Patent ID: 8631736

Claim:
Two-part piston ( 1 ) for an internal combustion engine, consisting of an upper part ( 2 ), and a lower part ( 3 ) screwed onto the upper piston part, having a piston crown ( 6 ) formed by the upper part ( 2 ), and a piston skirt ( 22 ) formed by the lower part ( 3 ), which skirt has two pin bores ( 23 , 24 ) that lie opposite one another, having a circumferential cooling channel ( 8 ) disposed radially on the outside, close to the piston crown ( 6 ), which is formed partly into the upper part ( 2 ) and partly into the lower part ( 3 ), which is delimited, radially on the outside, by a ring wall ( 9 ) connected with the piston crown ( 6 ), and a circumferential collar ( 27 ) affixed to the upper side of the lower part ( 3 ), and which is delimited, radially on the inside, partly by a circumferential upper ring rib ( 10 ) formed onto the underside of the upper part ( 2 ), facing away from the piston crown, and partly by a circumferential lower ring rib ( 11 ), affixed to the upper side of the lower part ( 3 ), on the side facing the piston crown, whereby the upper part ( 2 ) and the lower part ( 3 ) stand in contact with one another, partly by way of inner supporting surfaces ( 25 , 26 ) that delimit the underside of the upper ring rib ( 10 ) and the upper side of the lower ring rib ( 11 ), and partly by way of outer supporting surfaces ( 28 , 29 ) that delimit the underside of the ring wall ( 9 ) and the upper side of the collar ( 27 ), wherein at least one of the supporting surfaces ( 25 , 26 , 28 , 29 ) is covered with a chrome layer ( 30 ) that has a structured surface, having a plurality of elevations and depressions, and wherein the chrome layer is formed by application of an electrochemical method which triggers seed formation processes of the chrome on said at least one of the supporting surfaces by means of electrical voltage pulses, so that the structured surface has buds or nubs.