Over the last two decades, there have been many theoretical models presented for the feeding, melting, and melt pumping of thermoplastics in the single-screw extruder. Many of the models are amenable to computer analysis, but their complexity makes them impractical for industrial applications. The various melting models are reviewed. A model allowing for a deformable solid bed and bed acceleration is presented to show the limits of screw performance and operational stability. Comparisons are made between predicted and experimental data for processing various polyolefins and polystyrene. Final melt conditions can be estimated by a two-dimensional, nonisothermal developing melt flow model, and the influence of operating conditions and material properties are presented. Effects of barrier flights on the melting and melt mixing are discussed. Examples of the combined use of both programs to design the drive requirements and screw dimensions for processing various thermoplastics are also presented.

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