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Retrofitting always possible

Universally convertible machines allow flexible processes and are the basis for future-oriented investments

What has been tried and tested for mixers and batch dispersers for several years is now also being consistently applied to inline dispersers and powder wetting machines. By changing just two machine parts, the powder wetting machine is transformed into a six-ring inline disperser with shear speeds of up to 42 m/s. The conversion is quick and easy. The pipelines do not even need to be disconnected. The new tools also fit into older machines.

YSTRAL Multipurpose Multipurpose machine on lifting frame with quick coupling and interchangeable shafts

The process technician or production engineer is constantly faced with the question of which machine to integrate into their process. He knows the day-to-day business, he knows the current wishes and requirements, but he also knows that processes and requirements change frequently.

He cannot yet estimate whether the product range will be expanded in a year's time or whether new additives will be used that suddenly react more sensitively to shear and can therefore no longer be dispersed. Often the initiative also comes from the purchasing department, because it manages to procure a more cost-effective raw material, which is coarser-grained and now has to be dispersed much more.

Ultimately, customer requirements are changing. Quality requirements are constantly increasing. It makes no sense to purchase and install additional machines at a later date for each additional task. Retrofitting initially means project planning costs and loss of production during the conversion. Pipelines often have to be laid or new container flanges, TÜV approvals, extensions to the I&C technology and the control system are required. The follow-up costs are therefore very high. Forward-looking planning, convertibility, flexibility and future orientation are therefore important aspects when making an investment decision. With small laboratory appliances, it has long been common practice to design the tools to be quick and easy to change. The aim is to cover the entire range of similar processes with one device, which can be realized with the same drive, the same installation and the same control system. For this purpose, the drive is designed with a coupling so that the entire tool shank can be replaced quickly.

Interchangeable shanks for industrial machines

This concept has also proved very successful with industrial machines. The interchangeable shaft is designed in such a way that the mixer shaft is mounted completely separately from the motor. Sealing to the product is achieved via an integrated mechanical seal.

The coupling to the motor can be disconnected and reconnected in a few simple steps. The tool holder at the lower end of the interchangeable shaft is designed identically for all usable tools. It is therefore possible to replace the entire shaft including tool quickly and completely or, if you only have one interchangeable shaft, to remove the shaft and only change the tool according to the task.

A jet mixing head is used for completely homogeneous mixing and suspending. This generates vertical circulation without any baffles in the container and without rotation of the liquid. For intensive dispersing, on the other hand, the dispersing head is used. This works according to the rotor-stator principle of the gear rim dispersing machines and is used to crush particles or for emulsifying.

The Dispermix is a combination of disperser and mixer. While, as with the jet mixer, the entire contents of the container are mixed homogeneously, part of the product flowing through the mixing head is conveyed through the dispersing zone and intensively dispersed. This machine is particularly interesting because, unlike the simple disperser, it prevents an uneven distribution of the dispersing effect.

Without having to install a second mixer, the entire contents of the container can be dispersed homogeneously, even at higher viscosities. In addition to "normal" dispersing tasks, the Dispermix is therefore particularly suitable for quickly dissolving thickening agents and breaking down agglomerates. It is able to dissolve even highly thickening swelling agents (CMC, xanthan gum, guar, carbopol, etc.) quickly and absolutely agglomerate-free.

The Dispermix is also available in versions for breaking up very large lumps of solids in the liquid. Examples of this are the dispersing of fat or wax blocks or the dispersing of materials frozen in blocks. The Dispermix saves an enormous amount of time here.

With the three tool variants mentioned, all tasks from gentle mixing to intensive dispersing can be realized. A newly developed tool is the TDS suction mixer, which can be used on the Multipurpose machine. This mixer builds up a powerful vacuum in the center of its mixing head. With this, powders can be sucked into the liquid directly from the bag via a suction tube, dust-free and without losses. The bags do not need to be lifted and poured into the container. The powder is mixed in below the surface of the liquid. No crusts or adhesions form on the container wall.

Multifunctional machines in all sizes

However, the concept of changing the entire shaft using a coupling is not possible if the machines become too large and too heavy or are permanently installed in the container. But even in these cases, easily retrofittable multifunctional machines are available.

In this case, the tool holder is designed so that all available tool variants fit. The mixing head can then also be easily replaced. For retrofitting, it is usually necessary to change the mixing head in the container or to pull the machine out of the container. It is therefore important to pay attention to the "LDT multifunctional machine" feature when ordering a mixer or disperser. Although it is not possible to recommend such an LDT machine for every application, it is possible for most applications. Multifunction machines are designed in such a way that all screw heads, all connections and all threads are designed and sealed in accordance with GMP requirements. This is necessary for applications in the pharmaceutical or food industry. For applications in the chemical industry, this is a great advantage for cleaning.

Also as an inline disperser

The inline machines installed outside the container must also be as flexible, multifunctional and easy to convert as possible. Powder wetting machines of the Conti-TDS type have the task of sucking dust-free powder into the liquid and dispersing it. For this purpose, they have a dispersing chamber with at least three, sometimes even more connections: one or more inlets for the liquid, one or more inlets for the powder and an outlet for the finished product.

The machine is installed outside the container and conveys the liquid independently without an additional pump. It generates a massive vacuum in its dispersing zone, with which it can suck in powder or other liquids and disperse them very effectively.

The Conti-TDS-2 machine shown here is a smaller machine. The machines are available in various sizes up to 250 kW.

For tasks where no powder or other liquid is sucked in and where the entire output is to be used for dispersing, tools are now available that allow the powder wetting machine to be converted into a six-ring dispersing machine in just a few simple steps.

The conversion is very simple: only two screws need to be loosened and two components replaced. With the tools shown here, the result is a six-ring dispersing machine with shear rates of up to 42 m/s and shear gradients of up to 100,000 s-1.

The special feature of this machine concept is that the liquid connections do not even need to be disconnected for conversion. In contrast to all other inline dispersion machines, where the liquid inlet is located on the front of the machine and therefore has to be dismantled each time the machine is accessed, the Conti-TDS has the inlet on the motor side of the dispersion chamber. The connections for the liquid can therefore remain connected for conversion.

The fact that the liquid flows into the machine from the motor or seal side is not only an advantage during conversion, it is also a decisive advantage for the cleanability of the machine.

Conti-TDS-2 for feeding and dispersing powders in liquids

Powder depositing and dispersing machines with a vertically arranged shaft, in which the bearing and seal are positioned from below and the liquid flows into the machine from above, are the most difficult to clean. In these machines, the central area below the rotor is not sufficiently flushed either during operation or during cleaning. Old material collects, which can only be removed after complete disassembly. This is not the case with Conti-TDS machines. Here, the area behind the rotor is also flown through at maximum speed. The machine can be completely cleaned without disassembly.

ystral Fachartikel CAV Umrüsten

Magazine: cav
Issue: 01/2008
Author: Dr. Hans-Joachim Jacob

About the author

Dr. Jacob is Senior Expert Process and Applications at ystral. Dr. Jacob, who studied mechanical engineering, joined the company in 1990 as a process engineer and has since been responsible for our key accounts worldwide. His professional passion is the mixing and dispersion of powders in liquids. During his long career, he has gained experience in handling thousands of powders from a wide range of industries and is happy to share his expertise in various technical articles, online seminars and lectures.

About ystral

With our vast knowledge and many years of experience in Process- and Application Engineering we offer targeted, customer-oriented solutions across industries - from lab equipment to production machines or plants. Together with you, we develop concepts and implementations for your individual applications, which mean mmediately realisable and quantifiable added value for you.

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