Process for the manufacture of resin-coated refractory particles, preferably sand

A process for the preparation of a composition of refractory granules, comprising:

• 1. reacting 1 mole of at least one member selected from the group consisting of phenol, cresol and xylenol and 1 - 3 moles of at least one member selected from the group consisting of formalin and paraformaldehyde, in the presence of a catalytic amount of at least one member selected from the group consisting of ammonia, a primary amine and a secondary amine at 50.degree. - 70.degree.C for performing an addition-condensation reaction;
• 2. keeping the reaction mixture under reduced pressure at 70.degree.C or lower, as measured by the temperature of the products for dehydration until the products become substantially transparent;
• 3. further keeping the reaction mixture under reduced pressure for removal of aqueous condensate formed by self- condensation until the temperature of the reaction mixture reaches 90.degree. - 120.degree.C;
• 4. quenching the reaction mixture directly upon arrival of the temperature of the reaction mixture at the last mentioned temperature range, thereby forming a resol type phenolic resin having a softening point higher than 80.degree.C;
• and
• 5. thereafter mixing 70 - 100wt. % of said resol type phenolic resin with 0 - 30wt. % of a novalac-type phenolic resin, together with refractory granules kept at a temperature of at least 80.degree.C until the granules attain a freely flowing state.