Search

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 aim of the present study is to examine the antiwear, antifriction, and extreme pressure performance of castor oil with nano-additives by using a four-ball tester. CeO2 (~90 nm) and polytetrafluroethylene (~150 nm) nanoparticles were used as an additive in castor oil with four different concentrations in the range of 0.1-1.0% w/v. The suspension stability of the nanoparticles was improved by using sodium dodecyl sulfate as a dispersant. Different analytical tools were used to characterize the nanoparticles parameter (i.e. shape and size) as well as the worn surfaces. The additive concentration was optimized on the basis of tribological performance. The test results of antiwear and extreme pressure property have been reported on the basis of wear scar diameter and weld load, respectively. For the antiwear test, it was observed that the maximum reduction in the wear scar diameter was 37.4 and 35.3% at an optimum concentration of CeO2 and polytetrafluroethylene additive, respectively. Also, antifriction and load carrying properties of castor oil were significantly improved with the addition of nanoparticles as an additive in a small amount. The mechanism for such improvement in the tribological behavior has also been discussed. [ABSTRACT FROM AUTHOR]

This paper presents the enhancement of thermophysical and tribological properties of oil soluble Ni-promoted ultrathin MoS 2 nanocomposites blended with gear oil (SAE 75 W). The Ni-promoted ultrathin MoS 2 namely Ni-MoS 2 nanosheets was exfoliated chemically using ultrasonication and simple reflux techniques. The as-synthesized additives blended with gear oil (i.e., 0.5 wt% of micro MoS 2 , MoS 2 nanosheets and Ni-MoS 2 nanosheets) were tested for their thermophysical and tribological properties by using four ball wear tester according to ASTM D2783 standard. The obtained thermophysical and tribological characteristics reveals that the synergetic interaction of Ni and MoS 2 nanosheets have better dispersibility and more suitable lubricant additive for extreme pressure region. Thus, the above research enriches the tribological phenomena of transmission elements in the mechanical industry. [ABSTRACT FROM AUTHOR]

The aim of the present study is to highlight the particular behavior of the vegetable oils in relation with the additivation process. It is generally known that the lubricants are made by base oils and specific additives, both of these components playing an important role for achieving good quality lubricants. Many studies presenting the properties of the vegetable oils, emphasize the potential of these types of oils as base oils for lubricants, particularly for the eco friendly ones, due to their favorable characteristics as high biodegradability and renewability; there are also other experimental studies that are focused on the disadvantageous characteristics, as poor thermal stability and very low oxidation resistance. These studies and data are generally referring to the vegetable oils as such and not extend the evaluation of the vegetable oils in mixture with functional additives; this aspect is also very important in order to evaluate the potential of these types of oils to be improved by additivation. The additivation process involves a wide range of additives that are designed to improve different characteristics of the lubricants and, implicitly, to improve their performance and proper functioning. Some of the more usual types of additives are: antioxidant additives, depressant additives, antiwear and extreme pressure additives, anticorrosion and antirust additives. Usually a special attention is paid to oxidation resistance and to additives that improve this feature, but very important too, is the extreme pressure characteristic that has to be accomplished by many categories of lubricants like hydraulic oils, gear oils, bearing oils etc. Starting from the above mentioned considerations, the main propose of the research study was to evaluate the extreme pressure characteristic of the vegetable oils, as such and the influence of the specific additives that improve this feature, on the vegetable oils behavior. The experimental tests, performed for evaluation of the extreme pressure characteristic, were realized by a very relevant method, Four Ball Machine and highlighted an interesting behavior of the vegetable oils in comparison with the mineral oils type. [ABSTRACT FROM AUTHOR]

