Machinable polyimide is what you specify when PEEK would creep, PEI would soften and metal would contaminate. It holds 260–300 °C continuously, outgasses almost nothing in vacuum, and runs dry against steel without lubrication. It is also brittle, moisture-sensitive and expensive — all three shape how we machine it.
Figures for an unfilled Vespel SP-1 / Meldin 7001 class compound. Graphite and PTFE additions raise wear resistance and lower friction, but reduce strength by 20–40 %.
| Property | Value | Why it matters for machining |
|---|---|---|
| Glass transition | ~360 °C | No softening in the working range; the polymer stays glassy up to its decomposition limit |
| Continuous service temperature | 260–300 °C | Short excursions to 400 °C are tolerated in inert atmosphere |
| Tensile strength | 72–86 MPa | Good in compression, weaker in tension — design joints accordingly |
| Compressive strength | ~170 MPa | The property that sells PI: bushings and thrust washers carry real load at temperature |
| Flexural modulus | ~3.1 GPa | Stiff, but low elongation means little warning before fracture |
| Coefficient of thermal expansion | 45–55 µm/m·K | Closer to aluminium than PEEK; helps in mixed-material fixtures |
| Water absorption | ~1.5 % at saturation | The single biggest dimensional risk — condition the blank, then take the finish cut |
| Outgassing (TML / CVCM) | ~0.5 % / < 0.05 % | Qualifies for vacuum and semiconductor chambers without bake-out bake cycles |
| Wear / friction | Excellent, self-lubricating | Runs against stainless and ceramic without grease, at temperature |
| Chemical resistance | Excellent, with exceptions | Unaffected by fuels, oils and most solvents; attacked by strong alkalis and hot concentrated acids |
| Flammability | UL 94 V-0 | Very low smoke, used in aircraft and rail interiors |
| Cost index | 20–30 × PMMA | Order near-net blanks; a 20 % oversize plate can double the part cost |
Highest strength and electrical insulation, lowest outgassing. Default for semiconductor fixtures, insulators and analytical instrument parts where contamination is the concern.
Lower friction and thermal expansion, better dimensional stability under load. The general-purpose bearing grade for bushings, wear rings and slide pads.
Highest wear resistance and lowest CTE, at the cost of strength and impact. Used in high-load, low-speed bearings and seal rings.
Lowest coefficient of friction for unlubricated running against soft metals. Choose when start-up torque or stick-slip is the design driver.
Wafer contact rings, test sockets, vacuum chuck pads and plasma-etch fixtures: low particles, low outgassing, no metal ions.
Feedthrough insulators, thermal standoffs and valve seats that must not outgas and survive repeated cycling to 4 K.
Bushings, wear pads and seal supports near engines and APUs where 250 °C+ and dry running rule out PTFE and nylon.
Piston rings, rider rings and valve plates in oil-free compressors — the classic high-volume PI application.
GC and HPLC seals, ferrules and insulators that must stay inert at 300 °C with zero extractables.
High-temperature spacers, coil formers and slot liners where PI replaces ceramic and avoids brittle fracture.
PI is usually chosen for temperature plus wear. If either requirement is softer, a cheaper grade will do.
Tell us the service temperature, load and mating material. We will confirm the grade, the conditioning route and the tolerance that is actually achievable.
