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

Abstract

Low adhesion presents a major concern for many rail operators. Railway vehicles under these circumstances can experience a serious loss of braking capability giving rise to dangerous situations such as platform overruns and signals passed at danger. One cause of adhesion loss is autumn leaf fall [1]. Leaves are run over by the wheels of a train and a chemical reaction occurs between the leaf and the rail steel [2]. This forms a black layer on the rail which when wet causes very low friction. These leaf layers have also been shown to be isolating and can interfere with railway signalling systems. Traction enhancers (also referred to in this paper as traction gels) have been developed as an alternative solution to using sand alone. They consist of sand particles suspended in a water based gel and are designed to be delivered to the rail by the trackside or via mobile application systems. The aim of this work was to develop a technique for generating a representative leaf layer on the surface of a twin-disc rail specimen and using this to develop a test methodology for assessing the performance of a traction gel in terms of adhesion recovery, wear and its effect on wheel/rail isolation.

The low adhesion problem due to leaf contamination in the wheel/rail contact: Bonding and low adhesion mechanisms

“…Figure 1 (a) shows a general relationship between the slip and the traction coefficient, obtained in twin disc apparatus [4]. Figure 5: A general relationship between the rotational number and the traction coefficient in a twin disc apparatus, showing the long effect of wet leaves [24].…”

“…Main difference between a twin disc machine and a ball-on-disc machine is that the former produces a line contact and the latter produces a point contact. Figure 5 shows typical traction results of a twin-disc test performed under varying contamination conditions [24]. A leaf layer was created on the rail disc and then run against wheel disc.…”

“…In [4], leaves were continuously fed into the disc contact, keeping the friction level low, in contrast to the method used in [24]. As can be seen, both dry and wet leaves yield low traction levels at slip ratios between 0.5 and 5 %.…”

“…Traction enhancers (Adhesion enhancers), a type of product have been developed and tested recently, [12,24,35]. Traction enhancers aim to overcome low adhesion problems, in particular, leaf contamination.…”

“…Recently, new research approaches for the leaf film issue have been attempted, by analysing the bonding chemistry and mechanism between the leaf film and the rail surface [14,15,[24][25][26]. Several techniques for analysis, such as FT-IR (Fourier-Transform Infrared spectroscopy), GD-OES (Glow Discharge Optical Emission Spectroscopy) and EDX (Energy Dispersive Xray), have been carried out for leaf films obtained in both the laboratory and in the field.…”