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, calcium-copper-titanate (≈85 nm) and cerium oxide (≈90 nm) nanoparticles were blended in paraffin oil (PO) as an additive by varying the concentration from 0.1 to 1.0% w/v, and tribo-performance was evaluated with four-ball tester. The concentration 0.25% w/v of the nanoparticles in PO was found to be optimum in antiwear and antifriction property tests for both types of nanolubricants. At this particular concentration, the maximum reductions in the wear scar diameter were 38.4 and 26.1% for calciumcopper- titanate and cerium oxide-based nanolubricants, respectively. Also, the mean coefficient of friction was reduced by 17.3 and 29.6% at this optimum concentration for both types of lubricants. For extreme-pressure test, the loadcarrying capacity of the nanolubricants was improved from 126 to 160 kgf as compared with base PO. The worn surfaces were examined with scanning electron microscope, energy-dispersive spectroscopy, and atomic force microscope to study the physical phenomena that occurred during the sliding. [ABSTRACT FROM AUTHOR]

This paper investigates the tribological characteristics of modified jojoba oil (MJO) as a base stoke for SAE20W40 mineral oil (LO). In addition, a graphene nanoparticle was also added as an additive in MJO and studied for its performance. MJO was obtained from a two-stage transesterification process: acid esterification and base esterification. Six samples were formulated with the partial replacement of modified jojoba oil as 0, 10, 20, 30, 40 and 50 % by volume to the SAE20W40 mineral oil. Tribological tests were conducted on a four ball tribometer test rig under extreme pressure and anti-wear conditions with the formulated blends. Subsequently, 0.075 wt% of graphene nano additive was added in the above mentioned oil ratios and investigated once again in a four ball tester. Surface analysis was carried out, using scanning electron microscope (SEM). The experimental results showed that the blend of 20 % jojoba oil exhibited a lower wear scar diameter than other blends at extreme load conditions. An addition of 0.075 wt% of graphene nano-additive to the formulated blends also enhanced its lubrication properties. The surface characteristic study revealed that the addition of nano additives witnessed lesser wear scars with 10 and 20 % of jojoba blends. Among the blends, 20 % of jojoba oil was considered as an acceptable blend to enhance the mineral properties in comparison with SAE20W40 mineral oil. [ABSTRACT FROM AUTHOR]

A four-ball tester was used to evaluate the tribological performances of bismuth naphthenate (BiNap), sulfurized isobutene (VSB), and their combinations. The results show that the antiwear properties of BiNap and VSB are not very visible, but they possess good extreme pressure (EP) properties, particularly sulfur containing bismuth additives. Synergistic EP properties of BiNap with various sulfur-containing additives were investigated. The results indicate that BiNap exhibits good EP synergism with sulfur-containing additives. The surface analytical tools, such as X-ray photoelectron spectrometer (XPS) scanning electron microscope (SEM) and energy dispersive X-ray (EDX), were used to investigate the topography, composition contents, and depth profile of some typical elements on the rubbing surface. Smooth topography of wear scar further confirms that the additive showed good EP capacities, and XPS and EDX analyzes indicate that tribochemical mixed protective films composed of bismuth, bismuth oxides, sulfides, and sulfates are formed on the rubbing surface, which improves the tribological properties of lubricants. In particular, a large number of bismuth atoms and bismuth sulfides play an important role in improving the EP properties of oils. [ABSTRACT FROM AUTHOR]

Nanoparticles have been recently explored as lubricant additives for improving tribological performance of metal-forming tools. Halloysite clay nanotubes (HNTs) are naturally-occurring, low-cost, and non-toxic nanoparticles, making them attractive as green lubricant additives. In this study, HNTs were dispersed at varying concentrations (0.01, 0.05, and 0.10 wt%) within a polymeric lubricant for metal-forming applications. The ITeE-PIB Polish method for testing lubricants under scuffing conditions was conducted with a four-ball tribotester in order to obtain the scuffing load and load-carrying capacity ( p oz ) under extreme pressures (EP), as this method has demonstrated to be sensitive to extreme-pressure additives; a block-on-ring test was used to obtain wear volume loss and coefficient of friction (COF). Surface roughness of worn materials was characterized with an optical 3D-surface measurement system. Results showed that 0.05 wt% HNTs delayed scuffing initiation, and increased the scuffing load and load-carrying capacity by 50% and ~72%, respectively. Wear volume loss and COF were both lowered by ~70%, and surface roughness was reduced due to the formation of a tribofilm. The improved lubrication provided by environmentally-friendly HNT lubricant additives shown in this study may result in considerable cost savings through lower energy consumption and longer tool life. [ABSTRACT FROM AUTHOR]

