Influence of load and lubricants on EHD film thickness and rolling-contact fatigue lives of AISI 52100 steel balls

This work has evaluated the influence of load and type of lubricant on the thickness of the elastohydrodynamic (EHD) film and the rolling-contact fatigue lives of AISI 52100 steel balls. The lubricants studied have various viscosities and included two mineral oils and five synthetic oils from three families. Firstly, the central film thickness was determined in order to predict the lubrication regime. The stress—number of cycles fatigue curves were then calculated by means of Weibull plots, and the fatigue mechanism was evaluated. The test machine used for the analysis was a Seta-Shell 1980 four-ball EP lubricant tester. The 12.7 mm diameter test balls were made from a single batch of carbon-vacuum-deoxidised AISI 52100 steel with hardness RC65. Elastohydrodynamic film thickness estimation was carried out using pressure—viscosity coefficients (a). In this study, to calculate (X), a new interferometric technique, ultrathin film interferometry, was employed to measure the film thickness. A practical method was developed for evaluating EHD, mixed film, and solid lubrication processes. Micrographic mapping and energy dispersive spectroscopy (EDS) were used to analyse the rolling track of the test balls.     

抗磨添加剂对不同服役阶段润滑油摩擦学性能的影响

采用黏度测试仪测定新油及3种不同服役阶段润滑油的黏度,采用UMT-II摩擦磨损试验机考察其摩擦学性能,并同时考察3种在用润滑油添加抗磨添加剂后的摩擦学性能。研究结果表明:润滑油的黏度随着运行里程数的增加呈现先降后增的趋势;随润滑油运行里程数的增加,润滑油的摩擦因数增大,导致试验钢球的磨损量也增加;抗磨添加剂对不同服役阶段的润滑油的抗磨性能影响程度不同,在磨合磨损期和正常磨损期,加入抗磨添加剂后并不能改善润滑油的抗磨性能,而在异常磨损期,抗磨添加剂的加入可较好地改善润滑油的抗磨性能。     

Rolling contact fatigue life of AISI 52100 steel balls with mineral and synthetic polyester lubricants with PTFE nanoparticle powder as an additive

This work evaluates the rolling contact fatigue life of AISI 52100 steel bearing balls with mineral and synthetic oil, with and without additive, using a four-ball tester. IP 300/87 was applied with a total load of 600 kg (corresponding to a maximum Hertz stress of 8.709 MPa). SN-350 (a neutral mineral solvent) and TMP-05 (an environment friendly synthetic polyester) of the same viscosity were additivated with PTFE nanoparticle powder in different percentages. The total test time for each specimen was recorded and processed on Weibull probability plots. L₁₀ and L₅₀ are given for pure base oils and oils additivated with 1, 3 and 5 wt.% of PTFE powder. The results point to an increase in the fatigue life when additive-containing oils were used. In order to provide some understanding of the protection mechanism of the additive, the contact angle and the influence of the surface wettability on the lubricant unctuosity were analysed. Scanning electron microscopy and LINK techniques were used to study pitting, crack propagation, the chemical influence of additive and fluorine content.     

Evaluation of the antiwear performance of aged oils through tribological and physicochemical tests

Extending automotive engine drain intervals requires a good knowledge of the antiwear aspect of lubricant performance, which is often closely linked to the oxidative degradation of the oils. In this paper, we report the physicochemical analyses and tribological tests carried out on several oils oxidised by laboratory oxidation tests at different stages. An interesting correlation was found between the antiwear efficiency and some characteristics of the eletrochemical impedance spectra of such oxidised lubricants. A promising way of understanding the mechanisms of wear mitigation by aged engine oils is proposed.     

