Process for welding cylindrical container bodies

Abstract

The process relates to the welding of the cylindrical bodies of food cans in which the body is rolled with edges overlapping along a longitudinal welding line between resistance welding electrodes. The ratio of the radius of curvature of a first electrode with respect to the second is at least equal to 1.2. The material constituting the body is mild steel sheet having on one face at least, a protective conductive coating whose contact resistivity with respect to copper is at least 10.sup.-5 ohm/cm.sup.2. A material is selected having a ratio of the contact resistivity of a first face to that of the second at least equal to 1.2, and the material is rolled in such a way that the first face is in contact with the first electrode. The preferred materials have on each face a layer of tin of at the most 1.05 g/m.sup.2 and a composite layer of metallic chromium (5-140 mg/m.sup.2) and of chromium in oxidized form (1-30 mg/m.sup.2), the thickness of tin on the first face being less than that on the second and/or the thickness of chromium of the second face being less than that of the first. The use of the asymmetry of contact resistivity as defined, increases the latitude of welding (width of the range of angle of conduction of the welding voltage). Reversal of the asymmetry cancels the latitude of welding.