FLASH BUTT WEDGE REPAIR OF WELD HEAD DEFECTS

摘要

Transverse defects in the head of rail are the cause for many repair plug insertions and can lead to potential train stoppage if not repaired in a timely manner. In 2009, 76 train derailments were attributed to transverse head defects progressing to fracture in the rail. This phenomenon has been associated with the high axle loads found in mainly North American and heavy haul markets. Market trends are for increasing axle loads which may increase the occurrence of head defects. An efficient, high-performance repair for this defect has been sought for many years. For a truly effective repair, the loss of service time must be minimized to maintain cost effectiveness and the repair must perform as close to parent metal rail as possible. In early 2009 EWI and Holland entered into a joint development program to develop a repair for transverse defects in the rail head. Gas Metal Arc Welding, Resistance Brazing and flash butt welding with a wedge geometry piece were examined as methods for the repair. The flash butt welding process appeared most viable and is already associated with high-quality rail butt joints. The benefits of flash butt wedge welding include no rail cutting or removal, rapid on track repair time within 30-45 minutes, and the ability to modify the process using the computer-controlled flash butt welding system to accommodate different rail wear conditions. Additionally, cooling rates of the weld can be controlled such that the weld and heat-affected zone (HAZ) performance closely match the base metal. Special tooling and processing parameters were developed to use flash butt welding to place a wedge-shaped piece of matching rail material into a slot cut in the rail replacing the compromised area with matching rail material. Hardness testing, bend testing, and fatigue testing of joints produced with the final process all met AREMA performance objectives. Residual stress measurements of the weld showed a tendency for residual compressive stress in the rail head, although the level of residual stress was low. Currently, the first-generation welder with automated flash-removal equipment is being deployed in the field. Results of the qualification/performance tests show these welds perform very similarly to flash butt welds currently in rail. The use of this process is expected to enable railroads to quickly repair head defects in a more efficient manner.