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

Method for manufacturing one or more metal sealing caps comprising successively:

• a) providing a strip or sheet, of aluminum alloy, optionally having a roughness Ra in accordance with NF EN ISO 4287 standard (December 1998) of 0.2 to 0.8 μm, optionally from 0.2 to 0.6 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 at least two passes, optionally two or three passes, optionally two 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, optionally from 0.15 to 0.25 mm, over at least 20% of the length thereof starting from the bottom of the cap and optionally up to 60% of length thereof starting from the bottom of the cap, and comprising a continuous layer of varnish intact over an entire length of the skirt, on both inside and outside of the cap;
• d) optionally degreasing said cap;
• e) optionally printing and/or finishing varnishing for protection and/or decoration.