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.     

A new approach for polymer composite gear design

A new design method for polymer composite gear has been proposed in the current paper. This design method is based on the link between polymer gear wear rate and its surface temperature. It has been found from the tests that the polymer (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 one. The possible reason of the sudden increase in wear rate is due to the gear operating temperature reaching the material melting point under the critical load condition. Gear surface temperature has been then investigated in detail through 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. The method has been related to test results under different operating ambient temperature and gear geometries. Good agreement has been achieved between the proposed method predictions and experimental test results. Experimental investigation on polymer composite (glass fibre reinforced nylon with PTFE as internal lubricant) gears have also been carried out and two forms of failure have been found, root and pitch fractures.     

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.     

An Experimental Investigation of the Influence of the Lubricant Viscosity and Additives on Gear Wear

The influence of lubricant viscosity and additives on the average wear rate of spur gear pairs was investigated experimentally. The gear specimens of a comprehensive gear durability test program that made use of seven lubricants covering a range of viscosities were examined to measure gear tooth wear. The measured wear was related to the as-manufactured surface roughness, the elastohydrodynamic film thickness, and the experimentally determined contact fatigue lives of the same specimens. In general, the wear rate was found to be inversely proportional to the viscosity of the lubricant and to the lambda ratio (also sometimes called the specific film thickness). The data also show an exponential trend between the average wear rates and the surface fatigue lives. Lubricants with similar viscosities but differing additives and compositions had somewhat differing gear surface fatigue lives and wear rates.     

低速重载齿轮的磨损试验与研究

对圆周速度υ＝1～4m/s的齿轮传动进行了磨损试验。试验表明,υ＝1～4m/s低速重载齿轮均存在不同程度的齿面磨损,其磨损速率与圆周速度有关,且存在一最恶速度值,当齿轮处于最恶速度运动时磨损速率最大。对最恶速度现象进行了分析,认为边界润滑油膜仍具有一定的流变性,最恶速度现象与边界润滑油膜流变性形成的局部涡流有关。在试验条件下,最恶速度值为1.13～1.41m/s。为了提高齿轮的寿命,应避免齿轮在最恶速度及其附近运行。     

Influence of oil temperature on gear failures

Typical gear failures like wear, scuffing, micropitting and pitting are influenced by the oil temperature in the lubrication system. High temperatures lead to low viscosities and thus thin lubricant films in the gear mesh with generally detrimental influence on failure performance. On the other hand, for gear oils with additives higher temperatures correspond with higher chemical activity and, at least in some cases, with better failure performance of the lubricant. Last, but not least, at very high temperatures even metallurgical changes have been found with a reduction in material endurance limits. Examples for the influence of oil temperature on gear failure modes, as well as their introduction into load carrying capacity calculation methods are shown. With this background, the often-applied practice of increasing the severity of a gear oil test method by increasing the oil temperature has to be revised. Adequate solutions are discussed.     

The wear behaviour of polymer composite gears

In order to examine the wear of polymer composite gears, a test facility has been developed which has enabled the wear of gear trains to be measured continuously during gear operation. Brief details of the method are given. The purpose of this paper is to report some of the results obtained from this facility and, in particular, to discuss the effect of temperature on the wear of acetal gears.     

Durability improvement method for plastic spur gears

An experimental investigation of power-transmission plastic spur gears was performed by inspecting both the characteristics of wear and durability, and a durability improvement method is proposed that either drills an internal hole or inserts a steel-pin in the internal hole of the gear tooth, and this proposed method was verified. In the case of acetal gears, the amount of wear was observed to increase with the development of plastic deformation, and an increase in tooth stiffness occurred due to the brittle material property of acetal. On the other hand, in the case of nylon gears, the proposed method was shown to reduce the tooth temperature compared to the original gear, thus reducing the amount of wear and prolonging service life. Hence, the proposed method was proven to be practically applicable to plastic gears made from soft polymers that show visco-elastic properties such as nylon.     

反推齿轮胶合临界温度可靠性的试验研究

本文提出了用闪温准则反推齿轮胶合临界温度的计算方法，进行了大量齿轮抗胶合承载能力试验，根据试验结果对５０号机械油的临界温度进行了反推计算，分析和对比结果表明，该计算方法是可靠的，试验方案设计是合理的，为确定各类油品润滑时齿轮胶合临界温度奠定了基础。     

齿面粗糙度对低速重载齿轮磨损性能的影响

本文用自制磨损实验机对低速重载齿轮进行了滑动磨损模拟实验,通过实验研究了齿面粗糙度对低速重载齿轮磨损性能的影响,并得出了有益的结论。     

MoS2/Ti low-friction coating for gears

The applicability of a multilayer composite surface coating in gears is discussed in this work, mainly in what concerns to gear efficiency at normal operating conditions and to scuffing load capacity. The average friction coefficient between gear teeth is discussed and compared with uncoated steel gears.The disulfide molybdenum/titanium (MoS₂/Ti) composite coating is studied and the deposition procedure is described.Several screening tests, like Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, were performed to evaluate the adhesion to the substrate, the tribological performance of this coating and his applicability in heavy loaded rolling-sliding contacts, such as found in gears.FZG gear efficiency tests were performed using type C gears in order to evaluate the influence of the surface coating in gear efficiency, for a wide range of operating conditions. These tests in conjunction with a numerical model for the energetic balance of the FZG gearbox allowed the determination of the average friction coefficient between gear teeth, taking into account the presence of the surface coating.FZG gear scuffing tests were also performed using type C gears in order to evaluate the coating anti-scuffing performance, which proved to be very significant.     

