Tumble Mixers

Tumble mixers are composed of a rotating shell that contains the solids. The two most common shapes are the V-type and the twin cone. Another more recent shape is the diamondback blender. The primary mixing mechanism in a tumble mixer is the distribution of solids along the ever-changing angle-of-repose surface.
Mixing is affected by the container’s shape. The V-mixer, for example, tends to form two separate mixing chambers connected by a central cross-mixing zone. The twin-cone and diamondback blender shells converge all the solids toward the smaller diameter ends and, thus, greatly facilitate cross-mixing. The diamondback blender, with its one-dimensional convergence, tends to create a crisscross response angle as the solids slide from one portion of the blender to the other, producing additional cross-mixing.

The angle of repose is the primary demixing mechanism in tumble mixers. With a V-mixer, the low angle-of-repose component concentrates in the central cross-mixing region. The twin-cone and diamondback blenders tend to leave the lower angle-of-repose component in striations that, on discharge, may exit in high concentrations. The diamondback blender produces a bottom-to-top uniform flow across the cross-section that mixes striations effectively on discharge.

In general, tumble blenders are limited to moderately cohesive solids that do not have sifting or repose-angle demixing. However, running the diamondback blender at high speeds can extend the range of solids to those that would normally demix with sifting and repose-angle mechanisms.