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PBT
PBT (Polybutylene Terephthalate) is a semi-crystalline engineering thermoplastic in the polyester family, prized for its excellent electrical insulation properties, fast crystallization rate, and strong resistance to automotive fluids and chemicals. Its rapid crystallization enables short injection molding cycle times, making it highly productive for high-volume connector and electronic component manufacturing. PBT retains its mechanical and dielectric properties across a broad temperature range (–40°C to +150°C for reinforced grades), and its inherently good tracking resistance (CTI >400V) makes it one of the most specified materials for electrical connectors, switches, and automotive electrical systems.
Mechanical Properties
- Density: 1.31 g/cm³
- Tensile Strength: 55 MPa
- Yield Strength: 53 MPa
- Elongation at Break: 50–300%
- Flexural Modulus: 2,400 MPa
- Hardness: Rockwell M 118
- Heat Deflection Temperature: 150°C @ 1.8 MPa (unfilled); up to 210°C (30% glass-filled)
- Melting Point: 225°C
- Thermal Conductivity: 0.25 W/m·K
- Coefficient of Thermal Expansion: 6.5 × 10⁻⁵ /°C
- Water Absorption: 0.3%
- Flammability Rating: HB (UL94); flame-retardant grades available in V-0
Advantages
🟢 Excellent electrical insulation and arc tracking resistance — CTI >400V makes PBT the go-to material for high-voltage connectors, circuit breakers, and switch housings
🟢 Fast crystallization rate — enables short injection molding cycles (typically 30–50% faster than PET), boosting productivity for high-volume production
🟢 Outstanding chemical resistance — resists automotive fuels, oils, greases, and weak acids/bases; ideal for under-hood and electrical system components
🟢 Good mechanical properties at elevated temperatures — reinforced grades maintain stiffness and strength up to 150°C, suitable for demanding automotive and industrial environments
Machining & Manufacturing
| Parameter | Specification | Notes |
| Cutting Speed | Turning: 200–400 m/minMilling: 600–1,500 RPM (Ø6–Ø12 mm end mills) | Excess speed leads to local overheating and surface melting |
| Tooling | Unfilled PBT: Sharp carbide tools with 5°–15° positive rakeGlass-filled PBT: K10/K20 carbide or PCD inserts | Glass fiber is abrasive and shortens tool service life |
| Coolant | Glass-filled PBT: Water-based flood coolantUnfilled PBT: Air blastDrilling & tapping: Mist coolant | Controls heat and glass fiber dust |
| Chip Control | Unfilled PBT: Brittle semi-continuous chipsGlass-filled PBT: Abrasive powdery chips | Vacuum extraction is required for fiber dust protection |
| Surface Finish | Unfilled PBT turning: Ra 0.8–1.6 μmGlass-filled PBT: Ra 1.6–3.2 μm | Use fine-grit tools and light finishing cuts for better effect |
| Dimensional Considerations | Low thermal expansion for stable dimensions | Thin-walled parts may warp; stress relief at 150°C for 30 minutes is recommended |
Common Applications
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