Sandite

Sandite is a trade name for a type of rail-cleaning fluid used on railways to improve traction between the train wheels and the rails. It is primarily composed of silica sand suspended in a fluid carrier, typically a mixture of water, antifreeze (like glycol), and potentially some additives to aid suspension or prevent corrosion.

Sandite is applied to the rails by special equipment fitted to trains, typically referred to as "sandite applicators" or "rail head treatment trains" (RHTT). These applicators spray a thin layer of Sandite onto the railhead. The sand particles help to break down and remove contaminants like leaf debris, grease, oil, and water that can accumulate on the rail surface, especially during autumn (fall) when leaf fall is prevalent.

The presence of contaminants significantly reduces the coefficient of friction between the wheels and the rails, leading to wheel slip (where the wheels spin without propelling the train forward) or wheel slide (where the wheels lock up and slide along the rails). These issues can cause delays, increase wear and tear on the train and track, and compromise braking performance.

By increasing the friction between the wheels and the rail, Sandite improves acceleration, braking, and general adhesion. This allows trains to maintain their schedules more reliably, especially during adverse weather conditions.

While effective, the application of Sandite is a temporary solution. The fluid evaporates, and the sand is eventually dispersed by train traffic and environmental factors. Therefore, regular re-application is necessary to maintain optimal rail adhesion, especially during periods of heavy contamination.