Conveyor belt transfer points are a potential problem area for any bulk material handling operation. As tons of material per minute are quickly dropped with great force through transfer chutes onto a receiving conveyor, fugitive cargo often piles up around the frame and dust migrates throughout the area, collecting on idlers, pulleys and floors and affecting air quality. Moreover, workers have to continuously clean up the material before it encapsulates the belt, potentially exposing them to a hazardous work area around a moving conveyor, where even incidental contact can result in serious injury in a split second.
Conveyor operators need only take a broad look at the expense that fugitive material has on a system to realize the full cost that accompanies inefficient transfer point designs. Problems such as improper belt support, badly sealed chutes, damaged idlers and uneven cargo distribution can all result in spillage and belt mistracking, contributing to increased costs for maintenance and cleanup, the potential for injury and compliance issues. These factors raise the cost of operation and reduce profit margins.
In a properly-engineered transfer point, each component — from the chute design to the cradles and dust seals — is employed to maximize its specific function and contain dust and fines, while at the same time offering workers easy access for maintenance. The whole system works efficiently, retaining the maximum amount of cargo at the highest achievable volume, while still offering the safest work environment possible.
Airflow and Entrapment
With a constant stream of material crashing on the impact point of the receiving belt, the transfer point can be incredibly turbulent, and this turbulence must be contained. By slowing the airflow in the skirted area, suspended dust is allowed to settle onto the cargo path. To contain the mixture of air and disrupted material, a stable, well-supported belt is needed for the sealing components to seal against. Without a stable beltline, the belt will sag between idlers, and sealing components will not prevent air and fine material from escaping out of unsealed gaps, causing spillage and dust emissions.
There are typically two acceptable ways to support a belt in the confined area of a transfer point. The first is to use steel or impacting idlers — or a combination of both — that are spaced close together. Typically, idler spacing should be approximately 1 to 2 inches (2.5 to 5 cm), but the less spacing in between idlers, the better. The second way is to install adequate cradles with track-mounted idlers in between for total belt support.
A crucial requirement in any transfer point designed for reduced spillage and high efficiency is an effective skirting and wear liner sealing system at the edge of the belt. Older systems may have wear liners that are fastened to the inside of the chute wall — often welded — which poses a significant potential risk to maintenance workers doing adjustments or replacements. Since a grinder or torch is generally needed for this task, dust residue must be thoroughly washed from chute walls to avoid potential explosions.
A more modern design features external skirting, which establishes the tight belt seal needed to eliminate fugitive dust and fines. After elevating the chute box above the material flow, an abrasion-resistant liner plate is mounted on the outside of the chute, followed by the skirting seal. This system closes the gap between the liner and seal, eliminating abrasion from trapped material without interfering with existing supports. The external design requires minimal tools and no confined space entry to inspect, adjust or replace wear liners or skirts, and in most cases can be performed by a single worker.
With a properly trained staff and thoughtfully designed components, transfer point maintenance is easier and safer than ever before. Thanks to new component designs and advanced engineering capabilities, the work environment has been drastically improved in recent years, and operators are reducing downtime due to cleanup and broken equipment caused by fugitive material and dust. These gains should inspire operators to make time for a cost/benefit analysis of new transfer point technology and assess the long-term gains of both increased efficiency and workplace safety.