End jointing metal rods for reinforced concrete - by threading upset and hardened ends

摘要

The ends of metal rods, e.g. for reinforced concrete, are joined by heating the ends, upsetting them hot, and threading to fit a threaded jointing sleeve. Between upsetting and threading the hot end of a rod is quickly cooled. Water may be used, either by plunging the end of the rod into it, through jets. The cooling may produce a martensitic or bainitic structure all the way through the end of the rod. Alternatively it may be controlled to produce a surface quench only, to martensitic or bainitic structure, followed by self tempering by the heat remaining in the unquenched core.