GEAR MADE OF THERMOPLASTIC RESIN

摘要

PURPOSE:To obtain a gear excellent in dimensional accuracy within a short period by providing a hollow structure to the entire peripheries or a part of the root parts of the teeth of a gear made of a thermoplastic resin. CONSTITUTION:Hollow parts 6 are provided to the entire peripheries or a part of the root parts of teeth by introducing gas into the root parts 3 of teeth by a gas assist molding method. The gas assist molding method is a molding method injecting a thermoplastic resin into a mold cavity in injection molding and subsequently injecting gas in the resin to obtain a hollow molded product. The gas assist molding method is performed by the combination of an injection molding machine and a gas injection device. The root parts 3 of the teeth are parts having the same thickness as the tooth width present between the web part 4 usually applied in a gear made of a thermoplastic resin and a tooth bottom circle 2. By this constitution, the shape error due to the shrinkage of tooth parts is suppressed and the gear having excellent accuracy is obtained.