GB615675A - Improvements relating to the manufacture of bi-metal articles by a centrifugal casting operation - Google Patents

Abstract

In the manufacture of bi-metal brake drums and like articles composed wholly or in part of a plurality of integrally united layers of respectively different metals, including a layer of cast iron formed in situ by a centrifugal casting operation, a suitable flux to be applied to the surface on to which the cast iron is to be cast comprises a compound of boron, an alkali or alkaline earth metal, and oxygen (e.g. a borate such as borax, or a calcium salt of boric acid such as colemanite, borocalcite, boronatrocalcite), and a "deoxidiser" having a greater affinity for oxygen than has iron under the conditions of casting and whose oxides are stable under the said conditions in the presence of carbon (e.g. aluminium, calcium silicide, ferro-silicon, calcium manganese silicide, silicon-manganese-zirconium alloys such as that known as "S.M.Z.," or a mixture of any two or more of such substances). There may also be included in the flux boric acid in amounts up to that of the boron compound, an alkali metal silicate or carbonate up to 3 times the amount of the boron compound, reduced iron powder and/or glass up to 25 per cent of the weight of the flux, and a binder, e.g. shellac up to 2 per cent of the weight of flux. The flux may be applied in methylated spirit or other suitable volatile medium, or in water, or directly in powdered form by, for example, spraying. The material "S.M.Z." is said to comprise 60-65 per cent Si, 5-7 per cent Mn, 5-7 per cent Zr, and approximately 20 per cent Fe.