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Lubricating Grease
Dr. Raj Shah, Mr. Blerim Gashi Despite the current wide range of grease lubricating applications (rolling bearings, plain type bearings, gears, joints, electric motors and vehicles, heavy duty machinery) there remains an evident lack of sufficient research aimed towards understanding the underlying mechanisms of film formation, loss of film, and film separation [1]. Instead, a majority of tribological research of grease lubrication focuses on overcoming challenges or shortcomings as a matter of application parameters (adjusting speed, temperature, or contact load) and the resulting performance outputs rather than the fundamental mechanisms governing the inputs. Numerous tools can be utilized in order to enhance these property ranges and prevent lubrication failure, such as the incorporation of nanoadditives or polymer additives, as well as the improvement of oil distribution design, application frequency, and sealing performance in preventing contamination. Recent advances focused in the last three years have extended the applicability of greases in extreme conditions. This article will summarize the key findings and lessons within those research advancements. Though these efforts have been fruitful, this area of research remains a vital field for yielding further mechanical performance and overall profits. Grease Fundamentals Grease lubrication is the process by which a semi-liquid lubricant coated on a wide-variety of contacting surfaces reduces the mechanical wear, coefficient of friction, and prevents premature failure of machinery. Fundamentally, greases are complex semi-liquid lubricants primarily consisting of a base oil (mineral or synthetic oil), a thickening agent (metal soap), and various viscosity modifiers and/or additives. It is important to note that optimal utilization of greases relies on the correct type of grease used for specific requirements. The many types of greases consisting of various combinations of metal soap thickeners such as lithium, aluminum, sodium, or even clay contain a wide variety of temperature ranges, rust protection, and extreme pressure properties which are well understood [2]. Table 1 displays an assortment of some of the most common types of metal soaps utilized within industry today, as well as the key characteristics and applications of each respective thickener. - 46 NLGI Spokesman | VOLUME 85, NUMBER 5 | November/December 2021
