Bearing design under complex loads

At the core of modern industry, from high-speed aircraft engines to mining machinery that can withstand large vibrations, bearings, as key components of rotating systems, directly determine the reliability, efficiency, and lifespan of the entire equipment based on their performance. However, industrial application scenarios are becoming increasingly stringent, and bearings are often no longer only subjected to simple radial or axial forces, but are also in a complex load environment with multiple physical fields coupled. Dealing with this challenge has become a core issue in the field of bearing design.

1、 What is a complex load? ——Multidimensional mechanical challenges
Complex loads far exceed the scope of basic rated dynamic loads, usually manifested as the composite and dynamic superposition of multiple loads, mainly including:

Composite load: Radial load, axial load, and overturning moment acting simultaneously and in varying proportions. For example, the pitch bearings and main shaft bearings of a wind turbine need to simultaneously withstand the radial force generated by wind load, the axial force of rotor weight, and the moment caused by wind yaw.

Dynamic and impact loads: loads that rapidly change in size and direction over time. The bearings in equipment such as mining crushers and steel mills need to frequently withstand strong impacts and vibrations caused by ores or steel billets.

Extreme condition coupling: Load and extreme environmental factors (such as high temperature, low temperature, vacuum, corrosive media) act simultaneously. The main shaft bearings of aircraft engines are subjected to enormous centrifugal forces and aerodynamic loads, while also being subjected to high temperature environments, posing severe challenges to lubrication and material performance.

This multi-dimensional and dynamically changing load condition poses unprecedented challenges to the fatigue life, operational accuracy, stability, and reliability of bearings.

2、 Design Challenge: Starting from Failure Modes
Under complex loads, the traditional failure modes of bearings are exacerbated and may give rise to new problems:

Early fatigue spalling: The phenomenon of stress concentration is more prominent, and small design defects are amplified under alternating stress and impact, leading to premature fatigue spalling of the raceway and rolling elements.

Failure of the cage: Severe acceleration changes and vibrations may cause excessive stress on the cage, leading to problems such as fracture and increased wear, thereby causing the failure of the entire bearing.

Wear and corrosion: Under heavy loads, high speeds, or poor lubrication conditions, sliding friction increases, leading to accelerated surface wear. If there is pollution or corrosive media, wear and corrosion will promote each other.

Thermal runaway: If the frictional heat generated under high-speed and heavy load conditions cannot be dissipated in a timely manner, it will cause a sharp increase in bearing temperature, lubrication failure, and ultimately lead to locking and welding.

3、 Response strategies and innovative design
To conquer complex loads, modern bearing design has evolved from traditional geometric design to a systematic engineering that integrates materials science, tribology, dynamics, and intelligent manufacturing.

1. Advanced bearing selection and structural design

Innovation in bearing types: selecting the optimal solution for specific load types. For example, cross roller bearings are widely used in robot joints and precision turntables due to their compact structure and high moment stiffness; Double row tapered roller bearings and self-aligning roller bearings have become the preferred choice for heavy machinery due to their strong composite load-bearing capacity and self-aligning performance.

Internal geometry optimization: By finely optimizing the curvature of the raceway, the shape of the rolling elements (such as using logarithmic generatrix modification), and the contact angle, the stress distribution between the rollers and the raceway can be significantly improved, reducing edge stress concentration and greatly improving the life of the bearing under eccentric load and impact conditions.

2. Materials Science and Heat Treatment Technology

High performance steel: High cleanliness bearing steel produced by processes such as vacuum degassing and electroslag remelting, which reduces impurities and non-metallic inclusions from the source and improves the fatigue strength of the material.

Surface engineering: Heat treatment processes such as carburizing and case hardening can form a high hardness and high wear resistance surface layer on the bearing surface, while maintaining the toughness of the core and perfectly responding to impact loads. Coating techniques such as Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) can endow surfaces with lower friction coefficients and higher corrosion resistance.

3. Lubrication technology and sealing design

Lubricants and lubrication methods: Develop high-performance synthetic lubricating grease and special lubricating oil to meet the needs of wide temperature range and long service life. For extreme working conditions, forced lubrication methods such as oil air lubrication and spray lubrication are used to ensure that the lubricant reaches the contact area sufficiently and accurately, and carries away frictional heat.

Intelligent seal: The combination design of multi lip seal, labyrinth seal, and magnetic seal can effectively prevent external pollutants from entering and lubricant leakage, which is the key to ensuring the long-term operation of bearings in harsh environments.

4. Simulation and digital design

Modern design tools: Using finite element analysis (FEA) and multi-body dynamics (MBD) simulation, designers can simulate the mechanical behavior, thermal distribution, and lubrication state of bearings under real complex loads in a virtual environment, predict and optimize performance in advance, reduce dependence on physical prototypes, and accelerate the development process.

Digital Twin and Condition Monitoring: By combining with Internet of Things (IoT) sensors, a digital twin model is created for bearings in critical equipment to monitor their vibration, temperature, load, and other states in real-time, enabling predictive maintenance and early warning and intervention before faults occur.

4、 Conclusion
The design of bearings under complex loads is a continuous dialogue with physical limits. It is no longer an isolated design of a single component, but a comprehensive discipline that requires global consideration of system integration, operating condition prediction, and full lifecycle management. With the continuous breakthroughs in new materials, new processes, and digital technologies, future bearings will become more intelligent, durable, and reliable, providing indispensable core support for human industrial equipment to move towards higher efficiency, higher precision, and more demanding application environments.