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The feasibility of CuP as a multifunctional additive in lithium grease was evaluated for the first time. The experimental results indicated that the CuP significantly enhanced the friction reduction, antiwear properties, extreme pressure capabilities, and antimicrobial characteristics of lithium greases. The SRV test results suggested that the optimal tribological properties were obtained by adding 3 wt% of CuP to lithium greases, resulting in a decrease of the friction coefficient and wear volume by 28.25% and 34.98%, respectively. The four-ball results confirmed that the extreme pressure performance of the lithium grease with 3 wt% CuP was enhanced by a factor of 3.17. The bacterial inhibition rate of lithium grease with 3 wt% CuP was higher than 99.98%. The lubrication mechanism and antimicrobial mechanism was explained.

Extreme Pressure (EP) additives are commonly used in lubricants to reduce wear and prevent seizures at high temperatures and pressure. In terms of their mechanism, these build up a film on the surface with chemisorption. This film efficiently prevents metal-metal adhesion. Industrial statistics show that extreme pressure additives are mostly used in metalworking fluids, lubricating greases and engine oils. Sulfurized vegetable oils can be used as EP additives of lubricants. This type of EP additive is ashless, derived from renewable sources and has a lesser negative effect on the environment compared to those that are not derived from vegetable sources. Several technologies for the preparation of additives have been developed, of which the dark sulfurization process has been studied. Several physical and lubricating properties of the obtained additives have been investigated, based on which, it is possible to produce additives with favourable viscosity values and low copper corrosion grade. [ABSTRACT FROM AUTHOR]

The performance loss in industrial equipment due to friction and wear is one of the critical concerns among researchers. This drives the need to develop lubrication fluids that reduce friction to provide extended performance. The global sustainability movement drives the research towards novel bio-based oils to aid in lubrication. This study analyses the dispersion stability, tribological behaviour and antiwear properties of zinc oxide (ZnO), titanium dioxide (TiO2) and molybdenum di sulphide (MoS2) nanoparticles as an additive in hazelnut and sunflower oils. The viscosity index and flash point of the prepared nano lubricants were analyzed. The tribological test conducted on four ball tester resulted in a 12.6% and 35.8% reduction in coefficient of friction (COF) for 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil. The corresponding wear scar images were analysed. The extreme pressure (EP) test resulted that 1% MoS2 in sunflower oil exhibiting improved performance as it sustained a 1800N load. The kinematic viscosity of the 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil had an improvement against others. Therefore, infusion of nano additives in bio-oils offers enhanced tribological properties foreseeing sustainability in applications.

Abstract Lubricating approaches involving nanoparticles have a significant role in reducing friction and wear. Reducing friction is crucial for preserving energy, minimizing emissions, and protecting the environment. The present experimental study investigates green nano-lubricants prepared by dispersing various concentrations of CaCO3 nanoparticles in jojoba oil. The aim of the study is to assess the usability of a bio-sourced alternative nanolubricant to depleting conventional lubricants. The role of nanoparticle concentration and thermo-physical properties in improving the lubrication properties of jojoba oil was thoroughly investigated in the present study. The anti-wear and extreme-pressure behavior of jojoba oil dispersed with CaCO3 nanoparticles were evaluated as per the ASTM D4172 and ASTM D2783 test standards. The coefficient of friction, wear scar diameter, last non-seizure load, initial seizure load, weld point load, and load wear index of each sample were assessed. Compared with pure jojoba oil, the addition of CaCO3 nanoparticles in jojoba oil revealed remarkable anti-wear and extreme-pressure properties with significant improvements in the last non-seizure load, initial seizure load, weld point load, and load wear index, the average friction coefficient and the average wear scar diameter of the steel balls decreased by as much as 34.1% and 40.2%, respectively.

