The derailment of a high-speed train in Hatfield in the UK last week has led to a new focus on rail safety measures. If the problem is rail cracking, maybe they have the answer in the US…
According to Railtrack zone director Ray Price, although the exact reasons for the broken rail at Hatfield are still under investigation, the rail showed signs of a phenomenon known as ‘head checking’ or ‘gauge corner cracking’.
The condition itself typically comprises extremely fine hairline cracks on the surface of the rail where it comes into contact with the wheels of the train. According to Railtrack ‘it is a relatively new phenomenon’ and has been identified at locations where fast lines enter curves, particularly on lines with heavy rail traffic such as freight or heavy locomotives. On occasions, quite new rail has been affected.
As a precaution, Railtrack has imposed emergency speed restrictions at all sites where evidence of this condition has been found, and has pledged to bring forward its rail replacement programme to deal with these sites.These restrictions have also been implemented to ensure safe operation of trains while the inspections and renewal work are carried out.
The problem of rail cracking has been known for some time to researchers at the US’ Argonne National Laboratory. A year ago, they disclosed that they were working on laser glazing of steel rails, specifically to help out. When steel rails are laser glazed, trains travel on them with significantly reduced friction between the rails and train wheels. Although friction is needed on the top of rails for traction, the rubbing that occurs between the wheels and the side of the rail causes many problems. The drag forces it produces cause increased fuel consumption, wear away the rail, initiate cracking that can lead to rail fracture and derailment, and force the wheel to climb over the rail, another cause of derailments.
Liquid lubricants such as oil and grease currently used to reduce friction wash away in the rain, are environmentally unsound, and cause loss of traction if they migrate to the top of the rail. The solid state lubricant that results from laser glazing is durable, environmentally benign and stays where applied. In addition, it can be applied to rails in service or during fabrication.
To laser glaze a rail, a laser beam is passed along the rail surface to rapidly melt a thin layer of steel. This molten layer rapidly solidifies to form a hard, glassy surface elastic enough to distribute the load evenly to the underlayer.
Argonne researchers laser glazed surface regions of a six-foot length of unused rail and sent it to the Association of American Railroads’ test facilities for friction measurements.
The laser-treated surfaces remained intact, without cracking or delamination, after more than 30,000 back-and-forth cycles at typical loads. The treatment reduced friction coefficients by as much as 40 percent, which can reduce rail cracking by up to 75 percent.