Deterioration of lubricants

Due to the continuous input of thermal energy necessary to maintain mechanical work, tribological systems are in progressive equilibrium. In the tribosystem, the flow of energy is accompanied by an increase in entropy of the total system and is reflected by the tribochemical reactions and deterioration of lubricant quality. Our understanding of tribosystems has been seriously limited by a lack of kinetic information on critical reactions in hydrocarbon formulation and critical reactions at interfaces. 

Condition monitoring is an established technique which has been used by capital-intensive or high-risk industries to protect their investment. The concept has developed radically in recent years largely due to advances in computerization, which offer greater scope for sophisticated techniques. These fall into three types of monitoring vibration, performance and wear debris. The last monitors particulate debris in a fluid such as lubricating oil, caused by the deterioration of a component. 

In the pyrot area, paraffin is widely used in the manuf of book and wooden matches, as a protective coating to counteract possible surface deterioration of metal powders, as a lubricant and waterproofing agent for the interior surfaces of kraft paper flare and signal cases, and as a binder which tends to fill interstices between particles on press loading (Ref 7, pp 69, 71, 302 316)... 

The ZDDP deterioration By reference to Table 6.10 and the case study 2 Evaluation of ZDDPs , in field tests of 56 passenger car vehicles (taxi cabs) and laboratory analysis of lubricating data were included viscosity, TBN, TAN, ZDDP (active), dispersants, oil consumption rate, engine deposits, camshaft and valve lifter wear. Which of the major ZDDPs and ZDDPs mixtures provide the best antiwear and antioxidant performance ... 

The next chapter is a review of current practice in lubrication of internal combustion engines and lubricant design. The role of individual lubricant components and their use in mineral and synthetic formulations is covered. This is followed by a discussion of the tribochemical effects of additive interactions. The heart of the manuscript is chapters, "Tribochemical nature of antiwear film , "Surface tribochemistry and activated processes", and "Analytical techniques in lubricating practices". Topics covered include tribofilm formation, organomolybdenum compounds in surface protection, catalytic activity of rubbing surfaces, introduction of some techniques for evaluation of tribofilms composition and analytical techniques for evaluation of lubricant degradation. Examples of the application of basic concepts are introduced, eg., acidity and basicity in the process of lubricant deterioration. 

HA is the basis of the lubricant and "shock absorber" properties of synovial fluid. Osteoarthritis is the most common disease of joints, and correlates with a deterioration of synovial HA. Intra-articular administration of HA is a widely used therapy for OA, providing relief of pain, and other symptoms. The first arthroscopic viscosurgical application of HA was in 1989 [150]. There are several preparations of partially cross-linked HA that are now used in this context. However, only one preparation will be discussed here. Synvisc , also known as hylan G-F 20, is a viscoelastic fluid containing modified HA produced from rooster combs. Hylans are cross-linked derivatives of HA. Synvisc contains hylan A (average molecular size 6x10 Da) and hylan B, a hydrated gel in a buffered salt solution. 

API Category MT-1, issued in 1995, describes the performance requirements of lubricants intended for use in non-synchronized manual transmissions, such as those found in heavy-duty trucks and buses, particularly in the United States. Lubricants meeting this requirement give protection against the combination of thermal degradation, component wear and oil seal deterioration which is not provided by lubricants meeting the requirements of API GL-1 through to GL-5. 

If the ecolabelling scheme is extended to other types of lubricants such as engine oils, then there will need to be a recognition that different criteria, as far as prohibited substances, may be needed and that performance may be a major factor in contributing to environmental impact. Fit for purpose may not be good enough. The aim must be to establish a level of performance that does not represent a deterioration in standards and to have a means for discriminating between products. 

All bearings in the CRD are precision ball bearings which are lubricated with a special grease that has been developed for this type of low radiation and moderate temperature application. This lubricant, which is also used in the harmonic drive components, has been subjected to long duration tests in helium. Therefore, the possibility of bearing or speed reducer seizure from deterioration of the lubricant is minimized. Relubrication of these components at regular maintenance intervals is planned. 

Free-radical chain inhibitors are of considerable economic importance. The term antioxidant is commonly applied to inhibitors that retard the free-radical chain oxidations that can cause relatively rapid deterioration of many commercial products derived from organic molecules. Their function is particularly crucial in such organic materials as lubricating oils, which must remain chemically inert at relatively high temperatures. The basic chain mechanism for autoxidation is ... 

The deterioration of polymer properties by ESC has been studied for several decades. But the actual mechanism is not certainly established (Hansen 2002). It is believed that in the presence of the stress, the active fluid causes local plasticization that generates crazes and eventually catastrophic cracks. The ultimate result in many cases is brittle fracture, even in normal ductile polymers like polyethylene, ABS, and polycarbonate. Since failure by ESC can be induced by environmental fluids like cleaning agents and lubricants and the mechanical stress can be the residual (molded-in) stresses, it was considered to be a silent killer (Sepe 1999). 

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