Phenol-formaldehyde novolak binder for foundry sand - contg. urea cpd for increased build up and cure rates of moulds and cores

摘要

A resin coated sand, for foundry cores and moulds, comprises (a) particles of sand coated with 1-8, pref. 1-6 wt.% of P-F novalak resin, (b) curing agent, pref. hexaomethylene tetramine, and (c) 115, pref. 1.5-3.5 wt. % ( on P-F resin) of a urea cpd. selected from (ethylene) urea and/or propylene urea. The incorpn. of (c) increases the build up rate and cure rate of the coated sand and both the invest time and cure time can be reduced in the mfr. of cores and moulds by the shell process. Hot and cold tensile strength of cores and moulds are increased.