Southern California Plastics, Inc, a custom molder of engineering thermoplastics, has only just begun a large-scale changeover from conventional desiccant systems to Maguire's LPD™ vacuum resin dryers, but already the benefits are as clear as the now defect-free lenses that are among its products, according to the company. Southern California Plastics operates 24 injection molding machines, running polycarbonate, polyetherimide, and other engineering resins, offering moldmaking and design engineering services and maintaining clean-room molding and assembly areas for medical-device components.

The company began by using an LPD dryer on a trial basis and soon reported energy savings that on an annualized basis amounted to $28,000. Included in the figures were:

• savings resulting from a reduction of dryer energy consumption by 82%;


• elimination of the cost of generating compressed air for desiccant dryers;


• an energy-conservation rebate from Southern California Edison, the local electrical utility.

"If Edison hadn't given me a rebate, I would still be able to pay off the cost of the LPD dryer in less than a year. It's just incredible," said D.E. (Ernie) Rodriguez (pictured with dryer), president of Southern California Plastics. "We have 10 more LPD dryers on order, and with subsequent rebates for energy savings, I expect to be able to recover 40% of the investment cost."

Additional savings from elimination of compressed air have been an unanticipated benefit, according to Rodriguez. "Our 25 hp screw compressor was running nonstop and drawing lots of power," he said, "but the LPD vacuum dryer needs only a small amount of compressed air to run the vacuum generator."

Still another benefit is productivity and product quality. "We have to dry 100 lb an hour of polycarbonate for molding clear lenses," Rodriguez said. "With this new dryer we haven't had one single defect."

The reduction in defects is attributable to the much shorter heat history imposed on resin by the LPD dryer, according to B. Patrick Smith, Maguire vice president of marketing and sales.

"Besides requiring only 20% of the energy needed by a desiccant system to properly dry resin, the LPD dryer takes only about one-sixth of the time," Smith said. "This shorter heat history, combined with a more uniform and efficient drying process, reduces the likelihood of polymer discoloration or degradation."

The LPD dryer differs radically from conventional hot-air/desiccant dryers in two ways:

• instead of flowing hot, dry air over the pellets to slowly draw the moisture out, the patented LPD dryer uses vacuum to reduce the boiling point of water, quickly turn the moisture into water vapor, and literally pull the water vapor from within the pellets; and


• the LPD dryer carries out heating and vacuum drying simultaneously in separate stations, making possible small batches while in effect transforming a batch process into a continuous one that keeps pace with the throughput of the plastics processing machine.