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B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
B21C37/00—Manufacture of metal sheets, rods, wire, tubes, profiles or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
B21C37/06—Manufacture of metal sheets, rods, wire, tubes, profiles or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
B21C37/15—Making tubes of special shape; Making tube fittings
B21C37/20—Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes or tubes with decorated walls
B21C37/205—Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes or tubes with decorated walls with annular guides
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FR573873D1923-11-281923-11-28 Metal duct with a large radiant surface and its manufacturing processExpiredFR573873A (en)