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Analysis of Injection Molding Process of PC Plastics

TIME:2021-04-23 Share

PC is commonly known as polycarbonate. Because of its excellent mechanical properties, it is commonly known as bulletproof glue. PC has the characteristics of high mechanical strength, wide operating temperature range, good electrical insulation performance, good dimensional stability, and transparency. It is widely used in electrical products, electrical instrument housings, and electronic product structural parts. There are many modified PC products, usually glass fiber, mineral fillers, chemical flame retardants, and other plastics are added. PC has poor fluidity and high processing temperature, so the processing of many grades of modified materials requires a special plasticized injection structure.

Plastic treatment PC has a high water absorption rate. It must be preheated and dried before processing. Pure PC is dried at 120°C, and modified PC is generally dried at 110°C for more than 4 hours. The drying time cannot exceed 10 hours. Generally, the air extrusion method can be used to judge whether the drying is sufficient. The use ratio of recycled materials can reach 20%. In some cases, 100% recycled materials can be used, and the actual amount depends on the quality requirements of the product. Recycled materials can not be mixed with different masterbatch at the same time, otherwise it will seriously damage the properties of the finished product.

Design of injection mould and gate. The mold temperature of common injection molded parts is 80-100℃, and the glass fiber is 100-130℃. Small products can use needle gates. The gate depth should be 70% of the thickest part. Other gates have rings and rectangles. The larger the gate, the better to reduce defects caused by excessive shearing of the plastic. The depth of the vent hole should be less than 0.03-0.06mm, and the runner should be as short and round as possible. The draft angle is generally about 30'-1°.

The melt temperature can be used to determine the processing temperature by the air injection method. Generally PC processing temperature is 270-320℃, some modified or low molecular weight PC is 230-270℃.

plastic mould
1. Injection speed It is common to use faster injection speed for molding, such as electrical switch parts. Commonly it is slow → rapid prototyping.
2. Back pressure The back pressure of about 10bar can be appropriately reduced when there is no gas pattern and color mixing. 3. Retention time If the residence time is too long at high temperature, the material will degrade, release CO2, and turn yellow. Do not use LDPE, POM, ABS or PA to clean the barrel. Apply PS cleanup.
4. Matters needing attention Some modified PC, due to too many recycling times (lower molecular weight) or uneven mixing of various components, it is easy to produce dark brown liquid bubbles.

Selection of injection molding machine. Due to cost and other reasons, current PC products often use modified materials, especially electrical products, but also need to increase fire resistance. When flame-retardant PC and other plastic alloy products are molded, the requirements for the plasticization system of injection molded parts It is well-mixed and corrosion-resistant, which is difficult to achieve with conventional plasticizing screws. When purchasing, it must be stated in advance.

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