Field investigations into the adhesion recovery in leaf-contaminated wheel–rail contacts with locomotive sanders

Abstract

Locomotives of railways worldwide have been using sand since 1838 to improve the wheel-rail adhesion during traction and braking operations. In more recent years, sanders have also been fitted to electrical and diesel multiple units in some railways to fight (often in combination with traction control or wheel slide protection systems) the low-adhesion conditions, especially encountered in autumn due to leaf contamination. In spite of the worldwide broad use of sand, different standards on sanding practice appear to be used by different railways, while there is a lack of fundamental understanding on the influence of sanding parameters, such as particle size distribution, feed rate, and number of sanding axles (among others), on the adhesion recovery, wear, and train detection. In order to gain a better understanding of these interrelationships, the authors have carried out laboratory investigations in recent years. As a continuation of that work, the influence of the sand particle size on the adhesion recovery in leaf-contaminated contacts is investigated in this article by means of traction tests of an electrical locomotive in a stabling yard. Three differently sized silica sands are used in the testing. In addition to the particle size investigations, the standard sand currently used in the Dutch railways is also tested to quantify its effectiveness against leaf contamination. Besides the immediate adhesion improvement upon sanding, the remaining friction level left for subsequent tractive wheel passages is also investigated for all sands tested. Furthermore, baseline tests (i.e. without application of sand) are also performed to obtain some quantitative insight into the impact of leaf contamination on the wheel-rail adhesion in the field.

Tribology of the wheel–rail contact – aspects of wear, particle emission and adhesion

“…Leaf fall can also cause a lot disturbance to traffic on the network [45]. Research into leaf contamination and low adhesion has been carried out using various methods including actual trains [67], pin-on-disc [58,68], twin-disc [69,70] and ball-on-disc [71] test rigs. A comparison of these tests was discussed in [72], and is shown in Table 4.…”

“…It was pointed out that with increased thickness of the oxide layer on the railhead surface the friction coefficient reduces [72] although no definitive relationship was found between leaf contamination thickness and the friction levels [64]. [68] GallardoHernandez and Lewis [70] Li et al [69] Cann [71] Arias-Cuevas and Li [67] Test apparatus Pin-on-disc …”

“…These adhesion loss situations are usually short lived and in order to restore safe operation of a locomotive quickly high wear rates [77] and electrical isolation which can be caused by these products can be tolerated [78]. Arias-Cuevas et al [79,80] compared four types of sands with different grain sizes using a combination of laboratory (twin-disc) testing and field testing. Both test methods showed that medium sized sand particles are the most effective for adhesion recovery.…”

“…Removal of only the coated slippery layer is not enough to restore friction levels. A number of methods are used to combat adhesion problems due to leaf contamination including: sand [72,80], Sandite (a mixture of sand and aluminum oxide particles), high-pressure water jetting, high-powered lasers [70] and a magnetic track brake [83]. However, leaf contamination on the rail is very localized and the contaminated depth varies.…”

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

“…Consequently, low adhesion problems have been present in many railway networks in recent decades, especially those related to leaf contamination in autumn [1][2][3][4]. Recent field investigations have demonstrated that leaf layers in dry conditions can lead to low adhesion incidents as well as in humid conditions [5]. Since the beginning of railways, sanding from the locomotive has been a common practice to enhance the wheel-rail adhesion [6].…”