Drying of plastic resin can be a key step in the injection molding process, since too much moisture can cause a number of processing problems.
Most polymers exhibit at least some level of polarity and can absorb a certain amount of moisture from the air. How much impact that moisture has on the quality of a molded part usually is determined by the resin and the application.
When preparing resins for processing in injection molding, material should be properly dried to the manufacturers’ recommendations. If this is not done, part quality can be compromised. Issues that can occur include splay marks, irregular moldings, lower mechanical properties, brittleness, bubbles, and sink marks.
By drying resin before processing, shops can maintain the performance characteristics of the resin and maintain a competitive position.
Drying also can eliminate hydrolysis and part failure. Hydrolysis is a chemical reaction in the polymer that breaks the covalent bonds in its chain, reducing its mechanical properties.
However, using a drying system sometimes may not be enough to improve the quality and consistency of the injection molding process. On the shop floor, it is important to monitor the dew point and moisture content of resins to always ensure they meet the manufacturers’ recommendations for dryness.
A dew point monitor can be attached to the drying system at the hopper outlet to aid the process. Moisture can also be monitored by heating samples of resins and measuring the weight loss in the sample.
On the shop floor, processors seek energy-efficient drying machinery. Intelligent auxiliaries can point out the corrections to be made and automatically make them.
For more information on drying, visit these links on types of dryers, resin differences, installing dryers and maintenance.