In the demanding world of industrial sealing, where extreme temperatures, aggressive media, and critical pressures are daily challenges, the choice of gasket material is paramount. Among the high-performance solutions available, expanded graphite gaskets, also known as flexible graphite gaskets, have established themselves as a superior choice for a vast array of applications. Sourced from high-purity natural graphite and processed through exfoliation, expanded graphite gaskets deliver an exceptional combination of thermal resilience, chemical resistance, and reliable sealing force. At Kaxite Sealing, we specialize in manufacturing premium-grade expanded graphite gaskets engineered to meet the most stringent operational requirements across global industries.
Expanded graphite is created by treating natural flake graphite with intercalation agents and then rapidly heating it. This process causes the graphite crystals to expand or exfoliate perpendicular to the basal plane, creating a mat of vermiform (worm-like) particles. This mat is then calendered into sheets without the use of binders. These pure graphite sheets are the base material for expanded graphite gaskets. They can be used as plain sheets, die-cut into specific shapes, or combined with other materials to form composite gaskets, offering versatility and robust performance.
The widespread adoption of expanded graphite gaskets is driven by their unique set of material properties:
Kaxite Sealing provides expanded graphite gaskets in various forms to suit specific application needs. Below are the standard specifications for our core product lines.
| Parameter | Specification / Value | Test Standard |
|---|---|---|
| Material Grade | KX-Graphite 99, KX-Graphite HP (High Purity) | ASTM D7219 |
| Density Range | 0.9 g/cm³ to 1.15 g/cm³ | ASTM D7772 |
| Thickness Range | 0.5 mm (0.020") to 6.0 mm (0.250") | - |
| Temperature Range (Inert) | -240°C to 3000°C (-400°F to 5432°F) | - |
| Temperature Range (Oxidizing) | -240°C to 450°C (-400°F to 842°F) | - |
| Tensile Strength (MD) | 4.5 MPa (min) | ASTM D828 |
| Compression Set (at 50 MPa) | < 12% | ASTM F36 |
| Recovery | > 50% | ASTM F36 |
| Thermal Conductivity | 10 - 150 W/(m·K) (in-plane) | ASTM E1461 |
| pH Value | 5 - 7 (Neutral) | ASTM E70 |
| Sulfur & Chloride Content | < 50 ppm (for nuclear/aggressive service) | ASTM D4327 / D4208 |
For applications requiring enhanced mechanical strength, blow-out resistance, or handling ease, Kaxite offers reinforced variants:
| Composite Type | Core/Laminate Material | Typical Thickness | Key Application Benefit |
|---|---|---|---|
| Tanged Insert Gasket | 304, 316 Stainless Steel | 1.5 mm, 3.0 mm | High strength, anti-blowout, standard flange service |
| Double-Sided Foil Laminate | 304, 316, Inconel Foil (0.05mm) | 1.0 mm, 1.5 mm, 2.0 mm | Easy handling, no dusting, barrier against pitting media |
| Kammprofile Gasket | 304, 316, Carbon Steel Core | Varies (Core + Graphite Facing) | High pressure/temperature, thermal cycling, low bolt load |
The versatility of Kaxite expanded graphite gaskets makes them suitable for a broad spectrum of industries:
Q: What is the primary difference between expanded graphite and compressed non-asbestos (CNAF) gaskets?
A: The core difference lies in composition and temperature capability. Expanded graphite gaskets are made from nearly pure graphite (carbon), offering superior thermal conductivity and a much higher maximum service temperature (up to 450°C in air vs. typically 260-280°C for CNAF). CNAF gaskets are composite materials of aramid fibers, rubber binders, and fillers. While CNAF is excellent for general industrial service, expanded graphite is the choice for extreme heat, aggressive chemicals, and where long-term binder degradation is a concern.
Q: Can expanded graphite gaskets be used for oxygen service?
A: Generally, no. Standard expanded graphite is carbon-based and presents a combustion risk in high-pressure oxygen or strong oxidizing agent environments. Special, passivated grades may be available for specific low-risk applications, but this requires careful consultation with the manufacturer like Kaxite Sealing and adherence to strict industry standards like ASTM G94.
Q: Why do some expanded graphite gaskets have metal inserts or laminates?
A: Pure graphite sheets, while excellent sealants, can be delicate to handle and may lack sufficient mechanical strength for high-pressure or large-diameter flanges prone to bending. A metal tanged insert provides an internal skeleton, drastically improving tensile strength, torque retention, and resistance to blow-out. Metal foil laminates (e.g., stainless steel) make the gasket easier to handle, prevent graphite particle loss ("dusting"), and provide a metallic barrier against highly corrosive media that might attack graphite.
Q: How do I determine the correct density and thickness for my application?
A: Selection depends on flange conditions (surface finish, flatness), medium, pressure, temperature, and bolt load. As a general rule: Standard water, steam, and chemical services often use 1.5mm thick sheets with a density of 1.1 g/cm³. For higher pressures or uneven flanges, a thicker gasket (e.g., 3.0mm) with a slightly lower density can provide better conformability. For severe service (high P/T cycling), a reinforced composite like a Kammprofile is recommended. Always consult Kaxite Sealing's engineering team or refer to ASME PCC-1 guidelines for specific recommendations.
Q: What flange surface finish is recommended for expanded graphite gaskets?
A: A serrated finish is typically recommended to provide sufficient "bite" and prevent slippage. Common finishes include phonographic (spiral) serrated with a 0.06mm (2.5 mil) depth or concentric serrations. A smooth, polished finish (e.g., Ra < 1.6 µm) is not recommended as it may lead to poor grip and potential seal failure. The ideal roughness (Ra) is between 3.2 µm and 6.3 µm (125-250 µin).
Q: Are Kaxite expanded graphite gaskets suitable for spiral wound gasket replacement?
A: In many cases, yes, especially where thermal cycling or corrosion of the spiral wound metal windings is an issue. Expanded graphite gaskets, particularly reinforced types, offer excellent recovery and sealability under cycling conditions. However, this is not a direct substitution. It requires careful review of the flange design, pressure-temperature ratings, and bolt loads. Kaxite Sealing can provide technical support for retrofit evaluations.
Q: How should I store and handle expanded graphite gaskets?
A: Store in a cool, dry place away from direct sunlight and oxidizing agents. Keep in original packaging until ready for use. Handle with clean gloves to prevent contamination from oils and moisture. For pure graphite sheets, take care to avoid tearing or creasing. Use foil-laminated or reinforced grades if frequent handling is anticipated. Do not fold or bend the gaskets sharply.
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