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When solid with liquid ...

Mixing and dispersing powders with liquids

Mixing and dispersing powdery solids with liquids is no easy task. The raw materials often have to be added from different container shapes, the powder floats to the top of the container and incrustations form on the edges - all in all a time-consuming and costly process. A powder wetting and dispersing machine, such as the one used by a plastics chemicals company, can help here.

Ystral Conti-TDS cross-section Powder and liquid components are fed into the dispersing and mixing head of the Conti-TDS via separate inlets

Not everything that looks like chocolate pudding is actually chocolate pudding: the first glance into the large container still gives hope - at the latest when using the nose it becomes clear that this is pure chemistry, or more precisely plastic chemistry. The brown mass in the preparation container of the Conti-TDS system is a mixture of chalk, polyol and lightweight filler. Isocyanate is added to produce a resin that is pumped into molds, cured and then marketed as a modeling board. Sika Deutschland GmbH in Bad Urach, Swabia, specializes in these boards and recently commissioned the Conti-TDS system - in addition to an existing older system from the same manufacturer.

for us, the calculation is quite simple: "The Conti-TDS system from ystral saves us time and money," says Sika project manager Jürgen Haussier. The main problem in the manufacture of certain products is the large number of additives that have to be added to a batch as individual components in liquid or powder form - and often from different containers. The necessary working method is time-consuming and cost-intensive, as these processes can often only be carried out manually. our Conti-TDS system is able to carry out this manual work in a user-friendly and economical way," adds Hanspeter Kenk, responsible for system construction at ystral.

Dust-free feeding, residue-free emptying The Conti-TDS is a system for dust-free feeding and dispersing of powdery solids with liquids. The system consists of a preparation tank with jet mixer, anchor stirrer with scraper, a powder wetting machine and a vacuum vessel. "The principle is of course always the same, but basically," says plant manufacturer Kenk, "a special version is developed for each customer that is tailored to their product.

The contents of the container circulate continuously and the vacuum generated is used to transfer powder and liquid additives into the liquid phase without leaving any dust or residue. Powder and liquid components are fed into the dispersing and mixing head of the Conti-TDS via separate inlets.

All parts in contact with the product can be completely cleaned using an appropriate cleaning program. The rinsing time and process are adapted depending on the task. Plant manager Haussier explains: "To clean the system, we pump some polyol through the pipes and into the tank. We can simply use this polyol again in the next batch." Plant engineer Hanspeter Kenk adds: "In the food or pharmaceutical industry, of course, cleaning is a different matter. This process is often more demanding than the production itself - which is why such systems are also CIP-capable."

Saves personnel and space
Sika already had good experiences with the first ystral system, but opted for the additional new Conti-TDS for good reason. "We were simply no longer able to meet our needs with the old system," says project manager Haussier. "With the new system, the bagging task is much more convenient, the throughput is higher and, above all, the control system with visualization and recipe management makes work much easier." The entire system can now be operated by one worker from production, virtually on the side. Only the containers need to be moved, the bags filled and the process monitored. "We save on personnel and need fewer raw material roll containers," continues Jürgen Haussier.

The entire system is on load cells, "this is important for subsequent logging," says Hanspeter Kenk. Everything is dosed automatically via the recipe control system, and all relevant data (dosing quantities, speeds, temperature, etc.) can be documented via the logging system.

Know-how in the dispersion head
The special feature of the YSTRAL Conti-TDS system is the dispersing head on the powder wetting machine. Via the vacuum in the mixing head of the Conti-TDS, the raw materials are first sucked out of the powder bag into the dispersing head via a separate inlet under vacuum - an impressive 100 kg/minute. There the powder is wetted with the liquid - in this case the chalk with the polyol. "We have a vacuum of almost 90% here," explains Hanspeter Kenk, "so that the air expands between the powder particles."

This creates a large surface area, the particles expand and wetting can take place with a very high shear gradient. The powder is immediately wetted and dispersed and arrives in the boiler as a suspension. The suspension is constantly circulated so that it can become increasingly enriched with powder until the desired degree of saturation is reached. The valve to the dispersing head is then closed and re-dispersed. "With the Conti-TDS system, the user does not have the usual disadvantages such as hours of stirring, powder floating to the top, encrusted edges, inhomogeneous product, etc.," says Hanspeter Kenk.
In addition to the dispersing head, this sophisticated mixing concept includes the jet mixer and anchor stirrer components installed in the container, which ensure homogeneous mixing and improved heat transfer in the product. Mixing in the container also prevents short-circuit currents.

From mixer to process plant
Ystral has been on the market for 30 years with the jet mixer and for around 10 years with powder wetting machines. The first YSTRAL jet mixer for liquids and solids based on the rotor-stator system was developed back in 1959 and is now used worldwide for a wide range of mixing applications. The company now sees itself as a service provider for process technology, i.e. entire process engineering processes are developed in close cooperation with the customer.

At a time when mechanical engineering and large chemical companies can shake hands when it comes to the poor order situation, ystral is doing well. "We have been looking for ways to offer customers decisive advantages through new machines and processes," says Managing Director David Manke - and this has not only been successful at Sika in Bad Urach. Sales division manager Stephan Bizer adds: "For the development of the new Conti-TDS machine, we drew up a specification sheet in consultation with the customer: the powder should be sucked into the liquid via vacuum, the liquid must be pumped, the powder must be wetted and dispersed in the liquid, existing components should be used as far as possible, the price/performance ratio must be clearly convincing."

All points were met and the machine is now established on the market. The range of applications has been greatly expanded, and the Conti-TDS has led to enormous reductions in production times, quality improvements and improved working conditions, particularly in the case of laborious and complex production processes. In some areas, areas of application have been opened up for which there was previously no suitable solution.

ystral Fachartikel Verfahrenstechnik

Magazine: Process engineering
Issue: 07/2005

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