Mixer having a segmented helical mixing blade

A mixer for producing mixture comprising:

• an inside mixing means disposed at a center of a mixing vessel and connected to an inner shaft so that the inside mixing means is rotated;
• and
• an outside mixing means disposed around the periphery of said mixing vessel and connected to an outer shaft arranged coaxially with said inner shaft so that the outside mixing means is rotated;
• wherein the inside mixing means moves materials of mixture from the bottom of the center of said mixing vessel toward an upper portion of said center and thence toward an upper periphery of said mixing vessel, and then the outside mixing means moves the materials from the upper periphery toward a lower periphery of said mixing vessel and thence toward the bottom of the center of said mixing vessel, the mixer circulating and mixing the materials in said mixing vessel;
• and
• wherein said inside mixing means comprises a shaft body connected to said inner shaft and a predetermined number of mixing blade elements which are detachably fixed to said shaft body and overlaid to adjacent mixing blade elements in the axial direction, each mixing blade element being provided with a helical mixing blade piece for mixing and moving said materials, the adjacent mixing blade elements being disposed so that the mixing blade pieces of said adjacent mixing blade elements form one substantially continuous helical blade.