Review of Recent U.S.A. Publications on Lubricating Grease

Abstract

Recent lubricating grease research and technology in the U.S.A. has been a wide-ranging endeavor with fundamental research investigations on theories of structure (including complex soaps), permeability, electrical measurements, and electron microscopy adding much to the knowledge of grease structure. NLGI Fellowship studies have contributed significantly to this phase. Outstanding advances have also been made in manufacture and processing, giving greater efficiencies, shorter times of manufacturing and culminating in the first truly continuous manufacturing process. Radioactive tracing of additive mixing has been accomplished. Packaging has advanced with new materials, and new ingredients for greases have become available. Inventory and quality control has been marked by the use of computers. Mechanical testing and evaluation has been a major effort in supplementing simple non-bearing bench tests by providing laboratory rig tests using actual bearings and gears. Many new designs of testing equipment have been developed, and studies of the friction, wear and e.p. properties of lubricating greases, including ball joint testing, have been extended. Analysis and non-mechanical testing endeavors have included a critical look at the significance of the bomb oxidation test, the development of an instrumental method to measure color, and the use of infrared techniques for quantitative analysis of lithium soap in lubricating grease. Studies on flow and dispensing have been particularly active resulting in an advanced understanding of grease flow, both theoretical and in practical applications. In particular, apparent viscosity determinations have been correlated with flow in pipes in a very useful way. A continuing development of centralized lubricating systems has made for efficiency, economy and safety, and great expansions in bulk handling have come about through better understanding of grease flow. Formulation of lubricating greases has been marked by development of new thickeners in addition to complex soaps, and in the expanded use of molybdenum disulfide as a solid-film lubricating additive. The development and study of products for extreme environments including aerospace applications has resulted in some industrial spin-off. The new NLGI Reference Systems provide samples of the same formulation and manufacture which can be used for research and evaluation by laboratories with assurance of continuity, this being particularly valuable for co-operative investigations by technical societies. New discoveries have been made with old ingredients, such as the finding that high-soap-content greases give longer ball-bearing lives. A special grease has been formulated for the food industry. The application of lubricating greases and requirements for them have been marked by the development of rustproof applications from the “inside-out” rather than simply applying an asphaltic undercoating. The new grease-petrolatum-type products applied mainly with airless sprays have given much better rust protection for the life of the automotive vehicle than was obtained previously. Lubrication intervals for automotive chassis greases have continued to increase, although certain makes of cars have reverted to shorter periods and more grease fittings particularly when conventional greases are used. There has been an intensive development of aerospace applications with special greases such as the perfluorinated types coming into the picture where hard vacuum, high temperatures, and other extreme conditions must be resisted. However, it has been found that more conventional greases may work surprisingly well, not only where sealed against vacuum, but in vacuum environments. Improvements have been made in railroad lubrication particularly in the understanding of the functioning of journal roller bearing greases and effect of vibration on them, and the trend toward mild-e.p.-gear-oil traction-motor gear lubricants which give better heat transfer, resist thickening, and afford improved lubrication of gears. The issuance of a revised NLGI Glossary containing approximately 100 terms now agreed upon in the lubricating grease industry should help the understanding of these products by users and others. The NLGI Grade Classification has been made an American Standard and is being considered for international standardization. Production surveys made periodically by NLGI and recent marketing forecasts have resulted in very helpful statistics and the recognition of trends. Considerable thought has been given to better marketing techniques.