Which powder mixer concepts work well with standardised drums for small powder batches?
For small powder batches in standardised drums, drum and container mixers based on the free-fall principle work particularly well, provided the powders are readily flowable, largely free of agglomerates, and sufficiently similar in particle size, particle shape, bulk density and flow behaviour. In development work, rotating drum mixers, tumble mixers and 3D container mixers are particularly common. The sealed drum is held in a secure clamping fixture and moved as a complete mixing vessel by rotation, inversion, or a superimposed motion. Because no mixing tools enter the product space, the particle structure is treated comparatively gently. At the same time, the product remains in its original container, which limits transfer losses, product-contact equipment surfaces and the cleaning effort for the mixer frame. Drum mixers are also available for smaller containers; systems commonly available on the market cover, for example, drums up to around 220 litres as well as small laboratory vessels.
Pure rotational drum mixers are particularly simple in design. The drum is secured via clamping straps, form shells, adjustable clamping arms or interchangeable adapters at the shell or the drum rim, and moved about a defined axis. Tumble and 3D mixers extend the pure rotational motion with additional pivoting or inversion movements. This can improve the exchange between product regions. These concepts are often suitable for sensitive granulates and readily flowing powder mixtures, because the mechanical stress remains low and there are no product-contact mixing tools to clean.
However, these advantages should not obscure the fact that free-fall mixers are only of limited suitability for many demanding powder formulations. The mixing principle relies on the free movement of individual particles and on repeated pouring and avalanching motion. Strongly cohesive powders can be moved as coherent agglomerates or “clumps” without being sufficiently finely distributed. For such products, the shear energy introduced is often insufficient to reliably break up agglomerates; a dynamic mixer with tools and a defined shear effect may be required. Conversely, free-fall mixers can be prone to segregation with very free-flowing components. Differences in particle size, bulk density, shape or surface properties promote segregation during mixing and, in particular, during discharge.
For formulations with large differences between components, hard-to-dose minor components, strongly cohesive powders, a required liquid input, or high homogeneity requirements, dockable laboratory mixing heads are therefore often the better solution. The drum remains the product vessel, while an external mixing head is docked dust-tight from above. Suitable mixing tools include, for example, helical, propeller, anchor or dispersing tools. Such a system can introduce a substantially higher and more targeted shear effect than a free-fall mixer. It is therefore suitable for cohesive solids, moistening tasks, suspensions, and liquids with suspended solids. For liquid or pasty systems, the choice of tool must be matched to the flow behaviour of the specific medium.
Bottom docking and discharge stations are a further option where products from drums are to be dosed, homogenised, or processed as a suspension. The drum is positioned on a docking station and connected via a suitable discharge valve. An agitator can be introduced into the vessel from above or below to pick up sediment or homogenise a solids suspension before discharge. These solutions are particularly relevant where a product settles during storage, or where solids must be redistributed uniformly in a liquid before filling.
Dissolver and rotor-stator systems in drum designs are not primarily suited to dry powder mixing, but rather to producing dispersions, emulsions and suspensions. They generate high local shear forces and can finely disperse pigments, solid agglomerates or liquid-solid systems. Typical applications are found in paints, coatings, cosmetic formulations, adhesives and chemical-technical products. Compact planetary mixers or dual-shaft systems, in which tools move both about their own axis and along the vessel wall, can be used for pasty formulations. Such systems are suitable for pasty media, adhesives or sealing compounds; in this context, the term viscosity refers to the liquid or pasty continuous phase, not to dry powders.
Suitable fixing is essential for the safe processing of different drum sizes. Steel drums can generally be held using robust clamping or centring systems. Plastic drums and pails, by contrast, require distributed load-bearing support, for example via wide clamping straps, matched form shells or basket adapters, so that they do not deform under dynamic loading. Small laboratory containers can be securely held with reducing adapters. Acceleration and braking ramps should be set so that the container, closure fittings and product are not subjected to unnecessary dynamic loading. In addition, secure lid locking, a check of drum integrity, and, for dust-forming products, suitable protective measures against unintended release are required.
