Dispersion and Ultra-fine grinding Master of the Agitator Bead Mills

Related Vendors

Willy A. Bachofen AG

DÜPERTHAL Sicherheitstechnik GmbH & Co. KG

Glatt Ingenieurtechnik GmbH

Italvacuum, Srl

Chemical, pharmaceutical and food producers, colleges and universities all over the world use them: Wet-milling technology has been revolutionized by WAB with the development of its horizontal agitator bead mills. At this year’s Achema, the resourceful Swiss company was presenting the latest generation of its Dyno-Mill UBM (Universal Bead Mill).

What do a chicken plucking machine, a tobacco seedling setting machine, a knothole drilling machine and an agitator bead mill have in common? All these products can be found on a long list from the early 1980s of a Swiss company whose founder was tireless in thought and action. His personal secretary said of her boss: “Finding things is an art! He found gaps for innovations. He found the right people who could make things happen. He found new patents, new locations. He found his wife, he found agents for his machines and he found solutions to problems.” We are talking about Willy A. Bachofen (1912-2000), founder of the machine factory Willy A. Bachofen AG based in the city of Basel.

Even though the chicken plucking machine alone (which achieved world fame among experts) would be worthy of an article in its own right, in what follows here we devote our attention to the wet-milling technology.

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At the end of the 1960s, Willy A. Bachofen succeeded in bringing a new precept in dispersing and milling technology to the world market. The performance of wet-milling technology was significantly improved with the development of the DYNO-MILL, the first fully self-contained horizontal agitator bead mill. For the first time, it became possible to disperse and grind in a self-contained system, without the ingress of air.

In 1967, Bachofen secured the manufacturing rights — the beginning of a new era in the company’s history and the catalyst for a continuous upswing. Over the following decades, the mills were continuously developed, and today, the WAB Group offers a wide range of wet-milling solutions for applications in research, development, prototyping and production.

Green Chemistry: Agitator Bead Mill as a Reactor

Chemical transformation triggered by mechanical force, known as “mechanochemistry”, offers many opportunities for the development and production of new molecules as well as materials, and offers several advantages over conventional production processes. WAB is also convinced that mechanochemistry is an important technology for a greener future of the chemical industry and has been investing in its introduction for several years. Although long proven in research, the implementation into industrial application has not been successful so far, as no suitable and scalable devices were previously available. The innovative WAB Impa°Ct Reactor now closes this gap: the mechanical energy is introduced by means of grinding beads. An induction heater implemented into the grinding chamber heats the reactants directly and efficiently up to 160 °C. Conventional batch processes can be replaced by a continuous process with the WAB Impa°Ct reactor. The developers promise faster, more selective and innovative reactions, a significant saving of solvents, and industrial scale-up.

Depending on the task and the Dyno-Mill used, different reaction times can be realized with one or more pre-mixes. This saves valuable raw materials and time, as it significantly reduces the cleaning effort between the individual tests. Important process parameters, such as product temperature, pressure and flow rate, are controlled and logged. The system enables both single-pass and circulation processes, and can be used for liquid and viscous pumpable products as well as heterogeneous catalysts. Processing volumes start with one liter of suspension and can be scaled up to the larger models of the Dyno-Mill series, combining the three WAB Dyno-Mill technologies in one reactor: the Dyno-Accelerator, the patented Dyno-Disc BC agitator discs and the Dyno-Disc KD agitator discs. Together with the grinding beads, the technology guarantees a high and uniform mechanical energy input with simultaneous good mixing and thus surface renewal of the reactants.

Learn more about the WAB IMPA°CT Reactor

Supremacy of the Wet-Milling Technology

Agitator bead mills have long since gained a dominant position in the field of nano-scale and colloid wet grinding of, for example, lacquers, paints, pesticides, microbiological cell material and pharmaceuticals. Controlled deagglomeration, dispersion and true grinding of solid particles in a liquid medium are the principal focus of wet-milling technology. Particle sizes below 100 nanometers can thus be achieved, which other grinding techniques can often only achieve with restrictions.

Here’s how it works: The grinding suspension is placed together with the grinding beads in a horizontal (or vertical) cylindrical grinding container with an axial high-speed agitator shaft carrying several agitator discs. The suspension flows continuously through the grinding container and is ground by pressure and shear stress in a recirculating flow between the grinding beads as they are whirled around by the agitator. At the outlet of the machine, screens or separation gaps prevent the grinding beads from escaping along with the finished grinding suspension.

The grinding fineness depends on:

• the type and filling level of the grinding beads,

• the diameter ratio of the grinding beads to the particle size of the feed material,

• the type of grinding stock to be ground,

• the type of agitator elements,

• the average dwell time of the suspension in the grinding chamber.

Dispersing agents prevent the fine particles from agglomerating and stabilize the grinding suspension.

The Dyno-Mill Universal Bead Mill (UBM)

The new generation of WAB agitator bead mills highlighted at this year’s Achema covers the entire range from dispersion to ultra-fine grinding of small product quantities right up to the production of large volumes. Even highly viscous products can be processed with high throughput rates. One of the strengths of the Dyno-Mill UBM is the extremely even distribution of grinding beads in the active grinding chamber. This makes it easy to determine stable and efficient process parameters for both single-pass and recirculation modes.

