Effect of gate designs when molding thermoplastic elastomers

The depth, width, and land length of an edge gate were systematically varied in order to assess guidelines for gates used in injection molding of thermoplastic elastomers (TPEs) in comparison to conventional thermoplastics. Each gate design was evaluated using several classes of TPEs and a range of processing conditions. It was possible to predict flow instabilities using flow simulations in block copolymers while no correlation could be obtained in case of elastomeric blends and alloys. In general, gates for elastomers exhibited a narrower window and produced best results at depth of 60 to 65% of nominal wall thickness with twice the width and land length not more than 0.075 mm. Shore hardness of material played a prominent role on rheological and morphological characteristics affecting gate design while processing parameters did not affect the flow instabilities.