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Coin a phrase

Letters

Bob Hairsine will be pleased to hear that the criteria for rails are indeed stringent (NCE last week) - the problem is the rail's extreme duty, especially wear.

The contact area between rail and wheel is only the size of a small coin, amazingly therefore a typical rail vehicle is carried at speed on eight such small areas.

Consider what is happening on this small area; it carries a vertical load of up to 12.5t (plus dynamic and centrifugal effects), lateral loads due to steering effects and longitudinal loads due to braking and traction. If a 12 car train is travelling at 200km/h any point on the rail will experience the passage of 48 wheel loads in about five seconds!

Mill-heat treated rail is often used at critical locations such as tight curves to reduce the rate of wear. This produces 'normal' hardness rail steel in the web and foot, but a harder head. The downside is of course reduced ductility.

The result of all the foregoing is a risk of crack initiation, propagation and eventually fracture of the rail. This can be safely controlled by good engineering. Rail industry leaders need to appoint high quality engineers to positions of real influence, and listen to them.

Perhaps they should also superglue a small coin to their desks as a constant reminder of the pre-eminence of engineering in running a safe and efficient railway Tony Masters (F), admasters@posford.co.uk.

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