Abstract
Plastic materials can absorb moisture from the atmosphere even after drying. This absorbed moisture can cause many defects in the molding process. Conventionally, a dryer is used to reduce the moisture content. However, the use of a drying unit involves huge daily power consumption and is also time-consuming. Therefore, this study proposed a new method to reduce the impact of moisture on molded product part quality through the optimization of plasticization parameters while reducing drying time. Two plastic materials, polyurethane (TPU) and polycarbonate (PC), were used for the experimental verification. Key plasticization parameters, including back pressure, screw rotation speed, and barrel temperature were chosen; their influence was investigated by the design of experiments (DOE). Moisture-induced defects, such as air bubble area, part surface gloss, and appearance were measured and correlated with the plasticization parameters. It was found, after optimization via a three-level DOE and factorial design multivariate statistical analysis using TPU, that the gloss (GU) of the PC part without drying was very close to that (98.4 GU) of the fully dried PC. The proposed methodology may help molders to improve production efficiency and achieve cost savings.
Highlights
IntroductionThe molding principle is to plasticize plastic pellet particles, transforming the raw materials into a molten state by the action of external heat and the sheer heat generated by screw rotation
The traditional injection molding manufacturing process is still the mainstream processing method in the plastics industry due to its low processing cost, fast production speed, large production volume, and formable products with complex shapes.The molding principle is to plasticize plastic pellet particles, transforming the raw materials into a molten state by the action of external heat and the sheer heat generated by screw rotation
Plastic injection molding experiments were conducted on a Victor—VS100 injection molding machine (IMM) using the thermoplastic polyurethane (TPU), The effect of moisture content on the melted polymer was assessed by the formation of air bubbles in the product part
Summary
The molding principle is to plasticize plastic pellet particles, transforming the raw materials into a molten state by the action of external heat and the sheer heat generated by screw rotation. The molten polymer is injected into a pre-designed mold cavity through screw advancement and molded into the shape of the mold design. The output product quality [1] is a function of the processing conditions, melt quality, material property, mold design, and machine parameter setting; any changes in the above will deliver a defective product with short shot, flash, air bubbles, silver streaks, warpage, shrinkage, etc. In an injection molding process, factors [2] that affect the final quality of the product include the quality of the plastic pellets, the injection speed, the injection pressure, the packing pressure [3], the melt temperature, and the mold temperature. Among the many variable factors, plastic pellets determine the mechanical properties of the product [4]
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