METHOD AND APPARATUS FOR MAKING A GYPSUM BOARD

1 . 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.

2 . The gypsum board of claim 1 , wherein the back cover sheet moves along a downstream portion of the first path segment with movement along a slope defining an angle “A” between the back cover sheet in the downstream portion of the first path segment and the front cover sheet on the forming surface of 0 to 90 degrees.

3 . The gypsum board of claim 1 , wherein the discharge of calcined gypsum core slurry is in a direction of counter current flow with direction of movement of the back cover sheet, or the discharge of calcined gypsum core slurry is in a direction of concurrent flow with the direction of movement of the back cover sheet.

4 . The gypsum board of claim 1 , wherein the first transition roller changes the direction of movement of the back cover sheet to movement along a first portion of the second path segment that has a second horizontal movement component in the machine direction and a second vertical movement component, the second vertical movement component being upwards, or downwards, or neutral to provide movement only along the second horizontal movement component.

5 . The gypsum board of claim 1 , wherein the first transition roller is a freewheeling roller.

6 . The gypsum board of claim 1 , wherein the second path segment has a first portion and a second portion, wherein at a downstream end of the first portion of the second path segment the back cover sheet passes over a second transition roller to feed the back cover sheet to the second portion of the second path segment and change the direction of movement of the back cover sheet.

7 . The gypsum board of claim 1 , wherein at the downstream end of the second path segment the multilayer assembly includes the first portion of aqueous gypsum slurry layer on the front cover sheet, the second portion of aqueous gypsum slurry layer on the first portion of aqueous gypsum slurry layer, and the back cover sheet on the second portion of aqueous gypsum slurry layer.

8 . The gypsum board of claim 1 , wherein the forming of the layer of the aqueous gypsum slurry as a higher-density region in layer form contacting an upper surface of the front cover sheet comprises passing the front cover sheet under a slurry roller to spread the slurry of the higher-density region.

9 . The gypsum board of claim 1 , wherein the discharge of calcined gypsum core slurry is in a direction of concurrent flow with the first direction of back cover sheet travel.

10 . The gypsum board of claim 1 , the discharge of calcined gypsum core slurry is in a direction of counter current flow with the first direction of back cover sheet travel.

11 . The gypsum board of claim 1 , wherein the slurry mixer discharges the calcined gypsum core slurry onto a portion of the back-cover sheet supported by a back-plate.

12 . The gypsum board of claim 6 , wherein the second transition roller is a freewheeling roller or a driven roller.

13 . The gypsum board of claim 6 , wherein the second transition roller is a bare-center shaft roller having a central shaft of a first diameter and opposed cylindrical end portions of a second diameter, wherein the second diameter is larger than the first diameter.

14 . The gypsum board of claim 6 , wherein the second transition roller is at a sufficiently raised position relative to the front cover sheet moving along the forming surface for a head of aqueous gypsum slurry at the downstream end of the third path segment to be visible to an operator.

15 . The gypsum board of claim 1 , wherein the front cover sheet comprises at least one of a glass mat facer sheet or a paper facer sheet.

16 . The gypsum board of claim 1 ,

wherein the lower-density region resulting from the set gypsum lower-density region slurry has a thickness of 0.25 inches to 1.5 inches;

wherein the higher-density region has a thickness of about 0.02 inches to about 0.75 inches;

wherein the lower-density region has a density of 15 to 55 pounds/cubic foot, and

wherein the higher-density region has a density of 25 to 70 pounds/cubic foot.

17 . An apparatus to manufacture a gypsum board according to the method of claim 1 , comprising:

a forming surface for depositing thereon a front cover sheet and moving the front cover sheet horizontally in a machine direction along the forming surface;

a source of a first portion of the aqueous gypsum slurry in an unfoamed state for depositing the first portion of the aqueous gypsum slurry over the front cover sheet to form a layer of the aqueous gypsum slurry as a higher-density region in layer form contacting an upper surface of the front cover sheet, wherein the first aqueous gypsum slurry layer has a first slurry density,

a back cover sheet drive comprising a first transition roller for moving a back cover sheet along a back cover sheet path comprising a first path segment and a second path segment,

wherein the first path segment is adapted and configured for moving the back cover sheet 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,

a source of a second portion of the aqueous gypsum slurry, which is less dense than the first portion of the aqueous gypsum slurry, to contact a surface of the back cover sheet in the first path segment, wherein the second portion of the 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 second portion of the aqueous gypsum slurry,

the first transition roller at a downstream end of the first path segment for passing the back cover sheet 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, wherein the second path segment upstream end is at the first transition roller,