The performance loss in industrial equipment due to friction and wear is one of the critical concerns among researchers. This drives the need to develop lubrication fluids that reduce friction to provide extended performance. The global sustainability movement drives the research towards novel bio-based oils to aid in lubrication. This study analyses the dispersion stability, tribological behaviour and antiwear properties of zinc oxide (ZnO), titanium dioxide (TiO2) and molybdenum di sulphide (MoS2) nanoparticles as an additive in hazelnut and sunflower oils. The viscosity index and flash point of the prepared nano lubricants were analyzed. The tribological test conducted on four ball tester resulted in a 12.6% and 35.8% reduction in coefficient of friction (COF) for 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil. The corresponding wear scar images were analysed. The extreme pressure (EP) test resulted that 1% MoS2 in sunflower oil exhibiting improved performance as it sustained a 1800N load. The kinematic viscosity of the 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil had an improvement against others. Therefore, infusion of nano additives in bio-oils offers enhanced tribological properties foreseeing sustainability in applications. [ABSTRACT FROM AUTHOR]

Ammonia is a prospective zero-carbon-emission fuel for use in large marine diesel engines. Current research focuses on several technical aspects, such as injection strategies or exhaust gas aftertreatment options, but investigations regarding the impact of ammonia on engine oil degradation are largely absent from the literature. This study provides a methodology with which to evaluate this phenomenon via artificial oil alteration. By using an admixture of various contaminations to air, such as ammonia and its partial combustion product nitrogen dioxide, their respective impacts on chemical oil degradation were assessed. Subsequently, the lubricating performance of altered oils was investigated, with a focus on corrosion properties, deposit formation, and load-bearing capability. Although the application of a stoichiometric ammonia–air mixture resulted in less pronounced thermo-oxidative degradation compared to alteration with neat air, static and dynamic deposit formation as well as corrosion properties and load-bearing capability were severely impacted by the presence of ammonia. On the contrary, nitrogen dioxide contamination resulted in higher oxidation and acidification of the oil, but altered samples performed considerably better than ammonia-altered aliquots in terms of coking tendencies, corrosivity, and load bearing. [ABSTRACT FROM AUTHOR]

Extreme pressure (EP) and antiwear (AW) additives are necessary for boundary lubrication. However, their mechanisms and physical and chemical properties remain unclear. EP and AW additives were reviewed to fill gaps in theoretical and industrial applications. Compounds containing chlorine, sulfur, and phosphorus elements were first used in boundary lubrication because of thermal reaction with metal to form film characteristics. First, the mechanisms of traditional EP and AW additives were analyzed, the physical and chemical properties were compared, and properties affecting factors were studied. Traditional EP and AW additives are not environmentally friendly, but nanoparticle EP and AW additives are excellent substitutes. The mechanisms of nanoparticle EP and AW additives were summarized. The influence of nanoparticle structure parameters, concentration, and media polarity on properties was studied. Second, the influence law of non-polar chain length on traditional EP and AW additives was revealed. The improvement interval of traditional EP and AW additives on the performance of the base fluid was determined. The structural advantage of low crystallinity onion-like and multilayer sheet-like low wrinkle effect of nanoparticles was explained. The particle size design principle attached to the surface roughness and size-dependent melting inhibition mechanism was established. The influence of concentration and media polarity on nanoparticle properties was obtained. Finally, the research of minimum amount matching database and mathematical selection model for traditional EP and AW additives and the molecular dynamics analysis of surface-modified nanoparticles and the development of green general-purpose additives based on molecular design are prospected. [ABSTRACT FROM AUTHOR]

Rail lubrication is vital in determines the friction, wear and noise level in the wheel and rail contacts. In general, the primary function of a rail curve grease is to minimize friction between the contact as well as to protect side wear of rails on a curved track. In this study, three commercially applied railway greases were identified and the wear and friction behavior, as well as the load-carrying ability, were investigated. Before that, the grease's physiochemical properties in terms of the consistency and drop point, as well as the element content, were also examined. The tribological investigation of the greases was also carried out using four-ball wear tester. In this test, the wear preventive (WP) and extreme pressure (EP) properties of the grease were measured under sliding actions between the balls, and the wear surface analysis was also carried out. The tests results explained that the rail curve greases are very soft in texture yet have stable structure over a high-temperature range. The greases also presenting low friction coefficient; ranges between 0.070 to 0.090, and acceptable wear scar diameter indicating the good anti-friction and anti-wear properties. High load-carrying ability up to 400 kg is also the significant properties for a rail curve grease to perform as the desired functions.

