During plastic injection molding, the influence of moisture on quality of plastic material is great, which not only may result in plastic cracks, whitening, air bubble, but also degrades the plastics and decreases the performance. Therefore, it’s necessary to control the moisture of plastic materials in injection molding.
There are many factors affecting the moisture of plastic materials in the process of drying that mainly include the drying temperature, airflow and time, dew-point temperature and environment.
Drying temperature varies with different materials, which is critical for complete drying of the plastics. Insufficient temperature will lead to poor drying effect or prolong the drying time, while too high of the drying temperature will decompose the material and decrease the mechanical-physical properties.
Although the greater the drying airflow, the better the drying effect, it requires large consumption, and there’s slight difference between actual minimum airflows required by different materials for drying. The common airflow is 1.5~3.5m3/ (kg.hr), and specific requirements please refer to the table of physical properties for different materials; Dew-point temperature ≤-20°C that can completely dry ordinary plastics, and the lower the dew-point temperature of the dry air, the better the drying effect.