Towards a standard approach for the twin disc testing of top-of rail friction management products

A wheel/rail friction coefficient that is too low can result in damage to the wheel and rail due to slips and slides, delays and safety concerns. A friction coefficient that is too high can result in excessive wear, noise and rolling contact fatigue. Changing contact and environmental conditions cause variations in wheel/rail friction, so friction management products, applied via wayside or on-board applicators, are used to either increase or decrease the friction coefficient so that an improved level is reached. They can be split into three classes; traction enhancers, lubricants and top-of-rail products (including water-based, oil/grease-based and hybrid products). This paper focuses on top-of-rail products and describes the different apparatus, contact conditions, product application methods and result interpretation that have been used to test these products and highlights the requirement for a more standardised test method. A proposed test method is outlined, which uses a twin disc test rig to collect “effective level of friction” and “retentivity” data to assess product effectiveness. More comparable and standardised data will ensure that maximum benefit is obtained from each set of results and help both product development and the approvals process.