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A composite simulation model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder has been developed. The model is based on combining new melt conveying models with melting and solids conveying models, and the die is included into considerations. A general approach is applied using fully three-dimensional non-Newtonian FEM modeling for melt conveying to develop screw pumping characteristics which are implemented into the composite model. Several screw configurations are considered including non-classical elements. Computations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

Intermeshing counter-rotating twin screw extruders play an important role in polymer processing, especially for the extrusion of profiles and pipe, largely from polyvinyl chloride. There has been little effort on flow modeling of these machines and most of this has involved representing the machine as a “leaky” positive displacement pump and estimating leakages. In recent years, M.H. Hong and the authors have developed more general methods of simulation of flow in this machine and both applied and experimentally verified it for a few designs. Here we extend these efforts to a broader range of screw designs, especially with deeper screw channels where transverse shearing induced by the flights is important. Calculations are done for isothermal power law fluids. The results are compared with experiment. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

We have made a study of the development of phase morphology of an immiscible blend(75/25)(polypropylene–polyamide-6) for different types of continuous mixers including (i) Buss Kneader, (ii and iii) modular intermeshing corotating and counter-rotating twin screw extruders, and (iv) NEX-T Kobelco Continuous Mixer. Comparisons are made using different screw configurations for each machine. Generally, in comparison of the different machines, the intermeshing counter-rotating twin screw extruder produced the finest dispersed morphology. Using a droplet breakup kinetic model, we interpreted the blend dispersed phase droplet breakdown rate and coalescence rate. In comparison with our earlier study of the continuous mixing of agglomerates of CaCO3 particles the polymer droplet breakup rate was smaller than that of the particle agglomerates and the coalescence rates of droplets were many times greater than the particle reagglomerates rates. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Previous experimental studies of melting of pellets in an intermeshing counter-rotating twin-screw extruder have shown that melting is initiated both between the screws and at the barrel. Models are developed for melting in both those regions. The melting between the screws is initiated by frictional work on the pellets by the calendering stresses between the screws. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced.

We have developed non-Newtonian and nonisothermal flow simulation codes in twin screw extruders using the finite element method. These codes can simulate the fully filled part of several kinds of screw elements, such as full flight screws, kneading discs, rotors, and their combinations. In this paper, we describe how we applied them to simulate a counter-rotating nonintermeshing continuous mixer, LCM100G, by Kobe Steel, Ltd. The LCM100G is a Farrel-type continuous mixer that has two mixing stages. We focused on the second mixing stage, since the flow domain of this stage is almost filled by polymer melts. Numerical simulations at various flow rates were performed. We also carried out experimental observations to verify the numerical simulations. Pressure and temperature profiles from the simulations were found to be in good agreement with the experimental results.

Current residence time distribution models for counter-rotating extruders are mainly developed for fully filled machines. However, in practical situations, these extruders operate under starved conditions. To overcome this missing link in the current models, this paper describes the average degree of fill in the situation of starvation. This degree of fill is determined by the length over which the extruder is fully filled and the degree of fill in the partially filled zone. The comparison of the experiments with the theory shows that the existing theory underestimates the length of the fully filled zone by about 30%. The degree of fill in the partially filled zone is well predicted by taking into account all non-pressure driven leakage flows.

Extensive experimental studies of a starved flow modular tangential screw extruder are described. Die pressures and fill factor profiles along the screw axis are measured and used to determine screw characteristic curves Q vs. AP/L for individual screw elements of varying designs in a Leistritz twin screw extruder. Superior pumping characteristics of matched as opposed to staggered elements is found. The experimental screw characteristic curves are compared with the results of mathematical simulations of the flow. Agreement is generally good.