Evaluation of surface fatigue performance of gear oils

The effect of additive chemistry on the surface fatigue of gears was investigated using an FZG gear tester and fluids based on an API GL-5 grade gear oil. Surface fatigue lives were determined as a function of load and additive chemistry. At 1.52 GPa, the removal of the primary extreme pressure (EP) additive from the fully formulated gear oil decreased the fatigue life of gears slightly (4%). However, the removal of the primary antiwear (AW) additive decreased the fatigue life of gears significantly (83%). At 1.86 GPa, the removal of the EP additive from the fully formulated gear oil decreased the gear fatigue life by 27%. However, the removal of the primary AW additive decreased the fatigue life of gears significantly (75%). Micro-pitting was the dominant surface morphology in the dedendum of the gears tested with two oils at load stage eleven: one using the complete additive package, and a second where the EP additive had been removed. However, spalling was the primary failure mode of gears tested without an AW additive, independent of whether an EP agent was present. Surface analysis of the pinion gears showed the formation of a mixed phosphate/phosphite—oxide layer on the surface of gears tested with fluids containing an AW additive. Formation of this layer seems to be the key to a long fatigue life.     

Sulphurised vegetable oils as EP additives for industrial gear oil formulations

Renewable sources can provide, besides fuel, a wide range of feed stocks for the organic chemicals industry. Utilisation of non-edible vegetable oils and speciality chemicals has, therefore, become relevant in recent times. Sulphurisation of three triglyceride oils (karanja, rapeseed, and castor oils) and liquid wax (jojoba) has been investigated in detail in order to examine the potential of sulphurised vegetable oils for use as extreme-pressure (EP) additives for developing formulations for industrial gear oils. The capacity of these oils with respect to the uptake of sulphur, the limitations of some of the sulphurised products for use as EP additives, and the problems in developing such formulations for industrial gear oils, are discussed.     

A surface wear model for hypoid gear pairs

In this paper, a methodology was proposed for simulation of surface wear of face-milled or face-hobbed hypoid gear pairs. The methodology combines Archard's wear model with a finite-element based hypoid gear contact model. The wear model requires the sliding distances and contact pressures to be computed along the contact zones at each rotational gear position. Formulations were proposed for computation of sliding distance along the tooth contact zones based on hypoid gear kinematics and geometry of the tooth surfaces, and the contact model was used to predict the normal contact pressure distributions. An example hypoid gear pair was analyzed for its wear behavior. Influences of gear position errors on wear patterns were demonstrated. An approximate method that is computationally more efficient was also proposed at the end.     

Torque loss in a gearbox lubricated with wind turbine gear oils

In this study, four different fully formulated ISO VG 320 wind turbine gear oils were select: a mineral oil‐based, a polyalphaolefin‐based, an ester‐based and a polyalkyleneglycol‐based fluids. Their physical properties (viscosity, thermoviscosity, piezoviscosity etc.) were characterised for a wide range of operating temperatures. A two‐stage multiplying gearbox, with helical gears, was selected to evaluate the influence of the wind turbine gear oil formulation on torque loss with the gearbox operating at low speed (130–230 rpm) and high torque (500–1000 Nm). The results obtained showed that each wind turbine gear oil formulation generated very different torque losses, evacuated heat flows and operating temperatures, with differences above 20 °C under the most severe operating conditions. A numerical model was developed, simulating all power loss mechanisms inside the gearbox, in particular the churning and friction losses. The coefficients of friction, between gear teeth and between rolling elements and bearing raceways, were calculated for all the tested oils. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of temperature on the friction performance of gear oils in rolling–sliding and pure sliding contacts

The friction behaviour of five different gear oils in rolling–sliding and pure sliding contacts and how temperature influences their friction properties were investigated. It is found that increasing temperature decreases boundary friction with gear oils that contain friction modifiers while not for other gear oils, at all contact pressures investigated. In mixed lubrication region, temperature decreases friction at low contact pressures while increases friction at high contact pressures. The effect of slide–roll ratio on friction is significant in boundary lubrication region especially at higher temperature while less significant in mixed lubrication region at both low and high temperatures. The ranking of gear oils for friction in boundary and mixed lubrication regimes is similar both in rolling–sliding and pure sliding contacts, regardless of temperature. Copyright © 2013 John Wiley & Sons, Ltd.     

Calculation of sliding power loss in spur gear contacts

An engineering-level calculation model for sliding power loss in spur gear contacts is presented. Teeth contact through the line of action is modelled as a constantly changing roller contact whose radius, speed, and load can be calculated from the gear geometry under the given operating conditions. The gear mesh cycle is approximated by a large number of elastohydrodynamic contacts. A constant film thickness and a Hertzian pressure distribution are assumed in each contact. The model includes non-Newtonian lubricant behaviour together with temperature and mixed lubrication effects in contact. The numerical solver is reasonably fast in evaluating effectively the sliding power loss dependence on the essential gear and lubricant parameters. The features and behaviour trends of the calculated sliding power losses have a close similarity with published results obtained from measurements and experiment-based power loss models with mineral oil. The limiting shear stress of the lubricant is observed to have an essential role in the power loss behaviour especially at high loads.     

