Rigid graphite felts (boards) are shape-retentive insulating materials made of graphite fibers and carbon binder. Based on high purity graphite fibers which have been milled, carbonized, mixed with proprietary resins, and vacuum formed into boards.
The boards then go through a process polymerization and drying. They are then carbonized followed by a final heat treatment to between 1500 ºC and 2800 ºC depending on the process application.
Its properties are governed by the precursor, the type and quantity of the binder, its compression ratio and thermal treatment. The material is used in the form of self-supporting boards, cylinders and other components, mainly in high temperature furnace applications.
Rigid graphite board has excellent machining properties. It can be easily machined by such conventional methods as sawing, cutting, drilling or milling.
Strict process control ensures a homogeneous board with excellent thermal properties resulting in improved hot zone temperature uniformity. Thermal properties may be further enhanced by the application of a graphite foil coating.
Available Types, Sizes and Main Properties
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Type
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Thickness
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Width
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Length
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Pure surfaces (no foil or CFC)
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80mm (max)
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1000mm (max)
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1500mm (max)
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Graphite foil on one side
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Graphite foil on both sides
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CFC on one side
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CFC on both sides
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Graphite foil on one side, CFC on the other
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Properties
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Value
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Bulk density (g/cm³)
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≥0.28
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Flexural strength (MPa)
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2.5 - 3.2
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Thermal conductivity (W/mK)
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0.25 - 0.30
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Tensile strength (MPa)
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2.8 - 6.8
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Ash content (%)
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≤0.05
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Carbon content (%)
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≥98
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Processing temperature (°C)
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1500 - 2800
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Thermal expansion coefficient (10-6/K)
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0.8 - 6.9
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Characteristics and Benefits
- Low thermal conductivity allows high temperature furnaces to be designed and built with thin layers of insulating material. Moreover, the graphite foil-faced boards ensure heat reflection into the furnace interior, and the foil acts as a convection barrier
- Low heat capacity. The material has low density so the small mass of theheat insulating layer allows rapid heating and cooling of the furnace.
- High thermal stability. Rigid graphite boards are stable up to 2800 °C in vacuum and under inert atmospheres
- Shape-retention. The rigid boards do not compress or shrink under normal operating conditions. The bulk density thus remains unchanged throughout the entire insulating layer. The insulating properties stay constant, and no voids, channels or hot spots occur
- Low adsorption of gases and vapours. Due to their small specific surface area, rigid graphite boards adsorb only insignificant amounts of moisture. This allows short evacuation times in vacuum furnaces
- Erosion resistance. The carbon binder secures the felt fibers, thus reducing the amount of particulates entering the furnace atmosphere as a result of high gas velocities. Felts protected by CFC or graphite foil coated surfaces perform even better
- Excellent machining properties. Rigid graphite boards could be machined by using conventional methods such as cutting, drilling, sawing and milling. The clamping pressure should be distributed over large areas to reduce the risk of creating indentations
Applications
- Vacuum heat treatment
- Vacuum brazing
- Hard metal sintering
- Non-oxide ceramic production, e.g. aluminium-nitride, silicon-carbide, boron-nitride, etc.
- Precision casting units
- Carbon fiber production
