Spring engineering: recent research and findings

This article summarizes a series of spring-engineering research topics, from air springs for intercity trains and the dynamics of spring oscillators to contact fingers for draw-out circuit breakers and surface hardening of spring steel. The findings are presented in condensed form.

Fatigue of stainless steel compression springs

The results of a vacuum-outgassing test on cycling stainless steel compression springs show that the spring reel of a medium-sized industrial spring can be a source of a series of spring fractures. A rigid-flexible coupling dynamics model that accounts for the flexibility of a series of steel springs has been established to analyse the failure.

Air springs for intercity trains

In the development of an air spring for an Italian intercity train, the main technical parameter requirements, structural design and finite element analysis were established, and the spring type was verified experimentally. Product loading and application tests showed that the air spring functions meet the technical requirements.

Spring oscillator dynamics

For a spring oscillator moving in a lubricated horizontal plane, a nonlinear two-degrees-of-freedom differential equation model describes the motion. Related work on the void-seal design of springs reports how radial stiffness varies with different radial force angles and eccentric distances.

Archimedes spiral spring stiffness

The stiffness of the Archimedes spiral was analysed theoretically, giving an axial-stiffness formula, and a stiffness-stress coefficient was proposed to evaluate spring performance. The theory was then applied in finite element simulation: at the same axial stiffness, and compared with five spiral profiles, the Archimedes spiral showed a smaller maximum stress, making it suitable for long-life applications.

Spring contact fingers in draw-out circuit breakers

In a draw-out (handcart) circuit breaker, the excessive tightening force of the plum-contact hoop easily causes climbing as the handcart is pushed in. The causes of the climbing problem were analysed and, combined with the advantages of spring contact points and their good conductive function, a prototype was built and tested. In related work, the connecting-plate dimensions were optimized and a mathematical model of the spring actuation arrangement was established and simulated; the simulation results show that the output characteristics of the arrangement match the load requirements of the circuit breaker well, and the optimized contact spring pressure was confirmed.

Nitriding of spring steel

To improve the wear resistance of spring steel surfaces, the microstructure and friction behaviour of the nitriding layer were studied. Nitriding was carried out at different times and temperatures, and the microstructure, hardness and friction behaviour were tested. The results show that the nitriding layer forms an uncorroded bright compound layer, while the diffusion layer turns black because of the etching effect.