What should we do if there are dark spots on injection products?
Many defects will appear in the injection molding process, such as bubbles, sink marks, dark spots, etc. When injection molding defects occur, we should analyze the possible reasons for these defects and improve the injection product quality. We will analyze the reasons and solutions for dark spots that happen in the injection molding process.
1. High melting temperature will decompose the materials into carbides, causing dark spots in the molding process. For some heat-sensitive materials, the temperature of the barrel must be strictly controlled. When dark spots are found on the surface of the plastic part, you should check whether the temperature controller is working properly, and adjsut the barrel and mold temperature. Please noted that if the temperature is too low, such defects as silver streak will appear.
2. If the gap in the barrel is too large, some melted material will stay in the gap, resulting in dark spots during the injection molding process. In response to this case, lower the barrel temperature first and check whether the fault can be removed, or check whether there are dead corners in the barrel, near the nozzle and mold.
3. If the injection speed of the injection molding machine is too fast, and the injection pressure is too high, the related movement speed of the melted material and the cavity wall during molding filling will be high, and it is easy to generate friction and overheating, which will cause the material to decompose and produce black spots. In this regard, you should adjust the injection speed and injection pressure properly.
4. Poor exhaust of the barrel and injection mold, the residual gas in the material will cause combustion due to adiabatic compression, and black spots will appear on the surface of the plastic part. We can adjust the exhaust structure of the barrel and injection mold.