the first transition roller is spaced a distance above the higher-density region on the front cover sheet for passing the second portion of the aqueous gypsum slurry over the first transition roller to deposit a majority by weight of the second portion of the aqueous gypsum slurry that dropped away from the back cover sheet on the higher-density region on the front cover sheet,

wherein the first portion of aqueous gypsum slurry and second portion of aqueous gypsum slurry comprise a respective mixture of water and stucco, wherein the stucco comprises calcium sulfate hemihydrate, wherein the first portion of aqueous gypsum slurry and second portion of aqueous gypsum slurry respectively comprise a 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; and

the downstream end of the second path segment located for depositing the back cover sheet on the second portion of the aqueous gypsum slurry on the front cover sheet to form a multilayer assembly including the back cover sheet on the second portion of the aqueous gypsum slurry;

a forming station for forming the multilayer assembly;

setting the calcium sulfate hemihydrate to form a panel comprising a gypsum core comprising calcium sulfate dihydrate; and

wherein the first portion of the gypsum slurry is forms a higher-density region in layer form contacting the front cover sheet;

wherein the second portion of the gypsum slurry is in a foamed state as a lower-density region contacting the higher-density region, the higher-density region having a higher density than the lower-density region; and

wherein the board core comprises a set lower-density region comprising calcium sulfate dihydrate and a set higher-density region comprising calcium sulfate dihydrate, the set higher-density region being interposed as a layer between the set lower-density region and the front cover sheet.

18 . An apparatus to manufacture a gypsum board according to the method of claim 1 , comprising:

a mixer for preparing an aqueous gypsum slurry comprising a mixture of water, and stucco, wherein the stucco comprises calcium sulfate hemihydrate, wherein the aqueous gypsum slurry comprises a 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; and

a forming surface for depositing thereon a front cover sheet and moving the front cover sheet horizontally in a machine direction along the forming surface;

a source of a first portion of the aqueous gypsum slurry in an unfoamed state for depositing the first portion of the aqueous gypsum slurry over the front cover sheet to form a layer of the aqueous gypsum slurry as a higher-density region in layer form contacting an upper surface of the front cover sheet,

a back cover sheet drive comprising a first transition roller and a second transition roller for moving a back cover sheet along a back cover sheet path comprising a first path segment and a second path segment,

wherein the first path segment is adapted and configured for moving the back cover sheet 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,

a source of a second portion of the aqueous gypsum slurry, which is less dense than the first portion of the aqueous gypsum slurry, to contact a surface of the back cover sheet in the first path segment, wherein the slurry contacts the back paper at an angle of incidence “B” of 0 to 90 degrees relative to the surface of the back cover sheet contacted by the slurry,

the first transition roller at a downstream end of the first path segment for passing the back cover sheet around the first transition to feed the back cover sheet to the second path segment, wherein the second path segment has an upstream end and a downstream end, wherein the second path segment upstream end is at the first transition roller,

the first transition roller is spaced a distance above the higher-density region on the front cover sheet for passing the second portion of the aqueous gypsum slurry over the first transition roller to deposit a majority by weight of the second portion of the aqueous gypsum slurry that dropped away from the back cover sheet on the higher-density region on the front cover sheet,

the downstream end of the second path segment located for depositing the back cover sheet on the second portion of the aqueous gypsum slurry on the front cover sheet to form a multilayer assembly including the back cover sheet on the second portion of the aqueous gypsum slurry;

a forming station for forming the multilayer assembly;

setting the calcium sulfate hemihydrate to form a panel comprising a gypsum core comprising calcium sulfate dihydrate; and

wherein the first portion of the gypsum slurry is forms a higher-density region in layer form contacting the front cover sheet;

wherein the second portion of the gypsum slurry is in a foamed state as a lower-density region contacting the higher-density region, the higher-density region having a higher density than the lower-density region; and

wherein the board core comprises a set lower-density region comprising calcium sulfate dihydrate and a set higher-density region comprising calcium sulfate dihydrate, the set higher-density region being interposed as a layer between the set lower-density region and the front cover sheet.

19 . (canceled)

20 . The gypsum board of claim 1 , having a transverse width of 3 to 5 feet, wherein the set higher density region has;

an average thickness of 20-40 mil measured from the average of a series of 1 inch wide samples taken across the width a transverse cross section of the board,

the set higher density region thickness of each sample has a +/−20 mil difference from the average thickness,

the minimum set higher density region thickness of the samples is at least 10 mils thickness, and

the minimum thickness of the set higher density region of the samples/average thickness=40-100%, typically 40-90 or 40-80%.