Key points of fiberglass processing technology
1. Mixing:
Chopped glass fiber: Typically added with plastic pellets in a high-speed mixer or at the side feed port of a twin-screw extruder. Premix uniformity affects final dispersion.
Long-fiber pellets: Typically directly injected into the mold.
2. Extrusion pelletizing (for short fibers):
Screw design: Use a high-shear, multi-block twin-screw extruder. The glass fiber is typically added downstream of the melt zone to avoid excessive shear fracture.
Process control: Control screw speed, temperature, and vacuum exhaust. High speed and excessively high melt temperature can increase glass fiber breakage.
Dispersion and distribution: The goal is to evenly disperse the glass fibers in the matrix and maintain an appropriate length (typically 0.2-0.8mm for short fibers).
3. Injection molding (primary application):
Mold design: Gate design should avoid excessive shear fracture of the glass fibers (e.g., preventing the point gate from directly impacting the glass fiber bundle); consider venting (glass fibers carry a lot of air); and ensure that the runners and mold cavities are wear-resistant. Process Parameters:
Melt Temperature: Keep as low as possible while maintaining fluidity to minimize glass fiber breakage and resin degradation.
Injection Speed: Medium to high speeds promote glass fiber orientation and reduce floating fibers, but excessive speeds can increase shear fracture. A balance is necessary.
Holding Pressure/Time: Appropriate increases can help reduce shrinkage and warpage.
Mold Temperature: Appropriate increases in mold temperature (e.g., 80-120°C) can significantly improve surface quality (reduce floating fibers), reduce internal stress, and increase crystallinity (for crystalline plastics).
Back Pressure: Appropriate increases can help homogenize the melt, but excessive increases can increase glass fiber breakage.
4. Common Processing Problems and Solutions:
① Floating fibers/exposed glass fibers:
Solutions: Increase mold temperature, increase injection speed, optimize gate location/design, select an appropriate coupling agent/lubricant, adjust the formulation (e.g., add a flow improver or compatibilizer), and perform mold surface treatment (e.g., Teflon coating). ② Uneven glass fiber distribution/agglomeration:
Countermeasures: Optimize the screw assembly and glass fiber addition point, ensure uniform premixing, improve melt mixing, and adjust the process (e.g., back pressure).
③ Excessive glass fiber breakage:
Countermeasures: Reduce screw speed, lower melt temperature, reduce injection speed (front end), optimize screw design (reduce high shear zones), select glass fiber with a suitable aspect ratio, and consider long-fiber pellets.
④ Product brittleness/impact resistance:
Countermeasures: Optimize the interface (coupling agent), add toughening agents, select long-fiber pellets, and adjust glass fiber content and length.
⑤ Severe equipment wear:
Countermeasures: Use surface-hardened screws/barrels (e.g., bimetallic, spray-coated tungsten carbide), and use wear-resistant mold materials.