Characterizing the Mixing Efficiency of the Planetary Powder Mixer Triaxe® Through An Extended Power Consumption Study

While mixing processes have been largely employed in industry since a long time, a need of comprehensive studies of these processes is recently growing. Indeed modern materials are frequently performed in very tight intentions, especially in high added-values industries. It is usual to find formulations containing several tenths of ingredients, but for which end-use properties finally depend on the efficiency of a single mixing step.

Fig 1: Triaxe® mixing system

Planetary mixers take a large place among the proposal of equipment manufacturers. The combination of several motions ensures interesting mixing conditions and allows the mixer to be adapted to a wide range of raw material properties. The Triaxe® mixing system combines a gyration motion and a rotation motion of an impeller across a spherical tank, as shown in fig. 1. Previous studies from our group enhanced the versatility of this mixer, being able to achieve mixing of free-flowing or cohesive materials in a short mixing time. For a given product, mixing time and power consumption depend on gyrational and rotational speeds of the impeller. A characteristic speed, corresponding to the maximum tip speed of the impeller for given gyration and rotation conditions, is defined and its versatility is demonstrated. It is concluded from mixing and power consumption experiments that this speed governs agitation and mixing of free-flowing powders. In addition, some correlations involving dimensionless Power numbers and Froude numbers deduced from this characteristic speed are highlighted. This is enlarged to account for powders of very different flow characteristics, as well as their mixtures.