GB876493A - Improvements in or relating to the preparation of sand for moulding - Google Patents

Abstract

Production of resin coated sand particles for use in the production of shell moulds comprises, mixing the sand with a thermosettable phenol-formaldehyde condensation product, containing free steam-volatile phenol, at a temperature in excess of 100 DEG C. and above the melting point of the condensation product, adding water in an amount sufficient to remove the free phenol by vaporisation in association with the steam produced, continuing to mix the sand and condensation product until discrete sand particles individually coated with resin are formed, and adding hexamethylene-tetramine to the mixture in an amount sufficient to convert the condensation product to a thermoset resin on subsequent heating, during, or subsequent to, the water addition. Where hexamethylene-tetramine is added prior to the formation of discrete sand particles the temperature of the mixture is maintained at least at that obtaining at the time of addition of the hexamethylene-tetramine until particles are formed. A phenol-formaldehyde condensation product containing a molar ratio phenol:formaldehyde of 1:0.4 to 1:0.9 preferably 1:0.72 to 1:0.76 containing 2-10% wt. of free steam-volatile phenol is added in an amount of 2-10% wt. to sand preheated to a temperature of 120-160 DEG C., in a mechanical mixer. Sufficient water, preheated, if desired, to maintain the temperature of the mix, is added, and to facilitate rapid evaporation external heating by a steam jacket, a radiant heater, or hot air may be applied. Hexamethylene tetramine in amount from 5-20% wt. of the resin is added either as such subsequent to the water, or as a solution therein, and the temperature of the mix is maintained together with continued stirring until discrete particles are formed. Any small aggregates may be finally broken down by tumbling in a rotary drum. Specification 753,163 is referred to.