Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

Specification and Documentation of Rail Grinding Work in Europe (continued)

While wheels inevitably wear through wheel/rail interaction, proper maintenance can significantly reduce the amount of wear and surface damage that occurs to the rail. But if poor wheel conditions are a given, the only way to improve contact (and wear) conditions is to modify the rail head profile. With today's grinding technology, the rail can be shaped to meet virtually any desired contact geometry, including the high or low rails in curves, or both rails in tangent track (see Figure 3).

Grinding Practices
Earlier generation rail grinders were fitted with fixed grinding motors that required many grinding passes to remove short-pitch and short-wave corrugations, and improve rail surface conditions. Today, modern rail grinding equipment can achieve the desired rail profile and surface condition in a single pass.

The maintenance strategy has also changed. Where railway personnel once held sway, the contractor now is responsible for planning, execution and quality control. While the railway may indicate where to grind, it’s the contractor’s duty to plan and execute the grinding plan, and to document that the finished work meets the specification. Certification of such, accompanied by documentation, is required for payment.

Process versus Product Specification
Grinding programs are either "process-" or "product-" based. While both types of program require pre- and post-grind inspections, process-based grinding programs specify the process to be used — the type of pattern and number of passes required to bring the rail into an acceptable condition. Depending on the effectiveness of the selected pattern, the finished grind quality may be better-than or less-than expected.

Product-based specification, which identifies a specific profile to be achieved for each section of track, has become the favored European approach. Product-based grinding is typically performed following rail condition monitoring, when critical values exceed pre-set thresholds or at fixed intervals. If the grinding cycle is right, the specified profile can be reestablished without much difficulty.

Quality Control
Specifications, which specify the longitudinal and transverse profiles, metal-removal rates and finished rail surface conditions, also provide the basis for quality assurance upon completion of the work. Measurement tools are now available to continuously record the longitudinal and the transverse profile during grinding. Rolling contact fatigue can be measured through Eddy-Current-technology. Speno International has fitted two machines with such systems. Metal removal can be spot-checked by measuring the rail height before and after grinding at the same location.

In Europe, two quality standards are defined for the longitudinal profile over four wavelength bands, which range from 10mm to 1m. Maximum peak-to-peak variations after grinding may not exceed 0.01mm for short waves and 0.1mm for defects up to 1m in length. Since some locations cannot be ground completely, such as level crossings and short plugs, the specification allows some percentage of the recordings or of the measured total length to be outside these limits. Quality Class 1 requires 95% of the finished rail to be within the limits (90% of the long waves must be within the limits). On Class 2 track, which deals with 30mm – 100mm and 100mm – 300mm wavelengths, 90% of the recordings must be within the specifications.

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