In vertical manufacturing of plastic parts using point gate design, injection molding product surface exhibits a radiation system with varying color depth and luster, forming radiance lines centered around the gate. This phenomenon is mainly seen as dark lines on dark background, dark lines on dark background, and dense, whitish dark lines around the gate.
This defect is commonly observed in the manufacturing process of injection-molded polystyrene and modified polystyrene blends, closely linked to factors such as differences in rheology, coloring, etc., variations in flow rates between stratospheric and turbulent layers of the casting system, and differences in heating states. The generation of burnt filaments from plastic due to thermal decomposition, as well as interference of gaseous substances when plastic enters the mold, also contribute to this issue.
To address this problem, consider the following measures:
- When mixing plastics, ensure thorough mixing and homogeneity of plastic particles.
- Mix plastic and coloring agent evenly, and if necessary, add an appropriate amount of dispersant, achieving this through mechanical mixing.
- Ensure full plasticization of the plastic, with good plasticizing performance of the machine.
- Reduce injection pressure and speed, shorten injection and holding time, and simultaneously increase mold temperature and nozzle temperature while decreasing front furnace temperature.
- Prevent an increase in melt viscosity and the generation of coking material caused by plastic degradation. Check for dead-end wear in the screw and barrel, ensure proper control of the heating system, and avoid prolonged heating that may lead to plastic decomposition. Improve the situation by polishing the screw and barrel.
- Enhance gate design by enlarging gate diameter, changing gate position, transitioning the gate to a rounded shape, and experimenting with the addition of a cold material well at the flow channel end.