With a high degree of automation

Walter Sonntag

Vetimex is one of the leading manufacturers of animal pharmaceuticals in the Netherlands. Its facility in Bladel was equipped with two production lines for premixes and special mixes, a process involving the blending of carrier, active and auxiliary ingredients. The first task was to feed a 4000 l mixer with the basic ingredients at high precision.

The carrier ingredients – corn meal and corn flour – for premix production are delivered by silo lorries, and pneumatically transferred into indoor silos with a capacity of 45 m3 each. The silos are standard-equipped with the necessary filters, level measuring systems, pressure- and vacuum-relief valves. A vibration bottom and a dosing screw with integrated screening ensure reliable product discharge from the silos and feeding into the pneumatic vacuum weighing system. The weighing system transports the carrier ingredients into a conveyor scale located above the mixer and offering a capacity of 4000 l. With the help of coarse/fine switchover at the product inlet, very high accuracies of dosing and weighing are achieved even in large batches. Following electromechanical weighing, the batch of carrier ingredient is filled into the mixer.

For supplying the active ingredients – they are delivered in bags – three bag-tipping hopper stations are available, equipped with filter, vibration screen and suction for dust-free bag emptying (Fig. 1). The vibration screen prevents coarse contaminants getting into the production process, at the same time, it gently breaks any agglomerates. Three vacuum weighing systems with weighing ranges of 50 kg, 250 kg and 500 kg convey the active ingredients to the mixer.

Since some of the ingredients are poor-flowing bulk materials, these three conveyor scales were constructed as negative-weighing systems. The weighed batches are kept ready in the conveyor scales, and are consistently called off by the mixer via dosing screws. Systematic allocation to lines prevents contamination and division into different weight ranges leads to exact dosing and weighing results. This has a favourable effect on the quality of the mixes. Micro ingredients are weighed at a separate weighing station.

The modular control system (MCS) controls the entire production and mixing process (Fig. 2). At the correct time, it doses the weighed quantities into a vertical two-shaft precision mixer. This mixing principle, aided by two synchronously rotating, top-mounted, rotatin helical mixing blades, causes total integration of product flows in the mixer. While the material in the outer area are moved upwards, a downflow prevails at the centre of the vessel. This product interflow without dead zones makes for high effectiveness, ideal for mixing ingredients which differ greatly in bulk density and particle size. After only three to four revolutions at a circumferential speed of about 1m/s, theentire bulk material has been completely stirred once. This ensures ideal distribution of the mix material, regardless of mixing-tool speed. Even binders like oil and micro quantities of active ingredient can thus be thoroughly integrated. In all, three to five batches of 200 kg each are produced. The mixing time per batch is six minutes at the maximum. Experience has shown that product composition and mixer filling level do not affect the mixing process. The precision mixer is equipped with an automatic frequency control which saves energy at a rate of up

to eight per cent. Its construction is joint-free, which makes it possible to also handle, for example, microbiological substances. The mixer meets the 3-A standard and conforms to GMP regulations. Orbital tank-wash lances, which are used with aseptic snap locks, ensure fast and reliable cleaning with rotating mixing tools, despite the large volume. Mixer residue discharge to a degree of 99.97 % – the residue from a 2000 kg batch is about 600 g – reduces the risk of cross-contamination to a minimum.

A dosing screw moves the finished mixes directly to a bag-filling station. The thorough blending remains ensured for the duration of the entire discharge process as well. A sample is taken from each batch. Following satisfactory results of an analysis, and no sooner, the produced mix is released for sale. Vetimex currently produces 13 different formulas, with product changes several times a day being possible because of the cleaning ease.

On a second product line, special mixes of premix, active and auxiliary ingredients were to be produced. Due to the large number of formulas (some 100) with several ingredients each, and because of the frequent formula change, Vetimex realized a containment system.

The bagged material is preweighed using a feed hopper with a large-surface filter and suck-off system, and filled into a round interchangeable container with butterfly valve. Here, too, a vibration screen prevents coarse contaminants entering the container. Small quantities of active ingredient are weighed separately at a manual weighing station, and also fed into the container. For a control, the interchangeable container sits on a floor scale during the dosing process. After filling, the container is shut tight with a lid.

The container is pneumatically fixed in the holding device of the mixer. With a special, frequency-controlled mixing process, this system achieves very good blending results because the active and auxiliary ingredients are free-flowing and of similar bulk density. Additional mixing tools in the container are not required. The round shape of the container ensures high sturdiness (Fig. 3).

The interchangeable containers are deposited on a container discharge station above the filling machines, secured in place and docked via an inflatable sleeve for dust-free emptying. After opening the container, the mixture – now homogeneous – can be fed into the machine. The round interchangeable containers feature an optimum geometry for discharge, and can be equipped at any time with added vibration support in the case of poor-flowing bulk materials. The dosing screw integrated into the container discharge station receives a signal from the requester of the filling machine, which causes it to discharge the product at a consistent rate.

When the interchangeable container is empty, it is removed from the filling machine, and cleaned. Here again, the round construction proves an advantage. After cleaning, the interchangeable container can be used again. In all, ten interchangeable containers are used in this system. This enables high flexibility coupled with reduced cleaning work.

Azo

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Further information cpp-231