Bulk Material Loaders and Unloaders

Bulk materials loaders and unloaders are used to fill and remove powders, granular substances and other bulk solids from bags, bins, boxes, carts, drums, hoppers, railcars, trucks, and silos. They often include solids feeders and can break down clumps or arches to allow for more uniform distribution of bulk materials. Some bulk materials loaders and unloaders are designed to handle abrasives or ceramics, chemicals or fertilizers, cosmetics or pharmaceuticals, construction materials or cement, food products, metals or minerals, and paints or pigments. Others are designed to handle pulp and paper, wood chips, polymers, adhesives, molding, coal, or wastewater sludge. Dry or free-flowing devices can handle a variety of dry materials. Wet or bridging devices can handle moist materials, slurries and dispersions; flakes and fibers; and other bridged materials with high aspect ratios. 

There are many types of bulk materials loaders and unloaders. Belt or apron feeders dispense material from a serrated or smooth belt that receives material from a hopper and is driven by a roller. Bin sweep arms use an auger to sweep the bottom of a bin or silo and a screw to pull material into a well. Drum or roll feeders consist of a hopper atop a solid or hollow roll. Dumpers or tilters reposition or empty storage containers by tilting them. Inverters or upenders also empty containers, but by rotating them 180°. Load arms or layer loaders are long tubes which rotate to feed materials evenly. Load spouts consist of a telescoping tube with a funnel-shaped end for the dust-controlled loading of hoppers, storage bins, shipping vehicles, or packages. Pneumatic or vacuum feeders use pressure to fluidize bulk materials and then push them to the process unit or vessel. Star feeders consist of a paddle wheel-shaped rotor that rotates slowly in order to dispense bulk material into a hopper or process unit. Table feeders consist of a hopper, skirt and rotating disc. Vibratory feeders include a hopper on top of a metal tray and an unbalanced motor or other controlled vibration source.

Selecting bulk materials loaders and unloaders requires an analysis of flow control types, features, and applications. There are two basic flow control types: volumetric and gravimetric. Volumetric devices control bulk material flow in units such as cubic feet per hour. Gravimetric devices control bulk material flow in units such as pounds per hour. Depending on the flow control type, volumetric capacity and gravimetric capacity are important specifications to consider. For bulk materials loaders and unloaders that include feeders, load cells or scales are often used to provide continuous or batch weighing. Common features for loaders and unloaders include integral bins or hoppers; adjustment controls; vibrators, impactors, or agitators; aerators or fluidizers; and blending capabilities. Applications for bulk materials loaders and unloaders include conveyor feeding, dust collecting, filling, metering, bin discharging, and sampling.

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