Carnaud S.a.

Claude Mergey

Raymond Allouf

Patrice Robichon

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.

Process for welding cylindrical container bodies

The invention relates to mild steel sheet, having deposited on at least one of its major faces a sub-layer of tin in an amount of 0.1 to 1.05 g/l and a composite coating containing chronmium and chronmium oxide. The content of chromium in the composite coating is more than 5 .mu.g/cm.sup.2 while the content of chromium oxide in the coating, expressed in terms of chromium, is less than 2.5 .mu.g/cm.sup.2. The resultant sheets give improved welds when joined by electric welding and are particularly suited for making can bodies for food cans.

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Ville d'Avray, France

Claude Mergey