Worldwide, plastics processing is conducted on a massive scale, with raw materials produced, shipped, and handled in extremely large volumes. They are delivered to processing plants in large, skid-mounted cardboard boxes called gaylords; in oversized reinforced plastic bags (super sacks); in skidded stacks of paper bags; or by railcar or truckload. Once in the processing plant, these resins usually are handled with a pneumatic conveying system that typically consists of a system of pipes, manifolds, valves, and controls that derive their motive force from a high-velocity stream of air. Typically, this air stream moves as a result of a differential in vacuum pressure that is created at the head of the system by a vacuum pump. In smaller, self-contained conveying systems, the vacuum may be created by a motor or by a fast-moving stream of compressed air that is pulled past a venturi. When granular, pelletized, or powdered materials are exposed to this vacuum pressure differential, they are drawn into the pneumatic conveyor, suspended in the air stream, and moved to their destination.
There are many advantages to pneumatic conveyance in a plastics processing plant: Contamination is held to a minimum. Waste and spillage are minimized, resulting in a cleaner plant and lower housekeeping costs. Personnel accidents, from lifting, or moving resins, or from slips and falls on spilled resin can be virtually eliminated.