As a major contributor to formulation quality and consistency, feeder performance rightly deserves close attention and concern. Basically, feeding performance is composed of three major metrics:
- Repeatability (precision) – A measure of short-term discharge stream variability about its average value
- Linearity (accuracy) – A measure of a calibrated (spanned) feeder’s ability to produce a discharge stream whose average rate equals the desired (set) rate over its full operating range
- Stability (consistency) – A measure of a feeder’s ability to maintain accuracy and precision over extended periods of operation
The following screens address each of these metrics individually, but before detailing each dimension, it is important to appreciate that feeding performance is determined by more than the design of the feeder itself. In addition to selecting the right feeder for the job, the material and the operating environment impact performance.
The core factor in achieving and maintaining a high level of feeder performance is the design and configuration of the feeder itself. This includes not only the essential function-related subsystems of material handling, weighing and control, but also many other design elements related to robustness, durability, operational flexibility, maintenance and service.
The extreme diversity of materials and storage/handling characteristics encountered in today’s processing operations demand that close attention be paid to the assessment of materials early in the feeder specification and selection phase. Since the first step in assuring feeding accuracy is properly matching feeder and material, close consultation with the feeder supplier and possible laboratory testing to confirm the selection is typically recommended.
The Operating Environment
Attention paid to the environment in which a feeder is to operate will often reveal opportunities to assure optimal and reliable feeder performance. For example, wherever shock or vibration is a factor, measures can be taken to physically isolate the feeder. Extremes of temperature, humidity, wind, and other environmental factors should be evaluated and avoided or minimized where possible.