Effect of humidity on wear of M-50 steel with a branched perfluoropolyalkylether lubricant

Humidity is an uncontrolled variable in many tribology tests. This report shows that changes in relative humidity can affect wear for all perfluoropolyalkylethers regardless of their molecular structure. Using a Cameron–Plint tribometer under controlled environmental conditions, wear of M-50 steel with a Krytox (a branched perfluoropolyalkylether) lubricant was studied under boundary lubrication conditions at 150^°C in air with relative humidity ranging from 1 to 95%. Both wear and friction decreased sharply as humidity was increased from 1 to 20%, then were constant as the humidity was increased to 95%. Thus, wear is highly dependent on humidity when relative humidity is less than 20%. The similar effect of humidity on wear previously observed for Fomblin Z, a linear perfluoropolyalkylether containing difluoroacetal groups, and Demnum S, a linear perfluoropolyalkylether which does not contain difluoroacetal groups, indicates that this may be a general property of all commercially available perfluoropolyalkylethers, branched as well as linear ones. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of hard coated metals on the thermo‐oxidative stability of a branched perfluoropolyalkylether lubricant

M‐50 and carburized Pyrowear 675® (Carpenter Technology, Reading PA, USA) steel coupons deposited with commercially available physical vapour deposited TiN, TiCN, TiAlCN, TiCrCN/TiB₄C multilayer, electroless Ni (E‐Ni) TiN and E‐Ni TiCN coatings were immersed in a branched perfluoropolyalkylether (PFPAE), Krytox AC® (E.I. du pont de Nemours and Company, Wilmington DE, USA), in an oxidative environment at temperatures ranging from 315 to 360 °C for a duration of 24 hours and compared with uncoated coupons. Coated and uncoated Pyrowear 675® coupons demonstrated superior corrosion resistance compared with coated and uncoated M‐50 respectively. The coatings most resistant to chemical attack in the PFPAE fluid were TiCN, E‐Ni TiN and E‐Ni TiCN. Copyright © 2006 John Wiley & Sons, Ltd.     

Stabilization of a linear perfluoropolyalkylether fluid

The thermo‐oxidative stability of a linear perfluoropolyalkylether fluid has been improved by stressing the fluid at 371°C while bubbling air or nitrogen in an overboard configuration. It is believed that the minor amounts of less stable species present in the fluid, possibly hydrogen‐containing species, are degraded and removed during the process leaving the residual fluid with enhanced stability. Two antioxidation/corrosion additives, a substituted triphenyl phosphine and a substituted diphenyl ether, were formulated with the stressed fluid, and their behavior was compared with the same formulations in unstressed fluid. While the phosphine formulation in stressed fluid showed better stability than its formulation in unstressed fluid, no such effect was noticed with the diphenyl ether additive formulations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Development of a soluble lubricity additive for perfluoropolyalkylether fluids

A new lubricity additive for perfluoropolyalkylether (PFPAE) fluids was synthesized. A linear, unbranched fluid formulated with this additive was evaluated under boundary lubrication and elastohydrodynamic (EHD) lubrications. Performance of the base fluid imporved significantly with the incorporation of this additive.     

两种合成航空润滑基础油高温氧化衰变机理研究

为研究航空润滑油的热氧化安定性,模拟聚α-烯烃(PAO)和酯类油(DE)两种合成航空润滑基础油在发动机内的高温工况,借助傅里叶红外光谱(FTIR)、气相色谱/质谱(GC/MS)联用等仪器对反应油样的黏度和结构组成进行测试与分析.结果表明,PAO具有较差的热氧化安定性能,在200℃时就发生分解,而DE的分解温度可达到300℃.在两种航空润滑基础油的高温衰变中,均有不同的产物生成.PAO衰变产物主要包括烷烃和烯烃,而DE的衰变产物主要是含氧化合物.最后,根据实验结果分析了航空润滑基础油的高温衰变机理.     

增/减材柔性制造及加工系统构成形式

将柔性制造的思想引入到增/减材制造中,形成增/减材柔性制造工艺。阐述了该工艺的内涵及加工范围,确立了增/减材柔性制造工艺流程,描述了各组成工序的特点,详细阐述了增/减材柔性制造中材料沉积、材料去除两工序内部及其之间的多种柔性加工方式。在此基础上,确立了增/减材柔性制造系统的设备构成及其相互关系,给出了加工设备的总体布局。为进一步研究该工艺的加工序列规划及各种构成设备具体结构形式等方面打下基础。     

Carbonyl peak index technique in the study of lubricant oxidation

A technique known as the Carbonyl Peak Index (CPI) is used to assess the relative oxidation stabilities of two competing grades of commercial automotive crankcase oils, their base oils, and the oxidation characteristics resulting from oil/metal interactions. The CPI provided empirical data from the infrared spectra which enabled a more lucid explanation of the oil soluble acidity and sludge deposition characteristics of the oils. A combination of these parameters has confirmed that the hydrocarbon type composition of the oils gave some stability to the fully formulated monograde oil. Consequently, the monograde base oil was found to possess a greater stability towards oxidation than the multigrade base oil under the conditions of test. However, the fully formulated oils were found to be more stable than the base oils, mainly due to the added antioxidants. Metals in the oils acted as antioxidants initially, but later turned to pro-oxidants. The reversal of metal action from inhibition to autooxidative catalysis was also found to be base-oil hydrocarbon-type dependent and this has been related to the natural antioxidant capacity of the oils.     

