GB519931A - Improvements in or relating to methods for heating metals - Google Patents

Abstract

519,931. Heat-treating metals. NESS, H. J. July 27, 1938, No. 22333. [Class 51 (ii)] Furnace atmospheres. In the heat treatment of both ferrous and non-ferrous metals, lithium or a lithium compound such as the carbonate is introduced into the furnace atmosphere in sufficient quantity to prevent oxidation of the metal. In gas or oil fired furnaces the lithiumcontaining material may be injected with the fuel, or it may be supplied separately and combustion should be so controlled that the furnace gases contain a small percentage of carbon monoxide. In the case of electric furnaces the material is injected with powdered carbon or carbon monoxide is supplied to the furnace. The lining of the furnace should be resistant to the action of lithium at the operating temperature and it may be preconditioned by introducing the lithium-containing material while the furnace is at a high temperature or by painting it with an aqueous solution of the material and then heating-up the furnace. Magnesium oxide is preferably used for the lining, but silica-alumina, brick chromium oxide, zirconium oxide and silicon carbide are also suitable. The lining and the fuel should both be free from sulphur. The furnace shown for heating steel blanks 8 is preferably a gas burner 6 and the products of combustion escape through the offtake 7. The lithium-containing material is supplied through the pipe 9 from 'the mixing apparatus described in Specification 519,973, and the quantity is controlled to produce a rich scarlet-coloured flame. The coating of lithium carbonate which forms on the metal can be removed by weak hydrochloric or acetic acid. The lithiated atmosphere facilitates the welding or brazing of metals such as iron or steel by an intermediate metal such as copper, silver or alloys.