Optimizing Hopper Airflow and Temperature Controls in Plastic Processing
Hopper airflow rates of 0.8 to 1.2 m3/hr per kg/hr combined with a dew point below -40 C prevent hydrolytic degradation and guarantee uniform drying.
Moisture Equilibrium Limit
Meaning
Maximum water content represents the saturation point of a polymer resin exposed to a specific ambient temperature and relative humidity for an extended duration. Hygroscopic materials like polyamide or polyester eventually reach a stable state where the rate of water absorption equals the rate of evaporation. This moisture equilibrium limit determines the drying time required to reach a processable state.
Storage Condition
Pellets held in open gaylords absorb moisture based on the surrounding air quality. If the warehouse humidity increases, the moisture equilibrium limit of the resin rises, necessitating longer residence times in the desiccant hopper. Saturated material results in splay defects and reduced mechanical properties in the finished part.
Drying Target
Processors aim for a moisture level well below the point of saturation. Since the moisture equilibrium limit is often higher than the maximum allowable moisture for injection moulding, active drying is a necessity. Calculating the difference between the current percentage and the target percentage dictates the energy demand of the drying system.
Material Chemistry
Polar groups within the molecular chain attract water molecules through hydrogen bonding. Because of these chemical attractions, the moisture equilibrium limit for nylon 6 is higher than that of polyolefins like polyethylene. This ceiling on absorption is a fundamental material property defined in technical datasheets.