Metering Tube is Key to Precision, Accuracy Of TrueFeed™ Gravimetric Feeders from Conair

A patented rotating metering tube, built into the new TrueFeed™ gravimetric feeder from Conair, dispenses process ingredients with exceptional accuracy, even at rates as low as 0.02 gm/sec. This new metering technology eliminates the uneven delivery or “surging” that is associated with older auger-type feeders. Together with advanced control software, automated material weighing and flow-rate calibration capabilities, this unique feature helps the TrueFeed gravimetric feeders set a new standard of accuracy and performance.

Volumetric feeders, most of which use an auger screw to meter colorant and other expensive additives, are notoriously inconsistent. The amount of material dispensed in any given shot can vary widely (as much as ± 20% of setpoint) due to surging. Surging occurs because the flighted auger delivers material in an uneven and repeated pattern; similar to a cross-section of a sinusoidal wave that starts small, crests, and then falls off. Typically, there is a large amount of material dispensed at the mid-point of a rotation, with somewhat less material at the beginning and end. While surging does not affect the total amount of material delivered by a feeder over a long period of time, it can upset the consistency of mixes that depend on a consistently low rate of additive or color. Because the volume of the dispense rises, peaks, and falls through each cycle, surging can also make the process of sampling and calibration, which is critical to accuracy of volumetric feeders, more difficult.

To compensate for erratic feeding, processors often over-feed, setting rates higher to ensure that enough colorant is always dispensed. With some ingredients costing up to $50/lb or more, using even a small amount more than necessary can be quite expensive. On the other hand, with the digital precision of the TrueFeed, and the more accurate metering tube, processors can be certain that just the right amount of color or additive is dispensed.

The TrueFeed’s rotating metering tube ensures a steady stream of process ingredients by tumbling them over and over in the tube, where they form an unbroken stream that exits the feeder at the feed - throat adapter of the processing machine. To further enhance consistent dispensing, the stainless-steel tube is driven by a microprocessor-controlled stepper motor. The motor itself is significantly more precise in its start, stop, and rotation control than conventional DC motors that are used in auger and disk type feeding equipment. In addition, the microprocessor is capable of continuous self-calibration and fine-tuning based on sampling and recalculation of weight and material-flow data.

The accuracy of the TrueFeed is also enhanced by the fact that it is gravimetric, rather than volumetric. The ingredient hopper is weighed continuously. As material is dispensed, the weight loss is registered and the feeder runs until the exact amount has been delivered. Then it stops. If material characteristics (bulk density, particle geometry, etc.) change, the speed of the metering unit is adjusted automatically to compensate. The digital weighing unit is accurate even under vibration conditions.

With volumetric feeders, on the other hand, users are required to collect and weigh as many as a dozen material samples to calibrate how long the auger must turn to dispense a given weight. If the character of the material changes, the time-consuming calibration process must be repeated.

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