The largest Maguire low-pressure dryer (LPD) yet to be developed enables users of large injection moulding presses or medium-throughput blow-molding machines or extruders to achieve the cost savings and product-quality improvements made possible by a fundamentally new method of drying resin, Maguire Products, Inc announced.

Designed to accommodate maximum processing throughputs of 90 kg/hr. (200 lb./hr.), the new LPD 200 dryer is 178cm high, 79cm wide, and 81cm deep (70 by 31 by 32 in). Although it has double the capacity of the next-largest LPD dryer (the LPD 100, for throughputs up to 45 kg/hr, or 100 lb/hr), the new unit is only 25cm taller and 10 cm wider, the Aston, Pennsylvania-based company said.

This dimensional increase is proportionately smaller than would be necessary in going from a 45 to a 90 kg/hr model of a conventional dehumidifying dryer, according to B. Patrick Smith, vice president of sales and marketing. "The LPD dryer is smaller to start with than a conventional dryer of equivalent capacity, and it becomes even more affordable as capacity increases," Smith said.

"Because of its simpler design, smaller batch size, and shorter drying cycle, the LPD can be scaled up without the substantial increases in the size and weight of blowers and other components required for a dehumidifying dryer. This translates into a smaller increase in investment cost."

Even greater are the savings in operating costs, according to Smith, who noted that the LPD dryer makes possible reductions in energy consumption, increases in processing-machine uptime, and improvements in product quality in comparison with a conventional dryer. "One of our customers reports that an LPD 100 dryer paid for itself in less than three months simply by reducing the scrap rate for moulded automotive headlamp lenses," Smith said. "Because the LPD dryer imposes less heat history on the resin and dries it more efficiently than a dehumidifying dryer, the moulder produced fewer lenses with splay and other defects."

In comparative testing on two side-by-side injection molding lines, Smith added, the same customer used 87 per cent less energy with the LPD dryer than with a dehumidifying dryer.

The LPD dryer differs radically from conventional dehumidifying dryers in two ways: 1) instead of heating the resin and flowing dry air over the pellets to slowly draw the moisture out, the patented LPD dryer uses vacuum to literally pull moisture from within the pellets and 2) the new 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.

The small batch size and short drying cycle of the LPD dryer make it possible to shorten Monday morning cold startups from several hours to less than an hour, adding that much more to weekly production time.

Also increasing productivity is the three-station indexing system of the dryer, which makes possible color and material changes on the fly, eliminating downtime.

Another source of cost savings is the elimination of desiccant, which, in a conventional dryer, becomes saturated and must be regenerated by a heating and cooling process so it will again be able to absorb moisture. The energy used in this process is lost to the ambient environment. In addition, desiccant degrades over time and must be replaced on a regular basis.

Besides the LPD 200 and LPD 100 units, Maguire offers the LPD 30, which accommodates processing-machine throughputs of up to 23 kg/hr (50 lb/hr).