RAILWAY AGE MAY 2021 ISSUE: As a part of the Affiliation of American Railroads’ (AAR) Strategic Analysis Initiatives program, Transportation Expertise Middle, Inc. (TTCI) investigated the results of tread braking on wheel put on and tread floor harm by monitoring the efficiency of three articulated five-unit effectively vehicles and 5 coal hopper vehicles with disabled brakes working in in any other case regular income service circumstances.
The Federal Railroad Administration (FRA) granted an enforcement discretion for these eight vehicles to function with disabled brakes in income service between 2016 and 2020. Trains transferring these vehicles had been required to include sufficient vehicles to take care of a minimum of 95% operational brakes. This requirement offered ample security precautions as evidenced by the truth that no accidents, incidents or accidents occurred as a result of working these eight vehicles with disabled brakes for greater than three years in in any other case regular service.
Wheel put on and tread floor harm have lengthy been regarded as influenced by the abrasive contact and warmth developed by tread braking. Thermal mechanical shelling is the acceleration of near-surface rolling contact fatigue (RCF) harm on wheel treads as a result of elevated wheel temperatures. These outcomes present vital perception into the results of tread braking for the actual service environments being evaluated, however the outcomes don’t cowl the complete vary of working environments in North American freight service.
The air brakes on the D truck of the three effectively vehicles had been disabled together with the complete air brake system of the 5 coal hoppers. The E truck of the effectively vehicles and 5 further coal vehicles with usually functioning brakes had been included within the take a look at as management teams so the efficiency of the teams might be recognized with and with out air braking. None of those modifications affected the operation of the handbrakes.
New wheelsets had been used for each the take a look at and management teams to get rid of the affect of pre-existing circumstances. Researchers carried out periodic inspections of the take a look at vehicles, together with photo-documenting seen wheel tread harm and gathering wheel profile measurements for put on calculations. These inspections had been simpler to schedule on the coal vehicles touring in a unit prepare in contrast with the effectively vehicles that didn’t journey collectively. Restore information had been used to evaluate wheel longevity.
Along with the periodic inspections, detailed examinations had been carried out on a complete of 4 wheelsets eliminated as a result of excessive influence hundreds from one effectively automotive with disabled brakes and two coal vehicles with disabled brakes. These examinations included numerous combos of ultrasonic testing, magnetic particle inspection, optical microscopy, and metallurgical evaluation. All 4 wheelsets confirmed traits in step with typical RCF tread harm noticed on wheels in regular income service operations. The figures above present two examples of the tread harm discovered on wheels faraway from vehicles with disabled brakes. The investigation indicated the harm was as a result of RCF alone with no indication of the wheels sliding on the rail.
Upon examination of the locomotive occasion recorder information representing 1,200 miles from two eastbound journeys with the loaded coal vehicles, it was found that the air brakes had been utilized 91 instances at preliminary prepare speeds larger than 15 mph. Primarily based on the discount in brake pipe strain and prepare velocity, not one of the functions had been estimated to have generated wheel temperatures a lot in extra of 200°F.
In conclusion, this testing demonstrates that typical wheel shelling from RCF can and does happen impartial of heating from tread braking. Regardless of the appliance of the coal automotive brakes dozens of instances per journey, it’s not clear that the wheel temperatures had been heat sufficient to affect put on or shelling. In truth, neither automotive sort confirmed statistical variations in wheelset survival based mostly on the situation of the brakes. Though the impact of braking on the wear and tear charges of the effectively automotive wheels was inconclusive because of the information scatter and small pattern sizes, the coal automotive wheels didn’t present any put on penalty from tread braking.