Powder processing: mixing and flow under the spotlight

Paul Boughton

Japanese company Teijin Aramid is an international company that supplies customers throughout the world with the high-performance aramids Twaron, Technora and Teijinconex. These are available as yarn, fibre and pulp, and the aramid-based rubber ingredient Sulfron. Its production sites are mainly in Japan and the Netherlands.

Aramid fibres combine extremely high mechanical strength with heat and chemical resistance, providing long lasting solutions being essential for high cost efficiency. Today aramids are used in a wide variety of markets and applications. These include; the automotive market, for example tyres, hoses and belts; aerospace; civil engineering and construction; leisure goods; protective clothing; optical fibre cables; friction and sealing materials, and more.

The company is constantly striving to develop new friction materials and to this end its plant in Wuppertal, Germany, is making use of an FT4 powder rheometer from English company Freeman Technology. The FT4 is a universal powder tester that provides three complementary approaches in a single instrument: measurement of bulk properties including permeability, bulk density and compressability; shear property determination with automated shear cells; and dynamic flowability using patented methodology. Last year, it helped the company to win the coveted Queen’s Award for Enterprise in Innovation.

Teijin Aramid is using the FT4 to investigate the flow behaviour of friction materials containing Twaron pulp, with a view to designing formulations with specific properties.

Describing his experience with the FT4, Andreas Wodetzki, technical account manager at Teijin Aramid, said, “Non-asbestos organic friction material formulations include many variable raw materials all of which can affect the overall powder properties. We needed a highly repeatable method for measuring the flow behaviour of such formulations when changing the para-aramid pulp type and content. The FT4 gives us repeatable results that are both intuitive and highly informative.”

Using the FT4, the team at Teijin Aramid has demonstrated that different para-aramid pulp types have an influence on flowability, compressibility and permeability across the powder bed. This knowledge allows the development of friction material formulations having special features (Fig. 1). With cost saving being a major issue in the brake industry, standardised testing of friction material formulations should not only enable cost reductions both in development and during production, but also help optimise quality.

According to Wodezki, “The FT4 is bringing more science to understanding ‘black magic’ friction material formulations. We are continuing to generate data in order to learn from past experience and to better understand the influence of different raw materials.” 

Expanding product choice

Meanwhile leading powder and particle technology company Hosokawa Micron continues its expansion with opening of a new, 12-storey hq building at Hirakata, Osaka, Japan. The company says this is a key indicator of its intention to keep investing in the future of particle science and processing.

As part of this expansion, Hosokawa Micron has also added to its established range of Vrieco Nauta conical mixers with a mixer dedicated to laboratory use.

Designed for testing and experimental purposes, the Minimix produces small batches of product for test purposes, the results of which can be used for scaling-up to larger mixer sizes.

Using Vrieco Nauta mixing technology, the new mini mixer has been developed as a batch mixer for a wide range of powders, pastes and slurries, and meets all FDA, GMP and industry standards. The unit includes a compact drive unit, non-lubricated orbit arm and is designed for easy cleaning between batches.

With variable speeds on both the rotating screw and its orbital arm, the Minimix controls the continuous movement of product from the bottom of the vessel to the top whilst the orbital arm revolves the screw around the inner vessel wall. The product then flows downwards into the centre of the vessel, completing the intensive and highly efficient mixing action.

Manufactured from stainless steel and available in a range of sizes from 5 to 20 litres, the mixer includes exchangeable containers for quick and simple batch exchanges, helping avoid cross contamination between batches. Screw speed can be set between 120-300 rpm whilst the orbital arm rotates at 4-10 rpm

According to Hosokawa Micron, Vrieco Nauta conical mixers and Cyclomix agglomerators have become the mixers of choice for companies looking to mix metal powders prior to pressing. The short mixing times, thorough mixing, operational flexibility and excellent cleanability offered by them is creating cost advantages that make them popular, particularly in a highly competitive metals and alloys market, says the company.

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