GB798064A - Improvements in or relating to shell moulding sand - Google Patents

Abstract

A resin coated free-flowing sand is made by mixing in the absence of a condensation catalyst, a heat stable resin and a mass of sand heated sufficiently to cause said resin to coat the individual sand grains, mixing a second batch of sand, a condensation catalyst and a second resin capable of ready condensation when heated in the presence of said catalyst, said second mixing operation being conducted at a temperature too low to permit substantial condensation of said second resin, and mixing the two sand/resin mixtures while the heated mixture retains a substantial amount of heat. In Examples (1) and (2), sand is mulled with a liquid "A"-stage phenolformaldehyde resin in the presence of hexamethylene tetramine and ammonium hydroxide and mixed with a second batch of sand previously coated at 300 DEG F. with a phenol-formaldehyde novolak resin; (3) sand is mixed with an ammonium chloride catalysed novolak resin in the presence of hexamethylene tetramine and magnesium stearate and mixed with a second batch of sand previously mulled at 250 DEG to 350 DEG F. with a solid or liquid novolak resin; Example (4) is a modification of Example (1) in which part or all of the sand is omitted from the cold muller.ALSO:A pre-flowing moulding sand is made by mixing in the absence of a condensation catalyst, a heat stable resin and a mass of sand heated sufficiently to cause said resin to coat the individual sand grains, mixing a second batch of sand, a condensation catalyst and a second resin capable of ready condensation when heated in the presence of said catalyst, said second mixing operation being conducted at a temperature too low to permit substantial condensation of said second resin and mixing the two sand/resin mixtures while the heated mixture retains a substantial amount of heat. In Examples (1) and (2), sand is mulled with a liquid "A"-stage phenol-formaldehyde resin in the presence of hexamethylene tetramine and ammonium hydroxide and mixed with a second batch of sand previously coated at 300 DEG F. with a phenol-formaldehyde novolak resin; (3) sand is mixed with an ammonium chloride catalysed novolak resin in the presence of hexamethylene tetramine and magnesium stearate and mixed with a second batch of sand previously mulled at 250-300 DEG F. with a solid or liquid novolak resin; Example (4) is a modification of Example (1) in which part or all of the sand is omitted from the cold muller. The compositions are used for producing moulding shells.