To investigate whether the dense Kondo compound CeB6 might evolve into a topological insulator under sufficient pressure, four-point electrical resistivity measurements have been carried out over the temperature range 1.3 K-295 K in a diamond anvil cell to 122 GPa. The temperature Tmax of the resistivity maximum initially increases slowly with pressure but disappears between 12 and 20 GPa. The marked changes observed under pressure suggest that a valence and/or structural transition may have occurred. Synchrotron x-ray diffraction measurements, however, fail to detect any change in crystal structure to 85 GPa. Although a transition into an insulating phase is not observed, this dense Kondo system is completely suppressed at 43 GPa, leaving behind what appears to be a conventional Fermi liquid metal.

A research has been done to investigate the tribological performance of palm kernel oil (PKO) with addition of different percentage of pour point depressant, PPD (5w%, 10wt%, 20wt% and 30wt%) according to ASTM D2783. The main analyses that have been done in this research are low temperature performance ability of blended PKO, coefficient of friction (COF), wear scar diameter (WSD) and surface profile. The result of the experiment has shown that for low temperature performance, PKO with 20wt%PPD (A2-20%) and 30wt%PPD (A2-30%) show great performance in withstanding lower temperature (15℃). Under extreme pressure test, it can be seen that PKO can only withstand lower load (110kg) compared to mineral oil (140 kg). The sample 10wt%PPD (A2-10%) shows good lubricity performance in terms of COF as compared to other sample. 5wt%PPD (A2-5%) and 10wt%PPD show good lubricity performance in terms of anti-wear behaviour (A2-10%) by producing the lowest WSD when compared to other samples. From overall view, PPD is considered as successful in improving low temperature performance of PKO, but in terms of lubricity performance, adding PPD will slightly reduce the lubricity performance under extreme pressure if compared to pure PKO.

Palm oil olein and palm oil ester is well-known potential candidate in plant-based oil to replace the conventional mineral oil. Harvested all year round, the advantages and benefits initiate the palm oil to be used in varieties of application. In this paper, palm oil olein was tested on its capability as a lubricant to replace the mineral oil. To enrich the performance of this oil, different types of nanoparticles additives were added. Previous studies proved that by adding small size of additives into lubricating oil can lessen the friction and improve anti-wear properties. The adjustment of the lubricating oil with nanoparticle additives will reduce the friction between two contact surfaces and produce less heat. In his study, three type material of solid additives namely nanoclay and carbon nanotubes were used. Four ball tester following ASTM D4072-94 was conducted to determine the optimum concentration of each additives and its tribological properties under boundary lubrication (metal to metal contact). Result obtained shows that the addition of 0.04 wt% of carbon nanotubes recorded the lowest coefficient of friction with a 10.8% improvement compared to the pure palm oil. The additive also contributed to better wear scar diameters and possessed good anti-wear properties for palm oil. This thus shows the significant potential of carbon nanotubes as the wear preventive additive for palm oil olein. It is also discovered that 0.04 wt% of nanoclays additive is the optimum concentration of the mixture with coefficient of friction reduced 22.16% compared to mineral oil.

