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Special Flame-Retardant Material for New Generation of Dishwashers

Working in close cooperation with the Product Area Dishwashers of BSH Bosch und Siemens Hausgeräte GmbH in Dillingen, Germany, Bayer MaterialScience has developed a special flame-retardant PC/ABS (polycarbonate/acrylonitrile-butadiene-styrene) blend under the trade name Bayblend® FR 3008 HR (Hydrolysis Resistant), which is exceptionally resistant in extremely warm, humid environments.

It is used to protect the sensitive electronic parts for the latest generation of dishwashers from BSH and meets all the requirements for this application. Among other things, the appliance electronics are used in dishwashers with innovative zeolite technology. This technology makes it possible to keep drying cycle times to an absolute minimum, while ensuring optimized drying results and minimal energy consumption.

In order to meet the high quality standards of BSH, comprehensive aging experiments were carried out to simulate the actual life cycle of a dishwasher. These confirmed that, even after being stored in an 80 °C water bath in constant contact with steam for 60 days, Bayblend® FR 3008 HR remains extremely resistant to hydrolytic molecular degradation and thus retains the necessary product properties to a very high level. The yield stress of this blend (based on ISO 527-1 and -2) exhibits virtually no change throughout the entire storage period.

Such extreme conditions completely destroy test pieces made from other PC/ABS FR grades that do not undergo specific hydrolysis stabilization and are used, for example, in the housings of IT equipment and TV sets.

In order to recreate the stress on the materials during a washing cycle as accurately as possible, in addition to being subjected to pure steam, they were also exposed to common additives such as detergents and rinse aids, and to simulated fatty deposits. Bayblend® FR 3008 HR gave an impressive performance, demonstrating outstanding hydrolysis resistance and exceptional resistance to chemicals.

Bayer MaterialScience carried out a hydrolysis test in accordance with customer requirements. For this purpose plastic granules were kept at 80 °C and almost 100 percent humidity for 60 days, and the material degradation measured using the volume flow index. This confirmed the hydrolysis resistance of Bayblend® FR 3008 HR and its good correlation with the materials testing carried out by BSH.

To ensure reliable operation in the long term, Bayblend® FR 3008 HR had to undergo numerous other strict tests, such as mechanical thermal aging, checks of dimensional stability, examinations of chemical resistance and moisture absorption, and tests of optical quality characteristics based on color stability, for example.

High long-term heat resistance, excellent flame retardance
Another strength of Bayblend® FR 3008 HR is its long-term heat resistance. Following mechanical load testing with and without impact stress over a period of around 1.5 to 2 years, its relative thermal index (RTI) (UL 746 B) was established at 80 °C until 85 °C for wall thicknesses of 1.5 mm or over. A reliable UL 94 V-0 classification had to be achieved for a low wall thickness of 1.5 mm, even in the face of such high temperatures and an exposure period of over 5,000 hours. This Underwriters Laboratories (UL) test measures the maximum permissible long-term service temperature of the material in air. This high RTI value opens up a broad range of applications for our material and confirms that components made from it will function reliably and safely at high operating temperatures.

The manufacturer's extensive substance-specific material and function tests are enhanced by the requirements pertaining to the safety of electrical appliances as specified in the standard for household appliances ISO (EN) 60335-1. Only if it passes two glow-wire tests carried out on specimens may a thermoplastic be used directly to simulate overexposure to heat due, for example, to glowing contact elements or briefly overloaded electrical resistors for unsupervised household appliances, such as refrigerators, washing machines and dishwashers with rated currents in excess of 0.2 A.

It must have a GWFI (Glow Wire Flammability Index, IEC 60695-2-11 / IEC 60695-2-12) of at least 850 °C, and a GWIT (Glow Wire Ignition Temperature, IEC 60695-2-13) of 775 °C, both measured using test sheets. At the request of BSH, Bayer MaterialScience had Bayblend® FR 3008 HR officially certified by the VDE so that, as a preferred material, it fulfills the "preselection" criteria. This means manufacturers and suppliers do not have to carry out laborious tests on finished components. Passing these tests is often not only more difficult, but also time-consuming and more costly.

To avoid tracking currents for electrical insulating materials in extremely humid conditions and impurities, BSH demands a CTI A (comparative tracking index) > 250 based on IEC 60112 (test solution A). This value is far higher than the usual mains voltage. As it is classified as a resource of protection class II and has electrical insulation of 31 kV/mm, Bayblend® FR 3008 HR more than fulfills the requirement (2kV/mm) for reinforced or double insulation to prevent electric shocks as specified in IEC 60343-1.

In comprehensive materials testing, Bayblend® FR 3008 HR had no problems fulfilling BSH’s high quality requirements in terms of hydrolysis and chemical resistance, electrical safety, heat resistance and light stability. It also satisfies the high demands placed on the design and functionality of the component.

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