Method and apparatus for making a gypsum board

A method for manufacturing a gypsum board comprising:

• depositing a front first cover sheet, having first and second opposed surfaces, over a forming surface and moving the front first cover sheet horizontally in a machine direction along the forming surface;
• optionally depositing a first aqueous gypsum slurry on the front first cover sheet moving in the machine direction to form a first aqueous gypsum slurry layer as a higher-density region in layer form contacting an upper surface of the front first cover sheet, wherein the first aqueous gypsum slurry layer has a first slurry density of 75-100 lbs/ft3;
• depositing a second aqueous gypsum slurry in a foamed state on the first aqueous gypsum slurry layer, if the first aqueous gypsum slurry layer is present, or if the first aqueous gypsum slurry layer is not present depositing the second aqueous gypsum slurry in a foamed state on the front first cover sheet, to form a second aqueous gypsum slurry layer as a middle-density region in layer form contacting an upper surface of the first aqueous gypsum slurry layer, if the first aqueous gypsum slurry layer is present, or if the first aqueous gypsum slurry layer is not present contacting an upper surface of the front first cover sheet, wherein the second aqueous gypsum slurry layer has a second slurry density of 40-65 lbs/ft3, wherein if the first aqueous gypsum slurry is present the second slurry density is lower than the first slurry density, and
• depositing a third aqueous gypsum slurry in a foamed state on the second aqueous gypsum slurry layer to form a third aqueous gypsum slurry layer as a lower-density region in layer form contacting an upper surface of the second aqueous gypsum slurry layer, wherein the third aqueous gypsum slurry layer has a third slurry density of 30-55 lbs/ft3 which is lower than the second aqueous slurry density;
• wherein the optional first aqueous gypsum slurry, the second aqueous gypsum slurry and the third aqueous gypsum slurry comprise a respective mixture of water and stucco, wherein the stucco comprises calcium sulfate hemihydrate, wherein the optional first aqueous gypsum slurry, the second aqueous gypsum slurry and the third aqueous gypsum slurry each comprises a respective mixture of at least 60 wt. % said calcium sulfate hemihydrate on a dry (water free) basis, and the water at a weight ratio of water to the calcium sulfate hemihydrate of 0.2:1 to 1.2:1;
• passing a back second cover sheet, having third and fourth opposed surfaces, over a first transition roller spaced above the front first cover sheet, and subsequently applying the back second cover sheet over the third aqueous gypsum slurry layer, to form a multilayer assembly including the front first cover sheet, optionally the first aqueous gypsum slurry layer on the first cover sheet, the second aqueous gypsum slurry layer on the first layer, if the first layer is present, or if the first layer is not present then the second layer is on the first cover sheet, the third aqueous gypsum slurry layer on the second aqueous gypsum slurry layer, and the back second cover sheet over the third aqueous gypsum slurry layer, with the third surface of the second back cover sheet facing the third aqueous gypsum slurry layer;
• passing the multilayer assembly into a forming station for forming the multilayer assembly;
• setting the calcium sulfate hemihydrate respectively of the optional first aqueous gypsum slurry layer, the second aqueous gypsum slurry layer, and the third aqueous gypsum slurry layer by respectively reacting the calcium sulfate hemihydrate with the water of the optional first aqueous gypsum slurry layer, the second aqueous gypsum slurry layer, and the third aqueous gypsum slurry layer to form a panel comprising a gypsum core of an optional first board layer comprising calcium sulfate dihydrate, a second board layer comprising calcium sulfate dihydrate, and a third board layer comprising calcium sulfate dihydrate between the front first cover sheet and back second cover sheet,
• wherein the first board layer, if present, has a first board layer density, wherein the second board layer has a second board layer density, wherein if the first board layer is present the second board layer density is lower than the first board layer density, and wherein the third board layer has a third board layer density lower than the second board layer density;
• and
• cutting and drying the panel into the gypsum board;
• and
• wherein the method comprises:
• A) said depositing of the third aqueous gypsum slurry to comprise directing the third aqueous gypsum slurry on the third surface of the back second cover sheet, passing the back second cover sheet with the third aqueous gypsum slurry over the first transition roller spaced above the first front cover sheet, while the fourth surface of the back second cover sheet contacts the first transition roller, so that a majority of the third aqueous gypsum slurry falls off the back second cover sheet onto the second aqueous gypsum slurry over the front first cover sheet;
• or
• B) said depositing of the second aqueous gypsum slurry to comprise directing the second aqueous gypsum slurry on the third surface of the back second cover sheet, passing the back second cover sheet with the second aqueous gypsum slurry over the first transition roller spaced above the front first cover sheet, while the fourth surface of the back second cover sheet contacts the first transition roller, so that a majority of the second aqueous gypsum slurry falls off the back second cover sheet onto the deposited first aqueous gypsum slurry if present or, if the first aqueous gypsum slurry is not present, onto the front first cover sheet, and then depositing the third aqueous gypsum slurry onto the deposited second aqueous gypsum slurry.