What advantages do adaptable mixing tools offer for changing products in an industrial mixer?
Adaptable mixing tools increase the flexibility of an industrial mixer when products, formulations or batch sizes change. They make it possible to adapt mixing intensity, product movement, de-agglomeration, liquid introduction and wear protection specifically to the properties of the respective mix, without having to install a completely new plant for every task.
Process flexibility
With changing products, the requirements often differ considerably. Free-flowing powders mainly need even convective circulation. Cohesive powders can require additional de-agglomeration. Sensitive granules, fibres, coated particles or crystals, by contrast, should experience as little shear, impact and crushing stress as possible. Adaptable tool elements, such as paddles, blades, helices, knives, scrapers or intensive mixing tools, allow product movement to be adjusted to these differences.
Adaptability can be implemented in different ways here. With some mixers, tools are actually changed, for example when switching from a gentle paddle geometry to a more intensively acting tool. In other cases, the base tool stays in the apparatus and the process intensity is adjusted via rotational speed, direction of rotation, time-limited switching-on of choppers, dosing strategy or fill level. In practice, the second solution is often faster, because it requires no mechanical conversion and no renewed cleaning after a tool change.
Greater flexibility, however, does not automatically mean that every formulation can be run on the same plant without renewed testing. Where particle structure, cohesiveness, moisture, dosing fractions, formulation, fill level, product-contact materials or the required hygiene level change significantly, mixing time, rotational speed, homogeneity, emptying and cleaning must be checked for the new task.
Mixing quality and product protection
Tool geometry determines which mixing mechanisms dominate in the vessel. Large-area paddles, helices or ribbons mainly promote convective product streams and can circulate the entire batch volume relatively gently. Intensive knives, choppers or rotor-stator systems generate locally higher shear forces and are suitable for breaking up agglomerates or for finer distribution of a liquid addition. Scrapers can limit wall build-up with sticky or moist products and help include all product zones in the mixture.
The ability to select or combine these functions as needed helps resolve the conflict between fast homogenisation and product protection. A sensitive granule, for example, can first be homogenised at low rotational speed. If individual agglomerates need to be broken up, an intensive tool can be operated only for a short, defined phase. The batch is then mixed out again at low mechanical stress. This lowers the risk of particle breakage, fines formation, abrasion, unwanted heating and changes to the particle size distribution.
A tool configuration chosen appropriately for the product can shorten the mixing time, because the required product movement is generated in a targeted manner. This does not mean, however, that a more intensive tool is always better. Excessive rotational speed, too long a mixing time, or unnecessarily high shear can segregate the mixture again, damage sensitive particles, or increase the cleaning requirements. The optimal goal is therefore the smallest robust process window in which the required homogeneity is reliably achieved.
Cleaning and wear
Adaptable tools can improve cleaning and product changes when they are designed with smooth, readily accessible surfaces, defined tool-to-wall clearances and as few retention zones as possible. Suitable scraping and deflection geometries can limit wall build-up and base deposits. This reduces product residues, cleaning effort and the risk of cross-contamination. With allergen-critical, pharmaceutical or high-purity products, however, all product-contact areas – including shafts, seals, outlet fittings, lids, filters and dosing points – must still be included in the cleaning validation.
With abrasive mixes, modular or exchangeable wear elements can be economically worthwhile. Instead of replacing the entire rotor, particularly stressed paddles, blades, scrapers or protective segments can be replaced in a targeted way. Through a materials-appropriate choice, hardened steels, carbide, suitable plastics or ceramic coatings can be used only where technically necessary. Quick-change tools that can be used on both sides can reduce downtime as well as spare parts and maintenance costs. One example of a modular tool concept cites rapid replacement of all product-contact wear parts and lower wear costs through mixing blades usable on both sides.
Further process functions
Tool adaptation can be combined with further equipment options. Liquid lances, spray nozzles or two-fluid nozzles allow the targeted introduction of binders, oils, solutions or suspensions. The tool motion distributes these liquids throughout the product volume; with suitable design, this can bind fine fractions to coarser carrier particles, reduce dust, or produce granulation and coating effects.
Temperature-control jackets or temperature-controlled tools can be relevant where the product is to be heated, cooled, dried, conditioned or mixed at a defined temperature. Vacuum or inerting equipment can be necessary for solvent-containing, oxidation- or moisture-sensitive, or dust-explosible products. Inline sensors such as NIR, Raman, torque, temperature, moisture or pressure measurement can supplement the control system, provided the measurement point and the evaluation model are validated for the critical formulation.
Scale-up and validation
Adaptable mixing tools can ease the transition from laboratory to production scale, but they do not replace systematic scale-up development. In scale-up, vessel geometry, tool diameter, wall clearances, fill level, rotational speed, circumferential speed, power density and mixing time must be considered together. Geometric similarity, as well as characteristic values such as circumferential speed or specific power input, can provide important guidance. A constant circumferential speed or power density alone, however, does not guarantee that product flow, homogeneity and product protection transfer identically. Tool geometry and the actual product properties remain decisive.
Mixing trials with the original product are therefore the safest basis for determining the appropriate tool configuration and the process window. These should examine not only mixing quality and mixing time, but also particle breakage, fines content, temperature development, liquid distribution, abrasion, residual discharge, cleanability and the stability of the mixture after discharge and conveying. With product ranges of great variance, the most critical product should be tested in each case: for example the most cohesive, most abrasive, most sensitive or lowest-dosed formulation.
