The loading zone of a conveyor belt is one of the more difficult areas to seal against dust and fugitive materials. Because of the turbulent movements of these materials, both from their own fall and from air pressure within the transfer chute, they are prone to disperse upon contact with the belt.
This dispersal will cause a significant amount of material to roll toward the tail of the conveyor or fall along the sides near the loading zone. Materials can then build up on the pulley or on the ground around the supports and the tail of the conveyor.
One common solution is the addition of a seal behind the loading chute, generally made of plastic or rubber. Often these systems are loosely installed and generally insufficient to prevent the escape of material.
However, if a sealing system is placed tightly enough against the belt to prevent leakage out the back of the loading zone, the seal may instead act as a belt cleaner. In this instance, material adhered to the belt that were not previously removed by a belt cleaner at the discharge point can be dislodged behind the loading chute seal. These materials can eventually build up in the same way as fugitive materials, potentially falling off the conveyor around the tail pulley.
In either case, sealing the corners of the loading chute can prove even more difficult. Dust at the transfer point is generally under high pressure, often pushing it out past regular seals. Fluctuations in belt tension created by the impact of materials from the loading chute or wing-type tail pulleys can also allow the escape of dust and materials past the seal.
At present, multiple-barrier sealing boxes offer the primary solution for preventing the escape of materials at loading zones. These boxes are attached to the back wall of the loading chute, and reach to the area where the belt is flat as it crosses the tail pulley. A tail-sealing box is often installed on the transition are when retrofitting existing conveyors, though this is not recommended for new conveyors because of the difficulty in sealing the transition bend.
Rather than a firm seal that might act as a “belt cleaner,” these boxes will be backed by a strip of one-way seal that will prevent the escape of materials in the chute without applying enough pressure to scrape off materials adhered to the belt. The sides should be lined with a multi-layer skirt running continuously through the end of the conveyor’s skirt board, essentially removing concerns about high-pressure corners.
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