Mixing in the original drum offers clear organisational advantages in research and development. The drum can serve as the mixing, storage and transport container. This reduces the number of product transfers, which can lower losses and the risk of cross-contamination. In addition, trial batches can be processed quickly one after another, because the mixer frame has no product-contact interior surfaces when the container is closed. For toxic, dusty or solvent-containing substances, an enclosed, mechanically safe system is particularly important. Whether the drum clamping and the overall plant are suitable for the specific ATEX zone or a particular containment level must be assessed separately.
A straightforward scale-up from a laboratory drum to a production mixer is, however, not automatic. Transferability depends on the mixing principle, vessel geometry, fill level, motion path, rotational speed, product properties and the order of addition. Characteristic numbers such as the Froude number can provide orientation for rotating systems, but they do not replace trials at the relevant scale. Precisely because the degree of segregation can change with container size, fall height, air movement and discharge geometry, homogeneity should be checked both after mixing and after transport and discharge. Research shows that differences in particle properties, and particle size in particular, can significantly influence homogeneity and segregation risk.
amixon® drum and IBC mixing concepts
For small powder batches in standardised drums, amixon® offers the EM single-shaft mixer, a mixing concept that combines the advantages of drum logistics with a dynamic, precisely controllable mixing action. For larger batches and IBC-based material flows, the COM container mixer is available. Both systems differ fundamentally from free-fall or tumble mixers: the container is not rotated or inverted as a closed vessel, but remains vertical or in a defined tilted position during the process. Homogenisation is achieved by an actively driven mixing tool. This also allows products to be processed that are only of limited suitability for pure free-fall mixing systems, such as cohesive powders, moist solids mixtures, agglomerated raw materials, or mixtures with liquid addition.
The amixon® EM single-shaft mixer is designed for small development, small-production and just-in-time batches. Depending on the configuration, it covers batch sizes of approximately 5 to 200 litres and can be charged and emptied using standardised drums or lidded drums. The drum is brought to the mixer with a hand pallet truck and docked with low dust emission. The mixer is filled through a controlled tilting motion; once mixing is complete, the homogenised product can be transferred back into the drum via the same route. The drum thus serves as the transport and receiving container, while the actual mixing process takes place in the amixon® mixing chamber.
The EM's mixing chamber can be tilted for filling, discharge and process intensification. In the tilted position, the vertical product movement of the mixing tool is superimposed with a cross-flow. The product is conveyed upward in the peripheral region, guided back down in the central region, and simultaneously circulated laterally. This three-dimensional flow promotes uniform homogenisation, even at low fill levels. Depending on the product and configuration, the fill level can lie within a wide range of approximately 10 to 100 percent of the usable volume. The mixing intensity is adjustable: a low tool speed can be used for particularly gentle homogenisation tasks; where required, cutting rotors or HighShearBlades can be used to specifically break up agglomerates and support the incorporation of small quantities of active ingredients or additives.
The EM is particularly suitable for premixes and trituration. Such process steps are important when small quantities of highly concentrated active-ingredient, vitamin, mineral or trace-element components must first be premixed with a suitable carrier. The aim of the premix is to incorporate minor components completely and finely distributed into a sufficiently large proportion of a carrier powder. The resulting premix can subsequently be introduced into a larger final mixture. This approach is relevant, for example, for pharmaceutical products, nutraceuticals, dietetic mixtures and infant formula. The required mixing quality and the suitable sampling strategy must be demonstrated for each formulation.
Liquids can also be mixed into powder in a controlled manner in the EM. Suitable liquid dosing and, where applicable, a finely atomising feed device allow small liquid quantities to be distributed as uniformly as possible within the moving powder. For a robust design, wettability, cohesiveness, initial moisture, particle structure, dosing rate and possible agglomeration must be taken into account. For strongly cohesive powders or products with pronounced agglomerates, additional intensive mixing can support deagglomeration. As with all powder mixing processes, actual suitability should be confirmed through trials with the original product.