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating, and extreme pressures acting on the most critical regions of the step faces, near their outer edges. The pressure development along the chutes is presented, generally indicating an increase of the modulus of pressure coefficients up to the vicinity of the point of inception of air entrainment, and a decrease further downstream. The extreme pressure coefficients along the spillway are fitted by an empirical formula, and the critical conditions potentially leading to cavitation on prototypes are calculated. The correlation between the cavitation index and the friction factor is also applied for predicting the onset of cavitation on prototypes, and the results are compared with the pressure data-based method. Generally, the results obtained from those methods yield typical values for the cavitation index in the vicinity of the point of inception, varying approximately from 0.8 to 0.6, respectively. In light of these results, maximum unit discharges of about 15–20 m2/s are considered advisable on 53° sloping large-stepped spillways without artificial aeration, for step heights ranging from 0.6 to 1.2 m. For much higher unit discharges, a considerable reach of the spillway may potentially be prone to the risk of cavitation damage.

The lubricity of sweet almond oil (Prunus amygdalus var. Dulcis) was evaluated through Anti Wear (AW) properties and Extreme Pressure (EP) performance in a four-ball tribometer. The results were compared to those obtained with two mineral oils of contrasting viscosity, namely technical white mineral oil and delta 360 plasticizer, neither of them containing additives. Sweet almond oil was found to have greater lubricity than the mineral oils, as the spheres it lubricated had lower average wear track diameter and friction coefficient. In addition, sweet almond oil showed better performance under extreme pressure conditions and a greater weld point than mineral oils. Finally, an FT-IR spectroscopic analysis allowed determining that under the conditions of the current assays almond oil does not oxidize.

Abstract To enhance the lubricating and extreme pressure (EP) performance of base oils, two types of oil-soluble ionic liquids (ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate (ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10 (PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear (AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants.

Tribological properties of lithium potassium titanate (PT), molybdenum disulphide, and tungsten disulphide-dispersed mineral oil (MO) were investigated. The sample containing 2 wt.% WS2 exhibited the lowest coefficient of friction. However, the wear scar diameters of the additivated samples were very narrow. Extreme pressure properties of mineral oil were enhanced with the addition of additives. The rolling contact fatigue results exhibited better fatigue life of the balls in MoS2 and PT-dispersed MO. Surface characterization of the balls indicated more pitting on the balls of the MO and WS2-dispersed MO as compared to MoS2 and PT, indicating a stable film in the case of MoS2 and PT, which was confirmed by the presence of additives on ball surfaces by Raman spectrograph. The results of extended rolling contact fatigue tests proved that PT-added mineral oil provided the highest life cycles of the tested balls, followed by MoS2 and WS2-added mineral oil; thus, indicating PT as a plausible alternative to MoS2 and WS2.

The pressure-viscosity coefficient, α, is a measure of the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). There seems to be confusion around the understanding of the pressure-viscosity response in the inlet zone. In this paper the values of α were obtained from measurements of viscosity as a function of pressure and offers a understanding on the piezoviscous effect at various inlet pressures for those liquids. Moreover, the viscosities of several commercial engine oils and laboratory blends of mineral and synthetic base oils with polymer additives were measured at pressures up to 1 GPa and at temperatures of 40°, 75°, and 100°C. It was observed in some of these materials The significant changes within viscosity are temperature- and pressure-dependent. Analysis of the experimental results indicated that the solidification (significant increase viscosity) is due to liquid-solid phase transitions occurring in the lubricant's polymer additives. Thus, this paper gives evidence on the role of molecular weight and concentration of polymer and its influence on the pressure and temperature-dependent onset of the phase transitions. This transition has not been discussed in the open literature and is not accounted for in current bearing design using the Barus equation or the modified Yasatomi equation and may be the cause of some bearing damage modes.

