Understanding Rail Buckling: An Inside Look at Sun Kinks and Their Management

Railway infrastructure is subject to a variety of environmental impacts, with sun kinks being a notable issue observed during hot weather. This phenomenon, often referred to as rail buckling, is a common and well-documented issue not just in the UK but also in countries like the United States. This article delves into the reasons behind rail buckling, how it affects railway operations, and the strategies employed to manage it effectively.

What Causes Rail Buckling?

The expansion of rail due to heat is a natural occurrence worldwide, not unique to the United Kingdom or the US. Railways are made of steel, which expands when heated, leading to potential issues during hot weather. In the US, the term used for this condition is “sun kinks”. Railroad companies often avoid laying welded rail in cold months due to the higher expansion when temperatures rise. Additionally, sections of rail that can slide on themselves without causing buckling are strategically placed in tracks.

Experiences of Rail Expansion

As part of my experience working on a US railroad in the early 1980s, I encountered a few instances of sun kinks. One memorable incident occurred while I was a brakeman on the headend. We observed an upcoming sun kink on a straight track, about a half mile ahead. The rails appeared bent about 6 inches out of alignment. We were traveling at the speed limit of 50 mph. The engineer began setting the air brakes, slow us down, and then kicked off the brakes to ensure the train was free-rolling over the kink. This prevented the stresses of braking when encountering a sun kink, which can lead to jackknifing of railcars.

A more dramatic encounter happened during a vacation when my train crew hit a sun kink. The engineer, instead of gradually setting the brakes, applied emergency braking. After using this method, it’s impossible to kick off the brakes as the pressurized air in the brake line is expelled and takes time to re-build. The severe impact led to the train derailing in three places, with some tank cars catching fire and at least one exploding. Fortunately, the head and rear end crews were not injured. Mexican nationals riding illegally in a boxcar were also uninjured, though the experience was extremely frightening for them as their boxcar was derailed.

Management and Prevention Strategies

To manage the risks associated with rail buckling, railway operators employ several strategies. These include:

Preventive Maintenance: Regular inspections and maintenance are crucial to identify potential areas of concern. Trains are often limited to specific speeds in areas where sunlight hits the rails, known as solar zones. Track Design: Techniques such as the placement of expansion joints and slide bars enable the rails to move slightly without buckling. This helps to distribute the thermal stress evenly. Advanced Warning Systems: Modern technology has led to the development of early warning systems that can predict and alert railway operators about potential buckling incidents before they occur.

By understanding the causes and effects of rail buckling, railway operators can implement effective management strategies to ensure the safe and efficient operation of rail systems during hot weather.

Additionally, understanding the role of steel expansion and the presence of sun kinks can help in the development of better railway infrastructure. These insights can be invaluable in minimizing accidents and improving overall rail safety.