Gate design guidelines for injection molding of thermoplastic elastomers.

摘要

Design guidelines were developed for edge gates that produce fewer defects, such as jetting and gate blush, when molding thermoplastic elastomers. While these defects in thermoplastic material are influenced by gate dimensions and processing condition, in thermoplastic elastomers, the defects are very dependent on materials properties. For elastomeric block copolymers, defects levels increased with material hardness and occurred when the gate shear stress exceeded the critical shear stress suggested in simulation databases. In contrast, shear stress was not linked to defects in elastomeric blends and alloys. Defects increased with decreasing material hardness and were apparently associated with the elastic recovery of the melt as exited the gate. The blends may be slipping along the mold wall when the melt enters the cavity. Finally, shorter and wider gates cause defects in some materials to become very sensitive to processing conditions, and therefore, may not be desirable designs.