June, 2018
www.us-tech.com
Bubble-Free Potting of High-Voltage Capacitors for Medical Engineering
Continued from previous page
right potting material. “For our regular capacitors, we
use potting resins based on polyurethane. Since the high-voltage capacitors come into contact with liq- uids, such as transformer oil during operation, epoxy resins are more suitable,” says André Tausche, man- aging director of FTCAP. Polyurethane (PU) compounds
offer a broad and versatile range of properties. PU compounds can be processed by machines easily, and have low volume shrinkage and mod- erate flexibility after curing. But, PUs are very sensitive to moisture and must be stored and prepared in a vacuum before potting. Epoxy resins, however, offer
temperature stability, low flamma- bility and higher glow-wire ratings. Due to their hardness, high modulus of elasticity and mechanical stability when cured, these materials are well-suited for components used in harsh environments. Low-moisture absorption and excellent chemical resistance are other key benefits. The company chose a heat-cur-
ing, two-component epoxy resin from Wevo-Chemie GmbH, WEVOPOX 8260 FL/WEVODUR 1018. The epoxy exhibits long-term heat resistance and good flow properties. Due to its hardness, high degree of cross-linking and low water absorption, it is well- suited for potting high-voltage capaci- tors.
Selecting the System FTCAP turned to Scheugen -
pflug for a suitable potting system. “We came back to Scheugen -
pflug relatively quickly, as we al - ready use a system from the compa- ny and are very satisfied with it,” explains Tausche. “We were also con- vinced by the fact that Scheugen - pflug and Wevo-Chemie had already successfully completed a project with a similar material.” To choose the best system for
FTCAP’s potting process, Scheugen - pflug carried out dispensing tests with engineers from FTCAP and Wevo-Chemie at its in-house technol- ogy and application center. During the tests, Scheugen -
pflug’s VDS U potting system demon- strated excellent results, bubble-free operation and repeatability. This system is particularly useful for the series production of medium and large components. It also handles dif- ficult part shapes and complex cast- ing programs. The system is based on Scheugenpflug’s standard modular platform. This design offers users flexibility and short delivery times, as well as lower costs. Even in cramped production environments, the modular system can be tailored to a specific application easily. Since small series and custom-
made products make up a significant part of FTCAP’s portfolio, the compa- ny relies primarily on semiautomat- ed processes. “We focus more on nich- es in the market and on small-to- medium ser ies. A fully automated production environment would make little sense for us. Instead, we prefer workplaces that can be adapted quick- ly and easily,” explains Tausche. “Above all, we needed a system that offered us the necessary flexibility in this environment.”
The vacuum potting system is
particularly suitable for applications with a wide variety of components. With its 15.8 x 11.8 in. (40 x 30 cm) movable pallet drawer, parts with different sizes and shapes can be pot- ted in the same system. Three mov- ing axes allow the VDS U to encapsu- late several components in one run. This balances short cycle times with high potting quality. Scheugenpflug’s Dos P016 pis-
ton dispenser ensures the output of exact and reproducible material quantities. Not only does it cover a wide range of requirements, it also
VDS U vacuum dispensing sys- tem, shown here with the A310 preparation and feeding unit.
enables gentle dispensing of pres- sure-, moisture- or shear-sensitive potting media, without the risk of material changes. The Dos P016 is also equipped with a heating unit for both the metering head and mixing tube. This heats the material just before potting, reducing its viscosity and helping to reduce bubbling, even with complex part shapes. The A310 from Scheugenpflug
prepares and feeds the epoxy resin into the potting system. With this machine, large quantities of self-lev- eling potting materials can be
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See at SMT/Hybrid Pkg, Booth 4-421
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