9. Procedure
9.1 Cut elastomer coupons from standard, 2-mm thick, vulcanized sheets (Practice D3182) or, optionally, from AMS 3217/2B or AMS 3217/3A sheets. Do not include any part of the thicker, identification portion of the sheet as part of the coupon. Trim off any edge flashing, if present. The coupon dimensions should be approximately 50 by 25 mm, 35 by 35 mm, or, preferably, die-cut, 40-mm diameter. Coupons cut to these dimensions will maintain a consistent, elastomer-to-sample volume ratio.
9.1.1 When using the cutting die for coupon preparation, back up the elastomer slab with a suitable surface, such as a plastic (preferred) or hardwood kitchen cutting board. Strike the die with a hammer or, preferably, use an arbor press to cut out the coupon. The die should not be turned in a drill press as this can cause heat distress on the cut edges of the coupon. From time to time, inspect the cutting edge of the die and resharpen as required.
9.1.2 With a leather punch or cork borer, punch or cut a 4 to 5-mm diameter hole near the edge (near the center of a short edge if a rectangular coupon is used). Corners or small radiused notches can be cut for identification; do not cut V-notches.
9.2 Stack three coupons having the same configuration to obtain the requisite, minimum 6-mm thickness (see Section 6 of Test Method D2240). Using the Durometer presser foot, apply sufficient force to ensure intimate contact between the stacked coupons and that the stack remains flat after removal of the force. Determine the initial, Shore Durometer A hardness, Hi of the elastomer coupon in accordance with Test Method D2240.
9.3 The reagent water must be freshly boiled to prepare it for hydrostatic weighings. Pour a sufficient amount of reagent water into a clean, heat-resistant, glass beaker (600 mL or larger) and boil vigorously for approximately 5 min; cover the beaker with a clean watchglass, and cool to 20 to 25°C.
9.4 Weigh the hanger wire both in air and partially submerged (10 to 15 mm) in the prepared reagent water. The entire hook portion of the hanger wire is to be completely submerged. Record the immersion depth, as well as both mass determinations, for later reference. For these and all subsequent weighings, the mass determinations are to be to the nearest milligram, at least.
NOTE 8 - Marking the water level on the outside of the beaker can be beneficial in attaining the same immersion depth for the determination of M2 and M4 (see 9.6.5 and 9.21, respectively).
9.5 Wipe the coupon with n-heptane-wetted cheesecloth to remove any mold-release compound that may be present on the surface. Gently blow dry with nitrogen or clean, dry, pressurized air. Alternatively, blot dry with cheesecloth or filter paper. Remove any adhering cloth or paper fibers.
9.6 After the n-heptane has evaporated completely, determine the volume and relative density, RD, of the specimen by water displacement.
9.6.1 If the elastomer specification has a requirement for density or relative density but does not specify the test method for its determination, use the Hydrostatic Method described in Test Method D297. If the specification has neither a density nor a relative density requirement, determine relative density in accordance with 9.6.2 through 9.6.7.
9.6.2 Weigh the coupon in air to determine M1. The hanger wire may be included in the weighing; if it is used, subtract its mass in air from the combined mass to determine M1.
9.6.3 Using the hanger wire, dip the coupon successively in beakers of wetting agent solution and reagent water. Drain momentarily after each dipping by touching the lower edge of the coupon against the rim of the beaker.
9.6.4 Suspend the hanger wire and coupon from the balance hook so that the hanger is submerged in prepared reagent water to the same depth as in 9.4. Inspect the submerged coupon, and remove any adhering air bubbles. If the bubbles are difficult to remove, repeat 9.6.3. In uncommon instances, it may be necessary to devise a means of mechanically dislodging adherent air bubbles.
9.6.5 Weigh the combined mass of the submerged hanger and coupon, and calculate M2 by subtracting the mass of the hanger wire partially submerged in water to the same depth described in 9.4.
9.6.6 Dip the coupon in methanol and blot it dry with filter paper.
9.6.7 Calculate the relative density, RD, in accordance with 10.2. Discard the coupon if it does not meet the density or relative density requirements of the elastomer specification or as described in 9.7 or 9.8.
9.7 If the density or relative density is not specified, conduct replicate tests or tests with multiple lubricant samples only with coupons that are within 0.010 of the mean relative density to ensure satisfactory precision. Coupons outside these limits should be discarded.
