Synthetic oils - does their use really pay off?
Today, hardly any new vehicle is delivered whose engine has not already been filled with a low-viscosity, fully synthetic oil at the factory. Synthetic oils are also being used more and more frequently in the industry. Typical examples are hydraulic fluids for construction machinery or high-performance gear oils for wind turbines, but also special products such as high-temperature chain oils or circulating lubricating oils for paper machines.
Fully synthetic lubricants are manufactured on the basis of hydrocarbons. Starting products can be petroleum products as well as various other raw materials from which hydrocarbons can be extracted or synthetic fluids can be produced. During production, the molecular structures are modified in such a way that the desired lubricating properties result and the optimum viscosity situation is achieved. Appropriate additives are mixed in, which for most synthetic oils are almost identical to those for mineral oil-based base oils. As a rule, synthetic products are several times more expensive than the same amount of mineral oil-based, but their advantages can not be denied.
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Lower energy losses, better efficiency
Synthetic oils are significantly "thinner" than conventional mineral oils at the same ISO viscosity grade and low temperatures. One unit that makes this "multi-range characteristic" clear is the viscosity index (VI). This is usually in the range of 90 - 100 for mineral oil-based lubricating oils, while it is almost always above 140 for synthetic base oils. The higher the VI, the less energy is required for the same nominal viscosity at cold start or at low ambient temperatures. Since such oils flow more easily, they consume less valuable energy through reduced splashing and pumping losses.
Synthetic oils therefore help to save fuel or electrical energy. The lower the temperature, the more electrical energy is saved. By selectively adjusting the molecular structure, lower friction coefficients can be achieved with synthetic oils even without special additives, such as "friction modifiers". In practice, therefore, synthetic oils can save between 0.5 and 3% energy, not only because of their viscosity situation, but also thanks to their balanced formulation.
The potential savings can be significant, depending on the plant. The use of synthetic oils, which are often much more expensive, more than pays for itself in the long run through the energy-saving potential alone. Calculate for your plants how high your energy costs are and what savings effect you can achieve in your operation.
Longer oil life
When an oil is employed, it ages as it is used. Reactions of oil molecules, e.g. with oxygen, cause oils to oxidize. The oxidation process can be significantly slowed down with special additives, the "antioxidants".
Synthetic oils are also not exempt from the aging process. Yet they generally have significantly longer service lives than mineral oils. The aging of an oil charge, especially in the industrial sector, is significantly affected by the time of use and the temperature that the oil experiences during its use.
In addition, impurities such as water, dust or wear particles have an accelerating effect on the oxidation behavior of an oil. Oil oxidation and the content of "antioxidants" still present in used oil can only be determined with the aid of elaborate laboratory analyses using infrared spectroscopy or the RULER.
"Bad odor" alone is not a sign of oil aging. To reduce wear, almost all oils also contain sulfur compounds, the decomposition products of which smell like "rotten eggs" and clearly mask the "rancid" odor that occurs during oil aging.
Unlike mineral oils, synthetic oils do not have "imperfections" in the molecular structure where oxygen can attack and thus initiate aging. Synthetic oils already have considerably better oxidation stability than a mineral oil with equal additives due to the uniformity of the molecules and the stable molecular structure with respect to oxygen influence. In addition, the oxidation tendency of synthetic oils is inhibited with modern antioxidants based on phenols, amines or salicilates until this aging protection has been used up.
Therefore, synthetic oils can often remain in use several times longer than mineral oils. Only if synthetic oils are heavily contaminated by combustion residues or mixed with more than 5% mineral oil, as is the case in engine operation, does the aging stability decrease.
Formula for oil aging of mineral and synthetic oils
Just as vegetable oil becomes rancid as a function of temperature and time, so too does mineral oil, which was created from plants in primeval times.
- As a rule of thumb for the speed of oil aging, the following has been proven for non-mixed and contaminated mineral oils:
Every 10°C above a temperature of 50°C, the rate of oil aging doubles. Assuming that a well-refined mineral oil, such as that used in the production of turbine oils, can remain in service for at least 40,000 hours at 50°C, this time is reduced to 20,000 hours at 60°C and 10,000 hours at 70°C.
- When using synthetic oil, not only is the temperature for the onset of oil aging higher, but the speed of oil aging also slows down significantly. Thus, the following rule of thumb can be assumed for an uncontaminated and unmixed synthetic oil:
Every 15°C above 60°C, the expected oil life is halved. A synthetic hydraulic oil, such as that used in construction machinery, can remain in service for as long as 40,000 hours at temperatures in the hydraulic tank of 60°C, for example. At 75°C, this time is halved to 20,000 hours. At 90°C, a temperature at which many plants are operated today, the oil can still be used for 10,000 hours. In the case of construction machinery, this is virtually a lifetime filling.
Comparison of oil aging and oil life
| Temperature in °C when using mineral oil | Operating hours that the oil can be used without an oil change | Temperature in °C when using Synthetic oil |
|---|---|---|
| 50 | 40,000 | 60 |
| 60 | 20,000 | 75 |
| 70 | 10,000 | 90 |
| 80 | 5,000 | 105 |
| 90 | 2,500 | 120 |
| 100 | 1,250 | 135 |
| 110 | 625 | 150 |
| 120 | 312 | 165 |
| 130 | 156 | 180 |
Other advantages that speak for the use of synthetic-based lubricants and operating fluids:
- Low evaporation losses and thus less oil consumption compared to mineral oils of identical viscosity at oil sump temperatures of 100°C and above.
- Good air separation behavior lowers the tendency to cavitation, the oil is less compressible.
- Less air in the oil reduces oil aging. Less foaming because the same high-pressure properties can be achieved with lower levels of additives that can promote foaming.
- Good filterability because no long-chain, sticky molecular compounds of additives used to optimize viscosity-temperature behavior (VI-Improver).
