Gear Wear Research Articles

An investigation of misalignment effects on the performance of acetal gears

Abstract This paper concentrates on the effects of misalignment on meshing behaviour of acetal gears as hardly any misalignment investigations on polymer gears in the existing literature. The experimental results show that the wear of acetal gears is insensitive to radial and axial misalignments but sensitive to yaw and pitch misalignments which degrade the conjugate contact action. Yaw misalignment leads to ‘scoop’ wear marks near tooth pitch points. Pitch misalignment causes ‘superimposed palisade’ wear marks and micro cracks near tooth roots. Compared with metal gears, the effects of small pitch angle on acetal gears are insignificant which may be linked closely to polymer's low elastic modulus. Strikingly different wear striations and various debris morphologies are observed by using scanning electronic and optical microscope (SEM, OM) and misalignment effects can be noted.

Helical gear wear monitoring: Modelling and experimental validation

Gear tooth surface wear is a common failure mode. It occurs over relatively long periods of service nonetheless, it degrades operating efficiency and leads to other major failures such as excessive tooth removal and catastrophic breakage. To develop accurate wear detection and diagnosis approaches at the early phase of the wear, this paper examines the gear dynamic responses from both experimental and numerical studies with increasing extents of wear on tooth contact surfaces. An experimental test facility comprising of a back-to-back two-stage helical gearbox arrangement was used in a run-to-failure test, in which variable sinusoidal and step increment loads along with variable speeds were applied and gear wear was allowed to progress naturally. A comprehensive dynamic model was also developed to study the influence of surface wear on gear dynamic response, with the inclusion of time-varying stiffness and tooth friction based on elasto-hydrodynamic lubrication (EHL) principles. The model consists of an 18 degree of freedom (DOF) vibration system, which includes the effects of the supporting bearings, driving motor and loading system. It also couples the transverse and torsional motions resulting from time-varying friction forces, time varying mesh stiffness and the excitation of different wear severities. Vibration signatures due to tooth wear severity and frictional excitations were acquired for the parameter determination and the validation of the model with the experimental results. The experimental test and numerical model results show clearly correlated behaviour, over different gear sizes and geometries. The spectral peaks at the meshing frequency components along with their sidebands were used to examine the response patterns due to wear. The paper concludes that the mesh vibration amplitudes of the second and third harmonics as well as the sideband components increase considerably with the extent of wear and hence these can be used as effective features for fault detection and diagnosis.

Engineering modeling of wear profiles in tooth flank of polyamide spur gears

The present paper is a contribution in developing an engineering model expressing the evolution of tooth flank wear in polyamide spur gears as a function of number of cycles. The method is based on first observing the behavior of wear on tooth flanks in real test conditions. Then, progressive flank wear profiles are plotted in order to sort out the corresponding fitting curves together with the associated mathematical equations. The general engineering model controlling the evolution of wear profile is found of the form of quadratic equation where the variable is the circular thickness of a tooth at a given depth from the top land of the tooth. The respective parameters of the engineering wear equation are determined as a function of number of revolutions of the spur gear. A wear correction parameter k w is added in order to catch up the measuring errors when plotting the wear profile curves using the proposed engineering wear model for spur gears. The data are in good agreement with that obtained from experimental measurements.

The Effect of Selected Operating Parameters, Material Pairing, and Gear Size on the Wear Behavior of Grease Lubricated, Small Module Gears

The wear behavior of grease lubricated gears is significantly affected by a number of factors besides the composition of the grease that is used for lubrication. A main influence factor on the wear behavior of grease lubricated gears is the lubrication supply mechanism (“circulating” or “channeling”), which is, among other things, strongly affected by the rotational speed of the gears. Especially at higher rotational speed, the dominant grease lubrication supply mechanism for grease lubricated gears tends to be channeling, which generally promotes increased wear on account of limited lubricant availability in the mesh as well as limited heat dissipation from the mesh. Experimental investigations conducted herein have shown that the gear wear behavior, especially at higher rotational speed, can be influenced by the internal geometry of the gear casing as well as by the direction of rotation of the gears. Additional investigations that were conducted focus on the effect of the material pairing and heat treatment on the wear behavior of grease lubricated gears in comparison to a case-carburized reference gear set. Furthermore, the effect of the gear size on the lubrication supply mechanism and thus on the wear behavior was investigated. For both gear sizes investigated (mn = 1.0 mm and mn = 0.6 mm), circulating was observed at low rotational speeds. At high rotational speeds, channeling effects were dominant.