Proper lubricants and lubrication methods for rolling bearings are essential for providing sufficient bearing performance in high pressure applications. Main roles of molybdenum disulfide (MoS 2 ) grease lubricant in rolling bearing are reduction of friction and wear, removal of frictional heat, extension of fatigue life, and protection from corrosion. Traditional method to evaluate wear behaviour of grease is based on ASTM D2266 which evaluates the performance of grease at 75 °C, constant load and speed. However, actual applications may require bearings to be subjected to variable loading conditions where-in rotations per minute (rpm), load and duration of test are variables. 4 ball wear tests were conducted under these variable conditions using chrome-plated steel balls (Bearing-quality Aircraft Grade E52100), to examine the extent of wear and to predict its behaviour using 2 level design of experiment (DOE) factorial approach. In this paper wear and bearings grease deterioration with and without MoS 2 are shown and statistical equations to predict wear with respect to speed, MoS 2 concentration, and loads are calculated. Auger electron spectroscopy (AES), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) were used in order to highlight wear and friction for different lubricant blends and to understand the influence of MoS 2 and variable loads on grease. Results indicated that wear depend largely on loading conditions. It is believed that MoS 2 greases perform poorly under constant load and a reduced concentration of MoS 2 is sufficient to provide the same improved wear characteristics under variable loads and speeds for extreme pressure applications. [ABSTRACT FROM AUTHOR]

Water and lubricants interaction though not desirable but it is unavoidable. Water amplifies the corrosion at the lubricated contacts however its influence on the tribology of fuels, oils and greases is not clear, yet. Here, we have used the testing methods like Four Ball Tester (ASTM D2266, D2596) and Low Temperature Torque Tester (ASTM D1478) to investigate the effect of water on calcium sulfonate (CaS) grease, lithium (Li) grease and the test method HFRR (ASTM D6079) to study the effect of water on diesel fuel lubricity. Addition of water and an increase in its concentration in CaS and Li greases increases the roughness of friction profile and also the wear. For example, in CaS grease, the rougher friction profile indicates severe metal-to-metal contacts due to loss of boundary lubrication triggered by poor oil bleeding. This process, leading to increase in wear, is attributed to the emulsion stability that increases with an increase in water concentration, related to its interaction with CaCo 3 in CaS. Furthermore, such an interaction is the reason for an increase in the run-in torque with an increase in concentration of water molecules for CaS operating at – 30 °C. In the case of diesel lubricity, the water molecules interact with the polar groups in the fuel at high humidity and reduces its surface activity. As a result there is a rougher friction profile and an increase in the wear, similar to the tribological behavior of greases contaminated with water. Overall, the added water contamination hampers the lubrication by greases and fuel. Mainly, due to poor boundary lubrication that allow more metal-to-metal contacts and increase the wear. Therefore, a careful selection of the ingredients in greases and fuel is necessary to improve the behavior of bearings and diesel fuel pumps exposed to water. [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]

