Belt conveyor in an underground tunnel. Transportation of ore to the surface (Istock Image)
Introduction
Material that sticks to a conveyor belt after passing over the head pulley is known as carryback. This carryback falls off the belt as it passes over return idlers, creating piles that increase dust exposure, pose safety hazards, and shorten belt and component life. Addressing carryback at the head pulley helps keep the material in the main flow, minimizing dust emissions and cleanup needs. The primary approach to controlling carryback is to clean the belt immediately after material discharge, typically using mechanical scrapers, brushes, or washing systems.
Belt Scraping
There are numerous types of belt cleaners, but they all serve the same purpose: to reduce carryback on the belt after ore discharge. Belt cleaners either peel or scrape material from the belt. Primary cleaners are angled sharply toward the belt to peel off material, while secondary cleaners are angled in the direction of belt travel to scrape off remaining fines. Multiple cleaner systems are often used to maximize effectiveness and minimize belt wear, starting with a primary cleaner on the head pulley followed by one or more secondary cleaners along the belt return. When dust levels are high, two or three cleaners may be used in different locations. To ensure scrapings are returned to the primary material flow, chutes must be designed to capture and direct them effectively.
Belt Washing
In applications where minimal carryback is required, a belt washing system can be used when scraping alone is insufficient. A wash box system sprays water on the conveyor belt and scrapes it simultaneously, ensuring thorough cleaning. Spray bars soften carryback and lubricate the belt, allowing effective removal without excess wear. The configuration of nozzles and cleaners is tailored to the required cleanliness and the type of ore being conveyed.
Conclusion
Effectively managing carryback is crucial to reducing maintenance, improving safety, and extending the life of conveyor belts and components. Whether using scrapers, washing systems, or a combination, keeping conveyor belts clean minimizes downtime and keeps operations running smoothly.
Reference
NIOSH Mining Program Report of Investigations, «Dust Control Handbook for Industrial Minerals Mining and Processing», second edition.
