Viscosity is the single most critical physical property of a lubricant and should be a key consideration when selecting an industrial lubricant. Viscosity can influence lubricant life expectancy, the rate of equipment wear, energy consumption and resistance to flow and shear.
Viscosity, by definition is a lubricant’s resistance to flow and shear. Water, for example is a low viscosity fluid and syrup similar to lubricants is a high viscosity fluid. A lubricant’s viscosity is defined by the size of its molecules. The larger the molecular structure of a lubricant the higher the viscosity. The size and structure of mineral lubricant molecules vary; therefore, the average molecule size dictates the viscosity. As mineral oils age this structure changes resulting in viscosity changes over the service life of the lubricant. Synthetic lubricants, for example Mobil SHCTM Series lubricants are manufactured in such a way as to result in consistently sized molecules of an identical structure remaining consistent throughout service life.
The viscosity of a lubricant changes dependant on the temperature, pressure and actual shear stress of a lubricant as a result of it flowing between moving components. As the temperature rises viscosity decreases increasing flow rate. When a lubricant experiences colder temperatures the opposite occurs.
To determine a lubricants quality you must consider its Viscosity Index (VI). VI is a measure of the change in viscosity of a lubricant relative to temperature. Lubricants with a high VI will exhibit less change in viscosity at increased temperatures than lubricants with a lower VI. It is during the cold start where the concern is greatest owing to the heavy drag from high viscosity lubricants with a low VI number. It takes roughly 90 seconds for the lubricant to properly circulate in an engine following a dry start from cold. Lubricants with similar properties to that of Mobil SHC tend to have very little change in viscosity irrespective of temperature and stabilise at a much faster rate.
Industrial equipment does not operate under consistent conditions and Industrial operations are often subject to a wide variety of operating environments where extreme temperature changes can requently occur.
In order to withstand such dramatic variations in temperature it is recommended that industrial plant managers select and utilise a lubricant with a high VI formulated specifically to withstand temperature variation. Synthetic lubricants with high VI, such as Mobil SHC Series lubricants can aid in maintaining operating consistency, protect equipment from operating conditions and minimise failure. This type of lubricant is formulated to deliver superior protection across a greater range of operating temperatures in comparison to conventional, mineral-based lubricants. This improves equipment reliability and performance resulting in increased plant productivity.