The choice of plastic parts is mainly determined by the type of plastic (thermoplastic or thermosetting), the starting from, and the shape and size of the product. The manufacture of Automotive plastic structural parts generally uses molding, transfer molding, and injection molding. Lamination, molding, and thermoforming are the shaping of plastics on a flat surface. The above methods can be used for rubber processing. In addition, castings are using liquid monomers or polymers as raw materials. Among these methods, extrusion and injection molding are used the most and are also the most basic molding methods.
So what is the reason for the air marks of automotive plastic structural parts during the processing?
Air streak is a quality defect that is easy to produce and difficult to eliminate. Air streak will not only affect the appearance of the product but also affect the strength of the product. The remaining raw materials will be decomposed to generate gas due to the sheer force generated by the rotation of the screw and the heating of the barrel. There will be uneven heating of the melt, and it is difficult to form precision products. If the screw design is reasonable and matches the type of plastic to be processed, the molding process range will be relatively wide, otherwise, the processing and molding process range of automotive plastic structural parts may be very narrow or even unable to form products. Under high temperature and high pressure, the low-viscosity molten plastic suddenly passes through the narrow gate, and the molten raw material is injected into the mold cavity for a short time, and enters the cavity with a large free space, entraining the air existing in the runner and the cavity. The filling process of raw materials in the mold is also the process of gas being discharged. The parting surface of the mold lacks the necessary exhaust holes or the exhaust holes are insufficient, and the processing gaps such as thimbles are exhausted so that the air in the runner and cavity cannot be discharged. When the plastic enters and leaves at the same time, it is easy to cause the gas to be wrapped in the high-temperature melt. With the flow of the melt, the gas escapes from the surface of the melt to form flow traces.