Permanent Way (history) - Modern Edge Rails

Modern Edge Rails

The breakthrough came when John Birkinshaw of Bedlington Ironworks in Northumberland developed rolled wrought iron rails in 1820 in 15 feet (4.6 m) lengths, as used for the Stockton and Darlington Railway. This was strong enough to bear the weight of a locomotive and of a train of wagons (or carriages) pulled by it. This marks the beginning of the modern rail era.

This system was instantly successful, although some false starts took place. Some early rails were made in a T cross section, but the lack of metal at the foot limited the bending strength of the rail, which has to act as a beam between supports.

As metal technologies improved, these wrought iron rails were made progressively somewhat longer, and with a heavier, and therefore stronger, cross-section. By providing more metal in the foot of the rail, a stronger beam was created, achieving much better strength and stiffness, and a section was created similar to the bullhead rail section still visible today. This was expensive, however, and the promoters of early railways struggled with decisions about the appropriate weight (and therefore strength, and cost) of their rails.

At first the rail section was almost symmetrical top-to-bottom, and was described as a double-headed rail. The intention was to invert the rail after the top surface had become worn, but rails tend to develop chair gall, an attrition of the rail where it is supported in the chairs, and this would have made running on the former bottom surface impossibly noisy and irregular. It was obviously better to provide the extra metal on the top surface and gain extra wear there without the need to invert the rail at half life.

Many railways preferred a flat bottom rail section, where the rails could be laid directly on the ties (sleepers), representing a marked cost saving. Indenting of the sleeper was the problem, and where the traffic was heavy, it became necessary to provide a sole plate under the rails to spread the load on the tie, partly vitiating the cost saving. However in main line situations, this form found almost universal adoption in North America and Australia, and in much of continental Europe. The UK persisted with bullhead rail in main line use, with widespread introduction of flat-bottom rail only starting in about 1947.