Implementing Dribble Chutes and Auxiliary Systems
On conveyors where cleaning systems are positioned so that the material removed from the belt does not freely return to the main material body, a dribble chute, or fines chute, is usually required. This is a separate part of the discharge chute that directs the removed carryback back into the main material flow. This auxiliary chute must be large enough and designed with a steep enough wall angle to ensure the material falls away from the cleaning system and prevents the encapsulation of the cleaner in sticky materials. It is advisable to install a dribble chute with an angle as close to vertical as possible and to line it with a low-friction material such as Ultra-High Molecular Weight (UHMW) polyethylene. Incorporating flow aids to help move the carryback material away from the cleaners can also be useful.
One way to solve the problem of buildup on a dribble chute is to create a dynamic sub-floor inside the chute. This can be accomplished by mounting a sheet of smooth, low-friction, abrasion-resistant plastic, such as UHMW polyethylene, parallel to the chute floor with one end unsecured, allowing the sheet to move freely. A vibrator is mounted to this sheet, providing dynamic action to prevent material buildup. Because this vibrating sheet is isolated from the steel chute work by a rubber cushion, there is very little force applied to the structure, reducing the risk of metal fatigue.
An alternative system could include a flexible curtain or sheet of rubber used as a chute liner, which is periodically "kicked" with the discharge from an air cannon. This flexes the liner, causing any adhered material to drop away.
Access to the dribble chute should be provided to allow personnel to clear buildups and perform periodic washdowns to prevent blockages.