Analysis of the flow paths in a rubber internal mixer in dependency of different process parameters

• Applicant: Professor Dr.-Ing. Christian Hopmann
• Subject Area: Plastics Engineering
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 377803088

For the production of rubber products, the mixture components are compounded in a discontinuous internal mixer. In order to achieve a stable and efficient process with a short mixing time and a homogeneous product, the mixing procedure is usually developed empirically. This method is time consuming and requires specialised knowledge of experienced employees. To design a time efficient mixing process with high filler dispersion, it is necessary to have scientific knowledge about the flow paths in an internal mixer. Previous trials to describe the flow paths in the mixing chamber are based on simplifying assumptions, for example a fully-filled mixing chamber, or consider only the flow behaviour in the area between the rotor and the mixing chamber wall.The development of a method to visualise the flow behaviour in the area between the rotors of a tangential internal mixer is the aim of this research project. After completion the research projekt it will be possible for the first time to describe the flow process in an internal mixer completely. For this reason, different coloured as well as fibre filled compounds and multicomponent systems are used. After the compound is vulcanized in the mixing chamber, the chamber will be opened so that the flow behaviour can be analysed, for example due to the different colours of the flow paths.After the development of the method and the identification of the flow paths, the influence of different process parameters, for example the temperature of the mixing chamber, phase angle or the rotor speed, on the flow behaviour in the area between the tangential rotors is analysed. By a variation of the phase angle, the flow conditions in the area between the rotors will be varied, while the flow conditions between rotor and mixing chamber wall will remain almost constant. This would not be possible by changing rotor geometry as an example. Based on the results, a correlation between the varied process parameters and the flow paths is derived. Thus, it will be possible to predict the flow behaviour between the rotors of an internal mixer depending on the chosen process parameters. In addition, the correlation between the flow paths and the amount of material to the dominated mixing effects will be derived. This will enable to predict the quality of the mixing. To verify the developed method, the scientifically derived correlations between process parameters, flow paths and mixing effects are validated in further mixing tests, which differ regarding the mixing chamber sizes and process parameters. Based on the gained knowledge, it will be possible to explain and predict the effects of various process parameters on the flow conditions, which enables to design and develop mixing processes in tangential internal mixers more efficiently.

• DFG Programme: Research Grants