The influence of oxidation on the tribological performance of diester lubricant

The oxidative degradation test of di‐2‐ethylhexyl sebacate (DEHS) was carried out by a sealed stainless steel reactor. Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry (GC–MS) were utilised to characterise the chemical composition and molecular structure of the oxidation products. The results revealed that 2‐ethyl‐1‐hexanol and mono(2‐ethylhexyl)sebacate were major degradation products in the liquid phase. Tribological behaviour was measured using a four‐ball tester. Scanning electron microscopy was employed to investigate the morphologies of the worn surface. Tribological results showed that anti‐wear and friction‐reducing performances of DEHS were highly dependent on the chemical composition of the oxidation products generated during the test. The hydroperoxides formed during the initial oxidation process could deteriorate lubrication properties of DEHS. However, certain amount of highly polar degradation products (acids and alcohols) generated could significantly improve the friction‐reducing performance of DEHS by the formation of boundary adsorption films on the rubbing surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

The kinetics of lubricant penetration action during machining

A new model of cutting fluid penetration in the interface zone during metal cutting is proposed. This model includes three stages relating to processes in a single capillary: 1. liquid phase entry, 2. ‘micro-droplet explosion’, and 3. filling the capillary by gas phase lubrication. Calculations of model parameters have been done for two different liquids: water and castor oil. The correlation between model data and known experimental results is also given.     

Effect of temperature on tribological performance of a silicon nitride ball material with a linear perfluoropolyalkylether

The effect of temperature in rolling contact performance of a hot isostatically pressed (HIP) silicon nitride ball material with a linear perfluoropolyalkylether (PFPAE) was studied using a ball-on-rod type rolling contact fatigue tester. The test temperature ranged from ambient to 343°C for a period of 24 h at a stress of 5.5 GPa using thin dense chrome (TDC)-coated T-15 bearing races. The lubricant and its decomposition products, specifically acid fluoride and acids, attacked Si₃N₄ balls at all test temperatures resulting in corrosion pitting. The presence of metal fluoride on all the Si₃N₄, transferred from the races, was detected by X-ray photon spectroscopy (XPS). The thickness of the oxide layer formed on the balls, as determined by Auger electron spectroscopy (AES) increased with temperature. The changes in physical properties of post-test lubricant showed that the lubricant was stable at temperatures up to 288°C. The change in viscosity was constant up to 288°C and with a significant change above 288°C. The FTIR analysis of 316 and 343°C post-test lubricant showed the presence of carboxylic acid. The total acid number (TAN) increased linearly up to 288°C and accelerated at 316 and 343°C. The study indicates that the use of Si₃N₄ balls with a linear PFPAE results in an incompetent tribo system.     

The effect of lubricant inertia in externally pressurized bearings using a viscoelastic lubricant

The inertia effects in an externally pressurized bearing with a viscoelastic lubricant were considered using the methods of averaged inertia and of iteration. The inertia forces reduce the load-bearing capacity at a given flow rate. The effect of the elasticity of the liquid is to increase the pressure and the load-bearing capacity at any point. The effects of the elastic number S, the volume flow rate Q, the ratio σ of the inner radius of the bearing to the outer radius of the bearing and $\text{H =}\text{h}\text{a}$ on the pressure and the loadbearing capacity are presented graphically. The results obtained by the two methods are in good agreement.     

Development of engine crank-case oil formulations for oxidation stability using indigenously blended lubricant base-stocks

With changing engine design putting more emphasis on fuel economy, emissions control and low engine oil consumption, the quality levels of engine crank-case oils are changing fast. With this in view, experimental work has been carried out towards the development of engine crankcase-oil formulations meeting the required levels of oxidation stability. Three lubricant base-stocks meeting the physico-chemical characteristics of engine oils, prepared from lubricant streams obtained from different refined crude oils and one re-refined engine oil base-stock were used. The viscosity index of these base-stocks ranged from 84 to 98, and carbon residue from 0.06 to 2.2. The antioxidant used in the formulation was of ZDDP type, and the detergents were calcium and barium sulphonates. The base-stocks were evaluated using the IIP oxidation stability test, to determine their suitability in the formulation of engine crankcase oils. The base-stocks were then dosed with additives, and tested again by the IIP Oxidation Stability Bench Test, for their additive response. The final formulations were then tested on a CRC-L-38 standard engine test prescribed in Indian Standard 13656:1993 for IC Engine Crankcase Oils with respect to bearing corrosion and piston deposit tendencies. It was observed that higher VI lubricant base-stocks and the re-refined engine oil base-stock gave better test performance in both bench and standard engine tests.     

