How do I assess the mixability of a powder blend with large density differences in advance at laboratory scale?
Assessments of mixability at laboratory scale should be carried out with a small, readily reproducible preliminary trial. What matters is a clear measurand for homogeneity, for example a lead component or a tracer that can be recorded analytically without difficulty.
With powders that differ greatly in density, it is not sufficient to check the mixing state only immediately after mixing. What is also decisive is whether the mixture segregates again after discharge from the mixer. Bulk density, flowability and, where applicable, dust generation should therefore also be examined, particularly after filling, packaging and transport.
Take samples from several zones of the mix. Work with graduated mixing times and compare the results systematically. In this way you recognise from what point a sufficiently homogeneous mixture is achieved and whether this stability is retained in the further process.
How amixon® masters large differences in density and particle size when mixing
The mixability of a powder blend with large differences in density should be assessed at laboratory scale with a reproducible preliminary trial. Not only the differences in density are relevant here, but also the particle size distribution, the flow behaviour and cohesion. A defined tracer or a lead component as well as samples from several zones of the mix are suitable for the test.
What is critical is not only the mixing state in the mixer, but also the discharge. If discharge takes place in free fall, the mix can build up into a cone of repose and segregate in the process. A dense-phase discharge with little segregation into a filling plant, onto a conveyor belt or into a downstream process is more favourable.
Depending on the material system, amixon® uses different machines with vertically mounted helical mixing tools for such tasks. These include the twin-shaft mixer HM, the single-shaft mixer VM, the cone single-shaft mixer AM, the KoneSlid® mixer KS, the SpherHelics® mixer SH as well as the Gyraton® silo mixer GM for large batches up to 100 m³. These apparatus are designed to homogenise even heterogeneous mixtures with differing densities, particle sizes and flow properties in a controlled manner.
Verification in the amixon® pilot plant
amixon® checks in advance in the pilot plant whether the specific combination of density spread, particle size distribution and cohesion delivers the expected result: for this, 35 test units are available in Paderborn alone.