Pre-drying (injection moulding)
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A Pre-drying is a process needed during Injection Moulding process to remove moisture from polymer material. Plastics materials are hygroscopic and pre-drying is important before Injection moulding. Plastics materials are packed into bags which contain 25 kg and each material grade has a recommended maximum moisture content for defect-free processing. [1]
Allowable moisture content for different polymers
| Polymer Family | Acceptable Moisture content (%) |
|---|---|
| Acrylonitrile butadiene styrene | 0.1 |
| Polycarbonate | 0.02 |
| Polyamide | ≤ 0.2 |
| Polybutylene terephthalate | 0.03 |
| Polyethylene terephthalate | 0.02 |
| Styrene-acrylonitrile resin | 0.1 |
| Thermoplastic elastomers | 0.1 |
| Polycarbonate+ Acrylonitrile butadiene styrene | 0.04 |
| Description | Problems while moulding | Defects in moulded parts |
|---|---|---|
| Defects | Drooling | Silver streaks |
| Defects | Bubble in purge | Surface blemish |
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