Determination of synthetic lubricant concentrations in soil during laboratory-based biodegradation studies

The use of synthetic, biodegradable lubricants for two-stroke engines has become widespread due to increased concern over the build-up of hydrocarbons, derived from mineral oil-based lubricants, in the aquatic environment. A method for assessing the biodegradation potential of new lubricants was developed by the Co-ordinating European Council (CEC) for the Development of Performance Tests for Lubricants and Engine Fuels in 1982. However, this method deals only with the aquatic environment. The use of such lubricants in agricultural machinery led to a modification of the CEC method to assess the relative biodegradability of lubricants in soil. After incubation of oil-treated soil in a simple and inexpensive incubation assembly, samples were extracted with solvent and the level of lubricant determined by infrared spectroscopy. The method was found to be both accurate and reproducible, giving excellent recoveries. It compared favourably with a gravimetric method and was so sensitive that it gave appreciable blank values from untreated soils owing to their content of long chain aliphatic natural products. The incubation and extraction methods were used successfully to assess the biodegradability of a range of synthetic lubricants in soil in comparison to a mineral oil-based lubricant and a natural vegetable oil. The synthetic oils were found to degrade more rapidly and extensively than the mineral oil-based lubricant but not as rapidly or extensively as the vegetable oil. Amendment with nitrate considerably enhanced the loss of all the oil tested, indicating the importance of nitrogen availability when assessing the inherent biodegradability of hydrocarbons in soil. As the data generated is from laboratory-based studies the results do not necessarily translate directly to the field situation. However, the method is suitable for screening new materials and for comparative purposes.     

Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts

The wear and friction behaviour of an ionic liquid 1‐ethyl‐3‐hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X‐ray analyser attachment (SEM/EDS) and X‐ray photoelectron spectroscopy (XPS). A low friction coefficient (˜0.05) was recorded when lubricating with L206; a small amount of water (5 wt. %) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF₃, Al₂O₃, AlO(OH), and Al(OH)₃ formed during friction; there was no indication of boron on the worn surfaces.     

Analysis of a thrust bearing with a viscoelastic lubricant

The characteristics of a thrust bearing with a viscoelastic lubricant have been analysed. The elasticity of the lubricant, the volume rate of flow of lubricant and the ratio of the inner and outer radii of the bearing are characterized by the parameters α, β and σ. The effects of these parameters on the pressure distribution and the load-bearing capacity have been studied.     

Additive Mechanism Investigation of Perfluoropolyether Lubricants with a Phosphazene Additive

The tribological characteristics of magnetic thin film media coated with perfluoropolyether (PFPE) lubricants (ZDOL and AM300J) and a phosphazene additive (X-IP) were investigated in this study. The drag test results show that under ambient and hot/wet conditions the media coated with AM300J lubricant have higher retention on the test track than those coated with ZDOL 2000 PFPE lubricant. The phosphazene additive X-IP was observed to strongly anchored to the surface and was not as easily removed as PFPE lubricants alone. The retention characteristics of X-IP are independent of either AM or ZDOL. Secondary Ion Mass Spectroscopy (SIMS) depth profile data and Angle-Resolved X-Ray Photo-electron Spectroscopy (XPS) reveal that X-IP molecules were distributed near the disk surface in the X-IP and PFPE lubricants mixed layer, indicating a strong bonding/adhesion of X-IP to the disk surface. Together with the drag testing data, the authors conclude that the preferential distribution of X-IP close to the disk surface in the mixed layer helps to improve lubricant retention performance at the head-disk interface.     

Analysis of step bearings with a micropolar lubricant

Squeeze film step bearings lubricated with a micropolar fluid were analysed. It was found that the load capacities increase as the micropolar parameter $\text{}\text{?}\text{gm}{}_1$ increases or as $\text{M =}\text{h}{}^2\text{μ}\text{4γ}$ decreases. The load capacity also decreases as the step height increases.     

The unusual behaviour of a lubricant boundary layer

Oil starvation, finger formation and non-linear flow of the oil at the entry of a friction system are generally treated as problems of fluid dynamics. The present work attempts to show that an important, if not the most important, reason for these flow anomalies is the energetic interaction of the oil with the metallic surfaces and with the solid-like adsorbed layer. The experimental results obtained so far indicate that the behaviour of sliding bearings is inferior to that expected theoretically but that the gap can be sensibly reduced by modifying the interface relation between the contiguous phases that constitute the friction system.     

Measurement of lubricant flow in a gasoline engine

A residence time of approximately 60 s for lubricant in the piston ring pack of a gasoline engine, running at 1500 rpm, 50% throttle, has been measured by adding a hydrocarbon marker to the oil in the sump and monitoring its build up in oil extracted from the top ring groove. Comparison of the rate of increase of oxidised products in the sump with the level of oxidation in the ring pack allows a rate of flow of oil entering the ring pack from the sump to be calculated as approximately 0.4 cm³ min⁻¹ cylinder⁻¹, with at least 88% returning to the sump and the remainder lost into the combustion chamber. The volume of oil in the ring pack was determined as approximately 0.4 cm³ cylinder⁻¹, approximately one quarter of the free volume available between the top of the oil control ring and the top piston ring.