Carbon- and graphite-filled PTFE (25% C and 15% graphite)
Carbon- or graphite-filled PTFE for sliding in water, steam and chemicals
Carbon and graphite give PTFE compressive strength, heat conduction and low wear, including in water and steam, where bronze corrodes. These fillers are almost as chemically inert as PTFE itself and less abrasive than glass fiber. Carbon and graphite combinations are common in piston rings for oil-free compressors.
Designations and equivalents
| System | Designation |
|---|---|
| Abbreviation (ISO 1043) | PTFE + carbon / graphite |
| Trade names | Fibracon PTFE + 25% Carbon (Roechling); POLYFLON 25CAR (Daikin); Fibracon PTFE + 15% Graphite (Roechling); POLYFLON 15GR (Daikin) |
Standards by product form
| Form | Standard |
|---|---|
| Filled PTFE compound | ASTM D4745* |
| Molded rod, tube and sheet | Stock-shape manufacturer's specification |
| Machined part to drawing | ISO 2768 tolerance or as per drawing |
Composition and filler
Nominal composition by mass
| Component | Content |
|---|---|
| PTFE | 75% (carbon grade) or 85% (graphite grade) |
| Carbon (coke/fiber) | 25% by mass |
| Graphite | 15% by mass |
Mechanical properties
Typical values from the stock-shape manufacturer's catalog, 23 °C (25% carbon, 15% graphite); ISO/ASTM methods as per the source
| Property | Value |
|---|---|
| Tensile strength | 25% carbon: min. 15 MPa · 15% graphite: >13 MPa |
| Elongation at break | 25% carbon: min. 90% · 15% graphite: >180% |
| Compressive strength | 25% carbon: 10 MPa |
| Hardness | 25% carbon: Shore D 63 · 15% graphite: Shore D 55-59 |
Typical physical and thermal properties
| Property | Value |
|---|---|
| Density | 25% carbon: 2.10 ± 0.03 g/cm³ · 15% graphite: 2.05-2.25 g/cm³ |
| Maximum continuous service temperature | 260 °C |
| Minimum service temperature | -200 °C |
| HDT (1.8 MPa) | 25% carbon: 65 °C |
| Melting point or glass transition | 327 °C |
| Linear thermal expansion | 25% carbon: 95 µm/m·K |
| Thermal conductivity | 25% carbon: 0.64 W/m·K |
| Water absorption (24 h) | 25% carbon: 0.05% |
| Flammability (UL 94) | 25% carbon: V-0 |
Friction, wear and PV limit
| Property | Value |
|---|---|
| Dynamic coefficient of friction against steel | 25% carbon: 0.06 (dynamic, 0.8 m/s, 1 MPa, against stainless steel Ra 0.5 µm) |
| PV limit (pressure × velocity) | 25% carbon: 0.365 MPa·m/s (at 0.05 m/s); 0.46 MPa·m/s (at 0.5 m/s); 0.545 MPa·m/s (at 5 m/s) |
| Deformation under load (creep) | 25% carbon: 5-7% (deformation under load, ASTM D621) |
| Deformation under load (creep) | 25% carbon: 6.5% (total deformation under 14 MPa, 24 h) |
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 | Very good (Daikin cites resistance to hydrochloric acid) |
| Bases (alkalis) | Very good |
| Solvents | Very good |
| Hydrocarbons and oils | Very good |
| Steam and hot water | Very good; recommended for water applications (Daikin) |
Stock forms and sizes
- Rod (round bar)
- Sheet (plate)
- Tube and bushing
- Molded bushings and rings
- 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; minimum -200 °C (unloaded; under load, limited by HDT and creep). |
| Annealing (stress relief) | Stress-relief annealing before finish machining. |
| Bonding and welding | Cannot be welded; bonding only after chemical etching of the surface. |
| Machining | Machines well with carbide; carbon dust is conductive, so clean the machine. |
Typical applications
- Piston rings for oil-free compressors
- Bushings and bearings in water, steam and chemical media
- Pump seals
- Guide rings in water and emulsions
- Antistatic parts
Alternatives: Bronze-filled PTFE in oil hydraulics with high load; carbon-filled PEEK when load and temperature exceed the limits of PTFE.
Frequently asked questions
Which standards cover Carbon- and graphite-filled PTFE (25% C and 15% graphite)?
Filled PTFE compound: ASTM D4745*. Molded rod, tube and sheet: Stock-shape manufacturer's specification. Machined part to drawing: ISO 2768 tolerance or as per drawing.
Up to what temperature can Carbon- and graphite-filled PTFE (25% C and 15% graphite) be used?
Continuous service up to 260 °C; minimum -200 °C (unloaded; under load, limited by HDT and creep).
Which materials can replace Carbon- and graphite-filled PTFE (25% C and 15% graphite)?
Bronze-filled PTFE in oil hydraulics with high load; carbon-filled PEEK when load and temperature exceed the limits of PTFE.
Carbon or bronze in PTFE?
Carbon in water, steam, acids and media where bronze corrodes; bronze in hydraulic oil, with higher load and better heat conduction.
Does carbon-filled PTFE conduct electricity?
Partially: carbon fillers make PTFE dissipative, which is useful in antistatic parts. It is not an insulator like virgin PTFE.
