Carryback is material that adheres to the belt beyond the discharge point of the head pulley, accounting for most of the fugitive material present in conveyor systems. Material fines become dislodged along the return run of the conveyor and build-up beneath the belt. Carryback particles are typically less than 10mm in size.
Particles that make up carryback typically have a higher moisture content than the overall conveyed material. As the belt rolls over the idlers the belt vibrates creating a setting action. The smallest moisture rich fines sift to the bottom of the pile, where they can create an adhesive mixture that clings to the belt.
Fugitive material on walkways and underneath conveyor belts represent an increased risk to personal safety including slips, trips and falls, pinch points and manual handling.
Environmentally, there is an increased risk of conveyed materials falling outside the designated areas. This in turn increases dust. Which can be harmful, depending on the sensitivity in the surrounding environment (particularly around ship loading and associated stockpiling and feeders).
Carryback build-up on rolling components causes mistracking and blockages in head chutes, which in turn leads to spillage and off-centre loading. It also reduces efficiency, increases maintenance costs, reduces plant safety, reduces product quality, shortens belt life and leads to premature component failure. Fugitive material may bury idlers, conveyor components, or structural supports, requiring expensive clean-up labour and replacement parts.
Planned maintenance and shutdowns of conveyor belts are necessary to achieve effective and continual bulk handling operations. Installing a belt cleaner, or belt cleaning system, reduces carryback by removing the fines from the belt after the discharge point.
Properly installed, designed and maintained belt cleaning systems remove carryback and return it to the main material flow. Typically, belt cleaners are installed at or near the discharge point to remove residual fines.
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