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In the daily production of modified plastic injection molding, some problems are likely to occur. The more common defects mainly include dark spots, gloss differences and surface wrinkles. Generally speaking, these defects often occur near the gate, so today We analyze the causes of defects from the aspects of mold and molding process.
1. Gloss difference
For injection molded plastic products, the difference in gloss is most obvious on the surface of textured products. Even if the surface of the mold is very uniform, irregular gloss may appear on the product. In other words, the mold surface effect of some parts of the product is not well reproduced.
As the distance of the melt from the gate gradually increases, the injection pressure of the melt gradually decreases. If the far end of the gate of the product cannot be filled, the pressure there is the lowest, so that the texture of the mold surface cannot be copied to the surface of the product correctly. Therefore, the area where the cavity pressure is the highest (half of the fluid path from the gate) is the area where the gloss difference appears the least. To change this situation, you can increase the melt and mold temperature or increase the pressure, while increasing the pressure holding time can also reduce the difference in gloss.
Good design of plastic products can also reduce the chance of gloss differences. For example, drastic changes in the wall thickness of the product can cause irregular flow of the melt, which makes it difficult for the surface texture of the mold to be copied to the surface of the product. Therefore, the design of uniform wall thickness can reduce the occurrence of this situation, and excessive wall thickness or excessive ribs will increase the chance of gloss difference. In addition, insufficient venting of the melt is also a cause of this defect.
2. Dark spots
Dark spots appear near the gate, like a dim solar halo. It is especially obvious when producing plastic products with high viscosity and low fluidity materials, such as PC, PMMA or ABS. When the resin of the cooled surface layer is taken away by the resin flowing in the center, such visible defects may appear on the surface of the product.
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