Composite piston ring and process

Claim 1

A composite engine part comprising: a thermoplastic, amide-imide resinous polymeric piston ring having an inner piston-engaging surface for snap-fitting interlocking engagement with a piston and an outer bearing surface for reciprocatingly sliding against a wall of an engine cylinder, said thermoplastic piston ring providing an oil and exhaust gas-impervious barrier and seal between said piston and said cylinder wall for substantially preventing passage of oil and gas exhaust gases therethrough, said piston ring defining a generally radial access opening, said piston-engaging surface having a diameter slightly smaller than the groove-defining piston surface on which it fits, said piston ring comprising a reaction product of a trifunctional carboxylic acid compound and at least one diprimary aromatic diamine, said piston ring further comprising at least one of the following moieties: ##STR8## wherein one carbonyl group is meta to and one carbonyl group is para to each amide group and wherein Z is a trivalent benzene ring or lower-alkyl-substituted trivalent benzene ring, R 1 and R 2 are different and are divalent aromatic hydrocarbon radicals of from 6 to about 10 carbon atoms or two divalent aromatic hydrocarbon radicals of from 6 to about 10 carbon atoms joined directly or by stable linkages selected from the group consisting of --O--, methylene, --CO--, --SO 2 --, and --S-- radicals and wherein said R 1 and R 2 containing units run from about 10 mole percent R 1 containing unit and about 90 mole percent R 2 containing unit to about 90 mole percent R 1 containing unit and about 10 mole percent R 2 containing unit, and said amide-imide resinous polymeric piston ring comprising at least one of said moieties substantially maintaining its shape and structural integrity at engine operating conditions.