Mixing and stirring device, method, and method for manufacturing lightweight gypsum board, including chute with eccentric orifice passage

A method for mixing and stirring gypsum slurry, with use of a mixing and stirring device for the gypsum slurry having a circular casing forming a mixing area for mixing of the gypsum slurry, a rotary disc positioned in the casing and rotated in a predetermined rotational direction, and a chute for delivery of the gypsum slurry which is provided outside of the casing in order to feed the slurry of the mixing area to a sheet of paper for gypsum board liner and which generates an intratubular swirling flow for mixing the slurry with foam or foaming agent for adjustment of specific gravity,

• wherein the slurry effluent from the casing through a slurry outlet port positioned on said casing is caused to flow down gravitationally in an intratubular area of the chute, and the foam or foaming agent is mixed with the slurry by said intratubular swirling flow generated in the intratubular area, and the slurry is introduced from the chute into a discharge pipe portion through an orifice passage which locally constricts a cross section of the intratubular area, and
• wherein a centroid of a figure of a cross section of the orifice passage is located at a position eccentric with respect to a center axis of said intratubular area, so that an axisymmetric vortex flow in the intratubular area is at least partially broken down by the orifice passage, for restricting regeneration or generation of the intratubular swirling flow in said discharge pipe portion on a downstream side of the orifice passage.

A method for manufacturing lightweight gypsum boards having a specific gravity equal to or less than 0.8, wherein gypsum slurry is produced with use of a mixing and stirring device for the gypsum slurry, which has a circular casing forming a mixing area for mixing of the gypsum slurry, a rotary disc positioned in the casing and rotated in a predetermined rotational direction, and a tubular passage for delivery of the gypsum slurry provided outside of the casing in order to feed the slurry of the mixing area to a sheet of paper for gypsum board liner, and wherein the slurry of the mixing area is spouted onto said sheet of paper through a chute which allows the slurry to flow down gravitationally, comprising steps of:

• introducing said gypsum slurry of the mixing area effluent from the casing through a slurry outlet port disposed on the casing, into a tubular passage of said chute together with foam or foaming agent for adjustment of a specific gravity, and generating an intratubular swirling flow in an intratubular area of the chute by turning the slurry therein so that the slurry and the foam or foaming agent are mixed in the tubular passage by the intratubular swirling flow generated in the chute;
• introducing said gypsum slurry from the chute into a discharge pipe portion through an orifice passage which locally constricts a cross section of fluid passage of the intratubular area, and
• positioning a centroid of a figure of the cross section of the orifice passage at a position eccentric with respect to a center axis of said intratubular area for causing an axisymmetric vortex flow in said intratubular area to be at least partially broken down by the orifice passage, thereby restricting regeneration or generation of the intratubular swirling flow in an intratubular area of said discharge pipe portion located on a downstream side of said orifice passage.