PURPOSE: To obtain long metal tube which is free of discoloration by the method in which lubrication oil adhered to the inner wall surface of a long metal tube put in a continuous annealing furnace is decomposed to vapor and then the vaporized lubricating oil is removed by suction while introducing a reducing gas into the furnace through the tube.
CONSTITUTION: The long metal tube 3 is transported into the annealing furnace 1 by the holder 2, where during the transporting period for the tube in the temperature at the upset to 480°C, the exhaust pump 6 is actuated. Then, the reducing gas inside the annealing furnace 1 is sucked into the metal tube 3 from its one side and then discharged through the exhaust tube 4 and the flexible tube 5 to its another side. Thus, the decomposed lubricating oil gas is discharged with the reducing gas as a carrier gas. In this way the lubricating oil can be completely removed in the course of heating process for continuous annealing, thus assuring the annealing of long metal tube 3 having inner wall which is free of discoloration.
MATSUMOTO JIYOUJI
TODA KAZUO
