Key Points
- "Carbon" refers to material baked at 1000-1400°C without graphitization, with high hardness and wear resistance but poor lubricity
- "Graphite" refers to material graphitized at 2400-3000°C, with good self-lubrication and low friction coefficient
- "Carbon graphite" is a partially graphitized intermediate material balancing hardness and lubricity, the mainstream choice for seals
- Performance: carbon hardness HS 70-100, friction 0.15-0.30; graphite hardness HS 40-70, friction 0.04-0.15
- Selection principle: high load/wear → carbon or hard carbon; dry friction/oil-free → graphite or carbon graphite; corrosive media → impregnated carbon graphite
1. Terminology: Why the Confusion
In industrial contexts, terms like "carbon graphite," "graphite," "hard carbon" and "electrographite" are often used interchangeably, causing selection confusion for procurement and engineers. The root cause is that these are all carbon-based engineered materials differing in heat treatment temperature and crystal conversion degree:
- Carbon: baked at 1000-1400°C, carbon atoms primarily amorphous, no complete graphite crystals
- Graphite: graphitized at 2400-3000°C, carbon atoms rearranged into regular layered graphite crystals
- Carbon graphite: partially graphitized, crystal conversion between carbon and graphite
- Electrographite: fully graphitized in electric furnace, highest crystal conversion
English terminology follows the same hierarchy: Hard Carbon → Carbon Graphite → Electrographite, with increasing graphitization degree.
2. Essential Crystal Structure Difference
The fundamental difference lies in the sharpness of the (002) peak in X-ray diffraction, i.e., graphitization degree:
| Material | Baking temp | Graphitization | d₀₀₂ spacing | Crystal features |
|----------|-------------|----------------|---------------|------------------|
| Carbon (hard) | 1000-1400°C | <30% | 3.44-3.70 Å | Mostly amorphous |
| Carbon graphite | 2000-2400°C | 30%-80% | 3.36-3.44 Å | Partially regular |
| Electrographite | 2400-3000°C | >80% | 3.35-3.36 Å | Highly regular |
Higher graphitization means more complete layered structure, weaker inter-layer van der Waals forces and better self-lubrication; but hardness drops and wear resistance decreases. This is the core trade-off in material selection.
3. Performance Comparison
3.1 Mechanical Properties
- Carbon (hard): Shore hardness HS 70-100, compressive 200-400 MPa, excellent wear resistance but higher brittleness
- Carbon graphite: Shore hardness HS 40-90, compressive 150-340 MPa, balanced hardness and toughness
- Electrographite: Shore hardness HS 30-60, compressive 100-200 MPa, best toughness but lowest hardness
3.2 Tribological Properties
- Carbon: dry friction 0.15-0.30, poor self-lubrication, needs soft counterface or external lubrication
- Carbon graphite: dry friction 0.04-0.15, good self-lubrication, mainstream seal material
- Electrographite: dry friction 0.04-0.10, best self-lubrication but lower wear resistance than carbon graphite
3.3 Thermal and Chemical Properties
All three have high thermal conductivity (70-150 W/(m·K)), far superior to engineering plastics. Temperature resistance reaches 600°C+ in non-oxidizing media. Chemically, carbon and carbon graphite resist most acids, alkalis and salts but require impregnation due to higher porosity; electrographite has lower porosity but still needs impregnation for sealing.
4. Seal Selection Recommendations
4.1 High Load, Heavy Wear Conditions
For mining crusher bearings and heavy machinery bushings, choose carbon or hard carbon for high hardness and wear resistance. Note that carbon is more brittle and should not bear impact loads.
4.2 Dry Friction, Oil-Free Conditions
For food machinery, vacuum equipment and submersible pumps, choose graphite or carbon graphite for low friction and self-lubrication to avoid media contamination. PTFE or phenolic impregnation is commonly used.
4.3 High Temperature Oil Pumps
Choose antimony-impregnated carbon graphite for 400°C+ temperature resistance and load capacity, commonly grade M106K.
4.4 Highly Corrosive Chemical Service
Choose furan resin-impregnated carbon graphite for strong acid/alkali resistance; PTFE impregnation is needed for hydrofluoric acid service.
4.5 High-Speed Light-Load Sealing (Mechanical Seal Rings)
Carbon graphite is the mainstream choice as the soft face, paired with silicon carbide or hard alloy as the hard face. It balances hardness and self-lubrication for stable fluid film and wear resistance.
5. Procurement Recommendations
Confirm the following with your supplier to avoid material selection errors:
1.Material type: carbon/carbon graphite/electrographite (graphitization degree)
2.Impregnation type: resin/metal/un-impregnated
3.Performance indicators: hardness, compressive strength, porosity, friction coefficient
4.Service conditions: temperature, pressure, media, speed
5.Compliance with industry standards (e.g., JB/T 8896, API 682)
Huahao Sealing Co., Ltd. supplies carbon graphite seal rings, bushings and segmented rings in mainstream grades such as M106K, M254K and M179K, with custom machining from drawings or samples and material test reports.