Why is Moisture a Problem

In the Injection Molding Process

2/22/2024

Molding problems, particularly in humid months, often trace back to excessive moisture in the resin. Moisture in resin can cause degradation of certain materials used in injection molding, particularly hygroscopic plastics like nylon, ABS, and polycarbonate. It can lead to discoloration, molecular degradation, resulting in defects such as brittleness, reduced strength, surface imperfections and other undesirable effects in the final molded parts. This can lead to parts that are more prone to failure or deformation under stress.

Moisture absorption can affect the dimensional stability of the plastic during the molding process, leading to variations in the size and shape of the molded parts. This causes dimensional inaccuracies and warping, leading to deviation from the intended specifications and making them unfit for their intended application. The presence of moisture can cause variations in melt viscosity, flow behavior, and cooling rates, leading to inconsistencies in the molding process and resulting in fluctuations in part dimensions and properties.

To mitigate these issues, it’s essential to properly dry the plastic resin before the injection molding process. This is typically done using equipment such as desiccant dryers or hopper dryers, which remove moisture from the resin pellets prior to molding. Additionally, maintaining proper storage conditions for the resin, such as humidity-controlled environments and sealed containers, can help prevent moisture absorption before processing.

Desiccants can play a crucial role in injection molding processes, particularly when dealing with moisture-sensitive materials such as certain types of plastics. Desiccant captures moisture in its pores, which become blocked with contamination over time. And only fresh desiccant gives your dryers a chance to thoroughly dry your material in hot, humid weather. Dew Point Meters monitor and spot check the performance of the desiccant style drying equipment. Here’s how desiccants are typically used in injection molding:

1. Material Storage: Plastic pellets, can absorb moisture from the atmosphere over time. Desiccants are often used in material storage areas or containers to maintain low humidity levels and prevent moisture absorption by the plastic pellets.
2. Drying Hoppers: Before the plastic pellets are fed into the injection molding machine, they may need to be dried to remove any moisture absorbed during storage or transportation. Drying hoppers equipped with desiccant dryers are commonly used for this purpose. The desiccant absorbs moisture from the pellets as they are heated and dried before entering the molding machine.
3. Dehumidification Systems: In environments with high humidity levels, it may be necessary to use dehumidification systems to control the moisture content of the air within the injection molding facility. Desiccants can be incorporated into these systems to help remove moisture from the air, creating a dry environment conducive to high-quality molding.
4. Material Handling Equipment: Desiccants can also be integrated into conveyors or drying systems, to prevent moisture absorption during the transfer of plastic pellets between different stages of the injection molding process.
5. Mold Storage: Molds can also be susceptible to moisture-related issues if not stored properly. Desiccants can be used within mold storage containers or cabinets to maintain low humidity levels and prevent corrosion or other damage to the molds.

Overall, the use of desiccants in injection molding is essential for ensuring the quality and consistency of molded products, particularly when working with moisture-sensitive materials. By effectively controlling moisture throughout the molding process, manufacturers can minimize defects and optimize production efficiency.