Segregation problems when using a tumble blender: double cone blender and V-blender

29-07-2013

Q: we use a tumble blender and a ribbon blender mixer. I’ve heard that if you mix too long, you can undo the mixing result when using a tumble blender. What is this “demixing” and what causes it?

A: Unlike most liquid blends, in which mutually soluble form a stable blend that doesn’t degrade over time, dry mixtures have a tendency to segregate. This is because particles have different sizes, shapes, and densities. When the particles are in motion (as in mixing), the differences cause the particles to segregate. In a tumble blender, the ingredients are loaded in batches, often forming stratified layers in the vessel. Then the unit begins tumbling, and its symmetrical rotation creates a nonrandom mixing pattern. This pattern, when combined with the various particles’different trajectories, can demix or segregate the particles in a pattern different from that formed by the layers during loading. To avoid this segregation in the later mixing stages, it’s best to use a tumble blender for relatively short mixing times. A tumble blender can also be designed to provide asymmetrical rotation to minimize demixing caused by trajectory segregation. For instance, a V-blender can have one extended leg and a double cone mixer can have offset cones; by using such designs, you can shorten mixing times, improve mixing quality, and limit further segregation.

double cone blender, powder mixer
Double Cone Blender: a kind of tumble blender