PURPOSE: To obtain a good welded tube effectively without requiring any complicated forming equipment by introducing a beltlike material from large-diameter side entrance of a tube forming die, bending it continuously, and welding butted ends through a slit.
CONSTITUTION: The tube forming die 2 is formed of a forming section 4 having a circular truncated conical inner face 8 and a welding section 6 that continues to the small-diameter side exit of the forming section 4. The beltlike material H is introduced from the lrge-diameter side entrance of the forming section 4, advanced in the circular truncated conical inner face 8 and bent gradually to a cylindrical form. This skelp is introduced to the cylindrical inner face of the welding section 6, and butted ends are welded by a welding torch 20 through a welding hole of a slit 18 formed in the welding section 6. The welded part is shifted along the slit 18. By this way, even a thin tube can be manufactured at high roundness.
KUZUHARA HARUYA
OKUI MASAHISA
NANBA KEIZOU
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