Patent ID: 8641841
Filing Date: 2014-02-04
Classification: C21D,F27B,F27D,Y10T

Abstract:
1. A heat treatment method in which an atmosphere-control gas is introduced to a heating chamber having a heating zone, metal tubes are continuously loaded along an axial direction from a furnace entrance, and the metal tubes subjected to a heat treatment are taken out from a furnace exit, the heat treatment method comprising: providing a front chamber including a preheating zone on an entrance side of the heating chamber, the front chamber having seal curtains both at the entrance thereof and at the exit therefrom, setting an internal pressure of a front chamber at a pressure that is greater than atmospheric pressure owing to the in-between entrance seal curtains, but less than the heating chamber pressure owing to the in-between exit seal curtains, so that two levels of pressure are defined inside the furnace to provide a stepwise pressure gradient therein; performing the heat treatment for the metal tubes by heating the metal tubes to a temperature at which an adhered substance on inner and outer surfaces of the metal tubes can be vaporized in the front chamber to produce a contaminant gas and discharging the contaminant gas inside the metal tube to outside of the continuous heat treatment furnace through the rear end of the metal tube as a result of the pressure gradient between the front chamber and outside the continuous heat treatment furnace, and discharging the contaminant gas inside the metal tube through the rear end of the metal tube to the front chamber as a result of the pressure gradient between the heating chamber and the front chamber.