Orientation: Exchange market pressure (EMP) is the selling pressure of domestic currency or excess demand needed for foreign currency. Research purpose: The purpose of this study was to analyse EMP using extreme value theory (EVT) and to compare two commonly used EVT methods. Motivation for the study: To determine whether the EMP of two African countries can be modelled with EVT, and if so, which method would be best suited. To determine periods of extreme pressure or currency crisis by using these methods. Lastly, to study the individual components of the EMP index during these periods of stress of crises. Research design/approach and method: The monthly data of the three components of the EMP index for two African countries (Republic of South Africa [RSA] and Kenya) were studied for a period of 19 years (1999–2017). The data were modelled using the generalised Pareto distribution (GPD) with the peak over threshold (POT) method using maximum likelihood estimation. Moreover, the data were also modelled using the non-parametric Hill estimate. Appropriate estimated and empirical quantiles are reported in order to determine periods of extreme pressure or crises. The components of the EMP RSA data set were modelled with appropriate autoregressive moving averages and/or autoregressive conditional heteroscedasticity/generalised autoregressive conditional heteroscedasticity (ARMA/ARCH/GARCH) processes to ensure independent and identically distributed variables. Main findings: Reliable and accurate estimates were obtained for the scale and shape parameter using the GPD POT method for both countries. Positive shape parameters confirmed generalised extreme value distributions with heavy tails of the Frechet type. Similarly, accurate and reliable shape estimates were computed using the non-parametric Hill estimator for both countries. Practical/managerial implications: The GPD POT method more closely reflected estimates to the empirical qauntiles compared to the Hill method. It is feasible to model the EMP data of two African countries with EVT using both POT estimation methods. However, the GPD method using maximum likelihood estimation was more accurate compared to the non-parametric Hill estimate. Contribution/value-add: It is feasible to model the EMP data of two African countries using EVT using both POT methods. As a consequence periods of extreme pressure could be identified. Therefore the individual components of the EMP at those periods of extreme pressure could be studied more closely.

A research has been done to investigate the tribological performance of palm kernel oil (PKO) with addition of different percentage of pour point depressant, PPD (5w%, 10wt%, 20wt% and 30wt%) according to ASTM D2783. The main analyses that have been done in this research are low temperature performance ability of blended PKO, coefficient of friction (COF), wear scar diameter (WSD) and surface profile. The result of the experiment has shown that for low temperature performance, PKO with 20wt%PPD (A2-20%) and 30wt%PPD (A2-30%) show great performance in withstanding lower temperature (15°C). Under extreme pressure test, it can be seen that PKO can only withstand lower load (110kg) compared to mineral oil (140 kg). The sample 10wt%PPD (A2-10%) shows good lubricity performance in terms of COF as compared to other sample. 5wt%PPD (A2-5%) and 10wt%PPD show good lubricity performance in terms of anti-wear behaviour (A2-10%) by producing the lowest WSD when compared to other samples. From overall view, PPD is considered as successful in improving low temperature performance of PKO, but in terms of lubricity performance, adding PPD will slightly reduce the lubricity performance under extreme pressure if compared to pure PKO. [ABSTRACT FROM AUTHOR]

To enhance the lubricating and extreme pressure (EP) performance of base oils, two types of oil-soluble ionic liquids (ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate (ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10 (PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear (AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants. [ABSTRACT FROM AUTHOR]

Pressure fluctuations are a key issue in hydraulic engineering. However, despite the large number of studies on the topic, their role in spatial hydraulic jumps is not yet fully understood. The results herein shed light on the formation of eddies and the derived pressure fluctuations in stilling basins with different expansion ratios. Laboratory tests are conducted in a horizontal rectangular flume with 0.5 m width and 10 m length. The range of approaching Froude numbers spans from 6.4 to 12.5 and the channel expansion ratios are 0.4, 0.6, 0.8, and 1. The effects of approaching flow conditions and expansion ratios are thoroughly analyzed, focusing on the dimensionless standard deviation of pressure fluctuations and extreme pressure fluctuations. The results reveal that these variables show a clear dependence on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609

