Paint & Coatings Industry - March 2008 - (Page 71)

High shearing speeds break apart these stable, wet agglomerates (Figure 6) and new dry solid surfaces are released. Sub-level vacuum feeding or the condensation principle with gas exchange can be an acceptable solution to this problem. Figure 7 | Schematic close-up of the process details. Dispersion Technology By connecting the individual process stages within a small space, all processes are achieved within milliseconds to create an optimum dispersion. Figure 7 shows details of the process. The rotary valve attached to the solids feeding station seals off the dispersion chamber from the atmosphere and serves for dosing the powder. In the feeding tunnel under vacuum, the dry agglomerate is deaerated and fed to the atomizer. A hydro cyclone effect, similar in concept to a liquid ring vacuum pump, produces the vacuum effect. The pump transports a liquid stream tangentially to a ring-shaped acceleration chamber where it is hydraulically accelerated into rotation. The rotation corresponds approximately to the speed of the rotor, which prevents the liquid from splashing into the solids feeding tunnel. A “freefalling liquid curtain” is created and leveled by centrifugal forces. After about 100 mm, this liquid layer merges with the rotor, forming a seal and is discharged at high speed. The rotor rotates the finely atomized solids falling from above. It spins them towards the outside onto the liquid layer. Wetting occurs during the immersion of the individual solids and is assisted by the immediate increase in pressure. At the discharge of the machine, wetting is already perfect and cannot be improved by further processing with a disperser. The necessary rotary motion of the rotor leads to slight shearing, but this is negligible due to the wide gap between the rotor and the housing. These are also the reasons for the low induced specific power input of this technology. Micro cavitation occurs in a rapid transition from vacuum vapor phase to process overpressure, further improving the dispersion process. Also, the quickly flowing liquid surface, which is available with a surface of more than two square meters per second, aids the wetting process. The high liquid surface in relation to the specific surface of the atomized solid agglomerates explains the basic principle of the Ψ- MIX. Continuous dosing of liquids and solids or batch circulation with continuous powder feed are possible. Batch circulation is the most favorable method because it is easier to control the quality of the end product. liquid batches, difficult-to-wet solids and extremely fine solids. It processes temperature-sensitive products as well as low- to high-viscosity suspensions that are barely pumpable. Conclusion Innovative dispersion technology sets new benchmarks for modern production processes in all fields where micronized, pulverized solids have to be mixed as fine and as homogenously as possible. If the impression within the industry is that the development of dispersion technology has reached a standstill, the invention of the Ψ-MIX shows promise for the future. It may be difficult to fully integrate the concept of this new invention, but from a technical point of view there are no objections. This new concept may raise some conflicts with conventional mixing systems. For established dispersion systems, it may define a new era in the market for dispersing equipment, and manufacturers of mills will need to make adaptations to accommodate the higher throughput rates. This concept prompts rethinking about the dispersion process and a look at an innovative dispersion technology. For further information, e-mail info@nft.netzsch.com, visit http://grinding.netzschusa.com/, or call 484/879.2020, fax 610/280.1299. PA I N T & C O A T I N G S I N D U S T R Y 71 Variety of Applications This technology is ideal for processing products with a high-solids content, a low-solids portion in large http://grinding.netzschusa.com http://grinding.netzschusa.com

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Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Marketplace Quarterly Stock Watch Reaching Strict VOC Requirements With Outstanding Durability for Industrial Maintenance and Marine Coatings A Unique Fungicide for Wood-Filled Plastic deSigns of the Times: Slacking Off! From Rocks to Nanos Shear-Free Dispersion Process Fluorinated Oxetane Oligomers as Versatile Intermediates for Polymer Modification The Effects of TPO Composition on Adhesion and Proposed Chemical Mechanism Supplier Showcase Color Management Materials Watch Products Classifieds Advertiser Index

Paint & Coatings Industry - March 2008

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