Cylinder device and method of manufacturing piston rod

A method of manufacturing a piston rod of an automobile suspension device, in which

• a chrome-plated layer is formed on a sliding surface which slides in an axial direction while contacting with an oil seal,
• the sliding surface is configured to repeatedly move in and out between an inside and an outside of the cylinder, and
• the piston rod is configured to move in and out the cylinder accommodating a working fluid therein,
• the method comprising a polishing step performed after the chrome-plated layer is formed,
• wherein the polishing step includes:
• an initial polishing step of polishing with a first polishing film and polishing with a second polishing film having coarser mesh than the first film, to obtain an initial polished surface in which, as a characteristic evaluation parameter of a plateau structure surface described in JIS B 0671-2 (2002) and ISO 13565-2 (1996), a reduced valley depth Rvk is 0.06 μm or more and less than a plating thickness of the chrome plating;
• and
• a finish polishing step of polishing the initial polished surface with a third polishing film having a finer mesh than the first polishing film and the second polishing film to form a plateau surface in which, as lubricity parameters of the plateau structure surface,
• a reduced peak height Rpk is 0 μm or more and 0.04 μm or less, and
• a core roughness depth Rk is 0.08 μm or more and 0.16 μm or less.