The use of fluorinated mix catalyst (titanium fluoride: TiF3 + iron fluoride: FeF3) with polytetrafluoroethylene: PTFE in engine oil is increasingly a strategy to improve fuel economy and component durability to simultaneously provide low friction and excellent wear protection. The influence of these additives shows promising results during load bearing capacity testing and long-term durability experiments. This paper addresses the enhancement of friction and wear performances of 0.1% and 0.05% phosphorus plain zinc dialkyl dithiophosphate (ZDDP) oil and fully formulated engine oil when heated to 100°C for specific time under thermal and tribological conditions for moderate pressure loading (1.9 GPa Hertzian pressure or 180 N) which simulate the cold start of a car under 700 rpm rotational speed or the valve trains loading where most of the ZDDP are applied. Tests were performed in a ball on cylinder tribometer under boundary lubrication conditions. Surface analyses were carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results showed that the anti-wear additives (2 wt. % PTFE + 0.5 wt. % FeF3 + .5 wt. % TiF3) provided excellent wear protection to 0.1% phosphorus plain and fully formulated oil when cylinder is immersed in the desired lubricant and heated for a predetermined time but performed poorly in 0.05% phosphorus fully formulated oil under the same conditions. The transform of anti-wear coated material to the worn surfaces, which was a function of the anti-wear performance of additives, was shown to have an influence on friction performance. The wear reducing effect, which was observed in fluorinated additives tribological tests, indicated a positive contribution and good tribofilm formations. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Zinc Dialkyl Dithiophosphate (ZDDP) is a well-known multifunctional additive for soap based lubricating greases. Polymers are being studied for their performance as lubricating grease thickeners and rheology modifiers. In this work the tribological study of ZDDP was carried out in polypropylene (PP), maleated polypropylene (mPP) and linear low density polyethylene (PE) thickened lubricating greases. Performance of lithium grease was taken as a reference. The tribological properties were evaluated using a four ball tester for EP properties and Optimol SRV-III machine for coefficient of friction. The mechanism of action of ZDDP in polymer greases was established through analysis of the worn surface of steel balls with scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDAX). The results show that the performance of ZDDP depends on the thickener system. The antiwear and EP property exhibited by ZDDP varies from polymer to polymer. Poor performance was observed with PP type thickener whereas performance in PE and lithium grease was comparable. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose – This study aims to examine the effect of the antiwear resistance of plain zinc-dialkyldithiophosphate (ZDDP) oil in the presence of Titanium-fluoride/iron-fluoride/polytetrafluoroethylene (TiF3/FeF3/PTFE) in the time to tribofilm breakdown and extent of wear under extreme boundary lubrication using a contact load of 317 Newton and a rotational speed of 700 rpm to simulate the cold start of a car engine. The mechanism of tribofilm formation and breakdown was followed carefully by monitoring the friction coefficient for different surface roughnesses over the duration of several reproducible tests that were performed in a ball on cylinder tribometer. Design/methodology/approach – The heating time of the cylinder dipped in the specified lubricant blend then set for one minute before testing and the break in period of 2 minutes to cool the contacting metal to metal surfaces during tribological testing played important roles in minimizing friction and wear, and are directly proportional to the durability and time for breakdown of the tribofilm. This article addresses the improvement of water drop contact angles for different surfaces during heat treatment and the tribological enhancement of antiwear additives when optimum concentration of fluorinated catalysts and PTFE is used in connection with reduced surface roughness and break in period. Findings – Design of Experiment software, scanning electron microscopy, energy dispersive spectroscopy and nanoindentation were used in this study to evaluate the antiwear resistance films when using 0.05 per cent phosphorus ZDDP plain oil with 0.5 weight per cent TiF3 + 0.5 weight per cent FeF3 + 2 weight per cent PTFE and when applying 2 minutes break in time to cool down the contacting bodies when temperature rises. Results indicated that the coated film on the thermally treated surfaces that is reflected as white patches on the SEM images is a function of the antiwear additives contribution; it is also shown to have positive influence on the friction and wear performances during tribological testing. Originality/value – This research involved the study of lubricant and surface interactions with antiwear additives under boundary lubrication and extreme pressure loading. Several researchers studied these effects and submitted articles to the journal. This is the first time that a break in period was used with surface conditions to simulate car stops in heavy traffic conditions. [ABSTRACT FROM AUTHOR]

