Precautions for PFA Plastic Injection Molding

PFA (perfluoroalkoxy alkane) offers exceptional heat resistance, corrosion resistance, electrical insulation and high purity, making it widely used in semiconductor components, high-purity fluid pipelines, medical devices and other high-end fields. However, PFA has a narrow molding temperature window, high melt viscosity and strong thermal sensitivity. Improper processing can easily lead to bubbles, black spots, shrinkage cavities, cracking and even corrosive gas release. The following summarizes key precautions covering raw material treatment, mold design, processing parameters, quality control and safety management to ensure stable and qualified production.

1. Raw Material Preprocessing and Equipment Preparation

1.1 Drying and Cleanliness Control

Although PFA has low water absorption, surface moisture and contaminants can cause silver streaks, bubbles and surface defects. It is recommended to use vacuum drying at 120℃ for 4 hours or hot-air drying at 150℃ for 2 hours, ensuring the moisture content is below 0.02%. For high-purity applications such as semiconductor parts, production must be carried out in a Class 1000–10000 cleanroom to avoid dust contamination. Dried materials should be stored in sealed containers to prevent reabsorption of moisture.

1.2 Equipment Selection and Cleaning

The injection molding machine should be equipped with corrosion-resistant screws and barrels, preferably made of bimetallic or stainless steel materials. Before production, the barrel must be thoroughly purged with special cleaning resins to avoid residual contaminants. The nozzle should adopt an open check valve structure to reduce melt retention and thermal degradation. Ordinary lubricants and mold release agents are prohibited to prevent material contamination.

2. Mold Design and Maintenance

2.1 Mold Steel and Surface Treatment

PFA melt is slightly corrosive to metal and tends to adhere to mold surfaces. It is recommended to use corrosion-resistant mold steels such as S136 or H13, with mirror polishing to Ra ≤ 0.2μm. Hard chrome plating or nitriding treatment can further improve wear resistance and demolding performance. The overall mold precision should be controlled within ±0.005mm to meet the requirements of precision components.

2.2 Runner, Gate and Venting Design

PFA has high melt viscosity, so runners should be short, thick, circular and smooth with rounded corners to eliminate dead corners. The gate size should be appropriately enlarged; fan gates and side gates are preferred to avoid shear overheating. Gates should be placed near thick sections to reduce internal stress. Venting grooves with a depth of 0.02–0.03mm should be set at flow ends, weld lines and deep cavities. Vacuum venting is recommended for high-quality products.

2.3 Cooling and Demolding Structure

PFA crystallizes slowly and requires uniform cooling and stable mold temperature. Cooling channels should be arranged evenly and close to the cavity surface. The draft angle should be no less than 1° to facilitate demolding. Ejection should use large-area ejector pins, stripper plates or sleeves to avoid stress marks, white spots or cracking caused by concentrated force.

3. Core Molding Process Parameters

3.1 Temperature Control

PFA processing temperature ranges from 350℃ to 420℃; temperatures above 475℃ will cause decomposition and release corrosive fluorides. A three-stage gradient temperature setting is recommended:

Rear barrel: 310–330℃

Middle barrel: 340–360℃

Front barrel: 350–370℃

Nozzle: 370–400℃

Mold temperature: 150–200℃ (180–230℃ for thick products)

Melt residence time should be controlled within 15 minutes to avoid thermal degradation.

3.2 Injection, Holding Pressure and Cooling

Injection pressure is generally 60–100MPa, and 120–150MPa for thin-walled parts. Multi-stage injection speed is adopted to prevent jetting and air entrapment. Holding pressure is set to about 80% of injection pressure to compensate for shrinkage. Cooling time depends on product thickness, usually 20–60 seconds, to ensure stable dimensions before ejection.

3.3 Back Pressure and Screw Speed

Back pressure is controlled at 5–10MPa for uniform plasticization. Screw speed is 50–80rpm to avoid excessive shear heat. A screw with L/D ratio 18–22:1 and compression ratio 2.5–3:1 is suitable for PFA processing.

4. Production Control and Safety Management

During production, regular inspections should be conducted to monitor product appearance, dimensions and stability. Different grades of PFA should be produced separately to avoid performance fluctuations. High-purity products require strict anti-contamination measures throughout the process.

Since PFA releases toxic and corrosive gases when overheated, the workshop must be equipped with strong ventilation systems. Operators must wear heat-resistant gloves and goggles for protection. Waste materials and decomposed residues should be treated as hazardous waste to prevent environmental pollution.

5. Common Defects and Troubleshooting

6. Summary

Stable injection molding of PFA relies on precise temperature control, reasonable mold structure, sufficient venting, standardized material preparation and strict safety management. Each processing step must be strictly controlled to avoid thermal degradation, contamination and molding defects. For high-end applications, full-process traceability and cleanliness management are essential to ensure product performance and consistency in batch production.