![]() The disadvantages of synthetic oils include their price, which is up to 10 times higher, reduced compatibility with one other, and problematic behaviour with respect to seals, tubing, and coats of paint.Īlthough lubricants are usually miscible (with the exception of PAGs) – especially if they share the same nominal viscosity and are designed for the same purpose – they are not always compatible with each other. Their consistently high VI improves cold start behaviour, ensures a stable viscosity level over a wide temperature range, and simplifies control. Synthetic oils therefore minimise the risk of deposits and deliver a better filterability. ![]() These in turn cause deposits and lead to filtration problems. A natural viscosity index (VI) as high as in excess of 200 instead of 95 eliminates the need for multigrade additives, which, as non shear-stable additives, can result in the formation of reaction products. Hydraulic systems filled with these are easier to start, and demonstrate smaller energy losses at high temperatures. These oils are thinner at low temperatures and thicker at higher temperatures than conventional mineral oils. Synthetic base oils offer the advantage of better viscosity-temperature (VT) behaviour. These oils also contain modern antioxidants based on phenols, amines, or salicylates, which serve to further improve service life. Their molecular structure exhibits a lower reactivity with oxygen at higher operating temperatures. Pure synthetic oils can remain in use for far longer than previously used products. As base oils, these contain poly-alpha olefins (PAOs), saturated or unsaturated ester oils, or polyglycols (PAGs). In addition to hydrocracked oils, which are still very inexpensive, today fully synthetically produced fluids are used. The advantages of synthetic oils over conventional mineral oils can also be clearly proven using oil analysis. These high demands can often only be met by using synthetic multi-purpose hydraulic oils, which are more suited to long-term use. With improved base oils and corresponding additives, modern hydraulic fluids are mastering these higher temperature requirements, as well as increased mechanical strains, and are contributing decisively to the continuous operability of the systems involved. If only a few years ago oil suited to 400 bar of pressure was needed for hydraulic engines and cylinders, today it is not unusual to encounter demands for oil suited to over 600 bar of pressure. ![]() Temperatures are not only rising because the oil quantities are falling, but also because pressures are increasing. As such, the oxidation or ageing stability of oils is becoming ever more relevant. Due to oxidation, a mineral oil-based hydraulic oil that is changed after 10,000 operating hours at 60☌ must be changed after only 2,500 operating hours at 80☌. At a temperature of 10☌ higher, however, the increased oxidation tendency of mineral oils means that oil service life is halved. The oil consequently spends less time in the oil container, and has less time to cool to the ideal mineral oil temperature of less than 60☌. Systems are becoming ever more compact and designed for smaller oil quantities.
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