Plaster moulding prodn. avoiding premature setting - by dry mixing lignocellulose fibre and plaster, adding water contg. lignin-sulphonic acid, then accelerator and recycled material

摘要

Prodn. involves: (a) dry mixing fibrous lignocellulose material (I) and CaSO4.1/2H2O powder (II) and opt. storing; (b) adding water contg. ligninsulphonic acid (III) and mixing; (c) adding a mixt. of a latent plaster setting accelerator (IV) and finely ground trimmings (VA) and/or grinding dust (VB) from the mouldings and mixing just before spreading; and (d) spreading the moist and homogeneous compsn. to a moulding and compressing until the plaster has set. Pref. (I) consists of fluffed cellulose or waste paper; the setting retarder (III) is the Na or ammonium sa and (IV) is an alkali metal or ammonium sulphate or water glass and is used as soln. absorbed by a superabsorber (VI), which can absorb up to 34 times its own wt. of salt soln., or in capsules (VII) fractured on pressing. USE/ADVANTAGE - The process is used for making fibre-reinforced plasterboard. It prevents premature setting.