Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/490438
42 March - April 2015 | www.machinerylubrication.com Ask the ExpERTs Polyalkylene glycols or PAG base oils are a type of synthetic base stock. While synthetic engine oils are becoming increasingly common, they usually are not formulated with this type of base stock. Most of them are polyal- phaolefin or PAO base oils, with some being synthetic blends. Blending of synthetic oils is a precise science and is normally done to aid in the formulation with additives. That's not to say that PAG oils can't be made into engine oils. There have been studies done on using these types of synthetics for all types of automotive lubricants including gear, transmission and crankcase oils. Synthetic oils across the board offer a wide array of benefits in any application. More often than not they have a higher oxidative tolerance so they last longer in service. In mobile equipment that operates in extreme temperature envi- ronments, synthetics work well, as they generally have a higher viscosity index. The viscosity index is a measure of how much viscosity changes over a temperature spectrum. The higher the value, the less the viscosity is affected by a change in temperature. These synthetics have their own unique characteristics that set them apart from other synthetic oils. PAGs have excellent lubricity and a high viscosity index (typically 100 to 200, depending on the formulation). They also have great thermal and oxidative stability. This equates to longer service life and functionality in high-tem- perature applications. Along with the benefits, there are also drawbacks for any synthetic. These types of synthetics have the dubious reputation of not being miscible with mineral oils. PAG and standard mineral oils do not mix well and form an almost snot-like substance when they come in contact with each other. Not only can they not mix with mineral oils, but certain polymers and paints are also incom- patible with these fluids. PAGs can cause the shrinking or swelling of some seal materials, which can lead to leaks and/or allow contamination into the system. Before putting a PAG oil into any machine (engine, gearbox, hydraulic system, etc.), make sure all the materials are compat- ible. Likewise, if the system was previously filled with a mineral oil, the system should be flushed to ensure that all the mineral oil is removed to avoid any of the previously mentioned problems. So while synthetics are becoming more and more widespread, different synthetics are used in different applications. Although not traditionally used in engine oils, PAG oils are very common in refrig- eration oils, brake fluids and various gear oils. One of the biggest risks when switching from a mineral oil to a synthetic is the incom- patibility. This should always be kept in mind. "Can engine oils be formulated from polyalkylene glycols?" "What methodology should be used when deciding if you can extend pM intervals?" There are many methods for safely extending service intervals. Each depends on the exact preventive mainte- nance (PM) task you are trying to extend, but at the core of most is oil analysis. Repeatable and representative oil samples with the proper test slates are essential for evaluating the current practices and the possibility of extending service intervals. The first step is to take a deep look into the historical data you have for the component or group of equipment. Groups of equip- ment should be fundamentally the same and operate within the same environmental conditions. Depending on the type of equip- ment and PM task you are evaluating, certain trends and data will need to be analyzed. For example, if you want to extend drain inter- vals for a fleet of diesel engines, look at historical trends of spectrochemical analysis, fuel dilution, soot levels, oxidation, water, viscosity and base number. Next, you will need a good way to compare/compile the data, such as with a spreadsheet. Once the data is in a spreadsheet, check the number and type of abnormal samples as well as any trends that develop as the oil ages and how soon after a change-out that those trends appear. If the majority of results are deemed normal when the change-out occurs, the equipment may be a good candidate for extending the service. A good rule of thumb is to use a 25-percent increase in increment while verifying with more oil analysis. You want to ensure the new interval has not overextended the service, so a sample should be taken at the old interval and just before the change-out at the new interval. The decision to extend inter vals typically is driven by cost or savings. However, you will want to justif y these changes. To do so, consider the following: oil capacity, oil cost, disposal cost,