A vulcanized sheet S1 having formed therein annular articles P1 is prepared at first, which sheet comprises thick external bridges (16) in a thin annular zone (14) and at regular angular intervals so that the bridges connect an external flash (13) to a body (15) of the sheet. A recess (22) is formed centrally of an inner waste (20) surrounded by each article. Then, a guide lug (34) is inserted in the recess to correctly position the article, before tearing by means of a first punch (35) an inner breakable boundary (26) intervening between the article and the inner waste so as to remove the inner waste from the article. Next, a further guide lug (44) is inserted in a space from which the inner waste has been removed, a die having a bore (31a) of a diameter larger than the article supports the sheet, and finally a second punch (45) tears an outer breakable boundary (12) to separate the article from the sheet.