Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/875060
8 | September - October 2017 | www.machinerylubrication.com COVER STORY The test results for the blended fluids in the study (shown on page 7) indicate that the lubricants passed the foam criteria for compatibility at this concentration. Membrane Patch Test The formation of solids is a serious problem with lubricant compatibility. This is typically an additive issue in which one additive has poor solubility in the other lubricant's base stock, or the additives in one lubricant react with the additives in the other lubricant. If severe, this can be observed in visual testing. However, the concentrations are often too low for observation. ASTM D7843, commonly referred to as the membrane patch colorimetry (MPC) test, can be used to observe solid formation. Results are reported as a dE value based on the CIE Lab scale. The MPC results for most new lubricants are in the 2-5 dE range. The test results for the blended fluids in the study (shown below) indicate that the lubricants passed the liquid-solid criteria for compatibility at this concentration. Demulsibility Demulsibility is the lubricant's ability to separate from water. It is measured using ASTM D1401. This test blends 40 milliliters of water and oil, reporting the amount of oil, water and emulsion af ter a predetermined amount of time. According to ASTM D4304, a lubricant should have less than 3 milliliters of stable emulsion. The results for the blended fluids in the study are shown below and reveal that these lubricants failed the test. Rust When water limits are exceeded, most condition monitoring programs aler t users about the lubricant's condition due to potential rust issues. Since the studied lubricants were R&O fluids, passing a rust test was a primary concern. ASTM D4378 defines water as critical at 200 milligrams per gram (mg /g) of lubricant. The synthetic PAG lubricant failed this test. Even when blended, the lubricant's water levels still did not meet the recommended amount. The initial study evaluated the new lubricants (PAG, mineral oil 1 and mineral oil 2) and determined that they passed the rust criteria. The next step was to perform the tests with aged lubricants. For this, the lubricant was run to 75 percent to the end of a rotating pressure vessel oxidation test (RPVOT). This is based on ASTM D4378, which explains that a fluid is at its end of life when the RPVOT reaches 25 percent of the new fluid (75 percent to the end of the RPVOT). RPVOT adds excess water to the lubricant as part of the test, so water is already present to cause potential issues. The rust test (ASTM D665A) for the new and oxidation-tested lubricants showed passing results. The rust inhibitor in all three fluids was found to be sufficient to protect equipment even at high water levels. BLENDED LUBRICANTS dE VALUE 90% PAG/10% Mineral Oil 1 4.3 90% PAG/10% Mineral Oil 2 4.5 BLENDED LUBRICANTS AMOUNT OF WATER 90% PAG/10% Mineral Oil 1 3,900 mg/g 90% PAG/10% Mineral Oil 2 4,400 mg/g BLENDED LUBRICANTS OIL WATER EMULSION (TIME IN MINUTES) 90% PAG/10% Mineral Oil 1 1 mL 0 mL 79 mL (30) 90% PAG/10% Mineral Oil 2 2 mL 1 mL 77 mL (30) 5% Mineral Oil 2/95% PAG 1 mL 0 mL 79 mL (30) 95% Mineral Oil 2/5% PAG 0 mL 32 mL 48 mL (30) TESTING SERIES PAG MINERAL OIL 1 MINERAL OIL 2 Weight Change of Copper Panel (mg/cm 2 ) -0.367 -0.008 0.017 Appearance of Copper Panel Shiny IB Shiny IB Shiny IB Original Viscosity at 40°C (cSt) 24.70 33.35 31.36 40°C Viscosity After (cSt) 26.17 33.31 31.36 % Change in Viscosity (D445 at 40°C) 5.95% -0.12% 0.00% Original Acid Number (D974) (mg KOH/g) 0.06 0.08 0.03 Acid Number After (D974) (mg KOH/g) 2.44 0.05 0.13 Change in Acid Number (D974) (mg KOH/g) 2.38 -0.03 0.10 Total Acidity of Water Layer (mg KOH) 6.93 2.85 0.95 Percent Insolubles 0.004% 0.000% 0.012% End of Test Fluid ICP – Copper (ppm) 5 Nil Nil MPC test results Demulsibility test results Rust test results Hydrolytic stability results for the tested lubricants New Oils PAG 75% to EOT 2272 Mineral Oil 1 75% to EOT 2272 Mineral Oil 2 75% to EOT 2272 The results of the rust test include a visual rating of steel pins as shown above.