Wear Of Spur Gears Research Articles

Active learning strategy-based reliability assessment on the wear of spur gears

Active learning strategy-based reliability assessment on the wear of spur gears

Influence of tooth profile and surface roughness on wear of spur gears considering temperature

Influence of tooth profile and surface roughness on wear of spur gears considering temperature

Effect of Tooth Surface Roughness on Wear of Spur Gears

Since gears transmit motion by meshing teeth, it is hard to avoid problems which wear and damage to the tooth surface. Because Tooth surface wear is difficult to predict, the approach to the wear problem still often relies on empirical rules and symptomatic measures. If the undermining by wear can be predicted by mathematical formulas, it may allow engineers to solve wear issues in model-based development, or to consider wear resistance from the design state. Therefore, the development of wear prediction formulas seemed like a very valuable goal, so the authors decided to work on it. In this paper, as a step for the final goal, the gear driving test was conducted using multiple gears with different tooth surface roughness. Then to detect changes in tooth profile, the tooth profile error was measured, and wear depth was calculated. Moreover, surface roughness on teeth was measured, and the relationship between surface roughness and wear depth was investigated.

Classification of stages of wear in spur gears based on wear debris morphology

This work investigates the morphological changes in the wear debris, generated during the different stages of gear wear. Wear debris are generated at the mating load-bearing tooth surfaces having relative motion. The number and size of collected wear debris provide useful information for the gear fault diagnosis.
 In the present work, both online and offline analyses of wear debris are carried out for gear fault diagnosis. In the online analysis, the oil from the gear sump is passed through online wear debris counter (to estimate the number of wear particles per minute) and particle size bin. Along with the online process, the oil samples are collected periodically, and wear debris particle images are captured using a scanning electron microscope (SEM). These images are subsequently processed to determine the parameters related to the shape, size and boundary features of the particles. The results of the modified texture in different stages of gear wear are reported. The average wear mass calculated as the actual area of the wear particles is combined with particle per minute is used as the stage’s classification.
 The combined online and offline study provides a better prediction of mild wear progression along with the information on the wear mechanisms at different stages of wear. The presence of different type of particles (ferrous and non-ferrous) points to degradation of specific components.

Study on wear in spur gears based on an improved load distribution model considering the effects of corner contact

Gear surface wear is an unavoidable tooth profile deviation and can influence gear load distribution and transmission error. Because of that, it is necessary to study the interaction between them and wear. For that purpose, a modified wear prediction model has been established by combining the potential energy method, and an improved load distribution model considering the effect of corner contact. The load share ratio (LSR) obtained from the improved model is verified by the finite element method (FEM). And relative to the FEM, the proposed model is much more efficient. Besides, the influences of wear accumulation process and corner contact on loaded static transmission error (LSTE) and load distribution are discussed. The results show that considering the effect of corner contact is necessary and can improve the accuracy of the wear prediction. And, it can be observed that there is a significant time-varying characteristic on LSTE, LSR of worn gear, as well as a correlation between them. Furthermore, the influence of gear modulus and gear ratio is discussed as well and it is found that both can effectively reduce the wear depth and significantly influence the condition of corner contact.

Monitoring gear surface degradation using cyclostationarity of acoustic emission

Abstract This paper aims at establishing a correlation between gear wear in spur gears and the statistical properties of AE signals. A generalised Gaussian cyclostationary model is proposed for AE signals measured on gears. This choice is motivated by the characteristics of lubricated contact in spur gears, combining non-stationarity (i.e. cyclostationarity) and non-Gaussianity (i.e. impulsiveness). The former is due to the cyclic kinematics of gear tooth meshing, which leads to a periodicity in the statistics of the AE signal, while the latter is caused by rapid energy release from asperity deformation during gear tooth contact. Two gear wear indicators are defined and estimated based on this assumption (cyclic kurtosis and cyclic scale parameter) and their evolution is monitored against direct measurements of surface degradation in an endurance test. Results show that the proposed indicators are sensitive to monitoring wear phenomena on gear tooth surfaces.

