In the process of injection mold testing, a tricky situation often arises: although the mold seems to operate normally, the plastic products suffer from serious appearance quality issues. Specifically, there are radial white marks on the surface of the plastic products, and these white marks become more severe as the glass fiber content in the plastic material increases. This defect in plastic products is commonly known as “floating fibers” in the industry. For products with strict appearance requirements, the “floating fibers” phenomenon is absolutely unacceptable as it not only affects the aesthetics of the products but may also have potential impacts on their overall performance. So, what factors lead to the emergence of “floating fibers”? The following is a detailed analysis from multiple aspects.
1. Compatibility Differences in the Flow of Molten Plastic Material
During the flow of molten plastic material, there are significant differences in fluidity between glass fibers and plastics, and their material densities are also different. These differences prevent them from being fully compatible during the flow process. Due to the relatively low density of glass fibers, they tend to float on the surface during flow, while the denser plastic materials sink inward. This stratification phenomenon ultimately results in the exposure of glass fibers, leading to the formation of the “floating fibers” defect on the surface of plastic products. For example, in the production of engineering plastic products with high glass fiber content, this “floating fibers” phenomenon caused by compatibility differences is particularly evident, seriously affecting the appearance quality of the products.
2. Friction and Viscosity Changes during the Flow of Molten Material
As the molten plastic material flows, it is subjected to frictional forces from the injection molding machine screw, the nozzle of the precision injection mold, the runners, and the gates. These frictional forces not only cause differences in the viscosity of the molten material but also damage the surface of the glass fibers. When the viscosity of the molten material is low, it means it has stronger fluidity. However, at the same time, the damage to the surface of the glass fibers becomes more severe. The damaged glass fiber surface is more prone to interact with the surrounding environment, further exacerbating the uneven distribution of glass fibers on the surface of plastic products and thus making the “floating fibers” phenomenon more prominent. For instance, in the production of precision parts with high requirements for injection molding processes, improper control of frictional forces often leads to frequent occurrences of the “floating fibers” problem, increasing the defect rate of the products.
3. The “Fountain” Effect during Injection into the Mold Cavity and Cooling and Freezing
When the molten plastic material is injected into the cavity of the precision injection mold, a “fountain” – like effect occurs. During this process, the glass fibers flow from the interior to the periphery and come into contact with the surface of the mold cavity. Since the temperature of the surface of the precision injection mold cavity is relatively low, the glass fibers, which have a low density and cool quickly, are rapidly frozen. If these glass fibers are not fully surrounded by the subsequently injected molten material in time, “floating fibers” will form on the surface of the plastic products. This situation is particularly common in the production of large injection – molded parts because the cooling process of large injection – molded parts is relatively complex, and there are significant temperature differences in different parts of the mold cavity, which makes it more likely to cause uneven freezing of glass fibers and thus trigger the “floating fibers” problem.
In conclusion, the formation of the “floating fibers” defect is a complex process. It is closely related to the composition and characteristics of the plastic materials and is also influenced by multiple factors during the precision injection molding process. This complexity and uncertainty pose certain challenges to injection molding production. However, by deeply analyzing its formation causes, we can take targeted measures to optimize the production process, effectively reduce the occurrence of the “floating fibers” phenomenon, and improve the quality and pass rate of plastic products.