NOTE 9 - Although Test Method D 4289 provides no information regarding the precision of density or relative density measurements, operators are frequently concerned about the repeatability of their own determinations. Typically, good laboratory skills by an operator will be confirmed by a coefficient of variation (CV) of less than 0.05 % for a series of values obtained with one batch of elastomer. If the CV is significantly greater than 0.1 %, the operator should improve his technique.
9.8 When using SAE Reference Elastomers AMS 3217/2B or AMS 3217/3A (NBR-L or CR, respectively), the coupons must conform to the density (Test Method D297) and other requirements given in Table A1.1. Discard any reference elastomer coupons that do not meet the requirements shown in Table A1.1.
9.9 Lubricant samples should be homogeneous. Thoroughly mix fluid samples having potential for additive separation. Stir grease samples if separated oil is present.
9.10 If only grease samples are to be tested, skip to 9.12 to continue.
9.11 For Fluid Samples - Fill the beaker with the test fluid to the 80-mL mark. Place one coupon on a coupon suspension wire and insert into beaker making sure coupon is completely immersed.
9.11.1 If only fluid samples are to be tested, skip to 9.13 to continue.
9.12 For Grease Samples - When the physical properties of the grease will allow insertion of the coupon without occluding air, fill the beaker with test grease to the 80-mL mark, then insert the coupon in an upright position. Fill in all voids that may have been created while packing the test grease and coupon into the beaker.
9.12.1 Alternatively, distribute about 20 mL of the test grease in the bottom of the beaker, apply a thick coating (4 mm, min) of test grease on the elastomer coupon, and place the coupon upright in the beaker. Pack the test grease around the coupon, eliminating all air pockets to ensure intimate contact with the test coupon. Fill the beaker to the 80-mL mark with the test grease.
9.12.2 While packing grease into the beaker, great care must be taken to ensure that the coupon and test grease are in intimate contact; fill in all voids and minimize occlusion of air.
9.13 For All Samples - Although compatibility tests are frequently run in duplicate, do not place more than one coupon into a beaker of test sample in order to maintain a consistent elastomer-to-sample volume ratio.
9.14 Regardless of the filling technique or nature of the lubricant, the coupon shall be totally immersed in the test sample and shall not contact the beaker surfaces during the test.
9.15 Cover the beaker with an inverted aluminum beaker cover and press in the sides of the cover to closely conform to the beaker.
9.16 Place the beaker(s) in a suitable metal instrument tray; place in the center of a wire shelf located in the upper third of the oven preheated to the test temperature more or less 2.5°C (see 4.1).
9.16.1 Maintain the test temperature more or less 2.5°C for 70 more or less 0.5 h or as specified by the lubricant specification.
9.16.2 Some lubricant specifications may require immersion times other than 70 h. For times <70 h, the time tolerance shall be more or less 0.25 h, and for times >70 h, the tolerance shall be more or less 0.5 h.
9.17 After the immersion period, remove the beaker from the oven. Remove (and later discard) the beaker cover. Remove the coupon with forceps, place it in the beaker cover to cool to room temperature.
NOTE 10 - Certain combinations of sample and elastomer can form malodorous reaction compounds in this test method. Although unpleasant, such compounds are not believed to be hazardous. Nonetheless, it is recommended that the uncovering of beakers and the removal and cleaning of coupons be conducted in a fume hood.
9.18 Remove the bulk of the sample adhering to the coupon with the dull, side edge of a spatula. Wipe the coupon with dry cheesecloth followed by cleaning the coupon of residual sample with cheesecloth liberally wetted with n-heptane; pay particular attention to removing sample from the hanger hole, edges, and any notches. Blow dry the coupon with nitrogen or clean, dry, compressed (unheated) air, or blot it dry with filter paper.
9.19 Measure the final hardness, Hf, in the manner described in 9.2, and calculate the hardness change, DH, as described in 10.1.
9.20 If elastomer coupons were run in duplicate tests, the two coupons should be stacked on a third, but untested, coupon of like geometry in order to obtain the required thickness for Durometer measurements (see 9.2). If only one coupon was tested, it should be stacked on two untested coupons.
9.21 Determine M3 and M4 by weighing the coupon in air and in freshly prepared reagent water (9.3) at the same immersion depth noted in 9.4 and in the same manner used to determine M1 and M2 (9.6.2 through 9.6.7).
9.22 Calculate the volume change, DV, as described in 10.3.
10. Calculations
10.1 Calculate the hardness change as follows:
NOTE 11 - A negative DH value indicates that the coupon softened during the test; conversely, a positive value indicates that it hardened.
10.2 Calculate the relative density as follows:
10.3 Calculate the volume change as follows:
