What advantages do hollow-sphere mixers offer for sensitive, fragile agglomerates?
Hollow-sphere mixers belong to the category of vertical mixers. They are specially designed to homogenise sensitive or fragile agglomerates with a high mixing quality, without substantially impairing their particle size distribution and internal structure. This rests on their spherical geometry and a low-shear, gravity-based mixing kinematics.
Blending takes place primarily through the rotation of the centrally installed mixing tool. The bulk material is thereby moved by gravity and three-dimensional restratification.
Despite the low mechanical loading, an efficient axial, radial and diagonal redistribution is achieved through the three-dimensional movement of the spherical mixing chamber. Homogenisation rests on gentle restratification and the flowing of the material streams into one another at low circumferential speeds.
The closed, spherical geometry has no corners, edges or dead zones, which enables a geometry-related residual discharge and product protection. In combination with gravity, this enables an almost residue-free discharge, as occurs with flowable products such as water. This is not the case with customary powdered products.
Cleaning and GMP friendliness: smooth internal surfaces generally have only one or two shaft passages with seals. Hollow-sphere mixers can be cleaned about as well as cone or cylinder mixers.
Adaptable mixing intensity and good scalability: the energy input into the product can be set in a targeted manner via rotational speed, fill level and mixing time. The intensity can be reduced to such an extent that the particles merely slide gently – ideal for particularly brittle agglomerates. At the same time these process parameters scale well, so that gentle mixing conditions determined in the laboratory can be transferred reproducibly to the production scale.
Overall, hollow-sphere mixers thus offer a technologically suitable solution for homogenising mechanically sensitive agglomerates where grain preservation, product purity and a high, reproducible mixing quality are the priority – particularly where the main mixing tool is designed as a helical mixing tool. Mostly, however, hollow-sphere mixers are equipped with modified anchor stirring rings. They then push the powder masses ahead of them and compact the powders unintentionally.
The SpherHelics® hollow-sphere mixer SH from amixon® is the ideal solution for fragile agglomerates
Geometry against particle breakage
Owing to its hollow-sphere form, the SH avoids by design those areas in which fragile agglomerates could be damaged. There are no corners, edges or crushing zones. The helical mixing tool produces a three-dimensional product flow with short mixing times and low energy input. The mixing chamber and mixing tool are welded free of crevices and ground smooth. The mixing tool is also mounted and driven at the top only.
This enables gentle and product-protecting mixing.
The circumferential speed is adjustable in the range of approximately 0.8 to 3.5 m/s. In practice, SpherHelics® mixers are usually operated at low speed, so that spray-dried powders, fluid-bed granules, instant agglomerates and coatings retain their structure. Where required, the same apparatus can work in a targeted de-agglomerating manner with a switchable cutting rotor.
The product discharge is residue-free and free of segregation. ComDisc® elements sweep the floor in the final discharge phase, so that even the last remnants are discharged. The dead-space-free DosiFlap® fitting enables direct, low-dust filling. The sizes range from 100 to 7,000 litres usable capacity. The mixing chamber is designed for ATEX Zone 20 and is available EHEDG-, FDA- and 3-A-compliant on request. Programmable washing lances for wet cleaning are likewise available.
Alternative for extremely rapid residue-free discharge
Where a particularly rapid product discharge is required, the KoneSlid® KS suggests itself as a complement. It is designed for products from spray drying, fluid-bed drying and belt drying, achieves a good mixing quality after 20 to 30 revolutions and empties within seconds, without a cone of repose and without segregation. Which design offers the best combination of breakage rate and cycle time is clarified by amixon® in the pilot plant with the original product and documented trial results.
Verification in the amixon® pilot plant
Before an investment, suitability can be verified in the amixon® pilot plant. There, 35 test units of various sizes are available. They are complemented by pilot plants in Japan, India, Thailand, China, South Korea and the USA. The trials are carried out with the original product, at real fill levels and within the intended temperature and pressure range. Mixing quality, product protection, energy input, cleanability and reproducibility are assessed. The results are evaluated and documented together with the amixon® experts.
Hygienic design as the foundation
All the properties described rest on the amixon® hygienic design. The mixing chamber and mixing tool are welded free of crevices and ground smooth. The mixing tool is mounted at the top only, so that the contamination-critical lower shaft passage is eliminated. Large Clever-Cut® inspection doors with an OmgaSeal® seal provide good access to the product-contact surfaces. Dead-space-free discharge devices and integrated washing lances permit validatable dry and wet cleaning in accordance with the EHEDG, FDA and 3-A specifications.