Investigation of subsequent deposit growth on pre‐existing lubricant deposits: a substitutional growth model

The Penn State Micro‐Oxidation (PSMO) test was used in an inverse manner to pre‐cover metallic pan surfaces with polymeric, transitioning and carbonaceous films. These pre‐coated pans were then used as the initial test specimen/surface upon which fresh lubricant samples were aged. The effects of pre‐deposits of varied ages were gauged against the baseline of a virgin metallic surface to decouple the lubricant‐deposit system towards resolving their effect upon further deposit growth. From such data, a uniform deposition model describing deposit formation and aging was developed. Chemical characterisation of PSMO deposits by Fourier transform infrared‐attenuated total reflectance and energy‐dispersive X‐ray spectroscope analyses provide additional supporting evidence of changes in chemical bonding (alkyl C–H and carbonyl C=O bond stretching vibrations) and composition (C‐ and O‐atom content) as the deposits undergo deoxygenation and dehydrogenation reactions. Across different aged oils and films, the substitution tests show a declining activity towards mass deposition with film age, interpreted as decline in reactivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Nanolubrication: Characterization of patterned lubricant films on magnetic hard disks

Patterned lubricant films on magnetic hard disks offer potential advantages in controlled bonding sites, higher average shear strength, and longer durability. However, since the lubricant film thickness is at 1 or 2 nm, characterization of the pattern is difficult. Normal atomic force microscopic techniques can only image very small area in the nanometer range and the sharp tip can potentially modify the pattern. A wide area optical technique is needed to characterize the patterns. This paper examines patterned lubricant film using an optical surface analyzer (OSA) to image the bonded phase and mobile phase of an alcohol functionalized perfluoropolyether (PFPE) on magnetic hard disks. The phase shift signal and reflectivity intensity of the polarized light spectra provide clear optical images of the lubricant film at nanometer thickness. Optical images were successfully obtained before and after the buffing process and the ramp load and unload (L/UL) testing. Results of 100% bonded, 100% mobile, and 20% zigzag patterned lubricant films confirm that the patterned lubricant films can control the bonded/mobile ratio of such films better.     

Improvement of thermooxidative stability of non‐edible vegetable oils of Indian origin for biodegradable lubricant application

For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant‐related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non‐edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non‐edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd.     

Pulsed field gradient (PFG) NMR spectroscopy: An effective tool for the analysis of mixtures of lubricating oil components

In the presently reported work, the multinuclear two‐dimensional (2D) diffusionordered nuclear magnetic resonance (NMR) spectroscopy (DOSY) technique based on the pulsed field gradient (PFG) has been used in experiments to analyse mixtures of lubricating oil components. One‐dimensional (1D) PFG experiments have also been used to simplify and edit the NMR spectra of the mixtures. Such experiments provide a clean spectrum of the highest molecular weight (slower diffusing) component by eliminating the signals of lower molecular weight (faster diffusing) components, without any prior physical separation. These pulsed field gradient experiments not only facilitate the separation of resonance signals of different components, but also lead to their subsequent identification, and provide information about the number and structure of components in a mixture. Some examples of our initial efforts to establish 1D and 2D PFG‐based NMR experiments for the analysis of mixtures of lubricating oil components are given and assessed to illustrate the potential applications of such techniques in the field of lubricating oils.     

Experimental evaluation of palm oil as lubricant in cold forward extrusion process

Today, vegetable oil is much desired for its application as a lubricant in metal forming processes, because it is a renewable resource and has high biodegradability compared to mineral oil. According to the Organization for Economic Cooperation and Development for the European Union 301C (OECD) testing method, the biodegradability levels of vegetable oils are better compared to petroleum-based lubricants. Palm oil is used more often than other vegetable oils. Therefore, palm oil has the potential to fulfill the demand for vegetable-based lubricants. The purpose of this paper is to evaluate the viability of palm oil when used as a lubricant in cold work such as the forward plane strain extrusion process. The performances of palm oil were compared with additive-free paraffinic mineral oil. Experimental work with a plane strain extrusion apparatus with a symmetrical workpiece was carried out at room temperature. The material of the workpiece is annealed pure aluminum A1100. The visioplasticity method was used to calculate the velocities and effective strain in the deformation zone of the workpiece. The results obtained from the experimental work showed that palm oil has satisfactory lubrication performances, as compared to paraffinic mineral oil, and has advantages in reducing the extrusion load.     

