Selecting a screw feed device for low-rate loss-in-weight feeding
Low-rate feeding is a challenging segment of the bulk solids loss-in-weight feeding world. This article provides information about screw feed devices -- the most common metering device for low-rate feeders -- and explains how to choose one for your low-rate feeding application.
Low-rate feeders are finding increasing use in bulk solids processes that require highly precise, continuous feeding of small amounts of powders, granules, and pellets. A typical low-rate feeder operates by loss-in-weight -- that is, the feeder is controlled in a closed-loop system using feedback from a scale that measures weight loss. The unit's low feedrates usually fall into one of three challenging ranges -- from 0.04 to 1 lb/h (20 to 454 g/h), from 1 to 3 lb/h (454 to 1,361 g/h), and from 3 to 10 lb/h (1,361 to 4,536 g/h). To ensure that the feeder can feed the material at a highly precise, very low rate, it must have a feed device that can properly meter the material.