Online condition monitoring of misaligned meshing gears using wear debris and oil quality sensors

PurposeThis paper aims to investigate the effect of misalignment on wear of spur gears and on oil degradation using online sensors.Design/methodology/approachThe misalignment effect on gears is created through a self-alignment bearing, and is measured using laser alignment system. Several online sensors such as Fe-concentration sensor, moisture sensor, oil condition sensor, oil temperature sensor and metallic particle sensor are installed in the gear test rig to monitor lubricant quality and wear debris in real time to assess gearbox failure.FindingsOffset and angular misalignments are detected in both vertical and horizontal planes. The failure of misaligned gear is observed at both the ends and on both the surfaces of the gear teeth. Larger-size ferrous and non-ferrous particles are traced by metallic particle sensor due to gear and seal wear caused by misalignment. Scanning electron microscope (SEM) images examine chuck, spherical and flat platelet particles, and confirm the presence of fatigue (pitting) and adhesion (scuffing) wear mechanism. Energy-dispersive X-ray spectroscopy analysis of SEM particles traces carbon (C) and iron (Fe) elements due to gear failure.Originality/valueGear misalignment is one of the major causes of gearbox failure and the lubricant analysis is as important as wear debris analysis. A reliable online gearbox condition monitoring system is developed by integrating wear and oil analyses for misaligned spur gear pair in contact.

Measurement of mean wear coefficient during gear tests under various operating conditions

Seven wear tests were conducted on an FZG gear testing machine in order to ascertain the influence of basestock (PAO and mineral), specific film thickness and contact load on the wear of spur gears, particularly on the wear coefficient κ that is used in Archard׳s law. The results showed that load may have some influence on the wear coefficient. They also showed that the influence of specific film thickness on wear is very non-linear. The influence of basestock, even with oils of similar viscosity, is very significant, as much as any other parameter in isolation.

Assessment of surface contact fatigue failure in a spur geared system based on the tribological and vibration parameter analysis

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. The changes in operating conditions such as increase in temperature, load, reduction in viscosity result decrease in lubricant film thickness and degradation of lubricating oil thereby triggering several types of failures on tooth surfaces viz. pitting, scuffing, micro pitting, scoring, and spalling, these faults influence changes in vibration signals. This paper presents the results of experimental investigations carried out to assess wear in spur gears of single stage spur gear box under fatigue test conditions. The studies considered the lubricant film thickness analysis, wear mechanism studies on gear tooth surfaces, oil degradation analysis using Fourier transform infrared radiation (FTIR) method along with vibration signal analysis. The results provide a good understanding of tribological and vibration parameters as measures for effective assessment of wear in spur gears.

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.

The influence of contact stress distribution and specific film thickness on the wear of spur gears during pitting tests

One of the main gear damage mechanisms is the formation of pitting and spalling on the tooth flank. Several factors have significant influence on the damage formation, such as: contact stress level; tooth profile type; relative contact speed; surface finish and lubrication conditions. This work comprehends the global observation of all such parameters and was carried out to explain the phenomena related to this wear mechanism. The wear test equipment uses the power recirculation principle and is commonly known as FZG test rig. The gears were made from AISI 8620 steel and had two types of surface finishing (by shaving or by milling). The wear experiments were performed with two torque stages: 135 N.m (running-in) and 302 N.m (steady-state), and two test temperatures: 60oC (running-in) and 90oC (steady-state). The wear level was determined by using image analysis. In order to calculate the specific film thickness and friction coefficient, the roughness of tooth flank was measured at each test stop. After the experiments were completed, it was possible to confirm that, for both manufacturing processes, the boundary lubrication regime was adopted at the tooth flank and the specific film thickness presents a different behavior when compared to addendum, pitch diameter and deddendum regions. The wear on the gear flanks depended on the lubricant film thickness and it was higher for the milled gears.

