Blending powders is one of the oldest unit-operations in the solids handling industries. For many decades powder blending has been used just to homogenise bulk materials. Many different powder mixer machines have been designed in order to be able to handle materials with various bulk solids properties. On the basis of the practical experience gained with these different machines, engineering knowledge has been developed to construct reliable equipment and to predict scale-up and mixing behaviour. At present, the same mixing technologies are used for many more applications:

  1. Improve product quality.
  2. Coat particles.
  3. Fuse materials.
  4. Wet.
  5. Dispers in liquid.
  6. Agglomerate
  7. Alter functional material properties, etc.

       This wide range of applications of powder mixer equipment requires a high level of knowledge, long time experience and extended test facilities so as to come to the optimal selection of equipment and processes.

Mixing mechanisms

       In powder mixing, two different dimensions in the mixing process can be determined: convective mixing and intensive mixing. In the case of convective mixing material in the mixer is transported from one location to another. This type of mixing process will lead to a less ordered state inside the mixer, the components which have to be mixed will be distributed over the other components. With progressing time the mixture will become more and more randomly ordered. After certain mixing time the ultimate random state is reached. Usually this type of mixing is applied for free-flowing and coarse materials.

       On the other hand, the intensive mixing is needed then materials are cohesive, for convective mixing is no longer sufficient to obtain a randomly ordered mixture. The relative strong inter-particle forces will form lumps, which are not broken up by the mild transportation forces in the convective mixer. In order to decrease the lump size additional forces are necessary, which is intensive mixing. These additional forces can either be impact forces or shear forces.