Abstract: A piston for use in a hydraulic cylinder which is subject to sudden and extremely high shock load pressures and high temperature operating conditions is provided with a plurality of interlocking axially-spaced circumferential grooves. A relatively thin, flat washer of heat-formable fluoropolymer is snapped over a retaining ring integral with the piston and the piston is then moved axially through a heated hot-forming cylinder, causing the washer to conform to the cylindrical shape of the piston. At least one circumferential groove has a side wall which is undercut relative to its cylindrical surface to provide a locking angle. Preheating the washer prior to hot-forming the band and forming a sloping ramp in opposition to the undercut side wall result in improved flow of the fluoropolymer toward the undercut side wall. An additional advantage of the preheating is the formation of an improved band skirt with an improved, sharply-defined sealing edge.

Abstract: A piston for use in a hydraulic cylinder which is subject to sudden and extremely high shock load pressures and high temperature operating conditions is provided with a plurality of interlocking axially-spaced circumferential grooves. A band of a heat-formable fluoropolymer is snapped over a retaining ring integral with the piston and the piston is then moved axially through a heated hot-forming cylinder, causing the washer to conform to the cylindrical shape of the piston. At least one circumferential has a side wall which is undercut relative to its cylindrical surface to provide a locking angle. A method of washer preheating prior to hot-forming the band results in better flow of the fluoropolymer toward the undercut side wall. The method of preheating also produces a band skirt with a relatively sharply-defined sealing edge.