Understanding how moisture is accumulated in and on plastic resins is key to understanding how to solve the problems that it causes, such as defective molded plastics and interruptions in production. Furthermore, using the right equipment to eliminate the moisture can not only increase the production of usable plastics, but reduce energy consumption and maintenance requirements. All of these effect the bottom line - profit.

Most plastic resins, such as PA (Nylon), PC and PET, are hygroscopic materials. They adsorb moisture from humid ambient air and give moisture back to dry air. Every type of resin can hold a specific amount of moisture between its molecular chains. Additional amounts of moisture can be condensed on the surface of the pellets (surface moisture). Non-hygroscopic resins, such as PE, PP and PVC, do not adsorb any moisture, but they still can have surface moisture.

Adsorbed moisture in hygroscopic resins and surface moisture in non-hygroscopic resins are known to cause defects in molded plastics and they might lead to a complete production stop.

The compressed air dryer is the ideal continuous resin dryer. It combines the advantages of the hot air dryer and the desiccant dryer and avoids all the disadvantages of air dryers. Fasti's Compressed Air Resin Dryer (CARD) preheats the material with hot air and then uses a small amount of compressed air to remove the moisture from the resin. The compressed air is decompressed before it is heated and released at the bottom of the drying hopper. Standard quality of compressed air with a dew point of 5 °C [41 °F] or lower at 7 bar [100 psi] or higher is very sufficient for the job. The central air compressor in plastics processing facilities supplies air to multiple dryers saving expensive floor space in the manufacturing area and reducing the maintenance requirements. The energy consumption of the CARD is much lower than that of a desiccant dyer. In some applications, as in blow molding, the energy consumption can be reduced to nearly ZERO. The exhaust air from the process is used for drying and the heat can be recovered from the air compressor.

A Small Compressed Air Resin Dryer (SCARD) is also available and has many advantages:

• Low initial cost
• Energy savings between 22% and 60% when compared with desiccant dryers
• Excellent and constant drying results with no losses in efficiency over time
• Very compact dryer with little space requirements or direct installation on extruders
• Virtually no maintenance requirements