On the prediction of friction coefficient and wear in spiral bevel gears with mixed TEHL

A prediction model of the friction coefficient and wear of the spiral bevel gears in the mixed lubrication condition is proposed. Effect of a coupling thermo-elasto-hydrodynamic phenomenon on tooth surface should be considered comprehensively prior to the execution of tooth wear analysis. An effort is devoted to application of TEHL with rough surface contact to analyze the performance of spiral bevel gears in terms of the pressure, flash temperature, friction coefficient, and particularly wear rate. Wear mechanism and rules under a condition of the mixed lubrication are revealed to provide evidence for gear design and engineering application. And comparison of the prediction wear depth with the experimental measurements shows good agreement.

Virtual sensing for gearbox condition monitoring based on kernel factor analysis

Vibration and oil debris analysis are widely used in gearbox condition monitoring as the typical indirect and direct sensing techniques. However, they have their own advantages and disadvantages. To better utilize the sensing information and overcome its shortcomings, this paper presents a virtual sensing technique based on artificial intelligence by fusing low-cost online vibration measurements to derive a gearbox condition indictor, and its performance is comparable to the costly offline oil debris measurements. Firstly, the representative features are extracted from the noisy vibration measurements to characterize the gearbox degradation conditions. However, the extracted features of high dimensionality present nonlinearity and uncertainty in the machinery degradation process. A new nonlinear feature selection and fusion method, named kernel factor analysis, is proposed to mitigate the aforementioned challenge. Then the virtual sensing model is constructed by incorporating the fused vibration features and offline oil debris measurements based on support vector regression. The developed virtual sensing technique is experimentally evaluated in spiral bevel gear wear tests, and the results show that the developed kernel factor analysis method outperforms the state-of-the-art feature selection techniques in terms of virtual sensing model accuracy.

Adaptive Decoupling of Nonideal Machine and Sensor Properties for Extraction of Fine Details When Using the Motor Drive as a Diagnostic Sensor

This paper presents methods to enhance the quality of spatial information that can be extracted when using the motor drive as a diagnostic sensor. When using the state-of-the-art motor drive-based techniques for extracting spatial information related to the state of wear in a gear train driven by an ac machine, position sensor-induced periodic position measurement errors and machine-induced spatial harmonic torque ripple can degrade the quality and the detail of the information that can be extracted. In this work, this degradation of information is displayed experimentally, and it is demonstrated that the quality of the spatial information extracted can be significantly improved through implementation of existing model reference adaptive system (MRAS)-based nonideal sensor property decoupling techniques and newly developed MRAS-based spatial harmonic torque ripple decoupling techniques. Furthermore, it is identified and demonstrated in this work that by removing the gear mesh harmonic component from the gear wear information extracted using the state-of-the-art techniques, and then calculating the spatial rate of change of this new information, a new signal is generated that strongly correlates to local gear tooth defects in a gear train driven by an ac machine.

The Wear Behavior of Small Module Gears Lubricated with NLGI 1 Grease

ABSTRACTSmall module gears (mn ≤ 1 mm) are increasingly important in power transmitting gear applications due to ever more rigorous requirements regarding, for example, performance and weight. They can be found in numerous applications that are subject to very different operating conditions. Often, small module gear applications are grease lubricated. This results in the lubrication supply mechanism (i.e., circulating and channeling) playing an important role in regard to the resultant gear failure mode. In the experimental investigations conducted herein, the focus was on gear sliding wear. The influence of the operating conditions and the grease composition on the lubrication supply mechanism, and thus wear behavior, was investigated using case-carburized, small module gears (mn = 1 mm). The investigations show that the rotational speed has a significant effect on gear wear behavior. Increasing rotational speed does not necessarily lead to more favorable wear behavior of grease-lubricated gears. Furthermore, the grease composition was shown to affect wear behavior.

Enhancement of wear resistance on normal contact ratio spur gear pairs through non-standard gears

Tooth wear is considered to be one of the major causes of failure modes in gearing systems. The achieved service life of the geared unit mainly depends on the gear tooth strength and surface wear. Excessive wear is characterized by loss of tooth profile, which results in high noise and vibration, a minor loss of conjugate action and a reduction in efficiency. Hence, enhancement of gear life against wear becomes an important requirement for effective design detailing of gears. This article presents an idea to minimize the wear of the gear teeth by adopting non-standard gear. Non-standard gear is defined as one whose tooth thickness at the pitch circle is not equal to 0.5πm. In this study, the impact of the tooth thickness coefficient on tooth wear for standard and non-standard spur gears is numerically investigated. The non-standard tooth thickness in the pinion leads to enhancement of the tooth strength and leading to reduction of tooth wear. Finally, the influence of gear parameters such as gear ratio, pressure angle and pinion teeth number on wear depth, for non-standard pinion and gear has been investigated and the results of the parametric study are discussed.

