Real-time diagnosis of melting and mixing processes in internal mixer by ultrasound

An ultrasonic technology on melting and mixing processes in the internal mixer real-time, non-intrusively and non-destructively is investigated. Ultrasonic signatures, such as amplitude of transmission and reflection echoes, as well as visual observation, and mechanical torque measurement, were used for the diagnosis of the melting process of low-density polyethylene (LDPE) and the mixing processes of the melted LDPE with a calcium carbonate (CaCO3) powder. Phase change from solid to liquid, partially melted pellets, and distributing progress of CaCO3 powder during the melting and mixing processes were successfully monitored by ultrasound. Melting and mixing completions were determined when ultrasonic reflection echo reached its upper stable level. Larger amount of CaCO3 powder required longer mixing period. Higher temperature of mixing chamber and faster rotation speed of blades reduced mixing period. The presented ultrasonic technique can be utilized to optimize the melting and mixing processes.