Drying is a necessary criteria for quality processing of plastics. Improper and inadequate drying leads to bad finish, and can also lead to loss of structural strength, impact strength, tensile strength in addition to cosmetic defects-splay, silver streaking, etc. Resin Dryers hold the key to optimum performance of molded parts and prevents degradation.
There are 3 parameters that are responsible for quality drying: temperature (between 160 to 180ºC), air flow and dew point; of these the most critical is dew point. Dew point lowers the vapor pressure around the surface of the resin which in turn forces the moisture out. Moisture is responsible for the structural and cosmetic defects mentioned earlier.
There are several kind of drying technologies available in the market today for drying resins . Depending the need , a manufacturing facility could choose from Hot Air Drying Technology, Desiccant Dryers, and Compressed Air Drying Technology.
Types of Dryers
Hot air dryers are the oldest type of resin processors and work very simply. Hot air is produced inside a specialized chamber, into which the resin is placed. Moisture from the resin is pulled into this heated air and is then blown away with an industrial-sized fan. While hot air dryers are the least expensive type of resin processors, they are also the least efficient.
Desiccant dryers are very similar to hot air dryers, except they contain additional beds of desiccant material that help to absorb moisture from the resin. These dryers are more expensive than basic hot air drying processes but are much more economical in terms of space occupied and energy consumed. Desiccant dryers can also dehydrate the resin much quicker than simple hot air dryers.
Compressed air dryers are preferred by many manufacturers due to their quiet, smoothly-operating mechanisms and low-maintenance features. Standard plant compressed air is first pumped into an inner chamber of the dryer, where it undergoes several pre-filtering stages. The air then passes through a heated drying technology mechanism. Next, it is sent into another chamber where the resin awaits. The dried air absorbs moisture from the resin and is then pumped out of the machine. Compressed air dryers are the most expensive types of resin processors, but unlike desiccant and hot air dryers, they consist of no moving parts which must be cared for and maintained.
Dehumidified drying done via honeycomb wheel technology is the next level in resin drying and has an advantage in terms of energy saving, better dew point (-65º C), less maintenance, no contamination and lower life cycle cost.