PI · additive grade
PI 40% Graphite
Properties of the 40% Graphite condition, compared with the other PI grades.
Choose for the best dimensional stability, lowest CTE and highest thermal conductivity in high-load/high-speed bearings and seal rings.
What is PI 40% Graphite?
PI 40% Graphite is PI in the 40% Graphite grade — choose for the best dimensional stability, lowest CTE and highest thermal conductivity in high-load/high-speed bearings and seal rings. PI 40% Graphite has a tensile strength of 52 MPa (7.54 ksi), stronger than 56% of polymer grades. Elongation at break is 3% and the elastic modulus is 6.2 GPa (0.899 Msi). PI 40% Graphite has a density of 1.65 g/cm³ (0.0596 lb/in³), heavier than 93% of polymer grades. Its glass-transition temperature is 385°C (725 °F). Unfilled is the default condition FabDigit quotes; 40% Graphite is available on request or by drawing note.
Advantages
- Conducts heat well — 1.7 W/m·K (0.982 BTU/hr·ft·°F), better than 100% of polymer grades
- High service temperature — 300°C (572 °F), better than 99% of polymer grades
- Stiff — 6.2 GPa (0.899 Msi), better than 89% of polymer grades
- Good UV / weathering resistance — 60/100, better than 80% of polymer grades
Limitations
- Heavy — 1.65 g/cm³ (0.0596 lb/in³), worse than 93% of polymer grades
- High embodied carbon — 13 kg CO₂/kg, worse than 93% of polymer grades
- Difficult to weld — 5/100, worse than 90% of polymer grades
- Limited ductility — 3%, worse than 83% of polymer grades
- Limited formability — 15/100, worse than 80% of polymer grades
PI 40% Graphite properties
Typical room-temperature values for PI 40% Graphite — 13 properties are specific to this condition; the rest are grade-level values shared by every PI grade. Each bar shows where the value sits among the polymer grades in FabDigit's library — further right is higher.
Physical5
PI 40% Graphite has a density of 1.65 g/cm³ (0.0596 lb/in³), heavier than 93% of polymer grades. Its glass-transition temperature is 385°C (725 °F).
Mechanical15
PI 40% Graphite has a tensile strength of 52 MPa (7.54 ksi), stronger than 56% of polymer grades. Elongation at break is 3% and the elastic modulus is 6.2 GPa (0.899 Msi).
Thermal10
PI 40% Graphite is rated for continuous service to 300°C (572 °F). It conducts heat at 1.7 W/m·K (0.982 BTU/hr·ft·°F), better than 100% of polymer grades. Thermal expansion is 38 µm/m·K (21.1 µin/in·°F).
Electrical6
PI 40% Graphite is an electrical insulator with a dielectric strength of 22 kV/mm (558.8 V/mil) and a resistivity of 1×10¹⁴ Ω·m.
Chemical & Environmental3
Corrosion resistance is excellent (85/100), better than 63% of polymer grades. UV resistance is good.
Sustainability4
Producing a kilogram of PI 40% Graphite takes about 290 MJ of energy and emits 13 kg of CO₂ — more than 95% of polymer grades. Typical recycled content is 0%.
Manufacturability4
PI 40% Graphite's machinability is fair (45/100, worse than 77% of polymer grades); weldability not recommended (5/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other PI grades and fills
PI is also supplied in 7 other conditions. The full side-by-side table is on the PI overview.
- UnfilledDefaultPick when electrical insulation, maximum elongation/toughness and cleanliness matter more than wear life.86 MPa tensile
- FILMPick for flexible circuits, cable/motor insulation, thermal tape and high-voltage barriers where thin, tough, high-dielectric film is needed.231 MPa tensile
- CF30Choose for maximum stiffness, creep resistance and lowest CTE in structural high-temperature parts.100 MPa tensile
- TPIUse when complex net-shape parts must be injection molded and 240–260 °C service is enough; melt-processable unlike Kapton/Vespel PI.92 MPa tensile
- 15% GraphiteStandard bearing/wear grade: lower friction and wear rate than SP-1 with better dimensional stability, no longer an insulator.65 MPa tensile
- 40% GraphiteChoose for the best dimensional stability, lowest CTE and highest thermal conductivity in high-load/high-speed bearings and seal rings.52 MPa tensile
- 15% Graphite + 10% PTFEPick for the lowest dry coefficient of friction and best start-up/oscillating unlubricated sliding performance.44 MPa tensile
Working with PI 40% Graphite
Is PI easy to machine?
