Effect of sursulf treatment on the performance of 0.14% C steel gears

Sursulf-treated low carbon steel gears were tested in a back-to-back gear test rig. The failure of the gears is by pitting and the contact stress-pitting life curve has been established. Wear particle analysis of the lubricating oil was carried out to analyse the nature of the failure. The study reveals that Sursulf treatment on low carbon steel gears considerably improves their performance. The cumulative wear particle concentration at the pitting limit has been suggested as a basis for predicting the onset of failure of the gears.     

Durability and performance evaluation of surface treated worm drives of similar material pair

The present work is concerned with development and analysis on the performance of a similar material pair worm drive. Experiments were carried out on En-353 steel, case hardened worm mating with Sursulf treated wheel made of the same material. A constant value of limiting torque has been established at all tested speeds. It is found that at higher speeds (>1200 rpm) temperature increases progressively without attaining a stable value, leading to thermal instability. Beyond this, lubrication failure has been observed. Efficiency is relatively higher at intermediate torque levels. Reduced efficiency at higher torque level is due to ineffective lubrication. From the wear debris analysis, it was observed that no uncharacteristic mode of wear prevailed at any of the tested conditions. A fairly low value of coefficient of friction based on operating conditions is observed. This can be attributed to the presence of Sursulf treatment. The drive has not exhibited any tendency to scuffing or scoring within the range of tested conditions for continuous duty, largely attributed to Sursulf treatment.     

Surface integrity studies on shot-peened thermal-treated En 24 steel spur gears

En 24 steel spur gears in untreated and thermal-treated conditions with and without shot peening were tested in a back-to-back gear test rig. Surface finish at the pitch region and wear loss were monitored. Surface integrity studies and ferrographic analysis of wear debris enabled the interpretation of failure. The surface deterioration was less pronounced in the case of shot-peened gears and further they exhibited good steady-state wear characteristics compared to unpeened gears.     

基于拓展有限元的齿轮点蚀磨粒形态学特征模拟

疲劳点蚀是齿轮摩擦副的典型固有磨损特征,其产生的点蚀磨粒已经被用于理解疲劳磨损的发生和发展机理,由于缺乏理论模拟,基于磨粒特征的疲劳磨损机理判断还停留在经验分析层面。为此,拟通过齿轮接触疲劳点蚀的数值模拟,研究点蚀磨粒形态特征,为在线磨粒特征表征磨损状态的方法提供理论探索。在考虑弹流润滑的条件下,建立齿轮副局部接触模型,并采用拓展有限元法(Extended finite element method,XFEM)模拟表面萌生裂纹的拓展过程。进一步分析工况与点蚀磨粒形态特征的关系,结果表明,点蚀磨粒长轴尺寸随初始萌生裂纹的长度增加而增大,随载荷的增加而减小;点蚀磨粒的厚度随初始萌生裂纹的深度增加而增大。通过与已发表的试验结果进行对比,该模型所得到的点蚀形貌尺寸和形状与试验得到的点蚀形貌基本一致,从而验证了该模型的有效性。     

Contact endurance of gearing teeth subjected to ion-beam nitriding

Gears treated by intense nitrogen ion flows were calculated for preventing deep contact pitting, allowing for the real distributions of hardness in the depth of the hardened layer and reduced stresses. A method for calculating the contact endurance of gears hardened by ion-beam nitriding was proposed. The results of the calculations and experiments have shown that ion-beam nitriding leads to an increase in the load-carrying capacity of a gear 1.31 times in comparison with that of a gear with gears subjected to traditional nitriding; the wear resistance of the ion-nitrided gears is two times greater than that of hardened and tempered gears.     

