Rail grinding was initially developed as a corrective process to remove longitudinal irregularities such as corrugation or to restore crosssectional profile of the rail head. Work was typically programmed when the damage exceeded defined thresholds, or when the resources were available. Periodic preventive grinding work has proved beneficial for virtually all types of heavily-loaded lines. High speed lines are prone to RCF (rolling contact fatigue) as they are subjected to particularly high traction forces that damage high rails in curves and both rails in areas of strong acceleration. With heavy haul freight, axleloads greater than 25 tonnes can aggravate the development of RCF, and it was here that the first specific rail head profiles and cyclic grinding strategies were developed. Today, RCF is increasing on conventional lines, as the speeds of both passenger and freight trains are rising, and operators are making more use of the maximum axleload. Combined with slip-controlled locomotives capable of high acceleration, this is pushing the rails to the limit of their fatigue strength. In tackling RCF in switches and crossings, it is necessary to decide whether the corrective work should be completed in one visit or spread over several, which will determine the average metal removal rate. Aiming for a completely crack-free surface is complex, as RCF does not develop uniformly, but the specification of an acceptable residual crack depth after grinding looks set to be a topic of intense discussion for a long time to come. Depending on the location of the turnouts and the different traffic loads using the straight and diverging routes, wear patterns may vary significantly between the various rails. For example, if most traffic uses the straight track, this would see considerable vertical wear over time. As the switch blade only starts to wear where wheel forces transfer from the stock rail, the contact zone on the blade gradually moves forward towards the tip. And whilst the stock rail on the open side of the turnout will wear as a result of both traffic load and regular grinding, the corresponding open switch blade is less used, and its height will change very little. When the points are set for the diverging track, the switch blade on that side is higher than the stock rail, and is thus impacted by the wheel load closer to the tip. Following the grinding work, it is important to undertake visual inspection and measure the longitudinal and transverse profiles to ensure the switch and crossing meets the required specification. Longitudinal profile is usually recorded in up to four different wavelength classes, as defined in EN 13231 Part 3.
Controlling RCF in switches and crossings
Railway Gazette International ; 169 , 5 ; 55-58
2013
4 Seiten, 11 Bilder
Aufsatz (Zeitschrift)
Englisch
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