Encapsulating liq hardener in water-repellent powders - to promote hardening of casting compsns partic sand casting moulds and cores contg isocyanate or silicate binder

摘要

Hardening agent-contg. liqs. disclosed in Parent Patent are enclosed in microcapsules formed of water-repellent powder and admixed to moulding compsn. while charging to moulding box, e.g. by injection. Capsule walls are destroyed to release hardener, pref. consisting of aq. solns. of (i) tert. amines, tert. amine salts or quat ammonium cpds., partic. for moulding compsns. contg. isocyanate binders, or hexamethylene tetramine mixed with aromatic amines or aromatic hydroxycarboxylic acids, (ii) (in)org. acids, esp. for silicate binder-contg. compsns. Water-repellent powder may be (a) treated minerals with stratified layer structure, e.g. fatty amine-heated bentonite, (b) colloidal silicic acid derivs., (c) metal esp. Al salts of higher carboxylic acids and/or (d) waxy materials.