Carrydown of liquid friction modifier

Abstract

A small-scale laboratory apparatus was built to study liquid friction modifier (LFM) behavior in a top-of-rail application. A field experiment was also carried out to complement the laboratory findings. KELTRACK® (a water-based LFM) was used as the test fluid. Laser-induced fluorescence served to measure the LFM thickness left on the track after the passage of the wheel. The lab experiments show that the LFM cannot withstand the high wheel-rail contact pressure in the nip present in cargo rail situations. As a result, the liquid is squeezed out laterally and attaches to the edges of the wheel contact band. This “edge liquid” is then carried down the track on the wheel. Gravimetric measurements of the wheel contact band confirm this observation, and show that only a minute amount of liquid is carried through the nip in the valleys between surface roughness features. In the field experiment, the LFM is applied from a trackside unit on a tangent section of the track. About 500 m downstream of the application point, the track has a curved section. LFM cannot be detected anywhere on the track a short distance (∼200 m) past the application unit. However, LFM is detectable on the curved sections of the track up to approximately 2 km from the application unit. This LFM on the curved track is believed to be due to transfer of the “edge liquid” from the wheel to the track, caused by the movement of the contact band as the train rounds a curve. The presence of LFM on the curved track far downstream is consistent with prior measurements of reduced lateral force on the curved track downstream of LFM application sites.

Studying the transfer mechanisms of water based top-of-rail products in a wheel/rail interaction

“…One laboratory-based study has been carried out on TOR product pick-up, 17 but in this work, friction was not measured and mechanisms of pick-up/carry-down were not explored in detail. Recently field studies carried out have shown that TOR products do not appear to be carried down more than a few hundred metres on the rail 18,19 From this work, however, indications were that the product on the wheel could be effective for >3 km. This ties-up with lateral force measurements that have shown that TOR products have an effect 3 km from application.…”

“…For example, a 35% lateral force reduction was detected 3 km from the application point of a TOR-FM in field trial described previously. 19 While detection of product on the rail head can be achieved, checking wheels is difficult in normal field trials as the trains pass and go. In a recent track trial, using a locomotive running through the same puddle of product repeatedly, with the same lateral position for the wheels, 18 it was shown that product could only be detected using a swabbing technique for up to 450 m down the track.…”