Lubrication mechanism failure

One-shot metered lubrication is eminently suited to oiling systems and can be employed either in an all-loss arrangement or as part of a circulatory system. Sight-glasses or other indicators should be incorporated since such lubricating mechanisms are nowadays so reliable that a blockage or other failure might not be suspected until too late. 

The wear rate on liquid lubrication by electrolytes is defined only by metal dissolution and intensified friction, and can be varied in response to the corrosion rate under static conditions to a value that characterizes the mechanical failure of the metal. 

Experimental confirmation of the elastohydrodynamic lubrication theory has been obtained in certain selected systems using electrical capacitance, x-ray transmission, and optical interference techniques to determine film thickness and shape under dynamic conditions. Research is continuing in this area, including studies on micro-EHL or asperity lubrication mechanisms, since surfaces are never perfectly smooth. These studies may lead to a better understanding of not only lubricant film formation in high-contact-stress systems but lubricant film failure as well. 

Chemical Lubrication under Extreme Loads. So far the lubrication mechanisms discussed have involved ever thinner layers of lubricating liquid. The obvious limit to that progression is the complete absence of an external lubricant. When devices operate under extreme conditions of load, speed, temperature, and other parameters, conventional lubricants will usually begin to break down and drastic mechanisms must be employed to prevent complete seizure and failure of the machinery. One way to approach that problem has been the development of sacrificial lubricants, which, under extreme conditions, react with fresh metal surfaces formed by wear to produce a new inorganic chemical layer that can then be more easily sheared, thereby preventing seizure. 

Mechanical failures may occur for a number of reasons. Some are induced by cavitation, hydraulic instability, or other system-related problems. Others are the direct result of improper maintenance. Maintenance-related problems include improper lubrication, misalignment, imbalance, seal leakage, and a variety of others that periodically affect machine reliability. 

The author doubts if the comparison by making the dimensionless load parameter equal is better. He believes that the contact pressure better represents the real physics, which is more closely correlated with lubricant rheology, lubrication mechanism, material performance and efficiency evaluation as well as possible failures. If the dimensionless load parameter is kept constant, for example, but the contact ellipticity changes from 1/8 to 8, the contact pressure would be reduced down to about 11.7%, at which the contact and lubrication mechanisms may be completely different. On the contrary, when keeping the contact pressure and Rx the same, for the same ellipticity change the dimensionless load needs to be increased more than 620 times. Even for the same ellipticity, we believe that the contact pressure is better correlated with the physics and the failures. Also, comparison by making the dimensionless load equal only yields a small quantitative difference. 

Lubricating oil analysis, as the name implies, is an analysis technique that determines the condition of lubricating oils used in mechanical and electrical equipment. It is not a tool for determining the operating condition of machinery. Some forms of lubricating oil analysis will provide an accurate quantitative breakdown of individual chemical elements, both oil additive and contaminates, contained in the oil. A comparison of the amount of trace metals in successive oil samples can indicate wear patterns of oil wetted parts in plant equipment and will provide an indication of impending machine failure. 

The increasing demands being made on equipment by the requirement for increased output from smaller units create problems of lubrication, even in systems where full-fluid film conditions generally exist. For instance, at start-up, after a period of rest, boundary lubrication conditions can exist and the mechanical wear that takes place could lead to equipment failure. Anti-wear additives, by their polar... 

In literature, some researchers regarded that the continuum mechanic ceases to be valid to describe the lubrication behavior when clearance decreases down to such a limit. Reasons cited for the inadequacy of continuum methods applied to the lubrication confined between two solid walls in relative motion are that the problem is so complex that any theoretical approach is doomed to failure, and that the film is so thin, being inherently of molecular scale, that modeling the material as a continuum ceases to be valid. Due to the molecular orientation, the lubricant has an underlying microstructure. They turned to molecular dynamic simulation for help, from which macroscopic flow equations are drawn. This is also validated through molecular dynamic simulation by Hu et al. [6,7] and Mark et al. [8]. To date, experimental research had "got a little too far forward on its skis however, theoretical approaches have not had such rosy prospects as the experimental ones have. Theoretical modeling of the lubrication features associated with TFL is then urgently necessary. 

The failure of TFL only means a loss of mobility here, but monolayers can stay on solid surfaces to separate the solid surfaces in relative motion, and subsequently sustain a feasible boundary lubrication state [10]. Because the film thickness of TFL is of the nano scale or molecular order, from a mechanical point of view, TFL is the last one of the lubrication regimes where the Reynolds equation can be applied. 

The model has been applied successfully to predicting the performances of bearings, gears, seals, and engines [10-12]. A fundamental limitation of the statistic models is their inability to provide detailed information about local pressure distribution, film thickness fluctuation, and asperity deformation, which are crucial for understanding the mechanisms of lubrication, friction, and surface failure. As an alternative, researchers paid a great interest to the deterministic ML model. 

Bartz, W.J. and Xu, Jinfen, Wear Behaviour and Failure Mechanism of Bonded Solid Lubricants, Lubric. Eng., 43, 514, (1987). 

Ineffective lubrication remains one of the leading causes for machinery failure. Routine inspection of the machine s lubrication system is among the easiest and most productive ways to avoid equipment failure and should play a pivotal role in the pursuit of precision lubrication. This program allows the operators and the mechanics who perform the routine inspections to have a better awareness of the importance of effective lubrication, resulting in the improvement of the quality of lubricant application. ... 

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