Types of High-Temperature Engineering Plastics
High-temperature engineering plastics refer to engineering plastics capable of withstanding continuous use temperatures above 150°C. They are commonly used in aerospace, automotive, electronics, and medical fields. These materials offer excellent heat resistance, mechanical strength, and chemical stability, but they are more difficult to process and often require specialized injection molding techniques.
The following is a list of common high-temperature engineering plastics, organized by their continuous use temperature and typical applications:
| Material Name | Abbreviation | Continuous Use Temperature (°C) | Typical Characteristics and Applications |
|---|---|---|---|
| Polyetherimide | PEI (Ultem) | 170–217 | High strength, chemical resistance; used in optical devices and automotive parts. |
| Polyphenylene Sulfide | PPS | 220–240 | Heat and chemical resistant; electronic components, pumps, and valves. |
| Polyether Ether Ketone | PEEK | 250–260 | Extremely high mechanical strength, radiation resistant; medical implants, aerospace components. |
| Polyamide-imide | PAI (Torlon) | 250–275 | High wear resistance, high temperature; bearings, gears. |
| Polyimide | PI | 250–300+ | Extreme heat resistance, vacuum resistant; films, insulation materials. |
| Polytetrafluoroethylene | PTFE | 200–260 | Low friction, chemical resistant; seals, pipes. |
| Polybenzimidazole | PBI | 300–400+ | Highest heat resistance; fire-resistant materials, aerospace. |
| Polyphenylsulfone | PPSU | 180–200 | Impact resistant, steam resistant; medical devices. |
These materials are often reinforced with glass fiber (GF) or mineral fillers to enhance performance, but this increases abrasiveness. When selecting materials, consider specific temperature thresholds, cost, and processability. For example, PEEK and PAI are suitable for extreme environments, while PPS is more economical.
Considerations for Steel Selection in Injection Molds for High-Temperature Engineering Plastics
High-temperature engineering plastics (such as PEEK and PPS) typically have melt temperatures between 280–400°C or higher, which subject the mold to thermal stress, wear, and corrosion. Therefore, steel selection should prioritize heat resistance, hardness, wear resistance, and thermal fatigue resistance. Key considerations include:
- Heat Resistance and Thermal Fatigue Resistance The mold must withstand repeated heating/cooling cycles without cracking. Hot-work tool steels such as H13 (chromium-molybdenum hot-work steel) are recommended, with heat resistance up to 600°C or more. H13 is suitable for high-volume production and abrasive materials (e.g., glass-filled plastics). In contrast, P20 steel (pre-hardened) is suitable for moderate temperatures but tends to deform under high heat and is not recommended for PEEK and similar materials.
- Wear Resistance and Hardness High-temperature plastics often contain fillers (e.g., glass fiber) that accelerate mold wear. Choose high-hardness steels such as ASSAB UNIMAX (HRC 56–58). For highly corrosive plastics (e.g., fluorine-containing materials), use 420 stainless steel (corrosion-resistant tool steel) to prevent rusting.
- Thermal Conductivity and Uniformity The steel should have good thermal conductivity to ensure uniform mold temperature distribution and avoid localized overheating that causes material degradation. H13 offers better thermal conductivity than P20 and is ideal for complex molds. High-purity steels with uniform microstructure improve polishability and service life.
- Other Considerations For high production volumes, select H13 to extend mold life. For budget constraints, P20 can be used but requires surface treatments (e.g., chrome plating). Always verify the steel’s purity and heat-treatment condition to avoid premature failure due to impurities. For extreme high temperatures (e.g., PI), special alloys or coatings may be required.
Considerations for Gate Design in Injection Molds for High-Temperature Engineering Plastics
Gate design significantly affects melt flow, shear heat, and part quality. High-temperature plastics have high viscosity and are prone to degradation, so optimization is essential to avoid defects such as weld lines, flow marks, or yellowing. Key considerations include:
- Gate Type Selection Prefer larger gates such as tab gates or edge gates to facilitate filling of abrasive materials (e.g., glass-filled PPS) and reduce shear heat-induced degradation. Avoid small gates (e.g., pin gates) because high-temperature plastics have poor flow, which can cause short shots or excessive shear (leading to molecular degradation). For shear-sensitive materials, use hot runner systems to maintain melt temperature.
- Gate Location Place gates in non-visible areas (e.g., part bottom) and away from cores or pins to prevent uneven flow. Ensure simultaneous cavity filling to avoid weld lines. For complex shapes, locate gates in thicker wall sections to promote uniform cooling and reduce residual stress. Multi-gate designs can be used for large parts but require balanced flow.
- Gate Size and Shape Width should be based on cavity volume, and depth should be 50–80% of the part wall thickness (for PE/PP it can be as low as 50%). Gates that are too large may cause sink marks, while gates that are too small increase pressure and heat (exceeding the melt point of high-temperature plastics can cause degradation). The shape should be smooth and rounded to avoid sharp corners that induce turbulence. For high-temperature plastics, optimize to maintain polymer temperature and prevent flow marks.
- Other Considerations Control injection speed (medium speed to avoid excessive shear heat). Integrate uniform cooling channels to prevent localized overheating. Gates should be easy to remove during post-processing without visible marks. Use simulation software (e.g., Moldflow) to optimize the design and ensure part quality.