The innovators at WAB have developed a new generation of agitator discs — the Dyno-Disc BC (Bead Channel) — especially for the Dyno-Mill series. They have special grinding bead channels in combination with a closed outer contour. The channels ensure efficient acceleration of the grinding beads along a precisely defined path.

During operation, each of the channels create counter-rotating grinding circuits between the agitator discs. The outer contour of the new agitator discs is completely closed within the agitated bed of grinding beads. Therefore, these remain between the agitator discs and are evenly distributed in the active grinding chamber. This ensures that the bed of grinding beads is efficiently utilized. Dyno-Disc BC agitator discs are designed for high wear resistance and consistently high performance while simultaneously reducing maintenance costs.

The grinding or dispersing process with the Dyno-Mill can be run in different operating modes, and hence can be optimally adapted to the application and required product quality:

• In the single-pass process, the grinding suspension from the supply container passes through the mill in a single closed pass.

• In the simple circulation process, the grinding suspension passes through the mill several times until the required particle size is achieved.

• In the circulation process with start-up pass, the grinding suspension is first pumped into the mill from a pre-mixing container and only then does the simple circulation process start. Once it has been emptied, the pre-mixing container can be prepared for the next batch.

• In the circulation process with final pass, the grinding suspension is collected in a separate discharge container after the required particle size has been achieved.

• In pendulum operation (“multipass process”), the circulation process randomly “swings” between two different supply containers until the desired particle size is reached.

• Two mills can also be connected directly in series — without an intermediate container — in order to achieve particularly high particle finenesses. The second agitator bead mill can be equipped with smaller grinding beads.

Wide Range of Applications

The new generation of Dyno-Mill Universal Bead Mills offers the optimum wet-grinding unit for every type of wet-milling tasks — with grinding chamber volumes from 0.5 to 100 liters and particle finenesses down to below 50 nanometers. A variety of grinding bead materials (diameter 0.2 to 2.5 mm), e.g. ceramic or glass, are available. All machines are ergonomically designed and also have permanently installed stainless steel trays.

The range of applications for agitator bead mills is diverse: the special wet-milling technology ensures brilliant colors for all types of paints, optimally milled aromas for foodstuffs, targeted bioavailability of active medical substances, extraction of biological raw materials and much more. Three applications are given below as examples.

Active Pharmaceutical Ingredients

Many modern active pharmaceutical ingredients have poor solubility properties. Bioavailability can therefore become a challenge in product development. This is where the Dyno-Mill pharmaceutical wet-milling technology helps: by reducing the particle sizes during wet grinding, the available active ingredient surfaces increase exponentially and so improve the bioavailability of the active ingredient. Machines specially developed for sterile production are available for this purpose. The most important features are:

• cleaning in place (CIP) and sterilization in place (SIP),

• semi-automatic or fully automatic control of the CIP/SIP process,

• optionally available WAB Scada system (according to 21 CFR Part 11) for control, data acquisition and data processing,

• machine production in compliance with current Good Manufacturing Practice (cGMP) and EHEDG directive,

• material certificates in compliance with FDA requirements.

For all Dyno-Mill Pharma installations, the FDS, DQ, FAT, SAT, IQ and OQ qualification documents required for validation, plus the certificates for process-relevant machine components (calibration and material certificates) are available.

Plant Protection Products in Suspension

Plant protection products are chemical or biological active substances that protect plants from harmful organisms or prevent them from impacting plants. Whether these are herbicides, insecticides or fungicides: modern wet milling allows simple and dust-free handling of all types of active substances. Products with the smallest concentrations of solids in suspension have the following advantages:

• no clogging of the spraying apparatus,

• even distribution of the active substance,

• higher effectiveness and yield due to the larger area coverage,

• no sedimentation during transport or storage,

• easy dilution without re-agglomeration.

The Dyno-Mill agitator bead mills can easily mill large quantities of plant protection products to the desired particle size and are characterized by compact design and shorter cleaning times. The risk of cross-contamination is reduced.

Nail Polishes

Nail polishes are available in all color shades and special effects. Manufacturers are constantly developing new colors to go with the latest fashion trends. Besides the colors, the ease of application is important: The polish should spread easily during application and it should not drip. This allows for perfect drying.

The two basic components of modern nail polishes are usually a thixotropic base (gel) and a pigmented color paste. For grinding of the thixotropic base, the viscosity and gloss are of primary importance. For the separately ground color paste, the color properties (intensity and hue) and gloss are important. By combining all the properties, the two complement each other to create the finished nail polish. WAB offers the whole range of agitator bead mills for the manufacture of high-quality gels and color pastes.

WAB’s process experts will help customers to find the best solutions for their applications in one of the company’s local Process Technology Centers (PTCs). The reliable and technically competent customer service as well as the broad network of the WAB Group work together like the parts of a Swiss watch. 

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