Machines dry with sharp polished carbide (PCD for graphite/CF grades), light feeds and good chip clearance; brittle at edges so avoid sharp internal corners and stress-relieve/anneal after heavy cuts.
Can PI be welded?
Not weldable — non-melting (except TPI grades); join by high-temperature epoxy/polyimide adhesive, press-fit or mechanical fastening.
Can PI be formed, bent or molded?
Kapton-type film is cast/extruded and can be laminated or thermoformed only slightly; Vespel-type stock is direct-formed (isostatic pressing + sintering) and then machined; only thermoplastic PI can be injection molded (melt 400–420 °C, mold 180–230 °C, dry resin thoroughly).
What surface finishes work on PI?
Amber natural color needs no coating; can be plasma/alkaline-etch activated for metallization and adhesive bonding; polishes to a fine matte finish, no paint/anodize required.
PI chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| graphite15 % in SP-21, 40 % in SP-22 | 0 – 40 | 0 |
| PTFE10 % in SP-211 | 0 – 10 | 0 |
| MoS215 % in SP-3 (vacuum grade) | 0 – 15 | 0 |
| carbon fiberstructural CF-reinforced grades | 0 – 40 | 0 |
| polyimide resin (PMDA–ODA type aromatic pyromellitic dianhydride + 4,4'-oxydianiline backbone; unfilled default grade | balance | — |
PI 40% Graphite — frequently asked
What is PI 40% Graphite used for?
PI 40% Graphite is typically used for wire and cable insulation film, aerospace and satellite structural parts, unlubricated bushings and thrust washers, seal rings and piston rings for high-temperature service, semiconductor process components and flexible circuit substrates. In short: ultimate aerospace performance.
What is the tensile strength of PI 40% Graphite?
PI 40% Graphite has a typical tensile strength of 52 MPa (7.54 ksi) — stronger than 56% of polymer grades. Strength varies by condition: see the 8 listed tempers.
Is PI 40% Graphite easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 77% of polymer grades). Machines dry with sharp polished carbide (PCD for graphite/CF grades), light feeds and good chip clearance; brittle at edges so avoid sharp internal corners and stress-relieve/anneal after heavy cuts.
Can PI 40% Graphite be welded?
Not readily — weldability is rated not recommended (5/100). Not weldable — non-melting (except TPI grades); join by high-temperature epoxy/polyimide adhesive, press-fit or mechanical fastening.
What surface finishes work on PI 40% Graphite?
Amber natural color needs no coating; can be plasma/alkaline-etch activated for metallization and adhesive bonding; polishes to a fine matte finish, no paint/anodize required.
Can PI 40% Graphite be formed, bent or molded?
Kapton-type film is cast/extruded and can be laminated or thermoformed only slightly; Vespel-type stock is direct-formed (isostatic pressing + sintering) and then machined; only thermoplastic PI can be injection molded (melt 400–420 °C, mold 180–230 °C, dry resin thoroughly).
What is the maximum service temperature of PI 40% Graphite?
PI 40% Graphite is rated for continuous use to about 300°C (572 °F), and briefly to 480°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in PI 40% Graphite?
Yes — PI 40% Graphite is available for CNC machining, sheet metal and injection molding with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Vespel SP-1 / SP-21 / SP-22 / SP-211 / SP-3 polyimide parts and shapes design handbook — DuPont (2021)
- Kapton HN polyimide film — summary of properties — DuPont (2022)
- Duratron PI / CU60 polyimide stock shapes datasheet — Mitsubishi Chemical Advanced Materials (2022)
- Meldin 7001 / 7211 / 7220 polyimide datasheets — Saint-Gobain Performance Plastics (2021)
- AURUM thermoplastic polyimide product guide — Mitsui Chemicals (2020)
- Engineered Materials Handbook Vol. 2: Engineering Plastics — ASM International (1988)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.