Loading zones where impact resulting from lump size, material density and height of material free fall could seriously damage the belt, are generally furnished with impact idlers or sections to cushion the impacting force. The vertical velocity of the material dropped from various heights above the belt surface and the horizontal belt speed, will be different than the speed of the material when it contacts the belt, resulting in greater impact and shearing forces on the belt covers.
Lumpy materials can cause appreciable impact on the belt. The heavier the lump, the greater height of fall or the greater its angular velocity when it contacts the belt, the greater will be the energy tending to rupture the belt. When the material strikes the belt directly over a solid support, damage to the carcass can result from the crushing action of the lump against the solid support.
To minimize impact damage, every effort should be made to provide good loading conditions of the material being handled. CEMA provides an “Equivalent Free Fall Calculation”, and “Lump Weigh Factor Chart”. (CEMA, 7th Edition)
Air supported belt conveyors are provided with a solid trough for the entire length of the conveyor, eliminating all the troughing idlers. Therefore, it is especially important to protect both the belt and trough beneath the loading or impact zone.
The Hendrik Group, Inc. has designed a patented (7,281,624), air supported impact section, where a urethane pad is cast directly into the plenum bed to cushion the impact force and minimize belt top cover and carcass damage. The urethane pad has the same catenary curve profile of the plenum bed. Holes with the same diameter and spacing as the rest of the conveyor are cast into the impact pad to provide a continuous air film to support the belt and load. As material is dropped through the feed chute, it is centrally loaded onto the belt through The Hendrik Group, Inc.’s exclusive “belt loader.”
The impact section absorbs most of the “free falling energy”. Since the belt floats on a cushion of air, the volume of material is immediately lifted and exited from the loading zone, eliminating damage to both the belt and the plenum section.