Conical screw mixers use a rotating screw that progresses around the periphery of a conical hopper. The screw lifts solids from the bottom of the hopper to the top, where the mixture flows by gravity back into the screw. Mixing occurs around the open screw, where the solids transported by the screw exit at various levels and are replaced by other solids at that level. The screw’s shearing action also intimately mixes the various components. Gross mixing action occurs within the mixture by the velocity profile created in the conical hopper as it feeds the screw. With conical screw mixers, this gross mixing action is most effective when the solids move along the conical hopper walls.
Conical screw mixers are specified according to media, capacity, operating configuration, mix rate, and motor speed. There are three basic media types for conical screw mixers: liquid, liquid solid, and powder. Operating capacity is specified in gallons and feed rate is listed in gallons per minute (gpm). There are three parameters for configuration: operating condition, mounting style, and mixer location. Typically, the operating condition is batch, the mounting method is overhead, and the mixer location is top-entry. Specifications for mix rate and motor speed include accuracy and motor power. Operating temperature and pressure are additional specifications to consider.
Selecting conical screw mixers requires an analysis of available features. Some products have internal heating element or cooling element. Others are programmable, allowing operators to adjust settings for different ranges, materials, and levels. There are three display types for conical screw mixers: analog, digital and video display. Analog devices have a dial or indicator lights. Digital units have a digital, numerical display. Video displays that use a cathode ray tube (CRT), liquid-crystal display (LCD), or other multi-line display are also available.
Conical screw mixers may be designed for either atmospheric operation or vacuum operation. They often feature a single-speed screw and orbital arm. In terms of applications, conical screw mixers are used to process adhesives, chemicals, cosmetics, paints and coatings, and pharmaceutical products. Industrial mixers for chemical processing include products rated for general chemical heating, as well as devices designed for corrosive chemicals such as acids and solvents. Conical screw mixers are also used for water and wastewater treatment applications, including the mixing of carbon slurry and lime slurry.