Method for manufacturing long metal stopper caps comprising a skirt having a constant thickness

A method for manufacturing one or more metal sealing caps comprising successively:

• a) providing a strip or sheet, of aluminum alloy, having a roughness Ra in accordance with NF EN ISO 4287 standard (December 1998) of 0.2 to 0.8 μm, coated on both faces thereof with a layer of varnish;
• b) conducting a first cutting operation to obtain disks referred to as blanks;
• c) a stamping said blanks, in one or more passes, optionally using a stamping lubricant, so as to form a stamped preform, comprising a head and a skirt;
• c′) at least one drawing comprising passing the stamped preform through at least one drawing ring in order to lengthen the metal and make said metal thinner, so as to form a cap comprising a head and a skirt, the top of the cap being on a head side and a bottom of the cap on a side where the skirt ends, the skirt having a constant thickness of 0.12 to 0.27 mm, over at least 20% of the length thereof starting from the bottom of the cap, and comprising the continuous layer of varnish intact over an entire length of the skirt, on both inside and outside of the cap, wherein the skirt of the cap has a length of 40 to 85 mm;
• d) optionally degreasing said cap;
• e) optionally printing and/or finishing varnishing for protection and/or decoration.