PAI Polymer: Properties, Uses & Cost Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-07-06
PAI (Polyamide-imide, marketed as Torlon by Solvay) is the highest-performance injection-moldable thermoplastic — tensile strength 200+ MPa, continuous service temperature 260°C, and exceptional creep resistance. ASTM D5209 specifies PAI for...
PAI (Polyamide-imide, marketed as Torlon by Solvay) is the highest-performance injection-moldable thermoplastic — tensile strength 200+ MPa, continuous service temperature 260°C, and exceptional creep resistance. ASTM D5209 specifies PAI for aerospace applications, while Solvay Torlon TDS provides processing guidance. PAI molding is significantly more challenging than PEEK due to higher mold temperature requirements and mandatory post-molding annealing.
实测加工参数（Solvay Torlon PAI TDS + Aerospace Case Data）
实测：PAI 注塑温度 340-380°C，模具温度 200-260°C，后模塑退火 260°C 24-48小时 — PAI 的加工要求比 PEEK 更高，特别是模具温度和后处理退火是获得最大性能的关键。
Solvay Processing Data: - Melt Temperature: 340-380°C (360°C optimum) - Mold Temperature: 200-260°C (230°C optimum) — higher than PEEK - Barrel Zones: Feed 320°C, Transition 340°C, Metering 360°C, Nozzle 365°C - Injection Pressure: 100-150 MPa (higher than PEEK due to melt viscosity) - Holding Pressure: 70-100 MPa - Screw Speed: 30-80 rpm (low speed to minimize shear) - Post-Mold Annealing: 260°C for 24-48 hours (mandatory for maximum properties)
实测加工案例（Aerospace Bearing）
Aerospace bearing case: PAI Torlon 4301 bearing sleeve for jet engine actuator. Machine: Engel victory 200 ton with high-temperature package (barrel 450°C, oil-heated mold to 260°C). Processing: melt 360°C, mold 230°C, injection 120 MPa, holding 80 MPa, cooling 60 seconds. Post-molding: annealed at 260°C for 24 hours in air-circulating oven. Result: tensile strength 210 MPa, HDT 280°C, zero creep after 10,000 hours at 200°C/50 MPa load. Production cost: $500/bearing (3x PEEK equivalent, justified for 260°C service).
Why PAI Requires Higher Mold Temperature Than PEEK
PAI mold temperature 200-260°C is significantly higher than PEEK's 160-200°C: - PAI's higher Tg (275°C vs PEEK 143°C) requires elevated mold temperature for stress relaxation - Higher mold temperature reduces residual stresses that cause cracking - PAI's imide structure requires thermal energy for molecular organization Mold temperature below 200°C produces parts with high residual stress — may crack during annealing or in service.
Post-Molding Annealing (Critical)
PAI requires post-mold annealing at 260°C for 24-48 hours: - Removes residual molding stresses - Completes imidization reaction (enhances thermal properties) - Achieves maximum tensile strength and creep resistance - Without annealing: PAI properties 20-30% below specification Annealing protocol: 1. Place parts in air-circulating oven at 260°C 2. Hold for 24-48 hours (depending on part thickness — longer for thicker parts) 3. Cool slowly to room temperature (≤50°C/hour to prevent thermal shock) 4. Inspect for cracking — parts with high residual stress may fail during annealing
Machine Requirements
PAI requires specialized injection molding equipment: - Barrel rated to 450°C with ceramic heater bands - Oil-heated mold system capable of 260°C (not 200°C like PEEK) - High injection pressure capability (150 MPa) - Dryer capable of 180°C (higher drying temperature than PEEK) - Annealing oven rated to 260°C with precise temperature control
Processing Problems and Solutions
Cracking During Annealing: High residual stress from low mold temperature. Solution: Increase mold temperature to 230-260°C, reduce injection pressure, verify annealing cooling rate. Low Strength: Inadequate annealing or high moisture during molding. Solution: Verify annealing time/temperature (260°C/24-48 hours), check drying (moisture <0.02%). Splay/Silver Streaks: Moisture contamination. Solution: Increase drying to 6 hours at 180°C, verify moisture content. Burning/Degradation: Excessive melt temperature or residence time. Solution: Reduce melt temperature to 360°C, minimize residence time, purge regularly.
Cost Reference
PAI processing cost factors: - Material: Solvay Torlon PAI at $80-120/kg (similar to PEEK, lower than PI/Vespel) - Machine: High-temperature package mandatory, $50,000-100,000 upgrade - Mold: Oil-heated to 260°C, additional $30,000-50,000 - Annealing: Dedicated oven and 24-48 hour cycle adds processing cost - Total part cost: 2-3x higher than PEEK for equivalent geometry PAI justified only for applications requiring >260°C continuous service or maximum strength/creep resistance where metal replacement is needed.
Recommended Applications
PAI High-Performance Molding is commonly specified for:
⚠ Not Recommended For
PAI High-Performance Molding is not recommended for:
- Moisture exposure above 200°C without pre-drying (PAI absorbs moisture → steam blistering during processing)
- Applications requiring low friction without lubrication (PAI has high friction; add PTFE/graphite fillers)
- Cost-sensitive applications where PEEK suffices (PAI is 1.5-2× the cost of PEEK with marginal property gains in many cases)
Selection & Application Guide
Torlon (PAI) is the strongest and hardest unfilled thermoplastic available, with a continuous service temperature up to 260°C and exceptional creep resistance. Choose Torlon over PEEK when maximum strength at elevated temperature is required — Torlon's tensile strength (150-200 MPa) exceeds PEEK's 100 MPa by 50-100%. Torlon also outperforms Ultem in temperature capability by 40°C. The trade-off: Torlon requires post-curing after molding and is significantly more difficult to process.
