Article: Top Ten FAQ On Bulk Solids Feeders Accuracy

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•Article: Top Ten FAQ On Bulk Solids Feeders Accuracy

Accuracy for bulk solids feeders are a concern of any processor who has to control the flow of bulk solid material. This handy guide attempts to answer the most common questions surrounding the area of feeder accuracy, and should serve to form a working knowledge of the basics of continuous feeding.

While applications can range from the simple regulation of a single material to highly complex and sophisticated, multi-ingredient blending systems involving many feeders and processing lines, this discussion will limit its focus to individual feeder accuracy.

By combining a presentation of the principles of feeder accuracy along with the practical aspects of their application to real world process operation, it is hoped a more useful and rounded understanding is achieved.

1. "How is feeder accuracy defined?"
To fully define feeder accuracy it is necessary to address three separate and distinct areas of feeder performance: repeatability, linearity and stability. Repeatability reports how consistent the feeder's discharge rate is at a given operating point, linearity assesses how accurately the feeder discharges at the requested average rate over its full operating range, and stability gauges performance drift over time.

2. "How do I translate process requirements into feeder accuracy specifications?"
Bridging the gap between feeder-related performance and end product quality begins with an analysis of quality standards and specifications. On the basis of that data, appropriate feeder performance specifications can be determined by simply working backwards.

3. "How do I decide whether to choose volumetric or gravimetric feeders?"
By definition, gravimetric feeders measure the flow's weight in one fashion or another, and then adjust feeder output to achieve and maintain the desired setpoint. Volumetric feeders, again by definition, don't weigh the flow. Volumetric feeders operate by delivering a certain volume of material per unit time which is then translated into an inferred weight-based flow rate by the process of sampled calibration.

4. "What factors determine the accuracy of a volumetric screw feeder?"
As mentioned above, volumetric feeders operate by delivering a certain volume of material per unit time. Flow rate changes are accomplished by altering screw speed. A range of screw designs, sizes and geometries as well as agitation systems are available to optimize feeding the given material.

5. "How does a loss-in-weight screw feeder work and what issues affect its ability to perform accurately?"
The concept is simple, but the execution is challenging. A loss-in-weight feeder consists of a hopper and feeder that is isolated from the process so the entire system can be continuously weighed. As the feeder discharges material, system weight declines. The loss-in-weight feeder controller adjusts feeder speed to produce a rate of weight loss equal to the desired feed rate setpoint.

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•Article: Top Ten FAQ On Bulk Solids Feeders Accuracy