Method and apparatus for making a gypsum board

A gypsum board made according to a method for manufacturing a gypsum board comprising:

• depositing a front cover sheet having first and second opposed surfaces over a forming surface, the front cover sheet first surface being a lower surface facing the forming surface and the front cover sheet second surface being an upper surface facing away from the forming surface, and moving the front cover sheet horizontally in a machine direction along the forming surface;
• depositing a first portion of aqueous gypsum slurry over the front cover sheet to form a layer of the first portion of aqueous gypsum slurry as a higher-density region in layer form contacting the upper surface of the front cover sheet,
• moving a back cover sheet having third and fourth opposed surfaces along a back cover sheet path comprising a first path segment and a second path segment downstream of the first path segment, wherein the back cover sheet moves along the first path segment above the higher-density region on the front cover sheet with movement comprising a first vertical movement component and/or a first horizontal movement component, wherein the first vertical movement component being movement in a direction downwards towards the higher-density region on the front cover sheet, wherein the first horizontal movement component being movement in a direction opposite to the machine direction,
• depositing a second portion of aqueous gypsum slurry, which is less dense than the first portion of aqueous gypsum slurry, to contact the third surface of the back cover sheet in the first path segment, wherein the second portion of aqueous gypsum slurry contacts the back cover sheet at an angle of incidence “B” of 0 to 90 degrees relative to the surface of the back cover sheet contacted by the slurry,
• wherein the first portion of aqueous slurry and the second portion of aqueous slurry each comprise a respective mixture of water and stucco, wherein the stucco comprises calcium sulfate hemihydrate, wherein the first portion of aqueous slurry and the second portion of aqueous slurry each comprise 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;
• then at a downstream end of the first path segment passing the back cover sheet with the second portion of aqueous gypsum slurry over a first transition roller spaced a distance above the higher-density region on the front cover sheet, while the fourth surface of the back cover sheet contacts the first transition roller, to deposit a majority by weight of the second portion of aqueous gypsum slurry that dropped away from the back cover sheet on the higher-density region on the front cover sheet, to form a layer of the second portion of aqueous gypsum slurry in a foamed state as a lower-density region in layer form contacting an upper surface of the higher density region, the higher-density region having a higher density than the lower-density region;
• the back cover sheet then passes around the first transition roller to feed the back cover sheet to the second path segment, wherein the second path segment has an upstream end and a downstream end, the upstream end at the first transition roller, and
• at the downstream end of the second path segment depositing the back cover sheet on the second portion of the aqueous gypsum slurry on the face cover sheet to form a multilayer assembly including the back cover sheet on the second portion of the aqueous gypsum slurry;
• passing the multilayer assembly into a forming station for forming the multilayer assembly;
• setting the calcium sulfate hemihydrate of the respective first portion of aqueous gypsum slurry layer and second portion of aqueous gypsum slurry layer by reacting the calcium sulfate hemihydrate with the water of the respective first portion of aqueous slurry layer and the second portion of aqueous gypsum slurry layer to form a panel comprising a gypsum core of respective first and second board layers comprising calcium sulfate dihydrate between the front cover sheet and the back cover sheet;
• wherein the first board layer comprises a set higher-density region as a layer comprising calcium sulfate dihydrate and has a first board layer density;
• wherein the second board layer comprises a set lower-density region as a layer comprising calcium sulfate dihydrate and has a second board layer density lower than the first board layer density, the set higher-density region being interposed between the set lower-density region and the front cover sheet;
• and
• drying the panel and cutting the panel into the gypsum board.