Investigating the Lubricity and Electrical Insulation Caused by Sanding in Dry Wheel–Rail Contacts

Abstract

The adhesion (or available friction) in the wheel-rail contact is the most important parameter for the braking and traction operation of rail vehicles. Since the beginning of railway transportation, sanding from the locomotive has been a common practice to enhance the wheel-rail adhesion. In recent years, sanding from electrical multiple units (EMUs) and sand-based friction modifiers (FMs) have been adopted in some railway networks to overcome low adhesion incidents caused by leaf contamination in autumn. Although sanding has been proven to improve the adhesion under most of the typical contamination conditions, laboratory and field investigations have shown that sand may act as a solid lubricant in dry wheel-rail contacts. Nevertheless, the influence of the current sanding parameters on the solid lubrication effect has not been entirely investigated. Depending on the resulting adhesion coefficient, the traction and braking operations of rail vehicles could be affected. Furthermore, the influence of those parameters on the electrical insulation is also of special importance because it may affect the train detection. This article presents a laboratory investigation of the influence of three sanding parameters (i.e., feed rate, particle size, and slip) on the adhesion and electrical insulation in dry wheel-rail contacts. The tests have been carried out with a twin-disk roller rig in rollingsliding motion under closely controlled conditions. Three different slips representative of the actual traction and braking operations have been considered. Sands of four different sizes and up to five feed rates have been used. The results show that using smaller particle sizes and higher feed rates promotes the lubrication and causes more electrical insulation in the wheel-rail contact. Furthermore, the increase in slip is found to reduce the lubrication, leading to a higher adhesion coefficient.

New Insights into the Short Pitch Corrugation Enigma Based on 3D-FE Coupled Dynamic Vehicle-Track Modeling of Frictional Rolling Contact

“…The damage mechanism studied in this paper is wear; thus, the wheel and rail materials are assumed to be elastic. A Coulomb friction law is employed with a friction coefficient f C of 0.6 as in [31]. In the literature, the friction coefficient of dry wheel-rail contact is reported to be between 0.4 and 0.65 [32].…”

A new method for the assessment of traction enhancers and the generation of organic layers in a twin-disc machine

“…For these tests a supply of dead sycamore leaves was sourced. Sycamore leaves have been used in previous studies using leaf layers [7,9]. It was found in [5] that dead leaves showed significantly higher impedance than fresh ones, thus these tests would represent a worst case scenario.…”

“…Previous work has shown how sand in the contact can have adverse effects on track circuit isolation [4,5] and wheel/rail wear [5,6]. Friction modifiers (a different type of material with different purposes) have also been assessed before using the SUROS rig by Li et al [7] and leaf layers have also been generated on the SUROS specimens by Vasić et al [8] and Arias-Cuevas et al [9]. In this work we report development of a new method to generate a leaf layer and use of this method together with electrical isolation measurements to assess traction recovery performance with a traction gel.…”

Development of an innovative wheel–rail contact model for the analysis of degraded adhesion in railway systems

“…The performances of the contaminants have been compared to each other in [19]. Fundamental studies have been carried out through on-track railway tests too by taking into account natural contaminants [12] and artificial friction modifiers [10,11]. In that case, a comparison between the contaminants can be found in [17].…”