High mixing quality

Dipl.-Ing. Matthias Böning

The helical-blade agitator of the vertical single-shaft mixer generates a state of prevailing total flow in the mixing chamber by spiralling the materials in the mixer upward along the peripheral zone of the mixing chamber and allowing these to slide downward in the centre of the vessel. The blade-shaped mixing arms generate an additional lateral flow. In addition, the two synchronously rotating agitators of the vertical double-shaft mixer generate an even more intensive transverse flow and activation of the centre zone of the vessel. Moreover, the double-shaft mixer is suited to operation at low rotational speed thus enabling gentle stirring for high mixing qualities.

One example of mixing pharmaceutical products is a 5 m³ double-shaft mixer used for microfine dispersion of active substances in tablet masses with subsequent moistening. First the base and major components are automatically weighed and mixed. The mixing process becomes distributive and dispersive through the additional action of multi-stage cutting rotors. This step is followed by the addition of highly viscous liquids and suspended extract compounds. Other dry substances are added and applied to the moist particle surfaces during a very gentle stirring phase. Sub-sequently, the free-flowing mass is pressed for drying. The mixer is discharged free of segregation and with the most gentle treatment of particles possible. The level of residue is about 0.07%. The batches for one day can be mixed without requiring intermediate cleaning, apart from sweeping with a suitable broom or using an industrial vacuum cleaner.

To clean the orbital tank, washing lances are inserted in the opening provided and secured by means of an aseptic fastlock system. The CIP operation takes place automatically. The rotating agitators and the mixing chamber are sprayed completely. Due to the seamless detail design of all mixer components, the mixer offers a high standard of hygiene with low labour requirements. It is considered microbiologically controllable and is FDA-approved for the production of pharmaceuticals products and bacteria cultures. For mixing other high-grade products where mixing procedures are less demanding in terms of process engineering, the vertical single-shaft mixing system is chosen. This preci-sion mixer is particularly suited to effective mixing of large volumes. To achieve ideal mixing qualities, the residence time in the mixer is about 50 to 150% longer compared to the vertical double-shaft mixer.

A single-shaft mixer with a volume of 3 m³ processes batches of up to 10t consisting of granulated tablet masses, granulated sugar as well as finely dispersed powder and liquid additives, offering high mixing quality. Subsequently, the mixer product is filled into container carts by means of suction conveyors. The discharged product is free of segregation. The residue in the mixer is about 500 g. This corresponds to a discharge of about 99.99%. A successful CIP proce-dure is guaranteed by three orbital washing heads. For simple operating procedures and comprehensive quality assurance, six automatic washing programs have been included in the process control system. These are based on documented and verified cleaning procedures and are an integral component of the production process.

Ruberg Mischtechnik

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Further information cpp-203