DRYING: Vacuum Dryer’s Load Sensors Continuously Control Resin Levels

Addition to dryer line doubles capacity of previous model.

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The new VBD300 dryer from Maguire Products, Aston, Penn., has the capacity for general-purpose injection molding applications and low- to mid-throughput extrusion jobs. Throughputs ranging up to 300 lb (136 kg) per hour double the VBD150’s capacity (which proved to have greater capacity in testing after launch) and bring the benefits of vacuum resin drying to a broader range of applications.

The vacuum technology reduces the boiling point of water, causing moisture within the pellets to volatilize and be forced out into the low-pressure environment surrounding it. Maguire says that compared to desiccant systems, its vacuum dryers have lower operating costs, increased efficiency, and greater process control.

Key to that process control are the load cells, which were added in 2015, that the VBD line employs. These monitor material weight at two different points, giving control over material consumption and providing documentation of process conditions for certification purposes.

The load cells provide continuous control of the resin level in two of the three vessels in the drying system: the vacuum chamber and the retention hopper. Operating on a loss-in-weight basis, the load cells provide real-time data on material throughput and are unaffected by variations in bulk density, reportedly achieving accuracy of ± 0.5%.

Maguire says that compared to desiccant dryers, the VBD vacuum dryer consumes 60% less energy and drys resin in one-sixth the time, substantially reducing the polymer’s heat history. The VBD can provide properly dried polymer for production in 35 minutes after a cold start, according to Maguire.

VBD vacuum dryers use gravity to move material through three drying stages of the drying process—heating hopper, vacuum vessel, retention/takeaway hopper—which are arranged vertically. Material is moved from one stage to the next via high-speed slide-gate valves that dispense with an accuracy of ±4g.

Maguire says practically all resins can be processed via vacuum drying. The company is currently working on the VBD 600, which would have a throughput capacity of 600 lb per hour. The third model in the line, the VBD 1000, which has capacity of 1000 lb/hr, launched in 2013. 

The VBD 300 dryer has a touchscreen control that allows operators to manage all drying parameters from one screen, and like all Maguire equipment, the dryer comes with a five-year warranty.