Effect of Cross-Sectional Rotation of Molten Plastic Flow on the Weld Line of Plastic Injection Parts

This research examined the rotational flow position at the runner to rotate the crosssection of the plastic melt undergoing different shear rates before it flowed through the gate into the plastic injection mold cavity of PP, PS and HIPS tensile test specimens. The plastic injection molds use two gates in order to form weld line at the center of the specimen. The mold insert can be changed at runner in order to rotate the melt cross-section flow at different positions. There were 4 types of rotational flow positions: 1 no rotation flow, 2 before the runner, 3 in front of gate, and 4 mixed type 2 and 3. The specimens were examined the weldline quality using an optical microscope. It was found that the rotational flow affected the weld-line quality. The specimens of all three materials obtained from the mixed type provided the best weld-line quality.