Pressure fluctuations beneath hydraulic jumps potentially endanger the stability of stilling basins. This paper deals with the mathematical modeling of the results of laboratory-scale experiments to estimate the extreme pressures. Experiments were carried out on a smooth stilling basin underneath free hydraulic jumps downstream of an Ogee spillway. From the probability distribution of measured instantaneous pressures, pressures with different probabilities could be determined. It was verified that maximum pressure fluctuations, and the negative pressures, are located at the positions near the spillway toe. Also, minimum pressure fluctuations are located at the downstream of hydraulic jumps. It was possible to assess the cumulative curves of pressure data related to the characteristic points along the basin, and different Froude numbers. To benchmark the results, the dimensionless forms of statistical parameters include mean pressures (P*m), the standard deviations of pressure fluctuations (σ*X), pressures with different non-exceedance probabilities (P*k%), and the statistical coefficient of the probability distribution (Nk%) were assessed. It was found that an existing method can be used to interpret the present data, and pressure distribution in similar conditions, by using a new second-order fractional relationships for σ*X, and Nk%. The values of the Nk% coefficient indicated a single mean value for each probability.

The tribological performance of crude Nigeria-based castor oil has been investigated and compared with that of a foreign, 20W-50 high quality crankcase oil, to see its suitability as base oil for lubricating oils in indigenous vehicle and power plants engines. The experiment was conducted using a four ball tester. The results showed that unrefined castor oil has superior friction reduction and load bearing capability in an unformulated form than the commercial oil; can compete favourably with the commercial oil in wear protection when formulated with suitable antiwear agent, hence can be a good alternative base stock for crankcase oils suitable for Nigeria serviced vehicles, and plants engines from tribological, environmental, and non-food competitive points of view.

The lubricity of sweet almond oil (Prunus amygdalus var. Dulcis) was evaluated through Anti Wear (AW) properties and Extreme Pressure (EP) performance in a four-ball tribometer. The results were compared to those obtained with two mineral oils of contrasting viscosity, namely technical white mineral oil and delta 360 plasticizer, neither of them containing additives. Sweet almond oil was found to have greater lubricity than the mineral oils, as the spheres it lubricated had lower average wear track diameter and friction coefficient. In addition, sweet almond oil showed better performance under extreme pressure conditions and a greater weld point than mineral oils. Finally, an FTIR spectroscopic analysis allowed determining that under the conditions of the current assays almond oil does not oxidize. [ABSTRACT FROM AUTHOR]

In the present work, due to the key role played by the environmental compliance and the operators' safety when using Metalworking Fluids (MWFs), a novel Natural Origin (NO) lubricant has been comparatively investigated with a commercial Mineral Based (MB) one in terms of: (i) environmental impact and (ii) lubricating/anti-wear performance. As for the former aspect, the values of Non-Ionic Surfactants (NIS) and Chemical Oxygen Demand (COD) in the aqueous phase obtained after the chemical breaking of the emulsions were evaluated; as for the second aspect, the performance of emulsions with different concentrations and oil types (the mineral and the natural one) were assessed both in laboratory (tests using Falex tribometer) and in real production environment (tool flank wear evaluation during machining). The chemical breaking demonstrated that the aqueous phase extracted from the NO emulsion (fresh or after several months of working) was characterized by very low contents of NIS and COD (3 orders of magnitude and 3 times, respectively, less than the MB emulsion if considering fresh emulsions; 3 orders of magnitude and 4 times, respectively, less than the MB emulsion if considering emulsions after several months of working) thus making possible to re-use it in the production process. On the other hand, from the process point of view, tribological and wear tests revealed that the NO emulsion always led to a tool wear smaller than the one determined by MB: around 30% if using an oil content of 5% for both the emulsions; around 19% if using an oil content of 5% for NO and 9% for MB. [Display omitted] • A methodology for assessing lubricating/anti-wear performance has been defined. • Green lubricant, even with low oil content, can reduce remarkably the tool flank wear. • Green lubricant can reduce the oil consumption while improving the production process' efficiency. • The aqueous phase of the broken emulsion contains extremely low NIS and COD levels. • Circularity of the process is possible since the aqueous phase can be re-used. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ashless and non-corrosive organic disulfides derivatives. • Excellent anti-wear and extreme pressure performances. • Organic disulfides suitable to replace MCCP and ZDDP as EP additives. • FeS and FeSO 4 give effective protective film from organic disulfides. • The adsorption of π bond on the metal surface induce more sulfur molecules. Medium chain chlorinated paraffin (MCCP) and zinc dialkyl dithiophosphate (ZDDP) are widely used as extreme pressure (EP) additives in metalworking fluids (MWFs). Currently, sulfur-based EP additives are found to be more environmentally friendly and biodegradable. Although naphthenic base oil (NBO) is suitable to be used in MWFs due to its low pour point and better emulsified ability, there is a lack of study on the sulfur additives in this type of oil. In this study, two organo disulfides compounds namely dibenzyl disulfide (DBDS) and dioctyl disulfide (DODS) have been synthesized as EP additives. These DBDS and DODS demonstrate an excellent EP performance, non-corrosive, ashless, and good anti-wear (AW) properties in NBO. The DBDS shows 1961 N (EP value) and 6 mm2 (AW scar area) in NBO, which is superior to DODS, MCCP and ZDDP. This is due to the formation of sulfur-based tribofilm on the interface that acts as a protective sulfur layer thus, enhancing the property of EP. [ABSTRACT FROM AUTHOR]

