Volumetric feeding: Six common methods
Volumetric feeding is based on an invention more than 2,300 years old: Archimedes' screw. Though developed to move water, Archimedes' screw was adapted in the late 19th century to move dry materials; later, the screw was also used to feed dry materials by controlling their flow. Today, several volumetric feeding methods are used. This article first discusses volumetric feeding basics, then describes six common volumetric feeding methods and how to select a volumetric feeder. Other information discusses minimizing speed control and feedrate errors in volumetric feeding.
A feeder is a mechanical device that controls material flow from one point to another at some required rate. The device controls flow by weight [called a gravimetric feeder or weigh feeder] or by volume [called a volumetric feeder]. A gravimetric feeder feeds by directly measuring the material's weight [facilitated by sensing variations in the material's density] and then controlling the feedrate around the desired rate, or set-point, in units of weight per unit time. A volumetric feeder feeds a certain volume of material per unit time at a given motor speed, and its feedrate can be stated in units of volume per unit time [such as cubic feet per hour]. The feeder's material feedrate by weight [such as pounds per hour] must be inferred from motor speed assuming constant bulk density.