Influence of gelatin and bovine serum lubricants on ultra-high molecular weight polyethylene wear debris generated in in vitro simulations

Ultra-high molecular weight polyethylene (UHMWPE) wear debris induced osteolysis has a major role in the late aseptic loosening and ultimate failure of total hip replacements (THR). Clinically relevant in vitro simulations of wear are essential to predict the osteolytic potential of bearing surfaces in artificial hip joints. Newborn calf or bovine serum has been accepted as a boundary lubricant for such in vitro tests, but its biological stability has been questioned. This study compared the wear factors, number of wear particles and levels of microbial contamination produced in bovine serum and a gelatin-based lubricant. The wear factors produced by the two lubricants were not significantly different, however the wear debris morphology produced was substantially different. The bovine serum became contaminated with micro-organisms within 28 h, whereas the protein-based lubricant remained uncontaminated. The results showed that bovine serum was not a stable boundary lubricant. They also showed that although the wear factors for the two solutions were not significantly different, the protein-based lubricant was not a suitable alternative to bovine serum because the wear debris produced was not clinically relevant.     

Viscosity and working efficiency analysis of soybean oil based bio-lubricants

This article presents significant data about viscosity and working efficiency analysis for developing the soybean oil based bio-lubricants. A suitable viscosity or viscosity index (VI) plays a very important role in a lubricant, which can avoid collision and rubbing between components of mechanical devices in work as well as optimize working efficiency of a machine. In general, low friction between devices can increase working efficiency of a machine, but low viscosity of a lubricant will easily cause collision and rubbing between components of mechanical devices in work. A too viscous lubricant also requires a large amount of energy to move, but a too thin lubricant will easily cause rubbed devices and increased friction. To replace the mineral oils and syntholubes, the soybean oil is recently become one of the most actively studied oils due to its eco-friendly organic property and lower cost. This work used mixtures of the original soybean oil, the epoxidized soybean oil, and the hydrogenated soybean oil as the base oils. Applications are focused on developing engine bio-lubricants. The results show that the epoxidized soybean oil has extremely large viscosity in comparison with the engine lubricants as well as the original soybean oil, whereas the hydrogenated soybean oil is clearly opposite. This viscosity analysis offers good informations to fit viscosity of the engine lubricants by mixing the three soybean oils as base oils.     

Scuffing detection of TU3 cam–follower contacts by electrostatic charge condition monitoring

The increasing costs associated with lubricant development and qualification has driven the need for condition monitoring techniques to be deployed on test engines to maximise information gained from expensive testing programmes. This paper discusses the results from a motorised TU3 engine with electrostatic sensors focused on the cams. System characterisation tests and an oil starvation test were used to decouple charge mechanisms associated with a lubricated wear test, accelerated through the use of carbon black. Cross-correlation of various charge signal processing techniques, scanning electron microscopy and profilometry revealed that tribocharging dominated during running-in/mild wear and contact potential difference (CPD) dominated during the progression of severe adhesive wear. Tribocharging (the charge generated by a low conductivity fluid) has been shown to be affected by oil temperature, cam rotation speed and the presence of charged species within the lubricant. Contact potential differences was principally generated by the work function difference between oxidised and nascent regions associated with adhesive wear on the cam surface. Electrostatic monitoring which is sensitive to lubricant chemistry and wear, and can be implemented in an industry standard engine, has great potential for the lubricant industry.     