In this study an extreme pressure and anti-corrosion additive package for gear oils has been created. In this context three different organic molecules were synthesized. Methylene-bis (dibutyldithiocarbamate), Sulfured oleic acid and o,o-Dialkyldithio Phosphate. Mass spectrums and Elemental analyses were carried out for these three molecules. For each molecule 4-ball weld points (WP), 4-ball Wear Scar Diameter (WSD), Copper corrosion (CC) and salt spray tests (SS) were carried out. Antioxidant properties of synthesized molecules were determined. According to the test results eight different additive packages were prepared and WP, WSD, CC and SS tests were applied to each package to determine a suitable package content. The highest yield was obtained in the five and six additive package with 250, 300 kg weld point and 0.41, 0.53 mm scar diameter respectively. For all additive packages the extreme pressure and corrosion resistance properties of gear oil increase by increasing the percentage of Methylene-bis (dibutyldithiocarbamate). o,o-Dialkyldithio Phosphate showed the highest antioxidant activity and it has been obtained bets corrosion protection with Sulfured oleic acid. [ABSTRACT FROM AUTHOR]

To investigate whether the dense Kondo compound CeB 6 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 T max 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. [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]

This paper presents the experimental results for the extreme pressure characteristics of a palm oil-based trimethylolpropane (TMP) ester blended with paraffin oil obtained using a four-ball machine. The load and speed of the sample were set between 20–120 kg and 1770 rpm, respectively. TMP ester produced from palm oil is biodegradable and has high lubricity properties, such as a higher flash point temperature and viscosity index. It has an affinity to surface asperities, which reduces wear between sliding contacts. Based on the calculation, it was found that majority of the oils in boundary regime and mixed elastrohydrodynamic regime. For the same contact load, the film thickness with TMP100 is 70% thicker than that with paraffin oil. In addition to that, test results revealed that (1) for all the used lubrication oils, TMP ester blended with paraffin provide better surface protection compared to paraffin oil. (2) Even though, TMP100 has the highest film thickness, at low load the wear is higher. Surface morphology test was conducted using scanning electron microscope and surface roughness tester. It was found that severe corrosive wear occurred at TMP100 which is probably due to the high oxygen content compared to other lubricant. [ABSTRACT FROM PUBLISHER]

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]

Taking fluorinated graphene (FG) and polytetrafluorethylene (PTFE) as the typical models, this work aims to clarify the influences of carbon-skeleton structure and C F bond strength on their tribological performance and lubrication mechanism under extreme-pressure condition. As oil additives, the load-bearing capacity of PAO-6 increases from 300 N to 600 N with FG and 400 N with PTFE. Compared with the situation with the PTFE sub-microspheres, the wear rate of PAO-6 with FG nanosheets reduces by about 40%. Proved by the apparent difference in tribofilm formation ability of FG and PTFE, it is believed that the higher reactivity of the C F bond and adsorption ability of two-dimensional carbon-skeleton play a crucial role in FG's excellent tribological performance. • The honeycomb-like carbon structure of fluorinated graphene intensively improves its thermal stability. • The layered structure of FG exhibits better dispersion stability than the microsphere morphology of PTFE. • Due to its lower C F bond strength, it is easier for FG to from tribofilm over the friction surface than PTFE. • As lubricating oil additive, FG exhibits better extreme pressure and anti-wear properties than PTFE. [ABSTRACT FROM AUTHOR]

Abstract: A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20N, 1.82GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well. [Copyright &y& Elsevier]

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]

