MACHINERY LUBRICATION- INDIA NOVEMBER-DECEMBER 2019 | Page 19

MLI also be changed. Their advantage over mineral oils is that the change intervals are extended. Typically, the higher the operating temperature, the greater the benefit of using a synthetic lubricant. Base Stocks Used at High Temperatures The charts on page 29 compare the operating temperature ranges of different base stocks for mineral and synthetic lubricants. Note that these ranges represent normal values according to the base stock type. They do not reflect the comparative life of the lubricant. At high temperatures, the lifespan of synthetics is much longer than similar mineral oil products. There are also more synthetic base stocks that can work at high temperatures, such as diesters, polyglycols, polyolesters, etc. TYPE DROPPING POINT, °C MAXIMUM SERVICE TEMPERATURE, °C Simple Lithium 175 120 to 135 Lithium Complex 250+ 150 to 175 Polyurea 250+ 150 to 175 Calcium 90 60 to 70 Anhydrous Calcium 140 Calcium Complex 260+ 190 to 220 Modified Clay 280+ 190 to 220 Sodium 190 135 to 150 Sodium Complex 250+ 170 to 190 90 to 110 The table on the right can be used as a general reference for the maximum service application of greases according to the thickener in the formulation. The chart at the bottom of the page compares how grease consistency changes with temperature in two greases: simple lithium and lithium complex. The latter is classified as a high- temperature grease even in formulas with mineral oil. Remember, when selecting high-temperature lubricants, follow the appropriate methodology to determine the right option according to your equipment conditions and reliability objectives. Always weigh the pros and cons, and analyze the expected economic and operational benefits so you can be sure you are choosing the correct lubricant for your high- temperature application. Strengths and Weaknesses of High- temperature Lubricants About the Author When choosing a high-temperature lubricant, you must be aware of the potential drawbacks in order to select the best possible product. The table on page 30 provides the strengths and weaknesses of common synthetic lubricants. These charts are intended for general reference only, as various technologies in the marketplace may result in different specifications or performance. Alejandro Meza is a senior technical consultant with Noria Corporation. He has more than 20 years of experience in the lubricant industry, technical services, quality assurance, training, consulting and development in the United States, Brazil, Mexico and the Americas region. Contact Alejandro at [email protected] to learn how Noria can help you choose the right lubricant for your high-temperature applications. 1000 Complex vs. Simple Soaps LITHIUM COMPLEX 100 SIMPLE LITHIUM 10 Significa Significant nt Differn Difference ce 1 0 50 100 150 200 250 TEMPERATURE, °C Comparison of How Grease Consistency Changes with Temperature in Two Greases www.machinerylubricationindia.com | November - December 2019 | 17