The transparent plastic injection molding process should pay attention to the common problems
Transparent injection parts because of high transmittance. It is necessary to require strict surface quality of plastic products. Can not have any stripes, stomata, pan-white.
Fog halo, black spots, discoloration, poor gloss. And so on the entire injection process of raw materials, equipment, molds. Even product design, must pay attention to and put forward strict or even special requirements.
Second, as transparent plastic for a high melting point, fluidity is poor. So in order to ensure product surface quality. Often in the barrel temperature, injection pressure, injection speed, and other technical parameters for fine-tuning. So that the injection molding can not only fill the mold. But will not produce internal stress caused by product deformation and cracking. Injection molding process and product handling of raw materials to talk about matters needing attention.
The following on its preparation of raw materials, equipment, and mold requirements.
1，The preparation and drying of raw materials because the plastic contains little impurities. May affect the transparency of the product, and storage, transportation. The feeding process must pay attention to sealing, ensure that raw materials are clean. Especially raw materials containing moisture. After heating will not cause drying. So it is best to filter in the raw materials, after drying. The raw materials must be used in order to dry.
2，The cleaning of the barrel, screw, and its accessories to prevent the contamination of raw materials. And the deposit of the old material or impurities in the screw and the attachment sag. Special thermal stability of the resin exists, so before use, downtime after the application of screw cleaning agents to clean the pieces. So that it must not adhere to impurities. When there is no screw cleaning agent, can be PE, PS, and other resin cleaning screws.
3，In the mold design should pay attention to the problem (including product design) in order to prevent the return flow is not smooth. Or cooling is not all caused by poor plastic molding, surface defects, and deterioration. Generally in the mold design, should pay attention to the following. Wall thickness should be as uniform as possible, the de-molding gradient is large enough. The transition should be a gradual, smooth transition, Preventing sharp corners. Sharp edge generation, especially PC products must not have a gap. Gate, the flow channel as wide as possible, coarse short, and should be based on the contraction and condensation process set gate location. When necessary, should be added cold material wells. The mold surface should be smooth, low roughness (preferably less than 0.8). The vent groove must be sufficient to discharge air and melt gas in time.
4，Attention should be paid to the injection molding process (including the requirements of the injection molding machine).In order to reduce the internal stress and surface quality defects.
The following aspects should be paid attention to in the transparent plastic injection molding process:
⑴ The injection molding machine should be selected with a special screw and a separate temperature control nozzle.
⑵ The injection temperature is suitable for high injection temperature if the plastic resin does not decompose.
⑶ Injection pressure: generally higher, to overcome the defects of the molten material viscosity. But the pressure is too high, resulting in internal stress-causing dislocation and deformation.
⑷ Infusion speed: in the case of filling the mold. It is generally advisable to lower the injection rate.
⑸ Pressure protection time and molding cycle: in the case that the product is filled with mold, no-sag, or bubble is produced. It should be as short as possible so as to minimize the duration of the melt in the cylinder.
⑹ Screw speed and back pressure: should be as low as possible to avoid the possibility of a solution to the quality of plasticization.
⑺Mmperature: the quality of the product is greatly affected by the cooling of the product. So the mold temperature must be able to control the process accurately. If possible, the mold temperature should be higher.
Transparent plastic must first have a high degree of transparency. Followed by a certain strength and wear resistance, can impact, heat-resistant parts, chemical resistance to excellent, water absorption is small. Only in this way in the use, to meet the requirements of transparency and long-term unchanged.