Silicon Carbide Mechanical Seals

Topics Covered

Why Use Silicon Carbide?

Graphite Charged Silicon Carbide

Why Use Silicon Carbide?

Silicon carbide is a more expensive seal material the carbon, but it is often used in more demanding applications. For example, blistering is a critical concern with carbon bearing materials. Strangely, the reason why blistering sometimes occurs is not known for certain. The most popular explanation is that a certain amount of material becomes absorbed in the carbon substrate and expands because of frictional heat, thus creating a crater in the seal face. Blistering is most often found in applications involving heavy oils. In some cases, the use of silicon carbide as a mating surface will eliminate a blistering problem.

The surfaces of seal face components made from silicon carbide materials approach the hardness of diamonds and possess outstanding resistance to abrasion. These materials are particularly well suited to corrosive applications and can handle a wide range of temperature extremes. Silicon carbide is an excellent thermal conductor and can be specified where high strength and stiffness are required. One type of silicon carbide is made by exposing specially formulated graphite to silicon vapour. Another is reaction bonded (RBSC), a fine grain alpha silicon carbide matrix that has been infiltrated with molten silicon. A third type consists of high density silicon carbide in granular form that is moulded and sintered at high temperatures to form a solid part.

Graphite Charged Silicon Carbide

Graphite charged silicon carbide has been used as an alternative for hard surface against hard-surface applications. Bonding a silicon carbide matrix with graphite by an infiltration of molten silicon produces this material. It can be used for a high performance pressure-velocity applications and applications where resistance to the pumped solids is crucial.

Primary author: Lawrence Thorwart

Source: Abstracted from Materials World, vol. 2, pp. 519-21, 1994 “The materials key to seal performance”

For more information on Materials World please visit The Institute of Materials