Influencia de las condiciones de esmerilado sobre la aparición de capa blanca en rieles tipo R400HT para uso en el Metro de Medellín

Abstract

Rail grinding is a maintenance operation carried out to remove surface and subsurface defects in rails, mainly those associated with rolling contact fatigue (RCF) and corrugation. However, rail grinding could promote the formation of a hard and fragile layer at the surface known as White Etching Layer (WEL). The presence of this layer has been associated with the early onset of RCF cracks. In this study, R400HT rail samples were ground in laboratory under controlled conditions that promote the formation of the WEL. The samples were submitted to accelerated contact fatigue tests at 20,000 cycles (8,000 cycles dry + 12,000 cycles with water) in a twin-disc tribometer, in which the wear rate and the coefficient of friction were determined. The results showed that under different grinding conditions, all tested samples developed the WEL at the surface. The samples with WEL presented higher wear and density of cracks compared to WEL-free samples for the same number of cycles. The onset of cracking was influenced by the presence of the WEL since as the WEL-perlite interface was a preferential site for crack initiation.

El esmerilado de rieles constituye una operación de mantenimiento destinada a corregir defectos superficiales y subsuperficiales presentes en los mismos, especialmente aquellos derivados de la fatiga por contacto con rodadura (RCF) y a la formación de corrugaciones. Sin embargo, el esmerilado de rieles puede inducir la formación de una capa dura y frágil en la superficie conocida como capa blanca. La presencia de esa capa se ha asociado con una aparición temprana de grietas por RCF. En este trabajo, se esmerilaron muestras de rieles R400HT en laboratorio bajo condiciones controladas que promueven la formación de capa blanca. Se sometieron tanto muestras esmeriladas como no esmeriladas a pruebas de fatiga de contacto aceleradas a 20K ciclos (8K ciclos en seco + 12K ciclos con agua) en un tribómetro tipo disco-disco, con el objetivo de determinar la tasa de desgaste y el coeficiente de fricción. Los resultados revelaron que todas las muestras probadas, bajo diferentes condiciones de esmerilado, desarrollaron una capa blanca en sus superficies. Aquellas muestras con esta capa blanca exhibieron un mayor desgaste y una mayor densidad de grietas en comparación con las muestras sin esmerilar, para el mismo número de ciclos de fatiga. Además, se observó que el inicio del agrietamiento fue influenciado por la presencia de la capa blanca, dado que la interfaz entre la capa blanca y la perlita se convirtió en un sitio preferencial para el inicio de las grietas. (Tomado de la fuente)

Rail grinding is a maintenance operation carried out to remove surface and subsurface defects in rails, mainly those associated with rolling contact fatigue (RCF) and corrugation. However, rail grinding could promote the formation of a hard and fragile layer at the surface known as White Etching Layer (WEL). The presence of this layer has been associated with the early onset of RCF cracks. In this study, R400HT rail samples were ground in laboratory under controlled conditions that promote the formation of the WEL. The samples were submitted to accelerated contact fatigue tests at 20,000 cycles (8,000 cycles dry + 12,000 cycles with water) in a twin-disc tribometer, in which the wear rate and the coefficient of friction were determined. The results showed that under different grinding conditions, all tested samples developed the WEL at the surface. The samples with WEL presented higher wear and density of cracks compared to WEL-free samples for the same number of cycles. The onset of cracking was influenced by the presence of the WEL since as the WEL-perlite interface was a preferential site for crack initiation.