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Monday, 5 September 2011

Eleven good reasons to use synthetic gear oil

There’s an ever growing swing towards the use of synthetic gear oil, and in this article we’re going to examine eleven good reasons to use synthetic gear oil in your industrial transmission systems.

As manufacturers continue to push the limits of machine performance to increase productivity, reduce downtime and energy costs, suppliers need to offer increasingly creative solutions. Interestingly, one of the most effective ways to achieve these performance levels is also one most frequently overlooked: proper lubrication.

OEMs specify what lubricants should be used, and therefore it’s important for them to view lubricant as a machine element, in the same way that they consider material composition of the gears and bearing type. As with all the
other components, the right gear oil will allow the gearbox to achieve optimum performance; resulting in lower wear rates, lower operating temperatures, extended oil change intervals and importantly, improved energy efficiency.

Choosing the best synthetic gear oil
When selecting the proper synthetic gear oil it’s crucial the correct base oil viscosity is determined based on the following criteria:
• Operating speed (variable or fixed)
• Type of friction (sliding or rolling)
• Load and environmental conditions
• PAG (polyalkylene glycol) oils, are good for sliding friction but are not well suited for rolling friction.
• PAO oils are used for rolling friction and can cope with some sliding friction.
• Silicon and PFPE lubricants are typically used for extremely high temperatures.

Benefits of using synthetic gear oil.
Synthetic gear oil is usually selected to provide the following mechanical and chemical properties:
1) Extended drain intervals
Approximate oil change intervals of gear oils at an operating temperature of 176°F (80°C) are:
• Mineral oil: 5,000 operating hours
• SHC oil: 15,000 operating hours (extension factor 3)
• PAG oil: 25,000 operating hours (extension factor 5)
• The life extension factors of synthetic oils as compared to mineral oil are as follows:
• Mineral oil = 1
SHC = 9.5 times longer
PAG = 31 times longer
These extended intervals also reduce the effect of oil on the environment

2) Low/high-temperature viscosity performance
• Synthetic gear oil has a lower friction coefficient than mineral oil as well as a better viscosity-temperature relationship. This usually facilitates the use of lower viscosity grades as well as reducing oil operating temperature. In turn this leads to the life extension factors for oil change intervals of synthetic gear oils even longer than the values stated above, which reference fixed oil temperature. The following comparison of test results illustrates the effect on temperature after 300 operating hours:
• Mineral oil: 230°F (110°C)
SHC: 194°F (90°C)
PAG: 167°F (75°C)
• The 10K rule dictates that for every 10 degrees you increase the temperature of the lubricant, you halve its performance life.
3) Decreased evaporative loss
4) Reduced frictional losses
5) Reduced wear
6) Improved mechanical efficiency
7) Chemical stability
8) Resistance to oil sludge build up
9) Reduced operating costs resulting from less downtime
10) Reduced labour costs (Extended oil change intervals)
11) Measurable energy savings and increased output

The effect of synthetic gear oil on energy efficiency.
Even within the genre of synthetic gear oil there is a differences in energy efficiency due to friction performance. Polyglycols, for example, are the most efficient and lowest wear type of oils, particularly in high-sliding applications such as worm and hypoid gears. In these applications, PAGs offer a lower coefficient of friction within the gearbox, resulting in less power loss and lower temperatures.

Synthetic gear oil is also more energy efficient because of oxidation and thermal stability, which means the gear oil lasts much longer. Typically you’d change a mineral oil every 5,000 hours, whereas PAOs or synthetic hydrocarbon oils could last approximately 15,000 hours before a change. PAGs can last as long as 25,000 hours at similar temperatures.

As part of oil degradation over time, the Total Acid number changes, and the additives are used up. While changing the synthetic gear oil replenishes the additives and removes wear particles, it also adds maintenance downtime and costs to the equation. Choosing a high-performance synthetic gear oil from the start will reduce the oxidation rate and decrease the required number of oil changes and associated downtime.

The choice of gear oil affects several transmission design considerations, including the reliability and efficiency of the final product. How much the energy efficiency of a gearbox is improved by using high-quality synthetic gear oil, depends on the gear type.

Significant increases using synthetic gear oil can be realized in gear types that normally have lower efficiencies such as worm drives. As the efficiency increases, the temperature of the gearbox also drops and this decrease in temperature increases the life of the gear system.

So to conclude: In choosing high-quality synthetic gear oil, end users will save energy and reduce operating costs through reduced maintenance, longer oil change intervals, and less wear.

Image: Master isolated images /