Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/520842
www.machinerylubrication.com | May- June 2015 | 21 notorious for their incompatibility with mineral oils, although oil-soluble PAGs (usually called OSPs) largely remedy this drawback. In the event that mineral oils and PAG oils form an incompatible mix, the result is a gelatinous mass that clogs lines and can lead to lubricant starvation and ultimately machine failure. Other incom- patibilities for synthetics include paints, hose materials and some additives. Synthetic esters such as phosphate esters, polyol esters and di-esters are also at risk for hydrolysis. Hydrolysis is a water-induced chemical reaction that can cause a rise in acid number, loss of viscosity and an increase in varnish potential. Synthetic Types Polyalphaolefi ns have been identifi ed as the most common synthetic base oils. They are used in nearly every type of equipment with the exception of compressors that have high discharge pressures, where they have been known to leave deposits. PAOs are miscible with mineral oils and have good demulsibility characteristics. Polyalkylene glycol oils are used in some refrigeration compressor systems as well as brake fl uids, worm gear oils and gas turbine oils. They are unique in that they don't form deposits as the oil breaks down. PAGs also have a natural detergency and clean up varnish left behind by other fl uids. If the base fl uid is made by the polymerization of ethylene oxide, the resulting fl uid is water soluble and is often used in water-emulsion hydraulic fl uids. Di-esters are frequently used in compressor applications and are often paired with PAOs to help with additive solu- bility. Di-esters also tend to be hygroscopic in nature, which means they absorb mois- ture readily. They have a high viscosity index as well as a low pour point, so these oils will remain fl uid at low temperatures. Silicone base oils have the highest viscosity indexes and some of the highest levels of thermal and oxidative stability. These bases are used primarily in high heat applications and some brake fl uids. They are typically very costly. In addition, the oxidation byproducts are abrasive and can lead to added machine wear. Silicones are also chemically inert, which makes it diffi - cult to blend additives into them and still have them remain in solution. Overall, synthetic oils can be tremen- dous assets to any lubrication program, but they must be matched to the machinery's needs to get the optimum benefi t from them. When making the transition from mineral base fl uids to a synthetic base, be sure to fl ush the system to minimize any residual compatibility issues that may remain. By understanding the strengths and weaknesses of the synthetic base you are using, you will be well on your way to achieving all of the advantages associated with these fl uids. About the Author Wes Cash is a senior technical consultant with Noria Corporation. He holds a Machine Lubrication Technician (MLT) Level II certifi ca- tion and a Machine Lubricant Analyst (MLA) Level III certifi cation through the International Council for Machinery Lubrication (ICML). Contact Wes at wcash@noria.com. S y n t h e t i c s Synthetic oils can be tremendous assets to any lubrication program, but they must be matched to the machinery's needs to get the optimum benefit from them.