Weld Lines on High-Density Polyethylene Injection-Molded Products (Variant: Strengthened Measures)

Linear marks appear on the product surface where two or more melt streams converge, usually appearing as V-shaped grooves or color difference lines with low strength. Weld lines not only affect appearance but are also weak links of the product, and it is easy to crack from here when stressed. In particular, additional attention is needed on the original basis; this problem is more prominent and requires focused attention.

(1) The multi-gate design or complex product structure causes the melt to converge after splitting; the melt temperature at the convergence is low and the fusion is insufficient (2) The injection speed is too slow, the melt temperature drops too much during mold filling, and it cannot fully fuse when converging (3) The barrel temperature is too low, the melt fluidity is poor, and the pressure at the convergence is insufficient (4) The mold temperature is too low, the melt cools rapidly after contacting the mold wall, and the fusion strength of the convergence interface is low (5) Poor venting: the gas at the convergence cannot be discharged, forming a barrier layer (6) On the original basis, additional attention is needed: fluctuations in process parameters or changes in equipment status have aggravated this problem

(1) Increase the melt temperature to the higher value within the range of 180-260°C to improve melt fluidity (2) Increase the mold temperature to the higher value within the range of 30-80°C to delay melt cooling (3) Increase the injection speed, shorten the filling time, and reduce melt temperature loss (4) Adjust the gate position and number to minimize melt splitting; add overflow wells to remove weld lines when necessary (5) Improve mold venting, and set vent grooves or vent pins at the weld line position (6) Also strengthen process monitoring; on the original basis, additional attention is needed to pay special attention to parameter stability

Weld lines are a manifestation of poor melt convergence and fusion; the melt fusion quality is improved by increasing the melt temperature, injection speed, and mold temperature. Targeted preventive measures need to be taken in different production scenarios.