When it comes to correcting or maintaining the profile and surface condition of rail on North American railroads, there is one primary method: rail grinding. Rail milling, an established method in other parts of the world was recently introduced in a transit application in Canada (see p. 16), but at present, rail grinding is the method of choice. Freight railroads grind for two primary reasons: to maintain or manage rail shape (a fundamental aspect of wheel/rail interaction) and to minimize surface-initiated fatigue cracks that interfere with ultrasonic testing and can ultimately lead to rail defects. Transit systems grind for the same reasons, but also to control wheel/rail noise induced by rail corrugation. So, the goals of most grinding programs are to correct or maintain the desired rail profile; to remove surface damage, such rolling contact fatigue (RCF) and shells, spalls and corrugation (SSCs), which interfere with the ability of ultrasonic rail flaw detection systems to inspect the rail for internal defects. While there are shades of gray between them, the two primary approaches have been corrective and preventive grinding. Corrective grinding typically implies the application of multiple passes with heavy metal removal at lower speeds to restore the rail shape and/or surface to acceptable conditions; preventive grinding typically implies the application of fewer passes with less metal removal at higher grinding speeds to catch degrading surface and/or profile conditions on a more frequent basis before significant damage is done.
展开▼
