Research on Axle Box Springs in EMUs: Function, Classification, Fatigue Causes, Detection & Prevention

As the main model of modern railway transportation, the safety and stability of the operation of EMUs have an important impact on people’s travel, freight transportation and the development of the entire social economy. Among the important parts of EMUs, the axle box spring (railway spring) is one of the more core components. It can relieve the impact force between the wheels and the track and make the wheels fit the track, thereby ensuring the smooth travel and safe operation of the train. However, due to long-term and high-load operation, the contact fatigue problem of the axle box spring often occurs, causing unstable operation and safety risks for the train. Therefore, in-depth research on this problem and exploration of preventive measures has become one of the current focuses of research in railway transportation and related fields.

Function and classification of axle box springs

The role of railroad springs
The axle box spring is one of the core components of the suspension system of the EMU. Its role is to relieve the impact force between the wheels and the track, thereby reducing the friction between the wheels and the track while ensuring the smooth travel of the train; it can also reduce the wear of the track. The axle box spring can accept multi-directional forces, thereby realizing multi-directional shock absorption and suspension functions. In terms of shock absorption, the railroad spring stiffness and damping coefficient of the axle box spring directly affect the impact force between the wheel and the track, while in terms of suspension, the guide frame and connector of the railway spring are key components for achieving the turning maneuverability of heavy-load high-speed railway trains.

Classification of axle box springs
According to their different structural forms, axle box springs can be divided into four categories: leaf spring type, disc spring type, wrist type and gas spring type. The specific classification is as follows：

• Leaf spring axle box spring: Its structure is mainly composed of multiple thin steel plates put together and connected into an integral spring assembly with bolts, nuts, etc. It has the characteristics of large elastic stiffness and strong rigidity, but it is heavy.
• Disc spring axle box spring: Also known as spiral spring, it is a very common structural form. Its surface is twisted, which adapts to different road conditions. It has moderate stiffness and is relatively light.
• Wrist axle box spring: It mainly refers to the spring with the structural form of a ball head or ring seam fork, ball joint or wrist connection on the bearing surface. It has the characteristics of a compact structure, small spring stiffness and strong adaptability.
• Gas spring axle box spring: focuses on springs with gas as elastic elements, mainly used in the suspension system of light rail passenger trains. Its advantages are stable system elasticity, reversibility of fluid, and even the ability to change the elastic coefficient by adjusting the size of the air pressure.

Causes and influencing factors of contact fatigue

Causes of contact fatigue

The accumulation effect of constant friction and pressure on the small deformation of the contact surface causes the contact fatigue of the damping spring. After a certain number of cycles, this small deformation will exceed the fatigue limit of the material itself and cause the failure of the railroad spring. Among them, the fatigue strength and fatigue life of the axle spring directly affects the size and probability of contact fatigue. The main factors include the quality of spring steel, structural form, manufacturing process, ambient temperature and other factors.

Factors affecting contact fatigue

• Quality of spring material: The properties and quality of spring material play a vital role in the incidence of contact fatigue. With the continuous improvement of technology and optimization of steel, some axle box springs have made great progress in spring materials, manufacturing processes, etc., effectively reducing the risk of contact fatigue.
• Load size and frequency: Load size and frequency are one of the main factors that lead to contact fatigue of the axle box spring. With the increase of load and the acceleration of frequency, the working conditions of the damping spring will become more complex and harsh, and the probability of contact fatigue will also increase.
• Ambient temperature: The ambient temperature has a critical influence on the elastic coefficient and hardness of the axle box spring. Specifically, when in a high-temperature environment, the axle box spring is prone to plastic deformation or loosening, and when in a low-temperature environment, the axle box spring may suffer brittle fracture.

Common detection methods and preventive measures

Common detection method

• Nondestructive testing method: It mainly uses nondestructive testing technology, such as ultrasonic, magnetic powder, eddy current and other methods to detect spring defects, as well as measure parameters such as the surface hardness and fatigue resistance of the spring.
• Dynamic load test method: It mainly uses actual load tests to analyze the frequency response of the axle box spring under its working state and measure the stress and strain changes of the spring under different load conditions.
• Static load test method: mainly through gravity loaders, spring compressors and other equipment to directly test the strength, stiffness and fatigue resistance of the axle box spring.

Preventive measures

• Optimize spring materials: use high-quality steel and technology to improve the strength and stiffness of spring materials and increase the life and fatigue resistance of springs.
• Use appropriate matching and lubrication methods: by adjusting the matching clearance and surface lubrication method between the axle box spring and the axle box hole, reduce the occurrence of contact fatigue and extend the service life of the spring.
• Inspection and maintenance: regularly maintain and inspect the axle box spring, promptly discover and repair the defects and hidden dangers of the damping spring, and ensure its stability and reliability in operation.

Supplier

Luoyang Fonyo Heavy Industries Co., Ltd,founded in 1998,is a manufacturer in cast railway parts.Our factory covers an area of 72,600㎡, with more than 300 employees, 32 technicians, including 5 senior engineers, 11 assistant engineers, and 16 technicians.Our production capacity is 30,000 tons per year. Currently, we mainly produce casting, machining, and assembly for locomotive,railcar,high-speed trains, mining equipment,wind power,etc.Our products have been exported to Russia, the United States, Germany, Argentina, Japan, France, South Africa,Italy and other countries.
Contact: Stella Liu
Email:sales@railwaypart.com
Mobile:+8615515351287