GB491008A - Volatile welding and brazing fluxes - Google Patents

Abstract

In gas-welding or brazing metals and alloys with the aid of an alkyl borate flux mixed with the welding or brazing gas in the vapour state, the flux vapour is obtained by volatilization from a liquid flux consisting of pure alkyl borate or a pure mixture of alkyl borate and an alkyl alcohol which is capable of forming an azeotropic vapour with the borate or one of the borates present, the borate being present in the mixture in an amount sufficient to yield a vapour having a borate concentration at least as great as that in the azeotropic composition. The borate used is preferably methyl, ethyl, propyl, or isopropyl borate or mixtures thereof. For some purposes volatile silicates, e.g. methyl silicate, may be added to the liquid fluxes, to form silica in the welding flame to assist the action of the boron oxide. The compositions which will produce the required borate concentration in the vapour are shown for some mixtures in the drawings. It is preferred to use a liquid having a borate concentration slightly greater than that of the azeotrope, e.g. a mixture of 80 per cent methyl borate and 20 per cent of methyl alcohol. Pure dry compounds are preferably used in making the mixtures. Examples are also given of fluxes containing methyl or ethyl borate and various amounts up to 20 per cent of methyl silicate. The welding or brazing of copper, bronze, brass, low carbon steel, and high chromium ferrous alloys is referred to and the composition of various alloys which may be used for the welding rods is specified, e.g. an alloy containing copper, manganese, and silicon, and alloys containing, besides copper and tin, zinc, lead, or both zinc and lead, or, in another example, zinc, silicon, and iron. Other fluxes referred to in connection with comparative tests are: (a) a paste of boric acid and borax, (b) volatile fluxes obtained from mixtures of methyl alcohol and boric acid or boron oxide, the percentage of methyl borate varying from 7,2 to 76 per cent, and (c) a flux as in (b) containing 76 per cent of borate which has been contacted with activated carbon.