Method of making a rolled metal piston ring

In a method of forming a piston ring comprising a steel strip of split ring shape and having a pair of sidewalls extending radially outwardly of an intermediate wall and which piston ring has at its outer periphery a pair of axially spaced cylindrical surfaces each located at the outer end of converging radially outwardly extending portions of the strip and which portions have confronting surfaces which abut from the inner apex toward said intermediate wall for at least part of the outward radial extent of said converging portions to provide a pair of axially spaced rigid rims, the steps of providing a strip of steel of uniform width and thickness and which strip has opposite major sufaces and opposite edges, progressively moving said strip through a series of metal forming stations, forming said strip into a channel-form shape having parallel sidewalls extending in one direction with respect to an intermediate wall and a pair of parallel V-shaped projections extending in the opposite direction with respect to the intermediate wall, each V-shaped projection having converging portions, squeezing said converging portions of each of said projections to bring the inner surfaces thereof into abutting engagement by applying forces thereto acting transversely to the direction of movement of the strip to form a pair of transversely spaced rigid rims, and shaping the outer end of the first and second portions to provide a flat outer surface on each of the rigid rims.

In an apparatus for forming a piston ring for location in a circumferential groove in a piston movable in a cylinder bore of an internal combustion engine, which piston ring comprises a steel strip of split ring shape and having an intermediate wall portion and a pair of sidewalls extending radially inwardly therefrom, said ring having at its outer periphery a pair of cylindrical surfaces for engagement with the cylinder bore and which are located at the outer ends, respectively, of parallel solid rigid rims which extend radially outwardly with respect to the intermediate wall portion, and which apparatus includes means for forming a steel strip into a cross section having an intermediate wall portion and sidewalls extending in one direction therefrom and a pair of rims extending in the other direction therefrom, means for coiling the formed steel strip into a helical coil with the sidewall portions extending radially inwardly and the solid rigid rims extending radially outwardly, means for slitting said helical coil lengthwise to form individual piston rings, means for forming spaced vent openings in said intermediate wall portion prior to coiling said strip into a helical coil, means for hardening said steel strip, and means for surface finishing the piston ring coils, the improvement wherein said means for forming a steel strip comprises means for feeding a strip of steel of uniform width and thickness and which strip has opposite major faces and opposite edges through a series of metal forming stations, means at said stations for progressively bending said strip into a channel-form shape having an intermediate wall portion with sidewall portions extending in one direction therefrom and with a pair of parallel solid rigid rim portions extending in the opposite directon from said intermediate wall, said stations including roll means for deforming out of the intermediate wall portion a pair of parallel V-shaped projections each comprising converging portions having inner and outer faces terminating in and inner apex and an outer end, respectively, and separate roll means for bringing said inner faces into abutment with each other from said inner apex toward said intermediate wall for at least a portion of the distance between said inner apex and said intermediate wall, and roll means at one of said stations for forming flat surfaces at the outer end of each of said V-shaped projections during the progressive formation of said strip.