Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

Successful Grinding: Starting with the Basics
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Profile Measurement

Rail profile measurement systems can be mounted on geometry cars, small stand-alone hi-rail vehicles or integrated with larger hi-rail systems that have gauge restraint measuring systems (see Figure 5). Rail wear, rail flaw, track gauge and surface measurements can be integrated with a railway’s maintenance records and made available to track personnel. An under-utilized strength of these systems is their ability to forecast maintenance and capital requirements. Figure 6 shows a typical output indicating rates of change of rail wear, track gauge and rail cant.

The railway industry isn't about technology, it's all about money: capital and operating costs. Rail measurement systems provide information on current conditions and also show the rate of change from previous tests. Trends can be analyzed to determine optimum maintenance points and long-term capital requirements. Integrated systems can calculate the long-term lifecycle costs of track assets and provide information on depreciation (a non-cash component of operating ratio). They can also deliver present value cost/benefit on the use of lubricants/friction modifiers, grinding, defect detection, premium rail and fasteners, increased tonnage or axle load, etc.

Rail measuring systems have sufficient accuracy to be used for rail grinding both in profile selection and material removal calculation. These measurements bear directly on grinding contractor productivity and the unit cost of production. They are vital for quality control and location history. Figure 7 shows a typical output for rail grinding profile selection and optimum metal removal.

Effective as it is, rail grinding cannot correct or compensate for conditions such as wide gauge, which can have a combination of sources. Figure 8 shows a track where the low rail is severely canted to the field side. In this case, 1 in. of the 1-1/2 in. of wide gauge is due to rail cant. The grinding software will suggest a profile but this rail should not be ground until re-set.

Rail grinding will not economically compensate for excessive RCF or corrugation. The deterioration has to be caught in time. Serious effort should be spent on identifying areas where corrugation and RCF have started to form, and to develop a preventative grinding program. Left unchecked, impact loads from corrugation cause damage to roller bearings, traction motors, ballast and ties (concrete, in particular), and can result in early rail removal. Corrugation can also rapidly re-establish despite expensive multi-pass corrective grinding because the grind rarely gets deep enough into the parent metal. If preventive grinding is deferred, corrective grinding will be required at a significantly higher cost.

Work has been done to correlate surface crack length with defect development (1). Rail hardness, steel cleanliness and residual stresses each have an effect on the likelihood of defect development. Some rails with extensive surfacing cracking and shelling will not develop transverse defects (TDs). But wherever rail (type/manufacturer/year) has been shown to develop TDs from gauge-corner RCF, crack lengths should be measured and recorded during inspection. The data should be analyzed to predict future defects and to determine optimum grinding cycles.

Another issue related to surface cracking is that the stress at the crack tip is increased enormously when a “incompressible” liquid such as water from rain or snow or a lubricant is trapped at the end of a crack and compressed by a passing wheel set. This will cause surface shelling and flaking (see Figure 9). Areas around rail lubricators are particularly prone to this. A good practice is to ensure that areas around lubricators are prepared for the grind cycle, rather than being skipped over.

Preventive rail grinding in combination with lubrication can dramatically increase rail life (2). They must be combined because lubrication, alone, prevents the normal wear and removal of damaged surface material. Where a rail has well-developed surface cracks, liquid lubricants infiltrate the crack, reduce friction between the crack faces and accelerate crack propagation. The application of lubricants to damaged rail can increase the rate of crack growth.

Overall, an effective rail grinding program requires a comprehensive inspection/maintenance program. It requires inspectors to:
• Monitor tie and surface conditions.
• Utilize technology to obtain the lowest life-cycle cost of assets. Data can be used to make a case to management to support grinding and lubrication programs.
• Improve track and walking inspections.
• Inspect and perform maintenance at hot spots. The problems can’t all be found from a hi-rail vehicle traveling at 30 mph.
• Adopt effective preventive grinding and lubrication/friction modification programs to substantially increase rail life.

A simple summary is this: grinding maintains, lubrication sustains.

References
(1) Grassie, S., “Rolling contact fatigue on the British railway system. Treatment of rolling contact fatigue in rails: a guide to current understanding and practice,” RT/PWG/001 issue 1, Railtrack plc, London, February 2001.

(2) Eadie, D., Vidler, B., Hooper, N., Makowsky, T., “BC Rail Top of Rail Friction Control: Lateral Force And Rail Wear Reduction In A Freight Application,” International Heavy Haul Association Conference 2003.

Norman Hooper, P. Eng., is Principal, Hooper Engineering.

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