A PISTON OR PLUNGER AND A METHOD FOR MAKING THE SAME

摘要

A piston or plunger comprises a piston body (10), preferably made from metal, and a sleeve or sealing member (19) made from a deformable material, such as polytetrafluoroethylene (PTFE). The sealing member (19) is mounted on the piston body (10) by passing an annular sealing member blank (21) with an inner diameter, which is substantially smaller than the maximum diameter of the central outer cylindrical surface part (13), around a first end of the piston body and by moving it towards said first circular edge (11), while the sealing member blank (12) is deformed into tight engagement with the central outer cylindrical surface part (13) and into the grooves or depressions (13) formed therein. In this manner a tubular sealing member (19), which extends axially along the central outer surface part, and which has opposite first and second ends extending beyond said first and second circular edges (11, 12), respectively, is formed. Thereby both of these opposite end portions of the tubular sealing member may function as sealing lips (20). Preferably, the piston body has a stepped configuration with opposite end portions (14, 15) extending from said central outer cylindrical surface par (13), and the outer diameter of each of the end portions is smaller than the diameter of the central outer cylindrical. Thus, said first and second edges (11, 12) separate the central surface part (13) from the opposite end portions (14, 15).