This work presents the effects of five inorganic nanoparticles as additives, i.e., CNp (carbon nanotori particles), TiO 2 , MoS 2 , MoO 3 , and HcNT (halloysite clay nanotubes), in three different lubricants (oil-based, grease, and water-based). Nanolubricants were prepared by adding 1 wt% particles into each type of lubricant. Tribological properties of nanolubricants were determined and compared under anti-wear (AW) and extreme pressure (EP) conditions. CNp showed a decrease in coefficient of friction (COF) by 22% when added to water-based lubricant. Additionally, CNp demonstrated an improvement in limiting pressure of seizure (p oz) of 74%, 52%, and 1621% for oil-based lubricant, grease, and water-based lubricant, respectively. Comparing 1 wt% CNp added to water-based lubricant with oil-based lubricant and grease, the improvements become outstanding under EP conditions. An increase in p oz by 2479% compared to oil-based lubricant, and 789% compared to grease, was observed. In addition, a decrease of 66–69% in average wear scar diameter (AWSD) was obtained in comparison to oil-based lubricant and grease. Tribological mechanisms of carbon nanotori provide a rolling/sliding effect under AW conditions, and a load-bearing effect under EP conditions. [Display omitted] • Composites of water-, grease and oil-based lubricants were obtained. •Inorganic nanoparticles (CNp (carbon nanotori), TiO 2 , MoS 2 , MoO 3 , and HcNT (halloysite clay)) were used for tribological tests. •Carbon nanotori showed lowering the coefficient of friction by 22%. •MoS 2 and MoO 3 demonstrated good tribological performance for oil and grease based lubricants. •Anti-wear (AW) and extreme pressure (EP) conditions were applied for tribological tests. [ABSTRACT FROM AUTHOR]

Abstract: This work presents and discusses the extreme-pressure behaviour of nanoparticle suspensions in a polyalphaolefin (PAO 6). CuO, ZnO and ZrO2 nanoparticles were dispersed at 0.5, 1.0 and 2.0wt.% in PAO 6 using an ultrasonic probe during 2min and EP properties were obtained using a Stanhope Seta Shell Four-Ball EP Lubricant Tester according to ASTM D2783. The ball test material was AISI 52100 steel of 12.7mm diameter, with a hardness of about 65 HRC. The wear scar diameter (WSD) was measured with an optical microscope and scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis of the worn surface highlighted a number of conclusions: all concentrations of nanoparticles improved the EP properties of PAO 6; CuO nanoparticles exhibited the best EP behaviour and ZrO2 the worst; CuO and ZnO suspensions showed better results at 0.5% and 2.0wt.% of nanoparticles, respectively, while ZrO2 behaved identically regardless of nanoparticle concentration; all results were analysed according to the nanoparticles’ size and hardness, and their deposition on wear scar surface. [Copyright &y& Elsevier]

The lubrication mechanisms of water-based fluids are not yet well understood, especially when extreme load conditions are applied. The example of lamellar crystallite particles in water, provided by an emulsion-like technology, is described in this paper. It is shown, for the first time, that the presence of such nanostructures in the sliding interface can provide extreme-pressure lubrication. This water-based lubricant is particularly efficient when one of the two solid surfaces is made of brass. In this case, a multilayer is created in the contact. It is formed by a brass layer transferred to the counter face, the brass surface itself and a lamellar film adherent to the former layers. This lamellar system is able to sustain pressures up to a few GPa and to maintain a low friction coefficient. [ABSTRACT FROM AUTHOR]

To improve the lubricity of the as-prepared food-grade aluminum-based grease, the influence of two nano-additives (nano-PTFE and nano-CaCO 3) on the tribological properties is systematically investigated using four-ball and ball-disc wear testers. The results reveal that as-prepared food-grade aluminum-based grease possesses excellent tribological properties after the addition of both nano-additives. Compared with a single-additive food-grade grease, the presence of two-additive significantly improves maximal non-seizer load, weld point load, test stability, the average coefficient of friction and wear volume of the disc owing to the synergistic role of pure grease, nano-additive and rubbing surface. Moreover, pure grease and two-additives-containing grease are verified to be safe by the Listeria monocytogenes method. These results provide valuable insights into the development of novel food-grade lubricants. • The pure and dual-additive-containing greases were proved to be safe using the Listeria monocytogenes. • The adsorption property of nano-PTFE was stronger than that of nano-CaCO 3 on the disc surface. • Two-additive compound significantly improved the tribological properties of the base grease and testing stability. • The grease of 2wt.% nano-PTFE and 3wt.% nano-CaCO 3 compound would be greater potential application in the food machines. [ABSTRACT FROM AUTHOR]

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]