Putting the simple back into viscosity
Written by John Sander
Recent Trends
Fluid Lubricants
Because of its large volume and importance to so many consumers, the engine oil market drives many new trends that occur within the lubricant industry. Today, articles are being written discussing the possible demise of monograde engine oils. A number of years ago, straight grade engine oils, especially SAE 30 and SAE 40, were the most prevalent viscosity grades used by most consumers. SAE is considering adding either two or three new viscosity grades to the SAE J300 Viscosity Classification that was described previously. The reason all of this is occurring is because much attention is being paid to improving fuel economy and energy efficiency. Governments are pushing automotive and industrial OEMs to find ways to improve the efficiencies of the vehicles and equipment they produce. It is not completely surprising that lubricants have been considered as a means to decrease fuel and energy consumption. As viscosity is a measurement of the internal resistance of a fluid to flow, if the viscosity is decreased, then so is the internal resistance. Therefore attention is now being paid to decreasing the viscosity of various lubricants to reduce their detraction from efficiency. Improved efficiency results in less energy consumed, which results in lower emissions released into the environment.
Due to the improvement seen through the use of multigrade engine oils, studies have now been done that suggest that the same energy savings can be realized through the use of multigrade or synthetic industrial lubricants. The majority of the work has been done in hydraulic fluids, which not surprisingly, is the second largest category of lubricants by volume. In fact, one additive supplier has set up a Web site specifically to describe how viscosity can affect hydraulic system efficiency. This supplier has coined the term "Maximum Efficiency Hydraulic Fluids", a concept for which it won the 2010 American Institute of Chemical Engineers Energy Efficiency award.
Greases
So far, the products discussed have been fluids. What about greases? While energy efficiency studies may not be as easy to conduct and prove for greases, new viscosity-related research is occurring to better determine how greases will flow when used in an application. In fact, ASTM subcommittee D02.G has various active research projects, including some related to grease rheology. Rheology is the study of the deformation and flow of materials. Not surprisingly, this definition sounds very similar to the definition of viscosity. Much of this research is being conducted employing a tool called a rheometer. A paper has been published in which rheometer data has been compared to grease penetration data. The rheometer provides a new level of sensitivity above and beyond that of the penetrometer.
One last area of interest is the viscosity of used oils. Analyzing used oils is not new, but analyzing them under high- and low-temperature operating conditions is new. How will the effects of oxidation, contamination and shear affect the performance properties of the lubricant? A working group at ASTM has been formed, and it is planning a symposium to be held in the future to present research related to rheology (viscosity) of in-service lubricants.