Tribological Features of Refined,Deodorized, and Bleached Palm Olein with Mineral Oil Blend

Vegetable oils have been investigated to replace petroleum-based lubricants due to their environmentally friendly characteristics, and these oils have become an important source of biolubricants. For the purpose of ensuring the ability of vegetable oils as a neat or partial biolubricants, image processing techniques were employed to explore the tribological characteristics of vegetable oil with a mineral oil blend. Refined, bleached, and deodorized palm olein blended with mineral oils was investigated using a four-ball tribotester and design of experiments with volumetric blend ratios of 20 to 80%. An optimized value E53.11/RB46.89 was obtained from the investigation, in compliance with ASTM D4172 standard. From the results, the E53.11/RB46.89 blend reduces the friction coefficient and wear scar diameter as well as the material lost in comparison with neat mineral oil. It is concluded that the E53.11/RB46.89 blend could be a potential partial biolubricant due to its negligible negative impact on wear and it provides satisfactory performance as a lubricant.     

Study of some non-edible vegetable oils of Indian origin for lubricant application

Due to growing environmental concerns, eco-friendly processes and materials have become one of the key interests of research and in the area of tribology, natural esters are gaining popularity as lubricants. Natural esters are being used in many applications as eco-friendly lubricant base. In Europe, canola/rapeseed oil and sunflower oil are mainly used, whereas in the USA, soybean oil is in use for formulating environmentally friendly lubricants. Native and genetically modified high oleic varieties of these oils are being widely used. In the Indian scenario, since the above-mentioned oils are scarcely available for industrial applications, there is a need to look for other viable alternatives. Some candidate non-edible vegetable oils of Indian origin were selected which were unexplored or less explored in the field of lubricant application, and their suitability in lubricant application focusing mainly on physico-chemical characteristics, thermo-oxidative stability and lubrication characteristics was studied. These oils were found to be promising candidates for application in lubricants in view of their physico-chemical characteristics and better thermo-oxidative and hydrolytic stability. Copyright © 2007 John Wiley & Sons, Ltd.     

Anti-wear Chemistry of ZDDP and Calcium Borate Nano-additive. Coupling Experiments, Chemical Hardness Predictions, and MD Calculations

Zinc dialkyl dithiophosphate (ZDDP) is an anti-wear additive for steel surfaces currently used in engine oils. Its anti-wear performance (against abrasion) is due to tribochemical reaction of zinc polyphosphate with abrasive metal oxides nanoparticles, under the combined effect of pressure and shear. However, phosphorous and sulfur are nocuous for environmental issues. Borates are possible candidates to replace phosphates in engine oils. Friction reduction with borates is found to be better than ZDDP but the anti-wear efficiency of borates is lower. In this work, we show how chemical hardness model and computer simulation can explain these different behaviors. Also we show that molecular dynamics is able to predict accurately behavior of mixtures of phosphates and borate. Results show that mixtures of additives with a P:B ratio slightly above unity can be a good compromise to have both good tribological performance and low content of phosphorous and sulfur in the lubricant.     

Increased total knee arthroplasty ultra-high molecular weight polyethylene wear using a clinically relevant hyaluronic acid simulator lubricant

In this study, osteoarthritic and periprosthetic synovial fluid samples were rheologically and biochemically compared to develop a hyaluronic acid (HA) supplemented bovine serum (BS) lubricant that mimicked the properties of human joint synovial fluid. The effect of this BS + HA lubricant (50 per cent bovine calf serum + 1.5 g/l HA) on the wear rate of ultra-high molecular weight polyethylene (UHMWPE) during a total knee replacement wear test was then investigated. In conjunction with biochemical similarities, the rheological analysis showed that the BS + HA lubricant viscosity was not statistically different to aspirated total knee arthroplasty (TKA) revision joint fluid viscosity over a range of physiologic shear rates. Gravimetric results at 5 million wear testing cycles showed that the BS + HA lubricant produced an average of 6.88 times more UHMWPE wear than 50 per cent bovine serum lubricant alone. The BS + HA lubricated CoCr femoral component surfaces revealed pitting and surface roughening that was not observed using standard bovine serum only lubricants, but that was similar to the metallic surface corrosion observed on in vivo CoCr femoral component retrievals. These findings support the hypothesis that the addition of HA to simulator lubricant is capable of producing CoCr femoral component surface damage similar to that observed in vivo.     