含污染物油润滑条件下的磨粒磨损研究

概述了含污染物油润滑条件下的磨损试验方法，分析了磨粒尺寸、磨粒含量；材料硬度和材料表面粗糙度等试验参数对含污染物油润滑条件下材料的磨损性能的影响，结果表明其磨损机理主要是点蚀、犁削和熔着磨损，并提出了解决措施。     

Integrated wear prediction model for cylindrical gear with variable hyperbolic circular arc tooth trace under mixed elastohydrodynamic lubrication

Cylindrical gear with variable hyperbolic circular arc tooth trace (VH-CATT) is a new type of gear. Sliding wear is the main mode of the surface failure of multiple mechanical parts. Both the lubrication state and contact temperature considerably influence wear characteristics, which may aggravate the transmission performance of gear pairs. Wear, contact temperature, as well as lubrication states are jointly explored. Therefore, an integrated wear prediction model was proposed through taking into account flash contact temperature and surface roughness of VH-CATT cylindrical gears in mixed elastohydrodynamic lubrication. According to the equivalent ellipse contact model of VH-CATT cylindrical gears and tooth surface equation, normal curvature and velocity relations for VH-CATT cylindrical gears were observed, and the normal meshing force was obtained through the consideration of load sharing coefficients and quality grades. Flash contact temperature was estimated by using the literature. This study proposes analytical solutions for investigating how various surface roughness, operation, and geometric parameters affect asperity contact ratio (ACR), asperity contact pressure (ACP), flash contact temperature (FCT), as well as wear depth (WD) related to driving gears. ACR, ACP, FCT, as well as WD initially decrease and then increase from engaging-in to engaging-out processes. The minimum occurs at the pitch point. The WD declines as module, cutter radius, and rotational velocity increase while augmenting when surface roughness and torques increase. The maximum and minimum wear depths in driving gears occur at the dedendum and pitch point, respectively. Its overall wear is reduced by 23.16 % compared to the wear of spur gears. The results are valuable for the studies of tooth pitting, wear resistance, and fatigue life improvement for VH-CATT cylindrical gear. These studies can provide verification data and references required for engineering designs and VH-CATT cylindrical gear operations.

     

Intergranular cracking during pitting of gears

Pitting phenomenon in gears was studied using a power recirculating type test rig. The study of gear failure by pitting was made by micro-photographic analysis. Microscopical examination of pitted areas revealed transcrystalline cracks as well as intergranular cracking, a mode of failure not previously reported.     

Experimental studies on the effects of reduction in gear tooth stiffness and lubricant film thickness in a spur geared system

Gears are one of the most common mechanisms for transmitting power and motion and their usage can be found in numerous applications. Studies on gear teeth contacts have been considered as one of the most complicated applications in tribology. Depending on the application, the speed and load conditions of teeth may change triggering several types of failures on teeth surface such as wear, scuffing, micro-pitting and pitting. The above-mentioned faults influence changes in vibration and acoustic signals, due to changes in operating conditions such as increase in temperature and decrease in lubricant film thickness and specific film thickness. These abnormal changes result in cumulative effects on localised or distributed faults on load bearing surfaces of gears. Such damages cause reduction in tooth stiffness and severity of damage can be assessed by evaluating the same using vibration-based signals.This paper presents the results of experimental investigations carried out to assess wear in spur gears of back-to-back gearbox under accelerated test conditions. The studies considered the estimation of operating conditions such as film thickness and their effects on the fault growth on teeth surface. Modal testing experiments have been carried out on the same gear starting from healthy to worn out conditions to quantify wear damage. The results provide a good understanding of dependent roles of gearbox operating conditions and vibration parameters as measures for effective assessment of wear in spur gears.     

Thermal aspects of lubrication of concentrated contacts

Deterioration of gears occurs by abrasive wear, pitting (surface fatigue) or severe adhesive wear (scuffing). The effects of the latter mode may be mitigated by the use of extreme pressure (EP) additives but these sometimes accentuate the risk of pitting-type failure. Accordingly, EP lubricants are not recommended for industrial gearing. The introduction of elastohydrodynamic lubrication theory has demonstrated that it is possible to operate gears without physical contact between the interacting tooth faces. Under conditions of pure rolling (at the pitch point) there is good agreement between theory and experiment, but when relative sliding occurs the measured film thickness is lower than calculated. A recently derived theory, taking into account the effect of the heating arising from relative sliding on the hydrodynamic film thickness, has been applied to a set of industrial gears, from which it is deduced that the effect on load-carrying capacity of the gear is not serious. The theory has also been applied to some results obtained on the Institution of Automobile Engineers lubricant-testing machine.     

