Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/778560
34 | January - February 2017 | www.machinerylubrication.com comes to additive solubility, lubricity, seal shrinkage and film strength. Much like mineral oils, PAOs are widely employed for lubricating applications and are often the preferred option when higher tempera- tures are expected. Group V is assigned to all other base oils, particularly synthetics. Some of the most common oils in this group include diesters, polyolesters, polyalkylene glycols, phosphate esters and silicones. Diester (dibasic acid ester) is manufac- tured through a reaction of dibasic acid with alcohol. The resulting properties can be adjusted based on the types of dibasic acid and alcohol used. Polyolester is made through a reaction of monobasic acid with a polyhydric alcohol. Much like diesters, the resulting properties will depend on these two constituent types. Polyalkylene glycol (PAG) is produced through a reaction involving ethylene or propylene oxides and alcohol to form various polymers. A number of PAG prod- ucts are developed based on the oxide used, which will ultimately influence the base oil's water solubility. Phosphate ester is created through a reaction of phosphoric acid and alcohol, while silicones are formulated to have a silicon-oxygen structure with organic chains attached. Each of these synthetics has specific strengths and weaknesses, as shown in the table on page 34. Applications In general, synthetics can provide greater benefits when it comes to proper- ties influenced by extreme temperatures, such as oxidative and thermal stability, which can contribute to an extended ser vice life. In situations where the lubri- cant will encounter cold startups or high operating temperatures, synthetics like PAOs typically will perform better than mineral oils. PAOs also exhibit improved characteristics in relation to demulsibility and hydrolytic stability, which influence the lubricant's ability to handle water contamination. While PAOs are ideal for applications like engine oils, gear oils, bearing oils and other applications, mineral oil remains the predominant oil of choice due to its lower cost and reasonable service capabilities. With more than 90 percent usage in the industrial and automotive markets, mineral oil has solidified its place as the most common base oil in the majority of applications. Paraffinic mineral oil, which is repre- sented in Groups I, II and III, can offer a higher viscosity index and a higher flash point in comparison to naphthenic mineral oils, which have lower pour points and better additive solvency. Even though naphthenic oil is mineral-based, it is considered a Group V oil because it does not satisf y the API's qualifications for Group I, II and III. The unique character- istics of naphthenic mineral oils have of ten made them good lubricants for locomotive engine oils, refrigerant oils, compressor oils, transformer oils and process oils. Nevertheless, paraffinic oils continue to be the preferred option for high-temperature applications and when longer lubricant life is required. Ester-based synthetics, such as diesters and polyolesters, have advantages when it comes to biodegradability and misci- bility with other oils. In fact, it is common for diesters and polyolesters to be mixed with PAOs during additive blending to help accept more significant additive packages. Diesters and polyolesters are of ten deployed as the base oil for compressor fluids, high-temperature grease applications and even bearing or gear oils. Because they are known to perform well at higher temperatures, polyolesters have also been widely used for jet engine oils. Compared to other oils, polyalkylene glycols (PAGs) have a much higher viscosity index and good detergency, lubricity, and oxidative and thermal stability characteris- tics. PAGs can be formulated to be water soluble or insoluble and do not form deposits or residue during extreme oper- ating conditions. PAGs can be employed in a number of applications, such as compressor oil, brake fluid, high-tempera- ture chain oil, worm gear oil and LESSONS IN LUBRICATION 55% of lubrication professionals use both synthetic and mineral-based lubricants at their plant, according to a recent survey at MachineryLubrication.com