Lubricant Degradation Research Articles

The Development and Implementation of a Program to Improve the Performance of Reactor Trip Breakers after Salem

A program to improve the performance of reactor trip breakers after Salem is described. It consists of a maintenance program, a hardware program, and a followup program designed to correct the age-related lubrication degradation problem identified as a common mode failure mechanism by post-Salem investigations.

The Development and Implementation of a Program to Improve the Performance of Reactor Trip Breakers After Salem

A program to improve the performance of reactor trip breakers after Salem is described. It consists of a maintenance program, a hardware program, and a followup program designed to correct the age-related lubrication degradation problem identified as a common mode failure mechanism by post-Salem investigations.

The Reaction of Perfluoropolyalkylether Oil with FeF3, AlF3, and AlCl3at Elevated Temperatures

The interaction of perfluoropolyalkylether (PFPE) oil with ferric fluoride (FeF3) and other Lewis acids at elevated temperatures under inert atmosphere was investigated to determine whether the reaction results in lubricant degradation. At 35°C, ∼25°C below the onset of thermal degradation, PFPE'S reaction with FeF3 yields acyl fluoride and ketone degradation products and also a decrease in the oil's number-average molecular weight. In the presence of small quantities of water, the acyl halide products hydrolyze, resulting in carboxylic acids. The oil's reaction with aluminum fluoride at 350°C and aluminum chloride at 200°C also causes it to degrade measurably. The results indicate that PFPE oil can degrade at estimated bearing asperity contact temperatures in the presence of FeF3.

The DSC cell—a versatile tool to study thermal-oxidative degradation of lubricants and related problems

The versatility of a differential scanning calorimetry (DSC) cell in studying thermal and/or thermal-oxidative degradation of lubricants is shown using ester based aviation turbine oils as an example. The following applications are discussed: 1. quality control of used oils by pressure differential scanning calorimetry (PDSC); 2. influence of metal catalysis on oil degradation; 3. identification of volatile degradation products by PDSC—gas chromatography (GC)—mass spectrometry (MS) via a TENAX GC trap.

COBRA analysis of laboratory degraded synthetic turbine engine lubricants

AbstractThe Complete Oil Breakdown Rate Analyser (COBRA) is an instrument that detects ill‐defined electrochemical changes in synthetic ester‐based lubricants as those fluids are oxidatively degraded. In several Air Force field applications, the COBRA has proven useful in determining lubricant condition or in identifying abnormally operating engines in which excessive lubricant degradation occurred. In laboratory analyses of field samples from programmes involving several engine types, correlation of COBRA with total acid number or viscosity was poor, but consumption of one or more oxidants appeared to be consistently associated with high COBRA values. To determine if such correlation exists, this study was conducted to evaluate laboratory degraded synthetic lubricants. Results of the laboratory study indicate that COBRA increases rapidly after depletion of typical antioxidants, increases with higher total acid numbers and trends with viscosity data. The poor correlation observed between COBRA and total acid number and viscosity for field samples is attributed to differences in for example engine breather designs, and oxidative environments, which can significantly alter the properties of the residual engine lubricant analysed by COBRA. Due to the presumed test apparatus and engine design dependence of COBRA data, COBRA correlation must be established for each application.

Lubricant Degradation and Wear V. Reaction Products of a Zinc Dialkyldithiophosphate and Peroxy Radicals

Previous work has shown that reaction of zinc di-n-octyldithiophosphate with peroxy radicals in laboratory experiments led to products which were ineffective as antiwear agents. These products have now been identified and a material balance obtained by the application of several analytical techniques. The principal reaction product was the disulfide species tetra-n-octylthioperoxydiphosphate. This compound was synthesized, tested, and found to be less effective than zinc di-n-octyldithiophosphate as an antiwear agent.

