Patent ID: 7470338

Claim:
A process for manufacturing plasterboard, comprising the following steps: feeding a first addition into a screw conveyor at a first inlet, wherein the first addition comprises hydratable calcium sulphate and water, wherein the screw conveyor conveys in a downstream direction; withdrawing a first feed from a first outlet of the screw conveyor; withdrawing a second feed from a second outlet of the screw conveyor; feeding a second addition into the screw conveyor at second inlet, wherein the second inlet is downstream from the first inlet, first outlet and second outlet; withdrawing a third feed from a third outlet of the screw conveyor, wherein the third outlet is downstream from the second inlet, wherein the first and second feed have a different composition from the third feed; feeding the first feed into a first mixer; feeding the third feed into a second mixer that is independent of the first mixer; feeding in a facing; preparing a first gypsum slurry in the first mixer; preparing a second gypsum slurry in the second mixer; applying the first gypsum slurry onto the facing and forming a crude surface layer; applying the second gypsum slurry onto the crude surface layer and forming a crude core layer that has a different composition to that of the crude surface layer; feeding in a second facing; feeding the second feed into a third mixer; preparing a third gypsum slurry in the third mixer; wherein the third mixer is independent of first mixer and the second mixer; wherein the first, second and third mixers are arranged in parallel and not in series; applying the third gypsum slurry onto the second facing and forming a second crude surface layer with a different composition than that of the crude core layer; applying the second crude surface layer onto the crude core layer; forming a crude plasterboard; and hydrating and drying the plasterboard.