A method for producing a gypsum plasterboard comprising the steps of providing bundler dust obtained from gypsum plasterboard leftovers of a plasterboard trimming process by a trimming device, in particular by a bundler saw; and adding at least a part of the bundler dust to a gypsum slurry for producing the gypsum plasterboard.

A composition for forming molded mantels, columns and other decorative enhancement to fireplace openings is formed of a mixture of alpha hemihydrate gypsum plaster, cement, filler and milled fiber. By using this composition with water and acrylic binder a mixture is formed which sets and gains strength quickly and is an ideal material for manufacturing architectural and decorative structures. Advantageously, a casted piece can be removed from a mold within two to three hours after casting. The finished product has a desired finish that is similar to a casted gypsum cement, referred to sometimes as a honed finish which can withstand high heat, discoloration and cracking while maintaining suitable strength when exposed to typical temperatures of a fireplace surround in indoor applications.

Disclosed are product (e.g., panels), slurry, and methods relating to an uncooked starch having a mid-range peak viscosity (i.e., from about 120 Brabender Units to about 900 Brabender Units).

A method for continuously forming gypsum-based panels of high fixing strength comprises the steps of: forming a mixture comprising stucco, non-pregelatinized migratory starch, glass fibre, fluidizer and water; casting the mixture in a continuous band; maintaining the band under conditions sufficient for the stucco to form an interlocking matrix of set gypsum; cutting the band to form one or more wet panel precursors; and drying the wet panel precursor to form one or more gypsum-based panels. The weight ratio of water to stucco in the mixture is less than 0.7; the stucco is present in the mixture in an amount of over 60 wt % relative to the total solids content of the mixture; the starch is present in the mixture in an amount of over 3 wt % relative to the the stucco; the glass fibre is present in the mixture in an amount of over 1 wt % relative to the stucco; the fluidizer is is present in the mixture in an amount of at least 0.1 wt % relative to the stucco; and the density of the gypsum-based panel is greater than 700 kg/m.

A pressing assembly (10) and a method for forming a depression (105) within a moving, wet gypsum board (100) is disclosed. The assembly comprises a pressing head (16) comprising a pressing surface which is arranged to contact the board, and a support member (17), the pressing head (16) being arranged to compress a portion of the board between the pressing surface and the support member (17) to form a depression (105) within the board (10). The pressing surface comprises a first and second surface portion (24, 25) separated by a relief portion (27), which is arranged to press the board (100) toward the support head (17) with less compressive force than the first and second surface portion (24, 25). The assembly further comprises drive means (18, 19, 22) for moving the pressing head and the support member in a first direction which substantially corresponds with the direction of the moving board, and a second direction which is substantially perpendicular to a plane of the board, while the speed of the pressing assembly in the first direction substantially matches the speed of the board.

A mixer has a circular housing defining a mixing area for mixing and kneading of a gypsum slurry. A rotary disc is positioned in the housing and rotated in a predetermined rotational direction. A rotary driving shaft cointegrally connected with the rotary disc and a plurality of scrapers are positioned in the mixing area. A slurry discharge port is provided on an annular wall of the housing for feeding the gypsum slurry of the mixing area onto a sheet of paper for gypsum board liner. An opening of the slurry discharge port is divided into a plurality of narrow openings, so that fluid resistance on the gypsum slurry flowing out of the mixing area is increased. An annular basal part rotates integrally with the rotary disc and an inner end portion of the scraper is fixed to the annular basal part.

There are provided gypsum panels, sheets and multi-layer sheets as well as methods of preparation thereof. For example, there are provided cellulose filament-reinforced gypsum panels, sheets and multi-layer sheets and methods of preparation thereof. For example, in such gypsum panels, sheets and multi-layer sheets gypsum is bound with cellulose filaments to strengthen the gypsum panels, sheets and multi-layer sheets. The cellulose filament-reinforced gypsum panel can be, for example, a core comprising a honeycomb or corrugated structure. There are also provided aqueous suspensions comprising cellulose filaments and CaSO.sub.4.2H.sub.2O.

Disclosed are product (e.g., panels), slurry, and methods relating to an uncooked starch having a mid-range peak viscosity (i.e., from about 120 Brabender Units to about 900 Brabender Units).

Disclosed are product (e.g., panels), slurry, and methods relating to an uncooked starch having a mid-range peak viscosity (i.e., from about 120 Brabender Units to about 900 Brabender Units).

[Object] Behavior of a flow of foam or foaming agent ejected to a gypsum slurry can be stabilized, and a relatively large amount of foam or foaming agent can be homogeneously or uniformly dispersed in the slurry.

[Solution] A mixer (10) has a mixing area (10a) for preparing gypsum slurry (3), a slurry delivery section (4) for delivering the slurry from the mixing area, and a feeding port (60) for feeding foam (M) or a foaming agent to the slurry in the mixing area and/or the slurry delivery section under pressure. The slurry having the foam mixed therein is supplied to a production line (1) for forming gypsum boards or gypsum-based boards. The feeding port is provided with a partition member (62,64,65) dividing an ejecting region (61,61). The ejecting region is divided into a plurality of openings (63), which simultaneously eject the foam or forming agent to the slurry.