Key Process Points of Polycarbonate Injection Molding

Polycarbonate injection molding is a molding process in which thermoplastic polycarbonate material is melted at high temperature and injected into a mold under high pressure, and then cooled and solidified to obtain a product with specific shape and properties. The following is a detailed description of its key process points:

1. Raw material pretreatment: PC material is sensitive to moisture. Even trace amounts of moisture at high temperatures can lead to degradation, producing defects such as bubbles and silver streaks, and reducing product strength. Sufficient drying is required before molding. The drying temperature is typically 110-120℃, and the drying time is 4-24 hours, ensuring the moisture content is below 0.02%. The dried raw material should be sealed and stored to prevent re-absorbing moisture.

2. Molding temperature: PC is a non-crystalline polymer with no definite melting point; its melting temperature range is 240-320℃. The injection temperature needs to be adjusted according to the molecular weight of the raw material, the shape of the product, and the mold structure, generally controlled between 270-320℃. Too low a temperature will result in insufficient mold filling and a dull surface; too high a temperature may cause material decomposition, discoloration, or the formation of bubbles.

3. Mold temperature: Mold temperature has a significant impact on product performance and is typically controlled between 70-120℃. Increasing the mold temperature can improve the surface quality of the product, reduce internal stress, and facilitate the filling of thin-walled or long-flow products. However, excessively high mold temperatures can lead to prolonged molding cycles and increased sticking of the product to the mold.

4. Injection Pressure and Speed: PC melt has high viscosity and poor flowability, requiring high injection pressure to ensure complete mold filling. Excessive injection pressure may increase internal stress in the product and cause flash; insufficient pressure may result in incomplete mold filling. Injection speed needs to be adjusted according to the product wall thickness and gate design, generally using multi-stage injection (slow-fast-slow) to avoid defects such as bubbles and weld lines.

5. Screw and Barrel Design: PC injection molding requires a dedicated screw with a length-to-diameter ratio typically of 15-20 and a compression ratio of 1.5:1-3.0:1. The screw design must ensure sufficient plasticization of the material while avoiding shear overheating. The barrel needs to be equipped with a heating device, and the nozzle orifice should have a large diameter and a separate heating device to prevent melt solidification.

6. Molding Cycle and Holding Pressure: The molding cycle includes injection, holding pressure, and cooling time. The holding pressure is typically 40%-60% of the injection pressure. The holding time needs to be adjusted according to the product wall thickness to avoid shrinkage or deformation. Cooling time must ensure the product is fully cured for smooth demolding.

7. Post-processing: PC products are prone to cracking due to internal stress, especially those with complex shapes or metal inserts. Post-processing can eliminate internal stress through heat treatment. This involves placing the product in a drying oven, slowly heating to 120-130℃, holding at that temperature for 30-40 minutes, and then slowly cooling to below 60℃ before removal.

8. Mold design considerations: The mold runner should be short and wide, and the gate size should be large enough to reduce pressure loss. For thin-walled products, the mold temperature and injection speed need to be increased to ensure complete mold filling.

Qingdao Xueyu Molding Products Co., Ltd. is mainly engaged in the design and manufacturing of injection molds, injection molding and secondary processing (spraying, pad printing, ultrasonic welding, stamping), etc. For more information about polycarbonate injection molding, please contact us.

Website: www.xyzmould.com

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