Antiwear Action of Mineral Lubricants Modified by Conventional and Uncoventional Additives

The authors of this paper investigated the influence of esters of rapeseed oil fatty acids on the lubricating properties of mineral lubricants containing chosen AW/EP additives. Methyl esters, ethylene glycol esters, and glycerol esters as well as some commercial AW/EP packages based on zinc dialkyldithiophosphate, S–P organic compounds, and sulphurized esters of fatty acids were tested. The tribological tests were carried out with the use of a four-ball machine. Antiwear (AW) properties of tested compositions were determined using their limiting load of wear (G_oz(40)). It appears that the AW action of esters of rapeseed oil fatty acids depends on their structure. The best AW action is shown by compositions of mineral oil lubricants containing AW/EP additives and methyl esters of rapeseed oil fatty acids. The SEM/EDS analysis of the scar surface layer indicated that the presence of these esters in lubricants causes a change in the interaction between AW/EP additives and the metal surface. These observations were confirmed by the XPS surface analysis.     

Suitability of vegetable oils as industrial lubricants

This paper reports on the application‐relevant properties of sixteen commercially available vegetable oils tested without additives in accordance with established standards. Their performance was compared with each other and with that of mineral oil and synthetic esters. The basic characteristics of all the oils (density, viscosity, pour point, cloud point, flash point and fire point) were initially determined. A chemical analysis of the vegetable oils was carried out to determine the acid value, saponification and iodine numbers. Additionally, the oxidative stability of all the oils was tested. The tribological performance, lubrication, and wear protection of the oils were judged under abrasive as well as adhesive conditions. The comparative study of the test vegetable oils showed great differences in the properties of the oils. All the vegetable oils tested revealed weak points during testing, including rape seed and castor oils, which have established uses in industry. This study shows that certain vegetable oils, such as sesame oil and wheatgerm oil, may have potential for use in selected technical applications. The mineral oil and synthetic esters showed markedly superior performance when tested under adhesive conditions, but comparable behaviour to the other oils under abrasive conditions.     

硫代磷酸酯胺盐抗磨剂的性能及应用

硫代磷酸酯胺盐具有好的热氧化安定性,极压抗磨性,水解安全性,是一种性能较全面的抗磨添加剂。该剂与其他功能添加剂复配,可调制７５Ｗ／９０,８０Ｗ／９０,８５Ｗ／９０重负载车辆齿轮油,多种粘度级别的重负荷工业齿轮油和７０ＴＢＮ船用气缸油。     

A scuffing load capacity test with the FZG gear test rig for gear lubricants with high EP performance

Methods for the evaluation of the scuffing load capacity of EP lubricants of API GL-4 and GL-5 performance levels have been developed for the standard FZG gear test rig, which has a centre distance of a = 91.5 mm. Procedure A10/16.6R/90 is capable of discriminating between industrial gear oils and automotive gear oils up to GL-4 performance level while procedure S-A10/16.6R/90 can be applied to GL-4 and GL-5 lubricants. The test methods were verified with reference oils and commercial gear lubricants. The results of the tests can be used to give a relative ranking of reference and candidate lubricants. They can also be used as limiting values in the scuffing load capacity rating method according to DIN 3990 (ISO DIS 6336).     

含硫,磷极压抗磨添加剂与CeF3配伍后对摩擦表面反应膜的影响

作者利用Ｘ光光电子能谱（ＸＰＳ）仪和自动划痕试验机研究了锂基脂中ＣｅＦ３与含硫、磷 中剂配伍后对摩擦表面反应膜的影响。划痕试验结果表明，在所试验的六种添加剂中只有二烷基二硫代磷酸锌（ＺＤＤＰ）、磷酸三甲酚酯（ＴＣＰ）和二正丁基亚磷酸酯（ＤＢＰ）与ＣｅＦ３配伍可有效地改善摩擦表面反应膜的附着性。ＸＰＳ研究结果表明，ＺＤＤＰ可改善ＣｅＦ３的成膜能力，抑制ＣｅＦ３的摩擦水解反应。ＣｅＦ３与其它添加剂复合     

Thermo-elastohydrodynamic lubrication of an involute gear

This paper analyses the thermo-elastohydrodynamic lubrication on an involute spur gear tooth surface and the influence of the inlet temperature of the lubricant. The oil film temperature distribution shows a minimum near the point where the pressure distribution is a maximum and the energy loss a minimum. Then the temperature increases slightly in the outlet region. Calculated results show a decrease of a few percent in the maximum pressure distribution compared with an oil film on a rigid surface. Based on oil film thickness and gear tooth deflection, the load sharing coefficient and the relative transmitting errors are calculated. The behaviour of the oil film due to the variation of the normal tooth load at the transition point of the meshing is investigated also     

