A feeder's most basic mission is to handle the material and produce a uniform and consistent discharged stream. This section details various common solutions to achieving this fundamental requirement. Advantages and limitations of each approach are also discussed.
The first leg of the gravimetric feeding triangle, material handling, refers to a feeder’s ability to condition the material (if and as required) and produce a reliably consistent and uniform volumetric discharge stream. If the feeder’s material handling system can perform this essential task, appropriate control adjustments can then be applied (based on continuous weight data) to achieve and maintain the desired gravimetric discharge rate.
Well behaved materials, such as most plastic pellets or free-flowing, non-packing powders typically pose few handling problems, tend to maintain a consistent density when handled, and thus are readily controllable.
However, more difficult materials (compacting, poor flowing, sticky, clumpy, hygroscopic, floodable, etc.), often require feeding elements and density conditioning measures specially matched to meet the handling challenge.
To accommodate the broad range of plastics resins, additives, forms and handling characteristics, a spectrum of material handling strategies is required including: