Mixer including foam feeding port, mixing method, and method for producing lightweight gypsum board

A method for producing light-weight gypsum boards having a specific gravity equal to or less than 0.8, in which gypsum slurry is prepared in a mixing area of a mixer, the slurry is delivered out of the mixing area through a slurry delivery section of the mixer, foam is fed under pressure to the slurry in the mixing area and/or the slurry in the slurry delivery section, and a production line for forming gypsum boards is supplied with the slurry having the foam mixed therein, comprising steps of:

• positioning a feeding port of the foam for feeding the foam to said slurry, in the mixing area and/or the slurry delivery section,
• dividing an ejecting region of said port ejecting the foam to a flowing fluid of said slurry, by a partition member,
• delivering the foam to said port through a fluid passage of the foam, and
• ejecting said foam to said fluid of the slurry simultaneously through a plurality of openings defined by division of the ejecting region,
• wherein an amount of the foam to be ejected to said slurry is so set as to form a gypsum core of said gypsum board having a specific gravity equal to or less than 0.7.