Abstract: An innovative approach to improving the wear resistance and load-carrying capacity of surfaces is by development of novel systems featuring coating treatment. Evaluation of the tribological performance of three physical vapor deposition (PVD) coatings, namely, TiN, WC/C, and DLC (diamond-like carbon), is necessary to determine their suitability as coatings for high-speed and heavy-duty power-transmitting gears. The uncoated and coated steel balls were subjected to four-ball tests under lubricated conditions. An optical microscope and a scanning electron microscope were used to observe wear scars, and energy-dispersive X-ray analysis was performed to determine the chemical compositions of the materials; these methods were also used to analyze the wear mechanisms. The wear performance of the three coatings was compared, and a four-ball method extreme pressure test was performed to determine the last nonseizure load of each tribo-pair. The WC/C and DLC coatings showed excellent tribological performance under high contact pressures and thermal loads, and the benefits of these coatings increased with decreasing performance of the lubricating medium. Therefore, WC/C and DLC coatings are suitable for application in high-speed and heavy-duty gears. Oxidation wear and peeling, fatigue pitting, and adhesive transfer are the main coating failure modes of the TiN, WC/C, and DLC coatings, respectively. [Copyright &y& Elsevier]

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating, and extreme pressures acting on the most critical regions of the step faces, near their outer edges. The pressure development along the chutes is presented, generally indicating an increase of the modulus of pressure coefficients up to the vicinity of the point of inception of air entrainment, and a decrease further downstream. The extreme pressure coefficients along the spillway are fitted by an empirical formula, and the critical conditions potentially leading to cavitation on prototypes are calculated. The correlation between the cavitation index and the friction factor is also applied for predicting the onset of cavitation on prototypes, and the results are compared with the pressure data-based method. Generally, the results obtained from those methods yield typical values for the cavitation index in the vicinity of the point of inception, varying approximately from 0.8 to 0.6, respectively. In light of these results, maximum unit discharges of about 15–20 m2/s are considered advisable on 53° sloping large-stepped spillways without artificial aeration, for step heights ranging from 0.6 to 1.2 m. For much higher unit discharges, a considerable reach of the spillway may potentially be prone to the risk of cavitation damage. [ABSTRACT FROM AUTHOR]