润滑和载荷状态对聚甲醛齿轮服役性能的影响

基于齿轮耐久性能试验台开展了一系列干接触/油润滑下POM(聚甲醛)-POM齿轮副承载能力试验,并测量了服役过程中的轮齿温度、磨损量、齿廓精度和齿面形貌。试验发现,POM齿轮失效形式与载荷和润滑方式有关。通过对齿面微观形貌和磨屑表征,确认干接触下POM齿轮主要磨损模式为黏着磨损与磨粒磨损,而油润滑下POM齿轮失效形式为接触疲劳失效。由于润滑油减少了齿面摩擦,降低了运行温度,延缓了齿面劣化程度,因此POM齿轮在油润滑下的承载能力明显提高。     

Influence of lubricants on the pitting fatigue of gears

Using the FZG gear tester with heat-treated and case-hardened gears the effect of lubricants and additives on the incidence of pitting fatigue was investigated. The influence of base oil type and additives requires further investigation before general conclusions can be derived. From the results now available extreme pressure additives which increase the scuffing load carrying capacity of case-hardened gears allow increased load testing without surface pitting failure. Additives have a direct beneficial influence on retarding the pitting of heat-treated gears. Of the additives tested, the most effective in reducing pitting fatigue failure was MoS₂, but with a high concentration of about 1.5%.     

Spalling formation mechanism for gears

Though the basic phenomenon of wear on gear tooth contact surfaces is the removal of a piece of material from the working surface, the sizes of the wear debris may be different, due to the different physical causes in their formation processes. No common definitions have been established to distinguish spalling from pitting in the literature. This is probably due to the fact that the physical causes of pitting and spalling have not yet been established. In this paper, a brief literature review is presented with the intention to differentiate spalling from pitting. Three types of wear phenomena are defined. Furthermore, the results of a recent experimental study of gear tooth spalling formation in AISI 4340 gears in a test rig are also presented to demonstrate a possible process of spalling due to the development of cracks beneath the tooth contact surfaces and crack linkages in plastically-collapsed metal ligament between the crack tip and the adjacent tooth contact surface. These experimental results substantiated the ligament collapse spalling mechanism proposed by Ding et al. [Y. Ding, R. Jones, B.T. Kuhnell, Elastic-plastic finite element analysis of spall formation in gears, Wear 197 (1996) 197-205; M. Heems, F. Lagarde, R. Courtel, P. Sorin, C. R. Acad. Sci. 257 (3) (1963) 3293].     

Detection and diagnosis of surface wear failure in a spur geared system using EEMD based vibration signalanalysis

Gears are used for transmission of power, motion or both. Under increased power and higher speeds, tribological failures such as scuffing, pitting, mild wear and tooth breakage are of major concern. This paper presents the results of experimental investigations carried out to assess wear in spur gears of a back-to-back gear box under accelerated test conditions. The studies considered the estimation of specific lubricant film thickness and its effects on the fault growth on gear teeth surface. Ensemble empirical mode decomposition (EEMD) technique is used to extract the fault related features from the vibration signals acquired from the gearbox. The results highlight the advantage of EEMD technique for effective assessment of wear in spurgears.     

An Experimental Investigation of Micropitting Using a Roller Disk Machine

Micropitting is a microscopic form of progressive fatigue wear. It is most often associated with case hardened gears although such failures have also been reported for rolling element bearings. This paper reviews the micropitting phenomenon and reports the results of an experimental study conducted using a roller disk machine. Analysis of the micropitted test specimens confirmed that the roller disk machine experiments faithfully reproduce the failure mode as found on full size gears. The effect of various operating parameters was investigated. The results show that increasing load, decreasing specific film thickness and maintaining negative relative sliding all increased the rate of micropitting wear. The authors also found that micropitting is almost completely eliminated at a very low, but non-zero, slide-to-roll ratio.     

