NR NR/BS/LI/058 ISSUE 1 PDF

Introduction

The principal objectives of Switch and crossing grinding are as follows:

• To produce a regular and consistent running band on the crown of the rail.
• To impose and maintain a profile that reduces contact stresses on the gauge corner and shoulder of the rail.
• To remove localised misalignment at welds and other track features.
• To remove the fatigue damaged surface of the rail, which has or is likely to initiate rolling contact fatigue cracks.

The priorities for current train based grinding should be as follows until such time as grinding resources are available to control the initiation and early propagation of rolling contact fatigue.

1. New S&C installation, NB the S&C should always be tamped before grinding is performed
2. S&C with moderate RCF, poor rail profile, moderate damage to crossing nose
3. S&C with heavy or severe RCF, chipped switchblade tips and crossing nose
4. Grinding of other obstacles that the main line grinder cannot grind

Grinding should be targeted so that the highest priority S&C are ground approximately every 15 to 20 EMGT of traffic.

This following brief description of switch grinding methods is provided to give a better understanding of the performance expected from the switch grinding machines.

• The grinder shall have the capability of grinding the railhead surface between 45° on the field side to 75° on the gauge side, where 0° is normal to the vertical centre line of the rail.
• The grinder shall have the capability of removing side lipping and corrugations at level crossings.
• Different arrangements of grinding stones and motors will have limitations concerning the capability to grind within crossings, guard rails, lubricator sites,axle counters, hot axle box detectors, obstacles in level crossings, and other obstructions.
• The distance left un-ground by the main line grinders will define the limits of the switch grinding in terms of distances from the heel of the crossing and in front of the switch point. At present main line grinders can grind to within a nominal 30 meters of an obstruction. Once the S&C grinders are in full operation it is anticipated that these machines will have a scheduled grinding programme to follow the plain line grinders to complete the areas of track left unground by these machines.

These issues combined with the grinding machine metal removal capability will determine the grinding stone patterns, power and grinding pass speeds to be used on the switch grinding machines.