Machinery Lubrication

Machinery Lubrication November December 2016

Machinery Lubrication magazine published by Noria Corporation

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S y n t h e t i c L u b r i c a n t s B y A l e JA ndro me z A | Nori a Corpor at ioN PERSPECTIVE SELECTING Guidelines for High-temperature LUBRICANTS owadays most industries have processes that require machines to operate at high tempera- tures. These applications demand special lubricants that can handle extreme operating temperatures by maintaining their lubrication properties, keeping the system clean and providing a reasonable service life. The ultimate goal is to sustain high machine reliability while controlling maintenance costs. In many cases, a synthetic lubricant may be the best choice. What is Considered a High Temperature? Before selecting a high-temperature lubricant, you must first know when a temperature is considered to be high. Unfortunately, there is no single right answer to this question. For the sake of reference, generally an oil that is able to work at temperatures higher than 210-250 degrees F (100-120 degrees C) for a normal or extended drain interval may be assumed to be a high-temperature lubricant. Of course, other sources may have different opinions on this temperature range. The well-known Arrhenius rate rule, which relates to lubricant use versus temperature, states that for every increase of 18 degrees F (10 degrees C), the oil life is cut in half. This equation was originally formulated for mineral oils, but while the lifespan is different for various product technologies, the rule is applicable for both mineral and synthetic lubricants. This means that a mineral oil with a weak formulation may be used at higher temperatures if it is changed frequently, but that is not practical or cost-effective in most cases. The same principle applies to the base stocks used in greases. The grease's thick- ener influences the performance at higher temperatures due to its oxidation resis- tance, as well as the dropping point that it imparts to the grease. It is recommended to use a grease below its dropping point to ensure the lubricant stays in place. See the sidebar on page 30 for a few simple rules to help determine the maximum operating temperature based on a grease's dropping point. High-temperature Operation A lubricant's operating temperature will depend on several factors, such as the heat N 80% of lubrication professionals use high-temperature lubricants on the machines at their plant, based on a recent survey at MachineryLubrication.com

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