Countering Conveyor Clogs

As belt conveyor cargo travels over the idlers on the carry run, the weight of the cargo and the undulating surface causes dust and fines to adhere to the belt and lodge into cracks and gouges. Upon discharge, material that does not fall with the main cargo stream and remains clinging to the belt’s return is known as carryback. If it is not cleaned from the belt by a primary and secondary cleaner, the carryback falls from the belt and accumulates in piles under the belt, building up as spillage or becoming airborne dust. Studies have shown that mitigating carryback can reduce fugitive spillage and dust by up to 90%, while increasing idler and belt life by 25 – 30%.

Material that is cleared by a primary or secondary cleaner is collected on a slope in the rear of the head chute, referred to as a ‘dribble chute’. However, cleaning these fines increases the volume of material passing through the head chute and this can build up directly under the head pulley. To control buildup and chute clogging, a vibrating dribble chute and mounted air cannons were developed to reduce downtime from clogging and cleaning and increase production.

A clean belt is an efficient belt

If a belt has no cleaners, operators should expect to add labour to their budgets to clean spillage and replace fouled components from excessive dust and carryback. When spillage is left to build up, the belt rides on the dried pile of abrasive material, which prematurely erodes the belt covers and damages the unprotected return, resulting in a lower belt life. Further down the return path, carryback can foul rollers and spill into walkways, requiring regular maintenance to retain efficiency and uphold adequate workplace safety standards.

Without adequate cleaning, a belt in a heavy-duty dry bulk handling operation can carryback more than 0.5 t (0.45 t) of material per hour. The addition of just a primary cleaner will still experience carryback, leaving only an average of 0.02 lb/ft2 (100 g/m2) on the belt. Adding multiple cleaners can get the carryback level down to 0.01 – 0.004 lb/ft2 (50 – 20 g/m2) on the belt. Depending on the speed of the belt, length of the system and the space in which it is operating, this amount of average carryback would keep spillage levels sustainable and dust levels relatively compliant to workplace air quality regulations. Using a high quality belt cleaning system drastically reduces carryback, dust and spillage, but also introduces a design dilemma resulting in faster build up on the dribble chute. Depending on the characteristics of the application, the design of the dribble chute is an important consideration. Material buildup on them requires addressing in order to maximise production efficiency.2 Some heavy-duty applications might require two primary cleaners and a secondary cleaner between the discharge and snub pulleys, which can create a lot of buildup. Due to space restrictions from a small head pulley, tertiary cleaners might be the only option, so designers recommend a vertical dribble chute. Vertical dribble chutes are also prone to buildup and clogging and are difficult to clean. If only a tertiary cleaner is allowed, catch pans are often used to gather carryback from idlers when the conveyor path crosses environmentally sensitive areas, roads or walkways.

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