Range of application and influencing variables

Container mixers are used in the food industry across a broad performance range, from recipe development to large series production. The batch sizes and throughputs actually run depend essentially on the product properties (for example bulk density, flow behaviour, particle size distribution) as well as on the required homogeneity and hygiene requirements.

Typical batch sizes (container volume)

The batch size is determined primarily by the gross volume of the standard container used (IBC, intermediate bulk container) and by the permissible fill level.

Laboratory and pilot-plant scale: approximately 5–50 litres

Used for product and recipe development, sample production, process validation or highly concentrated additive mixtures.

Pilot and small series production: approximately 50–300 litres

Typical for niche products, food supplements, spice blends or premium and specialty mixtures in limited quantities.

Medium production sizes: approximately 300–1,500 litres

Frequently used for baking mixes, instant products, dry beverage powders, soup and sauce bases as well as functional food mixtures.

Large-scale production: approximately 1,500–4,000 litres

For high-volume applications such as staple food mixtures, feed premixes or bulk-oriented base mixtures.

In special cases, particularly in the high-performance pharmaceutical and food sector, larger container volumes are also possible (several thousand litres).

The usable fill level typically lies at 40–70 % of the container volume, in order to ensure sufficient free space (headspace) for movement of the mix and reliable homogenisation. The batch mass actually available in kg depends directly on the bulk density of the product.

Typical throughputs and times

Throughput results from batch size, mixing time and the total cycle time per batch (including handling processes).

Mixing times (pure mixing time)

Usually 2–15 minutes per batch; with typical dry powders and granules, many applications lie in the range of 3–8 minutes, depending on recipe, flow properties, homogeneity requirement and the mixing technology used (pure free fall versus additional mixing tools or intensive mixers).

Cycle times including handling

In practice approximately 10–30 minutes per batch, depending on docking, clamping, lifting/tilting, charging, discharging, any intermediate cleaning and the degree of automation of the container handling.

Batch frequency

• Semi-automated plants: typically 4–7 batches per hour.
• Fully automated systems with automatic container transport (for example AGVs) and quick-clamping systems: up to 10–12 batches per hour possible.

Practical mass throughputs (guide values):

• Small plants: approximately 100–500 kg/h
• Larger plants: approximately 500–3,000 kg/h

Example calculation

With a standard container of 1,000 litres at a usable filling level of approximately 70 % (approximately 700 litres) and a mean bulk density of 0.6 kg/l, a batch mass of around 420 kg results. Where 6 batches per hour are run, the theoretical throughput lies at approximately 2.5 t/h.

Factors influencing design and throughput

The specific throughput of a container mixing plant is determined by several technical and organisational factors.

Product properties

Bulk density (with food powders typically 0.3–1.2 kg/l), flow properties (fluidity; poorly flowing or cohesive powders often require longer mixing times or the use of choppers or intensive mixing tools to break up agglomerates), particle size distribution and sensitivity to mechanical stress.

Mixing quality requirements

Required homogeneity, for example a coefficient of variation (CV) frequently below 5 % for typical food applications; proportion of small added substances (flavourings, vitamins, colourings, functional additives) which may require a longer mixing time or special process management.

Recipe and process complexity

Upstream and downstream steps (weighing in, dosing, labelling, sampling) influence the rate at which new batches can be fed to the mixer; likewise the number of components per recipe and the frequency of recipe changes.

Hygiene and cleaning requirements

Hygienic design requirements (for example EHEDG-compliant design); cleaning strategy: with container mixers the main cleaning of the container takes place outside the machine, in container washing systems. The mixing apparatus itself is cleaned wet by docking a washing container which also handles the drying.

Degree of automation in container handling

Manual handling (pallet trucks, forklifts), semi-automatic handling with mechanical docking systems or fully automatic handling with AGVs, automatic docking, clamping and identification of the containers.