Hot piercing of ingots for tube mfr. - esp copper ingots, which are heated and rolled over mandrel in skew mill in protective atmos. of nitrogen to preclude oxidn. of ingots

摘要

Metal ingots prone to oxidn. when hot, e.g. Cu ingots, are heated in a protective gas atmos. and then fed in a protective atmos. to a skew rolling mill fitted with a stationary mandrel, so each ingot is rolled over the mandrel to make a tube. The pref. atmos. is nitrogen, which also enters the rolling gap so the hot ingot is also protected against oxidn. during rolling. The pref. plant consists of a heating furnace followed by a skew rolling mill; and nitrogen in the furnace flows along tubes surrounding the hot ingot so the latter is shielded from air while being rolled. Ingots with bright surfaces can be heated to the rolling temp. without oxidn. and rolled in the absence of air, so no oxide is rolled into the surface of the tubes.