Manufacture of gypsum board from FGD gypsum
AssigneeNational Gypsum Company
InventorEdward A. Burkard
Life of this patent
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Abstract
By-product gypsum, which is formed during a flue gas desulfurization process, (FGD gypsum) is carefully formed as an aqueous slurry of crystals having a mean particle diameter of between about 35 microns and 80 microns and filtered, which filter cake is substantially completely dried before calcination, without any substantial grinding action, the crystals are then flash calcined to a hemihydrate, then ground, to reduce consistency, and then formed into an aqueous slurry from which a paper-covered gypsum board is formed of superior core quality.
Claims18
The method of making gypsum wallboard comprising the steps of removing substantially all of the free moisture from an about 94% to 98% pure gypsum filter cake of about 35 to 80 micron average particle diameter FGD dihydrate gypsum while avoiding any substantial reduction of particle size of said gypsum other than the breaking up of agglomerates of particles, flash calcining said dried FGD gypsum to about 25% of the water of hydration producing FGD hemihydrate gypsum, grinding at least about 25% of said calcined gypsum to produce a Fisher surface area of material of at least about 2500 cm.sup.2 /gm, said surface area being measured on the product as ground if 100% of the calcined gypsum is ground and on a blend of the ground product with the unground portion if less than 100% of the calcined gypsum is ground, mixing said post-ground calcined gypsum with water and a lightweight aggregate, and forming the resultant aqueous slurry into board form between opposed paper face sheets.
Dependencies are inferred from the claim text.