Prediction of Steady State Adhesive Wear in Spur Gears Using the EHL Load Sharing Concept

The concept of load sharing between asperities and fluid film is applied in conjunction with lubricated sliding wear formulation proposed by Wu and Cheng (1991, “A Sliding Wear Model for Partial-EHL Contacts,” ASME J. Tribol., 113, pp. 134–141; 1993, “Sliding Wear Calculation in Spur Gears,” ASME J. Tribol., 115, pp. 493–500) to predict the steady state adhesive wear in gears. Thermal effects are included using a simplified thermoelastohydrodynamic analysis. The prediction of the model is verified by comparing simulation results with published experimental data pertinent to steady state wear rate. The main advantages of this method are the accuracy and the remarkable computational efficiency. The results of parametric simulation study are presented to investigate the effect of speed and surface roughness on a portion of load carried by asperities and wear rate.

Thermoelastohydrodynamic Analysis of Spur Gears with Consideration of Surface Roughness

Thermoelastohydrodynamic lubrication (TEHL) analysis for spur gears with consideration of surface roughness is presented. The model is based on Johnson’s load sharing concept where a portion of load is carried by fluid film and the rest by asperities. The solution algorithm consists of two parts. In the first part, the scaling factors and film thickness with consideration of thermal effect are determined. Then, simplified energy equation is solved to predict the surfaces and film temperature. Once the film temperature is known, the viscosity of the lubricant and therefore friction coefficient are calculated. The predicted results for the friction coefficient based on this algorithm are in agreement with published experimental data as well as those of EHL simulations for rough line contact. First point of contact is the point where the asperities carry a large portion of load and the lubricant has the highest temperature and the lowest thickness. Also, according to experimental investigations, the largest amount of wear in spur gears happens in the first point of contact. Effect of speed on film temperature and friction coefficient has been studied. As speed increases, more heat is generated and therefore film temperature will rise. Film temperature rise will result in reduction of lubricant viscosity and consequently decrease in friction coefficient. Surface roughness effect on friction coefficient is also studied. An increase in surface roughness will increase the asperities interaction and therefore friction coefficient will rise.

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.

Influence of Tip Relief Modification on the Wear of Spur Gears with Asymmetric Teeth

Recently, spur gears with asymmetric teeth have been considered a way of increasing performance while maintaining the gearbox dimensions. Asymmetric teeth have different pressure angles on drive and coast sides. They provide, among other advantages, a high bending strength and low vibration. In spur gears with asymmetric teeth, wear has been observed to be a major failure mode. In this study, the impact of tip relief modification and pressure angle on the wear of spur gears with asymmetric teeth is numerically investigated. Here, the focus is on sliding wear. A wear model based on Archard's equation is employed to predict wear depth. The pressure angle and the tip relief are parameterized. In the analysis, instantaneous contact loads and Hertz pressures are used in wear depth calculations. It is shown that as the amount of the tip relief increases, the wear depth, particularly at the beginning and end of the mesh, decreases. As the number of wear cycles increases, the effect of the tip relief modification on wear depths decreases slightly. It was also shown that with an increase in tip relief, the dynamic load decreases. However, if the amount of tip relief modification increases excessively, the maximum dynamic load also increases. Therefore, an excessive increase in tip relief modification should be avoided, whereby the level of excessive increase depends on the tip relief configuration.

Dynamic interaction between contact loads and tooth wear of engaged plastic gear pairs

This study investigates the interaction between the dynamic contact load and the tooth profile wear of POM and Nylon 66 plastic gear pairs. A dynamic model of a plastic gear pair is presented. This model incorporates the effects of position-varying tooth mesh stiffness, damping ratio, load sharing, tooth profile wear and temperature on the dynamic contact load. The tooth wear equation developed by Flodin and Andersson [Simulation of mild wear in spur gears. Wear 1997;207:16–23] is utilized to simulate tooth wear and tooth profile variation. The variation of the contact load generated by the cumulative tooth profile wear is simulated and examined. A computational algorithm is developed to simulate the interaction between a dynamic contact load and tooth profile wear. Numerical results demonstrate that the dynamic load histogram of an engaged plastic gear pair can change markedly due to tooth wear.

