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What advantages does a vertical twin-shaft mixer offer over a single-shaft mixer for large-volume batches?

For large-volume batches, a vertical twin-shaft mixer offers advantages above all in terms of mixing time, homogeneity and particle protection. This is particularly relevant where the mixture must not warm up, or where spray-agglomerated instant products, muesli formulations or other fragile structures are to be homogenised gently.

Higher mixing intensity in a short mixing time

Two vertically arranged, mutually interacting mixing shafts create overlapping zones of action with three-dimensional restratification and counter-flow effects. The material is circulated upwards, downwards and radially at the same time, with the result that:

  • the mixing time falls markedly compared with single-shaft systems (in practice often by around 50–70 %),
  • very high homogeneity is achieved even with complex formulations,
  • the specific energy input per tonne of product remains low, because speeds can be moderate despite the strong mixing action.

The overall cycle time is then determined more by filling, discharge and cleaning; the throughput advantage lies above all in the shorter actual mixing phase.

Particle protection and handling of heterogeneous formulations

The evenly distributed mixing action and the ability to work at low circumferential speeds allow sensitive particle structures to be mixed very gently:

  • porous, spray-agglomerated instant powders retain their instant properties,
  • baked or extruded cereals (e.g. muesli components) are distributed homogeneously without excessive breakage.

At the same time, vertical twin-shaft mixers achieve shorter mixing times and a more stable distribution with batches whose bulk densities, particle sizes or flow properties differ widely:

  • segregation is largely suppressed,
  • very small additive quantities can be homogenised reliably into large carrier quantities,
  • moist or pasty materials and conditioned mixtures can also be homogenised.

Economic aspects

With large-volume batches, vertical twin-shaft mixers offer economic advantages:

  • lower specific energy consumption per batch thanks to short mixing times and efficient flow guidance,
  • often a lower overall height in relation to batch size and a compact footprint compared with other high-performance mixing systems.

Set against this are higher investment costs and a more complex drive and synchronisation arrangement. In industrial practice, vertical twin-shaft mixers are therefore regarded as the technically superior solution for large-volume batches wherever high demands are placed on homogeneity, product protection, process flexibility and reproducible mixing quality.

How amixon® compares the HM vertical twin-shaft mixer with the VM single-shaft mixer for large-volume batches

Both the HM vertical twin-shaft mixer and the VM single-shaft mixer are based on the SinConcave®/SinConvex® helical mixing tool. They generate an upward flow at the periphery and a downward flow in the centre, producing a three-dimensional total flow. Both designs thus achieve a technically ideal random mixture across an exceptionally wide fill level range of approximately 10 to 100 % – with no loss of mixing quality. Both work at low speed, with circumferential speeds of approximately 0.8 to 3.5 m/s.

What makes the HM better than conventional vertical mixers

The HM uses two helical mixing tools arranged in parallel, whose flow fields overlap. As a result:

  • the mixing time is shortened compared with single-shaft systems, typically by a factor of 2–3,
  • the specific energy input into the product falls markedly,
  • very high levels of homogeneity are achieved in a short time while product protection remains at a maximum.

The two shafts permit a cubic, relatively flat vessel geometry. With large-volume batches, the available installation space is used more efficiently than with classic tall-cylinder vertical mixers. Residual discharge rates of approximately 99.997 % and better are realistically achievable – depending on the design and on ComDisc® tools – and exceed the typical values of many standard mixers.

The role and particular features of the VM

The VM achieves the same mixing quality as the HM, but requires roughly two to three times the mixing time and a correspondingly higher energy input. It is therefore appropriate where mixing time and energy input are less critical, or where investment costs are the priority. Both systems are available in finely graduated sizes between approximately 100 and 50,000 l and can be equipped with heatable or coolable jacket surfaces.

Hygienic design and cleanability

All the mixing systems named follow the amixon® hygienic design:

  • mixing chamber and mixing tool are welded free of crevices and ground smooth; the mixing tool is mounted exclusively at the top, and a contamination-critical lower shaft passage is eliminated.
  • Large Clever-Cut® inspection doors with OmgaSeal® seals provide ergonomic access and permanently dead-space-free closures.
  • Dead-space-free discharge devices, integrated washing lances and optional fully automatic wet cleaning support validatable cleaning to EHEDG, FDA and 3-A standards; the machines conform to ATEX Zone 20 and can be equipped with MultiPlane® tools.

The HM and VM thus offer a combination of an exceptionally wide usable fill level range, very high mixing quality, maximum product protection and exemplary hygienic design that goes beyond what typical vertical mixers deliver.