A foreign matter removing apparatus for removing foreign matter in a powder and granular material is provided. The foreign matter removing apparatus includes: a conveyance device configured to convey the powder and granular material from a supply port to a discharge port that are for the powder and granular material; and a foreign matter sedimentation device that is provided between the supply port and the discharge port on a conveyance path of the conveyance device, and is configured to sediment the foreign matter in the powder and granular material. The foreign matter sedimentation device includes both a foreign matter discharge port provided at a lowest position in a height direction and a bottom inclined toward the foreign matter discharge port.

A method of conditioning stucco comprises the steps of supplying a quantity of stucco particles to a reaction vessel, the stucco particles comprising calcium sulphate hemihydrate and/or calcium sulphate anhydrite, as well as calcium sulphate dihydrate; and conditioning the stucco particles at a temperature of at least 100? C. and a humidity of at least 70%. During the step of conditioning the stucco particles, the bulk density of the stucco particles within the reaction vessel is at least 1 g/cm.sup.3.

A method of conditioning stucco comprises the steps of supplying a quantity of stucco particles to a reaction vessel, the stucco particles comprising calcium sulphate hemihydrate and/or calcium sulphate anhydrite, as well as calcium sulphate dihydrate; and conditioning the stucco particles at a temperature of at least 100? C. and a humidity of at least 70%. During the step of conditioning the stucco particles, the bulk density of the stucco particles within the reaction vessel is at least 1 g/cm.sup.3.

A calcined gypsum treatment apparatus has an agitating type of cooler provided with a cooling region for cooling the calcined gypsum, and a moisture supplying device for incorporating moisture into the calcined gypsum. The moisture supplying device includes a humid gas-feeding port which introduces humid gas including moisture or steam, directly into the cooling region. The calcined gypsum is introduced through a calcined gypsum introduction port into the cooling region, and the moisture is incorporated into the calcined gypsum to modify the calcined gypsum. The humid gas-feeding port is positioned in vicinity to the calcined gypsum introduction port so as to allow the spouted or delivered flow of the humid gas to be brought into contact with the calcined gypsum immediately after introduced into the cooling region.

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.

The instant invention is concerned with the post-treatment of -hemihydrate plasters for the purpose of stabilization. The invention relies in the addition of a retardant to the calcined -hemihydrate. It is also the purpose of the invention to provide stabilized -hemihydrate plasters which exhibit advantageous properties.

The invention pertains to a method for stabilizing stucco wherein a fresh stucco is provided; water is added to the fresh stucco to obtain moistened stucco, and the moistened stucco is maintained at a temperature of at least 30 C. for a time interval of at least 30 minutes to obtain a stabilized stucco.
The process allows inter alia for an easy adjustment of the activity of the stabilized stucco, which is useful to e.g. adjust setting time of a corresponding stucco slurry. The invention further pertains to a method for producing gypsum plasterboards, wherein a stabilized stucco obtained with the above method is used.

Disclosed are various methods for reducing levels of elemental sulfur within gypsum products such as wall board. Gypsum sometimes includes increased levels of elemental sulfur. Such sulfur can be corrosive and otherwise harmful at elevated levels. The disclosure contemplates reacting the elemental sulfur with copper to copper sulfide. This reaction has the benefit of reducing the levels of elemental sulfur present within the final gypsum product. The copper can be added at any of a variety of locations in the manufacturing process. This is a very efficient method for reducing elemental sulfur in the production of gypsum products.

Disclosed are various methods for reducing levels of elemental sulfur within gypsum products such as wall board. Gypsum sometimes includes increased levels of elemental sulfur. Such sulfur can be corrosive and otherwise harmful at elevated levels. The disclosure contemplates reacting the elemental sulfur with copper to copper sulfide. This reaction has the benefit of reducing the levels of elemental sulfur present within the final gypsum product. The copper can be added at any of a variety of locations in the manufacturing process. This is a very efficient method for reducing elemental sulfur in the production of gypsum products.

A gypsum-based construction material can include gypsum core including a stucco component, a siloxane component at a content of not greater than about 2.0 wt. % relative to a content of the stucco component, and a calcium hydroxide catalyst at a content of at least about 0.01 wt. % and not greater than about 0.1 wt. % relative to the content of the stucco component. The gypsum-based construction material can have a pH of at least about 7.5 and not greater than about 10.