Container mixers using intermediate bulk containers (IBCs) are particularly suitable for contract mixing operations with variable batch sizes and frequent product changes. They combine process engineering, logistical and hygienic advantages in a modular system.

Some container mixers work as free-fall mixers. The vessel is rotated or tilted so that the product falls and rolls within the mixing chamber. These systems are suitable above all for free-flowing powders and granulates with similar bulk density, particle size distribution and flow properties. There are also container mixers with an actively moved mixing tool inside the vessel. These are regarded as precision mixers, can be used universally and are also suitable for more demanding formulations.

A central advantage is that the IBC itself serves as the mixing vessel. Filling, mixing, intermediate storage, transport and discharge all take place in the same container. Classic transfer operations are eliminated. Flexibility increases, product changes are accelerated and different batch sizes can be run with consistent quality.

IBC systems offer great freedom in batch size. Different container sizes – from smaller vessels to several thousand litres – allow batch sizes to be matched exactly to the order quantity without the mixing station having to be converted. Container mixers typically work with fill levels of approximately 40 to 80 per cent. If the batch quantity is matched to the container size, the fill level and thus the flow and mixing behaviour remain comparable. Stationary mixers, by contrast, are usually optimised for one nominal volume and lose mixing quality when underfilled. IBC systems circumvent this disadvantage.

Product changes benefit from the short set-up and cleaning times. A change essentially takes place by exchanging the container; the base machine is relatively easy to clean. The risk of cross-contamination falls considerably. Where required, each formulation can be assigned its own IBC. This makes such systems particularly interesting for areas with high hygiene requirements, for example in the food, pharmaceutical, paint or additive industries.

In process engineering terms, free-fall container mixers work very gently. Homogenisation takes place through rotation or a tumbling or tilting movement of the entire vessel, usually without internals in the product space. Shear loading, particle breakage and segregation with sensitive bulk materials are thereby reduced. Defined speeds, tilt angles and mixing times make reproducible results attainable, with target relative standard deviations in the low single-digit percentage range. The closed system reduces dust emissions and protects against exposure to critical dusts.

Logistically, IBC container mixers permit parallel operation. The filling, mixing, cleaning and discharge processes can be decoupled in time. While one batch is being mixed, a second container can be filled and a third cleaned. The mixing station thus becomes the central processing unit with high utilisation. At the same time the IBC functions as a storage, mixing and dosing vessel, so that transfers between batching and mixing vessels are eliminated. This saves time, reduces losses and lowers dust generation.

Traceability can be organised well. Each container can be given a batch identification and is thus traceable through the entire process. This supports GMP-compliant documentation and audit trails in contract manufacturing. The cleaning effort is concentrated on the vessel and a few interfaces rather than on complex stationary mixing geometries. Consumption of cleaning media and water and the working time required therefore fall.

From the point of view of occupational safety and environmental protection, the closed system minimises the exposure of personnel to dust. Atmospheric contamination of the surroundings is reduced, so that different products can be processed in parallel in one hall without influencing one another.