Treating sheet metal in open coil bobbins

摘要

An open coil bobbin 5 of sheet metal, e.g. steel is treated in a furnace 1, particularly to decarburize and denitride it so as to render it non-ageing, in which an internal rotary impeller 7 is used to blow gas, such as HNX gas supplied from gasometer 19, between the coils of the bobbin during heating up, by blocking the impeller inlet or outlet, e.g. with baffle 12 using weights and pulleys, and blowing wet hydrogen between the coils by means placed outside the furnace, such as reservoir 18, during soaking, e.g. at 700 DEG C. The inlet or outlet of the impeller may also be blocked during all or part of the heating up and cooling, during which HNX gas is circulated through the furnace via a refrigerator. A heat exchanger 14 may be used to transfer heat from gas leaving the furnace via duct 11 to gas entering via duct 9.