New dual-shaft design incorporates a special helical agitator and high-speed dispersion blade. The new combination of agitators provides improved axial and radial turnover of the materials being mixed, as well as high shear of the product. This feature is especially useful for viscous materials that have poor flow qualities, the addition of powders that have a tendency to float on the surface, and when heat transfer of the batch constituents is important. The helical agitator is designed for bi-directional operation. The mixer also includes a conical bottom vessel, special electrically actuated discharge valve, double mechanical seals, a 100 psig jacket for heating and cooling, a temperature probe and all stainless steel wetted parts.