Gypsum mould regeneration - by drying, breaking up, firing, grinding and stirring with water, strengthener and setting retarder

摘要

Regenerating spent or o d-range gypsum moulds, to gypsum mould comprises, esp. for ceramic industry, comprises (1) drying the spent moulds to 2 wt. % free water content, (2) breaking up to 2 cm grein-size, (3) firing to =200 degrees C until free from dihydrate and esp. contg. is approx. 2 wt.% water of crystallisation, (4) finely grinding to 200 mu grain-size while supplying cold air and (5) strongly stirring for 6-20 (8-14) min. with addn. of water, a strengtheners and a setting retarder. Pref. strengtheners are (a) strong liquefiers, esp. highly condensed, high mol wt. water-soluble aminoplasts based on melamine-HCHO modified at least at one NH2 by sulphite on sulphonic acid or by (in) organic amides or (b) water-soluble polysilicic acids, and are added in 0.4-1.5 wt. % concn., w.r.t. solids.