Injection Molding Raw Material Drying Standards and Quality Control Methods

In injection molding production, the drying of plastic raw materials is a critical process that directly affects part appearance, mechanical properties, and production stability. Hygroscopic materials easily absorb moisture during storage and transportation. Insufficient drying causes water to vaporize under high-temperature melting, resulting in bubbles, sliver marks, flow lines, brittleness, and poor dimensional stability. Therefore, establishing standardized drying parameters and strictly controlling key variables such as temperature, time, air volume, and material bed thickness are essential for consistent quality.

Common Drying Standards for Plastic Materials

Different plastics have distinct hygroscopicity and thermal stability, so their drying parameters must be set accordingly.

PC: 100–120°C, 3–4 hours, dehumidifying drying recommended.

PA6/PA66: 80–90°C, 4–6 hours, must use dehumidifying dryer with dew point ≤ -30°C.

PBT: 120–140°C, 3–4 hours, ensure uniform hot air circulation.

ABS: 70–85°C, 2–3 hours, keep sealed after drying to prevent re-absorption.

PMMA: 80–95°C, 2–4 hours, avoid overheating.

PP/PE: Generally no drying required; dry at 60–70°C for 1–2 hours only in high-humidity environments.

Drying Equipment and Environmental Control

Equipment performance and workshop environment directly determine drying reliability.

Hot-air dryers are suitable for low-hygroscopic materials; dehumidifying dryers are for PA, PC, PBT, etc.

Hoppers should be insulated; feeding systems use closed pipelines to reduce moisture contact.

Regularly clean hoppers, ducts, and heaters to prevent carbonization and contamination.

Maintain workshop humidity at 50%–60% and keep material storage areas dry and sealed.

Key Process Parameter Control

Temperature, time, air volume, and material thickness are the four core factors.

Temperature: Avoid yellowing, degradation, or sticking; control fluctuation within ±5°C.

Time: Ensure full moisture removal without over-drying.

Air volume: Provide sufficient and uniform penetration to avoid dead zones.

Material bed thickness: Keep moderate to ensure uniform drying.

Real-time monitoring and record-keeping enable traceable and stable production.

Drying Effect Evaluation and Quality Management

Visual inspection: pellets should be dry, loose, and free of clumping.

Mold trial: parts free of bubbles, sliver marks, and deformation.

Instrument measurement: use moisture analyzer for high-precision applications.

Establish standard operating procedures, operator training, and batch management systems.

Common Issues and Improvements

Insufficient drying: increase temperature or time, upgrade to dehumidifying dryer.

Yellowing or degradation: lower temperature, reduce drying time.

Uneven drying: adjust material thickness, optimize air distribution.

Recycled material: dry separately and control mixing ratio.

Drying is the first quality gate in injection molding. Scientific standards, stable equipment, strict parameter control, and effective management ensure high efficiency, low defect rates, and stable long-term production.