Requirements for equipment and moulds, injection moulding process and raw material processing of products are discussed.
Because there are any trace impurities in plastic bags, the preparation and drying of raw materials may affect the transparency of products, so storage and transportation.
During the feeding process, care must be taken to seal and ensure that the material is clean. Especially when the raw material contains water, it will deteriorate after heating. Therefore, it must be dry and dry funnel must be used for moulding. It is also important to give priority to air input for filtration and dehumidification in the drying process to ensure that it does not pollute raw materials.
Cleaning pipes, screws and accessories
In order to prevent the pollution of raw materials and the existence of old materials or impurities, screw and accessories, especially resin, have poor thermal stability. Therefore, before and after use, please use the screw cleaner to clean the impurities, so that they do not adhere to impurities. When there is no screw cleaner, use PE, PS resin to clean the screw.
When temporary shutdown occurs, in order to prevent material from falling at high temperature for a long time, the temperature of dryer and cylinder should be lowered, such as PC, PMMA, etc. the temperature of tube body should be lowered below 160 C. (PC hopper temperature should be below 100 C)
Problems in Die Design (including Product Design)
In order to prevent poor reflux or uneven cooling resulting in poor appearance plasticity, resulting in surface defects and deterioration;
In general, the following points should be paid attention to in die design:
The wall thickness should be as uniform as possible and the stripping slope should be large enough.
This shift should be gradual. Smooth transition to prevent sharp corners. Sharp edges, especially PC products, must be free of gaps.
Doorway. The passage should be as wide and short as possible, and the gate position should be set according to the shrinkage and condensation process. If necessary, additional cold wells should be added.
The surface of the die should be smooth with low roughness (preferably less than 0.8);
Exhaust. The tank must discharge air and gas from the melt in sufficient time.
Except for PET, wall thickness should not be too thin, generally not less than LMM.
Notes in Injection Molding Process (Including Injection Molding Machine Requirements)
In order to reduce the internal stress and surface quality defects, the following aspects should be paid attention to in the process of injection moulding:
Injection moulding machine with special screw and independent temperature control nozzle should be selected.
On the premise that the plastic resin does not decompose, the injection temperature should be higher.
Injection pressure: generally higher, overcome the shortcomings of high melt viscosity, but higher pressure will produce internal stress, resulting in difficult release and deformation of the die;
Injection speed: In the case of filling mode, the injection speed is generally low, and multi-stage injection speed should be adopted.
Pressure retention time and forming time: Satisfactory filling does not produce depressions and bubbles; it should be as short as possible to minimize the time spent on fuses;
Screw speed and back pressure: On the premise of satisfying the plasticizing quality, the possibility of pressure reduction should be reduced as much as possible.
Mold temperature: It has a great influence on the cooling quality and quality of products. Therefore, the die temperature must be able to accurately control the process. Mold temperature should be as high as possible.
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