20 - What other drying options are there?
As is the case with many fields of industry, when it comes to drying plastics, there are common, and less common, technologies. Here, we look at some of the latter.
Drying cabinets, which fall within the hot-air dryer category, are suitable for very small batches and microgranulate. It is important to keep in mind that drying cabinets use ambient air. As a result, that they are only suited to drying slightly hygroscopic or non-hygroscopic material. Granulate is spread out on trays, and hot air is passed over it, wicking away moisture.
When throughput is low, it is advisable to operate the dryer in conjunction with a blanketing bin to keep granulate clean and dry. Granulate is generally already dry when delivered; this state must simply be maintained. With the integrated control unit correctly configured, and a continuous supply of dry air, blanketing bins can easily keep granulate dry for several days. All that is required is a small quantity of expanded compressed air.
Thermal conduction is less important for infrared dryers, as infrared radiation penetrates the plastic material directly. For the granulate to be heated properly, a large surface area – and therefore a large drum – is required.
Vacuum dryers are essentially batch dryers. The term “vacuum” is slightly misleading, as these dryers operate with underpressure. This underpressure causes the moisture’s boiling point to increase, driving it from the granulate as vapor. A typical vacuum dryer has three bins, which go through the drying cycle in sequence. First, the granulate is heated to a defined temperature under atmospheric pressure. A partial vacuum is then created in the chamber, and the resulting water vapor is removed by suction. Vacuum dryers are unquestionably fast and efficient, but are not well suited to high-throughput batch drying.
You want to see different models of drying options? Find them on www.motan.com