Chemical Analysis of Hydrocarbon Grease from Spin Bearing Tests

The rotor bearing running torque levels of certain spin bearing units were found to increase significantly during extended life testing. Samples of the greases from these tests were analyzed to determine if lubricant degradation was linked with the increased torque levels. By means of chromatographic and spectroscopic techniques, we were able to determine that oxidation of some of the greases had occurred and that the oxidative degradation was most easily observed in the soap-thickener portion of the grease. A correlation between the disappearance of the fatty acid salts and the appearance of degradation products was observed. Polymerization of the greases war observed in all samples. We also determined that the grease degradation was symptom of adverse mechanical condition in the bearings and not the primary cause of mechanical problems. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in Washington, D.C., October 5–7, 1982

Kinetic approach to engine oil. 1. Analysis of lubricant transport and degradation in engine system

Kinetic approach to engine oil. 1. Analysis of lubricant transport and degradation in engine system

Hydrogen embrittlement of a stainless ball bearing steel

Ball bearing steels are susceptible to hydrogen embrittlement caused by lubricant degradation. It has been shown that hydrogen embrittlement of 440C stainless steels is associated with the existence of M 7C 3 carbides. The behaviour of M 7C 3 carbides during hydrogen embrittlement was investigated by classical rotating beam fatigue and tensile tests of specimens into which hydrogen had been introduced by cathodic charging. The effects of the current density, the time and the stress of charging and the relaxation time between charging and mechanical testing were assessed. The hydrogen embrittlement was characterized by using tritiated water. High resolution autoradiography and scanning electron microscopy were used to determine the location of the hydrogen in the martensitic matrix relative to the M 7C 3 carbides and to the interfaces between the M 7C 3 carbides and small M 23C 6 carbides.

Lubricant Degradation and Wear III. Antioxidant Reactions and Wear Behavior of a Zinc Dialkyldithiophosphate in a Fully Formulated Lubricant

Earlier model systems studies have shown that the products of the antioxidant reactions of a zinc Dialkyldithiophosphate (ZDTP) with peroxy radicals are ineffective as antiwear agents. Now a similar study has been carried out with a fully formulated synthetic hydrocarbon/ester engine oil aged in fleet tests. The results are consistent with those reported earlier and indicate that the previous conclusion can be extended to a fully formulated lubricant in service. It was found that base stocks containing esters can exhibit increased wear upon addition of ZDTP. However, this can be suppressed by other oil additives. A study of the wear behavior of admixtures of a ZDTP and a hindered phenol reacted with peroxy radicals showed that the hindered phenol did not protect the ZDTP from degradation by antioxidant reactions, a result consistent with analysis of IR spectra presented in the accompanying paper (1). Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

Molecular Degradation of Lubricants in Sliding Elastohydrodynamic Contacts

The extent of lubricant degradation in a sliding elastohydrodynamic contact has been investigated. The lubricant was subjected to peak Hertz pressures of approximately 109 N/m2 and average shear rates of 106 to 107 s−1. Hydrocarbon lubricants, bulk polymers and polymer containing hydrocarbon solutions were examined. Small samples (10−8m3) of test lubricant were extracted from the entrance and exit regions of the EHD contact. These samples were then analyzed to determine alterations in the molecular weight distribution. In addition, a microcapillary viscometer was developed to determine viscosity changes. Degradation resulting in up to a 70 percent viscosity loss was found in fluids which had molecular weights of over 1000. High degrees of correlation were found between molecular weight loss, viscosity loss and the energy dissipated in the contact.

Paper 3: Influence of the Atmosphere on the Endurance of Some Solid Lubricants Compared at Constant Layer Thickness

Friction and endurance of five powdered solid lubricants were studied on a pin and ring machine. Simple methods were developed to produce layers of constant thickness (1 μm). The ease of rubbing-in varies widely with structure and with particle size. Ease of layer formation is completely unrelated to endurance: NbSe2 is rubbed in readily, but is rubbed off directly on loading. Layers of constant thickness from MoS2, WS2, and WSe2 powders behave roughly similarly, but MoS2 has a much longer life. The lubricant films are gradually destroyed by oxidation and therefore endurance increases in the series oxygen, air, and nitrogen (with 100 p.p.m. oxygen). The process of lubricant degradation is the same for the synthetic crystalline powders as found previously for MoS2: blistering of the run-in film surface on release of loading. Oxygen accelerates this process, leading finally to descaling and the onset of seizure. The endurance of MoSe2 goes through a pronounced maximum in oxygen–nitrogen mixtures. It is suggested that oxygen plays a dual role, first by enhancing film formation, and second by causing oxidative embrittlement of the lubricant.

