???? >>?????????? >>Processing Carbon Graphite

Carbon graphites are created by combining the two forms of carbon with coal tar pitch. The coal tar pitch acts as a temporary binder that holds the two structures together during the compression moulding process in which near net shapes are formed. Following the moulding operation, the parts are sintered at temperatures high enough to carbonise the coal tar pitch. The result is a structure that is completely carbon bound and contains both carbon and graphite. This structure is extremely strong in compression and will not creep under load. The carbonisation of the temporary binder leaves holes in the structure - on a micro scale the sintered body is a black sponge.

The formation of holes during the processing of a carbon graphite composite has various advantages. The holes can be filled with resins, metals, carbon, or inorganic salts, depending on the planned use of the material, table 2. These fillers serve to improve the strength, thermal conductivity and tribological characteristics of the material. Additionally, carbon-graphite can be sintered to an even higher temperature to convert the entire structure to graphite to provide especially good performance in very high temperature, high speed applications.

Impregnation	Applications
Thermoset resin	General duty to 260°C in water, coolants, fuels, oils. Light chemical solutions, food and drug.
Antimony	Hot water, steam, light hydrocarbons.
Copper or silver	High pressure service to 20.7MNm-2.
Carbon	Highly corrosive environments.
Film formers (fluorides etc)	Extremely dry environments, vacuum or cryogenic.
Oxidation inhibitors (phosphates etc)	High temperature and/or high speed (to 538°C and 240ms-1).

Carbon-Graphites vs Traditional Lubricants
Carbon graphites are used in a wide range of applications where traditional lubricating methods are not appropriate. For example, a typical oil lubricated bearing struggles at temperatures below -40°C because of the high viscosity of the oil. Above 200°C oils carbonise, making them abrasive and ineffective. Graphite bearings are capable of extended use at temperatures above 600°C.

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