By Christine Banaszek
Solid-solid product formulations are mixed to meet a variety of objectives. These include blending of ingredients (such as in the preparation of animal feeds, fertilizer, glass batches, food products, etc), heating/cooling/drying (like in the processing of metal powders and plastics) and coating of solid particles with small amounts of liquid (similar to the manufacture of pigments, pharmaceuticals and chemical blends).
Three basic blenders can achieve the above objectives. These are small-scale random motion (diffusion), large-scale random motion (convection) and shear. Diffusion occurs readily for free-flowing powders. But for most rapid mixing, in addition to diffusive movement, large groups of particles should be able to intermix as well.
Among solid-solid blending systems, the three most common types are the horizontal ribbon blender, the cone screw vertical blender and the tumble blender. Of these three, the ribbon blender particularly demonstrates convective high speed mixing.
Aside from level of shear or ‘gentleness’, other factors help determine which type of blender will work most efficiently in a certain application. Following are some things to consider when choosing your blender.