Gear Wear Process Monitoring Using a Sideband Estimator Based on Modulation Signal Bispectrum

As one of the most common gear failure modes, tooth wear can produce nonlinear modulation sidebands in the vibration frequency spectrum. However, limited research has been reported in monitoring the gear wear based on vibration due to the lack of tools which can effectively extract the small sidebands. In order to accurately monitor gear wear progression in a timely fashion, this paper presents a gear wear condition monitoring approach based on vibration signal analysis using the modulation signal bispectrum-based sideband estimator (MSB-SE) method. The vibration signals are collected using a run-to-failure test of gearbox under an accelerated test process. MSB analysis was performed on the vibration signals to extract the sideband information. Using a combination of the peak value of MSB-SE and the coherence of MSB-SE, the overall information of gear transmission system can be obtained. Based on the amplitude of MSB-SE peaks, a dimensionless indicator is proposed to assess the effects of gear tooth wear. The results demonstrated that the proposed indicator can be used to accurately and reliably monitor gear tooth wear and evaluate the wear severity.

Gear wear monitoring by modulation signal bispectrum based on motor current signal analysis

Gears are important mechanical components for power transmissions. Tooth wear is one of the most common failure modes, which can present throughout a gear’s lifetime. It is significant to accurately monitor gear wear progression in order to take timely predictive maintenances. Motor current signature analysis (MCSA) is an effective and non-intrusive approach which is able to monitor faults from both electrical and mechanical systems. However, little research has been reported in monitoring the gear wear and estimating its severity based on MCSA. This paper presents a novel gear wear monitoring method through a modulation signal bispectrum based motor current signal analysis (MSB-MCSA). For a steady gear transmission, it is inevitable to exist load and speed oscillations due to various errors including wears. These oscillations can induce small modulations in the current signals of the driving motor. MSB is particularly effective in characterising such small modulation signals. Based on these understandings, the monitoring process was implemented based on the current signals from a run-to-failure test of an industrial two stages helical gearbox under a moderate accelerated fatigue process. At the initial operation of the test, MSB analysis results showed that the peak values at the bifrequencies of gear rotations and the power supply can be effective monitoring features for identifying faulty gears and wear severity as they exhibit agreeable changes with gear loads. A monotonically increasing trend established by these features allows a clear indication of the gear wear progression. The dismantle inspection at 477h of operation, made when one of the monitored features is about 123% higher than its baseline, has found that there are severe scuffing wear marks on a number of tooth surfaces on the driving gear, showing that the gear endures a gradual wear process during its long test operation. Therefore, it is affirmed that the MSB-MSCA approach proposed is reliable and accurate for monitoring gear wear deterioration.

Hydrogen Entry into an AISI 4135 High Strength Steel in Tribocorrosion Environment

Hydrogen entry into AISI 4135 high strength steel in tribocorrosion environment was studied in the present study. The samples were corroded in tribocorrosion environment using a pin-on-disk type wear gear equipped with a solution cell and in static corrosion environment, and the hydrogen content entered into the steel was measured using hydrogen thermal desorption analysis. The hydrogen content in tribocorroded sample was larger than that in corroded sample without wear. From the cathodic polarization curves and surface morphology, it is revealed that the main factor which increases the amount of entered hydrogen is solution flow. The solution flow enhances the supply of oxygen, and the difference of flow rate forms anodic and cathodic areas on the samples. Solution flow also enhances anodic dissolution and increases hydrogen generation reaction. As a result, hydrogen entry into the high strength steel is enhanced in tribocorrosion environment.

A technique for calculating tribotechnical characteristics of tractive cylindrical gear of VL-10 locomotive

A technique for the design calculations of the local strength, wear, and durability of tractive cylindrical double gear of VL-10 locomotive with angular tooth correction has been suggested. The technique allows for realistic engagement conditions (parity and wear-induced changes in the tooth profile curvature). The regularities of the effect that structural (angular engagement correction) and operational (linear tooth wear) factors have on these parameters for triple–double–triple tooth engagement in this gear have been revealed. It has been established that, when considering tooth correction, there are certain optimum displacement coefficients that maximize the durability compared to the uncorrected gear. It has been shown that, if one allows for changes in the tooth-profile due to wear are allowed for, the actual durability and bearing capacity of the gear is higher. The results have been presented graphically in order to help establish regularities of the effect of engagement conditions on the tribotechnical characteristics.

Wear and Reliability Life of Large Modulus Gear Rack

In this paper, based on the Archard wear theory, numerical simulation method and Hertz contact theory, the numerical simulation model of gear rack wear is established under the influence factor of load and hardness for the wear condition of large modulus gear rack. The simulation calculation of its wear process and wear life is realized through the Matlab software. Results show: Along the tooth profile, wear rate of tooth root is greater than the crown. Maximum wear position is decided by comprehensive influence of contact stress and slip distance. The analysis calculation of large module gear rack’s wear process and life can be solved through the method of combining experiment and numerical simulation for good engineering application.

