DRYING: Vacuum Dryer Adds Load Cells for Greater Accuracy

Originally titled 'DRYING: Load Cells Make Dryer More Accurate'

Load cells provide continuous control of the resin level in the vacuum chamber and retention hopper.

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Maguire Products Inc., Aston, Penn., says the addition of load cells to its patented line of VBD vacuum dryers allows level control to within ± 0.5%. Maguire will demonstrate the enhanced VBD dryer at NPE2015 (see previous coverage in March Keeping Up).


The VBD dryer now uses load cells to continuously control the resin level in two of the system’s three vessels—the vacuum chamber and the retention hopper. The load cells operate on a loss-in-weight basis, giving the machine’s control real-time data on material throughput that Maguire said is unaffected by variations in bulk density. Because of this, the dryers reportedly achieve the aforementioned accuracy of ±0.5%.


Furthermore, Maguire noted that the load cells impart enhanced control over material throughput to the dryer by enabling the microprocessor in the controller to monitor, display, and log throughput in real time. As the first batch of material is conveyed from the dryer to processing, a throughput rate is calculated and subsequently updated once per minute. Material usage documentation can be downloaded via USB port, making proactive monitoring of inventory possible. Load cells also enable the microprocessor to run a resettable flow totalizer, which is displayed on the screen and entered in the event log.


The load cells also contribute to energy savings, according to Maguire, thanks to improved control over throughput rate. By setting that rate to precisely match that of the process, processors can avoid an excess of dried material left over at the end of a run and can ultimately use less energy.


The load cells also give Maguire’s VBD dryers the option to run batches in addition to continuous flow operations. With the Batch Mode selected, if operators select, for example, 1,000 pounds, the VBD will run 1,000 pounds and then automatically shut down. That shutdown is anticipated so that the vacuum chamber and retention hopper are empty—a good operating practice at the completion of a batch run.


Maguire noted that as with previous versions of the VBD, the unique vacuum-drying process can cut energy use over desiccant systems by more than 60%, with resin exposed to drying for shorter periods of time, reducing overall heat history for the material. The system’s design also eliminates most moving parts, using gravity to move material through vertically arranged stages of the drying process.