PAI (Torlon® 4301) – polyamide-imide
The strongest thermoplastic up to 260 °C, bearing grade with PTFE and graphite
Polyamide-imide is the thermoplastic with the highest strength and stiffness up to about 260 °C, with very low creep. Grade 4301, with PTFE and graphite, is made for bearings and wear rings under high load and speed. It absorbs some moisture, which changes dimensions: precision parts require dry, stabilized material.
Designations and equivalents
| System | Designation |
|---|---|
| Abbreviation (ISO 1043) | PAI |
| Trade names | Torlon 4301 (Syensqo/Solvay, resin); Duratron T4301 PAI (MCAM); TECAPAI CM XP440 (Ensinger) |
Standards by product form
| Form | Standard |
|---|---|
| Rod, tube and sheet | Manufacturer's specification (Solvay Torlon; MCAM Duratron T4301) |
| Machined part to drawing | ISO 2768 tolerance or as per drawing |
Composition and filler
Nominal composition of the bearing grade
| Component | Content |
|---|---|
| PAI (polyamide-imide) | ≈ 85% |
| PTFE + graphite | ≈ 15% (grade 4301)* |
Mechanical properties
Typical values from the stock-shape manufacturer's catalog, 23 °C; ISO/ASTM methods as per the source
| Property | Value |
|---|---|
| Tensile strength | 103 MPa |
| Modulus of elasticity (tensile) | 6,210 MPa |
| Elongation at break | 3% |
| Compressive strength | 152 MPa |
| Hardness | Rockwell M 106 |
| Notched impact | 42.7 J/m |
Typical physical and thermal properties
| Property | Value |
|---|---|
| Density | 1.45 g/cm³ |
| Maximum continuous service temperature | 260 °C |
| Maximum short-term temperature | 270 °C |
| Minimum service temperature | -20 °C |
| HDT (1.8 MPa) | 279 °C |
| Melting point or glass transition | 275 °C |
| Linear thermal expansion | 25.2 µm/m·K |
| Thermal conductivity | 0.533 W/m·K |
| Water absorption (24 h) | 0.4% |
| Water absorption (saturation) | 1.5% |
| Flammability (UL 94) | V-0 |
Calculate the weight of PAI (Torlon® 4301) – polyamide-imide bar, plate or pipe →
Friction, wear and PV limit
| Property | Value |
|---|---|
| Dynamic coefficient of friction against steel | 0.2 (dynamic, dry against steel (MCAM QTM 55007)) |
| PV limit (pressure × velocity) | 1.4 MPa·m/s (MCAM QTM 55007, dry against steel, safety factor 4:1 already applied; original 40,000 psi·ft/min; requires post-cure); 0.326 MPa·m/s (ASTM D3702 (Ensinger USA), no safety factor stated; original 9,300 psi·ft/min (compression molded)) |
PV and friction depend on the test method, the mating surface (steel, stainless, roughness), lubrication and each manufacturer's safety factor: compare values from the same source and confirm by testing in critical applications.
Chemical resistance
| Medium | Resistance |
|---|---|
| Acids | Limited in strong acids; good in weak acids |
| Bases (alkalis) | Poor (strong alkalis unacceptable) |
| Solvents | Good (including chlorinated solvents, ketones, esters) |
| Hydrocarbons and oils | Good |
| Steam and hot water | Limited (absorbs water; steam above ~150 °C degrades it) |
Stock forms and sizes
- Rod (round bar)
- Tube and bushing
- Sheet (plate)
- Raw material: rod (round bar), sheet (plate) and tube, cut to size
- Machined part to drawing or sample, in the same order as the metal parts
- Lot certificate of conformity; FDA/EU 10/2011 declaration when the grade allows
Service temperature, machining and assembly
| Item | Usual practice |
|---|---|
| Service temperature | Continuous service up to 260 °C, short peaks up to 270 °C; minimum -20 °C (unloaded; under load, limited by HDT and creep). |
| Annealing (stress relief) | The material is supplied already post-cured by the manufacturer; anneal only as instructed by the manufacturer. |
| Bonding and welding | Bonding with epoxy after surface preparation. |
| Machining | Machines with carbide tooling; store dry before machining precision parts. |
Typical applications
- Bearings and wear rings with very high PV
- Transmission thrust washers
- Seal rings and piston rings
- Parts for packaging and semiconductor machinery
Alternatives: Bearing-grade PEEK (lower cost, less water absorption); PI (Vespel) above 260 °C.
Frequently asked questions
Which standards cover PAI (Torlon® 4301)?
Rod, tube and sheet: Manufacturer's specification (Solvay Torlon; MCAM Duratron T4301). Machined part to drawing: ISO 2768 tolerance or as per drawing.
Up to what temperature can PAI (Torlon® 4301) be used?
Continuous service up to 260 °C, short peaks up to 270 °C; minimum -20 °C (unloaded; under load, limited by HDT and creep).
Which materials can replace PAI (Torlon® 4301)?
Bearing-grade PEEK (lower cost, less water absorption); PI (Vespel) above 260 °C.
Torlon or PEEK?
Torlon (PAI) has higher strength, stiffness and PV; PEEK absorbs less water, has better chemical resistance and costs less. For a critical bearing under high load, PAI 4301 usually wins.
