TABLE OF CONTENTS When plastic materials are moulded in high volumes, the plastic pellets are usually fed from large holding bins or silos through conveying lines to a receiver, and then moved by vacuum to a loader. The loader may be located at the machine, on a dryer, or at a blending station. The silos may be located inside the plant, or if they are large, outside the plant.
An advantage of storing materials inside the plant during the cold season is that less heat is needed to heat the plastic from storage temperature up to its melt temperature. Heat is energy, and energy is expensive. A disadvantage of storing large quantities inside is the cost of space that might otherwise be used for additional moulding equipment or for secondary operations to produce additional products and income.
Bulk material handling systems may include mechanical conveyors or screw augers, but for longer distances, most use air pressure or vacuum to create a fast-moving stream of air inside a pipe to carry the material along. The highest volumes and longest distances are handled by air at moderate pressure from a blower.
Drying the material before it is moulded requires a dryer that can remove moisture down to the specified level (often measured in weight per cent) within the time allowed by the moulding machine s material demands. The drying of plastic materials depends on time, temperature, air flow, and how dry the air is that is going through the...
