Heating with “brains”, Panel made from Bayblend® FR 3010 used in control unit of gas-fired boiler
Tuesday - June 20, 2006, Leverkusen – Anyone building or renovating a house can now cut down on heating costs thanks to the “Heatronic II” from BBT Thermotechnik GmbH. The intelligent control system is the brains of the gas boiler and precisely tailors consumption to individual requirements, thus minimizing fuel costs. BBT Thermotechnik, a subsidiary of Bosch based in Wetzlar (Germany), uses Bayblend® FR 3010 from Bayer MaterialScience AG for the housing of the latest generation of the Heatronic II. The flame-retardant blend of polycarbonate and ABS (PC/ABS) meets stringent requirements for electrical safety, resistance to chemicals and hydrolysis, light stability, and heat resistance. It also satisfies the high demands placed on the design and functionality of the component. Compared with previous grades of Bayblend®, the PC/ABS material offers optimized processing.
Wide design freedom, easy processing
The control system is of modular design and can be used in a broad range of boilers. The geometry of the front panel is therefore suitably complex. In order to precisely fit the complicated inner workings of the control system and the numerous operating elements, the molding must display a minimal tendency to warp and have a high level of dimensional accuracy and stability. In this respect, Bayblend® FR 3010 provides the necessary design flexibility and integration potential. The material also offers advantages in terms of processing. “Thanks to its heat resistance of up to 110 °C (Vicat B 120), its high toughness and stiffness, the panels can easily be demolded at high temperatures. This minimizes injection-molding cycle time and thus increases productivity,” explains Burkhard Thuermer, who works in technical product support for flame-retardant PC/ABS blends at Bayer MaterialScience. The outgassing of volatile substances from the thermoplastic during processing is virtually non-existent. This minimizes the accumulation of deposits on injection molds, and thus benefits processing significantly. It also means longer periods between cleaning cycles.
Long-term heat resistance
Another strong point of Bayblend® FR 3010 is its long-term heat resistance. This ensures that the control equipment can function properly even when subjected to high temperatures during operation. One established means of assessing maximum long-term heat resistance in continuous service in air without permanent external loading is the relative temperature index (RTI) as specified in UL 746 B (Underwriters Laboratories). In the case of short-term mechanical stress caused by impact, the RTI of Bayblend® FR 3010 is 85 °C (at a wall thickness of 1.5 mm), which is 10 °C higher than that achieved by the previous panel material, thus providing greater safety.
Chemically resistant to hydrolysis, grease and oil
It is also important that the control housing is chemically resistant to a certain punching oil and potentiometer grease. If the appliance comes into contact with these media, no fractures should occur either during assembly or in long-term use. Bent strip testing according to EN ISO 4599 was carried out using substances supplied by BBT Thermotechnik. The client requested a maximum exposure period of 14 days at an elevated temperature of 60 °C, which approximately simulate the lifespan of the molded part. “Bayblend® FR 3010 satisfied the stringent requirements. There was no visual surface damage such as the appearance of fine cracks, fractures and discoloration,” says Dr. Thomas Eckel, product developer for flame-retardant PC/ABS blends at Bayer MaterialScience.
The high level of resistance to hydrolysis exhibited by the PC/ABS blend when exposed to a warm, moist atmosphere also ensures the long-term operation of the control unit and protects the in-built electronics. A highly informative accelerated test developed by Bayer MaterialScience is used to determine the hydrolysis behavior. “The plastic granules are stored for seven days at 95 °C and almost 100 percent humidity. The hydrolytic degradation at the end of this period can be measured using the MVR volume-flow rate. Our tests showed that Bayblend® FR 3010 outperformed the thermoplastic previously used,” observes Eckel.
Also colorfast in the long-term
As well as functional demands on the control unit, Bosch Thermotechnik customers attach great importance to the appearance of the panel. The surface finish of the lightly textured molding has to remain extremely color fast when exposed to light over the lifecycle of 12 years calculated by Bosch. In order to assess the color stability of Bayblend® FR, Bayer MaterialScience carries out various standardized tests for indoor applications. Results show that Bayblend® FR 3010 exhibits excellent color stability and easily fulfils the EN-ISO 4892 standard required by Bosch, even without UV stabilization. “It is worth pointing out that the radiation level of 92 MJ/m2 set in this test is more than double that of the globally accepted light aging standard to ASTM D 4459, known as the IBM test,” comments Thuermer.
The chlorine- and bromine-free flame retardance package means that the PC/ABS blend exhibits exceptional fire resistance. This enables it to satisfy not only the relevant UL standards, but also the glow-wire test to IEC 60695-2, which forms part of the often-quoted household appliance standard IEC 60335-1. A value of 960 °C in test thicknesses of 1.0 to 3.0 mm was recorded on the UL Yellow Card for the Glow Wire Flammability Index (GWFI) in line with IEC 60695-2-12. The Glow Wire Ignitability Temperature (GWIT) in line with IEC 60695-2-13 is 850 °C for the same wall thickness range.
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