Influence of lubricant on gear failures — test methods and application to gearboxes in practice

Base oil type, oil viscosity, and additive type and content have a strong influence on typical gear failures. As it is not possible to quantify the influence of a lubricant on load‐carrying capacity simply from a knowledge of the physical or chemical oil data, many test methods have been developed for the evaluation of mechanical—technological lubricant properties. Simple low‐cost bench test methods often show poor correlation with practice. From both experience and systematic investigation, it can be seen that testing of gear lubricants can be performed adequately only in gear test rigs using specified test gear geometry. The standard FZG back‐to‐back gear test rig has been developed over many years and improved for different types of gear failure simulation. The standard FZG oil test A/8.3/90 is widely used for the evaluation of the scuffing properties of industrial gear oils. Automotive gear oils of GL4 level can be tested in the step test A10/16.6R/90, and axle oils of GL5 level in the shock test S‐A10/16.6R/90. For slow‐speed regimes, the C/0.05/90:120/12 wear test can be used. The influence of lubricants on the micropitting performance of gears can be evaluated in the GF‐C/8.3/90 micropitting test. Different pitting tests are available, as single‐stage (PT‐C/9:10/90) or load spectrum (PT‐C/LLS:HLS/90) tests. The aim of this paper is to describe the influence of the lubricant on the different failure modes in gears, how to quantify this effect in adequate test methods, and how to introduce the results of such tests as determining values of the lubricant into load‐carrying capacity rating methods.     

Experimental measurement of strain and stress state at the contacting helical gear pairs

Contact stress evaluation in gears has been a complex area of research, due to its non-linear and non-uniform nature of stress distribution. The high contact stress on gears results in pitting and scuffing, which leads to tooth failure. Furthermore the effects of friction on gear contacts make the problem more complicated. Hence, in this paper, attempt has been made to study contact stress in gears. The experimental testing and analysis of the helical gear was carried out using Gear Dynamic Stress Test Rig (GDSTR). GDSTR is a newly designed test rig to compute the contact stresses on the gear pair contact, under real gear conditions. GDSTR uses the strain gauge and carbon slip rings to measure the surface contact stresses at the contacting points of a meshed gears. The experimental analysis showed promising results which have been verified by the finite element frictional contact analysis. The experimental testing was carried out on 5° and 25° helical gear pairs. Helical gear models with the same specifications and for different frictional coefficient conditions were also generated using FE modelling. The frictional contact stress analysis using FEM has been used for comparison with the experimental results.     

Influence of shot peening on the surface durability of thermomechanically treated En 24 steel spur gears

En steel, in untreated and thermal treated conditions, with and without shot peening, were tested in a back-to-back gear test rig. Their contact fatigue characteristics were studied and S–N curves have been established. Contact fatigue strength of shot peened gears for a given life showed an improvement in relation to unpeened gears.     

齿轮点蚀破坏中磨损与振动关系的试验研究

利用铁谱分析技术和振动分析技术中的时频分析方法研究了模拟点蚀故障齿轮磨损与振动的关系。分析结果表明点蚀齿轮磨损和4个时域特征值从一面一点、一面三点到多面多点依次变大,多面多点蚀齿轮磨损严重,磨粒数量最多;点蚀齿轮出现以输入输出端的啮合频率为中心,以转频为调制频率的边频带。齿轮磨损与振动相互关联,磨损量的变化率与振动方差变化率在3种点蚀齿轮中表现明显;但磨损量的增长率不仅与齿面点蚀的程度有关,还与点蚀的齿数有关;而齿轮的振动强度与齿轮齿面点蚀的程度最相关,即齿面点蚀破坏越厉害,振动越剧烈。     

Experimental simulation of gear contact along the line of action

In highly loaded gears, lubricated rolling/sliding contact conditions change greatly along the line of action. This leads to variation in gear frictional properties and to failures such as pitting and scuffing that take place in different positions along the tooth flank. Information on instant contact behavior is therefore very useful, but this kind of measurement in real gears is extremely complicated. Single spur gear geometry has been simulated at 38 steady-state measuring points along the line of action using a twin-disc test device focusing on the friction coefficient and on temperature and lubrication conditions. Twin-disc simulations were adjusted to match real gear experiments by using similar maximum Hertzian pressure and surface velocities. The results show that the curve shapes for the mean friction coefficient as a function of pitch line velocity are similar to the corresponding experimental results with real gears. Further, the calculated thermal Λ-values of real gears and the measured mean contact resistance correspond well. This approach shows potential for simulating gear friction and failure mechanisms along the line of action.