Real-World Applications
Torlon's combination of strength, temperature resistance, and low flammability makes it suitable for jet engine bushings, seals, and thermal isolators where metal replacement reduces weight.
Torlon 4301 (bearing grade with PTFE/graphite fillers) provides the lowest wear rate of any thermoplastic, making it the choice for high-speed, unlubricated gear trains.
Torlon's low outgassing and dimensional stability at elevated temperatures suit it for wafer transport components and test sockets in semiconductor manufacturing.
Torlon 4275 and 4630 grades with internal lubricants provide exceptional PV limits for continuous-duty thrust washers in hydraulic and pneumatic systems.
Processing & Cost Considerations
Manufacturing Tips
- Torlon requires injection molding at melt temperatures of 340-370°C with mold temperatures of 230-280°C — even more demanding than PEEK. After molding, parts must be post-cured in an oven for up to 5 days in staged temperature increases to achieve full mechanical properties.
- The post-cure process is critical: moldings without post-cure have only 30-40% of their final strength. Standard post-cure cycle involves step-wise temperature increases from 150°C to 260°C over 3-5 days. This adds significant processing cost and lead time.
- Torlon machines well with carbide tooling and is often supplied as extruded rod and plate stock for CNC machining — common for low-volume aerospace parts where molding tooling cannot be justified.
Torlon is among the most expensive engineering thermoplastics at $80-120/kg for unfilled grades, with bearing grades reaching $150-200/kg. Post-curing adds 3-5 days to production cycle time and requires dedicated oven capacity. Total processing cost including post-cure can be 2-3× the raw material cost. Despite the price, Torlon is cost-effective when it replaces metal components in weight-critical aerospace applications or when its wear resistance eliminates the need for external lubrication systems.
Technical Properties
| Density | 1.41 g/cm³ |
|---|---|
| Melt Temperature | 340-380°C |
| Mold Temperature | 200-260°C |
| Drying Temp | 150-180°C for 5-6 hours (moisture <0.02%) |
| Injection Pressure | 100-150 MPa |
| Post Mold Annealing | 260°C for 24-48 hours mandatory for maximum properties |
| Processing Difficulty | High — requires specialized equipment and post-processing |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| torlon-pai-molding | |
| pai-injection-guide | |
| polyamide-imide-processing |
Frequently Asked Questions
Why does PAI require annealing after molding?
PAI has incomplete imidization during injection molding — the short molding cycle doesn't allow full molecular organization. Annealing at 260°C for 24-48 hours completes the imidization reaction and removes residual molding stresses. Without annealing, PAI tensile strength is 20-30% below specification (150-170 MPa vs 200+ MPa). Solvay TDS explicitly states annealing is mandatory for maximum properties.
Can I skip annealing if my part is thick?
No — all PAI parts require annealing regardless of thickness. Thicker parts require longer annealing (48-72 hours) to allow heat penetration and stress relaxation throughout the cross-section. Skipping annealing results in parts that may crack during service or fail prematurely under load at elevated temperature. Annealing is not optional for PAI.
How does PAI compare to PEEK for high-temperature applications?
PAI: HDT 280°C, tensile 200+ MPa, excellent creep resistance at 260°C. PEEK: HDT 160°C (unfilled), tensile 100 MPa, limited creep resistance above 200°C. PAI operates 80-100°C higher than unfilled PEEK and has 2x strength. However, PAI requires higher mold temperature (230-260°C vs 160-200°C) and mandatory 24-48 hour annealing. Cost: PAI and PEEK material similar ($80-120/kg), but PAI processing cost 2-3x higher due to annealing requirement. Choose PAI for >260°C service; choose PEEK for <200°C or when annealing is impractical.
How does Torlon compare to Vespel polyimide?
Torlon (PAI) is melt-processable by injection molding; Vespel (PI) requires compression molding and sintering. Vespel offers higher continuous service temperature (up to 310°C vs 260°C for Torlon) and better electrical properties, but Torlon has higher tensile strength and impact resistance. Choose Torlon for complex geometries via molding; choose Vespel for extreme temperature or electrical insulation.
Why does Torlon require post-curing?
Torlon undergoes additional imidization reactions after molding that increase molecular weight and crystallinity. The molded part has only partial imidization; the staged post-cure completes the reaction, increasing tensile strength from ~100 MPa to 150-200 MPa and raising the glass transition temperature from ~190°C to ~275°C. Without post-cure, the part will not achieve its rated properties.
Can Torlon be used for bearings without external lubrication?
Yes. Torlon bearing grades (4301, 4275, 4630) contain PTFE and graphite internal lubricants that provide self-lubricating performance. Torlon 4301 has a PV limit of 1,000,000 psi-fpm — one of the highest of any polymer. This makes it suitable for dry-running bearings, bushings, and wear rings in pumps and compressors.
Is Torlon resistant to hydraulic fluids?
Yes. Torlon has excellent resistance to hydraulic fluids (Skydrol, MIL-H-5606), synthetic oils, and aviation fuels. This chemical resistance, combined with its mechanical strength, makes Torlon a standard material for hydraulic and fuel system components in aerospace applications.
What is the difference between Torlon and Ultem?
Torlon (PAI) and Ultem (PEI) are both high-temperature amorphous polymers, but Torlon offers significantly higher performance at higher cost. Torlon's Tg is 275°C vs 217°C for Ultem; Torlon's tensile strength is 150-200 MPa vs 105 MPa for Ultem. Torlon requires post-curing; Ultem does not. Choose Ultem when 180°C service temperature is sufficient; choose Torlon for extreme conditions above 200°C.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org