FT-NMR and FTIR applications in lubricant distillates and base stocks characterisation

Lubricant distillates undergo different stages of refining in order to produce the quality required of base stock for lubricating oil formulations, incorporating different additives in various doses. It is essential to monitor the degree of refining at different stages and additive response in base stocks, using fast and accurate techniques. FT-NMR and FTIR techniques offer a new dimension to the monitoring and characterisation of lubricant distillates and base stocks. In the present paper, an attempt is made to demonstrate the application of these techniques to deriving some average structural parameters and to correlate them with various physico-chemical characteristics of lubricant distillates and base stocks. These correlations could be used to optimise various process parameters during the refining of lubricant distillates. If the process parameters are constant, such correlations could be used to predict the quality of the base stocks obtained from any change in the composition of the lubricant distillates. Various applications of FTIR in base oil characterisation and its processing are also reviewed.     

The effect of water on the acid-base properties of new and used IC engine lubricating oils

The absolute values of total base number (TBN) were determined for several sets of both fresh and used engine oil samples. Basic and acidic compounds from these oils have been extracted into water, 7% sea water and ethanol-water (1:1, v/v) mixtures. The extracts have been determined by potentiometric titration as pH extracts, TBN (water extract) and alkalinity. The oil formulations are not resistant to the presence of water but basic additives in fresh oil are more resistant than those for used oils. The percentage of TBN extractable into water significantly increases with service life. The presence of significant amounts of water in lubricating oil is serious and should form part of any lubricant condition monitoring system. The case is argued for both the use of dehydration canisters in oil systems and for the development of a new method of water content determination for used formulated lubricating oils which is quick, accurate and suitable for automated condition monitoring systems. The pH of aqueous extracts for condition monitoring of lubricating oils is shown to be only meaningful for TBN values of 2 or less.     

Tribological Study of a Tetrahedral Diamond-Like Carbon Coating under Vegetable Oil–Based Lubricated Condition

Maintaining a clean environment is the major concern of industries that produce fuel and lubricants for automotive applications. Thus, vegetable-based oils are being explored for the preparation of biobased lubricants because of their biodegradability and nontoxicity. Despite their low thermal stability, vegetable oils show better tribological characteristics than mineral oils. Nonetheless, the thermal stability of vegetable oils could be improved by transesterification. In this study, three vegetable-based oils (sunflower, palm, and coconut) were used to investigate the tribological properties of ta-C diamond-like carbon (DLC) coating under DLC–steel contact condition. A BICERI ball-on-a plate tribotesting machine was used to conduct experiments. During the experiment, test contacts of tribopairs lubricated with sunflower oil exhibited better tribological characteristics than those using coconut oil as a lubricant.     

Total vegetable oil greases

A grease has two major constituents, namely, a lubricant, that performs the function of lubrication; and a gellant, that provides a solid continuous phase, occludes the lubricant, and gives apparent physical structure to the grease. Generally, the gellant is 5–30% and the lubricant 65–90%, additives and fillers making up the rest. In conventional greases, the gellant is a vegetable oil soap, and the lubricant is a liquid oil of petroleum origin or is a synthetic. Such greases have limited biodegradability, because the major constituent, i.e., the lubricant, is normally not biodegradable. In total vegetable oil grease, both the gellant and the lubricant are derived from vegetable oils, giving a grease of potentially high eco‐compatibility. Esters, dibasic acid esters, and alkylated esters of vegetable oil are known to be high‐quality lubricants. These can be used with soap stocks prepared from vegetable oils to give a grease of total vegetable oil origin. The vegetable‐oil based lubricants and soaps are prepared separately and combined in appropriate proportions to give a grease of the required specifications. Alternatively, esterification and saponification can be carried out simultaneously to give a grease of the desired specifications, where an alkali will be the catalyst for esterification, and reactant for saponification. In this paper, the process parameters, and kinetics of these simultaneous reactions are discussed. The results of experimental evaluation of some of these greases are also presented.