Paper 4: Effect of Environment on Bearing Performance

The life of bearings, components which allow relative motion between members of a mechanism, is greatly dependent upon the properties of the materials of construction, but the nature of the lubricant and the environment can have a dominant effect on the incidence of failure. Lubricant contamination and degradation can be deleterious. Additives which impart or reinforce some lubricant property desirable for a specific mechanism may be detrimental to other moving mechanisms. Water in lubricant, not adequately additive fortified, may be harmful. Solid additives such as MoS2 can be beneficial if used correctly. Incompatibility with other additives may have adverse effects. The role of material properties and surface treatments in counteracting deleterious lubricant effects is discussed. Aspects of specific environmental effects as well as failure mechanisms in general are dealt with.

Thermally Activated Seizure of Angular Contact Bearings

Equations have been developed relating friction-power to bearing element temperatures for the particular case of prelubricated or lightly lubricated ball bearings. An expression is derived for the change in relative dimensions of an angular contact bearing, as determined by the temperature gradient across the bearing. A second expression is found for the accommodation of the bearing to expansion, this accommodation resulting from elastic deformation and changes in contact angles. A comparison of these relationships reveals that unstable operating conditions may occur and lead to sudden uncontrollable increases in contact loads. These regions of unstable operation may occur as a result of lubricant degradation or bearing wear, as well as combinations of operating speed and housing dimensions.

Research Report 8: Current Status of Joint Lubrication

Properties of synovial fluid and cartilage are reviewed and some thought is given to the nature of joint lubrication. It does appear, at this stage, that neither the classical hydrodynamic theory of lubrication nor the boundary lubrication can permit an adequate description of the mechanism of joint lubrication; a possible solution lies in application of the elastohydrodynamic theory of lubrication, although this theory is not yet advanced enough to handle the total complexity of joint lubrication. It is suggested that, in principle, joint lubrication depends on the existence of thixotropic and elastic (normal stress phenomenon) fluid between the articular surfaces, that the area of the load-carrying film depends on the elasticity and resiliency of cartilage, and that the latter shows most variable, time- and load-dependent rheological behaviour. Pathological changes in synovial fluid leading to the change of its rheology to Newtonian, will result in a damage to the articular surfaces; on the other hand, a presence of a healthy synovial fluid per se is not sufficient to maintain an efficient lubrication. Resiliency of cartilage is responsible for the existence of elastohydrodynamic conditions; a degeneration of cartilage will lead to boundary lubrication and mechano-chemical degradation of synovial fluid. Complexity of the problems requires multi-disciplinary collaboration.

Degradation of high temperature lubricants and metals by fluoroelastomers : John J. Murray and Eugene P. Scanlan. ASLE Trans., 4 (1961) 220–226

Degradation of high temperature lubricants and metals by fluoroelastomers : John J. Murray and Eugene P. Scanlan. ASLE Trans., 4 (1961) 220–226

Degradation of High Temperature Lubricants and Metals by Fluoroelastomers

The structural and functional components of high temperature lubrication systems are metal assemblies, lubricants and elastomeric seals. How do combinations of these effect each other under the varying conditions of temperature and atmosphere? This question is often presented to the manufacturers of seals and of lubricants. A laboratory method for determining the answer is presented here. This method exposes combinations of lubricant, metal and elastomer to varying atmospheric conditions at a constant temperature. The degrading effects of temperature alone on each component of a lubricating system are known. This work was prepared to show that the proper selection of the sealing system components can prolong the life of the system.