How do you evaluate the scalability of a laboratory mixer for food supplements up to production sizes?
The scalability of a laboratory mixer is assessed via geometry, process parameters, material properties and product quality. The aim is that homogeneity, active ingredient distribution and content uniformity remain reproducible from laboratory to production scale.
Geometric and kinematic similarity
For a robust scale-up, laboratory, pilot and production mixers should be as geometrically similar as possible. Vessel dimensions, tool geometry as well as inlets and outlets are important here. In addition, the Froude number, the Newton number and the circumferential speed have to be considered, in order to keep particle movement, energy input and shear loading comparable.
The Froude number relates to rotating free-fall, drum and throw mixers as well as to systems with a horizontally mounted mixing tool. In vertical mixers with forced restratification it is not a design or scale-up criterion. What is decisive there is that the mixing principle remains the same across all sizes and that the restratification covers the entire mixing chamber independently of the fill level; transferability is secured in the pilot plant with the original product.
Material and process behaviour
Particle size, bulk density, flow behaviour, moisture and the tendency to segregate strongly influence the scaling behaviour. Depending on the formulation, a constant specific power input, a constant Froude number or a constant circumferential speed is used as the guiding variable. Temperature control and heat removal also become more important as the plant size increases.
Evidence of quality
The mixing quality should be checked at all scales with comparable analyses, for example via sampling and chromatographic or spectroscopic analysis. With low-dose formulations, wall adhesion, electrostatic effects and segregation are particularly critical. A pilot scale helps to recognise scaling effects early and to secure the process for production.
How amixon® secures the scale-up from the pilot plant into production
An identical mixing principle across all scales
The core of the amixon® approach: trial and production mixers work with the same mixing system. The SinConcave®/SinConvex® helical mixing tool conveys the mix upwards at the periphery and lets it flow downwards in the centre. This three-dimensional total flow remains the same irrespective of the size. Scaling takes place via the restratification formula, that is via the conveying volume flow of the helical mixing tool and the restratification frequency derived from it – not via the rotational speed alone. All sizes are operated within the same window of approximately 0.8 to 3.5 m/s, generally at low speed. The flow pattern, the mechanical loading of particles and the similarity conditions are thereby preserved between the scales.
Congruent geometries as the basis
Decisive for the scale-up is the congruence of the geometries between the pilot plant and production mixers. The vessel shape, the mixing tool geometry, the internals and the flow space remain in the same relationship to one another. This produces a comparable flow pattern that can be transferred reproducibly from laboratory to pilot plant and on to production scale.
Calculation formula for the flow
The conveying capacity of the vertical mixing helix can be described approximately by the following relationship:
I_V = (π/4) · (D² − d²) · Φ · S · n · ζ
Here I_V is the conveying capacity, D the outer diameter of the helix, d the inner diameter, Φ the fill level, S the pitch of the helix, n the rotational frequency and ζ the speed coefficient. This relationship shows that for the scale-up it is not the rotational speed alone that is decisive, but the resulting conveying capacity and circumferential speed.
Mixing quality independent of fill level
amixon® mixers achieve high mixing qualities even at a low fill level, approximately 10 %. The technically ideal random mixture cannot be improved further in practice. Batch sizes can vary within the same mixer without homogeneity having to be revalidated. This defuses the most critical moment in a scale-up, namely the first small production batches in the large machine.
A fine size range instead of jumps in scale
On request, amixon® manufactures mixer sizes in 100-litre increments from 100 to 50,000 litres for the VM, HM and AM types; the Gyraton® GM continues from 10 to approximately 100 m³ in 1 m³ increments. The step from the validated trial scale to the target size can thereby be chosen very finely. A forced jump to the next catalogue size is not necessary.
Validation before the investment
The amixon® pilot plant has 35 test units of various sizes available. Trials run with the original product, at real fill levels and within the planned temperature and pressure range. The parameters circumferential speed, mixing time and fill level flow directly into the design of the production machine.
Manufacture in Paderborn as the quality foundation
amixon® develops and manufactures exclusively at the Paderborn works with a high depth of manufacture and all components from Germany. As a certified welding company with European, Japanese, Korean and American qualifications, amixon® designs every apparatus as a one-off on the basis of the operator's URS. Quality control remains entirely in-house without gaps, and every specification can be documented down to component level. This manufacturing autonomy also secures long-term supply, since every component can be reproduced even decades later.