Acoustics Based Monitoring and Diagnostics for the Progressive Deterioration of Helical Gearboxes

Gearbox condition monitoring (CM) plays a significant role in ensuring the operational reliability and efficiency of a wide range of critical industrial systems such as wind turbines and helicopters.Accurate and timely diagnosis of gear faults will improve the maintenance of gearboxes operating under sub-optimal conditions,avoid excessive energy consumption and prevent avoidable damages to systems.This study focuses on developing CM for a multi-stage helical gearbox using airborne sound.Based on signal phase alignments,Modulation Signal Bispectrum (MSB) analysis allows random noise and interrupting events in sound signals to be suppressed greatly and obtains nonlinear modu-lation features in association with gear dynamics.MSB coherence is evaluated for selecting the reliable bi-spectral peaks for indication of gear deterioration.A run-to-failure test of two industrial gearboxes was tested under various loading conditions.Two omnidirectional microphones were fixed near the gearboxes to sense acoustic information during operation.It has been shown that compared against vibration based CM,acoustics can perceive the responses of vibration in a larger areas and contains more comprehensive and stable information related to gear dynamics vari-ation due to wear.Also,the MSB magnitude peaks at the first three harmonic components of gear mesh and rota-tion components are demonstrated to be sufficient in characterizing the gradual deterioration of gear transmission.Consequently,the combining of MSB peaks with baseline normalization yields more accurate monitoring trends and diagnostics,allowing the gradual deterioration process and gear wear location to be represented more consistently.     

Signature Response for Friction and Wear

An experimental study of signature response for friction and wear is carried out in a triplane ball-on-peg machine under varying load conditions. Photographs of worn roller test specimens at critical temperatures were taken to determine the nature of the wear surface under boundary lubricated conditions. Acoustic response in the beginning and at the point of scuffing has demonstrated a definite trend which follows a similar pattern as that of friction. The experiment was repeated with a combination of steel and brass and with steel and mild steel using as the lubricants hexadecane, MoS₂ and light stock oil. The scuffing load was accompanied by severe wear of the surface. A critical value for friction and that of acoustic response was observed with variations in temperature. Results obtained contribute to the assesment in the change in friction and wear values on sliding surfaces. This help comes from a knowledge of acoustic emission and the known condition of the surface and both components of the pair. The findings of these experimental results and the mode of signature response provides a good scope for further investigations aimed at understanding the mechanism and establishing a method for diagnostic maintenance.     

基于闪温法的传动齿轮抗胶合可靠度分析与计算

以Block闪温法为基础，论述了齿轮传动抗胶合可靠性分析模型和计算方法，并用实例加以说明，为探索可靠性技术在齿轮抗胶合承载能力计算中的应用进行了有益的尝试。     

车辆齿轮油承载能力的估算

从纳米摩擦学角度考察了车辆齿轮的四球机测定结果,发现最大无卡咬负荷ＰＢ和烧结负荷ＰＤ值不能很好地代表承载能力。阐明了由这两个指标难于预测车辆齿轮油承载能力的原因是：（１）钢球材质与实际摩擦副的不同;（２）钢球的接触方式是点接触;而齿轮是线接触;首次提出一套利用四球机测试估算车辆齿轮油承载能力的方法,指出实际选择齿轮油时可根据经的啮合压力来确定油品在四球机试验中应达到的比压力。     

机械设备新旧程度检测方法的研究(Ⅰ)——齿轮箱磨损试验

本文通过机械设备(齿轮箱)的磨损试验,获得机械设备运行过程中的磨损曲线。在定量分析的基础上,建立推断机械设备新旧程度的评定指标。     

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.     

考虑磨损的直齿轮啮合刚度计算与分析

基于能量法和Archard磨损模型,提出了一种考虑磨损的齿轮啮合刚度数值计算方法.根据展成法原理,建立了精确的齿廓曲线方程.利用能量法计算齿轮单齿啮合刚度,并通过分段1阶傅里叶级数拟合获得齿轮总啮合刚度.以Archard磨损模型为基础,计算得到齿面法向磨损量与啮合点处压力角的关系.计算分析了不同磨损量对齿轮啮合刚度的影...     

On the prediction of the design criteria for modification of contact stresses due to thermal stresses in the gear mesh

The mechanism of surface failure due to temperature rise is a very important problem in gear design. Thermal considerations have received considerable attention from the gear researchers but only for scoring failures when the destruction of lubrication film occurs as a result of temperature rise. In spite of the wealth of literature on this subject, this problem is not fully analyzed.The objectives of this paper are to consider the mechanisms of thermal stresses and the thermal cycling in contact zone, during the gear mesh. This research has been conducted for the first point of contact based on consideration of transient heat transfer, elastohydrodynamic lubrications, and surface roughness and gear material.A procedure presented in this paper evaluating the stresses (thermal and mechanical) and predicting the design criteria for modifying the contact stresses due to thermal stresses. The effect of the material, oil film thickness, surface roughness and geometric operating parameters on modification parameter is illustrated. Also the effects of a load on the temperature rise and the modification parameters are evaluated.     

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。