Abrasive wear occurs when there is contact between the side of the flange of a wheel and the gauge face of the rail. This contact usually takes place between the leading outer wheel of a vehicle bogey and the outer rail of a curve.
On curves careful periodic check must be carried out of the outer rail to ensure that side wear is kept within prescribed limits. Failure to do this could result in a derailment. Where curves are tighter than 200 metre radius, continuous check rails should be provided inside the inner rail. This check rail is to be set not more than about 50mm inside the running rail or at a distance that will ensure that the inside face of the flange of the inner wheels will bear on the check rail thus sharing the centrifugal force between the check rail and the outer rail through flange bearing. Abrasive wear of rails can be reduced by the use of rail lubricators placed at strategic positions. Great care needs to be exercised in the use of lubricators to ensure that only flanges are lubricated. Lubricant deposited on the top of rail heads can cause problems with braking, acceleration and wheel-spin. This is particularly important where trains are automatically driven or where stopping positions are critical such as when rolling stock doors have to line up with platform doors.
When wheels run along fairly straight track with flanges just clear of the rails, the contact area between wheel and rail is extremely small. In theory the contact would only be a point which would make contact pressures infinitely high. In practice both surfaces deform slightly to give a contact?patch'. Evensonlyso,anarea oftypicallyabout such ap 100 sq.mm under the heaviest wheel load. This gives pressures as high as 1200N/sq.mm which is higher than the yield point of the steel. This has the effect of causing the contact patch to become plastic and to flow causing various wear patterns and irregularities over time.
Where rails become side worn near to limit on curves, extra life can be obtained by either turning the high rail on jointed track or transposing the two rails on continuously welded rail. Close inspection of the existing inner rail outer edge must be carried out before transposing to ensure that there are no other defects present such as roll-over, ?lipping' would make the ride or plastic rough and precipitate failure of the new running edge.
If speeds in excess of 120 kph (75 mph) are expected, transposing should only be carried out if re-profiling of the existing inner rail is carried out. Wear on point and crossings needs to be carefully watched on a regular basis. Some repair of bad wear can be done by welding but in most cases components need to be changed.
In jointed track excessive wear often takes place at rail joints or fishbolt holes and is the main reason for re-railing. Joints also increase wear on rolling stock. This is one of the main reasons why main line railways are progressively changing to continuously welded rails.
When a derailment occurs on any railway at any location, rail wear must be fully investigated as this can often prove to be the root cause. All rails should be closely inspected including any tell-tale signs of where wheels ran at the time of and just prior to the derailment.