Simulation of wear in gears with flank interference—a mixed FE and analytical approach

Gears in precision mechanisms, such as industrial robots, are often designed to have no backlash. Deviations from the ideal gear geometries and unfavourable deformations during operation may cause interference between interacting tooth flanks, resulting in high and strongly varying friction. Mild wear of the tooth flanks may improve such conditions. Therefore, this theoretical study has been conducted of wear in spur gears with interference. A mixed finite element (FE) and analytical approach is used. The FE method is used to determine contact loads between the interacting gear teeth. The main drawback with FE analyses of this type of problem is normally the computation time needed. Therefore, a novel FE meshing method is used, giving a dense FE mesh in the contact regions and a coarse mesh in the rest of the teeth. Based on the FE determined loads between the interacting teeth, the contact pressures and the contact widths are then easily determined using analytical expressions based on Hertz theory. The wear of a point on a tooth flank is determined by integrating the product of sliding distance and contact pressure during the time it is in contact with its mating flank. The results show that the wear of the gear tooth flanks may eliminate the interference and consequently the high and strongly varying friction will decrease dramatically. However, the transmission error will change, since the gears will not preserve their accurate involute profiles.

Wear simulation of spur gears

AbstractThis paper deals with prediction of wear in spur gears, which has been calculated using an approach in which the wear depth on a tooth surface is integrated over time using the Euler integration method. Variations in pressure distribution over the surface have been considered, as well as changes in curvature and surface profile of the teeth as they wear. The paper focuses on the use of an appropriate wear model for simulating wear using calculated conditions between high‐performance slow‐running lubricated spur gears. A numerical model for prediction of surface interaction of spur gears developed earlier by the authors has been applied as the basis for the simulation of wear using different wear models. Owing to the nature of the wear models, methods of calculating the contact temperature have been investigated for the specific case of interacting gear teeth. It was found that a linear wear model, when compared with a more complex oxidation model and with a model based on adsorption of lubricant molecules, satisfactorily predicts wear. It was also found that it is the geometry of the gears that causes sliding velocity to be the dominant wear‐inducing factor, and so determines the general nature of the wear behaviour.

Simulation of mild wear in spur gears

Mild wear in gears is in most cases a smooth process giving initially improved contact conditions followed by a very slow and mild wear process. In some cases the mild wear may cause unfavorable changes of the surface topography, giving non-uniform gear rate, increasing dynamic effects and perhaps more severe forms of tooth failures. The knowledge about the interactions between mild wear, dynamic effects and other severe failures is rather limited. This paper therefore treats mild wear of spur gears, how it can be simulated and the effects of the same on contact conditions. A numerical model for wear prediction of spur gears is developed. The model can adopt any wear model although in this paper the wear simulations are based on a generalized Archard's wear equation. The running conditions for gear tooth surfaces are particularly considered and the contact between the surfaces are modelled by Winkler's elastic foundation model.

Studies on Friction and Wear of Spur Gears in High Vacuum. 1st Report. Case of Stainless Steel SUS 304.

In this report, the friction and wear of austenitic stainless steel spur gears of which the surface layer was thermally diffused after being Sn-plated were exammined in high vacuum. Gear tests were carried out under grease lubrication and dry friction in vacuum of about 2 x 10-3 Pa using a power-circulating gear test rig. From the tests, the following results were obtained. ( 1 ) In the case of grease lubrication, the ratio of the gear frictional loss torque to the transmitted torque was in the range of 0. 01 to 0. 05. ( 2 ) The time to reach destructive surface failure of the gears due to thermally diffused treatment was significantly long. This long time was observed in both dry friction test and grease lubrication one. The optimum diffused layer thickness was about 4 μm in the case of grease lubrication. ( 3 ) The acceleration of the gear box when the gear tests could not proceed due to destructive surface failure was significantly increased, and then the destructive surface failure could be detected by means of the measurement of acceleration due to vibration of the tested gear box.