An improved sand binder for steel castings

The demand for an environmentally improved sand binder system for steel which does not produce SO2 on casting was satisfied by using a discovery first made in the laboratories of Borden (UK) Ltd in 1952 that alkaline phenolic resins could be gelled using esters. Two processes were developed from this concept, one using liquid esters for the manufacture of small numbers of large castings in jobbing foundries, and the other using the vapour of a very reactive ester for mass–producing repetitive castings. Alkaline phenolic resins cured with esters are only partially crosslinked. On pouring molten metal the bond becomes plastic and absorbs sand expansion before being fully cured. Dimensionally accurate steel castings of excellent surface finish and free from mould–metal reactions and hot tearing are produced. Methods of recycling attrition–reclaimed sand at high levels and avoiding the use of blackings have recently been developed. The annual tonnage of ester–cured phenolic binder is now more than 20 000 tonnes worldwide, evidence of its rapid acceptance since its initial development in the period 1978–1982.