MATERIALS HANDLING
Top Left: Carryback dislodged from the
belt by a return idle. Top Right: Inadequate cleaning leads to carryback build up and potential encapsulation
To control buildup and
A vibrating dribble chute uses a low friction UHMW liner activated by rotary vibrator
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 to maximise production efficiency. Some heavy-duty applications
might require two primary cleaners and a secondary cleaner between the discharge and snub pulleys which can result in 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
chute clogging, a vibrating dribble chute and mounted air cannons were developed
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.
DRIBBLE CHUTES: CATCH OR RELEASE? Some methods of controlling carryback capture the material for cleanup and others aid flow and release it back into the cargo stream. Capture systems such as drip pans or catch pans are often designed to be lowered or hinged making cleanup faster but still expose the worker to hazards as large build ups can break loose while cleaning. Instead of catch pans, some
systems allow material to drop below the system and are cleared by drag chain or pusher conveyor. These can be effective in operations with larger aggregate but may run into
issues if loads are unbalanced or moist fines are left to harden during downtime. Operators who use this method have reported that the extra power required to run these systems is costly and more labour is needed to keep systems functioning than they previously predicted. The most basic flow aid is the use
of water to saturate the discharge and keep it flowing onto the receiving belt. Although some applications can attribute silica content, magnetic properties and surface friction for buildup, moisture is a large factor in adhesion (buildup on surfaces) and cohesion (buildup of material upon itself). Most bulk solids begin to lose adhesion strength at 15% moisture, so not using enough water makes the carryback stickier, whereas oversaturation could cause problems since many processes cannot tolerate the addition of water. One highly effective and field
proven method is installing a sloped chute with a low friction “active”
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