润滑脂中极压抗磨添加剂的研究进展

综述近年来多种类型的极压抗磨添加剂在润滑脂中的研究成果,包括:层片状、球粒状添加剂、微纳尺度的软、硬质点添加剂、微纳尺度的氧化物及其他化合物添加剂、环保型添加剂。总结其抗磨减摩的作用机制,并针对目前研究存在的问题,提出了润滑脂用极压抗磨添加剂研究的方向。     

Sliding wear performance of different polyimide formulations

Sliding wear studies on different polyimide (PI) formulations against hardened, smooth steel were conducted using a pin-on-ring testing facility. Contact pressure p was varied in such a way that for three different sliding velocities v (0.6, 1.5 and 3.0 m s⁻¹) two pv levels could be maintained (1.7 and 5.0 MPa m s⁻¹). The best results were achieved with a PI formulation containing 15 wt% graphite filler and 10 wt% fluorocarbon resin having a wear factor

Full-size image (<1K)

. This material was also superior to newly developed high performance thermoplastics, in particular polyetheretherketone (PEEK) and thermotropic liquid crystal polymers (LCP), even when the latter contained about 20 vol.% of short glass or carbon fibre reinforcement.     

Acetal gear wear and performance prediction under unlubricated running condition

Tests have shown that the acetal gear wear rate will be increased dramatically when the load reaches a critical value for a specific geometry. The gear surface will wear slowly with a low specific wear rate if the gear is loaded below the critical condition. The sudden increase in wear rate may be due to the gear operating temperature reaching the material melting point under the critical load condition. Gear surface temperature has been investigated in detail by studying three components: ambient, bulk and flash temperatures. Through extensive experimental investigations and modelling on gear surface temperature variations, a general relation has been built up between gear surface temperature and gear load capacity. A new design method for acetal gear has been proposed based on the link between polymer gear wear rate and its surface temperature. The method has been related to test results under different operating ambient temperature and gear geometries. Good agreements have been achieved between the proposed method predictions and experimental test results. The maximum torque the acetal gears can transmit is 9 Nm for both the driver and driven with a 2 mm module, 30 teeth and 17 mm face width. Copyright © 2006 John Wiley & Sons, Ltd.     

Fling-off cooling of gear teeth

In any machine there are unavoidable sources of frictional heat generation. In gear transmissions, for example, heat is generated by tooth friction, bearings and seals, and by jetting of superfluous oil from between the teeth. All of the components within a machine are interconnected in a thermal network - the pattern of which is characteristic of that machine - which contains heat sinks and thermal resistances as well as heat generators. The particular thermal resistance due to fling-off of oil from gear teeth has a complicated nature and forms the object of this study. The theory is discussed and the results of calculation and experiment reported and compared.     

无机纳米抗磨剂的摩擦学性能研究

用超声波纳米粉碎机制备了纳米级的粉料,借助透射电镜表征分析了颗粒的粒度及形状。根据正交试验找到了较好的分散悬浮剂,通过添加分散悬浮剂和采用超声波分散的方法制备出悬浮性、分散性良好的油基纳米抗磨剂。用环块磨损试验机测定了纳米抗磨剂的摩擦学性能,发现：将含一定量的纳米抗磨剂加入到基础油中,可提高其抗磨减摩性能。正常供油状态下,该纳米抗磨剂的摩擦因数和相对磨耗都有了一定的降低。停止供油状态下,进一步验证了该纳米抗磨剂在摩擦表面的沉积及随后的剪切作用下形成了具有抗磨减摩作用的膜。     

Antiwear film formation of neutral and basic ZDDP: influence of the reaction temperature and of the concentration

Both synchrotron radiation-based techniques (XANES) and transmission electron microscopy (EDX, EELS) are used to draw a comparison of antiwear and thermal films generated from neutral and basic ZDDP salts. Antiwear films were created in a pin-on-flat wear machine and the wear debris was collected. The analysis of the tribofilms did not show any substantial difference between neutral and basic ZDDPs. The wear scar diameter and the P and S chemical environment in the tribofilm were very similar. The chemical analysis of the wear debris revealed differences in the chemical composition. Wear debris from basic ZDDP seems to be mostly composed either of unreacted ZDDP or of a linkage isomer of ZDDP (LI-ZDDP), and zinc polyphosphate; whereas the wear debris as far as neutral ZDDP is concerned seems to be exclusively composed of zinc polyphosphate (and sulphur species). More iron was also detected in the wear debris with basic ZDDP – possibly an indication of the iron content of the tribofilm. Differences in chemical structure could also be detected in the thermal films. While neutral ZDDP reacted with the surface to form polyphosphates at 150°C, the same reaction products were obtained with basic ZDDP at 175°C. The concentration of ZDDP in oil is thought to be the main parameter to explain the differences in the thermal film formation. This revised version was published online in July 2006 with corrections to the Cover Date.