Metenova Academy is a series of articles, aiming to introduce and educate in the world of magnetic mixers. In this article we will describe what to consider when designing a vessel with a bottom mounted mag mixer.
Usage of bottom mounted mag mixers will require regular preventive maintenance. This normally contains inspecting of the mixing head, slide bearing components and replacing the gaskets used - at least once a year. However, the intervals differ between users and manufacturing plants.
When designing vessels to be used with a bottom mounted magnetic mixer there are some considerations that are crucial to achieve the optimal mixing performance. Typically, a lot of work is emphasized on positioning the mixer in the proper location in the bottom. The mixer location will drive the flow in the bottom region of the vessel. The placement is important in order to achieve proper mixing, avoid stagnation points compensate for other equipment’s effect on the flow pattern such as sensors, probes, vortex breakers. The proximity to other “welded in” components such as tank outlet valves also need to be considered in relation to available positions.
One thing that is often neglected is the fact that it is equally important to consider the relationship between the top openings and the mixer, located in the bottom. This has to do with accessibility and service ability from a top outside position. By paying attention to this in a design phase, a lot of maintenance and service hassle can be avoided. In the end it will save time and money for the end user.
In today’s pharma process, the users are more and more reluctant to do vessel entry during service of mixers. The reasons are many, but aspects like safety plays a large role. It is becoming increasingly more difficult and restricted to send down service staff, into a vessel.
By addressing the design of the top part of a vessel, the designer can make the vessel to be service friendly and thereby avoid the need of using vessel entry. Often the position of the manway is positioned by coincidence, rather than in relation to the placement of the mag mixer.
In addition to the service aspect, the top design can also be important for certain applications, where the feeding point of either liquid substances or powder substances are being fed. This is due to the fact that position of the feeding point can in some cases either enhance or restrict the blending process. Access point is determined by the vessel top design.
To perform service on a bottom mounted magnetic mixer, it is important to be able to access the mixer from a position that is well aligned with the vessel plate center line. This allows the operator to reach into the manway and remove the Mix Head with the Mix Head lifting tool in an aligned direction.
This is important since the mixers rotates around a sliding bearing and the mixing head needs to be lifted along the slide bearing axis. This means that the manway where the operator will work from is required to be in a position that gives the operator good alignment with the tank plate. If there are multiple mixers inside the vessel, it is even more important to find a good position. When having multiple mixers, the service point will have to be a position where all mixers can be accessed from.
Just as important, is the part of the slide bearing located on the tank plate, the male post. It also needs to be serviced from the outside preferably. Often the male post bearing is attached to the tank plate though a threaded hole or a threaded pin that holds the bearing in position on the tank plate. The assembly need to be tightened according to the manufacturer’s specification. To be able to firmly tighten and secure the bearing part alignment is crucial.
Alignment between manway access point and mixer tank plate is very important when performing service of a mag mixer!