3.3.2 Symbols used in the calculation of relative density (see Eq 2 in 10.2) and volume change (see Eq 3 in 10.3):
RD = relative density,
DV = volume change, %,
M1 = initial mass of coupon in air, g,
M2 = initial mass of coupon and hanger wire in water less mass of hanger wire partially submerged in water, g,
M3 = final mass of coupon in air, g,
M4 = final mass of coupon and hanger wire in water less mass of hanger wire partially submerged in water, g.