(237b) Modeling and Scale-up of Tumble Blenders for Highly Segregating Materials

Tumble blenders are one of the simplest and most common types of blenders for mixing powders and granular materials. Tumblers are commonly used for batch blending in a wide range of industries when low-shear, gentle mixing is sufficient to blend the formula components. Materials suitable for tumble blending are generally easy flowing, non-cohesive materials that don't form agglomerates when tumbled. By their nature these types materials are generally easy to mix, but they also represent a class of materials that can have strong segregation tendencies. Tumble blending binary or multi-component mixtures of granular solids with a wide size distribution can present unique challenges because the blending mechanisms at work in a tumbler (primarily shear and diffusion) are the same mechanisms that cause segregation. Shear that occurs during discharge of a tumble blender can cause demixing of materials that may be overlooked if samples are only collected from the blender before discharge. Blending materials such as plastic pellets and granular polymer materials for plastics compounding and solid surface manufacturing present some of the most extreme challenges for achieving blending and controlling segregation. Modeling the blending process using actual materials and correct sampling methods is the best way to ensure successful scale up to a production process. Two applications for blending coarse, free flowing plastic materials were modeled in pilot scale to determine optimum blender configuration and process parameters for blending. Scale-up parameters were applied to determine the full scale operating parameters and, in one case, testing the full scale equipment was done to confirm performance. The process led to successful scale up and avoided the potential for significant problems that could have resulted from segregation.