Adaptable mixing tools and equipment: the amixon® system for changing products
One tool principle, many operating conditions
For changing products, amixon® mixers generally require no mechanical conversion sets and no exchange of the mixing tools. The SinConvex® helical ribbon mixing tool remains in the mixer even when the bulk material characteristics change markedly – from coarse, sensitive particles to fine or nanostructured powders, from free-flowing bulk materials to cohesive, moist or suspended systems. What is decisive for mixing quality is not a change of tool, but an operating mode individually matched to the mixing task.
The SinConvex® geometry produces three-dimensional forced restratification. The product is conveyed upward near the wall, flows back downward under gravity at the centre, and is continuously guided back into the active mixing zone. This controlled product movement can be used for dry, moist and suspended solid systems. Even with strongly differing bulk densities and particle sizes, the operating parameters can be set so that the required homogeneity is achieved. For mixtures with large differences between the components, however, it must always be checked whether the mixture also remains stable during discharge, conveying and filling.
Adaptation takes place through the operating mode. This includes mixing time, tool rotational speed or circumferential speed, fill level, order of raw material additions, dosing locations, dosing times, direction of rotation where applicable, liquid addition, temperature and pressure. The tool circumferential speed can be set in a range of approximately 0.8 to 3.5 m/s, depending on the design and mixing task. For sensitive products, a particularly gentle, low-speed operating mode is chosen. With cohesive powders, agglomerates or minor components that are difficult to disperse, the intensity can be specifically increased. Where local de-agglomeration is required, cutting rotors or HighShearBlades can be switched on for a limited time. The base mixing tools remain unchanged; only the process condition is adjusted.
Liquid additions, too, can be integrated into product handling without a tool change. Lances, spray nozzles or two-fluid nozzles introduce binders, oils, solutions or suspensions into an active mixing zone. This enables, for example, the wetting of cohesive powders, the even distribution of additives, the binding of fine particles to coarser carriers, or the coating of solid particles. Quantity, droplet size, dosing time and post-mixing time are adapted to the respective formulation as part of the operating mode. For temperature-sensitive or thermally controlled processes, a double jacket supplements the process options through heating or cooling.
Each formulation is given its own mixing program in the PLC. This program can contain setpoints and tolerances for mixing time, rotational speed, intensive mixing phases, liquid addition, temperature, pressure, fill level and discharge sequence. A product change is thus implemented primarily by calling up a released recipe, not by a mechanical conversion of the mixing tool. This reduces changeover times, avoids errors in assembly or tool configuration, and eases reproducible batch handling. The actual cleaning time and the release required between two products continue to depend on the formulation, allergens, active ingredients, colour, odour, fat content and hygienic risk assessment.
Fill level and product range
The usable fill level range for amixon® mixers can cover approximately 10 to 100 per cent of the usable volume, depending on the design and product. This allows the same apparatus to process different lot sizes. Whether the technically ideal random mixture is achieved at every fill level and with every formulation must be demonstrated on a product-related basis. Particularly at very low fill levels, with nano-fine or strongly cohesive constituents, with extreme dosing ratios, or with formulations having large differences in density and particle size, mixing time, the intensity required and the tendency to segregate can change.
The same applies to the claim that no renewed validation is required. A change in process parameters within an already established and validated process window can be covered by the released PLC recipe. With a new formulation, significantly changed raw material quality, an extended fill level range, or a different homogeneity target, however, a renewed risk-based assessment is required. It can be kept lean where comparable products and robust prior trials exist, but should not be omitted entirely, particularly in quality-critical applications.
Design and retrofitting
Every amixon® apparatus is designed on the basis of a user requirement specification. Tool geometry, the possible number and position of cutting rotors, the location of liquid nozzles, materials, surfaces, seals, sensors, temperature-control surfaces, discharge concept and automation are matched to the intended product range. For abrasive products, for example, hardened tools, carbide inserts or ceramic coatings can be provided. For moist, reactive or temperature-sensitive products, temperature-control jackets, vacuum, pressure or inerting functions can be integrated.
If the product range is extended later, project-specific modernisations are possible. These can include additional dosing points, measurement points, liquid lances, temperature-control connections, sensors, cutting rotors, or adjustments to the discharge and cleaning periphery. Such retrofits, however, change the plant and must therefore be reassessed with regard to mechanics, tightness, hygiene, explosion protection, control and process quality. In many cases, the mixing helix itself does not need to be replaced.
Verification in the pilot plant
Suitability for a broad product range is verified in the amixon® pilot plant using the most critical original products. These include, for example, the product most sensitive to particle breakage, the most cohesive powder, the most abrasive material, a formulation with a very low dosing fraction, or a mixture with particularly large differences in density and particle size. The trials are carried out with realistic fill levels, mixing times, rotational speeds, addition sequences and, where applicable, temperature or pressure conditions.
Mixing quality, mixing time, de-agglomeration, particle protection, liquid distribution, energy input, residual discharge, cleanability and the stability of the mixture during discharge and in downstream process steps are assessed. The documented results form the basis for the design of the production mixer and for defining the PLC recipes. They help establish the process parameters so that a product change actually takes place via a mixing program rather than a mechanical tool change.
Hygienic design
The flexible operating mode is complemented by a cleaning-friendly construction. Mixing chambers welded free of crevices and ground smooth, mixing tools supported only at the top without a lower shaft passage in the product area, large CleverCut® inspection doors with OmgaSeal® seals, low-dead-space discharge elements and integrated washing lances improve accessibility, cleaning and product changes. Dry and wet cleaning can be designed and validated depending on the product, allergen profile, fat content and hygiene concept. Depending on the project, the construction can be aligned with EHEDG guidelines as well as FDA hygiene guidelines and 3-A Sanitary Standards.