Train’s wheels are made of steel and it is running on metal railway tracks. Metal to metal friction is very less. Due to the heavy weight of locomotive and wagons, a countable friction is created between wheel and track. This friction helps locomotive to move through rolling of wheels.
However, for any reasons, mainly during the rainy season, the rainwater comes between wheels and the railway track. This rainwater then works as lubricant and reduces the friction between wheels and track.
Thus, the wheel starts slipping. Traction motors roll the wheels but due to less tractive force causing less frictional force, locomotive cannot move. Loco wheels start rolling or slipping at one place of railway track.
These tyes of the phenomena are very harmful to both locomotive wheels and railways tracks. It creates skidding marks on wheels and tracks. Sometimes, the locomotive is unable to pull load and train become stall in a block section.
It hampers train movement in that section. Another light engine is to be sent this time to work as banking to clear the block section pushing from the rear.
It consumes time and all the trains run late. Railway always tries to avoid this situation.
Sand is an effective material to create extra friction and it is easily available. So railway engineers make arrangements to carry the sand with loco so that it can be used when required.
That’s why, sandbox is introduced near the wheels and sand must be filled up at the charge take over and made point of the train.
This sand is used by two types. One is automatic and another is manual. Loco pilot has to test the manual process of sanding at the time of taking charge through the manual pressing switch from the loco cab. Assistant Loco Pilot’s Duty is to check whether sandboxes are all full of sand or not. If not, sand is to be filled up.
Automatic sanding starts whenever Locomotive wheel slips through electrical arrangements. It energises the sanding switch automatically.
Credit : Quora
Picture Credit : Google