Carbon-Graphite Seals

Seal materials require high strength and a relatively high modulus of elasticity to withstand deformation at the interface. Carbon-graphite seal materials provide the strength and rigidity which are especially important in high pressure, zero leakage mechanical end-face seals. High thermal conductivity is essential in removing heat from the interface.

Seal wear is a result of adhesive wear, chemical wear, erosive wear and sometimes radioactive wear. Carbon-graphite is inert to most chemical reagents so it survives where other materials fail. However, chemical wear is evidenced in certain strong oxidising environments or where the additives are attacked by specific oxidising reagents.

Impregnation of Carbon-Graphite Seals
Impregnation of carbon seals can be done with a variety of materials to control permeability. In addition to thermoset resins, other types of impregnants include thermoplastics, metals, and inorganic salts or glasses. The temperature limit of the impregnant places an upper limit on the operating temperature of the carbon parts.

Metals such as antimony, silver, copper, nickel, and babbitt can improve the strength, thermal conductivity, and tribological characteristics of the materials. Impregnants made of inorganic salts usually phosphate or borate - and glasses are used in high temperature applications. Carbons impregnated with soluble salts must be handled carefully to avoid exudation, especially under humid conditions, but loss of impregnant rarely affects any physical property of a seal other than permeability.


Carbon-Graphite Seals in Aerospace Applications
Carbon-graphite and graphites are excellent materials for aircraft turbine engine mainshaft seals. The mainshaft in a turbine engine rotates at very high speeds and operates in an environment of changing high temperature conditions. Mainshaft bearing compartment seals are used to protect rotor support bearings from hot gases flowing through the engine and to prevent the loss of lubricant in the bearing compartments.