Thin-walled pyrolytic carbon mouldings - made by CVD on mandrel with pressure equalisation device minimising stress on moulding during cooling and shrinkage of mandrel

摘要

The mouldings are made by the thermal decompsn. of a hydrocarbon cpd. in a reactor, so a deposit is obtd. on a graphite mandrel. The assembly is then cooled so the moulding can be removed from the mandrel. As soon as cooling commences, the mandrel shrinks away from the moulded deposit to leave a cavity which is supplied by the reaction gas to equalise the pressure on both sides of the moulding. The mandrel pref. has an axial hole with a bottom gas inlet; and the top of the hole is closed by a plug. After deposition of the moulding and the commencement of cooling, the mandrel shrinks away from the plug, which adheres to the moulding, so a cavity is provided for pressure equalisation. When the mandrel does not shrink uniformly away from thin-walled mouldings, the latter are subjected to mechanical stress which can fracture the mouldings. The invention eliminates such problems.