About the stability of seamless rails

Since seamless lines eliminate a large number of rail joints, they have the advantages of balanced driving, low maintenance costs for locomotives and tracks, and long service life. They are one of the main contents of railway track modernization. However, to give full play to its superiority, it is necessary to meet the design requirements of strength and stability at the same time.

1. Temperature stress and temperature force

The rails expand and contract with heat. On seamless lines, the free expansion and contraction per unit length of welded long rails is equal to the product of the linear expansion coefficient and the rail temperature change amplitude. Once the welded long rails are "locked", the free expansion and contraction cannot be achieved or cannot be fully achieved due to the resistance of the joints at both ends and the resistance of the roadbed along the line.

At this time, the unrealized free expansion and contraction will be converted into temperature strains = with equal values ​​but opposite directions, thereby generating temperature stress = and temperature force = (for the elastic modulus of steel; for the cross-sectional area of ​​the rail) inside the rails.

In summer, when the rail temperature rises, the rails are bound to stretch, but because it cannot be achieved, it is converted into compressive strain, generating compressive stress inside the rails. In winter, the rail temperature decreases, and the rail is bound to shorten. However, since this cannot be achieved, it is converted into tensile strain, generating tensile stress inside the rail. This stress caused by the change in rail temperature is called temperature stress, and the force acting on the rail cross section is called temperature force.

2. Track laying temperature and locking rail temperature

The rail temperature most suitable for laying long welded rails is called track laying temperature. Because the rail temperature may fluctuate during the track laying process, an upper and lower fluctuation range is allowed when determining the track laying temperature. The locking rail temperature, also known as the stress-free rail temperature, is the rail temperature when the long welded rails are laid, the fasteners are tightened, and the anti-climbing equipment and joint splints are installed.

It must be within the allowable fluctuation range of the track laying temperature. The locking rail temperature should generally be slightly higher than the average of the local maximum and minimum rail temperatures to prevent excessive rail temperature pressure in the hot summer season, thereby reducing the potential danger of expansion track of the seamless line.

The local maximum rail temperature is generally 20C higher than the maximum temperature, while the minimum rail temperature is roughly equal to the minimum temperature. The locked rail temperature is the basis for calculating the range of rail temperature changes and must be recorded in detail and properly preserved. If changes are caused by line operations, they should be corrected in a timely manner.