SIGRAFINE® Fine-Grain Graphite

Synthetic graphite materials with a mean grain size less than four millimeters are labeled as fine and medium grain graphite. The ability to influence specific material properties by varying raw materials, their processing, and the manufacturing technology makes these an indispensable key material for many applications.

With isostatic, extruded, vibration and die molded graphite SGL Group’s portfolio comprises the whole range of fine and medium grain graphites. This allows us to select the best material for you requirements.

To extend the service life of our graphite components and to achieve high-purity surface structures, we also offer surface coating e.g. with silicon carbide (SiC).

All our fine and medium grain graphites are marketed under the new common brand name SIGRAFINE®. Materials were previously known under RINGSDORFF®, SIGRAFORM®, SIGRAMENT®, and CRYSTA-SIL®.

Fine-grain graphite manufacturing

The production processes for synthetic carbon and graphite materials are equivalent to those applied in the ceramic industry. The solid raw materials coke and graphite are first milled and then mixed with binder pitch in mixers. Afterwards the shaping process such as isostatic pressing, extrusion, vibration molding, or die molding takes place. The shaped bodies, called “green” material, are then carbonized in an oxygen free environment and graphitized before they can undergo further mechanical processing to be turned into complex shapes. Optional further refinements such as purification and coating e.g. with silicon carbide are possible.

More information

Isostatic graphite is an ultra fine grain graphite used for applications where the mechanical properties of other fine grain graphites are inadequate. Its name is derived from the method of production: During the forming process the material is isostatically pressed i.e. with equal pressure from every side. Therefore the material shows typically an isotropic property behavior. 

Typical properties of the material

  • Highly mechanically stable
  • High-dense
  • Isotropic
  • Little wettable

Extruded graphite is produced in an extrusion process. In contrast to isostatic graphite, extruded graphite has a coarser grain size and a lower strength but higher thermal and electrical conductivity.

Vibration molded graphite is characterized by a homogeneous structure and typically a medium grain size. The material shows a planar isotropic property behavior and can be produced in large formats.

Typical properties of the materials

  • Thermally and electrically conductive
  • Resistant to bending
  • Chemically resistant
  • Resistant to thermal shock

The material class of die molded carbon and graphite contains amorphous carbon as well as graphite and the so-called carbon graphite, a composite material containing both hard carbon and graphite.

The materials have a fine to ultrafine granulation and can also show a high anisotropy due to the axial forming process. Extremely wide property profiles result from this large material variety with regard to mechanical strength, friction, and conductivity.

Materials were designed for example to match specific tribological or electrical properties. These can be even further enhanced by impregnation with resins, phosphates, or metals. In contrast to the other synthetic graphite shaping processes the die molding technology also allows for applying the pressed to size technology (PTS). This near net shape pressing is highly efficient and is of considerable advantage since complex parts can be produced in high volumes, cost efficient, and with minimum material input.

Typical properties of the material

  • Excellent media resistant
  • Low-wear
  • Long term stable
  • Taylor made properties

With a SiC coating the service life of graphite components can be extended. At the same time high-purity, inert, and dense surface structures are realized, required e.g. in processing semiconductor materials. Typical coating thicknesses are in the range of 100 µm.

Typical properties of the material

  • Dense
  • Wear resistant
  • Temperature and oxidation resistant
  • Highly thermally conductive

SiC coating process

Silicon carbide is deposited as thin layers on fine grain graphite and carbon fiber-reinforced carbon by CVD (chemical vapor deposition). Deposition takes typically place at temperatures of 1200-1300 °C. The thermal expansion behavior of the substrate material should be adapted to the SiC coating to minimize thermal stresses. 

Main applications of our SIGRAFINE SiC Coating

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