Carbon Graphite Seals in Vacuum Equipment: A Full-Scenario Analysis from Molecular Pumps to Coating Machines

Vacuum technology is one of the core supporting technologies of modern high-end equipment manufacturing, widely applied in semiconductor fabrication, vacuum coating, aerospace simulation, photovoltaics, and precision metallurgy. In vacuum equipment, seal performance directly determines the system's ultimate vacuum level, pumping efficiency, and process stability. Carbon graphite materials, with their unique combination of low outgassing rate, self-lubrication, high-temperature resistance, and chemical inertness, have become irreplaceable key sealing materials in vacuum equipment. This article systematically introduces the typical application scenarios, technical requirements, and selection considerations for carbon graphite seals from Huahao Sealing Co., Ltd. in vacuum equipment.

1. Core Advantages of Carbon Graphite in Vacuum Equipment

1.1 Extremely Low Outgassing Rate

Vacuum systems impose stringent requirements on material outgassing rates. Ordinary rubber sealing materials typically have outgassing rates in the 10⁻³-10⁻² Pa·L/(s·cm²) range under vacuum, while degassed carbon graphite materials can achieve rates as low as 10⁻⁶-10⁻⁵ Pa·L/(s·cm²), three orders of magnitude lower than rubber. This means that in high-vacuum and ultra-high-vacuum systems above 10⁻⁶ Pa, carbon graphite seals can reduce the system's base pressure to the lowest possible level.

1.2 Self-Lubrication Eliminates Oil Contamination

Lubrication in vacuum environments is a global challenge. Traditional lubricating oils and greases volatilize rapidly under vacuum, not only contaminating the vacuum chamber and workpieces but also degrading the vacuum level. Carbon graphite requires no external lubrication — its layered crystal structure is itself a solid lubricant, maintaining stable low friction coefficients at ultra-high vacuum down to 10⁻⁸ Pa, completely solving the lubrication problem in vacuum environments.

1.3 Excellent High-Temperature Resistance

Equipment such as vacuum heat treatment furnaces and vacuum coating machines typically operates in the 800-1500°C temperature range, far exceeding the limits of conventional sealing materials. Carbon graphite can withstand temperatures above 2000°C in vacuum or inert atmospheres without structural changes, making it the preferred sealing material for high-temperature vacuum equipment.

2. Typical Vacuum Equipment Application Scenarios

2.1 Vacuum Molecular Pumps and Dry Pumps

In turbomolecular pumps, carbon graphite seal rings are used for high-speed shaft sealing, with operating speeds up to 30,000-60,000 rpm. Due to the extremely high rotational speeds, PV value capacity and dynamic balance precision requirements for seals are exceptionally demanding. Our M7N series antimony-impregnated carbon graphite seal rings undergo precision dynamic balance correction with unbalance controlled to G2.5 grade, meeting the high-speed sealing requirements of molecular pumps. In dry screw vacuum pumps, carbon graphite bushings serve as rotor support bearings, achieving long-life operation under oil-free lubrication conditions.

2.2 Vacuum Coating Equipment

In magnetron sputtering coaters and evaporative coaters, carbon graphite seals are primarily used for vacuum chamber door sealing, workpiece rotary axis sealing, and target material drive shaft sealing. Since coating processes are extremely sensitive to contamination, any organic volatilization can cause film defects. Pure carbon graphite (no impregnation) performs best in such applications, ensuring both sealing performance and elimination of contamination sources. Our carbonized carbon graphite has consistently achieved outgassing rates below 5×10⁻⁶ Pa·L/(s·cm²) in testing at multiple photovoltaic coating equipment manufacturers.

2.3 Semiconductor Manufacturing Equipment

Vacuum systems in semiconductor wafer fabrication equipment have the most stringent requirements for sealing materials. In addition to low outgassing rates, materials must be free of metallic impurities (especially alkali metals Na, K), as these metal ions contaminate wafers and alter device electrical properties. Our high-purity carbon graphite uses carefully selected low-ash raw materials, with alkali metal content controlled below 5 ppm, and has passed material certification at multiple semiconductor equipment manufacturers.

2.4 Vacuum Heat Treatment Furnaces

Vacuum quenching furnaces, vacuum annealing furnaces, vacuum sintering furnaces, and other heat treatment equipment widely use carbon graphite seals for furnace door sealing, electrode sealing, and fan shaft sealing. In high-temperature conditions above 1200°C, we recommend carbonized pure carbon graphite seal rings with specially optimized oxidation resistance, which maintain stable operation in vacuum environments with trace oxygen (oxygen partial pressure <10⁻³ Pa).

3. Selection Considerations for Vacuum Application Carbon Graphite

3.1 Impregnation Type Selection

Impregnation type selection is critical in vacuum applications. For ultra-high vacuum (<10⁻⁶ Pa) applications, pure carbon graphite or carbonized graphite without impregnation should be selected; for medium-to-high vacuum (10⁻¹-10⁻⁶ Pa), special low-volatility resin-impregnated graphite may be used; for strongly corrosive vacuum conditions, metal-impregnated (antimony, silver) graphite can be considered, but note that its outgassing rate is slightly higher than pure carbon graphite.

3.2 Degassing Pretreatment Process

Vacuum carbon graphite seals must undergo strict degassing pretreatment before shipment. Our standard process includes: holding at 250°C for 24 hours under 10⁻³ Pa vacuum, then holding at 400°C for 8 hours, progressively releasing gas molecules adsorbed inside the material. For ultra-high vacuum applications, higher temperature and longer duration degassing processes can be customized.

3.3 Surface Treatment and Cleanliness Control

Surface cleanliness of vacuum seals directly affects outgassing rate. All vacuum carbon graphite seals must be cleaned, dried, and vacuum-packaged in a Class 100 cleanroom after degassing to avoid surface organic contamination. Our vacuum-grade products undergo gas chromatography testing before shipment to ensure organic volatile content meets SEMI standards.

4. Performance Verification and Quality Control

4.1 Outgassing Rate Testing

We have established a comprehensive outgassing rate test platform using a quadrupole mass spectrometer to dynamically monitor the gas release spectrum of carbon graphite samples during heating. Each batch of vacuum-grade carbon graphite seals comes with an outgassing rate test report, including total outgassing rate and partial pressure data for each gas component (H₂, H₂O, CO, CO₂, N₂, O₂).

4.2 Sealing Performance Testing

Vacuum seals must pass helium mass spectrometer leak testing, with leak rate requirements typically <1×10⁻⁹ Pa·m³/s. Our test equipment can detect extreme leak rates down to 1×10⁻¹² Pa·m³/s, ensuring each product meets vacuum sealing requirements.

Conclusion

The application of carbon graphite seals in vacuum equipment exemplifies the critical role of materials science in high-technology equipment. From molecular pumps to coating machines, from semiconductors to aerospace simulation, carbon graphite provides irreplaceable support for vacuum technology breakthroughs through its combined advantages of low outgassing, self-lubrication, and high-temperature resistance. Huahao Sealing Co., Ltd. is committed to the research, development, and manufacturing of vacuum-grade carbon graphite seals, and looks forward to working with vacuum equipment manufacturers to advance the localization of vacuum technology.