Feature article: Top-mounted magnetic mixers for special stirring tasks

Magnetic agitators offer many advantages compared to agitators that have a mechanical seal. A further development of the top-mounted magnetic agitator using an internal magnetic coupling now enables areas of application that were previously not possible.

Magnetic agitators - efficient and easy to maintain

Magnetic agitators offer many advantages compared to conventional agitators that have a mechanical seal. In particular, the lower risk of contamination and the resulting lower operating costs are substantial arguments for the use of magnetic agitator technology. The field has developed rapidly in recent years. This enables its use for a large number of stirring processes, such as slurry stirring tasks. Magnetic agitators combine aseptic process capability with stable and precise operation and also enable a large amount of power to be transmitted.

Retrofitting for existing systems

New containers or bioreactors are not the only vessels that can be equipped with magnetic agitators. Replacing the conventional mechanically sealed agitator as part of a retrofitting of existing systems is also useful in many cases due to the many advantages of magnetic agitator technology.

Increased torques and better stability

ZETA has now brought a new product to the market in the field of ​​magnetic agitators driven from above, the so-called top-mounted magnetic agitators. ZETA's top-mounted magnetic agitators were mainly designed for magnetic couplings up to 8 newton-meters (Nm). The areas of application were limited to reactors in the laboratory sector and smaller process containers. The further development of the ZETA AMRi, a top-mounted magnetic agitator with an internal magnetic coupling, now enables application options on a larger scale and for installation positions inclined up to 20°. The optimized design leads to an increase in transmissible torques with better stability of the agitator shaft and journal.

Tailored for the pharmaceutical industry

In some agitation processes, depending on the container and agitator geometry, the installation of the agitator requires a certain tilt angle in order to achieve optimal flow dynamics. The AMRi has already proven itself for customers in systems having such an inclination of the agitator shaft.

A microfiltration system was supplied for a Swiss pharmaceutical company, with the geometry of the system being based, by customer request, on an existing system having a conventional agitator. Instead of the mechanically sealed agitator, however, a top-mounted magnetic agitator was installed here. This not only made the required tilt angle of 10 degrees possible, but tests before delivery also showed that the agitator can also be operated at an angle of 20 degrees. As part of an agitator expansion study, the best solution for a user-friendly and ergonomic design adapted to the spatial conditions was worked out together with the customer.

Sophisticated design for easy cleaning

Further advantages of the AMRi also include a simple construction of two parts - a unit that is installed with the flange fixed and a drive unit. The completely removable container lid also enables the agitator to be installed easily. Riboflavin tests carried out confirm that the container and agitator can be cleaned easily and efficiently.

Unprecedented fields of application

A top-mounted magnetic agitator is also used for a very special stirring task in a downstream process system for a customer in Vienna. A slurry of hydroxyapatite is stirred in a 700 L container, which is then pumped into the chromatography column to be packed via an outlet valve in the base of the container. However, the material easily settles and compacts. Up to now, there was no suitable stirring system for this challenge.

ZETA developed a solution with a three-stage AMRi agitator adapted to the container that ensures sufficient turbulence during emptying and also with low batch volumes. The new system was subjected to extensive tests that examined the slurry with regard to particle sizes and clumping. The efficiency and stability of the stirring system was thereby proven.

Agitators for potentially explosive environments

ZETA's top-mounted magnetic agitators comply with ATEX guidelines and can be certified for use in potentially explosive environments. One such project was carried out for a pharmaceutical manufacturer in Switzerland. Agitators for 22 containers with sizes of 50 or 100 L were used here, with the respective agitator shafts being installed at a tilt angle of 13 or 20 degrees. Equipping the containers with mechanically sealed agitators was out of the question for the customer, since the nitrogen supply for the gas-lubricated seals would have been very complex and would have required too much space.

• Reduced risk of contamination compared to mechanical seals
• Simple, inexpensive maintenance
• High stability even with an inclined agitator shaft
• High performance input possible
• ATEX certification possible
• Customized solutions for special tasks and challenges