Disc machine study of contact isolation during railway track sanding

Abstract

An experimental study has been carried out to investigate the effect of sanding on the electrical isolation of a wheel/rail contact. Sand is applied to the wheel/rail interface to increase adhesion in both braking and traction. Train detection, for signalling purposes, can be by means of track circuits. Signalling block occupancy is triggered by the wheelset of the train`shorting out' the track circuit. Sand in the wheel/rail interface means that contact between the wheelsets and the track may be compromised, inhibiting train identi®cation. Tests were performed on a twin-disc machine where rail and wheel steel discs are loaded together and driven under controlled conditions of rolling and slip. Sand was fed into the disc contact through a standard compressed air sanding valve. The electrical circuit used was a simpli®ed simulation of the TI21 track circuit. The application of sand with and without water to the discs was carried out under a range of mild and severe test conditions. The results indicated that a transition exists in the sand¯owrate below which there is a measurable, but not severe, change in voltage, but above which the contact conductance decreases by an order of magnitude and the voltage tends towards its open-circuit value. The total isolation time also showed a similar transition. Contact resistance was modelled assuming full disc separation by a sand layer and partial disc contact with some sand present. Traction was monitored during the tests. A wet contact showed approximately half the traction of a dry contact. The addition of sand increased the traction to levels observed in a dry contact. Idealizations inherent in the test method mean that it represents a severe case. The disc geometry is smaller than a wheel/rail contact and both are in rotational motion. The sand nozzle was placed closer to the interface, leading to greater sand entrainment and low inductance. A fast data acquisition rate made the test circuit more sensitive to small¯uctuations in isolation than an actual track circuit. Given these limitations, it is likely that the test method, at its present stage of development, should be used as a means to assess qualitatively the relative effects on electrical isolation of different contaminants.

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

“…The test discs are connected in parallel with R2 as shown in Figure 4. This circuit has been used in previous work [4,5]. When the test discs are brought into contact more current will be drawn through them due to the lower resistance of the contact (between 0.5 -0.6 ) compared to R2 (10 ).…”

“…More information on the development of the rig can be found in [3]. 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].…”

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

“…Unlike HPFs, VHPFs are used to restore adhesion under adhesion loss conditions. 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.…”

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

“…In order to monitor the electrical voltage across the disks contact area, an electrical circuit was installed on the roller rig so that voltage readings together with adhesion data could be obtained in the course of each test. Figure 3 depicts the electrical circuit, which had also been used for insulation studies on wheel-rail contacts in previous study [14]. In these tests, a nominal input voltage of 2 V was taken, but note that previous study demonstrated the negligible influence of the input voltage on the electrical insulation of the wheel-rail contact [14].…”

“…This has led railway organizations to establish standards on railway sanding that guarantee correct functioning of track circuits [13]. Lewis et al [14,15] investigated the electrical insulation of the wheel-rail contact caused by sanding in both static and dynamic tests. Their results showed that the electrical insulation of the wheel-rail contact varied with the sand feed rate, and complete electrical insulation may occur above a certain sand feed rate.…”