Tribology of gears

Why Tribology is Important in Mechanical Engineering


Gears are the mechanical transmission elements that are toothed to transfer the motion and power between any mechanical components. They are widely used in various devices such as automobile parts, clocks, mechanical machines, bicycles, etc. These are the most common type of power transmission elements used in various applications. They are classified based on their shape, gear tooth designs, axes of rotation, etc. Based on these factors the energy efficiency of the gears is determined for the desired applications. The gear tooth is continuously in contact with each other and there is a continuous motion between the interface of the gear hence there is an existence of friction. This friction if elevated at the interface leads to wear of the gear material and later the gear fails. Thus, it is important to analyze the gear tribology and study the tribological properties of the material used in manufacturing gears with the operating conditions to determine the suitable material [1].

Why Tribology is Important in Mechanical Engineering

Fig-1 The image of gear alignment [2]

Factors affecting gear tribology

Gear tribology depends on various factors such as surface roughness which is linked during the manufacturing of the gears. The materials used in manufacturing the gears should have good surface tribological properties and grain sizes which further affect the friction and wear of the gear. During the operation, lubricants are commonly used in the gear interface to reduce friction, and wear, and carry the wear debris, preventing corrosion and noise or vibration. The amount of lubricant at the gear tooth interface varies the gear life, when the tooths are not completely in contact or in non-conformal conditions then the gear interface is in Elastohydrodynamic lubrication and when they are in contact with each other with solid-solid contact then they are in boundary lubrication. Thus, studying the lubricant behavior of the gears helps in determining the type of lubricant that can be used for different applications [3].

Problems with Gear Tribology

Gear wear is one of the commonly seen issues in gear tribology, the gear wear is a progressive loss of material on the tooth surface due to the relative motion between the tooth surfaces. The common causes of gear wear are root cracks, bending fatigue, breakage, scuffing, micro pitting, spalling, etc. The gears are continuously in contact and rolling or sliding motion with the other gear tooth and under an applied load this motion leads to material reduction on the surface interface reducing the gear mass and causing the wear. There are different kinds of gear wear mechanisms studied such as abrasion, adhesion, fatigue, corrosion, erosion, fretting, etc [4].

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Fig-2 Types of failure on gear surface [5]

Abrasion on the gear surface occurs due to the contamination of particles and lack of lubrication at the sliding contacts. Since the materials used in the gears are the same the three-body abrasion takes place where the particles get entrapped in the sliding interface causing the wear. In the case of adhesion, the gear materials get transferred from one gear tooth to another due to tearing and micro-welding. The corrosive wear occurs on the gear tooth as surface deterioration due to an electrochemical reaction between the gear material and the lubricants used. Further surface fatigue is caused due to large cyclic loading at the gear tooth contact interfaces as micro/macro pitting. This pitting can be caused due to mechanical actions, electrical erosion, or corrosion on the surface during cyclic loading.

Gear wear monitoring

Monitoring the gear wear is very important to protect the gear material used because the material can easily get degraded which results in the failure of the transmission system. Understanding the gear wear propagation using gear wear monitoring in industrial systems will help in improving the life of the gears. This analysis is performed on the number of particles, shapes, sizes, and concentrations in wear debris at the lubrication used in the gear tooth interfaces. This method is called the gear oil particle analysis; however, this method is not real-time. Hence there are other different types of gear wear analysis techniques such as vibrational analysis, in the vibration analysis method the rotating machine is recorded, which under normal conditions is different when compared to the vibration under fault conditions. Thus, this change in the surface can be observed in the vibration which is a real-time wear analysis [3].

A review of vibration-based gear wear monitoring and prediction techniques  - ScienceDirect

Fig-3 Schematic representation of gear wear monitoring [3]


[1] Bergseth, E., 2012. On tribological design in gear tooth contacts (Doctoral dissertation, KTH Royal Institute of Technology).


[3] Feng, K., Ji, J.C., Ni, Q. and Beer, M., 2023. A review of vibration-based gear wear monitoring and prediction techniques. Mechanical Systems and Signal Processing182, p.109605.

[4] Feng, K., Smith, W.A., Randall, R.B., Wu, H. and Peng, Z., 2022. Vibration-based monitoring and prediction of surface profile change and pitting density in a spur gear wear process. Mechanical Systems and Signal Processing165, p.108319.


I am currently working as a Postgraduate Researcher at the University of Leeds. Previously I completed my master's under the prestigious Erasmus Mundus joint master's degree program (Master's in Tribology). I have also completed my bachelor's in Mechanical engineering from VTU, Belgaum, India. I am working as the social media manager for Tribnet and also I have my youtube channel Tribo Geek.

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