Understanding and Mitigating Carryback in Conveyor Systems
Carryback refers to any material that remains attached to the conveyor belt beyond the discharge point. This material constitutes a significant portion of all fugitive materials and poses substantial risks to conveyor systems, akin to transfer point spillage and other types of fugitive materials. These issues manifest as accumulations of fugitive material, leading to belt mistracking, shortened belt life, premature component failures, and other problems that result in conveyor downtime and costly repairs. Dust from carryback can also pose risks such as fire or explosion, as well as hazards like slips, trips, and falls. In some cases, this dust can present serious health risks to personnel.
Because carryback occurs unexpectedly, it often becomes highly visible, potentially drawing negative attention from neighbors and regulatory agencies regardless of where it settles. Carryback consistently indicates inefficiencies within conveyor systems.
To mitigate carryback, conveyor belts generally employ belt cleaning systems—blades specifically designed to scrape off fine material adhered to the belt beyond the discharge point. These belt cleaners are typically positioned to clean the belt as it passes around the head pulley.
Carryback typically consists of the worst-condition cargo for the belt. These particles are generally smaller in size and contain higher moisture levels compared to other conveyed materials, making them more adhesive. During the material conveying process, vibrations shake these small particles and excess moisture down to the lower portions of the belt, where they amalgamate into the substances responsible for carryback. When these materials dry, they can form a crude cement-like substance that proves challenging to remove, potentially causing damage to the belt and equipment, and possibly leading to clogs in transfer chutes.