Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/875060
12 | September - October 2017 | www.machinerylubrication.com It should be noted that the RPVOT life of the new mineral oil lubricants was more than 1,000 minutes, while the PAG lubricant was measured at 657 minutes. When the test for the PAG lubricant was extended to 1,000 minutes, the MPC for the fluid was measured to be 72.3 dE, which was still in the same range of the previous results. However, the viscosity was very high, making the MPC measurement difficult. In this case, the viscosity would be the most important value, as opposed to varnish. Acid Number Acid number, as defined by ASTM D974, has often been described as the criteria for a lubricant's end of life. For years, this was the condemnation standard for mineral oils. ASTM D4378 recommends a warning level of 0.3-0.4 milligrams of potassium hydroxide (KOH) per gram increase over the new oil's acid number. PAG lubricants have a suggested limit of 5 mg KOH/g. At 75 to 100 percent of the end of the RPVOT test, all three lubricants had an acid number in the range suggested by ASTM D4378 as the end of the fluid's life. The high acid number in these results might also explain the rust observed in the ASTM D665 test for the PAG lubricant. Elemental Analysis Elemental analysis is a test that isn't generally studied in relation to RPVOT. RPVOT uses a copper metal catalyst coil in the fluid. If the copper dissolves into the lubricant, it acts as an oxidation catalyst and could accelerate the test. If copper corrosion poses a potential problem at the end of the ASTM D2272 test, it should be seen in the elemental analysis as an increase in copper. The copper sensitivity found in the hydrolytic stability test for the PAG lubri- cant was again detected in this test. It was observed at a higher level due to the higher oxidation of the lubricants. This offers some distinguishing parameters for comparing the lubricants. RULER Oxidation is often studied in relation to the quantity of antioxidant remaining in the lubricant. This parameter is measured using the Remaining Useful Life Evaluation Routine (RULER) test (ASTM D6971). ASTM D4378 suggests a warning limit of less than 25 percent of the new lubricant's antioxidant level. Based on the test results shown in the table bellow, it was recommended to change Acid number test results Copper test results LUBRICANT ACID NUMBER PAG: New Oil 0.03 PAG: 75% RPVOT 2.36 PAG: RPVOT EOT 21.73 Mineral Oil 1: New Oil 0.01 Mineral Oil 1: 75% RPVOT 0.25 Mineral Oil 1: RPVOT EOT 4.26 Mineral Oil 2: New Oil 0.01 Mineral Oil 2: 75% RPVOT 0.47 Mineral Oil 2: RPVOT EOT 5.31 LUBRICANT COPPER (PPM) PAG: New Lubricant Nil PAG: 75% RPVOT 66 PAG: 100-minute RPVOT 793 Mineral Oil 1: New Lubricant Nil Mineral Oil 1: 75% RPVOT 11 Mineral Oil 2: New Lubricant Nil Mineral Oil 2: 75% RPVOT 5 Mineral Oil 3: New Lubricant Nil Mineral Oil 3: 75% RPVOT 24 RULER test results Questions to Ask When determining whether a lubricant has reached the end of its service life, several questions must be asked: Answers to these questions will be valuable in your decision-making process. • What should you do about lubricant replacement? • Do you put the same lubricant back in again? • W hat if the lubricant has been changed and no longer exists? • Do you rely on the new lubricant's promotional materials? • Do you rely on the experiences of your colleagues? • Should you obtain your own performance testing data? COVER STORY SAMPLE PEAK AREA % CHANGE FROM NEW SAMPLE PEAK AREA % CHANGE FROM NEW SAMPLE PEAK AREA % CHANGE FROM NEW ANTIOXIDANT CHEMISTRY PAG Mineral Oil 1 Mineral Oil 3 New Lubricant 46218.5 16617.5 (RUL1) Phenolic 5889 1783 (RUL2) Amine 75% RPVOT 22097.5 47.8% 9280 55.8% (RUL1) Phenolic 1633.5 27.7% 744 41.7% (RUL2) Amine RPVOT EOT 14767 32.0% 0 0.0% (RUL1) Phenolic 1550 26.3% 529 29.7% (RUL2) Amine 1,000-minute RPVOT 7325 15.8% (RUL2) Amine