ASTM D2782 Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Timken Method)
9. Procedure
9.1 Fill the reservoir of the tester to within 76 mm (3 in.) of the top (approximately 3 L or 3 qt) with the fluid to be tested. Preheat the fluid to 37.8 +/- 2.8°C (100 +/- 5°F).
NOTE 6 - The fluid may be heated by the use of an immersion heater located in the tester reservoir or by heating the fluid prior to filling the reservoir. If an immersion heater is used, localized overheating must be avoided. This may be done by stirring or by circulating prior to the assembly of the lever arm.
NOTE 7 - Fluids having a viscosity above about 5000 cSt (5000 mm2/s) at 40°C often cannot be tested at the prescribed fluid temperature of 37.8 +/- 2.8°C (100 +/- 5°F) because of inability of the pump to recirculate the fluid at this temperature. However, results from limited cooperative tests, covered in Tables A1.1 and A1.2, indicate that the starting fluid temperature could be increased to 65.6°C (150°F) to obtain adequate flow without affecting OK or score values. Testing of such high-viscosity fluids at room temperature in the Test Method D2509 grease feeder also appears valid but may be difficult because of fluid leakage.
9.2 Set the discharge valve at full open. Allow the lubricant to flood the test cup and block. When the sump is about half filled with the fluid, start the motor and run for 30 s to break-in. If the equipment used is equipped with acceleration control, start the motor and increase the spindle speed gradually to achieve 800 +/- 5 rpm after 15 s. Run for a further 15 s to complete the break-in.
9.3 After a break-in period of 30 s, start the timer and apply at 8.9 to 13.3 N/s (2 to 3 lbf/s), a load that is less than the expected score load. In the absence of a better estimate, a starting load of 30 lbf is recommended. The load-lever arm, spring-weight platform assembly is not considered a part of the applied load. In the event a lower starting load is used, it must be a multiple of 6. Then allow the machine to run at 800 +/- 5 rpm for 10 min +/- 15 s after load application is initiated, unless a score is detected before that period.
9.4 If, after the load has been applied, scoring is evident by vibration or noise, stop the tester at once, turn off the flow of lubricant, and remove the load. Since the excessive heat developed with deep scoring may alter the surface characteristics of the entire block, discard the test block.
NOTE 8 - Precaution: The machine and test pieces may be hot at this point and care should be exercised in their handling.
9.5 If no scoring is detected, allow the tester to run for 10 min +/- 15 s from the start of the application of the load. At the end of the 10-min +/- 15-s period, reverse the loading device and remove the load from the lever arm. Turn off the motor, allow the spindle to come to rest, then turn off the flow of fluid. Remove the load lever and inspect the condition of the test block surface at 1x magnification. Microscopical observations shall not be used to define when scoring has occurred. The lubricant has failed at the imposed load if the wear scar indicates any scoring or welding.
NOTE 9 - A microscope may be used to examine the wear scar for further information as required in 10.2
9.6 If no score is observed, turn the test block to expose a new surface of contact and, with a new test cup, repeat the test, as in 9.5, at 10-lbf increments until a load that produces a score is reached. At this point decrease the load by 5 lbf for the final determination.
NOTE 10 - Before each test in 9.6-9.8 cool the fluid in the reservoir to 37.8 +/- 2.8°C (100 +/- 5°F), cool the shaft to less than 65.6°C (150°F), install a new test cup, and turn the test block to expose a new surface of contact. When seizure has occurred, discard the entire test block since excessive heat, developed when scarring occurs, may alter the surface characteristics of the entire block.
9.7 If a score is produced at the 30-lbf load, reduce the load by 6-lbf decrements until no scoring is realized. At this point, increase the load by 3 lbf for the final determination.
9.8 When the wear scar evidence at any load stage makes the definition of the onset of scoring questionable, repeat the test at the same load. If the second test produces a score, record a score rating for this load. Similarly, if the second test produces no scoring, record a no score rating. If the second test again yields a questionable result, simply withhold judgment of the rating at this load stage and test the fluid at the immediately next higher load stage (see Annex A2). Then assign a rating to the load stage in question that is identical to the rating obtained at the immediately next higher load stage employed.
10. Calculation
10.1 When desired, the contact (unit) pressure that exists between the cup and block at the conclusion of the test can be calculated. After the OK value has been determined, remove the test block and wash with Stoddard solvent or White Spirit, rinse with acetone (Warning - See Note 2 and Note 3.), and blow dry. By means of a filar micrometer microscope, measure the width of the scars on those blocks which successfully carried this load. Make all measurements to 0.05 mm (0.002 in.). Calculate the contact pressure, C, as follows:
C, psi = [L(X + G)]/YZ or [20(X + G)]/Z
C, MPa = 9.81[L(X' + 0.454G)]/Y'Z'
where:
L = mechanical advantage of load-lever arm, 10,
G = load-lever constant (value is stamped on lever arm of each tester),
X = mass (weight) placed on the weight pan, lb,
X' = mass (weight) placed on the weight pan, kg,
Y = length of test scar ( 1/2 in.),
Y' = length of test scar (12.7 mm),
Z = average width of test scar, in., and
Z' = average width of test scar, mm.
10.2 For convenience, contact (unit) pressures in pounds per square inch are listed in Table X3.1.
