stacks are placed into each tool and multiple tools are then placed into a cvi furnace and heated to about 1100 u00b0 c while holding the temperature constant a mixture of 95 natural gas and 5 propane added is fed into the furnace and carbon is deposited into the pores created by carbonization of the matrix resin during the heat up cycle the gas is fed for a period of 100 hours after which the furnace is cooled and the tools are unloaded the rings are weighed and are found to have increased in weight by 25 and have attained a density of 1 45 gm cc each ring is then fed through an automated grinder system which removes the external surface layer deposited on both surfaces and brings the total thickness and parallelism within a tolerance of less than 0 001 34 a metal ring which may have gear teeth on the o d or i d is stamped from a steel sheet the steel sheet has been previously coated with a nitrile phenolic film adhesive such as is available from bfgoodrich adhesive systems the carbon carbon rings are placed on both sides of the adhesive coated metal ring a.