Abstract: Many problems such as health and environment issues are identified with the use of cutting fluids (CFs). There has been a high demand for developing new environmentally friendly CFs such as vegetable based cutting fluids (VBCFs) to reduce these harmful effects. In this study, performances of six CFs, four different VBCFs from sunflower and canola oils with different ratios of extreme pressure (EP) additives, and two commercial types of CFs (semi-synthetic and mineral) are evaluated for reducing of surface roughness, and cutting and feed forces during turning of AISI 304L austenitic stainless steel with carbide insert tool. Taguchi’s mixed level parameter design (L18) is used for the experimental design. Cutting fluid, spindle speed, feed rate and depth of cut are considered as machining parameters. Regression analyses are applied to predict surface roughness, and cutting and feed forces. ANOVA is used to determine effects of the machining parameters and CFs on surface roughness, cutting and feed forces. In turning of AISI 304L, effects of feed rate and depth of cut are found to be more effective than CFs and spindle speed on reducing forces and improving the surface finish. Performances of VBCFs and commercial CFs are also compared and results generally show that sunflower and canola based CFs perform better than the others. [Copyright &y& Elsevier]

Tribological properties of lithium potassium titanate (PT), molybdenum disulphide, and tungsten disulphide-dispersed mineral oil (MO) were investigated. The sample containing 2 wt.% WS2 exhibited the lowest coefficient of friction. However, the wear scar diameters of the additivated samples were very narrow. Extreme pressure properties of mineral oil were enhanced with the addition of additives. The rolling contact fatigue results exhibited better fatigue life of the balls in MoS2 and PT-dispersed MO. Surface characterization of the balls indicated more pitting on the balls of the MO and WS2-dispersed MO as compared to MoS2 and PT, indicating a stable film in the case of MoS2 and PT, which was confirmed by the presence of additives on ball surfaces by Raman spectrograph. The results of extended rolling contact fatigue tests proved that PT-added mineral oil provided the highest life cycles of the tested balls, followed by MoS2 and WS2-added mineral oil; thus, indicating PT as a plausible alternative to MoS2 and WS2. [ABSTRACT FROM AUTHOR]

Pressure fluctuations are a key issue in hydraulic engineering. However, despite the large number of studies on the topic, their role in spatial hydraulic jumps is not yet fully understood. The results herein shed light on the formation of eddies and the derived pressure fluctuations in stilling basins with different expansion ratios. Laboratory tests are conducted in a horizontal rectangular flume with 0.5 m width and 10 m length. The range of approaching Froude numbers spans from 6.4 to 12.5 and the channel expansion ratios are 0.4, 0.6, 0.8, and 1. The effects of approaching flow conditions and expansion ratios are thoroughly analyzed, focusing on the dimensionless standard deviation of pressure fluctuations and extreme pressure fluctuations. The results reveal that these variables show a clear dependence on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385 , where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins within this range. [ABSTRACT FROM AUTHOR]

Pressure fluctuations beneath hydraulic jumps potentially endanger the stability of stilling basins. This paper deals with the mathematical modeling of the results of laboratory-scale experiments to estimate the extreme pressures. Experiments were carried out on a smooth stilling basin underneath free hydraulic jumps downstream of an Ogee spillway. From the probability distribution of measured instantaneous pressures, pressures with different probabilities could be determined. It was verified that maximum pressure fluctuations, and the negative pressures, are located at the positions near the spillway toe. Also, minimum pressure fluctuations are located at the downstream of hydraulic jumps. It was possible to assess the cumulative curves of pressure data related to the characteristic points along the basin, and different Froude numbers. To benchmark the results, the dimensionless forms of statistical parameters include mean pressures (P*m), the standard deviations of pressure fluctuations (σ*X), pressures with different non-exceedance probabilities (P*k%), and the statistical coefficient of the probability distribution (Nk%) were assessed. It was found that an existing method can be used to interpret the present data, and pressure distribution in similar conditions, by using a new second-order fractional relationships for σ*X, and Nk%. The values of the Nk% coefficient indicated a single mean value for each probability. [ABSTRACT FROM AUTHOR]