What is flexible graphite sheet
Flexible graphite sheets are formed by chemical intercalation, high-temperature puffing, and roll/compression molding of natural flake graphite.
It retains the hexagonal layered structure of graphite, but transforms the originally hard and brittle scales into a soft, compressible, and resilient sealing material.
Also known in the industry as:
- Graphite Sheet / Paper
- Flexible Graphite Plate
- Expanded Graphite Gasket
Common thickness: 0.3/0.5/0.75/1.0/1.5/2.0/3.0 mm
Common density: 0.7/1.0/1.2/1.3/1.4 g/cm ³
Why choose flexible graphite sheets for industrial seals
The flange seal should withstand high temperature, high pressure, medium corrosion, and repeated start stop simultaneously.
| Characteristic | Numerical/Performance | Sealing significance |
| Heat-resistant | Oxidation atmosphere 450-500 ℃; Inert/Vacuum 2000 ℃+ | Steam, thermal oil, and flue gas systems can all be used |
| Chemical Resistance | Acid, alkali, salt, and most solvents resistant | General use of chemical, petrochemical, and power media |
| Soft and compressible | Compression rate 30-50%, rebound rate 15-45% | Paste legal blue surface, automatically compensate for unevenness |
| Self-sealing | Sealing micro leaks under low pressure by "squeezing deformation" | Low requirement for bolt pre tightening force |
| Non adhesive | Disassemble the non stick flange for easy cleaning | High maintenance efficiency |
| Anti-aging | No rubber aging, no PTFE creep issues | Long lifespan, long maintenance cycle |
| Conductive and Thermal Conductivity | Surface thermal conductivity 100-600 W/m · K | Can meet both grounding and uniform heating requirements |
Sealing mechanism of flexible graphite sheets
Flexible graphite sheets are sealed by "elastic-plastic deformation":
1. Bolt compression → Graphite sheet is compressed
2. Graphite sheets are squeezed into the micro pores and rough peaks on the surface of the flange
3. The contact surface forms a "graphite bonding layer" to block the leakage channel
4. The higher the medium pressure, the tighter the graphite sheet is compressed, and the sealing is actually better (self tightening effect)
That's why flexible graphite sheets are more reliable on high-pressure steam flanges than ordinary rubber pads and PTFE pads.
Application scenarios of flexible graphite sheets for industrial sealing
1. Flange gasket (core)
- Steam pipeline flange
- Heat transfer oil system
- Chemical piping
- Power plant boiler and turbine interface
Common forms:
- Pure graphite sheet cutting gasket
- Graphite+metal tooth shaped composite pad (Kammprofile)
- Graphite winding pad inner filling tape (the "flexible graphite filling layer" of the winding pad)
2. Pump valve seal
- Valve cover gasket
- Pump body sealing gasket
- Bottom gasket of high-temperature valve packing box
3. Heat exchanger
- Plate heat exchanger sealing gasket (replacing rubber, with higher temperature resistance)
- Pipe box flange gasket
4. Exhaust pipe/flue
- Engine exhaust pipe gasket
- Boiler flue flange
- Flue gas heat exchanger
5. Battery/Electronics (Extended)
- Fuel cell bipolar plate sealing
- Thermal insulation sealing gasket for battery pack
- Insulation and sealing of high-temperature electric heating elements
Key performance indicators
| Project | Typical requirements |
| Density | 0.7-1.4 g/cm ³ (commonly used for sealing 1.0-1.3) |
| Carbon content | ≥ 98% (sealing grade); ≥ 99% (high-purity grade) |
| Ash content | ≤ 2% (sealing grade); ≤ 0.1% (high-purity grade) |
| Sulfur content | ≤ 1000 ppm (normal); ≤ 50 ppm (low sulfur nuclear grade) |
| Chlorine content | ≤ 50 ppm (to avoid stress corrosion) |
| Compression ratio | 30–50%(ASTM F36) |
| Rebound rate | 15–45% |
| Tensile strength | 3-8 MPa (parallel to the surface) |
| Operating temperature | Oxidation at 450 ℃; Inert at 2000 ℃+ |
| Thickness tolerance | ±0.05–0.1 mm |
| Dimensional tolerance | ± 0.1-0.5 mm (cut piece) |
Shortcomings and remedies of flexible graphite sheets
| Shortcoming | Consequence | Remedial plan |
| Pure graphite sheet has low strength | High pressure flanges are prone to being squeezed out | Add metal toothed/corrugated skeleton (Kammprofile) |
| Oxidation atmosphere above 500 ℃ will cause erosion | The lifespan of high-temperature oxygen-containing media decreases | Use antioxidant coating or switch to metal pad |
| Pure graphite sheets have micropores | Gas medium may penetrate | High density pressing+surface impregnation |
| The rebound rate is not as good as that of metal wrapped pads | Possible relaxation after repeated start stop cycles | Add metal skeleton and control pre tension force |
| Surface powdering | Clean environment is not friendly | Surface coating, composite PI/PTFE membrane |
End
Flexible graphite sheet for industrial sealing = "soft graphite" formed by extruding natural flake graphite,
Relying on "pressing in, blocking leaks, high temperature resistance, and corrosion resistance" as the main sealing force in flanges, pump valves, and heat exchangers.
Choose based on four factors : density, thickness, carbon content/ash content, and sulfur and chlorine content.
Do not use the high-pressure flange bare, add a metal frame; Do not use it naked in high-temperature and oxygen-containing environments, and perform antioxidant treatment.