The simulation of influence of engagement conditions and technological teeth correction on contact strength, wear and durability of cylindrical spur gear of electric locomotive

The cylindrical spur tractive gear of the electric locomotive has been conducted using the author’s method of the calculation of maximum contact pressures, teeth wear and durability at technological correction of engagement at changeable, in the result of teeth wear and conditions of their contact. The regularities of tribocontact pressures change in engagement has been established after reaching the permissible wear depending on the shift coefficients in the phases of double–single–double tooth engagement. Considerable decrease of maximum tribocontact pressures is observed in the result of teeth wear in the entry phase of double-tooth engagement in comparison with their initial values. Depending on the shift coefficients, maximum (permissible) wear of wheel teeth would arise in different contact points: at the entrance into single-tooth engagement in non-corrected gear and at the exit in the presence of correction. Gear durability has its optimum at [Formula: see text] = 0.1 which is 1.22 times larger than in the absence of engagement correction.

Modelling and measurement of wear particle flow in a dual oil filter system for condition monitoring

Wear debris is an indicator of the health of machinery, and the availability of accurate methods for characterising debris is important. In this work, a dual filter model for a gear oil system is used in conjunction with operational data to indicate three different system operating states. The quantity of wear particles in gear oil is analysed with respect to system running conditions. It is shown that the model fits the data in terms of startup “particle burst” phenomenon, quasi-stationary conditions during operation, and clean-up filtration when placed out of operation.In order to establish boundary condition for particle burst phenomenon, the release of wear particles from a pleated mesh filter is measured in a test rig and included in the model. The findings show that a dual filter model, with startup phenomenon included, can describe trends in the wear particle flow observed in the gear oil. Using this model it is possible to draw conclusions on the filtration system performance and wear generation in the gears. Limitations of the proposed model are the lack of ability to describe noise and random burst spikes attributed to measurement error distributions. Trending of gear wear particle generation is made possible by model parameter estimation and identification of an unintended lack of filter change. The model may also be used to optimise system and filtration performance, and to enable continuous condition monitoring.

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.

Misalignment detection in induction motors with flexible coupling by means of estimated torque analysis and MCSA

In recent years, progress has been made in developing techniques to detect mechanical faults in actuators driven by induction motors. The latest developments show their capability to detect faults from the analysis of the motor electrical variables. The techniques are based on the analysis of the Motor Current Signature Analysis (MCSA) and the Load Torque Signature Analysis (LTSA), among others. Thus, failures such as misalignment between the motor and load, progressive gear teeth wear, and mass imbalances have been successfully detected. In case of misalignment between the motor and load, both angular and radial misalignment, the results presented in literature do not consider the characteristics of the coupling device. In this work, it is studied a mechanism in which the power transmission between the motor and load is performed by means of different types of couplings, mainly those most frequently used in industry. Results show that the conclusions drawn for a particular coupling are not necessarily applicable to others. Finally, this paper presents data of interest for the development of algorithms or expert systems for fault detection and diagnosis.

Design Optimization and Analysis of Industrial Gearbox Casing to Reduce Wear of Gear and Bearings Due to Vibrations: Review

Design Optimization and Analysis of Industrial Gearbox Casing to Reduce Wear of Gear and Bearings Due to Vibrations: Review

Applying thermophysics for wind turbine drivetrain fault diagnosis using SCADA data

Cost-effective wind turbine (WT) diagnosis using supervisory control and data acquisition (SCADA) data is a promising technology for future intelligent wind farm operation and management. This study presents a thermophysics-based method for WT drivetrain fault diagnosis. A synthesised thermal model is formed by incorporating thermal mechanisms of the drivetrain into a WT system model. Applications of the model are demonstrated in case studies of the gearbox and generator comparing simulation results and SCADA data analysis. The results show non-linearity of the gearbox oil temperature rise with wind speed/output power that can effectively indicate gearbox efficiency degradation, which may be attributed to gear transmission problems such as gear teeth wear. Electrical generator faults such as ventilation failure and winding voltage unbalance will cause changes to heat transfer and result in temperature changes that can be used for diagnosis purposes. This is shown by different patterns of stator winding temperature associated with power generation, while the simulation reveals the thermal mechanism. The method can be applied to diagnose some failure modes which are hard to identify from vibration analysis. The developed thermal model can play a central role for the purpose of fault diagnosis, by deriving relationships between various SCADA signals and revealing changes in the thermophysics of WT operation.