Patent ID: 7572344

Claim:
Method for the production of wear-resistant sides for a keystone ring for internal combustion engines, in which a rectangular ring is first formed, consisting of a steel strip having a rectangular cross-section as the base material, having an inner ( 5 a ) and an outer ( 5 b ) circumference surface as well as an upper and a lower side, which ring is subsequently nitrided on all sides by means of a nitriding process, and subsequently brought into its final shape and geometry by means of machining of the surfaces, whereby the base material is exposed at the ring sides ( 3 a , 3 b ) by means of the machining, wherein shaping to form a piston ring having a rectangular cross-section is followed by the following method steps: parallel grinding of the ring sides and grinding of the outer circumference surface to form its intended profile, and brushing of the inner circumference surface; grinding of the upper and lower ring side ( 3 a , 4 a ) to form the keystone ring, in such a manner that the piston ring still has parallel sides ( 3 b , 4 b ) as a stacking surface in the region of its outer circumference surface; complete nitriding of the piston ring surface by means of the gas nitriding process (GNS), to form a nitride layer; shaping of the nitrided piston ring by means of grinding and lapping, without machining of the nitrided sides of the piston ring; stacking of the piston rings by way of their parallel sides, under axial bias, to form a package, and coating of the outer circumference surface of the piston rings with a wear-resistant layer by means of PVD method(s); grinding of the nitride layer of the sides in the de-stacked state, in such a manner that a maximum of one-fourth of the total layer thickness of the nitriding layer is removed.