The amixon® COM container mixer can be used for larger batches. The container itself acts as the mixing chamber and remains upright or slightly tilted during the mixing process. A mixing tool immersed from above generates the required product movement. Mixing therefore does not occur through inverting the container, but through an actively driven mixing system within the closed vessel. amixon® describes the COM as a container mixer for high-value mixed products; depending on the configuration, it can be operated with standardised IBCs and special Mixtainer® containers.
A SinConvex® or MultiPane® mixing tool can be used with the COM. The mixing tool is introduced from above into the gas-tight closed container, homogenises the product, and is then withdrawn again in reverse. SinConvex® supports intensive three-dimensional flow and good product guidance right into the near-base and near-wall regions. MultiPane® is suitable for particularly gentle mixing processes and can be used where sensitive particle structures, granulates or agglomerates are to be preserved as far as possible. The COM can therefore be used for dry and moist powders, as well as for products with demanding homogeneity requirements. The specific mixing task, the achievable homogeneity, and the suitable fill level are determined through product trials.
A central advantage of both concepts lies in combining the mixing process with container logistics. Transfer steps are reduced, which can limit product losses, dust emissions and interfaces for possible cross-contamination. The container can be used for weighing, intermediate storage, internal transport and receiving the finished product. With the EM, the product is homogenised in the mixer and then returned to the standard drum. With the COM, homogenisation takes place directly in the container. This process organisation is particularly advantageous for small and changing batches, for contract mixers, and for operations with frequent product or formulation changes.
Cleanability is part of the plant design. With the EM, the mixing chamber can be tilted into an ergonomically favourable position for cleaning. With the COM, a Washtainer® can be docked for automatic wet cleaning of the mixing tool. For hygienically demanding applications, the mixing systems can be executed with low-dead-space geometries, readily accessible product-contact surfaces, and suitable sealing and cleaning functions. For the COM, amixon® cites, among other things, WIP fixtures with aseptic quick-release couplings and suitability for high hygiene requirements. Whether dry or wet cleaning is required, and how it must be validated, depends on the formulation, allergen or active-ingredient risk, product adhesion and operational requirements.
Mixing programs can be stored in a PLC and run reproducibly on a batch-by-batch basis. These can include mixing time, tool speed, intensive mixing phases, order of addition, liquid dosing and, where applicable, temperature profiles. A connection to an ERP or manufacturing execution system, together with barcode or RFID capture, can support the complete traceability of formulation, raw materials, container, batch, process parameters and cleaning status. This creates a robust basis for traceability, process validation and the evaluation of plant availability.
All hygienic properties are based on a construction designed to be cleaning-friendly. This includes low-seam welded and ground-smooth surfaces, top-mounted mixing tools without a product-contact lower shaft feedthrough, generously sized inspection doors, and low-dead-space discharge elements. CleverCut® inspection doors with OmgaSeal® seals can improve accessibility and support a permanently tight, cleaning-friendly design. Depending on the project, integrated wash lances or fully automatic wet-cleaning functions can also be provided. Execution to EHEDG guidelines, and taking FDA hygiene guidelines or 3-A Sanitary Standards into account, is possible depending on the project.
Before selecting a mixing system, verification with the original product comes first. More than 30 test units in various sizes are available at the amixon® pilot plant in Paderborn; additional pilot plants exist in Japan, India, Thailand, China, South Korea and the USA. The trials replicate real fill levels, batch sizes, and temperature and pressure conditions. Mixing quality, product protection, energy input, deagglomeration, liquid incorporation, dischargeability, cleanability and reproducibility in later operation are assessed. The documented results provide a sound basis for the technical and economic design of the chosen drum or IBC mixing solution.